18027-97-9Relevant articles and documents
Gold-catalyzed oxidative coupling of arylsilanes and arenes: Origin of selectivity and improved precatalyst
Ball, Liam T.,Lloyd-Jones, Guy C.,Russell, Christopher A.
supporting information, p. 254 - 264 (2014/01/23)
The mechanism of gold-catalyzed coupling of arenes with aryltrimethylsilanes has been investigated, employing an improved precatalyst (thtAuBr3) to facilitate kinetic analysis. In combination with linear free-energy relationships, kinetic isotope effects, and stoichiometric experiments, the data support a mechanism involving an Au(I)/Au(III) redox cycle in which sequential electrophilic aromatic substitution of the arylsilane and the arene by Au(III) precedes product-forming reductive elimination and subsequent cycle-closing reoxidation of the metal. Despite the fundamental mechanistic similarities between the two auration events, high selectivity is observed for heterocoupling (C-Si then C-H auration) over homocoupling of either the arylsilane or the arene (C-Si then C-Si, or C-H then C-H auration); this chemoselectivity originates from differences in the product-determining elementary steps of each electrophilic substitution. The turnover-limiting step of the reaction involves associative substitution en route to an arene π-complex. The ramifications of this insight for implementation of the methodology are discussed.
Gas-phase alkylation of phenyltrimethylsilanes. Using the trimethylsilyl group to probe proton shifts in gaseous arenium ions
Attina', Marina,Cacace, Fulvio,Ricci, Andreina
, p. 5937 - 5942 (2007/10/02)
The reactivity of (trimethylsilyl)benzene (TSB) and (trimethylsilyl)toluenes (TST) toward i-C3H7+ and (CH3)2F+ has been studied in the gas phase in the interval from 0.6 to 3040 Torr and from 37.5 to 100 °C by mass spectrometric and radiolytic techniques. The systematic investigation of the dependence of the relative rate of the alkylation and alkyldesilylation processes promoted by i-C3H7+ on the nature and the concentration of gaseous bases has allowed an evaluation of the rate constant of the isomerization via proton 1,2-shifts of the alkylated adducts from TSB into the corresponding ions protonated ipso to the SiMe3 group. The results, i.e., ki = 1.6 X 109 s-1 at 310 K and Ei? ≈ 9.5 kcal mol-1, represent the first experimental evaluation of the kinetic parameters of proton 1,2-shifts within gaseous arenium ions, generally too fast to be monitored by mass spectrometric techniques, and are in excellent agreement with theoretical and solution-chemistry studies of the model C6H7+ ion. The selectivity of the alkylation of TSB and of m- and p-TST is discussed, particularly as regards direct ipso substitution and the steric hindrance to deprotonation of the ortho-isopropylated adducts.
