Towards Selective Hydrogenation using Metal Nanocatalysts in Ionic Liquids

This work deals with the application of metal-nanoparticles (M-NPs) in ionic liquids (ILs) as catalyst systems for the selective hydrogenation reaction of different organic molecules. The focus of this work is, in particular, on the investigation of the influence of the functionalised imidazolium-based ILs, but also on the metal catalysts on the selectivity of the hydrogenation reactions of nitriles, N-heteroaromatic compounds and alkynes. In the hydrogenation reaction of alkynes using Ni-NPs dispersed in the nitrile-functionalised IL 1-(3-cyanopropyl)-2,3-dimethylimidazolium bis(trifluoromethanesulfonimide), (Z)-alkenes were obtained selectively under very mild reaction conditions. Secondly, N-heterocyclic compounds like pyridine-, pyrimidine-, pyrrole- and pyrazole-substructures were efficiently hydrogenated using Ru-NPs in ILs as catalyst systems. In the selective hydrogenation of quinoline using Ru-NPs in the diol-functionalised IL 1-(2,3-dihydroxypropyl)-2,3-dimethylimidazolium bis(trifluoromethanesulfonimide) excellent selectivity of up to 99% for 1,2,3,4-tetrahydroquinoline was achieved. In addition, selective hydrogenation reactions of nitriles revealed a dependency of the metal used to control the selectivity of this reaction. With the use of Ni-NPs in the IL 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonimide) selectively primary amines were obtained. Ru-NPs in the same IL catalysed a hydrogenative coupling reaction of nitriles with amines for the synthesis of secondary imines. Furthermore, Ni- and Ru-NPs in IL were tested for the selective hydrogenation of nitrobenzene to aniline as well as for hydrogenative coupling reactions of nitrobenzene with benzaldehyde. Moreover, in this work attempts were carried out for the preparation of bimetallic Ni-Ru structures in ILs, for a potential application in selective hydrogenation reactions. Apart from that, one part of this work deals with an overview about relevant research in the fields of the reductive formaldehyde syntheses and its derivatives starting from carbon dioxide and carbon monoxide.