Four-coordinate, monoradical-containing Co(iii) complexes participated in the non-innocent ligand driven homolytic cleavage of S-S and Se-Se bonds and catalyzed the conversion of RNCO (R = phenyl and naphthyl) to the corresponding urea derivatives (TON 480) in dry CHCl under sunlight stimulus.

The noninnocent ligand HL contained a bulky phenyl substituent at the ortho position to the aniline moiety. The ligand reacted with 0.5 equiv of CuCl·2HO in the presence of EtN under air and provided the corresponding Cu(II)-bis(imonosemiquinone) complex (1). The complex upon oxidation by a stoichiometric amount of ferrocenium hexafluorophosphate (FcPF) yielded the four-coordinate [Cu(II)-(imonosemiquinone)(iminoquinone)]PF complex (3), while the oxidation by an equivalent amount of CuCl·2HO produced the five-coordinate Cu(I)-bis(iminoquinone)Cl complex (2). Thus, a ligand-based oxidation followed by ligand-to-metal electron-transfer was realized for the latter oxidation process. Removal of the Cl ion from complex 2 rendered the four-coordinate complex 4. The oxidation state of both Cu(I) and iminoquinone moieties remained unaltered upon the change in the coordination number. All the complexes were characterized by X-ray crystallography. Complexes 2, 3, and 4 were diamagnetic with an S = 0 ground state as evident by electron paramagnetic resonance (EPR) and H NMR measurements. The UV-vis-NIR spectra of all the complexes were dominated by charge-transfer transitions. Two oxidations and two reductions waves were noticed in the cyclic voltammogram (CV) of complex 1. Complex 2 and complex 3 underwent one oxidation and three reductions. Unlike complex 3, which experienced ligand-based oxidation, in complex 2 the oxidation was metal-centered [oxidation of Cu(I)-to-Cu(II)]. UV-vis-NIR spectral changes during the fixed-potential coulometric one-electron oxidation and thereafter EPR analysis consolidated the metal-based oxidation in complex 2. Complex 2 was air stable; however, it oxidized KO to oxygen molecule, and complex 1 was formed in due course as evident by UV-vis-NIR spectral changes and EPR measurements. Time dependent density functional theory calculations have been incorporated to assign the transitions that appeared in the UV-vis-NIR spectra of the complexes.

2-Aminophenol appended pentadentate ligand HGan was synthesized by mixing equimolar amounts of 2-[bis(2-pyridylmethyl)aminomethyl]aniline (A) and 3,5-di-tert-butyl catechol in hexane in the presence of EtN under air. The ligand reacted with Fe(ClO)·6HO or Fe(ClO)·6HO in the presence of tetrabutylammonium perchlorate, and EtN under air and provided a μ oxo-bridged dinuclear iron complex (1). X-ray single-crystal analysis of complex 1 revealed the presence of a furan derivative, resulting from the oxidative aromatic C-C bond cleavage product of 2-aminophenol derivative, in the coordination sphere of each iron center. Mechanistic investigation for the formation of complex 1 established that in the absence of molecular oxygen no oxidation of the appended 2-amidophenolate unit took place. An iron(III)-amidophenolate complex, formed initially, further reacted with molecular oxygen and caused oxidative aromatic C-C bond cleavage via a putative alkylperoxo species.

Ausgehend vom Radikalkettenmechanismus der Speiseoleoxydation wird ein Zeitgesetz fur die photochemische Oxydation ohne Hydroperoxidzerfall abgeleitet. Die Korrelation mit Versumsergebnissen fur Sojaol (1. Phase] ermoglimt die B e r e h u n g der Quantenausbeute der photoehemischen Startreaktion und der Kettenlange. Mit Hilfe dieser kinetischen GroDen sowie der Quantenausbeute der Bruttoreaktion wird namgewiesen, daD die Oxydation des Sojaols in der 1. Phase nicht autokatalytisch verlaufen kann. Die autokatalytischen Oxydationen (Sojaol 2. Phase, Sonnenblumen-und ErdnuDol] werden durch Untersuchung ihrer Oxydationsgeschwindigkeit in Abhangigkeit vom absorbierten Quantenstrom diskutiert. Dabei zeigt sich, daD wegen der Anwesenheit von Antioxydantien der Ungesattigtheitsgrad der Ole nieht allein fur die Oxydationsbereitschaft verantwortlich ist. Influence of Light on the Oxidative Deterioration of Edible Oils V: Kinetics of ReactionA time law for the photochemical oxidation without the decomposition of hydroperoxides has been derived from the radical chain mechanism in the oxidation of edible oils. Quantum yield of the photochemical start reaction and of the chain length can be calculated from the experimental results for soybean oil in the first phase. Using these kinetic values as well as from the quantum yield of the brutto reaction it is proven that the first phase in the autoxidation of soybean oil does not proceed by autocatalysis. Autocatalytic oxidations, e. g. soybean oil in the second phase, sunflower oil, and peanut oil,, are discussed on the basis of investigations on the oxidation rate as a function of absorbed quantum current. It is found that owing to the presence of antioxidants, the degree of unsaturation of oils alone is not responsible for the readiness with which the oil is oxidized.

No abstract