A series of isolable silanoic thio-, seleno-, and telluroesters (LSi(=X)OR) with donor-supported Si=X double bonds (L=beta-diketiminate; X = S, Se, Te)

The first silicon analogues of carbonic (carboxylic) esters, the silanoic thio-, seleno-, and tellurosilylesters 3 (Si = S), 4 (Si = Se), and 5 (Si = Te), were prepared and isolated in crystalline form in high yield. These thermally robust compounds are easily accessible by direct reaction of the stable siloxysilylene L(Si:)OSi(H)L' 2 (L = HC(CMe)(2)[N(aryl)(2)], L'= CH[(C = CH2)CMe][N(aryl)](2),; aryl = 2,6-iPr(2)C(6)H(3)) with the respective elemental chalcogen. The novel compounds were fully characterized by methods including multinuclear NMR spectroscopy and single-crystal X-ray diffraction analysis. Owing to intramolecular N-Si donor-acceptor support of the Si-X moieties (X = S, Se, Te), these compounds have a classical valence-bond N+-Si-X- resonance betaine structure. At the same time, they also display a relatively strong nonclassical Si = X pi-bonding interaction between the chalcogen lone-pair electrons (n(pi) donor orbitals) and two antibonding Si-N orbitals (sigma*(pi) acceptor orbitals mainly located at silicon), which was shown by IR and UV/Vis spectroscopy. Accordingly, the Si = X bonds in the chalcogenoesters are 7.4 (3), 6.7 (4), and 6.9 % (5) shorter than the corresponding Si-X single bonds and, thus, only a little longer than those in electronically less disturbed Si-X systems (heavier ketones).