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Kinetics and Mechanism of Hydrogen‐Atom Abstraction from Rhodium Hydrides by Alkyl Radicals in Aqueous Solutions
Author(s) -
Pestovsky Oleg,
Veysey Stephen W.,
Bakac Andreja
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201100094
Subject(s) - kinetic isotope effect , radical , chemistry , flash photolysis , hydride , reaction rate constant , hydrogen atom abstraction , kinetics , hydrogen atom , isotopologue , photochemistry , rhodium , deuterium , medicinal chemistry , chemical kinetics , reaction mechanism , alkyl , hydrogen , catalysis , organic chemistry , molecule , physics , quantum mechanics
The kinetics of the reaction of benzyl radicals with [L 1 (H 2 O)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) × 10 7 M −1 s −1 (H) and (6.2±0.3) × 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 PhCH 3 and PhCH 2 D in a reaction of benzyl radicals with a mixture of rhodium hydride and deuteride. Similarly, the reaction of methyl radicals with {[L 1 (H 2 O)RhH] 2+ + [L 1 (H 2 O)RhD] 2+ } produced a mixture of CH 4 and CH 3 D 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 L 1 Rh.