Phenoxazinone Synthase‐like Catalytic Activity of Bi‐ and Trinuclear Copper(II) complexes with 2‐benzylethanolamine: Experimental and Theoretical study

The self‐assembly reaction of 2‐benzylaminoethanol (Hbae) with CuCl2 or Cu(NO3)2 leads to the formation of binuclear [Cu2(bae)2(Cl)2] (1) and [Cu2(Hbae)2(bae)2](NO3)2 (2) complexes, while the trinuclear [Cu3(Hbae)2(bae)2(dmba)2](NO3)2 (3) compound was obtained using the auxiliar bulky substituted 2,2‐dimethylbutyric acid (Hdmba). All three compounds act as catalysts for the aerobic oxidation of 2‐aminophenol to the phenoxazinone chromophore (phenoxazinone synthase‐like activity) with the maximum reaction rates up to 2.3 × 10–8 M s–1. The substrate scope involves methyl‐, nitro‐ and chloro‐substituted 2‐aminophenols, disclosing the negligible activity of nitro‐derivatives, while the 6‐amino‐m‐cresol substrate shows the highest activity with the initial reaction rate of 5.8 × 10–8 M s–1. The mechanism of the rate‐limiting reaction step (copper‐catalysed formation of 2‐aminophenoxyl radicals) was investigated at the DFT level. The combined DFT and CASSCF studies of the copper superoxo CuII–OO· radical species as possible unconventional reaction intermediates resulted in a rational mechanism of H‐atom abstraction, where the activation energies follow the experimental reactivity of substituted 2‐aminophenols. The TDDFT and STEOM‐DLPNO‐CCSD theoretical calculations of the absorption spectra of substrates, phenoxazinone chromophores and putative polynuclear species containing 2‐aminophenoxo ligand are reported.