Chemistry Reference
In-Depth Information
R
1
R
1
R
1
R
1
NN
R
1
NN
R
1
R
1
R
1
R
2
R
2
R
2
R
2
Cl
Pd
Cl
Cl
Pd
Cl
N
N
N
N
Cl
Pd
Cl
Cl
Pd
Cl
R
2
R
2
R
2
R
2
R
1
R
1
R
1
R
1
N
N
N
N
R
1
R
1
R
1
R
1
46a:NHC=IMes
46b :NHC =IPr
46c :NHC=IMes
46d :NHC=IPr
Figure 4.21
Structure of the PEPPSI-type dinuclear palladium complexes 46a-d
using pyrazine and DABCO linkers.
Table 4.16 Comparison of the activities of the new complexes with
[Pd(IPr)(PEPPSI)] and some in situ-generated systems.
Cl
Si(OMe)
3
[Pd] (0.5 mol%)
+
MeO
TBAF
Toluene, 12 0°C, 5 h
MeO
Entry
[Pd]
Yield (%)
1
46a
80
2
46b
88
3
46c
78
4
46d
84
5
[Pd(IPr)(PEPPSI)] (15)
86
6
Pd(OAc)
2
+ IMes
HCl
43
7
Pd(OAc)
2
+ IPr
HCl
51
and as good as [Pd(IPr)(PEPPSI)] for the challenging coupling between
4-chloroanisole and phenyltrimethoxysilane (Table 4.16). The scope of the
reaction was studied and was found to be similar to that in previous reports
in the field, affording the expected biaryl compounds in good yields with a
low catalyst loading of 0.5 mol% and the use of TBAF as the promoter.
4.3.2 Heck Reaction
Heck cross-coupling is one of the most widely employed reactions to create
C-C bonds. It involves the reaction between a halide or pseudohalide and an
alkene.
6,108
The coupling has found many applications through the years,
notably for the preparation of industrially applicable compounds
3
and nat-
ural products.
2
The mechanism of the reaction is depicted in
Scheme 4.33.
9d,109
The first steps of the catalytic cycle are similar to those
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