Homodinuclear Complexes Of [Cu(Dppf)](+) Or [Ru(Bpy)(2)](2+) With 1,4-Bis(Camphorquinoneimino)Benzene (Bcqb) As A Redox-Active Bridging Ligand

The product mu-bcqb from the reaction between p-phenylenediamine and two equivalents of camphorquinone has been used as a potentially conjugated molecular bridge between two complex fragments [Cu(dppf)](+), dppf=1,1'-bis(diphenylphosphino)ferrocene, to yield 1(2+), and between two [Ru(bpy)(2)](2+) moieties, resulting in 2(4+). The molecular structure of 1(BF4)(2) shows an intramolecular Cu-Cu distance of 8.04 angstrom and a torsionally twisted conformation of the bridge, while cyclic voltammetry, EPR, IR and UV-vis-NIR spectroelectrochemistry reveal two closely spaced one-electron reductions and a ferrocene-based two-electron oxidation. Compound 2(PF6)(4) exhibits at least three one-electron reduction waves and one 2e-oxidation, the former attributed to mu-bcqb and the latter assigned to metal-based processes showing no evidence for a Ru-Ru mixed-valent intermediate. However, intra-ligand based mixed valency with intense LLIVCT absorptions in the near infrared was observed for the metal coordinated mu-bcqb(.-) and mu-bcqb(.3-) bridges. The two examples 1(n+) and 2(n+) illustrate that a combination of physical methods is advantageous to analyze and define the correct electronic structures in complexes involving several metal centers and noninnocent ligand components.