61

Journal of Organornetallic Chemistry, 161 (19TS) 61-‘i3 @ Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands

STUDIES ON THE REACTIONS OF BIS(ACETYLACETONATO)PLATINUM(II) WITH LEWIS BASES

IV. PREPARATIONS AND CHARACTERIZATION OF NOVEL ACETYLACETONATO COMPLEXES [Pt(C5H602)L2]

TAKASHI IT0 and AK10 YAMAMOTO

Research Laboratory of Resources Utilization, Tokyo Institute of Technalogy, 4259 Nagatsuta, Xiciori-ku. Yokoflanla 227 (Japan)

(Received June rith, 19’iS)

Summary

Novel complexes [Pt(C5H602)Ll] (IVa, L = PPh,; IVb, L = PhIePh,, IVc, L = PMe,Ph) were prepared by the reactions of [Pt(acac),] with tertiary phosphines either at elevated temperature (when L = PPhR) or at room temperature (L = PMePh, and PMe,Ph), whereas AsPh, yielded [Pt(acac)(y-acac)AsPh3] (Id) by the rea&ion with [Pt(acac),] even under rigorous conditions. Complexes IV were characterized on the basis of their IR and NMR spectra, elemental analy- ses and chemical reactions, and a structure which possesses a chelate type “acetylacetonato” ligand involving n-osoallyl bonding is proposed.

In previous papers of this series we have reported that acetylacetonato (acac) ligands in [Pt(acac)?] which are bonded to platinum as chelate ligands via two oxygen atoms rearrange on reaction with Lewis bases to give complexes with unidentate central C-bonded or O-bonded acetylacetonato ligand(s) [l--3]. It was found that the mode of coordination of the resulting complex depended on the Lewis base employed, i.e., triphenylphosphine and tricyclohesylphos- phine afforded complex I [Pt(acac)(y-acac)L] :* (L = PPh3 (Ia) and P(cyclo- C6H11)3 (Ib)), in which one acac ligand rearmnged to the C-bonded form [ 11, whereas pyridine (py) gave two types of complexes, Ic (L = py) and II [Pt(y-

* Throughout this paper abbreviations for the acetylacetonato ligands in various modes of coordina- tion are used as follows: acac. acetylacetonato &and coordinated to the central metal in an en01

bidentate form through two ox>-gen atoms: y-acac, the diketo form of acetylacetonato ligand coor-

dinated to the metal in a unidentate way through the cer.tral (y-) carbon atom: 0-acac. acetylaceto-

nato ligand coordinated in a unidentate mode through an enolic oxygen atom; and “acetylaceto-

nato” denotes the l&and of the type Cjfi602 2-in which two protons are removed from acetYlaCe-

tone (Hacac).

62

acac)Jpy)J , dependin, Q on the reaction temperature [2]. Furthermore, the unidentate, O-bonded acetylacetonato complex of the type III [Pt(O-acac),- (PEt&], in which the acetylacetonato ligand is coordinated to Pt through one of two 0 atoms was obtained by the reaction of [ Pt( acac)l] with triethylphos- phine [3].

H,C -c* 0

(10) L = PPh, clI)

(Ib) L = P(cycLo-C,H,, 1 3 (ICI L = py

H, ,CH3

,c=c \

H&--C

-0

0 ,PEi3 ‘Pt

Et,P’ ‘0 O>/CH3

)c=c,

&C H

Continuation of this line of study resulted in the isolation of new complexes of the type [Pt(CSHA02)L2] (IVa, L = PPh3, IVb, L = PMePhz; IVc, L = PNIe,Ph) from the reaction of [Pt(acac),] with tertiary phosphines under more rigorous conditions, when L = PPh3, than those used for the synthesis of complex Ia.

Complexes IV appear to contain a chelated “acetylacetonato” ligand ( C5H602’-) presumably having an z--0xoally1 group. Although the iron complex with a chelated “acetylacetonato” (CsH602*-) ligand such as:

72

\

c

0 *--- ‘.

I_ (0 ;m2 .

.___ 0,’

C’-‘3

has been postulated as one of the possible products in the reductive decyanation of organic nitriles promoted by Fe(acac)s [4], there has been no precedent for the isolation of such a new type of “acetylacetonato” complex.

Results and discussion

Preparation of the complex -4s we have reported previously, [Pt(acac),] reacts with an equimolar

amount of triphenylphosphine in toluene or diethyl ether at room temperature

63

to yield [Pt(acac)(y-acac)PPh,1 (Ia) [I] _ Employment of more rigorous condi- tions, i.e., reflux in tetrahydrofuran (THF) for several hours, using more than 2 molar equivalents of PPh3, resulted -in the formation of a colorless crystalline solid whose analysis corresponded to the composition [Pt(CjH602)(PPh3)2] (IVa). Release of one mol of acetylacetone (Hacac) per mol of the complex in the reaction was confirmed by GLC. The reaction can be carried out silmilarly at elevated temperatures (loo-m-150” C) using a hydrocxbon solvent such as toluene, decalin or 1,5 cyclooctadiene (eq. 1). In contrast with this reaction, a similar reaction with [Pd(acac),] has been reported to give a palladium (0) complex [Pd(PPh,),] [5].

solvent [Pt(acac)J + 2 PPh3 F [ Pt( CSH607)( PPh3)2] + Hzcac (1)

(IVa)

Complex IVa can be obtained also by the reaction of either [Pt(acac)(r-acac)- PPh,] (Ia) with an equimolar amomlt of PPh, in boiling THF or of [Pt(y-acac)z- (py),] (II) with 2 molar equivalents of PPh3 in refluxing benzene. These facts, together with the observation that [PtEt(y-acac)(PPh,),] (V) rearranges t.o IVa with evolution of ethane on treatment with THF [l], suggest that the reaction represented in eq. 1 proceeds in a stepwise fashion, passing through the y-acac mode of coordination.

The diamagnetic, colorless complex IVa is highly soluble in chlorinated sol- vents such as CHC13 and CHJ&, and moderately soluble in pyridine and hot THF. The complex can be recrystallized from these solvents to give crystals containing each solvent (except CHCl,) which was difficult to remove even by prolonged pumping. Analytical results for these solvated and unsolvated com- pounds are listed in Table 1. The compleses are stable to air in the solid state, but they are slowly decomposed by air in solution.

T_aBLE 1

&IICRO.L\NALYSESAND IR ABSORPTIOXS (E;Br)OF[Pt(CjH602)L71,S(IV) -.-__-__

COrnPk?X hlicroanaiyses (Found(caIcd.) (5))

L S C H Others

_____

PPh3(IVa) 60.0 4.5

(60.2) (4.4)

PPhs(IVa) THF 60.2 4.8 (60.7) (50)

PPhx(IVa) CII?_Cl~ 55.9 4.5 Cl: 7.7 (55.9) (1.2) (7.9)

PPh3 (IVa) 1 z"Y 60.4 4.6 N: 1.0

(60.9) (4.5) (0.8)

PPh?_Me (IV%) 54.1 4.7

(53.7) (4.7)

PPhMe2 (lVc1 43.5 4.8 (44.3) (5.0)

__~ --~~

1650s. 1600~s. 1590(sh), 15iO(sh)

157os.1535s

TA

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2

1H N

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The use of PMePh, and PMe,Ph in place of PPh3 yielded analogous com- plexes, [Pt(C5H60z)(PMePh2)J (IVb) and [Pt(CsH60z)(Pi\Ie2Ph)?_l (NC), under milder conditions than those adopted for the synthesis of IVa (see Experimen- tal section). The analytical results for these complexes are included also in Table 1. It is interesting that PEt3, a more electron-donating tertiary phosphine, affords the unidentate 0-acac type complex III on reaction with LPt(acac),]

[31- In contrast to the tertiary phosphine ligands, triphenylarsine afforded only

the mono-y-acac complex, [Pt(acac)(y-acac)AsPh,l (Id), on reaction wit.11 [Pt(acac)J even under rigorous conditions. In view of the fact that type I com- plexes, [Pt(acac)(y-acac)L], were converted to “acetylacetonato” complexes of type IV (when L = PPh,) or to bis-y-acac complex of type II (when L = py) on further reaction with respective Lewis bases, the exceptional inertness of Id toward further attack of AsPh, is noteworthy.

[Pt(acac)z] + AsPh; reflus- [Pt(acac)(y-acac)AsPhJ] (2)

Attempts to obtain complex IV by the reaction of cis-[PtC1,L2] (L = PPh, and PMePhz) with acetylacetone in the presence of pyridine or triethylamine at 120” C failed and the reactants were recovered. Furthermore, neither [Pt(PPh,),] nor [Pt(PPh3)J reacted with acetylacetone even on heating at 110” C for 16 h in toluene, in spite of a brief report on the isolation of a com- plex with a platinacyclopropane rin, u from essentially the same system [6].

IR and ‘H NMR spectra The IR spectra of complexes of type IV show strong absorptions around

1600 cm -’ in addition to bands due to coordinated phosphine ligands. There was no band assignable to v(OH). As is shown in Table 1, the characteristic bands in the 1500--1700 cm-’ region are sensitive to the nature of ligand L and the attached solvent S, but they arp definitely different from those of the complexes of type [Pt(acac)(y-acac)L] (I) as there is no band below 1550 cm-’ in the spectra of the former. The absorptions of IV also differ distinctly from those of bis-y-acac complex II whose carbonyl absorptions appear above 1600 cm-‘.

The ‘H NMR spectra (Table 2) of IVa in CDC13 consisted of signals at 6 - 7.2 (30H) and 1.28 ppm (3H) together with three groups of multiplets each centered at 4.36, 3.12, and 2.66 ppm (total intensities corresponded to 3H). The complicated pattern of the last three blocks of signals (Fig. 1A) was simpli- fied considerably by irradiating the 3’P nucleus to remove its coupling. As illus- trated in Fig. lB, the ‘HC3’P} NMR spectrum suggests t,hat there exist three protons H,, I&,, H,, where H, couples with both Hb and H,, whereas no cou-

pling exists between Hb and H,, and that Hb and H, signals accompany the satellite bands due to coupling with 19’Pt. Although the higher counterpart. of the l& satellite bands is not discernible in the 100 MHz spectrum owing to overlapping with the H, signal, the 220 MHz spectrum of the same sample clearly resolved them, suggesting the validity of the assignments made on the 100 MHz spectrum. There was no appreciable change in the ‘H NMR signals

66

(B)

(A)

~

J(bHc)

3 Hz

HC Hb

J(PtH,) 36 Hz

?

J(PtH3) ti7H-z

J(HOHC)

A,h&W ’ A.36 3!12 2.66 ppm

Fig. 1. 1 H NbIR spectrum (A) and ‘H I. ‘~*P)xFRIR spectrum (B) of IPt(C5H602)(PPh3)zl W’a) (2-s

ppm region).

when the temperature was changed from --40 to 60” C. As is shown in Table 2, the ‘H NMR spectra of IVb and IVc possess the characteristic signals essentially similar to those of IVa except that there exist some complicated phosphine- methyl signals in the former. The fact that the methyl groups of PMePh2 in complex IVb appeared as two sets of doublets suggests that the complex has a square planar c&configuration with respect to two phosphine ligands.

The cis-configuration of IV was further supported by the 31P NMR spectral data of the PPh3 complex IVa. 3*P{1H} NMR spectrum of IVa in CDCl:, at 25” C

shows a pair of singlets at S 25.5 and 25.9 ppm (with respect to external PPh, reference, downfield positive) each accompanied by the satellite bands due to lg5Pt (‘J(Pt-P) 2880 and 3195 Hz, respectively). This means that the two phos- phine ligands in IVa are in different electronic environments due to the differ- ent tram substituents. The values for ‘J(Pt-P) are somewhat smaller than the reported value of 3875 Hz for cis-[PtClJPPh&] [7]. In 13C{*H} NMR spec- trum (in CDC13 at 25” C) there are three sets of fairly weak signals in addition to the strong multiplet at 6 127.7-134.0 ppm (downfield from internal Sih’le,) due to carbon atoms in the coordinated PPh3. The singlet at 31.0 ppm may be assigned to the methyl group as it changes to quartet by a “gated” decoupling experiment. Two dcublets at a low magnetic field (6 178.0 and 202.9 ppm, J(P-Cj 4.9 Hz) remained doublet on a “gated” decoupling experiment, hence

67

they were assigned to the carbon atoms attached to oxygen in the “acetylaceto- nato” ligand. The signals of the remaining two carbon atoms could not be dis- cerned in the 13C{‘H} NMR spectrum but might be either included in the multiplet signals of PPh3 or split into the multiplet clue to the coupling with phosphorus nuclei.

Some reactions of [Pt(CiHb01)(PPh3)2] (IVa) Complex IVa reacted with acetyl or benzoyl chloride at room temperature

to give the known dichloro complex, cis-[PtCl,(PPh,)J. This is in contrast to the behavior of [Pt(acac)(y-acac)PPhJ (Ia), which undergoes mono-chlorina- tion on a similar reaction with benzoylchloride to give [PtCl(acac)PPh,] [ 11. It is noteworthy that even dichloromethane, which was used as a solvent for recryst.allization of IVa, can readily chlorinate IVa in the presence of gaseous CO or CO2 to give the cis-dichloro complex.

The reaction of IVa with an excess of trifluoroacetic acid at room tempera- ture afforded [Pt(OOCCF3)Z(PPh3),I [S] and acetylacetone (eq. 3). The stoi-

[Pt(CjH602)(PPh&] + 2 CF,COOH + [ Pt(OOCCF,),( PPh3)J + CjHS02( Hacac)

(3)

chiometry of the reaction was confirmed on t.he basis of the ‘H NMR spectrum. That is, the ‘H NAIR signals of the samples prepaecl by dissolving [Pt(C5H60Z)- (PPh-,),]CH2ClZ in CF,COOH consisted of those ascribable to the coordinated P,Dh, at 6 7.5 ppm (multipiet, 30H), CH&l, at 6 5.28 ppm (singlet, 2H), and free acetylacetone (enol/keto l/l; enol-CH, at 6 2.27 ppm and keto-CH, at 6 2.54 ppm, total 6H; enol-CH at 6 5.82 ppm and keto-CH, at 6 4.03 ppm, total 1.5H; each singlet). The contents of each component in the reaction mis- ture was determined as 2.05 mol/mol of the initial complex for PPh,, O.SS mol for CHZCIZ and 0.93 mol for acetylacetone using 1,1,1’,1’-tet,rachloroethane as an internal standard_ When deuteriated trifluoroacetic acid, CF,COOD, was used in place of CF,COOH, signals due to the keto-CH, and the enol-CH of acetyl- acetone disappeared completely and the signal intensity of its methyl protons decreased by about 26%. These results indicate t.hat the “acetylacetonato” ligand of IVa may be such that one of the two methyl groups of acetylacetone is-participating in bonding to the platinum atom (eq. 4, 5).

[Pt(C5H602)(PPh3)J + 2 CF,COOD + [Pt(OOCCF,),(PPh3)7_]

:: OD 0 OD

CH?DCCH= &CH3 + excess CF,COOD + CH?D!CD= A-CH3

:: YD + CH,DCCH= C-C

(4)

(5)

Furthermore, no change was observed in the shape of the ‘H NMR signals due to t.he PPh3 ligand between two systems: IVa/CF,COOH and IVa/ CF,COOD. This fact suggests that there is no orthometallation involved in the bonding of PPh3 with platinum in comples IVa.

68

Possible structure for complex IV The spectral, chemical and elementary analytical results described above all

agree with the formula [Pt(C5H602)L2] for complexes IVa-IVc. Especially the results of the chemical reactions strongly suggest that IV contains an “acetyl- acetonato” ligand in which one of the two methyl groups of the acetylacetone participate in the bonding to the central metal. There are several possible struc- tures to meet these requirements as follows.

The first example of a compound which possesses a cis-diene diolate type acetylacetonato group, such as VI, has recently been reported and its molecular structure was determined by X-ray analysis [9] _ Although ‘H NMR data for the present complex IV (Table 2) are somewhat similar to those reported for the

Fh

mc)

“acetylacetonato” ligand in VI [9] (6 3.75 and 4.32 ppm (=CH,), 6 4.5s ppm (/)CH), and 6 1.25 ppm (-CH,); no data were given on the coupling constants of the signals) assignment of complex IV to structure I seems to be less prob- able since the strong IR absorptions observed around 1600 cm-’ for com- plex IV cannot be explained by structure A with an exocyclic methylene group.

H2=\

/ c-o

HC \pt/L

NC-O’ ‘L H3C"

(A)

Participation of the terminal methyl group(s) of the P-diketonato ligand in the form of a methylene group in the bonding to the metal has been reported for tellurium [lo] and palladium [ll] _ However, there is no precedent for the chelating fl-diketonato complex possessing both terminal CH; --metal and enol O---metal o-bonds similar to structure B. Structure B is not consistent with the

0

UC >C-CH2\ ,L

\

H3=

,C_olPt\L

‘H NMR parameters of IV (Fi,. CT 1 and Table 2). For example the CH2 group should be equivalent and have a large coupling with 195Pt.

Structure C which involves si-oxoallyl mode of coordination can be regarded as a delocalized intermediate between two structural extremes, A and B.

69

(Cl

Although some sr-osoallyl complexes of Co [ 12,131) Ru [ 141, Fe [13,15], and Ni [13] have been postulated as active intermediates in reactions involving organic carbonyl compounds, few examples of the unambiguous isoiation of such si-oxoallyl comples have been reported. Except the manganese comples of VII [ 161, whose structure has been confirmed through X-ray structural analysis [17], other r-osoallyl derivatives of Pd [18---201 and Fe [Zl] of type VIII so far reported have all been assumed on t.he basis of IR and ‘H NMR,

Mn-_CO

2

and/or mass spectrometry. A contradictory observation has been reported on their IR absorption, i.e., complexes VII [I61 and VIII (A,1 = Pd, R’ = Me and Ph, R’ = H, R3 = X = Cl) EZ.81 lack the v(C=O) band. whereas the rest of the complexes [ 19. -211 are claimed to show strong bands assignable t.o v(C=O) in the 1500--1580 cn-’ region. If one assumes that the very strong bands around 1600 cm- ‘, the region which is too high for structure A and too low for B, observed in the present complexes IV is due to the v(C=O) of ii--osoallyl group, its ‘H NMR spectral data (Table 2) can be explained reasonably well by con- sidering structure C, where H,, Hb and H, in Table 2 correspond to, respec- tively, the proton attached to vinylic carbon, anti, and s~‘rz pseudo-allylic protons_ Since there have been no ‘H NMR data reported which are relevant to structure C, the comparison was made between ‘H NMR data of IV and some reported 7r-(n~etl~)allylplatinum complexes, such as (sr-&H,)(T-allyl)Pt [ 221, [(sr-(meth)allyl)Pt(Pph,),l’ [23,24] and (sr-(meth)allyl)Pt(C&14H)(PPh,) [25] (Table 3). The only difficulty in assigning complexes IV to structure C is that there exists considerable coupling between H, and H,/H,, since such coupling is usually minimal when a carbon- -carbon single bond intervenes. Alternat.ively, structure D which is similar to that postulated by van Tamelen et al. for iron [a] ~ may also meet the requirement of these observed H- -H coupling constants as well as other ‘H NMR parameters.

CHz ..\ >,c--3, o,L

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The lack of success in prepaLxng a single crystal suitable for X-ray studies * so far prevents us frcm presenting a definite structure for complexes IV. How- ever, structure C or D seem to be most appropriate for the structure of IV on the basis of spectral, chemical, and analytical results.

Experimental

All manipulation were carried out under an atmosphere of nitrogen or argon. [Pt(acac),] was prepared accordin g to the reported method [26] _ Triphenyl- phosphine was kindly donated by Ihara Chemical Indu-:try Co. Ltd., to which we are indebted. Methyldiphenylphosphine [ 271 and clin~et.l~ylpl~enylpl~ospl~ine [2S] were prepared as described in the literat.ure. Triphenylarsine (Strem) was used as purchased.

Infrared spectra were recorded on a Hitachi 295 spectrometer as KBr discs. ‘H NMR (100 MHz) and 31P{‘H) NhiR (40.5 MHz) specka were measured by Mr. Y. Nakamura on JEOL PS-100 spectrometer which was operated in the Fclurier transform mode for the latter nucleus. 13C NMR spectra (15.1 MHz) was recorded on JEOL FX-60 by Mr. K. Kosaka of Japan Electron Optics Laboratory, Ltd., to whom the authors are indebted. The 220 MHz ‘H NMR spectra were measured on Yarian HR-220 spectrometer by T. Hattori of Kyoto University. Elemental analyses of carbon, hydrogen, nit.rogen and chlorine were performed by Mr. T. Saito of our reseaxh Laboratory.

Preparation of [Pt(CjHoO?_)(PPIl_3)J (IV,). A mixture of [Pt(acac),] (0.43 g, 1.09 mmol), PPh, (0.60 g, 2.29 mmol) and THF (10 ml) was heated under reflus for 5 h to give a yellow solution. GLC analysis (SDC-550, 5O”C, Hz as carrier gas, and di-n-propylketone as an internal standard) of the solution revealed that OS2 mol of acetylacetone per mol of the starting [Pt(acac),] vcas liberated in the solution_ On cooling the yellow solut.ion to room temperature, a white precipitate was deposited. In order to complete the precipitation, 10 ml of hesane was added to the system with stirring. The white precipitate was fil- tered, washed with hexane, and dried in vacua to give 0.83 g (93%) of unpurified [Pt(C,H,O,)(PPh,),]THF. Recrystallization of the white powcler from a l/2 misture of CH2C12 and hexane afforded white prisms of [Pt(C,H,,02)(PPllj)Z]- CH&l, (m-p., 210--220” C, with decomposition)_ Similarly, recrystallization of the crude product from either hot THF or pyricline/hexane gave crystals con- taining each solvent. A solvent-free comples was obtained by the analogous reaction in reflusing toluene or heptane or in decalin at 160” C or 1,5-cyclo- octadiene at 130°C. Analytical results of the solvated and unsolvatecl products are listed in Table 1.

Preparation of [Pt(C,H,O,)(P~~lePIll)ll (IVb). Stirring a diethyl ether (10 ml) solution of [Pt(acac),] (0.35 g, 0.90 mmol) and PhlePh, (0.50 ml, 2.66 mmol) at room temperature overnight afforded a pale yellow precipitate_ The precipi- tate was filtered, wasized with Et?_0 and hesane and dried in vacua. The crude product (0.41 g, 66%) was recrystallized from CH,ClJtoluene to give pale- orange crystals of [Pt(CSH60,)(PMePh,),].

Preparation of [Pt(CsH60z)(Pfile,Pl~)J (IVa). A similar reaction as above

* Good crystals of IVa we obtained from the CHClqIhcsane system were found to be twins.

72

was applied for the synthesis of IVc. The powdery, deep-yellow crude product was recrystallized from a l/3 mixture of CH,& and Et*0 to give pale-orange crystals. The product was characterized by elemental analysis, IR (Table 1) and ‘H NMR (Table 2) spectroscopy.

Reaction cf [Pt(acac)z/ with AsPh,. The pale-yellow suspension of [Pt-

(acac)?] (0.23 g, 0.59 mmol) and AsPh3 (0.50 g1 1.6 mmol) in 5 ml of toluene was heated under reflux for 11 11, affording a pale-yellow solution_ The solution was concentrated to ca. 0.5 ml in vacua to yield a cream precipitate. Hexane (5 ml) was added to the system to complete the precipitation. The cream pow- der (0.35 g) was filtered, washed with hexane and dried in vacua. The crude product was reprecipitated from CHICl,/hexane to give, again, the cream pow- der (0.22 g), the ‘H NMR spectrum of which in CDC13 indicated that it consists of [Pt(acac)(y-acac)AsPh,l (Id) (ca. 75%) and the starting [Pt(acac),] (25%). Characteristic IR absorptions of Id: P6S6s, 1675s, 157Os, 15X%, 1522s cm-‘. ‘H NMR data of Id (CDC13, 25°C): 6 1.63 (3H,s,acac-CH3 tram to y-acac lig- and), 2.01 (3H,s,acac-CH, tram to AsPh& 2.21 (GH,s,y-acac-CH3), 4.40 (lH,ss, y-acac-CH,J(PtH) 15 Hz) and 5.48 ppm (lH,s,acac-CH).

Reactions of [Pt(C,H,O,)(PPh,)J (IVa). Reaction with acetyl chloride and benzoyl chloride. On stirring the mixture of complex IVa (0.19 g, 0.23 mmol) and 7 ml of CH,COCl (98.5 mmol) at room temperature for 5 11, the initial cream suspension changed to a heterogeneous, pink mixture. The pink precipi- tate was filtered, washed with hexane and dried in vacua. The pale-pink powder thus obtained was identified as [PtC12(PPh&] on the basis of its IR spectrum (0.145 g, 90%). The product was further purified by recrystallization from CH,Cl,/toluene. The reaction of IVa with benzoyl chloride, which gave the same dichloro complex, was carried out similarly.

Reaction with methylexe chloride in the presence of carbon dioxide and car- bon monoxide. Carbon dioxide was passed through the CHICI1_ (10 ml) solution of IVa (0.17 g) at room temperature. The initial yellow solution gradually charlgecl t.o green. _4fter 4 h of reaction, the resulting deep green solution was concentrated to ca. 5 ml. Addition of hexane to the solution yielded a greenish white precipitate, which was filtered, washed with hexane and dried in vacua. It was purified by recrystallization from CH,C& to give off-white crystals, which were identified as [PtClJPPh&] (the yield was almost quantitative) on the basis of its IR spectrum and elemental analysis_

When the same reaction was carried out in the presence of 2 molar equi- valents of added PPh,, a similar reaction proceeded, although a color change to deep green was not observed in this case.

The use of carbon monoxide in place of carbon dioxide resulted in the for- mation of the same dichloro complex as above without appreciable color change.

Reac2on with CF&OOH. To the white suspension of IVa (0.10 g, 0.12 mmol) in THF (2 ml), trifluoroacetic acid (0.5 ml, 6.7 mmol) was added to produce a yellow solution. The solution was stirred at room temperature for 17 h, during which period the system became heterogeneous with formation of a white precipitate. Six ml of hexane was added to complete the precipitation. The white precipitate was filtered, washed with hexane and dried in vacua. The white powder thus obtained was characterized as [Pt(CF,COO),(PPh,),] (yield

73

was almost quantitative) on the basis of its IR spectrum (v,,~, (C02), 1730~s and 1700s; v~~~(CO~), 1400s cm-‘) and elemental analysis (Found: C, 50.5; H, 3.3.

C4,,F6H300.$ZPt calcd.: C, 50.8; H, 3.2%). The release of acetylacetone in this reaction was confirmed qualitatively by GLC analysis (SCD-550, 50°C) of the colorless filtrate_

AcknowIedgement

The authors express appreciation to Mr. T. Kiriyama for his esperimental assistance_ We are indebted to Professors N. Kasai and N. Yasuoka and their colleagues at Osaka University for helpful advice on the crystallization of the sample of compound IVa and for attempting its preliminary X-ray analysis.

References

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