Synthesis and catalytic activities of copper(II) complexes derived from a tridentate pyrazole-containing ligand. X-ray crystal structure of [Cu2(μ-dpzhp-O,N,N′)2][Cu(MeOH)Cl3]2

The synthesis of the new tridentate ligand 1,3-bis(3,5-dimethylpyrazol-1-yl)propan-2-ol (Hdpzhp) and a number of its copper(II) complexes are described. The complexes, which have the form [Cu2(μ-dpzhp-O,N,N′)2]X2 with X=Cu(MeOH)Cl3, NO3, and BF4, and [Cu2(μ-dpzhp-O,N,N′)(μ-OH)Cl2] have been characterized by elemental analysis, IR spectroscopy, ligand field and ESI mass spectrometry, showing the ligand to be dinucleating and to act as an N2O donor set with a bridging alkoxo group. The single-crystal X-ray structure of [Cu2(μ-dpzhp-O,N,N′)2] [Cu(MeOH)Cl3]2 shows the copper ions in the dinuclear cation in distorted square-planar environments of two oxygen and two nitrogen atoms from two different ligands with Cu–N distances of 1.932(7) to 1.992(6) Å and with Cu–O distances of 1.873(6)–1.976(6) Å. Additionally, one chlorine of each anion is semicoordinated to one of the two copper ions. Solid-state magnetic measurements show that the dinuclear unit is strongly antiferromagnetic, and paramagnetic in its CuCl3(MeOH) anions. The compound [Cu2(μ-dpzhp-O,N,N′)2](BF4)2 is catalytically active in the oxidative coupling of 2,6-dimethylphenol and leads to a high selectivity in poly(1,4-phenylene ether) (PPE) over the unwanted side product, 4-(3,5-dimethyl-4-oxo-2,5-cyclohexadienylidene)-2,6-dimethyl-2,5-cyclohexadienone.