Multinuclear Cobalt-Salen complexes with phenylene linker for epoxide polymerizations

Di-and trinuclear cobalt (Co)-salen complexes with a benzene ring as a rigid linker were explored for epoxide polymerizations. The dinuclear Co-salen complex with a 1,2-phenylene linker showed higher catalytic activity than the dinuclear Co-salen complex with a 1,3-phenylene linker and the trinuclear Co-salen complex with a 1,3,5-benzenetriyl linker for the copolymerization of propylene oxide (PO) with carbon dioxide. A combination of the absolute configuration of the two Co-salen moieties was found to affect its catalytic activity. The optimized dinuclear Co-salen complex with a heterochiral combination demonstrated highest activity and maintained its catalytic activity under a low catalyst concentration. The heterochiral dinuclear Co-salen complex also showed high activity for the copolymerization of PO with cyclic anhydride.