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

Abstract

Four new macrocyclic ligands of varying ring size, [22] (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 N 5 O 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). #

Catecholase Activity of a Copper(II) Complex with a Macrocyclic Ligand: Unraveling Catalytic Mechanisms

“…However, it is liable that in the course of the catalytic reaction the original dicopper(II) core undergoes substantial modification, as the carbonate bridge is likely to be cleaved by the incoming catecholate, as proposed in Scheme 1. Our earlier studies on other dicopper complexes with structurally related macrocyclic ligands [38,39] indicate that the macrocyclic cavity has a sufficient flexibility to bring two copper ions within a short distance of each other, required for a didentate bridging coordination mode of catechol. As a result, in the absence of the rigid carbonate bridge the substrate can bind to both copper(II) ions in a bridging fashion, pushing the catalytic reaction towards the cycle B, whereas the relative influence of mechanistic pathway A becomes negligible after a few minutes of the reaction.…”

“…The macrocyclic ligand [22]pr4pz was synthesized as previously described. [38] The single crystals of [H 2 [22]pr4pz]A C H T U N G T R E N N U N G (ClO 4 ) 2 suitable for X-ray crystal structure determination were obtained by diffusion of diethyl ether into a solution containing one equivalent of [22]pr4pz and two equivalents of perchloric acid in methanol. The solution ligand-field spectra were recorded on a Varian Cary 50 Scan UV/Vis spectrophotometer and on a Zeiss MCS500 Diode-Array spectrometer (l = 0.5 cm).…”

Aerobic Copper-Catalyzed Organic Reactions

“…767 The tetradentate X4 forms a binuclear complex that gives PPE in 80% conversion from 2,6-dimethylphenol. 768 While the steric bulk around X5 increases the reaction rate, it is not as effective as N -methylimidazole. 769 Similarly, the bidentate X6 benefits from steric bulk, but the conversion to PPE is less than 50%.…”

Catalytic Applications of Pyridine‐Containing Macrocyclic Complexes

“…These complexes were competent catalysts for the oxidative coupling of 2,6‐dimethylphenol (DMP). Full conversion of the substrate was never observed, probably because of the formation of inactive copper hydroxide species …”