A Prediction of Proton‐Catalyzed Hydrogenation of Ketones in Lewis Basic Solvent through Facile Splitting of Hydrogen Molecules. Issue 5 (16th December 2016)

• Record Type: Journal Article
• Authors: Heshmat, Mojgan; Privalov, Timofei
• Is Part Of: Chemistry. Volume 23:Issue 5(2017)
• Page Start: 1036
• Page End: 1039
• Publication Date: 2016-12-16
• Subjects: Lewis acids -- Lewis bases -- hydrogen activation -- hydrogenation -- metal-free catalysis; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201605443
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: A ketone's carbonyl carbon is electrophilic and harbors a part of the lowest unoccupied molecular orbital of the carbonyl group, resembling a Lewis acidic center; under the right circumstances it exhibits very useful chemical reactivity, although the natural electrophilicity of the ketone's carbonyl carbon is often not strong enough on its own to produce such reactivity. Quantum chemical calculations predict that a proton shared between a ketone and the Lewis basic solvent molecule (dioxane or THF) activates carbonyl carbon to the point of enabling a facile heterolytic splitting of H2 . Proton‐catalyzed hydrogenation of a ketone in Lewis basic solvent is the result. The mechanism involves the interaction of H2 with the enhanced Lewis acidity of a carbonyl carbon and the free Lewis basic solvent molecule polarizes H2 and enables the hydride‐type attack on carbonyl carbon, which is very strongly influenced by the proton shared between a ketone and solvent. The hydride‐type attack on carbon is reminiscent of the splitting of H2 by singlet carbenes except that, in this case, a Lewis base from the surrounding environment (solvent) is necessary for polarization of H2 and acceptance of the proton resulting from the heterolytic splitting of H2 . Abstract : Transition‐state calculations predict that the proton shared between a ketone and the Lewis basic solvent (dioxane or THF) activates carbonyl carbon to the point of enabling facile heterolytic splitting of H2, that is, one‐step transformation of a ketone to the corresponding alcohol with complete recovery of the solvent‐bound proton that awakens the Lewis acidic character of carbonyl carbon of the substrate ketone.