Rate-Limiting Step of the Rh-Catalyzed Carboacylation of Alkenes: C–C Bond Activation or Migratory Insertion?

• Published in: Journal of the American Chemical Society 2012-01, Vol.134 (1), p.715-722
• Main Authors: Lutz, J. Patrick, Rathbun, Colin M, Stevenson, Susan M, Powell, Breanna M, Boman, Timothy S, Baxter, Casey E, Zona, John M, Johnson, Jeffrey B
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja210307s

Rhodium-catalyzed intramolecular carboacylation of alkenes, achieved using quinolinyl ketones containing tethered alkenes, proceeds via the activation and functionalization of a carbon–carbon single bond. This transformation has been demonstrated using RhCl­(PPh3)3 and [Rh­(C2H4)2Cl]2 catalysts. Mechanistic investigations of these systems, including determination of the rate law and kinetic isotope effects, were utilized to identify a change in mechanism with substrate. With each catalyst, the transformation occurs via rate-limiting carbon–carbon bond activation for species with minimal alkene substitution, but alkene insertion becomes rate-limiting for more sterically encumbered substrates. Hammett studies and analysis of a series of substituted analogues provide additional insight into the nature of these turnover-limiting elementary steps of catalysis and the relative energies of the carbon–carbon bond activation and alkene insertion steps.