Chemistry Reference
In-Depth Information
Pd(OAc)
2
(15 mol %)
t
-Bu-Amphos (15 mol %)
Cs
2
CO
3
toluene/MeOH/H
2
O (1:1:1)
rt, 15 h
O
O
O
N
(HO)
2
B
N
NMe
3
Cl
-
O
O
t
-Bu
2
P
+
MeO
2
C
I
MeO
2
C
O
t
-Bu-Amphos
6
7
72%
Scheme 14.7
Pd(OAc)
2
(2 mol%)
DTBPPS (2 mol%)
CsOH, H
2
O/CH
3
CN (1:1)
80 °C
t
Bu
+
P
SO
3
-
Ph
MeO
Cl
MeO
t
Bu
H
DTBPPS
73%
Scheme 14.8
OH
O
HO
HO
OH
NH
PCy
2
OMe
OH
OH
N
HOH
2
C
PCy
2
MeO
O
PCy
2
OH
OH
O
9
8
SO
3
Na
10
Scheme 14.9
sulfonate group to provide water solubility.
30
Computational studies
showed that the ionization potential (IP) of Pd(DTBPPS) was lower than that
of Pd(Pt-Bu
3
), whereas Pd(t-Bu-Amphos) had a higher IP. The anionic
DTBPPS provides effective catalysts for the Suzuki and Sonogashira coupling
of aryl bromides and chlorides (Scheme 14.8).
The dialkyl(2-biphenyl)phosphines developed by Buchwald and co-
workers are highly effective ligands for a variety of cross-coupling reactions.
Carbohydrate-modified 2-(dicyclohexylphosphino)biphenyl analogs with
gluconamide (8)
31
and glucosamine (9)
32
moieties were synthesized and
applied to Suzuki couplings of aryl bromides and chlorides in water
(Scheme 14.9). Anderson and Buchwald reported the synthesis of a water-
soluble ligand by sulfonation of SPhos.
33
The sulfonated SPhos (10) provides
an effective catalyst for the Sonogashira coupling of aryl chlorides in water-
acetonitrile. Plenio's group developed a highly water-soluble 9-dicyclohexyl-
fluorenyl ligand (11) that provides active palladium catalysts for Suzuki and
Sonogashira couplings of aryl and heteroaryl bromides and chlorides
(Scheme 14.10).
34
14.2.1.2 Palladium-Catalyzed Cross-Coupling with Hydrophilic
NHC Ligands
Stable carbenes, such as 2-imidazolylidenes and 2-imidazolinylidenes are
highly effective ligands for palladium-catalyzed cross-coupling that provide
similar steric and electronic properties to electron-rich trialkylphosphines.
35
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