18033-75-5Relevant articles and documents
Fast kinetics study of the reactions of transient silylenes with alcohols. Direct detection of silylene-alcohol complexes in solution
Leigh, William J.,Kostina, Svetlana S.,Bhattacharya, Adroha,Moiseev, Andrey G.
scheme or table, p. 662 - 670 (2010/05/15)
The kinetic behavior of dimethyl-, diphenyl-, and dimesitylsilylene in hexanes solution in the presence of methanol (MeOH), tert-butanol (t-BuOH), and the respective O-deuterated isotopomers has been studied, with the goal of elucidating a detailed mechanism for the formal O-H insertion reaction of transient silylenes with alcohols in solution. The data are in all cases consistent with a mechanism involving the intermediacy of the corresponding silylene-alcohol Lewis acid-base complexes, which have been detected directly for each of the SiMe2-ROL and SiPh2-ROL (L = H or D) systems that were studied. Complexation proceeds effectively irreversibly (Keq ≥ 2 x 105 M-1) and at close to the diffusion-controlled rate in these cases. In contrast, the kinetic and spectroscopic behavior observed for SiMeS2 in the presence of these alcohols indicates the SiMeS2-ROL complexes are involved as steady-state intermediates, formed reversibly and 10-100 times more slowly than is the case with SiMe2 and SiPh2. Product formation from the silylene-alcohol complexes is shown to proceed via catalytic proton transfer by a second molecule of alcohol, the rate of which exceeds that of unimolecular intracomplex H-migration in all cases, even at submillimolar alcohol concentrations. The catalytic rate constants range from 109 to 1010 M-1 s-1 for the SiMe2-ROH and SiPh2-ROH complexes, sufficiently fast that the isotope effect ranges from ca. 2.5 to close to unity for all but the SiPh2-t-BuOL complex, where it is remarkably large (kHH/kDD = 10.8 ± 2.4). The value is consistent with a mechanism for catalysis involving double proton transfer within a cyclic five-membered transition state. The isotope effects on the ratio of the rate constants for catalytic proton transfer and dissociation of the SiMeS2-MeOH and SiMeS2-t-BuOH complexes suggest that a different mechanism for catalytic proton transfer is involved in the case of the sterically hindered diarylsilylene.
Radiochemical study of the gas phase reaction of nucleogenic diethylsilylium ions with methanol and butanol
Kochina,Vrazhnov,Ignatyev
, p. 258 - 261 (2007/10/03)
The gas phase ion-molecule reactions between alcohols (methanol and n-butanol) and nucleogenic diethylsilylium ions generated by the β-decay of the tritiated diethylsilane were studied by the radiochromatographic method. Among the labelled neutral product
Ion-molecular reactions of free ethylsilicenium ions with alcohols in the gas phase
Kochina,Shchukin,Nefedov,Sinotova
, p. 885 - 888 (2007/10/03)
Ion-molecular reactions of free ethylsilicenium ions with methanol and isobutanol in the gas phase were studied radiochemically. Within the reaction time the ethylsilicenium ion completely isomerizes into the dimethylsilicenium ion. The reaction mechanism was suggested.
Substituent effects on the reactivity of the silicon-carbon double bond. Resonance, inductive, and steric effects of substituents at silicon on the reactivity of simple 1-methylsilenes
Leigh, William J.,Boukherroub, Rabah,Kerst, Corinna
, p. 9504 - 9512 (2007/10/03)
The reactivities of a series of substituted 1-methylsilenes RMeSi=CH2 (R = H, methyl, ethyl, t-butyl, vinyl, ethynyl, phenyl, trimethylsilyl, and trimethylsilymethyl) in hydrocarbon solvents have been investigated by far- UV (193-nm) laser flash photolysis techniques, using the corresponding 1- methylsilacyclobutane derivatives as silene precursors. Each of these silacyclobutanes yields ethylene and the corresponding silene, which can be trapped as the alkoxysilane RSiMe2OR' cleanly upon 193- or 214-nm photolysis in solution in the presence of aliphatic alcohols. UV absorption spectra and absolute rate constants for reaction of the silenes with methanol, ethanol, and t-butyl alcohol have been determined in hexane solution at 23°C. The rate constants vary from a low 3 x 107 M-1 s-1 for reaction of 1- methyl-1-trimethylsilylsilene with t-BuOH to a high of 1 x 1010 M-1 s- 1 for reaction of 1-ethynyl-1-methylsilene with MeOH. In several cases, rate constants have been determined for addition of the deuterated alcohols, and for addition of methanol over the 0-55°C range. Invariably, small primary deuterium kinetic isotope effects and negative Arrhenius activation energies are observed. These characteristics are consistent with a mechanism involving reversible formation of a silene-alcohol complex which collapses to alkoxysilane by unimolecular proton transfer from oxygen to carbon. Silene reactivity increases with increasing resonance electron-donating and inductive electron-withdrawing ability of the substituents at silicon and is significantly affected by steric effects within this series of compounds. This is suggested to be due to a combination of effects on both the degree of electrophilicity at silicon (affecting the rate constants for formation and reversion of the complex) and nucleophilicity at carbon (affecting the partitioning of the complex between product and free reactants). Two 1- methyl-1-alkoxysilacyclobutanes were also investigated, but proved to be inert to 193-nm photolysis.
Mercury-sensitized photolysis of Me2SiH2 the disproportionation reactions of the Me2SiH radical
Kerst,Potzinger
, p. 1071 - 1078 (2007/10/03)
Mercury-sensitized photolysis of Me2SiH2 yields in the primary step an Me2HSi radical and an H atom with a quantum yield of one. The Me2HSi radicals undergo a combination reaction [k(2)] as well as two kinds of disproportionate reactions leading to dimethylsilylene [k(3)] and 1-methylsilaethene [k(4)]. The following branching ratios have been determined: k(3)/[k(2) + k(3) + k(4)] = 0.64 ± 0.10 and k(4)/[k(2) + k(3) + k(4)] ≥ 0.007. For Me3Si radicals the branching ratio for disproportionation was also determined and a value of 0.063 was obtained.
Direct detection and characterization of a transient 1-silaallene derivative in solution
Kerst, Corinna,Rogers, Cerrie W.,Ruffolo, Ralph,Leigh, William J.
, p. 466 - 471 (2007/10/03)
Direct irradiation of ((trimethylsilyl)ethynyl)pentamethyldisilane in hydrocarbon solution affords a mixture of reactive intermediates which have been detected and identified using laser flash photolysis techniques and trapped as the methanol adducts in steady state irradiation experiments. Flash photolysis of air-saturated hexane solutions of the disilane allows detection of transient species assigned to 1,1-dimethyl-3,3-bis(trimethylsilyl)-1-silaallene and dimethylsilylene, along with a non-decaying species assigned to 1,1-dimethyl-2,3-bis(trimethylsilyl)-1-silacyclopropene. These were identified on the basis of their UV absorption spectra and reactivity toward various reagents. The 1-silaallene is a minor photoproduct, but it is readily observable in transient absorption experiments because it is relatively long-lived (τ = 2.4 μs in air-saturated solution) and absorbs strongly, with absorption maxima considerably to the red of those of the 1-silacyclopropene. The 1-silaallene exhibits characteristic silene reactivity; it reacts with methanol, acetic acid, acetone (κ = 106-108 M-1 s-1) and oxygen (κ~108 M-1 s-1), exhibits low reactivity toward aliphatic dienes and tert-butyl alcohol, and decays with second-order kinetics in the absence of quenchers. With methanol and acetic acid, it has been shown that reaction in hexane occurs with the monomeric ROH species only. Steady state irradiations in the presence of methanol afford methanol-addition products consistent with the formation of the silaallene, silacyclopropene, and silylene, along with bis(trimethylsilyl)acetylene as the major product.
Photolysis of 1,1,2,2-tetramethyl-1,2-bis-(2'-thienyl)disilane
Hu, Shui-Sheng,Weber, William P.
, p. 155 - 164 (2007/10/02)
Photolysis of 1,1,2,2-tetramethyl-1,2-bis-(2'-thienyl)disilane (I) in methanol/benzene leads to dimethyl-bis-(2'-thienyl)silane (III), 2-methoxydimethylsilylthiophene (IV) and 2-dimethylsilylthiophene (V) as a major products.The mechanism of this reaction, has been explored by use of methanol-d4.The predominant pathway leading to IV and V appears to involve direct reaction of methanol with the photoexcited state of I.
INSERTION OF DIMETHYLSILYLENE INTO O-H AND N-H SINGLE BONDS
Gu, Tai-Yin Yang,Weber, William P.
, p. 7 - 11 (2007/10/02)
Dimethylsilylene, generated by photolysis of dodecamethylcyclohexasilane, inserts efficiently into O-H single bonds of alcohols to yield alkoxydimethyl-silanes.Use of ethanol-O-d1 yields ethoxydimethylsilane-Si-d1.Dimethylsilylene also inserts into O-H single bonds of water or D2O to yield respectively tetramethyldisiloxane or tetramethyldisiloxane-Si2-d2.Dimethylsilylene also inserts into N-H bonds of primary and secondary amines to yield aminodimethylsilanes.This reaction provides an efficient route to difunctional silanes.
Solvent Modified Reactivity of Dimethylsilylene
Steele, Kent P.,Weber, William P.
, p. 6095 - 6097 (2007/10/02)
The insertion of dimethylsilylene into the oxygen-hydrogen single bond of alcohols to yield alkoxydimethylsilanes has been used to probe the effect of solvent on dimethylsilylene reactivity.Competition reactions between pairs of alcohols for dimethylsilylene in various solvents have been carried out.The selectivity of dimethylsilylene is influenced by solvent.Dimethylsilylene is more selective in ether than in hydrocarbon solvents.This difference may result from the formation of complexes between donor solvents and dimethylsilylene.These complexes can deliver dimethylsilylene which is less reactive and more selective than free dimethylsilylene.
