In Situ Studies of Arylboronic Acids/Esters and R(3)SiCF(3) Reagents: Kinetics, Speciation, and Dysfunction at the Carbanion-Ate Interface.
In Situ Studies of Arylboronic Acids/Esters and R(3)SiCF(3) Reagents: Kinetics, Speciation, and Dysfunction at the Carbanion-Ate Interface.
复制标题
芳基硼酸/酯和R（3）SiCF（3）试剂的原位研究：碳离子-Ate界面的动力学、形态和功能障碍。
DOI：
10.1021/acs.accounts.2c00113
复制
发表时间：
2022-05-03
影响因子：
18.3
通讯作者：
Lloyd-Jones, Guy C.
中科院分区：
文献类型：
--
作者：
Garcia-Dominguez, Andres;Leach, Andrew G.;Lloyd-Jones, Guy C.
试剂的不稳定性降低了化学过程的效率，尽管人们在反应优化方面投入了大量精力，但对试剂分解的机理原因关注较少。实际上，反应通常是简单地使用过量的试剂。具有普遍存在的实例的两个反应类别是硼酸/酯的Suzuki-Miyaura交叉偶联和从Ruppert-Prakash试剂TMSCF 3转移CF 3或CF 2。这个帐户描述了我们对它们分解的机械研究的一些总体特征。在第一部分中，我们总结了（杂）芳基硼酸的具体实例如何通过水溶液脱硼过程分解：Ar-B（OH）2 + H2O → ArH + B（OH）3。分析的关键是一个动力学模型，其中pH值控制硼形态和杂环质子化状态的发展。该方法揭示了六种不同的protodeboronation途径，包括自催化时，pH值接近的硼酸的pKa，和protodeboronation通过一个短暂的芳基茴香醚途径高度缺电子芳烃。通过二醇酯化的硼酸的“保护”程度被示出为非常依赖于二醇身份，六元环酯导致比母体硼酸更快的protodeboronation。在帐户的第二部分中，我们描述了TMSCF 3与酮、氟代芳烃和烯烃的反应动力学的19 F NMR光谱分析。由亚化学计量的“TBAT”（[Ph 3SiF 2][Bu 4 N]）引发的过程涉及阴离子链式反应，其中低浓度的[CF 3]−从硅醇盐储层[TMS（CF 3）2][Bu 4 N]中快速且可逆地释放。增加TMSCF 3浓度会降低[CF 3]−浓度，从而抑制CF 3转移速率。计算和动力学表明，TMSCF 3分子间从[CF 3]−中提取氟化物以生成CF 2，否则将是吸能α-氟化物消除。从[CF 3]−和CF2开始，涉及全氟烯烃同系化的级联反应导致受阻全氟碳负离子[C11 F23]−的产生和抑制。从TMSCF 3生成CF 2更有效地由NaI介导，与TBAT相反，该过程经历自动加速。该过程涉及NaI介导的α-氟化物从[CF 3][Na]中消除，生成CF2和[NaI·NaF]链载体。链支化，由[（CF2）3 I][Na]原位生成（CF2 + TFE + NaI），导致自动加速。有效捕获CF2的烯烃减弱了链支化，抑制了自动加速，并导致不太快的二氟环丙烷化。该账户还强调了实验和计算的协作方法如何实现对过程控制的机械见解。
Reagent instability reduces the efficiency of chemical processes, and while much effort is devoted to reaction optimization, less attention is paid to the mechanistic causes of reagent decomposition. Indeed, the response is often to simply use an excess of the reagent. Two reaction classes with ubiquitous examples of this are the Suzuki–Miyaura cross-coupling of boronic acids/esters and the transfer of CF3 or CF2 from the Ruppert–Prakash reagent, TMSCF3. This Account describes some of the overarching features of our mechanistic investigations into their decomposition. In the first section we summarize how specific examples of (hetero)arylboronic acids can decompose via aqueous protodeboronation processes: Ar–B(OH)2 + H2O → ArH + B(OH)3. Key to the analysis was the development of a kinetic model in which pH controls boron speciation and heterocycle protonation states. This method revealed six different protodeboronation pathways, including self-catalysis when the pH is close to the pKa of the boronic acid, and protodeboronation via a transient aryl anionoid pathway for highly electron-deficient arenes. The degree of “protection” of boronic acids by diol-esterification is shown to be very dependent on the diol identity, with six-membered ring esters resulting in faster protodeboronation than the parent boronic acid. In the second section of the Account we describe 19F NMR spectroscopic analysis of the kinetics of the reaction of TMSCF3 with ketones, fluoroarenes, and alkenes. Processes initiated by substoichiometric “TBAT” ([Ph3SiF2][Bu4N]) involve anionic chain reactions in which low concentrations of [CF3]− are rapidly and reversibly liberated from a siliconate reservoir, [TMS(CF3)2][Bu4N]. Increased TMSCF3 concentrations reduce the [CF3]− concentration and thus inhibit the rates of CF3 transfer. Computation and kinetics reveal that the TMSCF3 intermolecularly abstracts fluoride from [CF3]− to generate the CF2, in what would otherwise be an endergonic α-fluoride elimination. Starting from [CF3]− and CF2, a cascade involving perfluoroalkene homologation results in the generation of a hindered perfluorocarbanion, [C11F23]−, and inhibition. The generation of CF2 from TMSCF3 is much more efficiently mediated by NaI, and in contrast to TBAT, the process undergoes autoacceleration. The process involves NaI-mediated α-fluoride elimination from [CF3][Na] to generate CF2 and a [NaI·NaF] chain carrier. Chain-branching, by [(CF2)3I][Na] generated in situ (CF2 + TFE + NaI), causes autoacceleration. Alkenes that efficiently capture CF2 attenuate the chain-branching, suppress autoacceleration, and lead to less rapid difluorocyclopropanation. The Account also highlights how a collaborative approach to experiment and computation enables mechanistic insight for control of processes.
登录
查看更多内容
影响因子：
15
作者：
Hayes, Hannah L. D.;Wei, Ran;Lloyd-Jones, Guy C.
通讯作者：
Lloyd-Jones, Guy C.
影响因子：
1.8
作者：
Harlow, Richard L.;Benet-Buchholz, Jordi;Grushin, Vladimir V.
通讯作者：
Grushin, Vladimir V.
影响因子：
12.9
作者：
Garcia-Dominguez, Andres;de Oliveira, Pedro H. Helou;Jones, Guy C. Lloyd
通讯作者：
Jones, Guy C. Lloyd
影响因子：
3.6
作者：
Cammidge, AN;Crépy, KVL
通讯作者：
Crépy, KVL
影响因子：
12.9
作者：
Ball, Liam T.;Corrie, Tom J. A.;Lloyd-Jones, Guy C.
通讯作者：
Lloyd-Jones, Guy C.