The isolable cation radical of disilene: Synthesis, characterization, and a reversible one-electron redox system

The highly twisted tetrakis(di-tert-butylmethylsilyl)disilene 1 was treated with Ph₃C⁺·BAr₄^- (BAr₄^-: TPFPB = tetrakis(pentafluorophenyl)borate) in toluene, producing disilene cation radical 3 upon one-electron oxidation. Cation radical 3 was isolated in the form of its borate salt as extremely air- and moisture-sensitive red-brown crystals. The molecular structure of 3 was established by X-ray crystallography, which showed a highly twisted structure (twisting angle of 64.9°) along the central Si-Si bond with a bond length of 2.307(2) Å, which is 2.1% elongated relative to that of 1. The cation radical is stabilized by σ-π hyperconjugation by the four tBu2MeSi groups attached to the two central sp²-Si atoms. An electron paramagnetic resonance (EPR) study of the hyperfine coupling constants (hfcc) of the ²⁹Si nuclei indicates delocalization of the spin over the central two Si atoms. A reversible one-electron redox system between disilene, cation radical, and anion radical is also reported.