75736-66-2Relevant articles and documents
Visible-Light-Enhanced Cobalt-Catalyzed Hydrogenation: Switchable Catalysis Enabled by Divergence between Thermal and Photochemical Pathways
Mendelsohn, Lauren N.,MacNeil, Connor S.,Tian, Lei,Park, Yoonsu,Scholes, Gregory D.,Chirik, Paul J.
, p. 1351 - 1360 (2021/02/01)
The catalytic hydrogenation activity of the readily prepared, coordinatively saturated cobalt(I) precatalyst, (R,R)-(iPrDuPhos)Co(CO)2H ((R,R)-iPrDuPhos = (+)-1,2-bis[(2R,5R)-2,5-diisopropylphospholano]benzene), is described. While efficient turnover was observed with a range of alkenes upon heating to 100 °C, the catalytic performance of the cobalt catalyst was markedly enhanced upon irradiation with blue light at 35 °C. This improved reactivity enabled hydrogenation of terminal, di-, and trisubstituted alkenes, alkynes, and carbonyl compounds. A combination of deuterium labeling studies, hydrogenation of alkenes containing radical clocks, and experiments probing relative rates supports a hydrogen atom transfer pathway under thermal conditions that is enabled by a relatively weak cobalt-hydrogen bond of 54 kcal/mol. In contrast, data for the photocatalytic reactions support light-induced dissociation of a carbonyl ligand followed by a coordination-insertion sequence where the product is released by combination of a cobalt alkyl intermediate with the starting hydride, (R,R)-(iPrDuPhos)Co(CO)2H. These results demonstrate the versatility of catalysis with Earth-abundant metals as pathways involving open-versus closed-shell intermediates can be switched by the energy source.
Diastereofacial selectivity in reactions of substituted cyclohexyl radicals. An experimental and theoretical study
Damm,Giese,Hartung,Hasskerl,Houk,Hüter,Zipse
, p. 4067 - 4079 (2007/10/02)
The diastereofacial selectivity in reactions of a series of alkyl-substituted cyclohexyl radicals has been investigated. In additions of cyclohexyl radicals to alkenes, it has been found that only substituents bound at the olefinic center being attacked by the radical influence the equatorial-axial selectivity. Substituents bound to the radical center or axial substituents β to the radical center lead to increased axial attack. Equatorial β-substituents or axial γ-substituents increase the amount of equatorial attack. The same trends are observed for halogen and hydrogen abstraction reactions; the amount of axial reaction product is usually somewhat higher than in the addition reactions. The stereoselectivities can be explained with steric and torsional effects very similar to those suggested for nucleophilic addition reactions to cyclohexanones. A MM2 force field has been parameterized to gain further insight into the stereochemistry of the reaction.
Hydrogenolyse en phase liquide des epoxydes du t-butyl-4 methylene-cyclohexane sur divers catalyseurs metalliques supportes
Accrombessi, Georges,Geneste, Patrick,Olive, Jean-Louis,Pavia, Andre Armand
, p. 19 - 23 (2007/10/02)
Epoxides of 4-t-butylmethylenecyclohexane have been hydrogenolised on various supported metal catalysts: Pd, Pt, Rh, Ni, at ordinary temperature and 1 atm pressure in various solvents.All these catalysts present a good regioselectivity, leading to preferential cleavage of the more substituted C-O bond.In the isomerisation process the order of reactivity is Ni Pt Pd = Rh with a yield in aldehydes of 60 percent for Pd and 80 percent for Rh and an important percentage of configuration inversion.The reaction could be used as a good method for preparing cis or trans 4-t-butylcyclohexanecarboxaldehyde.On Pt and Ni, hydrogenolysis yields primary alcohols with cleavage of the oxiran ring by trans or cis addition of hydrogen.
