1,1′-Binaphthyl-2-methylpyridinium-based peroxophosphotungstate salts: Synthesis, characterization and their use as oxidation catalysts

Article abstract of DOI:10.1002/ejic.200900682

A series of 1,1'-binaphthyl-2-methylammonium and pyridinium salts 6, 7, and 8 was synthesized through the coupling reaction of 2-(bromomethyl)-1,1'- binaphthalene (5) with the dendritic tetraallyl pyridinedicarbinol dendron 2 as well as triethylamine and 4-tert-butylpyridine. Tetraallyl pyridinedicarbinol dendron 2 was prepared by allylation of commercially available diethyl pyridine-3,5-dicarboxylate (1). The allylation of 2 with, allyltrimethylsilane in the presence of boron trifluoride was unsuccessful, as tetraallyl pyridinedicarbinol trifluoroboron adduct 3 was obtained instead of expected hexaallylpyridine compound 4. The catalytic hydrogenation of allyl groups of the ammonium salt of 2, namely, tetraallyl 1,1'-binaphthyl-2-methylpyridinium salt 6, successfully led to the corresponding tetra-n-propyl 1,1'-binaphthyl-2- methylpyridinium salt 9. The reaction between salts 7, 8, and 9 and the heteropolyacid H₃PW₁₂O₄₀ in the presence of a large excess of hydrogen peroxide afforded the corresponding 1,1'-binaphthyl-2-methylammonium-based polyoxometalate salts 10, 11, and 12, which, contain a catalytically active trianionic [H₃PW ₁₂O₄O]^3- in the core. These binaphthyl-POM salts are soluble in commonly used organic solvents, and their IR and ³¹P NMR spectroscopic and elemental analysis data indicate the presence of the POM unit in the frameworks. These POM hybrids are efficient, recoverable, and reusable catalysts in the oxidation of thioanisole, cyclooctene, and cyclohexanol, with H₂O₂ as the oxidant. A study of the countercation effects indicated that the reaction kinetics and the selectivity are sensitive to the structure of the cation. Two cycles of catalytic reactions were performed without a discernible loss in activity. Wiley-VCH Verlag GmbH & Co. KGaA.

Full text of DOI:10.1002/ejic.200900682

FULL PAPER
DOI: 10.1002/ejic.200900682
1,1Ј-Binaphthyl-2-methylpyridinium-Based Peroxophosphotungstate Salts:
Synthesis, Characterization, and Their Use as Oxidation Catalysts
Claire Jahier,[a] François-Xavier Felpin,[a] Catherine Méliet,[b]
Francine Agbossou-Niedercorn,[b] Jean-Cyrille Hierso,[c] and Sylvain Nlate*[a]
Keywords: Dendrimers / Polyoxometalates / Oxidation / Homogeneous catalysis
A series of 1,1Ј-binaphthyl-2-methylammonium and pyrid-
inium salts 6, 7, and 8 was synthesized through the coupling
reaction of 2-(bromomethyl)-1,1Ј-binaphthalene (5) with the
dendritic tetraallyl pyridinedicarbinol dendron 2 as well as
triethylamine and 4-tert-butylpyridine. Tetraallyl pyridined-
icarbinol dendron 2 was prepared by allylation of commer-
cially available diethyl pyridine-3,5-dicarboxylate (1). The
allylation of 2 with allyltrimethylsilane in the presence of bor-
on trifluoride was unsuccessful, as tetraallyl pyridinedicarbin-
ol trifluoroboron adduct 3 was obtained instead of expected
hexaallylpyridine compound 4. The catalytic hydrogenation
of allyl groups of the ammonium salt of 2, namely, tetraallyl
1,1Ј-binaphthyl-2-methylpyridinium salt 6, successfully led
to the corresponding tetra-n-propyl 1,1Ј-binaphthyl-2-meth-
ylpyridinium salt 9. The reaction between salts 7, 8, and 9
and the heteropolyacid H3PW12O40 in the presence of a large
excess of hydrogen peroxide afforded the corresponding
1,1Ј-binaphthyl-2-methylammonium-based polyoxometalate
salts 10, 11, and 12, which contain a catalytically active tri-
3–
anionic [H3PW12O40
]
in the core. These binaphthyl–POM
salts are soluble in commonly used organic solvents, and
their IR and 31P NMR spectroscopic and elemental analysis
data indicate the presence of the POM unit in the frame-
works. These POM hybrids are efficient, recoverable, and re-
usable catalysts in the oxidation of thioanisole, cyclooctene,
and cyclohexanol, with H2O2 as the oxidant. A study of the
countercation effects indicated that the reaction kinetics and
the selectivity are sensitive to the structure of the cation. Two
cycles of catalytic reactions were performed without a dis-
cernible loss in activity.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
properties that make them particularly attractive for appli-
cations in homogeneous catalysis, in biology, in magnetism,
in optic, and in medicine.[8] The properties of anionic
POMs, in dendritic POM frameworks, such as their sta-
bility, solubility, catalytic efficiency, their recycling poten-
tial, and overall their catalytic efficiency, are closely related
to the structure of the dendrimer. For instance, dendritic
POM compounds in which the POM unit is encapsulated
into the dendritic structures were found to be more stable
than their homologues functionalized at the periphery with
POM units.[6h] In addition, the quest for new catalytic and
highly enantioselective processes is one of the most inten-
sively studied areas in chemical synthesis. Chiral ligands are
crucial asymmetric inductors in active metal–organic cata-
lysts.[9] Therefore, the design of suitable innovative chiral
ligands for a particular application remains a formidable
challenge. In this context, we are interested in the synthesis
of chiral dendritic polyoxometalate catalysts for asymmetric
transformations. Binaphthylamino-containing ligands were
chosen to introduce chirality into the dendritic structure.
After the discovery of practical asymmetric catalysis by
Knowles[10] and Kagan,[11] optically active binaphthyl-con-
taining ligands of C2 symmetry were confirmed to be of
the highest interest for asymmetric catalysis.[12] From the
development of binap [2,2Ј-bis(diphenylphosphino)-1,1Ј-bi-
Introduction
Dendritic catalysts have been developed during the last
decade as a result of their potential applications in various
areas.[1] The use of these macromolecules in molecular ca-
talysis, pioneered by van Leeuwen,[2b,2d] is an emerging field
of research. Their large size and molecular weight allow the
easy recovery of the catalysts, an essential feature for reac-
tion efficiency, resources economy, and environmental con-
cern.[2] In this context, a variety of dendritic compounds
have been synthesized and used in different domains such
as supramolecular chemistry,[3] nanosciences,[1c] drug deliv-
ery,[4] and catalysis.[2,5] Some relevant examples based on
polyoxometalates (POMs) have been reported recently.[6]
POMs are effective catalysts in the oxidation of organic
substrates such as alkenes, alcohols, and sulfides. POMs[7]
are a large class of inorganic compounds with interesting
[a] ISM, UMR CNRS No. 5255, Université Bordeaux I,
351 Cours de la Libération, 33405 Talence Cedex, France
Fax: +33-5-40006994
E-mail: s.nlate@ism.u-bordeaux1.fr
[b] Université de Lille 1-Sciences et Technologies, UCCS UMR
CNRS No. 8181, ENSCL(CHIMIE), Bât C7,
BP 90108, 59652 Villeneuve d’Asq Cedex, France
[c] ICMUB UMR CNRS N° 5260, Université de Bourgogne
9 Avenue Alain Savary, 21078 Dijon Cedex, France
5148
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1,1Ј-Binaphthyl-2-methylpyridinium-Based Peroxophosphotungstate Salts
naphthyl] chemistry by Noyori in 1980,[13] binaphthyl, bi-
phenyl, and other biaryl groups have been used as chiral
sources to introduce many highly efficient asymmetric envi-
ronments.[14] A fine-tuning of the stereoelectronic properties
of such ligands is easy to perform through the use of either
substituted and/or partially hydrogenated aromatic units,
resulting in spectacular variations in the efficiency and
selectivity of the corresponding catalysts. In the case of den-
drimers, the dihedral angles of the biaryl ligands have
proven to exert a decisive influence on the reaction kinetics
and/or enantioselectivity.[15] It was found that the size of
the dendritic wedges influenced the reactivity and/or the
enantioselectivity of the catalytic species. Similar effects
might be anticipated in the case of catalytic systems incor-
porating chiral dendritic POMs. Contrary to chiral den-
dritic binaphthylphosphane ligands that have been exten-
sively used in asymmetric catalysis, binaphthylamino-con-
Scheme 1. Syntheses of tetraallyl pyridinedicarbinol compounds 2
taining ligands have been only scarcely reported.[16] Thus, and 3.
pursuing our investigation on the synthesis and catalytic ap-
plications of dendritic POM frameworks, we report the syn-
thesis and characterization of dendritic and nondendritic carbenium ion generated in the ionization process of the
1,1Ј-binaphthyl-2-methylammonium-based
peroxophos- carbinol with boron trifluoride, thus avoiding the allylation
photungstate [H3PW12O40]3– salts[6d–6h,17] in their racemic reaction. Dendritic pyridine compound 2 and boron adduct
form. These organic–inorganic hybrids have shown to be 3 were characterized by standard NMR spectroscopic and
efficient, recoverable, and reusable catalysts in the oxidation mass spectrometric analysis. Whereas the aromatic region
1
of thioanisole, cyclooctene, and cyclohexanol with hydrogen of 2 in its H NMR spectrum exhibits two singlet at δ =
peroxide. We have investigated the synthesis of the racemic 8.53 (2H) and 7.74 ppm (1 H) assigned to the two different
mixtures of dendritic POM hybrids with the intention to aromatic protons of the pyridine moieties, the spectrum of
extend this synthetic route to enantiomerically pure den- tetraallyl dicarbinol boron adduct 3 exhibits a broad doub-
dritic 1,1Ј-binaphthyl-based POM frameworks.
let at δ = 8.77 ppm and a singlet at δ = 8.30 ppm assigned
to the aromatic protons of the pyridine group. In addition,
1
the H NMR spectrum of boron adduct 3 shows a marked
downfield shift of the two aromatic signals, probably due to
the coordination of dendritic pyridine 2 (Lewis base) to bo-
ron trifluoride (Lewis acid). Further data in support of the
formation of 3 were obtained by 11B NMR (broad quadru-
plet at δ = 0.21 ppm) and 19F NMR (broad multiplet at
–151.6 ppm) spectroscopy. Attempts to prepare n-propyl
compound 2a by catalytic hydrogenation of the allyl groups
of 2 by using a Pd/C catalyst failed. Presumably, the pyr-
idine moieties are potentially poisonous ligands for the Pd/
C catalyst and possibly act as activity inhibitors. Thus, ac-
cess to n-propyl pyridine derivatives was not possible under
the reaction conditions. The mass spectrometric analysis of
boron adduct 3 shows prominent peaks at m/z = 300.18
Results and Discussion
Synthesis and Spectroscopic Characterization of 1,1Ј-
Binaphthyl-2-methylpyridinium and 1,1Ј-Binaphthyl-2-
methyltriethylammonium Salts
The strategy used to prepare 1,1Ј-binaphthyl-2-methyl-
pyridinium salts involved the coupling reaction of 2-(bro-
momethyl)-1,1Ј-binaphthalene (5)[18] with designed den-
dritic pyridine compounds.
Synthesis of the Tetraallyl Pyridinedicarbinol Compound 2
The synthesis of tetraallyl pyridine 2 was based on the (calcd. 300.42) [M – BF3 + H]+ and 322.17 (calcd. 322.40)
allylation of commercially available diethyl pyridine-3,5-di- [M – BF3+Na]+. For compound 2, four prominent peaks
carboxylate (1) as summarized in Scheme 1. This strategy, where obtained in the mass spectrum at m/z = 300.18
recently reported by our group, enables a large-scale prepa- (calcd. 300.42) [M + H]+, 322.17 (calcd. 322.40) [M +
ration of aryl polyallyl dendrons and dendrimers.[19]
Na]+, 621.35 (calcd. 621.81) [2M + Na]+, and 920.57 (calcd.
The reaction of 1 with allylmagnesium bromide led to 921.22) [3M + Na]+. We assume these prominent peaks to
tetraallyl pyridinedicarbinol compound 2 in 75% yield. The be the mono(pyridine), bis(pyridine), and tris(pyridine) ad-
reaction of 2 with allyltrimethylsilane in the presence of ducts of sodium. In contrast to 2, the mass spectrum of
Et2O·BF3 led to tetraallyl dicarbinol boron adduct 3. Ex- tetraallylpyridine boron adduct 3 shows only an extra peak
pected hexaallylpyridine compound 4 was not obtained, assigned to the bis(pyridine) adduct of sodium. In this case,
even in the presence of a large excess of allyltrimethylsilane. the formation of the bis- and tris(pyridine) adducts of so-
The coordination of the pyridine moiety to the electron- dium in the mass spectrometer is probably avoided by the
withdrawing boron atom prevented the formation of the presence of the nitrogen–boron bond.
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Synthesis of 1,1Ј-Binaphthyl-2-methylpyridinium and 1,1Ј-
Binaphthyl-2-methyltriethylammonium Salts
troscopic techniques, as well as elemental analysis. The data
are consistent with the structure proposed for these pyrid-
inium salts.
The 1,1Ј-binaphthyl-2-methylammonium salts were syn-
thesized by using the strategy described in Scheme 2. The
amino derivative (tetraallyl pyridinedicarbinol 2, triethyl-
amine, and p-tert-butylpyridine) was treated with 2-(bro-
momethyl)-1,1Ј-binaphthalene (5) and the corresponding
1,1Ј-binaphthylpyridinium compounds 6, 7, and 8 were ob-
Synthesis and Characterization of 1,1Ј-Binaphthyl-2-
methylpyridinium and 1,1Ј-Binaphthyl-2-
methyltriethylammonium POM Salts
The 1,1Ј-binaphthyl-based POM-cored salts were synthe-
tained in 96, 71, and 81% yield, respectively. Triethylammo- sized according to the procedure involving peroxide-medi-
nium salt 7 and tert-butylpyridinium salt 8 were synthesized ated decomposition of the heteropolyacid H3PW12O40 in
to point out the effect of the dendritic cation on the anionic the presence of H2O2 to form the dinuclear peroxotungstate
POM species in dendritic POM frameworks. The hydrogen- [WO(O2)2(H2O)O]2– and the trianionic peroxotungstate
ation of 6 with the use of a Pd/C catalyst (10% Pd) gave [PO4{WO(O2)2}4]3–. The latter reacts selectively with den-
the tetra-n-propyl 1,1Ј-binaphthyl-2-methylpyridinium salt dritic 1,1Ј-binaphthyl-2-methylpyridinium salt 9 as well as
9 in 90% yield. Interestingly, whereas compound 2 was nondendritic pyridinium salt 8, and triethylammonium salt
found to be inert towards hydrogen in the presence of the 7 in a biphasic mixture of water and dichloromethane to
Pd/C catalyst, its ammonium derivative reacted with hydro- give dendritic 1,1Ј-binaphthyl-2-methylpyridinium POM
gen under similar conditions to give 9. Thus, the prepara- framework 10, nondendritic tert-butylpyridinium POM salt
tion of the ammonium salt is an essential step before the 11, and triethylammonium POM salt 12 containing the tri-
catalytic hydrogenation of alkenes groups, possibly because anionic [PO4{WO(O2)2}4]3– at the core (Scheme 3).
it avoids poisoning of the ligands by the Pd/C catalyst that
In the dendritic series, we only considered the synthesis
could inhibit the hydrogenation reaction under these condi- and investigation of the catalytic properties of n-propyl
tions (Scheme 2). Access to n-propyl-based pyridinium salts 1,1Ј-binaphthylpyridinium POM salt 10, because of its high
is essential, as they increase the solubility of POM frame- solubility in organic solvents, contrary to insoluble poly-
works in organic solvents, an important feature for their epoxy–POM hybrids usually obtained from polyallyl am-
use in homogeneous catalysis. Characterization of all the monium salts. All the POM compounds described herein
compounds was carried out by using standard NMR spec- wereisolatedfromtheCH2Cl2 layerandfullycharacterizedby
Scheme 2. Syntheses of the tetraarmed 1,1Ј-binaphthyl-2-methylpyridiniumdicarbinol salts 6 and 9.
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1,1Ј-Binaphthyl-2-methylpyridinium-Based Peroxophosphotungstate Salts
Scheme 3. Syntheses of 1,1Ј-binaphthyl-2-methylpyridinium POM salts 10 and 11 and 1,1Ј-binaphthyl-2-methyltriethylammonium POM
salt 12.
NMR spectroscopy, elemental analysis, and IR spec-
troscopy. The data obtained (see Experimental Section) are
fully consistent with the proposed structures.
Oxidation of Sulfides, Alkenes, and Alcohols by Using 1,1Ј-
Binaphthyl-Based POM Salts 10–12
The performances of 1,1Ј-binaphthyl-based POM salts
10–12 were tested in the oxidation of thioanisole (13), cyclo-
octene (14), styrene (15), and cyclohexanol (16) (Scheme 4).
The results reported in Tables 1 and 2 clearly show that
compounds 10–12 oxidize 13 to corresponding sulfoxide 17
and sulfone 18. The oxidation of 13 presumably gives, in a
first step, sulfoxide 17, which is in turn oxidized into sulfone
18 either through a POM-catalyzed process or directly by
the action of hydrogen peroxide.
Scheme 4. Catalytic oxidation of thioanisole (13), cyclooctene (14),
styrene (15) and cyclohexanol (16) with the use of 1,1Ј-binaphthyl-
based POM salts 10–12.
In order to optimize the selectivity of sulfoxide 17 forma-
tion, we carried out a series of experiments, which are sum- drogen peroxide had clearly a great effect on the kinetics
marized in Table 1. When 13 was treated with H2O2 at and the selectivity of the reaction (Figure 1). For the oxi-
30 °C without a catalyst, only 4% of sulfoxide was obtained dations mentioned so far, the POM was allowed to react
after 5 d (Table 1, Entry 1). When the reaction was carried with hydrogen peroxide for 30 min at room temperature be-
out in the presence of POM compound 12 and H2O2 fore addition of the substrate. Following the evolution of
(2.8 equiv.) it was completed within 1 h, with a selectivity the reaction mixture with time indicated that preactivation
of 31% for sulfoxide 17 and 69% for sulfone 18 (Table 1, of POM catalyst 12 with H2O2 gave an active species. How-
Entry 2). By diminishing the oxidant/substrate ratio down ever, when the substrate was added immediately after hy-
to 1.1, we observed an increase in the selectivity of the sulf- drogen peroxide, an increase in the activity and selectivity
oxide (Table 1, Entries 3 and 4). The concentration of hy- was observed (Table 1, Entry 5).
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Table 1. Catalytic oxidation of thioanisole (13) by using H2O2.[a]
Entry
Catalyst
H2O2
(equiv./substrate)
Time[c]
Conversion[d]
[%]
Yield of 17[d]
Yield of 18[d]
50% conversion
[min]
[%]
[%]
1
2
3
4
5
6
7
8
9
–
1
5 d
4
100
100
99
80
80
98
100
96
4
31
56
82
75
42
90
53
92
–
69
44
17
5
38
8
–
–
5
7.5
3
4
9
13
13
12[b]
12[b]
12[b]
12
2.8
2.4
1.1
1.1
2.8
1.1
2.8
1.1
60 min
60 min
210 min
30 min
35 min
75 min
65 min
75 min
11
11
10
47
4
10
[a] Catalytic conditions: in CH2Cl2 at 30 °C under vigorous stirring, reactants were added as follows: catalyst (0.4 mol-%), H2O2 (35% in
H2O), CH2Cl2, and substrate (1 mmol). [b] The catalysts were activated through reaction with H2O2 over 30 min at room temperature
before addition of the substrate. [c] Nonoptimized reaction times. [d] Determined by GC analysis with an Alltech EC5 capillary column.
Figure 1. Kinetics of thioanisole (13) oxidation with 1,1Ј-bi-
Figure 2. Kinetics of the oxidation of sulfoxide 17 into sulfone 18
naphthyl-2-methyltriethylammonium POM salts 12.
with H2O2 without any POM salt.
This result indicates that the preactivation of the catalyst
The reaction was found to be extremely slow, with only
was not necessary, as half conversion of thioanisole was 0.8% (GC yield) of sulfone obtained after 90 min. This rate
reached within 3 min without activation of the catalyst increased with barely a 20% conversion of sulfoxide 17 into
(Table 1, Entries 4 and 5).
sulfone 18 within 33 h, supporting the fact that there is no
To evaluate the ability of hydrogen peroxide to oxidize significant contribution of an uncatalyzed process to this
sulfoxide into sulfone without any assistance of the POM over oxidation. Thus, when adapting the amount of oxidant
catalyst, we investigated the oxidation of sulfoxide 17 into to that of the substrate, the selectivity of sulfoxide 17 can
sulfone 18 with H2O2 at 30 °C (Figure 2).[20]
be quite high (Table 1, Entries 7 and 9).
Table 2. Catalytic oxidation of cyclooctene (14), styrene (15), and cyclohexanol (16) using H2O2.[a]
Entry
Catalyst
Substrate
Time
Conversion[c]
[%]
Product, yield
[%]
50% conversion
[h]
1
2
3
4
5
6
7
8
9
–
12[b]
11[b]
11
14
14
14
14
14
14
15
15
15
16
16
3 d
48 h
72 h
49 h
24 h
49 h
8 d
8 d
8 d
3 d
3 d
4
100
100
83
100
60
–
–
–
69
55
19, 100
19, 100
19, 100
19, 100
19, 100
19, 100
20, 0
–
5
13
13
11.5
10[b]
10
12
–
–
–
9.5
48
11
20, 0
10
20, 0
21, 100
21, 100
10
11
11
10
[a] All catalytic reactions were performed in CH2Cl2 at 30 °C under vigorous stirring. The reactants were added as follows: catalyst
(0.4 mol-%), H2O2 (35% in H2O, 3.2 equiv./substrate), CH2Cl2, and then the substrate (1 mmol). [b] The catalysts were activated through
reaction with H2O2 over 30 min at room temperature before addition of the substrate. [c] Determined by GC with an Alltech EC5 capillary
column.
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1,1Ј-Binaphthyl-2-methylpyridinium-Based Peroxophosphotungstate Salts
benzophenone under an argon atmosphere immediately prior to
Dendritic 1,1Ј-binaphthyl-2-methylpyridinium POM 10
and nondendritic tert-butylpyridinium POM salt 11 also
oxidized thioanisole into sulfoxide with good selectivities
(90 to 92%; Table 1, Entries 7 and 9). In comparison to
nondendritic POM catalysts 11 and 12, the highest selectiv-
ity of sulfoxide 17 (92%; Table 1, Entry 9) was obtained
with dendritic compound 10. Interestingly, a discernible
negative dendritic effect was observed on the reaction kinet-
ics, as 13 min were needed to convert 50% of the substrate
use. Acetonitrile (CH3CN) was stirred under an argon atmosphere
overnight over phosphorus pentoxide, distilled from sodium car-
bonate, and stored under an argon atmosphere. Methylene chloride
(CH2Cl2) was distilled from calcium hydride just before use. All
1
other chemicals were used as received. The H, 13C, 31P, 11B, and
19F NMR spectra were recorded at 25 °C with a Bruker AC, 400
FT spectrometer (11B 128.38 MHz, 19F 376.46 MHz), 250 FT spec-
trometer (1H 250.13, 13C 62.91 MHz), or a Bruker AC 200 FT spec-
trometer (1H 200.16, 13C 50.33, 31P 81.02 MHz) at the CESAMO
with dendritic catalyst 10 (Table 1, Entry 9), whereas half (Bordeaux, France). All chemical shifts are referenced to Me4Si
(TMS). Mass spectra were performed by the CESAMO with a
QStar Elite mass spectrometer (Applied Biosystems). The instru-
ment is equipped with an ESI source, and spectra were recorded in
the positive mode. The electrospray needle was maintained at
4500 V and operated at room temperature. Samples were intro-
conversion of sulfide 13 was reached after 9 min in the case
of 11 (Table 1, Entry 7). This negative effect is probably
caused by the increased bulk around the catalytic center.
Two cycles of catalytic reactions were performed with the
use of 13 and dendritic catalyst 10, without a discernible
loss in activity or selectivity.
We also performed the oxidation of cyclooctene (14), styr-
ene (15), and cyclohexanol (16) with POM salts 10–12 with
the use of H2O2 as oxidant (Scheme 4). The experimental
duced by injection through
a 10-µL sample loop into a
200 µLmin–1 flow of methanol from the LC pump. Elemental
analyses were carried out at the Vernaison CNRS center. The infra-
red spectra were recorded in KBr pellets with an FTIR Paragon
1000 Perkin–Elmer spectrometer, unless otherwise indicated. Or-
results summarized in Table 2 clearly showed the efficiency ganic oxidation products were identified by correlation to authentic
samples. The synthesis and characterization of 2-(bromomethyl)-
1,1Ј-binaphthalene (5) were performed according to a literature
procedure.[18]
of all the binaphthyl–POM salts in the oxidation of cyclo-
octene (14) into corresponding epoxide 19 (Table 2, En-
tries 2–6). Styrene (15) was not oxidized into epoxystyrene
(20) with this series of catalysts (Table 2, Entries 7–9), Tetraallyl Pyridinedicarbinol 2: In a Schlenk tube, a solution of
diethyl pyridine-3,5-dicarboxylate (1) (3.53 g, 15.84 mmol) in
CH2Cl2 (10 mL) was added to a Schlenk tube containing allylmag-
nesium bromide (1  in diethyl ether, 79.2 mL, 79.2 mmol) at 0 °C.
After 12 h stirring at room temperature, a solution of NH4Cl (6 ,
30 mL) was added to the reaction mixture. The product was ex-
tracted with CH2Cl2 (3ϫ30 mL), and the organic phase was dried
with sodium sulfate. The solvent was removed under vacuum, and
the product was purified by column chromatography on silica gel
(petroleum ether/diethyl ether, 1:1) to afford 2 as an orange oil.
whereas cyclohexanol (16) led to corresponding ketone 21
with 55 to 69% conversion after 3 d with POM salts 11 and
10. In comparison to our initial experiments investigating
the properties of POM-cored dendrimers, especially their
solubility and catalytic efficiency,[6g–6h] the results described
here with a new series of POM compounds confirm that
the microenvironment of the POM unit has a great effect
on its properties.
1
Yield: 3.6 g (75%). H NMR (250.13 MHz, CDCl3): δ = 8.53 (s, 2
H, o-H pyridine), 7.74 (s, 1 H, p-H pyridine), 5.55 (m, 4 H, CH
allyl), 5.08 (m, 8 H, CH2 allyl), 2.65 (m, 8 H, CH2 allyl) ppm. 13C
NMR (62.91 MHz, CDCl3): δ = 145.3 (CH, pyridine), 140.6 (Cq,
pyridine), 132.7 (CH=CH2), 131.3 (C, pyridine), 119.7 (CH=CH2),
74.2 (C-OH), 46.7 (CH2) ppm. MS (ESI): m/z = 300.18 [M]+,
322.17 [M + Na]+, 621.35 [2M + Na]+, 920.57 [3M + Na]+.
C19H25NO2 (299.41): calcd. C 76.22, H 8.42; found C 76.01, H
8.58.
Conclusions
Dendritic and nondendritic 1,1Ј-binaphthyl-2-methylpyr-
idinium- and 1,1Ј-binaphthyl-2-methyltriethylammonium-
based POM salts were prepared in their racemic form and
used in the oxidation of thioanisole, cyclooctene, and cyclo-
hexanol with hydrogen peroxide. The corresponding sulfox-
ide, epoxide, and ketone, respectively, were obtained with
good to excellent conversion and selectivity. Among these
POM catalysts, it was observed that the reaction kinetics
and the selectivity were sensitive to the structure of the cat-
ion. Despite the racemic form of these POM hybrids, we
have set up an efficient protocol to recoverable 1,1Ј-bi-
naphthyl-2-methyl-based polyoxometalate frameworks and
showed their efficiency in the oxidation of a variety of sub-
strates such as sulfides, alkenes, and alcohols. We believe
that this synthetic procedure represents a promising ap-
proach to enantiopure dendritic 1,1Ј-binaphthyl-2-methyl-
based POM salts that should be used as recoverable and
highly enantioselective catalysts in oxidation reactions.[21]
Further work in this area is in progress.
Pyridinedicarbinol Boron Adduct 3: In a Schlenk tube, allyltrimeth-
ylsilane (3.81 g, 33.40 mmol, 5.3 mL) was dissolved in anhydrous
CH2Cl2 (8 mL), and the solution was cooled to –78 °C. Then, a
solution of BF3 (1  in Et2O, 33.40 mmol, 33.40 mL) was added to
the reaction mixture. Then, a solution of 2 (1 g, 3.34 mmol) in
CH2Cl2 (8 mL), also cooled to –78 °C, was added to the reaction
mixture. After 12 h stirring, the solution was evaporated under vac-
uum and Et2O (10 mL) was added. The product was extracted with
CH2Cl2 (3ϫ20 mL) and dried with sodium sulfate. The solvent was
removed under vacuum, and the product was purified by column
chromatography on silica gel (petroleum ether/diethyl ether, 9:1) to
1
give an orange oil. Yield: 878 mg (71%). H NMR (250.13 MHz,
3
CDCl3): δ = 8.77 (br. d, JH,B = 1.5 Hz, 2 H, o-H pyridine), 8.30
(s, 1 H, p-H pyridine), 5.64 (m, 6 H, CH=CH2), 5.11 (m, 12 H,
CH=CH2), 2.65 (m, 12 H, CH2) ppm. 13C NMR (62.91 MHz,
CDCl3): δ = 146.5 (CH, pyridine), 141.6 (Cq, pyridine), 138.2 (CH,
pyridine), 131.5 (CH=CH2), 121.7 (CH=CH2), 74.8 (C-OH), 46.4
(CH2) ppm. 11B NMR (128.38 MHz, CDCl3): δ = 0.21 (br. q, BF3)
ppm. 19F NMR (376.46 MHz, CDCl3): δ = –151.6 (br. m, BF3)
Experimental Section
General Remarks: Reagent-grade tetrahydrofuran (THF) and di-
ethyl ether were predried with Na foil and distilled from sodium–
Eur. J. Inorg. Chem. 2009, 5148–5155
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S. Nlate et al.
FULL PAPER
ppm. MS (ESI): m/z = 300.18 [M + H – BF3]+, 322.17 [M + Na –
H, CHpyr), 8.95–6.95 (m, binaphthyl), 5.74 (br. m, CH2-N), 1.72
BF3]+. C19H25·BF3NO2 (367.21): calcd. C 62.15, H 6.86; found C (br., CH and CH2), 1.21 (br., CH2), 0.76 (br., CH3) ppm. 13C NMR
62.20, H 6.89.
(62.91 MHz, CDCl3): δ = 150.4–125.0 (Cpyr and Cbinaphthyl), 75.8
(C-OH), 63.2 (CH2-N), 43.9 (CH2), 16.8 (CH2), 14.3 (CH3) ppm.
MS (ESI): m/z = 574.20 [M – Br]+. C40H48BrNO2 (654.73): calcd.
C 73.38, H 7.39, N 2.14; found C 73.46, H 7.18, N 2.06.
Tetraallyl 1,1Ј-Binaphthyl-2-methylpyridiniumdicarbinol Salt 6: In a
Schlenk tube, a mixture of 5 (0.290 g, 0.84 mmol) and the corre-
sponding amine in acetonitrile (5 mL, 0.500 g, 1.67 mmol) was
stirred for 12 h at 80 °C. After removal of the solvent under vac-
uum, the residue was washed with diethyl ether and dried under
vacuum to afford the ammonium salt as a brown light solid. Yield:
Dendritic n-Propyl 1,1Ј-Binaphthyl-2-methylpyridinium POM 10:
H2O2 (35% in water, 14 mL) was added to a solution of commercial
heteropolyacid H3PW12O40 (804 mg, 0.280 mmol) in water
(0.500 mL). The mixture was stirred at room temperature for
1
515 mg (96%). H NMR (250.13 MHz, CDCl3): δ = 8.70 (s, 1 H,
p-H pyridine), 8.62 (s, 2 H, o-H pyridine), 8.20–7.02 (m, bi-
naphthyl), 5.78 (dd, 2 H, CH2-N), 5.61 (m, 4 H, CH=CH2), 4.96
(m, 8 H, CH=CH2), 2.56 (br. m, 8 H, CH2) ppm. 13C NMR
(62.91 MHz, CDCl3): δ = 147.05 (Cq, pyridine), 140.81 (Cq, bi-
naphthyl), 140.37 (CH, pyridine), 138.74 (CH, pyridine), 134.14
(Cq, binaphthyl), 133.72 (Cq, binaphthyl), 133.62 (Cq, binaphthyl),
133.01 (Cq, binaphthyl), 132.99 (Cq, binaphthyl), 132.30
(CH=CH2), 132.29 (Cq, binaphthyl), 129.84 (CH, binaphthyl),
129.27 (CH, binaphthyl), 128.86 (CH, binaphthyl), 128.55 (CH, bi-
naphthyl), 128.19 (CH, binaphthyl), 127.43 (CH, binaphthyl),
127.22 (CH, binaphthyl), 127.12 (CH, binaphthyl), 126.70 (CH, bi-
naphthyl), 127.32 (CH, binaphthyl), 125.88 (CH, binaphthyl),
125.40 (CH, binaphthyl), 125.07 (CH, binaphthyl), 119.91
(CH=CH2), 75.14 (Cq-OH), 63.00 (CH2-N), 45.84 (CH2) ppm. MS
(ESI): m/z = 566.30 [M – Br]+, 567.31 [M + H – Br]+. C40H40BrN
(646.66): calcd. C 74.29, H 6.13, N 2.17; found C 74.13, H 6.05, N
2.03.
30 min.
A solution of ammonium bromide salt 9 (450 mg,
0.730 mmol) in CH2Cl2 (3 mL) was added, and the mixture was
stirred for 40 min. The CH2Cl2 layer was washed with water and
dried with sodium sulfate. The product was obtained by removing
the solvent under vacuum to give a yellow solid. Yield: 652 mg
(84%). 1H NMR (300 MHz, CDCl3, broad signal): δ = 9.00 (br.,
CHpyr), 8.44 (br., CHpyr), 8.13–6.96 (br. m, binaphthyl), 5.83 (br.,
CH2-N), 1.67 (br., CH and CH2), 1.25 (br., CH2), 0.79 (br., CH3)
ppm. 13C NMR (62.91 MHz, CDCl3): δ = 148.2 (Cpyr), 139.96
(Cpyr), 139.06 (Cpyr), 134.5–125.0 (binaphthyl), 75.05 (C-OH),
63.74 (CH2-N), 42.94 (CH2), 16.7 (CH2), 14.4 (CH3) ppm. 31P
NMR (81.02 MHz, CDCl3): δ = 2.97 (br., PO4) ppm. MS
(MALDI-TOF): m/z = 2868.31 [M]+. FTIR (KBr): ν = 1094.72 (P–
˜
O), 944.42 (W=O), 864.05 (O–O), 605.32 and 525.46 {[W(O)2]s,as
}
cm–1. C120H144N3O30PW4 (2874.83): calcd. C 50.14, H 5.05, P 1.08,
W 25.58; found C 50.02, H 4.85, P 1.1, W 25.82.
1,1Ј-Binaphthyl-2-methylpyridinium POM 11: H2O2 (35% in water,
8.0 mL) was added to a solution of commercial heteropolyacid
H3PW12O40 (465 mg, 0.161 mmol) in water (0.300 mL). The mix-
ture was stirred at room temperature for 30 min. A solution of
ammonium bromide salt 8 (200 mg, 0.420 mmol) in CH2Cl2 (3 mL)
was added, and the mixture was stirred for 40 min. The CH2Cl2
layer was washed with water and dried with sodium sulfate. The
product was obtained by removing the solvent under vacuum to
give a yellow solid. Yield: 356 mg (94%). 1H NMR (200 MHz,
CDCl3, broad signal): δ = 9.15 (br., CHpyr), 8.70 (br., CHpyr), 8.22–
7.07 (binaphthyl), 5.95 (br. m, CH2-N), 0.99 (s, CH3) ppm. 13C
NMR (62.91 MHz, CDCl3): δ = 143.6 (Cpyr), 138.83 (Cpyr), 134.4–
123.9 (binaphthyl), 63.10 (CH2-N), 36.0 (Cq, tBu), 29.8 (CH3) ppm.
31P NMR (81.02 MHz, CDCl3, broad signal): δ = 3.06 (br., PO4)
1,1Ј-Binaphthyl 2-Methyltriethylammonium Salt 7: In a Schlenk
tube, 5 (0.717 g, 2.06 mmol) was dissolved in triethylamine (4 mL)
and stirred for 12 h at 80 °C. After removal of the solvent under
vacuum, the residue was washed with diethyl ether and dried under
vacuum to afford the corresponding ammonium salt as a brown
1
light solid. Yield: 659 mg (71%). H NMR (250.13 MHz, CDCl3):
δ = 7.97–7.09 (m, binaphthyl), 4.62, (d, 2 H, CH2-N), 3.24 (m, 6
H, CH2), 0.91 (t, 9 H, CH3) ppm. 13C NMR (62.91 MHz, CDCl3):
δ = 141.8–123.9 (binaphthyl), 59.1 (CH2-N), 53.7 (CH2-N), 46.25
(CH2), 10.2 (CH3) ppm. MS (ESI): m/z = 368.22 [M – Br]+, 369.24
[M + H – Br]+. C27H30BrN (448.44): calcd. C 72.32, H 6.74, N
3.12; found C 71.98, H 6.56, N 3.01.
1,1Ј-Binaphthyl 2-Methylpyridinium Salt 8: In a Schlenk tube, 5
(0.524 g, 1.51 mmol) was dissolved in acetonitrile (2 mL) with 4-
tert-butyltylpyridine (0.45 mL, 0.408 g, 3.02 mmol) and stirred for
12 h at 80 °C. After removal of the solvent under vacuum, the resi-
due was washed with petroleum ether and dried under vacuum to
afford ammonium salt 8 as a brown light solid. Yield: 580 mg
ppm. FTIR (KBr): ν = 1111.96 and 1053.06 (P–O), 954.33 (W=O),
˜
830.66 (O–O), 590.95 and 508.25 {[W(O)2]s,as
}
cm–1.
C90H84N3O24PW4 (2357.99): calcd. C 45.84, H 3.59, P 1.31, W
31.19; found C 45.66, H 3.48, P 1.1, W 31.40.
1
(81%). H NMR (250.13 MHz, CDCl3): δ = 8.41 (d, CHpyr), 8.18
1,1Ј-Binaphthyl-2-methyltriethylammonium POM 12: H2O2 (35% in
water, 8.0 mL) was added to a solution of commercial heteropolya-
cid H3PW12O40 (498 mg, 0.173 mmol) in water (0.300). The mixture
was stirred at room temperature for 30 min. A solution of ammo-
nium bromide salt 7 (200 mg, 0.450 mmol) in CH2Cl2 (3 mL) was
added, and the mixture was stirred for 40 min. The CH2Cl2 layer
was washed with water and dried with sodium sulfate. The product
was obtained by removing the solvent under vacuum to give a yel-
(d, CHpyr), 8.00–6.962 (m, binaphthyl), 6.10 (dd, CH2-N), 1.316 (s,
9 H, CH3) ppm. 13C NMR (62.91 MHz, CDCl3): δ = 170.0 (Cpyr),
143.7 (CHpyr), 138.98 (CHpyr), 134.4–123.8 (binaphthyl), 62.76
(CH2-N), 36.2 (Cq, tBu), 29.89 (CH3) ppm. MS (ESI): m/z = 402.20
[M – Br]+, 403.22 [M + H – Br]+. C30H28BrN (482.46): calcd. C
74.69, H 5.85, N 2.90; found C 74.60, H 5.74, N 2.81.
Tetra-n-propyl 1,1Ј-Binaphthyl-2-methylpyridiniumdicarbinol Salt 9:
10% Pd/C catalyst (35 mg, 0.324 mmol) was added to a THF solu-
tion (5 mL) of ammonium compound 6 (0.350 g, 0.504 mmol) in a
thick-walled tube capped with a Young’s stopcock. The tube was
flushed, pressurized with hydrogen, and sealed, and the mixture
1
low solid. Yield: 370 mg (95%). H NMR (200 MHz, CDCl3): δ =
7.92–7.04 (binaphthyl), 4.51 (br. m, CH2-N), 3.12 (br., CH2-N),
0.86 (br., 9 H, CH3) ppm. 13C NMR (62.91 MHz, CDCl3): δ =
141.5–124.7 (binaphthyl), 58.9 (CH2-N), 53.89 (CH2-N), 8.21
was stirred at room temperature for 3 h. The solvent was removed (CH3) ppm. 31P NMR (81.02 MHz, CDCl3): δ = 2.77 (PO4) ppm.
under vacuum, and the residue was extracted with dichloromethane
and filtered through Celite. After evaporation of dichloromethane,
9 was obtained as a brown light solid. Yield: 315 mg (90%). 1H
NMR (250.13 MHz, CDCl3): δ = 8.95 (s, 1 H, CHpyr), 8.63 (s, 2
FTIR (KBr): ν = 1117.28 and 1048.59 (P–O), 956.44 (W=O),
˜
828.02 (O–O), 603.26 and 523.04 {[W(O)2]s,as
}
cm–1.
C81H90N3O24PW4 (2255.94): calcd. C 43.12, H 4.02, P 1.37, W
32.60; found C 42.87, H 3.97, P 2.03, W 32.11.
5154
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Eur. J. Inorg. Chem. 2009, 5148–5155

1,1Ј-Binaphthyl-2-methylpyridinium-Based Peroxophosphotungstate Salts
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General Procedure for the Catalytic Oxidation Reactions with the
Use of Ammonium POM Salts 10–12 and Catalyst Recovery Experi-
ments: To a CH2Cl2 solution of the catalyst (0.4 mol-%) was added
the substrate (1 mmol) and the corresponding equivalents of 35%
H2O2. The reaction mixture was stirred at 30 °C and monitored by
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CH2Cl2 layer was separated and concentrated under vacuum. The
catalyst was precipitated by addition of Et2O. The solid was filtered
and washed with Et2O, giving quantitatively the POM catalyst. The
catalyst recycling was carried out following the typical procedure
and conditions described above for the first cycle, CH2Cl2 and reac-
tants being adjusted to the amount of catalyst used. The reaction
was performed with thioanisole (13) by using dried recovered den-
dritic compound 10. The catalyst was completely dissolved in
CH2Cl2, and the reactants were added to the solution. After com-
pletion, the kinetics remained unchanged, as the data collected
were comparable to that summarized in Table 1 for the first cycle.
The catalyst was recovered and checked by 1H and 31P NMR spec-
troscopy.
Acknowledgments
Financial support from the Agence Nationale de la Recherche
(ANR-06-BLAN-0215), the University of Bordeaux, and the Cen-
tre National de la Recherche Scientifique (CNRS) is gratefully ac-
knowledged. The authors thank E. Gérard and G. Lefrançois for
some catalytic experiments.
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Received: September 1, 2009
Published Online: October 9, 2009
Eur. J. Inorg. Chem. 2009, 5148–5155
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5155