Formation of the CuII–Phenoxyl Radical by Reaction of O2 with a CuII–Phenolate Complex via the CuI–Phenoxyl Radical

Takashi Suzuki, Hiromi Oshita, Tatsuo Yajima, Fumito Tani, Hitoshi Abe, Yuichi Shimazaki

Research output: Contribution to journalArticle

Abstract

Reaction of Cu(ClO4)2⋅6 H2O with a tripodal 2N2O ligand, H2Me2NL, having a p-(dimethylamino)phenol moiety, in CH2Cl2/MeOH (1:1 v/v) under basic conditions under an inert gas atmosphere gave [Cu(Me2NL)(H2O)] (1). The same reaction carried out under aerobic conditions gave [Cu(Me2NL)(MeOH)]ClO4 (2), which could be obtained also from the isolated complex 1 by reaction with O2 in CH2Cl2/MeOH. The X-ray crystal structures of 1 and 2 revealed similar square-pyramidal structures, but 2 showed the (dimethylamino)phenoxyl radical features. Complex 1 exhibits characteristic CuII EPR signals of the d x2-y2 ground state in CH2Cl2/MeOH at 77 K, whereas 2 is EPR-silent. The EPR and X-ray absorption fine structure (XAFS) results suggest that 2 is assigned to the CuII–(dimethylamino)phenoxyl radical. However, complex 1 showed different features in the absence of MeOH. The EPR spectrum of the CH2Cl2 solution of 1 exhibits distortion from the dx2-y2 ground state and a temperature-dependent equilibrium between the CuII–(dimethylamino)phenolate and the CuI–(dimethylamino)phenoxyl radical. From these results, CuII–phenoxyl radical complex 2 is concluded to be formed by the reaction of 1 with O2 via the CuI–phenoxyl radical species.

Original languageEnglish
Pages (from-to)15805-15814
Number of pages10
JournalChemistry - A European Journal
Volume25
Issue number69
DOIs
Publication statusPublished - Dec 10 2019

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Paramagnetic resonance
Ground state
Noble Gases
X ray absorption
Inert gases
Phenol
Phenols
Crystal structure
Ligands
X rays
phenoxy radical
Temperature
perchlorate

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Organic Chemistry

Cite this

Formation of the CuII–Phenoxyl Radical by Reaction of O2 with a CuII–Phenolate Complex via the CuI–Phenoxyl Radical. / Suzuki, Takashi; Oshita, Hiromi; Yajima, Tatsuo; Tani, Fumito; Abe, Hitoshi; Shimazaki, Yuichi.

In: Chemistry - A European Journal, Vol. 25, No. 69, 10.12.2019, p. 15805-15814.

Research output: Contribution to journalArticle

Suzuki, Takashi ; Oshita, Hiromi ; Yajima, Tatsuo ; Tani, Fumito ; Abe, Hitoshi ; Shimazaki, Yuichi. / Formation of the CuII–Phenoxyl Radical by Reaction of O2 with a CuII–Phenolate Complex via the CuI–Phenoxyl Radical. In: Chemistry - A European Journal. 2019 ; Vol. 25, No. 69. pp. 15805-15814.
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abstract = "Reaction of Cu(ClO4)2⋅6 H2O with a tripodal 2N2O ligand, H2Me2NL, having a p-(dimethylamino)phenol moiety, in CH2Cl2/MeOH (1:1 v/v) under basic conditions under an inert gas atmosphere gave [Cu(Me2NL)(H2O)] (1). The same reaction carried out under aerobic conditions gave [Cu(Me2NL)(MeOH)]ClO4 (2), which could be obtained also from the isolated complex 1 by reaction with O2 in CH2Cl2/MeOH. The X-ray crystal structures of 1 and 2 revealed similar square-pyramidal structures, but 2 showed the (dimethylamino)phenoxyl radical features. Complex 1 exhibits characteristic CuII EPR signals of the d x2-y2 ground state in CH2Cl2/MeOH at 77 K, whereas 2 is EPR-silent. The EPR and X-ray absorption fine structure (XAFS) results suggest that 2 is assigned to the CuII–(dimethylamino)phenoxyl radical. However, complex 1 showed different features in the absence of MeOH. The EPR spectrum of the CH2Cl2 solution of 1 exhibits distortion from the dx2-y2 ground state and a temperature-dependent equilibrium between the CuII–(dimethylamino)phenolate and the CuI–(dimethylamino)phenoxyl radical. From these results, CuII–phenoxyl radical complex 2 is concluded to be formed by the reaction of 1 with O2 via the CuI–phenoxyl radical species.",
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AB - Reaction of Cu(ClO4)2⋅6 H2O with a tripodal 2N2O ligand, H2Me2NL, having a p-(dimethylamino)phenol moiety, in CH2Cl2/MeOH (1:1 v/v) under basic conditions under an inert gas atmosphere gave [Cu(Me2NL)(H2O)] (1). The same reaction carried out under aerobic conditions gave [Cu(Me2NL)(MeOH)]ClO4 (2), which could be obtained also from the isolated complex 1 by reaction with O2 in CH2Cl2/MeOH. The X-ray crystal structures of 1 and 2 revealed similar square-pyramidal structures, but 2 showed the (dimethylamino)phenoxyl radical features. Complex 1 exhibits characteristic CuII EPR signals of the d x2-y2 ground state in CH2Cl2/MeOH at 77 K, whereas 2 is EPR-silent. The EPR and X-ray absorption fine structure (XAFS) results suggest that 2 is assigned to the CuII–(dimethylamino)phenoxyl radical. However, complex 1 showed different features in the absence of MeOH. The EPR spectrum of the CH2Cl2 solution of 1 exhibits distortion from the dx2-y2 ground state and a temperature-dependent equilibrium between the CuII–(dimethylamino)phenolate and the CuI–(dimethylamino)phenoxyl radical. From these results, CuII–phenoxyl radical complex 2 is concluded to be formed by the reaction of 1 with O2 via the CuI–phenoxyl radical species.

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