Electrochemistry of Oxygenation Catalysts. 3.¹ Thermodynamic Characterization of Electron Transfer and Solvent Exchange Reactions of Co(salen)/[Co(salen)]⁺ in DMF, Pyridine, and Their Mixtures

Abstract

Redox and ligand exchange reactions of the oxygenation catalyst (N,N '-bis(salicylidene)ethylenediaminato)cobalt(II), Co(salen), and its one-electron oxidation product, Co(salen)(+), are investigated in DMF, pyridine, and mixtures of these solvents. Electron transfers and solvent exchange reactions involving three neutral Co(II) and three cationic Co(III) complexes with different axially bound solvent molecules (two DMF, one DMF and one pyridine, or two pyridine molecules) form a three-rung ladder scheme. All formal potentials E(0) and equilibrium constants K in this scheme are determined from electrochemical or spectrophotometric experiments or the construction of thermodynamic cycles. The latter are also used to prove consistency of the results. Values for the E(0) and K are discussed in terms of the Co coordination geometry, solvent effects on the potentials, the thermodynamics of cross reactions, and the distribution of Co(II) and Co(III) species as a function of the solvent composition. Some peculiarities found in the oxygenation of flavonols and indoles are explained.

Metal–Salen Schiff base complexes in catalysis: practical aspects

“…Organic substrates containing donor atoms (phenols, indoles, and amines) are more easily oxidized. 39 As in Nature, Schiff base metal complexes were designed to include a cavity, in order to accommodate dioxygen or some small ligands. 40 However, as already presented in this review, non-covalent secondary interactions are essential in order to obtain selective and efficient catalysts with Salen metal complexes.…”

Synthesis and electrochemistry of M(II) N2O2 schiff base complexes: X-Ray structure of {Ni[Bis(3-chloroacetylacetone)ethylenediimine]}

“…The electrochemical studies of cobalt(II) Salen type Schiff bases showed that the major species in the solution were Co(Schiff baes)(Solvent) 2 in DMF and DMSO [6,8]. The following redox reaction is proposed for Co(II) BBE complex in dimethylformamide [12,[23][24][25].…”

“…Cyclic voltammetry has been a useful instrument to study the mechanisms of the catalysis property of metal Schiff base complexes and their reactivity [2,[4][5]. To explore the catalytic activity, the electrochemical properties of Co(III) BAE and Salen Schiff base complexes were studied intensively [6][7][8][9][10][11][12]. Also, the electrochemical *Corresponding author.…”

Evaluation of antioxidant and antiproliferative activities of 1,2‐bis (p‐amino‐phenoxy) ethane derivative Schiff bases and metal complexes

“…Also, some Schiff complexes find different application areas. For example, such as the oxidation of platinum complexes, the use of oxygen as the oxygen carrier model for cobalt complex oxygenation and transport reactions, the oxidation of phenols and olefins catalytic reactions, the use of Mn and Ru complexes in water catalyzed photolysis, and iron complexes catalyzed by cathodic oxygen which is known to be used as a catalyst . The catalytic activity of complexes of Schiff’s complexes with transition metal ions has also shown considerable interest in some industrial and biochemical events …”