Abstract
The controversy in the reported kinetics for the hydrogen-atom abstraction reaction by methyl radicals for cis- and trans-[(Cyclam)RhIIIHCl]+ and trans-[(Cyclam)(H2O)RhIIIH]2+ has been resolved by studying several feasible mechanistic pathways with density functional theory. The only low-energy reaction mechanism predicted by these calculations involves a single-step radical-propagation mechanism in which the methyl radical simply abstracts the Rh bound H atom from the complex to form methane and the reduced Rh product. Previous experimental work on the chloride and aquo complexes suggested contradictory kinetic isotope effect (KIE) values of 0.66 ± 0.30 and 1.42 ± 0.07 as well as rate constants for the reaction differing by four orders of magnitude. The calculated mechanism predicts a KIE value of 1.08 and a high reaction rate. The alternative mechanisms are described briefly.
The controversy in the reported kinetics for the hydrogen-atom abstraction reaction bymethyl radicals for cis- and trans-[(Cyclam)RhIIIHCl]+ and trans-[(Cyclam)(H2O)RhIIIH]2+ has been resolved by studying several feasible mechanistic pathways with density functional theory.
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