Hydrogen-Bonding-Mediated Selective Hydrogenation of Aromatic Ketones over Pd/C in Ionic Liquids at Room Temperature

Abstract

Selective hydrogenation of aromatic ketones without hydrogenation of aromatic rings over Pd/C is very interesting but still challenging. Herein, we report a hydrogen-bonding-mediated strategy for selective hydrogenation of aryl ketones to either aryl alcohols or aryl alkanes at room temperature, which is achieved over Pd/C in imidazolium-based ionic liquids (ILs) via altering the IL anions from [Cl]− to [BF4]−. 1-Butyl-3-methyl-imidazolium ([BMIm]+) ILs with [Cl]− and [BF4]− anions show high performances, affording a series of aromatic alcohols or alkanes with 100% selectivity and high yields, respectively. Mechanism investigation indicates that the π–π interaction between the ILs and the aromatic ring of the ketones may inhibit the hydrogenation of the aromatic ring, and the dual H-bonding interaction of the IL cation and anion with the resultant alcohol from the ketone hydrogenation mediates the hydrogenation selectivity. This catalytic protocol is simple, highly efficient, and selective toward target products, which may have promising applications.

Acidic Ionic Liquids as Metal-Free and Recyclable Catalysts for Direct Reduction of Aromatic Allylic Alcohol in Dimethyl Carbonate via Hydrogen Transfer

“…Based on our results and previous reports, − we proposed a plausible mechanism depicted in Scheme . The sulfonic group on the side chain of the cation and trifluoromethanesulfonate as the anion were essential for the reaction (Table , entries 16–18), which illustrated their synergistic effects.…”

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

“…Additionally, in some cases, ILs can stabilize catalytically active species in high oxidation states, , preventing them from being deactivated. Moreover, ILs can also activate several substrates via C–H···π interactions, π-stacking interactions, and ion-pair formation, thus facilitating their catalytic transformation. , ILs that contain aromatic cations can activate unsaturated substrates with H-bonding acceptor or donor sites through strong interactions between the cation and the substrate’s functionalities, which typically include double and triple bonds, as well as O-, N-, and aromatic groups. ,,− These interactions can involve C–H···π interactions, π-stacking interactions, and ion-pair formation in the presence of a catalyst. Several representative examples include the carbonation of epoxides and the hydrogenation of arenes and ketones.…”

Intramolecular Dehydration of Cyclic Alcohols to Cyclic Alkenes via Cation- and Anion-Confined Catalysis over Ionic Liquids

“…In previous reports, several transformations have been achieved via interactions by selecting proper C + and A – . For example, Pd/C in combination with [BMIm]­[BF 4 ] and [BMIm]­[Cl], respectively, can achieve selective hydrogenation of acetophenone to ethylbenzene and 1-phenylethanol due to the different hydrogen bonding interactions provided by C + and A – . , [HO-EtMIm]­[OTf] could efficiently catalyze intramolecular dehydration of diols to cyclic ethers via the dual hydrogen bonding effect …”