An Ion-Responsive Pincer-Crown Ether Catalyst System for Rapid and Switchable Olefin Isomerization

Area of Science:

• Organometallic Chemistry
• Catalysis
• Supramolecular Chemistry

Background:

• Iridium-catalyzed reactions are crucial in organic synthesis.
• Controlling catalyst activity and selectivity remains a key challenge.
• Macrocyclic ligands offer unique coordination environments.

Purpose of the Study:

• To develop a highly controllable iridium-catalyzed isomerization of allylbenzenes.
• To investigate the role of alkali metal cations in modulating catalytic activity.
• To understand the mechanism of catalyst activation and tuning.

Main Methods:

• Synthesis and characterization of an iridium complex with a pincer-crown ether ligand.
• Investigation of catalytic activity in allylbenzene isomerization.
• Spectroscopic and kinetic studies to elucidate reaction mechanisms.
• Systematic variation of alkali metal cations and counterions.

Main Results:

• A chloride-ligated iridium complex was activated by sodium salt addition.
• Lithium cation addition resulted in up to a 1000-fold rate enhancement.
• Catalyst activity was modulated across several orders of magnitude by varying alkali metal salts and additives.
• Mechanistic studies indicated that substrate binding is key to the observed tunability.

Conclusions:

• Tunable hemilability through alkali metal cation binding provides exquisite control over iridium catalysis.
• This system offers a novel platform for developing highly selective and active catalysts.
• The findings open new avenues for catalyst design in organic transformations.