An electron poor iridium pincer complex for catalytic alkane dehydrogenation

Area of Science:

• Organometallic Chemistry
• Catalysis
• Ligand Design

Background:

• Alkane dehydrogenation is a crucial transformation in chemical synthesis.
• Development of efficient and stable catalysts is essential for industrial applications.
• Phosphinite ligands play a role in tuning the properties of metal catalysts.

Purpose of the Study:

• To synthesize and characterize a novel electron-deficient diphosphinite ligand.
• To investigate the catalytic activity of the resulting iridium pincer complex in alkane dehydrogenation.
• To study the mechanistic aspects of the catalytic cycle, including resting state identification.

Main Methods:

• Synthesis of 4,6-bis(trifluoromethyl)-1,3-phenylene diphosphinite ligand.
• Preparation and characterization of iridium chloro(hydride) pincer complex using NMR spectroscopy.
• X-ray crystallography for structural elucidation of key complexes.
• Evaluation of catalytic performance in alkane dehydrogenation reactions.

Main Results:

• Successful synthesis of the novel diphosphinite ligand (ligand 4) and its corresponding iridium pincer complex (complex 5).
• Complex 5 exhibited a higher turnover number (TON) in alkane dehydrogenation compared to related phosphinite pre-catalysts.
• Formation and characterization of cyclooctene (COE) and tert-butylethylene adducts, with the COE adduct identified as the catalyst's resting state.

Conclusions:

• The electron-deficient diphosphinite ligand enables the formation of a highly active iridium pincer catalyst for alkane dehydrogenation.
• The developed catalyst demonstrates superior performance, highlighting the ligand's beneficial electronic and steric properties.
• Understanding the resting state provides insights into the catalytic mechanism and potential for further optimization.