Electronic structure and reactivity studies of a nonsymmetric one-electron oxidized CuII bis-phenoxide complex

Linus Chiang, Erik C. Wasinger, Yuichi Shimazaki, Victor G Young, Tim Storr, T. Daniel P. Stack

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Abstract

The tetradentate mixed imino/amino phenoxide ligand (N-(3,5-di-tert-butylsalicylidene)-N′-(2-hydroxyl-3,5-di-tert-butylbenzyl))-trans-1,2-cyclohexanediamine (salalen) was complexed with CuII, and the resulting Cu complex (2) was characterized by a number of experimental techniques and theoretical calculations. Two quasi-reversible redox processes for 2, as observed by cyclic voltammetry, demonstrated the potential stability of oxidized forms, and also the increased electron-donating ability of the salalen ligand in comparison to the salen analogue. The electronic structure of the one-electron oxidized [2]+ was studied in detail, and Cu K-edge X-ray Absorption Spectroscopy (XAS) measurements confirmed a CuII-phenoxyl radical complex in solution. Resonance Raman (rR) and variable temperature 1H NMR studies, coupled with theoretical calculations, showed that [2[rad]]+ is a triplet (S = 1) CuII-phenoxyl radical species, with localization of the radical on the more electron-rich aminophenoxide. Attempted isolation of X-ray quality crystals of [2[rad]]+ afforded [2H]+, with a protonated phenol bonded to CuII, and an additional H-bonding interaction with the SbF6 counterion. Stoichiometric reaction of dilute solutions of [2[rad]]+ with benzyl alcohol showed that the complex reacts in a similar manner as the oxidized CuII-salen analogue, and does not exhibit a substrate-binding pre-equilibrium as observed for the oxidized bis-aminophenoxide CuII-salan derivative.

Original languageEnglish (US)
Pages (from-to)151-158
Number of pages8
JournalInorganica Chimica Acta
Volume481
DOIs
StatePublished - Sep 1 2018

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Electronic structure
reactivity
electronic structure
Electrons
Ligands
analogs
Benzyl Alcohol
ligands
X ray absorption spectroscopy
electrons
Phenol
Hydroxyl Radical
phenols
Phenols
Cyclic voltammetry
isolation
absorption spectroscopy
alcohols
Alcohols
x rays

PubMed: MeSH publication types

  • Journal Article

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Electronic structure and reactivity studies of a nonsymmetric one-electron oxidized CuII bis-phenoxide complex. / Chiang, Linus; Wasinger, Erik C.; Shimazaki, Yuichi; Young, Victor G; Storr, Tim; Stack, T. Daniel P.

In: Inorganica Chimica Acta, Vol. 481, 01.09.2018, p. 151-158.

Research output: Contribution to journalArticle

Chiang, Linus ; Wasinger, Erik C. ; Shimazaki, Yuichi ; Young, Victor G ; Storr, Tim ; Stack, T. Daniel P. / Electronic structure and reactivity studies of a nonsymmetric one-electron oxidized CuII bis-phenoxide complex. In: Inorganica Chimica Acta. 2018 ; Vol. 481. pp. 151-158.
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abstract = "The tetradentate mixed imino/amino phenoxide ligand (N-(3,5-di-tert-butylsalicylidene)-N′-(2-hydroxyl-3,5-di-tert-butylbenzyl))-trans-1,2-cyclohexanediamine (salalen) was complexed with CuII, and the resulting Cu complex (2) was characterized by a number of experimental techniques and theoretical calculations. Two quasi-reversible redox processes for 2, as observed by cyclic voltammetry, demonstrated the potential stability of oxidized forms, and also the increased electron-donating ability of the salalen ligand in comparison to the salen analogue. The electronic structure of the one-electron oxidized [2]+ was studied in detail, and Cu K-edge X-ray Absorption Spectroscopy (XAS) measurements confirmed a CuII-phenoxyl radical complex in solution. Resonance Raman (rR) and variable temperature 1H NMR studies, coupled with theoretical calculations, showed that [2[rad]]+ is a triplet (S = 1) CuII-phenoxyl radical species, with localization of the radical on the more electron-rich aminophenoxide. Attempted isolation of X-ray quality crystals of [2[rad]]+ afforded [2H]+, with a protonated phenol bonded to CuII, and an additional H-bonding interaction with the SbF6 − counterion. Stoichiometric reaction of dilute solutions of [2[rad]]+ with benzyl alcohol showed that the complex reacts in a similar manner as the oxidized CuII-salen analogue, and does not exhibit a substrate-binding pre-equilibrium as observed for the oxidized bis-aminophenoxide CuII-salan derivative.",
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AU - Stack, T. Daniel P.

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AB - The tetradentate mixed imino/amino phenoxide ligand (N-(3,5-di-tert-butylsalicylidene)-N′-(2-hydroxyl-3,5-di-tert-butylbenzyl))-trans-1,2-cyclohexanediamine (salalen) was complexed with CuII, and the resulting Cu complex (2) was characterized by a number of experimental techniques and theoretical calculations. Two quasi-reversible redox processes for 2, as observed by cyclic voltammetry, demonstrated the potential stability of oxidized forms, and also the increased electron-donating ability of the salalen ligand in comparison to the salen analogue. The electronic structure of the one-electron oxidized [2]+ was studied in detail, and Cu K-edge X-ray Absorption Spectroscopy (XAS) measurements confirmed a CuII-phenoxyl radical complex in solution. Resonance Raman (rR) and variable temperature 1H NMR studies, coupled with theoretical calculations, showed that [2[rad]]+ is a triplet (S = 1) CuII-phenoxyl radical species, with localization of the radical on the more electron-rich aminophenoxide. Attempted isolation of X-ray quality crystals of [2[rad]]+ afforded [2H]+, with a protonated phenol bonded to CuII, and an additional H-bonding interaction with the SbF6 − counterion. Stoichiometric reaction of dilute solutions of [2[rad]]+ with benzyl alcohol showed that the complex reacts in a similar manner as the oxidized CuII-salen analogue, and does not exhibit a substrate-binding pre-equilibrium as observed for the oxidized bis-aminophenoxide CuII-salan derivative.

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