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 μ-aryl dicopper complexes [Cu2(μ-η(1):η(1)-Ar)DPFN]X (Ar = C6H5, 3,5-(CF3)2C6H3, and C6F5; DPFN = 2,7-bis(fluoro-di(2-pyridyl)methyl)-1,8-naphthyridine; X = BAr4(-) and NTf2(-); Tf = SO2CF3) was achieved by treatment of a dicopper complex [Cu2(μ-η(1):η(1)-NCCH3)DPFN]X2 (X = PF6(-) and NTf2(-)) with tetraarylborates. Structural characterization revealed symmetrically bridging aryl groups, and (1)H NMR spectroscopy evidenced the same structure in solution at 24 °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 [Cu2(μ-η(1):η(1)-Ph)DPFN](NTf2)2 in high yield. The solid-state structure of the mixed-valence μ-phenyl complex exhibits inequivalent copper centers, despite a short Cu···Cu distance. Electronic and variable-temperature electron paramagnetic resonance spectroscopy of the mixed-valence μ-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.