Carbazole functionalized luminescent silver( i ), gold( i ) and gold( iii )–N-heterocyclic carbene complexes: a new synthetic disproportionation approach towards Au( i )–NHC to provide Au( iii )–NHC

Synthetic, structural and photophysical properties of carbazole functionalized novel procarbenic species 1-(methyl/picolyl)-3-(N-ethylcarbazolyl)-1H benzimidazoliumhexaflurophosphate (1 and 2) and their N-heterocyclic carbene (NHC) complexes of Ag(I) (3 and 4), Au(I) (5 and 6) and Au(III) (7 and 8) are described. According to the solid-state structures, a linear coordination geometry of Ag(I)–NHC (4) and Au(I)–NHC (6) has been established by X-ray diffraction studies; whereas the Au(III)–NHC complex (7) adopts the square planar geometry. The Au(III)–NHC (7 and 8) complexes have been synthesized from Au(I)–NHC (5 and 6) by capitalizing on a novel disproportionation protocol. Furthermore, the Au–Ccarbene bonds in complexes 7 and 8 are inert towards changes in the oxidation state of the metal atom. All the proligands (1 and 2) and complexes (3–8) are luminescent at room temperature.