Cobalt‐Mediated Switchable Catalysis for the One‐Pot Synthesis of Cyclic Polymers

Abstract A cobalt salen pentenoate complex [salen=( R , R )‐ N , N ′‐bis(3,5‐di‐tertbutylsalicylidene)‐1,2‐cyclohexanediamine] is rationally designed as the catalyst for the ring‐opening copolymerization (ROCOP) of epoxides/anhydrides/CO 2 . Via migratory insertion of carbon monoxide (CO) into the Co−O bonds, the ROCOP‐active species α‐alkene‐ω‐O‐Co III (salen) can be rapidly and quantitatively transformed into α‐alkene‐ω‐O 2 C‐Co III (salen) telechelic linear precursors. Upon dilution of reaction mixtures, the homolytic cleavage of Co−C bonds induced by visible light generates α‐alkene acyl radicals that spontaneously undergo intramolecular radical addition to afford organocobalt‐functionalized cyclic polyesters and CO 2 ‐based polycarbonates with excellent regioselectivity. The cyclic products can either react with radical scavengers to generate metal‐free cyclic polymers or serve as photo‐initiators for organometallic‐mediated radical polymerization (OMRP) to produce tadpole‐shaped copolymers.