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+ .