Symmetrically bridged bis-N-heterocyclic carbene rhodium (I) complexes and their catalytic application for transfer hydrogenation reaction

Bridged rhodium(I) bis(NHC) complexes of the formula [bis-(NHC)Rh(I)PF6] (1c–5c) were synthesized and applied as catalysts in the transfer hydrogenation of acetophenone in 2-propanol. The activity of the rhodium(I) complexes largely depends on the nature of the N-substituents and the applied bases. The synthesized compounds were characterized by elemental analysis, 1H and 13C NMR-spectroscopy and mass spectrometry. The structure of complex 2c was exemplary determined by X-ray analysis.

Graphical abstractBridged rhodium(I) bis(NHC) complexes can be applied as catalysts for transfer hydrogenation. Bearing the possibility for immobilization in the ligand backbones may pare the way for recyclable, stable catalysts.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Rhodium(I) complexes are easily obtained with a variety of bridged NHC ligands. ► The complexes are catalysts for transfer hydrogenation reactions. ► Catalyst recycling compensates its lower activity.