Hexamethyldisilane, electron

Compound 14 is diamagnetic and represents the first tetrasodium-dication cluster that is stabilized by two sterically congested silyKflu-orosilyl)phosphanide counterions (see Section II,D). It has been also independently synthesized through sodium consumption of 13 in the presence of styrene as catalyst in 24% yield. The electron reservoir of the Na) cluster can serve for reduction processes, that is, it reduces Me3SiCl to hexamethyldisilane (see Section II,F). The fact that 14 is intensely yellow, and not red or blue as observed for Na-loaded zeolites (28), suggests that the residual metal electrons are probably much less delocalized. 

The electrochemical oxidation of hexamethyldisilane in acetonitrile results in the cleavage of the Si-Si bond and the formation of a short lived intermediate shown in Scheme 28. The number of electrons transferred is calculated as being 2. 

A variety of new methods for the selective reduction of pyridine Ar-oxides to the corresponding pyridine have been developed. A procedure that is limited to the reduction of relatively electron-rich pyridine Ar-oxides utilizes hexamethyldisilane in the presence of methyllithium in THF/HMPA <1999JOC2211>. This reduction can also be performed on quinoline and isoquinoline Ar-oxides. Tris(2-carboxyethyl)phosphine (TCEP) can be used to... 

Tanaka et al. have reported platinum-catalyzed site-selective silylation of aromatic aldimines with hexamethyldisilane [91]. This silylation reaction proceeds exclusively at the position ortho to the imino group. In the case of the reaction of an imine having an electron-withdrawing group at the para position, the yield of the desired silylated product improves (Eq. 45). The key to this site selectivity is the coordination of the imino nitrogen with the platinum atom. 

Other examples of the application of CIDNP spectroscopy to radical additions and substitutions include the self-substitution of quinones in the presence of tertiary aliphatic amines [111], the photoreactions between hexamethyldisilane and quinones [112], and the allylation of quinones via photoinduced electron transfer from allylstannanes [113] (see also Section V.E). Cycloadditions via radical ions are treated in a separate section (V.D.3). 

Mizuno and his co-workers reported the photosilylation of electron-deficient alkenes by use of hexamethyldisilane and unsymmetrical disilanes. The photoreaction of l,l-dicyano-2-phenylethene and disilanes in acetonitrile in the presence of phenanthrene affords sily-lated dicyanoethanes in good yields. A key intermediate in this process is the silyl radical, generated by solvent (nucleophile)-assisted cleavage of the radical cation of disilanes. Silyl radical attack at the radical... 

A study of the molecular structure of disilane, hexachloiodisilane, and hexamethyldisilane has been carried out (2) with the aid of electron diffraction, and the Si—Si bond lengths obtained (2.32 0.03, 2.32 0.06, and 2.34 0.10 A, respectively) are roughly the same as that in elementary silicon. No information is available on the bond lengths of higher organo-polysilanes. 

During the silylation with hexamethyldisilane, the reductive dehalogenation and the formation of a biaryl are common side-reactions. However, these can be minimized by using potassium carbonate as the base in the case of electron-rich substrates, or with potassium fluoride in the reactions with electron-poor substrates. The arylsilanes produced by any of above mentioned reactions can be cross-coupled with aryl hahdes by employing the following methods. Table 9. 

Silylation of Aryl Halides. In the presence of HMPA and a catalytic amount of Pd(PPh3)4, hexamethyldisilane reacts with various electron-deficient aryl and heteroaryl bromides, such as p)Tidine and quinoline, to give the corresponding aryl and... 

Very few examples were described in this class and the formation of the aryl-silicon bond was obtained analogously to the alkylation of aryl nitriles presented in Section 4.3.3 by ipso-substitution reaction induced by an initial electron transfer process. Thus, tetracyanobenzene in the presence of hexamethyldisilane was in part silylated... 

Igarashi, M., Uedo, T., Wasaka, M., and Sakaguchi, Y, Photoinduced electron transfer reaction between hexamethyldisilane and quinones as studied by CIDNP technique, /. Organomet. Chem., 421, 9,1991. 

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