UC Irvine

There are very few reports of ruthenium complexes for olefin polymerization and the active species are unknown. In this dissertation we explore a series of new ruthenium II and IV complexes for olefin polymerization catalysis. We synthesized an arene-tethered ruthenium complex (eta6-C6H5(CH2)3SCH3RuCl2) capable of catalyzing ethylene polymerization using AlMe2Cl as cocatalyst. Homologous dimethylated eta6-C6H5(CH2)3SCH3Ru(CH3)2 complex in the presence of ethylene also yielded polyethylene when activated with HBArF ([H(Et2O)2]+[BAr'4]- (where Ar'=3,5-(CF3)2C6H3)). Mechanistic studies by 1H-NMR and mass spectrometry support a ruthenium cationic [eta6-C6H5(CH2)3SCH3Ru(oligomer)]+ complex as the polymerization active species. This has unambiguously demonstrated for the first time a ruthenium complex as the active species for catalyzing olefin insertion polymerization.

We also studied heteroatom effect eta6-Arene tethered ruthenium (II) complexes on polymerization activity. Complexes (eta6-C6H5(CH2)3SCH3RuCl2), (eta6-C6H5(CH2)3N(CH3)2RuCl2), and [(eta6-C6H5(CH2)3OCH3RuCl2)]2 with coordinating oxygen, sulfur, and nitrogen heteroatoms in the tethered arms have been compared for olefin polymerization. Nitrogen and sulfur-containing complexes are active for olefin polymerization while oxygen-containing complex is inactive. The nitrogen-containing complex is 1.5-fold more active than the sulfur-containing complex. The polymers obtained are composed of two different fractions, a high molecular weight fraction (55-161 kg*mol-1) and a low molecular weight fraction (276-761 g*mol-1). The polydispersities of both fractions are narrow, indicating a single-site catalyst. DFT calculations were carried out on to determine the migratory insertion barriers. Nitrogen-containing complex was found to have a migratory insertion barrier of the chain propagation of 19.4 kcal*mol-1 while sulfur-containing was found to be 21.8 kcal*mol-1. Theoretical calculations are in agreement with the experimental polymerization activity results.

We hypothesize that a more electron deficient ruthenium complex will be more active. We synthesized Ru(IV) dimethyl complex [Cp*(k2-S2CNMe2)RuIVMe2] that polymerizes ethylene with higher activity. The polymers obtained were linear with high molecular weights (up to 322 kg*mol-1) and narrow monomodal molecular weight distributions (Mw/Mn=1.69-2.50). Pronounced counterion effects were observed: the methylaluminoxane activator gave the highest productivities, whereas HBArF resulted in no activity. These results are further supported by DFT calculations, which indicate a low migratory insertion barrier for chain propagation (9.8 kcal*mol-1) but high ethylene uptake energies (15.6 kcal*mol-1).