Switchover of the Mechanism between Electron Transfer and Hydrogen-Atom Transfer for a Protonated Manganese(IV)-Oxo Complex by Changing Only the Reaction Temperature

• Published in: Angewandte Chemie International Edition 2016-06, Vol.55 (26), p.7450-7454
• Main Authors: Jung, Jieun, Kim, Surin, Lee, Yong-Min, Nam, Wonwoo, Fukuzumi, Shunichi
• Format: Article
• Language: English
• Subjects: bioinorganic chemistry; Deuterium; Electron transfer; hydrogen atom transfer; Hydroxylation; Isotope effect; Manganese; manganese(IV)-oxo complex; mechanism switchover; Mesitylene; Temperature; Temperature effects; Toluene; Triflic acid
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201602460

Hydroxylation of mesitylene by a nonheme manganese(IV)–oxo complex, [(N4Py)MnIV(O)]2+ (1), proceeds via one‐step hydrogen‐atom transfer (HAT) with a large deuterium kinetic isotope effect (KIE) of 3.2(3) at 293 K. In contrast, the same reaction with a triflic acid‐bound manganese(IV)‐oxo complex, [(N4Py)MnIV(O)]2+‐(HOTf)2 (2), proceeds via electron transfer (ET) with no KIE at 293 K. Interestingly, when the reaction temperature is lowered to less than 263 K in the reaction of 2, however, the mechanism changes again from ET to HAT with a large KIE of 2.9(3). Such a switchover of the reaction mechanism from ET to HAT is shown to occur by changing only temperature in the boundary region between ET and HAT pathways when the driving force of ET from toluene derivatives to 2 is around −0.5 eV. The present results provide a valuable and general guide to predict a switchover of the reaction mechanism from ET to the others, including HAT. The switchover of the reaction mechanism from electron transfer (ET) to hydrogen‐atom transfer (HAT) for a protonated nonheme manganese(IV)–oxo complex was investigated. The switchover occurs in the presence of triflic acid by changing only the reaction temperature in the boundary region between ET and HAT pathways. KIE=kinetic isotope effect; black=mesitylene, red=[D12]mesitylene.