Catalytic Nitrous Oxide Reduction with H₂ Mediated by Pincer Ir Complexes

Area of Science:

• Catalysis
• Green Chemistry
• Organometallic Chemistry

Background:

• Nitrous oxide (N₂O) is a potent greenhouse gas requiring effective decomposition methods.
• Hydrogenation of N₂O to N₂ and water offers an environmentally benign pathway.

Purpose of the Study:

• To develop and investigate novel iridium complexes for N₂O hydrogenation.
• To understand the catalytic mechanism and identify pathways for catalyst deactivation.

Main Methods:

• Synthesis and testing of iridium complexes with proton-responsive pincer ligands.
• Catalytic hydrogenation of N₂O under mild conditions.
• Reaction monitoring using NMR spectroscopy.
• Mechanistic insights via Density Functional Theory (DFT) calculations.

Main Results:

• Iridium complex 4, featuring a lutidine-derived CNP pincer ligand, exhibited the highest catalytic activity (TOF = 16.4 h^-1 at 55 °C).
• NMR studies revealed initial deprotonation and regeneration of the active catalyst, but also identified a deactivation pathway involving a dinitrogen Ir(I) complex (7).
• DFT calculations supported complex 4 as the turnover frequency-determining intermediate and identified the rate-limiting transition state.

Conclusions:

• Proton-responsive pincer iridium complexes are effective catalysts for N₂O hydrogenation.
• Complex 4 is a highly active catalyst, though catalyst deactivation can occur.
• Understanding the mechanism and deactivation pathways is crucial for optimizing catalytic performance.