A Noninnocent Cyclooctadiene (COD) in the Reaction of an 'Ir(COD)(OAc)' Precursor with Imidazolium Salts

The reactions between [Ir(COD)(μ-OAc)]2 and the functionalized imidazolium salt 1-mesityl-3-(pyrid-2-yl)imidazolium bromide (MesIPy·HBr) or 1-benzyl-3-(5,7-dimethylnaphthyrid-2-yl)imidazolium bromide (BnIN·HBr) at room temperature afford the COD-activated IrIII–N-heterocyclic carbene (NHC) complexes [Ir(1-κ-4,5,6-η-C8H12)(κ2C,N-MesIPy)Br] (1) and [Ir(1-κ-4,5,6-η-C8H12)(κ2C,N-BnIN)Br] (2), respectively. In contrast, the methoxy analogue [Ir(COD)(μ-OMe)]2 on reaction with MesIPy·HBr under identical conditions affords the IrI–NHC complex [Ir(COD)(κ2C,N-MesIPy)Br]. Treatment of [Ir(COD)(κ2C,N-MesIPy)Br] with sodium acetate does not lead to COD activation. Further, use of 2,2′-bipyridine (bpy) with [Ir(COD)(μ-X)]2 (X = MeO or AcO) in the presence of [nBu4N][BF4] affords exclusively [Ir(bpy)(COD)][BF4] (3). Metal-bound acetate is shown to be an essential promoter for activation of the COD allylic C–H bond. An examination of products reveals the following transformations of the precursor components: cleavage of ...