Cobalt-Schiff Base Complex Catalyzed Oxidation of Para-Substituted Phenolics. Preparation of Benzoquinones

Mechanistic Insights into the Oxidation of Veratryl Alcohol with Co(salen) and Oxygen in Aqueous Media: An in‐situ Spectroscopic Study

“…According to the literature, the peroxo bridge most probably forms through a mononuclear superoxo complex. [8,12] Oxygen molecule binds first to one cobalt center as a superoxo radical, which then binds to another cobalt complex forming a peroxo species. At these reaction conditions the dinuclear species is more stable and it forms fast.…”

“…[4,11] It has been suggested that the mononuclear superoxo species is usually responsible for catalyst activity in the oxidation of phenolic substrates, but no direct evidence is yet available. [3,4,[12][13][14] There are less examples on the oxidation of benzylic substrates. It has been noted that the reaction mechanisms de-mation of a μ-peroxo bridge between two such Co(salen) substrate units is observed in the UV/Vis spectra.…”

“…Selective oxidation of lignin would be attractive for catalytic pulp bleaching [16][17][18] and for the search of renewable raw materials. [3,12] This reaction proceeds in the presence of molecular oxygen to reach TOF = 10-15 at optimum conditions (TOF = turnover frequency, moles of product per mol of catalyst per hour). [16] The effect of reaction conditions observed previously for this system suggest that a mononuclear superoxo complex is not responsible for catalytic activity.…”

Studies on the oxidation of phenols catalyzed by a copper(II)–Schiff base complex in aqueous solution under mild conditions

“…19 -22 Although the exact reasoning is not known, the donor ligand of imidazole (and pyridine) in the axial position of the complex probably plays an important role in the stability of the high oxidation state of metal complex, as was noted by us previously, and in other studies. 20,22 Imidazole (and pyridine) would chelate Cu 2+ in the axial position of the complex to form a 'new' metal complex, which would stabilize the high oxidation state of the metal complex and activate H 2 O 2 binding to the complex, hence the oxidation of phenol is accelerated.…”

From Salicylaldehyde to Chiral Salen Sulfonates – Syntheses, Structures and Properties of New Transition Metal Complexes Derived from Sulfonato Salen Ligands

“…[1][2][3][4] Salen-type complexes have been used in many reactions like alkene epoxidation, [5,6] epoxide ring opening, [7] cyclopropanations, [8] aziridination [9] and other reactions. [10][11][12] They can also serve as metalloprotein models, as these complexes are efficient oxygen carriers.…”