Access to Well-Defined Dimeric Formally Copper(III) Pyrazolates and XPS Characterization of Dicopper(III) Trifluoromethyl Complexes

Treatment of the copper(III) heterocubane [Cu(CF3)2(OH)]4 with pyrazoles under mild conditions resulted in the formation of dimeric copper(III) pyrazolates (F3C)2Cu(μ2-Pz)2Cu(CF3)2·3MeCN and (F3C)2Cu(μ2-Pz)2Cu(CF3)2·H2O. The structures of these complexes and their substituted 4-chloro- and 4-nitropyrazolate analogs have been unambiguously confirmed by X-ray crystallography and characterized by NMR and IR spectroscopy. Irradiation of pyrazolate with a blue LED results in trifluoromethyl group transfer to the ortho-position of the pyrazole ring furnishing 3-trifluoromethylpyrazole. The high oxidation state of copper in the entire family of cubane-derived dimeric Cu(III) trifluoromethyl complexes is supported by XPS spectroscopy. A Cu 2p3/2 binding energy range of 935–937 eV is characteristic of the Cu(III) oxidation state, which corroborated the spectrum obtained for the O-donor copper(III) tellurate complex [Cu(H2TeO6)2]5– devoid of covalent copper–carbon bonds.