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

Rotthowe, Nils; Linseis, Michael; Vogelsang, Lars; Orth, Nicole; Ivanovic-Burmazovic, Ivana und Winter, Rainer F. (2021): A Pretender Croconate-Bridged Macrocyclic Tetraruthenium Complex: Sizable Redox Potential Splittings despite Electronically Insulated Divinylphenylene Diruthenium Entities. In: Molecules, Bd. 26, Nr. 17, 5232

Abstract

Careful optimization of the reaction conditions provided access to the particularly small tetraruthenium macrocycle (Ru2Ph)-Ru-2-Croc, which is composed out of two redox-active divinylphenylene-bridged diruthenium entities {Ru}-1,4-CH=CH-C6H4-CH=CH-{Ru} (Ru2Ph;{Ru} = Ru(CO)Cl((PPr3)-Pr-i)(2)) and two likewise redox-active and potentially non-innocent croconate linkers. According to single X-ray diffraction analysis, the central cavity of (Ru2Ph)-Ru-2-Croc is shielded by the bulky (PPr3)-Pr-i ligands, which come into close contact. Cyclic voltammetry revealed two pairs of split anodic waves in the weakly ion pairing CH2Cl2/NBu4BAr24F (BAr24F = [B{C6H3(CF3)(2)-3,5}(4)](-) electrolyte, while the third and fourth waves fall together in CH2Cl2/NBu4PF6. 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 Ru2Ph entities within (Ru2Ph)-Ru-2-Croc, 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. (Ru2Ph)-Ru-2-Croc 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 (Ru2Ph)-Ru-2-Croc a true pretender.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Chemie und Pharmazie
• Themengebiete: 500 Naturwissenschaften und Mathematik > 540 Chemie
• Sprache: Englisch