Rate-Limiting Step of the Rh-Catalyzed Carboacylation of Alkenes: C–C Bond Activation or Migratory Insertion?
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)(2)Cl](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.
Lutz, Patrick J., Colin M. Rathbun, Susan M. Stevenson, Breanna M. Powell, Timothy S. Boman, Casey E. Baxter, John M. Zona and Jeffrey B. Johnson. "Rate-Limiting Step of the Rh-Catalyzed Carboacylation of Alkenes: C–C Bond Activation or Migratory Insertion?" Journal of the American Chemical Society 134, no. 1.00 (2012): 715-722.