Synthesis and Reactivity of Ampy-Based Ruthenium(II) Catalysts for Transfer Hydrogenation of Ketones

Four ruthenium­(II) complexes of the motif, cis-RuCl2[Ph2P­(CH2)4PPh2]­(ampy-L) and trans-RuCl2[Ph2P­(CH2)4PPh2]­(ampy-L) (ampy = 2-(aminomethyl)­pyridine; L = Cl or OMe), were synthesized for potential catalytic applications. The complexes were fully characterized using NMR spectroscopy, UV–vis spectroscopy, X-ray crystallography, and electrochemical analyses. The trans-isomer was observed to undergo isomerization to the cis-isomer, and kinetic studies of the isomerization reaction showed that subtle changes in ampy-L electron density did not impact the rate of trans-to-cis isomerization. To probe the utility of these complexes toward catalysis, transfer hydrogenation reactions were performed for the reduction of a variety of ketones. All three cis-complexes showed high rates and yields toward ketone transfer hydrogenation.