Theory‐Based Extension of the Catalyst Scope in the Base‐Catalyzed Hydrogenation of Ketones: RCOOH‐Catalyzed Hydrogenation of Carbonyl Compounds with H2 Involving a Proton Shuttle. Issue 72 (7th December 2017)

• Record Type: Journal Article
• Authors: Heshmat, Mojgan; Privalov, Timofei
• Is Part Of: Chemistry. Volume 23:Issue 72(2017)
• Page Start: 18193
• Page End: 18202
• Publication Date: 2017-12-07
• Subjects: carbonyl compounds -- hydrogenation -- Lewis acids -- Lewis bases -- metal-free catalysis -- proton shuttles; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201702149
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: As an extension of the reaction mechanism describing the base‐catalyzed hydrogenation of ketones according to Berkessel et al., we use a standard methodology for transition‐state (TS) calculations in order to check the possibility of heterolytic cleavage of H2 at the ketone's carbonyl carbon atom, yielding one‐step hydrogenation path with involvement of carboxylic acid as a catalyst. As an extension of the catalyst scope in the base‐catalyzed hydrogenation of ketones, our mechanism involves a molecule with a labile proton and a Lewis basic oxygen atom as a catalyst—for example, R−C(=O)OH carboxylic acids—so that the heterolytic cleavage of H2 could take place between the Lewis basic oxygen atom of a carboxylic acid and the electrophilic (Lewis acidic) carbonyl carbon of a ketone/aldehyde. According to our TS calculations, protonation of a ketone/aldehyde by a proton shuttle (hydrogen bond) facilitates the hydride‐type attack on the ketone's carbonyl carbon atom in the process of the heterolytic cleavage of H2 . Ketones with electron‐rich and electron‐withdrawing substituents in combination with a few carboxylic and amino acids—in total, 41 substrate–catalyst couples—have been computationally evaluated in this article and the calculated reaction barriers are encouragingly moderate for many of the considered substrate–catalyst couples. Abstract : Transition‐state calculations indicate that a proton shuttle could make it possible for species with the carboxyl functional group (:−C(=O)OH) to act as both the Lewis base and the Brønsted–Lowry acid in heterolytic H2 splitting at the electrophilic carbonyl carbon atom of a ketone/aldehyde, R′R′′C=O. Transition‐state calculations for 41 plausible molecular systems give moderate barrier heights.