Complexos monometálicos de zircônio(IV) e zinco(II) com bases de Schiff tridentadas tipo ONN derivadas da diaminomaleonitril: síntese, caracterização e estudos como catalisadores em reações de oxidação

Abstract

It is known that transition metal complexes are compounds with a wide range of applications, due to, for example, its structural versatility and variability of electronic properties. A wide range of these compounds have vital functions in living organisms, being found in enzymes, proteins and cofactors. So, the potentiality of such complexes for the catalytic activity is related to the presence of possible active sites for substrate coordination and the occurrence of the catalyzed reaction. In search for inorganic compounds that act as mimetic models for the enzyme Catechol Oxidase, there were synthesized monometallic zirconium (IV) and zinc (II) complexes. The ligands used were tridentate Schiff base originated by the reaction between diaminomaleonitrile and salicylaldehyde, or 4-substituted salicylaldehyde. Those compounds were characterized through techniques such as solubility tests, melting point tests, molar conductivity measures, vibrational and electronic spectroscopies and 1H nuclear magnetic resonance. The complexes were tested for its functional mimetic activity for the enzyme Catechol Oxidase by conducting the reaction between 3,5-di-tert-butylcatechol and O2, to form 3,5-di-tert-butyl-ortho-quinone. It was found that in 24 h the zinc complex without substituent on the aromatic ring of the ligand has a catalytic behavior, resulting in a conversion 17 % higher than that observed in the test without catalyst. The results for all other complexes suggested inhibitory activity and the tested zirconium complex was the one which the inhibition effect was more pronounced. In the first four hours of reaction it presented conversions of 5 % of the converted in the test without catalyst.