Pyridylamido Hafnium and Zirconium Complexes: Synthesis, Dynamic Behavior, and Ethylene/1-Octene and...

Published: May 25, 2011

r 2011 American Chemical Society 3318 dx.doi.org/10.1021/om200167h |Organometallics 2011, 30, 3318–3329

ARTICLE

pubs.acs.org/Organometallics

Pyridylamido Hafnium and Zirconium Complexes: Synthesis,Dynamic Behavior, and Ethylene/1-Octene and PropylenePolymerization ReactionsKevin A. Frazier, Robert D. Froese, Yiyong He, Jerzy Klosin,* Curt N. Theriault, Paul C. Vosejpka,and Zhe Zhou

Corporate R&D, The Dow Chemical Company, 1776 Building, Midland, Michigan 48674, United States

Khalil A. Abboud

Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States

bS Supporting Information

’ INTRODUCTION

The last two decades have seen extensive research devoted tothe development of non-Cp-based molecular catalysts for olefinpolymerization.1�3 We have been interested recently in imino-amido4�6 and imino-enamido7 type catalysts and uncovered aninteresting diversity of polymerization characteristics. Closelyrelated to the imino-amido catalyst family are catalysts contain-ing the pyridylamido ligand framework, which were developedinitially at Union Carbide8 (generation 1) and further elabo-rated via a joint collaboration between Symyx Technologies andThe Dow Chemical Company9,10 (generation 2). The generalstructures of the pyridylamido catalysts and the chiral procata-lyst 1 used in this work are depicted in Figure 1. This catalystfamily has been the subject of much research due to unusualcatalyst and polymer properties.

Pyridylamido catalysts form high molecular weight, isotacticpolypropylene, which is very unusual for the C1/Cs-symmetriccatalysts.2d,11 This catalyst family was also identified as veryeffective for the preparation of olefin block copolymers due totheir ability to undergo reversible and efficient chain-transferreactions with some metal alkyl complexes (e.g., ZnEt2) duringolefin polymerization.3,12 Pyridylamido catalysts were also

recently reported to exhibit living character.11 Interestingly, theformation of a multimodal polymer is often observed withcatalysts of this type, indicating the lack of a single site. Theactivation mechanism of these catalysts is unusual and hasbeen studied extensively via experimental and computationalmethods.13,14 It has been hypothesized that the active catalyticspecies is formed by insertion of an ethylene or R-olefin into theHf�aryl bond, leading to a modified catalyst, 1a (Figure 1). Inethylene/1-octene and propylene polymerization reactions, in-sertion of the olefin(s) into the Hf�aryl bond can lead tomultiple species, which results in the formation of multiple activepolymerization sites generating a mixture of polymers.

Most of the catalytic and mechanistic work reported thus farhas focused on the study of chiral and achiral hafnium complexes.It was of interest to us to evaluate the zirconium8,15 analogue of 1for both ethylene/1-octene and propylene polymerizations andcompare its polymerization characteristics to that of 1. Depend-ing on the ligand framework, zirconium and hafnium complexescan exhibit quite different polymerization behaviors; thus

Received: February 21, 2011

ABSTRACT:Hafnium and zirconium pyridylamido complexeswere prepared by the reaction of deprotonated ligand withMCl4 followed by alkylation withMeMgBr. 1HNMR analysis ofthe isolated products revealed the presence of two complexes ineach sample in about a 93:7 ratio. Both complexes were shownby 1D NOESY experiments to be in dynamic equilibrium witheach other at ambient temperature. An analysis of the chemicalshift differences between major and minor isomers together with low-temperature NOE experiments revealed that the differencebetween major and minor isomers is due to the rotation of the 2-iPr-phenyl group attached to the chiral center. Magnetizationtransfer experiments conducted at temperatures between 10 and 40 �C yieldedΔH‡ andΔS‡ of 14.3(6) kcal/mol and�11(2) cal/mol 3K, respectively. Density functional theory calculations resulted in very similar activation parameters. Additionally, this fluxionalprocess was calculated to occur in the cationic species with a rate comparable to that of propylene propagation kinetics. Bothcomplexes have been studied as procatalysts for ethylene/1-octene copolymerization and propylene polymerization reactions. 13CNMR analysis of polypropylene obtained under high-temperature polymerization conditions allowed for the unequivocaldetermination of the identity of a second 2,1-regioerror.

3319 dx.doi.org/10.1021/om200167h |Organometallics 2011, 30, 3318–3329

Organometallics ARTICLE

synthesis and evaluation of 3 was warranted. In addition to thecomplications with catalyst activation mentioned above, ithas been known that there is a persistent additional species inprocatalyst 1, composition of which was unknown. This workwill shed light on the identity of this additional species,

ultimately adding an additional level of complexity to thisintriguing catalyst family.

’RESULTS AND DISCUSSION

Previously, complex 1 was prepared by refluxing the corre-sponding ligand (2) with Hf(NMe2)4 followed by the reaction ofthe isolated triamide derivative, 2-Hf(NMe2)3, with AlMe3. Wedesired to prepare 1 and its Zr analogue by a more easily scalable

Figure 1. Pyridylamido procatalysts and their activation.

Scheme 1. Synthesis of Procatalysts 1 and 3

Figure 2. 1H NMR spectrum of 1. Asterisks indicate some resonances of the minor component.

Figure 3. Thermal ellipsoid drawing of 3 at the 40% probability level.Hydrogen atoms have been removed for clarity.



method and developed an improved synthesis as outlined inScheme 1. Ligand 216 was reacted with one equivalent of n-BuLiat ambient temperature in toluene followed by the reaction of theresulting anion with hafnium or zirconium tetrachloride at110 �C for 1 h. The in situ formed trichloride intermediate wasreacted with three equivalents of MeMgBr at ambient tempera-ture to produce the desired complexes, 1 and 3. Both complexeswere characterized by elemental analysis, 1D (Figure 2) and 2DNMR spectroscopy, and single-crystal X-ray analysis. X-raystructures of 1 and 3 are isostructural, and only the molecularstructure of 3 is shown here (Figure 3).16 Interestingly, all regionsof the 1H NMR spectra of both complexes 1 and 3 revealed thepresence of a minor component at a level of about 7% (Figure 2).Since ethylene/1-octene copolymers with a broad polydispersityindex (PDI) have been observed previously with 1, it wasreasoned that the minor component might be catalytically active

and directly responsible for polymer bimodality. Thus, it wasimportant to us to determine the identity of this minorcomponent.

This minor component appeared to be structurally similar to1, as all of its resonances exhibited very similar chemical shiftsand multiplicity to those observed in 1. In an effort to identifythese resonances, a comprehensive NMR analysis was carriedout. The most important and unexpected piece of informationthat allowed for determining the structure of this minorcomponent in the spectra of 1 came from 1D NOESY experi-ments. In addition to the expected positive NOEs, 1D NOESYspectra also revealed negative EXSY peaks between 1 and theminor component. This fact clearly indicates that the minorcomponent is in chemical exchange with 1. Full analysis of theNOE and TOCSY data allowed for the full assignment of allresonances of the minor component, which from now on will be

Figure 4. Rotational isomers 1 and 10.

Figure 5. 1H NMR and 1D NOESY spectra of 1 and 10 (in C6D6) at 7 �C (mixing time = 0.7 s). Asterisk designates residual toluene.



referred to as either the minor isomer or 10. The three-dimensional structures of 1 and 10 were shown to differ in theorientation of the (2-iPr)Ph group relative to the remaining partof the ligand framework (Figure 4). This conclusion wasreached from several independent pieces of data. The first clueas to the three-dimensional structure of the minor isomer camefrom the analysis of the chemical shift differences between bothisomers. The chemical shift difference between most of theresonances of 1 and 10 was found to be small (within 0.05 ppm)except for the resonances associated with the (2-iPr)Ph groupattached to the chiral center (C14) and its neighboring proton

H14.17 For example, the difference between the chemical shiftsof H10/H100, H11/H110, H14/H140, and H18/H180 are 0.68,0.26, 0.44, and 0.56 ppm, respectively.

If the (2-iPr)Ph fragment has two different orientations asdepicted in Figure 4, then the NOE experiments might be able toprovide unequivocal evidence for it. To minimize contributionsfrom EXSY peaks, NOE NMR experiments were conducted at alower temperature (7 �C). The 1HNMR and 1DNOESY spectraobtained at 7 �C are shown in Figure 5. Fortuitously, at 7 �C theH14 and H9 resonances are adequately separated (they overlapat 30 �C) such that they can be independently irradiated. Sincethe distance between protons H9/H14 in the major isomer isapproximately the same as that of H90/H140 in the minor isomer(the DFT-calculated distances are 2.67 Å for H9/H14 and 2.68 Åfor H90/H140), it was expected that irradiation of H14 and H140would result in a similar intensity of NOEs for H9 and H90,respectively (internal check). In the first NOE experiment, theH14 resonance was irradiated, resulting in strong NOEs of H9,H18, H20, and H25 (Figure 5, middle spectrum). It is importantto note that strong NOEs are observed for two out of threemethine resonances. There is also NOE enhancement for theH10 resonance, but its intensity is very small. On the other hand,irradiation of H140 resulted in very strong NOEs for H90, H100,H200, and H250 (Figure 5, bottom spectrum). The appearance of

Figure 6. 1D NOE array spectra of 1 and 10 (in toluene-d8) at 30 �C.

Figure 7. Calculated structure of 1 (major isomer).

Figure 8. Calculated structure of 10 (minor isomer).

Figure 9. Calculated transition state (TS) for the interconversion of1 and 10.



a strong NOE for H100 and the disappearance of the NOE forH180 is a strong indication that the difference between 1 and 10 isdue to the different disposition of the (2-iPr)Ph fragment relativeto the rest of the molecule.

To evaluate the activation parameters for this fluxional pro-cess, a series of magnetization transfer experiments was con-ducted between 10 and 40 �C. An example set of arrayed 1DNOESY spectra is shown in Figure 6.18 The obtained rateconstants and corresponding Eyring plot are shown in theSupporting Information. Data analysis results in ΔH‡ and ΔS‡

of 14.3(6) kcal/mol and �11(2) cal/mol 3K, respectively. In-tegration of the resonances corresponding to the major andminor isomers in the 1H NMR spectrum gives an equilibriumconstant (Keq) of 14 at 30 �C, which corresponds to a free energy(ΔG�) difference of 1.6 kcal/mol. For comparison, the rateconstant for interconversion of 3 and 30 was measured at 30 �Cusing magnetization transfer experiments. The measured rate of1.66(3) s�1 is slightly faster than that of interconversion between1 and 10, which was determined to be 1.22(2) s�1 at the sametemperature.

The calculated structures of 1, 10, and the transition state (TS)for their interconversion are shown in Figure 7�9, respectively.19

Selected bond lengths and angles for the calculated structures arecollected in Table 1. Except for the orientation of the (2-iPr)Phfragment, both structures 1 and 10 are very similar. However,the transition state is distorted significantly compared to thetwo minima. First, the five-membered ring containing Hf�N1�C34�C14�N2 is relatively planar in 1 and 10 but isnoticeably puckered in the TS. The Hf�N1�C34�C14 torsionangles for 1, 10, and TS are �14.9�, �8.4�, and �38.7�,respectively. Second, the 2,6-diisopropylphenyl fragment is tiltedaway from the (2-iPr)Ph fragment in the TS. The C30�C38�N2�C14 torsion angles for 1, 10, and TS are 105.7�,107.7�, and 122.8�, respectively. Another notable aspect is thatthe (2-iPr)Ph fragment could rotate in either direction in the TS,but prefers to reside toward the pyridine rather than beingdirected toward the sterically encumbered 2,6-diisopropylphenylgroup (see Figure 9). Thus the equilibrium process, 1 T 10,

involves a windshield wipermotion (back and forth) rather than afull rotation.

The enthalpy and entropy of activation as calculated usingdensity functional theory are ΔH‡ = 16.9 kcal/mol and ΔS‡ =�9.9 cal/mol 3K. These values agree well with the experimentallydetermined kinetic parameters of ΔH‡ = 14.3 kcal/mol andΔS‡ = �11 cal/mol 3K. Reaction thermodynamics for the iso-merization process from 1 to 10 are computed to be ΔH� = 1.7kcal/mol and ΔS� = �1.5 cal/mol 3K, which at room tempera-ture equates to an equilibrium mixture of 97:3. This value agreesvery well with the experimentally determined equilibrium ratio(93.3:6.7).

These same isomerization barriers were also determined forthe cationic catalyst, formed by the removal of one methylgroup, as well as the likely active catalyst,13 the olefin appendedspecies (see 1a in Figure 1). Themethyl cation is not necessarilythe best representation of the active catalyst, as the opencoordination site could be occupied by a solvent molecule,olefin, β-agostic interaction (in a longer polymer chain), or thecounterion. However, our goal was to determine if there weregross differences for the rotation of the (2-iPr)Ph fragment inthe dimethyl neutral catalyst (1) and the two cationic repre-sentations of active species. The isomerization processes for theneutral procatalysts 1 and 10 and their corresponding cationicspecies are depicted in Figure 10. The computed barrier for thecationic systems were determined to be even lower than that ofthe neutral species with ΔH‡ = 12.9 kcal/mol for activated 1andΔH‡ = 13.9 kcal/mol for ethylene-appended 1 (Figure 10).While the calculations for the active cationic catalysts are onlyestimates, these barriers are low and one would expect thecorresponding rotation of the (2-iPr)Ph group to be as fast, ifnot faster, than the rate of polymerization. The relative rate atwhich the (2-iPr)Ph group rotates is important since the twopossible procatalysts, 1 and 10, are structurally different enough

Table 1. Selected Bond Lengths and Angles for the Calcu-lated and Experimentally Determined Molecular Structuresa

bond/angle 1 1 (X-ray) 10 TS

Hf�N2 2.325 2.295(2) 2.331 2.328

Hf�N1 2.094 2.081(2) 2.099 2.122

Hf�C27 2.220 2.223(3) 2.218 2.220

Hf�C28 2.230 2.210(3) 2.226 2.217

Hf�C32 2.287 2.256(2) 2.288 2.294

N2�C14 1.469 1.475(3) 1.469 1.491

N2�C38 1.442 1.444(3) 1.444 1.443

C14�C34 1.515 1.501(3) 1.514 1.522

C31�C32 1.399 1.391(3) 1.398 1.395

C31�C33 1.480 1.489(3) 1.480 1.478

C27�Hf�C28 107.8 105.7(2) 106.2 111.1

N1�Hf�C32 69.6 69.56(8) 69.4 69.6

N1�Hf�N2 71.5 72.12(7) 71.5 72.3

C34�C14�N2 108.7 109.2(2) 109.1 105.2

C35�C14�N2 114.6 114.1(2) 117.2 112.7aMetric parameters are based on the geometries shown in Figure 7�9for the calculated structures.

Figure 10. Isomerization of 1/10 and the anticipated activation stepsand possible isomerizations of various cationic species.



that they are likely to produce different types of polymers. Thestructural differences between the two isomers have alreadybeen discussed, but as an example of the contrasting geome-tries, one can compare the distance between the methineproton of the (2-iPr)Ph group and the hafnium atom. In 1,this distance is 5.570 Å, while in 10 this distance has beenreduced to 3.050 Å, indicating a more sterically crowdedenvironment. Since even achiral versions of pyridylamidecatalysts {without (2-iPr)Ph)} produce multimodal polymersas a result of ligand modification,13 it is unclear what the role ofthe (2-iPr)Ph rotation is in 1 and 3 with regard to polymerproperties.Ethylene/1-Octene Copolymerization Study. Ethylene/1-

octene copolymerization reactions was also conducted in a 2 Lbatch reactor at 120 �C containing 460 psi ethylene pressureand 250 g of 1-octene. In addition to complexes 1 and 3, (η5-C5Me4)(SiMe2-N-tBu)TiMe2 (CGC) was also included in thestudy for comparison. Procatalysts were activated with 1.2equivalents (relative to procatalyst) of [HNMe(C18H37)2]-[B(C6F5)4] activator. All polymerization reactions were car-ried out for 15 min and stopped by venting the ethylenepressure. At a polymerization temperature of 120 �C, thecatalytic activity of 1 is about 60% higher than that of thezirconium analogue 3, but is 18 times lower than the catalyticactivity of CGC. At 150 �C, the activity decreases but therelative activity trends between catalysts remain almost thesame. The hafnium complex 1 is a good 1-octene incorporator,leading to polymers with 1-octene levels that are higher thanthose produced by 3 but somewhat lower than those producedby CGC (at both polymerization temperatures). The same1-octene incorporation trends (hafnium leads to higher in-corporation of 1-octene than the zirconium analogue) wereobserved also within the imino-amido and imino-enamidofamilies of catalysts.4,7 Pyridylamido complex 1 is a better1-octene incorporator than hafnium imino-amido and

imino-enamido catalysts.4,7 The most remarkable polymeriza-tion data included in Table 2 are the molecular weight ofpolymers produced by 1 and 3. At a polymerization tempera-ture of 120 �C, procatalyst 1 gives an ultrahigh molecularweight ethylene/1-octene copolymer with a Mw of 1422 kDa,which is about 30 times higher than that produced by the CGCcatalyst. The molecular weights of polymers produced by 1 at120 �C are not only higher than those produced by CGC butalso higher than those generated by hafnium imino-enamidocomplexes, which have Mw of about 1000 kDa under verysimilar polymerization conditions. The zirconium complex 3results in polymers with high Mw that is about half of thatproduced by the Hf analogue. Procatalyst 1 is a very rareexample of a catalyst that is capable of producing ethylene/1-octene copolymers at 120 �C with a Mw above 1000 kDa.Propylene Polymerization Study. Propylene polymeriza-

tion reactions were conducted in a 1.8 L batch reactor undertwo different sets of conditions. The first set of experimentswas conducted under high propylene concentration and

Table 2. Ethylene/1-Octene Copolymerization Data for Complexes 1, 3, and CGCa

run # poly. temp (�C) catalyst (μmol) yield (g) catalyst activityb Tm (�C) Mw � 10�3 (kDa) Mw/Mn octene content (mol %)

1 120 1 (1.5) 19.9 13 267 53.8 1420 3.1 12.1

2 120 3 (1.5) 8.4 8400 68/106 867 3.3 8.5

3 120 CGC (0.2) 46.7 233 500 59.1 50.2 2.2 15.6

4 150 1 (2.5) 17.5 7000 51.1 565 8.2 12.7

5 150 3 (2.0) 7.6 3800 71/114 301 136 8.4

6 150 CGC (0.4) 47.5 118 750 55.4 28.6 1.8 14.6a Polymerization conditions: 533 mL of Isopar-E; 250 g of 1-octene; ethylene pressure = 460 psi; procatalyst:activator:MMAO = 1:1.2:10; activator:[HNMe(C18H37)2][B(C6F5)4]; hydrogen = 10 mmol; reaction time 15 min. bActivity: g of polymer/mmol cat. CGC = {(η5-C5Me4)(SiMe2-N-tBu)}TiMe2. 1-Octene content determined by FTIR.

Table 3. Propylene Polymerization Data for Complexes 1and 3 (high propylene concentration)a

run

#

catalyst

(μmol)

yield

(g)

catalyst

activitybTm

(�C)%

mmmm

Mw � 10�3

(kDa) Mw/Mn

7 1 (1) 23.8 23 800 153.9 94.2 198 3.0

8 3 (1) 10.9 10 900 146.6 92.6 63.4 2.9a Polymerization conditions: temp = 90 �C; 667mL of Isopar-E; 286 g ofpropylene; hydrogen = 8.3 mmol; procatalyst:activator:MMAO =1:1.2:10; activator: [HNMe(C18H37)2][B(C6F5)4]; reaction time10 min. bActivity: g of polymer/mmol cat.

Figure 11. 3D structures of four possible 2,1-insertion regioerrorsin iPP.



90 �C reactor temperature (Table 3). The data indicate thatthe zirconium complex 3 exhibits about 50% lower activitythan 1. The Zr catalyst yields isotactic polypropylene (iPP)with significantly lower Mw and slightly lower tacticityas shown by a reduced melting point and 13C NMRanalysis.Previous studies2d,20 showed that pyridylamido catalyst 1

led to a 2,1-insertion regioerror (RE3, Figure 11), which isstructurally different from the regioerrors observed in poly-mers prepared by standard C2-symmetric metallocene catalysts(RE1 and RE2). Initially, very low levels of the minor 2,1-insertion regioerror in the polymers from 1made it impossibleto determine conclusively its nature. We decided to prepareseveral iPP samples under different reaction conditionsusing catalysts 1 and 3 in an effort to generate samples withsignificantly higher amounts of secondary minor 2,1-regioerrors,in order to allow us to establish its stereochemistry unambigu-ously. The second set of propylene polymerization reactions wasperformed at lower propylene pressure and two different reactortemperatures (60 and 120 �C), as shown in Table 4. Gratifyingly,13C NMR analysis of polymers produced at the higher tempera-ture (120 �C) (runs 9 and 10) reveals significant formation of the

minor regioerror (Figure 12, label with # symbol). Chemical shiftanalysis of resonances of this minor regioerror suggests that theybelong to either the RE1 or the RE4 microstructure. In order toassign this regioerror, a 2DHOESY experiment of iPP from run 9was conducted (Figure 13). It was expected that the chemicalshift difference of the two protons attached to carbons F and f(Figure 12) in RE1 and RE4, respectively, should be about0.4 and 0.13 ppm, respectively. The chemical shift differencefound in the sample from run 9 is 0.48 ppm (Figure 13), whichindicates that this minor 2,1-regioerror belongs to the RE1

Table 4. Propylene Polymerization Data for Complexes 1and 3 (low propylene concentration)a

run

#

temp

(�C)catalyst

(μmol)

yield

(g)

catalyst

activitybTm

(�C)Mw � 10�3

(kDa)

Mw/

Mn

9 120 1 (0.5) 4.9 9800 144.7 88.7 2.7

10 120 3 (2.0) 2.8 1400 139.1 67.4 4.3

11 60 1 (0.5) 2.2 4400 156.7 702 2.2

12 60 3 (1.0) 7.2 7200 150.2 168 1.9a Polymerization conditions: 300 mL of Isopar-E; propylene = 80 g;hydrogen = 9.6 mmol; procatalyst:activator:MMAO = 1:1.2:10; activa-tor: [HNMe(C18H37)2][B(C6F5)4]; reaction time 10 min. bActivity:g of polymer/mmol cat.

Figure 12. 13C NMR of iPP prepared at 120 �C (run 9, top spectrum) and iPP prepared at 60 �C (run 13, bottom spectrum). Asterisks and numbersymbols designate RE3 and RE1 2,1-insertions, respectively.

Figure 13. HOESY (1H�13C) of iPP (resonances F and f) prepared at120 �C (run 9). Mixing time is 100 ms.



microstructure.20 The presence of RE1 and RE3 regioerrors iniPP produced by 1 and 3 indicates that these misinsertions arenot triggered by the preceding stereoerror in the growingpolymer chain and are formed by enchainment of 2,1-propylenecoordinated with both enantiofaces to the metal center. Sinceprocatalysts 1 and 3 can result in the formation of more than oneactive catalyst under polymerization conditions, it is not obviousif both regioerrors (RE3 and RE1) are formed by the same ordifferent catalytic species.

’CONCLUSIONS

This work revealed that the second component present in thehafnium and zirconium pyridylamido procatalysts is a result of thepresence of a minor diastereoisomer that is in dynamic equilibriumwith the primary complex at ambient temperature. Analysis ofchemical shift differences between the isomers together with low-temperature NOE experiments and computational work showedthat the difference between the major and minor isomers is due tothe rotation of the 2-isopropylphenyl ring attached to the chiralcenter. Activation barriers obtained experimentally (ΔH‡ and ΔS‡

of 14.3(6) kcal/mol and�11(2) cal/mol 3K, respectively, for theHfcomplex) for this fluxional process compared favorably withcomputational data. Copolymerization studies of ethylene and1-octene showed pyridylamide hafnium procatalyst 1 exhibitsmoderate activity at 120 �C, but it produces ultrahigh molecularweight (1420 kDa) copolymers at this temperature. Complex 1 is avery rare example of a procatalyst capable of producing such highmolecular weight copolymers at temperatures above 100 �C. Thezirconium analogue 3 gives lower activity and leads to polymers witha lower molecular weight and reduced 1-octene content comparedto 1. Polypropylene produced by the pyridylamido zirconium 3 hasslightly lower tacticity and lowermolecular weight than the polymerprepared by the hafnium complex 1. Propylene polymerization athigher reactor temperature (120 �C) resulted in the formation ofpolypropylenewith twodistinct 2,1 insertion regioerrors. Theminorregioerror was determined to be the same regioerror as the oneobserved in iPP produced by metallocene catalysts.

’EXPERIMENTAL SECTION

General Considerations. All syntheses and manipulations of air-sensitive materials were carried out in a nitrogen-filled glovebox. Solventswere first saturated with nitrogen and then dried by passage throughactivated alumina and Q-5 catalyst prior to use. Deuterated NMR solvents(toluene-d8, C6D6) were dried over sodium/potassium alloy and filteredprior to use unless otherwise noted. NMR spectra were recorded on VarianInova 300 (FT 300 MHz, 1H; 75 MHz, 13C) and VNMRS 500 (FT 500MHz, 1H; 126 MHz, 13C) spectrometers. 1H NMR data are reported asfollows: chemical shift, integration, multiplicity (br = broad, s = singlet, d =doublet, t = triplet, q = quartet, p = pentet, hept = heptet, andm=multiplet)and assignment. Chemical shifts for 1H NMR data are reported inppm downfield from tetramethylsilane (TMS, δ scale) using residual protonsin the deuterated solvents (C6D6, 7.15 ppm, C6D5CD3, 2.09 ppm) asreferences. 13C NMR data were determined with 1H decoupling, and thechemical shifts are reported in ppm vs tetramethylsilane (C6D6, 128 ppm,toluene-d8, 20.4ppm).2,6-Bis(1-methylethyl)-N-[[6-(1-naphthalenyl)-2-pyr-idinyl]methylene]benzenamine and 2-isopropylphenyllithium were preparedaccording to published procedures.10c Sublimed grade HfCl4 was obtainedfrom Strem, and the naphthylboronic acid used was obtained from FrontierScientific. Elemental analyses were performed by Midwest Microlab, LLC.Preparation of N-[2,6-Bis(1-methylethyl)phenyl]-R-[2-(1-methylethyl)-

phenyl]-6-(1-naphthalenyl)-2-pyridinemethanamine (2). The 2,6-bis(1-

methylethyl)-N-[[6-(1-naphthalenyl)-2-pyridinyl]methylene]benzenamine(2.20 g, 5.6 mmol) was magnetically stirred as a slurry in 60�70 mL of dryether under a nitrogen atmosphere. An ether solution of 2-isopropylphe-nyllithium (1.21 g, 9.67mmol in 25mLof dry ether) was added slowly usinga syringe over a period of 4�5 min. After the addition was complete, a smallsample was removed and quenched with 1 N NH4Cl, and the organic layerwas analyzed by high-pressure liquid chromatography (HPLC) to check forcomplete consumption of starting imine. The remainder of the reactionmixture was quenched by the careful, slow addition of 1 NNH4Cl (10mL).The mixture was diluted with more ether, and the organic layer was washedtwice with brine, dried (anhydrousNa2SO4), filtered, and stripped of solventunder reduced pressure. The crude product, obtained as a thick red oil (2.92g; 100% yield), was used without further purification. 1H NMR (500 MHz,toluene-d8): δ 8.14 (m, 1H), 7.68 (dd, 1H, J = 7.5, 1.5 Hz), 7.64�7.56 (m,2H), 7.46 (dd, 1H, J=7.1, 1.2Hz), 7.29�7.20 (m, 3H), 7.19�7.09 (m, 4H),7.08�7.00 (m, 5H), 5.66 (s, 1H,H14), 4.80 (s, 1H,NH), 3.29 (hept, 1H, J=6.8 Hz, CH(CH3)2), 3.22 (hept, 2H, J = 6.8 Hz, CH(CH3)2), 1.08�1.03(m, 6H, CH(CH3)2), 1.01 (d, 3H, J = 6.9 Hz, CH(CH3)2), 1.00 (d, 6H,J = 6.9 Hz, CH(CH3)2), 0.95 (d, 3H, J = 6.8 Hz, CH(CH3)2).

1H NMR(500 MHz, C6D6): δ 8.20 (m, 1H), 7.75 (m, 1H), 7.68�7.60 (m, 2H),7.51 (dd, J = 7.1, 0.9 Hz, 1H), 7.30�7.23 (m, 3H), 7.21�7.05 (m, 8H),7.02 (d, J = 7.6Hz, 1H), 5.73 (s, 1H), 4.87 (s, 1H), 3.33 (hept, J = 6.8 Hz,1H), 3.27 (hept, J = 6.7 Hz, 2H), 1.07 (d, J = 6.8 Hz, 6H), 1.02 (d, J = 6.8Hz, 9H), 0.97 (d, J = 6.8 Hz, 3H). 13C{1H} NMR (126 MHz, C6D6):δ 163.01, 159.07, 146.71, 143.44, 143.41, 141.00, 138.86, 136.78, 134.55,131.85, 129.24, 128.64, 128.52, 127.78, 127.68, 126.55, 126.53, 126.27,126.00, 125.81, 125.33, 124.41, 123.96, 122.91, 120.19, 67.10, 28.85, 28.12,24.36, 24.23, 23.81. 13C{1H} NMR (126 MHz, toluene-d8): δ 162.98(quat), 159.06 (quat), 146.69 (quat), 143.47 (quat), 143.34 (quat), 141.04(quat), 138.80 (quat), 136.73 (CH), 134.55 (quat), 131.83 (quat), 129.20(CH), 128.62 (CH), 128.48 (CH), 127.70 (CH), 127.63 (CH), 126.54(CH), 126.45 (CH), 126.22 (CH), 125.90 (CH), 125.73 (CH), 125.22(CH), 124.37 (CH), 123.86 (CH), 122.84(CH), 120.09 (CH), 67.12 (CH),28.85 (CH(CH3)2), 28.11 (CH(CH3)2), 24.32 (CH(CH3)2), 24.23(CH(CH3)2), 24.20 (CH(CH3)2), 23.78 (CH(CH3)2). ES-HRMS (m/e):calcd for C37H41N2 (M þ H)þ 513.326, found 513.327.

Preparation of [N-[2,6-Bis(1-methylethyl)phenyl]-R-[2-(1-methylethyl)-phenyl]-6-(1-naphthalenyl-kC2)-2-pyridinemethanaminato(2-)-kN1,kN2]dimethylhafnium (1, 10). Inside a nitrogen-filled glovebox a glassjar was charged withN-[2,6-bis(1-methylethyl)phenyl]-R-[2-(1-methyl-ethyl)phenyl]-6-(1-naphthalenyl)-2-pyridinemethanamine (10.21 g,19.92 mmol) dissolved in 100 mL of toluene. To this solution was addednBuLi (8.4 mL of 2.5 M solution in hexanes, 21.0 mmol) by syringe. Thissolution was stirred for 1 h; then solid HfCl4 (6.41 g, 20.00 mmol) wasadded. The jar was capped with an air-cooled reflux condenser, and themixture was heated to 100 �C for 2 h. After cooling, MeMgBr (23.2 mL of3 M solution in diethyl ether, 69.7 mmol, 3.5 equivalents) was added bysyringe, and the resulting mixture stirred overnight at ambient temperature.Solvent was removed from the reaction mixture using a vacuum systemattached to the drybox. To the residue was added toluene and the mixturewas filtered. The residue was washed with additional toluene (8 washes of∼50mL; until the eluent flowwas colorless). Recovered eluentwas strippedto dryness under vacuum, and hexane (30mL)was added, then removed byvacuum. Hexane (50 mL) was again added, and the resulting slurry wasstirred for 30 min. The suspension was filtered and the collected productwas washed with cold hexane (50 mL) to give the desired product as abright yellow powder (11.2 g, 15.46 mmol, 78%). 1: 1H NMR (500MHz, C6D6, 30 �C): δ 8.57 (d, 1H, 3J = 7.5 Hz, H1), 8.25 (d, 1H, 3J = 8.5Hz, H6), 7.81 (d, 1H, 3J = 7.5 Hz, H2), 7.71 (dd, 1H, 3J = 7.7 Hz, 3J = 1.7Hz, H3), 7.51 (d, 1H, 3J = 8.0Hz, H7), 7.34 (m, 1H,H10), 7.30 (m,H5),7.27 (m, H4), 7.17 (dd, 1H, 3J = 7.5 Hz, 4J = 1.9, H17), 7.13 (t, 1H, 3J =7.5 Hz, H16), 7.07 (dd, 1H, 3J = 7.5 Hz, 4J = 1.9, H15), 7.07 (m, 1H,H13), 7.00 (m, 2H, H11/H12), 6.84 (t, 1H, 3J = 7.5 Hz, H8), 6.57 (s,1H, H14), 6.55 (d, 1H, 3J = 7.5 Hz, H9), 3.82 (sep., 1H, 3J = 6.8



Hz, H19), 3.37 (sep., 1H, 3J = 7.0 Hz, H20), 2.89 (sep., 1H, 3J = 6.8 Hz,H18), 1.38 (d, 3H, 3J= 7.0Hz, H25), 1.36 (d, 3H, 3J= 7.5Hz,H24), 1.17(d, 3H, 3J = 6.5 Hz, H21), 1.14 (d, 3H, 3J = 6.5 Hz, H26), 0.94 (s, 3H,H27), 0.689 (d, 3H, 3J = 6.5 Hz, H22), 0.685 (s, 3H, H28), 0.38 (d, 3H,3J = 6.5 Hz, H23). 10: 1H NMR (C6D6, 30 �C): δ 8.55 (d, 1H, 3J = 7.5Hz, H10), 8.30 (d, 1H, 3J = 8.5 Hz, H60), 7.77 (d, 1H, 3J = 8.0 Hz, H20),7.69 (d, 1H, 3J = 8.0 Hz, H30), 7.55 (d, 1H, 3J = 8.0 Hz, H70), 7.30 (tm,1H, 3J = 8.5 Hz, H50), 7.25 (tm, 1H, 3J = 7.0 Hz, H40), 7.18 (d, 1H, 3J =7.5 Hz, H130), 7.07 (tm, 1H, 3J = 7.0 Hz, H120), 6.86 (t, 1H, 3J = 7.5 Hz,H80), 6.75 (t, 1H, 3J = 7.5 Hz, H110), 6.68 (d, 1H, 3J = 8.0 Hz, H100),6.48 (d, 1H, 3J = 7.5 Hz, H90), 6.13 (s, 1H, H140), 3.92 (sep., 1H,3J= 7.0Hz,H190), 3.45 (sep., 1H, 3J=6.8Hz,H180), 3.18 (sep., 1H, 3J=6.8Hz, H200), 1.41 (d, 3H, 3J = 7.0 Hz, H240), 1.40 (d, 3H, 3J = 7.0 Hz, H250),1.27 (d, 3H, 3J= 6.5Hz,H220), 1.18 (d, 3H, 3J= 6.5Hz,H260), 0.88 (s, 3H,H270), 0.67 (s, 3H,H280), 0.48 (d, 3H, 3J = 6.5Hz, H210), 0.29 (d, 3H, 3J =7.0 Hz, H230). 1: 13C{1H} NMR (126 MHz, C6D6, 30 �C): δ 206.04(C32), 170.53 (C34), 164.32 (C33), 147.35 (C37), 146.68 (36), 146.36(C39), 145.55 (C38), 143.98 (C31), 140.81 (C35), 140.75 (C8, 1JCH =163.6 Hz), 135.70 (C29), 134.11 (C1, 1JCH = 158.6 Hz), 130.72 (C30),130.09 (C10), 129.92 (C3), 129.86 (C2), 127.95 (CH), 126.90 (C5),126.79 (CH), 125.99 (C16), 125.46 (CH), 125.41 (C4), 125.14(C17), 124.47 (CH), 124.17 (C6), 120.36 (C7, 1JCH = 166.2 Hz, 2JCH =6.7Hz),), 119.48 (C9, 1JCH = 166.4Hz,

2JCH = 6.7Hz), 76.75 (C14, 1JCH =133.5 Hz), 66.89 (C28, 1JCH = 111.6 Hz), 62.85 (C27, 1JCH = 112.8 Hz),28.70 (C20), 28.63 (18), 28.12 (C19), 27.44 (C24), 25.77 (C25), 25.44(C26), 25.16 (C21), 23.73 (C23), 23.02 (C22). Anal. Calcd forC39H4HfN2: C, 65.12; H, 6.17; N, 3.89. Found: C, 65.56; H, 5.93, N, 3.73.Preparation of [N-[2,6-Bis(1-methylethyl)phenyl]-R-[2-(1-methylethyl)-

phenyl]-6-(1-naphthalenyl-kC2)-2-pyridinemethanaminato(2-)-kN1,-kN2]dimethylzirconium (3, 30). A solution ofN-[2,6-bis(1-methylethyl)-phenyl]-R-[2-(1-methylethyl)phenyl]-6-(1-naphthalenyl)-2-pyridi-nemethanamine (2.25 g, 4.39 mmol) in hexane (40 mL) was cooled in aglovebox freezer (�40 �C). nBuLi solution (1.93 mL of 2.5 M nBuLi inhexane, 4.83 mmol) was added by syringe, and the suspension was stirredfor about 2 h after reaching ambient temperature. The reaction mixturewas cooled again in the freezer, filtered, washed with cold hexane, andvacuum-dried overnight. The lithium amide product (2.38 g) as a light tansolid powder was carried on to the next step without further treatment orpurification (quantitative recovery was assumed). This lithium salt (2.38 gcrude from the previous reaction, 4.38 mmol) was stirred in toluene(∼50 mL) with ZrCl4 (1.02 g, 4.38 mmol). After mixing, the mixturebecame clear and darkened. The solutionwas heated to reflux for 2 h, thenwas allowed to cool to ambient temperature. The reaction solution waschilled slightly below ambient temperature in the glovebox freezer justprior to the addition of MeMgBr solution (5.06 mL of 3 M solution inether, 15.18 mmol), which was added via syringe. This mixture was stirredat ambient temperature overnight. The solvents were removed completelyunder vacuum; then toluene (50 mL) was re-added and the mixture wasfiltered. The residual dark sludgewaswashedwith toluene until thewasheswere almost colorless. The collected toluene solution was stripped todryness under vacuum, and a crude product was obtained as a dark brownpowder. Hexane (∼30 mL) was added to the crude product, and it wastriturated briefly at ambient temperature before being cooled to�40 �C,filtered, and washed with additional cold hexane. The solid productrecovered from the hexane filtering (1.36 g, 49% yield) was furtherpurified by recrystallization (toluene/hexane) to provide X-ray qualitycrystals. 1H NMR (500 MHz, C6D6) δ 8.59 (d, 1H, J = 7.6 Hz, H1), 8.24(d, 1H, J = 7.6 Hz, H6), 7.76�7.69 (m, 2H, H2/H3), 7.50 (d, 1H, J =7.9 Hz, H7), 7.36 (m, 1H, H10), 7.32�7.25 (m, 2H, H4/H5), 7.19�7.10(m, 2H, H16/H17), 7.09�7.05 (m, 2H, H13/H15), 7.04�6.97 (m, 2H,H11/H12), 6.83 (t, 1H, J = 7.8Hz, H8), 6.54 (d, 1H, J = 7.7Hz, H9), 6.44(s, 1H, H14), 3.84 (hept, 1H, J = 6.9Hz, H19), 3.40 (hept, 1H, J = 6.7Hz,H20), 2.92 (hept, 1H, J= 6.7Hz,H18), 1.38 (d, 3H, J= 6.8Hz,H25), 1.36(d, 3H, J = 6.9 Hz, H24), 1.19 (s, 3H), 1.18 (d, 3H, J = 7.3 Hz, H21), 1.13

(d, 3H, J = 6.8 Hz, H26), 0.85 (s, 3H), 0.69 (d, 3H, J = 6.7 Hz, H22), 0.38(d, 3H, J = 6.7 Hz, 3H). 13C{1H} NMR (126 MHz, C6D6): δ 192.35(C32), 170.24 (C34), 164.34 (C33), 147.42 (quat), 146.47 (quat),146.43 (quat), 144.71 (quat), 142.74 (quat), 140.78 (quat), 140.74(C8), 135.76, 133.34 (C1), 130.25 (C10), 130.00, 129.89, 129.38,127.93, 126.85, 126.82, 126.29, 125.45, 125.32, 125.23, 124.56, 124.18(C6), 120.16 (C7), 119.65 (C9), 76.71 (C14), 53.61 (ZrCH3), 49.77(ZrCH3), 28.86 (C20), 28.68 (C18), 28.17 (C19), 27.47 (C24), 25.83(C25), 25.33 (C26), 25.04 (C21), 23.84 (C23), 23.15 (C22). Anal. Calcdfor C39H4ZrN2: C, 74.12; H, 7.02; N, 4.43. Found: C, 74.22; H, 7.15,N, 4.42.PolymerizationProcedures andPolymerCharacterizations.

Ethylene/1-Octene Copolymerization. A 2 L Parr reactor was usedin the polymerizations. All feeds were passed through columns ofalumina and Q-5 catalyst (available from Engelhard Chemicals Inc.)prior to introduction into the reactor. Procatalyst and cocatalyst(activator) solutions were handled in the glovebox. A stirred 2 L reactorwas charged with about 533 g of mixed alkanes solvent and 250 g of1-octene comonomer. Hydrogen was added as a molecular weightcontrol agent by differential pressure expansion from a 75 mL additiontank at 300 psi (2070 kPa). The reactor contents were heated to thepolymerization temperature of 120 �C and saturated with ethylene at460 psig (3.4 MPa). Catalysts and cocatalysts, as dilute solutions intoluene, were mixed and transferred to a catalyst addition tank andinjected into the reactor. The polymerization conditions were main-tained for 10 min with ethylene added on demand. Heat was continu-ously removed from the reaction vessel through an internal cooling coil.The resulting solution was removed from the reactor, quenched withisopropyl alcohol, and stabilized by addition of 10 mL of a toluenesolution containing approximately 67 mg of a hindered phenol anti-oxidant (Irganox 1010 from Ciba Geigy Corporation) and 133 mg of aphosphorus stabilizer (Irgafos 168 from Ciba Geigy Corporation).Between polymerization runs, a wash cycle was conducted in which850 g of mixed alkanes was added to the reactor and the reactor washeated to 150 �C. The reactor was then emptied of the heated solventimmediately before beginning a new polymerization run. Polymers wererecovered by drying for about 12 h in a temperature-ramped vacuumoven with a final set point of 140 �C. Melting and crystallizationtemperatures of polymers were measured by differential scanningcalorimetry (DSC 2910, TA Instruments, Inc.). Samples were firstheated from room temperature to 180 at 10 �C/min. After being heldat this temperature for 2�4 min, the samples were cooled to �40 at10 �C/min, held for 2�4 min, and then heated to 160 �C. Weightaverage molecular weights (Mw) and polydispersity values (PDI) weredetermined by analysis on a Viscotek HT-350 gel permeation chroma-tographer (GPC) equipped with a low-angle/right-angle light-scatteringdetector, a 4-capillary inline viscometer, and a refractive index detector.The GPC utilized three Polymer Laboratories PLgel 10 μm MIXED-Bcolumns (300 � 7.5 mm) at a flow rate of 1.0 mL/min in 1,2,4-trichlorobenzene at either 145 or 160 �C. To determine octeneincorporation, 140 μL of each polymer solution was deposited onto asilica wafer, heated at 140 �C until the trichlorobenzene had evaporated,and analyzed using a Nicolet Nexus 670 FTIR with 7.1 version softwareequipped with an AutoPro auto sampler.Propylene Polymerization. Propylene polymerization was con-

ducted in a 1.8 L SS batch reactor. This reactor was manufactured byBuchi AG and sold by Mettler and is heated/cooled via the vessel jacketand reactor head. Syltherm 800 was the heat transfer fluid used and wascontrolled by a separate heating/cooling skid. Both the reactor and theheating/cooling system are controlled and monitored by a Camile TGprocess computer. The bottom of the reactor was fitted with a largeorifice bottom dump valve, which empties the reactor contents into a 6 LSS dump pot. The dump pot was vented to a 30 gal blowndown tank,with both the pot and the tank N2 purged. All chemicals used for



polymerization or catalyst makeup were run through purificationcolumns, to remove any impurities that may effect polymerization.The propylene, toluene, and IsoparE were passed through two columns,the first containing A2 alumna, the second containing Q5 reactant. TheN2 and H2 were passed through a single Q5 reactant column. Thereactor was cooled to 50 �C for chemical additions. The Camile controlsthe addition of IsoparE, using a micromotion flowmeter to accuratelyadd the desired amount. The addition of H2 was accurately achieved bypressuring up a 50 mL shot tank to 240 psi and slowly adding H2 untilthe desired decrease was reflected in the shot tank pressure. Thepropylene was then added through the micromotion flowmeter.After the chemicals were in the reactor, the reactor was heated to thepolymerization temperature. The activator(s) and catalyst were handled inan inert glovebox,mixed together in a vial, drawn into a syringe, and pressuretransferred into the catalyst shot tank. This was followed by three rinses oftoluene, 5 mL each. Immediately after catalyst/activator addition, the runtimer began. Usually within the first 2 min of successful catalyst runs, anexotherm was observed, as well as decreasing reactor pressure. Thesepolymerizations were run for 10 min; then the agitator was stopped, thereactor pressured up to ∼500 psi with N2, and the bottom dump valveopened to empty reactor contents to the dump pot. The dumppot contentswere poured into trays placed in a lab hood, where the solvent wasevaporated off overnight. The trays containing the remaining polymer werethen transferred to a vacuumoven, where theywere heated to 145 �Cundervacuum to remove any remaining solvent. After the trays cooled to ambienttemperature, the polymers were weighed for yield/efficiencies and sub-mitted for polymer testing. Weight average molecular weights (Mw) andpolydispersity values were determined by analysis on a SYMYXhigh-throughput gel permeation chromatographer. The GPC utilized threePolymer Laboratories PLgel 10 μmMIXED-B columns (300� 10 mm) ata flow rate of 2.5 mL/min in 1,2,4-trichlorobenzene at 160 �C.Melting andcrystallization temperatures of polymers were measured by differentialscanning calorimetry (DSC 2910, TA Instruments, Inc.). Samples werefirst heated from room temperature to 210 at 10 �C/min. After beingheld at this temperature for 4 min, the samples were cooled to �40 at10 �C/min and were then heated to 215 at 10 �C/min after being heldat �40 �C for 4 min.Magnetization Transfer Experiments.18 NMR measurements

were performed on a Varian VNMRS 500 (FT 500 MHz) spectrometerusing toluene-d8. The rate of this chemical exchange was measured byfollowing transfer of magnetization (by measuring areas under theexchanging resonances) as a function of mixing time. A two-siteexchange process is illustrated in eq 1. The rate laws for this two-siteexchange are shown in eqs 2 and 3. Integration of these rate laws leads toexpressions 4 and 5, where At and Bt are peak intensities (integrals) ofresonances A and B at time t,Ao and Bo are peak intensities (integrals) ofA and B at t = 0, k is the chemical exchange rate constant, t is the mixingtime, and Ra and Rb are relaxation rates for A and B.21

relaxationrsRa

Ahka

kbB sf

Rbrelaxation Keq ¼ ka=kb ð1Þ

DADt

¼ kb½B� � ka½A� � Ra½A� ð2Þ

DBDt

¼ ka½A� � kb½B� � Rb½B� ð3Þ

At ¼ 12Ao 1þ Ra � Rb þ ka � kb

La � Lb

� �e�Lb�t

"

þ 1þRa � Rb þ ka � kbLa � Lb

� �e�La�t

�þB0

kbLa � Lb

ðe�Lb�t�e�La�tÞ� �

ð4Þ

Bt ¼ A0ka

La � Lbðe�Lb�t � e�La�tÞ

� �

þ 12Bo 1þ Ra � Rb þ ka � kb

La � Lb

� �e�Lb�t þ 1� Ra � Rb þ ka � kb

La � Lb

� �e�La�t

" #

La¼ 12

ðRa þ Rb þ ka þ kbÞ þffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi½ðRa � Rb þ ka � kbÞ2þ4kakb�

q� �

Lb¼ 12

ðRa þ Rb þ ka þ kbÞ �ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi½ðRa � Rb þ ka � kbÞ2þ4kakb�

q� �ð5Þ

Magnetization transfer experiments were performed on a VarianVNMRS 500 (FT 500 MHz) spectrometer equipped with a pulse-fieldgradient probe using NOESY1D pulse sequences (double pulse fieldgradient spin echo NOE (DPFGSE-NOE) method22). Magnetizationtransfer data were collected at 10, 20, 30, and 40 �C. The resonance at6.12�6.15 ppm was selectively excited in each of these experiments, andits return to equilibrium together with its exchange with the peak at6.57�6.59 ppm was followed as a function of time (mixing time). Probetemperature was calibrated using ethylene glycol. Acquisition time wasset to 2 s with a delay time of 1 s. Line broadening of 0.5 was used. Thenumber of transients collected for each spectrum was set from 128 to856. All the resonances were integrated and tabulated. Chemicalexchange rate constants (k) were obtained by fitting time-dependentintegrated values of both signals to eqs 4 and 5 using a nonlinear least-squares routine. Five parameters (Ao, Bo, ka, kb, Ra, and Rb) were variedin order to minimize the sum of the squared deviations between theexperimental and calculated data. Microsoft Excel solver was used toperform this least-squares analysis. Thermodynamic parameters (ΔH‡

and ΔS‡) were obtained by least-squares analysis of the nonlinear formof the Eyring equation.23 In this procedure, rate constants are calculatedusing the nonlinear form of the Eyring equation, and the ΔH‡ and ΔS‡

are adjusted until the sum of the error squared between the observed andcalculated rate constants reaches a minimum.Microsoft Excel solver wasused to perform this least-squares analysis. Errors were obtained bynonlinear error analysis using SolvStat macro.24

13C NMR Analysis of Polypropylene Samples. The samplewas prepared by adding approximately 2.7 g of stock solvent to a0.21�1.2 g sample in a 10mmNMR tube and then purging in anN2 boxfor 2 h. The stock solvent was made by dissolving 4 g of PDCB para-dichlorobenzene in 39.2 g of ortho-dichlorobenzene with 0.025 Mchromium acetylacetonate (relaxation agent). The sample was dissolvedand homogenized by heating the tube and its contents at 140�150 �C.The data were collected using a Bruker 400MHz spectrometer equippedwith a Bruker Dual DUL high-temperature CryoProbe.25 For 1D 13CNMR, the data were acquired using 320 transients per data file, a 7.3 spulse repetition delay (6 s delayþ1.3 s acq. time), 90 degree flip angles,and a modified inverse gated decoupling26 with a sample temperature of120 �C. All measurements were made on nonspinning samples in lockedmode. Samples were homogenized immediately prior to insertion intothe heated (125 �C) NMR changer and were allowed to thermallyequilibrate in the probe for 7 min prior to data acquisition.

’COMPUTATIONAL DETAILS

Calculations were carried out with the Gaussian0327 program. Alloptimizations and frequencies used the hybrid density functional theory(DFT) method, B3LYP.28 These calculations were performed with theLANL2TZ(f)29 basis set on hafnium, which includes triple-ζ functionson the valence and added f-functions, while the inner electrons areapproximated by the LANL2DZ effective core potential. All other atomsutilize the 6-311G** basis set.30 Unless otherwise stated, energies arecompiled in kcal/mol, and free energies are quoted at 298 K.



Structure Determination of 1 and 3. Data for both structureswere collected at 173 K on a Siemens SMART PLATFORM equippedwith a CCD area detector and a graphite monochromator utilizing MoKR radiation (λ = 0.71073 Å). Cell parameters were refined using up to8192 reflections in each case. A hemisphere of data (1381 frames) wascollected using theω-scanmethod (0.3� framewidth) for each structure.The first 50 frames were remeasured at the end of data collection tomonitor instrument and crystal stability (maximum correction on I was<1%). Absorption corrections by integration were applied on the basis ofmeasured indexed crystal faces.

The structures were solved by the direct methods in SHELXTL631

and refined using full-matrix least-squares. The non-H atoms weretreated anisotropically, whereas the hydrogen atoms were calculated inideal positions and were riding on their respective carbon atoms. For 1,in the final cycle of refinement, 6234 observed reflections with I > 2σ(I)were used to refine 387 parameters, and the resulting R1, wR2, and S(goodness of fit) were 2.31%, 5.33%, and 1.03, respectively. A correctionfor secondary extinction was not applied. For 3, in the final cycle ofrefinement, 21 193 observed reflections with I > 2σ(I) were used to refine379 parameters, and the resulting R1, wR2, and S (goodness of fit) were3.7%, 8.54%, and 0.924, respectively. A correction for secondary extinctionwas not applied due to the small crystal size. Refinement was done using F2.Structure Determination of 2.The crystal,mounted on aMitegen

Micromount, was automatically centered on a Bruker SMART X2S bench-top crystallographic system. Intensity measurements were performed usingmonochromated (doubly curved silicon crystal) MoKR radiation (0.71073Å) from a sealed microfocus tube. Generator settings were 50 kV, 30 mA.Data were acquired using three sets of omega scans at different phi settings.APEX2 software was used for preliminary determination of the unit cell.Determinations of integrated intensities and unit cell refinement wereperformed using SAINT. Data were corrected for absorption effects withSADABS using the multiscan technique. The structure was solved with XS,and subsequent structure refinements were performed with XL.

’ASSOCIATED CONTENT

bS Supporting Information. NMR spectra, X-ray data for 1,2, and 3 including CIF file, table with total energies for allcomputed structures, mol file containing xyz data for all com-puted structures, and Excel spreadsheet containing magnetiza-tion transfer calculations. This material is available free of chargevia the Internet at http://pubs.acs.org.

’AUTHOR INFORMATION

Corresponding Author*E-mail: [email protected].

’REFERENCES

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