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

Abstract

A series of ruthenium acetylide complexes [Ru­(BPI)­(PPh₃)₂(CCR)] (BPI = 1,3-bis­(2-pyridylimino)­isoindolate; R = −C₆H₅ (<b>2</b>), −Cp₂Fe (<b>3a</b>), −C₆H₄C₆H₄CCCp₂Fe (<b>3b</b>)) and bis­(acetylide)-linked binuclear ruthenium complexes [{Ru­(BPI)­(PPh₃)₂}₂(CCRCC)] (R = none (<b>4</b>), 1,4-benzenediyl (<b>5</b>), 1,4-naphthalenediyl (<b>6</b>), 9,10-anthracenediyl (<b>7</b>)) 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 <b>3</b>–<b>7</b> with 1 equiv of ferrocenium perchlorate afforded the corresponding one-electron-oxidized complexes <b>3</b>⁺–<b>7</b>⁺. In contrast to the case for <b>3a</b>^<b>+</b>, where spin density is localized at the Fe center due to moderate electronic communication between Ru^II and Fe^III centers along the Ru–CC–Cp₂Fe backbone, the spin density is primarily populated on Ru for <b>3b</b>^<b>+</b> without an appreciable electronic interaction between Ru^III and Fe^II across the quite long bridging system RuCCC₆H₄C₆H₄CCCp₂Fe. For bis­(acetylide)-linked binuclear ruthenium complexes <b>4</b>–<b>7</b>, 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. <b>4</b>⁺ displays highly electronically delocalized behavior, whereas <b>5</b>⁺–<b>7</b>⁺ are on the borderline of electronic delocalization