Triethylsilane

Form Supplied in colorless liquid widely available. 

Introduction. Triethylsilane serves as an exemplar for organosilicon hydride behavior as a mild reducing agent. It is frequently chosen as a synthetic reagent because of its availability, convenient physical properties, and economy relative to other organosilicon hydrides which might otherwise be suitable for effecting specific chemical transformations. 

50 atm of carbon monoxide to give a 50% yield of a mixture of the (Z)- and ( )-enol silyl ether isomers in a 1 2 ratio (eq 3). Hydrolysis yields the derived acylsilane quantitatively.  

A number of metal complexes catalyze the hydrosilylation of various carbonyl compounds by triethylsilane. Stereoselectivity is observed in the hydrosilylation of ketones as in the reactions of 4-t-butylcyclohexanone and triethylsilane catalyzed by ruthenium, chromium, and rhodium metal complexes (eq 4). Triethylsilane and Chlorotris(triphenylphosphine)rho-dium(I) catalyst effect the regioselective 1,4-hydrosilylation of Q ,/3-unsaturated ketones and aldehydes. Reduction of mesityl oxide in this manner results in a 95% yield of product that consists of 1,4- and 1,2-hydrosilylation isomers in a 99 1 ratio (eq 5). This is an exact complement to the use of phenylsilane, where the ratio of respective isomers is reversed to 1 99.  

Hydrosilylations. Addition of triethylsilane across multiple bonds occurs under the influence of a large number of metal catalysts. Terminal alkynes undergo hydrosilylations easily with triethylsilane in the presence of platinum, rhodium, ruthenium, osmium, or iridium catalysts. For example, phenylacety-lene can form three possible isomeric hydrosilylation products with triethylsilane the (Z)-/3-, the and the a-products 

Synonyms silicon triethyl hydride, triethyl-silicon hydride 

Triethylsilane is used as a redncing agent in many organic synthetic reactions. 

Colorless liqnid boils at 109°C (228°F) density 0.73 g/mL insoluble in water 

It does not ignite spontaneously in air, bnt it can explode on heating. The ease of oxidation of this compound is relatively lower than mono- and dialkylsilanes. Reaction with oxidizing snbstances, however, can be violent. Reaction with boron trichloride conld be explosive at room tempera-tnre. Even at —78°C (—108°F), mixing these reagents cansed pressnre buildup and com-bnstion (Matteson 1990). 

C2H5Br + Mg C2H5MgBr 3C2H5MgBr + HSiCl3 (C2H5)3SiH + 3MgBrCl Whitmore, Pietrusza, and Sommer, J. Am. Chem. Soc., 69, 2108 (1947). 

Silane Alcoholysis. Triethylsilane reacts with alcohols in the presence of metal catalysts to give triethylsilyl ethers. The use of dirhodium(II) perfluorobutyrate as a catalyst enables regioselective formation of monosilyl ethers from diols (eq 6). 

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Reaction of triethylsilane with a, /3-unsaturated aldehydes catalyzed by Pd on carbon gives a /raff5-l,4-adduct as the main product. Reaction of acrolein gave the adduct in 86% yield, in which the 1,4-adduct 48 was 97% and the 1,2-adduct was 3%[44]. 

Primary organic amines react with triethylsilane in the presence of the appropriate potassium amides to produce organoaminotriethylsilanes with yields of 82-92%. 

Tin tetrachloride has been used to prepare the stericaHy hindered triisopropylchlorosilane [13154-24-0] (119). Organobromosdanes are obtained under similar conditions through reaction with cupric and mercuric bromide. These reactions are most suitable for stepwise displacement of hydrogen to form mixed hydridochlorosilanes or in systems sensitive to halogen (120). Hydrides have also been displaced using organic bromides. Heating triethylsilane and... 

Geminal polyhahdes also react with organosilanes under peroxide catalysis. For example, triethylsilane affords triethylchlorosilane in good yield upon reaction with carbon tetrachloride in the presence of benzoyl peroxide (bpo) at 80°C (94,100,102). 

A catalyst, usually acid, is required to promote chemoselective and regioselective reduction under mild conditions. A variety of organosilanes can be used, but triethylsilane ia the presence of trifiuoroacetic acid is the most frequendy reported. Use of this reagent enables reduction of alkenes to alkanes. Branched alkenes are reduced more readily than unbranched ones. Selective hydrogenation of branched dienes is also possible. 

The so-called ionic method for hydrogenating thiophenes (78T1703) is a further illustration of the chemical consequences of protonation. Protonation of the thiophene ring renders the ring susceptible to hydride ion attack, conveniently derived from triethylsilane (Scheme 12). 

Triethylsilane [617-86-7] M 116.3, b 105-107", 107-108", d 0.734, n 1.414. Refluxed over molecular sieves, then distilled. It was passed through neutral alumina before use [Randolph and Wrighton J Am Chem Soc 108 3366 1986],... 

A teehnique that is a convenient source of radieals for study by EPR involves photolysis of a mixture of di-t-butyl peroxide, triethylsilane, and the alkyl bromide corresponding to the radieal to be studied. Photolysis of the peroxide gives t-butoxy radieals, whieh selectively abstract hydrogen from the silane. This reactive silicon radieal in turn abstracts bromine, generating the alkyl radieal at a steady-state eoncentration suitable for EPR study. 

For the acetoxy radical, the for decarboxylation is about 6.5 kcal/mol and the rate is about 10 s at 60°C and 10 s at —80°C. Thus, only very rapid reactions can compete with decarboxylation. As would be expected because of the lower stability of aryl radicals, the rates of decarboxylation of aroyloxy radicals are slower. The rate for p-methoxybenzoyloxy radical has been determined to be 3 x 10 s near room temperature. Hydrogen donation by very reactive hydrogen-atom donors such as triethylsilane can compete with decarboxylation at moderate temperatures. 

The arylcopper reagents couple with 1-iodoarylacetylenes to give the unsym-metrical diarylacetylenes [25(S] (equation 176) Reaction with tetrabromoethyl- ene gives bis(pentafluorophenyl)acetylene in 66% yield [25S] (equation 177) Pen-tafluorophenyl copper couples with (bromoethynyl)triethylsilane to give C6F5C=CSi(C2H5)3 in 85% yield [259]... 

Because of Us high polarity and low nucleophilicity, a trifluoroacetic acid medium is usually used for the investigation of such carbocationic processes as solvolysis, protonation of alkenes, skeletal rearrangements, and hydride shifts [22-24] It also has been used for several synthetically useful reachons, such as electrophilic aromatic substitution [25], reductions [26, 27], and oxidations [28] Trifluoroacetic acid is a good medium for the nitration of aromatic compounds Nitration of benzene or toluene with sodium nitrate in trifluoroacetic acid is almost quantitative after 4 h at room temperature [25] Under these conditions, toluene gives the usual mixture of mononitrotoluenes in an o m p ratio of 61 6 2 6 35 8 A trifluoroacetic acid medium can be used for the reduction of acids, ketones, and alcohols with sodium borohydnde [26] or triethylsilane [27] Diary Iketones are smoothly reduced by sodium borohydnde in trifluoroacetic acid to diarylmethanes (equation 13)... 

The reduction is general for a variety of substituted benzophenones Such substituents as CH3 OH, OCH3, F, Br. N(CH3)2, NO2. COOH, COOCH3, NHCOC Hreaction conditions and do not alter the course of the reduction Diarylmethanols are reduced to diarylmethanes under the same conditions and probably are the intermediates in the reduction of ketones [26] Triethylsilane also can be used as a reducing agent in trifluoroacetic acid medium [27J This reagent is used for the reduction of benzoic acid and some other carboxylic acids under mild condiUons (equation 14) Some acids (phthalic, sue cinic, and 4-nitrobenzoic) are not reduced under these conditions [27]... 

BF3-Et20, NaCNBHs, THF, reflux 4-24 h, 65-98% yield. Functional groups such aryl ketones and nitro compounds are reduced and electron-rich phenols tend to be alkylated with the released benzyl carbenium ion. The use of BF3 Et20 and triethylsilane as a cation scavenger is also effective." ... 

Carboxamides and esters of arenecarboxylic acids are obtainable directly by reacting arenediazosulfones (Ar — N2 —S02 —Ar ) with CO and amines or alcohols, respectively, in the presence of Pd catalysts (Kamigata et al., 1989). Aromatic aldehydes are formed if the reaction is carried out in the presence of triethylsilane (Kikukawa et al., 1984). In an analogous way, arenediazonium salts can be transformed into ketones (ArCO —R R = CH3, C2H5, or C6H5) in the presence of stan-nanes, R4Sn (Kikukawa et al., 1982). 

A neat mixture of the /l-unsaturated ketone (10mmol), triethylsilane (11 mmol), and tris(triphenylphosphine)rhodium(i) chloride (0.01 mmol) was stirred at 50°C for 2h, and the product silyl enol ether was distilled directly (yields 90-98%). 

Triethylamine, 61,83,87,88,94,99,100,112 Triethylamine N-oxide, 84 Triethylbenzylammonium chloride, 49 Triethylsilane, 104,127.128 Trifluoroacetic acid, 59 Trimethyi-m-dimethylaminophenylsilane, 40 Trimethyl orthoformate, 109... 

To a solution of 4-t-butylcyclohexanone (lmmol), tris(triphenylphos-phine)ruthenium(n) chloride (0.05 mmol) and silver trifluoroacetate (0.05 mmol) in toluene (5 ml) was added triethylsilane (1.5 mmol). The mixture was heated under reflux for 20 h, and concentrated under reduced pressure. The residue was diluted with hexane (3 ml), filtered and distilled to give a mixture of triethylsilyl ethers (0.96mmol, 96%), b.p. 70°CI 0.1 mmHg. G.l.c. analysis shows an axial (cis) equatorial (trans) ratio of 5 95—a result comparable to the best LAH results. 

Note. Use of tris(triphenylphosphine)rhodium(i) chloride/triethylsilane gave somewhat poorer results in terms of stereoselectivity, ca. 10 90. 

The most common way to generate sulfonyl radicals for spectroscopic studies has been the photolysis of solutions containing di-t-butyl peroxide, triethylsilane and the corresponding sulfonyl chloride in a variety of solvents (equations 4-6). The slowest step in this sequence is the reaction between t-butoxyl radicals and triethylsilane (ks = 5.3 x 106m 1s-1)26 since that for chlorine abstraction (equation 6) is extremely efficient (cf. Table 4). 

Noell et al. reported the preparation of silica-poly(ether ether ketone) hybrid materials with improved physical properties.155 An amine-end-capped poly(ether ether ketone) was used to react with isocyanatopropyltriethoxysilane in tetrahydrofuran (THF). The triethylsilane-end-capped poly (ether ether ketone) was mixed with tetraethoxysilane (TEOS) in THF. Quantitative amounts of water were introduced into die system, and the mixture was reduxed at 80°C. The entire reaction mixture was allowed to further react in Tedon molds. Tough transparent materials were obtained by diis approach. 

The reaction of thiyl radicals with silicon hydrides (Reaction 8) is the key step of the so-called polariiy-reversal catalysis in the radical chain reduction. The reaction is strongly endothermic and reversible with alkyl-substituted silanes (Reaction 8). For example, the rate constants fcsH arid fcgiH for the couple triethylsilane/ 1-adamantanethiol are 3.2 x 10 and 5.2xlO M s respectively. 

The low reactivity of alkyl and/or phenyl substituted organosilanes in reduction processes can be ameliorated in the presence of a catalytic amount of alkanethiols. The reaction mechanism is reported in Scheme 5 and shows that alkyl radicals abstract hydrogen from thiols and the resulting thiyl radical abstracts hydrogen from the silane. This procedure, which was coined polarity-reversal catalysis, has been applied to dehalogenation, deoxygenation, and desulfurization reactions.For example, 1-bromoadamantane is quantitatively reduced with 2 equiv of triethylsilane in the presence of a catalytic amount of ferf-dodecanethiol. 

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