An expedient synthesis of perfluorinated tetraazamacrocycles: New ligands for copper-catalyzed oxidation under fluorous biphasic conditions

Article abstract of DOI:10.1002/ejoc.200600523

Conjugate additions of cyclam to perfluorohexyl vinyl sulfone and sulfoxide, which act as efficient fluorous Michael acceptors, readily give access to new fluoro-ponytail tetraazamacrocycles in good yields. The solubility of the N-tetrasubstituted macrocy

Full text of DOI:10.1002/ejoc.200600523

FULL PAPER
DOI: 10.1002/ejoc.200600523
An Expedient Synthesis of Perfluorinated Tetraazamacrocycles: New Ligands
for Copper-Catalyzed Oxidation under Fluorous Biphasic Conditions
Augustin de Castries,[a] Emmanuel Magnier,[a] Sophie Monmotton,[a] Hélène Fensterbank,[a]
and Chantal Larpent*[a]
Keywords: Fluorinated ligands / Azamacrocycles / Biphasic catalysis / Oxidation / Michael addition
Conjugate additions of cyclam to perfluorohexyl vinyl sul-
fone and sulfoxide, which act as efficient fluorous Michael
acceptors, readily give access to new fluoro-ponytail tet-
raazamacrocycles in good yields. The solubility of the N-tet-
rasubstituted macrocycles depends dramatically on the na-
ture of the polar function (SO or SO2): the sulfoxide cyclam
derivative is soluble in perfluorodecaline (pfd) and perfluo-
romethylcyclohexane (pfmc) while the sulfonyl derivative is
almost insoluble in organic or fluorous solvents. In agreement
with the well known affinity of cyclam for copper(II) ions,
stable copper complexes of the fluorous macrocyclic ligands
have been isolated and characterized. In chloroform/meth-
anol, complexes with four perfluorinated tails have been ob-
tained from reaction of the tetra-N-perfluorohexylsulfinyl-
substituted macrocycle with copper nitrate and copper per-
specifically gives copper complexes of the tri-N-substituted
macrocycle. Complexes with three and four fluorous tails as-
sociated with perfluorocarboxylate counteranions are soluble
in fluorous solvents (pfd and pfmc). These copper complexes
were tested as catalysts for the oxidation of cyclohexene by
molecular oxygen in the presence of tert-butyl hydroperox-
ide (tbhp). The oxidation reactions proceed under fluorous
biphasic conditions and the catalyst can be recovered and
reused. Quenching experiments indicate that cyclohexenyl
hydroperoxide is the main oxidation product of the reaction
performed with or without tbhp. Interestingly, these perfluo-
rinated copper complexes are good, recyclable catalysts for
the oxidation of cyclohexene by molecular oxygen without
tbhp at room temperature and 65 °C.
fluorocarboxylate. In trifluoroethanol,
Michael reaction has been observed and the same reaction
a
selective retro-
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
main an important challenge and there is still a great de-
mand for new fluorous ligands and fully characterized ro-
bust transition metal complexes. In this context, additional
methodologies are required to introduce perfluorinated tags
onto various backbones. We anticipated that conjugate ad-
dition of amines to perfluorinated Michael acceptors would
be a straightforward, general, and versatile approach for the
synthesis of fluorous ligands. This reaction introduces
methylene spacers between the heteroatom of the ligand
and the fluorous tail, which should mitigate the strong elec-
tron-withdrawing effect of the perfluoroalkyl group and
preserve the metal-binding properties of the heteroatom.
Moreover, this method allows the introduction of the fluo-
rous tags in the final step of the synthetic route and hence
avoids cumbersome purification steps. Hetero-Michael ad-
ditions have proven to be useful synthetic tools for the func-
tionalization of various amines and phosphanes.[9–14] Al-
though some conjugate additions to fluorinated acceptors
have been reported,[15] hetero-Michael additions have sel-
dom been used to introduce perfluorinated chains.[16]
Introduction
During the last decade fluorous biphasic chemistry has
evolved into a rich and fruitful research area due to its po-
tential as a new paradigm for green chemical processes.[1,2]
In the fluorous biphasic system approach, the low misci-
bilities of fluorocarbons with most organic solvents allow
the separation of catalysts or reagents modified with perflu-
orinated tags in the fluorocarbon phase from substrates or
products dissolved in the organic phase. The development
of various fluorous reagents and catalysts has enabled fluo-
rous technology to be increasingly applied to the isolation
of reaction products and the recovery of recyclable catalysts
or reagents.[1,2] Since its introduction by Horváth et al.,[3]
fluorous biphasic catalysis (FBC) has been applied to a
variety of catalytic reactions.[1,2,4–7] More recently, the
thermomorphic properties of light fluorous compounds
have been used to develop separation processes without
using fluorous solvents.[8]
Although numerous fluoro-ponytail phosphane and
amine ligands have been prepared,[1–8] their syntheses re-
We recently disclosed a multi-gram scale preparation of
vinyl tridecafluorohexyl sulfoxide (1) and vinyl tridecafluo-
rohexyl sulfone (2) in four steps starting from commercially
available mercaptoethanol.[17] Our synthetic plan avoids the
[a] Institut Lavoisier, UMR-CNRS 8180, Université de Versailles
Saint-Quentin-en-Yvelines,
45 avenue des Etats-Unis, 78035 Versailles cedex, France
E-mail: larpent@chimie.uvsq.fr
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A. de Castries, E. Magnier, S. Monmotton, H. Fensterbank, C. Larpent
FULL PAPER
use of toxic reagents and could be extended to various per- in agreement with the lower reactivity of the double bond
fluorinated chain lengths (Figure 1). Compounds 1 and 2 compared to that of vinyl sulfone 1.[9,10] The addition of
have proven to be good dienophiles in Diels–Alder cycload- water as a co-solvent favors the Michael addition[12,20] and
ditions, with an enhanced reactivity compared to non-fluo- allows the isolation of cyclam derivative 6 by filtration in
rous analogs such as phenyl vinyl sulfoxide.[18]
good yield (86%; Scheme 1). In order to compare the reac-
tivity of our fluorous vinyl sulfone and sulfoxide with classi-
cal Michael acceptors, as well as the stability and the prop-
erties of the corresponding fluorous macrocycles, the
macrocycle 7 was prepared from the commercially available
perfluorinated acrylate 4. Under similar experimental con-
ditions, the tetra-N-substituted macrocycle was obtained in
lower yield. The lower reactivity of acceptor 4[14] as well as
the partial solubility of 7 in the reaction medium, which
renders its isolation more tedious, both account for the
poor isolated yield.
Figure 1. Vinyl tridecafluorohexyl sulfoxide (1) and vinyl tride-
cafluorohexyl sulfone (2).
Since non-fluorous α,β-unsaturated sulfones and sulfox-
ides are excellent Michael acceptors and react with a
number of carbon and heteroatom nucleophiles,[9,10,12–14]
we anticipated that 1 and 2 would be valuable fluorous rea-
gents for the preparation of fluoro-ponytail amine ligands.
We first focused on a well known and widely studied macro-
cyclic ligand, namely 1,4,8,11-tetraazacyclotetradecane (cy-
clam, 3). Cyclam and its N-substituted derivatives have high
affinities for transition metal cations, with a marked selec-
tivity for copper(II) ions, and give very stable copper com-
plexes [the stability constants (logK) are 27.2 and 18.3,
respectively, for cyclam and tetramethylcyclam].[19] This
suggests that fluoro-ponytail macrocycles resulting from the
conjugate addition of cyclam to 1 and 2 will provide robust
catalysts for fluorous biphasic catalysis. Only a few exam-
ples of fluorocarbon-soluble macrocycles have been re-
ported so far. They include a perfluoro(oxy)alkenic cyclam
derivative obtained by N-alkylation with the corresponding
tosylate[6] and a fluoro-ponytail derivative of 1,4,7-triaza-
cyclononane prepared by N-alkylation with C8F17-
(CH2)3I.[7] These macrocycles have been found to be effec-
tive ligands in metal-catalyzed oxidations of hydrocarbons
and alcohols.
Scheme 1. Synthesis of fluoro-ponytail tetraazatetracyclotetrade-
canes.
All the macrocycles were fully characterized. In each
case, elemental analyses and mass spectra confirmed the
grafting of four fluorous tails onto the cyclam skeleton. The
observed numbers of NMR signals are in agreement with
the symmetry of the macrocycles.
Although their fluorine contents are quite similar, the
solubility and stability of macrocycles 5–7 in organic and
fluorous solvents depend dramatically on the polar function
(X) of the Michael acceptor. The main solubilities of fluori-
nated azamacrocycles 5–7 are summarized in Table 1. The
tetra-perfluorinated ester derivative 7 is soluble in most or-
ganic solvents as well as in perfluoromethylcyclohexane
(pfmc). Nevertheless, the presence of a perfluorocarbon
chain close to the ester function makes it sensitive to trans-
esterification and hydrolysis, and we observed that fast
transesterification occurs in methanol or trifluoroethanol
(tfe) and that partial hydrolysis readily takes place in the
presence of water.
We describe here the straightforward syntheses of new
perfluorinated macrocycles by hetero-Michael addition of
cyclam, as well as preliminary studies of the catalytic ac-
tivity of their copper complexes for the oxidation of cyclo-
hexene under FBC conditions.
Results and Discussion
Synthesis of Perfluorinated Tetraazamacrocycles
The tetrasulfone 5 is not soluble, even at high tempera-
As depicted in Scheme 1, the perfluorinated vinyl sulfone tures, in most organic and perfluorinated solvents, except
and sulfoxide 1 and 2 proved to be excellent Michael ac- benzotrifluoride (btf). On the other hand, sulfoxide 6 exhib-
ceptors and afforded fluoro-ponytail macrocycles 5 and 6, its enhanced solubilities with a thermomorphic behavior, as
respectively. The tetra-N-substituted perfluorinated cyclam expected from its fluorine content (about 55%). Macrocycle
derivative 5 is readily obtained by treating cyclam 3 with 6 can be dissolved in hot chloroform or hot thf, and is
vinyl sulfone 1 in 2-propanol at room temperature. Com- rather soluble in polar fluorous solvents such as perfluo-
pound 5 precipitates out of the reaction mixture and is con- romethylcyclohexane (room temp.) and perfluorodecaline
veniently isolated by filtration in 78% yield; the excess of (pfd; 80 °C) but poorly soluble in nonpolar fluorinated sol-
fluorous Michael acceptor can be recovered. Under the vents like Fluorinert® and perfluorohexane.[1h]
same experimental conditions (iPrOH, room temp., 36 h),
Macrocycle 6 is stable in either cold or warm solutions
the reaction of cyclam with vinyl sulfoxide 2 affords the of organic and fluorous solvents. Nevertheless, it is worth
fluoro-ponytail macrocycle 6 in a slightly lower yield (66%), noting that in trifluoroethanol, both sulfone 5 and sulfoxide
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New Ligands for Copper-Catalyzed Oxidation under Biphasic Conditions
FULL PAPER
Table 1. Solubilities of perfluorinated macrocycles 5–7 and copper complexes 9 and 10 in different solvents.[a]
wt.-% F Fluorinert® pfd[b]
pfmc[c]
btf[d]
CHCl3
toluene
Acetone thf
EtOAc
CH3CN MeOH
dmf
tfe[e]
5[f]
53.6
55.6
56.5
N
N
N
N
N
N
N
N
N
N
N
N
N
nd
N
S
N
N
N
N
S
N
nd
S
S
S
S
S
P
S
N
N
P
N
N
S
N
P[h]
N
P
S
S
nd
nd
N
N
N
P[i]
N
N
N
N
S
N
N
N
S
S
S
nd
nd
N
P
N
N
N
N
N
N
N
S
nd
nd
N
N
N
N
N
N
N
N
N
S
nd
nd
N
N
S
S
S
S
S
S
S
P
P
S
S
S
S
5[g]
6[f]
6[g]
7[f]
7[g]
S
S
9a[f]
10a[f]
9b[f]
9b[g]
10b[f]
10b[g]
50.3
47.2
57.9
N
N
S
S
N
S
nd
nd
N
N
N
N
S
S
S
57.1
N
S
S
[a] 8×10–3 ; S = soluble, P = partly soluble, N = not soluble, nd = not determined. [b] Perfluorodecaline. [c] Perfluoromethylcyclohexane.
[d] Benzotrifluoride. [e] Trifluoroethanol. [f] At room temperature. [g] At 80 °C. [h] Partly soluble in hot toluene, not soluble in hot CHCl3.
[i] Partly soluble in hot CHCl3, not soluble in hot toluene.
6 are soluble, but after a short period of time (1 h), retro- bands at 624 and 674 nm, respectively, consistent with a
Michael reactions occur that generate a complex mixture of copper(II)–N4 square-planar complex.[21] The absorption
mono-, di-, and trifunctionalized cyclams.
wavelength and the extinction coefficient for complex 9a
Of the three new perfluorinated macrocycles 5–7, the are close to those of other copper(II) complexes of tetra-N-
sulfoxide derivative 6 appears to be the most suitable ligand substituted cyclams associated with nitrate or triflate
for use in catalytic processes owing to its stability and solu- counteranions.[21] The red shift of the absorption band ob-
bility.
served for complex 9b may result from coordination of the
perfluorocarboxylate anion (in one or both of the axial po-
sitions).
Synthesis of Perfluorinated Copper Complexes
Surprisingly, when the fluorous macrocycle 6 was treated
Copper complexes 9a and 9b, with nitrate or perfluo- with copper nitrate or copper perfluorocarboxylate in tfe or
rocarboxylate counteranions, respectively, were readily ob- in a tfe/methanol mixture, the tri-N-substituted complexes
tained by treating the fluorous macrocycle 6 with copper 10a or 10b were selectively isolated in good yields
nitrate or copper perfluorocarboxylate (8)[7a] in chloroform/ (Scheme 2). This result is important considering the diffi-
methanol (Scheme 2): the complexes precipitate out of the culties encountered in building trifunctionalized cyclam
reaction medium and are readily isolated as pure com- skeletons in short reaction sequences. A close examination
pounds (blue powders) in fairly good yields. Elemental of the reaction in tfe revealed that the tetrasubstituted com-
analysis confirmed the stoichiometry and the purity of plex 9b is first formed and then slowly decomposes into 10b.
complexes 9a and 9b. Their ESI mass spectra display a sig- An acid-catalyzed retro-Michael process may account for
nal at m/z 920–921, which is assigned to the [6 + Cu]2+ ion, the formation of complex 10b. Nevertheless, we have not
i.e. to the 1:1 complex, without counteranion. The visible observed this specific retro-Michael process in other sol-
spectra of complexes 9a and 9b show broad adsorption vents, even in the more acidic hexafluoroisopropanol.[22]
Scheme 2. Preparation of perfluorinated copper(II) complexes 9a,b and 10a,b.
Eur. J. Org. Chem. 2006, 4685–4692
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A. de Castries, E. Magnier, S. Monmotton, H. Fensterbank, C. Larpent
FULL PAPER
The fluorine and copper contents of 10a and 10b confirm amine ligands,[6,7] we investigated the oxidation of cyclohex-
the presence of three fluorous tails as well as the 1:1 stoichi- ene 11 by molecular oxygen in the presence of tert-butyl
ometry of the copper complex. The ESI mass spectra of 10a hydroperoxide (tbhp) catalyzed by complexes 9b and 10b
and 10b display a signal at m/z 723–724, which is assigned under biphasic fluorous conditions (Scheme 3).
to the 1:1 doubly charged copper complex without
The oxidation results are presented in Table 2. All the
counteranion. The visible spectra of N-trisubstituted com- experiments were carried out at room temperature under
plexes 10a and 10b show adsorption bands at 583 and biphasic conditions and O2 atmospheric pressure: the cata-
635 nm, respectively. Their absorption wavelengths are lyst was solubilized in pfd (or pfmc) and the organic phase
lower than those of the tetra-N-substituted complexes 9a was the substrate itself; no additional solvent was used. In
and 9b (vide supra). This is in good agreement with pre- typical experiments (Table 2), the molar ratios between the
viously reported characteristics of non-fluorous cyclam substrate (cyclohexene 11), tbhp, and the catalyst were
complexes, whereby the introduction of N-substituents 40:0.5:0.008 (i.e. 0.02 mol-% catalyst and 1.25 mol-% tbhp).
tends to produce a change in the ligand field properties and GC analysis of the organic phase showed that the oxidation
a shift to higher wavelengths is observed as the number of of cyclohexene gave a mixture of cyclohexenol (12) and cy-
N-substituents is increased.[21a]
As can be seen in Table 1, fluoro-ponytail copper com- ene oxide were also detected.
clohexenone (13; Table 2). In some cases, traces of cyclohex-
plexes 9 and 10 are almost insoluble in organic solvents.
In the presence of copper perfluorocarboxylate (8), mild
Their solubility in fluorous solvents mainly depends on the oxidation of cyclohexene is observed but the conversion de-
nature of the counteranion and is not significantly affected creases dramatically when the fluorous phase is recycled
by the number of fluorous tails. As expected, perfluorocar- (entries 2 and 3). This can be rationalized by the poor sta-
boxylate complexes 9b and 10b exhibit the highest affinities bility of complex 8 and demonstrates that stable complexes
for fluorous phases and are soluble in pfmc and pfd. Nitrate are required.
complexes 9a and 10a are not soluble in perfluorinated sol-
The stable copper complexes 9b and 10b show catalytic
vents.
activity with oxidation yields and turnover numbers (TON)
The experimental conditions developed for the synthesis similar to those previously reported for other fluoro-pony-
of complexes from 6 could not be applied to the synthesis tail ligands derived from cyclam, tacn, or bipyridine.[6,7]
of complexes derived from ligand 5 due to the poor solubil- Complex 9b gave oxidation yields of 320–550% (with re-
ity of this macrocycle. Thus, treatment of 5 with the cop- spect to tbhp) and TONs of 200–350. More importantly,
per(II) perfluorocarboxylate 8 in btf gave an insoluble pur- the fluorous phase can be recovered and recycled, with
ple powder. Nevertheless, a careful analysis of this powder good preservation of the catalytic activity, for up to five
revealed the presence of a complex mixture of the expected runs (entries 4–8, 9, and 10). The catalytic activity decreases
copper complex accompanied by vinyl sulfone 2 and other slightly to around 80–85% in the second run and then re-
retro-Michael products. Attempts to synthesize copper mains constant in further experiments, thus indicating a re-
complexes from the macrocycle 7 bearing perfluorinated es- markable stability of the macrocyclic copper complex. The
ter tails also failed and led to complex mixtures of partially decrease of activity for the second run can be easily ex-
hydrolyzed and transesterified azamacrocycles derivatives, plained by some leaching of complex 9b into the organic
whatever the experimental conditions tested.
phase during the first experiment. As complex 9b is not
soluble in cyclohexene, this phenomenon stopped after the
second run. Complex 10b, which bears three perfluorinated
tails, shows a slightly lower activity than 9b, with oxidation
yields of about 200% and a TON of 100 (entries 15–17).
Oxidation of Cyclohexene (11) Catalyzed by Copper
Complexes 9b and 10b under Fluorous Biphasic Conditions
Macrocycle 6 gives access to stable copper complexes 9 Its catalytic activity decreased significantly during recycling
and 10 bearing four or three perfluorinated chains, respec- (60% and 50% of its initial value for the second and third
tively, which are soluble in fluorous solvents as perfluo- runs, respectively).
rocarboxylate derivatives 9b and 10b. In order to test the
The catalytic oxidation of cyclohexene was further inves-
potential of the fluoro-ponytail azamacrocycle 6 and to tigated in the presence of the most efficient catalyst (9b) in
compare its performance with previously reported fluorous order to improve the oxidation yields and to get further
Scheme 3. Catalytic oxidation of cyclohexene.
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New Ligands for Copper-Catalyzed Oxidation under Biphasic Conditions
FULL PAPER
Table 2. Catalytic activity of copper complexes 9b and 10b for the FBC oxidation of cyclohexene.[a]
Entry
Catalyst
Run
Solvent
Vol.
[mL]
Cat[b]
[mol-%]
Product
mmol
Selectivity [%][c]
Conversion[d] TON[e]
12
13
1
2
3
4
5
6
7
8
–
8
–
1
2
1
2
3
4
5
1
2
1
2
1
2
1
2
3
1
pfd[f]
pfd
4
4
–
0.02
0.4
0.7
0.3
2.8
1.7
1.6
1.7
1.6
2.0
1.6
2.7
0.5
1.2
0.9
0.9
0.5
0.4
1.7
56
40
42
37
35
29
30
31
23
37
44
38
39
45
42
37
38
36
27
54
47
58
58
57
56
56
71
60
51
55
57
51
53
57
55
59
73
136
53
–
85
33
9b
pfd
4
0.02
556
336
312
345
319
394
329
548
108
240
181
177
107
88
347
210
195
216
199
246
206
86
9
9b
pfd
2
4
4
4
0.02
0.08
0.02
0.02
10
11
12
13
14
15
16
17
18
9b
pfd
17
9b
pfmc[g]
pfd
150
113
110
67
55
53
10b
10b
pfmc
4
0.08
340
[a] Unless otherwise mentioned: cyclohexene (40 mmol, 4 mL), tbhp (500 µmol, 55 µL), catalyst (8 µmol), molar ratios 5000:62.5:1, 48 h,
room temperature. [b] With respect to cyclohexene. [c] Traces of cyclohexene oxide are present. [d] Conversion (%) calculated relative to
tbhp. [e] Turnover Number: mol of substrate oxidized/mol of catalyst. [f] Perfluorodecaline. [g] Perfluoromethylcyclohexane.
mechanistic insights. Oxidation yields and TON for the first oxide is the main oxidation product it is completely or partly
and second runs were quite similar when the experiments decomposed in the GC to produce a mixture of alcohol and
were carried out in pfd or pfmc (entries 4–6, 13–14), which ketone. On the other hand, the addition of PPh3 before GC
are both good solvents for 9b. Since the solubility of molec- analysis reduces the hydroperoxide into the corresponding
ular oxygen is higher in the latter,[23] these results seem to alcohol, which can be properly quantified. The results of
indicate that the concentration of molecular oxygen in the GC analyses after quenching with PPh3 clearly demonstrate
fluorous phase is not a limiting parameter, as previously that 14 is the main oxidation product (Table 3). Moreover,
reported.[24] On the other hand, for a given amount of cata- the quantification of 12 allows a precise quantification of
lyst, reducing the volume of the fluorous phase by a factor the real oxidation yield: with 1.25 mol-% of tbhp (standard
of two results in a marked improvement in the oxidation procedure) the oxidation yields reach 1044, 558, and 540%,
yield, up by about 400%, and of the TON, up by about 250 with TONs of 652, 348, and 329, respectively, for the first,
(entries 9 and 10) with 80% of activity remaining in the second and third runs (Table 3, entry 1). In the presence of
second run. An increased interfacial area under these condi- smaller amounts of tbhp (0.05 mol-%) oxidation yields of
tions, which could favor contact between the substrate and more than 22000% with a TON of 515 were achieved. The
the catalyst, may account for these results. Experiments per- catalytic activity decreases to around 50–55% in the second
formed in the presence of 0.08 mol-% of complex 9b give run and then remains constant in further experiments
higher conversions but low TONs, with a marked fall in (Table 3, entry 2). More unexpectedly, we found that the
activity for the second run (entries 11 and 12). A large leak- FBC oxidation of cyclohexene catalyzed by complex 9b can
age of the catalyst to the organic phase could be the origin be performed without tbhp with a TON of about 460 and
of this observation.
with 50–55% of remaining catalytic activity for the second
It is known that the tbhp/O2 oxidation process is an au- and third runs (Table 3, entry 3). Quenching experiments
toxidation process involving cyclohexene hydroperoxide show that 14 is also the main oxidation product in the ab-
(14): tbhp acts as an initiator to generate alkoxy or peralk- sence of tbhp at room temperature.
oxy radicals, which react with cyclohexene to produce a cy-
High oxidation yields are obtained when the catalytic re-
clohexenyl radical that is trapped by O2 and induces propa- actions are performed at 65 °C without tbhp − TONs
gation of the radical reaction.[6,7,25] In agreement with this higher than 1300 are achieved and the catalytic activity re-
proposed mechanism, the amount of tbhp can be signifi- mains constant for the second and third runs (Table 3, en-
cantly reduced: experiments performed at low tbhp/cyclo- try 4). At 65 °C cyclohexenone and cyclohexenol, which re-
hexene molar ratios (0.25 and 0.05 mol-%) gave very high sult from the decomposition of cyclohexene hydroperoxide,
oxidation yields (2050 and 6400%) and TONs of 240 and are the main oxidation products. Further studies are cur-
330 (Table 3). The formation of 14 as the major oxidation rently under way to investigate the possible mechanism of
product in the catalytic oxidation is clearly evidenced by this direct oxidation and to determine the role of the perflu-
quenching the reaction mixture with PPh3 (Table 3).[25] As orinated medium, which has recently been proved to boost
recently emphasized by Shul’pin et al.,[25] when a hydroper- autoxidation processes.[26]
Eur. J. Org. Chem. 2006, 4685–4692
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FULL PAPER
Table 3. FBC oxidation of cyclohexene: influence of the quantity of tbhp and comparison of the results before and after quenching of
the reaction by addition of PPh3.[a]
Entry
tbhp[b]
[mol-%]
Conversion[c]
No PPh3
Run 1
With PPh3
Run 1
Run 2
Run 3
Run 2
Run 3
1
1.25 (55 µL)
n
12
13
2.8
37
58
1.7
35
58
1.6
29
57
5.2
91
7
2.8
96
0
2.7
95
0
TON
n
12
13
TON
n
12
13
TON
n[d]
12[d]
13[d]
TON[d]
347
2.6
39
210
1.4
40
195
1.5
36
652
4.1
93
348
2.2
96
329
2.3
96
2
3
4
0.045 (2 µL)
55
54
56
4
0
0
330
3.8
34
175
1.0
38
185
1.2
38
516
3.7
93
273
1.8
95
285
1.9
97
0
61
53
54
4
0
1
472
5.0
30
70
1262
125
5.7
41
58
1434
149
5.4
41
59
1356
457
5.4
30
70
1344
222
5.3
44
54
1316
244
5.4
42
58
1350
0[e]
[a] Reaction conditions: perfluorodecaline: 4 mL; cyclohexene: 40 mmol; catalyst 9b: 8 µmol; variable amounts of tbhp; 48 h; room tem-
perature. [b] With respect to cyclohexene; volume in brackets. [c] n: Amount of oxidation products (mmol); relative molar ratios (%) of
cyclohexenol (12) and cyclohexenone (13). [d] After 24 h. [e] At 65 °C.
the residual peak of CHCl3 (δ = 7.27 ppm) as an internal standard.
Conclusions
19F NMR spectra were recorded with a Bruker AC300 (282 MHz)
A convenient and ready access to fluoro-ponytail tet-
or AC200 (188 MHz) spectrometer using CFCl3 as external stan-
raazamacrocycles through a conjugate addition of cyclam dard. 13C NMR were recorded with a Bruker AC300 (75 MHz) or
AC200 (50 MHz) spectrometer with the central peak of CDCl3 (δ
= 77 ppm) as an internal reference. Mass spectra were obtained
with a HP MS 5989B spectrometer. IR spectra were recorded for
samples in KBr on an Impact 400D Nicolet spectrophotometer.
The elementary analyses were performed at the Laboratoire Cen-
tral d’Analyses, (Vernaison, France). Melting points were deter-
mined on a Mettler FP61 melting point apparatus. UV/Vis mea-
surements were performed at 25 °C using a Perkin–Elmer Lambda
19 spectrophotometer. GC analyses were performed with a Shim-
adzu GC-14A equipped with a column Chrompack CP Sil 19 CB
to perfluorohexyl vinyl sulfone (2) and sulfoxide (1) has
been described. Perfluorohexyl vinyl sulfone and sulfoxide
have been revealed to be excellent Michael acceptors and
the application of this methodology for the preparation of
other fluorous ligands is currently in progress in our labora-
tory. The solubility of the tetra-N-substituted fluorous
macrocycles depends dramatically on the nature of the po-
lar groups in the fluorous tails. The macrocycle bearing per-
fluorinated sulfinyl arms (6) is soluble in fluorous solvents
like pfd and pfmc, while the tetrakis(perfluorohexylsul- (30 m×0.25 mm; film thickness: 0.25 µm). Chromatograms were
recorded and integrated with a Shimadzu C-R5A Chromatopac.
The temperature of the oven was programmed as follows: 50 °C
(for 2 min) then raised from 50 °C to 250 °C (rate: 10 °Cmin–1),
and finally 250 °C for 10 min. The injector and detector tempera-
tures were set to 270 °C. Hydrogen, air, and helium pressures were
0.5, 0.5, and 1 kgcm–2, respectively.
fonyl)cyclam derivative 5 is almost insoluble in organic or
fluorous solvents. The linkage of fluorous tails via an ethyl-
sulfinyl spacer does not affect the metal-binding ability of
the macrocycle: stable copper complexes with three and
four perfluorinated tails have been isolated from macrocycle
6, depending on the solvent used for the preparation.
Copper complexes associated to perfluorocarboxylate
counteranions are soluble in fluorinated solvents like pfd or
pfmc and have been successfully used in fluorous biphasic
catalysis. Fluorous copper complex 9b catalyzes the oxi-
dation of cyclohexene by molecular oxygen. This catalyst
is robust and can be recovered and reused with acceptable
conservation of the catalytic activity. Further application of
these fluorous complexes to other transformations is now
in progress.
Perfluorooctylethylcopper(II) dicarboxylate (8) was prepared ac-
cording to the procedure described by Fish.[7a] Perfluorohexyl vinyl
sulfone and sulfoxide were synthesized as described previously.[17]
1,4,8,11-Tetrakis(2-perfluorohexylsulfonylethyl)-1,4,8,11-tetraaza-
cyclotetradecane (5): A solution of 2-(perfluorohexylsulfonyl)ethene
(2; 3.18 mmol, 1.30 g) and cyclam (0.5 mmol, 0.1 g) in 2-propanol
(20 mL) was stirred at room temperature for 40 h. The precipitate
was filtered and washed with dichloromethane (50 mL) to give a
white powder (0.39 mmol, 0.72 g) in 78% yield; Rf = 0.5 (CH2Cl2/
MeOH, 95:5); m.p. decomposes at 158 °C. 1H NMR (200 MHz,
3
3
PhCF3, CDCl3): δ = 3.48 (t, JH,H = 6.0 Hz, 8 H), 3.20 (t, JH,H
=
6.0 Hz, 8 H), 1.78 (m, 4 H), 1.71 ppm (m, 16 H). IR (KBr): ν =
˜
2928, 2800, 1357, 1235, 1209, 1145 cm–1. C42H36F52N4O8S4
(1840.1): calcd. C 27.40, H 1.97, N 3.04, S 6.97; found C 27.45, H
1.92, N 3.07, S 7.44.
Experimental Section
All chemicals were purchased from Sigma, Aldrich, or Fluka and
were used without further purification. Organic solvents were pur-
chased from SDS and perfluorinated solvents from Apollo (includ-
ing trifluoroethanol). 1H NMR spectra were recorded with a
1,4,8,11-Tetrakis(2-perfluorohexylsulfinylethyl)-1,4,8,11-tetraaza-
cyclotetradecane (6): A solution of 2-(perfluorohexylsulfinyl)ethene
Bruker AC300 (300 MHz) or AC200 (200 MHz) spectrometer using (1; 9.62 mmol, 3.79 g) and cyclam (1.65 mmol, 0.33 g) in a mixture
4690
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Eur. J. Org. Chem. 2006, 4685–4692

New Ligands for Copper-Catalyzed Oxidation under Biphasic Conditions
FULL PAPER
of 2-propanol (14 mL) and water (7 mL) was stirred at room tem-
perature for 20 h. The precipitate was filtered and washed with
dichloromethane (50 mL) to give a white powder (1.38 mmol,
2.45 g) in 86% yield; Rf = 0.5 (CH2Cl2/MeOH, 95:5); m.p. decom-
1147 cm–1. UV/Vis (trifluoroethanol): λmax (ε) = 583 nm, 345. MS
(ESI+): m/z (100) 723–724 [M2+]. C34H33CuF39N6O9S3 (1569.0):
calcd. C 26.00, H 2.12, Cu 4.05, F 47.18, N 5.35; found C 26.47,
H 2.24, Cu 3.77, F 47.46, N 4.83.
1
poses at 150 °C. H NMR (200 MHz, CDCl3): δ = 3.18–2.47 (m,
[1,4,8-Tris(2-perfluorohexylsulfinylethyl)-1,4,8,11tetraazacyclo-
tetradecane]copper(II) Bis[3-(perfluorooctyl)propionate] (10b): A
solution of 8 (5.63×10–2 mmol, 58.8 mg) and 6 (5.63×10–2 mmol,
100 mg) in trifluoroethanol (4 mL) was stirred for 5 d. After fil-
tration, the filtrate was concentrated in vacuo, stirred in chloroform
( 2 0 m L ) f o r 1 h a n d f i l t e r e d t o g i v e a b l u e p o w d e r
(4.90×10–2 mmol, 95 mg) in a yield of 87%; m.p. decomposes at
32 H), 1.78 ppm (m, 4 H). 19F NMR (188 MHz, CDCl3): δ =
–80.89 (m, 3 F), –115.4 (m, 1 F), –119.5 (m, 3 F), –122.0 (m, 2 F),
–122.9 (m, 2 F), –126.2 ppm (m, 2 F). IR (KBr): ν = 2960, 2809,
˜
1362, 1235, 1199, 1147, 692 cm–1. MS (ESI+): m/z (%) 889 [M +
2+
2H+], 729 (100) [M – C6F13
]
2+, 705 (25) [M – SOC6F13
]
.
C42H36F52N4O4S4 (1776.1): calcd. C 28.39, H 2.04, F 55.60, N 3.15,
S 7.22; found C 28.53, H 1.99, F 55.57, N 3.08, S 7.83.
135 °C. IR (KBr): ν = 3428, 1598, 1363, 1245, 1199, 1147, 661 cm–1.
˜
UV/Vis (trifluoroethanol): λmax (ε) = 635 nm (263 –1 cm–1), 302
(6309). MS (ESI+): m/z 723–724 (100) [M2+]. C56H41CuF73N4O7S3
(2427.0): calcd. C 27.70, H 1.70, Cu 2.62, N 2.31, S 3.96; found C
27.23, H 1.71, Cu 2.80, N 2.31, S 3.89.
1,4,8,11-Tetrakis[2-(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluoro-
octylpropionyloxy)ethyl]-1,4,8,11-tetraazacyclotetradecane (7): The
acrylate 4 (1.36 g, 3.0 mmol) was added to a solution of cyclam
(0.1 g, 0.5 mmol) in 2-propanol (20 mL). This solution was stirred
for 1 d and then left to stand for another day at room temperature.
The precipitate was then filtered and the insoluble material washed
with methanol (10 mL) to give a white powder (0.44 g, 0.22 mmol)
in 44% yield; Rf = 0.5 (CH2Cl2/MeOH, 90:10); m.p. decomposes
Reaction Between 8 and 5: A solution of 8 (5.44 × 10–2 mmol,
56.8 mg) and 5 (5.44×10–2 mmol, 100 mg) in (trifluoromethyl)ben-
zene (10 mL) was stirred for 48 h at room temperature. Concentra-
tion in vacuo gave a violet powder (5.44×10–2 mmol, 156.9 mg);
m.p. decomposes at 104 °C. The TLC analysis revealed the presence
1
3
at 117 °C. H NMR (200 MHz, [D6]acetone): δ = 4.86 (t, JH,F
=
13.8 Hz, 8 H), 2.77 (t, 3JH,H = 6.0 Hz, 8 H), 2.52 (t, 3JH,H = 6.0 Hz,
24 H), 1.58 ppm (m, 4 H). 13C NMR (50 MHz, [D6]acetone): δ =
of vinyl sulfone 1. IR (KBr): ν = 2781, 1352, 1230, 1194 cm–1. UV/
˜
Vis (trifluoroethanol): λmax (ε) = 320 nm (272 –1 cm–1), 298 (1706).
MS (ESI+): m/z 1574 (C26H30F26N4O4S2[Cu(O2CCH2CH2-
C8F17])+. C64H44CuF86N4O12S4 (2885.): calcd. C 26.63, H 1.54, Cu
2.20, N 1.94, S 4.44; found C 27.28, H 1.78, Cu 2.25, N 2.05, S
4.30.
171.7, 59.7 (t, JC,F = 26 Hz), 52.3, 52.1, 50.1, 32.8, 25.1 ppm. 19F
2
NMR (188 MHz, [D6]acetone): δ = –77.0 (m, 3 F), –115.2 (m, 2
F), –117.9 (m, 4 F), –118.7 (m, 2 F), –119.1 (m, 2 F), –122.2 ppm
(m, 2 F). IR (KBr): ν = 2965, 2934, 2806, 1752 cm–1. MS (ESI+):
˜
m/z (%) 1009 (100) [M + 2H+]. C54H44F60N4O8 (2016.2): calcd. C.
32.16, H 2.20, N. 2.78; found C 32.08, H 2.24, N 2.82.
General Procedure for Fluorous Biphasic Catalysis: Catalyst 9b
(22.6 mg, 8 µmol) and perfluorodecaline (4 mL) were added to a
Schlenk tube followed by cyclohexene (4.0 mL, 40 mmol), 1,2-
dichlorobenzene (0.25 mL, 2 mmol, internal standard), and tert-bu-
tyl hydroperoxide (55 µL, 0.5 mmol). These were then placed under
an oxygen atmosphere. The reaction mixture was then stirred
(1250 min–1) for 48 h at room temperature. The reaction was moni-
tored by GC. After 48 h a 50-µL sample was taken from the organic
phase, diluted with diethyl ether (25 µL) and 0.1 µL of this solution
was injected into the GC.
[1,4,8,11-Tetrakis(2-perfluorohexylsulfinylethyl)-1,4,8,11-tetraaza-
cyclotetradecane]copper(II) Dinitrate (9a): A solution of copper ni-
t r a t e t r i hy d r a t e ( 5 . 6 3 × 1 0 – 2 m m o l , 1 3 . 6 m g ) a n d 6
(5.63×10–2 mmol, 100 mg) in a mixture of chloroform (3.2 mL)
and methanol (2.1 mL) was stirred for 24 h. The precipitate was
filtered then washed with methanol (10 mL) to give a blue powder
(5.0×10–2 mmol, 98 mg) in 89% yield; m.p. decomposes at 179 °C.
IR (KBr): ν = 2975, 2929, 1362, 1235, 1203, 1143, 666 cm–1. UV/
˜
Vis (trifluoroethanol): λmax (ε) = 624 nm (199 –1 cm–1), 308 (5495).
MS (ESI+): m/z (%) 920–921 (100) [M2+]. C42H36CuF52N6O10S4
(1964.5): calcd. C 25.68, H 1.85, F 50.29, N 4.28; found C 25.95,
H 1.89, F 50.1, N 4.51.
For experiments with reduction of the intermediate cyclohexenyl
hydroperoxide an excess of solid PPh3 (PPh3 was slowly added until
the end of exothermic phenomena) was added to the sample 10 min
before injection into the GC. The amounts of oxidation products
were determined using 1,2-dichlorobenzene as the internal stan-
dard.
[1,4,8,11-Tetrakis(2-perfluorohexylsulfinylethyl)-1,4,8,11-tetraaza-
cyclotetradecane]copper(II) Bis[3-(Perfluorooctyl)propionate] (9b):
A solution of 8 (5.63 × 10–2 mmol, 58.8 mg) and 6 (5.63 × 10–2
mmol, 100 mg) in a mixture of chloroform (0.67 mL) and methanol
(0.45 mL) was stirred for 24 h. The precipitate was filtered then
washed with chloroform (40 mL) to give a blue powder
(4.3 × 10–2 mmol, 120.8 mg) in 76 % yield; m.p. decomposes at
Acknowledgments
176 °C. IR (KBr): ν = 2812, 1363, 1294, 1204, 1137 cm–1. UV/Vis
We would like to thank Dr. Jean-Claude Blazejewski for fruitful
discussions, Aude Escande for technical assistance, and Karen
Wright for improvement of the English in this manuscript. A. C.
thanks the French M.E.N.R.T. for a PhD grant.
˜
(trifluoroethanol): λmax (ε) = 674 nm (646 –1 cm–1), 328 (3800)
p p m . M S ( E S I + ) : m / z ( % ) 9 2 0 – 9 2 1 ( 2 7 ) [ M 2 + ] .
C64H44CuF86N4O8S4 (2821.0): calcd. C 27.23, H 1.57, Cu 2.25, N
1.98; found C 26.74, H 1.55, Cu 2.80, N 2.11.
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˜
Eur. J. Org. Chem. 2006, 4685–4692
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4691

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Received: June 16, 2006
Published Online: August 22, 2006
4692
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Eur. J. Org. Chem. 2006, 4685–4692