Wirelike Dinuclear Ruthenium Complexes Connected by Bis(ethynyl)oligothiophene

Preparation and characterization of a series of rodlike binuclear ruthenium polyynediyl complexes capped with redox-active organometallic fragments [(bph)(PPh3)2Ru]+ (bph = N-(benzoyl)-N‘-(picolinylidene)-hydrazine) or [(Phtpy)(PPh3)2Ru]2+ (Phtpy = 4‘-phenyl-2,2‘:6‘,2‘ ‘-terpyridine) have been carried out. The length of the molecular rods is extended by successive insertion of 2,5-thiophene or 1,4-phenylene spacers in the bridging ligands. Oxidation of thiophene-containing Ru2II,II complexes induces isolation of stable Ru2II,III or Ru2III,III species. Electrochemical and UV−vis−NIR spectral studies demonstrate that the polyynediyl bridges with 2,5-thiophene units are more favorable for metal−metal charge transfer compared with those containing the same number of 1,4-phenylene units. Successive increase of thiophene spacers in mixed-valence complexes {RuII}−C⋮C(C4H2S)mC⋮C−{RuIII} (m = 1, 2, 3) induced a smooth transition from almost electronic delocalization (m = 1) to localization (m = 3). For binuclear ruthenium complexes with intramolecular electron transfer transmitted across nine Ru−C and C−C bonds, electronic conveying capability follows {Ru}−C⋮C(C⋮C)2C⋮C−{Ru} > {Ru}−C⋮C(C4H2S)C⋮C−{Ru} > {Ru}−C⋮C(C6H4)C⋮C−{Ru} > {Ru}−C⋮C(CHCH)2C⋮C−{Ru}. It is revealed that molecular wires capped with electron-rich (bph)(PPh3)2Ru endgroups are much more favorable for electronic communication than the corresponding electron-deficient (Phtpy)(PPh3)2Ru-containing counterparts. The intermetallic electronic communication is fine-tuned by modification of both the bridging spacers and the ancillary ligands.