Diruthenium Complexes with π‑Extended Bridging Bis(alkenyl)arylene Ligands, A Derived Metallamacrocycle, and Their Oxidized Forms

We report on dinuclear alkenylruthenium complexes with
π-extended trans,trans-distyrylbenzene
(1-V) or 1,4-(2-phenylethynyl)­benzene (1-A) linkers akin
to oligophenylvinylene and oligophenylethynylene oligomers (OPV-3
and OPE-3, respectively) and the macrocylic analogue 2-A. All compounds were characterized by NMR spectroscopy and high-resolution
ESI-MS. Their electrochemical and spectroscopic properties were examined.
The efficacy of intramolecular through-bond electron transfer in their
mixed-valent, one-electron-oxidized radical cations was probed by
UV/vis/NIR and EPR spectroscopy as well as by density functional theory
calculations. The terminally appended diruthenium tags of the present
compounds add IR spectroscopy to the available toolbox and provide
resolved hyperfine splittings to the 31P nuclei in the
EPR spectra of their one- and two-electron-oxidized radical cations
and dications. Our results indicate charge localization on one {Ru}–CHCHAr
site on the IR time scale for [1-A]•+ and [2-A]••2+ and a small
degree of charge delocalization in [1-V]•+. On the slower time scale of EPR spectroscopy, [1-V]•+ and [1-A]•+ become
valence-detrapped or nearly so. The near breakdown of electronic coupling
on fast time scales is also indicated by the finding that the chromophores
present in [1-V]•+ and [1-V]2+, in [1-A]•+ and [1-A]2+, and in [2-A]••2+ and [2-A]4+ are mutually identical.