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

N-1-substituted 3,5-dimethylpyrazole (dmpz) namely, methyl-3,5-dimethyl pyrazole-1-dithioate (L-1) and benzyl-3,5-dimethyl-pyrazole-1-dithioate (L-2) were reacted with zinc(II), copper(II) and cadmium(II) chloride to study their coordination behavior. Ligands L-1 and L-2 produced isostructural complexes with composition [Cu-I(L-1)(2)][(CuCl2)-Cl-I] (1) and [Cu-I(L-2)(2)][(CuCl2)-Cl-I] (2), respectively when reacted with CuCl2 center dot 2H(2)O. Copper (I) (d(10) 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 O-2 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 d(10) cations, zinc(II) and cadmium(II) the ligand L-1 and/or L-2 undergoes dissociation into parent pyrazole unit i.e., 3,5-dimethylpyrazole (dmpz) during formation of a monomeric tetrahedral Zn(dmpz)(2)Cl-2 (3) complex and a helical 1-D polymeric chain, [Cd(dmpz)(2)Cl-2](n)(4). The possible role of intramolecular hydrogen-bonding induced helicity has been explored in 4. (C) 2016 Elsevier Ltd. All rights reserved.