Synthesis of iridium pyridinyl N-heterocyclic carbene complexes and their catalytic activities on reduction of nitroarenes

Coordination of iridium(I) metal ions with a pyridinyl imidazol-2-ylidene ligand [R = Me, mesityl(2,4,6-trimethylphenyl)] that processes bulky substituents has been investigated. The iridium carbene complexes [(C)IrCl(COD)] (COD = 1,5-cyclooctadiene) are prepared via transmetalation from the corresponding silver carbene complexes. Upon the abstraction of chloride, the chelation of becomes feasible, resulting in the formation of [C,N-Ir(COD)](BF4)). The coordinated COD of complex can be replaced by carbon monoxide to yield the corresponding carbonyl species [C,N-()Ir(CO)(2)](BF4). The labile nature of the pyridinyl nitrogen donor is readily replaced by acetonitrile, as is evidenced by the NMR study. All iridium complexes show catalytic activity on the hydrogen-transfer reduction of carbonyl and nitro functionalities. By manipulation of the reaction conditions, the iridium-catalyzed reduction of nitroarenes can selectively provide aniline or azo compounds as the desired product.