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Kinetics and Mechanism of Hydrogen-Atom Abstraction from Rhodium Hydrides by Alkyl Radicals in Aqueous Solutions

TitleKinetics and Mechanism of Hydrogen-Atom Abstraction from Rhodium Hydrides by Alkyl Radicals in Aqueous Solutions
Publication TypeJournal Article
Year of Publication2011
AuthorsPestovsky O, Veysey SW, Bakac A
Journal TitleChemistry-A European Journal
Volume17
Pages4518-4522
Date Published04
Type of ArticleArticle
ISBN Number0947-6539
Accession NumberISI:000290159000020
Keywordscomplexes, dihydrogen, hydrides, hydrogen atom abstraction, isotope effects, kinetics, PORPHYRINS, pulse-radiolysis, reaction mechanisms, REDUCTION, rhodium, water
Abstract

The kinetics of the reaction of benzyl radicals with [L-1(H2O)RhH{D}](2+) (L-1 = 1,4,8,11-tetraazacyclotetradecane) were studied directly by laser-flash photolysis. The rate constants for the two isotopologues, k=(9.3 +/- 0.6) x 10(7)M(-1)s(-1) (H) and (6.2 +/- 0.3) x 10(7)M(-1)s(-1) (D), lead to a kinetic isotope effect k(H)/k(D)= 1.5 +/- 0.1. The same value was obtained from the relative yields of PhCH3 and PhCH2D in a reaction of benzyl radicals with a mixture of rhodium hydride and deuteride. Similarly, the reaction of methyl radicals with {[L-1(H2O)RhH](2+) + [L-1(H2O)RhD](2+)} produced a mixture of CH4 and CH3D that yielded k(H)/k(D)= 1.42 +/- 0.07. The observed small normal isotope effects in both reactions are consistent with reduced sensitivity to isotopic substitution in very fast hydrogen-atom abstraction reactions. These data disprove a literature report claiming much slower kinetics and an inverse kinetic isotope effect for the reaction of methyl radicals with hydrides of (LRh)-Rh-1.
URL<Go to ISI>://000290159000020
DOI10.1002/chem.201100094
Alternate JournalChem.-Eur. J.