Heterolytic dihydrogen activation by "antagonistic" Lewis pairs

点击翻译按钮获取中文摘要

Hydroboration of a series of enamines with Piers’ borane gave new intramolecular vicinal N/B frustrated Lewis pairs (FLPs). These examples feature weak intramolecular nitrogenboron interactions. The activation barrier for ring opening to the active FLPs was determined for chiral examples by dynamic 19F NMR spectroscopy. Similar P/B FLPs were prepared and the activation barrier of the cleavage of their weak P−B bonds determined as well. Many of these new systems cleave dihydrogen heterolytically under mild conditions. Some serve as metal-free catalysts for the hydrogenation of electron-rich unsaturated substrates (enamines, dienamines, imines, etc.). We have also developed a protocol for FLP catalyzed hydrogenation of electron-poor olefins and alkynes (bulky ynones and enones). This has considerably extended the application potential of these new metal-free main-group element dihydrogen activators.