Formation of a Ruthenium(V) - Imido Complex and the Reactivity in Substrate Oxidation in Water through the Nitrogen Non-Rebound Mechanism

Tomoya Ishizuka, Taichi Kogawa, Misaki Makino, Yoshihito Shiota, Kazuaki Ohara, Hiroaki Kotani, Shunsuke Nozawa, Shin Ichi Adachi, Kentaro Yamaguchi, Kazunari Yoshizawa, Takahiko Kojima

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Abstract

A RuII - NH3 complex, 2, was oxidized through a proton-coupled electron transfer (PCET) mechanism with a CeIV complex in water at pH 2.5 to generate a RuV=NH complex, 5. Complex 5 was characterized with various spectroscopies, and the spin state was determined by the Evans method to be S = 1/2. The reactivity of 5 in substrate C-H oxidation was scrutinized in acidic water, using water-soluble organic substrates such as sodium ethylbenzene-sulfonate (EBS), which gave the corresponding 1-phenylethanol derivative as the product. In the substrate oxidation, complex 5 was converted to the corresponding RuIII - NH3 complex, 3. The formation of 1-phenylethanol derivative from EBS and that of 3 indicate that complex 5 as the oxidant does not perform nitrogen-atom transfer, in sharp contrast to other high-valent metal-imido complexes reported so far. Oxidation of cyclobutanol by 5 afforded only cyclobutanone as the product, indicating that the substrate oxidation by 5 proceeds through a hydride-transfer mechanism. In the kinetic analysis on the C-H oxidation, we observed kinetic isotope effects (KIEs) on the C-H oxidation with use of deuterated substrates and remarkably large solvent KIE (sKIE) in D2O. These positive KIEs indicate that the rate-determining step involves not only cleavage of the C-H bond of the substrate but also proton transfer from water molecules to 5. The unique hydride-transfer mechanism in the substrate oxidation by 5 is probably derived from the fact that the RuIV - NH2 complex (4) formed from 5 by 1e-/1H+ reduction is unstable and quickly disproportionates into 3 and 5.

Original languageEnglish
Pages (from-to)12815-12824
Number of pages10
JournalInorganic chemistry
Volume58
Issue number19
DOIs
Publication statusPublished - Oct 7 2019

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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