Novel non-chelated cobalt(II) benzimidazole complex catalysts: Synthesis, crystal structures and cocatalyst effect in vinyl polymerization of norbornene

Abstract

The novel non-chelated monodentate benzimidazole (BI) complexes CoCl2(BI)(2) (1)-(3), where BI = 1-(2-methoxybenzyl)-2-(2methoxyphenyl)-1H-benzimidazole ( 1), BI = 2-(2,6-difluorophenyl)-1H-benzimidazole ( 2) and 2-methyl-1H-benzimidazole ( 3) were synthesized and characterized by single X-ray crystallography. Unexpectedly, in solid state these complexes show similar coordination behavior to their analogue nickel(II) benzimidazole complexes such as inter-molecular H-bonding pattern and presence of acetonitrile solvent molecules per unit of complex molecule. Moreover, among these cobalt catalysts 1 - 3, similar trend to that of nickel catalysts is observed for metal-to-nitrogen ( M - X) coordination bond length and halogen - metal - halogen ( X - M - X) bond angle. But unlike nickel( II) benzimidazole complexes, these catalysts show very low activity for vinyl polymerization of norbornene ( NB) upon activation with methylaluminoxane (MAO); however, the activity abruptly increased in modified methylaluminoxane (MMAO). The presence of a small amount of toluene strongly hampered the activity, and the use of dry methylaluminoxane (dMAO) as a cocatalyst did not result in a high activity. The use of toluene-free solid modified methylaluminoxane (sMMAO) is found to be the best cocatalyst, where the highest activity of value 3.9 x 10(7) g of PNB mol(Co)(-1)h(-1) was achieved for 3/sMMAO at 30 degrees C. (c) 2007 Elsevier B. V. All rights reserved.