Noninnocent Ligand Behavior in Diruthenium Complexes Containing a 1,3-Diethynylbenzene 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 metal phenylacetylide acceptor rather than in terms of IVCT transitions.