Highly regio- and stereo-selective copolymerization of CO2 with racemic propylene oxide catalyzed by unsymmetrical (S,S,S)-salenCo(III) complexes

A novel unsymmetrical ( S,S,S )-salen ligand bearing a derived chiral-BINOL was synthesized by the reaction of the condensation product of (1 S ,2 S )-1,2-diaminocyclohexane mono(hydrogen chloride) with 3-adamanyl-5- tert -butyl-2-hydroxybenzaldehyde and 3-formoyl-2-hydroxy-2′-alkyloxy-1,1′-binaphthyl, which originated from ( S )-1,1′-bi-2-naphthol via a four-step reaction. The cobalt complexes of this ligand, in conjunction with a nucleophilic cocatalyst, exhibited excellent activity in catalyzing asymmetric, regio- and stereo-selective copolymerization of CO 2 and racemic propylene oxide. The highest record of kinetic resolution coefficient ( K rel ) was obtained with the use of binary catalyst system consisting of ( S,S,S )-salenCo(III) complex 1c and bulky bis(triphenylphosphine)-iminium chloride (PPNCl). The resulting poly(propylene carbonate)s have more than 99% carbonate linkages and more than 98% head-to-tail content.