Insoluble perfluoroalkylated polymers: New solid supports for supported fluorous phase catalysis

Article abstract of DOI:10.1002/adsc.201000196

New perfluoroalkylated polystyrene resins have been prepared by the suspension polymerisation of 4-(perfluoro-n-octyl)styrene. The evaluation of these highly fluorinated insoluble materials as catalyst supports for rhodium-catalysed hydrogenation of styre

Full text of DOI:10.1002/adsc.201000196

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DOI: 10.1002/adsc.201000196
Insoluble Perfluoroalkylated Polymers: New Solid Supports for
Supported Fluorous Phase Catalysis
Nicolas Audic,a Philip W. Dyer,b Eric G. Hope,a Alison M. Stuart,a,*
and Samuel Suharda
a
Department of Chemistry, University of Leicester, Leicester, LE1 7RH, U.K.
Fax : (+44)-(0)116-252-3789; e-mail: Alison.Stuart@le.ac.uk
Centre for Sustainable Process Chemistry, Department of Chemistry, Durham University, Durham, DH1 3LE, U.K.
b
Received: March 13, 2010; Revised: July 14, 2010; Published online: September 8, 2010
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.201000196.
Abstract: New perfluoroalkylated polystyrene resins ments in the recycling of the perfluoroalkylated cata-
have been prepared by the suspension polymeri- lysts as compared to that achieved using fluorous re-
sation of 4-(perfluoro-n-octyl)styrene. The evaluation verse-phase silica gel.
of these highly fluorinated insoluble materials as cat-
alyst supports for rhodium-catalysed hydrogenation
of styrene and palladium-mediated Suzuki–Miyaura Keywords: perfluoroalkylated polystyrene; rhodium-
carbon-carbon bond forming reactions with 4-bromo- catalysed hydrogenation; supported fluorous phase
ACHTUNGTRENNUNGacetophenone and 4-bromoanisole revealed improve- catalysis; Suzuki–Miyaura reaction
Introduction
though the catalytic activity decreases upon recycling
in organic solvents, the behaviour is completely differ-
Although fluorous biphase catalysis has emerged as a ent in water where significantly higher TONs are re-
possible methodology for the immobilisation, recov- ported.[3] Similarly, Nishikido reported excellent recy-
ery and reuse of organometallic catalysts,[1,2] the pro- cling results with perfluoroalkylated Lewis acid cata-
hibitive cost of the perfluorocarbon solvents makes it lysts immobilised on fluorous reverse-phase silica gel
impractical for industrial purposes. Supported fluo- for Baeyer–Villiger and Diels–Alder reactions in
rous phase catalysis is an alternative method for recy- water.[4] Successful recycling of perfluoroalkylated
cling perfluoroalkylated catalysts that avoids the use Grubbs–Hoveyda alkene metathesis initiators was re-
of the expensive and environmentally persistent per- ported by two independent groups.[5,6] The key to the
fluorocarbon solvents. Here, non-covalent adsorption catalyst recovery was a solvent switch to a polar or-
of a fluorous-functionalised catalyst onto a support ganic solvent at the end of the reaction that allowed
material, generally silica, which has been modified the fluorinated species to re-adsorb on to the fluorous
with long perfluoroalkyl groups, allows catalysis to be silica before filtration, but even with this solvent
performed in conventional organic solvents and the switch, ~8% catalyst leaching into the organic phase
solid supported catalyst to be recovered by simple fil- was detected. Immobilised perfluoroalkylated chiral
tration, prior to recycle.
copper bis(oxazolines) catalysed successfully the
There have been a number of reports of supported enantioselective glyoxylate-ene reactions, but chiral
fluorous phase catalysis in the literature.[3–9] One of induction decreased substantially by the third catalyst
the most utilised strategies has employed fluorous recycle, something that the authors ascribe to an un-
functionalised silicas as the immobilising agent, al- favourable influence of the silica gel.[7] Likewise,
though this approach has a number of limitations in Biffis[8] and ourselves[9] reported signs of catalyst de-
terms of both catalyst recycle and stability. For exam- composition and the fluorous silica support changing
ple, Bannwarth has described the use of an air-stable, colour in the solventless silylation of 1-octanol using
perfluoroalkyl functionalised Pd(II) complex immobi- dirhodium(II) perfluorocarboxylates and the hydroge-
lised onto fluorous reverse-phase silica gel for nation of styrene with perfluoroalkylated analogues
Suzuki–Miyaura reactions in DME and water. Al- of Wilkinsonꢀs catalyst respectively, whilst Pozziꢀs flu-
Adv. Synth. Catal. 2010, 352, 2241 – 2250
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orous chiral Co
G
Although Yoshino managed to prepare the per-
tive for the hydrolytic kinetic resolution of terminal fluoroalkylated styrene 4 directly from alcohol 2 by
epoxides when it was supported on fluorous silica.[10]
heating at 958C for 18 h in the presence of potassium
The problems described above have led us and hydrogen sulfate, only a 4% yield of the expected sty-
others[11,12] to prepare new, non-silica based, well-de- rene was obtained in our hands and most of the alco-
fined, highly fluorinated solid supports for transition hol 2 was recovered intact at the end of the reaction.
metal based fluorous catalysts. In this regard, Bann- However, by increasing the temperature to 1308C,
warth reported high activities across two recycles for the perfluoroalkylated styrene 4 and a by-product 5,
Suzuki coupling reactions using a perfluoroalkylated resulting from condensation of two molecules of 2,
palladium(II) catalyst immobilised on perfluoroalky- were obtained in a 1:1 ratio with complete conversion
lated PEG dendrimers, but unfortunately without of 2 (Scheme 2). Using column chromatography sty-
metal leaching data.[11] In a parallel study, Gladysz de- rene 4 was separated from the by-product 5, which
scribed the use of commercial Teflon tape as an in- consisted of two diastereomers; 5a contains an anti
soluble fluorinated support for facile separation of a
thermomorphic rhodium hydrosilylation catalyst, in
which catalytic activity was maintained over two recy-
cles, but with some ligand (11%; cycle 1) and metal
(5%; cycle 2) losses.[12] Here, we report the synthesis
and applications of lightly cross-linked perfluoroalky-
lated polystyrene beads. Such systems are not only
thermally robust and insoluble, but also chemically
inert, something that will mitigate unwanted catalyst-
support reactions.
Scheme 2. Dehydration of 1-[4’-(perfluoro-n-octyl)phenyl)]-
ethanol (2).
Results and Discussion
Synthesis of 4-(Perfluoro-n-octyl)styrene
configuration and is a pair of enantiomers (the single
crystal X-ray structure is reported in the Supporting
The four step synthesis of 4-(perfluoro-n-octyl)styrene Information), whilst 5b contains a syn configuration
(4) is outlined in Scheme 1. A copper-mediated cross- and is a single meso compound. The ratio of 4 to 5
coupling reaction between 4-bromoacetophenone and was improved to 91:9 by further increasing the reac-
perfluoro-n-octyl iodide delivered 4-(perfluoro-n-oc- tion temperature to 1858C, decreasing the reaction
tyl)acetophenone (1), which was reduced with lithium time to 2 h and running the reaction under a con-
aluminium hydride to give compound 2 in an excel- trolled vacuum (80 mbar) in order to remove the
lent yield using modifications of procedures described water produced during the reaction. However, 4 was
by Yoshino.[13]
only isolated in 56% yield because polymerisation
also occurred at this elevated temperature. In an at-
tempt to counter this problem, the radical inhibitor
hydroquinone was added but did not prevent signifi-
cant loss of styrene via polymerisation.
A much better method for the formation of 4 was
to convert the alcohol 2 into the corresponding mesy-
late 3, which was then treated with potassium hydro-
gen sulfate and hydroquinone in benzotrifluoride
(BTF) at 1308C for 2 h to give the desired styrene 4
in 82% isolated yield (Scheme 1). In summary, 4-(per-
fluoro-n-octyl)styrene 4 was prepared in 4 steps from
4-bromoacetophenone with an overall yield of 76%
and only one purification step was required during
the whole synthesis.
Polymer Synthesis and Characterisation
A series of highly and lightly cross-linked polystyrene
Scheme 1. Synthesis of 4-(perfluoro-n-octyl)styrene (4).
polymers (P1a–P8c) was prepared by radical-initiated
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Insoluble Perfluoroalkylated Polymers: New Solid Supports for Supported Fluorous Phase Catalysis
Table 1. Synthesis of perfluoroalkylated polystyrene beads by suspension polymerisation.
Code DVB [%] Rf8-styrene [%] Styrene [%] Diluent Suspension Stabilizer[a] Stirring [rpm] Conditions Yield [%]
Method A
P1a
P2a
P3a
50
25
10
5
50
75
90
95
0
0
0
0
C6H5CF3
C6H5CF3
C6H5CF3
C6H5CF3
1% PVA
1% PVA
1% PVA
1% PVA
500[b]
500[b]
500[b]
500[b]
808C, 8 h
808C, 8 h
808C, 7 h
808C, 20 h
95
85
65
67
P4a
Method B
P5b
P6b
5
2
95
98
0
0
None
None
1% PVA, 2% NaCl
1% PVA, 2% NaCl
700[c]
700[c]
708C, 16 h
708C, 16 h
78
70
Method C
P7c
P8c
10
5
60
60
30
35
C6H5CF3
C6H5CF3
1% PVA, 2% NaCl
1% PVA, 2% NaCl
545[b]
545[b]
708C, 12 h
708C, 12 h
55
55
[a]
The suspension stabilizer solutions were prepared as 1 or 2% solutions by mass.
Overhead mechanical stirrer.
Magnetic stirrer bead.
[b]
[c]
suspension polymerisation[14,15] of 4-(perfluoro-n-oc- ployed, a mixture of PVA and NaCl was used as the
tyl)styrene (4), styrene and 1,4-divinylbenzene (DVB) suspension stabiliser and a magnetic stirrer bead was
using one of three different methods (Table 1). When utilised instead of an overhead mechanical stirrer.
benzotrifluoride was used as the diluent and 1% poly- Polymers P7c and P8c were prepared using Method
vinyl alcohol (PVA) was used as the suspension stabil- C, which combined using benzotrifluoride as the di-
iser in Method A, spherical polystyrene beads were luent with PVA/NaCl as the suspension stabiliser. The
obtained in all cases, except for polymer P4a. Lightly fluorine content of the latter two lightly cross-linked
cross-linked polymeric beads containing 2–5% di- polymers (5–10% divinylbenzene) was varied by in-
vinylbenzene were synthesised successfully when corporating some styrene as well as the fluorinated
Method B was used. In Method B no diluent was em- monomer 4.
Figure 1. (a) Solid-state 19F NMR spectrum of P3a. (b) Solid-state 13C NMR spectrum of P3a.
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The polymeric products were characterised by ele- ing Information. This low level of swelling appears at
mental analysis as well as by solid-state 13C and odds with the relatively low degree of cross-linking
19F NMR spectroscopy. The 13C NMR spectrum of and is something that has been attributed to the high
polymer P3a is shown in Figure 1 and is typical for a degree of functionalisation of the aromatic rings.[16]
lightly cross-linked polystyrene with broad resonances
at 40 ppm for the CH/CH2 signals, at 128 ppm for the
aromatic CH signals and at 149 ppm for the ipso car- Screening of Support Materials
bons. The 19F NMR spectrum, however, is more infor-
mative since it clearly shows the incorporation of the The new perfluorinated polystyrene-derived resins
long perfluoro-n-octyl group with signals for the ter- were evaluated initially as solid supports for the per-
minal CF3 (À81 ppm), the CF2 attached directly to fluoroalkylated palladium pre-catalyst
the aromatic ring (À110 ppm) and the mid-chain Suzuki–Miyaura reaction between 4-bromonitroben-
CF2ꢀs (À122 to À126 ppm). zene and phenylboronic acid (Table 2). The palladium
6
in the
Analysis of the various functionalised polymer complex 6 was first loaded onto each of the fluorinat-
resins by scanning electron microscopy (Figure 2) re- ed polymers by stirring a benzotrifluoride solution of
vealed that the lightly cross-linked polymers, which 6 with the fluorinated solid support for 15 min, before
contain ꢀ25% divinylbenzene content, are smooth, removing the solvent under vacuum and drying the
regular-sized beads, whereas the highly cross-linked polymer-supported catalyst (1 mg of catalyst/1 g of
polymer, P1a, has an irregular surface, a sign of a support) under reduced pressure. Catalytic reactions
more mechanically fragile structure. Unfortunately, were then performed with a 0.2 mol% palladium
the new fluorinated polymers showed limited swelling loading in DME at 808C for 12 h. After cooling the
behaviour in a range of different organic solvents (the reaction mixture to 08C, the liquid phase was re-
average increase in the volume of the beads is only moved carefully, worked up and analysed by GC. In
70%); the swelling data are reported in the Support- the meantime, the polymer beads were washed with
Figure 2. SEM of P2a (top) and P1a (bottom).
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Insoluble Perfluoroalkylated Polymers: New Solid Supports for Supported Fluorous Phase Catalysis
Table 2. Recycling results for the perfluoroalkylated palladium(II) catalyst 6 supported on the perfluorinated polymer resins
in the Suzuki–Miyaura reaction.
Solid Support
Monomer Content [%]
Rf8-Styrene
Conversion [%]
Run 2
DVB
Styrene
Run 1
Run 3
P4a
P5b
P2a
P8c
P7c
P1a
P4a[a]
5
5
25
5
10
50
5
95
95
75
60
60
50
95
0
0
0
35
30
0
99
99
89
99
99
99
99
97
15
67
86
61
10
15
23
1
29
40
28
0
0
0
[a]
[PdCl2ACHTUNGTRENNUNG(PPh3)2] was supported on polymer P4a.
DME and water, and dried for 2 h before being teria, polymers P7c and P8c were chosen from the ini-
reused in two further catalytic runs.
tial screening.
When the perfluoroalkylated palladium(II) pre-cat-
alyst 6 was supported on polymer P4a, which contains
the highest fluorine content (61%) of these fluorinat- Supported Suzuki–Miyaura Reaction
ed solid supports, nearly quantitative conversion was
obtained in runs 1 and 2, but only 23% conversion The Suzuki–Miyaura reaction with the more challeng-
was obtained in the third cycle. Kinetic studies on this ing substrates, 4-bromoacetophenone and 4-bromo-
supported catalyst system revealed a reaction profile,
ACHTUNGTRENaNGNU nisole, was undertaken in an in-depth investigation
which was much slower (quantitative conversion after of polymers P7c and P8c as materials for supported
approximately 10 h) than that for the homogeneous catalysis; comparisons with fluorous reverse-phase
system (2 h), consistent with heterogenisation of the silica gel (FRPSG) for the same reactions were under-
catalyst on the support materials. Reasonable recy- taken in parallel (Table 3). Both of the perfluorinated
cling results were also obtained with the lightly cross- polymers, P7c and P8c, gave recycling results with
linked polymers P2a, P8c and P7c, which contain 54– reasonable catalytic activity observed in the third run
57% fluorine content. In contrast, polymers P5b and for both substrates, better than those obtained with
P1a gave less efficient recycles due to their poorer FRPSG. These results are entirely consistent with pre-
mechanical properties, powdering very easily. Notably, vious observations from us[9,17] and others[8,10] on
the requirement for a perfluoroalkylated catalyst is metal-catalysed reactions using FRPSG, which high-
clear since little or no recycle was possible using non- light the poor recyclability of such systems, something
fluorinated [PdCl2ACHTNUGTRENUNG(PPh3)2] in association with polymer that has been ascribed to catalyst decomposition on
P4a. As expected, the non-fluorinated catalyst was re- the acidic silica surface. For all of the fluorinated sup-
tained less effectively by the perfluorinated polymer ports the amount of palladium leaching into the or-
with only 15% conversion achieved in the second run, ganic phase was monitored by ICP-OES for each cat-
compared to 97% conversion for the perfluoroalkylat- alytic run and reported as a percentage of the original
ed complex.
charge. In general, there was less than 2% palladium
Notwithstanding the efficacy of the new fluorinated leaching into the organic phase per catalytic run and
resins as catalyst supports, as determined from the re- there appeared to be slightly less palladium leaching
cycling results shown in Table 2, the mechanical sta- with polymer P7c compared to that with polymer
bility of the polymer support and the fluorine content, P8c. However, even with these polymeric supports,
both of which would affect the overall price of the im- the reduction in activities by the third run cannot be
plementation of these polymers, were also taken into ascribed solely to the catalyst leaching, but rather sug-
consideration when analysing the results from the pre- gest some catalyst degradation.[3]
liminary screening. Based on these three different cri-
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Table 3. Recycling results from the Suzuki–Miyaura reaction.
Fluorinated Support
R
Conversion [%]
Run 2
Pd Leaching [%]
Run 2
Run 1
Run 3
Run 1
Run 3
P8c
P7c
COMe
COMe
COMe
COMe
99
99
99
99
99
23
85
99
54
4
2.8
1.7
2.6
–
1.4
0.7
0.2
–
0.7
0.4
0.3
–
FRPSG
FRPSG[a]
>98
14
P8c
P7c
OMe
OMe
OMe
OMe
99
99
23
70
85
99
0
68
56
0
0.7
0.1
–
0.7
0.3
–
0.4
0.1
–
FRPSG
FRPSG[b]
10
0
–
–
–
[a]
Results taken from ref.[3] with 0.1 mol% catalyst loading.
Results taken from ref.[3] with 0.3 mol% catalyst loading.
[b]
Supported Rhodium-Catalysed Hydrogenation of
Styrene
supported catalyst 7, heating to 638C under 1 atmos-
phere of hydrogen before adding styrene and stirring
the reaction for a further hour at 638C. At the end of
The well-established hydrogenation of styrene with this time, the reaction mixture was cooled to 08C and
fluorinated analogues of Wilkinsonꢀs catalyst has the organic layer was removed for GC and ICP-OES
become a benchmark for comparing the efficacy of analysis (Table 4). For comparative purposes a set of
different fluorous-based catalyst/product separation identical experiments in the presence of FRPSG and
techniques[9,18–20] and was used here to evaluate the in the absence of a support was also undertaken.
performance of the new fluorous-functionalised poly-
In the absence of the polymer beads the thermo-
styrene resins in a second phase of testing. To this morphic rhodium catalyst precipitates as a waxy solid
end, the supported rhodium catalyst 7 was prepared in the reaction vessel allowing the product phase to
by the reaction of [RhClACHTNUGTRNE(UNG C2H4)2]2 with the perfluor- be decanted and the catalyst to be reused with good
oalkylated triarylphosphine in toluene in the presence retention of activity. When 7 was immobilised on
of the fluorinated beads followed by removal of the FRPSG, the catalytic activity is similar but reduces by
solvent under reduced pressure. The catalytic experi- 10% on recycling, presumably as a consequence of
ments were then performed by adding toluene to the catalyst decomposition on the support. In contrast,
Table 4. Recycling studies of the supported perfluoroalkylated Wilkinsonꢀs catalyst.
Fluorinated Support
Rate [mmolLÀ1 hÀ1]
Rh Leaching [%]
Run 2
Run 1
Run 2
Run 3
Run 1
Run 3
No support
FRPSG
P8c
220
220
250
284
216
218
249
285
220
203
250
294
0.06
0.30
0.12
0.06
0.07
0.38
0.04
0.08
0.11
0.22
0.04
0.09
P7c
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Insoluble Perfluoroalkylated Polymers: New Solid Supports for Supported Fluorous Phase Catalysis
analyses were performed by the Elemental Analysis Service
the rhodium catalyst can be recycled without loss in
catalytic activity when supported on perfluoroalkylat-
ed polymers P7c and P8c and furthermore displays
enhanced catalytic activity. The main advantage of
the fluorinated resins arises from the more straightfor-
ward handling/reuse of the catalyst, which is retained
on the functionalised polymer beads. Throughout the
hydrogenation recycling studies low levels of rhodium
leaching into the organic product were observed with
<0.1% per catalytic run for polymers P7c and P8c,
and <0.4% per catalytic run for FRPSG (Table 4).
Notably, Gladysz reported much higher rhodium
leaching levels (run 1 – 0.6%, run 2 – 5%) when the
at the University of North London. Mass spectra were re-
corded on a Kratos Concept 1H mass spectrometer. GC
analyses were performed using a Perkin–Elmer Clarus 500
GC fitted with a PE-5 column for the Suzuki–Miyaura reac-
tions and a SGE SE30 capillary column for the rhodium-cat-
alysed hydrogenations. Inductively coupled plasma optical
emission spectra (ICP-OES) were carried out using an
Uttima 2 ICP-OES spectrometer.
Dichloromethane and triethylamine were dried by reflux-
ing over calcium hydride, whilst diethyl ether was refluxed
over sodium wire, and benzotrifluoride and toluene were
both dried by refluxing over phosphorus pentoxide under di-
nitrogen. All of the solvents were distilled under dinitrogen,
stored in a closed ampoule over 4 ꢂ molecular sieves and
freeze-pumped-thawed three times to remove all dissolved
gases. Before use, 80% divinylbenzene (25 mL) was washed
with a 1% sodium hydroxide aqueous solution (2ꢃ50 mL)
and distilled water (3ꢃ25 mL), dried over magnesium sul-
fate and filtered. The suspension stabiliser solution used in
Method A in Table 1 (aqueous 1% PVA solution) was pre-
pared as follows: 2.5 g of polyvinyl alcohol (MW=72,000,
98% hydrolysed) were dissolved while stirring in 250 mL of
boiling water in a volumetric flask. The suspension stabiliser
solution used in Methods B and C (aqueous 1% PVA, 2%
NaCl solution) was prepared as follows: 2.5 g of polyvinyl
alcohol (MW=72,000, 98% hydrolysed) and 5 g of sodium
chloride were dissolved while stirring in 250 mL of boiling
water in a volumetric flask. The solutions were filtered just
before use to remove the eventual dusts in suspension.
more
highly
fluorophilic
rhodium
catalyst,
[RhCl{P(CH2CH2C6F13)3}3], was supported on Teflon
tape for ketone hydrosilylation.[12]
Conclusions
As well as developing a more efficient method for the
synthesis of 4-(perfluoro-n-octyl)styrene (4), a series
of insoluble, perfluoroalkylated polymer supports was
prepared by the suspension polymerisation of 4-(per-
fluoro-n-octyl)styrene. In the Suzuki–Miyaura reac-
tion with 4-bromoanisole and 4-bromoacetophenone,
higher conversions were obtained in the third cycle
when the perfluoroalkylated palladium catalyst pre-
cursor 6 was supported non-covalently on the per-
fluorinated polymer supports, P7c and P8c, compared
to using FRPSG as the solid support. However, even
with these polymeric supports, the reduction in activi-
ty for the third runs cannot be ascribed solely to the
catalyst leaching, but probably indicate some catalyst
degradation. In contrast, the highly fluorinated rhodi-
um hydrogenation catalyst 7 was recycled without loss
The perfluoroalkylated palladium catalyst, [PdCl2{P(4-
C6H4C2H4C8F17)3}2] 6, and rhodium catalyst [RhCl{P(4-
C6H4C6F13)3}3] 7 were prepared by the literature proce-
dures.[21,19] Fluoroflashꢄ silica gel (40 mm) was purchased
from Fluorous Technologies and H2 (BOC) used in the hy-
drogenation experiments was used without purification.
4-(Perfluoro-n-octyl)acetophenone (1)
in catalytic activity when it was supported on the fluo- A suspension of perfluoro-n-octyl iodide (61.9 g, 110 mmol),
4-bromoacetophenone (20.3 g, 100 mmol) and copper
powder (31.8 g, 500 mmol) in DMSO (100 mL) was heated
with vigorous stirring under a nitrogen atmosphere for 20 h
at 1108C. The hot mixture was filtered rapidly to remove
excess copper. Diethyl ether (500 mL) and water (500 mL)
were added to the filtrate. After 5 min vigorous stirring, the
resulting emulsion was filtered through Celite and the resi-
due was washed with diethyl ether (2ꢃ100 mL). The organic
layer was separated, washed with water (2ꢃ500 mL) to
remove DMSO and dried over magnesium sulfate. After re-
moving the solvent and 1 h of drying under oil pump
vacuum (0.2 mbar), 1 was obtained as an off-white solid;
yield: 53.2 g (99%); mp 64–668C (lit.,[13] 63.5–648C); anal.
calcd. for C16H7F17O: C 35.7, H 1.3%; found: C 35.7, H
1.3%. 1H NMR (300 MHz, CDCl3): d=2.67 (3H, s,
COCH3), 7.72 (2H, d, 3JH,H =8.4 Hz, ArH), 8.09 (2H, d,
3JH,H =8.4 Hz, ArH); 19F NMR (282 MHz, CDCl3): d=
rinated polymers P7c and P8c with <0.1% rhodium
leaching in each cycle. In summary, we have demon-
strated that supported fluorous phase catalysis could
offer an alternative recycling protocol for perfluori-
nated catalysts, but further optimisation is required to
reduce the metal leaching to acceptable levels.
Experimental Section
Proton, 19F and 13C NMR spectroscopies were carried out on
a Bruker DPX300 spectrometer at 300.14, 282.41 and
75.47 MHz, respectively, and were referenced to external
SiMe4 (1H), external CFCl3 (19F) and to external SiMe4 (13C)
using the high frequency positive convention. The highly
coupled 13C NMR signals of the fluorinated carbons are not
listed below. CPMAS 19F and 13C NMR spectroscopies were
also carried out on a Bruker ARX300 spectrometer at
282.09 and 75.40 MHz, respectively, and were referenced to
external CFCl3 and external SiMe4 respectively. Elemental
À126.03 (2F, m, CF2), À122.63 (2F, m, CF2), À121.71 (6F,
4
m, 3ꢃCF2), À121.11 (2F, m, CF2), À111.13 (2F, t, JF,F
=
4
14.1 Hz, a-CF2), À80.70 (3F, t, JF,F =9.9 Hz, CF3); 13C NMR
(75 MHz, CDCl3): d=26.7 (CH3), 127.3 (t, 3JC,F =6.0 Hz,
CH), 128.4 (CH), 133.0 (t, 2JC,F =24.1 Hz, C), 139.8 (C),
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196.9 (C); MS (EI): m/z=538.02262 (M+) (calcd. for
C16H7F17O: 538.02255), 523 (100).
4-(Perfluoro-n-octyl)styrene (4)
Method 1: A 50-mL round-bottomed flask was charged with
1-[4’-(perfluoro-n-octyl)phenyl]-ethanol 2 (13.5 g, 25 mmol),
potassium hydrogen sulfate (6.8 g, 50 mmol) and hydroqui-
none (138 mg, 1.25 mmol) and was connected to a column
filled with blue indicating silica gel (12.5 g). The reaction
mixture was then put under vacuum (80 mbar) and heated
in an oil bath (1858C) for 2 h with vigorous stirring. After
cooling the reaction mixture to room temperature, the or-
ganic products were extracted with hexane (3ꢃ25 mL) and
the combined extracts were dried over magnesium sulfate,
filtered and the solvent was removed to give a brown oil.
The crude mixture was purified by flash chromatography on
silica gel using hexane as eluant and after drying under oil
pump vacuum pure 4 was obtained as a white crystalline
solid; yield: 7.3 g (56%); mp 25–268C (lit.[13] colourless
liquid); anal. calcd. for C16H7F17: C 36.8, H 1.35%; found: C
1-[4’-(Perfluoro-n-octyl)phenyl]-ethanol (2)
A solution of 4-(perfluoro-n-octyl)acetophenone 1 (53.2 g,
99 mmol) in dry diethyl ether (100 mL) was added dropwise
to
a suspension of lithium aluminium hydride (4.0 g,
100 mmol) in dry diethyl ether (100 mL) stirring at 208C
under a nitrogen atmosphere. After the reaction mixture
had refluxed for 12 h, water (3 mL) was added very slowly
(dropwise) with stirring at 08C, followed by an aqueous
sodium hydroxide solution (15%, 3 mL) and water (9 mL).
The resulting heterogeneous mixture was filtered through
Celite and the aluminium salts were washed with hot THF
(4ꢃ100 mL). After removing the solvent, the residue was di-
luted with diethyl ether and the organic phase was washed
with brine, dried over magnesium sulfate, filtered and con-
centrated under reduced pressure to give 2 as an off-white
solid; yield: 51.1 g (96%); mp 58–598C (lit.,[13] 58.5–598C);
anal. calcd. for C16H9F17O: C 35.6, H 1.7%; found: C 35.6, H
1
36.7, H 1.3%. H NMR (300 MHz, CDCl3): d=5.41 [1H, d,
3
3JH,H =10.8 Hz, CH=CH(Z)H(E)], 5.88 [1H, d, JH,H
=
17.7 Hz, CH=CH(Z)H(E)], 6.77 (1H, dd, 3JH,H =17.7 Hz,
3JH,H =10.8 Hz, CH=CH2), 7.54 (4H, m, ArH); 19F NMR
(282 MHz, CDCl3): d=À126.03 (2F, m, CF2), À122.64 (2F,
m, CF2), À121.81 (6F, m, 3ꢃCF2), À121.17 (2F, m, CF2),
1
3
1.5%. H NMR (300 MHz, CDCl3): d=1.53 (3H, d, JH,H
=
=
3
6.6 Hz, CH3), 1.75 (1H, br s, OH), 4.99 (1H, q, JH,H
4
4
À110.59 (2F, t, JF,F =14.1 Hz, a-CF2), À80.70 (3F, t, JF,F
=
6.6 Hz, CHCH3), 7.53 (2H, d, 3JH,H =8.4 Hz, ArH), 7.59
9.6 Hz, CF3); 13C NMR (75 MHz, CDCl3): d=115.6 (CH2),
3
(2H, d, JH,H =8.4 Hz, ArH); 19F NMR (282 MHz, CDCl3):
2
125.3 (CH), 126.1 (t, 3JC,F =6.0 Hz, CH), 127.1 (t, JC,F
=
d=À126.05 (2F, m, CF2), À122.65 (2F, m, CF2), À121.78
24.1 Hz, C), 134.6 (CH), 140.2 (C); MS (EI): m/z=
522.02764 (M+) (calcd. for C16H7F17: 522.02763), 503 (41),
153 (100).
4
(6F, m, 3ꢃCF2), À121.20 (2F, m, CF2), À110.45 (2F, t, JF,F
=
4
14.1 Hz, a-CF2), À80.73 (3F, t, JF,F =9.6 Hz, CF3); 13C NMR
(75 MHz, CDCl3): d=25.2 (CH3), 69.8 (CH), 125.5 (CH),
127.0 (t, 3JC,F =6.0 Hz, CH), 128.0 (t, 2JC,F =24.1 Hz, C),
149.9 (C); MS (EI): m/z=540.03822 (M+) (calcd. for
C16H9F17O: 540.03820), 525 (100).
By-product anti (5a): Rf =0.71 (hexane/diethyl ether, 95/
5); mp 80–828C; anal. calcd. for C32H16F34O: C 36.2, H
1
1.5%; found: C 36.3, H 1.45%. H NMR(300 MHz, CDCl3):
3
d=1.42 (6H, d, 3JH,H =6.6 Hz, CH3), 4.31 (2H, q, JH,H
=
3
6.6 Hz, OCH), 7.43 (4H, d, JH,H =8.1 Hz, ArH), 7.60 (4H,
d, 3JH,H =8.1 Hz, ArH); 19F NMR (282 MHz, CDCl3): d=
À126.09 (4F, m, CF2), À122.69 (4F, m, CF2), À121.85 (8F,
m, 2ꢃCF2), À121.66 (4F, m, CF2), À121.25 (4F, m, CF2),
Methanesulfonic Acid 1-[4’-(Perfluoro-n-octyl)-
phenyl]ethyl Ester (3)
4
4
À110.39 (4F, t, JF,F =14.1 Hz, a-CF2), À80.78 (6F, t, JF,F
=
Methanesulfonyl chloride (4.65 mL, 60 mmol) was added
dropwise to a solution of 1-[4’-(perfluoro-n-octyl)phenyl]-
ethanol 2 (27.0 g, 50 mmol) and triethylamine (8.45 mL,
60 mmol) in dry dichloromethane (300 mL) at 08C under a
nitrogen atmosphere. The reaction mixture was stirred at
08C for 30 min and at 258C for a further 2.5 h before being
washed with an aqueous citric acid solution (5%, 2ꢃ
300 mL). This aqueous phase was extracted with dichloro-
methane (100 mL) and the combined organic phases were
washed with brine, dried over magnesium sulfate, filtered
and the solvent removed to give 3 as a pale yellow solid;
yield: 30.0 g (97%); mp 70–728C; anal. calcd. for
C17H11F17O3S: C 33.0, H 1.8%; found: C 33.1, H 1.7%.
9.3 Hz, CF3); 13C NMR (75 MHz, CDCl3): d=24.5 (CH3),
3
74.7 (CH), 126.4 (CH), 127.2 (t, JCF =6.0 Hz, CH), 128.2 (t,
2JCF =24.2 Hz, C), 148.2 (C); MS (EI): m/z=1047 (1), 693
(8), 539 (62), 523 (100). Crystals suitable for X-ray crystal-
lography were grown by slow evaporation from a solution of
5a in diethyl ether.
By-product syn (5b): Rf =0.44 (hexane/diethyl ether, 95/
3
5). 1H NMR (300 MHz, CDCl3): d=1.50 (6H, d, JH,H
=
3
6.6 Hz, CH3), 4.57 (2H, q, JH,H =6.6 Hz, OCH), 7.35 (4H, d,
3JH,H =8.1 Hz, ArH), 7.50 (4H, d, 3JH,H =8.1 Hz, ArH);
19F NMR (282 MHz, CDCl3): d=À126.09 (4F, m, CF2),
À122.69 (4F, m, CF2), À121.61 (12F, m, 3ꢃCF2), À121.27
4
(4F, m, CF2), À110.53 (4F, t, JF,F =14.5 Hz, a-CF2), À80.76
4
1H NMR (300 MHz, CDCl3): d=1.75 (3H, d, JH,H =6.6 Hz,
(6F, t, JF,F =10.0 Hz, CF3); 13C NMR (75 MHz, CDCl3): d=
3
3
3
CHCH3), 2.86 (3H, s, SO2CH3), 5.81 (1H, q, JH,H =6.6 Hz,
23.3 (CH3), 75.3 (CH), 126.3 (CH), 126.8 (t, JC,F =6.0 Hz,
CH), 127.9 (t, JCF =24.2 Hz, C), 148.2 (C); MS (EI): m/z=
2
CHCH3), 7.60 (4H, m, ArH); 19F NMR (282 MHz, CDCl3):
d=À125.91 (2F, m, CF2), À123.07 (2F, m, CF2), À122.11
1047 (1), 693 (2), 539 (8), 523 (100).
4
(6F, m, 3ꢃCF2), À121.24 (2F, m, CF2), À110.81 (2F, t, JF,F
=
Method 2: Methanesulfonic acid 1-[4’-(perfluoro-n-octyl)-
phenyl]-ethyl ester 3 (12.4 g, 20 mmol), potassium hydrogen
sulfate (5.5 g, 40 mmol), hydroquinone (110 mg, 1 mmol)
and benzotrifluoride (100 mL) were heated in an oil bath
(1308C) for 2 h with vigorous stirring under a nitrogen at-
mosphere. After cooling the reaction mixture to room tem-
perature, the mixture was filtered and the solvent was re-
4
14.1 Hz, a-CF2), À80.72 (3F, t, JF,F =9.9 Hz, CF3); 13C NMR
(75 MHz, CDCl3): d=23.3 (CH3), 38.9 (CH3), 79.2 (CH),
2
126.5 (CH), 127.5 (t, 3JC,F =6.5 Hz, CH), 129.5 (t, JC,F
=
24.5 Hz, C), 143.7 (C); MS (EI): m/z=618.01559 (M+)
(calcd. for C17H11F17O3S: 618.01575), 539 (100), 523 (84), 503
(18), 153 (40).
2248
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Adv. Synth. Catal. 2010, 352, 2241 – 2250

Insoluble Perfluoroalkylated Polymers: New Solid Supports for Supported Fluorous Phase Catalysis
moved to give a brown oil. The crude mixture was purified
by flash chromatography on silica gel using hexane as eluant
and after drying under oil pump vacuum pure 4 was ob-
tained as a white crystalline solid; yield: 8.6 g (82%).
708C for 16 h at 700 rpm with a magnetic stirrer bead. After
cooling the solution to 258C, the liquid phase was removed
using a pipette. The beads were washed with water (3ꢃ
30 mL) and acetone (2ꢃ30 mL), using a pipette to remove
the liquid phase, before being washed for 24 h with acetone
in a Soxhlet apparatus. After drying for 12 h at 508C under
oil pump vacuum, polymer P5b was obtained as spherical
transparent beads; yield: 1.97 g (78%); anal. calcd.: C 37.5,
H 1.4, F 61.0%; found: C 37.8, H 1.5, F 61.6%. CP MAS
19F NMR (235 MHz, 298 K, C6D6): d=À81.73 (CF3),
À110.81 (ArCF2), À122.41 (CF2), À126.73 (CF2CF3);
CPMAS 13C NMR (75 MHz, 298 K): d=40.8 (CH and CH2),
127.7 (ArCH), 148.9 (ArC).
Polymer P6b: The same procedure was used with 4-(per-
fluoro-n-octyl)styrene (2.56 g, 4.9 mmol) and divinylben-
zene, 80% (16 mg, 0.1 mmol) to give polymer P6b as spheri-
cal, transparent beads; yield: 2.15 g (70%); anal. calcd.: C
37.1, H 1.4, F 61.5%; found: C 37.3, H 1.3, F 61.35%.
General Procedure for the Synthesis of the Perfluoro-
alkylated Polystyrene Beads (Table 1); Method A
(for divinylbenzene content from 50% to 5%)
Polymer P2a: A cylindrical glass vessel[14] was charged with
an aqueous 1% PVA solution (40 mL), 4-(perfluoro-n-oc-
tyl)styrene (3.92 g, 7.5 mmol) and divinylbenzene, 80%
(407 mg, 2.5 mmol) in solution in benzotrifluoride (8 mL)
and AIBN (16 mg, 0.1 mmol) in solution in benzotrifluoride
(2 mL). The vessel was flushed with nitrogen and the mix-
ture was stirred at 808C for 8 h at 500 rpm with an overhead
mechanical stirrer. After cooling the solution to 258C, the
liquid phase was removed using a pipette. The beads were
washed with water (3ꢃ50 mL) and acetone (2ꢃ50 mL),
using a pipette to remove the liquid phase, before being
washed for 24 h with acetone in a Soxhlet apparatus. After
drying for 12 h at 508C, polymer P2a was obtained as spher-
ical transparent beads; yield: 3.70 g (85%); anal. calcd.: C
41.1, H 1.9, F, 57.1%; found: C 42.4; H 2.0, F 53.0%.
CPMAS 19F NMR (282 MHz, 298 K): d=À81.56 (CF3),
À110.30 (ArCF2), À121.54 (CF2), À122.58 (CF2), À126.21
(CF2CF3); CPMAS 13C NMR (75 MHz, 298 K): d=40.6 (CH
and CH2), 127.5 (ArCH).
Polymer P1a: The same procedure was used with 4-(per-
fluoro-n-octyl)styrene (2.61 g, 5.0 mmol) and divinylben-
zene, 80% (814 mg, 5.0 mmol) to give polymer P1a as spher-
ical beads; yield: 3.25 g (95%); anal. calcd.: C 47.9, H 2.6;
found: C 48.05, H 2.65. CPMAS 19F NMR (282 MHz,
298 K): dF =À81.04 (CF3), À110.12 (ArCF2), À121.54 (CF2),
À125.87 (CF2CF3); CPMAS 13C NMR (75 MHz, 298 K):
dC =40.4 (CH and CH2), 127.3 (ArCH), 146.8 (ArC).
Polymer P3a: The same procedure was used with 4-(per-
fluoro-n-octyl)styrene (3.29 g, 6.3 mmol) and divinylben-
zene, 80% (114 mg, 0.7 mmol) to give polymer P3a as spher-
ical, transparent beads; yield: 2.20 g (65%); anal. calcd.: C
38.3, H 1.5; found: C 38.4, H 1.4%. CPMAS 19F NMR
(282 MHz, 298 K): dF =À81.56 (CF3), À110.46 (ArCF2),
À121.71 (CF2), À122.56 (CF2), À126.21 (CF2CF3); CPMAS
13C NMR (75 MHz, 298 K): d=40.0 (CH and CH2), 128.1
(ArCH).
General Procedure for the Synthesis of the Perfluoro-
alkylated Polystyrene Beads (Table 1); Method C (for
divinylbenzene content from 10 to 5%)
Polymer
P7c:
4-(Perfluoro-n-octyl)styrene
(3.00 g,
5.7 mmol), styrene (0.30 g, 2.9 mmol), divinylbenzene
(156 mg, 1.2 mmol) and AIBN (20 mg, 0.1 mmol) were in-
troduced into a cylindrical glass reactor[14] that was preheat-
ed at 408C. The aqueous suspension stabiliser solution (1%
PVA, 2% NaCl, 38 mL) and benzotrifluoride (2 mL) were
then added. The reaction mixture was stirred with an over-
head mechanical stirrer (545 rpm) at 708C for 12 h under ni-
trogen. The resulting polymer beads were washed with
water (3 times) before being washed for 24 h with acetone
in a Soxhlet apparatus. After drying for 24 h at 608C, poly-
mer P7c was obtained as spherical transparent beads; yield:
1.90 g (55%); anal. calcd.: C 44.2, H 2.2, F 53.6%; found: C
43.6, H 2.1, F 55.0%. CPMAS 19F NMR (235 MHz, 298 K,
C6D6): d=À82.2 (CF3), À122.4 (CF2), À126.8 (CF2CF3).
Polymer P8c: The same procedure was used with 4-(per-
fluoro-n-octyl)styrene (3.00 g, 5.7 mmol), styrene (0.35 g,
3.4 mmol), divinylbenzene (78 mg, 0.6 mmol), AIBN (20 mg,
0.1 mmol), aqueous suspension stabiliser solution (1% PVA,
2% NaCl, 39 mL) and benzotrifluoride (1 mL) to give P8c
as spherical transparent beads; yield: 1.88 g (55%); anal.
calcd.: C 43.8, H 2.2, F 54.0%; found: C 43.2, H 2.1, F
50.4%. CPMAS 19F NMR (235 MHz, 298 K, C6D6): d=
À82.2 (CF3), À122.4 (CF2), À126.9 (CF2CF3).
Polymer P4a: The same procedure was used with 4-(per-
fluoro-n-octyl)styrene (3.35 g, 6.42 mmol) and divinylben-
zene, 80% (55 mg, 0.34 mmol) to give polymer P4a; yield:
2.27 g (67%); anal. calcd.: C 37.5, H 1.4%; found: C 38.1, H
1.1%.
General Procedure for the Suzuki–Miyaura Reaction
using Supported Catalysts (Table 2 and Table 3)
Polymeric beads were sieved before use and only those in
the 40–100 mesh (425–150 mm) range were used in order to
avoid recovery problems.
General Procedure for the Synthesis of the Perfluoro-
alkylated Polystyrene Beads (Table 1); Method B (for
divinylbenzene content from 5% to 2%)
A
Schlenk tube was charged with polymeric beads
Polymer P5b: A cylindrical glass vessel[14] was charged with
AIBN (16 mg, 0.1 mmol), 4-(perfluoro-n-octyl)styrene
(2.48 g, 4.75 mmol) and divinylbenzene, 80% (41 mg,
0.25 mmol). The mixture was gently warmed until a liquid
phase was obtained. An aqueous 1% PVA, 2% NaCl solu-
tion (30 mL) was added and the vessel was sealed under a
nitrogen atmosphere. The reaction mixture was stirred at
(330 mg) and a solution of [PdCl2{P(4-C6H4C2H4C8F17)3}2] 6
in benzotrifluoride (33 mM, 3 mL, 1 mmol) and stirred for
15 min at 208C. The solvent was evaporated and the result-
ing polymer-supported catalyst 6 (1 mg of catalyst/1 g of
solid) was dried for 3 h under oil pump vacuum.
Phenylboronic acid (67 mg, 0.55 mmol) and aryl halide
(0.51 mmol) were introduced into the Schlenk tube contain-
Adv. Synth. Catal. 2010, 352, 2241 – 2250
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asc.wiley-vch.de
2249

Nicolas Audic et al.
FULL PAPERS
ing the polymer-supported catalyst 6 (330 mg, 1 mmol) under References
argon and the resulting mixture was degassed three times
(vacuum/argon). Degassed DME (5 mL) was added to the
reaction mixture followed by a degassed solution of sodium
carbonate (1m, 2.5 mL, 2.5 mmol). The reaction mixture was
stirred for 12 h at 808C before being cooled to 08C with an
ice bath. The liquid phase was removed carefully with a Pas-
teur pipette and the polymer beads were washed successive-
ly with DME (2ꢃ10 mL), water (2ꢃ10 mL) and DME (2ꢃ
10 mL) and were dried for 2 h under oil pump vacuum
before being reused in a further reaction. All the liquid
phases were combined, diluted with brine (50 mL) and were
extracted twice with ethyl acetate (2ꢃ50 mL). The organic
phase was dried over magnesium sulfate, filtered and con-
centrated under vacuum to give the crude organic mixture
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General Procedure for the Hydrogenation of Styrene
using Supported Catalysts (Table 4)
The highly fluorinated support (250 mg) was introduced into
a Schlenk flask and was dried under oil pump vacuum for
24 h. After adding tris(4-tridecafluoro-n-hexylphenyl)phos-
phine (78 mg, 0.06 mmol) to the solid support under nitro-
gen via a glove box, a solution of [RhClACTHNUTRGNEG(UN C2H4)2]2 in toluene
(2 mL, 3.93 mM, 7.86 mmol) was added to the Schlenk flask
and the reaction was stirred for 15 min at 208C in order to
prepare [RhCl{P(4-C6H4C6F13)3}3] 7. The solvent was re-
moved under vacuum and the resulting polymer-supported
catalyst 7 (60 mg of catalyst/250 mg of solid support) was
dried for 30 min under oil pump vacuum.
After adding toluene (5 mL) to the solid-supported cata-
lyst 7, the reaction mixture was degassed three times
(vacuum/hydrogen) and the tube was sealed under a hydro-
gen atomostphere (1 atm). The reaction mixture was heated
to 638C, then styrene (1 mL, 8.7 mmol) was added and the
reaction mixture was stirred for an hour before being
quenched by cooling down to 08C with an ice bath. The or-
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Acknowledgements
We would like to thank the Royal Society (AMS) and the
EPSRC (NA and SS) for financial support. We would also
like to thank John Fawcett and Kuldip Singh (University of
Leicester) for the single crystal X-ray structure of compound
5a. Dr. David Apperly of the EPSRC Solid-State NMR ser-
vice (Durham University) is gratefully acknowledged for the
recording and analyses of the solid-state NMR spectra.
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2250
asc.wiley-vch.de
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2010, 352, 2241 – 2250