Ethylene and propylene polymerization by cationic monocyclopentadienyl titanium catalysts containing the weakly coordinating anion [B(C6F5)4]-

Article abstract of DOI:10.1016/S0022-328X(98)01209-1

The compounds Cp*TiMe₂E (Cp=η⁵-C₅Me₅; E=Me, C₆F₅, OC₆F₅, Cl) react with trityl tetrakis(perfluorophenyl)borate, [Ph₃C][B(C₆F₅)₄], to form the thermally unstable dititanium complexes [(Cp*TiMeE)₂(μ-Me)][B(C₆F₅) ₄], all of which behave as sources of the highly electrophilic species [Cp*TiMeE]⁺. An investigation of the activities of these [B(C₆F₅)₄]^- salts as ethylene and propylene polymerization catalysts shows that they are more active than the analogous compounds Cp*TiMeE(μ-Me)B(C₆F₅)₃, as anticipated since [B(C₆F₅)₄]^- is a poorer ligand than is [BMe(C₆F₅)₃]^-. However, contrary to current perceived wisdom, substitution of a methyl ligand of [Cp*TiMe₂]⁺ by the more electron withdrawing C₆F₅, OC₆F₅ and Cl ligands in these monocyclopentadienyl systems does not generally result in catalysts exhibiting lower activities and producing lower molecular weight polymers. An EPR study of the Cp*TiMe₃/[Ph₃C][B(C₆F₅) ₄] system in chlorobenzene at room temperature indicates that <0.01% of the titanium is present occasionally during polymerization as a complex of titanium(III), suggesting that a contribution to the catalytic processes by titanium(III) species is unlikely.