Taming Silicon Congeners of CO and CO₂: Synthesis of Monomeric Si^II and Si^IV Chalcogenide Complexes

Abstract

The synthesis of the unprecedented monomeric Si II selenide complex (bis-NHC)Si=Se!GaCl 3 2 (bis-NHC = bis-Nh eterocyclic carbene,H 2 C[{NC(H)=C(H)N(Dipp)}CD] 2 , Dipp = 2,6-iPr 2 C 6 H 3 ), bearing the elusive SiSe ligand as ah eavy CO homologue by the reaction of the silylone-GaCl 3 adduct (bis-NHC)Si!GaCl 3 1 with elemental selenium in acetonitrile,isreported. The similar conversion of 1 with excess selenium conducted in THF afforded the SiSe 2 complex (bis-NHC)Si(=Se)Se!GaCl 3 3.Remarkably,the reaction of 1 with Te=P(nBu) 3 as agentle Te transfer reagent led to the isolation of the monomeric SiTe 2 complex (bis-NHC)SiTe 2 4,t he first structurally characterized Lewis acid free heavy CO 2 homologue complex. The isolated compounds 2, 3,and 4 have been fully characterized,i ncluding single-crystal X-ray diffraction analyses.T heir electronic structures and spectroscopic data have also been studied by quantum-chemical calculations.Carbonmonoxide,CO, featuring amonomeric structure and Angewandte Chemie Communications 6299

NHCs in Main Group Chemistry

“…In addition, treating CAAC adduct 661 with 1 equiv of NHC results in the formation of the NHC-and CAACstabilized iodosilyliumylidene iodide 663, which is strongly related to the conversion of (IDipp)SiI 2 (606) to the NHC adduct 641 observed by the Filippou group. These results will be discussed in detail below.…”

“…603 The same group used their bis-NHC-stabilized monatomic zerovalent silicon complex (silylone) 582 604 (vide infra) as a suitable precursor for the synthesis of the unprecedented silicon dichalcogenides 578−581. 605,606 This chemistry has recently been reviewed in a comprehensive report and is therefore not discussed in detail here. 607 Oxidation of 582 with elemental sulfur yields the first-ever isolated monomeric SiS 2 complex 578.…”

“…Reduction of the former in THF gives the silicon(II) compound 605 in moderate yield. 546 They also characterized the first Si(II) diiodide complex (IDipp)SiI 2 (606), starting from the triiodosilylimidazolium salt 507 and using the same synthetic approach. Reaction of 507 with a molar excess of potassium graphite affords the corresponding NHC-stabilized diiodosilylene 606 as yellow crystals in high yield.…”

“…Treating the NHC-supported Si(II) diiodide complex (IDipp)SiI 2 (606) with additional σ-donating NHC ligands results in the formation of ionic products via iodide separation. In this manner, the iodosilyliumylidene cation NHC adduct 641 and the NHC-stabilized silicon(II) dication 642 were isolated and will be discussed thoroughly later.…”

“…Moreover, reaction of (IDipp)SiI 2 (606) with an excess of the less sterically demanding NHC IMe 4 results in the formation of the rare example of a Si(II) dication 642 via a carbene substitution reaction in high yield. 547 The novel dicationic silicon NHC complex 642 shows an even stronger highfield chemical shift (δ = −89.9 ppm) in the 29 Si NMR spectrum as compared to the NHC-supported iodosilyliumylidene 641, due to the highly shielded silicon nucleus by the three coordinating NHC ligands.…”