Influences of Alkyl and Aryl Substituents on Iminopyridine Fe(II)- and Co(II)-Catalyzed Isoprene Polymerization.

A series of alkyl- and aryl-substituted iminopyridine Fe(II) complexes 1a⁻7a and Co(II) complexes 2b, 3b, 5b, and 6b were synthesized. The activator effect, influence of temperature, and, particularly, the alkyl and aryl substituents' effect on catalytic activity, polymer molecular weight, and regio-/stereoselectivity were investigated when these complexes were applied in isoprene polymerization. All of the Fe(II) complexes afforded polyisoprene with high molecular weight and moderate cis-1,4 selectivity. In contrast, the Co(II) complexes produced polymers with low molecular weight and relatively high cis-1,4 selectivity. In the iminopyridine Fe(II) system, the alkyl and aryl substituents' effect exhibits significant variation on the isoprene polymerization. In the iminopyridine Co(II) system, there is little influence observed on isoprene polymerization by alkyl and aryl substituents.