Efficient route for cyclic olefin polymerization: Nonchelated monodentate benzimidazole Nickel(II) complex catalysts for vinyl polymerization of norbornene

Abstract

We developed a series of nonchelated monodentate benzimidazole nickel complexes, bis[2-(2,6-difluorophenyl)-1H-benzimidazole]nickel (II) dibromide (1), bis[]-(2,6-difluorobenzyl)-2-(2,6-difluorophenyl)1H-benzimidazole]nickel(II) dibromide (2), bis[2-methyl-]H-benzimidazole]nickel(II) dibromide (3), and bis[1(2-methoxybenzyl)-2-(2-methoxyphenyl)-1H-benzimidazole]nickel(11) dibromide (4), upon activation with methylaluminoxane (MAO), which are found to be highly active for vinyl polymerization of norbornene (Nb). The polymerization activity displayed by 4 is as high as 1.68 x 10(9) g of PNb center dot mol(Ni)(-1)center dot h(-1) at very high Nb/Ni ratio of 1 x 10(5). Moreover a small amount of MAO is required to achieve such activity with high yield. The comparable high activity of 4.96 x 10(8) g of PNb center dot mol(Ni)(-1)center dot h(-1) for the simplest complex 3 reveals the significance of nonchelation in this catalyst series. It is observed that the use of toluene as solvent inhibits the catalytic activity strongly. The in situ NMR analyses indicate that the ligand is still intact with the active species. and hence the difference in activity is indeed being associated with the change in ligand.