(NHCMe)SiCl4: a versatile carbene transfer reagent – synthesis from silicochloroform

Abstract

A new synthetic pathway for the N-heterocyclic carbene adduct (NHC^Me)SiCl₄ (2) (NHC^Me = 1,3-dimethylimidazolidin-2-ylidene) using silicochloroform is presented. Supported by DFT calculations, the energy for dissociation of 2 into the carbene and the SiCl₄ fragment was found to be comparable to carbene transfer reagents based on silver(I) chloride. Compound 2 was used to transfer the NHC ligand to three different phosphorus(III) chloro compounds, resulting in the neutral complexes (NHC^Me)PCl₃ (3a), (NHC^Me)PCl₂Ph (3b) and (NHC^Me)PCl₂Me (3c). The sterically non-demanding NHC ligand allowed the phosphorus(III) in complex 3a to be oxidized to phosphorus(V) without loss of the NHC ligand, and afford (NHC^Me)PF₄H (4). Furthermore, bis-carbene complexes of Ni(II) (5) and Pd(II) (6) were obtained by reacting 2 with the respective metal chlorides.