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

Abstract

The oxidation of dinuclear AuI complexes containing cyclophane‐bis(NHC) ligands by SOCl2, Br2 and I2 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 1H and 13C NMR spectroscopy. When the AuI complex contained an ortho‐cyclophane framework (dictating short intra‐cation Au···Au distances), oxidation resulted in dinuclear AuII complexes of the form X–AuII(NHC)2–AuII(NHC)2–X (X = Cl, Br, I), the Au···Au distance being in the range 2.6055(3)–2.6501(1) Å. These AuII complexes are strongly luminescent. When the AuI complex contained an meta‐cyclophane framework (dictating longer intra‐cation Au···Au distances), oxidation with SOCl2 or Br2 resulted in dinuclear complexes containing AuI and AuIII centres of the form X–AuIII(NHC)2–X–AuI(NHC)2. NMR studies showed that interconversion of the AuI and AuIII sites within the complexes occurred at rates comparable to the NMR timescale.