Hydrogen-atom transfer from transition metal hydroperoxides, hydrogen peroxide, and alkyl hydroperoxides to superoxo and oxo metal complexes

TitleHydrogen-atom transfer from transition metal hydroperoxides, hydrogen peroxide, and alkyl hydroperoxides to superoxo and oxo metal complexes
Publication TypeJournal Article
Year of Publication2007
AuthorsVasbinder MJ, Bakac A
Journal TitleInorganic Chemistry
Volume46
Pages2921-2928
Date PublishedApr
Type of ArticleArticle
ISBN Number0020-1669
Accession NumberISI:000245135900073
KeywordsABSTRACTION, acylperoxyl radicals, cross-disproportionation, ELECTRON-SPIN RESONANCE, kinetics, LOG K-VALUES, mechanism, OXOCHROMIUM(IV) ION, oxygen, thermodynamics
Abstract

Superoxochromium(III) complexes L(H2O)CrOO2+ (L = (H2O)(4) and 1,4,8,11-tetraazacyclotetradecane) oxidize hydroperoxo complexes of rhodium and cobalt in an apparent hydrogen-atom transfer process, i.e., L(H2O)CrOO2+ + L(H2O)RhOOH2+ -> L(H2O)CrOOH2+ + L(H2O)RhOO2+. All of the measured rate constants fall in a narrow range, 17-135 M-1 s(-1). These values are about 2.5-3.0 times smaller in D2O, where the hydroperoxo hydrogen is replaced by deuterium, and coordinated molecules of water by D2O. The failure of the back reaction to take place in the available concentration range places the O-H bond dissociation energy in RhOO-H2+ at <= 320 kJ/mol. The rates of oxidation of L(H2O)RhOOH2+ by CraqOO2+ are comparable to those for the oxidation of the corresponding hydrides despite the great difference (>= 80 kJ/mol) in the driving force for the two types of reactions. A chromyl ion, (CraqO2+)-O-IV, oxidizes L(H2O)RhOOH2+ and the cobalt analogs to the corresponding superoxo complexes. The rate constants are similar to 10(2)-fold larger than those for the oxidation by CraqOO2+. The oxidation of tert-BuOOH by (CraqO2+)-O-IV has k = 160 M-1 s(-1) and exhibits an isotope effect k(BuOOH)/k(BuOOD) = 12. Hydrogen atom transfer from H2O2 to CraqOO2+ is slow, k approximate to 10(-3) M-1 s(-1).

DOI10.1021/ic070015z
Alternate JournalInorg. Chem.