Examination of the ligand effect on the H2O2-oxidation of lignin model compounds catalyzed by a series of Cu(II) complexes

FERREYRA, J.; PALOPOLI, C.; SIGNORELLA, S. R.

Viña del Mar

Encuentro; VIII Latin American Meeting on Biological Inorganic Chemistry; 2023

U. de Santiago de Chile

In this work, we studied the ability of a series of Cu(II) complexes that differ in the identity of the donor atoms (N2O2 vs. N4) and in the electronic properties of the metallic center to catalyse the H2O2-oxidation of phenol, 2-methoxyphenol (guaiacol) and 2,6-dimethoxyphenol (2,6-DMP) as structural models of lignin. The different complexes were synthesized and fully characterized, and the oxidation of lignin models was monitored spectrophotometrically by following the absorbance increase at the absorption maxima of the main products, at 25°C. Additionally, oxidation products distribution and selectivity for each of the most active catalysts were determined by HPLC-UV-MS. It was found that there is a high correlation between redox potentials of Cu(II) complexes and their catalytic performances in phenol oxidation: in comparison to an N2O2-coordination environment, one of the N4-type enhances redox potential of the Cu(II)/Cu(I) couple, increasing the oxidizing power of the metallic center. On the contrary, in the oxidation of substituted phenols (guaiacol and 2,6-DMP) ligand arrangement around the metal is a more important factor to consider than Cu(II)/Cu(I) redox potential in order to explain the observed differences in catalytic activities.