Recoverable cationic Pd-catalyzed Heck reaction under thermomorphic mode

Article abstract of DOI:10.1016/j.jorganchem.2011.08.028

The reaction of allylpalladium chloride dimer and 4,4′-bis(R _fCH₂OCH₂)-2,2′-bpy, 1a-c, in the presence of AgOT_f resulted in the synthesis of cationic complex, [Pd(η³-allyl)(4,4′-bis-(R_fCH

Full text of DOI:10.1016/j.jorganchem.2011.08.028

Journal of Organometallic Chemistry 696 (2011) 3637e3642
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Recoverable cationic Pd-catalyzed Heck reaction under thermomorphic mode
*
Chieh-Keng Li, Ajay Ghalwadkar, Norman Lu
Institute of Organic and Polymeric Materials, National Taipei University of Technology, Taipei 106, Taiwan
a r t i c l e i n f o
a b s t r a c t
The reaction of allylpalladium chloride dimer and 4,40-bis(RfCH2OCH2)-2,20-bpy, 1aec, in the presence of
AgOTf resulted in the synthesis of cationic complex, [Pd(h3-allyl)(4,40-bis-(RfCH2OCH2)-2,20-bpy)](OTf),
2aec where Rf ¼ C9F19 (a), C10F21 (b), C11F23 (c), respectively. The solubility curves of 2aec which began
from virtually zero below ꢀ40 ꢁC and increased dramatically at slightly higher temperature were
quantitatively measured. Upon changing from ꢀ40e90 ꢁC there was several orders of magnitude
increase of solubility for 2aec. The cationic Pd-catalyzed Heck arylation of methyl acrylate was selected
to demonstrate the feasibility of recycling usage with 2b,c as the catalyst using DMF as the solvent at
140 ꢁC for 3 h in each run. At the end of each cycle, the product mixtures were cooled to ꢀ30 ꢁC, and then
catalysts were recovered by decantation. The products were quantified by GC analysis or by the isolated
yield. The Heck reaction of C6H5I with methyl acrylate could be catalyzed by 2b with good recycling
results for a total of 15 times and also with a 100% selectivity favoring the trans product. To our
knowledge, this is the first example of cationic Pd-catalyzed Heck reaction under the thermomorphic
mode.
Article history:
Received 22 June 2011
Received in revised form
10 August 2011
Accepted 18 August 2011
Keywords:
Cationic palladium complex
Heck reaction
Thermomorphic mode
Homogeneously
Heterogeneously
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
Pd-catalyzed Heck reaction has become one of the most
important reactions in developing new drugs, biologically active
Homogeneous catalysis offers several advantages like high
efficiency, better tuning of chemoselectivity, regioselectivity and/or
stereoselectivity of the catalysts [1]. However, the majority of
homogeneous catalysts have not been commercialized because of
its difficulty of separation from the reaction system. In other words,
it is important to develop scientifically rewarding methodology
that could bridge both homogeneous and heterogeneous reaction
systems [2]. Thermomorphic catalysis [3e6] is one of the new
approaches to solve the problems of separation and catalytic effi-
ciency with or without the fluorous solvents. Thermomorphic
catalysis has the exclusive property that the reaction mixture is
homogeneous when it is heated during the reaction; and the
product mixture becomes phase separated when cooled after the
reaction. Bergbreiter et al. used a polymer-based thermomorphic
system whose polymeric supporter was not totally dissolved at
high temperature. Gladysz et al. [5,6] and Yamamoto et al. [7,8]
have published the fluorinated compounds to catalyze the addi-
tion reaction of unsaturated substrates without the use of expen-
sive fluorous solvents. Fan et al. have also reported the use of the
thermomorphic system with a non-fluorous catalyst for asym-
metric hydrogenation [9].
compounds and many industrially useful chemicals or materials
[10]. A number of applications have been developed in the labo-
ratory and commercial level on this reaction. In particular, the
scientist R. F. Heck won the Nobel Prize in 2010 for this important
discovery sharing with E.I. Negishi and A. Suzuki reported by R.F.
Service in Science [11]. So far most of the efforts in this field are to
deal with the Pd catalysts, substrates, mechanisms etc. [12e15], but
to develop a recyclable reaction system for the Heck reaction is still
rare [16]. Previously we have reported the fluorous-ponytailed Pd
complexes for the Heck arylation [17e19]. Reported here are the
recyclable cationic Pd-catalyzed Heck reactions. The solubility
properties of cationic Pd complexes, 2aec, are interesting and have
been studied at different temperatures ranging from ꢀ40e90 ꢁC in
polar organic solvents. In addition, the catalyst 2b shows greater
stability and its activity has been demonstrated by reusing up to 15
recycles with 100% selectivity to trans product.
2. Results and discussion
The solubility of cationic Pd complex 2aec and neutral Pd
complex 3a,b [17e19] in DMF as a function of temperature is shown
in Fig. 1. The solubility was measured by the variable temperature
NMR spectrometer, where the temperatures were varied
from ꢀ40e90 ꢁC. We recorded the NMR integration of the peak of
the C5(50)-protons in 2,20-bpy and compared its value to that of the
* Corresponding author. Tel.: þ886 2 2771 2171x2417; fax: þ886 2 2731 7174.
E-mail address: normanlu@ntut.edu.tw (N. Lu).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.08.028

3638
C.-K. Li et al. / Journal of Organometallic Chemistry 696 (2011) 3637e3642
Table 1
18
16
14
12
10
8
Recycling results of 2b-catalyzed Heck reaction under thermomorphic mode.
2a
2b
2c
3a
3b
Run
Time (h)
Temperature (ꢁC)
Yield (%)
TON
1
2
3
4
5
6
7
8
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
6
9
10
11
12
13
14
15
4
2
0
-2
Reaction conditions: DMF (5 ml); 4a (2.54 mmol, 517.79 mg), 5b (5.08 mmol,
437.01 mg), NEt3 (7.61 mmol, 770.48 mg), 0.1 mol % 2b (4.00 mg).
-60
-40
-20
0
20
40
60
80
100
Temperature, 0C
Fig. 1. Plot of solubility curves of 2aec and 3a,b as a function of temperature. It is note
that the extent of solubility change of 2aec with temperature is much greater than
that of 3a,b.
mixtures were cooled to below ꢀ20 ꢁC and centrifuged, and the
catalysts recovered by decantation. The recovered 2b,c was added
with DMF, substrates, and base to proceed to the next cycle. The
products were quantified with GC analysis by comparison to
internal standard (NMP). The results of Heck reaction exhibited
a 100% selectivity favoring the trans product in just 3 h. As one
example shown in Table 1, the Heck reaction of C6H5I (4a) with
methyl acrylate (5b) could be catalyzed by 2b with good recycling
results for a total of 15 times with the same trans selectivity and
high TON. To our knowledge, this is the first example of fluorous
cationic Pd-catalyzed Heck reaction under the thermomorphic
mode with such a high yield and recyclability. Table 2 shows results
of Heck reaction of 4a and 5b using neutral Pd complex 3b as
a catalyst for comparison. This complex also shows 100% selectivity
with high TON, but it shows less recyclability up to 8 times as
compared to cationic complex 2b with extended reaction time of 6-
7 h. It is well-known that Heck reaction starts with the oxidative
addition of aryl halide to the active Pd catalyst center, so the
oxidative addition is then favored by the electron rich Pd center.
Although the Pd center in neutral complex 3b is more electron rich
than in cationic complex 2b,c, complexes 2b and 2c showed the
enhanced activity and recyclability than the former one, 3b. The
possible rationales are because the cationic complex 2b or 2c as
shown in Fig. 1 demonstrates the higher degree of solubility in
polar solvent due to their ionic nature which allows them for better
dissociation in the solvent and better catalytic activities. This
property offsets the disadvantage of electron deficiency in metal
center, so cationic 2b,c can give rise to higher activity than neutral
3b in the overall catalytic outcomes.
peak integration of
u-proton (from terminal HCF2 group) of the
standard, HCF2(CF2)3CH2OH. It was shown that compound 2a was
slightly soluble in DMF at ꢀ30 ꢁC, but 2b and 2c were totally
insoluble below ꢀ30 ꢁC. The solubility of 2a in DMF began from
virtually zero at ꢀ30 ꢁC, increased with the temperature from ꢀ30
to 10 ꢁC and increased remarkably at temperature >10 ꢁC. The
solubility curves of 2b and 2c, however, began from virtually zero
at ꢀ20 ꢁC and 0 ꢁC, respectively; then increased dramatically at
higher temperature (>23 ꢁC). As shown in Fig. 1, the solubility of
2aec significantly increased with the increasing temperature
from ꢀ40e90 ꢁC while the solubility change of 2a was the greatest.
Because 2a is still slightly soluble in DMF at ꢀ30 ꢁC, it is more
difficult to work with 2a during the recycling procedures. There-
fore, cationic Pd complex 2b,c was then selected as a good candi-
date for the subsequent catalytic experiments to examine the
recyclability of Heck reactions here under fluorous biphasic system
(FBS) or the thermomorphic mode.
The solubility of neutral palladium complex 3a,b [17e19] in
DMF was reported before, and was also incorporated in Fig. 1 for
comparison. It was known that the solubility of 3a,b started from
virtually zero at 20 ꢁC and then increased by several orders when
temperature was raised up to 90 ꢁC. Because of this thermomorphic
property, the Heck reactions catalyzed by 3a,b can be efficiently
carried out, easily separated and recovered at room temperature for
eight times [17]. It was surprising to note that the extent of solu-
bility change of 2aec with temperature is at least three times
greater than that of 3a,b.
The 2b-catalyzed Heck reaction of 4a and 5b using very low
loading of catalyst of only 0.001 mol% is shown in Table 3. It was
observed that catalyst 2b was effective at such a low amount with
very high TON of 100000 in 32 h.
In addition, the cationic Pd catalyst 2b was also studied for Heck
arylation of 4a and 5b under fluorous biphasic system (FBS) and the
results were summarized in Table 4. The catalyst could be
As shown in Scheme 1, the Pd-catalyzed Heck arylation of
methyl acrylate with aryl iodides was selected to demonstrate the
feasibility of recycling usage with 2b,c or 3b as the catalyst using
DMF as the solvent under thermomorphic mode, at ca. 140e150 ꢁC
for 3e7 h varying in each run. At the end of each cycle, the product
Thermomorphic mode
2b/3b
catalyst
O
140-150 o
NEt3
C
R
I
O
O
+
+
HNEt3I
R'
O
R'
R
H
R'
5a H
5b
4a
4b OMe
Me
Scheme 1. The cationic Pd-catalyzed Heck reaction under thermomorphic mode.

C.-K. Li et al. / Journal of Organometallic Chemistry 696 (2011) 3637e3642
3639
Table 2
Recycling results of 3b-catalyzed Heck reaction under thermomorphic mode.
Table 5
Recycling results of 2b-catalyzed Heck reaction under thermomorphic mode.
Run
Time (h)
Temperature (ꢁC)
Yield (%)
TON
Run
Time (h)
Temperature (ꢁC)
Yielda (%)
TON
1
2
3
4
5
6
7
8
5
6
7
7
7
7
7
7
140
140
140
140
140
140
140
140
100
100
100
100
100
100
100
100
1000
1000
1000
1000
1000
1000
1000
1000
1
2
3
4
5
6
7
8
3
3
3
3
3
3
3
3
140
140
140
140
140
140
140
140
100
100 (100)
100
100 (98)
100
100
1000
1000
1000
1000
1000
1000
1000
1000
100 (99)
100
Reaction conditions: DMF (5 ml), 4a (2.5 mmol, 610 mg), methyl acrylate 5b
(5.0 mmol, 355 mg), NEt3 (5.0 mmol, 510 mg), 0.1 mol % 3b (3.64 mg).
Reaction conditions: DMF (5 ml), 4-iodoanisol (4b) (2.54 mmol, 594.01 mg), 5b
(5.08 mmol, 437.01 mg), NEt3 (7.61 mmol, 770.48 mg), 0.1 mol % 2b (4.00 mg).
a
Isolated yields which are in good agreement with GC data are given in
parentheses.
Table 3
Recycling results of 2b-catalyzed Heck reaction under thermomorphic mode.
using NPr3 as a base compared with using NEt3. Furthermore, this
cationic 2b-catalyzed Heck reaction of aryl chloride which is known
to be much difficult to react had been successfully tested one time,
but the recovery and reuse of the catalyst still remained as a chal-
lenging task in this case.
Run
1
Time (h)
32
Temperature (ꢁC)
140
Yield (%)
100
TON
100,000
Reaction conditions: DMF (5 ml); 4a (63.45 mmol, 12.94 g), 5b (126.80 mmol,
10.93 g), NEt3 (190.36 mmol, 19.26 g), 0.001 mol % 2b (1.00 mg).
However, when the neutral 3b was used as a catalyst, the results
showed the opposite base effect on catalytic activity of 3b-cata-
lyzed Heck reaction. Tables 11 and 12 showed the results of 3b-
catalyzed Heck reaction of 4-nitrobromobenzene (4c) using NEt3 or
NPr3 as a base. The 3b-catalyzed Heck reaction showed good
activities using NEt3 as a base with almost same reactivity for 5
runs, but in contrast, when NPr3 was used as a base, the reactivity
dropped significantly after 3 cycles.
The similar trends of base effects have also been observed in the
case of 3b-catalyzed Heck reaction of 4-bromoacetophenone (4d).
These results are listed in supplementary material (see Table II & III
in Supplementary material).
The amount of residual Pd catalyst in the product solution after
centrifugation from the specific run was determined by ICP-MS, the
results indicating that the recovery of Pd catalyst left ca. 4% of the
Pd catalyst in solution as shown in Table 13. The amounts of Pd
recovered are 95.13, 94.33 and 97.79% for 4e2, 4e4 and 4e5,
respectively. In comparison, the data from Table 14 showed the
residual Pd present in the solution where neutral 3b was used.
Thus, the amounts of residual Pd present from the cationic Pd-
catalyzed Heck reaction were few percentages, although these
numbers are higher than 0.02% which is the average amount of
residual Pd present from neutral Pd-catalyzed reaction shown in
Table 14. The reason why product of Heck reaction catalyzed by the
cationic 2b,c contained more residual Pd than that catalyzed by the
neutral 3b,c is very likely due to the good solubility of cationic Pd
complexes 2b and 2c (data for 2c-catalyzed Heck reaction was
shown in Table I and IV of supplementary material.) From the Fig. 1,
it is known that the dissolution of cationic 2b,c in DMF at e 20 ꢁC is
successfully recycled for only 6 times, but it took a longer time to
complete (i.e. 25 h for the 6th run). These results indicated that
cationic Pd catalyst was more favored in thermomorphic condition
than in FBS.
With electron releasing OMe substituents on iodobenzene (4b),
excellent yields and recyclabilities could also be achieved for the
2b-catalyzed Heck arylation of 5b under the thermomorphic mode
(Table 5). The results (see supplementary material; Table I, 2c-
catalyzed Heck arylation) of Heck reaction catalyzed by 2c were
very similar to those by 2b, although in the case of 2c the reaction
temperature required about 10 ꢁC higher. Overall, complex 2b,c
could be easily recovered and reused in the Pd-catalyzed Heck
arylations of methyl acrylate under the thermomorphic mode.
Furthermore, the results shown in Table 6 obtained from 3b-cata-
lyzed Heck reaction were also similar to those from 2b-catalyzed
reaction, although it needed both higher temperature (ca. 10 ꢁC
higher) and longer time (mainly 7 h) to complete.
The cationic Pd complex 2b was also found to be effective in the
Heck arylation of less reactive aryl bromide under thermomorphic
mode as shown in Scheme 2. Tables 7 and 8 show the results of
Heck reaction of the NO2-containing aryl bromide (4c) with methyl
acrylate (5b) using tripropylamine (NPr3) or triethylamine (NEt3) as
a base. The catalyst shows better catalytic activity using NPr3 as
a base with high TON of ca. 1000 and could be recycled for almost 7
times. In contrast, using NEt3 as a base, it lowers the activity of the
cationic 2b which shows the poor recyclability as shown in Table 8.
The same effect of the base was also observed on Heck arylation
of 4-bromoacetophenone (4d) when 2b was used as a catalyst. As
shown in Tables 9 and 10, the results from 2b-catalyzed Heck
reaction of 4d with methyl acrylate gives rise to better recyclability
Table 6
Recycling results of 3b-catalyzed Heck reaction under thermomorphic mode.
Run
Time (h)
Temperature (ꢁC)
Yielda (%)
TON
Table 4
Recycling results of 2b-catalyzed Heck reaction under the FBS mode.
1
2
3
4
5
6
7
8
6
7
7
7
7
7
7
7
150
150
150
150
150
150
150
150
100 (100)
100
100
100 (99)
100
100 (99)
100
1000
1000
1000
1000
1000
1000
1000
1000
Run
Time (h)
Temperature (ꢁC)
Yield (%)
TON
1
2
3
4
5
6
7
3
6.5
10
12
14
25
27
140
140
140
140
140
140
140
100
100
100
100
100
100
36
1000
1000
1000
1000
1000
1000
360
100 (99)
Reaction conditions: DMF (5 ml), 4-iodoanisol (4b) (2.5 mmol, 585.1 mg), 5b
(5 mmol, 355 mg), NEt3 (5 mmol, 510 mg), 0.1 mol % 3b (3.64 mg).
a
Reaction conditions: DMF (3 mL), C8F18 (3.00 ml), 4a (2.54 mmol, 517.79 mg), 5b
(5.08 mmol, 437.01 mg), NEt3 (7.61 mmol, 770.48 mg), 0.1 mol % 2b (4.00 mg).
Isolated yields which are in good agreement with GC data are given in
parentheses.

3640
C.-K. Li et al. / Journal of Organometallic Chemistry 696 (2011) 3637e3642
Thermomorphic mode
catalyst 2b/3b
140-150 o
C
O
Y
Br
Y
O
O
+
+
HNEt3Br
or
HNPr3Br
O
NEt3 or NPr3
Y
4c
NO2
5b
4d COMe
Scheme 2. Cationic/neutral Pd-catalyzed Heck reaction of aryl bromide under thermomorphic mode.
Table 7
Table 10
Recycling results of 2b-catalyzed Heck reaction using NPr3 as a base under ther-
Results of 2b-catalyzed Heck reaction using NEt3 as a base under thermomorphic
momorphic mode.
mode.
Run
Time (h)
Temperature (ꢁC)
Yield (%)
TON
Run
1
Time (h)
40
Temperature (ꢁC)
150
Yield (%)
98
TON
980
1
2
3
4
5
6
7
8
3
20
15
15
15
15
15
20
140
140
150
150
150
150
150
150
100
95
100
98
>99
96
99
1000
950
1000
980
>990
960
990
Reaction conditions: DMF (5 ml), 4d (2.54 mmol, 505.20 mg), methyl acrylate (5b)
(5.08 mmol, 437.01 mg), NEt3 (7.61 mmol, 770.48 mg), 0.1 mol % 2b (4.00 mg).
Table 11
Recycling results of 3b-catalyzed Heck reaction using NEt3 as a base under ther-
momorphic mode.
95
950
Reaction conditions: DMF (5 ml), 4c (2.54 mmol, 512.72 mg), 5b (5.08 mmol,
437.01 mg), NPr3 (7.61 mmol, 1090.89 mg), 0.1 mol % 2b (4.00 mg).
Run
Time (h)
Temperature (ꢁC)
Yield (%)
TON
1
2
3
4
5
3
21
44
35
40
150
150
150
150
150
100
100
100
100
100
1000
1000
1000
1000
1000
Table 8
Recycling results of 2b-catalyzed Heck reaction using NEt3 as a base under ther-
momorphic mode.
Run
Time (h)
Temperature (ꢁC)
Yield (%)
TON
Reaction conditions: DMF (5 ml), 4c (2.74 mmol, 554.31 mg), methyl acrylate (5b)
(5.49 mmol, 472.46 mg), NEt3 (8.23 mmol, 832.98 mg), 0.1 mol % 3b (4.00 mg).
1
2
3
4
15
15
140
140
140
100
90
25
1000
900
250
unique property of complex 2b,c gives high efficiency and good
recyclability very close to ideal recoverable catalyst [25,26]. By
showing homogeneous catalytic activity at the elevated tempera-
ture they can be easily recovered by freezing the solution to ꢀ20 ꢁC
(or lower) followed by decantation. For example, Heck arylation of
aryl iodide with methyl acrylate was easily achieved with very high
TON under thermomorphic condition. It turned out that cationic Pd
complexes of this type were also the efficient catalysts for Heck
arylation of less reactive aryl bromides with good activity and
reusability.
Reaction conditions: DMF (5 ml), 4c (2.54 mmol, 512.72 mg), 5b (5.08 mmol,
437.01 mg), NEt3 (7.61 mmol, 770.48 mg), 0.1 mol % 2b (4.00 mg).
much better than that of neutral 3b,c, so during the work-up, more
residual Pd from cationic catalyst 2b,c could leak out to the solution
than that from neutral catalyst 3b,c when the lower temperature
was difficult to maintain throughout the procedures.
3. Conclusions
In summary, the new series of cationic palladium complexes
(2aec) containing fluorous-ponytailed bipyridyl ligands were
synthesized and successfully evaluated for Heck arylation under
the thermomorphic mode or FBS. This type of Pd complexes shows
excellent activities and reusabilities for a total of 15 recycles under
thermomorphic mode [21e24]. The cationic Pd complexes 2aec
whose good thermomorphic property is attributed to their ionic
nature show the even greater degree of solubility in polar solvents
at high temperature than the neutral Pd complexes 3a,b. This
4. Experimental
4.1. General procedures
Gas chromatographic/mass spectrometric data were obtained
using an Agilent 6890 Series gas chromatograph with a series 5973
mass selective detector. The reaction was monitored with a HP
6890 GC using a 30 m ꢂ 0.250 mm HP-1 capillary column with
a 0.25 mm stationary phase film thickness. The flow rate was 1 mL/
min and splitless. Samples analyzed by fast atom bombardment
(FAB) mass spectroscopy were done by the staff of the National
Central University (Taiwan) mass spectrometry laboratory. Infrared
Table 9
Results of 2b-catalyzed Heck reaction using NPr3 as a base under thermomorphic
mode.
Run
Time (h)
Temperature (ꢁC)
Yield (%)
TON
Table 12
1
2
3
4
5
6
7
8
3
20
15
15
15
15
15
20
140
140
150
150
150
150
150
150
100
95
100
98
>99
96
99
1000
950
1000
980
>990
960
990
Recycling results of 3b-catalyzed Heck reaction using NPr3 as a base under ther-
momorphic mode.
Run
Time (h)
Temperature (ꢁC)
Yield (%)
TON
1
2
3
4
3
35
20
55
150
150
150
150
100
86
100
46
1000
860
1000
460
95
950
Reaction conditions: DMF (5 ml), 4d (2.54 mmol, 505.20 mg), 5b (5.08 mmol,
437.01 mg), NPr3 (7.61 mmol, 1090.89 mg), 0.1 mol % 2b (4.00 mg).
Reaction conditions: DMF (5 ml), 4c (2.74 mmol, 554.31 mg), methyl acrylate (5b)
(5.49 mmol, 472.5 mg), NPr3 (8.23 mmol, 1179.38 mg), 0.1 mol % 3b (4.00 mg).

C.-K. Li et al. / Journal of Organometallic Chemistry 696 (2011) 3637e3642
3641
Table 13
Percentage (%) of residual Pd present after 2b-catalyzed Heck reaction.
4.1.1. Starting materials
Chemicals, reagents and solvents employed were commercially
available and used as received. C9F19CH2OH, C10F21CH2OH and
C10F23CH2OH were purchased from Aldrich and SynQuest.
Table
Pd (in ppm)
detected
Wt of the
sample
(mg)
Theoretical value
of Pd (in ppm)
before recovery
Recovery
(%)b
no.- Run no.a
from ICP
4e2
4e4
4e5
27.78
32.30
22.44
473.30
474.20
265.90
570.32
569.24
1015.17
95.13
94.33
97.79
4.2. Preparation of cationic Pd complexes 2aec where Rf ¼ n-C9F19
(a), n-C10F21 (b), and n-C11F23 (c)
Note:
As shown in Scheme 3, the reaction of allylpalladium(II) chlo-
ride dimer and AgOTf with three highly fluorinated bipyridine
derivatives, 4,40-bis(RfCH2OCH2)-2,20-bpy (1aec) in different reac-
tions were charged into a round bottomed flask, and CH2Cl2 (3 mL)
added as the solvent. The solution color changed from red to
yellow after mixing for several min. The solution was further stir-
red at 60 ꢁC for 24 h before the solvents and volatiles were
removed under vacuum, resulted in the synthesis of cationic
complex, [Pd(h3-allyl)(4,40-bis-(RfCH2OCH2)-2,20-bpy)](OTf) 2aec,
as the pale yellow solid, where Rf ¼ n-C9F19 (a), n-C10F21 (b), n-
C11F23 (c), respectively. In addition, the complex 3a,b, {PdCl2[4,40-
bis-(n-RfCH2OCH2)-2,20-bpy]} where Rf ¼ n-C9F19 (a), n-C10F21 (b)
was also synthesized by the procedure reported elsewhere [20].
The results obtained from cationic Pd complex 2aec and neutral Pd
catalyst 3a,b were also compared.
a
Taking 4e2 for example, 4-2 stands for data from Run No. 2 of Table 4.
Because 2c is slightly less soluble in polar solvent than 2b at the same
b
temperature, the recovered Pd is higher in average percentage from 2c case (96.99%)
than that from 2b case (95.75%). (The residual Pd data present in 2c-catalyzed Heck
reaction was shown in Table IV of supplementary material.)
Table 14
Percentage (%) of residual Pd present after 3b-catalyzed Heck reaction.
Table
No.- Run No.
Pd (in ppm)
detected
from ICP
Wt of the
sample
(mg)
Theoretical value of
Pd (in ppm)
before recovery
Recovery
(%)
2e5
2e6
2e7
0.135
0.147
0.157
781
781
781
681.129
680.994
680.847
99.98
99.98
99.98
Analytical data of 2a: Yield: 76.52%; 1H NMR (500 MHz, d-DMSO,
80 ꢁC),
d
(ppm):
d
8.43 (s, 2H, H3), 8.95 (d, 2H, 3JHH ¼ 5.3 Hz, H6), 7.71
spectra were obtained on a Perkin Elmer RX I FT-IR Spectrometer.
NMR spectra were recorded on Bruker AM 500 using 5 mm sample
tubes. D-toluene, deuterated DMF and deuterated Me2SO were the
references for both 1H and 13C NMR spectra; and FreonÒ 11 (CFCl3)
was the reference for 19F NMR spectra.
3
(d, 2H, JHH ¼ 5.3 Hz, H5), 4.97 (s, 4H, bpy-CH2), 4.39 (t, 4H,
3JHF ¼ 14.5 Hz, CH2CF2,), 6.07 (m, 1H, allyl Hcentral), 4.40 (bd, 2H, allyl
H
syn), 3.59 (bd, 2H, allyl Hanti); 19F NMR (470.5 MHz, d-DMSO, 80 ꢁC),
d
(ppm):
d
ꢀ125.7, ꢀ122.9, ꢀ122.4, ꢀ121.7, ꢀ121.6, ꢀ121.5, ꢀ119.1
Rf
O
Rf
O
N
N
1a-c
Rf
Rf
a
CF3(CF2)8
a
b
CF3(CF2)8
CF3(CF2)9
b
CF3(CF2)9
c CF3(CF2)10
A
B
Cl
Pd Pd
Cl
[Pd(CH3CN)2Cl2]
AgOTf
Rf
Rf
Rf
O
Rf
O
O
O
N
N
N
N
Pd
Pd
OTf
Cl
Cl
3a-b
2a-c
Scheme 3. (A) Synthesis of 2aec; (B) Synthesis of 3a,b.

3642
C.-K. Li et al. / Journal of Organometallic Chemistry 696 (2011) 3637e3642
3
(eCH2(CF2)8CF3, 16F), ꢀ80.6 (t, 6F, JFF ¼ 9.7Hz, eCF2CF3), ꢀ77.9(3F,
OTf): 13C NMR (126 MHz, d-DMSO, 80 ꢁC),
(ppm): 71.0 (bpy-CH2),
66.8 (CH2CF2), 120.3, 125.0, 151.5, 153.8, 153.9 (bpy), 100.7e148.5
(C10F19), 119.6 (s, allyl C2), 62.3 (s, allyl C1,3); FT-IR (cmꢀ1): 1617,
CF2 stretch, s); FAB: (M-
cooled to ꢀ30 ꢁC by the cold bath (for convenient operation,
the ꢀ20 ꢁC freezer was frequently used.) and the precipitated
catalyst was centrifuged and quickly recovered by decantation at
room temperature after each run. The recovered Pd catalyst was
washed with 2 mL DMF (or CH2Cl2) 3 times before proceeding to
the next cycle.
d
d
n
1561, 1454 (nbpy, m), 1266, 1211, 1152 (n
OTf)þ: C35H19F38N2O2Pd, calcd m/z 1327.9, found m/z 1327.5; (M
-OTfꢀ C3H5)þ: C32H14F38N2O2Pd, calcd m/z 1288.0, found m/z 1288.5.
Analytical data of 2b: Yield: 63.51%; 1H NMR (500 MHz, d-
Acknowledgments
DMSO, 80 ꢁC),
d
(ppm):
d
8.42 (s, 2H, H3), 8.95 (d, 2H, 3JHH ¼ 5.3 Hz,
H6), 7.71 (d, 2H, 3JHH ¼ 5.3 Hz, H5), 4.97 (s, 4H, bpy-CH2), 4.37 (t, 4H,
Authors thank the National Science Council (NSC 98-2113-M-
027-002-MY3) in Taiwan for the financial support.
3JHF ¼ 14.5 Hz, CH2CF2,), 6.07 (m, 1H, allyl Hcentral), 4.40 (bd, 2H, allyl
H
syn), 3.59 (bd, 2H, allyl Hanti); 19F NMR (470.5 MHz, d-DMSO,
80 ꢁC),
(18F, eCH2(CF2)9CF3), ꢀ80.6 (t, 6F, JFF ¼ 9.0 Hz, eCF2CF3,), ꢀ77.8
(OTf, 3F); 13C NMR (126 MHz, d-DMSO, 80 ꢁC),
(ppm): 71.0 (bpy-
CH2), 66.8 (CH2CF2), 120.3, 125.0, 151.5, 153.8, 153.9 (bpy),
100.7e148.5 (C10F21), 119.6 (s, allyl C2), 62.3 (s, allyl C1,3); FT-IR
d
(ppm):
d
ꢀ125.7, ꢀ122.9, ꢀ122.4, ꢀ121.6, ꢀ121.4, ꢀ119.1
3
Appendix. Supplementary material
d
d
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2011.08.028.
n
(cmꢀ1): 1617, 1561, 1454 (
nbpy, m), 1266, 1211, 1152 (nCF2 stretch, s);
FAB: (M-OTf)þ: C37H19F42N2O2Pd, calcd m/z 1427.9, found m/z
1427.9; (M-OTf-C3H5)þ: C34H14F42N2O2Pd, calcd m/z 1388.9, found
m/z 1388.8.
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Analytical data of 2c: Yield: 60.22%; 1H NMR (500 MHz, d-
DMSO, 80 ꢁC),
d
(ppm):
d
8.63 (s, 2H, H3), 9.06 (d, 2H, 3JHH ¼ 5.3 Hz,
H6), 7.83 (d, 2H, 3JHH ¼ 5.3 Hz, H5), 5.10 (4H, s, bpy-CH2), 4.49 (t, 4H,
3JHF ¼ 14.5 Hz, CH2CF2), 6.17 (m, 1H, allyl Hcentral), 4.52 (bd, 2H, allyl
H
syn), 3.59 (bd, 2H, allyl Hanti); 19F NMR (470.5 MHz, d-DMSO,
80 ꢁC),
d
(ppm):
d
ꢀ126.1, ꢀ123.2, ꢀ122.6, ꢀ121.6 w ꢀ121.9
3
(6CF2), ꢀ119.7 [(eCH2(CF2)10CF3, 18F)], ꢀ81.4 (t, 3F, JFF ¼ 9.0 Hz,
eCF2CF3), ꢀ78.6 (OTf, 3F); 13C NMR (126 MHz, d-DMSO, 80 ꢁC),
d
(ppm): d 72.5 (bpy-CH2), 68.3 (CH2CF2), 121.6, 126.1, 153.1, 155.0,
155.4 (bpy),101.7e119.5 (C11F23),120.9 (s, allyl C2), 63.1 (s, allyl C1,3);
FT-IR n nbpy, m), 1266, 1211, 1152 (nCF2
(cmꢀ1): 1617, 1561, 1458 (
stretch, s); FAB: (M-OTf)þ: C39H19F46N2O2Pd, calcd m/z 1527.9,
found m/z 1527.9; (M-OTf-C3H5)þ: C36H14F46N2O2Pd, calcd m/z
1486.9, found m/z 1486.9.
4.3. Recycling studies of the Heck reaction with Pd complex 2b (or
2c) as a catalyst under thermomorphic mode
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In a typical run, the reaction vessel was charged with DMF
(5 mL), 4aed, methyl acrylate (2 eq.), triethylamine or tripropyl-
amine (3 eq.) and the 0.1 mol % Pd complex 2b (about 4 mg). Then
the reaction mixture was set to react at ca. 130e150 ꢁC for 3e7 h
before GC analysis. After the reaction, the product mixtures were
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