N. Nowrouzi et al. / Tetrahedron Letters 57 (2016) 348–350
349
and
Table 1
Effect of different reaction parameters on the coupling reaction of iodobenzene
1.0 mmol) and chlorodiphenylphosphine (1.0 mmol) in the presence of tetrabuty-
Table 2
Phosphorylation of aryl halides with chlorophosphines in the presence of PdCl
TBAB
2
(
lammonium bromide (0.5 mmol)
PdCl
4
Entry Catalyst (mol %) Base (2.0 mmol) T (°C) Time (h) Yielda (%)
2
Ph
or
PhPCl2
2
PCl
2
Ph PAr
or
PhPAr
2
n-Bu NBr
ArI
+
1
2
3
4
5
6
7
8
9
1
1
1
5
5
5
5
5
5
5
5
3
1
10
3
NaOH
Na CO
CO
120
120
120
120
120
120
100
140
120
120
120
120
0.5
24
24
24
24
0.5
3
0.5
0.5
24
0.5
24
60
NaOH
120 °C
2
3
Trace
Trace
—
—
93
80
91
93
30
Ca
Bu
—
2
3
3
N
Yieldc (%)Ref.
Entry
ArX
Ph
Ph
n
PCl3Àn
Time (h)
0.5
b
b
b
b
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
I
1a
9310
2
PCl
I
0b
1
2
2a
906
Ph
Ph
2
PCl
PCl
1
b
91
—
b,c
I
a
b
c
3a
806
Isolated yield.
1.2
2
The reactions were carried out under an argon atmosphere.
TBAB was removed from the reaction mixture.
MeO
I
4a
7913
8710
Ph
2
PCl
1.5
6
O
2
N
the coupling reaction was performed under argon (Table 1, entry
). A temperature of 120 °C was optimal for this reaction (Table 1,
6
I
5a
entry 1). When the reaction temperature was lowered to 100 °C,
the yield also decreased (Table 1, entry 7). Higher temperatures
2
Ph PCl
(
Table 1, entry 8) did not improve the conversion and yield of
the desired product. Next, the reaction was carried out with differ-
ent amounts of PdCl (1, 3, 10 mol %). As shown in entries 9–11, at
20 °C, 3 mol% of the catalyst was sufficient to catalyze the reac-
6a
7a
Ph
Ph
PCl
PCl
1
906
—
2
I
S
2
Br
1
2
24
tion efficiently. In this case, the corresponding product was
obtained in 93% yield within 0.5 h (Table 1, entry 9). Finally, the
optimized reaction was performed in the absence of TBAB. How-
ever, when TBAB was removed from the reaction mixture, the reac-
tion did not occur (Table 1, entry 12).
Br
8a
Ph
Ph
2
PCl
PCl
24
24
—
O
2
N
Cl
Having the optimized conditions; aryl halide (1.0 mmol), Ph
1.0 mmol), NaOH (2.0 mmol), PdCl (0.03 mmol) and TBAB
0.5 mmol) at 120 °C under an argon atmosphere (Table 1, entry
), the phosphorylation reactions proceeded efficiently for
2
PCl
9a
—
2
(
(
9
2
NC
I
0b
8510
1
PhPCl
PhPCl
2
2
3
iodobenzene and iodobenzenes bearing either an electron-
withdrawing or an electron-donating group at the para-position
I
11b
4.5
8214
7515
(Table 2, entries 1–4). The methodology was further extended
to the coupling of sterically hindered aryl iodides such as 2-iodoto-
luene (Table 2, entry 5). We found that ortho-substituted iodide
also coupled well with this protocol. We also tried to use this
method for the coupling of chlorodiphenylphosphine with bromo-
and chlorobenzene. Although the cross coupling reaction pro-
ceeded efficiently for iodobenzenes, the reactions did not proceed
with bromo and chloro derivatives even with an electron-with-
drawing group at the para-position (Table 2, entries 7–9). These
I
1
2b
PhPCl
PhPCl
PhPCl
2
2
2
5
MeO
I
13b
15
24
8016
Br
reactions did not proceed even in the presence of PPh
3
as ligand
4b
1
—
or with increasing the amount of PdCl from 3 mol % to 10 mol %.
2
2
O N
Instead of chlorodiphenylphosphine, we also examined this
method for the coupling of dichlorophenylphosphine with iodoben-
zenes. The reactions proceeded efficiently and the corresponding
products were obtained in high yields (Table 2, entries 10–13).
The role of TBAB in this reaction is crucial. It is well established
that the presence of TBAB not only makes the catalytic system stable
a
Reaction conditions: aryl halide (1.0 mmol), chlorodiphenylphosphine
1.0 mmol), n-Bu NBr (0.5 mmol), PdCl (3 mol %), NaOH (2.0 mmol), 120 °C under
argon.
(
4
2
b
Reaction conditions: aryl halide (2.0 mmol), dichlorophenylphosphine
4 2
(1.0 mmol), n-Bu NBr (0.5 mmol), PdCl (6 mol %), NaOH (4.0 mmol), 120 °C under
argon.
c
17
Isolated yield.
by preventing the formation of palladium black but also acts both
as a reducing agent for the generation of Pd(0)1
2b,18
and as an ionic
observed for three runs. From the fourth run, a loss of the activity
of the system was observed (Table 3).
liquid solvent to make the reaction mixture homogeneous.
The recyclability of this system was also examined in the reac-
tion of iodobenzene with chlorodiphenylphosphine. For this pur-
pose, after completion of the reaction and extraction of the
product using diethylether, iodobenzene, chlorodiphenylphos-
phine and base were added to the remaining layer containing Pd
As shown in Table 1, entry 5, the reaction did not occur in the
absence of NaOH. Moreover, in a control experiment, we observed
that Ph
under the reaction conditions.
According to the above observations, a proposed mechanism is
shown in Scheme 1.
À
2
PO was produced in the reaction of Ph
2
PCl and NaOH
(
0)/TBAB and the reaction mixture was worked-up after 35 min.
Quantitative conversion to the corresponding phosphine was