Catalytic hydrogenation with frustrated Lewis pairs: selectivity achieved by size-exclusion design of Lewis acids |
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Authors: | Eros Gábor Nagy Krisztina Mehdi Hasan Pápai Imre Nagy Péter Király Péter Tárkányi Gábor Soós Tibor |
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Institution: | Institute of Biomolecular Chemistry, Chemical Research Center of Hungarian Academy of Sciences, P.O. Box 17, Budapest 1525, Hungary. |
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Abstract: | Catalytic hydrogenation that utilizes frustrated Lewis pair (FLP) catalysts is a subject of growing interest because such catalysts offer a unique opportunity for the development of transition-metal-free hydrogenations. The aim of our recent efforts is to further increase the functional-group tolerance and chemoselectivity of FLP catalysts by means of size-exclusion catalyst design. Given that hydrogen molecule is the smallest molecule, our modified Lewis acids feature a highly shielded boron center that still allows the cleavage of the hydrogen but avoids undesirable FLP reactivity by simple physical constraint. As a result, greater latitude in substrate scope can be achieved, as exemplified by the chemoselective reduction of α,β-unsaturated imines, ketones, and quinolines. In addition to synthetic aspects, detailed NMR spectroscopic, DFT, and (2)H isotopic labeling studies were performed to gain further mechanistic insight into FLP hydrogenation. |
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Keywords: | chemoselectivity hydrogenation Lewis acids Lewis bases size exclusion |
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