Synthesis, Structures, and Catalytic Properties of Dinuclear Iridium(I) Complexes with a Hexadentate Macrocyclic Diamine‐Tetracarbene Ligand

Two dinuclear macrocyclic Ir I NHC complexes, [Ir 2 (L 1 )(COD) 2 ](PF 6 ) 2 ( 1 , COD = 1,5‐cyclooctadiene) and [Ir 2 Cl(L 1 )(COD)]Cl ( 2 ), were prepared by the reaction between [{IrCl(COD)} 2 ] and macrocyclic N‐heterocyclic carbene (NHC) ligand precursor (H 4 L 1 )(PF 6 ) 4 containing four benzimidazolium and two secondary amino groups. Furthermore, 1 and 2 were carbonylated to give [Ir 2 (L 1 )(CO) 4 ](PF 6 ) 2 ( 3 ) and [Ir 2 Cl(L 1 )(CO) 2 ]Cl ( 4 ), respectively. Notably, 1 can capture the chloride ion to turn itself into 2 with accompanying transformation from cis to trans configuration. Complexes 2 and 4 have unusual five‐coordinate Ir I centers, which are rarely reported for Ir I NHC complexes. The catalytic properties of 1 , 2 , and related mononuclear Ir I complex [Ir(L 2 )(COD)](PF 6 ) ( 5 , L 2 = bis‐NHC ligand) were evaluated in 1,4 conjugate addition reactions of arylboronic acids to cyclohex‐1‐en‐2‐one. These three complexes are the first examples of Ir I NHC species showing such catalytic properties in 1,4‐addition reactions, and have higher catalytic activities than the reported Ir I complex [Ir(hydroquinone)(COD)]BF 4 .