Chem. Rev. 2002, 102, 3543

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Applications of Sol−Gel-Processed Interphase Catalysts

Zhong-lin Lu, Ekkehard Lindner,* and Hermann A. Mayer*

Institut fur Anorganische Chemie, Universitat Tubingen, Auf der Morgenstelle 18, 72076 Tubingen, Germany

Contents I. Introduction 3543

II. Organic Groups as Reactive Centers 3545A. Solid Acids 3545B. Solid Bases 3546C. TEMPO-Modified Sol−Gel Materials 3549

III. Metal Complexes as Reactive Centers 3549A. Titanium Complexes 3549B. Chromium Complexes 3550C. Manganese Complexes 3550D. Iron and Ruthenium Complexes 3551

1. Iron Complexes 35512. Ruthenium Complexes 3552

E. Cobalt, Rhodium, and Iridium Complexes 35581. Cobalt Complexes 35582. Rhodium Complexes 35593. Iridium Complexes 3568

F. Palladium and Platinum Complexes 35701. Palladium Complexes 35702. Platinum Complexes 3572

IV. Enzymes as Reactive Centers 3572V. Summary and Outlook 3573

VI. Acknowledgments 3575VII. List of Abbreviations 3575

VIII. References 3575

I. Introduction

Mank ind’s ever-growing dem an d for energy an draw m aterials is gradually pushing natu ral resourcesto th eir l imits, giving rise to more environmentalp r ob le m s . I n t h i s r e ga r d , ch e m is t r y h a s p la y ed acontradictory role, although it represents one of themost su ccessful and diverse sectors of ma nu factu ringindustries in m any regions of the world. The r angeof chemical products is enormous, and they makeinvaluable contr ibutions to our quality of life. H ow-e ve r , t h e s e m a n u f a ct u r i n g p r oce s se s a l so l ea d t omillions of tons of waste. As a consequence, the roleof chemistry is not generally accepted by govern-ments or the public; chemistry is actually consideredb y m a n y a s t h e ca u s e of t h e p r ob le m s . H e n ce , t h eso-called “green chemistry” becomes increasinglyimporta nt, with t he objective to creat e new products,processes, an d services tha t achieve s ocietal, eco-nomic, and environmental benefits.1-5

The challenge for chemists include the discoverya n d e va l u a t ion of n e w s yn t h e t i c p a t h w a y s u s in galternative feedstocks, the elaboration and employ-m e n t of m or e fa v or a b le r e a ct i on con d it i on s a n dsolvents for improved selectivity as well as energyminimization, and the design of less toxic and inher-ently sa fer chemicals.6 In chemical synthesis, th eideal will be the combination of a number of environ-mental, h ealth, safety, a nd economic tar gets. Cat a-lysts are able to meet this lofty goal because theyhave widely recognized benefits s thermodynami-cally favorable reactions that have no low-energypathways can be rendered possible under mild condi-t i on s . M or e ov er , ca t a l ys t s a r e m a n d a t or y i n t h e

manu facture of a vast a rray of chemicals an d fuelsan d a s su ch significan tly contr ibute t o our economyand high l iving stan dards.7-10 In addition, catalystsprovide importa nt environmental advantages, forexample, in catalytic convert ers for a ut omobiles.5,11

Moreover, impr oved cata lytic processes could lead t omore efficient consumption of energy a nd natu ralresources as well as sequestra tion of the greenh ousegas CO2.

Homogeneous catalysts have uniform and well-d e fi n ed r e a ct i ve ce n t e r s, w h ich l ea d t o h i gh a n dreproducible selectivities.12-17 The activity and ef-ficiency of these catalysts are generally high. How-ever, one of the major problems is the separation of

the catalyst from the reaction mixture. This proce-dure often generates large volumes of waste eluentand devours a lot of energy. Also, t he process of extracting an expensive catalyst m ay lead to decom-position. Thus, elimination of th is step would befavorable and is one of the major goals in moderncatalyst research.

To solve th is pr oblem, several concepts h ave beentested to combine the advantages of homogeneousan d het erogeneous catalysis. These include su pportedliquid-phase cata lysts,18,19 biphasic catalysts,20-23

ionic liquids a s solvent s in catalysis,24-27 the applica-tion of supercrit ical fluids,28-31 d e n d r im e r ca t a -lysts,32,33 na nofiltra tion-coupled cata lysis,34 and sup-

p or t e d ca t a l ys t s .35-52 A d r a w b a ck of s u p p or t e dcatalysts is the loss of homogeneity due to minorchan ges in the structure, which many reactive cen-ters suffer from. This leads t o a redu ced activity an dselectivity of the immobilized catalysts.53 In severalcases the in fluence of th e ma tr ix on t he final outcomeof the reactivity and selectivity is not known. This isdue to th e lack of structural knowledge a bout boththe reactive centers a nd the polymer matr ix.

The application of surface-modified inorganic andorganic materials has been less successful because

* Aut hor t o whom correspondence sh oul d be addressed (fax0049-7071-295306; e-mail ekkeha [email protected],herma nn.ma [email protected]).

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of (i) the sh ort lifetimes of these cata lysts caused bythe leaching of the reactive centers (poor anchoring),(ii) reduced accessibility of the catalysts, (iii) sterice ffe ct s of t h e m a t r i x, (i v) i n h om og en e it y of t h erea ctive center s, an d (v) difficulties in controlling t hedensity of the reactive centers on the surface. 53,54

With t he a im t o develop h igh-performa nce heter o-genized homogeneous cat alysts, t he concept of chem-

istry in interphases has recently been introduced.55

This term was imported from chromatography intothe area of supported transition metal complexes in1995.56 An interphase is defined as a region withina material in which a stationary and mobile compo-nent penetrate each other on a molecular level (seeFigure 1). The stationary phase is composed of aninert matrix, a flexible spacer, and an active center,whereas the mobile phase consists of a solvent or agaseous, liquid, or dissolved r eactant . In th e case of chromatography, the active center fulfills the functionof an interaction center, whereas in catalysis, thea ct i ve s it e i s a r e a ct i ve ce n t e r , f or e xa m p le , a norganometallic complex. In an ideal interphase, thereactive center is uniform, well-defined, and highly

mobile. Therefore, an interphase is able to simulatehomogeneous reaction conditions, and at the sametime it has the advantage of a heterogeneous catalyst.Rigid but highly porous materials can as well serveas supporting matrix provided that sufficiently longspacers lead to a satisfactory mobility of the reactivecenter s. Major dr awbacks of conventional su pportedcata lysts such as leaching, poor selectivity, an drestricted accessibility of the reactive centers can beovercome. These systems combine m any advan ta gesof homogeneous (high activity, high selectivity, highreproducibility) and heter ogeneous (easy sepa ra tiona n d r e cov er y of t h e ca t a l ys t s fr om t h e r e a ct i onmixture) catalysis. In this review, the term “inter-

Zhong-lin Lu, born in 1968 in Gansu Province (China), studied chemistryat Lanzhou University and earned his M.S. degree in 1993. He receivedhis Ph.D. degree in 1997 at Nanjing University with Prof. Xiao-zeng You.In 1996, he worked 8 months at the University of Hong Kong in the groupof Prof. Andreas Mayr. After two years of postdoctoral work with Prof.Bei-sheng Kang at Zhongshan University, he joined the group of Prof.Rudi van Eldik at the University of Erlangen-Nurnberg as a HumboldtFellow. At present he works as a Humboldt Fellow with longer-cooperationfellowship in the group of Prof. Ekkehard Lindner at the University ofTubingen. His main research interests include coordination chemistry(transition metal and lanthanide complexes with tripodal ligands, aroyl-hydrazones, isocyanide, ether-phosphines), kinetics and mechanisms ofmetal complexes, and homogeneous and heterogeneous catalysis withruthenium complexes.

Ekkehard Lindner, born in 1934 in Rottweil/Neckar (Germany), studiedchemistry at the then Technische Hochschule in Munchen and completedhis Ph.D. thesis in 1962 with Walter Hieber on perfluorinated organo-cobaltcarbonyls. After his dissertation, he joined the group of H. Behrensat the University of Erlangen-Nurnberg and completed his Habilitation in1967 with work on reactions of acid halides with Lewis acids and Lewisbases. In 1966 he was appointed Oberassistent and in 1970 Wissen-schaftlicher Rat. In the same year he was awarded the Dozentenstipen-dium of the Fonds der Chemischen Industrie. In 1971 he accepted aposition in the inorganic chemistry department (Anorganische Chemie II)

at the Universitat Tubingen. His main research interest is organometallicchemistry (transition metal mediated organic syntheses, macrocycles withreactive transition metal centers and their host / guest chemistry) and itsapplication in homogeneous and heterogeneous catalysis (complexes withhemilabile ligands, chemistry in interphases). He is the author of about450 publications.

Hermann A. Mayer was born in Heidelberg (Germany) in 1954 andreceived his Ph.D. degree in 1986 at the University of Tubingen withProf. Dr. E. Lindner. After two years of postdoctoral work with Prof. Dr.W. C. Kaska at the University of California, Santa Barbara, he returnedto the University of Tubingen. In 1994 he finished his Habilitation andwas appointed Professor of Inorganic Chemistry in 2000. His researchinterests include the design of polyphosphine ligands, transition organo-metallic chemistry, concepts for catalyst immobilization, and the applicationof multinuclear NMR spectroscopy to organometallic chemistry in solutionand in solid state.

F i g u r e 1 . S chem atic repres entation of an interphas e.

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phase catalysts” is introduced. The matrix is thatp a r t of t h e i n t er p h a s e ca t a l ys t w h ich a ffe ct s t h ecross-linking and therefore the insolubility of thesupport. Ma inly, element-oxygen-element and car-bon-carbon bonds form the polymer backbone. Thespacer provides the linkage between the matrix andth e rea ctive center. It usu ally consists of a chemicallyinert chain of variable length l ike hydrocarbonsw it h ou t or w it h h e t e r oa t om s e n s u r in g s u ffi ci en t

mobility of the reactive center . The reaction cent ersare catalytically active groups, including organicmoieties, meta l complexes, or enzymes. Most of th etypical homogeneous catalysts can be embedded intostat ionar y ph ases by su itable T-silyl-fun ctiona lizedligands.

F o r t h e p r e p a r a t i o n o f i n t e r p h a s e c a t a l y s t s , t h esol-gel process is a powerful t ool.55,57-60 Suitablepolysiloxane networks (hybrid polymers) are obtainedunder smooth and low-temperature conditions. Si-multaneous co-condensation of T-silyl-functionalizedmetal complexes or ligands with various alkoxysi-lanes provide materials in which, in the case of ani de a l i n t er p h a s e , t h e r e a ct i ve ce n t e r s a r e n e a r ly

homogeneously distributed across a chemically andt h e r m a l ly i n er t ca r r i e r m a t r i x. D ep e n di n g o n t h ekind of application, sol-gel materials util ized incatalysis are either microporous or mesoporous. Itshould be stressed that the term “interphase cata-lysts” may be different in the literature. Encapsula-t i on of ca t a l yt i c g r o u p s i n t o s ol-g el m a t e r i a ls ,sol-gel-entrapped catalytic materials, immobilizedcata lysts, supported metal or organometallic com-p le xe s , e t c. , h a v e m a n y t h i n gs i n com m on w it hinterphase catalysts. Fu rtherm ore, in m any cases i ti s d iffi cu l t t o d is t in g u is h a com p le x t h a t i s ju s timmobilized on a sup port from a n int erpha se catalystas described above. The main criterion should be the

mobility of the r eactive centers, which also dependson the flexibility of the spacer in the solvent used.Very often it is laborious to judge whether supportedcom p le xe s r e p or t e d i n t h e l it e r a t u r e m e et t h e r e -quiremen t of high m obility u nder reaction conditions.For th ese reasons in this r eview a re discussed onlythose mat erials tha t h ave been prepar ed by polycon-densa tion or poly-co-cond ensa tion of monomeric fun c-tionalized ligands, metal complexes, or other cata-lytically active groups by the sol-gel process. It willb e d e m on s t r a t e d t h a t t h e w a y a m a t e r i a l wa s s yn -thesized has a high impact on the per forma nce of thecatalyst. Therefore, in this review, emphasis is puton the preparation of catalytic systems r elated to

chemistry in interphases, their catalytic activities,and in particular their recycling ability.

II. Organic Groups as Reactive Centers

Acids, bases, and oxidants are fundamental andimportant catalysts applied in a wide spectrum of organ ic conversions, for example, in addition, con-densation, and redox reactions. However, the produc-tion of large amounts of waste and the costly sepa-r a t i on a n d ca t a l ys t r e cov er y h a v e a l wa y s ca u s e dproblems. An additional intricacy is that some or-ganic acids, such as peroxoacids, are not stable andtherefore are unsafe for use on a large scale. Clearly,

the immobilization of a cids, bases, a nd oxidantswithin a solid support is a major advantage in theprolonged quest for heterogeneous catalysts for or-ganic reactions, which results in an improvementwith respect to workup, r ecycling, and sta bility.61-67

A. Solid Acids

A typical example is the preparation of uniformlymodified polysilsesquioxanes from 1,4-bis(tr ieth oxy-

silyl)but-2-ene an d HP O(OEt)2 to get 1,4-bis(trieth-oxysilyl)-2-(diethylphosphonato)butane via a radicaladdition reaction, which was then transferred to aninsoluble product by an acid-catalyzed sol-gel pro-cess (Schem e 1).68 The corr esponding ph osphonic acid

modified polysilsesquioxane 1 was isolated aftert r e a t m e n t of t h e p h os p h on a t e w it h con ce n t r a t e dhydrochloric acid an d cha racterized by m ultinu clearsolid-stat e n uclear magn etic resonance (NMR) spec-troscopy.

Polymer 1 offers a new class of solid acids, whichhas been considered as a catalyst in the pinacol-

pinacolone rea rr an gement. Treat ment of pina col with1 at 140 °C resulted in a high conversion to pina-colone after 12 h (eq 1a). The same cata lyst was a lsosuccessful in the dehydration of cyclohexanol at 120°C, but with low activity (eq 1b; Table 1). Controlexperiments with mesoporous or microporous silica

S c h e m e 1

T a b l e 1 . P e r f o r m a n c e o f C a t a l y s t s 1-4

cat a-lyst

type of ca ta lysis eq

yield(%)

select-ivity(%)a r ef com m en ts

1 rearrangement b 1a 80 68 n o r ecyclin g t estdehydrationc 1b 15

2a epoxidationd 2a 55 100 69 2b was u sed for

2b 2a 57 88 secon d r u n

2b 57e 77 e

56 f 77 f

3 2a 62 96

4 deh ydr obr om - 3a 3 0 75 n o r ecyclin g t estinationg 3b 34

a Selectivity to the oxide. b Reaction conditions: 0.2 g of catalyst, 6.0 g of pinacol, T ) 140 °C, t ) 1 2 h . c Reactioncondit ions: 0.25 g of cat alyst, 25 mL of cyclohexanol, T ) 12 0°C, t ) 12 h. d Reaction conditions: 4 mmol of alkene, 50 mLof chloroform, 0.75 g of catalyst, T ) 30 °C, t ) 24 h. e Firstr u n . f S e cond r un. g Reaction conditions: 9 × 10-3 mol of substrate, catalyst prepared from 13.2 × 10-3 mol of TMOSand 6.8 × 10-3 mol of 3-(diethoxysilyl)propylamine, 5 mL of benzene, reflux, t ) 8 h .

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under the same conditions afforded no products forthe above-mentioned two r eactions. I t should bepointed out that industrial processes for the accessto cyclohexene require high temperatures and pres-sur es wher e cyclohexanol is fed to a ctivat ed cata lystssuch as sil ica, alumina, or zinc aluminate at 380-450 °C. Neat phosphoric acid in large excess is alsoactive between 160 and 170 °C.

Peroxoacids function as active straightforward

epoxidation reagents with wide applications. Theyar e often employed for th e epoxidat ion of un function-alized a lkenes and do not require further cata lysts.To immobilize peroxoacid, in a first step polysiloxane-supported nitriles are prepared by sol-gel processingof (2-cyanoethyl)triethoxysilane (CETS) in the pres-ence of tetraethyl orthosilicate (TEOS) (Scheme 2).69

Subsequent hydrolysis by aqueous sulfuric acid af-forded the polysiloxane-anchored car boxylic acids.Treatment of these m aterials with methan esulfonica ci d a n d h y d r og en p e r ox id e g a ve t h e s u p p or t e d

peroxocar boxylic acids 2a ,b . Both 2a a n d 2b weresynthesized in CETS/TEOS ratios of 1:1 and 1:2,respectively. In the case of (3-cyanopropyl)triethox-ysilane (CPTS), the supported peroxocarboxylic acid3 was genera ted in a rat io of CPTS/TEOS ) 1:1. Thenumber of peroxoacid groups was determined byreductive t i tration with 0.1 M aqueous Na 2S2O3 inthe presence of iodide.

All three acids 2a ,b a n d 3 were successfully appliedin th e epoxidation of alken es (eq 2). In p ar ticular, cis-cyclooctene an d cyclohexene were converted withhigh to excellent selectivities (see Table 1). Alth ough2b affords a lower selectivity th an 2a , after recyclinga n d t r e a t m e n t w it h h y d r og en p e r ox id e /m e t h a n e -

sulfonic acid, 2b was still capable of epoxidizingcyclohexene. Compa red to polymer-support ed sys-tems,70 oxygen transfer efficiencies of silica materialswere much higher (48 vs 76-91% for 2a ,b a n d 3,respectively). At the same time 2a ,b have loadingsa n d a ct i vi t ie s t h a t a r e cl os e t o t h os e fou n d forconvent iona l homogeneous per oxoacids, and th ey arestable under anhydrous conditions at room temper-a t u r e .

B. Solid Bases

The preparation of organically modified silica-bearing amine groups via the sol-gel method has

been known for some time, but their application assimple catalysts and reagents for organic synthesisis much less developed.71-74 In pa rticular, th e groupof Avnir wa s inter ested in t he pr epara tion of propyl-amine-anchored silica 4 ob t a in e d b y t h e s ol-ge lprocess of tetram ethoxysilane (TMOS) and 3-(di-ethoxymethylsilyl)propylamine (Scheme 3).75

The a ctivity of supported a mine 4 was determinedby dehydrobromination of 2-phenylethyl bromide or10-bromo-10,11-dihydro-5 H -dibenzo[a,d]-cycloheptan-5-one (eq 3; Table 1). Considering th at the substr atehas been added in excess and that some of the aminesare inaccessible du e to m icroporosity a nd th e kn own

i n t er a ct i on of s u c h a m i n es w it h t h e s il a n ol s, t h econvers ion of the a ctual cat alytic active site is h ighert h a n t h e ov er a l l y ie ld . T h is s t u d y u n e q u iv oca l lydemonstr at ed t he feasibility of organ oamine m odifiedsol-gel materials as recoverable catalysts and re-agents.

Michael additions are essential carbon-carbonbond forma tion processes. A base is always requiredas catalyst to form the intermediate carbanion byabstracting a proton from an activated methyleneprecursor. Frequently th is reaction serves a s a testto study the catalytic activity of solid bases. Twonovel cat alysts based on hexagonal m esoporous silica(H M S ) a n d N , N -dimethyl-(3-aminopropyl)trimeth-

S c h e m e 2

S c h e m e 3


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oxysilane were prepared using a templated sol-ge lmethod and varying the amine-to-silane ratio.76 Inthis way catalysts 5a ,b (Scheme 4) with TEOS/ N , N -dimethyl-3-aminopropyltrimethoxysilane ratios of 9:1and 4:1, respectively, are accessible. Their charac-terization by thermogravimetric analysis revealed agood thermal stabili ty. Surface areas and loadingsof th e functional groups resulted from Bruna uer,Emmett, and Teller (BET) methods and acid t i tra-tions. They were furt her chara cterized by diffusereflectance Fourier transform infrared (FT-IR) spec-

tr oscopy (DRIFT).Both cat alysts 5a ,b were evaluated in t he rea ction

of nitroalkanes with R, β-unsaturated carbonyl com-pounds (eq 4) and showed high selectivities and evenh i gh e r a ct i vi t ie s t h a n t h os e p r e pa r e d w it h a m or -phous silica (see Table 2). Rates are approximately

3 t imes faster compared to catalysts with similarloadings. No enantioselectivity was observed in the

reaction between 2-cyclohexen-1-one and nitroethane/ nitropropane. Altogether th ere is a lmost no differencein performance between 5a a n d 5b . After recovery,5a ,b continued t o cat alyze th e rea ctions th ree t o fivetimes. High yields were achieved even in a secondor third repeated use.

Mesoporous mixed titania-silica materials driedby semicontinuous extraction with supercritical CO 2

turned out to be excellent catalysts for the epoxida-tion of alkenes, alkenols, and alkenones with alkylhydroperoxides.77-79 T h e s t r u c t u r e a n d a c t i v i t y o f these aerogels were controlled by adjustment of thesol-gel preparat ion and drying procedure. The acid-i t y o f t h e m i xe d ox id e i s cr u c ia l t o a ct i va t e t h e

peroxide but can also result in acid-catalyzed sidereactions of reactants and products.80 T u n i n g t h ea ci di t y w it h w ea k l y b a s ic or g a n ic a n d i n or g a n icadditives considerably impr oved th e p erforma nce of the m ixed t i tania-silica systems. Especially, amineaddition en ha nced epoxide forma tion. Thus, selectivi-ties of up to 98% in the demanding epoxidation of 3-meth ylcyclohex-2-en-1-ol wer e achieved with highreaction rates.81 The positive influence was explained

b y t h e n e u t r a l iz a t ion of s om e a ci d s i t es t h a t a r epresent in the aerogels.

Baiker’s group reported on th e synt hesis of novelorganically modified mesoporous mixed titania-silicap o l y m e r s w i t h a t a r g e t s t r u c t u r e a s i l l u s t r a t e d i nScheme 5.80 The functional groups were introduced

via Si-C bonds during the sol-gel process and notonly change the surface properties with respect topolarity an d a cidity but also are su pposed t o inter actdirectly with the t i tanium active site as electron-d on a t i n g l ig a n d s. T h e m e n t ion e d p ol ym e r s w er einvestigated by thermal analysis a nd BET methodsas well as by FT-IR, DRIFT, and NMR spectroscopy.

tert -Butyl hydroperoxide (TBHP) served as a pr obe

for t he cat alytic potent ial of th e organ ically modifiedtitania-silica aer ogels 6a-c in t he epoxidation of cyclohexene an d cyclohexenol (eq 5). Differencesamong 6a-c refer to initial rat es in t he epoxidationof cyclohexen e/cyclohexenol, which decrease in th eseries 6b > 6c > 6a (see Table 3). With regard tothe epoxidat ion of cyclohexene, a ll catalysts wereactive. However, due to the rapid consecutive reac-t i on s , w h i ch ca n b e t r a ce d b a ck t o r e s i du a l H C lreta ined in the solid, no yield an d selectivities werefoun d for 6a . For the epoxidat ion of cyclohexenol,experiments with 6a-c were condu cted un der exactlythe same conditions to ensure a direct comparisonw it h t h e u n m o di fi ed a e r og el . T h u s , t h e e pox id e

productivity of 6a-c is similar to or even better tha nthat of the unmodified aerogel and correlates wellwith the high initial a ctivities. By organic modifica-tion a remarkable enhancement has been achievedin t he epoxide s electivity of olefins, r eachin g 94% for6c with 91% peroxide conversion. Only a methyl-modified titan ia-silica aerogel afforded a higherolefin selectivity (98% after 10 min ) and also a higheraverage rate. Compared to former studies the reac-tant-to-peroxide ratio in this work was improved. 82,83

Several advantages thus are realized by introducingorgan ic fun ctional groups t o titan ia-silica catalysts.The materials combine the high activity of mesopo-rous t i tania-silica aerogels with high epoxide selec-

S c h e m e 4

S c h e m e 5

T a b le 2 . M ic h a e l A d d i t io n R e a c t i o n s C a t a ly z e d b y5 a ,b ( E q u a t i o n 4 ) ( D a t a f r o m R e f e r e n c e 7 6 ) a

eq 4a eq 4b

cata-lyst R

tim e(h )

yieldb

(%) Rtim e

(h )yield

(%) com m en t s

c H 7 58 H 13 58CH 3 7.5 72 CH 3 5 65CH 3CH 2 6.5 76 CH 3CH 2 8 82 5a was reused

3-5 tim es;5a H 3 70 H 6 62 n o specific

CH 3 2 92 CH 3 4.5 72 da ta a re pr e-CH 3CH 2 2 90 CH 3CH 2 5 86 sen t ed

5b H 4 8 0 H 4 90CH 3 1.2 94 CH 3 1.5 88CH 3CH 2 1.5 95 CH 3CH 2 2.5 93

a Typical rea ction conditions: 0.5 g of cat alyst 5a , 25 mL of nitroethane, 20 mmol of but-3-en-2-one, reflux. b Yields of products by GC ana lysis. c N , N -Dimethyl-3-aminopropyl-silicaprepared by postmodification.


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tivities. Furthermore, a reduction of the TiO 2 contentbelow 10 wt % is possible without loss of activitywhen compared to the unmodified aerogel possessing20 wt % of TiO 2.

G u a n i d i n e s a r e v e r s a t i l e s t r o n g b a s e s a n d a l s ocan didates for su pported catalysts. Previous work h as

demonstrated that guanidines can be supported, buttheir successful application in organic synthesis islimited. Novel guanidine bases supported on silicaor micelle-templated silica (MTS) are typical ex-amples (Scheme 6).84

To prepare such systems, (chloropropyl)trimethoxy-silane was sol-gel processed with TE OS in eth an ol.Subsequent trimethylsilylation of the surfaces wasachieved with N ,O-bis(trimethylsilyl)acetamide. Treat-ment of this ma terial with 1,1,3,3-tetra methylguani-

dine (TMG) an d 1-meth yl-1,5,9-tr iazabicyclo[4.4.0]-decane gave the final product 7, w h i ch h a s b ee ncharacterized by BET methods and 13C magic-anglespinning (MAS) NMR spectroscopy.

Cyclohexenone was reacted with hydrogen peroxidein m ethanol at 20 °C to probe the catalytic activity(eq 6; Table 3). Excellent conversions and selectivities(89%) toward epoxides were achieved, whereas previ-ously supported guanidines led to a conversion of only42%.85 Similar results were obtained with cyclopen-tenone. Repeated use of the recovered catalyst indi-cates a significantly poorer performance, possibly dueto t he adsorption of small quantit ies of byproductssuch as diols at the active site.

T a b le 3 . P e r f o r m a n c e o f C a t a l y s t s 6-8

selectivity (%)

catalysttype of

ca t a ly si s e q t im e (h )initialr a t ea yield (%) S olefin

b S peroxidec r ef com m en t s

6a epoxidationd 5a 2 1.8 80 n o r ecyclin g t est s wer e r epor t ed5b 2 1.8 67 81 83

1 60 80 826b 5a 2 8.1 90 97 90

5b 2 8.2 75 74 751 97 82 76

6c 5a 2 3.1 75 96 865b 2 3.3 70 93 70

1 91 94 70

7 epoxidatione 6a 2 65 89 56 84 r eu se of ca t a lyst s in dica t ed a poor er per for m a n ce12 85 65 7

2 f 34 93 522g 20 81 198g 51 78 6

6b 2 60 8 7 54

8 oxidation h 7 4 95 87 8 retained its a ctivity an d selectivity within fourrun s, no specific data a re present ed

a mmol g-1 m in -1. b S olefin ) 100% [epoxide]/([olefin]0 - [olefin]). c S peroxide ) 100% [epoxide]/([peroxide]0 - [peroxide]). d Reactionconditions: 70 mg of cata lyst, 20 mmol of olefin, decane or penta ne a s int ernal st andar d, 2 mL of toluene, 5 mmol of TBHP, T )90 °C. e Typical reaction conditions: 10 m mol of 2-cyclohexenone, 10 mL of methan ol, 0.1 g of cata lyst, T ) 20 °C, hydrogenperoxide was added dropwise. f Using 2-propanol as solvent. g 0.2 g of silica was added. h Reaction condit ions: 2.15 g of cat alyst

(0.5 m mol of radical), 10 mm ol of MGP, 60 mL of H2O containing KBr (1.4 mmol), 10% excess of 1.19 M NaOCl, pH 9.3, t )

4 h .

S c h e m e 6


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C. TEMPO-Modified Sol−Gel Materials

Stable organic nitroxyl radicals belonging to the

2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) family

are outstanding catalysts for selective oxidations. 86

The radicals are soluble in water (∼1% w/w) where,

i n t h e p r e se n ce of a l k a l in e (p H 9-1 0 ) N a O C l a s

primary oxidant along with a catalytic amount of

bromide, they mediate the conversion of -CH 2OH

groups into car boxylic fun ctions with complete se-lectivity for the primar y a lcohols. Blum’s group h as

recently disclosed that sol-gel-processed TEMPO is

an effective catalyst for the oxidation of sugars with

N a O B r i n t o u r o n a t e s (S ch e m e 7 ).87 T h e T E M P O

moiety was tethered to (MeO)3Si(CH 2)3NH 2 by reduc-

tive a mina tion of 4-oxo-TEMPO (TEMPON). Then

the radical monomer was homogeneously entrapped

within a sil ica matrix by the sol-gel process with

TMOS as a co-polycondensation agent to produce 8.

Catalyst 8 promoted the oxidation of methyl R-D-

glucopyranoside to the corresponding uronic acid (eq

7 ) . I n e a c h r u n n o o t h e r p r o d u c t s a p a r t f r o m t h e

u r on a t e (t h e con t e n t of w h i ch w a s a l so m e a s u r e d

with the colorimetric test for uronic acids) were

detected in th e reaction mixture. In four consecutive

reaction cycles the catalyst retained its activity, as

well as its sh ape a nd a ppearan ce. Interestingly, after

each run a higher degree of oxidation (∼95%) was

found (Table 3). Fur thermore, n o leaching of en-

tra pped ra dicals into th e solut ion wa s detected (with

a spectroscopic limit of 10 ppm). This is important

because many heterogeneous oxidations can actuallybe promoted by catalysts leached into the solution.

By separating th e cata lyst from th e reaction m ixtur e

shortly (30 min) after the beginning of the oxidation,

t h e m ot h e r l iq u or h a s b ee n i n ve s t ig a t ed , w h ich

indicated no extra format ion of uronate. The r euse

activity of 8 was also confirmed by electron spin

resonan ce (ESR) spectroscopy prior to and after

consecutive reaction runs. Detailed aspects affecting

the catalytic properties of 8 (including the ratio of

metal to water, amount of alcohol, pH value, tem-

perature, drying t ime, and other important param-

eters) have been patented.88

III. Metal Complexes as Reactive Centers

A. Titanium Complexes

Group 6 metallocences were discovered by Kamin-sky and Sinn and viewed as the next generation of catalysts for olefin polymerization.89-91 It was soonr e a li ze d t h a t t h e or i gi n a ll y h om og en e ou s m e t a l-locenes had to be heterogenized to avoid reactorfouling and to provide products with large, uniformparticle sizes and higher bulk densities. Moreover,the facile control of the polymer particle morphologyis achieved by using established technologies knownfrom common Ziegler-Natta catalysts.92-94 However,these systems will not be discussed here in detailb e c a u s e t h e a c t u a l a c t i v e c a t a l y s t s r e m a i n i n t h epolymer and are not recovered.

Polymer-anchored cyclopentadienyl- and penta-methylcyclopentadienyltitanium catalysts were de-scribed by Cermak et al.95 Polysiloxane-boun d penta -methylcyclopentadiene was prepared by polycon-densation of C5H Me 4CH 2Si(OEt)3 with TEOS. Sub-sequent ly, th e obtained micropar ticulate polysiloxane

w a s r e a ct e d w it h C p Ti Cl3 and Cp*TiCl3 (Cp*)

pentamethylcyclopentadienyl) in the presence of alarge excess of n -butyllithium , resp ectively, to afford9a ,b (Scheme 8). The h ydrogenat ion potential of 9a

in the case of 1-octene [tur nover frequency (TOF) )14.5 min-1] w a s 6 .5 t i m e s l o w e r t h a n t h a t o f t h ehomogeneous system Cp*CpTiCl2 but could be main-tained even after a prolonged period of time (eq 8).Recycling was possible four times with gradu al lossof activity (TOF cha nged from 14.5 m in-1 in th e firstrun to 5.1 min-1 in the second r un and to 1.0 min-1

in the fourth run) without leaching of titanium. For

S c h e m e 7

S c h e m e 8


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9b , the hydrogenation activity (TOF ) 28.8 min-1)was slightly higher than that of the homogeneous

system Cp 2*TiCl2. I t was sti l l active in the absenceof butylli thium and could be reused. The authorssuggested that the variance in catalytic activity isattributed to variable methods of anchoring of thetitanium complexes using different qualities of TEOS,which lead to altered morphologies of the polysilox-anes and hence different availabilities for the cata-lytically active centers.95 Because in dependence onsynthetic procedures th e a ctive sites a re inside th ematrix and not on the surface of the materials, thereaction conditions need to be selected carefully sotha t the accessibility of the reactive centers is m ain-tained.

B. Chromium ComplexesA well-known heter ogeneous chromium system is

the Phillips catalyst (CrO 3 /SiO2), which has playedan importan t role in t he production of polyolefinssince i t was discovered by Hogan and Banks moret h a n 4 0 y e a r s a g o.96 Considering the concept of interphase, th is process is not discussed in moredetail.

Organometallic chromium complexes are effectivein the regio- and stereoselective hydrogenation of various unsaturated systems.97,98 Polysiloxane-boundchromium complexes were applied in the hydrogena-tion of meth yl sorbat e, 3-nonene-2-one, an d 1-octyne.As a catalyst served 10 , which was obtained by co-

condensation of η6-C6H 5Si(OEt)3Cr(CO)3 with TMOSand subsequent curing (Scheme 9; eq 9).99 As meth -

ods for its characterization served X-ray photoelec-tron spectroscopy (XPS), BET an alysis, a nd infrared

spectr oscopy. Detailed hydrogenation da ta for th eabove-ment ioned t hree su bstra tes ar e listed in Ta ble4. The activity of 10 was retained through severalcycles and showed good regio- and stereoselectivities.C ycl oh e xa n e a s a s ol ve n t i s s u p e r i or t o T H F i nrecovering t he cata lytic activity u pon r ecycling of 10 .Experimental r esults indicate t hat the r eaction h astaken place within the polymer pores.

C. Manganese Complexes

Metalloporphyrins, mainly of iron(III) and manga-nese(III), represent versatile oxidation cata lysts an d

S c h e m e 9

T a b l e 4 . P e r f o r m a n c e o f C a t a l y s t 1 0 i n H y d r o g e n a t i o n R e a c t i o n s ( D a t a f r o m R e f e r e n c e 9 9 ) a

selectivity (%)

eqsubstr a te(mol L-1) s olve nt [ca t alyt st ]/[s ub st r at e]

r u nn o.

tim e(h )

yield(%) Z isomer E isom er com m en ts

b 0.2 cycloh exa n e 1:20 2 96 100 10 showed good9a 0.10 1:20c 1 6 74 96 4 r ecyclin g a bilit y

4 5 47 95 40.16 1:20d 1 8 97.5 96 4

4 8 38 64 360.2 1:20 1 5 95 97 3

4 5 96 98 2

0.2 TH F 1:20 1 3 100 95 14 3 21 90

b 0.11 cycloh exa n e 1:10 24 929b 0.11 1:10 1 16 95

5 17 80

b 0.11 cycloh exa n e 1:10 38 94 100e

9c 0.11 1:10 1 41 63 82e 18 f

5 44 96 82e 18 f

a Reaction conditions: 0.1-0.2 mol L-1 of substrate, 200-250 mL of solvent, p[H 2] ) 430 psi. b Homogeneous reaction withcomplex (EtO)3SiPhCr(CO)3. c Using catalyst prepared from commercial silica. d Using uncured catalyst 10 . e Pr oduct is 1-octene. f Product is 1-octane.


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have been designed as models for monooxygenasesbased on cytochrome P-450.100-109 Hybrid polymerscontaining manganese porphyrins as reactive centerswere introduced by Iamamoto et al .110 A t e t r a k is -(pentafluorophen yl)porphyrin ma ngan ese(III) com-

plex served as start ing material and was reacted with(3-aminopropyl)triethoxysilane (APTES) to afford aT-silyl-fun ctionalized man ganese porphyrin precur-sor. Subsequent poly-co-condensation with TEOS inthe presence of nitrogen ba ses gave catalysts 11 a-c(Scheme 10), which were characterized by ultraviolet-visible (UV-vis) absorption spectr oscopy, th ermo-gravimetric analysis (TGA), electron paramagneticresonane (EPR), and electron spectroscopy imaging(ESI). Polymers 11 a-c were active in the epoxidationof ( Z )-cyclooctene u sing P hIO as oxidan t (eq 10). Thecatalytic activities of 11 a-c were less than those of the corresponding h omogeneous system, and the rat eof conversion was also lower (Table 5).

Another modified tetrakis(2,6-dichlorophenyl)por-phyrinmanganese species was heterogenized in thepresence of TEOS to give 12 a ,b (Schem e 10).111 Theseimmobilized complexes catalyzed the epoxidation of cyclooctene, using PhIO as oxidant (eq 10). In gen-eral, the reactions were complete after 24 h withyields of cyclooctene oxide bet ween 69 a nd 96% (Table5). It is obvious that the catalytic activity of 12 a ,b isb e t t e r t h a n t h a t o f 11 a-c . No leaching of the met-a l lop or p h y r in fr om t h e s t a t i on a r y p h a s e w a s ob -served during the reaction. Hydrogen peroxide asoxygen donor was also probed, but the yield was verylow.

D. Iron and Ruthenium Complexes

1. Iron Complexes

As models for cytochrome P-450, iron porphyrinshave received much attention. Heterogenized cata-l ys t s b a s ed on i r on p h or p h y r in s a d s or b e d or co-valently boun d t o inorgan ic polymers h ave a lso beenreported.100,103-107,112-119 In several cases they were

S c h e m e 1 0

T a b l e 5 . P e r f o r m a n c e o f C a t a ly s t s 1 1 a-c, 12a,b,15 a-c , a n d 1 6 a-c i n t h e E p o x i d a t io n o f ( Z) -C y c l o o c t e n e ( E q u a t i o n 1 0 a ) a

yieldb (%)

ca t a lyst solven t 1 h 24 h r ef com m en ts

c CH 2ClCH 2C l 8 4 8 4 1 10 n o r ecy cli ng t e st s for11 a 0 34 ca t a lyst s 11 a-c ,11 b 7 27 12 a ,b , 15 a-c , a nd11 c 7 30 16 a-c

c CH 2Cl2 70 70 11112 a 35 9612 b 20 69

c CH 2ClCH 2Cl 89 89 1 1015 a 43 8515 b 7 3115 c 14 50

16 a CH 2Cl2 97 100 11116 b 10 4716 c 13 100

a R e a ction conditions: 1 m L of solve nt, 150 µL o f ( Z )-cycloocten e, 5 µL of cyclohexanone as internal standard, 5.0mg of PhIO, 10 m g of catalyst, 25 °C. b Yield is based on P hIO.c Homogeneous reaction with the corresponding metal com-plexes without T-silyl groups.


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obtained from su rface-supported or entr apment meth-ods.100,103,117,120 Earlier work to incorporate iron por-phyrins into interphases originates from Battioni etal., and they designated their system as metallopor-phyrinosilica.121 Respective catalysts 13 a ,b a n d 14 a ,bwere obtained as outlined in Scheme 10. From (3-amin opropyl)tr iethyoxysilane an d meso-tetrakis(pen-tafluorophenyl)porphyrin t he monomer was formed.Subsequent hydrolysis and polycondensation in abiphasic CH 2Cl 2 /H 2O s ys t e m i n t h e p r e se n ce of acatalyst (HF or 1-methylimidazole) afforded 13 a ,b ,whereas 14 a a n d 14 b were produced by hydrolysisand co-condensation of modified porphyrin withTEOS in EtOH. The content of porphyrin in 13 a ,bwas higher th an in 14 a ,b . However, 13a ,b exhibitedlower specific sur face ar eas (30-1 0 5 m 2 g-1) t h a n14 a ,b (>6 90 m 2 g-1). Al l o f t h e m ca t a l yz ed t h eepoxidation of cyclooctene in high yields (>90%) aswell as th e hydr oxylation of cyclohexan e an d h eptan ewith PhIO with yields of ∼50% (eq 10; Ta ble 6). Thehybrid p olymers 14 a ,b promoted a lso the epoxidation

of cyclooctene with t -BuOOH in a yield between 45and 64%. Interestingly, the corresponding homoge-n e ou s ca t a lys t w a s d ea ct iva t e d u n d er t h e s a m ereaction condition. Some pr eliminar y results werealso described in the oxidation of an adamantane/ cyclohexane mixture (1:1) with PhIO. It was foundthat the adamantane/cyclohexane oxidation productr a t i o w a s m u ch h i gh e r for 14 a ,b t h a n for 13 a ,b ,which is tr aced back t o the difference in the specificsur face area . Hydr oxylation of cyclohexan e, which isless reactive an d bulky, was th us favored in t he caseof 13a ,b , where the metal center is less accessible.Similar results were achieved for the oxidation of acyclododecane/cyclohexane mixture (1:1). Catalysts

14 a ,b led to cyclododecanol/cyclohexanol ratios of ∼

2,whereas 13a ,b gave a ratio of 1.

Iam amoto et al. prepa red t he ironporphyrinosilica15 a-c 110 a n d 16a-c 111 according to Scheme 10 andcompared their properties with those of the corre-sponding manganese porphyrins (vide supra, Scheme10). The porphyrins 15a-c proved to be more activet h a n 11 a-c in the epoxidation of ( Z )-cycloocten e withPhIO as oxidant (eq 10; Table 5). The best perfor-mance was obtained by 15 a in which pyridine wasused as a template and t he yield was similar to thatof the homogeneous iron porphyrin. In particular,15 b ,c led to a lower product yield, caused by thereduction of iron(III) to iron(II) during the catalyst

preparation. The properties of 16 a-c were similarto those of 12 a ,b , and the catalytic epoxidation of cyclooctene was possible using PhIO as oxidant (eq10). After a reaction time of 24 h, 16a ,c gave yieldsof 100% (Table 5). In contrast to surface-supportediron porphyr ins,115 no leaching in 15 a-c a n d 16 a-cwas observed during the reaction, which was con-firmed by UV-vis spectroscopy and further epoxi-dation tests of the filtered reaction mixture. Unfor-tu na tely, no recycling of th e catalysts wa s men tioned.

2. Ruthenium Complexes

Ruthenium complexes incorporated into interphases ys t e m s a r e d is cu s s ed i n t h e s e qu e n ce of e t h e r-phosphine-, phosphorus-, and nitrogen-containingligands.

a. Ether -Phosphine Ligands. Hemilabile ether-phosphines have been extensively investigated in

T a b le 6 . P e r f o r m a n c e o f C a t a l y s t s 1 3 a ,b a n d 1 4 a , b ( D a t a f r o m R e f e r e n c e 1 2 1)

yield (%)

catalysteq 10ba

(epoxidation)eq 10cb

(epoxidation)eq 10dc

(hydroxylation)eq 10c + 10e (ratio)d

(hydroxylation)eq 10c + 10f (ratio)e

(h yd roxyla t ion ) com m en t s

13 a 48 64 41 54 (5.6) 30 (1.1) ca t a lyst s sh owed13 b 47 45 49 64 (9.9) 52 (1.1) sh a pe14 a 41 54 45 50 (12) 38 (1.7) select ivit y14 b 44 50 47 57 (17) 45 (2.0)

a Reaction conditions: molar ra tio of hydr ocarbon/ t -BuOOH/catalyst ) 600:200:1, 1 mL of CH 2Cl 2 /CH 3OH (1:3), yield based on

t -BuOOH.b

Reaction conditions: molar ra tio of hydrocarbon/PhIO/catalyst ) 800:20:1, 1 mL of CH2Cl 2, [catalyst] ) 1 mmol L-1

,T ) 20 °C, t ) 2 h; yields were based on PhIO and referred to cyclohexanol and cyclohexanone. c Reaction conditions: molar ratioof hydrocarbon/PhIO/catalyst ) 2100:20:1, 1 mL of CH 2Cl 2 /CH 3CN (1:1), yields referred to heptanols and heptanones. d Molarratio of adamantane/cyclohexane/PhIO/catalyst ) 200:200:20:1, 1 mL of CH 2Cl 2, total yields (adam an tan ols/cyclohexanol in molarratio). e Molar rat io of cyclododecane/cyclohexane/Ph IO/cat alyst ) 400:400:20:1, 1 mL of CH 2Cl 2, total yields (cyclododecanol/ cyclohexanol in molar ratio).


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organometallic chemistry as a tool to stabilize emptycoordination sites at reactive centers. 122 Ligands of this t ype form a close conta ct to the meta l center viat h e p h os ph or u s a t om s o t h a t t h e lig an d ca n n ot

dissociate completely from the metal center. At thes a m e t i m e t h e ox yg en a t om in t h e e t h er m oie t ycoordinates to the metal in a labile manner and isinvolved in a n opening an d closing mechan ism ta kingover the function of an intramolecular solvent. It isimporta nt for cata lysis tha t t he hem ilabile char acterof eth er-phosphines is present not only in homoge-neous but also in inter phase systems. 123-127 With theaim to correlate structural and dynamic propertiesof various interphase catalysts with their cata lyticactivity, many polysiloxane matrices in which ruthe-nium complexes were covalently bound via silyl-modified ether-phosphines have been synthesizedand characterized.56,128,129 Ph ysical pr operties of these

stationary phases can be varied in a wide range byemployment of different co-condensation agents, forexample, TEOS, MeSi(OMe)3 (MTMS), Me2Si(OMe)2

(DMOS), (MeO)2SiMe(CH 2)6MeSi(OMe)2, a n d Al-(OiP r )3, as well as with ether-phosphine ligands thatcontain different spacer lengths. The loading of thematr ix with metal centers within t he mat rix can bea d ju s t ed b y a n a p pr op r ia t e a m ou n t of t h e co-condensation agent. Multinuclear CP/MAS solid-stateNMR spectroscopy gave insight into the stereochem-istry of the metal complexes, the integrity of thespacer, th e polymer ba ckbone, an d th e mobility of th ereactive centers. In addition, extended X-ray absorp-tion fine structure (EXAFS), X-ray diffraction (XRD),

etc. were also applied to characterize these inter-phase systems.

Approximat ely 10 years ago, the first polysiloxan e-supported ether-phosphine r ut henium (II) complexes

of t h e t yp e 17 were introduced (Scheme 11).130

(MeO)3Si(CH 2)6PPh(CH 2CH 2OMe) was t reated with[RuCl2(CO)2]n , a nd the resulting complex was poly-co-condensed with TEOS to afford 17 . Catalyst 17was active in the heterogeneous hydrogenation of crotonaldehyde with comparatively high selectivities(eq 11; Table 7). Moreover, n o loss of meta l or ligand

Table 7. Performance of Catalysts 17, 19a,b, 20a-i , a n d 2 1 a-i i n t h e H y d r o g e n a t i o n o f 2 - B u t e n a l ( E q u a t i o n 1 1 ) a

selectivity (%)

2-butenol

catalyst T (°C)t i me

(h )r u nn o.

yield(%) bu ta na l tra n s isomer cis isomer n -bu t a n ol r ef com m en t s

17 120 3.3 1 5 1.3 37.2 32.2 4.6 25.9 130 17 was reused in4 50.1 37.1 44.4 4.1 14.3 fou r cycles

19 a 80 4 1 20 19 73 4 4 131 ca t a lyst s 19 a ,b a n d 20 a-i150 1 1 65 23 51 5 21 wer e r ecover ed, bu t det a ils

2 63 22 55 5 18 wer e given on ly for 19 a ,

19 b 80 4 1 20 19 72 4 5 20 a , and 20 c150 1 1 81 18 46 4 32

20 a b 120 1 1 35 28 60 12 13220 b 1 52 17 62 2120 c c 1 71 11 65 2420 d 1 37 23 63 1420 e 1 48 18 63 1920 f 1 69 12 64 2220 g 1 38 23 60 1720 h 1 47 18 59 2220 i 1 60 15 64 21

21 a 80 4 1 5 38 58 4 133 ca t a lyst s 21 a-i were recovered,21 b 1 21 28 63 9 bu t det a ils wer e given on ly21 c 1 44 20 65 15 for 21 g a n d 21 i21 d 1 15 28 62 1021 e 1 27 20 64 1621 f 1 45 12 64 2221 g 1 21 27 64 921 h 2 20 26 65 9

3 20 26 64 101 26 24 66 10

21 i 1 51 19 64 172 35 22 67 11

d 3 34 23 66 111 34 29 41 30

a Reaction conditions: p[H 2] ) 50 bar, Ru/ n -butenal ) 1:250 for catalyst 17 , 1:1000 for cata lysts 19-21 . b Second run with 33%yield, third run with 34% yield. c Second ru n with 65% yield, third run with 64% yield. d Homogeneous reaction with monomericcomplex.

S c h e m e 1 1


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from the support occurred, which was confirmed byatomic absorption spectroscopy (AAS).

Via exchange reactions between HRuCl(CO)(PPh 3)3

a n d e t h er-p h os p h in e l ig a n d s s u ch a s (M eO )3Si -(CH 2)3(Ph)PCH2Do (Do ) methoxymethyl, tetrah y-

drofuryl, and 1,4-dioxanyl), three different P-coordi-na ted t rimet hoxysilyl-functiona lized ru th enium com-plexes of the type HRuCl(CO)(P∼O)3 w er e p r e -pared.125 Poly-co-condensation of the monomeric spe-cies with variable a mounts of TEOS under varioussol-gel conditions gave t he polymeric (ether-phos-phine)ruth enium(II) complexes 18 a-c (Schem e 12).

Small amounts of magnesium salts were introducedin t o t h e m a t r ix t o in cr e a se t h e p ol ar it y of t h enetwork, which led to an improved product/catalystseparabili ty. These materials were used in the hy-drogena tion of n -butyraldehyde (eq 12; Table 8).Catalysts with a higher a mount of Q-silyl speciescould be well separated from t he reaction mediumbut suffered from a lower activity due to the non-flexibility of the matrices and occlusion of the com-plexes. Those with lower Q-type silicons and a small

particle size were highly active, but separation waspossible only by the addition of nonpolar solvents.Mg 2+-d op e d ca t a l ys t s w er e fe a t u r e d b y a h i gh e ractivity and were completely recovered by centrifuga-tion after t he hydrogenat ion. No leaching of ruth e-

nium took place in these interphase systems as wasdetermined by AAS measu rement. Constant ana lyticvalues of the materials after several catalytic runshave been found, and no loss of activity was estab-lished for Mg2+-doped catalysts.

To tra nsfer distinct properties of polysiloxanes topoly(alumosiloxane) matrices and to incorporate ioncharges into network builders, poly(alumosiloxane)-bound ether-phosphine ruthenium complexes haveb ee n p r e pa r e d i n a s im u l t a n e ou s s ol-gel process(Scheme 13).131 Two different amoun ts of Al(OiP r )3

acting as an aluminum-containing precursor werehydrolyzed in meth an ol. The r esulting sols were co-condensed with mixtures of th e m onomeric complexcis-Cl(H)Ru(CO)(P∼O)3 [P∼O ) PhP(CH 2CH 2OC H 3)-(CH 2)3Si(OMe)3)] an d TE OS to a fford catalysts 19 a ,b .Both systems were applied to the hydrogenation of trans-crotonaldehyde (eq 11). At 80 °C conversionsof 20% were observed with chemoselectivities beingh ig h er t h a n 3 :1 w it h r e ga r d t o t h e for m a t ion of

T a b le 8 . P e r f o rm a n c e o f C a t a l y s t s 1 8 a-c i n t h e H y d r og e n a t i o n o f n -B u t y r a l d e h y d e ( E q u a t i o n 1 2 ) ( D a t a f r o mR e f e r e n c e 1 2 5 ) a

catalyst T (°C) t im e (m in ) r u n n o. yield (%) TOF (m in-1) com m en t s

18 a b 80 60 1 62.2 10.4 18 a-c showed good recycling2 10.0 a bilit ies in t h e secon d

150 60 1 99.5 22.1 a n d t h ir d r u n s18 b b 50 60 1 2.4 0.04

150 60 1 98.5 18.02 16.93 17.0

18 c b 100 60 1 32.5 3.9150 45 1 100 22.2

18 c c 150 60 1 91.8 15.218 c d 150 60 1 74.9 12.518 c e 150 15 1 100 66.6

2 65.9

a Reaction condit ions: 0.1 mmol of catalyst with respect t o Ru, 7.2 g (100 mmol) of n -butyra ldehyde, start ing H 2 pr e ssur e ) 50ba r . b Ru/TEOS ) 1:6. c Ru/TEOS ) 1:10. d [Ru]/TEOS ) 1:30. e [Ru]/TEOS ) 1:6, and the matrix was doped with Mg 2+.

S c h e m e 1 2

S c h e m e 1 3


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u n s a t u r a t e d a l coh ol s. I n cr e a s in g t h e t e m p er a t u r efrom 120 to 150 °C resulted in conversions of up to81% (see Table 7). However, the chemoselectivitiesdecreased a nd considerable am oun ts of the h ydroge-nat ion pr oduct n -butyl alcohol was formed. The betteractivities of 19b compared to 19 a at elevated tem-peratures are traced back to the stronger polarity of 19 b . Both materials 19a ,b could be recovered fromthe reaction mixture by simple centrifugation, and

after being washed with acetone and n -hexane, theyrevealed the same catalytic activities in the secondr u n .

Fu rt her poly(alum osiloxane)-boun d rut henium (II)complexes were made accessible by sol-gel pr ocess-ing of the trimethoxysilyl-functionalized ruthenium-(II) complexes cis-Cl(H)Ru(CO)(P∼O)3 [P∼O ) P h P -(CH 2CH 2OC H 3)(CH 2)n Si(OMe)3, n ) 3, 6, 8] with t hedifferent co-condensation agents TEOS, MTMS,DMOS, a nd aluminu m-2-propanolate [Al(OiP r )3](Schem e 14).132 All materials 20 a-i proved to be

successful as hydrogenation catalysts for 2-butenal(eq 11; Table 7). Catalysts 20 a , 20d , a n d 20 g dis-played conversions in t he ra nge of 35-38%, and theselectivities in the formation of unsaturated alcoholscompared to saturated aldehydes were approximately2.5:1. Variation of the matrices led to higher conver-sions (∼70% for cat alysts 20 c , 20 f , a n d 20 i) a n d

chemoselectivities toward th e h ydrogenat ion of car-bonyl double bonds (20 c : 2-butenol/ n -butanol ) 6:1).Dynamic solid-state NMR investigations indicatedtha t t he mobility of the rea ctive centers is determinedby the length of the spacers and not by the type of th e co-condensa tion a gent . Complete recycling of th ecatalysts from the reaction mixture by simple cen-trifugation after a catalytic run and a re-employmentwith constant activity after washing with acetone andn -hexane was demonstra ted.

Several (ether-phosphine)ruthenium(II) complexesof th e type cis-Cl(H)Ru(CO)(P∼O)3 [P∼O ) PhP(CH 2-CH 2OC H 3)(CH 2)nSi(OMe)3, n ) 3 , 6 , 8 ] w e r e co-condensed with TEOS, MTMS, and DMOS, respec-

tively, to afford nine polysiloxane-boun d rut heniumspecies 21 a-i (Scheme 15).133 Further studies wereor i en t e d w it h r e s pe ct t o t h e h y d r og en a t i on of n -buten al (eq 11). The most rigid mat erial 21a showed

hardly any catalytic activity at the applied reactionconditions. Increasing the spacer length from n -propyl to n -hexyl or n -octyl a fforded conver sions from15 t o 21% (see Table 7). The more flexible cat alysts21 g-i displayed even a higher activity and selectivity

with conversions between 44 and 51%. In the case of corresponding homogeneous cata lysts, the overallconversion wa s less a nd th e selectivities were poorer .An importan t point is the fact th at the activities of sol-gel-immobilized r ut henium complexes can beadjusted by the properties of the carrier m atrix an dthe spacer. Enh an ced mobility increased th e activityand selectivity of 21 g-i . It was also concluded thatthe diffusion of the substrate into the matr ix is notthe rat e-determining st ep. Moreover, th ese cat alystscould be easily recovered from th e r eaction mixtureby precipitat ion of t he highly swollen gels withn -hexane followed by simple fi ltrat ion. The samecatalytic activity was found after three consecutive

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runs for 21 g , whereas 21 i loses some of its activityin the first reuse. However, after the second run theactivity remains constant.

b. Phosphorus Ligand s. Sol-gel-derived rut heniu m

cat alysts for t he synt hesis of N , N -dimethylformamide(DMF) from supercritical carbon dioxide were re-p or t e d b y t h e g rou p of B a ik er .134,135 As ligands,T-silyl-functionalized phosphines of the type Ph 2P -(CH 2)2Si(OEt)3 a n d M e2P(CH 2)2Si(OMe)3 w e r e a p -plied (Scheme 16).13 4 Co-condensa tion with TEOS

produced the ruthenium(II) catalysts 22 a-d . Under

the r equired rea ction conditions both can didates werestable a nd able to produce DMF with 100% selectivity(eq 13a). Independent of the prepar at ion conditions,the employment of methylphosphine 22c ,d resultedin higher activities, as compared to the phenylphos-phine congeners 22 a ,b (Table 9). For 22 c ,d a maxi-mum turnover number (TON) of 110800 correspond-i n g t o a T O F o f 1 8 6 0 h-1 at 100% selectivity wasatta ined under specific conditions (see Table 9).Leaching of active species from the catalysts couldbe neglected, because the filtrate exhibited no cata-lytic activity in subsequent activity t ests. Moreover,using the same catalyst for three consecutive experi-ments resulted in a marked increase of activity for

the second run, and i t remained stable in the thirdexperiment. The stabilizing effect of sol-gel-pro-cessed h omogeneous complexes was su pported by t helong-lastin g a ctivity of 22 a-d . However, no data for

turn over numbers were presented in th e literatu re.134

Fresh and used hydridometal catalysts, which werereinstalled for catalytic testing after storage underair for one year, showed no loss of activity. This is incontra st t o the findings with homogeneous ana logues,with which the reaction mixtures rapidly changedtheir color or precipitated, indicating decomposition.

Inter estingly the above-ment ioned cat alyst 22 c wa salso active in the generation of methyl formate in100% selectivity (eq 13b; Table 9). The TOF maxi-mum of 115 h-1 wa s >2 t i m e s h i g h e r t h a n f o r t h ebest reported homogeneous systems.

In addition, the effects of reaction variables on the

rea ctivity a nd selectivity of 22 a by varying th e initialconcentrat ion of the catalyst an d dimethylamine, th epartial pressures of hydrogen and carbon dioxide, thetemperature, and the stirring frequency were stud-ied.13 6 With r egard t o the in fluence of reaction time,it was found that there is a nearly constant reactionrate as long a s enough dimethylamine is available.Below 100 min-1, t h e t u r n o ve r fr e qu e n cy of t h ereaction increased with the stirring frequency. Be-tween 100 and 300 min-1, th e kind of stirring doesnot influence the turn over frequency, indicating anegligible influence of externa l mass t ra nsport on thereaction rate under standa rd reaction conditions.W it h r e s pe ct t o t h e e ffe ct of d im e t h yl a m in e , t h e

reaction rate appeared to be of first order at lowerconcentr ation a nd of zero order at higher concentra -tion. The carbon dioxide partial pressure seemed tobe negligible in th e ra nge investigated. Kinetic dataindicated an approximately 0.6th order with regardto the dependence of the ra te on th e hydrogen par tialpressu re. An a ctivat ion en ergy of 69.8 ( 2.4 kJ mol-1

w a s ca l cu l a t ed for t h e s yn t h e s is of D M F i n t h etemperature range between 333 and 413 K. Above413 K, the formation of byproducts and the decom-position of the catalyst were observed.

Recently Baiker synthesized the mesoporous hy-brid aerogels 23 a ,b (Schem e 17).137 A functionalizedbidentate ruthenium(II) phosphine complex was used

T a b le 9 . P e r f o rm a n c e o f C a t a l y s t s 2 2 a ,b a n d 2 3 a , b

ca t a lyst t ype of ca t a lysis eqyield

(%)selectivity

(%) TON aTO F(h-1) r ef com m en t s

22 a b syn t h esis of DMF 13a 25 100 3230 220 134 r eu sed in t h r ee cycles, n o det a iled22 b b 35 100 4420 290 da t a wer e pr esen t ed22 c b 94 100 13670 90022 c c 82 100 110800 186022 d b 84 100 11800 790

22 c d syn t h esis of m et h yl for m a t e 13b 1740 115 TOF s for 22 c d a n d 23 a e are higher

tha n t hose in homogeneous23 a e synthesis of N , N -diet h ylfor m a m ide 13a 18400 137 ph a se23 b e 2210

a Tur nover n um ber [mol(DMF)/mol(cat alyst )] for eq 13a, a nd [mol(met hyl format e)/mol (cat alyst )] for eq 13b. b Reaction condit ionsfor reaction eq 13a with 22 a-d : 500 mL stainless steel autoclave; n [Me 2NH ] ) 0.71 mol; p[H 2] ) 8.5 MPa; p[CO 2] ) 13.0 MPa ;T ) 373 K; t ) 15 h; st ir r ing r a te ) 300 min-1; n [catalyst] ) 5 × 10-5 mol (Ru). c n [Me 2NH ] ) 6.4 mol; T ) 406 K; t ) 60 h;stir r ing r a te ) 500 min-1; n [catalyst] ) 1.8 × 10-5 mol (Ru). H 2 a nd C O2 were recharged regularly to keep constant pressure.d Reaction conditions for eq 13b with 22 c : 500 mL sta inless steel autoclave; n[MeOH] ) 0.75 mol; p[H 2] ) 8.5 MPa; p[CO 2] )13.0 MPa; T ) 373 K; t ) 15 h; st ir r ing r a te ) 300 min-1; n [catalyst] ) 1.77 × 10-5 mol (Ru). e Reaction conditions: T ) 110 °C;tota l pr e ssur e ) 18 M P a ; n [catalyst] ) 7.5 × 10-7 mol.

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a s p r ecu r s or t o r e a ct w it h T MO S v ia a s ol-gelprocess. Aerogel 23 a was isolated by extra ction of the

solvent with supercritical CO2 from t he p roduced gel,and xerogel 23 b was obtained by slow evaporationof the solvent. Polymers 23 a ,b were used to prepare N , N -diethylformamide from CO2, H 2, a n d d i e t h y -lamine (eq 13a; Table 9). Depending on the condi-tions, turn over frequencies up to 18400 h-1 wereachieved with aerogel 23 a . U n d e r t h e s a m e c on d i-tions t he microporous xerogel 23 b afforded only 2210h-1. The difference was attributed to the favorabletexture properties of the aerogel, eliminating intra-par ticle diffusion limitat ions. The m easur ed tu rn overfrequency for 23 a was even significantly higher thant h a t for t h e m on om e r ic c on g en e r u n d e r t h e s a m econditions (3130 h-1).

c. Nitrogen Ligands. P r e p a r a t i ve a n d ca t a l yt i cstudies on nitr ogen-boun d ru then ium complexes areof considerable relevance, because of their potentialapplications in cata lysis a s well as in functionalmaterials.138,139 Typical examples are sol-gel-pro-cessed η6-arene r ut hen ium(II) complexes coordinat edwith functionalized pyridine. 4-Vinylpyridine and[RuCl2( p-Me2CH C6H 4Me)]2 served as st arting mat eri-als for the access to the catalyst precursor. 140,141 Amixture of hybrid polymers was prepared by freeradical polymerization of the precursor species andthe hydrolysis product of (3-meth acryloxypropyl)-tr imethoxysilane (MEMOS). The polymers were t henco-condensed with TEOS, Ti(OiP r )4, Zr(On P r )4, a n d

Al(OsecBu )3 i n t h e p r e se n ce of a n a ci d t o a ffor d24 a-d (Schem e 18),14 1 which were characterized byFT-IR spectroscopy. The different meta ls incorpo-rated in the polymer function as network builders.When catalysts 24 a-d were checked for the cycliza-

tion of ( Z )-3-methylpent-2-en-4-yn-1-ol (eq 14; Table10), th ey showed a r educed activity compar ed to th ehomogeneous congener, but they offered the advan-tage of a heterogeneous catalyst. Further details aresummarized in Table 10.

An ot h e r i m por t a n t con t r i bu t i on i s t h e s ol-ge ls yn t h e s is of t h e r u t h e n i u m (I I ) com p le xe s 25a ,bcontaining a polysiloxane-boun d imidazole ligand(Schem e 19).142 3-(4,5-Dihydroimidazol)-1-yl-propyl-trieth oxysilan e was employed as a coordinating a gentwith (η6-ar ene)ruth enium(II) complexes to synt hesizethe catalyst precursor, which was polycondensed orpoly-co-condensed with TEOS to afford 25 a ,b . Meth-ods for chara cterization were FT-IR spectroscopy,

T a b le 1 0 . P e r f o r m a n c e o f C a t a l y s t s 2 4 a-d a n d 2 5 a , b i n t h e C y c l i z a t i o n o f ( Z)-3-Methylpent-2-en-4-yn-1-ol( E q u a t i o n 1 4 ) a

ca t a lys t t im e (h ) y ie ld (%) t im e (h ) yi el d (%) T OF (h-1) r ef com m en t s

b 1.5 77 6 80 141 ca t a lyst s 24 a-d were reused, but no specific24 a 15 63 72 88 da t a wer e pr esen t ed24 b 15 27 72 8524 c 15 20 70 6524 d 15 66 70 80

25 a 45-89 10-96 142 ca ta lyst s 25 a ,b were reused 5 times, but no specific

25 b 76-

92 64-

230 da t a wer e pr esen t eda Reaction condit ions: 0.1 g of catalyst , 100 mg of ( Z )-3-methylpent-2-en-4-yn-1-ol, T ) 80 °C. b Homogeneous reaction with

[Ru(η6-Me 2CH C6H 4Me - p)(4-ethenylpyridine)Cl2].

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differential thermal analysis (DTA), TGA analysis,

NMR, Raman spectroscopy, and BET measurement s.Their catalytic activity was tested for the cyclizationof ( Z )-3-meth ylpent-2-en-4-yn-1-ol to 2,3-dimet hyl-furan (eq 14). At room temperature i t was low butraised when t he tempera tur e was increased to 80 °C.The catalysts were recovered by microporous filtra-tion and reused five times without significant loss of activity or selectivity. The kind of preparation andt h e a m ou n t of e m p loy ed T E O S a l so a ffe ct e d t h ecat alytic property. In most cases th e performa nce of 25 b i s s u p e r i o r t o t h a t o f 25 a , l e a d i n g t o h i g h e rproduct yields and tu rnover nu mbers (see Table 10).This effect is traced back to the higher surface areaof 25b .

E. Cobalt, Rhodium, and Iridium Complexes

1. Cobalt Complexes

An attractive topic is the nondestructive immobi-lization of cobalt Schiff base complexes (Scheme20).143 As an example, in a first step a cobalt (salen)compound was obtained by reaction of cobalt acetatewith a solut ion of aminopropyltrieth oxysilane andsalicylaldehyde. Then the silyl-modified salen com-plex was poly-co-condensed with TEOS to give 26 .Using cobalt (salen) as starting material in the sol-gel process n ot only avoided t he reverse Schiff basereaction but also accelerated the gelation rate due

to autocatalysis. The polysiloxane 26 was chara cter-ized by FT-IR, UV-vis, and XPS spectroscopy, lasera b la t ion I CP -M S, E P R , B E T, a n d T GA s t u die s.Oxidation of eth ylbenzene t o acetophenone (eq 15a;Table 11) by 26 was carr ied out in DMSO or DMF a t130 °C under an oxygen atmosphere in the presenceof pyridine and potassium tert -butoxide. After 72 h,

th e convers ion a chieved a value of 99.9%. Dur ing th ecatalytic reaction the rate of conversion decreased,which was attributed to a competitive adsorption of the reactants and products at the active sites. Ethyl-benzene oxidation could be conducted without anysolvent un der oxygen. Removal of water produceddur ing th e rea ction was necessary. Leaching of cobaltanalyzed with ICP-AES in th e fil trate amounted t o<0.1 wt %.

In another investigation i t was highlighted thatimmobilized cobalt (III) complexes a ct a s oxidat ioncatalysts (Scheme 21).144 Cyanoethylsilica was formed

b y a s o l-gel reaction of TEOS and cyanoethyltri-

T a b le 1 1 . P e r f o rm a n c e o f C a t a l y s t s 2 6 a n d 2 7 i n t h e O x i d a t i o n o f A lk y l b e n z e n e s

selectivity (%)

ca t alys t eq t im e (h ) yielda (%) r a t eb -onec -old r ef com m en t s

26 e 15a 1.5 6.4 0.35 71.9 28.1 143 n o r ecyclin g t est s wer e r epor t ed24 70.4 0.24 75.2 8.048 89.9 0.15 77.0 4.272 99.9 0.11 78.7 2.3

27 f 15a 22 76 n a g 9 4 1 44 ca t alys t w as r eu sed by a dd in g a s ma ll a m ou n t of p yr id in e,15b 22 25 100h but no detailed data were presented

15c 22 6

a Total yields of products. b Rate conversion (mol L-1 h-1). c Acetophenone. d Methylphenylmethanol. e Reaction conditions: 0.6g of catalyst, 40 g of ethylbenzene, T ) 130 °C. f Reaction conditions: 0.8 g of cata lyst, 400 mL of substrat e, stirring ra te at 700rpm, air stream ra te 400 mL min-1, T ) 130 °C for eq 15a,b, T ) 100 °C for eq 15c. g Not available. h The product is 4-chlorobenzoicacid.

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ethoxysilane in water in the presence of N -dodecyl-a m in e a s t e m pla t e . T r ea t m e n t of t h e p olym e r icmaterial with aqueous sulfuric acid transformed thecyano group to a carboxylic acid function. Complex-ation of cobalt to the modified matrix proceeded viarea ction of the polymer wit h Co(NO3)2‚6H 2O, sodiumacetate, pyridine, and hydrogen peroxide in waterun der r eflux. Atomic absorpt ion a na lysis, optical an dscan ning electron microscopy, BE T, powder X-ra y

diffraction, F T-IR, and U V-vis studies together witha comparison of the corresponding homogeneouscom p le x a l low ed t h e ch a r a c t er i za t i on of t h e i m -mobilized catalyst 27 containing a complicated cobaltspecies with two pyridine and two carboxylato ligandsper cobalt atom. Immobilized 27 was applied in t heaerial oxidation of neat ethylbenezene, chlorotoluen e,and toluene (eq 15a-c). After 22 h , 76% of eth ylben-

zene was oxidized with a selectivity to acetophenoneof 94% (Table 11). The rate of oxidation was almostlinear up to 70% conversion. U nder the same condi-tions 25% of pure 4-chlorobenzoic acid was isolated.Toluene was also oxidized to benzoic acid at 100 °Cin t he presence of 1% benzaldehyde a s a promoter,but th e yield was only 6% after 22 h . No leaching of cobalt took place in the above-mentioned reactionsas detected by atomic absorption spectroscopy. How-ever, pyridine was completely lost during the reac-tion, which resu lted in a failur e of repeat ed use. Upontreatment of the recovered catalyst with pyridine, the

cata lytic activity r eturned to close to i ts originalvalue.

Cobalt phthalocyanine complexes can also be an-chored to titanium dioxide (Scheme 22). 14 5 Cobalt-(II) tetrasulfonylphthalocyanine and cobalt(II) tetra-(chlorosulfonyl)phtha locyan ine were co-condensedwith titanium alkoxides upon sol-gel procedures toform 28 a-c a n d 29 a-d . S u lfi de a n d e t h a n e t h iolliquid-phase oxidations using the above-mentionedcatalysts were investigated in the presence of oxygen(eq 16; Table 12). In the oxidation of Na 2S, the mainproduct was elemental su lfur together with smallquantities of thiosulfate. Remarkably, the catalyticactivity did not change dur ing repeated u se. Catalyst

28 a was t he m ost active for sodium sulfide oxidation,the rate of th e conversion was 35.3 mol(S2-)/mol-(catalyst)‚min. In the oxidation of ethanethiol 28 a

a n d 29d showed the h ighest activities. They were a llstable in the reaction media, and no leaching of theactive component was established by checking t heactivity of the filtrate.

2. Rhodium Complexes

Rhodium complexes incorporated into interphasesystems can be arranged according to T-silyl-modifiedphosphorus, cyclopentadienyl, nitrogen, sulfur, andoxygen ligands.

a. Phosphorus Ligands. Brzezinska et al. describedthe application of polymeric siloxyphosphine rhodiumcomplexes as cata lysts for the hydrogenat ion of olefins, in particular, styrene. Hydrolysis of rhodium

complexes with the phosphines Cl3Si(CH 2)nP P h 2 (n) 2, 8) either with trichloromethylsilane or in thepresence of excess ligands afforded 30 a-c (Scheme23).146 The authors noticed that these materials wereeffective in the hydrogenation of olefins, but someactivity got lost on recycling (eq 17; Table 13).147

Polymer 30 c lost half of its activity after five cyclesand wa s the best candidate. The aut hors noticed tha tthe per formance and the activity were always higherfor catalysts conta ining a longer spacer, which isconsistent with the interphase concept.

Compared to Rh(CO)Cl[PPh 2CH 2CH 2Si(OEt)3]2, thesol-gel-processed rhodium complexes 31a ,b exhib-ited higher stability and better catalytic properties

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in the hydrosilylation of 1-hexene (Scheme 24; eq18).148 There is no significant loss of rh odium inrepeated uses. Poly- and oligosilanes from hydrosi-

lanes wer e also formed by 31 a ,b . Interestingly, 31 a ,bcatalyzed the CO oxidation and the water-gas shiftreaction, wherea s t he homogeneous complex Rh(CO)-Cl(PR3)2 normally does not work under the selectedreaction conditions.

I t s h ou l d b e m e n t ion e d t h a t Av n ir , B l u m , a n dSchu man n h ave carried out several investigations int h e h e t e r og en i za t i on of s ol u bl e t r a n s i t ion m e t a lcatalysts by employing the sol-gel process.75,87,149-152

A remarkable part of their work is devoted to theentrapment of catalytically active complexes intoplain SiO2 sol-gel mat rices. Cat alysts 32a ,b wereobtained by poly-co-condensat ion of TEOS with[(EtO)3SiCH 2CH 2P P h 2]4Rh 2(CO)2( µ-pz)2 an d [(Et O)3-

SiCH 2CH 2P P h 2]4Rh 2(CO)2( µ-Cl)2, respectively, ands h ow ed h i gh e r t h e r m a l s t a b il it y (S ch e m e 2 5).153

However, the ability to isomerize allylbenzene wasnot satisfying compared to physically encapsulatedcomplexes (eq 19; Table 13).

As already men tioned due t o its broad a vailability,carbon dioxide was intr oduced as a st ar ting mat erialfor the synthesis of valuable chemicals. Transferringi t i n t o D M F a n d m e t h y l f o r m a t e i s a n i n t e r e s t i n groute. To find an efficient and reusable catalyst fort h i s t r a n s for m a t i on , K r oe ch e r a n d B a ik e r e t a l .employed sol-gel-derived silica-anchored rhodium,

T a b le 1 2 . P e r f o r m a n c e o f C a t a l y s t s 2 8 a-c a n d 2 9 a-d i n t h e S u l f i d e a n d E t h a n e t h i o l O x i d a t i o n ( D a t a f r o mR e f e r e n c e 1 4 5 ) a

ca ta lyst t ype of ca ta lysis eq t im eb (min) V m c (mL/min) V (O2)d (m L) T OF e comments

28 a su lfide oxida t ion 16a 9 16.4 35.3 secon d r u n wit h fr esh ca t a lyst in 1:128 b 16.5 19.9 16.2 r a t io sh owed n o decr ea se in a ct ivit y,28 c 24 19.6 11.3 bu t n o fu r t h er specific da t a wer e29 a 18.5 18.7 10.6 pr esen t ed29 b 18 27.1 9.929 c 19 16.2 8.529 d 31 17.8 7.1

28 a et h a n et h iol oxida t ion 16b 2.1 80.3 >3 runs for each catalyst, data represent29 a 1.1 15.4 a ver a ge r esu lt s29 b 2.2 31.429 d 2.2 84

f 0.25 3.53g 0.25 3.52h 1.7 33.1

a Reaction condit ion for eq 16a : 25 °C, pH 7.3, [Na 2S] ) 5 × 10-2 M, molar rat io [Na 2S]/[catalyst] ) 110. Reaction conditionsfor eq 16b: 25 °C, pH 11, [eth an eth iol] ) 7.5 × 10-2 M, molar ratio [ethanethiol]/[catalyst] ) 110. b Time for complete oxidation.c Amount of oxygen consu med. d Maximum oxygen consum ption per m inute. e For eq 16a [mol(S 2-)/mol(catalyst) min]; for eq 16b[mol(HS)/mol(cat alyst) min ]. f Without catalyst. g Filtrate after four runs of 28 a , molar rat io [etha neth iol]/[catalyst] ) 300. h CoPc(4-SO 2X)4 on activated charcoal.

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iridium, palladium, platinum, and ruthenium com-plexes for the solvent-free synth esis of DMF fromcar bon dioxide, hydrogen, a nd dimethylamine und ersupercritical conditions.134,135 Textural and structuralproperties of the hybrid gels were characterized bymeans of NMR spectroscopy, EXAFS, XRD, TEM,and BET measurements. In the case of the rhodiumspecies 33 only low activity was detected and thecatalyst decomposed under the reaction conditions(Scheme 26; Table 13; eq 13a).134

To study the accessibili ty of reactive centers ininterphase catalysts, organometallic model reactionsand cat alytic investigations of polysiloxane-bound

(ether-phosphine)rhodium(I) complexes 34 a ,b havebeen carried out (Scheme 27).154,155 Treatment of thetrimethoxysilyl-functionalized ether-phosphine ligandCyP(CH 2CH 2OC H 3)(CH 2)3Si(OMe)3 w it h [ µ-ClRh-(COE)2]2 afforded ClRh(P∩O)(P∼O), which was fur-ther reacted with the co-condensation agent MeSi-(OMe)2(CH 2)6(MeO)2SiMe to give the desired materials34 a ,b . Complexes 34 a ,b are efficient catalysts in thehydrogenation of diphenylacetylene in organic sol-vents under mild conditions, typically at 303 K and5 b a r of h y dr og en p r e s su r e (e q 2 0; T a b l e 1 4 ).15 5

T a b le 1 3 . P e r f o r m a n c e o f C a t a l y s t s 3 0 a-c, 32a,b, and 33

conversion (%)

catalysttype of

ca ta lysis eq r at eat ot al

yieldss a t u r a t e d

productisomerized

p rod uct T ON b r ef com m en t s

30 a hydrogenationc 17a 8.1 8.1 146 30 a-c were recycled; 30 c lost half of its activity17b 88.5 88.5 a ft er 5 cycles a n d wa s t h e best ca ndida t e17c 86.4 46.3 40.1

8 88.8 42.9 45.930 b 17a n ad

30 c 17a n a

e isomerization f 19 3.44 98 1079 153 n o r ecycling t est s wer e r epor t ed for 32 a ,b32 a 0.55 28 187g 0.33 43 27632 b 0.71 32 734

33 h 13a 4 530 134 decom posed u n der t h e r ea ct ion con dit ions

a I nitia l r a te in m m ol m in-1. b Turnover number [mol (prod.)/mol(cat.)]. c Reaction conditions: 3 m mol of olefin, benzene a ssolvent , p[H 2] ) 1 atm, 1.33 × 10-2 mmol of cata lyst, T ) 25 °C, t ) 23h. d Not available. e Physical entrapment of the reactivemetal complex in 32 a . f Reaction condit ions: T ) 120 °C, 0.05 mmol of catalyst, 2 mL of allylbenzene. g Physical entrapment of the reactive metal complex in 32 b . h Synthesis of N , N -dimethylformamide, reaction conditions: 500 mL stainless steel autoclave;n [Me 2NH ] ) 0.71 mol; p[H 2] ) 8.5 MPa; p[CO 2] ) 13.0 MPa; T ) 373 K; t ) 15 h; stirring rate ) 300 min-1; n[catalyst] ) 5 × 10-5

mol (Rh).

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Fa vora bly the selectivity toward cis-stilbene was high(usually 98%), as long as the conversion of tolan didnot exceed 95%. When the cata lyst was recoveredfrom the reaction mixture and used again, hydroge-nation was observed with identical selectivity andonly slightly sm aller conversions. This finding de-

pends m ar kedly on the am oun t of th e co-condensationagent and on the polarity of the solvent. Raising therat io of th e co-condensat ion agent MeSi(OMe)2-(CH 2)6(MeO)2SiMe from 2:1 (catalyst 34 a ) t o 8 : 1(catalyst 34b ) l e d t o a n i n cr e a s e o f t h e t u r n o ve rfrequency (see Table 14). It can be seen that turnovernumbers and frequencies rise with increasing solventpolarity. The lower concentration of reactive centersin 34 a ,b prevented a dimerization of the catalysts,which resulted in a higher a ctivity compar ed to th eirmonomeric congener. To study leaching effects, thereaction solutions of four consecutive hydrogenationrun s were separ ated from th e polymer, concentrat ed,and subjected to catalysis. No hydrogenation of tolan

took place. To further check the accessibility of thereactive cent ers, r eactions of 34 a in solid/gaseous andsolid/liquid int erph ases with sma ll molecules such asCO, CH 2dCH 2, CS 2, a n d H 2 /pyridine were also in-vestigat ed. All reactions proceeded qua ntita tively,showing that the coordination centers were readily

accessible for the mentioned substrates, which is avaluable precondition for catalysis.15 5

To achieve recyclable catalysts in the hydroformy-l a t ion of ol efi n s , t h e p r e pa r a t i on of t h e s ol-gel-processed rhodium complexes 35a-c was described(Scheme 28).156 The bifun ctiona l co-condensa tionagent (MeO)3Si(CH 2)6Si(OMe)3 and a carbonylhydri-do(trisphosphine)rhodium complex with T-silyl-func-tionalized diphenyl phosphine l igands containingthree- or six-membered hydrocarbon spacers wereemployed as starting materials. The polymer-boundcomplexes 35 a-c a r e e xce ll en t ca t a l ys t s for t h ehydroformylation of 1-hexene in th e pr esence of awide variety of solvents (eq 21; Table 15). Polar

T a b le 1 4 . P e r f o rm a n c e o f C a t a l y s t s 3 4a , b i n t h e H y d r o g e n a t i o n o f T o l a n ( E q u a t i o n 2 0 ) ( D a t a f ro m R e f e r e n c e 1 5 5)

catalystreaction

condit ions conversion (%) cis -stilbene (%) trans-stilbene (%) bibenzyl (%) TONa TO F b comments

34 a c 61.9 99.0 1.0 96 288 ca t a lyst 34 a was reusedd 88.3 97.6 1.4 1.0 137 411 in 4 cyclese 85 96.8 2.2 1.0 132 395 f 89.9 98.3 1.3 0.4 899 449tolueneg 19.9 95.4 4.6 31 93TH F g 34.2 98.6 1.1 0.3 53 159ethanolg 75.8 99.3 0.7 117 352

methanol g 94.3 96.1 3.3 0.6 146 438cycle 1h 92.1 97.8 1.8 0.4 143 190cycle 4h 82.5 98.2 1.5 0.3 128 171

34 b c 74.7 99.2 0.7 0.1 116 347

a Turnover number [mol(substrate)/mol(catalyst)]. b Turnover frequency [mol(substrate)/mol(catalyst) h]. c Standard reactionconditions: T ) 303 K, t ) 20 min, 5 bar of H 2, 30 mL of methanol/toluene ) 1:1, tolan/rhodium ) 155:1. d See footn ote c except p[H 2] ) 40 ba r . e See footnote c except T ) 333 K. f See footn ote c except tolan/rhodium ) 1000:1, t ) 120 min. g See footnote cexcept using different solvent. h See footnote c except t ) 45 min.

T a b le 1 5 . P e r f o r m a n c e o f C a t a l y s t s 3 5 a-c a n d 3 6 a-d i n t h e H y d r o f o r m y l a t i o n o f A l k e n e s

ca ta lyst eq solven tconversion

(%)isomeri-

zation (%)hydroformyl-

ation (%) n /(n + is o) TON a TO F b r ef com m en t s

35 a 21 a c t olu en e 52.2 31.8 67.0 73.0 521 156 n o r ecyclin g t est s wer eTH F 52.5 19.3 79.7 75.0 525 r epor t eda cet on e 38.9 10.2 88.1 77.5 389

ethanold 49.2 19.4 79.6 71.4 492et h a n ol 58.6 12.7 85.0 84.7 586ethanole 77.2 67.3 12.1 96.9 772m et h a n ol 85.5 19.5 80.5 76.7 854wa t er 50.2 20.6 77.1 69.7 52

35 b et h a n ol 41.0 5.0 92.4 93.4 41035 c et h a n ol 29.6 6.2 90.9 86.4 29635 c 21 bc et h a n ol 29.0 3.4 92.0 84 29035 c 21 cc et h a n ol 20.6 2.7 96.1 84.9 206

f 21 a g t olu en e 100 17.4 82.6 0.57 13216 777 157 n o r ecyclin g t est s wer e36 a 100 33.7 66.3 0.67 10608 624 pr esen t ed36 b 100 20.9 79.1 0.58 12656 73436 c 100 5.3 94.7 0.53 15152 89136 d 100 7.5 92.5 0.53 14800 870 f dich lor om et h a n e 66.5 27.7 72.3 0.69 7496 45136 a 88.9 49.5 50.5 0.72 7184 42336 b 69.3 30.7 69.3 0.69 7680 451

36 c 100 13.0 87.0 0.58 13920 81936 d 100 23.9 76.1 0.65 12176 716

a Turnover numbers for catalysts 35 a-c [mol(substrate)/mol(catalyst)]; for catalysts 36 a-d [mol(ald.)/mol(catalyst)]. b Turnoverfrequencies [mol(ald.)/mol(catalyst) h]. c Reaction conditions except indicated: 10 bar of CO, 10 bar of H2, 20 mmol of alkene, 20 µmol of catalyst, 20 mL of solvent, T ) 373 K, t ) 150 min. d T ) 353 K. e T ) 393 K. f Homogeneous reaction with monomericmetal complex. g Reaction condit ions: 30 bar of CO, 30 bar of H2, 10 mL (80 mmol) of 1-hexene, 5 µmol of catalyst, T ) 70 °C, t ) 1020 min.


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s ol ve n t s s u ch a s m e t h a n ol a ffor d e d t h e h i gh e s tactivities, whereas t he selectivity t owar d t he forma-tion of 1-hept an al was optimal in solvents of mediumpolarity such as ethanol or acetone. Application of materials with non-coordinated l igands raised theselectivity toward hydroformylation up to 92% andt h e n/ iso r a t i o t o 1 4 :1 w it h a n a v er a g e t u r n o ve rfrequency of 164 mol(sub) m ol(cat )-1 h-1. D u e t olonger spacers, 35 c was expected to exhibit a highermobility and thus an improved selectivity. However,t h e n / n + is o rat io and t urn over frequencies obtainedwith 35 c were inferior to those observed with 35 b(see Table 15). The behavior was attributed to the

lower actual concentr ation (millimoles of P pervolume unit of swollen catalyst bead) of phosphinefun ctions in 35 c (constan t P/Rh) in the swollenpolymer. Olefins higher tha n 1-hexene were a lsohydroformylated with 35 c , a n d s im ila r t u r n ove rfrequencies an d selectivities wer e obtained. 31P C P / MAS and (1H , 31P) wide-line separ at ion (WISE) NMRspectr oscopic investigations gave an insight int o thedynamic behavior and mobility of these materials.

Other examples are the hybrid polymers 36 a-d(Scheme 29).157 A novel T-silyl-fun ctiona lized tri-phenylphosphine ligand had to be prepared to intro-d u ce t h e s p a ce r i n t h e p a r a -p os it i on of o n ly on ephenyl ring, which reacted with a rhodium precursor

to give the catalytically active T-silyl-functionalizedrh odium (I) compound ClRh(CO)[PP h 2C6H 4NHCONH-(CH 2)3Si(OEt)3]2. The m odified complex wa s t hen co-con d en s ed w it h (M eO )2MeSi(CH 2)6SiMe(OMe)2,(MeO)2MeSi(CH 2)3(1,4-C6H 4)(CH 2)3SiMe(OMe)2,(MeO)3Si(CH 2)6Si(OMe)3, a n d (M eO )3Si(CH 2)3(1,4-C6H 4)(CH 2)3Si(OMe)3. Stru ctur al an d mobility inves-t i ga t i on s of t h e s e n ov el s t a t i on a r y p h a s e s w er ecarried out by multinuclear solid-state NMR spec-troscopy (13C, 29Si, 31P). Complexes 36 a-d weresuccessfully employed in th e hydroformylation of 1-hexene with good tur nover nu mbers (eq 21; Table15). The cata lytic activity mainly depends on themobility of th e ma trices and the reactive center s. No

leaching of th e tra nsition meta l complexes dur ing thereactions was observed by atomic absorption spec-troscopy.

O f p a r t i cu l a r i n t er e s t a r e t h e s il ica -s u p p or t e d ,switchable, and recyclable hydroformylation/hydro-genation catalysts 37 a ,b (Scheme 30).158 They wereobtained from [Rh(A)CO]+ (A ) the correspondingligand system in Scheme 30) and TMOS and char-acterized by means of 31P and 29Si CP/MAS NMR, FT-

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IR, a nd X-ray photoelectron spectroscopy. In depen-dently, complexes 37a ,b a n d t h e s a me ca t a lys tsupported on commercial silica were applied in thehydroformylation of 1-octene (eq 22a). It was shown

t h a t t h e d iffe r en t p r e pa r a t i on p r oce d u r es l ed t odifferent performan ces of t he catalysts, which aresummarized in Table 16. Supported 37 a showed anoverall selectivity for l inear aldehydes of 94.6%(linear t o bra nched aldehyde ra tio of 65, whereas t ha tfor 37 b is only 2.4). The authors attributed the high

selectivity of 37 a to its larger P-Rh-P bite an gel of 108° compar ed t o 93° for 37 b . Recycling capabilitiesof 37 a ,b were uncovered from a series of consecutiveruns. Selectivities remained high, and no leachingw a s fou n d b y r h od iu m e le m en t a l a n a l ys is of t h eproduct. Also, 37 a w a s r e m a r k a b ly s t a b le u n d e rcatalytic conditions and worked for more than twoweeks without any loss of activity. From detailedstudies it was evaluat ed th at 1-nonanol, obtained viathe hydrogenat ion of the corresponding aldehyde,was formed as a n u nexpected byproduct (3.6% at 20%conversion). Under sta nda rd hydroformylation condi-tions, 37 a and its hydrido species HRh(A)(CO)2

coexisted on the support. This dual system acted as

a hydroformylation/hydrogenat ion sequence cata lyst,giving selectively 1-nonanol from 1-octene; ulti-mately, 98% of 1-octene was converted to mainly1-nonana l and 97% of the nonan al was hydrogenatedto 1-nonanol (eq 22b). Addition of 1-propanol to ther e a ct i on m i xt u r e ch a n g e d t h e s ys t e m t o a h y d r o-formylation catalyst, which produces 1-nonanal withan overall selectivity of 93%, a nd completely sup-pressed the reduction reaction. If the atmosphere was

changed from CO/H 2 t o H 2, the system switched tothe hydrogenation mode, which showed a clean andcomplete hydrogenation of 1-octene and 1-nonanalwithin 24 h. Active 37 a was recycled, and the systemcou l d b e r e ve r s ib ly s w it ch e d b et w ee n t h e t h r e e“catalyst modes”, hydroformylat ion/hydrogenat ion,hydroformylation, and hydrogenation, completelyretaining the excellent performance in each mode (seee n t r ie s 1 4-1 8 i n T a ble 1 6). W it h r e ga r d t o t h esurface-supported catalysts with the same reactivecenter, 37a showed a good recoverability and easycontrol in its cat alytic performan ce.

b. Cyclopentadienyl-Derived Ligands. Cyclopenta-dienylmeta l complexes have experienced wide a p-

p li ca t i on s i n h om og en e ou s a n d h e t e r og en e ou scatalysis;93,159-162 however, polysiloxane-bound con-geners were reported only recently.8,163,164 Schumanne t a l. p r ep a r ed t h r e e s ol-gel-processed rhodiumcomplexes 38 a-c (Schem e 31).165 With C5H 4CH 2CH 2-

Si(OMe)3 as well a s two different precursors [Rh-(CO)2Cl]2 and [Rh(COD)Cl]2 a s s t a r t i n g m a t e r i a l s ,T-silyl-functiona lized cyclopenta dienyl rh odium(I)complexes were attained. The monomeric precursorswere t hen poly-co-condensed with TEOS to give thedesired hybrid polymers 38 a-c , which catalyzed thehydrogenation of alkenes, in aromatic as well as inaliphatic hydrocarbons (eq 17b; Table 17). I t wasestablished that the reaction rates with 38 a-c wereeither the same or somewhat lower than those of the

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soluble cata lysts. However, they were air sta ble andrecyclable in nu merous r un s an d were leaching-proof.

On the contra ry, the corresponding homogeneouscatalysts could be handled only with exclusion of airand in a single catalytic run. Th e activities of 38 a-cwere super ior to th ose of physically entra pped r hod-ium complexes, which deactivated gradu ally in con-secutive run s because either t he pores conta ining themetal nuclei were blocked or the complexes werep a r t i a ll y r e d u ce d t o m e t a ll ic r h o di u m . C a t a l ys t s38 a ,c a l s o p r o m ot e d t h e h y d r og en a t i on of n i t r ocompounds (eq 23; Table 17).

An ot h e r e xa m p l e of a s ol-gel-processed Cp-Rhcomplexes 39 was pr esented by Cermak et a l. (Scheme32).166 The pr ecur sor complex was obtained from th ecorresponding alkoxysilyl-substituted tetr amet hyl-

cyclopenta diene an d chloro(1,5-cyclooctadien e)rhod-ium(I) dimers. The resulting complexes were then

included as components in the sol-

gel preparationsof polysiloxan es. Ca ta lysts 39 a ,b were char acterizedb y B E T a n d 13C CP/MAS NMR spectroscopy. Thehydrogenation of crotonic a cid in water by 39a ,bshowed a moderate activity up to 1.6 mol (mol of Rh )-1 m in-1 (eq 24; Table 17). The TOFs did notchange dramatically with the substrate/catalyst ratio,and turnover numbers were improved by increasingthe substrate/catalyst ratio (Table 17). Analysis byreversed-phase H PLC r evealed t hat the hydrogena-tion produced butyric acid as the only product.

c. Nitrogen Ligands. O t h e r t h a n i n t er p h a s e ca t a -lysts with phosphorus ligands, those with nitrogen-con t a i n i n g r h o di u m (I ) com p le xe s a r e r e la t i ve ly

T a b le 1 6 . P e r f o r m a n c e o f C a t a l y s t s 3 7 a ,b i n t h e H y d r o f o r m y l a ti o n / Hy d r o g e n a t i o n o f 1 -O c t e n e ( E q u a t i o n 2 2 ) ( D a t af r o m R e f e r e n c e 1 5 8)

n o.catalyst

(cycle)reaction

conditionsat i me

(h )conversion

(%) TOF bn -alde-

hydeis o-alde-

hyderat i o

(n / is o) 1-alcohol

octeneisomers

and oct ane(%) com m en t s

1 37 a (1) A 2 20 18 94.6 1.5 65 3.6 0.2 37 a was recycled and t he2 37 a (4) 2 12 12 89.6 1.6 62 8.8 0 syst em cou ld be3 37 a (1) 18 38 23 61.0 4.1 2 2 29.6 5.3 r ever sibly swit ch ed4 37 a (2) 18 30 17 7 7.9 3.7 25 15.1 3.43 bet ween t h e t h r ee5 37 a (1) B 24 69 35c 92.8 3.0 32 2.5 1.7 “ca t a lyst m odes”6 37 a (8) 24 63 33c 95.0 2.6 37 0.5 2.0 h ydr ofor myla tion /h ydr ogen a t ion ,7 37 b 24 72 119c 70.0 28.9 2.4 0.1 1.0 h ydr ofor m yla t ion , a n d8 H Md 24 19 283c 93.3 2.9 32 0 3.7 h ydr ogen a t ion9 P E e 24 64 175c 26.3 16.3 1.6 0 57.410 SC1 (1) f A 22 37 13 90.7 2.6 37 5.1 1.611 SC1 (3) f 72 61 8 79.9 3.5 27 13.2 3.412 SC2 (1)g 23 24 8 85.5 4.5 19 0 9.913 SC2 (4)g 72 44 5 84.8 5.4 16 0 9.814 37 a A 172 97 75h 18.5 3.6 23 66.7 11.2i

15 37 a A j 24 100 100h 0 0 100 100i

16 37 a A 68 60 16h 65.2 4.5 18 13.7 16.6i

17 37 a A j 2 98 10h 0 0 9.7 98i

18 37 a B 96 96 0h 90.7 5.1 18 0 4.3i

a Reaction conditions: (A) p(CO/H 2) (1:1) ) 50 ba r , T ) 80 °C, ligand/Rh ) 10, substra te/Rh ) 637:1, Rh content ) 1 × 10-5

mol, 1 mL of octene, 13 mL of toluene, 1 m L of decane as interna l reference; (B) 1 mL of 1-propanol was added t o the catalystmixtu re of A. b Average tu rn over frequencies were calculated as [mol(product)/mol(cat alyst)h]. c Initial t urn over frequencies were

calculated at 10-20% conversion. d Homogeneous reaction with monomeric complex in Scheme 30. e P hysica l e ntr a pm e nt of [Rh(acac)(CO)2] without T-silyl-functionalized diphosphine in polycondensed TMOS. f Silica-supported catalyst: the correspondingligand in 37 a was covalently tethered to silica and then modified with dimethoxydimethylsilane, subsequently reacted with[Rh(acac)(CO) 2]. g Silica-supported catalyst: the corresponding ligand in 37 a was reacted with [Rh(acac)(CO)2], then covalentlytethered to silica. h Conversion of aldehyde (%). i Yield of octane (%). j Addition of 1 mL of 1-nonanal and p[H 2] ) 50 bar insteadof p[CO/H 2] ) 50 ba r .

T a b le 1 7 . P e r f o r m a n c e o f C a t a l y s t s 3 8 a ,b a n d 3 9 a , b i n H y d r o g e n a t i o n s

ca t a lyst eq t im e (h ) yield (%) ca t a lyst eq t im e (h ) yield (%) r ef com m en t s

a 17 bb 3 76 a 23 b 40 46 165 38 a-c were recycled, but no38 a 4 54 38 a 40 10 specific da t a wer e r epor t edc 3 100 d 40 10038 b 4 59 38 c 40 100d 3 10038 c 4 100

ca t a lyst eq e TO F f TO N g r ef com m en t s

39 a 24 h 0.017 1.61 65 166 n o r ecyclin g t est s wer e39 b 0.025 0.23 13 ca r r ied ou t

0.050 0.14 140.098 0.14 9

a Homogeneous reaction wit h T-silyl-functionalized rh odium complex in 38 a . b Reaction conditions: 2.5 mmol of substr at e, 6.25× 10-2 mmol of rhodium catalyst, 3 m L of benzene, 14 atm H 2, T ) 80 °C for styrene and 90 °C for nitrobenzene. c Homogeneousreaction with T-silyl-functionalized rhodium complex in 38 b . d Homogeneous reaction with T-silyl-functionalized rhodium complexin 38 c . e Ratio of catalyst/substrate. f In [mol(H 2)/mol(Rh) min]. g In [mol(H 2)/mol(Rh)]. h Reaction conditions: substrate concentra-tion 0.25 M, 60 °C, p(H 2) ) 127.7 kPa.


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r a r e .167,168 Capka and Schubert et al. reported on theapplication of sol-gel-processed rh odium(I) com-plexes with pyridine-cont aining ligan ds.168 With 2-(2-trimethoxysilylethyl)pyridine (TMEP) as start ingmaterial , the hybrid catalysts 40 a ,b were preparedby two rout es: (i) treat ment of [Rh(CO)2Cl]2 with apolycondensate prepared by hydrolysis and conden-sation of a m ixture of TMEP an d TEOS an d (ii) sol-gel processing of TEOS with a rhodium(I) complexcoordinated to TMEP (Scheme 33). With 40 a ,b t h e

methan ol carbonylation was investigated (eq 25).Although the r eaction r ates (the highest r ate wa s 1.3

× 10-4

mol s-1

g(Rh)-1

) were lower t han th ose of thehomogeneous an alogues, 40 b displayed good catalyticperformances. Compared to the surface-supportedcatalysts prepared from the same monomeric rhod-ium complex and commercial silica, the stability of 40 a ,b was m uch better according to time-dependentmeasurements of the rhodium concentration in theoutlet of the plug reactor.168

New a nd diverse selective cata lytic mat erials ar isefrom the sol-gel route to hybrid organic-inorganicsolids. Examples are stud ies of mater ials containingchiral diamine ligands.167 Catalysts 41 a n d 42 wereprepared by reaction of silylated amines with [Rh-(COD)Cl]2 i n e t h a n ol , a n d t h e ob t a in e d p r e cu r s or

materials were poly-co-condensed with TEOS withoutany catalyst (Scheme 34). They were characterized

by elemental analysis, UV-vis, multinuclear solid-state N MR spectra, and BET measurements. Subse-quently, supported 41 a n d 42 were applied as cata-lysts in the asymmetric hydride transfer reductionof acetophenone a nd o-methoxyacetophenone (eq 26;Table 18). The ee values were higher compared tothose found for the soluble catalytic species. A relatedmat erial accessible by immobilization of diamine-

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rhodium complexes at the surface of silica showed amuch lower activity (see Table 18).

By employing primary amines as templates, theimmobilized chiral rhodium complexes 43a-d wereaccessible (Scheme 35).169 The monosilylated deriva-

tive of (1 R ,2 R )-diam inocyclohexan e w as cohydr olyzedwith TEOS un der different conditions. Treatmen t of the immobilized chira l ligands with [Rh(COD)Cl]2

afforded 43a-d . Th e en an tioselective redu ction of acetophenone served to screen th e cata lytic activityof 43 a-d (eq 26a). For 43 a-d , conversions between82 and 97% were achieved after 20-2 4 h a t 8 5 ° C

(Table 18). The alcohol was obtained with low eevalues between 10 and 16%. Conversions and enan-tioselectivities were similar to those observed inhomogeneous phase. The efficiency of 43 a-d is muchhigher than that of 41 a n d 42 , which is attributed tothe h igher porosity of the templat ed mat erials 43 a-d , having higher BET surface areas between 700 and1100 m 2 g-1. Twice-recycled 43 c s h o w e d t h e s a m econversion and enantiomeric excess. EDX analysesof the catalysts collected after the reaction indicatedthat their chemical composition did not change. Itw a s c o n c l u d e d t h a t t h e t e m p l a t e d m a t e r i a l s h a v emuch higher activities and stabili t ies than the re-lated non-templated species.

d . S u l f u r L i g an d s . In the quest for new ancillaryligan ds for cata lytic processes, Tiripicchio et al. wer e

interested in xerogels modified with sulfur ligandsand their rhodium(I) complexes.17 0 The potentiallybidentate benzoylthiourea (EtO)3Si(CH 2)3NHC(S)-NHC(O)Ph was synth esized as a precursor of thefunctionalized xerogels and then sol-gel-processede it h e r w it h T E OS or a l on e . An ch or i n g of [R h -(COD)Cl]2 and [Rh(CO)2Cl]2 with the above-men-tioned xerogels resulted in the hybrid catalysts 44 a ,b(Scheme 36), which were active in the hydroformy-

S c h e m e 3 6

T a b le 1 8 . P e r f o r m a n c e o f C a t a l y s t s 4 1-43

catalysttype of

ca t a lysis eq t im e con ver sion (%) eea (%) r ef com m en t s

b reduction c 26a 5 da ys 95 14 167 n o r ecyclin g t est s wer e41 5 da ys 80 25 r epor t edd 5 da ys 95 2642 5 da ys 75 58e 14 da ys 10 2242 26b 7 da ys 30 80

43 a reduction f 26a 20 h 91 15 169 43 c showed t he sam e activity

43 b 24 h 97 10 in 3 r u n s43 c 18 h 82 1643 c g 24 h 90 1343 d 20 h 87 12h 24 h 10

a Determined u sing HPLC on a chiral colum, (S )-phenyletha nol was obtained with ( R , R )-diamine ligand. b Homogeneous reactionusing [Rh(COD)Cl(L)], where L ) silyldiamine ligand in 41 . c Reaction condit ions: 8.3 mmol of acetophenone or o-methoxyac-etophenone, 20 mL of 2-propanol, 2.5 mm ol of KOH, T ) 25 °C, catalyst containing 1 mol % of rhodium. d Homogeneous reactionusin g [Rh(COD)Cl(L)], wh ere L ) silyldiamine ligand in 42 . e Catalyst prepared by immobilization of diaminerhodium complexin 42 at the surface of silica gel. f Reaction condit ions: 12 mL of 2-propan ol, 2 mmol of acetophenone, 2 mol % (0.04 mmol) of th erhodium cont aining cata lyst, 0.24 mmol of KOH, T ) 85 °C. g Using twice-recycled catalyst 43 c . h Corresponding rhodium catalystprepared from silyldiamine and TEOS in molar ratio 1:20.

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lation of styrene (eq 27). Styrene was qu an titat ivelyconverted into the corr esponding linear a nd bra nchedaldehydes under relatively mild conditions. Afterfiltration, 44 a ,b could be r eused with out a ny loss of a ct i vi t y. I t w a s fou n d t h a t t h e a n ch or e d s p eci esu n d er w en t m a jor ch a n g es d u r in g t h e ca t a ly t iccycles.170 The th iourea to complexes in 44 b appearedto be more sta ble than those in 44 a , and no degrada-tion to oxidized rhodium species was detected by XPS

after three cycles. However, some metal and sulfurleaching occurred in 44b as indicated by EDX mea-surements, but no detailed data were reported.

Recently, Tiripicchio a nchored rh odium(I) com-plexes to thiourea-functionalized xerogels and sils-esquioxanes a nd st udied th e mat rix effects dependen ton the selectivity in the hydroformylation of st y-rene.171 Catalysts 45 a-f were prepa red a ccording toScheme 37 and contain (EtO)3Si(CH 2)3NCS, (EtO)3Si-

(CH 2)3N H 2, P h N H 2, PhNCS, 1,4-diaminobenzene,1,4-phen ylenediisocyan at e, [Rh(COD)Cl]2, [Rh(CO)2-Cl]2, and TEOS as building blocks. As their above-mentioned relatives, 45 a-f were active in the hydro-formylation of styrene at 80 °C and 60 atm with a

1:1 mixture of CO/H 2 (eq 27). Styren e wa s completelyconverted into th e bra nched and l inear aldehyde.Only traces of ethylbenzene were detected, and noalcohols were form ed. However, n o data for TOFs an dT ON s w er e p r e se n t e d. S om e ca t a l ys t s s h ow ed avariat ion in r egioselectivity when applied in consecu-tive cata lytic ru ns. Recovery of 45 a-f was possible,and prior to repeated use, they have been investi-gated by XPS and EDX. A change in regioselectivity

was a scribed to mat rix effects. It was elucidated tha tth e sur face leaching of rh odium complexes forced th ecata lytic process to m ove t o the inside of the mat eri-als.

e. Oxygen Ligand s. With the intention to improvethe stabili ty of heterogenized catalysts to oxygen,Capka et al. designed a rhodium(I) complex boundt o s u p p or t s w it h ox yg en -con t a i n i n g a n c h or i n gligands.172 To solve this problem alkoxysilyl-substi-tuted 2,4-pentanediones of the type (RO)3Si(CH 2)n-CH(COCH 3)2 were coordinated to rhodium(I) com-pounds and immobilized via a sol-gel process (Scheme38). Th e cata lytic activities of 46 a-c were probed for

the hydrogena tion an d hydrosilylation of 1-octene(eqs 8 and 28; Table 19). Notably 46 a-c showedlower activities t ha n th e corresponding silica-sup-ported cata lysts, which is at tributed t o the low meta lloading of 46a an d t he imperfect a ccessibility of thereactive centers in 46b ,c due t o the small pore sizeof the polymers.

3. Iridium Complexes

Becau se of the rema rka ble chemical sta bility of Ti-O-P bonds, Maillet et al. considered phosphonate-based supported iridium(I) complexes as catalysts(Schem e 39).173 Fu nctiona lized 2,2′-bipyridine ligandscont aining two phosphonic acid m oieties were reacted

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with [Ir(COD)Cl]2 in basic media. Co-condensationof the resulting iridium(I) precursor with Ti(O iP r )4

afforded 47 , which wa s applied in th e hydrogenationof acetophenone. Optimizations of reaction conditionsfor the access to 47 were based on pH effects, themolar rat io of titanium/phosphorus, titan ium precur-sors, a nd solvents. The best experiment al conditionswere achieved by the following para meter s: pH 9.4,Ti/P ) 5.6, Ti(OiP r )4 as t i tanium pr ecursor, iP r O H / H 2O as solvent. These boundary conditions resultedin an acetophenone conversion of 94% (eq 29; Table19). This work clearly indicates t ha t reaction condi-t i on s i n t h e p r e pa r a t i on of i n t e r p h a s e ca t a l ys t sgreatly influence their performance.

A furth er example of a polysiloxane-supportedphosphine-iridium complex should be mentioned

and was introduced by Parish et al .174 The T-silyl-

fun ctiona lized ph osphine ligan ds (EtO)3Si(CH 2)nP P h 2

(n ) 2, 3) were co-condensed with TEOS, and the

resulting polymer was characterized by solid-state

NMR spectroscopy. Treat ment of these polymer-

anchored l igands with [Ir(COD)Cl]2 afforded the

hybrid catalysts 48 a ,b (Scheme 40), which showed a

significant activity in the hydrogenation of 1-hexene

(eq 30; Table 19). Although 48 a ,b are subjected to

some decomposition on repeated use, these systems

were still active after 10 cycles.

T a b le 1 9 . P e r f o r m a n c e o f C a t a l y s t s 4 6-48

conversion (%)

catalysttype of

ca ta lysis eqinitialr a t ea catalyst

type of ca ta lysis eq

TO N b

(s-1) 10 m in 120 m in r ef com m en t s

46 a hydrogenation c 8 2.9 46 a hydrosilylation d 28 0 0 0 172 n o r ecyclin g t est s46 b 4. 9 46 b 0 0 246 c 1. 2 46 c 0 0 8e 4. 9 e 0 0 37 f 12.5 f 2.5 45 72g 13.1 g 33 68 81

47 h h ydr ogen a t ion 29 94 173 n o r ecyclin g t est s

48 a i 30 11 174 ca t a lyst s wer e r eu sed, bu t48 b j 31 n o specific da t a wer e

presented

a [Mol(product)/mol(catalyst) min]. b B a sed on initia l r a te s in t he f ir st 5 m in. c Reaction condit ions: 6.4 mmol of 1-octen e, 10 µmol of catalyst (Rh), p[H 2] ) 110 kP a , 3 m L of tolue ne , T ) 65 °C. d Reaction conditions: 10 mmol of 1-octene, 10 m mol of triethoxysilane, 3 × 10-4 mmol of catalyst, T ) 100 °C. e T-silyl-functionalized rh odium complex. f Silica-supported catalyst fromT-silyl-functionalized rh odium complex. g Silica-supported catalyst from T-silyl-functionalized ligand and rhodium complex.h Reaction conditions: 5 mL of meth an ol, 40 bar of H2, Ir/substrat e 2.5%, NaOH /Ir ) 5:1, room t emperatu re, t ) 21 h. i Reactionconditions: 150 mg of catalyst 48 a (16 µmol of Ir), 2 mmol of 1-hexene, 3.5 mL of ethanol. j Reaction conditions: 100 mg of catalyst 48 b (32 µmol of Ir), 4 mmol of 1-hexene, 18 mL of ethanol.

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F. Palladium and Platinum Complexes

1. Palladium Complexes

An area of intense research has been oriented tosupported palladium cata lysts for cross-couplingreactions, which repr esent excellent m ethods for t hesynthesis of various organic molecules.128,175-181 Clark

et a l. developed a ra nge of heterogeneous palladiumcatalysts based on chemically modified mesoporoussilica gel, which was either commercially availableor prepared via sol-gel technology. The hybrid pal-ladium catalyst 49 was prepar ed by rea ction of sol-gel-processed aminopropyl-modified micelle-templat-ed silica (3-aminopropyl-MTS) with pyridinecarbalde-hyde, followed by complexation with palladium ac-etate (Scheme 41).182 To ensure stabili ty in subse-

quent reactions, 49 was h eated in different solvents.The activity of 49 w a s i n ve s t ig a t ed i n t h e H e ck rea ction of aryl iodides with olefins in an acetonitr ilesuspension (eq 31a; Table 20). In the first 6 h theconversion rate was ∼4% h-1 after a n inductionperiod of ∼1 h . S u pp os ed ly t h e d ecr e a se of t h eactivity after 6 h to 2% h-1 is due to the congestionof the gel pores by the products. By decanting theliquid from the reactor the active polymer 49 could

b e r e cy cl ed a n d w a s fu r t h e r a p p li ed w it h ou t a n yconditioning and regeneration. Only after five ad-ditional runs (corresponding to a turn over num berof >2000) was a significan t dr op in activity observed.T h e r e w a s n o i n du ct i on p e r iod on r e p ea t e d u s e .Analysis by atomic absorption spectroscopy cor-roborated that no detectable amounts of palladiuml ea ch e d d u r i n g t h e r e a ct i on . N o con v er s ion w a sobserved in the hot fi l trate, which further implied

that the transition metal species did not dissociatefr om t h e s u p p or t d u r i n g t h e r e a ct i on . T h e s a m epolymer 49 was also successful in th e H eck r eactionof aryl iodides with allylic alcohols to give carbonylcompounds (see Table 20). Repeated use of 49 oc-cur red without noticeable loss of activity.

In the Suzuki C-C coupling between phenylboronicacid and bromobenzene in xylene in the presence of potassium carbonate a s a base catalyst 49 was alsoreported to give excellent results concerning theactivity and recycling ability (eq 31b; Table 20). 183

High yields of biaryls were obtained at 95 °C. Stablepalladium complex 49 was also effective for substi-tut ed br omobenzenes (see Table 20).

With th e aim t o mimic th e sur face of silica but withproperties that are more readily controlled than thoseof silica, heter ogenized homogeneous palladium(II)complexes on polysiloxanes with controlled solubilityha ve been pr epared a nd char acterized (Scheme 42).184

(MeO)3Si(CH 2)11N 3 a s s t a r t i n g m a t e r ia l p r od u ce dsilica fragments small enough to be soluble in con-ventional organic solvents by incomplete acid hy-drolysis. Subsequent silylation with tr imethylsilylchloride and substitution with P(2-py)3 afforded apolysiloxan e ma tr ix with a n NH P(O)(2-py)2 function-ality. By coordination of both pyridyl groups topalladium acetate, the soluble, anchored palladium-

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(II) catalyst 50a was available. Progressive hetero-genization was conducted by further treatment of 50 awith HCl to yield 50 b , which wa s insoluble in organ icsolvents. Both materials displayed excellent activitiesfor various alkyne cyclotrimerizations (eq 32; Table

20). Monitoring experiments of the cyclotrimeriza-tions by 1H NMR spectroscopy corroborated that 50 awas stable against decomposition and palladiumleaching. Neither color chan ge nor precipitationoccurred during the reaction under similar condi-tions. Lack of any pa lladium species det ected by AASin the filtrate of the reaction solution further verifiedt h a t 50 b resisted leaching. Both species 50 a ,b wereregioselective in t he case of asymmet ric alkynes su chas 2-hexyne and phenylacetylene. Regarding catalystrecycling, 50 a a n d 50 b were tested for the cyclotri-merization of 4-octyne. Both of them exhibited goodstability with a 4-octyne conversion of 99% in sixcycles.

Various ether-phosph ine pa lladium(II) complexesw er e t r a n s fe r r ed in t o t h e in t e r ph a s e.170,178,185-187

Trea tm ent of 2 equ iv of T-silyl-fun ctiona lized et her-phosphines with PdCl2(COD) afforded monomericcomplexes, which were sol-gel-processed with vari-able amounts of TEOS to give th e hybrid mat erials51 a ,b (Schem e 43).185 They revealed high activity an dselectivity in the hydrogenation of tolan and 1-hexyne(eqs 20 and 33). The hydrogenat ion of 1-hexynesucceeded without any solvent. Within 10-20 minthe H 2 upt ake wa s finished with conversions of >99 %between 65 a nd 70 °C. Turn over frequencies dependo n t h e h y d r o g e n p r e s s u r e a t t h e b e g i n n i n g o f t h ereaction. Repeated use up to 10 times without notice-

able loss of th e activity wa s possible. Leaching of 0.2-

1 % o f t h e or i gi n a l p a l la d iu m q u a n t i t y w a s e s t a b-lished after each run. Because the recovered reactionsolut ion is ina ctive in t he h ydrogenat ion of 1-hexyne,it was suggested that palladium stil l embedded inthe polysiloxan e mat rix was the a ctive cata lyst rat herthan the palladium species in the reaction solution.Lower amounts of the co-condensation agent TEOS( x ) 4, 12) influenced th e selectivity with respect to1-hexene, ranging from 96 to 98% during seven runs.However, the selectivity decreased to 62% with highamoun ts of TEOS ( x ) 36). The decomposition of th epolymeric palladium complexes 51 a ,b d u r i n g t h ehydrogenation resulted in a r eaction a t th e bounda ryphase solid-l iquid, and the desired reaction in the

T a b le 2 0 . P e r f o r m a n c e o f C a t a l y s t s 4 9 a n d 5 0 a ,b

catalysttype of

ca t a lysis eq R1 R2t im e

(h )catalyst/

substr a teyielda

(%) r ef com m en t s

49 Heck reaction b 31a H CO2CH 3 24 82 182 ca t a lyst 49 was reused, but no specificH O CO2CH 3 24 31 da t a wer e pr esen t edH CH 2OH 24 21H O CH 2OH 24 15H CH OH CH 3 24 41H O CH OH CH 3 24 27

Suzuki reaction c 31b H 1 83 75d 18 3 49 showed good performance in 5 runs

H 1 83 96e

H 1 83 45 f

H 3 833 98CN 2 167 98Cl 3 167 98OMe 6 167 82CH 2Br 6 167 79

50 a cyclotrimerizationg 32 Me Me 12 94 184 50 a a n d 50 b exhibited stability withn P r Me 16 96h >99% 4-octyne conversionE t E t 16 91 t h r ou gh 6 cyclesn P r n P r 16 93 i

P h H 16 94 j

P h P h 16 9550 b Me Me 12 94

n P r Me 16 86k

E t E t 16 94n P r n P r 16 95 i

P h H 16 92 l

P h P h 16 90

a For eq 31 yields were measured from GC, for eq 32 yields are based on the purified products by flash chromatography onSi O2. b Reaction conditions: 30 mm ol of substra te, 0.2 g of catalyst, 30 mm ol of triethylamine, 30 mL of acetonitrile, T ) 82 °C.c Reaction condit ions: 13 mL of xylene, 5 mmol of bromobenzene, 7.3 mm ol of phenylboric acid, 10 mmol of K2CO 3, T ) 95 °C.d First cycle. e Fifth cycle. f Sixth cycle. g Reaction condit ions: 0.56 mmol of alkyne, 3 m L of CHCl3, catalyst loading ) 4 mol %,T ) 62 °C. h Product ratio A / B ) 91:9. i Yield > 99% in cycles 1-6 were determined by NMR spectroscopy at 62 °C. j Productr a tio A / B ) 81:19. k Product ratio A / B ) 90:10. l Product ratio A / B ) 79:21.


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interph ase failed. This was confirmed by h igh-resolu-tion scanning electron microscopy, 31P CP/MAS NMRspectra, and XPS studies. In the hydrogenation of tolan toluene served as a solvent (eq 20). Within alimited time (1 h) the conversion of diphenylacetylene

w a s s t r on g ly d e pe n d en t on t h e t e m p er a t u r e , b u tselectivities were const ant : 89% of cis -stilbene, 5%of trans-stilbene, and 6% of the fully hydrogenatedp r od u ct s . I t w a s f ou n d t h a t a h ig h er a m ou n t of ethanol in an ethanol/toluene solvent mixture ac-celerates th e conversion.

2. Platinum Complexes

Due to economic considerations, the recovery of platinum catalysts is a bsolutely indispensable.188-190

Hilal et al . synthesized su pported 52 a ,b (Scheme44 )191 a n d e va l u a t e d t h e ca t a l yt i c a c t iv it y for O -silylations. In the first step a T-silyl-modified amineligand and TEOS were sol-gel-processed to afford

the solid polymer. Subsequent treatment with H 2-P t C l6 or Na 2P t C l4 resulted in the formation of 52 aa n d 52b . E ffects of the substr ates, solvents, concen-trat ions, and temperatur e on the catalytic O-silyla-tion of R3Si-H compounds were studied in detail (eq34). Regarding the substrate, two factors affect thereactivity: (i) the st eric factor in th e sequence n PrOH> iP r O H > t BuOH and (ii) the electronic factor withregar d t o th e n ucleophilicity of alcohols; for exam ple,

ethanol is less reactive than propanol. The reactionrate is slowed when polar solvents are used and isfaster at higher temperature. Furthermore, catalystsu s e d a t h i gh e r t e m p er a t u r e s w er e l es s a ct i ve onrecovery than samples used at lower temperaturesdue to decomposition. 52 a s h ow ed a r e m a r k a b lecatalytic activity, whereas 52 b was inactive. Withrespect to recovery and repeated u se, 52 a partiallyretained i ts activity after three different runs, andthe catalytic activity was highly reproducible withinthe same batch.

IV. Enzymes as Reactive Centers

The immobilization of biological catalysts (e.g.,enzymes, cata lytic antibodies, and whole cells) inrobust matrices to enhance their lifetime as well astheir recovery and repeated use have been the focusof att ention for several years. 192,193 From economicaland ecological points of view, such catalysts areimport ant if they can be separa ted from t he rea ctionproducts and used again without significant loss of activity. A common approach is the encapsulation of ca t a ly t ic s p ecie s in s id e s ili ca v ia t h e s ol-ge lprocess.19 4-19 6 Although this is on the borderline of the concept of chemistr y in int erpha ses, some int er-esting examples are summar ized in this section. In1995, Reetz et al . demonstrated the entrapment of

lipases into t he hydrophobic sol-gel mat erials, whichresulted in interphase catalysts with long-term sta-bili ty as well as pronounced degrees of enhancedactivity in esterificat ions an d t ra nsester ificat ions inorganic solvents.197 The catalysts were prepared viaa base-promoted hydrolysis of tr ialkoxysilanes RSi-(OMe)3 (R ) alkyl) or mixtur es of these or others il a n es w it h T MO S i n t h e p r e se n ce of a l ip a s e.Relative activities of 500-800% in esterificationr e a ct ion s w it h r e sp ect t o t h e t r a d it ion a l u s e of corresponding enzyme powders in organic solventswere achieved. The aut hors foun d th at incorporat inghydrophobic alkyl groups in the silicon oxide matrixmarkedly improved the activity. Recently, they re-

ported also on the entr apment of certain lipases suchas SP 625 (Candida antactia B) or S P 523 ( Humicolalanuginosa) in sol-gel mat erials.194 The preparationm e t h od s a r e t h e s a m e a s t h o se a b ov e-m e n t ion e d .D iffe r e n t a l k ox ys i la n e s s u ch a s T M OS , M TM S ,n -C3H 7Si(OMe)3 (PTMS), HO[Me2SiO]nSiMe2OH(PDMS), or mixtures of them were chosen as sol-gel precursors. As a test reaction the hydrolysis of the propionic acid 4-nitrophenyl est er was selected.Relative enzyme activities of 93, 107, an d 110% forthe entrapped lipase in PDMS/TMOS (1:3), PDMS/ (MTMS (1:3), and PTMS/TMOS (5:1), respectively,were found. This means that enzyme activities inhomogeneous and heterogeneous systems are actu-

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ally compara ble. In optimal cases, it was possible torecycle th e catalysts with l it t le or no decrease inenzyme activity. The catalysts with hydrophobic alkylgroups also showed higher activities.

Several difficulties emerge in the synthesis of sol-gel-encapsulat ed biological cat alysts. The resultingalcohol from the hydrolysis of SiOR functions oftenirreversibly decomposes the catalyst. Its activity isalso reduced by a reaction between silica precursors

and the active centers. In addition, shrinkage of thegel upon drying leads to localized pressure a nd areduction in enzyme activity and poor diffusionchara cteristics. Investigations of Gill an d Ba llester oshave highlighted a general approach to this prob-lem.198 An import an t key to th eir success was t o moveaway from stan dar d silica pr ecur sors su ch a s TMOSand TEOS, since both of th em eliminate alcoholsdecomposing the catalysts. Glycerol, which was liber-a t e d d u r in g t h e p r ep a r a t ion of t h e m a t e r ia ls , isbiocompatible and helps the gel to dry in a controlledfashion, leading t o stable matr ices for the enzyme.For a range of enzymes and whole cells (yeast, R .miehei, a n d P. oleovorans were all successfully en-

capsulated) th e a ctivity of the en capsulat ed catalystsis between 83 and 98% of the native material . Theamounts of biomaterial (20-30 wt %) encapsulatedi s m u c h h i gh e r t h a n w it h t r a d i t ion a l m e t h od s . Astriking example of the importance of the glycerol-based route over the traditional method is given bythe hydrolysis of the nerve a gent diethyl 4-nitrophe-nyl phosphat e by a ph osphata se enzyme. A hydrolysisof >95% was achieved under continuous conditionsover a period of 700 h, compared to 35-40% withconventional materials. Under the same conditionspolyurethane-encapsulated materials, initially veryactive, ha d lost ∼30% of th eir original a ctivity.

V. Summary and Outlook Chemistry in int erpha ses offers a versatile method

t o com b in e t h e a d va n t a g e s of h om og en e ou s a n dheter ogeneous catalysis. As such it ha s opened a widearea of heterogenized catalysts. By careful designhomogeneous cata lysts can be tr ansferred to inter-phase systems. In the case of highly swellable orporous polymeric materials a solution-like state isi m i t a t e d i n w h i c h t h e r e a c t i v e c e n t e r s a r e n e a r l yhomogeneously distributed across the entire polymerand ther efore are similarly a ccessible as in h omoge-neous phase.55 The polymeric part of the stationarypha se consists mainly of flexible polysiloxan es, bu t

oxides of alum inum, as well as polyalumosiloxanes,titan ium, an d phosphorus, were also introduced intothe framework.55,131,132,141,145,173 As a consequence of these favorable circumstan ces the activity of suchhybrid catalysts is markedly improved. Furthermore,they can be separated from the reaction products andreused with a considera ble reduction of the commondrawbacks. On the basis of these latest scientificfindings this review presents a survey of the prepa-rat ions a nd a pplications of new interph ase catalysts,w it h a n e m p h a s is on t h e ir r e cy cl a bi li t y. I t w a shighlighted th at the r eactive centers may r ange fromfunctional organic groups t o t ransition metal com-plexes an d also enzymes. Hybrid polymers, which ar e

provided with metal complexes as reactive centers,constitute the dominant part of this paper. Metalse n com p a s s t i t a n iu m , ch r o m iu m , m a n g a n e se , a n dm os t of t h e g r ou p 8 m e t a ls . A s p eci a l a p p e a l of interphase catalysts is that they are able to promoteseveral kinds of reactions, such as specific hydrogena-tions,99,125,130-133,155,165-167,173 oxidations,69,87,110,111,121,143-145

hydroformylations,155-158,170,171 coupling rea ctions,182,183

an d O-silylations. 191 As has been demonstrated hy-

brid catalysts may be m ore efficient and displaybetter performances than their homogeneous coun-t e r p a r t s .133,137,158 Furthermore, embedding a highlyactive center into a polymer network often improvedits stabili ty and resulted in better handling.69,134,135

This not only enha nces the safety but also offersbetter storage possibilities over a longer period of t i m e, w h ich m a k e s t h e m a t t r a c t iv e f or i n du s t r i a lapplications.

An evaluation of Tables 1-2 0 r e ve a ls t h a t t h ecomparison of t he performan ce of th e catalysts isexceedingly difficult. The large variety of catalysts,the different preparation methods, and the diverselevels of char acterization of the hybrid polymers

complicate the extraction of common factors affectingthe catalytic activity. Furthermore, the complexityof the reaction system is increased as the influenceof the support is not well understood. As an example,th e BET sur face area an d th e pore size volume (Table21) ar e generally accepted par am eters t o cha ra cterizeth e su pport of immobilized catalysts; for example, th ecatalytic activity is enhanced the higher the surfaceand the larger the pore size volume are. In contra stto t his, if th e amount of organic building blocks isincreased in the so-gel-processed m at erials, in somecases th e BET su rface ar ea is st rongly reduced an dh a r d l y a n y p o r e s i z e i s g e n e r a t e d a s l o n g a s t h ematerial is dry. However, in an appropriate solventthe swelling ability of th is organ ic/inorganic hybridpolymer is improved, which can lead to an extremelygood performa nce of the cat alyst.15 5 Some rules arebecoming obvious as to how the catalytic performanceis related to chemistry in interphases. The length of the spacer, the density of the reactive centers, andthe a mount a nd k ind of copolymer a s well as t he waythe sol-gel process is performed have an impact onthe activity a nd selectivity of the active site. U nfor-tunately, each parameter has to be optimized for awant ed catalytic system. In genera l, compar ed to th ehomogeneous congeners the fixed catalysts in sta-tionary phases display lower reaction rates (TOF).

T h is i s m o r e t h a n com p e n s a t ed b y m u c h l on g erl ife t im e s of t h e a ct i ve s it e (T ON ), a s h a s b ee ndemonstrated in many cases. In part this is due tothe reduced leaching of these materials, which is aresu lt of th e sol-gel process because th is prepar at ionm e t h od i n cor p or a t e s t h e a ct i ve ce n t e r s i n t o t h evolume of a material.

Although some salient aspects of interphase cata-lysts have already been developed, it is apparent thata great number of opportun ities, challenges, an dapplications are to be expected. Thus, the fact t hatthere are examples of sol-gel-processed active cen-ters which promote reactions while their homoge-neous counterparts are inactive implies that there


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is a huge potential of synergism between supportedcatalyst an d mat rix.55,57,59,60,192,199 Therefore, in futu re,more emphasis should be put on the preparation of t h e h y br i d ca t a l ys t s b y ca r e fu l ly d e si gn i n g a n dm od ify in g t h e r e a ct i ve ce n t e r s , t h e con d e n s a bl egroups, and the wa y the sol-gel process is performed.Along with this impr oved an d new p hysical met hodshave to be developed and applied to study in moredetail the structure of stationary phases and of thereactive center s as well as all of the inter actions t ha tt a k e p la ce b et w ee n t h e h yb r id m a t e ria l a n d t h esubstr ates. Th is will lead to th e development of new

materials that are capable of promoting more thanone reaction or even allow sequences of catalyticconversions to be performed in one batch. 200,201 H y-brid polymers with more than one supported type of ca t a l ys t w il l b e w or k e d ou t . I n t h i s con t e xt n e wclasses of nanostru ctu red m ater ials with well-definedporosities and shapes will have potential applica-tions. As an example, the shape of the pores willd et e r min e t h e d iffu s ion of t h e s u bs t r a t e t o t h eembedded catalyst a nd will thu s h ave an impact onthe selectivity of the conversion. Due to the manyfactors affecting cata lytic properties an d t he dema nds

T a b le 2 1 . P h y s i c a l D a t a o f C a t a l y s t s 1-52

catalyst S BE Ta V b d c ld r ef ca t alys t S BE Ta V b d c ld r ef

1 354 0.192 e 3.87 68 22 a 460 2.8 1.7 1342a 42 6 f 3.54 69 22 b 200 3.4 2.82b 1080 f 2.88 22 c 510 2.3 1.93 59 7 f 3.31 22 d <5 3.74 75 23 a 670 1.74 1375a 92 5 ≈5 1.2 76 23 b 1000 0.445b 37 0 >10 2.2 24 a-d 14 16a 228 0.27 5.8 80 25 a 14 8-222 142

6b 251 1.61 16.7 25 b 10 5-55 06c 312 1.01 11.6 26 620 1.35 j 14 37 1281 2.4 1.4 84 27 528 0.315 0.668 1448 400 10-20 0.24 87 28 a-c 14 59a 4.53 95 29 a-c 14 59b 1.25 30 a-c 14 610 321.5 99 31 a 719 0.69 1.9 2.7 14811 a 132 3g 11 0 31 b 415 0.31 1.5 2.011 b 142 2g 32 a ,b 15 311 c 159 2g 33 800 2.4 2.0 13412 a 66 18g 11 1 34 a 1.6 15512 b 674 5g 34 b 0.913 a 60 59h 12 1 35 a 0.6 4.02 15613 b 105 61h 35 b 2.06 2.8214 a 690 15h 35 c 1.05 2.6914 b 770 16h 36 a-d 15 715 a 142 3g 37 a ,b 15 815 b 152 2g 38 a-c 16 515 c 141 2g 39 a 360 1.0 16616 a 19 9g 39 b 305 1.816 b 37 8g 40 a 1.2 16816 c 85 9g 40 b 0.617 41 10.8 16718 a 5-9 5-15 i 7.55 42 16.018 b 1-10 10-20 i 6.72 43 a 676 0.31 16918 c 1-14 0.5-30 i 6.99- 43 b 808 0.36 13.8

3.43 43 c 686 0.32 1919 a 60 0.1-0.5 i 5.75 43 d 869 0.45 12.219 b 70 0.1-0.5 i 5.10 44 a ,b 21.8 17020 a 60 5.90 45 a-f 17 120 b 120 6.39 46 a 127 0.78 12.3 0.09 17220 c 75 6.93 46 b 104 0.47 9.0 4.4020 d 45 5.01 46 c 205 1.16 15.8 0.11

20 e 60 5.32 47 17 320 f 50 6.14 48 a ,b 17 420 g 50 4.03 49 18 220 h 70 4.90 50 a 25 18420 i 75 5.12 50 b 19 021 a 15-20 133 51 a 2.8 9.31 18521 b 3-8 51 b 3.521 c 1-3 51 c 28 021 d 15-20 7.11 52 a 3.4 19121 e 3-8 6.39 52 b 1.6-6.421 f 1-3 8.1521 g 15-20 6.9121 h 3-8 5.9521 i 1-3 8.11

a In m 2 /g. b Pore volume in cm 3 /g. c Pore size in n m. d Loading of reaction centers in m mol/g for catalysts 1-8 and t he percentageof metal in other cata lysts except indicated. e Microporosity. f Determined for the parent COOH-silica. g Content of porphyrin in

the catalysts in m/m. h Content of porphyrin in the catalysts in m/m(%). i In µm . j Average pore volume between 1.7 and 300 nm.


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in accelerating the discovery of new catalysts, par-allelization and high-throughput screening methodswill have to be applied.202-204 Tools from informationsciences will be relevant to handling the multipa-rameter space.205

VI. Acknowledgments

We th ank the Deutsche Forschun gsgemeinschaft

(Forschergruppe FOR 184/3-1 and GraduiertenkollegChemie in Interphasen, Grant GRK 441/2-01), Bonn,Bad Godesberg, the Fonds der Chemischen Industrie,Frankfurt/Main, and the Alexander von HumboldtFoundation for generous financial support.

VII. List of Abbreviations

AAS a t om ic a bsor pt ion sp ect r os cop yAD a sym met ric dih ydr oxyla tionAP T E S 3 -(a m in op r op yl )t r ie t h ox ys il a neBE T m et hod a ccor din g t o Br un au er , E mm et t,

and TellerCE TS (2 -cya n oe th yl)t r ie th oxys ila n eCOD 1,5-cyclooct adien e

COE cyclooct en eCp cyclopen t a dien ylCp * 1 ,2 ,3,4 ,5 -p en t a me th ylcyclop en t a die nylCP/MAS NMR cross-polar ization magic-angle spinn ing

N MRCP TS (3 -cya n op r op yl)t r ie th oxys ila n eDM F N , N -dimethylformamideDMOS d im et h yld im et h oxysila n eDMSO dim et hyl su lfoxideD RI F T d iffu s e r efle ct a n ce in fr a r ed F ou r ie r t r a n s-

form spectroscopyD-s ilyl d ifu n ct ion a l-s ilylDTA differ en tia l t her ma l a na lysisE DX en er gy-d is per sive X-r a y a n alys isE PR elect ron pa ra ma gn et ic r eson an ceE SI elect ron spect roscopy im agin gE SR elect r on spin r eson a nceE XAF S e xt e n de d X-r a y a b sor p t ion fin e s t r u ct u r eF T-I R F ou r ie r t r a ns for m in fr a r ed s pe ct r os cop yH MS h exa gon al m esopor ou s silicaI CP -AE S i n d u ce d cou p le d p la s m a a t o mi c e m is s ion

spectroscopyI CP -M S in d uce d cou ple d p la s ma m a ss s pe ct r os -

copyM E MO S (3 -m e t h a cr y lox yp r op yl )t r i m e t h ox ys il a n eMTMS m et hylt rim et hoxysila neMTS m icelle-t em pla ted silicaN MR n uclea r m agn et ic r eson an ceP DMS H O[Me2SiO]nSiMe2OHP∼O m on oden ta te coor din at ed et her-phos-

phine ligand

P∩O biden t at e coor din at ed et her-phosphineligand

PTMS n -propyltrimethoxysilanepy pyr idin epyz pyr a zin eQ-s ilyl q ua dr ifu n ct ion a l-s ilylsalen N , N ′-ethylenebis(salicylideniminato)TBHP tert -butyl hydroperoxideTE M t r an sm is sion elect r on m icr os cop yT E MP O 2 ,2 ,6 ,6 -t e t r a m e t h yl pi pe r id in e -1 -ox ylT E MP O N 4 -ox o-2 ,2 ,6 ,6 -t e t r a m e t h yl pi pe r id in e -

1-oxylTE OS t et ra et hoxysila neTGA t her mogr avim et ric a na lysisTH F t et r a h ydr ofu r a n

T ME P 2 -(2 -t r im e t hy ls il yl et h yl )p yr id in eTMG 1,1,3,3-t et r am et h ylgu a nid in eTMOS t et ra met hoxysila neTOF t u r n over fr equ en cyTON t u r n over n u m berT-s ilyl t r ifu n ct ion a l-silylU V-vis u lt r a violet-visibleW IS E N M R w id e -l in e s e pa r a t i on N M RXP S X-r a y p hot oelect r on s pect r oscop yXRD X-r a y diffr a ct ion

VIII. References

(1 ) C la rk , J. H . Pure Appl. Chem. 2001 , 73 , 103.(2 ) C la rk , J. H . Green Chem. 1999, 1, 1.(3) Ghosh, A.; Gupta, S. S.; Bartos, M. J .; Hangun , Y.; Vuocolo, L.

D .; S te in h off, B . A. ; N o se r, C . A .; H o rn e r, D . ; Ma y er, S . ;Inderhees, K.; Horwitz, C. P.; Spatz, J.; Ryabov, A. D.; Mondal,S.; Collins, T. J . Pure Appl. Chem. 2001, 73 , 113.

(4) Loch, J. A.; Crabtree, R. H. Pure Appl. Chem. 2001, 73 , 119.(5) Green Ch emistry: Challenging Perspective; Tundo, P., Anast as,

P. T., Eds.; Oxford Science: Oxford, U .K., 1999.(6) Gladysz, J . A. Pure Appl. Chem. 2001, 73 , 1319.(7) Hoelderich, W. F. Catal. Today 2000, 62 , 115.(8) H latky, G. G. Coord. Chem. Rev. 2000, 19 9, 235.(9) H latky, G. G. Chem. Rev. 2000, 10 0, 1347.

(10) Chemistry of Waste Minimisation ; C la rk , J. H . , E d . ; Ch a p m a nand H all: London, U.K., 1995.

(11) Heck, R. M.; Farrauto, R. J. CATTECH 1997, 1, 117.(12) Clarke, M. L. Polyhedron 2001, 20 , 151.(13) Vankelecom, I. F. J .; Jacobs, P. A. Catalyst Immobilization on

Inorganic Supports; de Vos, D., Vankelecom, I. F. J., Jacobs, P.A., Eds.; VCH: Wienhein, Germany, 2000; p 19.

(14) Blaser, H . U.; Indolese, A.; Schnyder, A. Curr. Sci. 2000, 78 ,1336.

(15) Baker, R. T.; Tuma s, W. Science 1999, 284 , 1477.(16) J essop, P. G.; Ikariya, T.; Noyori, R. Chem. Rev. 1999, 99 , 475.(17) Chauvin, Y.; Vedrine, J . C. Actual. Chim. 1996, 58.(18) Arends, I. W. C. E .; Sheldon, R. A. Appl. Catal. A 2001, 21 2,

175.(19) Arhan cet, J. P.; Davis, M. E.; Merola, J. S.; Hanson, B. E. Nature

1989, 33 9, 454.(20) De Campo, F.; Lastecoueres, D.; Vincent, J . M.; Verlhac, J . B.

J. Org. Chem. 1999, 64 , 4969.(21) Cornils, B.; Herrm ann, W. A. Applied Homogeneous Catalysis

with Organometallic Compounds: A Comprehensive Handbook i n T wo Vo lu me s; C o rn ils, B . , H e rrm a n n , W. A . , E d s. ; V C H :

Weinhein, Germany, 1996.(22) Horvath, I. T.; Rabai, J. S cience 1994 , 266 , 72.(23) Wende, M.; Meier, R.; Gladysz, J. A. J . Am . Ch em. S oc . 2001,

123 , 11490.(24) Guernik, S.; Wolfson, A.; Her skowitz, M.; Greenspoon, N.;

Geresh, S. Ch em. Comm u n . 2001, 2314.(25) Wasserscheid, P.; Keim, W. Angew. Chem., Int. Ed. 2000, 39 ,

3772.(26) Li, R.; Wang, J. Hu a x u e S h i ji 2001, 23 , 211.(27) Berger, A.; de Souza, R. F.; Delgado, M. R.; Dupont, J . Tetra-

hedron Asymm etry 2001, 12 , 1825.(28) Zhang, J .; Wu, X.; Cao, W. Huaxue T ongbao 2001, 353.(29) Chemical S ynthesis Using S upercritical Fluids; J e s s op , P . ,

Leitner, W., Eds.; Wiely-VCH: Weinheim, German y, 1999; p 480.(30) Sellin, M. F.; Webb, P. B.; Cole-Hamilt on, D. J. Ch em. Comm u n .

2001, 781.(31) Fan, L.; Fujimoto, K. Appl. Catal. A 1999, 186 , 343.(32) Oosterom, G. E.; Reek, J . N. H.; Kamer, P. C. J.; van Leeuwen,

P. W. N. M. Angew. Chem., Int. Ed. 2001, 40 , 1828.

(33) Astruc, D.; Charda c, F. Chem. Rev. 2001, 10 1, 2991.(34 ) D e S m e t, K .; A e rts, S . ; C e u le m a n s, E . ; V a n k e le com , I. F . J. ;J acobs, P. A. Ch em. Co mmu n . 2001, 597.

(3 5 ) C ru d d e n , C . M. ; A lle n , D . ; Mik o lu k , M. D . ; S u n , J. Chem.Co mmu n . 2001, 1154.

(36) Brunel, D.; Bellocq, N.; Sutra, P.; Cauvel, A.; Lasperas, M.;Moreau, P.; Di Renzo, F.; Galarn eau, A.; Fajula, F. Coord. Chem.

Rev. 1998, 180 , 1085.(37) Har tley, F. R.; Vezey, P. N. Adv. Organomet. Chem. 1977, 15 ,

189.(38) Iwasawa, Y. Tailored Metal Catalysis; Ugo, R., James, B. R.,

Eds.; Reidel: Dordrecht, The Net herlands, 1986; p 333.(39) Merckle, C.; Haubrich, S.; Bluemel, J. J. Organomet. Chem.

2001, 62 7 , 44.(40 ) S a n d e e, A . J. ; P e tra , D . G . I . ; R e e k , J. N . H . ; K a m e r, P . C . J . ;

van Leeuwen, P. W. N. M. Ch em. Eu r . J . 2001, 7 , 1202.(41) Tsiavaliaris, G.; Haubrich, S.; Merckle, C.; Bluemel, J . Synlett

2001, 391.(42) de Miguel, Y. R. J. Chem. Soc., Perkin Trans. 1 2000, 4213.


8/3/2019 Chem. Rev. 2002, 102, 3543


(43 ) H e se m a n n , P . ; More a u , J . J . E . Tetrahedron Asymm etry 2000,11 , 2183.

(44) Price, P. M.; Clark, J. H.; Macquarr ie, D. J . J. Chem. S oc., DaltonTrans. 2000, 101.

(45) de J ong, K. P. Curr. Opin. Solid S tate Mater. S ci. 1999, 4, 55.(46) Protzmann , G.; Luft, G. Appl. Catal. A 1998, 17 2, 159.(47) Pugin, B. J. Mol. Catal. A: Chem. 1996, 107 , 273.(48) Capka, M. Collect. Czech. Chem. Commun. 1990, 55 , 2803.(49) Augustine, R. L.; Liu, J. J. Mol. Catal. 1986, 37 , 189.(50) Altava, B.; Burguete, M. I.; Garcia-Verdugo, E.; Luis, S. V.;

Vicent, M. J .; Mayoral, J . A. React. Funct. Polym. 2001, 48 , 25.(51 ) H a rtle y , F . R . Supported Metal Complexes. A New Generation

of Catalysts; Reidel: Dordrecht, The N etherlands , 1985; p 318.(52) Driessen-Hoelscher, B.; Keim, W. Han dbook of H eterogeneous

Catalysis; Er tl, G., Knoezinger, K., Weitkamp, J ., Eds.; Wiley-VCH: Weinhein, Germany, 1997; p 231.

(53) Bhalay, G.; Dunstan , A.; Glen, A. Synlett 2000, 1846.(54) Choplin, A.; Quignar d, F. Coord. Chem. Rev. 1998, 18 0, 1679.(55) Lindner , E.; Schneller , T.; Auer, F.; Mayer, H. A. Angew. Chem.,

Int. Ed. 1999, 38 , 2155.(56) Lindner, E.; Kemmler, M.; Schneller, T.; Mayer, H. A. Inorg.

Chem. 1995, 34 , 5489.(57) Baiker, A.; Grun waldt, J . D.; Muller, C. A.; Schmid, L. Chimia

1998, 52 , 517.(58) Huesing, N.; Schubert , U. Angew. Chem., Int. Ed. Engl. 1998,

37 , 23.(59) Moreau, J. J. E.; Man, M. W. C. Coord. Chem. Rev. 1998, 180 ,

1073.(60) Schubert, U. Ne w J . Ch e m. 1994, 18 , 1049.(61) Clark, J . H.; Lambert, A.; Macquarr ie, D. J .; Nightingale, D. J.;

Price, P. M.; Shorrock, J. K.; Wilson, K. Spec. Publ.- R. Soc.Chem. 2001, 266 , 48.

(62) Wilson, K.; Clark, J . H. Pure Appl. Chem. 2000, 72 , 1313.(63) Wilson, K.; Shorrock, J. K.; Renson, A.; Hoyer, W.; Gosselin, B.;

Ma c q u a rrie , D . J. ; C la rk , J. H . S t u d . S u r f . S c i . Ca t a l . 2000 ,130D, 3429.

(64 ) B a rto n , T . J. ; B u ll, L . M. ; K lem p e re r, W. G .; L oy , D . A .;McEnaney, B.; Misono, M.; Monson, P. A.; Pez, G.; Scherer, G.W.; Vartuli, J. C.; Yaghi, O. M. Chem. Mater. 1999, 11 , 2633.

(65) Molnar, A.; Keresszegi, C.; Torok, B. Appl. Catal. A 1999, 18 9,217.

(66) Wilson, K.; Clark, J . H. Ch em. Comm u n . 1998, 2135.(67) Clark, J . H.; Butterworth, A. J.; Tavener, S. J .; Teasdale, A. J.

J. Chem. Technol. Biotechnol. 1997, 68 , 367.(68) J urado-Gonzalez, M.; Ou, D. L.; Orm sby, B.; Sullivan, A. C.;

Wilson, J. R. H. Ch em. Co mm u n . 2001, 67.(69) Elings, J. A.; Ait-Meddour, R.; Clark, J . H.; Macquarrie, D. J .

Ch em. Comm u n . 1998, 2707.(70) Har rison, C. R.; Hodge, P. J. Chem. S oc., Perkin T rans. 1 1976,

605.

(71) Abramson, S.; Laspera s, M.; Galarn eau, A.; Desplantier-Giscar d,D.; Brunel, D. Ch em. Co mm u n . 2000, 1773.(72) Bellocq, N.; Abram son, S.; Lasper as, M.; Brun el, D.; Morea u, P.

Tetrahedron Asymm etry 1999, 10 , 3229.(73) Brunel, D. Microporous Mesoporous Mater. 1999, 27 , 329.(74) Lasperas, M.; Bellocq, N.; Bru nel, D.; Moreau, P. Tetrahedron

As y mm. 1998 , 9, 3053.(75) Sarussi, L.; Blum, J.; Avnir, D. J. Sol-Gel Sci. Technol. 2000,

19 , 17.(76) Mdoe, J. E. G.; Clark, J. H .; Macquarrie, D. J. Synlett 1998 , 625.(77) Mueller, C. A.; Schneider, M.; Mallat, T.; Baiker, A. Appl. Catal.

A 2000, 20 1, 253.(78) Figueras , F.; Kochkar , H.; Caldar elli, S. Microporous Mesoporous

Mater. 2000, 39 , 249.(79) Kochkar, H.; Figueras, F. J. Catal. 1997, 17 1, 420.(80) Mueller, C. A.; Schneider, M.; Mallat, T.; Baiker, A. J. Catal.

2000, 18 9, 221.(81) Dusi, M.; Mueller, C. A.; Mallat, T.; Baiker, A. Ch em. Co mm u n .

1999, 197.

(82) Dusi, M.; Mallat, T.; Baiker, A. J. Mol. Catal. A: Chem. 1999,138 , 15.(83) Mueller, C. A.; Maciejewski, M.; Mallat , T.; Baiker , A. J. Catal.

1999, 18 4, 280.(84) Blanc, A. C.; Macquarr ie, D. J.; Valle, S.; Renard , G.; Quinn , C.

R.; Brunel, D. Green Chem. 2000, 2, 283.(85) Rao, Y. V. S.; de Vos, D. E .; Wouters , B.; Grobet, P . J .; Ja cobs,

P. A. Stud. Surf. Sci. Catal. 1997, 11 0, 973.(86) Brunel, D.; Fajula, F.; Nagy, J . B.; Deroide, B.; Verhoef, M. J .;

Veum, L.; Peters, J. A.; van Bekkum, H. Appl. Catal. A 2001,213 , 73.

(87) Ciriminn a, R.; Pagliar o, M.; Blum, J .; Avnir, D. Chem. Commun.2000, 1441.

(8 8 ) P a g lia ro , M. ; A v n ir, D . ; D e g a n e llo , G . ; B lu m , J. WO P a te n t9947258, 1999; Chem. Abstr. 1999, 131 , 244813.

(89) Kaminsky, W.; Kuelper, K.; Brintzinger, H. H .; Wild, F. R. W.P . Angew. Chem., Int. Ed. Engl. 1985, 24 , 507.

(90) Deng, H.; Winkelbach, H.; Taeji, K.; Kaminsky, W.; Soga, K. Macromolecules 1996, 29 , 6371.

(91) Kaminsky, W.; Arrowsmith, D.; Laban, A.; Lemstra , P. J .; Loos,J.; Weingarten, U. Chem. E ng. T echnol. 2001, 24 , 1124.

(92) Hungenberg, K. D.; Kerth , J .; Langhauser, F .; Marczinke, B.;Schlund, R. Ziegler Catalysts: Recent S cientific Innovations and Technological Improvements; Fink, G., Muelhaupt, R., Brintz-inger, H. H, Eds.; Springer-Verlag: Berlin, Germany, 1995; p363.

(93) Soga, K.; Shiono, T. Prog. Polym. S ci. 1997 , 22 , 1503.(94) Dai, L.; Hu ang, N.; Tang, Z.; Hungenber g, K. D. J. Appl. Polym.

Sci. 2001, 82 , 3184.(95) Cerm ak, J .; Kvıcalova, M.; Blechta, V.; Capka , M.; Ba stl, Z. J .

Organomet. Chem. 1996, 509 , 77.(96) Hogan, J. P. U.S. Pat ent 2951816, 1960; Chem. Abstr. 1960, 55 ,

5564.(97) Chandira n, T.; Vancheesan, S. J. Mol. Catal. 1994, 88 , 31.(98) Sodeoka, M.; Ogawa, Y.; Kirio, Y.; Shibasa ki, M. Chem. Pharm.

Bull. 1991, 39 , 309.(99) Ophir , R.; Shvo, Y. J. Mol. Catal. A: Chem. 1999, 140 , 259.

(100) Evans, S.; Smith, J. R. L. J. Ch em. S oc., Perkin T rans. 2 2001,174.

(101) Sacco, H. C.; Iamam oto, Y.; Smith , J. R. L. J. Ch em. S oc., PerkinTrans. 2 2001, 181.

(102) Doro, F. G.; Smith , J. R. L.; Ferr eira, A. G.; Assis, M. D. J. M ol.Catal. A: Chem. 2000, 16 4, 97.

(103) Schiavon, M. A.; Iama moto, Y.; Nasciment o, O. R.; Assis, M. D. J. Mol. Catal. A: Chem. 2001, 174 , 213.

(104) Mansu y, D.; Battioni, P. Metallophorphyrins in Catalytic Oxida-tions; Dekker: New York, 1994; Chapter 4, p 99.

(105) Lindsay-Smith, J . R. Metalloporphyrins in Catalytic Oxidations;Dekker: New York, 1994; Chapter 11, p 325.

(106) Bedioui, F. Coord. Chem. Rev. 1995, 144 , 39.(107) Meunier, B. Chem. Rev. 1992, 92 , 1411.

(10 8 ) D e n ia u d , D . ; S p y rou lia s, G . A .; B a rto li , J . F . ; B a tt ion i, P . ;Mans uy, D.; Pinel, C.; Odobel, F.; Bujoli, B. New J. Chem. 1998 ,22 , 901.

(109) Mart inez-Lorente, M. A.; Battioni, P.; Kleemiss, W.; Bartoli, J.F.; Mansuy, D. J. Mol. Catal. A: Chem. 1996 , 113 , 343.

(11 0 ) C iu ffi, K . J. ; S a cco , H . C .; B ia zz otto , J. C .; V id oto , E . A .;Nascimento, O. R.; Leite, C. A. P.; Serra, O. A.; Iamamoto, Y. J .

Non-Cryst. Solids 2000, 273 , 100.(111) Sacco, H. C.; Ciuffi, K. J .; Biazzott o, J. C.; Zuccki, M. R.; Leite,

C. A. P.; Nascimento, O. R.; Serra, O. A.; Iamamoto, Y. J . No n -Cryst. Solids 2000, 27 3, 150.

(112) de Oliveira, D. C.; Sacco, H. C.; Nascimento, O. R.; Iam amoto,Y.; Ciuffi, K. J . J. Non-Cryst. Solids 2001, 284 , 27.

(113) Sacco, H. C.; Ciuffi, K. J .; Biazzott o, J. C.; Mello, C.; de Oliveira ,D. C.; Vidoto, E. A.; Nascimento, O. R.; Serra, O. A.; Iamamoto,Y. J. Non-Cryst. Solids 2001 , 284 , 174.

(114) Ciuffi, K. J .; Sacco, H. C.; Valim, J . B.; Manso, C. M. C. P.; Serra ,O. A.; Nascimento, O. R.; Vidoto, E. A.; Iamamoto, Y. J . No n -Cryst. Solids 1999, 24 7 , 146.

(115) Pr ado-Manso, C. M. C.; Vidoto, E. A.; Vinha do, F. S.; Sacco, H.C.; Ciuffi, K. J .; Martins, P. R.; Ferr eira, A. G.; Lindsay-Smith,J . R.; Nascimento, O. R.; Iamamoto, Y. J. Mol. Catal. A: Chem.1999, 15 0, 251.

(116) de Lima, O. J .; de Aguirr e, D. P.; de Oliveira, D. C.; da Silva, M.A.; Mello, C.; Leite, C. A. P.; Sacco, H. C.; Ciuffi, K. J . J. Mater.Chem. 2001, 11 , 2476.

(117) Molina ri, A.; Amad elli, R.; Antolini, L.; Maldotti, A.; Battioni,P.; Mansuy, D. J. Mol. Catal. A: Chem. 2000 , 158 , 521.

(118) Bat tioni, P.; Iwan ejko, R.; Mans uy, D.; Mlodnicka, T.; Poltowicz,J.; Sanchez, F. J. Mol. Catal. A: Chem. 1996, 109 , 91.

(119) Battioni, P.; Bart oli, J . F.; Mansu y, D.; Byun, Y. S.; Traylor, T.G. J. Chem. Soc., Chem. Commun. 1992, 1051.

(120) Sorokin, A. B.; Tuel, A. Ne w J . Ch e m. 1999, 23 , 473.(121) Batt ioni, P.; Cardin, E.; Louloudi, M.; Schollhorn, B.; Spyroulias,

G. A.; Mansuy, D.; Traylor, T. G. Ch em. Co mm u n . 1996, 2037.(122) Bader, A.; Lindner, E. Coord. Chem. Rev. 1991, 108 , 27.(123) Lindner, E .; Ja eger, A.; Wegner, P.; Mayer, H . A.; Benez, A.;

Adam, D.; Plies, E. J. Non-Cryst. Solids 1999, 255 , 208.

(124) Lindner , E.; Wielandt , W.; Baum ann , A.; Mayer, H. A.; Reinoehl,U.; Weber, A.; Er tel, T. S.; Bert agnolli, H. Chem. Mater. 1999,11 , 1833.

(125) Lindner, E.; Kemmler, M.; Mayer, H. A.; Wegner, P. J . A m .Chem. S oc. 1994, 116 , 348.

(126) Lindner, E.; Kemmler, M.; Mayer, H. A. Z. A norg. Allg. Chem.1994, 62 0, 1142.

(127) Lindner, E.; Kemmler, M.; Mayer, H. A. Chem. B er. 1992, 12 5,2385.

(128) Lindner, E.; Schreiber, R.; Kemmler, M.; Schneller, T.; Mayer,H. A. Chem. Mater. 1995, 7 , 951.

(129) Lindner, E .; Jaeger, A.; Schneller, T.; Mayer, H. A. Chem. Mater.1997, 9, 81.

(130) Lindner , E.; Bader, A.; Mayer, H. A. Z. An org. Allg. Chem. 1991,598 / 59 9, 235.

(13 1 ) L in d n e r, E . ; J a e g er, A .; K e m m le r, M.; Au e r, F . ; We gn e r, P . ;Mayer, H. A.; Benez, A.; Plies, E. Inorg. Chem. 1997, 36 , 862.

(13 2 ) L in d n e r, E . ; J a e ge r, A. ; A u e r, F . ; We g n e r, P . ; Ma y e r, H . A .;Benez, A.; Adam, D.; Plies, E. Chem. Mater. 1998, 10 , 217.


8/3/2019 Chem. Rev. 2002, 102, 3543


(133) Lindner, E.; J aeger, A.; Auer, F.; Wielandt, W.; Wegner, P. J . Mol. Catal. A: Chem. 1998, 129 , 91.

(134) Kroecher, O.; Koeppel, R. A.; Froeba, M.; Baiker, A. J. Catal.1998, 17 8, 284.

(135) Kroecher, O.; Koeppel, R. A.; Baiker, A. Ch em. Co mmu n . 1996,1497.

(136) Kroecher, O.; Koeppel, R. A.; Baiker, A. J. Mol. Catal. A: Chem.1999, 14 0, 185.

(137) Schmid, L.; Rohr, M.; Baiker, A. Ch em. Comm u n . 1999, 2303.(138) Holder, E.; Schoetz, G.; Schurig, V.; Lindner, E. Tetrahedron

Asymmetry 2001, 12 , 2289.(139) Egelhaaf, H. J .; Holder, E.; Herman , P.; Mayer, H. A.; Oelkrug,

D.; Lindner, E. J. Mater. Chem. 2001, 11 , 2445.

(140) Seckin, T.; Cetinkaya, B.; Oezdemir, I. Polym. Bull. 2000, 44 ,47.

(141) Cetinka ya, B.; Seckin, T.; Oezdemir, I.; Alici, B. J. Mater. Chem.1998, 8, 1835.

(142) Seckin, T.; Ozdemir, I.; Cetinka ya, B. J. Appl. Polym. Sci. 2001 ,80 , 1329.

(143) Mur phy, E. F.; Schmid, L.; Buergi, T.; Maciejewski, M.; Baiker ,A.; Guenth er, D.; Schneider, M. Chem. M ater. 2001 , 13 , 1296.

(144) Das, B. K.; Clark, J. H. Ch em. Comm u n . 2000, 605.(145) Stuchinskaya, T.; Kundo, N.; Gogina, L.; Schubert , U.; Lorenz,

A.; Maizlish, V. J. Mol. Catal. A: Chem. 1999, 140 , 235.(146) Brzezinska, Z. C.; Cullen, W. R. Ca n . J . Ch e m. 1980, 58 , 744.(147) Brzezinska, Z. C.; Cullen, W. R.; Stru kul, G. Can. J. Chem. 1980 ,

58 , 750.(148) Schubert, U.; E gger, C.; Rose, K.; Alt, C. J. Mol. Catal. 1989,

55 , 330.(149) Blum, J .; Gelman , F.; Abu-Reziq, R.; Miloslavski, I.; Schum ann ,

H.; Avnir, D. Polyhedron 2000, 19 , 509.(150) Gelman, F.; Blum, J .; Avnir, D. J . Am . Ch em. S o c. 2000, 12 2,

11999.(151) Blum, J .; Avnir, D.; Schuma nn, H. CHEM TECH 1999, 29 , 32.(152) Sertchook, H.; Avnir, D.; Blum, J .; Joo, F.; Kath o, A.; Schum ann ,

H.; Weimann, R.; Wernik, S. J. Mol. Catal. A: Chem. 1996 , 108 ,153.

(153) Rosenfeld, A.; Blum, J .; Avnir, D. J. Catal. 1996, 16 4, 363.(154) Lindner, E.; Schneller, T.; Mayer, H. A.; Bertagnolli, H.; Ertel,

T. S.; Horner, W. Chem. Mater. 1997, 9, 1524.(155) Lindner, E.; Schneller, T.; Auer, F .; Wegner, P .; Mayer, H. A.

Ch em. Eu r . J . 1997, 3, 1833.(156) Lindner, E.; Auer, F.; Bauma nn, A.; Wegner, P .; Mayer, H . A.;

Bertagnolli, H.; Reinoehl, U.; Ertel, T. S.; Weber, A. J . M o l .Catal. A: Chem. 2000, 15 7 , 97.

(157) Lindner, E.; Salesch, T.; Brugger, S.; Hoehn, F.; Wegner, P.;Mayer, H. A. J. Organomet. Chem. 2002, 641 , 165.

(158) Sandee, A. J.; Reek, J. N. H .; Kamer, P. C. J.; van Leeuwen, P.W. N. M. J . Am . Ch em. S o c. 2001, 123 , 8468.

(159) Alt, H. G.; Koppl, A. Chem. Rev. 2000 , 100 , 1205.(160) Ciardelli, F.; Altomare, A.; Michelotti, M. Catal. Today 1998,

41 , 149.(161) dos Sant os, J. H. Z.; Ban, H . T.; Teran ishi, T.; Uozumi, T.; Sano,

T.; Soga, K. J. Mol. Catal. A: Chem. 2000, 158 , 541.(162) Metallocene-Based Polyolefins; Scheir, J., Kaminsky, W., Eds.;

Wiley: Chichester, West Su ssex, U.K., 2000.(163) Alt, H. G.; Schert l, P.; Koppl, A. J. Organomet. Chem. 1998 , 568 ,

263.(164) Arai, T.; Ban, H. T.; Uozum i, T.; Soga, K. J. Polym. Sci., Part A:

Polym. Chem . 1998, 36 , 421.(165) Schuman n, H.; Hasan , M.; Gelman, F.; Avnir, D.; Blum, J . Inorg.

Chim. Acta 1998, 28 0, 21.(166) Cerm ak, J .; Kvicalova, M.; Blechta, V. Appl. Organomet. Chem.

2000, 14 , 164.(16 7 ) A d im a , A .; Mo rea u , J . J . E . ; Ma n , M. W. C . J . M a t er . Ch e m.

1997, 7 , 2331.(16 8 ) C a p k a , M. ; S c h u b ert, U . ; H e in rich , B . ; H jortk ja e r, J . Collect.

Czech. Chem. Commun. 1992, 57 , 2615.(169) Bied, C.; Gauth ier, D.; Moreau, J . J . E.; Man, M. W. C. J . S o l-

Gel Sci. Technol. 2001, 20 , 313.

(170) Cauzzi, D.; Lanfran chi, M.; Mar zolini, G.; Predier i, G.; Tiripic-chio, A.; Costa, M.; Zanoni, R. J. Organomet. Chem. 1995, 488 ,115.

(171) Cauzzi, D.; Costa , M.; Gonsa lvi, L.; Pellinghelli, M. A.; Pr edieri,G.; Tiripicchio, A.; Zanoni, R. J. Organomet. Chem. 1997, 54 1,377.

(172) Capka, M.; Czakoova, M.; Urbaniak , W.; Schubert, U. J. Mol.Catal. 1992 , 74 , 335.

(173) Maillet, C.; J anvier, P.; Pipelier, M.; Pra veen, T.; Andres, Y.;Bujoli, B. Chem. Mater. 2001, 13 , 2879.

(174) Par ish, R. V.; Habibi, D.; Moham ma di, V. J. Organomet. Chem.1989, 36 9, 17.

(17 5 ) L in d n er, E . ; E n d e rle , A .; B a u m a n n , A . J. Organomet. Chem.

1998, 55 8, 235.(176) Schlenk, C.; Kleij, A. W.; Frey, H.; van Koten, G. Angew. Chem.,

Int. Ed. 2000, 39 , 3445.(177) Yan, Y. Y.; Zuo, H. P.; J in, Z. L. React. Funct. Polym. 1997, 32 ,

21.(178) Lindner, E.; Schreiber, R.; Kemmler, M.; Mayer, H. A.; Fawzi,

R.; Steimann, M. Z. A norg. Allg. Chem. 1993, 619 , 202.(179) Centi, G. J. Mol. Catal. A: Chem. 2001, 173 , 287.(180) Bedford, R. B.; Cazin, C. S. J .; Hurst house, M. B.; Light, M. E.;

Pike, K. J .; Wimperis, S. J. Organomet. Chem. 2001, 63 3, 173.(181) Richmond, M. K.; Scott, S. L.; Alper, H. J. Am . Chem. S oc. 2001,

123 , 10521.(182) Clark, J . H.; Macquar rie, D. J.; Mubofu, E. B. Green Chem . 2000,

2, 53.(183) Mubofu, E. B.; Clark, J . H.; Macquar rie, D. J. Green Chem . 2001,

3, 23.(184) Fu, Y. S.; Yu, S. J . Angew. Chem., Int. Ed. 2001, 40 , 437.(185) Lindner, E.; Schreiber, R.; Schneller, T.; Wegner, P .; Mayer, H.

A.; Goepel, W.; Ziegler, C. Inorg. Chem. 1996, 35 , 514.

(186) Lindner, E.; Bru gger, S.; Steinbrecher, S.; Plies, E.; Mayer, H.A. Z. A norg. Allg. Chem. 2001, 627 , 1731.

(187) Lindner, E.; Baum ann, A.; Wegner, P .; Mayer, H . A.; Reinoehl,U.; Weber, A.; Er tel, T. S.; Berta gnolli, H. J. Mater. Chem. 2000 ,10 , 1655.

(188) Fan g, P. F.; Chen , Y. Y.; Gong, S. L.; Guo, L.; Lu, Q. S.; Zhu , L.Chin. J. Polym. Sci. 1999, 17 , 441.

(189) Rosenfeld, A.; Avnir, D.; Blum, J . J. Chem. Soc., Chem. Commun.1993, 583.

(190) Hu , C.-Y.; Han, X.-M.; J iang, Y. J. Mol. Catal. 1986, 35 , 329.(191) Hilal, H. S.; Rabah, A.; Khatib, I. S.; Schreiner, A. F. J. Mol.

Catal. 1990 , 61 , 1.(192) Reetz, M. T. Adv. Mater. 1997, 9, 943.(193) Guenter, W. Chem. Rev. 2002, 102 , 1.(194) Reetz, M. T.; Wenkel, R.; Avnir, D. Synthesis 2000, 781.(195) Reetz, M. T.; Zonta , A.; Vijayakrishna n, V.; Schimossek, K. J .

Mol. Catal. A: Chem. 1998, 134 , 251.(196) Reetz, M. T.; Waldvogel, S. R. Angew. Chem., Int. Ed. Engl. 1997,

36 , 865.

(197) Reetz, M. T.; Zonta , A.; Schimossek, K.; Liebeton, K.; Ja eger,K. E. Angew. Chem., Int. Ed. Engl. 1997, 36 , 2830.

(198) Gill, I.; Ballest eros, A. J . Am . Ch em. S oc . 1998, 120 , 8587.(199) Fodor, K.; Kolmschot, S. G. A.; Sheldon, R. A. Enantiomer 1999,

4, 497.(200) Hafez, A. M.; Taggi, A. E.; Dudding, T.; Lectk a, T. J . Am. Ch e m.

S oc. 2001, 123 , 10853.(201) Wack, H.; Taggi, A. E.; Hafez, A. M.; Drur y, W. J.; Lectka, T. J .

Am. Chem. Soc. 2001, 123 , 1531.(2 0 2 ) K in g sb u ry , J. S . ; G a rb e r, S . B . ; G ifto s, J. M. ; G ra y , B . L . ;

Okamoto, M. M.; Farrer , R. A.; Fourkas, J . T.; Hoveyda, A. H. Angew. Chem., Int. E d. 2001, 40 , 4251.

(203) Kobayashi, S. Curr. Opin. Chem. Biol. 2000, 4, 338.(204) Mueller, M.; Mathers, T. W.; Davis, A. P. Angew. Chem., Int.

Ed. 2001, 40 , 3813.(205) Hoehn, F.; Herm le, T.; Lindner, E .; Rosenstiel, W.; Mayer, H .

A. J. Chem. Inf. Comput. Sci. 2002, 42 , 36.

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