Aryl Group Transfer from Tetraarylborato Anions to an Electrophilic Dicopper(I) Center and Mixed-Valence μ-Aryl Dicopper(I,II) Complexes

The synthesis of discrete, cationic binuclear mu-aryl dicopper complexes [Cu-2(mu-eta(1):eta(1)-Ar)DPFN]X (Ar = C6H5, 3,5-(CF3)(2)C6H3, and C6F5; DPFN = 2,7-bis(fluoro-di(2-pyridy1)methyl)-1,8-naphthyridine; X = BAr4- and NTf2-; Tf = SO2CF3) was achieved by treatment of a dicopper complex [Cu-2(mu-eta(1):eta(1)-NCCH3)DPFN]X-2 (X = PF6- and NTf2-) with tetraarylborates. Structural characterization revealed symmetrically bridging aryl groups, and H-1 NMR spectroscopy evidenced the same structure in solution at 24 degrees C. Electrochemical investigation of the resulting arylcopper complexes uncovered reversible redox events that led to the synthesis and isolation of a rare mixed-valence organocopper complex [Cu-2(mu-eta(1):eta(1)--Ph)DPFN](NTf2)(2) in high yield. The solid-state structure of the mixed-valence mu-phenyl complex exhibits inequivalent copper centers, despite a short Cu center dot center dot center dot Cu distance. Electronic and variable-temperature electron paramagnetic resonance spectroscopy of the mixed-valence mu-phenyl complex suggest that the degree of spin localization is temperature-dependent, with a high degree of spin localization observed at lower temperatures. Electronic structure calculations agree with the experimental results and suggest that the spin is localized almost entirely on one metal center.