Mechanistic basis for tuning iridium hydride photochemistry from H(2) evolution to hydride transfer hydrodechlorination

The photochemistry of metal hydride complexes is dominated by H(2) evolution, limiting access to reductive transformations based on photochemical hydride transfer. In this article, the innate H(2) evolution photochemistry of the iridium hydride complexes [Cp*Ir(bpy-OMe)H](+) (1, bpy-OMe = 4,4ʹ-dimethoxy-2,2′-bipyridine) and [Cp*Ir(bpy)H](+) (2, bpy = 2,2ʹ-bipyridine) is diverted towards photochemical hydrodechlorination. Net hydride transfer from 1 and 2 to dichloromethane produces chloromethane with high selectivity and exceptional photochemical quantum yield (Φ ≤ 1.3). Thermodynamic and kinetic mechanistic studies are consistent with a non-radical-chain reaction sequence initiated by “self-quenching” electron transfer between excited state and ground state hydride complexes, followed by proton-coupled electron transfer (PCET) hydrodechlorination that outcompetes H–H coupling. This unique photochemical mechanism provides a new hope for the development of light-driven hydride transfer reactions.