Silylene-Functionalized N-Heterocyclic Carbene (Si-NHC).

The synthesis, structure, and reactivity of the first silylene-functionalized N-heterocyclic carbene (Si-NHC), {(L )Si}(L ), (3) (L =PhC(NtBu) , L =CCH(CNAr) C:, Ar=2,6-diisopropylphenyl) are reported. The ditopic carbanionic-NHC (dc-NHC), [Li(L )] (1) reacts with the monochlorosilylene (L )SiCl (2) to afford 3. The HOMO of 3 is the silylene lone-pair orbital, whereas the HOMO-1 is located at the carbene carbon atom. Both Si and C functionalities of 3 undergo reactions with chalcogens to give heavier ketone derivatives {(L )Si(E)}L (E) (E=S, 4; Se, 5; and Te, 6). Compounds 4-6 feature a highly polarized Si -E bond with a formal charge of -0.72 (4), -0.64 (5), and -0.50 e (6) on the E atom. The Wiberg bond indices of 1.64 (4), 1.66 (5), and 1.63 (6) for the Si-E bond however indicate a moderate p -p interaction between Si and E atoms. Compound 3 functions as a reducing agent and induces disproportionation of Si Cl to yield the silyl-functionalized NHC, {(L )SiCl }(L ) (7). Treatment of 3 with HSiCl leads to the formation of the silyl-functionalized imidazolium salt [{(L )SiCl }(L H)]Cl (8). The silylene moiety of 3 readily forms the iridium-silylene complex [{(L )(L )Si}Ir(cod)Cl] (9) featuring a free NHC ligand on treatment with [Ir(cod)(μ-Cl)] .