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0.25 mol % RhH(PPh
3
)
4
0.5 mol % dppBz
+
SR
X
F
RS
X
SR
0.5 equiv PPh
3
PhCl, reflux
X
R
Yield (%)
C(O)Ph
m
-CH
3
OC
6
H
4
89
C(O)Ph
p
-ClC
6
H
4
90
C(O)Ph
p
-CH
3
OC
6
H
4
87
CN
p
-CH
3
OC
6
H
4
91
NO
2
p
-CH
3
OC
6
H
4
86
C(O)CH
3
p
-CH
3
OC
6
H
4
91
Scheme 6.25
5 mol % [RhCl(COD)]
2
10 mol % PPh
3
toluene, NaO
Ar-I
+
RSH
Ar-SR
t
Bu, 100 °C
Ar
R
Yield (%)
p
-CH
3
C
6
H
4
p
-ClC
6
H
5
86
C
6
H
5
C
6
H
5
98
p
-BrC
6
H
4
C
6
H
5
67
p
-NH
2
C
6
H
4
C
6
H
5
94
p
-CF
3
C
6
H
4
C
6
H
5
91
p
-CH
3
C
6
H
4
C
6
H
11
73
Scheme 6.26
of alkyl thiols were reported, all of which provided lower yields than aryl
thiols. The use of aryl bromides in this chemistry was not reported.
6.7 Conclusion and Outlook
The transition metal-catalyzed formation of carbon-oxygen and carbon-
sulfur bonds via cross-coupling reactions of aryl halides and alcohols or
thiols has helped transform the way in which synthetic chemists design
strategies to prepare small molecules. Early catalyst development for
carbon-oxygen bond formation involved the use of palladium complexes
containing bulky, electron rich phosphine ligands that are thought to sta-
bilize highly reactive, coordinatively unsaturated metal complexes. New
generations of catalysts led to the development of palladium complexes that
can couple aryl halides with primary and secondary alcohols. For carbon-
sulfur bond cross-coupling reactions, typical catalyst systems contain
strongly chelating ligands, which prevent thiolate attack at the metal center
and subsequent catalyst deactivation. Other methods for attenuation of
thiolate nucleophilicity have also been advanced,
including employing
catalytic Lewis acids to chaperone the thiolate anion.
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