Molecular Coordination-Switch in a New Role: Controlling Highly Selective Catalytic Hydrogenation with Switchability Function

A molecular coordination-switch controlled by acid–base input has been developed and utilized in switchable catalysis. The molecular switch consists of a hybrid pyridylidene–benzimidazole ligand bound to an IrIIICp* moiety wherein the benzimidazole functionality has been utilized for acid/base controlled reversible coordination, switching between an IrIII-benzimidazole species (form I; neutral imino-type N-coordination) and an IrIII-benzimidazolate species (form II; anionic amido-type N–Ir bonding). Owing to the distinctly different nature of the metal–ligand bonding, it has been demonstrated that while the form I is almost inactive (TOF 1 h–1) in catalytic hydrogenation of imine under ambient pressure and temperature, the form II is greater than an order of magnitude more efficient (TOF 15.8 h–1) in the same catalysis. Moreover, the catalysis could be switched OFF and ON efficiently for several cycles with the addition of acid and base, respectively. Spectroscopic studies and kinetics have been performed to understand the switching activity.