Asymmetric Mixed‐Valence Complexes that Consist of Cyclometalated Ruthenium and Ferrocene: Synthesis,Characterization, and Electronic‐Coupling Studies

Three bis‐tridentate ferrocene‐containing cyclometalated ruthenium complexes, (Fcdpb)Ru(tpy)]⁺ ( 1 ⁺), (Fctpy)Ru(dpb)]⁺ ( 2 ⁺), and (Fcdpb)Ru(Fctpy)]⁺ ( 3 ⁺), have been prepared and characterized, where Fcdpb is the 2‐deprotonated form of 1,3‐di(2‐pyridyl)‐5‐ferrocenylbenzene, tpy is 2,2′:6′,2“‐terpyridine, dpb is the 2‐deprotonated form of 1,3‐di(2‐pyridyl)benzene, and Fctpy is 4′‐ferrocenyl‐2,2′:6′,2”‐terpyridine. Single crystals of compounds 2 ⁺ and 3 ⁺ have been studied by X‐ray analysis. Complexes 1 ⁺ and 2 ⁺ displayed two anodic redox waves, whilst three well‐separated redox couples were observed for compound 3 ⁺. A combined experimental and computational study suggested that the ferrocene unit on the Fcdpb moiety in compounds 1 ⁺ and 3 ⁺ was oxidized first. In contrast, the order of the oxidation of ruthenium and ferrocene in complex 2 ⁺ was reversed. Metal‐to‐metal‐charge‐transfer transitions (MM′CT) have been observed for the singly oxidized states 1 ²⁺, 2 ²⁺, and 3 ²⁺ in the near‐infrared region. Hush analysis showed that the metal–metal electronic couplings in compounds 1 ²⁺ and 3 ²⁺ were much stronger than those in compound 2 ²⁺.