Stable N-Heterocyclic Carbene Adducts of Arylchlorosilylenes and Their Germanium Homologues

The first N-heterocyclic carbene adducts of arylchlorosilylenes are reported and compared with the homologous germanium compounds. The arylsilicon(II) chlorides SiArCl(Im-Me-4) [Ar=C6H3-2,6-Mes(2) (Mes=C6H2-2,4,6-Me-3), C6H3-2,6-Trip(2) (Trip=C6H2-2,4,6-iPr(3))] were obtained selectively on dehydrochlorination of the arylchlorosilanes SiArHCl2 with 1,3,4,5-tetramethylimidazol-2-ylidene (Im-Me-4). The analogous arylgermanium(II) chlorides GeArCl(Im-Me-4) were prepared by metathetical exchange of GeCl2(Im-Me-4) with LiC6H3-2,6-Mes(2) or addition of Im-Me-4 to GeCl(C6H3-2,6-Trip(2)). All compounds were fully characterized. Density functional calculations on ECl(C6H3-2,6-Trip(2))(Im-Me-4), where E = Si, Ge, at different levels of theory show very good agreement between calculated and experimental bonding parameters, and NBO analyses reveal similar electronic structures of the two aryltetrel(II) chlorides. The low gas-phase Gibbs free energy of bond dissociation of SiCl(C6H3-2,6-Trip(2))(Im-Me-4) (Delta G(calcd)degrees=28.1 kJ mol(-1)) suggests that the carbene adducts SiArCl(Im-Me-4) may be valuable transfer reagents of the arylsilicon(II) chlorides SiArCl.