A Fully Charge-Delocalized Two-Dimensional Porphyrin System with Two Different Class III States

Understanding of charge-delocalization over two-dimensional (2D) frameworks is a further step in the path towards the development of molecular nanodevices and nanomaterials. Here, we report a porphyrin-nickel complex with four peripheral redox-active ruthenium pendants (1). A cyclic voltammogram of compound 1 displays reversible five-electron, four redox waves with large potential separations, suggesting that one-electron- (1⁺ ) and two-electron-oxidized species (1²⁺ ) are thermodynamically stable with respect to disproportionation. The paramagnetic one-electron-oxidized species 1⁺ prepared by a comproportionation reaction of compounds 1 and 1²⁺ , turns out to be a highly charge-delocalized two-dimensional class III compound as clearly indicated by its characteristic intervalence charge-transfer (IVCT) band as is further supported by IR and ESR spectroscopy as well as DFT and time-dependent (TD) DFT calculations. Furthermore, the diamagnetic dicationic species 1²⁺ has a spin-paired electronic structure with a fully charge-averaged class III character. The substantial contribution of the cumulenic structures to compound 1²⁺ is confirmed by ¹³ C NMR and IR spectroscopy as well as X-ray structure analyses. Such unique electronic features of the 2D systems provide a clue to development of nanoscale molecular devices.