Imino-Amido Hf and Zr Complexes: Synthesis, Isomerization, and

Organometallics 2011, 30, 251–262 DOI: 10.1021/om1008742

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Imino-Amido Hf and Zr Complexes: Synthesis, Isomerization, and Olefin Polymerization Robert D. J. Froese, Brian A. Jazdzewski, Jerzy Klosin,* Roger L. Kuhlman, Curt N. Theriault, and Dean M. Welsh 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 Received September 8, 2010

New hafnium and zirconium imino-amido complexes containing trimethylethylidene bridging groups are reported. Investigation into the thermal stability of these complexes revealed that they undergo facile rearrangement of the ligand backbone at 80 °C to produce isomeric imino-amido complexes. Mechanistic experiments and DFT calculations indicate that this isomerization reaction proceeds via a direct 1,2-methyl shift rather than a multistep mechanism involving the metal center. The initial imino-amido complexes (pre isomerization) exhibit high ethylene/1-octene copolymerization activities and generate polymers with very high molecular weights and relatively low comonomer contents. On the other hand, the isomerized complexes display significantly lower polymerization activities and give polymers with lower molecular weights and broad molecular weight distributions, indicative of multisite behavior.

Introduction There has been considerable research in the last 15 years in the area of non-Cp-based molecular catalysts1 for olefin *To whom correspondence should be addressed. E-mail: jklosin@ dow.com. (1) (a) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed. 1999, 38, 428–447. (b) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283–316. (c) Makio, H.; Kashiwa, N.; Fujita, T. Adv. Synth. Catal. 2002, 344, 477–493. (d) Park, S.; Han, Y.; Kim, S. K.; Lee, J.; Kim, H. K.; Do, Y. J. Organomet. Chem. 2004, 689, 4263–4276. (2) (a) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100, 1169–1203. (b) Tian, J.; Hustad, P. D.; Coates, G. W. J. Am. Chem. Soc. 2001, 123, 5134–5135. (c) Bollmann, A.; Blann, K.; Dixon, J. T.; Hess, F. M.; Killian, E.; Maumela, H.; McGuinness, D. S.; Morgan, D. H.; Neveling, A.; Otto, S.; Overett, M.; Slawin, A. M. Z.; Wasserscheid, P.; Kuhlmann, S. J. Am. Chem. Soc. 2004, 126, 14712–14713. (d) Boussie, T. R.; Diamond, G. M.; Goh, C.; Hall, K. A.; LaPointe, A. M.; Leclerc, M. K.; Murphy, V.; Shoemaker, J. A. W.; Turner, H.; Rosen, R. K.; Stevens, J. C.; Alfano, F.; Busico, V.; Cipullo, R.; Talarico, G. Angew. Chem., Int. Ed. 2006, 45, 3278– 3283. (3) Arriola, D. J.; Carnahan, E. M.; Hustad, P. D.; Kuhlman, R. L.; Wenzel, T. T. Science 2006, 312, 714–719. (4) (a) De Waele, P.; Jazdzewski, B. A.; Klosin, J.; Murray, R. E.; Petersen, J. L.; Theriault, C. N.; Vosejpka, P. C. Organometallics 2007, 26, 3896–3899. (b) Kuhlman, R. L.; Klosin, J. Macromolecules 2010, 43, 7903–7904. (5) (a) Mashima, K.; Ohnishi, R.; Yamagata, T.; Tsurugi, H. Chem. Lett. 2007, 36, 1420–1421. (b) Tsurugi, H.; Ohnishi, R.; Kaneko, H.; Panda, T. K.; Mashima, K. Organometallics 2009, 28, 680–687. (6) For main group imino-amido compounds see: (a) Klerks, J. M.; Stufkens, D. J.; v. Koten, G.; Vrieze, K. J. Organomet. Chem. 1979, 181, 271–283. (b) Jastrzebski, J. T. B. H.; Klerks, J. M.; v. Koten, G.; Vrieze, K. J. Organomet. Chem. 1981, 210, C49–C53. (c) Kaupp, M.; Stoll, H.; Preuss, H.; Kaim, W.; Stahl, T.; v. Koten, G.; Wissing, E.; Smeets, W. J. J.; Spek, A. L. J. Am. Chem. Soc. 1991, 113, 5606–5618. (d) Wissing, E.; Jastrzebski, J. B. H.; Boersma, J.; v. Koten, G. J. Organomet. Chem. 1993, 459, 11–16. (e) Wissing, E.; v. Gorp, K.; Boersma, J.; v. Koten, G. Inorg. Chim. Acta 1994, 220, 55–61. (f) Bruce, M.; Gibson, V. C.; Redshaw, C.; Solan, G. A.; White, A. J. P.; Williams, D. J. Chem. Commun. 1998, 2523–2524. r 2010 American Chemical Society

polymerization, resulting in the discovery of previously unknown polymerization behaviors2 and new polymeric materials.2a,3 Recently, we4 and researchers from Osaka University5 have been interested in group 4 imino-amido complexes,6 a class of olefin polymerization catalysts that was originally introduced by Murray and co-workers at Union Carbide.7 These complexes are of interest due to several factors, including ease of synthesis, good polymerization characteristics, and dependence of catalyst reactivity toward R-olefins on the metal and/or ligand substitutions. We recently described the synthesis of these imino-amido complexes (e.g., 1 and 3) in high yields via the reaction of hafnium or zirconium alkyls with bis-imines, as shown in Scheme 1.4a The use of complexes such as 1 as procatalysts for olefin polymerization is limited because these complexes are thermally unstable and can undergo dibenzyl elimination via a radical pathway to form ene-diamido complexes (2).4a This conversion is particularly facile for Zr complexes, occurring even at ambient temperature. In complexes such as 3, additional reaction pathways also may be observed.4a,5a For example, not only does thermal treatment of 3 lead to the formation of an ene-diamido complex (5), but a related imino-amido complex (4) is also observed. This species forms following an isomerization of the imino-amido fragment, presumably via a 1,2-hydrogen shift. A similar ligand framework rearrangement was proposed in the synthesis of an imino-amido manganese complex.8 Even though (7) (a) Murray, R. E. U.S. Patent 6,096,676, 2000. (b) Murray, R. E.; George, V. M.; Nowlin, D. L.; Schultz, C. C.; Petersen, J. L. Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 2002, 43, 294–295. (c) Murray, R. E. Int. Pat. Appl. 2003051935, 2003. (8) Riollet, V.; Coperet, C.; Basset, J.-M.; Rousset, L.; Bouchu, D.; Grosvalet, L.; Perrin, M. Angew. Chem., Int. Ed. 2002, 41, 3025– 3027. Published on Web 12/29/2010

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Froese et al. Scheme 1

good polymerization activities are observed for some group 4 imino-amido procatalysts,4a the high polymer polydispersity (Mw/Mn) values observed suggest that multiple species may be present during polymerization. We have recently focused our attention on a subclass of imino-amido complexes containing the trimethylethylidene bridging group (e.g., 6, 7). We hypothesized that complexes bearing these ligands would be more thermally stable and lead to polymerization catalysts that displayed improved olefin polymerization behavior.

Scheme 2. Synthesis of Complexes 10a and 11a

We have recently demonstrated that such complexes (6, 7) not only lead to very active olefin polymerization catalysts but, more importantly, also are capable of undergoing reversible chain transfer reactions with diethylzinc in the production of various types of olefin block copolymers.4b Because of our previous experience with the thermal reactivity of complexes 1 and 3, investigations of the thermal behavior of group 4 imino-amido complexes containing trimethylethylidene bridging groups were warranted.

formation reaction9 between keto-amine 87c,10 and ethyl amine in toluene (Scheme 2). Reaction of 9a with either hafnium or zirconium tetrabenzyl in toluene gives complex 10a or 11a, respectively, in good yields. Both complexes exhibit Cs symmetry in solution, as shown by NMR spectroscopy. For example, the 1H NMR spectrum of 10a (in toluene-d8, Figure 1) shows only one i-Pr methine signal at 3.33 ppm and two doublets appearing at 1.33 and 1.21 ppm, corresponding to the i-Pr methyl groups. This indicates that both isopropyl groups have the same chemical environment in solution. The appearance of two separate resonances for the i-Pr methyl groups is indicative of hindered rotation of the 2,6-diisopropylphenyl fragment (DIP) along the N-C(ipso)

Results and Discussion Synthesis of Ligands and Complexes. For the purpose of this study we chose to explore the synthesis, characterization, and polymerization behavior of complexes related to 6 (vide supra). Ligands bearing an N-ethyl substituent were favored over the N-n-octyl found in complex 6, as it was believed that the group 4 complexes derived from this ligand would possess lower solubility in nonpolar solvents such as hexane, thus facilitating purification by crystallization. The desired ligand 9a was synthesized via the titanium tetrachloride-induced imine

(9) (a) Carlson, R.; Nilsson, A. Acta Chem. Scand. 1984, B 38, 49–53. (b) Armesto, D.; Bosch, P.; Gallego, M. G.; Martin, J. F.; Ortiz, M. J.; Perez-Ossorio, R.; Ramos, A. Org. Prep. Proc. Int. 1987, 19, 181–186. (c) De Kimpe, N.; D'hondt, L.; Stanoeva, E. Tetrahedron Lett. 1991, 32, 3879–3882. (d) Carlson, R.; Larsson, U.; Hansson, L. Acta Chem. Scand. 1992, 46, 1211–1214. (e) Klosin, J. U.S. Patent 6,617,407, 2003. (10) See Supporting Information for single-crystal X-ray analysis of this compound.

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Figure 1. 1H and NOESY 1D NMR spectra of 10a (toluene-d8).

bond.11 This leads to different chemical environments of the methyl groups, pointing either toward or away from the trimethylethylidene bridge. Signals corresponding to the three methyl groups of the ligand’s bridge resonate as singlets at 1.21 ppm (3H) and 0.66 ppm (6H), further confirming the Cs molecular symmetry of the complex in solution. Methylene protons of the three benzyl groups appear as a sharp singlet at 2.14 ppm (6H), indicating fast exchange of the benzyl groups on the NMR time scale. To further confirm the structure in solution, a series of NOE experiments was conducted (Figure 1). Irradiation of the quartet at 2.84 ppm (corresponding to the methylene protons of the N-ethyl substitutent) results in the observation of strong NOEs with the triplet at 0.75 ppm (corresponding to the methyl protons of the N-ethyl substituent), the singlet at 2.14 ppm (benzyl methylene protons, as described above), and the singlet at 1.21 ppm (corresponding to one methyl group attached to the imine carbon of the ligand backbone). As expected, no NOE enhancement is observed between this quartet and the singlet observed for the two equivalent methyl groups attached to the ligand backbone appearing at 0.66 ppm. Similar NMR spectroscopic characteristics also are observed for complex 11a in solution. Gratifyingly, both complexes 10a and 11a were found to be highly crystalline relative to 6 and are readily crystallized from the toluene/hexane solvent mixtures, facilitating the further characterization of complex 10a via singlecrystal X-ray analysis (vide infra). To investigate the thermal stability of the newly prepared complexes, 10a was dissolved in toluene-d8 and heated for 16 h at 90 °C. The 1H NMR spectrum of the reaction mixture shows complete disappearance of 10a and clean formation of a new complex, which displays the same number of resonances and coupling patterns as 10a, but different chemical shifts. The identity of the product, 10b, was determined to be a constitutional isomer of 10a (Scheme 3), initially established by NOE experiments. The most revealing NOE data are observed upon irradiation of the quartet resonating at 3.13 ppm, corresponding to the methylene of the N-ethyl group (Figure 2). NOEs similar to those of 10a are observed (11) Hindered rotation of the 2,6-diisopropylphenyl fragment is observed commonly in bis-imine complexes. For examples see: (a) Schleis, T.; Spaniol, T. P.; Okuda, J.; Heinemann, J.; M€ ulhaupt, R. J. Organomet. Chem. 1998, 569, 159–167. (b) Bianchini, C.; Giambastiani, G.; Rios, I. G.; Mantovani, G.; Meli, A.; Segarra, A. M. Coord. Chem. Rev. 2006, 250, 1391–1418.

Scheme 3. Isomerization of 10a and 11a

with one significant difference: unlike in the case of 10a, there is no trace of NOE enhancement of the methyl group attached to the imine carbon (singlet at 1.35 ppm, 3H). Instead, a strong NOE enhancement of the singlet corresponding to two equivalent methyl groups attached to the ligand’s bridge (0.91 ppm, 6H) is observed. These data clearly indicate that the ethyl group is in close proximity to the gem-dimethyl fragment, indicative of an isomerized complex resulting from the migration of the methyl group. The identity of 10b was corroborated by a single-crystal X-ray analysis and full characterization of the independently synthesized complex 10b. Ligand 9b (the expected ligand of 10b) was prepared in two steps starting from 3-bromo-3-methylbutan-2-one (12) as shown in Scheme 4. Reaction of 9b with hafnium tetrabenzyl in toluene solution gives 10b in close to quantitative yield. The thermal rearrangements of 10a and 11a in solution were studied extensively utilizing NMR spectroscopy. These reactions are found to follow first-order kinetics with kobs values of 5.1 10-5 s-1 (t1/2 = 228 min) and 9.6 10-5 s-1 (t1/2 = 120 min) at 80.4 °C, respectively. Full kinetic analysis of 10a gives ΔH‡ and ΔS‡ of 29.1(7) kcal/mol and 4(2) cal/mol 3 K, respectively. Mechanism of Isomerization of 10a and 11a. We considered two plausible isomerization mechanisms for the conversion of 10a to 10b and 11a to 11b. One mechanism involves a direct 1,2-methyl shift (Scheme 5), whereas the other mechanism involves participation of the metal center (Scheme 6). The latter mechanism was proposed by Copert and co-workers to account for the observed product from the reaction of an aryl bis-imine and a neopentyl manganese complex.8 These two pathways can be distinguished by following the isomerization reaction of the Hf(CD3)3 derivative. A direct 1,2-shift should occur without scrambling between CH3 and CD3 groups, whereas the metal

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Froese et al.

Figure 2. 1H and NOESY 1D NMR spectra of 10b (toluene-d8). Scheme 4. Synthesis of 9b

Scheme 5. Reaction Diagram for the Direct 1,2-Methyl Shifta

Scheme 6. Possible Hf-Assisted Isomerization Pathwaysa

a DFT enthalpies (in kcal/mol) relative to 14a (0.0) on the potential energy surface are provided in parentheses.

participation mechanism (Scheme 6) would lead to replacement of some CD3 groups with CH3, an event that could be easily detected by 1H NMR spectroscopy. To investigate the mechanism operating in the isomerization of 10a, the perdeuteromethyl metal-alkyl analogue 14a was prepared as shown in Scheme 7. Complex 10a was reacted with three equivalents of iodine in methylene chloride at ambient temperature to produce the triiodo derivative 15. This reaction is very fast at ambient temperature, as evidenced by the rapid disappearance of the purple color of added iodine. Reaction between 15 and three equivalents of CD3MgI gives the desired 14a. Complex 14a was fully characterized both by NMR spectroscopy and single-crystal X-ray analysis.10 The 1H NMR spectrum of the isolated 14a in toluene-d8 is shown in Figure 3 (top spectrum). The 2H NMR spectrum of 14a shows a singlet at 0.31 ppm corresponding to three equivalent metal-bound CD3 ligands. An NMR tube containing 14a was heated at 80 °C for 24 h, revealing that complex 14a isomerizes with the first-order rate constant, kobs, of 2.3 10-5 s-1 (t1/2 = 492 min). This reaction rate is approximately 50% lower than the conversion of 10a to 10b. The 1H NMR spectrum shows about 90% conversion of 14a to 14b (Figure 3, bottom spectrum), but no Hf-CH3 resonances are observed around 0.3 ppm. Since the chemical shift of protons in

a DFT enthalpies (kcal/mol) relative to 14a (0.0) of various minima and transition states on the potential energy surface are provided in parentheses.

the 1H NMR spectrum is very similar to the equivalent deuterons in 2H NMR, the expected chemical shift for the Hf-CH3 resonances was close to 0.30 ppm. Additionally, an analogue of 14a with CH3 instead of CD3 groups attached to hafnium was prepared (14a-CH3) by the salt metathesis route and subsequently thermolyzed to give 14b-CH3. The chemical shifts of the Hf methyl groups in 14a-CH3 and 14b-CH3 were found to resonate in toluene-d8 at 0.30 and 0.25 ppm, respectively. The absence of any CH3 resonances in this region during thermolysis

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Figure 3. 1H NMR spectra (toluene-d8) of 14a (top spectrum) and reaction mixture after 90% conversion of 14a to 14b (bottom spectrum). The resonance at 4.00 ppm belongs to ferrocene used as an internal standard. Scheme 7. Synthesis of 14a

of 14a rules out the metal-assisted mechanism and therefore favors the 1,2-methyl shift. Computational Study.12 A series of calculations was performed to estimate activation parameters for the different isomerization pathways. The relative enthalpies of the direct 1,2-methyl shift and the Hf-assisted isomerization pathways for 14a are presented in Schemes 5 and 6, respectively. The direct 1,2-methyl shift from 14a to 14b proceeds across transition state TS1 with a ΔH‡ of 26.3 kcal/mol (Scheme 5).

The computed enthalpy of activation for the tribenzyl derivative 10a is slightly lower (24.7 kcal/mol), consistent with the faster reaction rate observed experimentally for this complex compared to its trimethyl analogue, 14a. Two possible Hf-assisted (12) Three-dimensional structures of all calculated compounds are included (in sd file format) in the Supporting Information. SD files can be read by the free Mercury program available at http://www.ccdc.cam. ac.uk/products/mercury/.

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Scheme 8. Calculated Energies (kcal/mol) for Imino-Amido Complexes and Associated Transition States

Froese et al. Table 1. Relative Energies (ΔH in kcal/mol) of the Nine Important Structures on the Potential Energy Surface for the Neutral (LMMe3) and the Cationic (LMMe2þ) Speciesa

a b c d TS1 TS2 TS3 TS4 TS5

pathways are shown in Scheme 6. The first pathway, involving the formation of bis-amido complex 14d by methyl transfer from Hf to the ligand, requires traversing TS2 with a ΔH‡ of 37.2 kcal/mol. Coincidently, intermediate 14d has the same ground-state energy as 14b. The second pathway involves the formation of a bis-imine-Hf complex 14c, which is a highly endothermic process (ΔH° = 22.4 kcal/mol). This observation helps explain why the reverse reaction, addition of bis-imines to hafnium tetrabenzyl, leads to benzyl-inserted complex. The formation of bis-imine complex 14c from 14a has a barrier (TS3) of 46.4 kcal/mol, whereas the reverse reaction (14c to 14a) occurs with a barrier of 24.0 kcal/mol. These computational data clearly indicate that the lowest barrier for isomerization of 14a to 14b occurs for the direct 1,2-methyl transfer, which is lower by 10.9 and 20.1 kcal/mol compared to the processes proceeding via bis-amido and bis-imine intermediates, respectively. The conclusions from this computational study are in full agreement with the experimental data, which indicate that Hf-assisted isomerization does not occur during interconversion of 14a to 14b. The computed activation parameters of ΔH‡ = 26.3 kcal/mol and ΔS‡ = 3.5 cal/mol 3 K for the direct 1,2-methyl shift agree well with those determined experimentally (ΔH‡ = 29.1(7) kcal/mol and ΔS‡ = 4(2) cal/mol 3 K). It is possible that the same direct 1,2-methyl shift might be taking place in the case of isomerization of the manganese imino-amido complex.8,13 The driving force for the isomerization of 14a to 14b is the increased stability of isomer 14b, which was calculated to be 2.9 kcal/mol (ΔH°) lower in energy than 14a.14 To examine the reasons for this thermodynamic preference, the energies of two additional sets of complexes were computed (Scheme 8). The first set contains N-Ph instead of N-DIP substituents, and the second group contains three hydrogen atoms instead of three methyl groups in the backbone of the ligand. In both cases, the ground-state energies are reversed; that is, complexes with amide-aryl substituents are more stable than their amide-alkyl counterparts. The opposite trend observed for 14a and 14b is most likely due to unfavorable steric interactions between the gem-dimethyl and the isopropyl groups of DIP in 14a, which lead to destabilization of 14a relative to 14b. For the ligand itself, DIP prefers to reside adjacent to the imine, as this species (9b) was calculated to be more stable than the DIP-amide (9a) by 5.0 kcal/mol. While isomerization of the neutral species is important for stability of the catalyst precursor, we were also interested in examining the stability of the dimethyl cationic species as a (13) A detailed computational study is currently underway in our laboratory to gain insight into the isomerization mechanism of these manganese complexes. (14) Calculated enthalpy of reaction from 10a to 10b is -4.5 kcal/ mol.

a

neutral HfMe3 (14)

cationic HfMe2 (16)

neutral ZrMe3 (17)

cationic ZrMe2 (18)

0.0 -2.9 22.4 -2.9 26.3 37.2 46.4 38.7 43.3

0.0 -4.8 4.3 19.1 25.6 38.6 46.5 37.6 43.5

0.0 -4.5 21.5 -3.3 25.1 36.9 43.8 37.7 40.3

0.0 -4.5 5.3 15.6 26.8 37.6 45.5 37.3 42.8

The labeling scheme is consistent with Schemes 5 and 6.

representative for the active catalyst to determine if the isomerization barriers change significantly. Even though the cationic active catalyst species may live only for a few minutes under polymerization conditions, the active catalyst may experience very high polymerization temperatures (120-160 °C), which might lead to the isomerization of the catalyst before its deactivation and thus influence its performance. The relative energies of the neutral and cationic hafnium and zirconium species for the different structures are collected in Table 1. A number of trends can be observed from these data. The isomerization from 14a to 14b is an exothermic process for both the cationic and neutral systems. For the cationic species, the direct 1,2-methyl shift (via TS1) also is favored over the bisimine or bis-amide pathways. The barrier for this isomerization process is comparable to those found for the neutral systems. Thus if the experimentally measured kinetic parameters are used and a similar isomerization rate for the cationic system is assumed, the half-life for catalyst conversion at 120 °C would be ∼3 min, which is in the range of the lifetime of the catalyst under polymerization conditions. It is interesting to note that, relative to 14a, the neutral bisamide (14d) is significantly more stable than the cationic bisamide (16d). The electrophilic cationic transition metal complexes prefer to have a saturated metal center (four-coordinate 16a is favored over three-coordinate 16d), while the neutral systems prefer less ligation of the metal (four-coordinate 14d is favored over five-coordinate 14a). The barrier for bis-imine formation is high for both neutral and cationic complexes. However, the reaction from the imino-amido to the bis-imine complex is more likely to occur in the cationic system, where the electrophilic nature of the metal can better support the extra ligation. The reaction to form the bis-imine (16c) from the imino-amido (16a) for the cationic system is still endothermic (4.3 kcal/mol), but it is substantially less than that computed for the neutral species (22.4 kcal/mol). Similar trends are calculated for the analogous neutral (17) and cationic (18) zirconium complexes. Single Crystal X-ray Structures of 10a and 10b. Molecular structures of complexes 10a (Figure 4) and 10b (Figure 5) each show a five-coordinate hafnium atom bound to two nitrogen donors and three benzyl groups. Metallacycles composed of Hf, two carbon (C1, C2) atoms, and two nitrogen (N1, N2) atoms are almost coplanar with mean deviation from the plane of 0.026 and 0.066 A˚ for 10a and 10b, respectively. A comparison of bond lengths within metallacycles in 1, 10a, and 10b is shown in Figure 6. The X-ray crystal structure of 10a reveals a considerably longer Hf-N(imino) bond (2.301(3) A˚) as compared to the Hf-N(amido) bond (2.074(3) A˚). Noticeably greater bonding asymmetry was observed in complex 10b, with

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Figure 4. Molecular structure of 10a. The hydrogen atoms have been omitted for clarity. Thermal ellipsoids are shown at the 40% probability level. Selected bonds (A˚) and angles (deg): Hf-N1 = 2.074(3), Hf-N2 = 2.301(3), C1-N1 = 1.497(4), C2-N2 = 1.270(5), C1-C2 = 1.508(5), N2-Hf-N1 = 72.6(1).


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Figure 6. Comparison of important bond lengths (A˚) in 1, 10a, and 10b. Table 2. Polymerization Data for Complexes 10a, 10b, 11a, 11b, and CGCa

run #

catalyst (μmol)

1 2 3 4 5

10a (0.25) 10b (1.00) 11a (0.25) 11b (1.00) CGC (0.20)

octene content polymer catalyst yield (g) activity Mw 10-3 Mw/Mn Tm (mol %) 35.2 6.7 22.9 5.5 113.8

140 800 6700 91 600 5500 569 000

633 520 782 294 108

3.1 5.2 2.8 60 2.6

102 112 112 120 60

3.8 3.3 1.7 2.9 14.9

a Polymerization conditions: 120 °C; 533 mL of Isopar-E; 250 g of octene; ethylene pressure: 460 psi; procatalyst:activator:MMAO = 1:1.2:10; activator: [HNMe(C18H37)2][B(C6F5)4]; reaction time 15 min. Activity: g of polymer/mmol cat. CGC = {(η 5 -C5 Me4 )(SiMe 2 -Nt-Bu)}TiMe2.

Figure 5. Molecular structure of 10b. The hydrogen atoms have been omitted for clarity. Thermal ellipsoids are shown at the 40% probability level. Selected bonds (A˚) and angles (deg): Hf-N1 = 2.380(4), Hf-N2 = 2.030(4), C1-N1 = 1.291(6), C2-N2 = 1.454(6), C1-C2 = 1.515(6), N2-Hf-N1 = 68.9(1).

Hf-N(imino) and Hf-N(amido) bond lengths of 2.380(4) and 2.030(3) A˚, respectively. The differences in bonding in both complexes can be better visualized by comparing the HfN(imido) and Hf-N(amido) bond differences of 0.227 A˚ for 10a and 0.350 A˚ for 10b. A very long Hf-N(imino) bond of 2.423(3) A˚ also was observed in complexes 1 with aryl (DIP) substituents attached to both imino and amido nitrogen atoms.4 The significant elongation of the Hf-N(imido) bond in 10b and 1 is likely due to the presence of the aryl (DIP) substituent, which presumably competes for nitrogen electron density, thus weakening Hf-N(imido) bonding. A similar description pertains to the case of Hf-N(amido) bond lengths in 10a and 10b, but the effect is less pronounced. The Hf-N(amido) bond in 10a is identical within experimental error to that in 1 (2.070(3) A˚). The Hf-C-Cipso bond angles in both complexes

are in the range of 110.1° and 121.7°, indicating a η1-bonding mode for all benzyl groups. Polymerization Study. Complexes 10a, 10b, 11a, and 11b were evaluated as catalysts for ethylene/1-octene copolymerization in a 2 L batch reactor at 120 °C containing 460 psi ethylene pressure and 250 g of 1-octene. (η5-C5Me4)(SiMe2-N-t-Bu)TiMe2 (CGC) also was included in the study for comparison. Procatalysts were activated with 1.2 equivalents (relative to procatalyst) of [HNMe(C18H37)2][B(C6F5)4] activator. All polymerization reactions were carried out for 15 min and stopped by venting the ethylene pressure. The data presented in Table 2 show that the imino-amido complexes 10a and 11a (runs 1 and 3) result in active catalysts upon activation, with complex 10a possessing higher activity. While the hafnium complex 10a was found to be 50% more active than zirconium analogue 11a, it is less active by a factor of 4 than the titanium-based CGC. Complexes 10a and 11a give very high molecular weight copolymers albeit with low 1-octene incorporation, with zirconium-based catalyst 11a giving the highest (783 K) weight average molecular weight. This molecular weight is much higher than that produced by CGC (Mw of 107 K), although caution needs to be applied when comparing molecular weight capabilities of catalysts having very different reactivity toward R-olefins. Since CGC is a much better 1-octene incorporator than 10a and 11a (Table 2) and it is known15 that 1-octene leads to

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molecular weight reduction during ethylene/1-octene copolymerization reactions with CGC,16 the effect of R-olefin on Mw needs to be considered. The main objective, however, was to determine whether isomerized complexes 10b and 11b are competent as catalysts in olefin polymerization reactions and, if so, what type of polymer microstructure is produced. It was found that complexes 10b and 11b do, indeed, lead to polymer production, but exhibit activities about 20 times lower than their isomeric counterparts and produce polymers with lower molecular weights (e.g., compare entry 1 to entry 3 in Table 2). GPC traces of polymers clearly show at least bimodal distribution for 10b and at least trimodal distribution in the case of 11b. The multimodality exhibited by polymers produced by 10b and 11b implies that these complexes undergo further transformation(s) during activation and/or polymerization. Perhaps the enhanced bonding asymmetry observed in the X-ray structure of 10b leads to higher reactivity of such complexes, which contributes to their higher susceptibility to undergo conversion into other, active species.

Conclusions Imino-amido complexes can be very active for olefin polymerization and can give very high molecular weight polymers. This behavior, coupled with their ability to chain shuttle with metal alkyl reagents, makes them an interesting family of olefin polymerization catalysts. Previously, we had shown that group 4 complexes bearing imino-amido ligands possessing benzyl substituents at the ligand backbone are unstable, leading to the formation of ene-diamido complexes. In an attempt to address instability of such complexes, we shifted our attention to imino-amido complexes containing a trimethylethylidene backbone. Imino-amido complexes containing different substituents on the imino and amino nitrogen atoms (e.g., 6, 10a, and 11a) are more thermally robust, but do undergo related isomerization reactions at higher temperatures. In these cases, we propose that the mechanism involves a direct 1,2-methyl shift of one of the methyl groups at the ligand backbone to form structurally analogous complexes. However, we found that these new complexes exhibit significantly reduced catalytic activity upon activation and produce less uniform polymer compositions. While procatalysts such as 6, 10a, and 11a exhibit very good polymerization characteristics, their propensity to undergo isomerization is not a desirable feature. A more attractive option would be the development of group 4 imino-amido complexes that are resistant to thermal rearrangement but maintain excellent olefin polymerization catalytic properties (e.g., high activity, high polymer molecular weight, and chain shuttling capability). The discovery of such catalysts is an active research area in our laboratory.

Experimental Section General Considerations. All solvents and reagents were obtained from commercial sources and used as received unless otherwise noted. Toluene, hexanes, CH2Cl2, and C6D6 were dried and degassed according to published procedures. NMR spectra were recorded on Varian Mercury-Vx-300 and VNMRS-500 spectrometers. 1H NMR data are reported as follows: chemical shift (multiplicity (br = broad, s = singlet, d = doublet, t = triplet, (15) Wang, W.-J.; Kolodka, E.; Zhu, S.; Hamielec, A. E. J. Polym. Sci., Part A: Polym. Chem. 1999, 37, 2949–2957. (16) Noticeable chain termination is observed after 1,2- and 2,1-octene insertion during ethylene/1-octene copolymerization with CGC, as evidenced by the appearance of vinylidene and vinylene chain ends.15

Froese et al. q=quartet, p=pentet, hept = heptet, and m=multiplet), integration, coupling constant in Hz, and assignment). Chemical shifts for 1 H NMR data are reported in ppm downfield from internal tetramethylsilane (TMS, δ scale) using residual protons in the deuterated solvent (C6D6, 7.15 ppm; toluene-d8, 2.09 ppm; C2D2Cl4, 5.99 ppm) as references. 13C NMR data were determined with 1H decoupling, and the chemical shifts are reported in ppm versus tetramethylsilane (C6D6, 128 ppm; toluene-d8, 20.4 ppm; C2D2Cl4, 73.8 ppm). All metal complexes were synthesized and stored in a Vacuum Atmospheres inert atmosphere glovebox under a dry nitrogen atmosphere or by using standard Schlenk and vacuum line techniques unless otherwise noted. Elemental analyses were performed at the Midwest Microlab, LLC. Preparation of 3-[[2,6-Bis(1-methylethyl)phenyl]amino]-3methyl-2-butanone (8). This compound has been reported previously.7c A modified procedure is described below. A solution of N,N0 -(1,2-dimethyl-1,2-ethanediylidene)bis[2,6-bis(1-methylethyl)benzenamine] (17.0 g, 40.0 mmol) in MeOH (500 mL) was treated with H2O (250 mL), causing the formation of a colorless precipitate. A 1.0 M (aq) solution of H2SO4 (160 mL) was then added dropwise over 1 h. The reaction mixture was refluxed for 1 h, resulting in the formation of a light yellow solution. This solution was cooled to ambient temperature and cautiously treated with KOH (slow addition of solid pellets) until pH = 14. The resulting mixture was extracted with Et2O (3 75 mL), and the combined organic fractions were dried over anhydrous MgSO4. The solvent and liberated 2,6-diisopropylaniline were removed under reduced pressure at 40 °C, resulting in the isolation of an off-white solid. Addition of a minimum amount of warm hexamethyldisiloxane (HMDSO) (∼10 mL) and storage at 0 °C resulted in the precipitation of a colorless solid. Multiple crops of the colorless solid were collected, combined, and washed with cool (∼-70 °C) HMDSO (5 1 mL). The resulting colorless solid was dried under reduced pressure to yield the desired compound, 4.3 g (41%). 1H NMR (300 MHz, CDCl3): δ 7.07 (br s, 3H), 3.70 (br s, 1H), 3.11 (hept, J = 6.6 Hz, 2H), 2.37 (s, 3H), 1.22 (s, 6H), 1.17 (d, J = 6.6 Hz, 12H) ppm. 13C{1H} NMR (75 MHz, CDCl3): δ 212.8, 145.4, 139.5, 124.7, 123.1, 63.6, 28.2, 25.3, 24.0, 23.9 ppm. HREIMS: calcd for C17H27NO m/z = 284.199, found m/z = 284.195. Preparation of N-[1,1-Dimethyl-2-(ethylimino)propyl]-2,6-bis(1-methylethyl)benzenamine (9a). In a glovebox, a Schlenk flask was charged with 3-[[2,6-bis(1-methylethyl)phenyl]amino]-3methyl-2-butanone (2.78 g, 10.68 mmol) dissolved in toluene (75 mL). Addition of 1.0 M TiCl4 in toluene (8.00 mL, 8.01 mmol) resulted in the formation of a bright orange solution and the deposition of an orange solid. The reaction mixture was transferred from the glovebox to a Schlenk line, and anhydrous ethylamine was bubbled through the solution. Within 5 min the color of the reaction mixture had bleached and a colorless precipitate had formed. Bubbling of ethylamine was continued for 2 h at ambient temperature. The reaction mixture was then poured into a solution of saturated Na2CO3 (aq; 150 mL), resulting in a slight exotherm and the deposition of additional colorless precipitate. The suspension was filtered and the filtrate was extracted with Et2O (3 20 mL). The combined organic fractions were dried over anhydrous MgSO4 and evaporated under reduced pressure to yield the desired product as a pale yellow liquid, 2.71 g (88%). 1H NMR (300 MHz, C6D6): δ 7.12 (br s, 3H), 5.24 (br s, 1H), 3.64 (hept, J = 6.9 Hz, 2H), 3.08 (q, J = 7.5 Hz, 2H), 1.46 (s, 3H), 1.23-1.18 (m, 15H), 1.13 (s, 6H) ppm. 13C{1H} NMR (75 MHz, C6D6): δ 172.2, 148.8, 142.2, 124.8, 123.4, 64.1, 45.3, 28.2, 26.8, 24.4, 16.2, 12.7 ppm. HREIMS: calcd for C19H32N2 m/z = 311.246, found m/z = 311.241. Synthesis of [N-[1,1-Dimethyl-2-(ethylimino-KN)propyl]-2,6bis(1-methylethyl)benzenaminato-KN]tris(phenylmethyl)hafnium (10a). To a vial containing N-[1,1-dimethyl-2-(ethylimino)propyl]-2,6-bis(1-methylethyl)benzenamine (0.9835 g, 3.41 mmol) dissolved in 20 mL of toluene was added HfBn4 (1.8513 g, 3.41 mmol) followed by addition of 10 mL of toluene. The reaction mixture was stirred overnight. The solution was concentrated to a volume of 10 mL. During solvent removal a white solid appeared.

Article To this suspension was added 30 mL of hexane, causing further precipitation of product. The solid was collected on the frit, washed with hexane (2 5 mL), and dried under reduced pressure to give 1.45 g of product. The filtrate was put into a freezer for 3 days, resulting in formation of large crystals. The solvent was decanted, and the crystals were washed with 2 mL of cold hexane and dried under reduced pressure to give 0.290 g of product. Combined yield: 69%. 1 H NMR (C6D6, 300 MHz, 23 °C): δ 7.15 (m, 9H), 6.84 (m, 9H), 3.34 (sept, 2H, 3JH-H=6.6 Hz, CH(CH3)2), 2.81 (q, 2H, 3JH-H= 7.2 Hz, CH2CH3), 2.21 (s, 6H, CH2Ph), 1.34 (d, 6H, 3JH-H = 6.6 Hz, CH(CH3)2), 1.21 (d, 6H, 3JH-H = 6.6 Hz, CH(CH3)2), 1.17 (s, 3H, CH3), 0.68 (t, 3H, 3JH-H=7.2 Hz, CH2CH3), 0.65 (s, 6H, CH3). 1H NMR (400 MHz, toluene-d8): δ 7.16-7.13 (m, 3H, DIP), 7.11 (t, J = 7.7 Hz, 6H, meta-Ph), 6.84 - 6.76 (m, 9H, ortho,paraPh), 3.33 (hept, J = 6.6 Hz, 2H, CH(CH3)2), 2.84 (q, J=7.2 Hz, 2H, CH2CH3), 2.14 (s, 6H, CH2Ph), 1.33 (d, J = 6.7 Hz, 6H, CH(CH3)2), 1.28 (s, 3H, CH3), 1.21 (d, J = 6.6 Hz, 6H, CH(CH3)2), 0.75 (t, J = 7.2 Hz, 3H, CH2CH3), 0.66 (s, 6H, CH3). 13 C{1H} NMR (C6D6, 75 MHz, 23 °C): δ 191.63 (NdC), 148.68 (quat), 147.69 (quat), 142.81 (quat), 128.51 (CH), 126.92 (CH), 126.36 (CH), 125.28 (CH), 121.66 (CH), 83.89 (CH2Ph, 1JCH = 116.7 Hz), 76.53 (quat), 44.32 (CH2CH3), 28.43 (CH(CH3)2), 27.47 (CH(CH3)2), 27.06 (2CH3), 25.38 (CH(CH3)2), 15.80 (CH3), 13.78 (CH2CH3). 13C NMR (101 MHz, toluene-d8): δ 191.63 (NdC), 148.67 (quat), 147.64 (quat), 142.86 (quat), 128.44 (CH), 126.93 (CH), 126.38 (CH), 125.24 (CH), 121.62 (CH), 83.88 (CH2Ph), 76.55 (quat), 44.35 (CH2CH3), 28.46 (s), 27.48, 27.10, 25.38, 15.79 (CH3), 13.84 (CH2CH3). Peak assignments were facilitated by HSQC, COSY, and APT spectra. Anal. Calcd for C40H52HfN2: C, 64.98; H, 7.09; N, 3.79. Found: C, 64.90; H, 7.03; N, 3.63. Preparation of (N-(1,2-Dimethyl-2-(ethylamino-KΝ)propylidene)-2,6-bis(1-methylethyl)benzenaminato-KΝ)tris(phenylmethyl)hafnium (10b). Method 1. An NMR tube was charged with 138 mg of 10a, which was dissolved in 0.7 mL of toluene-d8. The sample was heated overnight at 85 °C. Upon cooling to ambient temperature, hexane (3 mL) was added. After standing overnight, the solvent was decanted, and the formed crystals were washed with hexane (2 2 mL) and dried under reduced pressure to give 97 mg of product. Yield: 70.0%. Method 2. A solution of N-(3-(ethylamino)3-methylbutan-2-ylidene)-2,6-diisopropylbenzenamine (9b) (0.206 g, 0.714 mmol) in toluene (1 mL) was treated with a solution of HfBn4 (0.388 g, 0.714 mmol) in toluene (5 mL) to form a yellow solution. The reaction mixture was stirred at ambient temperature for 30 min, and the solvent was removed under reduced pressure. The resulting tan solid was redissolved in CH2Cl2 (1 mL), hexanes were added (3 mL), and the solution was filtered. Storage at ambient temperature overnight led to the deposition of off-white crystals. The mother liquor was decanted, and the crystals were dried under reduced pressure. A second crop of material was isolated upon storage of the mother liquor at -40 °C overnight. The solids were combined to yield the final product, 0.230 g (44%). 1 H NMR (400 MHz, C6D6): δ 7.22-7.16 (m, 6H, meta-CH2Ph), 7.07-6.99 (m, 3H, DIP), 6.98 (d, J = 7.1 Hz, 6H, ortho-CH2Ph), 6.86 (tt, J = 7.6, 1.2 Hz, 3H, para-CH2Ph), 3.15 (q, J = 6.8 Hz, 2H, CH2CH3), 2.51 (hept, J = 6.6 Hz, 2H, CH(CH3)2), 2.05 (s, 6H, CH2Ph), 1.30 (s, 3H, CH3), 1.25 (d, J = 6.8 Hz, 6H, CH(CH3)2), 1.02 (t, J = 6.8 Hz, 3H, CH2CH3), 0.91 (d, J = 6.8 Hz, 6H, CH(CH3)2), 0.88 (s, 6H, CH3). 1H NMR (400 MHz, toluene): δ 7.14 (tm, J = 7.7 Hz, 6H, meta-CH2Ph), 7.06-6.97 (m, 3H, DIP), 6.91 (d, J = 7.2 Hz, 6H, ortho-CH2Ph), 6.82 (t, J = 7.3 Hz, 3H, para-CH2Ph), 3.13 (q, J = 6.8 Hz, 2H, CH2CH3), 2.50 (hept, J = 6.8 Hz, 2H, CH(CH3)2), 1.97 (s, 6H, CH2Ph), 1.35 (s, 3H, CH3), 1.26 (d, J = 6.8 Hz, 6H, CH(CH3)2), 1.04 (t, J = 6.8 Hz, 3H, CH2CH3), 0.93 (d, J = 6.8 Hz, 6H, CH(CH3)2), 0.91 (s, 6H, CH3). 13 C NMR (75 MHz, C6D6) δ 200.69 (CdN), 147.92 (quat), 144.98 (quat), 139.03 (quat), 128.29 (meta-CH2Ph), 127.63 (ortho-CH2Ph), 127.43 (para-DIP), 124.59 (meta-DIP), 121.57 ( para-CH2Ph), 83.09 (CH2Ph), 72.46 (quat), 35.98 (CH2CH3), 28.84 (CH(CH3)2), 26.55 (2CH3), 24.28 (CH(CH3)2), 23.78 (CH(CH3)2), 19.61 (CH3), 19.00 (CH2CH3). 13C{1H} NMR


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(101 MHz, toluene-d8): δ 200.68 (CdN), 147.86 (quat), 145.08 (quat), 139.07 (quat), 128.23 (CH), 127.66 (CH), 127.49 (CH), 124.58 (CH), 121.53 (CH), 83.08 (CH2Ph), 72.54 (s), 36.06 (CH2CH3), 28.89 (s), 26.57 (s), 24.29 (s), 23.79 (s), 19.62 (s), 19.03 (s). Peak assignments were facilitated by HSQC, COSY, and APT spectra. Anal. Calcd for C40H52HfN2: C, 64.98; H, 7.09; N, 3.79. Found: C, 64.66; H, 6.96; N, 3.74. Preparation of [N-[1,1-Dimethyl-2-(ethylimino-KN)propyl]-2, 6-bis(1-methylethyl)benzenaminato-KN]tris(phenylmethyl)zirconium (11a). A colorless solution of N-[1,1-dimethyl-2-(ethylimino)propyl]-2,6-bis(1-methylethyl)benzenamine (0.250 g, 0.870 mmol) in toluene (10 mL) was added to a solution of ZrBn4 (0.396 g, 0.870 mmol) in toluene (10 mL). The resulting orange solution was stirred at ambient temperature for 3 h, and the solvent was removed under reduced pressure to yield a sticky orange residue. This residue was dissolved in toluene (15 mL), and hexanes (30 mL) were added. The resulting solution was filtered and stored at -30 °C overnight, resulting in the deposition of yellow crystals. The mother liquor was decanted, and the crystals were dried under reduced pressure to yield a yellow solid, 0.280 g (49%). 1H NMR (400 MHz, C6D6): δ 7.16 (s, 3H, DIP), 7.12 (tm, J = 7.7 Hz, 6H, meta-Ph), 6.88 (tm, J = 7.3 Hz, 3H, para-Ph), 6.83 (dm, J = 7.1 Hz, 6H, ortho-Ph), 3.41 (hept, J = 6.6 Hz, 2H, CH(CH3)2), 2.85 (q, J = 7.2 Hz, 2H, CH2CH3), 2.38 (s, 6H, CH2Ph), 1.33 (d, J = 6.7 Hz, 6H, CH(CH3)2), 1.26 (s, 3H, CH3), 1.19 (d, J = 6.6 Hz, 6H, CH(CH3)2), 0.74 (s, 6H, CH3), 0.72 (t, J = 7.3 Hz, 3H, CH2CH3). 13C NMR (101 MHz, C6D6): δ 190.56 (NdC), 148.20 (quat), 147.37 (quat), 143.75 (quat), 128.97 (meta-CH2Ph), 126.49 (ortho-CH2Ph), 126.43 (DIP), 125.22 (DIP), 121.59 (para-CH2Ph), 75.37 (quat), 75.14 (CH2Ph), 44.60 (CH2CH3), 28.53 (CH(CH3)2), 27.44 (2CH3), 27.23 (CH(CH3)2), 25.57 (CH(CH3)2), 15.58 (CH3), 13.91 (CH2CH3). Peak assignments were facilitated by HSQC, COSY, and APT spectra. Anal. Calcd for C40H52N2Zr: C, 73.68; H, 8.04; N, 4.30. Found: C, 74.05; H, 7.97; N, 4.22. Preparation of (N-(1,2-Dimethyl-2-(ethylamino-KΝ)propylidene)-2,6-bis(1-methylethyl)benzenaminato-KΝ)tris(phenylmethyl)zirconium (11b). A solution of N-(3-(ethylamino)-3-methylbutan2-ylidene)-2,6-diisopropylbenzenamine (9b) (0.200 g, 0.693 mmol) in toluene (1 mL) was added to a solution of ZrBn4 (0.316 g, 0.693 mmol) in toluene (9 mL) to form an orange solution. The reaction mixture was stirred at ambient temperature for 3 h, and the solution was concentrated (to ∼7 mL) at reduced pressure. The reaction mixture was then filtered and stored at -40 °C for 2.5 days, resulting in the formation of a yellow microcrystalline solid. The mother liquor was decanted, and the yellow solid was dried under reduced pressure. Additional crops of product were isolated upon crystallization either from a minimum amount of toluene or a 3:5 toluene/hexanes mixture at -40 °C. The crops were combined to afford the desired product as a yellow solid, 0.260 g (58%). 1H NMR (500 MHz, C6D6): δ 7.15 (t, J = 7.7 Hz, 6H, meta-Ph), 7.10-7.01 (m, 3H, DIP), 6.94 (d, J = 7.3 Hz, 6H, ortho-Ph), 6.88 (t, J = 7.3 Hz, 3H, para-Ph), 3.07 (q, J = 6.7 Hz, 2H, CH2CH3), 2.57 (hept, J = 6.7 Hz, 2H, CH(CH3)2), 2.27 (s, 6H, CH2Ph), 1.36 (s, 3H, CH3), 1.27 (d, J = 6.8 Hz, 6H, CH(CH3)2), 1.04 (t, J = 6.7 Hz, 3H, CH2CH3), 0.94 (d, J = 6.8 Hz, 6H, CH(CH3)2), 0.86 (s, 6H, CH3). 13C NMR (126 MHz, C6D6): δ 198.46 (CdN), 147.46 (quat), 145.21 (quat), 138.96 (quat), 128.64 (meta-CH2Ph), 127.35 (orthoCH2Ph), 127.26 (DIP), 124.64 (DIP), 121.43 (para-CH2Ph), 72.46 (quat), 72.08 (CH2Ph), 36.81 (CH2CH3), 28.77 (CH(CH3)2), 25.99 (2CH3), 24.32 (CH(CH3)2), 23.85 (CH(CH3)2), 19.43 (CH3), 19.30 (CH2CH3). Peak assignments were facilitated by HSQC, COSY, and APT spectra. Anal. Calcd for C40H52N2Zr: C, 73.68; H, 8.04; N, 4.30. Found: C, 74.05; H, 7.97; N, 4.22. Preparation 3-Bromo-3-methyl-2-butanone (13). In a 500 mL, three-neck, round-bottom flask equipped with a Teflon-coated thermocouple, an addition funnel, and a reflux condenser connected to a NaOH trap, 3-methylbutan-2-one (46.4 g, 0.5 mol) and acetic acid (75 mL) were combined. Bromine (78.3 g, 0.5 mol) and acetic acid (25 mL) were combined and placed in the addition

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funnel. The flask was placed in a cold water bath (15 °C), and the bromine solution was added dropwise. The rate of addition was controlled so the bromine color disappeared before the next drop was added. After the bromine addition was complete, the reaction mixture was stirred at ambient temperature overnight. Water (100 mL) was added to the reaction mixture. The solution was transferred to a separatory funnel, more water was added (100 mL), and the water layer was extracted with Et2O (3 150 mL). The combined Et2O layers were washed with cold, saturated NaHCO3 solution (3 200 mL). The Et2O layer was dried with anhydrous MgSO4, and the solvent was removed in vacuo to yield the crude product as a yellow oil (95% pure by GC). The product was further purified by vacuum distillation (33 °C, ∼25 mmHg) to yield a colorless oil, 59.0 g (74%). 1H NMR (300 MHz, CDCl3): δ 2.44 (s, 3H), 1.86 (s, 6H) ppm. 13C{1H} NMR (75 MHz, CDCl3): δ 203.4, 63.8, 29.6, 24.2 ppm. GC purity: 98%. Preparation of 3-(Ethylamino)-3-methyl-2-butanone (12). In a 500 mL, three-neck, round-bottom flask equipped with a nitrogen inlet, 3-bromo-3-methyl-2-butanone (19.8 g, 120.0 mmol), DMF (50 mL), and MgO (8.4 g, 210.0 mmol) were combined. A solution of ethyl amine in THF (2 M, 90 mL, 180 mmol) was added via syringe, and the mixture was stirred at ambient temperature overnight. The temperature was increased to 60 °C and the mixture was stirred for 18 h. After cooling, the mixture was filtered and the filtrate was concentrated under reduced pressure. The residue was dissolved in Et2O (100 mL) and washed with water (3 100 mL). The Et2O layer was dried with anhydrous MgSO4, and the solvent was removed under reduced pressure to yield an orange oil. The oil was dissolved in Et2O (40 mL), and a 2.0 M solution of HCl in Et2O was added to form the yellow HCl salt. The salt was recrystallized from ethanol/ethyl acetate to yield white crystals. The free base was obtained by treating the salt with NaOH to yield the product as a colorless oil, 3 g (19%). GC purity >99%. 1 H NMR (toluene-d8, 300 MHz): δ 4.74 (s, 1H), 2.21 (q, J = 7.2 Hz, 2H), 1.86 (s, 3H), 0.99 (s, 6H), 0.90 (t, J = 7.2 Hz, 3H) ppm. 13 C{1H} NMR (d8-toluene, 75 MHz): δ 211.7, 137.5, 62.9, 38.3, 24.3, 23.8, 16.1 ppm. Preparation of N-(3-(Ethylamino)-3-methylbutan-2-ylidene)2,6-diisopropylbenzenamine (9b). In a 100 mL, three-neck, roundbottom flask equipped with a nitrogen inlet, 3-(ethylamino)3-methyl-2-butanone (1.6 g, 12.0 mmol), 2,6-diisopropylaniline (6.8 mL, 36.0 mmol), and toluene (25 mL) were combined. A solution of TiCl4 in toluene (1 M, 6.0 mL, 6.0 mmol) was added via syringe, and the mixture was stirred at ambient temperature for 18 h. The mixture was filtered, and the filtrate was transferred to a separatory funnel with water (150 mL). The water layer was washed with toluene (2 100 mL). The water layer was treated with aqueous NaOH solution (5 N) until it became basic and then extracted with Et2O (3 100 mL). The combined Et2O layers were dried with anhydrous MgSO4, and the solvent was removed under reduced pressure to yield a pale brown oil, 1.4 g (40%). 1H NMR (C6D6, 300 MHz): δ 7.14-7.17 (m, 2H), 7.05-7.11 (m, 1H), 2.83 (hept, J = 6.9 Hz, 2H), 2.53 (q, J = 7.2 Hz, 2H), 1.54 (s, 3H), 1.30 (s, 6H), 1.17 (d, J = 6.9 Hz, 6H), 1.16 (d, J = 6.9 Hz, 6H), 1.02 (t, J = 7.2 Hz, 3H) ppm. 13C{1H} NMR (C6D6, 75 MHz): δ 176.2, 147.2, 135.8, 123.5, 123.2, 60.4, 38.3, 28.4, 26.4, 23.3, 23.0, 16.3, 15.6 ppm. Preparation of [N-[1,1-Dimethyl-2-(ethylimino-KN )propyl]2,6-bis(1-methylethyl)benzenaminato-KN]tri(methyl-d3)hafnium (14a). To 458 mg (0.54 mmol) of 15 dissolved in 20 mL of THF was added 1.89 g of CD3MgI as a 1 M solution in ether. During the CD3MgI addition, a white precipitate appeared. After stirring for 2 h, the solution was filtered and the solvent was removed under reduced pressure. The residue was dissolved in 6 mL of hexane, and the solution was filtered. The filtrate was put into the freezer overnight (-40 °C). The solvent was decanted, and the white crystals that formed were washed with cold hexane (2 2 mL) and then dried under reduced pressure to give 125 mg of product. Yield: 44.4%. 1H NMR (300 MHz, C6D6, 23 °C): δ 7.20 (m, 3H), 3.65 (hept, 2H, 3JH-H = 6.9 Hz, CH(CH3)2), 3.27 (q, 2H, 3JH-H = 6.3 Hz, CH2CH3), 1.39 (d, 6H, 3JH-H = 6.9 Hz, CH(CH3)2), 1.29

Froese et al. (s, 3H, CH3), 1.28 (d, 6H, 3JH-H = 6.9 Hz, CH(CH3)2), 0.93 (s, 6H, CH3), 0.86 (t, 3H, 3JH-H = 6.3 Hz, CH2CH3). 1H NMR (500 MHz, toluene-d8, 30 °C): δ 7.19-7.10 (m, 3H), 3.61 (hept, J = 6.8 Hz, 2H, CH(CH3)2), 3.30 (q, J = 7.3 Hz, 2H, CH2CH3), 1.39 (s, 3H, CH3), 1.34 (d, J = 6.8 Hz, 6H, CH(CH3)2), 1.27 (d, J = 6.7 Hz, 6H, CH(CH3)2), 0.95 (s, 6H, CH3), 0.90 (t, J = 7.3 Hz, 3H, CH2CH3). 2H NMR (toluene-d8, 76.8 MHz, 30 °C): δ 0.31 (s, CD3). 13C{1H} NMR (C6D6, 75 MHz, 23 °C): δ 189.12 (NdC), 149.19 (quat), 140.33 (quat), 126.30 (CH), 124.70 (CH), 76.40 (quat), 44.67 (CH2CH3), 28.59 (CH(CH3)2), 27.57 (2CH3), 26.95 (CH(CH3)2), 24.78 (CH(CH3)2), 15.38 (CH3), 13.67 (CH2CH3). 13 C NMR (126 MHz, toluene-d8, 30 °C): δ 189.17, 149.18, 140.41, 126.30, 124.63, 76.27, 44.56, 28.41, 27.45, 26.74, 24.60, 15.11, 13.47. Peak assignments were facilitated by HSQC, COSY, and APT spectra. Anal. Calcd for C22H31D9HfN2: C, 50.80; H, 7.75; N, 5.39. Found: C, 50.26; H, 7.78; N, 5.26. NMR Spectra for (N-(1,2-Dimethyl-2-(ethylamino-KΝ)propylidene)-2,6-bis(1-methylethyl)benzenaminato-KΝ)tri(methyl-d3)hafnium, 14b. 1H NMR (500 MHz, C6D6, 30 °C): δ 7.07-7.00 (m, 3H), 3.56 (q, J = 6.9 Hz, 2H, CH2CH3), 2.50 (hept, J = 6.8 Hz, 2H, CH(CH3)2), 1.40 (s, 3H, CH3), 1.32 (t, J = 6.8 Hz, 3H, CH2CH3), 1.20 (d, J = 6.8 Hz, 6H, CH(CH3)2), 1.12 (s, 6H, CH3), 0.93 (d, J=6.9 Hz, 6H, CH(CH3)2). 1H NMR (500 MHz, toluened8, 30 °C): δ 7.02-7.00 (m, 3H), 3.55 (q, J=6.9 Hz, 2H, CH2CH3), 2.50 (hept, J=6.8 Hz, 2H, CH(CH3)2), 1.45 (s, 3H, CH3), 1.31 (t, J = 6.8 Hz, 3H, CH2CH3), 1.19 (d, J = 6.8 Hz, 6H, CH(CH3)2), 1.15 (s, 6H, CH3), 0.95 (d, J = 6.9 Hz, 6H, CH(CH3)2). 2H NMR (toluene-d8, 76.7 MHz, 30 °C): δ 0.27 (s, CD3). 13C{1H} NMR (126 MHz, C6D6, 30 °C): δ 199.09 (CdN), 145.73 (s), 138.69 (s), 126.73 (s), 124.04 (s), 72.43 (s), 35.58 (s), 28.69 (s), 27.66 (s), 24.12 (s), 23.49 (s), 20.11 (s), 18.85 (s). Preparation of [N-[1,1-Dimethyl-2-(ethylimino-KN)propyl]-2,6bis(1-methylethyl)benzenaminato-KN]triiodohafnium (15). Iodine (0.9109 g, 3.59 mmol) was dissolved in CH2Cl2 (10 mL) and added to a solution of 10a (0.87 g, 1.18 mmol) in CH2Cl2 (10 mL) within 10 min. Rapid discoloration occurred during I2 addition until the final addition of the iodine solution. After the addition was complete, the reaction mixture was stirred for 2 h. Solvent was removed under reduced pressure, leaving a yellow solid. This solid was crystallized from a methylene chloride/hexane mixture (8 mL/ 20 mL) at -40 °C to give 0.70 g of product as a light yellow solid. Yield: 70.3%. 1H NMR (C2D2Cl4, 300 MHz, 23 °C): δ 7.37 (dd, 1H, 3JH-H=8.4 Hz, 3JH-H=7.2 Hz), 7.23 (d, 2H, 3JH-H=7.8 Hz), 3.89 (q, 2H, 3JH-H =7.2 Hz, CH2CH3), 3.46 (hept, 2H, 3JH-H = 6.6 Hz, CH(CH3)2), 2.21 (s, 3H, CH3), 1.55 (t, 3H, 3JH-H=7.2 Hz, CH2CH3), 1.43 (d, 6H, 3JH-H =6.6 Hz, CH(CH3)2), 1.32 (s, 6H, CH3), 1.26 (d, 6H, 3JH-H = 6.6 Hz, CH(CH3)2). 13C{1H} NMR (C2D2Cl4, 75 MHz, 23 °C): δ 192.90 (NdC), 147.81 (quat), 136.70 (quat), 128.13 (CH), 125.52 (CH), 79.05 (quat), 47.48 (CH2CH3), 28.35 (CH3), 27.08 (CH3), 26.89 (CH3), 25.16 (CH3), 15.38 (CH3), 13.67 (CH3). Peak assignments were facilitated by COSY and APT spectra. Anal. Calcd for C19H31HfI3N2: C, 26.95; H, 3.69; N, 3.31. Found: C, 26.76; H, 3.95; N, 3.16. Preparation of the Lithium Salt of N-[1,1-Dimethyl-2-(ethylimino)propyl]-2,6-bis(1-methylethyl)benzenamine. A light yellow solution of N-[1,1-dimethyl-2-(ethylimino)propyl]-2,6-bis(1methylethyl)benzenamine (0.784 g, 2.723 mmol) in hexanes (5 mL) was treated with 2.5 M n-butyllithium in hexanes (1.2 mL, 3.0 mmol), resulting in the formation of a yellow solution. The reaction mixture was stirred at ambient temperature for 5 min, resulting in the formation of a colorless precipitate. This suspension was stored at -40 °C overnight, the solid material was removed via filtration, and the filter cake was washed with cold (∼-40 °C) hexanes (3 2 mL) and dried under reduced pressure to yield a colorless solid, 0.5 g (62%). Material of higher purity may be obtained upon recrystallization from hexanes at -40 °C. 1 H NMR (300 MHz, C6D6, ambient temperature): δ 7.187.07 (m, 3H), 3.87 (br s, 2H), 3.04 (br d, 2H), 1.44 (s, 3H), 1.29 (br d, 6H), 1.20-1.07 (br m, 12H), 0.97 (t, J = 7.2 Hz, 3H) ppm. 1H NMR (300 MHz, d8-THF, ambient temperature): δ 6.67

Article (d, J = 7.5 Hz, 2H), 6.22 (t, J = 7.5 Hz, 1H), 3.67 (hept, J = 6.9 Hz, 2H), 3.28 (q, J = 7.5 Hz, 2H), 1.93 (s, 3H), 1.24 (t, J = 7.5 Hz, 3H), 1.22 (s, 6H), 0.99 (br s, 12H) ppm. Anal. Calcd for C38H62Li2N4: C, 77.51; H, 10.61; N, 9.52. Found: C, 77.82; H, 10.74; N, 9.19. Synthesis of ([N-[1,1-Dimethyl-2-(ethylimino-KN )propyl]-2,6bis(1-methylethyl)benzenaminato-KN]trimethylhafnium (14a-CH3). A pale yellow solution of the lithium salt of N-[1,1-dimethyl2-(ethylimino)propyl]-2,6-bis(1-methylethyl)benzenamine (0.312 g, 0.532 mmol) in toluene (5 mL) was treated with HfCl4 (0.341 g, 1.063 mmol) as a solid. The resulting suspension was stirred at ambient temperature overnight, forming a brown suspension. This suspension was treated with 3.0 M MeMgBr in Et2O (1.20 mL, 3.60 mmol) and stirred at ambient temperature for 2 h, forming a dark brown-black suspension. The reaction mixture was dried under reduced pressure, and the solid residue was extracted with hexanes (3 15 mL). The combined hexanes fractions were dried under reduced pressure to yield a yellow solid. This solid was dissolved in the minimum amount of hexanes and stored at -40 °C for 2.5 days, resulting in the formation of colorless crystals. Multiple crops of the crystals were isolated for a total yield of 0.21 g of colorless solid (40%). 1H NMR (500 MHz, C6D6): δ 7.22-7.16 (m, 3H), 3.64 (hept, J = 7.0 Hz, 2H), 3.27 (q, J = 7.5, 2H), 1.38 (d, J = 7.0 Hz, 6H), 1.29 (s, 3H), 1.27 (d, J = 7.0 Hz, 6H), 0.93 (s, 6H), 0.86 (t, J = 7.5 Hz, 3H), 0.39 (s, 9H) ppm. 1H NMR (400 MHz, toluened8, 30 °C): 7.19-7.10 (m, 3H), 3.61 (hept, J = 6.8 Hz, 2H, CH(CH3)2), 3.31 (q, J = 7.3 Hz, 2H, CH2CH3), 1.39 (s, 3H, CH3), 1.34 (d, J = 6.8 Hz, 6H, CH(CH3)2), 1.27 (d, J = 6.7 Hz, 6H, CH(CH3)2), 0.95 (s, 6H, CH3), 0.90 (t, J = 7.3 Hz, 3H, CH2CH3), 0.30 (s, 9H, HfCH3). 13C{1H} NMR (125 MHz, C6D6): δ 189.3 (CdN), 149.2, 140.5, 126.3, 124.7, 76.2, 56.8, 44.6, 28.4, 27.4, 26.8, 24.6, 15.2, 13.5 ppm. Anal. Calcd for C40H40N2Hf: C, 51.70; H, 7.89; N, 5.48. Found: C, 51.59; H, 7.58; N, 5.58. NMR Spectra for (N-(1,2-Dimethyl-2-(ethylamino-KΝ)propylidene)-2,6-bis(1-methylethyl)benzenaminato-KΝ)trimethylhafnium (14b-CH3). 1H NMR (400 MHz, toluene-d8, 30 °C): δ 7.03-6.99 (m, 3H), 3.55 (q, J = 6.9 Hz, 2H, CH2CH3), 2.50 (hept, J = 6.9 Hz, 2H, CH(CH3)2), 1.45 (s, 3H, CH3), 1.31 (t, J = 6.8 Hz, 3H, CH2CH3), 1.20 (d, J = 6.8 Hz, 6H, CH(CH3)2), 1.15 (s, 6H, CH3), 0.95 (d, J = 6.8 Hz, 7H, CH(CH3)2), 0.25 (s, 9H, HfCH3). 13 C{1H} NMR (100 MHz, toluene-d8, 30 °C): δ 199.02 (CdN), 145.76, 138.69, 126.79, 124.02, 72.48, 56.60 (HfCH3), 35.70, 28.73, 27.66, 24.14, 23.48, 20.14, 18.82. Decomposition Kinetics of 10a. A stock solution was prepared by dissolving 180 mg of 10a in 4.0 mL of toluene-d8. Spectra were collected at 60.4, 70.6, 80.4, and 90.4 °C using the following parameters: number of transients = 32 and acquisition time = 6 s. Rate constants (k) were obtained by least-squares analysis of a nonlinear form of a first-order equation.17 In this procedure concentrations at the given time interval are calculated using a nonlinear form of a first-order equation [A = Ao e-kt], and the rate constant (k) and initial concentration (Ao) are optimized by least-squares using Microsoft Excel solver. Thermodynamic parameters (ΔH‡ and ΔS‡) were obtained by least-squares analysis of a nonlinear form of the Eyring equation. In this procedure rate constants are calculated using a nonlinear form of the Eyring equation and the ΔH‡ and ΔS‡ are adjusted until the sum of the error squared between the observed and calculated rate constants reaches a minimum. Microsoft Excel solver was used to perform this least-squares analysis. This analysis gave ΔH‡ and ΔS‡ of 29.1(7) kcal/mol and 3.8(2.2) cal/mol 3 K, respectively. Errors were obtained by nonlinear error analysis using SolvStat macro.18 Ethylene-1-octene Polymerization Procedures and Polymer Characterizations. Ethylene-1-octene Copolymerization. A 2 L (17) Espenson, J. H. Chemical Kinetics and Reaction Mechanisms, 2nd ed.; McGraw-Hill: New York, 1995. (18) This was accomplished using SolvStat macro included in the book: Billo, E. J. Excel for Chemists, 2nd ed.; Wiley-VCH: Weinheim, 2001; Chapter 12.


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Parr reactor was used in the polymerizations. All feeds were passed through columns of alumina and Q-5 catalyst prior to introduction into the reactor. Procatalyst and cocatalyst (activator) solutions were handled in the glovebox. A stirred 2 L reactor was charged with about 533 g of mixed alkanes solvent and 250 g of 1-octene comonomer. Hydrogen was added as a molecular weight control agent by differential pressure expansion from a 75 mL addition tank at 300 psi (2070 kPa). The reactor contents were heated to the polymerization temperature of 120 °C and saturated with ethylene at 460 psig (3.4 MPa). Catalysts and cocatalysts, as dilute solutions in toluene, were mixed and transferred to a catalyst addition tank and injected into the reactor. The polymerization conditions were maintained for 15 min with ethylene added on demand. Heat was continuously removed from the reaction reactor through an internal cooling coil. The resulting solution was drained from the reactor, quenched with isopropyl alcohol, and stabilized by addition of 10 mL of a toluene solution containing approximately 67 mg of a hindered phenol antioxidant (Irganox 1010 from Ciba Geigy Corporation) and 133 mg of a phosphorus stabilizer (Irgafos 168 from Ciba Geigy Corporation). Between polymerization runs, a wash cycle was conducted in which 850 g of mixed alkanes was added to the reactor and the reactor was heated to 150 °C. The reactor was then emptied of the heated solvent immediately before beginning a new polymerization run. Polymers were recovered by drying for about 12 h in a temperature-ramped vacuum oven with a final set point of 140 °C. Melting and crystallization temperatures of polymers were measured by differential scanning calorimetry (DSC 2910, TA Instruments, Inc.). Samples were first heated from room temperature to 180 °C at 10 °C/min. After being held at this temperature for 2-4 min, the samples were cooled to -40 at 10 °C/min, held for 2-4 min, and then heated to 160 °C. Molecular weight distribution (Mw, Mn) information was determined by analysis on a custom Dow-built robotic-assisted dilution high-temperature gel permeation chromatographer (RAD-GPC). Polymer samples were dissolved for 90 min at 160 °C at a concentration of 30 mg/mL in 1,2,4-trichlorobenzene (TCB) stabilized by 300 ppm BHT, while capped and with stirring. They were then diluted to 1 mg/mL immediately before a 400 μL aliquot of the sample was injected. The GPC utilized two Polymer Laboratories PLgel 10 μm Mixed-B columns (300 10 mm) at a flow rate of 2.0 mL/min at 150 °C. Sample detection was performed using a PolyChar IR4 detector in concentration mode. A conventional calibration of narrow polystyrene (PS) standards was utilized, with apparent units adjusted to homopolyethylene (PE) using known Mark-Houwink coefficients for PS and PE in TCB at this temperature. Absolute Mw information was calculated using a PDI static low-angle light scatter detector. To determine octene incorporation, 140 μL of each polymer solution was deposited onto an IR transparent silicon wafer, heated at 140 °C until the trichlorobenzene had evaporated, and analyzed using a Nicolet Nexus 670 FTIR with 7.1 version software equipped with an AutoPro auto sampler. Structure Determination of 10a and 10b. X-ray intensity data were collected on a Bruker SMART diffractometer using Mo KR radiation (λ = 0.71073 A˚) and an APEXII CCD area detector. Raw data frames were read by the program SAINT19 and integrated using 3D profiling algorithms. The resulting data were reduced to produce hkl reflections and their intensities and estimated standard deviations. The data were corrected for Lorentz and polarization effects, and numerical absorption corrections were applied on the basis of indexed and measured faces. The structure was solved and refined in SHELXTL6.1, using full-matrix least-squares refinement. The non-H atoms were refined with anisotropic thermal parameters, and all of the H atoms were calculated in idealized positions and refined (19) Sheldrick, G. M. SHELXTL6.1, Crystallographic Software Package; Bruker AXS, Inc.: Madison, WI, USA, 2008.

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riding on their parent atoms. The refinement was carried out using F2 rather than F values. R1 is calculated to provide a reference to the conventional R value, but its function was not minimized. Structure Determination of 9 and 14a. A crystal, mounted on a Mitegen Micromount, was automatically centered on a Bruker SMART X2S benchtop crystallographic system. Intensity (20) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, M. G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, H.; Ehara, M.; Toyota, M. K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision C.02; Gaussian, Inc.: Wallingford, CT, 2004. (21) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785. (c) Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Chem. Phys. Lett. 1989, 157, 200. (22) (a) Dunning, T. H., Jr.; Hay, P. J. In Modern Theoretical Chemistry; Schaefer, H. F., III, Ed.; Plenum: New York, 1976; Vol. 3, p 1. (b) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270. (c) Wadt, W. R; Hay, P. J. J. Chem. Phys. 1985, 82, 284. (d) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299. (e) Roy, L. E.; Hay, P. J.; Martin, R. L. J. Chem. Theory Comput. 2008, 4, 1029.

Froese et al. measurements were performed using monochromated (doubly curved silicon crystal) Mo KR radiation (0.71073 A˚) from a sealed microfocus tube. Generator settings were 50 kV, 1 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 were performed using SAINT. Data were corrected for absorption effects with SADABS using the multiscan technique. The structure was solved with XS, and subsequent structure refinements were performed with XL. Computational Details. Calculations used the Gaussian0320 program. All optimizations were carried out with the hybrid density functional theory (DFT) method B3LYP.21 The geometry optimizations were performed with the LANL2TZ(f)22 basis set on hafnium/zirconium and 6-31G* (5d)23 on all other atoms (denoted B3LYP/6-31G*). Frequency calculations confirmed the nature of the stationary points and provided entropic and thermal corrections. Single-point energies using the B3LYP method and the LANL2TZ(f) basis set on hafnium/zirconium and the 6-311þG** basis set on the remaining atoms were also used. Supporting Information Available: Isomerization kinetics of 10a, additional computational data including SD file containing coordinates for all the computed structures, NMR spectra, and X-ray data. This material is available free of charge via the Internet at http://pubs.acs.org. (23) (a) Ditchfield, R.; Hehre, W. J.; Pople, J. A. J. Chem. Phys. 1971, 54, 724. (b) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972, 56, 2257. (c) Gordon, M. S. Chem. Phys. Lett. 1980, 76, 163.

Imino-Amido Hf and Zr Complexes: Synthesis, Isomerization, and

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