Selective Hydrogenation of α,β‐Unsaturated Aldehydes and Ketones by Air‐Stable Ruthenium NNS Complexes

Abstract

The selective hydrogenation of the carbonyl functionality of α,β-unsaturated aldehydes and ketones is catalysed by ruthenium dichloride complexes bearing a tridentate NNS ligand as well as triphenylphosphine. The tridentate ligand backbone is flexible, as evidenced by the equilibrium observed in solution between the cis- and trans-isomers of the dichloride precatalysts, as well as crystal structures of several of these complexes. The complexes are activated by base in the presence of hydrogen and readily hydrogenate carbonyl functionalities under mild conditions. Despite the activation by base, side reactions are negligible, even for aldehyde substrates, because of the low amount of base. Thus, the corresponding allylic alcohols can be isolated in very good yields on a 10-25 mmol scale. Turnover numbers up to 200 000 were achieved.

Phosphine free Mn-complex catalysed dehydrogenative C–C and C–heteroatom bond formation: a sustainable approach to synthesize quinoxaline, pyrazine, benzothiazole and quinoline derivatives

“…1 H NMR (600 MHz, CDCl3) δ 8.09 (s, 1H), 8.04 (s, 1H), 2.99 (q, J = 7.4 Hz, 2H), 2.71 (s, 3H), 1.39 (t, J = 7.4 Hz, 3H). 13 5,6,7,8-tetrahydroquinoxaline (6u) 13 Colourless Oil (151mg, 72%) 1…”

“…White solid (236 mg, 82%)1 H NMR (600 MHz, CDCl3) δ 7.40 -7.39 (m, 4H), 7.29 -7.27 (m, 6H), 3.08 -3.05 (m, 4H), 2.00 -1.98 (m, 4 H). 13 C NMR (150 MHz, CDCl3) δ 150.65, 149.65, 139.06, 129.73, 128.29, 128.22, 31.91, 22.91.…”

Inexpensive Ruthenium NNS‐Complexes as Efficient Ester Hydrogenation Catalysts with High C=O vs. C=C Selectivities

“…Recently, we reported on the development of a class of ruthenium NNS‐pincer complexes which showed high selectivity in the hydrogenation of unsaturated aldehydes and ketones to the corresponding unsaturated alcohols . These findings encouraged us to employ complex C1 a (Scheme ) in the hydrogenation of methyl cinnamate ( 1 a ).…”

“…This can be useful in cases where conventional hydrolysis is not feasible. We previously reported that the RuNNS catalyst selectively hydrogenates the aldehyde functionality in methyl 4‐formylbenzoate in methanol . Indeed, when this reaction was performed in toluene, both aldehyde and ester were reduced (entry 7).…”

Reduction of Aldehydes with Formic acid in Ethanol using Immobilized Iridium Nanoparticles on a Triazine‐phosphanimine Polymeric Organic Support

“…Interestingly, this catalyst system showed good activity in the hydrogenation of α,β-unsaturated aldehydes (2q). [34] We also tested the selectivity of this method in the hydrogenation of aldehyde group in the presence of other carbonyl groups and moderate to good selectivity was observed and products were obtained in satisfactory yields (2r-t). We also, checked the reduction of ketones and esters but no alcohol product was detected, demonstrating this catalyst group is selective for reduction of aldehyde group under our optimized conditions.…”