Photocatalytic Generations of Secondary and Tertiary Silyl Radicals from Silylboranes Using an Alkoxide Cocatalyst
Photocatalytic Generations of Secondary and Tertiary Silyl Radicals from Silylboranes Using an Alkoxide Cocatalyst
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DOI：
10.1021/acs.joc.2c01885
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发表时间：
2022-10-10
影响因子：
3.6
通讯作者：
Tanaka, Ken
中科院分区：
文献类型：
--
作者：
Arai, Ryo;Nagashima, Yuki;Tanaka, Ken
硅烷基自由基是制备各种有机硅化合物的重要物种。然而，与稳定的叔甲硅烷基自由基不同，仲甲硅烷基自由基的使用由于其不稳定性而在甲硅烷基化反应中存在问题。在这里，我们提出了光催化原位生成的二级和叔甲硅烷基自由基的单电子氧化的酯络合物，形成从甲硅烷基硼烷和醇盐助催化剂，实现高效的氢化硅烷化和氘代硅烷化的富电子烯烃和二烯以及缺电子烯烃。理论研究表明，用醇盐活化的阴离子硼酸盐络合物具有比中性硼酸盐络合物更低的氧化电位，允许形成仲甲硅烷基自由基。计算的反应途径表明，阴离子条件下使用的共轭酸碱对的NaOEt（助催化剂）和乙醇（溶剂）的硅烷基自由基和烯烃的范围扩大的关键。
Silyl radicals are valuable species to prepare diverse organosilicon compounds. However, unlike stable tertiary silyl radicals, the use of secondary silyl radicals has been problematic in silylation reactions due to their instability. Here, we present photocatalytic in situ generations of both secondary and tertiary silyl radicals by one-electron oxidation of ate complexes, formed from silylboranes and an alkoxide cocatalyst, achieving highly efficient hydrosilylation and deuterosilylation of electron-rich alkenes and dienes as well as electron-deficient alkenes. The theoretical studies show that anionic borate complexes activated with an alkoxide have lower oxidation potentials than neutral borate complexes, allowing the formation of secondary silyl radicals. The calculated reaction pathways reveal that anionic conditions using the conjugate acid-base pair of NaOEt (cocatalyst) and EtOH (solvent) are the key to expanding the scope of silyl radicals and alkenes.