title: Metal-free hydrogenation catalyzed by an air-stable borane: use of solvent as a frustrated Lewis base.
abstract: 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.
authors.affiliation: Department of Chemistry, Imperial College London, London, SW7 2AZ (UK) http://www3.imperial.ac.uk/people/a.ashley.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Scott
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Fuchter
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Ashley
mesh_terms: D000388:Air; D000588:Amines / Q000138:chemical synthesis* / Q000737:chemistry; D001880:Boranes / Q000737:chemistry*; D002384:Catalysis; D006865:Hydrogenation; D007097:Imines / Q000737:chemistry; D058115:Lewis Bases / Q000737:chemistry*; D015394:Molecular Structure; D012997:Solvents / Q000737:chemistry
chemical_list: D000588:Amines; D001880:Boranes; D007097:Imines; D058115:Lewis Bases; D012997:Solvents
keywords: boranes; frustrated Lewis pairs; heterocycles; hydrogenation; solvent effects
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