The Silicon Version of Phosphine Chalcogenides: Synthesis and Bonding Analysis of Stabilized Heavy Silaaldehydes

The synthesis of chalcogena-silaaldehydes (Ch = S, Se, Te), 15, stabilized by interaction with N-heterocylic carbenes (NHCs) is reported. Compounds 15 are formed by reaction of the NHC-stabilized hydridosilylene 13a with elemental chalcogens in moderate yields. X-ray diffraction analysis of all three variants of the chalcogena-silaaldehydes, 15, revealed short Si/Ch distances which are close to expected values for Si═Ch double bonds. The results of natural bond orbital and natural resonance theory analyses indicate strongly polarized Si-Ch bonds and suggest the occurrence of negative hyperconjugation, which is responsible for the short Si/Ch distances. These results indicate the isolobal relation between NHC-stabilized heavy silaaldehydes 15 and the well-known phosphine chalcogenides, R3PCh.