chapter 2 palladium catalysts in suzuki cross- coupling reaction

CHAPTER 3
THE HETEROGENEOUS SUZUKI CROSS-COUPLING
REACTIONS
Two types of catalysts are used in the Suzuki reactions; heterogeneous catalysts
where metallic Pd is supported on a carrier and homogeneous catalysts consisting of
mononuclear Pd (ligand) complexes.
Homogeneous palladium catalysts are widely used in many cross-coupling
reactions. These catalytic systems generally exhibit better activity and selectivity than
heterogeneous systems. Although homogeneous techniques are certainly important in
terms of their substrate tolerance, catalyst loading and reactivity, their complexity
preclude the large-scale applications. Palladium ligands and precursors are also
expensive, which severely restrict their industrial use and it is often difficult to remove
these reagents at end of reactions (Ruiz et al. 2006). Moreover, undesired byproducts
and/or scrambled products may also form in the presence homogeneous catalysts (Kotha
et al. 2002) (Figure 3.1.).
R
B(OH) 2
Pd(PPh 3) 4
R
HO
R
R
R
self-coupling
product
scrambled
product
hydrolysis
product
Figure 3.1. Generally observed side-reactions with Pd-catalyzed Suzuki-Miyaura crosscoupling
(Source: Kotha et al. 2002)
In this aspect, heterogeneous catalysts have many advantages over homogeneous
counterparts so that it can be easily removed from reaction mixtures and re-used several
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