N‐Heterocyclic Carbene (NHC)‐Stabilized Silanechalcogenones: NHC→Si(R 2 )E (E=O, S, Se, Te)

A series of N‐heterocyclic carbene‐stabilized silanechalcogenones 2 a , b (SiO), 3 a , b (SiS), 4 a , b (SiSe), and 5 a , b (SiTe) are described. The silanone complexes 2 a , b were prepared by facile oxygenation of the carbene–silylene adducts 1 a , b with N 2 O, whereas their heavier congeners were synthesized by gentle chalcogenation of 1 a , b with equimolar amounts of elemental sulfur, selenium, and tellurium, respectively. These novel compounds have been isolated in a crystalline form in high yields and have been fully characterized by a variety of techniques including IR spectroscopy, ESIMS, and multinuclear NMR spectroscopy. The structures of 2 b , 3 a , 4 a , 4 b , and 5 b have been confirmed by single‐crystal X‐ray crystallography. Due to the NHC→Si donor–acceptor electronic interaction, the SiE (E=O, S, Se, Te) moieties within these compounds are well stabilized and thus the compounds possess several ylide‐like resonance structures. Nevertheless, these species also exhibit considerable SiE double‐bond character, presumably through a nonclassical SiE π‐bonding interaction between the chalcogen lone‐pair electrons and two antibonding SiN σ* orbitals, as evidenced by their high stretching vibration modes and the shortening of the Si–E distances (between 5.4 and 6.3 %) compared with the corresponding SiE single‐bond lengths.