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.