Precursor transformation during molecular oxidation catalysis with organometallic iridium complexes

Area of Science:

• Organometallic Chemistry
• Catalysis
• Inorganic Chemistry

Background:

• Homogeneous oxidation catalysts often require specific ligand designs for optimal activity and stability.
• Iridium complexes are known for their catalytic versatility in oxidation reactions.

Purpose of the Study:

• To investigate the role of the Cp* ligand in [Cp*Ir(III)(chelate)X] oxidation catalysts.
• To elucidate the structure and reactivity of the active catalytic species.

Main Methods:

• UV-vis and 1H NMR spectroscopy
• Mass spectrometry (MALDI-MS)
• Electrophoresis, TEM-EDX, XPS, 17O NMR, resonance-Raman spectroscopy
• Density Functional Theory (DFT) calculations

Main Results:

• Cp* ligand is rapidly and irreversibly lost, forming active blue solutions.
• The active species is identified as a bis-μ-oxo di-iridium(IV) complex.
• The di-iridium(IV) complex catalyzes water and CH-oxidation without an induction period.
• DFT calculations provide insights into the electronic structure of the resting state.

Conclusions:

• Cp* functions as a sacrificial placeholder ligand, facilitating catalyst activation.
• The identified di-iridium(IV) species represents a stable and highly active catalytic form.
• [(cod)Ir(I)(chelate)] precursors are effective precatalysts for oxidation reactions.