Mechanism and Design Principles for Controlling Stereoselectivity in the Copolymerization of CO2/Cyclohexene Oxide by Indium(III) Phosphasalen Catalysts

Copolymerization of CO2 with cyclohexene oxide (CHO) creates a sustainable polymer that has been a target for homogeneous catalysis. In particular, indium­(III) phosphasalen catalysts generate high proportions of carbonate linkages in isotactic product poly­(cyclohexene carbonate) (iPCHC). We use theory here to characterize the initiation and propagation steps for these indium­(III) catalysts, which involve mononuclear mechanisms for CO2 insertion and CHO ring opening that are distinct from copolymerization mechanisms previously reported for other metal-based catalysts. We find that phosphasalen ligand interactions with CHO and the carbonate-terminated growing chain lead to stereoselection for high levels of isotacticity and suggest further modifications to the ligand that might tune this.