Density Functional Study of Ethylene Polymerization Catalyzed by a Zirconium Non-Cyclopentadienyl Complex, L2ZrCH3+. Effects of Ligands and Bulky Substituents

Abstract

To elucidate the role of electronic and steric effects on catalytic activities and to gain some guidance for the design of catalysts, we applied the hybrid density functional B3LYP and integrated molecular orbital + molecular mechanics (IMOMM) methods to study the mechanism of the chain initiation/propagation reaction of L2ZrMe+-catalyzed ethylene polymerization for several bidentate non-cyclopentadienyl ligands [L = −O−CHCH−CHNH− (1 (trans), 2 (cis)), HCO2 (3), HC(NH)2 (4), HC(O)(NH) (5 (cis), 6 (trans)), −O−CHCH−N(CH2) (7)], tBu-4 [L = HC(NtBu)2], and tBu-5 [L = HCO(NtBu)]. It was shown that for model catalysts 1−7 the barrier for chain initiation reaction is 11−21 kcal/mol. Reactant, π-complex, and product have either eclipsed or nearly untwisted ligands L, depending on the size of L−Zr ring, whereas the insertion transition state has the planes of the two ligands L twisted with respect to each other. Bulky substituents in catalysts tBu-4 and tBu-5 lead to a significant twisting of the ligands L in the...