Kinetics of oxidation of nitroxyl radicals with superoxometal complexes of chromium and rhodium

TitleKinetics of oxidation of nitroxyl radicals with superoxometal complexes of chromium and rhodium
Publication TypeJournal Article
Year of Publication2007
AuthorsVasbinder MJ, Bakac A
Journal TitleInorganic Chemistry
Volume46
Pages2322-2327
Date PublishedMar
Type of ArticleArticle
ISBN Number0020-1669
Accession NumberISI:000244798800055
KeywordsACID-CATALYZED OXIDATION, ATOM-TRANSFER, CYCLIC NITROXIDES, derivatives, electron-transfer, ions, mechanism, METAL-COMPLEXES, POLYMERIZATION, STYRENE
Abstract

In acidic aqueous solutions, nitroxyl radicals (X)TEMPO (X = H, 4-OH, and 4-oxo) and 3-carbamoyl-PROXYL readily reduce CraqOO2+ and Rh(NH3)(4)(H2O)OO2+ to the corresponding hydroperoxo complexes. The kinetics are largely acid independent for CraqOO2+, but acid catalysis dominates the reactions of the rhodium complex. This emerging trend in oxidations with superoxometal complexes seems to be directly related to the thermodynamics of electron transfer. The weaker the oxidant, the more important the acid-assisted path. The rate constants for the oxidation of (X)TEMPO by CraqOO2+ are 406 M-1 s(-1) (X = H), 159 (4-OH), and (20. 6 + 77.5 [H+]) (4-oxo). For the rhodium complex, the values are (40 + 2.20 x 10(3) [H+]) (X = H), (25 + 1.10 x 10(3) [H+]) (4-HO), and 2.21 x 10(3) [H+] (4-oxo). An inverse solvent kinetic isotope effect, k(H)/k(D) = 0.8, was observed in the reaction between (O)TEMPO and (NH3)(4)(H(D))(2)O)RhOO2+ in 0.10 M H(D)ClO4 in H2O and D2O.

DOI10.1021/ic062010s
Alternate JournalInorg. Chem.