COPPER(II) AND COPPER(I) COMPLEXES STABILIZED BY PHOSPHINE OXIDES - SYNTHESIS AND CHARACTERIZATION OF THE CATIONIC COMPLEXES [CU(ODPPF)(2)(ETOH)](2+) AND [CU(ODPPF)(2)](2+), PRECURSORS OF THE NOVEL COPPER(I) ADDUCT [CU(ODPPF)(2)](+) (ODPPF=1,1'-BIS(OXODIPHENYLPHOSPHORANYL)FERROCENE) - CRYSTAL-STRUCTURE OF [CU(ODPPF)(2)(ETOH)](BF4)(2) AND [CU(ODPPF)(2)](BF4)(2)

The ferrocenylbis(phosphine) dioxide complexes [Cu(odppf)(2)(EtOH)](BF4)(2) (1) and [Cu(odppf)(2)](BF4)(2) (2) (odppf = 1,1'-bis(oxodiphenylphosphoranyl)ferrocene have been prepared and characterized in the solid state by X-ray analysis and in solution by a combination of ESR, visible, and LR-spectroscopies and electrochemical techniques. The complexes crystallize in the monoclinic system, space group P2(1)/c, with Z = 4, and a = 19.484(2) and 12.325(2) Angstrom, b = 13.450(2) and 33.137(3) Angstrom, c = 25.477(2) and 17.608(2) Angstrom, and beta = 93.9(1) and 108.7(2)degrees, far complexes 1 and 2, respectively. In the cations the four O atoms of two odppf ligands are directly bonded to the metal center with Cu-O distances ranging from 1.92 to 2.076 Angstrom. In complex 1 the metal is pentacoordinate with the five donor atoms at the vertices of a distorted trigonal bipyramid formed by two chelated odppf moyeties and one molecule of ethanol, occupying an equatorial position, as the fifth ligand. In complex 2 the coordination geometry around the metal atom is distorted square-planar with the two odppf moieties acting as chelating ligands with a bite angle of about 153 degrees. The lability of EtOH ligand allows complex 1 to be easily and reversibly converted into complex 2 upon dissolution in noncoordinating solvents. ESR data in frozen solution of 1 in ethanol and of 2 in dichloroethane point to the confirmation of the Square-planar stereochemistry for complex 2 and to the conversion of the trigonal-bipyramidal structure of 1 into a square-pyramidal one. ESR parameters clearly indicate that ca 95% of the unpaired electron resides in the metal center, thus revealing a scarcely covalent character of the Cu-II-O bonds. A single well-defined oxidation process involving the two ferrocene cores has been detected by cyclic voltammetry for complex 2 in dichloroethane, while two discrete single electron reductions centered on the copper atom were observed under the same conditions. The one-electron reduction product was identified as the remarkable species [Cu(odppf)(2)](+) (3) which, although extremely reactive toward dioxygen, turned out to be quite stable toward valence disproportionation in aprotic solvents.