Noninnocent ligand behavior in diruthenium complexes containing a 1,3-diethvnvlbenzene bridge

The electronic structures of 1,3-{trans-Cl(dppe)₂RuC≡C} ₂C₆H₄ (3) and 1, 3 - {Cp*(dppe) RuC≡C}₂C₆H₄ (4) in their available redox states have been investigated using a combination of UV- vis-near-IR and IR spectroscopy and computational methods. In contrast to the case for closely related iron compounds, for the ruthenium complexes 3 and 4 the bridging aryl moiety is heavily involved in the oxidation process, and consequently descriptions of the electronic structures and electronic transitions in terms of the language developed for mixed-valence systems with clearly identifiable metal oxidation states are not appropriate. Consequently, the unique low-energy (near-IR) absorption bands observed for the asymmetric cations [3]⁺ and [4]⁺ are better described as arising from charge transfer transitions from a metal acetylide donor to a metalphenylacetylide acceptor rather than in terms of IVCT transitions.