Bimetallic mechanism operating in the copolymerization of propylene oxide with carbon dioxide catalyzed by cobalt–salen complexes

Dinuclear Co–salen complexes (R,R)-(S,S)-1–4 were synthesized and compared with their mononuclear counterpart rac-5 to suggest that a bimetallic mechanism is in charge for the alternating copolymerization of propylene oxide with CO2 in the absence of onium salt while a monometallic mechanism is more probable in its presence.