Arsenic silyls

Silyl and polysilyl radicals also combine with nitrogen, arsenic, and other main group 5 elements, as with sulfur and selenium. 

Several of the originally planned chapters, on comparison of silicon compounds with their higher group 14 congeners, interplay between theory and experiment in organisilicon chemistry, silyl radicals, recent advances in the chemistry of silicon-phosphorous,-arsenic,-antimony and -bismuth compounds, and the chemistry of poly silanes, regrettably did not materialize. We hope to include these important chapters in a future complementary volume. The current pace of research in silicon chemistry will certainly soon require the publication of an additional updated volume. 

It has been pointed out previously that silylation of ylides leads to stabilized products and that this is only one example of the very general phenomenon of carbanion stabilization through silicon (34, 61, 72). This effect was also found for arsenic ylides (34, 73), and is the basis for the preparation of other compounds of this series. The influence of silicon is by no means solely an electronic effect. In many cases, where alkylsilyl substituents are introduced, a steric effect may well dominate, which may reduce lattice energies for salts in transylidation reactions, preventing intermolecular contacts in decomposition processes, and rendering the formation of salt adducts unfavorable. This steric effect is reduced to a minimum, but not eliminated, if simple SiH3 groups are employed (61). Even then, however, a pronounced silicon effect is found, which must be based on electronic influences (49, 60, 61). 

In arsenic ylides, As—C multiple bonding seems to be strongly reduced and the nonbonding interactions are also likely to be less important. The proposed nonplanar geometry may well account for this. Because in silylated arsenic ylides the silicon atoms would meet with unfavorable... 

A number of crystalline arsenic compounds of the type R3As(X)OSiPh3 have been obtained by the reaction of triphenylarsane with silyl hypo-halites, Ph3SiOX (X = Cl, Br) (42). 

Similarly, permethylated silaarsanes with one to three arsenic atoms bound to silicon suffer bond cleavage, but only the silyl ethers analogous to 21a are formed (i). 

The silyl phosphorus and arsenic compounds react with a variety of reagents and form adducts more readily with Lewis acids than the silyl amines (Scheme 57). ... 

Protonic acid (HX) cleavage of arsenic-group IVB (Si, Ge, Sn) bonds in silyl-, germyl- or stannylarsines yields AsHj or Me AsH ... 

Figure 22 shows results obtained in the gas chromatography of a silylated mixture of aliphatic acids, phenylarsenic acid and hydrocarbons using a flame ionization detector and a glow discharge detector set at the silicon and arsenic wavelengths. 

For some applications it is desirable to have Si-dopped GaAs. Kikkawa and coworkers found Bu AsH2 a particularly useful arsenic MOCVD precursor because of the high concentration of the ASH2 species produced in the initial pyrolysis step. The AsH2 formed a silyl species as shown in their proposed scheme. 

Silyl and stannyl anions react with arsenic halides to give the corresponding As—Si and As—Sn compounds, respectively (equations 225 and 226 ). 

Early reports describing the preparation of i-block arsenides such as Ca(AsH2)2 and Ca(AsHMe)2 provided few details on their properties. That situation has changed with the use of silyl-substituted arsenic ligands, and compounds containing them display considerable structural diversity. This area has been reviewed. ... 

The compounds 8 and 10 are formed by the reaction of IS2Sip2 with two equiv [LiEH2(DME)] (E = P, As DME = 1,2-dimethoxyethane) they show no tendency to eliminate LiF in THF solution, surely because of the inherent strength of the Si-F bond. Silylation/germylation of 8 furnished the compounds 9 and 11, respectively, which were subsequently lithiated on phosphorus and arsenic to yield 1 and 3, respectively. In the first instance, the nature of the substituent at phosphorus determines the structures of the precursors 1 and 3, respectively. This has been demonstrated by a study of a structure-reactivity relationship for several compounds 1 [6]. The latter investigation... 

The arsenal for hydroxy protection has been considerably enriched by the introduction of silyl ethers in the early 1970s and many of the decisive developments in this area were made by Corey et al. Since then a boom of applications has emerged, and in numerous complex total syntheses to date a silyl protecting group has teen involved. Natural product synthesis, in particular the construction of prostaglan-... 

As in the case of monocyclic 1,3-azaphospholes/arsoles (Section 3.16.4.1.4) tris(trimethyl-silyl)phosphine/arsine provides the phosphorus/arsenic ring member by replacing the oxygen atom of an oxazolium ring. 

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