Mechanism of Anion-Catalyzed C-H Silylation Using TMSCF3: Kinetically-Controlled CF3-Anionoid Partitioning As a Key Parameter
Mechanism of Anion-Catalyzed C-H Silylation Using TMSCF3: Kinetically-Controlled CF3-Anionoid Partitioning As a Key Parameter
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DOI：
10.1021/acscatal.1c00033
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发表时间：
2021-02-22
期刊：
影响因子：
12.9
通讯作者：
Jones, Guy C. Lloyd
中科院分区：
文献类型：
--
作者：
Garcia-Dominguez, Andres;de Oliveira, Pedro H. Helou;Jones, Guy C. Lloyd
采用均相TBAT引发、原位和停流F-19 NMR谱、H-2-KIE、LFER、氘标记交叉、结构选择性定量（TMSCF 3/TESCF 3）、卡宾捕获和DFT计算研究了R3 SiCF 3试剂催化的C-H硅烷化反应机理。1，3-二氟苯（2）的反应动力学分析以及ArSiMe 3和Me 3SiF的生成作为[2]、[TMSCF 3]和[TBAT]浓度的函数，表明CF 3-苯胺是活性中间体。CF 3-阴离子从硅醇盐[（CF 3）（2）SiMe 3]-中可逆释放，并通过限速芳烃去质子化（H-1/H-2 KIE 9.5）进行分配，生成ArSiMe 3（通过瞬时芳基阴离子）和氟仿（CF 3 H），与F-阴离子竞争转移到TMSCF 3，生成CF 2和TMSF。[2]/[TMSCF 3]浓度比直接且成比例地控制分配的动力学，有利于C-H去质子化。较高浓度的TBAT和较低浓度的TMSCF 3导致更快的ArSiMe 3生成速率。同系TESCF 3试剂的使用导致更快的阴离子催化速率和对C-H去质子化的增加的选择性。由CF2原位生成的全氟烯烃捕获CF 3-阴离子，导致阴离子催化的逐步抑制。通过使用苯乙烯添加剂来捕获CF2来抑制，并且通过缓慢添加TMSCF 3（1）来提高该过程的效率以保持高浓度比[2]/[1]。
The mechanism of anion-catalyzed C-H silylation by R3SiCF3 reagents has been investigated using homogeneous TBAT-initiation, in situ and stopped-flow F-19 NMR spectroscopy H-2-KIE, LFER, deuterium-labeled crossover, structure-selectivity quantitation (TMSCF3/TESCF3), carbene trapping, and DFT-calculations. Analysis of the kinetics of reactions of 1,3-difluorobenzenes (2), and the generation of ArSiMe3 and Me3SiF as a function of the concentration of [2], [TMSCF3], and [TBAT], show that a CF3-anionoid is the active intermediate. The CF3-anionoid is reversibly released from siliconate [(CF3)(2)SiMe3]- and undergoes partitioning through rate-limiting arene deprotonation (H-1/H-2 KIE 9.5) to generate ArSiMe3 (via a transient aryl anionoid) and fluoroform (CF3H), in competition with F-anion transfer to TMSCF3 to generate CF2 and TMSF. The [2]/[TMSCF3] concentration ratio directly and proportionally controls the kinetics of the partition, in favor of C-H deprotonation. Higher concentrations of TBAT and lower concentrations of TMSCF3 lead to faster rates of ArSiMe3 generation. Use of the homologous TESCF3 reagent leads to faster rates of anion catalysis and an increased selectivity toward C-H deprotonation. Perfluoroalkenes, generated in situ from CF2, capture the CF3-anionoid leading to progressive inhibition of the anion-catalysis. Inhibition is suppressed by using a styrene additive to trap the CF2 and the efficiency of the process enhanced by slow-addition of TMSCF3 (1) to maintain a high concentration ratio [2]/[1].