Structural Diversity of the Tris(di-<i>tert-</i>butylmethylsilyl)stannyl Anion: Monomeric vs Dimeric, Lithium Coordinated vs Lithium Free

Abstract

The one-electron reduction of the tris(di-tert-butylmethylsilyl)stannyl radical (tBu2MeSi)3Sn• was studied in a variety of solvents: polar, nonpolar, and aromatic. The structure of the resulting tris(di-tert-butylmethylsilyl)stannyl anion depends on the reaction conditions. Thus, the reduction of 3 with potassium in the presence of [2.2.2]cryptand resulted in the formation of the free anion 5, whose structure is very similar to that of the THF-solvated stannyllithium species 4. The reduction of 3 with lithium in heptane produced the dimeric structure 6, whereas the reduction in benzene gave 7 as an anion complexed with Li(η6-benzene). The 119Sn NMR spectrum of 7 at room temperature showed a quartet at −819.8 ppm due to the 119Sn−7Li coupling. This gives evidence for the existence of a covalent Sn−Li bond in solution, even at room temperature.