Sang Ruocheng, Han Wangyujing, Zhang Hanwen, Saunders Carla M, Noble Adam, Aggarwal Varinder K
School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, U.K.
J Am Chem Soc. 2023 Jul 19;145(28):15207-15217. doi: 10.1021/jacs.3c02185. Epub 2023 Jul 6.
Borylations of inert carbon-hydrogen bonds are highly useful for transforming feedstock chemicals into versatile organoboron reagents. Catalysis of these reactions has historically relied on precious-metal complexes, which promote dehydrogenative borylations with diboron reagents under oxidant-free conditions. Recently, photoinduced radical-mediated borylations involving hydrogen atom transfer pathways have emerged as attractive alternatives because they provide complimentary regioselectivities and proceed under metal-free conditions. However, these net oxidative processes require stoichiometric oxidants and therefore cannot compete with the high atom economy of their precious-metal-catalyzed counterparts. Herein, we report that CuCl catalyzes radical-mediated, dehydrogenative C(sp)-H borylations of alkanes with bis(catecholato)diboron under oxidant-free conditions. This is a result of an unexpected dual role of the copper catalyst, which promotes oxidation of the diboron reagent to generate an electrophilic bis-boryloxide that acts as an effective borylating agent in subsequent redox-neutral photocatalytic C-H borylations.
惰性碳氢键的硼化反应对于将原料化学品转化为多功能有机硼试剂非常有用。这些反应的催化作用在历史上一直依赖于贵金属配合物，其在无氧化剂条件下促进与双硼试剂的脱氢硼化反应。最近，涉及氢原子转移途径的光诱导自由基介导的硼化反应已成为有吸引力的替代方法，因为它们提供了互补的区域选择性并且在无金属条件下进行。然而，这些净氧化过程需要化学计量的氧化剂，因此无法与贵金属催化反应的高原子经济性相竞争。在此，我们报道了CuCl在无氧化剂条件下催化自由基介导的烷烃与双（邻苯二酚）二硼的脱氢C(sp)-H硼化反应。这是铜催化剂意外的双重作用的结果，它促进双硼试剂的氧化以生成亲电双硼氧化物，该双硼氧化物在随后的氧化还原中性光催化C-H硼化反应中作为有效的硼化剂。
