A DFT study on the reaction mechanisms of N-heterocyclic carbene catalyzed homodimerization of styrenes

In this study, the reaction mechanisms of selective tail-to-tail homodimerization of styrene catalyzed by N-heterocyclic carbene (NHC) have been firstly investigated using density functional theory (DFT). Four possible reaction channels (including the direct reaction channel and three NHC-catalyzed reaction channels) have been suggested and investigated in detail. Our calculated results indicate that one of the NHC-catalyzed channels is the most energetically favorable channel, which contains five reaction steps: the nucleophilic attack by NHC, DBU-assisted proton transfer, the dimerization, the direct [1,4]-proton transfer, and the regeneration of NHC. This work should be helpful for people to understand the dimerization at molecular level, and the novel DBU-assisted proton transfer process provides valuable insights on rational design of the suitable Brønsted acid/base catalysts for promoting this type of reaction. AMS subject classifications: 92E99