Taming Silicon Congeners of CO and CO2 : Synthesis of Monomeric SiII and SiIV Chalcogenide Complexes.

The synthesis of the unprecedented monomeric SiII selenide complex (bis-NHC)Si=Se→GaCl3 2 (bis-NHC=bis-N heterocyclic carbene, H2 C[{NC(H)=C(H)N(Dipp)}C:]2 , Dipp=2,6-iPr2 C6 H3 ), bearing the elusive SiSe ligand as a heavy CO homologue by the reaction of the silylone-GaCl3 adduct (bis-NHC)Si→GaCl3 1 with elemental selenium in acetonitrile, is reported. The similar conversion of 1 with excess selenium conducted in THF afforded the SiSe2 complex (bis-NHC)Si(=Se)Se→GaCl3 3. Remarkably, the reaction of 1 with Te=P(nBu)3 as a gentle Te transfer reagent led to the isolation of the monomeric SiTe2 complex (bis-NHC)SiTe2 4, the first structurally characterized Lewis acid free heavy CO2 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.