Electrocatalytic oxygenation of alkenes by a sterically hindered water-soluble iron porphyrin in aqueous solutions

Iron(III) tetrakis(N-methyl-2-pyridyl)porphyrin (Fe-III(2-TMPyP)) undergoes one-electron electro-oxidation to form O=Fe-IV(2-TMPyP) and O=Fe-IV(2-TMPyP)(OH) in pH 9.0 and 14.0 solutions respectively. A series of water-soluble carboxylic alkenes was used as substrates to investigate the catalytic reactivity and selectivity of the iron porphyrin. Both oxo-ferryl porphyrins oxidized alkenes via a pathway of allylic hydrogen abstraction. Molecular oxygen is also involved and the final product was identified to be an ene-one. The spectroelectrochemical method has indicated that the axial hydroxide ligand weakens the oxo-ferryl bond and facilitates the chemical reaction.