132536-24-4Relevant articles and documents
Supported palladium nanoparticles as heterogeneous ligand-free catalysts for the Hiyama C-C coupling of vinylsilanes and halobenzenes leading to styrenes
Grirrane, Abdessamad,Garcia, Hermenegildo,Corma, Avelino
, p. 49 - 57 (2013/06/27)
The Hiyama C-C coupling reaction of a wide range of aryl iodides and vinylsilanes has been performed using ligand-free solid catalysts based on supported palladium nanoparticles. Among the supports tested (Mg, TiO 2, CeO2 and active carbon), the most active catalysts were those in which palladium is supported on MgO and TiO2. Analogous Pt and Au materials were inefficient to promote this reaction. Leaching tests suggest that there is some contribution of dissolved Pd since Pd in solution has been detected and the scavenging test decreases the initial reaction rate. Although the solid Pd catalysts can be reused, it was, however, observed that they undergo a certain deactivation upon use that can be attributed to several factors including the presence of inorganic compounds on the catalyst, Pd leaching or agglomeration of Pd NPs.
Mechanism of Thermal Eliminations. Part 30. Pyrolysis of 2-Trimethylsilylethanol and 1-Aryl Derivatives
Taylor, Roger
, p. 1703 - 1706 (2007/10/02)
The Arrhenius parameters (Eact = 45.57 kcal mol-1, log A/s-1 = 12.865) and rate coefficient at 600 K (1.84 * 10-4 s-1) for the cis β-thermal elimination of trimethylsilanol from 2-trimethylsilylethanol are identical (within experimental error) with those reported in the literature for elimination of methyl trimethylsilyl ether from 1-methoxy-2-(trimethylsilyl)ethane.This indicates that the driving force for the reaction, formation of the Si-O bond, is such that alteration of the nucleophilicity of oxygen has little effect on the reaction rate.A series of 1-aryl-2-trimethylsilylethanols have been prepared and their rates of elimination determined.The activating effect of the 1-aryl substituent (5.2-fold) is much less than the corresponding effect in the pyrolysis of ethyl acetates (63-fold) and 2-trimethylsilylethyl acetates (87-fold).Breaking of the α-C-O bond is thus kinetically less important than in the other reactions, and this conclusion is confirmed by a correlation of the rate data with the Yukawa-Tsuno equation which gives ρ = -0.4, r = 0.3.Si-O bond formation in the reaction is thereby shown to be of over-riding kinetic importance.For the 4-methylphenyl- and 4-methoxyphenyl compounds a minor competing reaction was the elimination of water to give the corresponding 1-aryl-2-trimethylsilylethene, and this has a higher activation energy than for the elimination of trimethylsilanol.NMR spectra for the 1-aryl-2-trimethylsilylethanols show that interaction between the OH and SiMe3 groups inhibits free rotation about the C(1)-C(2) bond.Preparation of 1-aryl-2-trimethylsilylethanols gave 1,3-diaryl-4-trimethylsilylbutyl trimethylsilyl ethers as byproducts arising from elimination of water from two molecules of the alcohols in a process believed to be two-step.
