Rhenium(i) sapphyrins: Remarkable difference between the C₆F₅ and CF₃-substituted derivatives

Despite sapphyrins being the first ever reported extended porphyrins, their coordination chemistry remains quite limited. The newly gained access to meso-alkyl-substituted sapphyrins encouraged the study of their rhenium chelates in comparison with meso-aryl-substituted derivatives. Both the CF₃- and C₆F₅-substituted sapphyrins act as bidentate/monoanionic ligands, with the coordination sphere of the rhenium(i) ion completed by three carbonyls. Three pyrrole moieties are not involved in metal binding and all were disclosed to be "normal" with their N atoms within the macrocycle's core of the C₆F₅-substituted sapphyrin, while in the CF₃-substituted sapphyrin one pyrrole ring is "inverted" with its N atom on the periphery. These structural differences are demonstrated to affect both the optical and electrochemical properties of the Re(i) sapphyrins.