TY - JOUR
T1 - A Manganese(V)-Oxo Complex
T2 - Synthesis by Dioxygen Activation and Enhancement of Its Oxidizing Power by Binding Scandium Ion
AU - Hong, Seungwoo
AU - Lee, Yong Min
AU - Sankaralingam, Muniyandi
AU - Vardhaman, Anil Kumar
AU - Park, Young Jun
AU - Cho, Kyung Bin
AU - Ogura, Takashi
AU - Sarangi, Ritimukta
AU - Fukuzumi, Shunichi
AU - Nam, Wonwoo
N1 - Publisher Copyright:
© 2016 American Chemical Society.
PY - 2016/7/13
Y1 - 2016/7/13
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=84978771825&partnerID=8YFLogxK
U2 - 10.1021/jacs.6b03874
DO - 10.1021/jacs.6b03874
M3 - Article
C2 - 27310336
AN - SCOPUS:84978771825
SN - 0002-7863
VL - 138
SP - 8523
EP - 8532
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 27
ER -