Low-Valent, High-Spin Chromium-Catalyzed Cleavage of Aromatic Carbon–Nitrogen Bonds at Room Temperature: A Combined Experimental and Theoretical Study
作者:Xuefeng Cong、Fei Fan、Pengchen Ma、Meiming Luo、Hui Chen、Xiaoming Zeng
DOI:10.1021/jacs.7b08579
日期:2017.10.25
inexpensive chromium(II) chloride as precatalyst, accompanied by an imino auxiliary, the selective arylative and alkylative C–C coupling of C(aryl)–N bonds can be achieved. Crossover experiments indicate that a low-valent chromium species, formed in situ by reduction of CrCl2 with Grignard reagent, is responsible for the catalytic cleavage of C(aryl)–N bonds. DFT calculations show that facile insertion of the
过渡金属催化的芳香碳氮键的裂解具有很高的合成价值,因为这种键在有机化学中很常见。但是,很少有金属催化剂可用于选择性地破坏电子中性分子中的C(芳基)–N键。我们在这里报告了室温下电子中性苯胺衍生物中C(芳基)–N键的第一个低价,高旋转铬催化裂解。通过使用简单且廉价的氯化铬(II)作为预催化剂,并辅以亚氨基辅助剂,可以实现C(芳基)-N键的选择性芳基化和烷基化C-C偶联。交叉实验表明,低价铬物质是通过还原CrCl 2原位形成的与格氏试剂一起,负责C(芳基)–N键的催化裂解。DFT计算表明,铬(0)容易插入C(芳基)–N键,可以在高纺丝五重态(S = 2)基态下发生,而低纺丝单重态(S = 0)和三重态(S = 1)状态在能量上是不可访问的。发现高自旋铬(0)的d 6壳层中唯一配对的d电子对C(芳基)–N键的反键轨道的供体以及氮与金属中心的孤键结作用对在零价铬物种裂解C(芳基)–N键中起重要作用。