Abstract
The reaction between (tbbpy)~2~Ru(tmbiH~2~)~2~ (tbbpy = 4,4′‐di‐tert‐butyl‐2,2′‐bipyridine; tmbiH~2~ = 5,5′,6,6′‐tetramethyl‐2,2′‐dibenzimidazole) and LiMe/CuI affords the tetranuclear complex 1 containing the dication [{(tbbpy)~2~Ru(tmbi)}~2~Cu~2~]^2+^. The X‐ray structure of 1 shows that the two [(tbbpy)~2~Ru(tmbi)] units coordinate the two Cu atoms in a twofold monodentate manner. Each copper atom is surrounded by two N‐donor atoms of different ruthenium(II) units with N–Cu–N angles of 167.3°. The Cu···Cu separation (2.72 Å) indicates intranuclear contacts. LiMe/[(allyl)PdCl]~2~ reacts with the starting Ru complex to form 2, which contains the tetranuclear dication [{(tbbpy)~2~Ru(tmbi)}~2~{Pd(η^3^‐allyl)}~2~]^2+^. Its crystal structure shows that the Ru^II^ units act as twofold monodentate ligands as well. Each Pd^II^ is in an essentially planar coordination environment containing two nitrogen atoms of two different dibenzimidazolates in the cis position with the η^3^‐bonded allyl group occupying the two remaining positions. In contrast to 1, where the Ru–Cu–Cu–Ru unit forms an essentially planar structure, a strongly bent structure is formed in compound 2. ESI mass spectra of 1 and 2 clearly show that the tetranuclear complexes are present in solution as well. Both complexes are luminescent. In addition, 2 catalyses the Heck coupling at 120 °C in N,N‐dimethylacetamide. In contrast to 1 and 2, the homodinuclear complex [(tbbpy)~2~Ru(tmbi)Ru(tbbpy)~2~] (3) contains the dibenzimidazolate as a twofold chelating ligand that forms two five‐membered chelate rings with the Ru centres. Electrochemical measurements of 2 show two reversible, one‐electron oxidation steps, the difference between which (Δ__E__ = 89 mV) is distinctly larger than the pure entropic effect. Furthermore, four reduction steps are observed, the first two of which are fully reversible. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)