Rokob Tibor András, Hamza Andrea, Stirling András, Pápai Imre
Chemical Research Center of HAS, P.O. Box 17, H-1525 Budapest, Hungary.
J Am Chem Soc. 2009 Feb 11;131(5):2029-36. doi: 10.1021/ja809125r.
The reaction mechanism for the transition metal free direct hydrogenation of bulky imines catalyzed by the Lewis acid B(C6F5)3 is investigated in detail by quantum chemical calculations. A recently introduced mechanistic model of heterolytic hydrogen splitting that is based on noncovalent association of bulky Lewis acid-base pairs is shown to account for the reactivity of imine-borane as well as amine-borane systems. Possible catalytic cycles are examined, and the results provide solid support for the imine reduction pathway proposed from experimental observations. In addition, the feasibility of an autocatalytic route initiated by amine-borane hydrogen cleavage is demonstrated. Conceptual issues regarding the notion of frustration are also discussed. The observed reactivity is interpreted in terms of thermally induced frustration, which refers to thermal activation of strained dative adducts of bulky Lewis donor-acceptor pairs to populate their reactive frustrated complex forms.
通过量子化学计算详细研究了路易斯酸B(C6F5)3催化的大位阻亚胺无过渡金属直接氢化反应机理。一种最近引入的基于大位阻路易斯酸碱对非共价缔合的异裂氢裂解机理模型，被证明可以解释亚胺-硼烷以及胺-硼烷体系的反应活性。研究了可能的催化循环，结果为基于实验观察提出的亚胺还原途径提供了有力支持。此外，还证明了由胺-硼烷氢裂解引发的自催化途径的可行性。还讨论了与受挫概念相关的概念性问题。观察到的反应活性是根据热诱导受挫来解释的，热诱导受挫是指大位阻路易斯供体-受体对的应变配位加合物的热活化，以形成其反应性受挫络合物形式。
