Steric effect on the photoreaction of chromium(III) porphyrin complexes with imidazole ligands

Abstract

The steric effect in the photoreaction and ligand substitution reaction of axially coordinated imidazole ligands in chromium(III) porphyrin complexes was investigated in toluene. Imidazole ligands that have various alkyl substituents at the carbon atom [Formula: see text] to the coordinating nitrogen atom were used. The quantum yield of the photodissociation reaction of the axial imidazole ligand shows a remarkable steric effect. Reflecting the steric bulkiness, the magnitude of the quantum yield is isopropyl > ethyl > methyl > (H). The steric effect also appears in the thermal ligand substitution reactions. The mechanism of the steric effect on reactivity will be discussed in terms of the steric hindrance between the porphyrin ligand and the alkyl substituents of imidazole.