Isolable anion radical of blue disilene (^tBu₂MeSi) ₂Si=Si(SiMe^tBu₂)₂ formed upon one-electron reduction: Synthesis and characterization

The highly twisted tetrakis(di-tert-butylmethylsilyl)disilene 4 was prepared and reacted with ^tBuLi in THF, producing disilene anion radical 5 upon one-electron reduction. The anion radical 5 was isolated in the form of its lithium salt as extremely air- and moisture-sensitive red crystals. The molecular structure of 5 was established by X-ray crystallography, which showed a nearly orthogonal structure (twisting angle of 88°) along the central Si-Si bond, with a length of 2.341(5) Å, which is 3.6% elongated relative to that of 4. The interesting feature of 5 is that one of the central Si atoms has radical character, whereas the other Si atom has silyl anion character. An electron spin resonance (ESR) study of the hyperfine coupling constants of the ²⁹Si nuclei indicates that rapid spin exchange occurs between these central Si atoms on the ESR time scale.