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

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Title: Electronic structure and reactivity studies of a nonsymmetric one-electron oxidized CuII bis-phenoxide complex.
Authors: Chiang, Linus1, Stack, T. Daniel P.1, Wasinger, Erik C.2, Shimazaki, Yuichi3, Jr.Young, Victor4, Storr, Tim5
Source: Inorganica Chimica Acta. Sep2018, Vol. 481, p151-158. 8p.
Subjects: Cyclic voltammetry, Electronic structure, Phenol, Phenoxides, Electrons
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 Cu II , 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 Cu II -phenoxyl radical complex in solution. Resonance Raman (rR) and variable temperature 1 H NMR studies, coupled with theoretical calculations, showed that [ 2 ] + is a triplet ( S = 1) Cu II -phenoxyl radical species, with localization of the radical on the more electron-rich aminophenoxide. Attempted isolation of X-ray quality crystals of [ 2 ] + afforded [ 2 H] + , with a protonated phenol bonded to Cu II , and an additional H-bonding interaction with the SbF 6 − counterion. Stoichiometric reaction of dilute solutions of [ 2 ] + with benzyl alcohol showed that the complex reacts in a similar manner as the oxidized Cu II -salen analogue, and does not exhibit a substrate-binding pre-equilibrium as observed for the oxidized bis-aminophenoxide Cu II -salan derivative. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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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 Cu II , 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 Cu II -phenoxyl radical complex in solution. Resonance Raman (rR) and variable temperature 1 H NMR studies, coupled with theoretical calculations, showed that [ 2 ] + is a triplet ( S = 1) Cu II -phenoxyl radical species, with localization of the radical on the more electron-rich aminophenoxide. Attempted isolation of X-ray quality crystals of [ 2 ] + afforded [ 2 H] + , with a protonated phenol bonded to Cu II , and an additional H-bonding interaction with the SbF 6 − counterion. Stoichiometric reaction of dilute solutions of [ 2 ] + with benzyl alcohol showed that the complex reacts in a similar manner as the oxidized Cu II -salen analogue, and does not exhibit a substrate-binding pre-equilibrium as observed for the oxidized bis-aminophenoxide Cu II -salan derivative. [ABSTRACT FROM AUTHOR]
ISSN:00201693
DOI:10.1016/j.ica.2017.09.042