Acetamidine complexes as catalysts for ethylene polymerization

The reaction of (2,6-diisopropyl-phenyl)-acetimidoyl chloride or (2,6-dimethyl-phenyl)-acetimidoyl chloride with 2,6-dimethylaniline in the presence of triethylamine yields a mixture of isomers N'-(2,6-diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N'-(2,6-dimethyl)-acetamidine (1a) and N-(2,6-diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N'-(2,6-dimethyl)-acetamidine (1b), and N,N'-bis-(2,6-dimethyl-phenyl)-N-[1-(2,6-dimethyl-phenylimino)ethyl)]-acetamidine (2), respectively. The addition of isomers (1a + 1b) to nickel (II) dibromide 2-methoxyethyl ether, (NiBr2 [O-(C2H4OMe)(2)]) gives a mixture of new nickel complexes, [NiBr2{N'-(2,6-diisopropyl-phenyl)-N-[1(2,6-diisopropyl-phenylimino)-ethyl]-N-(2,6-dimethyl)-acetamidine}] (3a) and [NiBr2{N-(2,6-diisopropylphenyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N'-(2,6-dimethyl)-acetamidine}] (3b). Similarly, ligand 2 reacts with nickel (II) dibromide 2-methoxyethyl ether to afford the complex [NiBr2{N,N-bis-(2,6-dimethyl-phenyl)-N-[1-(2,6-dimethyl-phenylimino) ethyl)]-acetamidine}] (4). The structures of the ligands and nickel complexes have been determined by single crystal X-ray diffraction. The addition of MAO to these complexes generates catalytically active species for the homopolymerization of ethylene. The polymer products are high molecular weight (80-169 K). At temperatures of up to 60 degrees C both catalysts are a single site giving a monomodal molecular weight distribution. However, at 70 degrees C the mixture (3a + 3b) shows a bimodal molecular weight distribution. (C) 2008 Elsevier B.V. All rights reserved.