Energy and Materials Laboratory, School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, United Kingdom.
Dalton Trans. 2013 Jan 21;42(3):782-9. doi: 10.1039/c2dt31622f.
We report a kinetic and mechanistic study into the one-electron reduction of the archetypal Lewis acid tris(pentafluorophenyl)borane, B(C(6)F(5))(3), in dichloromethane and 1,2-difluorobenzene. Electrochemical experiments, combined with digital simulations, DFT computational studies and multinuclear NMR analysis allow us to obtain thermodynamic, kinetic and mechanistic information relating to the redox activity of B(C(6)F(5))(3). We show that tris(pentafluorophenyl)borane undergoes a quasi-reversible one-electron reduction followed by rapid chemical decomposition of the B(C(6)F(5))(3)˙(-) radical anion intermediate via a solvolytic radical pathway. The reaction products form various four-coordinate borates of which B(C(6)F(5))(4) is a very minor product. The rate of the follow-up chemical step has a pseudo-first order rate constant of the order of 6 s(-1). This value is three orders of magnitude larger than that found in previous studies performed in the donor solvent, tetrahydrofuran. The standard reduction potential of B(C(6)F(5))(3) is reported for the first time as -1.79 ± 0.1 V and -1.65 ± 0.1 V vs. ferrocene/ferrocenium in dichloromethane and 1,2-difluorobenzene respectively.
我们报告了一个动力学和机理研究，研究了典型的路易斯酸三（五氟苯基）硼烷，B（C（6）F（5））（3），在二氯甲烷和 1,2-二氟苯中的单电子还原。电化学实验，结合数字模拟、DFT 计算研究和多核 NMR 分析，使我们能够获得与 B（C（6）F（5））（3）的氧化还原活性有关的热力学、动力学和机理信息。我们表明，三（五氟苯基）硼烷经历准可逆的单电子还原，随后 B（C（6）F（5））（3）˙（-）自由基阴离子中间体通过溶剂解自由基途径迅速发生化学分解。反应产物形成各种四配位硼酸盐，其中[B（C（6）F（5））（4）]（-）是非常少量的产物。后续化学步骤的速率具有约 6 s（-1）的拟一级速率常数。这个值比在先前在给体溶剂四氢呋喃中进行的研究中发现的速率常数大三个数量级。B（C（6）F（5））（3）的标准还原电位首次报道为-1.79 ± 0.1 V 和-1.65 ± 0.1 V 相对于二氯甲烷和 1,2-二氟苯中的 ferrocene/ferrocenium。
