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

• Published in: Journal of the American Chemical Society Vol. 143; no. 7; pp. 2792 - 2800
• Main Authors: Camp, Andrew M, Kita, Matthew R, Blackburn, P. Thomas, Dodge, Henry M, Chen, Chun-Hsing, Miller, Alexander J. M
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 24.02.2021
• Subjects: catalysts; drugs; iridium; mechanistic models; olefin; positional isomerization; regioselectivity; stereoselectivity
• ISSN: 0002-7863; 1520-5126; 1520-5126
• DOI: 10.1021/jacs.0c11601

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.