Transformation of a Tetrasila-1,3-dienide to Its Valence Isomers

A tetrasila-1,3-dien-1-ide (2, a tetrasila-1,3-dien-1-yl
anion) generated by desilylation of the corresponding 1,4-bis(trimethylsilyl)tetrasila-1,3-diene
(1) with potassium tert-butoxide undergoes
transformation to provide a mixture of its valence isomers, a bicyclo[1.1.0]tetrasilan-2-ide
(4) and a cyclotetrasilen-3-ide (5) at room
temperature. The structures of the obtained valence isomers were characterized
by NMR spectroscopy and single-crystal X-ray diffraction analysis.
Equilibrium between 4 and 5 is observed
in solution. The isomerization routes between the valence isomers
are also found by DFT calculations of model compounds.