Water Exchange Controls the Complex-Formation Mechanism of Water-Soluble Iron(III) Porphyrins: Conclusive Evidence for Dissociative Water Exchange from a High-Pressure17O NMR Study

Abstract

The water-exchange reactions of three modified iron(III) porphyrins were studied in acidic medium as a function of temperature and pressure using 17O NMR spectroscopic techniques. The positive activation entropies and activation volumes support a dissociative mechanism (see scheme showing the transition state; L=nucleophile, H2O, NO). A comparison with available literature data reveals that the rate and mechanism of complex-formation reactions of such metal porphyrins are controlled by the water-exchange process.