TY - JOUR
T1 - Tuning Electron-Transfer Reactivity of a Chromium(III)-Superoxo Complex Enabled by Calcium Ion and Other Redox-Inactive Metal Ions
AU - Devi, Tarali
AU - Lee, Yong Min
AU - Nam, Wonwoo
AU - Fukuzumi, Shunichi
N1 - Funding Information:
This work was supported by the NRF of Korea through CRI (NRF-2012R1A3A2048842 to W.N.), GRL (NRF-2010-00353 to W.N.), Basic Science Research Program (2017R1D1A1B03029982 to Y.-M.L. and 2017R1D1A1B03032615 to S.F.), and the Grants-in-Aid (no. 16H02268 to S.F.) from MEXT.
Publisher Copyright:
© 2019 American Chemical Society.
PY - 2020/1/8
Y1 - 2020/1/8
N2 - Calcium ion plays an indispensable role for water oxidation by oxygen-evolving complex (OEC) composed of a manganese-oxo cluster (Mn4CaO5) in Photosystem II. In this context, the effects of Ca2+ ion and other redox-inactive metal ions on the redox reactivity of high-valent metal-oxo and metal-peroxo complexes have been studied extensively. Among metal-oxygen intermediates involved in interconversion between H2O and O2, however, the effects of Ca2+ ion and other redox-inactive metal ions (Mn+) on the redox reactivity of metal-superoxo complexes have yet to be reported. Herein, we report that electron transfer (ET) from octamethylferrocene (Me8Fc) to a mononuclear nonheme Cr(III)-superoxo complex, [(Cl)(TMC)CrIII(O2)]+ (1), occurs in the presence of redox-inactive metal ions (Mn+ = Ca2+, Mg2+, Y3+, Al3+, and Sc3+); in the absence of the redox-inactive metal ions, ET from Me8Fc to 1 does not occur. The second-order rate constants (ket) of ET from Me8Fc to 1 in the presence of a redox-inactive metal ion increased with increasing concentration of Mn+ ([Mn+]), exhibiting a second-order dependence on [Mn+]: ket = kMCET[Mn+]2, where kMCET is the fourth-order rate constant of metal ion-coupled electron transfer (MCET). This means that two Mn+ ions are bound to the one-electron reduced species of 1. Such a binding of two Mn+ ions associated with the ET reduction of 1 resulted in a 92 mV positive shift of the one-electron reduction potential of 1 (Ered) with increasing log([Mn+]). The log kMCET values increased linearly with the increasing Lewis acidity of Mn+ (ΔE), which was determined from the g values of O2 •--Mn+ complexes. The driving force dependence of log ket of MCET from ferrocene derivatives to 1 in the presence of Mn+ has been well-evaluated in light of the Marcus theory of electron transfer.
AB - Calcium ion plays an indispensable role for water oxidation by oxygen-evolving complex (OEC) composed of a manganese-oxo cluster (Mn4CaO5) in Photosystem II. In this context, the effects of Ca2+ ion and other redox-inactive metal ions on the redox reactivity of high-valent metal-oxo and metal-peroxo complexes have been studied extensively. Among metal-oxygen intermediates involved in interconversion between H2O and O2, however, the effects of Ca2+ ion and other redox-inactive metal ions (Mn+) on the redox reactivity of metal-superoxo complexes have yet to be reported. Herein, we report that electron transfer (ET) from octamethylferrocene (Me8Fc) to a mononuclear nonheme Cr(III)-superoxo complex, [(Cl)(TMC)CrIII(O2)]+ (1), occurs in the presence of redox-inactive metal ions (Mn+ = Ca2+, Mg2+, Y3+, Al3+, and Sc3+); in the absence of the redox-inactive metal ions, ET from Me8Fc to 1 does not occur. The second-order rate constants (ket) of ET from Me8Fc to 1 in the presence of a redox-inactive metal ion increased with increasing concentration of Mn+ ([Mn+]), exhibiting a second-order dependence on [Mn+]: ket = kMCET[Mn+]2, where kMCET is the fourth-order rate constant of metal ion-coupled electron transfer (MCET). This means that two Mn+ ions are bound to the one-electron reduced species of 1. Such a binding of two Mn+ ions associated with the ET reduction of 1 resulted in a 92 mV positive shift of the one-electron reduction potential of 1 (Ered) with increasing log([Mn+]). The log kMCET values increased linearly with the increasing Lewis acidity of Mn+ (ΔE), which was determined from the g values of O2 •--Mn+ complexes. The driving force dependence of log ket of MCET from ferrocene derivatives to 1 in the presence of Mn+ has been well-evaluated in light of the Marcus theory of electron transfer.
UR - http://www.scopus.com/inward/record.url?scp=85076955064&partnerID=8YFLogxK
U2 - 10.1021/jacs.9b11014
DO - 10.1021/jacs.9b11014
M3 - Article
C2 - 31800223
AN - SCOPUS:85076955064
SN - 0002-7863
VL - 142
SP - 365
EP - 372
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 1
ER -