A Manganese(V)-Oxo Complex: Synthesis by Dioxygen Activation and Enhancement of Its Oxidizing Power by Binding Scandium Ion

Seungwoo Hong, Yong Min Lee, Muniyandi Sankaralingam, Anil Kumar Vardhaman, Young Jun Park, Kyung Bin Cho, Takashi Ogura, Ritimukta Sarangi, Shunichi Fukuzumi, Wonwoo Nam

Research output: Contribution to journalArticlepeer-review

90 Scopus citations

Abstract

A mononuclear non-heme manganese(V)-oxo complex, [MnV(O)(TAML)]- (1), was synthesized by activating dioxygen in the presence of olefins with weak allylic C-H bonds and characterized structurally and spectroscopically. In mechanistic studies, the formation rate of 1 was found to depend on the allylic C-H bond dissociation energies (BDEs) of olefins, and a kinetic isotope effect (KIE) value of 16 was obtained in the reactions of cyclohexene and cyclohexene-d10. These results suggest that a hydrogen atom abstraction from the allylic C-H bonds of olefins by a putative MnIV-superoxo species, which is formed by binding O2 by a high-spin (S = 2) [MnIII(TAML)]- complex, is the rate-determining step. A Mn(V)-oxo complex binding Sc3+ ion, [MnV(O)(TAML)]--(Sc3+) (2), was also synthesized in the reaction of 1 with Sc3+ ion and then characterized using various spectroscopic techniques. The binding site of the Sc3+ ion was proposed to be the TAML ligand, not the Mn-O moiety, probably due to the low basicity of the oxo group compared to the basicity of the amide carbonyl group in the TAML ligand. Reactivity studies of the Mn(V)-oxo intermediates, 1 and 2, in oxygen atom transfer and electron-transfer reactions revealed that the binding of Sc3+ ion at the TAML ligand of Mn(V)-oxo enhanced its oxidizing power with a positively shifted one-electron reduction potential (ΔEred = 0.70 V). This study reports the first example of tuning the second coordination sphere of high-valent metal-oxo species by binding a redox-inactive metal ion at the supporting ligand site, thereby modulating their electron-transfer properties as well as their reactivities in oxidation reactions.

Original languageEnglish
Pages (from-to)8523-8532
Number of pages10
JournalJournal of the American Chemical Society
Volume138
Issue number27
DOIs
StatePublished - 13 Jul 2016

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