Synthesis of gold(I) diaminocarbene complexes by the addition of amines across coordinated isocyanoferrocene

Gold(I) acyclic diaminocarbene complexes of the [AuCl{C(NHFc)(NR2)}] type (Fc = ferrocenyl) were conveniently synthesized by a one-pot procedure. In this method, 1 equiv. of isocyanoferrocene (FcNC) and an excess of primary or secondary amines R2NH (dimethylamine, morpholine, methylamine, cyclohexylamine, and p-toluidine) are sequentially added to [AuCl(SMe2)] as a gold source in dichloromethane. The stepwise synthesis, in which [AuCl(FcNC)] is the isolated intermediate, worked equally well but generated lower overall yields due to compound loss during the two purification steps. The approach was further extended to synthesize the corresponding cationic biscarbene complexes [Au{C(NHFc)(NR2)}2]Cl simply by using 2 equiv. of FcNC during the "first" reaction step. The compounds form conformational isomers in solution that differ by the orientation of substituents at the carbene units. Based on DFT calculations, these isomers exhibit similar energies (energy difference <= 5 kcal mol-1). The crystal structures revealed symmetrical carbene units and the dominant role of the N-H & sdot;& sdot;& sdot;Cl interactions in the crystal assemblies in all cases, which also control the tendency for a particular conformation in the solid state.