Synthesis, Structure, Spectroscopic, and Electrochemical Properties of Highly Fluorescent Phosphorus(V)–meso-Triarylcorroles



The synthesis, spectroscopic, and electrochemical properties of seven new PVmeso-triarylcorroles (17) are reported. Compounds 17 were prepared by heating the corresponding free-base corroles with POCl3 at reflux in pyridine. Hexacoordinate PV complexes of meso-triarylcorroles were isolated that contained two axial hydroxy groups, unlike the PV complex of 8,12-diethyl-2,3,7,13,17,18-hexamethylcorrole, which was pentacoordinate, or the PV complex of meso-tetraphenylporphyrin, which was hexacoordinate with two axial chloro groups. 1H and 31P NMR spectroscopy in CDCl3 indicated that the hexacoordinated PVmeso-triarylcorroles were prone to axial-ligand dissociation to form pentacoordinated PVmeso-triarylcorroles. However, in the presence of strongly coordinating solvents, such as CH3OH, THF, and DMSO, the PVmeso-triarylcorroles preferred to exist in a hexacoordinated geometry in which the corresponding solvent molecules acted as axial ligands. X-ray diffraction of two complexes confirmed the hexacoordination environment for PVmeso-triarylcorroles. Their absorption spectra in two coordinating solvents revealed that PVmeso-triarylcorroles showed a strong band at about 600 nm together with other bands, in contrast to PV–porphyrins, which showed weak bands in the visible region. These compounds were easier to oxidize and more difficult to reduce compared to PV–porphyrins. These compounds were brightly fluorescent, unlike the weakly fluorescent PV–porphyrins, and the quantum yields for selected PV–corroles were as high as AlIII and GaIII corroles, which are the best known fluorescent compounds among oligopyrrolic macrocycles.