Ruthenium-Catalyzed Hydroamination of Unactivated Terminal Alkenes with Stoichiometric Amounts of Alkene and an Ammonia Surrogate by Sequential Oxidation and Reduction

Hydroamination of alkenes catalyzed by transition-metal complexes is an atom-economical method for the synthesis of amines, but reactions of unactivated alkenes remain inefficient. Additions of N–H bonds to such alkenes catalyzed by iridium, gold, and lanthanide catalysts are known, but they have required a large excess of the alkene. New mechanisms for such processes involving metals rarely used previously for hydroamination could enable these reactions to occur with greater efficiency. We report ruthenium-catalyzed intermolecular hydroaminations of a variety of unactivated terminal alkenes without the need for an excess of alkene and with 2-aminopyridine as an ammonia surrogate to give the Markovnikov addition product. Ruthenium complexes have rarely been used for hydroaminations and have not previously catalyzed such reactions with unactivated alkenes. Identification of the catalyst resting state, kinetic measurements, deuterium labeling studies, and DFT computations were conducted and, together, strongly suggest that this process occurs by a new mechanism for hydroamination occurring by oxidative amination in concert with reduction of the resulting imine.

过渡金属配合物催化的烯烃氢胺化反应是合成胺类化合物的原子经济性方法，但未活化烯烃的氢胺化反应仍存在效率低下的问题。此前已有研究报道以铱、金及镧系催化剂催化N-H键加成至此类烯烃的反应，但此类反应均需要使用过量的烯烃底物。若采用此前极少应用于氢胺化反应的金属开发新型反应机制，有望提升这类反应的效率。本工作报道了钌催化的多种未活化端烯烃分子间氢胺化反应，无需过量烯烃底物，以2-氨基吡啶作为氨替代物，即可得到马氏加成产物。钌配合物极少被用于氢胺化反应，且此前从未被用于催化未活化烯烃的此类氢胺化反应。本研究通过鉴定催化剂驻态、开展动力学测量、氘标记实验以及密度泛函理论（DFT）计算，综合所有结果强烈表明，该反应通过一种全新的氢胺化机制进行：即氧化胺化过程与生成的亚胺还原过程协同发生。