A DFT study on the mechanism for polymerization of ?-valerolactone initiated by N-heterocyclic carbene (NHC) catalysts

• NHCs catalyzes polymerization of lactones by acting as a base. Electronic effects determines the activation energy. Electron withdrawing groups on decreases catalytic activity. Highly basic may change reaction mechanism. HOMO energy correlates with eneregy. Polymerization reactions using renewable raw material substrate (namely, ?-valerolactone) and N-heterocyclic carbenes (NHC) organocatalysts to form polyesters were investigated computational approaches. Two routes for reaction, either NHC Brønsted base activating an alcohol used co-initiator or direct nucleophilic attack carbonyl carbon lactone, forming zwitterionic intermediate. In agreement previous studies, lowest pathway leading is that where activates co-initiator, yielding partially charged alkoxide then performs lactone. The proton affinity shows high correlation enthalpy first step. Thus, stabilize intermediate make lactone ring-opening rate-determining step reaction.