Preparation of New Olefin Polymerization Precatalysts by Facile Derivatization of Imino–Enamido ZrMe₃ and HfMe₃ Complexes

A novel strategy for polyolefin catalyst development was explored, in which imino–enamido zirconium and hafnium trimethyl complexes were used as synthons to produce a diverse array of new dimethyl derivatives. Specifically, reactions of the trimethyl precursors with protic reagents (i.e., imidazolimines, phosphinimines, and phenols) or unsaturated organic reagents (i.e., diisopropyl ketone and diisopropylcarbodiimide) resulted in the formation of new complexes wherein a single methyl group is replaced by a heteroatom-based ligand. In total, ten new dimethyl complexes were prepared and isolated in high yields utilizing these synthetic approaches. The new complexes were evaluated as precatalysts in ethylene/1-octene copolymerization reactions at 120 °C. Seven complexes were found to be competent catalysts under these conditions, and the resulting copolymers comprised a wide range of molecular weights and octene contents. The best catalysts of the series comprised imino–enamido complexes containing a phosphine-imidato ligand, which exhibited remarkably high activities, had high ethylene selectivities, and produced ethylene/1-octene copolymers with exceptionally high molecular weights. This work demonstrates that the replacement of one of the alkyl groups from trialkyl complexes can be a very effective approach for accessing a variety of new dialkyl precatalysts that can exhibit diverse polymerization behavior.