烷氧基自由基在铈催化的 C-H 官能化中通过 H 原子抽取的中介作用已得到明确证实。已经合成了催化相关的 Ce(IV)-醇盐络合物,并通过 X 射线衍射对其进行了表征。分离的五氯 Ce(IV) 醇盐的原位电子顺磁共振和瞬态吸收光谱实验将烷氧基自由基确定为通过配体到金属电荷转移 (LMCT) 激发产生的唯一以杂原子为中心的自由基物种。烷氧基自由基介导的氢原子转移 (HAT) 已通过动力学分析、密度泛函理论 (DFT) 计算和严格无氯条件下的反应得到验证。这些实验结果明确地确立了烷氧基自由基在 Ce-LMCT 催化中的关键作用,并明确排除了氯自由基的参与。这项研究还强化了选择性烷氧基自由基介导的 HAT 中酒精与 Ce 的高相对比例的必要性,因为酒精与 Ce 的相对比例看似微不足道的变化可能导致截然不同的机制途径。重要的是,之前提出的氯自由基-醇络合物假设解释了该系统中烷氧基自由基启用的选择性
Use of spin traps in the study of silyl radicals in the gas phase
作者:Harish Chandra、Iain M. T. Davidson、Martyn C. R. Symons
DOI:10.1039/f19837902705
日期:——
this study was to probe the utility of the spin-trapping technique for the identification and estimation of radicals derived from organosilicon compounds in the gasphase. The methods of generation comprised electric discharge and mercury-sensitized photolysis; the traps were Me3 C—NO and PhCNN(O)CMe3. After establishing that the procedures were satisfactory, using toluene and n-hexane as radical sources
The formation of fluoroalkyl radicals in liquid chlorofluorocarbons (CF2Cl-CFCl2, CFCl3, CFCl2-CH3, CHF2-CF2-CF2Cl,CF3-CFH-CF3 and CCl4) has been investigated by means of the spintrapping technique and ESR spectroscopy. It is shown that the primary fluoroalkyl radicals which were generated in these compounds by ionising radiation are preferably formed by bond cleavage at carbon atoms attached to one
This paper reports the spin trapping of radicals in liquid CCl4 irradiated with low-energy X-rays of different wavelengths, using phenyl-t-butylnitrone (PBN) as a spin trap. The unstable PBN-Cl adduct and the relatively stable PBN-CCl3 adduct have been detected. X-rays of energy above the K-edge for chlorine produce significantly more trapped radicals than those having energies below this K-edge value
A new role for nitrone (PBN:N-tert. Butyl alpha-phenyl nitrone) spin-trap in single electron transfer (SET) reactions is proposed. (C) 1998 Elsevier Science B.V. All rights reserved.