the novel five-membered heterocycles 4a, 5b and 6b. In 5b and 6b, derived from thiazole and 4-methyl-thiazole, zwitterionic structures result which can be regarded as borane adducts of carbenes. All new compounds were characterised by 1H-, 11B-, 13C-, 14/15N- and 29Si-NMR spectroscopy
β‐disilyl‐substitutedvinylcations were prepared by intramolecular addition of transient silylium ions to CC triple bonds. The vinylcations were isolated from hydrocarbon solutions as tetrakis(pentafluorophenyl) borates at room temperature. The substituents directly attached to the positively charged carbon atom were varied from tert‐butyl‐ to trialkylsilyl‐ to trialkylgermyl groups. The cations were
通过将瞬时甲硅烷离子分子内加成到 CC 三键上,制备了一系列 β,β-二甲硅烷基取代的乙烯基阳离子。乙烯基阳离子在室温下以四(五氟苯基)硼酸盐的形式从烃溶液中分离出来。直接连接到带正电荷的碳原子上的取代基从叔丁基到三烷基甲硅烷基到三烷基锗基不等。阳离子通过其特征13 C 和29 Si NMR 数据进行鉴定。NMR 研究揭示了 β,β-二甲硅烷基-α-锗基和三甲硅烷基取代的乙烯基阳离子具有高度动态的结构,其中两个乙烯基碳原子在室温下在 NMR 时间尺度上进行快速的分子内交换过程。核磁共振研究使用双重13 C 标记的乙烯基阳离子表明,作为该交换过程的机制,二碳炔 CC 2-单元在由三个阳离子甲硅烷基片段定义的三角形内旋转。因此,三甲硅烷基或二甲硅烷基锗基取代的乙烯基阳离子的动态结构与母体乙烯基阳离子质子化乙炔的情况相似。
Hydroboration of alkyn-1-yl(methyl)silanes bearing functional substituents at silicon
作者:Bernd Wrackmeyer、Heidi E Maisel、Wolfgang Milius、Moazzam H Bhatti、Saqib Ali
DOI:10.1016/s0022-328x(02)02219-2
日期:2003.3
Alkyn-1-yl(methyl)silanes Me-2(H)Si-Cequivalent toC-R (1), Me(H)(Cl)Si-Cequivalent toC-R (2) and Me-2(Cl)Si-Cequivalent toC-R (3) [R = Bu (a), Bu-t (b), Ph (c), SiMe3 (d)] react with 9-borabicyclo[3.3.1]nonane (9-BBN) by 1,2-cis-hydroboration to give selectively (except of 3d) the alkenylsilanes 4 (from 1), 5 (from 2), and 6 (from 3), in which the boryl group has become attached to the carbon atom adjacent to the silyl group bearing functional substituents. In the case of 3d, a mixture consisting of the alkenes 6d and the isomers 7d, 8d and 9d is obtained. All products were characterised by NMR spectra (H-1-, B-11-, C-13 and Si-29-NMR) in solution, and in the cases of 5c and 6c, the molecular structures in the solid state were determined by X-ray analysis. (C) 2003 Elsevier Science B.V. All rights reserved.