The First Silastannene >SiSn<: A New Doubly-Bonded System of Heavier Group 14 Elements

The reaction of bis[di-tert-butyl(methyl)silyl]dilithiosilane 1 with dichlorobis(2,4,6-triisopropylphenyl)stannane in THF at room temperature yielded highly air- and moisture-sensitive deep violet crystals of 1,1-bis[di-tert-butyl(methyl)silyl]-2,2-bis(2,4,6-triisopropylphenyl)-1-sila-2-stannaethene 2 with a SiSn double bond. The molecular structure of 2 was established by X-ray crystallography, which showed a trans-bent structure (bending angles of 26.2° for the sp2 Si atom and 9.6° for the sp2 Sn atom) with a >SiSn< bond length of 2.4188(14) Å and a twisting angle of 34.6°. The geometry and regioselectivity of the addition reaction of PhEH (E = O and S) corresponds to the polarity of the double bond Siδ-Snδ+, which is also supported by theoretical calculations on the model silastannene (H3Si)2SiSnPh2.