Synthesis, characterization, and transfer hydrogenation of Ru(II)-N-heterocyclic carbene complexes

Abstract

A new series of ruthenium(II) N-heterocyclic carbene complexes [RuL^1,2,3(p-cymene)Cl₂] (3a–c) (where L is a N-heterocyclic carbene), have been synthesized via transmetalation. The new ruthenium(II)-NHC complexes were applied to transfer hydrogenation of acetophenone derivatives and aldehydes using 2-propanol as a hydrogen source and KOH as a co-catalyst. The results show that the corresponding alcohols could be obtained in good yield with high catalyst activity (up to 100%) under mild conditions. [RuL¹(p-cymene)Cl₂] (3a) is much more active than the other complexes in transfer hydrogenation. Reactions, catalyzed by 3a–c, showed the highest reaction rates and yields of alcohol when the substrates bear more electron-withdrawing substituents. All new compounds were characterized by IR, elemental analysis, LC–MS (ESI), and NMR spectroscopy.

Graphical Abstract

Keywords:

• Ruthenium
• Silver
• N-Heterocyclic carbine
• Transfer hydrogenation
• Transmetalation

Acknowledgement

This work was financially supported by Gaziosmanpasa University Research Fund (GOP. B.A.P: 2010/84, 2011/51 and 2011/105).