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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• Complexes immobilized <strong>in</strong> zeolite super cages may have almost the same<br />
activity as the free complexes <strong>in</strong> solution.<br />
• The zeolite microstructure (micro-reactor) could help to overcome the<br />
problems of metal leach<strong>in</strong>g.<br />
• Zeolites are capable of stabiliz<strong>in</strong>g <strong>in</strong>termediate active species reta<strong>in</strong>ed <strong>in</strong><br />
their cavities and may show the product shape-selectivity.<br />
• They should regenerate the catalyst after deactivation.<br />
In the literature, [Pd]-loaded NaY zeolites were used for C-C coupl<strong>in</strong>g <strong>reaction</strong>s<br />
for the first time by Djakovitch and Koehler (Figure 3.15) (Djakovitch and Koehler<br />
1999). They reported that the <strong>catalysts</strong> exhibited a high activity and selectivity toward<br />
the Heck <strong>reaction</strong> of aryl bromides with olef<strong>in</strong>s <strong>in</strong> low <strong>palladium</strong> concentrations (0.1<br />
mol% of Pd). In another study, the Heck <strong>reaction</strong>s were performed for <strong>in</strong>dustrially more<br />
<strong>in</strong>terest<strong>in</strong>g chloroactophenone with styrene at 100 ºC (Djakovitch et al. 1999). The<br />
authors observed that the <strong>catalysts</strong> could be separated from the <strong>reaction</strong> mixture.<br />
However it could not be reused with same activity. The catalyst used <strong>in</strong> a first run at<br />
100 ºC was regenerated by <strong>in</strong>creas<strong>in</strong>g temperature to 140 ºC under <strong>reaction</strong> conditions<br />
(Djakovitch and Koehler 2001).<br />
R<br />
Br<br />
+ [Pd] zeo<br />
R = H, F, NO 2, CH 3CO<br />
R<br />
trans and cis-isomers<br />
+<br />
Figure 3.15. The Heck <strong>reaction</strong>s of aryl bromides with olef<strong>in</strong>s<br />
(Source: Djakovitch and Koehler 1999)<br />
The leach<strong>in</strong>g test was also performed and it was found that only small amount of<br />
<strong>palladium</strong> was leached, depend<strong>in</strong>g on temperature of the <strong>reaction</strong> and the nature of the<br />
Pd species immobilized <strong>in</strong> the zeolite cage. For the [Pd(NH3)4] 2+ -NaY which we also<br />
R<br />
39