A Highly Reactive Chromium(V)-Oxo TAML Cation Radical Complex in Electron Transfer and Oxygen Atom Transfer Reactions

Young Hyun Hong, Yuri Jang, Roman Ezhov, Mi Sook Seo, Yong Min Lee, Bhawana Pandey, Seungwoo Hong, Yulia Pushkar, Shunichi Fukuzumi, Wonwoo Nam

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

We report the synthesis, characterization, and electron-transfer (ET) oxidation reactivity of a chromium(V)-oxo TAML cation radical complex binding Sc3+ ion, {[CrV(O)(TAML•+)]-Sc3+}3+ (2-Sc). Its precursors, such as [CrV(O)(TAML)]- (1) and {[CrV(O)(TAML)]-Sc3+}2+ (1-Sc), were also characterized spectroscopically and/or structurally. In ET and oxygen atom transfer (OAT) reactions, while 1 and 1-Sc were sluggish oxidants, 2-Sc was a highly reactive oxidant with an extremely small reorganization energy. For example, in ET oxidation reactions, nanosecond laser-induced transient absorption measurements were performed to examine the fast ET from electron donors (e.g., ferrocene derivatives) to 2-Sc, affording a small reorganization energy (λ = 0.26 eV) of ET, which is even much smaller than the λ values reported in the ET reduction of heme Compound I (Cpd I) models and non-heme metal-oxo complexes. Such a small reorganization energy is ascribed to the TAML ligand centered ET reduction of 2-Sc. The λ value of 0.26 eV was also obtained in the electron self-exchange reaction between 2-Sc and 1-Sc. In OAT reactions, the rate constants of the sulfoxidation of thioanisole derivatives by 2-Sc at -40 °C were much greater than those reported in the oxidation of thioanisoles by heme Cpd I and non-heme metal-oxo complexes. The reactivity of 2-Sc in hydrogen atom transfer (HAT) reactions is also discussed briefly. To the best of our knowledge, this Cr(V)-oxo TAML cation radical complex binding Sc3+ ion, {[CrV(O)(TAML•+)]-Sc3+}3+, with an extremely small reorganization energy is one of the most powerful high-valent metal-oxo oxidants in ET and OAT reactions.

Original languageEnglish
Pages (from-to)2889-2901
Number of pages13
JournalACS Catalysis
Volume11
Issue number5
DOIs
StatePublished - 5 Mar 2021

Keywords

  • chromium(V)-oxo complex
  • electron transfer
  • oxygen atom transfer
  • redox-inactive metal ion
  • reorganization energy

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