O atom transfer from nitric oxide catalyzed by Fe(TPP).

Area of Science:

• Inorganic chemistry
• Organometallic chemistry
• Reaction mechanisms

Background:

• Nitrosyl iron porphyrins (NO-Fe(TPP)) are important in coordination chemistry.
• Understanding the reaction pathways of NO-Fe(TPP) with nitric oxide (NO) is crucial for catalytic applications.

Purpose of the Study:

• To elucidate the reaction mechanism of NO-Fe(TPP) with low pressures of NO gas.
• To identify key intermediates and their roles in the transformation processes.
• To investigate the potential for catalytic production of nitrous oxide (N2O).

Main Methods:

• Spectroscopic analysis, including IR spectroscopy, was used to identify transient intermediates.
• Isotope labeling experiments (14N/15N) were employed to track atom transfer and coupling.
• Kinetic studies and mechanistic proposals were developed based on experimental observations.

Main Results:

• A transient N--N-coupled (NO)2 adduct intermediate was identified.
• The formation of NO(NO2)Fe(TPP) was observed, suggesting a pathway involving free NO2.
• Catalytic production of N2O was achieved by using a competitive oxygen atom acceptor (PPh3).
• Cross-labeling experiments confirmed the equivalence of oxygen atoms in the intermediate.
• IR spectroscopy confirmed transient, isotope-sensitive bands indicative of the intermediate.

Conclusions:

• The reaction proceeds through a distinct N--N-coupled adduct intermediate.
• A proposed mechanism explains the formation of nitrite and N2O.
• Oxygen atom transfer from the intermediate is efficient and involves equivalent oxygen atoms.
• The study provides insights into the reactivity of NO-Fe(TPP) and potential catalytic cycles.