Xu Qing-Hao, Wei Li-Pu, Xiao Bin
Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China.
Angew Chem Int Ed Engl. 2022 Mar 28;61(14):e202115592. doi: 10.1002/anie.202115592. Epub 2022 Feb 10.
Single-electron transfer (SET) oxidation of ionic hypervalent complexes, in particular alkyltrifluoroborates (Alkyl-BF ) and alkylbis(catecholato)silicates (Alkyl-Si(cat) ), have contributed substantially to alkyl radical generation compared to alkali or alkaline earth organometallics because of their excellent activity-stability balance. Herein, another proposal is reported by using neutral metalloid compounds, Alkyl-GeMe , as radical precursors. Alkyl-GeMe shows comparable activity to that of Alkyl-BF and Alkyl-Si(cat) in radical addition reactions. Moreover, Alkyl-GeMe is the first successful group 14 tetraalkyl nucleophile in nickel-catalyzed cross-coupling. Meanwhile, the neutral nature of these organogermanes offset the limitation of ionic precursors in purification and derivatization. A preliminary mechanism study suggests that an alkyl radical is generated from a tetraalkylgermane radical cation with the assistance of a nucleophile, which may also result in the development of more non-ionic alkyl radical precursors with a metalloid center.
与碱金属或碱土金属有机金属化合物相比，离子型高价配合物，特别是烷基三氟硼酸盐（Alkyl-BF₃）和烷基双（儿茶酚）硅酸盐（Alkyl-Si(cat)₂）的单电子转移（SET）氧化反应，由于其出色的活性-稳定性平衡，在烷基自由基的生成方面做出了重大贡献。在此，本文报道了另一种方法，即使用中性类金属化合物Alkyl-GeMe₃作为自由基前体。Alkyl-GeMe₃在自由基加成反应中表现出与Alkyl-BF₃和Alkyl-Si(cat)₂相当的活性。此外，Alkyl-GeMe₃是镍催化交叉偶联反应中首个成功的第14族四烷基亲核试剂。同时，这些有机锗烷的中性性质弥补了离子型前体在纯化和衍生化方面的局限性。初步机理研究表明，在亲核试剂的协助下，四烷基锗自由基阳离子会生成烷基自由基，这也可能促使开发更多具有类金属中心的非离子型烷基自由基前体。
