College of Chemistry and Chemical Engineering, Xiamen University , Xiamen 361005, People's Republic of China.
Department of Chemistry and Biochemistry, University of Notre Dame , Notre Dame, Indiana 46556, United States.
J Am Chem Soc. 2016 Jul 20;138(28):8774-80. doi: 10.1021/jacs.6b02769. Epub 2016 Jul 6.
Based on a metal-templated approach using a rigid and globular structural scaffold in the form of a bis-cyclometalated octahedral iridium complex, an exceptionally active hydrogen-bond-mediated asymmetric catalyst was developed and its mode of action investigated by crystallography, NMR, computation, kinetic experiments, comparison with a rhodium congener, and reactions in the presence of competing H-bond donors and acceptors. Relying exclusively on weak forces, the enantioselective conjugate reduction of nitroalkenes can be executed at catalyst loadings as low as 0.004 mol% (40 ppm), representing turnover numbers of up to 20 250. A rate acceleration by the catalyst of 2.5 × 10(5) was determined. The origin of the catalysis is traced to an effective stabilization of developing charges in the transition state by carefully orchestrated hydrogen-bonding and van der Waals interactions between catalyst and substrates. This study demonstrates that the proficiency of asymmetric catalysis merely driven by hydrogen-bonding and van der Waals interactions can rival traditional activation through direct transition metal coordination of the substrate.
基于金属模板方法，使用刚性和球状结构支架的形式，即双环金属化八面体铱配合物，开发出一种非常活跃的氢键介导的不对称催化剂，并通过晶体学、NMR、计算、动力学实验、与铑同系物的比较以及在存在竞争氢键供体和受体的情况下的反应来研究其作用模式。仅依靠弱相互作用力，即可在催化剂负载低至 0.004 mol%（40 ppm）的情况下执行硝基烯烃的对映选择性共轭还原，其周转率高达 20 250。确定催化剂的速率加速为 2.5×10(5)。催化作用的起源可以追溯到通过催化剂和底物之间精心协调的氢键和范德华相互作用，有效地稳定了过渡态中发展的电荷。这项研究表明，仅仅由氢键和范德华相互作用驱动的不对称催化的效率可以与通过底物的直接过渡金属配位的传统活化相媲美。
