A heptadentate ligand possessing two phenol groups: Its diverse coordination chemistry and the catalytic behaviors of its transition complexes towards benzene oxidation

Reacting the heptadentate ligand 2,2′-(((pyridine-2,6-diylbis(methylene))bis((pyridin-2-ylmethyl)-azanediyl))bis(methylene))diphenol (H2L) with one equivalent of CuCl2·6H2O, NiCl2·6H2O and FeCl3·6H2O, followed by anion exchange with PF6−, BPh4− and ClO4− formed three mononuclear complexes [Cu(H2L)](Cl)(PF6) (1), [Ni(HL)](BPh4) (2) and [Fe(L)](ClO4) (3), respectively. Their structures in the solid state were determined by X-ray crystallography. The three metal centers in complexes 1–3 adopt distorted tetragonal pyramidal (Cu2+), octahedral (Ni2+) and pentagonal bipyramidal (Fe3+) geometries, respectively. In addition, the electrochemistry and their catalytic activity in the oxidation reaction of benzene to phenol by H2O2 were investigated.

Graphical abstractTreatment of the heptadentate ligand H2L, possessing pyridinyl and phenolate groups, with one equivalent of Cu2+, Ni2+ and Fe3+ ions, through non-, partial and complete deprotonation of the hydroxyl groups of the phenols in the ligand, led to a penta-coordinated copper(II), a hexa-coordinated nickel(II) and a hepta-coordinated iron (III) complex, respectively.Figure optionsDownload full-size imageDownload as PowerPoint slide