chapter 2 palladium catalysts in suzuki cross- coupling reaction

times for the transformation of a large amount of reactants until they become eventually
deactivated (Baleizao et al. 2003, Kim et al. 2002, Corma et al. 2002). That’s why,
heterogeneous catalysts are preferred for industrial processes and heterogenization
methods have been also investigated (Smith and Notheisz 1995).
The commonly used two methods for homogeneous system to heterogenize is
immobilization to liquid phase and insoluble support.
3.1. The Immobilization to Liquid Phase
The immobilization of catalysts in liquid phases has been widely used in the
coupling reactions. The principle of the liquid/liquid biphasic catalysis system is related
to solubility of reaction components like aryl, allyl or benzyl halogenides and boronic
acids as well as their coupling products. The most important advantage of such
processes is the facile recovery of catalysts from the reaction mixture, which is done by
a simple phase separation of two immiscible solutions, of which one contains the
product of the catalytic transformation and the other one palladium catalyst. Moreover,
this approach also limits contamination of the organic products by catalyst metal
(Heiden and Plenio 2004, Paetzold et al. 2001).
There are several different concepts studied by research groups; organic/organic
liquid biphasic catalysis often with polymer-supported catalysts, fluorous/organic
systems, ionic liquids, supercritical solvents, and aqueous/organic solvent systems
(Heiden and Plenio 2004, Paetzold et al. 2001).
Phosphines which commonly used in cross-coupling reactions as homogeneous
ligands can be converted into water-soluble derivatives by introduction of polar groups,
including carboxylate, sulfonate and ammonium, providing easy removability from
reaction mixture by extraction with organic solvent (Figure 3.2).
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