Synthesis and characterisation of stable carbene-indium(III) halide complexes

The reaction of the stable carbene, :CN(Prⁱ)C₂Me₂NPrⁱ, with InX₃, X = Cl or Br, yielded either the 1:1 or 1:2 complexes, [InX₃{CN(Prⁱ)C₂Me₂NPrⁱ}] and [InX₃{CN(Prⁱ)C₂Me₂NPr ⁱ}₂], depending upon the stoichiometry employed. X-Ray crystallography showed one of the 1:1 adducts, X = Br, to be monomeric and tetrahedral. The 2:1 adducts have a trigonal-bipyramidal geometry with two halides axial and one equatorial. Conductivity and NMR studies suggested all these complexes retain their neutrality in solution. Treatment of InX₃ with I equivalent of CN(Prⁱ)C₂Me₂NPrⁱ and half an equivalent of water afforded the ionic compounds [HCN(Prⁱ)C₂Me₂NPrⁱ] [InX₄{CN(Prⁱ)C₂Me₂NPrⁱ}] which are fluxional in solution at room temperature. The crystal structures of both compounds show the anion to be trigonal bipyramidal with two axial and two equatorial halides.