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‐Me4) [Ar=C6H3‐2,6‐Mes2 (Mes=C6H2‐2,4,6‐Me3), C6H3‐2,6‐Trip2 (Trip=C6H2‐2,4,6‐iPr3)] were obtained selectively on dehydrochlorination of the arylchlorosilanes SiArHCl2 with 1,3,4,5‐tetramethylimidazol‐2‐ylidene (Im‐Me4). The analogous arylgermanium(II) chlorides GeArCl(Im‐Me4) were prepared by metathetical exchange of GeCl2(Im‐Me4) with LiC6H3‐2,6‐Mes2 or addition of Im‐Me4 to GeCl(C6H3‐2,6‐Trip2). All compounds were fully characterized. Density functional calculations on ECl(C6H3‐2,6‐Trip2)(Im‐Me4), 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‐Trip2)(Im‐Me4) (Δ${G{{{\circ}\hfill \atop {\rm calcd}\hfill}}}$=28.1 kJ mol−1) suggests that the carbene adducts SiArCl(Im‐Me4) may be valuable transfer reagents of the arylsilicon(II) chlorides SiArCl. The first monomeric arylsilicon(II) chlorides, SiArCl(Im‐Me4), are reported in which Ar is C6H3‐2,6‐Mes2 (Mes=C6H2‐2,4,6‐Me3) or C6H3‐2,6‐Trip2 (Trip=C6H2‐2,4,6‐iPr3)] and Im‐Me4 is the N‐heterocyclic carbene 1,3,4,5‐tetramethylimidazol‐2‐ylidene. Their molecular (see picture) and electronic structures are compared with those of the homologous germanium compounds.