Core modified meso-aryl corrole: first examples of Cu^II, Ni^II, Co^II and Rh^I complexes

Abstract

A variety of metal complexes of 5,10,15-triphenyl-21-monooxa-corrole 4 have been investigated. This monooxa corrole, where one of the pyrrole ring is replaced by a furan moiety, is synthesized by the α-α coupling reaction of 16-oxa tripyrrane and dipyrromethane. The single crystal X-ray structure of 4 indicates only small deviation of the inner-core heteroatoms from planarity and this macrocycle arrange themselves into a columnar structure. Insertion of metals further flattens the corrole framework. Specifically, oxacorrole 4 binds to Ni^II, Cu^II, and Co^II with the participation of all heteroatoms in the coordination. However, Rh^I ion binds to only one imino and one amino nitrogen of the macrocycle. The bond angles at the metal center in the Ni^II and Rh^I complexes reveal square planar geometry completed by two CO molecules for Rh^I. The EPR spectra of the paramagnetic that Cu^II and Co^II complexes display significant decreases in the metal hyperfine couplings compared with the corresponding porphyrin complexes. The presence of superhyperfine coupling in the CuII complex suggests delocalization of unpaired electron density into the ligand orbitals. Electrochemical studies reveal easier oxidations and harder reductions relative to the corresponding porphyrin derivatives while, the metallated derivatives did not show their characteristic metal reductions due to the high energy of their LUMO.