Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, 610 Taylor Road, Piscataway, New Jersey 08854-8087, USA.
J Am Chem Soc. 2012 Feb 15;134(6):3300-11. doi: 10.1021/ja211945m. Epub 2012 Feb 7.
The intermolecular hydroaminoalkylation of unactivated alkenes and vinyl arenes with secondary amines occurs readily in the presence of tantalum and niobium binaphtholate catalysts with high regio- and enantioselectivity (up to 98% ee). Mechanistic studies have been conducted in order to determine the kinetic order of the reaction in all reagents and elucidate the rate- and stereodetermining steps. The effects of substrate steric and electronic properties on the overall reaction rate have been evaluated. The reaction is first order in amine and the catalyst, while exhibiting saturation in alkene at high alkene concentration. Unproductive reaction events including reversible amine binding and arene C-H activation have been observed. The formation of the metallaaziridine is a fast reversible nondissociative process and the overall reaction rate is limited either by amide exchange or alkene insertion, as supported by reaction kinetics, kinetic isotope effects, and isotopic labeling studies. These results suggest that the catalytic activity can be enhanced by employing a more electron-deficient ligand backbone.
在钽和铌联萘醇酸盐催化剂的存在下，仲胺很容易与未活化的烯烃和乙烯基芳烃发生分子间氢氨基烷基化反应，具有高区域和对映选择性（高达 98%ee）。为了确定所有试剂中反应的动力学顺序并阐明速率和立体决定步骤，进行了机理研究。评估了底物的空间和电子性质对总反应速率的影响。该反应对胺和催化剂均为一级，而在高烯烃浓度下，烯烃呈饱和状态。已经观察到包括可逆胺结合和芳基 C-H 活化在内的非生产性反应事件。形成金属氮丙啶是一个快速可逆的非解离过程，并且酰胺交换或烯烃插入是总反应速率的限制步骤，这得到了反应动力学、动力学同位素效应和同位素标记研究的支持。这些结果表明，通过采用更缺电子的配体骨架可以增强催化活性。
