Silylmercurials

Transmetalation of silylmercury compounds with lithium (equation 3) ... 

The silylmercury compounds are most conveniently available by reacting a chlorosilane with sodium amalgam. In contrast to the two methods mentioned above, which in most cases require polar, aprotic solvents such as THF, DME or HMPA, transmetalation reactions can be performed in nonpolar solvents and often result in better yields than when performed in ethereal solvents. 

TABLE 5. Metalated oligosilanes prepared by mercury-pounds and alkali metals metal exchange between silylmercury com- ... 

Transmetallation of silylmercury compounds, which are most easily available via the reaction of a silane with (/-Bu)2llg, appears to be the most convenient method for the preparation of cyclic potassium oligosilyl compounds c-(MegSis)K (19)83c as well as c-(MenSi6)K (20)84 were obtained by Hengge and coworkers from the corresponding mercury compound by means of a Na/K alloy in THF (equation 33). 

Doubtless, in these reactions unstable intermediate silylmercury compounds such as [H2(CH3)Si]2Hg and [H(CH3)2Si]2Hg are first produced which then undergo decomposition. The formation of the trisilane and higher polysilanes from the reaction of (CH3)2SiHBr with Na/Hg may be rationalized by the insertion into [H(CH3)2Si]2Hg of dimethylsilylene, (CH3)2Si , which is probably produced during the reaction through decomposition of an unstable intermediate species (CH3)2SiHg, followed by decomposition of the adducts. The generation of dimethylsilylene and its insertion into the... 

Silyllithium compounds may also be prepared by the transmetalation reaction between silylmercury and Li. The requisite silylmercury may be prepared from the corresponding chlorosilane or hydrosilane. The latter can be applied to the synthesis of polysilanyllithium. Equation (17) is an example. ... 

Convenient and inexpensive Me3SiCl can be used as solvent for the relative stable silylmercury. Displacement occurs smoothly and the thermally labile germylmercury species may be kept at low temperatures or prepared in situ. Their use in Ge-metal synthesis is discussed in S.8.4.S the other application is in the synthesis of digermanes or silylgermanes by elimination of mercury... 

Enantiomeric silylmercury compounds are obtained from reaction of diorganomercurys with an optically active hydrosilane [Eq. (6)] (76). The configuration is retained predominantly at silicon. These compounds, however, racemized readily when sublimed during purification. 

Several dimerization rates of alkyl-substituted silyl radicals were measured earlier [8]. However, the dimerization rates of silyl-substituted silicon-centered radicals have not previously been determined. In this study we have measured, using EPR spectroscopy, the rate constants for the recombination of four silyl radicals (lb, 2b, 3b, and 4b), to produce the corresponding disilane dimers of type a (i.e. la, 2a, 3a, and 4a respectively). This dimerization reaction is shown as the backward reaction of Eq. 2 in Scheme 1. Radicals lb, 2b, and 3b were generated photochemically fiom the corresponding disilane dimers of type a (Scheme 1, Eq. 2), while radical 4b was generated photochemically from the corresponding silylmercury compound 4c (Scheme 1, Eq. 1). 

At RT, solutions of (Me3Si)2Hg or (Me3Ge)2Hg show a single H-NMR resonance flanked by Hg satellites. As the temperature is raised the satellite signals broaden and finally collapse as the exchange rate becomes rapid on the NMR time scale. Exchange reactions between different silylmercurials and between silylmercurials and mercury dialkyls are elucidated by NMR, e.g. ... 

The chemistry of mercury(II) is dominated by the stability of two-coordinated compounds but in silylmercury compounds three- and four-coordinated anions, [(R3Si)3Hg] and [(R3Si)4Hg] are formed. 

Most isolable silylmercury compounds have three organic groups bonded to silicon, but the formation of H3SiHg derivatives is achieved by ... 

These silyl mercurials are stable over several days at RT, but as solids they react with traces of air or H2O. Organo(chloro)silylmercurials, (R Cl3 Si)2Hg (n = 0-2), also are known... 

The equilibrium lies to the left at 20°C (red color) and to the right at low T (green color). The structures of the related silylmercury complexes, Li[(Me2PhSi)3Hg] and Li2[(Me2PhSi)4Hg], contain a symmetrical, planar monoanion and a T dianion. 

Where hydrogen is also bonded to Si the stability of the silylmercury product is reduced, and with chlorosilanes the formation of (H3Si)2Hg can only be inferred from the final products ... 

The same polymeric silylmercurial can be obtained as a viscous oil, stable to 60°C, by ... 

Unsymmetrical silylmercurials can be cleaved with formation of a second Si—Hg bond these reactions are followed by a disproportionation step ... 

Unsymmetrical silylmercurials are more resistant to symmetrization than dialkylmercur-ials, RR Hg. The low steric factor in these silane substitution reactions is apparent in the reaction ... 

Most bis-silylmercurials are of the organo-(R3Si)2Hg type, but compounds with one to three Si—Cl bonds are known. They are thermally stable but sensitive to photodecomposition ... 

Anionic silylmercurials (see 5.7.3.1) are also formed by the reaction of (EtjS jHg with KCN in the presence of crown ethers, the products being Et3SiCN and K3[Hg(SiEt3)J. 

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