Evidence for C−H···X−Ir (X = Cl or I) Hydrogen Bonding between Imidazolium Salts and Iridium-Bound Halides and Formation of Ir(I) NHC Complexes

Reactions between an N,N′-adamantyl-substituted bis(imidazolium) diiodide (CH_imidCHCH_imid)I₂ (1) and the dinuclear iridium(I) complex ([Ir(μ-X)(cod)]₂ [X = Cl, I (prepared in situ)] in the absence of a base yielded the hydrogen-bonded complexes [(CH_imidCHCH_imid)I]⁺[IrCl(I)(cod)]⁻ (2) and [(CH_imidCHCH_imid)I]⁺[IrI₂(cod)]⁻ (2′). The charge-assisted intermolecular C−H···X−M hydrogen-bonding interactions between the [(CH_imidCHCH_imid)I]⁺ cations and the [IrX(I)(cod)]⁻ (X = Cl or I) anions involve two (C2-)H atoms of the imidazolium salt precursors and a halogen atom terminally bound to iridium. These hydrogen-bonded compounds can be converted to the monometalated iridium(I) N-heterocyclic carbene (NHC) complexes [IrCl(cod)(CH_imidCHC_NHC)]I (3) and [IrI(cod)(CH_imidCHC_NHC)]I (3′) by strong or weak bases. On the basis of our experimental results, we suggest an explanation for the influence of the imidazolium counteranions on the metalation reactions. The reaction between the bis(imidazolium) diiodide and [Ir(μ-Cl)(cod)]₂ in the presence of excess Cs₂CO₃ in refluxing acetonitrile directly afforded the monometalated iridium(I) NHC complex 3. The crystal structures of 2′·MeCN and 3/3′·MeCN have been determined by X-ray diffraction.