Selecting Double Bond Positions with a Single Cation-Responsive Iridium Olefin Isomerization Catalyst

Area of Science:

• Organic Chemistry
• Catalysis
• Organometallic Chemistry

Background:

• Catalytic double bond transposition is crucial for synthesizing valuable alkenes used in fragrances, chemicals, and pharmaceuticals.
• Achieving selective synthesis of specific alkene isomers often necessitates developing unique catalysts for each desired product, posing a significant challenge.

Purpose of the Study:

• To develop a single, versatile catalyst capable of selectively producing different internal alkene isomers.
• To demonstrate cation-responsive control over alkene isomerization pathways using a single iridium catalyst.

Main Methods:

• Synthesis of novel iridium pincer-crown ether catalysts incorporating an aza-18-crown-6 ether moiety.
• Investigation of catalyst performance in the presence and absence of sodium cations (Na+).
• Utilizing experimental and computational studies to elucidate the reaction mechanism and selectivity.

Main Results:

• A single iridium catalyst selectively produced 2-alkenes from 1-butene derivatives via single positional isomerization in the absence of salts, exhibiting high regioselectivity and stereoselectivity.
• The same catalyst, in the presence of Na+, mediated two positional isomerizations to yield 3-alkenes.
• The catalyst's cation-responsive behavior was attributed to the integrated aza-18-crown-6 ether, enabling precise control over isomerization pathways.

Conclusions:

• Developed a novel cation-responsive iridium catalyst for selective alkene synthesis.
• Demonstrated a strategy for controlling alkene isomer production using noncovalent modifications and cation interactions.
• The findings offer insights into designing advanced catalysts for targeted chemical synthesis.