Cobalt-catalysed alkene hydrogenation: a metallacycle can explain the hydroxyl activating effect and the diastereoselectivity

Abstract

A new non-redox metallacycle mechanism explains the substrate preference, the diastereoselectivity, and the hydroxyl activating effect in cobalt-catalyzed alkene hydrogenation.

Syntheses and Catalytic Hydrogenation Performance of Cationic Bis(phosphine) Cobalt(I) Diene and Arene Compounds

“…[8] Both 1-NBD + and 1-C6H6 + were also active for the hydrogenation of the tri-substituted enamide, (Z)-2acetamido-3-phenylacrylate(MAC), and produced the (S)hydrogenation product in excellent yield and enantioselectivity (Scheme 4B). The enantioselectivity for MAC hydrogenation with Co(I) + is higher than that obtained with the Co(II) dialkyl precatalyst, (R,R)-( iPr DuPhos)Co(CH2SiMe3)2 (92.7% ee), [22] suggesting different catalytic pathways and origins of enantioselection for Co(I) + and Co(II) precatalysts. Because of the exceptional performance of 1-NBD + for the asymmetric hydrogenation of MAA and MAC, studies were conducted to gain insight into the substrate-catalyst interaction.…”

“…For the directed hydrogenation of terpinenol, [20] computational studies support formation of metallocycles arising from the Co(II) oxidation state being maintained throughout the catalytic cycle. [22] An alternative pathway involving a more traditional Co(0)-Co(II) [23] cycle was also computed and while energetically reasonable, was higher in energy than the metallocycle pathway and does not explain the observed diastereoselectivity. Despite these advances, cationic bis(phosphine) cobalt(I) complexes have remained elusive and motivated our studies to explore their catalytic performance and compare them to the neutral cobalt examples as well as the well-established rhodium congeners.…”

Syntheses and Catalytic Hydrogenation Performance of Cationic Bis(phosphine) Cobalt(I) Diene and Arene Compounds

“…[8] Both 1-NBD + and 1-C 6 H 6 + were also active for the hydrogenation of the tri-substituted enamide,( Z)-2-acetamido-3-phenylacrylate (MAC), and produced the (S)-hydrogenation product in excellent yield and enantioselectivity (Scheme 4B). Thee nantioselectivity for MACh ydrogenation with Co I is higher than that obtained with the Co II dialkyl precatalyst, (R,R)-( iPr DuPhos)Co(CH 2 SiMe 3 ) 2 (92.7 % ee), [22] suggesting different catalytic pathways and origins of enantioselection for Co I and Co II precatalysts.…”

“…[20,21a-c] Fort he directed hydrogenation of terpinenol, [20] computational studies support formation of metallocycles arising from the Co II oxidation state being maintained throughout the catalytic cycle. [22] An alternative pathway involving am ore traditional Co 0 -Co II [23] cycle was also computed and while energetically reasonable,w as higher in energy than the metallocycle pathway and does not explain the observed diastereoselectivity.D espite these advances, cationic bis(phosphine) cobalt(I) complexes have remained elusive and motivated our studies to explore their catalytic performance and compare them to the neutral cobalt examples as well as the well-established rhodium congeners.…”

Cobalt-catalyzed highly enantioselective hydrogenation of α,β-unsaturated carboxylic acids

“…Early studies have showed the potential application of cobalt catalysts in the asymmetric alkene hydrogenation [58][59][60][61] However, these systems suffer from limited enantioselectivities, and in many cases H 2 could not be used as the stoichiometric reductant. Appreciable progress has been made in recent years, employing cobalt-based complexes for asymmetric hydrogenation of alkenes [62][63][64][65][66][67][68][69][70][71][72] . Chirik and coworkers report the highly enantioselective hydrogenation of styrene derivatives, cyclic alkenes, and enamides with cobalt complexes bearing C 1 -symmetric PNN-type pincer ligand or chiral diphosphine ligands 65,71,72 .…”