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Evaluation of Zirconium and Hafnium Complexes that Contain the Electron-Withdrawing Diamido/Donor Ligand [(2,6-Cl 2 C 6 H 3 NCH 2 CH 2 ) 2 NCH 3 )] 2 - for the Polymerization of 1-Hexene

2005; American Chemical Society; Volume: 24; Issue: 5 Linguagem: Inglês

10.1021/om040113h

1520-6041

Richard R. Schrock, J. Adamchuk, Klaus Ruhland, Lourdes Pia H. Lopez,

Carbon dioxide utilization in catalysis

The triamine (2,6-Cl2C6H3NHCH2CH2)2NMe (H2[ArClN2NMe]) can be prepared through the Pd-catalyzed coupling between 2-bromo-1,3-dichlorobenzene and (H2NCH2CH2)2NH to give (2,6-Cl2C6H3NHCH2CH2)2NH, followed by methylation of the central nitrogen with MeI. Zirconium and hafnium complexes that were prepared include [ArClN2NMe]M(NMe2)2 (M = Hf or Zr), [ArClN2NMe]MCl2, [ArClN2NMe]MMe2, [ArClN2NMe]HfCl(i-Bu), [ArClN2NMe]HfMe(i-Bu), and [ArClN2NMe]Hf(i-Bu)2. An X-ray crystal structure shows [ArClN2NMe]Hf(i-Bu)2 to be a square pyramid in which one of the isobutyl groups occupies the apical position. Activation of dimethyl species with {Ph3C}{B(C6F5)4}, B(C6F5)3, or {PhNMe2H}{B(C6F5)4} yielded {[ArClN2NMe]MMe}+ cations paired with {B(C6F5)4}- or {MeB(C6F5)3}- anions; these species are active for the polymerization of 1-hexene. Activation of [ArClN2NMe]Hf(i-Bu)2 with {Ph3C}{B(C6F5)4} or B(C6F5)3 produced {[ArClN2NMe]Hf(i-Bu)}{B(C6F5)4} and {[ArClN2NMe]Hf(i-Bu)}{HB(C6F5)3}, which are also active for the polymerization of 1-hexene. Isobutene was found to insert slowly into the M−R bond of these initiators in a 1,2 manner and was oligomerized at high concentrations of isobutene. Activation of [ArClN2NMe]HfMe(i-Bu) with B(C6F5)3 resulted in selective abstraction of a methyl group to generate 95% {[ArClN2NMe]Hf(i-Bu)}{MeB(C6F5)3}. The rate of consumption of 1-hexene followed a first-order dependence on 1-hexene (and hafnium or zirconium), and zirconium was faster than hafnium. Although poly[1-hexene] generated by the zirconium catalyst was characteristic of a living system, significant β-hydride elimination was observed in polymerizations by hafnium catalysts. The hafnium product of β-hydride elimination was observed to reinitiate the polymerization of 1-hexene. We conclude that by replacing the mesityl substituents in the analogous [(MesitylN2NMe]2- ligand with 2,6-Cl2C6H3 groups, decomposition is attenuated significantly, although living behavior is observed for zirconium catalysts only.