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

Abstract

The synthesis, structure, and reactivity of the first silylene-functionalized N-heterocyclic carbene (Si-NHC), {(L1 )Si}(L2 ), (3) (L1 =PhC(NtBu)2 , L2 =CCH(CNAr)2 C:, Ar=2,6-diisopropylphenyl) are reported. The ditopic carbanionic-NHC (dc-NHC), [Li(L2 )]∞ (1) reacts with the monochlorosilylene (L1 )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 SiII and CII functionalities of 3 undergo reactions with chalcogens to give heavier ketone derivatives {(L1 )Si(E)}L2 (E) (E=S, 4; Se, 5; and Te, 6). Compounds 4-6 feature a highly polarized Siδ+ -Eδ- 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 pπ -pπ interaction between Si and E atoms. Compound 3 functions as a reducing agent and induces disproportionation of Si2 Cl6 to yield the silyl-functionalized NHC, {(L1 )SiCl2 }(L2 ) (7). Treatment of 3 with HSiCl3 leads to the formation of the silyl-functionalized imidazolium salt [{(L1 )SiCl2 }(L2 H)]Cl (8). The silylene moiety of 3 readily forms the iridium-silylene complex [{(L2 )(L1 )Si}Ir(cod)Cl] (9) featuring a free NHC ligand on treatment with [Ir(cod)(μ-Cl)]2 .