Synthesis and structural investigation of R2Si (R = Me, Ph) bridged di-N-heterocyclic carbenes

Abstract

Functionalization of the C4 carbon of an imidazol-derived N-heterocyclic carbene (NHC) may allow fine-tuning of the electronic and steric properties of the C2 carbene center. A facile route to silyl-functionalized di-N-heterocyclic carbenes (Di-NHCs) is described. Treatment of the polymeric lithiated NHC, {Li(IPr^H)}_n (1) (Li(IPr^H) = {(N-2,6-iPr₂C₆H₃)₂CHCLi}C:) with a dichlorosilane affords monomeric silyl-functionalized Di-NHCs, R₂Si(IPr^H)₂ (R = Ph, 2; Me, 3). Interestingly, silyl-functionalized mono-NHC, Ph₂(Cl)Si(IPr^H) (4) with a pendant chloro-substituent can also be exclusively isolated maintaining the reactants 1 and Ph₂SiCl₂ ratio. NHCs 2 and 4 readily form copper complexes, Ph₂Si{(IPr^H)CuCl}₂ (5) and Ph₂(Cl)Si{(IPr^H)CuCl} (6), on reaction with CuCl. Straightforward conversion of an NHC to a Di-NHC (2 or 3) via C4 functionalization is reported for the first time. Molecular structures of 2, 4, 5 and 6 have been established by single crystal X-ray diffraction studies.