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

Journal Article · Tue Mar 22 04:00:00 EDT 2011 · Chemistry--A European Journal

DOI:https://doi.org/10.1002/chem.201100094· OSTI ID:1025116

Pestovsky, Oleg; Veysey, Stephen W; Bakac, Andrej

The kinetics of the reaction of benzyl radicals with [L{sup 1}(H{sub 2}O)RhH{l_brace}D{r_brace}]{sup 2+} (L{sup 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{sup 7} M{sup -1} s{sup -1} (H) and (6.2 {+-} 0.3) x 10{sup 7} M{sup -1} s{sup -1} (D), lead to a kinetic isotope effect k{sub H}/k{sub D}=1.5 {+-} 0.1. The same value was obtained from the relative yields of PhCH{sub 3} and PhCH{sub 2}D in a reaction of benzyl radicals with a mixture of rhodium hydride and deuteride. Similarly, the reaction of methyl radicals with {l_brace}[L{sup 1}(H{sub 2}O)RhH]{sup 2+} + [L{sup 1}(H{sub 2}O)RhD]{sup 2+}{r_brace} produced a mixture of CH{sub 4} and CH{sub 3}D that yielded k{sub H}/k{sub 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 L{sup 1}Rh.

• Research Organization: Ames Laboratory (AMES), Ames, IA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: AC02-07CH11358
• OSTI ID: 1025116
• Report Number(s): IS-J 7592
• Journal Information: Chemistry--A European Journal, Journal Name: Chemistry--A European Journal Journal Issue: 16 Vol. 17; ISSN 0947-6539
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ALKYL RADICALS
AQUEOUS SOLUTIONS
ATOMS
BENZYL RADICALS
HYDRIDES
HYDROGEN
ISOTOPE EFFECTS
ISOTOPIC EXCHANGE
KINETICS
METHYL RADICALS
MIXTURES
PHOTOLYSIS
REACTION KINETICS
RHODIUM
RHODIUM HYDRIDES
SENSITIVITY