Synthesis and structural characterization of N-heterocyclic carbene gold(I) complexes

A series of N-heterocyclic carbene Au(NHC)Cl complexes (NHC = IMes (1), SIMes (2), IPr (3), SIPr (4), IPrMe (5), IMe (6), ICy (7), IAd (8), ITPh (9)) have been synthesized either through reaction of the corresponding imidazol-2-ylidene carbene with [Au(SMe2)Cl] or by transmetalation of the respective Ag(I)-NHC complex in the presence of 1 equiv of [Au(SMe2)Cl]. All of the gold(I) complexes [Au(IMes)Cl] (10), [AU(SIMeS)Cl] (11), [Au(IPr)Cl] (12), [Au(SIPr)Cl] (13), [Au(IPrMe)Cl] (14), [Au(IMe)Cl] (15), [Au(ICy)Cl] (16), [Au(IAd)Cl] (17), and [Au(ITPh)Cl] (18) have been characterized spectroscopically and structurally by X-ray diffraction. The C-13 chemical shifts of the carbene carbon have been compared through subtraction of the corresponding imidazol-2-ylidene carbene and suggest that there is little difference in donor ability of the NHC ligands bound to gold(I). Crystal structure analysis reinforces this notion, with no obvious change in Au-C(NHC) bond length on going from saturated and unsaturated NHC ligands. For complexes 14, 17, and 18 Au center dot center dot center dot H-C interactions were observed from the sidearm substituents on the NHC ligand. Furthermore, the triazolium complex 18 also contains Au center dot center dot center dot Au interactions as well as head-to-tail pi-pi stacking of the phenyl sidearm substituent from neighboring molecules.