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Catalytic Hydrogenation with Frustrated Lewis Pairs: Selectivity Achieved by Size‐Exclusion Design of Lewis Acids

2011; Wiley; Volume: 18; Issue: 2 Linguagem: Inglês

10.1002/chem.201102438

1521-3765

Gábor Erős, Krisztina Nagy, Mehdi Hasan, Imre Pápai, Péter R. Nagy, P. Király, Gábor Tárkányi, Tibor Soós,

Organometallic Complex Synthesis and Catalysis

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.