Oxidative catalytic evolution of redox- and spin-states of a Fe-phthalocyanine studied by EPR

Highlights: ⿢EPR spectroscopy reveals that under oxidative catalysis Fe-phthalocyanine evolves via multiple redox/spin paths. ⿢Low-spin [Fe-imidazole] states evolve faster than high-spin Fe states. ⿢[Bis-Imidazole Fe-phthalocyanine] is catalytically inactive. The catalytic-oxidative evolution of the redox/spin states of a Fe-phthalocyanine (Fe-Pc) catalyst was studied by electron paramagnetic resonance spectroscopy. Under oxidative catalytic conditions, Fe-Pc may evolve via multiple redox/spin conformations. Axial ligation of imidazole, O₂ or t-Bu-OOH as oxidant, results in a complex multipath redox/spin landscape that was determined in detail herein. The high-spin conformations of Fe-Pc/imidazole evolve more slowly than the low-spin conformations. Catalytically active vs. inactive conformations were distinguished. A unified physicochemical catalytic reaction mechanism is discussed herein based on the distinct role of the various structural, spin and redox forms.