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Keywords = aerobic o-aminophenol oxidation

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24 pages, 58766 KiB  
Article
Tetranuclear Copper Complexes with Bulky Aminoalcohol Ligands as Catalysts for Oxidative Phenoxazinone Synthase-like Coupling of Aminophenol: A Combined Experimental and Theoretical Study
by Oksana V. Nesterova, Armando J. L. Pombeiro and Dmytro S. Nesterov
Catalysts 2022, 12(11), 1408; https://doi.org/10.3390/catal12111408 - 10 Nov 2022
Cited by 8 | Viewed by 2682
Abstract
The new copper(II) complexes [Cu4(pa)4(Bae)4]·H2O (1) and [Cu4(eba)4(Buae)4]·H2O (2) (Hpa = propionic acid, HBae = 2-benzylaminoethanol, Heba = 2-ethylbutyric acid and HBuae = [...] Read more.
The new copper(II) complexes [Cu4(pa)4(Bae)4]·H2O (1) and [Cu4(eba)4(Buae)4]·H2O (2) (Hpa = propionic acid, HBae = 2-benzylaminoethanol, Heba = 2-ethylbutyric acid and HBuae = 2-butylaminoethanol) were synthesizsed by the interaction of a copper salt with a methanol solution of the respective ligands. The single-crystal X-ray diffraction analysis reveals that both compounds have a {Cu43-O)4} cubane-like core. Both compounds show pronounced phenoxazinone synthase-like activity towards the aerobic oxidation of o-aminophenol to phenoxazinone chromophore, with the maximum initial rates W0 up to 3.5 × 10−7 M s−1, and exhibit complex non-linear W0 vs. [catalyst]0 dependences. DFT//CCSD theoretical calculations (B3LYP/ma-def2-TZVP//DLPNO-CCSD(T)/ma-def2-TZVPP) were employed to investigate the most challenging steps of catalyst-free and copper-catalysed o-aminophenol oxidation (formation of o-aminophenoxyl radical). QTAIM analysis was used to study the key intermediates and weak interactions. Geometries and energies of intermediates and transition states were benchmarked against a series of popular DFT functionals. The results of the calculations demonstrate that a CuII–OO• copper-superoxo model catalyst decreases the calculated activation barrier from 28.7 to 19.9 kcal mol−1 for the catalyst-free and copper-catalysed abstraction of the H atom from the hydroxyl group of o-aminophenol, respectively. Finally, both complexes 1 and 2 were studied as catalysts in the amidation of cyclohexane with benzamide to give N-cyclohexyl benzamide and N-methyl benzamide employing di-tert-butyl peroxide (DTBP) as the oxidant, with a conversion of 16%, and in the oxidation of cyclohexane to cyclohexanol with aq. H2O2, with a conversion of 12%. Full article
(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)
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