Silica Supported Organometallic Ir^I Complexes Enable Efficient Catalytic Methane Borylation

Area of Science:

• Organometallic Chemistry
• Catalysis
• Materials Science

Background:

• Methane (CH4) conversion via C-H borylation is crucial for producing valuable building blocks from the most abundant hydrocarbon.
• Existing homogeneous catalysts for CH4 borylation often exhibit low turnover numbers and conversions, potentially due to inactive metal hydride agglomerates.
• Developing robust and efficient catalysts for methane functionalization remains a significant challenge in synthetic chemistry.

Purpose of the Study:

• To enhance the performance of methane C-H borylation by heterogenizing a bisphosphine iridium precatalyst.
• To investigate the role of catalyst immobilization in preventing deactivation pathways and improving catalytic efficiency.
• To achieve high turnover numbers and selectivity for the monoborylated methane product.

Main Methods:

• Heterogenization of a [(dmpe)Ir(cod)CH3] bisphosphine molecular precatalyst onto amorphous silica.
• Catalytic testing of the supported catalyst for methane borylation at 150 °C.
• Characterization using X-ray absorption and dynamic nuclear polarization-enhanced solid-state NMR spectroscopy.
• Analysis of product selectivity for mono- vs. diborylation.

Main Results:

• The heterogenized catalyst demonstrated a 12-fold increase in efficiency compared to the standard catalyst, achieving over 2000 turnovers in 16 hours.
• High selectivity for monoborylation (91.5%) was observed, with improved yields (>82.8%) and selectivity (>99%) at higher catalyst loadings (1255 turnovers).
• Spectroscopic studies confirmed the supported precatalyst as an Ir(I) species and indicated the absence of multinuclear Ir polyhydrides post-catalysis, suggesting prevention of bimolecular decomposition.

Conclusions:

• Immobilization of the homogeneous Ir(I) fragment onto amorphous silica is a simple and effective strategy to enhance the turnover number (TON) and longevity of methane borylation catalysts.
• Heterogenization prevents catalyst deactivation via bimolecular pathways, leading to significantly improved catalytic performance.
• This approach offers a promising route for the sustainable and efficient utilization of methane as a chemical feedstock.