A kinetic study of the electron-transfer-initiated carbon-silicon bond cleavage reactions of benzyltrialkylsilanes promoted by dodecatungstocobalt(III)ate ion
摘要:
The reactions of some ring-substituted benzyltrimethylsilanes (1Z), (p-methylbenzyl)triethylsilane (2), (p-methylbenzyl)triisopropylsilane (3), and (p-methoxybenzyl)triisopropylsilane (4) with potassium 12-tungstocobalt(III)ate, K5[CoIIIW12O40] (CO(III)W), have been studied in AcOH-H2O. In all cases desilylated products, benzyl acetates, and benzyl alcohols have been obtained, with a 2:1 oxidant to substrate stoichiometry. A kinetic investigation has shown that the reactions of 1Z and 2 are strictly first order in Co(III)W and first order in the substrate. Added salts (NaClO4, NaOAc) decrease the rate, whereas no retarding effect by Co(II)W has been noted. In contrast, the reaction of 4 is no longer first order in Co(III)W and the rate is significantly decreased by added Co(II)W. These data have been interpreted in terms of an electron-transfer mechanism, in which a benzyltrialkylsilane radical cation is formed and then undergoes a C-Si bond cleavage to form a benzyl radical. Reaction of this radical with Co(III)W leads to the products. In the reactions of 1Z and 2 the rate-determining step is the transfer of the electron from the substrate to Co(III)W, whereas in the reaction of 4 the slow step is the one where the C-Si bond cleavage takes place. The mechanistic changeover is probably related to the much lower rate of C-Si bond cleavage in 4+. than in 1Z+. and 2+., due to the fact that in the former cation radical nucleophilic attack at silicon is made difficult by the bulky isopropyl groups. The kinetic data for the reactions of 1Z and 2 fit the Marcus equation for a reorganization energy lambda of 43 +/- 1 kcal mol-1. From this value a lambda-value of 61 kcal mol-1 for the couple ArCH2SiMe3+./ArCH2SiMe3 has been evaluated, which is somewhat higher than that found for a number of ArCH3+./ArCH3 Systems. The possible reasons for this difference are discussed on the basis of ab initio calculations (STO-3G) concerning bond distances and angles in PhCH3+. and PhCH2SiH3+..
Iron Porphyrin Catalyzed Insertion Reaction of <i>N</i>-Tosylhydrazone-Derived Carbenes into X–H (X = Si, Sn, Ge) Bonds
作者:En-Hui Wang、Yuan-Ji Ping、Zong-Rui Li、Hongling Qin、Zhen-Jiang Xu、Chi-Ming Che
DOI:10.1021/acs.orglett.8b01931
日期:2018.8.3
An efficient Fe(TPP)Cl catalyzed insertionreaction of in situ generated benzylic carbenes from N-tosylhydrazones into X–H (X = Si, Sn, Ge) was developed. Silanes bearing tertiary, secondary, and primary (3°, 2°, and 1°) Si–H bonds all reacted well to afford insertion products in moderate to high yields (up to 97%), and the reaction time could be significantly shortened to 1 h under microwave irradiation
One-Pot Rapid Access to Benzyl Silanes, Germanes, and Stannanes from Toluenes Mediated by a LiN(SiMe<sub>3</sub>)<sub>2</sub>/CsCl System
作者:Yaqi Yuan、Yuanyun Gu、Yan-En Wang、Jiali Zheng、Jiaying Ji、Dan Xiong、Fei Xue、Jianyou Mao
DOI:10.1021/acs.joc.2c01612
日期:2022.11.4
Organo-silanes, germanes, and stannanes are considered to be conducive to the development of cross-coupling reactions because they are stable, nontoxic, and easy to handle. Using feedstock toluenes, one-pot direct benzylic C–H silylations, germylations, and stannylations are developed. Simply combining toluenes, LiN(SiMe3)2/CsCl, and R3MCl (M = Si, Ge, Sn) generates a diverse array of bench-stable
Efficient deoxygenative silylation of C(sp3)–O bonds with hydrosilanes by supported Au catalysts is described. Goldnanoparticlessupported on TiO2 enabled various hydrosilanes to be used as sources of silyl groups in C–Si cross-coupling reactions. A variety of alkyl acetates and propargyl carbonates participated in the Au-catalyzed reactions to furnish the corresponding alkyl and allenylsilanes in
描述了负载型 Au 催化剂对 C(sp 3 )–O 键与氢硅烷的有效脱氧硅烷化。负载在 TiO 2上的金纳米粒子使各种氢硅烷能够在 C-Si 交叉偶联反应中用作甲硅烷基的来源。各种乙酸烷基酯和碳酸炔丙酯参与了金催化的反应,以高产率提供相应的烷基和烯丙基硅烷。此外,Au/TiO 2对环醚的开环甲硅烷基化也有效。详细的机理研究证实标题反应涉及甲硅烷基和烷基自由基中间体的形成,而 Au 纳米颗粒作为单电子转移催化剂与金属氧化物表面的路易斯酸位点的合作是氢硅烷异常反应性的原因特定的 C(sp 3 )–Si 键形成。