Scott Daniel J, Fuchter Matthew J, Ashley Andrew E
Department of Chemistry, Imperial College London, London, SW7 2AZ (UK) http://www3.imperial.ac.uk/people/a.ashley.
Angew Chem Int Ed Engl. 2014 Sep 15;53(38):10218-22. doi: 10.1002/anie.201405531. Epub 2014 Aug 11.
In recent years 'frustrated Lewis pairs' (FLPs) have been shown to be effective metal-free catalysts for the hydrogenation of many unsaturated substrates. Even so, limited functional-group tolerance restricts the range of solvents in which FLP-mediated reactions can be performed, with all FLP-mediated hydrogenations reported to date carried out in non-donor hydrocarbon or chlorinated solvents. Herein we report that the bulky Lewis acids B(C6Cl5)x(C6F5)(3-x) (x=0-3) are capable of heterolytic H2 activation in the strong-donor solvent THF, in the absence of any additional Lewis base. This allows metal-free catalytic hydrogenations to be performed in donor solvent media under mild conditions; these systems are particularly effective for the hydrogenation of weakly basic substrates, including the first examples of metal-free catalytic hydrogenation of furan heterocycles. The air-stability of the most effective borane, B(C6Cl5)(C6F5)2, makes this a practically simple reaction method.
近年来，“受阻路易斯酸碱对”（FLPs）已被证明是用于许多不饱和底物氢化反应的有效无金属催化剂。即便如此，有限的官能团耐受性限制了可进行FLP介导反应的溶剂范围，迄今为止报道的所有FLP介导的氢化反应均在非给体烃类或氯化溶剂中进行。在此，我们报道了大位阻路易斯酸B(C6Cl5)x(C6F5)(3-x)（x = 0 - 3）能够在强给体溶剂四氢呋喃（THF）中，在不存在任何额外路易斯碱的情况下实现氢分子的异裂活化。这使得无金属催化氢化反应能够在给体溶剂介质中在温和条件下进行；这些体系对于弱碱性底物的氢化反应特别有效，包括呋喃杂环的首例无金属催化氢化反应。最有效的硼烷B(C6Cl5)(C6F5)2的空气稳定性使得这成为一种实际操作简单的反应方法。
