Synthesis, structure, spectral 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 POCl₃ 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. ¹H and ³¹P NMR spectroscopy in CDCl₃ 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 CH₃OH, 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.