Syntheses, Characterization, Redox Properties, and Mixed-Valence Chemistry of Tetra- and Hexanuclear Diyndiyl Complexes

A series of RuII2FeII2 heterotetranuclear σ-acetylide complexes [{Cp(dppf)Ru}2(C⋮C−R−C⋮C)] (dppf = 1,1‘-bis(diphenylphosphino)ferrocene, R = 0, 1; 1,4-benzenediyl, 2; 1,4-naphthalenediyl, 3; 9,10-anthracenediyl, 4) were prepared and characterized by elemental
analyses, ES-MS spectrometry, IR, 1H and 31P NMR, and UV−vis−NIR spectroscopy, and
cyclic and differential pulse voltammetry. Reaction of 1 with [Cu(MeCN)4](ClO4) gave RuII2FeII2CuI2 heterohexanuclear compound [{Cp(dppf)Ru}2{Cu(MeCN)}2(C⋮C−C⋮C)](ClO4)2
[5(ClO4)2] through π-bonding of the acetylides to CuI centers. The structures of 1 and 5(ClO4)(SbF6) were determined by X-ray crystallography. Chemical oxidation of 1, 3, and 4 with an
equivalent of ferrocenium hexafluorophosphate gave one-electron-oxidized species [{Cp(dppf)Ru}2(C⋮C−R−C⋮C)](PF6) [R = 0, 1a(PF6); 1,4-naphthalenediyl, 3a(PF6); 9,10-anthracenediyl, 4a(PF6)] with Ru2II,III mixed valence. Electrochemical and visible−infrared spectral
studies revealed that the electronic delocalization depends on the R substituent in the
bridging ligand C⋮C−R−C⋮C. While the mixed-valence compound 1a(PF6) (R = 0) displays
an electronically delocalized behavior (class III mixed-valence system), 3a(PF6) (R = 1,4-naphthalenediyl) and 4a(PF6) (R = 9,10-anthracenediyl) may belong to borderline compounds
between electronic localization and delocalization.