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

• Published in: Chemistry, an Asian journal an Asian journal, 2013-01, Vol.8 (1), p.138-147
• Main Authors: Wu, Si-Hai, Shen, Jun-Jian, Yao, Jiannian, Zhong, Yu-Wu
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Chemistry; cyclometalation; ferrocene; mixed-valent compounds; redox-active compounds; ruthenium
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.201200900

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 12+, 22+, and 32+ in the near‐infrared region. Hush analysis showed that the metal–metal electronic couplings in compounds 12+ and 32+ were much stronger than those in compound 22+. Penny mix: Three bis‐tridentate ferrocene‐containing cyclometalated ruthenium complexes have been prepared and characterized, in which the ferrocene units are either substituted on the NNN ligand, on the NCN ligand, or on both sides. A combined experimental and computational study has shown that the electronic coupling between the iron and ruthenium sites is strongly dependent on the connection mode between the two redox‐active centers.