Reactivity of tris(trimethylsilyl)silane toward diarylaminyl radicals

Absolute rate constants for the reaction of tri-tert-butylphenoxyl radical (ArO*) with (TMS)(3)SiH were measured spectrophotometrically in the temperature range 321-383 K. Rate constants for the hydrogen abstraction from (TMS)(3)SiH by diarylaminyl radicals of type (4-X-C(6)H(4))(2)N* were determined by using a method in which the corresponding amines catalyze the reaction of ArO* with (TMS)(3)SiH. At 364.2 K, rate constants are in the range of 2-50 M(-)(1) s(-)(1) for X = H, CH(3), CH(3)O, and Br, whereas the corresponding value for ArO* is 3 orders of magnitude lower. A common feature of these reactions is the low preexponential factor [log(A/M(-1)s(-1)) of 4.4 and 5.2 for ArO* and Ph(2)N*, respectively], which reflects high steric demand in the transition state. A semiempirical approach based on intersecting parabolas suggests that the observed reactivity is mainly related to the enthalpy of the reaction and allowed to estimate activation energies for the reaction of (4-X-C(6)H(4))(2)N* and ArO* radicals with a variety of silicon hydrides.     

The mass spectra of some tris(trimethylsilyl)acylsilanes and tris(trimethylsilyl)silanes

While tris(trimethylsilyl) alkanoylsilanes fragment in the acylsilane form yielding [(Me₃Si)₃SiCO]⁺ by α-cleavage, the molecular ions of their aryl counterparts rearrange to ionized silaethenes prior to cleavage, paralleling known photochemical behaviour. Sila-allyl type structures are attributed to the stable [M? Me˙]⁺ ions obtained by subsequent cleavage. Metastable ion characteristics reveal the identity of the structures of the monomeric silaethene ions obtained from one of the aroylsilanes and a 1,2-disilacyclobutane. The non-compliance of the alkanoylsilanes with their photochemical behaviour is attributed to a preferred elimination of the stable alkyl radical (R˙) from the molecular ions. Several polysilanes display abundant odd-electron ions which may possess a disilene structure.     

Synthesis of 2,4-disubstituted piperidines via radical cyclization: unexpected enhancement in diastereoselectivity with tris(trimethylsilyl)silane

A novel approach to 2,4-disubstituted piperidines is reported, involving the radical cyclization of 7-substituted-6-aza-8-bromooct-2-enoates. Cyclization with tributyltin hydride affords the trans piperidines with trans/cis diastereomeric ratios ranging typically from 3:1 to 6:1. Cyclization with tris(trimethylsilyl)silane affords the same products with diastereomeric ratios of up to 99:1 in certain cases. The enhancement in diastereoselectivity results from the selective rearrangement of the minor stereoisomer through a cascade process involving radical cyclization to the piperidine radical, 1,5-radical translocation, and attack of the translocated radical onto the sulfonamide with extrusion of SO2 in a Smiles-type rearrangement. Slower trapping of the piperidine radical by tris(trimethylsilyl)silane compared to tributyltin hydride accounts for the occurrence of the rearrangement cascade in the former case.     

Safe, facile radical-based reduction and hydrosilylation reactions in a microreactor using tris(trimethylsilyl)silane

A highly efficient system for tris(trimethylsilyl)silane (TTMSS) mediated deoxygenation, dehalogenation and hydrosilylation reactions is described in a microstructured device; this convenient platform enables the scale up of radical-based processes.     

Synthesis of high-purity tris(trimethylsilyl) borate

A method was developed for synthesis of high-purity tris(trimethylsilyl) borate by reaction of trimethylacetoxysilane with powdered boric acid.     

Synthesis of bifunctional tetrakis(trimethylsilyl)silane derivatives

Bifunctional derivatives (XMe₂Si)₂Si(SiMe₃)₂ (X = H, Cl, or OH) were synthesized for the first time by the reaction of tetrakis(trimethylsilyl)silane with SbCl₅. The molecular and crystal structure of bis(hydroxydimethylsilyl)bis(trimethylsilyl)silane was established by X-ray diffraction. The fragmentation of the resulting compounds under electron impact was studied by mass spectrometry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 461–466, March, 2006.     

Synthesis of some tris(trimethylsilyl)germyl compounds

A variety of compounds containing the tris(trimethylsilyl)germyl group were prepared and characterized spectroscopically. Photolysis of adamantoyltris(trimethylsilyl)germane failed to yield the isomeric germene: in CCl₄ the photolysis appeared to occur by a Norrish type 1 process.     

Air-initiated hydrosilylation of unactivated alkynes and alkenes and dehalogenation of halohydrocarbons by tris(trimethylsilyl)silane under solvent-free conditions

A highly efficient air-initiated hydrosilylation of unactivated alkynes and alkenes and dehalogenation of halohydrocarbons with tris(trimethylsilyl)silane ((TMS)₃SiH) as a reducing agent has been established under solvent-free conditions. These observations demonstrate that the potential and versatility of air to function as a competent initiator for Si-H bond activations. It can rival organic initiators and metal catalysts in its efficiency and is a superior initiating system from economic, environmentally sound and practical perspectives.     

Transient Silenes as Versatile Synthons – The Reaction of Dichloromethyl‐tris(trimethylsilyl)silane with Organolithium Reagents

Treatment of dichloromethyl‐tris(trimethylsilyl)silane (Me₃Si)₃Si–CHCl₂ ( 1 ), prepared by the reaction of tris(trimethylsilyl)silane with chloroform in presence of potassium tertbutoxide, with organolithium reagents (molar ratio 1 : 3) affords the bis(trimethylsilyl)methyl‐disilanes Me₃SiSiR₂–CH(SiMe₃)₂ ( 12 a–d ) ( a : R = Me, b : R = n‐Bu, c : R = Ph, d : R = Mes). The formation of 12 a–d is discussed as proceeding through an exceptional series of isomerization and addition reactions involving intermediate silyl substituted carbenoids and transient silenes. The carbenoid (Me₃Si)₂PhSi–C(SiMe₃)LiCl ( 8 c ) is moderately stable at low temperature and was trapped with water to give (Me₃Si)₂PhSi–CH(SiMe₃)Cl ( 9 c ) and with chlorotrimethylsilane affording (Me₃Si)₂PhSi–CCl(SiMe₃)₂ ( 7 c ). For 12 d an X‐ray crystal structure analysis was performed, which characterizes the compound as a highly congested silane with bond parameters significantly deviating from standard values.     

Elimination of bis(trimethylsilyl)stannylene from tris(trimethylsilyl)stannylated zirconocene and hafnocene chlorides

Reactions of (Me₃Si)₃SnK with Cp₂MCl₂ (M = Zr, Hf) give the respective stannylated metallocene chlorides. These complexes display a tendency to eliminate bis(trimethylsilyl)-stannylene under Cp₂M(Cl)SiMe₃ formation.     

The Synthesis of tert‐Butyl(dichloromethyl)bis(trimethylsilyl)silane and (Dibromomethyl)ditert‐butyl(trimethylsilyl)silane and their Reactions with Organolithium Derivatives

tert‐Butyl(dichloromethyl)bis(trimethylsilyl)silane ( 4 ), prepared by the reaction of tert‐butylbis(trimethylsilyl)silane with trichloromethane and potassium tert‐butoxide, reacted with 2,4,6‐triisopropylphenyllithium (TipLi) (molar ratio 1 : 2) at room temperature to give (after hydrolytic workup) the silanol tBu(2,4,6‐iPr₃C₆H₂)Si(OH)–CH(SiMe₃)₂ ( 15 ). The formation of 15 is discussed as proceeding through the indefinitely stable silene tBu(2,4,6‐iPr₃C₆H₂)Si=C(SiMe₃)₂ ( 13 ), but attempts to isolate the compound failed. Treatment of (dibromomethyl)ditert‐butyl(trimethylsilyl)silane ( 7 ), made from tBu₂(Me₃Si)SiH, HCBr₃ and KOtBu, with methyllithium (1 : 3) at –78 °C afforded tBu₂MeSi–CHMeSiMe₃ ( 19 ); 7 and phenyllithium (1 : 3) under similar conditions gave tBu₂PhSi–CH₂SiMe₃ ( 20 ). The reaction paths leading to 15 , 19 and 20 are discussed. Reduction of 7 with lithium in THF produced the substituted ethylene tBu₂(Me₃Si)SiCH=CHSitBu₂SiMe₃ ( 21 ). For 21 the results of an X‐ray structural analysis are given.     

三(三甲硅基)环戊二烯基三羰基钼负离子的反应性

三(三甲硅基)环戊二烯基三羰基钼负离子锂盐[{η^5-(Me~3Si)~3C~5H~2}Mo(CO)~3]^-Li^+(1), 分别与MeI、phCH~2Cl及ClCH~2COOC~2H~5反应生成相应的烃基化钼衍生物[{η^5-(Me~3Si)~3C~5H~2}Mo(CO)~3R,] (R=-CH~3, 2; -CH~2ph, 3;-CH~2COOC~2H~5, 4)。1与PCl~3反应除得到预期的钼氯化物[{η^5-(Me~3Si)~3C~5H~2}Mo(CO)~3Cl](5)外, 主要得到钼磷氯化物[{η^5-(Me~3Si)~3C~5H~2}Mo(CO)~3PCl~2] 6; 1与碘反应得到钼碘化物[{η^5-(Me~3Si)~3C~5H~2}Mo(CO)~3I] 7; 1与HOAc作用后分别和CCl~4、NBS室温反应, 仅分离到脱去一个Me~3Si的钼卤化物[{η^5-(Me~3Si)~2C~5H~2}Mo(CO)~3X], (X:Cl, 8; Br, 9)。     

Tris(trimethylsilyl)silyl versus tris(trimethylsilyl)germyl: Radical reactivity and oxidation ability

A comparison of the tris(trimethylsilyl)silyl I and tris(trimethylsilyl)germyl II radical reactivity is provided. Their formation as well as their reactivity encountered in a large variety of chemical processes (addition to double bond, halogen abstraction, peroxyl radical formation…) is examined by laser flash photolysis, quantum mechanical calculations and electron spin resonance (ESR) experiments. The starting compound (TMS)₃GeH is more reactive than (TMS)₃SiH toward the t-butoxyl, the t-butylperoxyl and the phosphinoyl radicals. A similar behavior is noted for an aromatic ketone triplet state. II exhibits a lower absolute electronegativity: accordingly, the addition to electron rich alkenes is less efficient than for I. Radical II is also found less reactive for both the peroxylation and the halogen abstraction reactions. The rearrangement of is slower than for ; this is related to the respective exothermicity of the processes.     

Pd-catalyzed couplings of (α-fluoro)vinyl tris(trimethylsilyl)germanes

The (α-fluoro)vinyl tris(trimethylsilyl)germanes undergo Pd-catalyzed cross-couplings with aryl and alkenyl halides upon oxidative treatment with hydrogen peroxide under basic aqueous conditions to give access to fluoroalkenes and fluorodienes with retention of stereochemistry.     

Radical-mediated silyl- and germyldesulfonylation of vinyl and (alpha-fluoro)vinyl sulfones: application of tris(trimethylsilyl)silanes and tris(trimethylsilyl)germanes in Pd-catalyzed couplings

[reaction: see text] Radical-mediated silyl- and germyldesulfonylations of various vinyl and (alpha-fluoro)vinyl sulfones with tris(trimethylsilyl)silane and germanium hydrides provide access to vinyl and (alpha-fluoro)vinyl silanes and germanes. Upon oxidative treatment with hydrogen peroxide in basic aqueous solution, the vinyl tris(trimethylsilyl)silanes and -germanes undergo Pd-catalyzed cross-couplings with aryl halides.     

Addition of tris(trimethylsilyl) phosphite to N-substituted 4-piperidone

Russian Journal of General Chemistry - Convenient methods for the synthesis of functionalized phosphonic acids containing piperidine moieties via the reaction of tris(trimethylsilyl) phosphite with...     

A voltammetric study of some tris(trimethylsilyl)-methyltin derivatives

Classical d.c. polarography, supplemented by other voltammetric techniques, is used to elucidate the mechanism of reduction of di- and tri-halide derivatives of tris(trimethylsilyl) methyltm, despite the difficulties encountered in work at very negative potentials in ethanolic solutions. The dihalides are reduced in two irreversible one-electron steps; the trihalides are reduced in three one-electron steps, the first of which is quasi-reversible, the other two being irreversible. The first step in each case is adsorption-controlled while the others are diffusion-controlled. D.c. polarography is suitable for the determination of these compounds down to 5 × lO^-5 M.     

Application of vinyl tris(trimethylsilyl)germanes in Pd-catalyzed couplings

The oxidative treatment of vinyltris(trimethylsilyl)germanes with hydrogen peroxide (NaOH/H(2)O/THF) or tert-butyl peroxide (KH/THF) generates reactive germanol or germanoxane species that undergo Pd-catalyzed cross-couplings with aryl and alkenyl halides and aryl triflates in the presence of Pd(PPh(3))(4). Vinylgermanes having either a conjugated or isolated double bond serve as versatile transmetalation reagents. The E-germanes undergo coupling with retention of stereochemistry under aqueous and anhydrous conditions, while coupling of Z-germanes occurs with less stereoselectivity to produce a mixture of E/Z products.