Nonheme Iron Catalyst Selectively Activates Oxygen to Hydrogen Peroxide.

Area of Science:

• Coordination Chemistry
• Catalysis
• Electrochemistry

Background:

• Iron complexes exhibit high reactivity in the oxygen reduction reaction (ORR).
• ORR can proceed via two pathways: 2e-/2H+ to H2O2 or 4e-/4H+ to H2O.
• Selective ORR catalysis remains a significant challenge in chemistry.

Purpose of the Study:

• To design and synthesize novel iron complexes with secondary coordination sphere interactions.
• To investigate the influence of these interactions on ORR selectivity.
• To explore the catalytic activity and reaction mechanisms of the designed complexes.

Main Methods:

• Synthesis of two novel iron complexes: [Py2Py-(afaCy)2Fe]-OTf2 and [N-(afaCy)3Fe]-OTf2.
• Evaluation of catalytic activity using decamethylferrocene as a reductant.
• Monitoring reaction progress via absorbance spectroscopy and kinetic measurements.

Main Results:

• [Py2Py-(afaCy)2Fe]-OTf2 showed ORR selectivity similar to iron porphyrins but with slower kinetics.
• [N-(afaCy)3Fe]-OTf2 demonstrated exceptional selectivity for the 2e-/2H+ pathway, producing hydrogen peroxide.
• Kinetic analysis indicated second-order kinetics for [N-(afaCy)3Fe]-OTf2 with a rate constant of 81 mM-1 s-1.

Conclusions:

• Secondary coordination sphere interactions can effectively tune ORR selectivity in iron complexes.
• [N-(afaCy)3Fe]-OTf2 represents a rare example of a nonheme iron complex with high 2e-/2H+ ORR selectivity.
• The proposed rate-determining step involves electron transfer and proton transfer processes, followed by peroxide dissociation.