Scope and Mechanism of the Intermolecular Addition of Aromatic Aldehydes to Olefins Catalyzed by Rh(I) Olefin Complexes

Amy H. Roy, Christian P. Lenges, and Maurice Brookhart*
Contribution from the Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290
J. Am. Chem. Soc., 2007, 129 (7), pp 2082–2093
DOI: 10.1021/ja066509x
Publication Date (Web): January 31, 2007
Copyright © 2007 American Chemical Society
*

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

, mbrookhart@unc.edu

Abstract

Abstract Image

Rhodium (I) bis-olefin complexes Cp*Rh(VTMS)2 and CpRh(VTMS)2 (Cp* = C5Me5, Cp = C5Me4CF3, VTMS = vinyl trimethylsilane) were found to catalyze the addition of aromatic aldehydes to olefins to form ketones. Use of the more electron-deficient catalyst CpRh(VTMS)2 results in faster reaction rates, better selectivity for linear ketone products from α-olefins, and broader reaction scope. NMR studies of the hydroacylation of vinyltrimethylsilane showed that the starting Rh(I) bis-olefin complexes and the corresponding Cp*/Rh(CH2CH2SiMe3)(CO)(Ar) complexes were catalyst resting states, with an equilibrium established between them prior to turnover. Mechanistic studies suggested that CpRh(VTMS)2 displayed a faster turnover frequency (relative to Cp*Rh(VTMS)2) because of an increase in the rate of reductive elimination, the turnover-limiting step, from the more electron-deficient metal center of CpRh(VTMS)2. Reaction of Cp*/Rh(CH2CH2SiMe3)(CO)(Ar) with PMe3 yields acyl complexes Cp*/Rh[C(O)CH2CH2SiMe3](PMe3)(Ar); measured first-order rates of reductive elimination of ketone from these Rh(III) complexes established that the Cp ligand accelerates this process relative to the Cp* ligand.

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History

  • Published In Issue February 21, 2007
  • Received September 8, 2006

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