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

Abstract

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