Highly Enantioselective Alternating Copolymerization of Propene with Carbon Monoxide Catalyzed by a Chiral Phosphine-Phosphite Complex of Palladium(Ⅱ)

摘要

Alternating copolymerization of α-olefins with carbon monoxide catalyzed by chiral transition metal complexes is an attractive methodology to obtain optically active polymers because (1) main-chain chirality can be efficiently built from the prochiral monomers and (2) the polymer contains ketonic groups that are capable of further functionalization. Recently, a few examples of successful asymmetric alternating copolymerization of CO with α-olefins catalyzed by chiral palladium-(Ⅱ) complexes have been reported by Sen, Consiglio, and Brookhart. In all those reports, however, the highest stereo-regularities have been obtained with C_2 symmetric chiral cis bidentate ligands. Here we report a highly enantioselective alternating copolymerization of propene and carbon monoxide catalyzed by Pd(Ⅱ) complexes bearing the unsymmetrical phosphine-phosphite ligand (R,S)-BINAPHOS. The important roles played by the two nonequivalent coordination sites in the chain-growth steps are also revealed.