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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As a result, organic group or hydride is transferred to Pd (Figure 2.7.). A driv<strong>in</strong>g force<br />
for the <strong>reaction</strong> called transmetallation, is due to the difference <strong>in</strong> the electro negativities<br />
of two metals (Tsuji 1995).<br />
L<br />
R X<br />
Pd<br />
L<br />
M - R'<br />
L<br />
R<br />
L<br />
R'<br />
Pd M<br />
X<br />
Figure 2.7. Transmetallation<br />
(Source: Tsuji 1995)<br />
L<br />
R R'<br />
Pd<br />
L<br />
+<br />
MX<br />
M: ma<strong>in</strong> group metal<br />
In Suzuki <strong>reaction</strong>s, transmetallation between organo<strong>palladium</strong> (II) halides and<br />
organoboron compounds does not occur readily due to the low nucleophilicity of<br />
organic group on boron atom. However, the nucleophilicity of organic group on boron<br />
atom can be enhanced with base giv<strong>in</strong>g the correspond<strong>in</strong>g “ate” complexes (Miyaura<br />
and Suzuki 1995).<br />
2.2.1.3. Reductive Elim<strong>in</strong>ation<br />
Reductive elim<strong>in</strong>ation is simply the reverse <strong>reaction</strong> of oxidative addition. In<br />
this step, two carbon metal bonds are broken (Tsuji 1995). The catalytic cycle is<br />
completed by reduction of the Pd II species <strong>in</strong>to a Pd 0 species and f<strong>in</strong>ally coupl<strong>in</strong>g<br />
product forms (Figure 2.8.).<br />
L<br />
L<br />
Pd II<br />
R<br />
R' 2L<br />
L<br />
L<br />
Pd 0<br />
Figure 2.8. Reductive Elim<strong>in</strong>ation<br />
(Source: Tsuji 1995)<br />
L<br />
L<br />
+<br />
R R'<br />
11