chapter 2 palladium catalysts in suzuki cross- coupling reaction
chapter 2 palladium catalysts in suzuki cross- coupling reaction
chapter 2 palladium catalysts in suzuki cross- coupling reaction
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<strong>in</strong>volves the use of a catalyst <strong>in</strong> a different phase from the reactants. Typical examples<br />
<strong>in</strong>volve a solid catalyst with the reactants as either liquids or gases.<br />
Catalyst is a compound that affects the transition state and activation path by<br />
complex<strong>in</strong>g one of the reagents. Due to their partially filled-orbitals, transition metals<br />
are used as <strong>catalysts</strong>, provid<strong>in</strong>g electrons or withdraw<strong>in</strong>g electrons from the transition<br />
state of the <strong>reaction</strong>. Dur<strong>in</strong>g the <strong>reaction</strong> the transition metal ion is oxidized by one<br />
reactant to a higher oxidation state then reduced back to the orig<strong>in</strong>al form by another<br />
reactant.<br />
The study of catalysis dates back to the early 1800’s. Faraday was one of the<br />
first scientists to exam<strong>in</strong>e the ability of plat<strong>in</strong>um to facilitate oxidation <strong>reaction</strong>s (Smith<br />
and Notheisz 1995). Until now, many transition metals have been used <strong>in</strong> organic<br />
synthesis, but it is widely recognized that <strong>palladium</strong> is the most versatile <strong>in</strong> promot<strong>in</strong>g<br />
or catalyz<strong>in</strong>g <strong>reaction</strong>s, particularly those <strong>in</strong>volv<strong>in</strong>g carbon-carbon bond formation,<br />
which is not always easy to achieve with other transition metals (Tsuji 1995).<br />
2.1. Palladium Metals as Catalysts <strong>in</strong> Organic Syntheses<br />
2.1.1. Palladium as a Transition Metal<br />
Palladium is, as a d 10 element, one of the n<strong>in</strong>e elements <strong>in</strong> Group 8 of the<br />
periodic table. It was discovered by William Hyde Wollaston <strong>in</strong> 1803.<br />
Modern <strong>palladium</strong> chemistry started <strong>in</strong> 1960 with the <strong>in</strong>vention of an <strong>in</strong>dustrial<br />
process for acetaldehyde production by the air oxidation of ethylene, catalyzed by PdCl2<br />
and CuCl2, which is called the Wacker process (Tsuji 1995).<br />
In addition to its use as a catalyst, there are many other applications of<br />
<strong>palladium</strong>;<br />
• Gold is decolorized by addition of <strong>palladium</strong>, form<strong>in</strong>g white gold.<br />
• Hydrogen easily diffuses through heated <strong>palladium</strong>. Thus, it purifies the<br />
gas.<br />
• Telecommunications switch<strong>in</strong>g-system equipments use <strong>palladium</strong>.<br />
• Palladium is also used <strong>in</strong> dentistry, watches, <strong>in</strong> aircraft spark plugs and <strong>in</strong><br />
the production of surgical <strong>in</strong>struments and electrical contacts.<br />
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