Electrochemical, Spectroscopic, and Theoretical Studies on Diethynyl Ligand Bridged Ruthenium Complexes with 1,3-Bis(2-pyridylimino)isoindolate

A series of ruthenium acetylide complexes [Ru­(BPI)­(PPh3)2(CCR)] (BPI = 1,3-bis­(2-pyridylimino)­isoindolate; R = −C6H5 (2), −Cp2Fe (3a), −C6H4C6H4CCCp2Fe (3b)) and bis­(acetylide)-linked binuclear ruthenium complexes [{Ru­(BPI)­(PPh3)2}2(CCRCC)] (R = none (4), 1,4-benzenediyl (5), 1,4-naphthalenediyl (6), 9,10-anthracenediyl (7)) were synthesized and characterized by ESI-MS spectrometry, IR, 1H and 31P NMR, and UV–vis–near-IR spectroscopy, and cyclic and differential pulse voltammetry. Oxidation of 3–7 with 1 equiv of ferrocenium perchlorate afforded the corresponding one-electron-oxidized complexes 3+–7+. In contrast to the case for 3a+, where spin density is localized at the Fe center due to moderate electronic communication between RuII and FeIII centers along the Ru–CC–Cp2Fe backbone, the spin density is primarily populated on Ru for 3b+ without an appreciable electronic interaction between RuIII and FeII across the quite long bridging system RuCCC6H4C6H4CCCp2Fe. For bis­(acetylide)-linked binuclear ruthenium complexes 4–7, electrochemical, UV–vis–near-IR spectral and TD-DFT computational studies reveal that electronic delocalization along the bridging RuCCRCCRu backbone is highly dependent on the R spacer. It is demonstrated that with the gradual increase of a π-conjugated system in aromatic R spacer, the electronic delocalization shows progressive enhancement along the Ru–CCRCC–Ru backbone due to an increasing participation of the bridging ligand. 4+ displays highly electronically delocalized behavior, whereas 5+–7+ are on the borderline of electronic delocalization.