Figure 1. UV-vis spectral change during the addition of aq Fischer
carbene solution to aq K PdCl solution. Pd/Fischer carbene molar
ratio: (a) 1:0, (b) 1:0.087, (c) 1:0.174, (d) 1:0.261, (e) 1:0.348, (f)
:0.435, respectively.
2
4
1
9
0
on catalysis of the Hiyama reaction using arylalkoxysilane.
Such a coupling reaction uses organosilicon compounds
1
that have greater stability than organozinc or organomag-
nesium compounds, and they are less toxic than tin reagents.
They are often preferred to organoboron compounds which
are either unstable or difficult to purify and frequently lose
boron to give undesirable homocoupling products. Although
detection of nanoparticles of palladium in Hiyama reaction
Figure 2. (a) TEM image of the palladium nanoparticles (Pd/PEG
:2). (b) Electron diffraction pattern of palladium nanoparticles.
c) Plot of the size of a nanoparticle as a function of Pd/PEG molar
8
b
catalyzed by ligand-supported palladium complexes has
1
(
(6) For nanoparticle-catalyzed Stille reactions, see: (a) Kim, N.; Kwon,
ratio and % yield of the coupled product.
K. S.; Park, C. M. Tetrahedron Lett. 2004, 45, 7057-7059. (b) Zhao, D.;
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2
004, 126, 15876-15882. (c) Garcia-Martinez, J. C.; Lezutekong, R.;
raised a question about their possible involvement as a
catalyst, no conclusive evidence is yet available to substanti-
Crooks, R. M. J. Am. Chem. Soc. 2005, 127, 5097-5103. (d) Cal o´ , V.;
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1
1
6
044. (e) Li, J.- H.; Tang, B.-X.; Tao, L. -M.; Xie, Y.-X.; Liang, Y.; Zhang,
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M.-B. J. Org. Chem. 2006, 71, 7488-7490.
8a
reaction catalyzed by the Pd-Ni nanoclusture prompted
(7) For nanoparticle-catalyzed Suzuki reactions, see: (a) Reetz, M. T.;
Westermann, E. Angew. Chem. Int. Ed. 2000, 39, 165-168. (b) El-Sayed,
us to disclose the first example of palladium nanoparticle
catalysis for Hiyama reaction in water where palladium
nanoparticles were prepared by employing a Fischer carbene
M. A.; Collard, D. M.; Hong, X. M.; Li, Y. Org. Lett. 2000, 2, 2385-
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388. (c) Choudary, B. M.; Madhi, S.; Chowdari, N. S.; Kantam, M. L.;
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complex as the reducing agent for K PdCl . The major
3
532. (e) Thathagar, M. B.; Beckers, J.; Rothenberg, J. J. Am. Chem. Soc.
advantage of the protocol is 3-fold: all operations are
performed in water; no additive other than a small amount
of PEG is required; and the temperture of the reaction is
usually lower than 100 °C. The products are obtained in
excellent yields (>90% for most of the examples, see Table
2
002, 124, 11858-11859. (f) El-Sayed, M. A.; Narayanan, R. J. Am. Chem.
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(
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(
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