Structure and Spectroelectrochemical Response of Arene–Ruthenium and Arene–Osmium Complexes with Potentially Hemilabile Noninnocent Ligands

Nine of the compounds [M­(L2–)­(p-cymene)] (M = Ru, Os, L2– =
4,6-di-tert-butyl-N-aryl-o-amidophenolate)
were prepared and structurally characterized (Ru complexes) as coordinatively
unsaturated, formally 16 valence electron species. On L2–-ligand based oxidation to EPR-active iminosemiquinone radical complexes,
the compounds seek to bind a donor atom (if available) from the N-aryl substituent, as structurally certified for thioether
and selenoether functions, or from the donor solvent. Simulated cyclic
voltammograms and spectroelectrochemistry at ambient and low temperatures
in combination with DFT results confirm a square scheme behavior (ECEC
mechanism) involving the Ln ligand as
the main electron transfer site and the metal with fractional (δ)
oxidation as the center for redox-activated coordination. Attempts
to crystallize [Ru­(Cym)­(QSMe)]­(PF6) produced
single crystals of [RuIII(QSMe•–)2]­(PF6) after apparent dissociation of the
arene ligand.