Electron-Rich Diruthenium Complexes with π-Extended Alkenyl Ligands and Their F4 TCNQ Charge-Transfer Salts.

Abstract

The synthesis of dinuclear ruthenium alkenyl complexes with {Ru(CO)(P i Pr3)2(L)} entities (L=Cl− in complexes Ru2‐3 and Ru2‐7; L=acetylacetonate (acac−) in complexes Ru2‐4 and Ru2‐8) and with π‐conjugated 2,7‐divinylphenanthrenediyl (Ru2‐3, Ru2‐4) or 5,8‐divinylquinoxalinediyl (Ru2‐7, Ru2‐8) as bridging ligands are reported. The bridging ligands are laterally π‐extended by anellating a pyrene (Ru2‐7, Ru2‐8) or a 6,7‐benzoquinoxaline (Ru2‐3, Ru2‐4) π‐perimeter. This was done with the hope that the open π‐faces of the electron‐rich complexes will foster association with planar electron acceptors via π‐stacking. The dinuclear complexes were subjected to cyclic and square‐wave voltammetry and were characterized in all accessible redox states by IR, UV/Vis/NIR and, where applicable, by EPR spectroscopy. These studies signified the one‐electron oxidized forms of divinylphenylene‐bridged complexes Ru2‐7, Ru2‐8 as intrinsically delocalized mixed‐valent species, and those of complexes Ru2‐3 and Ru2‐4 with the longer divinylphenanthrenediyl linker as partially localized on the IR, yet delocalized on the EPR timescale. The more electron‐rich acac− congeners formed non‐conductive 1 : 1 charge‐transfer (CT) salts on treatment with the F4TCNQ electron acceptor. All spectroscopic techniques confirmed the presence of pairs of complex radical cations and F4TCNQ.− radical anions in these CT salts, but produced no firm evidence for the relevance of π‐stacking to their formation and properties.