Hydrogen atom transfer reactions of a ruthenium imidazole complex: hydrogen tunneling and the applicability of the Marcus cross relation.
作者： Adam Wu , James M. Mayer
DOI: 10.1021/JA805067H
关键词: Thermochemistry 、 Electron transfer 、 Photochemistry 、 Kinetic isotope effect 、 Chemistry 、 Reaction rate constant 、 Deuterium 、 Hydrogen atom 、 Hydrogen 、 Ruthenium
摘要: The reaction of RuII(acac)2(py-imH) (RuIIimH) with TEMPO• (2,2,6,6-tetramethylpiperidine-1-oxyl radical) in MeCN quantitatively gives RuIII(acac)2(py-im) (RuIIIim) and the hydroxylamine TEMPO-H by transfer H• (H+ + e−) (acac = 2,4-pentanedionato, py-imH 2-(2′-pyridyl)imidazole). Kinetic measurements this UV−vis stopped-flow techniques indicate a bimolecular rate constant k3H 1400 ± 100 M−1 s−1 at 298 K. proceeds via concerted hydrogen atom (HAT) mechanism, as shown ruling out stepwise pathways initial proton or electron due to their very unfavorable thermochemistry (ΔG°). Deuterium from RuII(acac)2(py-imD) (RuIIimD) is surprisingly much slower k3D 60 7 s−1, k3H/k3D 23 3 Temperature-dependent deuterium kinetic isotope effect (KIE) show large difference between apparent activation energies, Ea3D − Ea3H 1.9 0.8 kcal mol−1. ΔEa values appear ...
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