Synthesis, structure and catalytic properties of tripodal amino-acid derivatized pyrazole-based ligands

A synthesis of five functional multidendate ligand: methyl 2-(bis((3,5-dimethyl-1H–pyrazol-1-yl)methyl)amino)acetate L1, methyl 2-(bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)amino)-propanoate L2, methyl 2-(bis((3,5-dimethyl-1H-pyrazol-1-yl) methyl) amino)-3-methylbutanoate L3, methyl 2-(bis((3,5-dimethyl-1H-pyrazol-1-yl) methyl) amino)-3-methyl- pentanoate L4 and methyl 6-(bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)amino)hexanoate L5 is reported. Copper (II) complexes of these compounds were examined for their catalytic properties. The in situ generated copper (II) complexes were suitable catalysts for the catalytic oxidation of catechol substrate to quinone with dioxygen at ambient condition. All complexes catalyze the oxidation reaction with the rate varying from a high of 11.8250 μmol L−1 min−1 for the L2[Cu(CH3CO2)2] complex to a weaker rate of 0.7875 μmol L−1 min−1 for L3[Cu(NO3)2].

Graphical abstractThe syntheses of amino acid functional tridentate pyrazolyl ligands with good and excellent yields. The oxidation of catechol is very efficient to give quinone by various copper (II) salts and these ligands, which were generated in situ. The ester side chain and the anion have a large effect on the oxidation reaction rate.Figure optionsDownload full-size imageDownload high-quality image (96 K)Download as PowerPoint slide