Synthesis and characterizations of a phenolato coordinate gallium(III) porphyrin: A metalloporphyrin with stabilized axial ligand bonding

Abstract

To obtain stable metal–ligand bonding in metalloporphyrins, a phenolato-coordinated gallium(III) porphyrin (Ga³⁺Por) was designed, synthesized, and characterized. The strategy behind this chemistry is that the hard acid Ga³⁺ forms a stable bond with the hard base phenolato, PhO⁻. The title complex was synthesized through a dehydration reaction between phenol and the hydroxo complex of Ga³⁺Por. The stability of the Ga-O coordination bond facilitates the detection of the parent ion signal in atmospheric pressure chemical ionization mass spectrometry, as well as in conventional experimental techniques, such as recrystallization from a hot solvent under ambient conditions. Single-crystal diffraction studies revealed that the coordination geometry of the ligand resulted in a five-coordinate Ga³⁺Por. In addition to the usual spectroscopic studies, including absorption and emission spectra, electrochemical analyses were also performed. The positively shifted oxidation potential can be explained by the incorporation of gallium, which has an insufficient shielding effect because of its filled d-electrons.