Preparation and characterization of iminopyrrolyl hafnium complexes as catalyst precursors for α-olefin polymerization

Abstract

Amido, chloro, and benzyl hafnium complexes bearing 2-( N-aryliminomethyl)pyrrole [(R-pyr)H, 1a: R = DIP = 2-{ N-(2,6-diisopropylphenyl)iminomethyl}, 1b: R = XYL = 2-{ N-(2,6-dimethylphenyl)iminomethyl}, 1c: R = ANI = 2-{ N-(4-methoxyphenyl)iminomethyl}, 1d: R = TOL = 2-{ N-(4-methylphenyl)iminomethyl}] were prepared and characterized. The coordination modes of (R-pyr) 2Hf(NMe 2) 2 ( 2a– d) depend on the bulkiness of the aromatic substituent at the imine nitrogen of the ligands. In contrast, all (R-pyr) 2HfCl 2 ( 3a– d) have a C 2-symmetric octahedral structure. These diamido- and dichloro-bis(iminopyrrolyl)hafnium complexes, when combined with MMAO, become active catalysts for ethylene polymerization. Two types of hafnium benzyl complexes, (DIP-pyr)Hf(CH 2Ph) 3 ( 4a) and (DIP-pyr) 2Hf(CH 2Ph) 2 ( 5a), were prepared by the alkane elimination reaction from reactions of Hf(CH 2Ph) 4 with controlled amounts of iminopyrrole ( 1a). The mono(iminopyrrolyl)hafnium tribenzyl complex ( 4a) exhibited a high catalytic activity for 1-hexene polymerization.