The mechanism and impact of mono/bis(iodoimidazolium) halogen bond donor catalysts on Michael addition of indole with trans -crotonophenone: DFT calculations.

Bidentate halogen bond donor catalysts in organic reactions have attracted great attention in recent years. In this work, the catalytic mechanism of mono/bis(iodoimidazolium) halogen bond donor catalysts in the Michael addition reaction is investigated and bis(iodoimidazolium) halogen bond donor catalysts show a good catalytic performance. Catalyzed by these bidentate catalysts, the studied reaction can occur under mild conditions. The whole catalyzed reaction contains two steps. The formation of a carbon-carbon bond in the first step is a nucleophilic reaction of a C-nucleophile. The following proton transfer process contains two possible reaction pathways. Compared to the direct transfer pathway, the pathway of indirect hydrogen proton transfer has a lower energy barrier, and it is more prone to occur. The halogen bond donor catalysts increase the charge transfer of LP(O) → BD*(C-I), thereby accelerating the charge transfer during the formation of the C-C bond and reducing the reaction energy barrier.