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F
F
1mol%dtbpfPdCl
2
(HO)
2
B
MeO
2
C
MeO
2
C
+
N
KH
2
PO
4
,DME/H
2
O
rt, 73 %
Boc
Br
N
Boc
12 kg scale
F
MeO
2
C
HN
Scheme 3.26
Suzuki-Miyaura coupling using unstable 2-boronic acid N-Boc-
pyrrole.
OH
N
XantPhosPdCl
2
N
73 %
Br
O
O
N
l
B
N
l
+
N
N
Br
dtbpfPdCl
2
OH
HO
86 %
Scheme 3.27 Pd-catalyzed chemoselective Suzuki-Miyaura cross-coupling.
0.1 mol% XantPhosPdCl
2
1.3 equiv Et
3
N
O
N
N
l
50 psig CO
MeOH, 100 °C, 5h
O
99 % conversion
Scheme 3.28 Pd-catalyzed carbonylation of aryl chlorides.
XantphosPdCl
2
has also been found to be an effective precatalyst for
carbonylation reactions.
94
Despite the challenge of carbonylation of aryl
chlorides, this transformation was carried out with excellent conversion
using the Xantphos-based catalyst (Scheme 3.28).
3.7 Generation of LPd(0) Catalysts
The metal-to-ligand ratio seems to have a profound influence on certain
cross-coupling reactions, although this is not the case in all chemistries. For
in situ-generated catalysts involving monodentate ligands, a few reports
suggest a more active system when the metal-to-ligand ratio is 1 : 1, rather
than with the more traditional approach where excess ligand is used.
95,96
However during the mixing of Pd with ligand, more than one ligand can
coordinate with the Pd. Therefore, precatalysts engineered with a precise 1 : 1
ratio of phosphine (or other ligand) to palladium are of increasing interest.
Currently, there are three main classes of precatalysts providing this ratio;
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