Formation of Dinuclear AuII and AuI/AuIII Mixed-Valence Complexes is Directed by Structural Constraints Imposed by Cyclophane-NHC Ligands

The oxidation of dinuclear Au-I complexes containing cyclophane-bis(NHC) ligands by SOCl2, Br-2 and I-2 has been investigated. The outcome of the oxidation was dependent on the nature of the cyclophane-NHC framework. The new complexes were fully characterised by X-ray diffraction and H-1 and C-13 NMR spectroscopy. When the Au-I complex contained an ortho-cyclophane framework (dictating short intra-cation Au center dot center dot center dot Au distances), oxidation resulted in dinuclear Au-II complexes of the form X-Au-II(NHC)(2)-Au-II(NHC)(2)-X (X = Cl, Br, I), the Au center dot center dot center dot Au distance being in the range 2.6055(3)-2.6501(1) angstrom. These Au-II complexes are strongly luminescent. When the Au-I complex contained an meta-cyclophane framework (dictating longer intra-cation Au center dot center dot center dot Au distances), oxidation with SOCl2 or Br-2 resulted in dinuclear complexes containing Au-I and Au-III centres of the form X-Au-III(NHC)(2)-X-Au-I(NHC)(2). NMR studies showed that interconversion of the Au-I and Au-III sites within the complexes occurred at rates comparable to the NMR timescale.