Sun Wei, Li Ming-Peng, Li Lu-Jie, Huang Qiang, Hu Meng-Yang, Zhu Shou-Fei
Frontiers Science Center for New Organic Matter, State Key Laboratory and Institute of Elemento-Organic Chemistry, College of Chemistry, Nankai University Tianjin 300071 China
Haihe Laboratory of Sustainable Chemical Transformations Tianjin 300192 China.
Chem Sci. 2022 Feb 10;13(9):2721-2728. doi: 10.1039/d1sc06727c. eCollection 2022 Mar 2.
Iron-catalyzed organic reactions have been attracting increasing research interest but still have serious limitations on activity, selectivity, functional group tolerance, and stability relative to those of precious metal catalysts. Progress in this area will require two key developments: new ligands that can impart new reactivity to iron catalysts and elucidation of the mechanisms of iron catalysis. Herein, we report the development of novel 2-imino-9-aryl-1,10-phenanthrolinyl iron complexes that catalyze both -Markovnikov hydrosilylation of terminal alkenes and 1,2--Markovnikov hydrosilylation of various conjugated dienes. Specifically, we achieved the first examples of highly 1,2--Markovnikov hydrosilylation reactions of aryl-substituted 1,3-dienes and 1,1-dialkyl 1,3-dienes with these newly developed iron catalysts. Mechanistic studies suggest that the reactions may involve an Fe(0)-Fe(ii) catalytic cycle and that the extremely crowded environment around the iron center hinders chelating coordination between the diene and the iron atom, thus driving migration of the hydride from the silane to the less-hindered, terminal end of the conjugated diene and ultimately leading to the observed 1,2--Markovnikov selectivity. Our findings, which have expanded the types of iron catalysts available for hydrosilylation reactions and deepened our understanding of the mechanism of iron catalysis, may inspire the development of new iron catalysts and iron-catalyzed reactions.
铁催化的有机反应一直吸引着越来越多的研究兴趣，但相对于贵金属催化剂，其在活性、选择性、官能团耐受性和稳定性方面仍存在严重局限性。该领域的进展需要两个关键的发展方向：能够赋予铁催化剂新反应活性的新型配体以及对铁催化机理的阐明。在此，我们报道了新型2-亚氨基-9-芳基-1,10-菲咯啉基铁配合物的开发，这些配合物可催化末端烯烃的反马氏硅氢化反应以及各种共轭二烯的1,2-反马氏硅氢化反应。具体而言，我们首次实现了用这些新开发的铁催化剂对芳基取代的1,3-二烯和1,1-二烷基1,3-二烯进行高度1,2-反马氏硅氢化反应。机理研究表明，这些反应可能涉及Fe(0)-Fe(ii)催化循环，并且铁中心周围极其拥挤的环境阻碍了二烯与铁原子之间的螯合配位，从而促使氢化物从硅烷迁移至共轭二烯位阻较小的末端，最终导致观察到的1,2-反马氏选择性。我们的研究结果扩展了可用于硅氢化反应的铁催化剂类型，并加深了我们对铁催化机理的理解，可能会激发新型铁催化剂和铁催化反应的开发。
