Mechanism of oxidation of alkyl and superoxo complexes of chromium(III) by aquamanganese(III) ions

TitleMechanism of oxidation of alkyl and superoxo complexes of chromium(III) by aquamanganese(III) ions
Publication TypeJournal Article
Year of Publication2010
AuthorsJee JE, Pestovsky O, Hidayat I, Szajna-Fuller E, Bakac A
Journal TitleJournal of Coordination Chemistry
Volume63
Pages2578-2585
Date Published07
ISBN Number0095-8972
Accession NumberISI:000281031100017
Keywordsaqueous-solutions, benzyl radicals, chromium, homolysis, kinetics, manganese, manganese(3), nickel(iii) complexes, oxidation, oxygen, REDUCTION, thermodynamics
Abstract

The reaction between aqueous manganese(III) ions, Mn(H2O)(6)(3+), and (H2O)(5)CrOO2+ has a 1:1 stoichiometry and generates Cr(H2O)(6)(3+) and O-2 as products. The mixed second-order rate constant exhibits an [H+] dependence that identifies the hexaaquamanganese ion as the reactive form at 0.5 <=[H+]<= 3.0molL(-1), k(H)=350 +/- 10(molL(-1))(-1)s(-1). The reactivity of (H2O)(5)MnOH2+ is negligible under these conditions, most likely because the much lower reduction potential of this hydrolytic form results in unfavorable thermodynamics for the overall reaction. Mn(H2O)(6)(3+) also oxidizes a benzylchromium ion,(H2O)(5)CrCH2Ph2+, with a rate constant k=273 +/- 13(molL(-1))(-1)s(-1) in 3.0molL(-1) HClO4. The reaction has a 2:1 [Mn(H2O)(6)(3+)]/[(H2O)(5)CrCH2Ph2+] stoichiometry and generates benzyl alcohol as the sole organic product. The data are consistent with oxidative homolysis which generates benzyl radicals followed by rapid oxidation of the radicals with the second equivalent of Mn(H2O)(6)(3+). The unexpected similarity between the rate constants for the Mn(H2O)(6)(3+) oxidation of (H2O)(5)CrOO2+ and (H2O)(5)CrCH2Ph2+ is discussed.

URL<Go to ISI>://000281031100017
DOI10.1080/00958972.2010.498510