Dinuclear copper(II) complexes of four new pyrazole-containing macrocyclic ligands are active catalysts in the oxidative coupling of 2,6-dimethylphenol

Four new macrocyclic ligands of varying ring size, [22]py4pz, [22]pr4pz, [18]py2pz and [20]py2pz, containing four or two endocyclic pyrazole groups, form dinuclear copper compounds. The single crystal X-ray structures of [Cu(pr2pz)(ClO4)(2)] (A), [Cu-2([22]pr4pz)Cl-4](MeOH) (B), [Cu-4([18]py2pz)(2)(mu-Cl)(4)Cl-2]Cl-2 (C) and [Cu-2([18]py2pz)(CH3CN)(4)(ClO4)(2)](ClO4)(2)(CH3CN)(1.6) (D), show the pyrazole groups and the amine nitrogens all to be involved in the coordination of the copper(II) ions. In the mononuclear compound A the copper ion is in a distorted octahedral geometry, with the equatorial plane formed by four nitrogen donor atoms from the ligand and the axial positions occupied by two oxygen atoms from mono-coordinated perchlorate anions. In compound B each copper ion is in a distorted square pyramidal environment, with the three ligand nitrogens and a chloride atom in the equatorial plane and another chloride atom in the axial position. The cation of compound C contains four copper centers. Two bridging Cl atoms connect the two central copper atoms to form a centrosymmetric four membered ring. Two macrocyclic units are present in the cation, each containing two copper atoms bridged by a chloride atom. One copper is fivefold coordinated and the second copper is distorted octahedral. In compound D both copper(II) ions are in a distorted octahedral N5O environment, with the equatorial plane formed by the three ligand nitrogens and a nitrogen from an acetonitrile molecule. A second acetonitrile molecule and a mono-coordinated perchlorate anion are weakly bound in the axial positions. The copper nitrate compounds of these new ligands are to some degree active catalysts in the oxidative coupling of 2,6-dimethylphenol with molecular dioxygen to poly(2,6-dimethyl-1,4-phenylene ether). (C) 2003 Elsevier B.V. All rights reserved.