5325-97-3Relevant articles and documents
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Durland,Adkins
, (1938)
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Intramolecular Cobalt-Mediated Cycloaddition of Linear Enediynes. A Useful Synthetic Entry into Cobalt-Protected Tricyclic Dienes and Their Synthetic Elaboration
Sternberg, Ethan D.,Vollhardt, K. Peter C.
, p. 1564 - 1573 (1984)
CpCo(CO)2 undergoes reaction with the linear α,δ,ω-enediynes 4, 10, 18, 22 and 25 to give the CpCo-complexed tricyclic dienes 5, 11, 19, 20, 23, 24, 26, and possibly 27.The free ligands may be obtained in good yield by oxidative demetalation.Treatment of the dienylsilane 12 with bromine gave the desilylated aromatic 13, whereas reaction with m-chloroperbenzoic acid furnished the dienol 14 and α-trimethylsilyl β,γ-enone 15.The latter rearranged to the desilylated α,β-enone 17 with acid.Some mechanistic discussion is presented concerned with the course of the cobalt-mediated cyclization reaction.Hydride abstraction from 11 resulted in the cation 28 which underwent unexpected nucleophilic addition to both ligands, in addition to deprotonation to benzene complex 32 and the free aromatic ligand 31.
Ligand-enabled and magnesium-activated hydrogenation with earth-abundant cobalt catalysts
Han, Bo,Jiao, Hongmei,Ma, Haojie,Wang, Jijiang,Zhang, Miaomiao,Zhang, Yuqi
, p. 39934 - 39939 (2021/12/31)
Replacing expensive noble metals like Pt, Pd, Ir, Ru, and Rh with inexpensive earth-abundant metals like cobalt (Co) is attracting wider research interest in catalysis. Cobalt catalysts are now undergoing a renaissance in hydrogenation reactions. Herein, we describe a hydrogenation method for polycyclic aromatic hydrocarbons (PAHs) and olefins with a magnesium-activated earth-abundant Co catalyst. When diketimine was used as a ligand, simple and inexpensive metal salts of CoBr2in combination with magnesium showed high catalytic activity in the site-selective hydrogenation of challenging PAHs under mild conditions. Co-catalyzed hydrogenation enabled the reduction of two side aromatics of PAHs. A wide range of PAHs can be hydrogenated in a site-selective manner, which provides a cost-effective, clean, and selective strategy to prepare partially reduced polycyclic hydrocarbon motifs that are otherwise difficult to prepare by common methods. The use of well-defined diketimine-ligated Co complexes as precatalysts for selective hydrogenation of PAHs and olefins is also demonstrated.
Metallic Barium: A Versatile and Efficient Hydrogenation Catalyst
Stegner, Philipp,F?rber, Christian,Zenneck, Ulrich,Knüpfer, Christian,Eyselein, Jonathan,Wiesinger, Michael,Harder, Sjoerd
supporting information, p. 4252 - 4258 (2020/12/22)
Ba metal was activated by evaporation and cocondensation with heptane. This black powder is a highly active hydrogenation catalyst for the reduction of a variety of unactivated (non-conjugated) mono-, di- and tri-substituted alkenes, tetraphenylethylene, benzene, a number of polycyclic aromatic hydrocarbons, aldimines, ketimines and various pyridines. The performance of metallic Ba in hydrogenation catalysis tops that of the hitherto most active molecular group 2 metal catalysts. Depending on the substrate, two different catalytic cycles are proposed. A: a classical metal hydride cycle and B: the Ba metal cycle. The latter is proposed for substrates that are easily reduced by Ba0, that is, conjugated alkenes, alkynes, annulated rings, imines and pyridines. In addition, a mechanism in which Ba0 and BaH2 are both essential is discussed. DFT calculations on benzene hydrogenation with a simple model system (Ba/BaH2) confirm that the presence of metallic Ba has an accelerating effect.
