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

Abstract

Two dinuclear macrocyclic IrI NHC complexes, [Ir2(L1)(COD)2](PF6)2 (1, COD = 1,5‐cyclooctadiene) and [Ir2Cl(L1)(COD)]Cl (2), were prepared by the reaction between [{IrCl(COD)}2] and macrocyclic N‐heterocyclic carbene (NHC) ligand precursor (H4L1)(PF6)4 containing four benzimidazolium and two secondary amino groups. Furthermore, 1 and 2 were carbonylated to give [Ir2(L1)(CO)4](PF6)2 (3) and [Ir2Cl(L1)(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 IrI centers, which are rarely reported for IrI NHC complexes. The catalytic properties of 1, 2, and related mononuclear IrI complex [Ir(L2)(COD)](PF6) (5, L2 = 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 IrI NHC species showing such catalytic properties in 1,4‐addition reactions, and have higher catalytic activities than the reported IrI complex [Ir(hydroquinone)(COD)]BF4.