[CoH1(salen)(DMF)2]+ X" salts [X = PF6, C104; salen = bis(salicyliden)ethylendiiminato; DMF = dimethylformamide] have been synthesized by electrochemical and chemical (air) oxidation of Co"(salen). Their monomeric structure with two DMF molecules in the axial positions in both the solid state and DMF solution is shown by X-ray crystal structure analysis, thermal analysis, mass spectroscopy, and 'H and l3C NMR spectroscopy. The electrochemical reduction of the [Coni(salen)(DMF)2]+ cation is investigated by cyclic voltammetry and com pared to the oxidation of the neutral CoH(salen). The redox reaction connecting the cobalt(II) and the cobalt(III) species appears to be a quasi-reversible electron transfer. These properties make the [Co1 1 (salen)(DMF)2]+ X-salts starting materials for the analysis of the interaction of basic substrates with cobalt(III) species in the context of the biomimetic oxygenation reactions catalyzed by such complexes.
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.
Possible intermediates in the oxygenation of anilines 1 in the presence of complexes such as 2 are represented by adducts of these components. The formation constants for these complexes (single and double exchange of axial dmf ligands by 1) were determined quantitatively by cyclic voltammetry and by 1H NMR spectroscopy.
Es wird über Komplexe von Schiffschen Basen aus substituierten o‐Hydroxybenzophenonen und α,ω‐Diaminoalkanen nNN(OH)2Ph(OMe), die als Extraktionsmittel für 3d‐Metalle eingesetzt werden können, berichtet. Die Struktur dieser Komplexe hängt von n, der Länge der Alkylenkette der eingesetzten Diamine, ab. In den planaren, mononuklearen 1,1‐Chelaten mit Kupfer(II), Nickel(II), Kobalt(II) Und Eisen(III) koordiniert 2NN(OH)2Ph(OMe) als Dianion. Das flexiblere 3NN(OH)2Ph(OMe) kann als ebene – in den planaren 1,1‐Chelaten – aber auch als verdrillte Species – in Ni3[3 NNO2Ph(OMe)]2(CH3COO)2 und Fe[3 NN(OH)2Ph(OMe)]Cl3 – gebunden werden. Die Tendenz zur Komplexbildung nimmt beim übergang zu den Liganden 4 NN(OH)2Ph(OMe) und 6 NN(OH)2Ph(OMe) ab, nur mit Kupfer(II) konnten feste Species isoliert werden.
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