Catechol oxidase mimetic activity of copper(I) complexes of 3,5-dimethyl pyrazole derivatives: Coordination behavior, X-ray crystallography and electrochemical study

N1-substituted 3,5-dimethylpyrazole (dmpz) namely, methyl-3,5-dimethyl pyrazole-1-dithioate (L1) and benzyl-3,5-dimethyl-pyrazole-1-dithioate (L2) were reacted with zinc(II), copper(II) and cadmium(II) chloride to study their coordination behavior. Ligands L1 and L2 produced isostructural complexes with composition [CuI(L1)2][CuICl2] (1) and [CuI(L2)2][CuICl2] (2), respectively when reacted with CuCl2·2H2O. Copper (I) (d10 system) analogues, 1 and 2, exhibit prominent catechol oxidase activity in which a nice correlation-the easily oxidizable copper(I) center favoring the oxidation of 3,5-DTBC (3,5-ditertiary butyl catechol) is observed. Most importantly, these two compounds represent the class of copper(I) compounds that are rarely employed for the study of catecholase activity. The kinetics study exhibits a deuterium kinetic isotope effect in the catalytic oxidation of 3,5-DTBC by O2 as evidenced by about 1.9 times rate retardation in the deuterated solvent, suggesting the hydrogen atom transfer in the rate-determining step from the substrate hydroxy group to the metal-bound superoxo species. With other d10 cations, zinc(II) and cadmium(II) the ligand L1and/or L2 undergoes dissociation into parent pyrazole unit i.e., 3,5-dimethylpyrazole (dmpz) during formation of a monomeric tetrahedral Zn(dmpz)2Cl2 (3) complex and a helical 1-D polymeric chain, [Cd(dmpz)2Cl2]n(4). The possible role of intramolecular hydrogen-bonding induced helicity has been explored in 4.

Isostructural copper(I) complexes of methyl-3,5-dimethyl pyrazole-1-dithioate (L1) and benzyl-3,5-dimethyl-pyrazole-1-dithioate (L2) were synthesized. The same ligands formed tetrahedral Zn(dmpz)2Cl2 and a helical 1-D polymeric chain, [Cd(dmpz)2Cl2]n following dissociation of the parent ligand into 3,5-dimethyl pyrazole (dmpz). The copper (I) (d10 system) analogues exhibited mimetic catecholase oxidase activity.Figure optionsDownload as PowerPoint slide