Electron-Rich Diruthenium Complexes with π-Extended Alkenyl Ligands and Their F 4 TCNQ Charge-Transfer Salts.

The synthesis of dinuclear ruthenium alkenyl complexes with {Ru(CO)(P i Pr 3 ) 2 (L)} entities (L=Cl - in complexes Ru 2 -3 and Ru 2 -7; L=acetylacetonate (acac - ) in complexes Ru 2 -4 and Ru 2 -8) and with π-conjugated 2,7-divinylphenanthrenediyl (Ru 2 -3, Ru 2 -4) or 5,8-divinylquinoxalinediyl (Ru 2 -7, Ru 2 -8) as bridging ligands are reported. The bridging ligands are laterally π-extended by anellating a pyrene (Ru 2 -7, Ru 2 -8) or a 6,7-benzoquinoxaline (Ru 2 -3, Ru 2 -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 Ru 2 -7, Ru 2 -8 as intrinsically delocalized mixed-valent species, and those of complexes Ru 2 -3 and Ru 2 -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 F 4 TCNQ electron acceptor. All spectroscopic techniques confirmed the presence of pairs of complex radical cations and F 4 TCNQ .- radical anions in these CT salts, but produced no firm evidence for the relevance of π-stacking to their formation and properties.