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Metal‐Free Hydrogenation Catalyzed by an Air‐Stable Borane: Use of Solvent as a Frustrated Lewis Base
Author(s) -
Scott Daniel J.,
Fuchter Matthew J.,
Ashley Andrew E.
Publication year - 2014
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201405531
Subject(s) - frustrated lewis pair , heterolysis , lewis acids and bases , borane , chemistry , catalysis , furan , solvent , boranes , metal , organic chemistry , polymer chemistry , photochemistry , boron
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(C 6 Cl 5 ) x (C 6 F 5 ) 3− x ( x =0–3) are capable of heterolytic H 2 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(C 6 Cl 5 )(C 6 F 5 ) 2 , makes this a practically simple reaction method.