Insights into the Origin of High Activity and Stability of Catalysts Derived from Bulky, Electron-Rich Monophosphinobiaryl Ligands in the Pd-Catalyzed C−N Bond Formation

Eric R. Strieter, Donna G. Blackmond,* and Stephen L. Buchwald*;
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, and Department of Chemistry, University of Hull, Hull HU6 7RX, UK
J. Am. Chem. Soc., 2003, 125 (46), pp 13978–13980
DOI: 10.1021/ja037932y
Publication Date (Web): October 28, 2003
Copyright © 2003 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.

, d.g.blackmond@hull.ac.uk, ; , sbuchwal@mit.edu

Abstract

Abstract Image

A comparative kinetic examination of catalyst systems based on several monophosphinobiaryl ligands is reported. The bulk of the phosphine ligand controls the catalytic activity and the rate of catalyst activation with the catalyst based on 2-dicyclohexylphosphino-2‘,4‘,6‘-triisopropylbiphenyl providing the greatest activity and fastest activation. In the case where catalyst activation is slow (i.e., use of the smaller ligands such as 2-dicyclohexylphosphino-2‘-methylbiphenyl in combination with Pd(OAc)2) stirring the amine with the catalyst/base mixture prior to the commencement of the reaction increases the reaction rate along with the rate of catalyst activation. Kinetic isotope effects established that the catalyst activation process occurs through a β-hydride elimination pathway.

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History

  • Published In Issue November 19, 2003
  • Received August 14, 2003

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