Chemistry Reference
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HO
3
S
HSO
4
-
Na
2
PdCl
4
(1 mol %)
11
(2 mol %)
O
H
O
P
Cy
2
+
K
2
CO
3
H
2
O/
i
-PrOH (1:1)
90 °C, 8 h
N
N
Br
SO
3
H
91%
11
Scheme 14.10
-
O
3
S
SO
3
-
R
R
Na
+
-
O
3
S
N
N
SO
3
-
N
N
Na
+
R
R
R = Me:
12
R =
i
-Pr:
13
14
Scheme 14.11
NaO
3
S
SO
3
Na
Cl
-
1) ClSO
3
H, 100 °C
2) NaOH
Cl
-
N
N
N
N
69%
Scheme 14.12
CO
2
H
N
N
N
N
Pd
Cl
Cl
N
N
Pd
N
N
Br
Bu
Bu
HO
2
C
CO
2
H
Br
-
15
16
Scheme 14.13
There are fewer examples of water-soluble N-heterocyclic carbene (NHC)
derivatives and their use in aqueous solvents. In part, this is due to the high
basicity of the free carbene. Metal-NHC complexes are typically stable in
water, which allows the use of Pd-NHC complexes in aqueous-phase
catalysis. Sulfonated analogs of Mes and IPr imidazol(in)ium (12-14) were
prepared starting from sulfonated aniline derivatives (Scheme 14.11).
36
The
protonated NHC salts in combination with Na
2
PdCl
2
gave effective catalysts
for the Suzuki coupling of aryl chlorides in water at 100 1C. Imidazol(in)ium
precursors of NHCs are suciently stable to tolerate electrophilic sulfon-
ation, which provides an alternative method to the synthesis of sulfonated
NHC precursors (Scheme 14.12).
37
The carboxylate-substituted bis(NHC)-palladium complex 15
(Scheme 14.13) provides an active catalyst for the Suzuki coupling of aryl
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