Alkylsilanes synthesis

Organosilicon compounds are widely used in our daily life as oil, grease, rubbers, cosmetics, medicinal chemicals, etc. However, these compounds are not naturally occurring substances but artificially produced ones (for reviews of organosilicon chemistry, see [59-64]). Hydrosilylation reactions catalyzed by a transition-metal catalyst are one of the most powerful tools for the synthesis of organosilicon compounds. Reaction of an unsaturated C-C bond such as alkynes or alkenes with hydrosilane affords a vinyl- or alkylsilane, respectively (Scheme 16). 

The chemistry of silicone halides was recently reviewed by Collins.13 The primary use for SiCU is in the manufacturing of fumed silica, but it is also used in the manufacture of polycrystalline silicon for the semiconductor industry. It is also commonly used in the synthesis of silicate esters. T richlorosilane (another important product of the reaction of silicon or silicon alloys with chlorine) is primarily used in the manufacture of semiconductor-grade silicon, and in the synthesis of organotrichlorosilane by the hydrosilylation reactions. The silicon halohydrides are particularly useful intermediate chemicals because of their ability to add to alkenes, allowing the production of a broad range of alkyl- and functional alkyltrihalosilanes. These alkylsilanes have important commercial value as monomers, and are also used in the production of silicon fluids and resins. On the other hand, trichlorosilane is a basic precursor to the synthesis of functional silsesquioxanes and other highly branched siloxane structures. 

Orendorff, C.l. and Pemberton, J.E., Alkylsilane-based stationary phases via a displaceable surface template approach synthesis, characterization, and chromatographic performance. Ana/. Chem., 77, 6069, 2005. 

Olah and co-workers reported the synthesis of nitroalkanes and nitroalkenes from the nitrodesilylation of alkylsilanes and allylsilanes, respectively, with nitronium salts. 

Electrochemical synthesis of various cyclic alkylsilanes has been performed similarly113. It should be noted that 5-silaspiro[4,4]nonane is formed despite the high probability of polymer formation due to the high functionality of the silicon. Such high selectivity in the electrochemical ring closure seems to be due to the orientating effect of an electrode in the course of an irreversible reduction of a carbon-halogen bond in the monosilylated intermediate (equations 87 and 88). 

Figure 3.29 Synthesis of a PMO derivative with the use of a siloxane-based oligomer that consists of an alkylsilane nucleus (white) and three branching trimethyoxysilyl groups (light grey) This precursor acts simultaneously both as organosilica source and surfactant. The alkyl chain length (n) determined the phase of the composite for n = 10a2Dhexagonalphaseisformed for n = 16, a lamellar phase is obtained. This approach can also be employed as co-condensation reaction together with TMOS.

A facile synthesis of cyclic alkylsilanes consisting in the electrochemical reduction of aliphatic dibromides in the presence of polychlorosilanes of the formula R SiCl4 ( = 0, 2) affords heterocyclic compounds in good yields <1995JOM213>. According to the procedure described in Equation (8), the compound 26 was obtained in 57% yield. In contrast to nonelectrochemical methods, which are based on the ring closure of terminal unsaturated compounds, the electrochemical route is claimed to be more efficient and selective. 

Allylsilane 59 was obtained by initial reaction of the succinimide 55 with the corresponding Grig-nard alkylsilane and a subsequent simple sequence of reactions. This allylsilane was readily cyclized in formic acid at room temperature to 60, which was subjected to a Wacker oxidation (Tsuji 1984) to afford the dihydroanatoxin-a derivative 28. The nitrogen deprotection step with iodotrimethylsilane (Melching et al. 1986) funushedthe ( )-dihydroanatoxin-a, which was reprotected with oc according to the previously discussed Rapoport methodology (Sardina et al. 1989) to furnish the racemic ( )-anatoxin-a. The overall yield of this synthesis was 7% from the succinimide. 

This synthesis, which employs the relatively stable and commonly available metal carbonyls, is normally rapid, leading to generally air-sensitive products with high specificity in good to excellent yield. Some representative reactions, with RjSiH and R2SiH2 are listed in Table 1, and are seen to involve silanes with electronegative substituents. Attempted syntheses with alkylsilanes do not lead to stable products. However, use of alkyl-substituted disilanes does provide stable complexes, in which the disilane moiety forms a ring. Thus, ultraviolet irradition of Fe(CO)j... 

As a general mle, unless an anion-stabilizing group, such as phenyl, or a heteroatom such as sulfur is present, the alkylsilane is not readily deprotonated. The a-halosilane can be deprotonated but, unlike the readily available chloromethyltrimethylsilane, there are few general methods to this approach. Al-kyllithium reagents add to vinylsilanes ( ) to produce the carbanion (287). Silyl derivatives with heteroatoms, such as sulfur, selenium, silicon or tin, in the a-position (288) may be transmetallated (Scheme 41). Besides the difficulty in synthesizing the anion, alkene formation lacks specificity for simple di- and tri-alkyl-substituted alkenes. As a result, the Peterson reaction of an a-silyl carbanion with a carbonyl has found the greatest utility in the synthesis of methylene derivatives, (as discussed in Section 3.1.3), heterosubstituted alkenes and a,p-unsaturated esters, aldehydes and nitriles. 

Tannenbaum,SKaye G. F.Lewenz,J ACS 75, 375>57(1953), (Synthesis and Properties of Some Alkyl Silicanes) (17 refs) 7) R.L.Schalla G.E.McDonald,NACA Tech Note No 3405(1955) CA 49, 7248(1955) 8)R.L.Schalla et al, Combustion Studies of Alkylsilanes, paper reportedin the 5th Symp on Combust,Reinhold,NY( 1955),705 10(7 refs)... 

The first three methods are especially suitable for the synthesis of symmetrical alkylsilanes. Hydrosilylation offers a wide variety of applications which give rise to a large number of non-symmetrical organosilanes to be discussed in a separate section (vide infra). 

The encapsulation of enzymes in a sol gel matrix is an immobilization method in which the enzymes are incorporated into hybrid organic-inorganic hydrophobic materials (alkylsilanes) [13]. The sol-gel process can easily be recognized because it is the synthesis route in which at a certain time, there is the transition from the sol to the gel system. In contrast to the conventional methods, which require high temperatures for the fusion of vitreous silica, the sol-gel technique uses low temperatures for the hydrolysis and... 

Just as carbon-based alkyl groups can be oxidized, a silicon-based silane unit can be oxidized under certain conditions. Alkylsilanes can be converted to a hydroxy unit, but either an aryl group (R—SiR 2Ar) or another silyl group (RSi—SiR 3) must be attached to silicon. In an early version of this reaction, Fleming used a two-step process to transform the silane unit to an alcohol unit, treatment with mercuric acetate and peroxyacetic acid, followed by reduction with lithium aluminum hydride (see sec. 4.2.A for reductions with LiAlHq). Comins et al. used this procedure to convert dimethylphenylsilane (397) to alcohol 398 in 93% yield for the two steps, which was part of a synthesis of A-acetyl-A-methylphlegmarine. ... 

The first examples of the electrophilic acylolysis of alkylsilanes constitute a new, convenient method for ketone synthesis (Scheme 9). ... 

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