Mechanistic investigation of zwitterionic MOF-catalyzed enyne annulation using UNLPF-14-MnIIIas catalyst

Hybrid quantum mechanics/molecular mechanics calculations were performed to elucidate how [MnIIIporphyrin]+X−-based metal-organic frameworks (MOFs) catalyze the [2 + 1] cycloisomerization of enynes and why zwitterionic MOFs exhibit strong activity in Lewis acid catalysis. The calculations showed that zwitterionic MOFs have a “pure cationic active center” leading to a concerted nucleophilic attack pathway with lower barriers. In contrast, metals with coordinating anions have reduced electrophilicity, resulting in a stepwise radical-type pathway with much higher barriers. Further calculations showed the nature of catalysis was strongly depended on the charge on the anion ligand. A good linear relationship between the NPA charge and barrier was found, and verified by 73 anions with small derivations, which presents a universal adaptive character for various coordinated anions.