Transfer Hydrogenation of Ketones and Activated Olefins Using Chelating NHC Ruthenium Complexes

Abstract

N‐Heterocyclic carbene (NHC) ruthenium complexes consisting of different donor substituents attached to the NHC ligand efficiently catalyse the transfer hydrogenation of ketones and of activated olefins in α,β‐unsaturated ketones to give saturated alcohols. The most active catalyst precursor contains a tethered olefin as a hemilabile donor site. This complex also converts nitriles and, depending on the reaction conditions, either benzylamines are produced by means of transfer hydrogenation, or amides from formal addition of H2O. Kinetic analysis of the double hydrogenation of α,β‐unsaturated ketones indicates fast isomerisation of the enol intermediate to its saturated ketone tautomer prior to the second hydrogenation.

Transfer hydrogenation of unfunctionalised alkenes using N-heterocyclic carbene ruthenium catalyst precursors

“…AgBF 4 in order to abstract one chloride ligand from the precursor. 9,10 ‡ Transfer hydrogenation under these conditions was significantly accelerated, reaching 81% dodecane 65 formation after 5 h (cf 61% with 1). The increased catalytic activity is also reflected by the higher turnover frequency at 50% conversion, TOF 50 = 12 h -1 for 1 and 19 h -1 for activated 4.…”

Synthesis, structural characterization, electrochemistry and catalytic transfer hydrogenation of ruthenium(II) carbonyl complexes containing tridentate benzoylhydrazone ligands

“…Among the various metal complexes employed for transfer hydrogenation reaction, ruthenium-based complexes have gained immense attention and have proven to be effective homogeneous catalysts [15,16]. Varying levels of efficiency were observed for ruthenium complexes containing cyclometallated and N-heterocyclic carbene ligands [17,18], pincer ligands [19], Schiff base ligands [20,21], tripodal ligands [22,23], arene ligands [24,25] and phosphine-or amine-based ligands [26,27] as homogeneous catalysts for this transformation.…”

Ruthenium (II) and iridium (III) complexes of N-heterocyclic carbene and pyridinol derived bidentate chelates: Synthesis, characterization, and reactivity

“…The Ru-C carbene , Ru-N, and Ru-Cl bond distances are all quite similar to each other and to similar complexes in the literature. [91–96] The C-Ru-N bite angles are all similar and range from 76.0(1)° to 76.5(1)°.…”