Copolymerization of Epoxides and CO2 by Cobalt(II) Oxaporphyrins with Mechanistic Explorations on Poly(Propylene Carbonate) Formation

Abstract Two cobalt(II) oxaporphyrins (OTPPCoCl and OTPPCoSbF 6 ) are synthesized in this work and are characterized, including by X‐ray crystallography. Both complexes are tested as catalysts in the copolymerization of propylene oxide (PO)/cyclohexene oxide (CHO) and CO 2 . Polycarbonate is obtained in CHO/CO 2 copolymerization with OTPPCoCl as a catalyst, whereas in the case of PO, cyclic carbonate (CC) is majorly formed. An anion exchange from Cl − to SbF 6 − of the cobalt(II) oxaporphyrin leads to a drastic change in the product selectivity: sole polyether is afforded for both epoxides. The polyether formation by OTPPCoSbF 6 is postulated to proceed via a cationic mechanism. Further, an equivalent admixture of OTPPCoCl and OTPPCoSbF 6 allows the formation of poly(propylene carbonate). In this copolymerization, the latter catalyst acts as a PO activator, while OTPPCoCl functions as the initiator. In addition, density functional theory (DFT) calculations reveal a lower ring‐opening energy of PO by OTPPCoSbF 6 , compared with the usual propagating species, OTPPCo‐alkoxides and OTPPCo‐carbonates.