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
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
2.1.2. The Coord<strong>in</strong>ation Geometry of Organo<strong>palladium</strong> Compounds<br />
The geometry of organo<strong>palladium</strong> compounds depends on the oxidation state of<br />
<strong>palladium</strong>. In the organo<strong>palladium</strong> compounds, the transition metal may have 0, +2, +3,<br />
+4 oxidation state. All possible geometries of <strong>palladium</strong> depend<strong>in</strong>g upon its oxidation<br />
states are shown <strong>in</strong> Table 2.1.<br />
Table 2.1. The geometries of organo<strong>palladium</strong> compounds<br />
Oxidation Step Electronic Configuration Geometry<br />
0 d 10 Tetrahedral<br />
2+ d 8 Square planer<br />
4+ (rarely) d 6 Octahedral<br />
2.1.3. The Characteristic Features of Pd and Pd-C Bonds<br />
The most characteristic feature of the Pd-C bonds <strong>in</strong> <strong>in</strong>termediates of catalytic<br />
<strong>reaction</strong>s is their <strong>reaction</strong> with nucleophiles. Pd(0) is generated by accept<strong>in</strong>g two<br />
electrons from nucleophiles. Unlike <strong>palladium</strong>, some other metal-carbon bonds such as<br />
those with Mg, Al, Zn are attacked by electrophiles and metals are oxidized to M(II).<br />
Therefore, <strong>reaction</strong> can not carried out with a catalytic amount of these metals.<br />
Whereas, the catalytic <strong>reaction</strong> is possible via the regeneration of an active Pd (0)<br />
catalyst. In this respect, Pd is very unique.<br />
Organo<strong>palladium</strong> species tolerate many functional groups, such as carbonyl and<br />
hydroxyl groups, (except alkene, alkynes and iodide and bromides attached to sp 2<br />
carbons), which allows them to be employed <strong>in</strong> the synthesis of highly complex<br />
molecules. Thus, Pd-catalyzed <strong>reaction</strong>s do not need any protection of these functional<br />
groups. They are also not sensitive to water, alcohols and carboxylic acids.<br />
Pd is much less expensive a compared to other metals such as Rh, Pt, and Ir and<br />
its toxicity has posed no problem so far. Pd forms complexes with a wide variety of<br />
organic ligands with P, N, and O atoms; many of these complexes are relatively easy to<br />
5