3306
Organometallics 2007, 26, 3306-3314
Cyclopropanation of Cyclohexenone by Diazomethane Catalyzed by
Palladium Diacetate: Evidence for the Formation of Palladium(0)
Nanoparticles
Ona Illa,† Cristo´bal Rodr´ıguez-Garc´ıa,† Carles Acosta-Silva,† Isabelle Favier,‡
David Picurelli,‡ Antonio Oliva,† Montserrat Go´mez,*,‡,§ Vicenc¸ Branchadell,*,† and
Rosa M. Ortun˜o*,†
Departament de Qu´ımica, UniVersitat Auto`noma de Barcelona, 08193 Bellaterra, Barcelona, Spain,
Departament de Qu´ımica Inorga`nica, UniVersitat de Barcelona, Mart´ı i Franque`s, 1-11,
08028 Barcelona, Spain, and Laboratoire He´te´rochimie Fondamentale et Applique´e, UMR CNRS 5069,
118 Route de Narbonne, 31062 Toulouse Cedex 9, France
ReceiVed February 13, 2007
The diazomethane-mediated cyclopropanation of cyclohexenone using Pd(OAc)2 and different sources
of Pd(0) species as precatalysts has been studied. In the presence of an excess of diazomethane, Pd-
(OAc)2 rapidly evolves to the formation of palladium nanoparticles (less than 1 min), which are active
as catalysts in the cyclopropanation process. The nature of these particles has been analyzed through
transmission electron microscopy showing a size distribution between 6 and 40 nm. These nanoparticles
generated in situ are more active than Pd(0) complexes, preformed nanoparticles, and commercial palladium
powder. Cyclic voltammetry measurements of the reaction solution after completion show the presence
of Pd(0) species. This is the first time that Pd(0) nanoparticles are evidenced in a cyclopropanation reaction.
Moreover, the reduction of Pd(OAc)2 to Pd(0) in the presence of diazomethane has been theoretically
studied through density functional calculations. The formation of methyl and allyl acetates as organic
byproducts has been predicted by the theoretical calculations, and these species, as well as oligomers
derived from them, have been detected by spectrometric and spectroscopic techniques (MS, NMR,
and IR).
molecular palladium species, as proposed by Dupont10 and in
agreement with the results obtained by de Vries using ligand-
free palladium catalysts.11
Introduction
For metal-catalyzed processes, many studies have been
reported to establish the true nature of the catalyst. From the
point of view of the reactivity, it is more appropriate to classify
catalysts as homogeneous or heterogeneous depending on
whether the substrate interacts with one or many types of active
sites.1 Recently, tests commonly used to evaluate the nature of
the catalyst have been reviewed.2,3 However, when metal
nanoparticles are involved, it is even more difficult to conclude
about the catalyst nature, because they are placed at the frontier
between classical homogeneous and heterogeneous catalysts.4
This dilemma has been found in many palladium-catalyzed
reactions.5,6 In the last years, the possible formation of palladium
nanoparticles has been postulated for several catalytic pro-
cesses.7,8 In particular, for Pd-catalyzed C-C coupling reac-
tions,9 palladium nanoparticles seem to act as a reservoir of
Cyclopropanation of olefins with diazoalkanes catalyzed by
metal complexes is a widely used synthetic method.12-29
(9) For a general review concerning the Pd catalyst nature in Heck and
Suzuki couplings, see: Phan, N. T. S.; van der Sluys, M.; Jones, C. W.
AdV. Synth. Catal. 2006, 348, 609.
(10) Cassol, C. C.; Umpierre, A. P.; Machado, G.; Wolke, S. I.; Dupont,
J. J. Am. Chem. Soc. 2005, 127, 3298.
(11) (a) Reetz, M. T.; de Vries, J. G. Chem. Commun. 2003, 1787. (b)
de Vries, A. H. M.; Mulders, J. M. C. A.; Mommers, J. H. M.; Henderickx,
H. J. W.; de Vries, J. G. Org. Lett. 2003, 5, 3285.
(12) Doyle, M. P. Chem. ReV. 1986, 86, 919.
(13) Tomilov, Y. V.; Dokichev, V. A.; Dzhemilev, U. M.; Nefedov, O.
M. Russ. Chem. ReV. 1993, 62, 799.
(14) Doyle, M. P. In ComprehensiVe Organometallic Chemistry 2, Vol
12; Hegedus, L. S., Ed.; Pergamon: New York, 1995; p 387.
(15) Lautens, M.; Klute, W.; Tam, W. Chem. ReV. 1996, 96, 49.
(16) Davies, H. M. L. Aldrichim. Acta 1997, 30, 107.
(17) Doyle, M. P.; Protopopova, M. N. Tetrahedron 1998, 54, 7919.
(18) Doyle, M. P.; Forbes, D. C. Chem. ReV. 1998, 98, 911.
(19) Herndon, J. W. Coord. Chem. ReV. 2000, 206, 237.
(20) Lebel, H.; Marcoux, J.-F.; Molinaro, C.; Charette, A. B. Chem. ReV.
2003, 103, 977.
(21) Paulissen, R.; Hubert, A. J.; Teyssie´, P. Tetrahedron Lett. 1972,
1465.
(22) Mende, U.; Radu¨chel, B.; Skuballa, B.; Vorbru¨ggen, H. Tetrahedron
Lett. 1975, 629.
* Corresponding authors. E-mail: (M.G.) gomez@chimie.ups-tlse.fr;
(V.B.) vicenc@klingon.uab.cat; (R.M.O.) rosa.ortuno@uab.es.
† Universitat Auto`noma de Barcelona.
‡ Universitat de Barcelona.
§ Laboratoire He´te´rochimie Fondamentale et Applique´e.
(1) Schwartz, J. Acc. Chem. Res. 1985, 18, 302.
(2) Widegren, A.; Finke, R. G. J. Mol. Catal. A: Chem. 2003, 198, 317.
(3) Dyson, P. J. Dalton Trans. 2003, 2964.
(4) Astruc, D.; Lu, F.; Ruiz Aranzaes, J. Angew. Chem., Int. Ed. 2005,
44, 7852.
(5) Amatore, C.; Jutand, A. Acc. Chem. Res. 2000, 33, 314.
(6) Phan, N. T. S.; Van Der Sluys, M.; Jones, C. W. AdV. Synth. Catal.
2006, 348, 609.
(23) Kottwitz, J.; Vorbru¨ggen, H. Synthesis 1975, 636.
(24) Suda, M. Synthesis 1981, 714.
(25) Anciaux, A. J.; Hubert, A. J.; Noels, A. F.; Petinot, N.; Teyssie´, P.
J. Org. Chem. 1980, 45, 695.
(26) Ortun˜o, R. M.; Ibarzo, J.; AÄ lvarez-Larena, AÄ .; Piniella, J. F.
Tetrahedron Lett. 1996, 37, 4059.
(7) de Vries, J. G. Dalton Trans. 2006, 421.
(8) Thathagar, M. B.; ten Elshof, J. E.; Rothenberg, G. Angew. Chem.,
Int. Ed. 2006, 45, 2886.
(27) Denmark, S. E.; Stavenger, R. A.; Faucher, A. M.; Edwards, J. P.
J. Org. Chem. 1997, 62, 3375.
10.1021/om070141a CCC: $37.00 © 2007 American Chemical Society
Publication on Web 05/27/2007