Planar Tetracoordinated Silicon (ptSi): Room-Temperature Stable Compounds Containing Anti-van't Hoff/Le Bel Silicon

While a variety of compounds containing planar tetracoordinated carbon (ptC), the so-called anti-van't Hoff/Le Bel carbon, are known experimentally, stable systems containing planar tetracoordinated silicon (ptSi) are barely known. As part of our studies on the application of stereoelectronically well-defined transition-metal fragments to stabilize silicon in unprecedented bonding modes, we report herein the synthesis and full characterization of a series of thermally stable complexes of the general formula [Tp'(CO)(2)MSiC(R-1)C(R-2)M(CO)(2)Tp'] (M = Mo, W; R-1 = R-2 = Me or R-1 = H, R-2 = SiMe3, Ph; Tp' = kappa-N,N',N ''-hydridotris(3,5-dimethylpyrazolyl)borate), which incorporate a ptSi atom in addition to two ptC atoms. The complexes were obtained by reacting the metallasilylidyne complexes [Tp'(CO)(2)M Si-M(CO)(2)(PMe3)Tp'] with alkynes (RC)-C-1 CR2 and were comprehensively analyzed by experimental studies and quantum chemical calculations. The analyses revealed that the ptSi atom is embedded in a tricyclic trapezoidal core featuring one internal SiC2 and two outer M-Si-C three-membered rings, which are fused via two Si-C bonds. The structural peculiarities evoked by the presence of an anti-van't Hoff/Le Bel ptSi center, such as the short M-Si bonds, a nearly linear M-Si-M spine, long M-C bonds, and the presence of two planar tetracoordinated carbon atoms were elucidated by a detailed analysis of the electronic structure, suggesting that one factor for the stabilization of the ptSi geometry is the aromaticity of the central SiC2 ring having two delocalized pi electrons. Remarkably, the results further indicate the existence of both anti-van't Hoff/Le Bel carbon and silicon centers next to each other in the isolated complexes.

Automated summary

The synthesis and full characterization of thermally stable complexes containing planar tetracoordinated silicon (ptSi) and planar tetracoordinated carbon (ptC) atoms have been reported. Experimental and quantum chemical studies revealed that the aromaticity of the central SiC2 ring plays a role in stabilizing the ptSi geometry. Remarkably, the complexes contain both anti-van't Hoff/Le Bel carbon and silicon centers.