Synthesis, Structures, and Transfer Hydrogenation Catalysis of Bifunctional Iridium Complexes Bearing a C-N Chelate Oxime Ligand

We have synthesized a series of organometallic oxime complexes as novel metal-ligand cooperating bifunctional catalysts. The reaction of [{Cp*IrCl(mu(2)-Cl)}(2)] with ketoximes in the presence of sodium acetate afforded the half-sandwich chlorido iridium complexes 6 bearing a C-N chelate oxime ligand with a protic OH group in the beta-position to the metal. Complex 6a, derived from acetophenone oxime, reacted with silver triflate to give the triflate complex 7 and cationic nitrile complex 8 depending upon the reaction solvent. Complexes 6 also reacted with a base in dichloromethane to afford the oximato-bridged dinuclear complexes 9, which were converted back to the chlorido complexes 6 upon treatment with an amine hydrochloride. In contrast, dehydrochlorination of 6 in 2-propanol as well as the reaction of 9 with 2-propanol yielded the hydrido-bridged dinuclear oxime-oximato complexes 10. Crossover experiments revealed that 10 dissociates into the mononuclear hydrido-oxime complex 11 and unsaturated oximato complex 12, which are interconvertible by reactions with hydrogen donors and acceptors. Owing to the metal-ligand cooperation, 10 effectively catalyzed transfer hydrogenation of ketones with 2-propanol.