Designing metal-free frustrated Lewis pairs for dihydrogen activation based on a carbene–borane system

Abstract

Activation of small molecules by metal-free frustrated Lewis pairs (FLPs) is gaining much attention. In this regard, quantum chemical calculations have been carried out in benzene medium to design some intramolecular FLPs based on a carbene–borane system for activation of dihydrogen. Different carbenes, such as normal, abnormal and remote, has been considered in designing these FLPs. The designed FLPs are found to have lower activation barriers compared to the previously reported analogous systems. A FLP having a remote carbene is found to have the lowest activation barrier. However, the reversibility is most pronounced in case of normal carbene based FLPs, having a lower aromatization effect. The electronic feature associated with the activation process has been thoroughly studied and it is found that the synergism between donation and back-donation is responsible for activation of the HH bond.