Tetranuclear Copper Complexes with Bulky Aminoalcohol Ligands as Catalysts for Oxidative Phenoxazinone Synthase-like Coupling of Aminophenol: A Combined Experimental and Theoretical Study

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 HBuae 2-butylaminoethanol) were synthesizsed by the interaction of a copper salt with methanol solution respective ligands. single-crystal X-ray diffraction analysis reveals that both compounds have {Cu4(μ3-O)4} cubane-like core. Both show pronounced phenoxazinone synthase-like activity towards aerobic oxidation o-aminophenol to chromophore, maximum initial rates W0 up 3.5 × 10−7 M s−1, exhibit complex non-linear vs. [catalyst]0 dependences. DFT//CCSD theoretical calculations (B3LYP/ma-def2-TZVP//DLPNO-CCSD(T)/ma-def2-TZVPP) employed investigate most challenging steps catalyst-free copper-catalysed (formation o-aminophenoxyl radical). QTAIM was used study key intermediates weak interactions. Geometries energies transition states benchmarked against series popular DFT functionals. results demonstrate CuII–OO• copper-superoxo model catalyst decreases calculated activation barrier from 28.7 19.9 kcal mol−1 for abstraction H atom hydroxyl group o-aminophenol, respectively. Finally, 1 2 studied as catalysts in amidation cyclohexane benzamide give N-cyclohexyl N-methyl employing di-tert-butyl peroxide (DTBP) oxidant, conversion 16%, cyclohexanol aq. H2O2, 12%.