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 (CHimidCHCHimid)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 [(CHimidCHCHimid)I]+[IrCl(I)(cod)]− (2)
and [(CHimidCHCHimid)I]+[IrI2(cod)]− (2′). The charge-assisted
intermolecular C−H···X−M hydrogen-bonding
interactions between the [(CHimidCHCHimid)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)(CHimidCHCNHC)]I (3) and [IrI(cod)(CHimidCHCNHC)]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.