Anionic N -Heterocyclic Carbene Gold(I) Complexes from Sydnones as a Precarbenic Unit: A Comprehensive Study of the Au–C sp 2 Bond Stability Compared to Its “Relative” Imidazole

Abstract

A series of sydnones was used as N-heterocyclic carbene (NHC) precursors to synthesize gold(I) complexes by a two-step reaction. The first reaction step involves the deprotonation of the sydnone to obtain the corresponding anionic NHC. Second, the metal precursor was added to afford the corresponding gold(I) complex. At this point, the complex obtained depends on the nature of the metal precursor. The use of AuCl(tht) allows one to obtain the monocarbene complex (sydnone−Au−tht), and by contrast, the use of a gold(I) imidazole complex allows one to obtain the bis-carbene complex (syndone−Au−imidazole). Furthermore, the use of sydnone as a metal precursor (sydnone−Au−tht) yields the formation of asymmetric bis-sydnones complexes (sydnone−Au−sydnone’). All gold(I) complexes have been characterized by NMR, Fourier transform infrared spectroscopy (FT-IR), ultraviolet−visible (UV−vis), and elemental analyses. Density functional theory (DFT) methods were used in order to theoretically establish a structure/stability relationship and describe the catalytic effect of these complexes and their imidazole analogues.