Journal of the American Chemical Society, Vol.124, No.14, 3614-3621, 2002
Mechanism of propylene insertion using bis(phenoxyimine)-based titanium catalysts: An unusual secondary insertion of propylene in a group IV catalyst system
A highly regioselective secondary enchainment of propylene in a group IV catalyst system is reported. End-group analysis of polypropylene formed using the phenoxyimine-based titanium catalysts revealed a reversal in the regioselectivity of insertion for this class of catalysts. To the best of our knowledge, bis(phenoxyimine)-based titanium complexes are the only known group IV catalysts that insert propylene with exclusive 2,1-regiochemistry. Insertion of propylene into the initiating titanium hydride occurs with high 1,2-regiochemistry. Subsequent insertions into primary titanium alkyls are regiorandom, while insertions into secondary titanium alkyls proceed with high 2,1-regioselectivity. Cyclopolymerization and ethylene/ propylene copolymerization strategies are employed to support this proposal.