Dinuclear gold(i) complexes with propylene bridged N-heterocyclic dicarbene ligands: synthesis, structures, and trends in reactivities and properties

Four novel dinuclear N-heterocyclic dicarbene gold(I) complexes with a propylene linker between the carbene moieties have been synthesized and their luminescence and electrochemical properties, together with their reactivity towards bromine oxidative addition, have been screened. All the complexes emit in the solid state in the blue-green spectral range (400–500 nm) with appreciable intensities (Φem up to ≈10%). In cyclic voltammetry, the Au(I)/Au(0) peak splits at low temperature into two separate peaks relative to the couples Au(I)–Au(I)/Au(I)–Au(0) and Au(I)–Au(0)/Au(0)–Au(0), thus indicating the presence of an Au⋯Au interaction in the dinuclear complex. Oxidative addition of bromine affords as a major or unique product Au(II)–Au(II) complexes most likely as a consequence of the interaction between the two gold centres favoured by the propylene linker.