18027-97-9Relevant academic research and scientific papers
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.
A new route to organoboron polymers via highly selective polymer modification reactions
Qin, Yang,Cheng, Guanglou,Achara, Obianuju,Parab, Kshitij,Jaekle, Frieder
, p. 7123 - 7131 (2007/10/03)
We have developed a highly efficient new method for the introduction of Lewis acidic boron centers into the side chains of organic polymers. Our methodology involves three steps: (i) the controlled polymerization of the functional monomer 4-trimethylsilylstyrene (S-Si), (ii) the exchange of the silyl groups in poly(4-trimethylsilylstyrene) (PS-Si) with BBr3 to give the reactive polymer poly(4-dibro-moborylstyrene) (PS-BBr), and (iii) the fine-tuning of the Lewis acidity of the individual boron centers through substituent exchange reactions with nucleophiles. Treatment of PS-BBr with ethoxytrimethylsilane and THF respectively yields the moderately Lewis acidic poly(arylboronate)s PS-BOR (R = Et, 4-bromobutyl). The alkoxy groups in PS-BOR have been exchanged with pinacol to form the air-stable polymer PS-BPin (Pin = pinacolato). Treatment of PS-BBr with 2-thienyltrimethyltin and pentafluo-rophenylcopper respectively gives the well-defined highly Lewis acidic triarylborane polymers PS-BTh and PS-BPf (Th = 2-thienyl, Pf = 2,3,4,5,6-pentafluorophenyl), which contain triarylborane moieties at every repeat unit along the polymer chain. All polymers have been studied by multinuclear NMR spectroscopy and differential scanning calorimetry. The molecular weights of the arylboronate polymers PS-BOR have been determined by gel permeation chromatography, and the highly selective formation of polymer PS-BPin has been confirmed by static light scattering.
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.
