Synthesis and structure of copper (II) complexes with L–OH (L–OH = 2,6-bis-[N-(2-pyridylethyl)-formidoyl]-4-methyl-phenol)

The synthesis and molecular structures of three new copper (II) complexes with the ligand 2,6-bis-[N-(2-pyridylethyl)-formidoyl]-4-methyl phenol (L–OH) are reported. The complexes were prepared by reaction of L–OH with CuX2 · nH2O, affording [Cu2(L–O)(μ-OH)(μ-ClO4)](ClO4) (I); X=CLO4-, with KOH in the reaction media; or [Cu2(L–O)(μ-Cl)2][Cu2Cl6]0.5 (II); X = Cl, in neutral conditions. The presence of methyl 3,4-dihydroxy-benzoate (CAT-(OH)2) during the synthesis of I leads to the complex [Cu2(L–O)(μ-OH)(CH3OH)][Cu(CAT-O2)2]0.5(ClO4) (III). This compound exhibits an uncommon anion consisting of a bis-(catecholate) cuprate (II) moiety. The complete series of complexes show bridging phenoxo groups between the copper centers, together with hydroxo and perchlorate bridges found in I or two chlorides found in II. Compound I exhibit a rather low catalytic activity for the oxidation of 3,5-ditertbutyl catechol under aerobic conditions (12% quinone formation after 48 h at room temperature, in methanol solution 1 × 10−3 M in catalyst and 1 × 10−2 M in catechol), which could be ascribed to steric limitations of the catechol to coordinate the central Cu2O2 core.

Graphical abstractThe synthesis and molecular structure of three new copper (II) complexes: [Cu2(L–O) (μ-OH)(μ-ClO4)] (ClO4) (I), [Cu2(L–O) (μ-Cl)2][Cu2Cl6]0.5 (II) and [Cu2(L–O)(μ-OH)(CH3OH)]2[Cu(CAT-O2)2]0.5(ClO4)2 (III), with the ligand 2,6-bis-[N-(2-pyridylethyl)-formidoyl]-4-methyl phenol (L–OH) is reported. Compound I shows a very poor catecholase activity. Compounds II and III show very uncommon anions: a hexachloro dicuprate (II) and a bis-catecholate cuprate (II) moieties, respectively.Figure optionsDownload full-size imageDownload as PowerPoint slide