Immobilization of a N-substituted azaphosphatrane in nanopores of SBA-15 silica for the production of cyclic carbonates

Article abstract of DOI:10.1039/c4ta01500b

A novel N-substituted azaphosphatrane molecular precursor bearing an alkyne tether was synthesized using a multi-step strategy and covalently immobilized onto SBA-15 type silica through triazole linkages by means of the well-known click chemistry. The resulting hybrid material, [7]@SBA-15, was characterized well by methods appropriate to molecular species (e.g. solid state ¹³C, ³¹P and ²⁹Si NMR, infrared spectroscopy and elemental analysis) as well as techniques more commonly associated with the characterization of mesoporous solids (nitrogen sorption isotherms, powder X-ray diffraction, TGA analysis). The catalytic activity of [7]@SBA-15 was then evaluated in the coupling of CO₂ with two epoxides (styrene oxide and epichlorohydrin) and compared to its monotriazole modified AZAP molecular analog, 8. This work represents the first example of silica modified N-substituted azaphosphatrane for the production of cyclic carbonates. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4ta01500b

Journal of
Materials Chemistry A
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PAPER
Immobilization of a N-substituted
azaphosphatrane in nanopores of SBA-15 silica
for the production of cyclic carbonates†
Cite this: J. Mater. Chem. A, 2014, 2,
4164
1
a
a
a
a
Bastien Chatelet, Lionel Joucla, Jean-Pierre Dutasta, Alexandre Martinez*
b
and Veronique Dufaud*
´
A novel N-substituted azaphosphatrane molecular precursor bearing an alkyne tether was synthesized
using a multi-step strategy and covalently immobilized onto SBA-15 type silica through triazole linkages
by means of the well-known click chemistry. The resulting hybrid material, [7]@SBA-15, was
13
31
29
characterized well by methods appropriate to molecular species (e.g. solid state C, P and Si NMR,
infrared spectroscopy and elemental analysis) as well as techniques more commonly associated with the
characterization of mesoporous solids (nitrogen sorption isotherms, powder X-ray diffraction, TGA
Received 28th March 2014
Accepted 25th June 2014
2
analysis). The catalytic activity of [7]@SBA-15 was then evaluated in the coupling of CO with two
epoxides (styrene oxide and epichlorohydrin) and compared to its monotriazole modified AZAP
molecular analog, 8. This work represents the first example of silica modified N-substituted
azaphosphatrane for the production of cyclic carbonates.
DOI: 10.1039/c4ta01500b
www.rsc.org/MaterialsA
could also act as versatile phase transfer catalysts in a number
of alkylation, oxidation and cyclopropanation organic reac-
1
. Introduction
12
Proazaphosphatranes Verkade's superbases have recently tions and more interestingly that they could efficiently
attracted considerable interest as highly active and selective promote the coupling of carbon dioxide, a renewable feedstock,
basic or nucleophilic catalysts in a wide range of organic with epoxide to produce cyclic carbonates under atmospheric
1–9
13
transformations. These cyclic aminophosphines, built from pressure. Although homogeneous catalysts are ideal for ne-
the tris(2-aminoethyl)-amine (tren) scaffold, exhibit strong tuning reactivity and selectivity of a specic transformation,
basicity (pK ꢀ 32) owing to their ability to become protonated their separation from the reaction mixture and subsequent
a
on their phosphorus atom rather than on the nitrogen atoms, purication are energy-consuming and oen troublesome,
unlike all the commonly used non-ionic bases. As a result, the generating a large amount of wastes. Heterogeneous catalysts,
tricyclic conjugated acids thus obtained, called azaphospha- on the other hand, provide easier separation, recovery and
tranes (AZAP), are remarkably stable. It is perhaps because they reusability of the catalyst and are more suited for use in
are so stable that few synthetic or catalytic studies involving industrial processes and continuous-ow operations. One
these molecules have been undertaken as opposed to the widely promising approach to combine the advantages associated with
studied conjugated base proazaphosphatranes. For instance, both types of catalysts is the direct immobilization of relevant
one can cite their use as procatalysts in combination with homogeneous catalytic species onto insoluble supports whether
1
0
sodium hydride for the conversion of bromoalkanes to alkenes
organic or inorganic. Several methodologies are currently
11
or their ability to promote Michael and Strecker reactions. We available for this purpose including entrapment, adsorption,
have recently demonstrated that these azaphosphatrane salts ion-pair formation and covalent binding, thus leading to a wide
14–18
variety of hybrid catalytic materials.
Surprisingly, examples
of solid-supported azaphosphatranes are rare. To the best of our
knowledge, there are only two papers dealing with the immo-
bilization of azaphosphatranes onto polymeric supports. In
those reports, the covalent link to the surface was achieved by
a
´
Laboratoire de Chimie, Ecole Normale Sup ´e rieure de Lyon, CNRS, UCBL, 46 all ´e e
d'Italie, 69364 Lyon, France. E-mail: Alexander.Martinez@ens-lyon.fr; Fax: +33
4
b
727 28860; Tel: +33 4727 28863
Laboratoire de Chimie, Catalyse, Polym `e re, Proc ´e d ´e s (C2P2), CNRS, Universit ´e
Claude Bernard Lyon1, CPE Lyon, 43 Bd du 11 novembre 1918, 69616 Villeurbanne reacting one of the equatorial amino groups with a chloro-
Cedex, France. E-mail: Veronique.Dufaud@univ-lyon1.fr; Fax: +33 4724 31795; Tel: methylated Merrield's peptide resin under fairly drastic
+
33 4724 31792
ꢁ
conditions (DMF, 110 C, 6 days). The resulting solid catalyst
†
Electronic supplementary information (ESI) available: Synthesis of molecular
was successfully applied in various organic transformations
3
model 8, NMR data of compounds 7 and 8. For [7]@SBA-15 and parent [N ]
10
11
29
(dehydrohalogenation, Michael and Strecker reactions ) and
was found to be highly recyclable.
@
SBA-15 hybrids: physical properties, solid-state Si NMR, TGA, elemental
analyses and FT-IR. TEM/EDX for [7]@SBA-15. See DOI: 10.1039/c4ta01500b
14164 | J. Mater. Chem. A, 2014, 2, 14164–14172
This journal is © The Royal Society of Chemistry 2014

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Journal of Materials Chemistry A
Although interesting, this approach is exclusively limited to was synthesized from p-hydroxybenzaldehyde and 3-bromo-1-
23
non-substituted azaphosphatranes. We have recently shown propyne according to a procedure described in the literature.
that the substitution pattern on the AZAP catalyst greatly affects
13
its activity and stability in the synthesis of cyclic carbonates.
2
.2 Synthesis of molecular compounds
Thus, diversifying the electronic and steric properties of aza-
phosphatranes, notably by changing auxiliary groups on the
Synthesis of compound 2. p-Anisaldehyde (9.6 mL, 78.9
equatorial nitrogen atoms, is highly desirable to test for struc- mmol) was added to a solution of protected tren 1 (8.00 g, 32.5
ture–activity relationships and optimize the catalyst properties. mmol) in 250 mL of methanol. The reaction mixture was stirred
4
In our approach to provide a graable anchor while keeping overnight. NaBH (5.96 g, 157.8 mmol) was then added to the
the substitution versatility, we chose to desymmetrize the ice-cooled solution. The mixture was allowed to warm up to
substituents on the equatorial amines of the tren unit. As we room temperature and the solvent was evaporated. 10%
shall see, the synthesis of such molecular precursors involves a aqueous NaOH (250 mL) was then added and the mixture was
multistep protection/deprotection strategy using appropriately extracted with dichloromethane (3 ꢃ 200 mL). The combined
functionalized aldehydes. Further immobilization onto SBA-15 organic phases were dried over Na SO , ltered and the solvent
2
4
type silica was achieved through covalent bonding using the was removed under vacuum. The crude compound was puried
well-known click chemistry since this reaction proceeds with by column chromatography on silica gel using a (90 : 10 : 2)
19
high yields under mild conditions. Beyond recycling and mixture of dichloromethane, methanol and triethylamine as an
separation advantages, the immobilization of AZAP in the inner eluent to give compound 2 as a yellow oil (12.18 g, 77%). nmax
ꢂ1
space of mesoporous SBA-15 silica may provide benecial cm 3305 (br), 2962, 2933, 2832, 1707 s (C]O), 1513 s, 1247,
changes in reactivity owing to its high specic surface area (up 1174 (C–N), 813. dH (500.1 MHz; CDCl ) 7.22 (4H, d, J 8.77,
3
3
2
ꢂ1
to 1000 m g ) and tunable ordered pore systems (2–100 nm). ArH), 6.84 (4H, d, J 8.77, ArH), 3.78 (6H, s, OCH ), 3.70 (4H, s,
3
3
The state of the solid structure and the integrity of the immo- NCH Ar), 2.66–2.63 (5H, m, NCH CH N), 2.60–2.57 (5H, m,
2
2
2
bilized azaphosphatrane were characterized by several methods NCH CH N), 2.55–2.53 (2H, m, NCH CH N), 1.43 (9H, m,
2
2
2
2
including X-ray powder diffraction at small angles, elemental NBoc). d
analysis, thermogravimetric analysis, infrared spectroscopy, (CAr), 129.5 (CArH), 113.9 (CArH), 78.9 (C(CH
C
(125.7 MHz; CDCl
3
) 158.7 (C]O), 156.3 (CAr), 131.9
), 55.3 (OCH ),
multi-nuclei solid state NMR spectroscopy, nitrogen sorptions 54.1 (NCH Ar), 54.0 (NCH CH N), 53.1 (NCH CH N), 46.8
3
)
3
3
2
2
2
2
2
and transmission electron microscopy (TEM). Finally, the (NCH CH N), 39.07 (NCH CH N), 28.5 ((–CH ) ). ESI-MS m/z
2
2
2
2
3 3
+
catalytic performance of the resulting organic–inorganic hybrid obsd 487.3271 [M + H] , calcd 486.3206 for C H N O .
2
7
42 4 4
material was examined in the cycloaddition of CO
2
to epoxides
Synthesis of compound 3. To an ice-cooled solution of
and compared to its soluble clicked analogue. To the best of our compound 2 (12.18 g, 25.03 mmol) in 80 mL of dry THF was
knowledge, this work represents the rst example of silica added triethylamine (9.8 mL, 72.58 mmol). o-Nitro-
modied N-substituted azaphosphatrane for the production of benzenesulfonylchloride (12.59 g, 56.82 mmol) was then added
cyclic carbonates.
portion-wise to the mixture. The reaction mixture was allowed to
warm up to room temperature and stirred overnight. The solvent
was removed under vacuum and the residue was dissolved with
2. Experimental
1
0% aqueous K
dichloromethane (3 ꢃ 250 mL). The combined organic phases
All manipulations were conducted under a strict inert atmo- were dried over Na SO , ltered and the solvent was removed
2 3
CO (250 mL) prior to be extracted with
2.1 General
2
4
sphere or vacuum conditions using Schlenk techniques under vacuum. The crude compound was puried by column
including the transfer of the catalysts to the reaction vessel. The chromatography on silica gel using a 98 : 2 mixture of
solvents were dried using standard methods and stored over dichloromethane and methanol as the eluent to give compound
ꢂ1
˚
activated 4 A molecular sieves. Tetraethoxysilane (TEOS) and 3 as a yellow oil (17.34 g, 77%). nmax cm 3419 (br), 2975, 2935,
poly(ethyleneoxide)–poly(propyleneoxide)–poly(ethyleneoxide) 2836, 1706 s (C]O), 1544 (CAr–NO ), 1513, 1367 (CAr–NO ), 1249,
block copolymer (Pluronic 123, M 5000) were purchased from 1160 (S]O), 1033 (C–N), 779. d (500.1 MHz; CDCl ) 7.95 (2H, d,
Aldrich Chemicals. CO of a purity of 99.99% was commercially 7.60), 7.70–7.63 (6H, m, ArH), 7.14 (4H, d, J 8.59, ArH), 6.81
obtained and used without further purication. (3-Chlor- (4H, d, J 8.59, ArH), 4.36 (4H, s, NCH Ar), 3.77 (6H, s, OCH ),
2
2
w
H
3
2
J
3
3
3
2
3
opropyl)triethoxysilane was purchased from ABCR. (3-Iodo- 3.17 (4H, t, J 7.50, NCH CH N), 2.90–2.89 (2H, m, NCH CH N),
3
2
2
2
2
propyl)triethoxysilane was prepared by reacting (3-chloropropyl) 2.30–2.27 (6H, m, NCH
2
CH
2
N), 1.43 (9H, m, NBoc). d
C
(125.7
triethoxysilane with NaI in reuxing acetone for 72 hours MHz; CDCl
3
) 159.5 (C]O), 156.0 (CAr), 148.0 (CAr), 133.5 (CArH),
according to the method described by Matsura et al. (3-Azi- 133.4 (CAr), 131.9 (CArH). 130.9 (CArH), 129.9 (CArH), 127.4 (CAr),
dopropyl)triethoxysilane was synthesized by reacting 3-iodo- 124.2 (CArH), 114.2 (CArH), 79.0 (C(CH ), 55.3 (OCH ), 53.9
N), 51.8 (NCH CH N), 45.5
N), 28.4 (–C(CH ). ESI-MS m/z
20
)
3 3
3
propyltriethoxysilane with an excess of sodium azide (5 eq.) in (NCH
2
Ar), 52.3 (NCH
CH N), 38.3 (NCH
2
CH
CH
2
2
2
ꢁ
dry DMF at 50 C for 72 hours by adapting a procedure (NCH
described elsewhere. Azidobutane was prepared by reacting obsd 857.2809 [M + H] , calcd 857.2844 for C H N O S .
2
2
2
2
3 3
)
21
+
3
9
49 6 12 2
ꢁ
1-bromobutane and sodium azide in dry DMF at 60 C for
Synthesis of compound 4. To an ice-cooled solution of
2
4 hours. Compound 1 was synthesized by following a proce- compound 3 (17.24 g, 20.12 mmol) in 135 mL of dichloro-
22
dure described in the literature. p-Propargyloxybenzaldehyde methane was added 135 mL of triuoroacetic acid. The reaction
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ꢁ
mixture was stirred for one hour at 0 C and then allowed to organic phases were dried over Na
2
SO
4
, ltered and the solvent
warm up to room temperature. The solvents were evaporated. was removed under vacuum to give 6 (5.433 g, 57%) as a yellow
ꢂ1
Aqueous 10% NaOH was added and the mixture was extracted oil. nmax cm 3390 (br), 3288 (^C–H), 2958, 2931, 2832, 2111 w
with dichloromethane (3 ꢃ 250 mL). The combined organic (C^C), 1610, 1511 s, 1454, 1245, 1031 (C–N). dH (500.1 MHz;
phases were dried over Na
2
SO
4
, ltered and the solvent was CDCl
3
) 7.19–7.15 (6H, m, ArH), 6.87 (2H, d, J
3
8.58, ArH), 7.81
C^C), 3.77 (6H, s,
5.50, NCH CH N),
2.35, C^C–H). d (125.7
) 158.7 (CAr), 156.7 (CAr), 132.9 (CAr), 131.8 (CAr),
.80 (4H, d, J 8.73, ArH), 4.35 (4H, s, NCH Ar), 3.76 (6H, s, 129.5 (C H), 129.5 (C H), 114.8 (C H), 113.8 (C H), 78.6
removed under vacuum to give 4 as a yellow oil (14.71 g, 97%). (4H, d, J
3
8.65, ArH), 4.62 (2H, d, J
), 3.66 (6H, s, NCH Ar), 2.66 (6H, t, J
) 7.98 2.58 (6H, m, NCH CH N), 2.49 (1H, t, J
8.73, ArH), MHz; CDCl
4 2
2.35, OCH
ꢂ1
n
max cm 3348 (br), 2935, 2836, 1542 (CAr–NO
2
), 1511, 1346 OCH
(500.1 MHz; CDCl
7.60), 7.67–7.60 (6H, m, ArH), 7.14 (4H, d, J
3
2
3
2
2
(C
Ar–NO
2
), 1160 (S]O), 1031 (C–N). d
H
3
2
2
3
C
(2H, d, J
3
3
3
6
3
2
Ar
Ar
Ar
Ar
OCH ), 3.25 (3H, t, J 7.22, NCH CH N), 2.66 (2H, t, J 5.50, (C^C–H), 75.6 (C^C–H), 55.8 (OCH C^H), 55.3 (OCH ), 54.1
3
3
2
2
3
2
3
NCH CH N), 2.45–2.43 (3H, m, NCH CH N), 2.29 (4H, t, J 7.22, (NCH Ar), 54.0 (NCH Ar), 53.1 (NCH CH N), 46.9 (NCH CH N),
2
2
2
2
3
2
2
2
2
2
2
+
NCH
2
CH
2
N). d
C
(125.7 MHz; CDCl
3
) 159.5 (CAr), 147.9 (CAr), 46.8 (NCH
2
CH
2
N). ESI-MS m/z obsd 531.3318 [M + H] , calcd
1
33.6 (CArH), 133.1 (CAr), 132.1 (CArH), 130.9 (CArH), 130.0 531.3330 for C32
ArH), 127.4 (CAr), 124.2 (CArH), 114.2 (CArH), 55.3 (OCH ), 54.0 Synthesis of propargyl azaphosphatrane 7. In an ice-bath
N), 45.8 cooled round bottomed ask, tris(dimethylamino)phosphine
N). ESI-MS m/z obsd 757.2315 [M + (1.340 mL, 7.37 mmol) was dissolved in acetonitrile (70 mL).
43 4 3
H N O .
(
(
(
C
NCH
NCH
3
2
Ar), 52.4 (NCH
2 2 2 2
CH N), 51.7 (NCH CH
2
CH N), 38.5 (NCH CH
2
2
2
+
H] , calcd 757.2320 for C H N O S .
Phosphorus trichloride (0.322 mL, 3.69 mmol) was then added
3
4
41 6 10 2
ꢁ
Synthesis of compound 5. p-Propargyloxybenzaldehyde drop-wise. The reaction mixture was vigorously stirred at 0 C for
3.708 g, 23.15 mmol) was added to a solution of compound 4 0.5 h, and a solution of 6 (5.33 g, 10.05 mmol) in acetonitrile (35
14.60 g, 19.29 mmol) in 80 mL of methanol. The reaction mL) was introduced drop-wise. The reaction mixture was then
(
(
4
mixture was stirred overnight. NaBH (1.751 g, 46.30 mmol) was stirred for 2 days at room temperature. The solvent was removed
then added to the ice-cooled solution. The mixture was then under reduced pressure and the resulting yellow oil was puried
allowed to warm up to room temperature and the solvent was by column chromatography on silica gel using a 15 : 1 mixture of
evaporated. 10% aqueous NaOH (250 mL) was added and the dichloromethane and methanol as the eluent to give compound
ꢂ1
mixture was extracted with dichloromethane (3 ꢃ 200 mL). The 7 as an orange oil (3.41 g, 60%). nmax cm 3390 (br), 3291
combined organic phases were dried over Na SO , ltered and (^C–H), 2111 w (C^C), 1610, 1511, 1245, 1120, 1034, 740. dH
2
4
the solvent was removed under vacuum. The crude compound (500.1 MHz; CDCl ) 7.08 (2H, d, J 8.64, ArH), 7.06 (4H, d, J 8.60,
3
3
3
was puried by column chromatography on silica gel using a ArH), 6.94 (2H, d, J
3
8.64, ArH), 6.85 (4H, d, J
3
8.68), 5.79 (1H, d,
1
3
9
6 : 4 mixture of dichloromethane and methanol as the eluent
J
P-H 497), 4.68 (2H, d, J
N), 4.06 (4H, d, JP-H 17.10, ArCH
), 3.60–3.58 (6H, m, NCH CH N), 3.07–3.03 (6H, m,
CH N), 2.53 (1H, t, J 2.35, C^C–H). d (125.7 MHz; CDCl
4
2.38, OCH
2
C^C), 4.11 (2H, d, JP-H
ꢂ1
3
to give compound 5 as a yellow oil (16.19 g, 93%). nmax cm
16.90, ArCH
2
2
N), 3.80 (6H, s,
3
390 (br), 3286 (^C–H), 2933, 2836, 2119 w (C^C), 1542 s (CAr
–
OCH
3
2
2
NO ), 1346 (CAr–NO ), 1247, 1160 (S]O), 1027 (C–N). d (500.1 NCH
2
2
H
2
2
4
C
3
)
MHz; CDCl ) 7.95–7.93 (2H, m, ArH), 7.70–7.61 (6H, m, ArH), 159.4 (C ), 157.3 (C ), 130.2 (C ), 129.1 (C ), 128.8 (C H), 128.8
3
Ar
Ar
Ar
Ar
Ar
7
.30 (2H, d, J 8.54, ArH), 7.10 (4H, d, J 8.73, ArH), 6.91 (2H, d, J
(C H), 115.5 (C H), 114.5 (C H), 78.4 (C^C–H), 75.9 (C^C–H),
Ar Ar Ar
3
3
3
8
.65, ArH), 6.78 Hz (4H, d, J 8.73), 4.66 (2H, d, J 2.35), 4.33 (4H, 56.0 (OCH C^H), 55.5 (OCH ), 50.9 (NCH Ar, d, J 16.1), 50.8
3
3
2
3
2
3
s, NCH
2
Ar), 3.75 (8H, s, OCH
3
and NCH
2
Ar), 3.17 (4H, t, J
3
7.30, (NCH
2.35, (NCH
2
Ar, d, J
3
16.1), 47.1 (NCH
(202.4 MHz; CDCl
2
CH
2
N, d, J
3
7.3), 39.3
1
NCH
NCH
2
2
CH
CH
2
N), 2.51 (1H, t, J
N), 2.29 (4H, t, J
3
2.35, C^C–H), 2.48 (4H, t, J
7.30, NCH CH N). d
3
2 2
CH N, m). d
P
3
) ꢂ12.16 (d, JP-H 497). ESI-
+
+
2
3
2
2
C
(125.7 MHz; MS m/z obsd 559.2829 [M] , calcd 559.2833 for C32
H
N O
40 4 3
P .
CDCl
3
) 159.5 (CAr), 157.2 (CAr), 148.0 (CAr), 133.3 (CAr), 133.6
Synthesis of clicked model 8 (Scheme S1† in ESI). To a
(CArH), 133.2 (CAr), 132.0 (CArH), 130.9 (CArH), 130.0 (CArH), solution of compound 7 (274 mg, 0.460 mmol) in 6 mL of
1
28.6 (C H), 127.4 (C ), 124.3 (C H), 115.0 (C H), 114.2 dichloromethane was added diisopropylethylamine (0.5 mL,
Ar
Ar
Ar
Ar
(
(
(
C H), 78.6 (C^C–H), 75.7 (C^C–H), 55.9 (OCH C^H), 55.3 2.76 mmol), 92 mg of azidobutane (0.92 mmol) and a catalytic
Ar 2
OCH ),53.5 (NCH Ar), 52.6 (NCH N), 52.3 (NCH CH N), 51.7 quantity of CuI. The reaction mixture was stirred overnight. The
3
2
2
2
2
NCH
2
CH
2
N), 46.1 (NCH
2
CH
2
N), 45.7 (NCH
2
CH
2
N). ESI-MS m/z organic phase was washed with a diluted aqueous ammonia
solution, twice with water, dried over Na SO , ltered and the
+
obsd 901.2873 [M + H] , calcd 901.2895 for C44
H
49
N
6
O
11
S
2
.
2
4
Synthesis of compound 6. To a solution of compound 5 solvent was removed under vacuum. The crude compound was
16.09 g, 17.86 mmol) in 300 mL of DMF was added Na CO puried by column chromatography on silica gel using a 10 : 1
(
(
2
3
18.08 g, 170.5 mmol). Thiophenol (10.1 mL, 98.68 mmol) was mixture of dichloromethane and methanol as the eluent to give
ꢂ1
added under vigorous stirring. The reaction mixture was heated compound 8 as a brown oil (220 mg, 69%). nmax cm 2930,
ꢁ
to 50 C for 24 hours. The solvent was evaporated and water (300 2862, 1609, 1509, 1240, 1169, 1102, 1029. d (500.1 MHz; CDCl )
H
3
mL) was added to the residue and the mixture was extracted 7.65 (s, triazole), 7.11–7.08 (6H, m, ArH), 6.98 (2H, d, J 8.52,
3
with dichloromethane (3 ꢃ 300 mL). The solvent was evapo- ArH), 6.87 (4H, d, J
rated up to 200 mL and the organic phase was extracted with 1 N OCH , triazole), 4.37 (2H, t, J
P-H 16.92, ArCH N), 3.81 (6H, s, OCH
aqueous phases until pH 12 was reached. The solution was NCH CH N), 3.10 (6H, m, NCH CH N), 1.90 (2H, q, J
extracted with dichloromethane (3 ꢃ 200 mL). The combined triazoleCH CH ), 1.37 (2H, sex, J 7.45, triazoleCH CH
3
8.56, ArH), 5.79 (1H, d, JP-H 497), 5.21 (2H, s,
7.33, triazoleCH ), 4.13 (6H, d,
), 3.52 (6H, m,
7.43,
CH ),
2
3
2
3
aqueous HCl. NaOH pellets were added to the combined
J
2
3
2
2
2
2
3
2
2
3
2
2
2
14166 | J. Mater. Chem. A, 2014, 2, 14164–14172
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Paper
Journal of Materials Chemistry A
0.96 (3H, t, J
3
7.45, triazoleCH
2
CH
2
CH
2
CH
3
). d
C
(125.7 MHz; experiments were performed on a Bruker DSX 500 spectrometer
CDCl ) 159.4 (C ), 158.2 (C ), 143.9 (C ), 129.9 (Ctriazole] using a 4 mm double resonance Bruker MAS probe at spectral
3
Ar
Ar
Ar
2
9
13
CtriazoleH), 129.2 (C ), 129.0 (C H), 123.0 (Ctriazole]CtriazoleH), frequencies of 99.3 and 125.7 MHz for respectively Si and
C
Ar
Ar
1
15.5 (C H), 114.6 (C H), 62.3 (OCH , triazole), 55.6 (OCH ), nuclei. Chemical shis were referenced to TMS. The spinning
Ar
Ar
2
3
5
1.1 (NCH
2
Ar), 50.4 (triazoleCH
2
), 47.9 (NCH
2
CH
19.9
). d
) ꢂ11.19 (d, JP-H 497). ESI-MS m/z obsd 658.3602 and 2 ms respectively, number of scans: 3000 to 25 000 and
2
N), 39.5 rate was 10 or 15 kHz and samples were spun at the magic angle
2
9
13
(
NCH
azoleCH
MHz; CDCl
2
CH
2
N),
32.4
(triazoleCH
2
CH
2
),
(tri- using ZrO
2
rotors. The experimental details for the Si and
C
2
CH
2
CH
2
), 13.6 (triazoleCH
2
CH
2
CH
2
CH
3
P
(202.4 CP-MAS NMR experiments were as follows: contact time: 5 ms
1
3
+
31
[M] , calcd 658.3629 for C36
H
49
N
7
O
3
P.
repetition time: 2 s. P MAS NMR spectra were recorded on a
Bruker DSX-500 spectrometer operating at 202.4 MHz with a
classical 4 mm probehead allowing spinning rates up to 10 kHz.
The spectra were obtained by direct irradiation of phosphorus
and proton decoupling. In all cases it was checked that there was
a sufficient delay between the scans (5000) allowing a full
relaxation of the nuclei. The chemical shis are given relative to
2
.3 Hybrid silica materials
One-pot synthesis of azide functionalized SBA-15 silica, [N
SBA-15. SBA-15 mesoporous silica containing azidopropyl
3
]
@
groups was prepared by a one-pot co-condensation procedure.
In a typical experiment, P123 (5.06 g, 0.87 mmol) was weighed
into a Teon bottle. Then 2.0 M HCl (150 mL, 300 mmol) and
H O (7.5 mL, 416.66 mmol) were added and the mixture was
stirred at 40 C until the P123 was fully dissolved. TEOS (9.6 g,
3 4
external 85% H PO . Liquid NMR spectra of molecular
compounds were recorded on a Bruker AC-500 spectrometer and
2
1
13
referenced as following: H (500.1 MHz) and C (125.7 MHz)
ꢁ
1
13
chemical shis were measured relative to residual H or
resonances in CDCl : d 7.26 ppm for H, 77 ppm for C and
C
P
ꢁ
4
6.08 mmol) was then added to the reaction and stirred at 40 C
1
13
31
3
for 1 hour prehydrolysis time. (3-Azidopropyl)triethoxysilane
(
202.4 MHz) referenced to external 85% H
3
PO
4
at d ¼ 0.00 ppm.
(0.20 g, 0.60 mmol) was introduced dropwise into the reaction
Data are reported as follows: chemical shi, number of equiva-
lent nuclei, multiplicity (s ¼ singlet, d ¼ doublet, t ¼ triplet, q ¼
quartet, sex ¼ sextuplet, m ¼ multiplet), coupling constant (J in
Hz), and assignment. During catalytic runs, yields were esti-
ꢁ
mixture which was subsequently stirred at 40 C for 20 hours,
aged at 100 C for 24 hours, and then cooled to room temper-
ature. The resulting solid was ltered and repeatedly rinsed
with H O and Et O. The solid was then allowed to dry overnight
on an aspirating lter. The dried solid was Soxhlet extracted
with MeOH for 24 hours to remove P123. The white solid was
ꢁ
2
2
1
mated by H NMR with a Bruker Avance 300 spectrometer at
300.1 MHz. Mass spectral analyses were performed on a Nermag
R10-10C for exact mass. Elemental analyses were obtained from
the University of Bourgogne and the Research Institute on
Catalysis and Environment of Lyon. C, N, P elemental analyses
determinations were performed by ICP-AES (Activa Jobin Yvon)
spectroscopy from a solution obtained by treatment of the solid
ꢁ

nally dried overnight at 60 C under vacuum and stored under
nitrogen, [N
Click reaction of azaphophatrane 7 onto [N
SBA-15 (3 g) was suspended in dry THF (70 mL) followed by
3
]@SBA-15.
3
3
]@SBA-15. [N ]
@
subsequent addition of azaphosphatrane 7 (590 mg, 0.850
mmol), diisopropylethylamine (10 equivalents) and a catalytic
quantity of CuI (0.2 equivalent). The reaction was stirred for 2
days at room temperature. Aer ltration, the solid was washed
thoroughly with THF. The resulting solid was then contacted
with 0.1 M of N,N-diethyldithiocarbamate sodium in MeOH
catalyst with a mixture of HF, HNO
3
and H
2
SO
4
in a Teon
ꢁ
reactor at 150 C. Fourier transform infrared spectra (FT-IR) were
recorded using a JASCO FT/IR-4200 (JASCO) spectrometer in the
transmittance mode. Transmission electron microscopy (TEM)
was performed with a 200 kV JEOL 2100F microscope, with a
point to point resolution of 0.23 nm. This instrument was
equipped with an EDS X-ray analyzer LINK-ISIS. The preparation
of the sample was performed by dispersing the catalyst powder
on a microscopy copper grid (3.05 mm; 200 mesh) previously
coated with a holey-carbon lm.
(15 mL) to remove CuI and further washed with methanol (20
mL), THF (10 mL) and acetone (10 mL). The nal hybrid
material denoted [7]@SBA-15 was dried overnight at 60
under vacuum and stored under nitrogen.
ꢁ
C
2.4 Characterization
2.5 Catalytic testing
Small-angle X-ray powder diffraction (XRD) data were acquired
on a Bruker D5005 diffractometer using Cu Ka monochromatic [7]@SBA-15 (597 mg containing 0.05 mmol of azaphosphatrane)
˚
radiation (l ¼ 1.5418 A). Nitrogen adsorption–desorption or compound 8 (34.7 mg, 0.05 mmol), epichlorohydrin or
isotherms at 77 K were measured using a Micromeritics ASAP styrene oxide (5 mmol), 2,4-dibromomesitylene (used as
2
1
020M physisorption analyzer. The samples were evacuated at internal standard) and toluene (1 mL) were loaded into a 30 mL
20 C for 24 h before the measurements. Specic surface areas stainless autoclave. The reactor was ushed three times at room
ꢁ
2
were calculated following the BET procedure. Pore size distri- temperature with 10 bar of CO to remove air from the vessel
bution was obtained by using the BJH pore analysis applied to before being further charged to 20 bar of CO
the desorption branch of the nitrogen adsorption–desorption 80 C. Aer the desired reaction time (24 hours), the reactor was
isotherm. A Netzsch thermoanalyser STA 409 PC was used for cooled to room temperature and then in an ice bath and nally
2
and raised to
ꢁ
simultaneous thermal analysis combining thermogravimetric the excess of CO was carefully released. In the case of [7]@SBA-
2
(
1
TGA) and differential thermoanalysis (DTA) at a heating rate of 15, the solid was washed with chloroform and the mixture was
ꢁ
ꢂ1
ꢁ
0
C min
in air from 25–900 C. Solid state CP-MAS centrifuged. The procedure was repeated three times and the
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3
1
supernatant was collected. Reaction yields were determined by case of 7, P NMR conrmed the successful incorporation of
1
31
H NMR aer removal of the solvent.
the phosphorus atom in the tren ligand as the P NMR spec-
trum exhibits a single resonance at ꢂ12.2 ppm typical of the PH
site for AZAP derivatives (ESI, Fig. S3†).
3. Results and discussion
3.1 Synthesis of the AZAP precursor containing a clickable
anchor
3.2 Synthesis of the AZAP organic–inorganic hybrid material
Among the different methods reported in the literature for In the design of hybrid materials, the inuence of host matrix
anchoring organic molecules onto oxide surfaces, we have parameters such as pore size and morphological topology can
identied the copper(I)-catalyzed azide–alkyne 1,3-dipolar be effectively controlled and adapted to the guest size. In this
26
cycloaddition as a highly efficient and reliable ligation process regard, SBA-15 silica, which possesses a regular hexagonal 2D
19
to create robust linkages. The rst step to attain this purpose structure, represents an attractive host for the immobilization
was the synthesis of a N-substituted AZAP molecular precursor of catalytically relevant species. Because of its high surface area
bearing an alkyne tether. This was achieved using a multi-step and high silanol density, SBA-15 is easy to functionalize, and its
strategy which allowed for the selective introduction of various large pore diameter allows for large molecules to enter the pores
substituents at the nitrogen atoms of the tren unit, as depicted with less mass transfer limitation than materials with a smaller
in Scheme 1. The synthesis starts from commercially available pore size (i.e. MCM-41 silica). In this study, we used a two-step
tren, whose one of the amine functions was selectively procedure to prepare clean azaphosphatrane functional silica
22
monoprotected with a Boc group, 1. The two remaining free surfaces (Scheme 2). SBA-15 mesoporous silica modied by
amines were then reacted with p-methoxybenzaldehyde via a azidopropyl groups was rst synthesized by the one-pot co-
reductive alkylation to afford 2 in 77% yield. In order to prevent condensation route since this approach provides for greater
reaction of the two newly formed secondary amines with homogeneous distribution of functional groups within the
27
3
p-propargyloxybenzaldehyde, these latter were subsequently solid. Aer removal of the P123 structure directing agent, [N ]
protected with o-nitrobenzenesulfonylchloride to yield N,N- @SBA-15 was reacted with azaphosphatrane 7 under classical
disubstituted-2-nitrobenzenesulfonamide 3. The N-Boc pro-
tected group could then be selectively removed with triuoro-
acetic acid and the resulting free amine cleanly reacted with
p-propargyloxybenzaldehyde to give the N-alkylated product 5.
ꢁ
Upon treatment with PhSH and Na
deprotection of 5 via a S
2
CO
3
in DMF at 50 C, facile
24
N
Ar reaction mechanism was carried
out leading to the formation of functionalized tren ligand 6.
Finally, the phosphorus could be inserted following the clas-
25
sical procedure described by Verkade to give the dissymmetric
propargyl azaphosphatrane 7 in 60% yield. Structural charac-
terization of compounds 1–7 was assessed using FT-IR, multi-
nuclei NMR spectroscopy and electrospray ionisation mass
Scheme
2
Immobilization of azaphosphatrane through click
spectrometry (ESI-MS) (Experimental section). In the particular chemistry.
Scheme 1 Synthesis strategy to alkyne-containing azaphosphatrane.
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Journal of Materials Chemistry A
isotherms and pore size distributions are depicted in Fig. 2.
Both materials showed type IV isotherms and H1 hysteresis loop
characteristic of mesoporous solids and SBA architectures. A
steep capillary condensation step appearing at P/P ¼ 0.6–0.8
0
(Fig. 2, top) indicated the presence of regular mesopores in the
samples which was further conrmed by a narrow pore size
distribution in the mesopore range (Fig. 2, bottom). Upon
derivatization of [N
3
]@SBA-15 with azaphosphatrane 7, no
˚
change in pore diameter was observed (ꢀ58 A) whereas a
2
ꢂ1
Fig. 1 X-ray powder diffraction patterns of the azide functionalized
SBA-15 silica material before and after click reaction of 7.
marked decrease in the BET surface area (from 594 m g to
2
ꢂ1
ꢂ1
3
ꢂ1
4
0
15 m g , Table S1†) and pore volume (from 0.89 cm g to
3
.65 cm g , Table S1†) was noted which is consistent with the
presence of a signicant amount of azaphosphatrane on the
interior mesopore surfaces.
click conditions in the presence of diisopropylethylamine and a
catalytic amount of CuI, yielding hybrid [7]@SBA-15.
3
The successful incorporation of 7 in [N ]@SBA-15 was
The physicochemical and textural properties of hybrid
materials derived from powder XRD and sorption measure-
ments are summarized in Table S1† (ESI). Small angle powder
XRD patterns of SBA-15 materials collected before and aer
click reaction of 7 are displayed in Fig. 1. Both solids exhibited
typical diffractograms characteristic of hexagonally ordered
mesophases with the presence of three well resolved peaks in
13
31
further conrmed by solid-state C and P NMR spectroscopy.
13
Examination of the C NMR spectrum of [7]@SBA-15 showed
the presence of two key peaks at 122 and 145 ppm typical of the
triazole ring suggesting that 7 has been efficiently attached to
the azide linker without measurable degradation as most
resonances of the azaphosphatrane fragment were also
discernible (Fig. 3).
ꢁ
the 2q-range of 0.6 to 2 attributed respectively to (100), (110)
Further information concerning the phosphorus environ-
and (200) reexions. The presence of higher order reexions
indicates that the chemical bonding procedure did not
diminish the long-range structural ordering in the materials
although a slight decrease in intensity of the d100 reection was
observed for [7]@SBA-15. The ordering was also clearly evident
in the TEM/EDX imagery with a homogeneous distribution
of azaphosphatrane 7 throughout the solid (ESI, Fig. S7 and
Table S2†).
31
ment in [7]@SBA-15 was obtained from CP MAS P NMR. As
shown in Fig. 4, a single broad resonance centered at ꢂ12.8
ppm along with spinning side bands was observed. The absence
31
of signicant shi when compared to the liquid P spectrum of
7
suggests that the AZAP moiety remained intact upon click
reaction. The P–H site seems unaffected by inclusion of the
AZAP moiety in the silica matrix probably due to the protection
provided by the lipophilic pocket formed by a ring of
substituted benzyl-amino groups around the central PH unit.
Nitrogen adsorption–desorption measurements were used to
examine the textural properties of the hybrid materials. Typical
29
The Si CP MAS spectrum of [7]@SBA-15 showed no
signicant changes compared to the parent [N ]@SBA-15 (ESI,
3
13
Fig. 2 Nitrogen adsorption–desorption isotherms (top) and pore size Fig. 3 CP MAS C NMR of [N
3
]@SBA-15 before and after click reaction
]@SBA-15 and clicked silica materials of 7 and the liquid C NMR spectrum of molecular azaphosphatrane, 7
for comparison. S and * denote respectively CDCl and P123.
13
distributions (bottom) of azide [N
7]@SBA-15.
3
[
3
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This atom-efficient industrial process which utilizes CO
2
as a
raw material to value-added products has lately attracted
28
considerable interest (Scheme 3). Organic carbonates are
important building blocks that have been widely applied as
polar aprotic solvents, electrolytes for lithium batteries, mono-
mers for polycarbonates and copolymers synthesis and as
useful intermediates in the ne chemical and pharmaceutical
29
industries. Metal-free catalytic processes have existed for over
0 years, based mainly on quaternary ammonium or phospho-
5
30
nium salts, but they require fairly drastic reaction conditions
high temperatures and pressures) and the use of relatively pure
CO . Other viable processes based on more reactive transition
(
2
31
metal catalysts are productive under milder conditions, but in
this case metal contamination of nal products as well as
catalyst separation and disposal becomes both an environ-
mental and economic drawback. Therefore, the development of
new technologies and metal-free catalysts that operate under
mild reaction conditions is a priority to minimize costs and
greenhouse gas emissions and provide true viable alternatives
for fossil fuel-based chemicals.
3
1
Fig. 4 Liquid P NMR spectrum of molecular azaphosphatrane 7 and
31
MAS P NMR of [7]@SBA-15. * denotes spinning side bands.
Fig. S8†), indicating that the Si sites did not undergo any
chemical changes during the course of the click reaction.
Specically, the peaks associated with organosiloxanes (T-type
silicates) in the spectral region ranging from ꢂ60 to ꢂ75 ppm
remained unchanged which is a clear indication that covalent
bonding in [N ]@SBA-15 was unaffected by subsequent surface
derivatization.
Quantitative determination of organic content was obtained
from nitrogen and phosphorus elemental analyses. Thus, the
functional group loading corrected from sample humidity, that
is by considering the SiO
was found to be 0.17 and 0.10 mmol g dry silica for respec-
3
tively [N ]@SBA-15 and [7]@SBA-15 (Table S3†, ESI). This
suggests that 60% of the surface azido groups in [N ]@SBA-15
were successfully attached to 7 through the triazole ring. This
result was further conrmed by FT-IR, in particular by the
decrease in intensity upon click reaction of the stretching
vibration mode at 2117 cm typical of organic azide (Fig. S9†,
ESI). Thermogravimetric analysis before and aer click reaction
of 7 was also performed under owing air from room temper-
ature to 1000 C (ESI, Fig. S10†). In general, similar thermal
patterns, composed of three weight loss regions, were observed
for both hybrids: the weight loss due to desorption of phys-
isorbed water occurring before 170 C was followed by a
progressive weight loss comprised between 170 and 700
which was ascribed to organic species decomposition. Because
of the presence of the remaining P123 structure directing agent
in both solids, as evidenced by C NMR, this weight loss could
not be taken as a reliable estimate of the total amount of
organics. The third weight loss region which took place above
00 C was attributed to the release of water formed from the
In this regard, we have recently described the use of aza-
phosphatranes as original and tunable catalysts for the
3
synthesis of cyclic carbonates from CO
2
and epoxides, hence
demonstrating their utility as single components, metal-free
13
alternatives to current state-of-the-art catalysts. In particular,
we have shown that the substitution around the reactive P–H
site could have an impact on catalyst activity and stability. Thus,
a molecular analog of the triazole linked supported catalyst was
also synthesized to allow for meaningful comparative catalytic
studies. It was obtained by reacting n-butylazide with AZAP 7 to
afford a dissymmetric monotriazole modied AZAP 8, in which
the SBA-15 surface of [7]@SBA-15 has been replaced by a methyl
group (Scheme S1†, ESI).
ꢁ
2
content of the TGA run at 1000 C,
ꢂ1
3
In this paper, the comparison of the triazole-linked AZAP
hybrid catalyst to the molecular analog was accomplished
under identical conditions of temperature, CO2 pressure,
substrate concentration and, notably substrate/AZAP molar
ratio using two epoxide substrates: styrene oxide and epichlo-
ꢂ1
ꢁ
rohydrin. Typical reaction conditions were as follows: 80 or 100
ꢁ
2
C, 24 h, catalyst loading of 1 mol%, and 20 bar CO . Lower
ꢁ
pressures (1 and 10 bar) were attempted but yields of product
were insufficient for our purpose. Table 1 shows the test results.
One can see that the molecular catalyst 8 leads to near-quanti-
tative conversion of both phenyl-substituted and chloro-
methylene-substituted epoxides to the corresponding cyclic
carbonates under these reaction conditions. The supported
catalyst [7]@SBA-15 was reactive and revealed that there was a
substrate structural effect, the conversion of styrene oxide being
limited to 21% whereas with epichlorohydrin a conversion of
ꢁ
C
1
3
ꢁ
7
condensation of silanols in the silica matrix. Examination of the
DTA curve of [7]@SBA-15 reveals the presence of an additional
sharp decomposition peak around 255 C which could likely
ꢁ
arise from the AZAP moiety desorption.
2
3.3 Coupling of CO and epoxides to cyclic carbonates
As previously mentioned, the reactivity of the resulting organic–
inorganic hybrid material [7]@SBA-15 was then examined in the
Scheme 3 Synthesis of cyclic carbonates from epoxides and carbon
coupling of CO
2
with epoxides to produce cyclic carbonates. dioxide.
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Journal of Materials Chemistry A
a
Table 1 Coupling of CO
2
and epoxides to cyclic carbonates
Notes and references
ꢁ
Substrate
Temperature ( C)
Catalyst
7]@SBA-15
Yield (%)
1
2
J. G. Verkade, Acc. Chem. Res., 1993, 26, 483–489.
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[
21
99
8
3 J. G. Verkade, Top. Curr. Chem., 2002, 233, 1–44.
100
4
J. G. Verkade and P. B. Kisanga, Tetrahedron, 2003, 59, 7819–
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8
7]@SBA-15
49
99
7858.
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80
6
K. Wadhwa, V. R. Chintareddy and J. G. Verkade, J. Org.
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a
Conditions: epoxide (5.0 mmol), catalyst (0.05 mmol), toluene (1 mL),
2
(20 bar), and 24 hours. Yields were determined by H NMR using
1
CO
2
,4-dibromomesitylene (1.0 mmol) as an internal standard.
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8
3
4
9% could be achieved even at lower reaction temperature (80
9 P. Kisanga, X. Fei and J. Verkade, Synth. Commun., 2002, 32,
1135–1144.
ꢁ
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32
systems as a key parameter for improved reactivity.
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6 C. E. Song and S.-G. Lee, Chem. Rev., 2002, 102, 3495–3524.
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4
. Conclusion
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2
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Acknowledgements
The authors would like to acknowledge funding from the 26 (a) C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and
French Ministry of Research (Project ANR-2010JCJC 7111
(Sup) Base]). Sandrine Denis-Quanquin, Christine Lucas
and Philippe Arquilli `e re are also greatly thanked for
their help in respectively solid-state NMR and TEM
experiments.
J. S. Beck, Nature, 1992, 359, 710–712; (b) J. S. Beck,
J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge,
K. D. Schmitt, C. T.-W Chu, D. H. Olson, E. W. Sheppard,
S. B. McCullen, J. B. Higgins and J. L. Schlenker, J. Am.
[
3
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14172 | J. Mater. Chem. A, 2014, 2, 14164–14172
This journal is © The Royal Society of Chemistry 2014