A Manganese(V)-Oxo Complex: Synthesis by Dioxygen Activation and Enhancement of Its Oxidizing Power by Binding Scandium Ion.
A mononuclear non-heme manganese(V)-oxo complex, [Mn(V)(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 Mn(IV)-superoxo species, which is formed by binding O2 by a high-spin (S = 2) [Mn(III)(TAML)](-) complex, is the rate-determining step. A Mn(V)-oxo complex binding Sc(3+) ion, [Mn(V)(O)(TAML)](-)-(Sc(3+)) (2), was also synthesized in the reaction of 1 with Sc(3+) ion and then characterized using various spectroscopic techniques. The binding site of the Sc(3+) 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 Sc(3+) 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.
Department of Chemistry and Nano Science, Ewha Womans University , Seoul 03760, Korea.
Seungwoo
S
Hong
Department of Chemistry and Nano Science, Ewha Womans University , Seoul 03760, Korea.
Yong-Min
YM
Lee
Department of Chemistry and Nano Science, Ewha Womans University , Seoul 03760, Korea.
Muniyandi
M
Sankaralingam
Department of Chemistry and Nano Science, Ewha Womans University , Seoul 03760, Korea.
Anil Kumar
AK
Vardhaman
Department of Chemistry and Nano Science, Ewha Womans University , Seoul 03760, Korea.
Young Jun
YJ
Park
Department of Chemistry and Nano Science, Ewha Womans University , Seoul 03760, Korea.
Kyung-Bin
KB
Cho
Picobiology Institute, Graduate School of Life Science, University of Hyogo , Hyogo 678-1297, Japan.
Takashi
T
Ogura
Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory , Menlo Park, California 94025, United States.
Ritimukta
R
Sarangi
Department of Chemistry and Nano Science, Ewha Womans University , Seoul 03760, Korea.
Shunichi
S
Fukuzumi
Department of Chemistry and Nano Science, Ewha Womans University , Seoul 03760, Korea.
Wonwoo
W
Nam
D060326:Chemistry Techniques, Synthetic; D004579:Electron Transport; D008345:Manganese / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*
D009942:Organometallic Compounds; D008345:Manganese; D010100:Oxygen