Cobalt(III) Complexes of Various Salen-Type Ligand Bearing Four Quaternary Ammonium Salts and Their Reactivity for CO2/Epoxide Copolymerization

Abstract

Ligand variation was carried out on a cobalt(III) complex of Salen-type ligand comprised of 1,2-cyclohexenediamine and salicylaldehyde bearing a methyl substituent on 3-position and -[CMe(CH2CH2CH2N + Bu3)2] on 5-position, which is a highly active catalyst for CO2/propylene oxide copolymerization. Replacement of the methyl substituent with bulky isopropyl group resulted in alteration of the binding mode, consequently lowering turnover frequency significantly. Replacement with an ethyl group preserved binding mode and activity. Replacement of the tributylammonium unit with trihexylammonium or trioctylammonium, or replacement of 1,2-cyclohexenediamino unit with -NC(Me)2CH2N- decreased activity, even though the binding mode was unaltered.