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 (pyNwedgeC-R) [R=Me, mesityl(2,4,6-trimethylphenyl)] that processes bulky substituents has been investigated.  The iridium carbene complexes [(C-pyNwedgeC-R)IrCl(COD)] (COD=1,5-cyclooctadiene) are prepared via transmetalation from the corresponding silver carbene complexes.  Upon the abstraction of chloride, the chelation of pyNwedgeC becomes feasible, resulting in the formation of [C,N-(pyNwedgeC-R)Ir(COD)](BF4) (4).  The coordinated COD of complex 4 can be replaced by carbon monoxide to yield the corresponding carbonyl species [C,N-(pyNwedgeC-R)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.