Axial ligand exchange of iron(III) tetramesitylporphyrin phenolate complexes

The axial ligand of a series of iron(III) 5,10,15,20-tetramesitylporphyrin phenolate complexes was found to exchange with added carboxylic acids and alcohols. The rates of axial ligand exchange with carboxylic acids were found to be dependent on acidity of the carboxylic acid, basicity of the phenolate, and the steric bulk of both the carboxylic acid and the phenolate axial ligand. The rates of axial ligand exchange with alcohols were found to be dependent on the nucleophilicity of the alcohol, leaving group ability of the phenolate, and the steric bulk of both the alcohol and the phenolate axial ligand. Different mechanisms for ligand exchange are proposed for carboxylic acids and alcohols.