Taming Silicon Congeners of CO and CO : Synthesis of Monomeric Si and Si Chalcogenide Complexes.

The synthesis of the unprecedented monomeric Si selenide complex (bis-NHC)Si=Se→GaCl 2 (bis-NHC=bis-N heterocyclic carbene, H C[{NC(H)=C(H)N(Dipp)}C:] , Dipp=2,6-iPr C H ), bearing the elusive SiSe ligand as a heavy CO homologue by the reaction of the silylone-GaCl adduct (bis-NHC)Si→GaCl 1 with elemental selenium in acetonitrile, is reported. The similar conversion of 1 with excess selenium conducted in THF afforded the SiSe complex (bis-NHC)Si(=Se)Se→GaCl 3. Remarkably, the reaction of 1 with Te=P(nBu) as a gentle Te transfer reagent led to the isolation of the monomeric SiTe complex (bis-NHC)SiTe 4, the first structurally characterized Lewis acid free heavy CO homologue complex. The isolated compounds 2, 3, and 4 have been fully characterized, including single-crystal X-ray diffraction analyses. Their electronic structures and spectroscopic data have also been studied by quantum-chemical calculations.