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1) 2
n
-BuLi, TMEDA
hexanes, reflux
PR
2
PCl
2
4 RLi or 4 RMgX
Fe
Fe
Fe
2) 2 ClP R
2
THF,
THF,
−
40 °C
PR
2
PCl
2
40 °C
−
R = Me, Et,
i
-Pr,
t
-Bu, Cy, Aryl, 2-Furyl, etc.
Synthesis of symmetrical 1,1
0
-bis(phosphino)ferrocenes.
Figure 2.20
Table 2.7
Superior activity of (dtbpf)PdCl
2
in Suzuki-Miyaura coupling.
[Pd] (1 mol %)
K
2
CO
3
EtOH-H
2
O
80 °C, 12 h
MeO
F
MeO
F
PhB(OH)
2
X
Ph
Entry
Catalyst
X
Yield (%)
1
(PPh
3
)
2
PdCl
2
Br
93
2
(PCy
3
)
2
PdCl
2
Br
100
3
(dppe)PdCl
2
Br
100
4
(dppf)PdCl
2
Br
100
5
(dippf)PdCl
2
Br
100
6
(PPh
3
)
2
PdCl
2
Cl
2
7
(PCy
3
)
2
PdCl
2
Cl
2
8
(dppe)
2
PdCl
2
Cl
5
9
(dppf)PdCl
2
Cl
4
10
(dippf)PdCl
2
Cl
9
11
(dtbpf)PdCl
2
Cl
65
12
a
(dtbpf)PdCl
2
Cl
100
a
Run in DMF at 120 1C. dppe
¼
bis(diphenylphosphino)ethane.
Adapted with permission from T. J. Colacot and H. A. Shea, Org. Lett., 2004, 6, 3731. Copyright
2008 American Chemical Society.
In 2004, Colacot and Shea demonstrated for the first time that 1,1
0
-bis(di-
tert-butylphosphino)ferrocenepalladium dichloride [(dtbpf)PdCl
2
]
48
is very
active in Suzuki-Miyaura reactions utilizing unactivated aryl bromides and
chlorides.
81
Importantly, this air-stable complex seemed to be uniquely re-
active compared with similar catalysts including 1,1
0
-bis(diisopropylphos-
phino)ferrocenepalladium [(dippf)PdCl
2
], indicating that the balance of the
electronic and steric nature of the ligand in combination with the large bite
angle (104.21)
29
is integral to the catalyst activity (Table 2.7). By comparison,
the bite angle of (dippf)PdCl
2
(103.61)
80d
nearly matches that of the tert-butyl
analog; however, the isopropyl groups are both less electron-donating and
sterically demanding.
The superior activity of (dtbpf)PdCl
2
relative to other similar catalysts was
also observed by Itoh et al. in Suzuki-Miyaura reactions to generate 2-aryl-
purines with unprotected NH
2
groups.
82
As mentioned above, Hartwig and co-workers identified dtbpf as a com-
petent ligand for a-arylation reactions.
51
Regardless of the mode of ligand
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