Synthetic, Structural, and Mechanistic Studies on the Oxidative Addition of Aromatic Chlorides to a Palladium (N-Heterocyclic Carbene) Complex:  Relevance to Catalytic Amination

Alexandra K. de K. Lewis,† Stephen Caddick,*† F. Geoffrey N. Cloke,*† Norman C. Billingham,† Peter B. Hitchcock,† and John Leonard‡;
Contribution from the The Chemistry Laboratory, CPES, University of Sussex, Falmer, Brighton BN1 9QJ, UK, and AstraZeneca Pharmaceuticals, Mereside, Macclesfield, Cheshire SK10 4TF, UK
J. Am. Chem. Soc., 2003, 125 (33), pp 10066–10073
DOI: 10.1021/ja035565k
Publication Date (Web): July 26, 2003
Copyright © 2003 American Chemical Society
†

 University of Sussex.

,
*

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

,
‡

 AstraZeneca Pharmaceuticals.

, f.g.cloke@sussex.ac.uk, ; , s.caddick@sussex.ac.uk

Abstract

Abstract Image

The oxidative addition products trans-[Pd(NHC)2(Ar)Cl] (NHC = cyclo-C{NtBuCH}2; Ar = Me-4-C6H4, MeO-4-C6H4, CO2Me-4-C6H4) have been isolated in good yields from the reactions of ArCl with the amination precatalyst [Pd(NHC)2] and structurally characterized. The former undergo reversible dissociation of one NHC ligand at elevated temperatures, and a value of 25.57 kcal mol-1 has been determined for the Pd−NHC dissociation enthalpy in the case where Ar = Me-4-C6H4. Detailed kinetic studies have established that the oxidative addition reactions proceed by a dissociative mechanism. Rate data for the oxidation addition of Me-4-C6H4Cl to [Pd(NHC)2] compared to that obtained for the [Pd(NHC)2]-catalyzed coupling of morpholine with 4-chlorotoluene are consistent with a rate-determining oxidative addition in the catalytic amination reaction. The relative rates of oxidative addition of the three aryl chlorides to [Pd(NHC)2] (CO2Me-4-C6H4Cl > Me-4-C6H4Cl > MeO-4-C6H4Cl) reflect the electronic nature of the substituents and also parallel observed trends in coupling efficiency for these aryl halides in aminations.

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History

  • Published In Issue August 20, 2003
  • Received April 10, 2003

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