Ligand-Promoted Bifunctional Cobalt-Catalyzed Carbonylation-Polymerization of Epoxides: One Step to Polyhydroxyalkanoates

Poly(3-hydroxyalkanoates) (PHAs) are an important category of biodegradable plastics with properties similar to those of conventional ones. The development of a simple and efficient catalytic system for PHAs from the most abundant chemicals is economically important. Now we report an in situ generated bifunctional cobalt-catalyzed direct carbonylation-polymerization of epoxides in high efficiency in the presence of a diphosphine oxide ligand WenPhos oxide, which can be easily made from diphenyl sulfone in three steps with regular reagents. In addition, this ligand can promote the disproportionation of Co2(CO)8 to [Co(CO)4]- and Co(II) which is coordinated with phosphine oxide and sulfone oxide. Mechanistic studies indicate that this reaction is not from the ring-opening polymerization of in situ generated beta-lactone. Instead, the phosphine oxide coordinated cobalt cation and [Co(CO)4]- anion pair catalyzed direct carbonylation-polymerization of epoxide was proposed based on previous studies, some control experiments, and X-ray structures of the cobalt complexes.