- Microwave-assisted Lewis acid catalysis: Application to the synthesis of alkyl- or arylhalogermanes
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Under microwave irradiation, alkyl- or arylhalogermanes RnGeX4-n (R = Et, Bu, Ph; X = Cl, Br) are obtained by redistribution reactions of R4Ge with GeX4. These experimental conditions permit the synthesis of such compounds in good yield in a few minutes at atmospheric pressure. The direct Friedel-Crafts germylation of benzene and toluene by germanium tetrachloride also has been performed, but yields were low.
- Laurent, Régis,Laporterie, André,Dubac, Jacques,Berlan, Jacques
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p. 2493 - 2495
(2008/10/08)
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- Absolute Rate Constants for Some Intermolecular and Intramolecular Reactions of α-, β-, and γ-Silicon-Substituted Radicals
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Rate constants for hydrogen atom abstraction from n-Bu3GeH (kGeH) by Me3SiCH2. (1.), Me3SiCH2CH2. (2.), and Me3SiCH2CH2CH2. (3.) and from n-Bu3SnH (kSnH) by 1. and 3. have been determined at ambient temperatures.The order of decreasing radical reactivity is 1. > n-alkyl > 3. > 2..However, for bromine abstraction from the parent bromides by n-Bu3Sn. and n-Bu3Ge., the order of decreasing reactivity is 1-Br > 2-Br > 3-Br ca. n-alkyl bromide.The Arrhenius equations for reaction of 1. and 3. with n-Bu3SnH were also determined: log (kSnH(1.)/(M-1 s-1)) = (10.2 +/- 0.5) - (3.90 +/- 0.62)/Θ and log (kSnH(3.)/(M-1 s-1)) = (8.4 +/- 0.7) - (2.81 +/- 0.95)/Θ, where Θ = 2.3RT kcal/mol.These kinetic data are discussed in relation to previously measured rate constant ratios, kc5+6/kSnH and kexo5/kendo6, where kc5+6 corresponds to the cyclization of α-, β-, and γ-dimethylsilyl-substituted 5-hexenyl radicals to form 5-membered (kexo5) and 6-membered (kendo6) silacycloalkylmethyl radicals.
- Wilt, James W.,Lusztyk, J.,Peeran, Mehoob,Ingold, K. U.
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p. 281 - 287
(2007/10/02)
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- METAL-HALOGEN BONDING STUDIES WITH GROUP IV A TRIALKYLMETAL HALIDES
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Halogen redistribution reactions have been found to take place between benzyl bromide or benzyl iodide and the Group IV A silicon, germanium, tin, and lead containing trialkylmetal chlorides.However, for the reactions of the Si, Ge and Sn compounds, a quaternary ammonium halide catalyst was necessary to enable the equilibria to be established at reasonably rapid rates.The equilibrium constants at 50 deg C have been measured for each of these halogen redistributions.They have been found to increase gradually on going down in Group IV A from silicon to lead, being conside rably less than unity in the case of silicon and somewhat greater than unity in the case of lead for both the R3MCl + BzBr and R3MCl + BzI reactions.The ΔG0 values for these equilibria have been calculated, and it is suggested that their differences may be explained in terms of the relative importance of p?-d? contributions to the halogen-metal bonding in the various Group IV A trialkylmetal halide systems.
- Friedrich, Edwin C.,Abma, Charles B.,Vartanian, Paul F.
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p. 203 - 212
(2007/10/02)
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