A "Pretender" Croconate-Bridged Macrocyclic Tetraruthenium Complex: Sizable Redox Potential Splittings despite Electronically Insulated Divinylphenylene Diruthenium Entities.

Careful optimization of the reaction conditions provided access to the particularly small tetraruthenium macrocycle , which is composed out of two redox-active divinylphenylene-bridged diruthenium entities {Ru}-1,4-CH=CH-CH-CH=CH-{Ru} (RuPh; {Ru} = Ru(CO)Cl(PPr)) and two likewise redox-active and potentially non-innocent croconate linkers. According to single X-ray diffraction analysis, the central cavity of is shielded by the bulky PPr ligands, which come into close contact. Cyclic voltammetry revealed two pairs of split anodic waves in the weakly ion pairing CHCl/NBuBAr (BAr = [B{CH(CF)-3,5}] electrolyte, while the third and fourth waves fall together in CHCl/NBuPF. The various oxidized forms were electrogenerated and scrutinized by IR and UV/Vis/NIR spectroscopy. This allowed us to assign the individual oxidations to the metal-organic RuPh entities within , while the croconate ligands remain largely uninvolved. The lack of specific NIR bands that could be assigned to intervalence charge transfer (IVCT) in the mono- and trications indicates that these mixed-valent species are strictly charge-localized. is hence an exemplary case, where stepwise IR band shifts and quite sizable redox splittings between consecutive one-electron oxidations would, on first sight, point to electronic coupling, but are exclusively due to electrostatic and inductive effects. This makes a true "pretender".