VIII-B-1 Intramolecular Benzylation of an Imino Group of Tridentate 2,5-Bis(N-aryliminomethyl)- pyrrolyl Ligands Bound to Zircnoium and Hafnium Gives Amido-Pyrrolyl Complexes That Catalyze Ethylene Polymerization

We already reported that an intramolecular benzylation of the imino moiety of bidentate iminopyrrolyl ligands afforded an amido-pyrrolyl complexes 1 and they exhibited better catalytic activity for ethylene polymerization compared to the corresponding bis(iminopyrrolyl) dichloro complexes of zirconium. In this contribution, we prepared amido-pyrrolyl complexes of zirconium (3a-d) and hafnium (4a-f) by the reaction of tetrabenzyl-zirconium and -hafnium with 2,5-bis(N-aryliminomethyl)pyrrole ligands (2a-e), respectively. During the course of the reaction, one of two imino moieties of the ligand was selectively benzylated to give unique dianionic tridentate ligands, which stabilized dibenzyl complexes of zirconium and hafnium. The coordinative unsaturation around the metal center was compensated by not only the donation of the imino moiety but also the η2-coordination of one of the two benzyl ligands, as confirmed by spectral data together with X-ray analysis of 3b and 3c. The zirconium complexes 3b and 3c bearing bulky substituents at the nitrogen atoms of the ligand exhibited high catalytic activities (3b, 131 (kg-PE)(mol-cat)–1h–1 at 60 °C; 3c, 458 (kg-PE)(mol-cat)–1h–1 at 75 °C) upon combined with 1000 equiv. of MMAO. Lewis-base free cationic alkyl complexes 5b, 5c, 6b, and 6c were prepared by alkyl abstruction from the corresponding dibenzyl complexes of zirconium 3b,c and hafnium 4b,c and the resulting cationic complexes 5c and 6c were found to catalyze the ethylene polymerization without MMAO. 149 Annual Review 2004