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

The catalytic transposition of double bonds holds promise as an ideal route to alkenes of value as fragrances, commodity chemicals, and pharmaceuticals; yet, selective access to specific isomers is a challenge, normally requiring independent development of different catalysts for different products. In this work, a single cation-responsive iridium catalyst selectively produces either of two different internal alkene isomers. In the absence of salts, a single positional isomerization of 1-butene derivatives furnishes 2-alkenes with exceptional regioselectivity and stereoselectivity. The same catalyst, in the presence of Na+, mediates two positional isomerizations to produce 3-alkenes. The synthesis of new iridium pincer-crown ether catalysts based on an aza-18-crown-6 ether proved instrumental in achieving cation-controlled selectivity. Experimental and computational studies guided the development of a mechanistic model that explains the observed selectivity for various functionalized 1-butenes, providing insight into strategies for catalyst development based on noncovalent modifications.

Automated summary

This study successfully achieved the selective production of different internal alkene isomers using a single cation-responsive iridium catalyst, demonstrating exceptional regioselectivity and stereoselectivity under salt-free conditions. The development of new iridium pincer-crown ether catalysts played a key role in achieving cation-controlled selectivity, providing insights for catalyst development strategies based on noncovalent modifications.