Arylsilane radical anions

Arylsilane radical anions undergo cleavage and coupling reactions, usually under conditions where excess reducing agent is available. Reduction of phenylsilane, diphenylsilane, or triphenylsilane with sodium-potassium alloy under preparative conditions gives high yields of tetraphenylsilane (7). In the reduction of phenylsilanes, the appearance of 1,4-bis(silyl)benzene radical anions is frequently observed (135, 35, 86, 97, 75, 120, 100). Typical results are shown in Table II. 

In subsequent reactions, the arylsilyl anion (VI) can react with other arylsilanes to give the 1,4-coupling product or with DME to give a methyl-substituted derivative that, under the reaction conditions, may be further reduced to new radical anions (135) ... 

Preparative electrochemical reduction of arylsilanes in methylamine gives Birch-type products [Eq. (56)] [198]. The hydrogen atom is introduced preferentially on the carbon adjacent to the silyl group, and this regioselectivity is explained in terms of the stabilization of the radical anion by the neighboring silyl group. 

The perturbation of the yr-systems of radical anions of R3M substituted naphthalenes, formed by polarographic reduction, is discussed in terms of their ionization potentials, charge transfer excitations, reduction potential, and e.s.r. spin distribution. Base cleavage of arylsilanes is consistent with the formation of the carbanion XCeH4 as the rate determining step. The nature of the Ar—M... 

The initial electron transfer to form the anion radical species seems to be reversible. For example, Allred et al. investigated the ac polarography of bis(trimethylsilyl)benzene and its derivatives which showed two waves in di-methylformamide solutions [71] the first one is a reversible one-electron wave, and the second one corresponds to a two-electron reduction. Anion radicals generated by electrochemical reduction of arylsilanes have been detected by ESR. The cathodic reduction of phenylsilane derivatives in THF or DME at — 16° C gives ESR signals due to the corresponding anion radicals [5] (See Sect. 2.2.1). 

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