Pyridine‐Stabilized Rhodium Nanoparticles in Ionic Liquids as Selective Hydrogenation and Transfer Hydrogenation Catalysts

Abstract

Rhodium nanoparticles (RhNPs) stabilized with pyridine‐based ligands in the ionic liquid [BMIM][BF4] (RhNPs‐I to III) were synthesized from the organometallic precursor [Rh(µ‐OMe)COD]2 under dihydrogen pressure. The pyridine‐stabilized RhNPs showed smaller size compared to the ligand free RhNPs‐V and presented higher activity and selectivity in the hydrogenation of acetophenone to 1‐phenylethanol. In the case of pyridine‐capped RhNPs‐I, the system was reused for several runs without loss of activity and selectivity. Nitrobenzene was reduced to aniline with dihydrogen in the presence of RhNPs‐I with moderate activity. When the hydrogen source was formic acid‐Et3N azeotrope (transfer hydrogenation) the reaction was completed within minutes with high selectivity. Under transfer hydrogenation conditions, it was possible to apply the catalytic system RhNPs‐I in multistep processes for the generation of substituted arylic amines through the reductive N‐alkylation of nitrobenzene and benzaldehyde; and the synthesis of substituted pyrroles through the nitroarene reduction/Paal‐Knorr condensation.