The frustrated Lewis pair-mediated reversible hydrogen activation is studied as a function of the electron-donor quality of a series of phosphines. The increasing acidity of the generated phosphonium species leads to a stepwise lowering of the temperature for the highly reversible H2-activation and permits concrete classification for the first time. The influence of the acid strength on the metal-free hydrogenation of selected olefins is investigated by kinetic experiments and quantum chemical calculations. Detailed information for the rate-determining steps fully support our mechanistic model of a protonation step prior to hydride transfer. The rate of hydrogenation is strongly dependent on the electronic nature of the phosphine and of the acidity of the corresponding phosphonium cation. A careful balance of these two factors provides highly efficient metal-free hydrogenation catalysts. The provided findings are used to revise the reactivity of Lewis bases in the hydrogenation of imines, one of the most recognized applications of FLPs.
受挫的刘易斯对介导的可逆氢活化作用被研究为一系列
磷化合物的电子给体质量函数。生成的
磷化合物的酸度增加导致高度可逆的H2活化温度逐步降低,并首次允许进行具体分类。通过动力学实验和量子
化学计算研究了酸强度对所选烯烃的无
金属氢化作用的影响。有关速率决定步骤的详细信息完全支持我们在
氢化物转移之前质子化步骤的机理模型。氢化速率在很大程度上取决于
磷化合物的电子性质和相应
磷阳离子的酸度。仔细平衡这两个因素可提供高效的无
金属氢化催化剂。所提供的发现被用于修改路易斯碱在
亚胺氢化反应中的反应性,这是FLP最广为人知的应用之一。