Sol-gel immobilized aryl iodides for the catalytic oxidative α-tosyloxylation of ketones

Article abstract of DOI:10.1016/j.reactfunctpolym.2012.10.011

New hybrid silica materials M1-M4, derived from mono and bis-silylated aryl iodides, have been prepared via sol-gel processes, either by the hydrolytic polycondensation of a bis-silylated monomer or by the co-gelification of a monosilylated precursor with

Full text of DOI:10.1016/j.reactfunctpolym.2012.10.011

Reactive & Functional Polymers 73 (2013) 192–199
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Reactive & Functional Polymers
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Sol–gel immobilized aryl iodides for the catalytic oxidative
of ketones
a-tosyloxylation
a,
Wusheng Guo a, Amàlia Monge-Marcet a, Xavier Cattoën b, Alexandr Shafir a, , Roser Pleixats
⇑
⇑
a Department of Chemistry, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Barcelona, Spain
b Institut Charles Gerhardt Montpellier (UMR 5253 CNRS-UM2, ENSCM-UM1), 8 rue de l’école normale, 34296 Montpellier, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 July 2012
Received in revised form 19 October 2012
Accepted 22 October 2012
Available online 29 October 2012
New hybrid silica materials M1–M4, derived from mono and bis-silylated aryl iodides, have been pre-
pared via sol–gel processes, either by the hydrolytic polycondensation of a bis-silylated monomer or
by the co-gelification of a monosilylated precursor with tetraethylorthosilicate. They have been fully
characterized by elemental analysis, 13C and 29Si CP-MAS solid state NMR, IR, TGA, and nitrogen-sorption
measurements. These organosilicas have been successfully applied as supported catalysts in the
tosyloxylation of aliphatic ketones in the presence of m-chloroperbenzoic acid (m-CPBA) as an oxidant,
with the corresponding -tosyloxyketones obtained in moderate to good isolated yields. The recyclability
of the supported catalysts by a simple filtration has also been investigated.
Ó 2012 Elsevier Ltd. All rights reserved.
a-
Keywords:
a
Hypervalent iodine
Hybrid silica
Recyclable catalyst
Sol–gel
Oxidative a-tosyloxylation
1. Introduction
on the PhI-catalyzed
and Togo recently reported that iodobenzene also catalyzes the
oxidative -tosyloxylation of ketones (as illustrated in Scheme 1)
a-acetoxylation of ketones [7], Yamamoto
Oxidative CAH functionalization at the
a
position of carbonyl
a
compounds to form new CAO bonds is an attractive transformation
under mild conditions using m-CPBA as an oxidant [8–10], with
promising results achieved at 10 mol% of iodobenzene [8]. The
authors also tested polystyrene-supported iodoarenes [9,10] as
potentially recyclable heterogeneous catalysts. It should be noted
that polymer-supported iodobenzene had also previously been
used in the same laboratory for the preparation of a polymeric Ko-
ser reagent [11]. However, in most cases, although recovery and re-
use in a second cycle was indeed possible, considerable amounts of
the material (>0.5 equiv of ArI) were necessary to achieve moder-
that provides rapid access to -hydroxycarbonyl building blocks.
a
Among other methods, the use of hypervalent organoiodine(III) re-
agents such as the Koser reagent, PhI(OH)(OTs), has proven espe-
cially effective for introducing the AOTs group at this position
[1]. Indeed, the synthetic use of hypervalent organoiodanes has be-
come a hot topic in the last two decades due to their unique reac-
tivity beyond that of a simple oxidant. In addition, the use of a
hypervalent iodine reagent may, in a number of cases, obviate
the need for a metal additive, a particularly attractive feature in
pharmaceutical chemistry.
In processes employing hypervalent iodine, the iodoarene
side-product may, in principle, be easily removed at the end of
the reaction [2,3] and could, once again, be converted to a hyperva-
lent iodane through a simple oxidation. Interestingly, several re-
ate yields of the
a-tosyloxylated ketones. In addition to polymer-
based systems, ionic liquid-supported iodobenzene had also been
suggested by the same group in 2007 for use as a homogeneous
recyclable catalyst [12].
In search of a more efficient recyclable iodoarene, a hybrid silica
gel-based iodoarene was considered. The formation of hybrid silica
materials or organosilicas is an attractive strategy for the immobi-
lization of organocatalysts, since such materials combine the
advantages of a silica matrix, such as thermal and mechanical sta-
bility and chemical inertness, with the reactivity of an embedded
organic precursor [13–16]. Bridged silsesquioxanes [17,18] repre-
sent an interesting class of organosilicas, obtained by the sol–gel
cent publications describe
a modification of this process,
whereby catalytic quantities of the aryl iodides are used in the
presence of a cheaper terminal oxidant, which ensures the in situ
regeneration of the organoiodine(III) reagent [4]. This budding area
of research was recently the subject of two minireviews [5,6]. In
particular, following a 2005 publication by Ochiai and coworkers
hydrolysis-condensation of monomers containing
a variable
organic bridging fragment previously decorated with two or more
trialkoxysilyl groups. These materials feature inherently high
homogeneity and permit high loading of organic units, the
⇑
Corresponding authors. Fax: +34 93 5812477.
E-mail addresses: alexandr.shafir@uab.cat (A. Shafir), roser.pleixats@uab.cat
(R. Pleixats).
1381-5148/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.reactfunctpolym.2012.10.011

W. Guo et al. / Reactive & Functional Polymers 73 (2013) 192–199
193
shifts are referenced to the 13C resonance of the solvent. N2-sorption
isotherms were obtained on a Micromeritics ASAP2020 analyzer at
the Institut Charles Gerhardt in Montpellier after degassing the
materials at 55 °C for 30 h under high vacuum. The surface areas
and pore size distributions were calculated from the desorption
branch by the Brunauer-Emmett-Teller (BET) transform and the
Barrett–Joyner–Halenda (BJH) method, respectively. High resolu-
tion mass spectra were determined at the Servei d’Anàlisi Química
of the Universitat Autònoma de Barcelona using a Bruker Daltonic
MicroTOFQ spectrometer (Bremen, Gemany) equipped with an
ESI inlet. Elemental analyses were performed at the Serveis Cientí-
fico-Tècnics of the Universitat de Barcelona, and the Si content was
determined by inductively coupled plasma optical emission spec-
troscopy (ICP-OES) using a multichannel Perkin Elmer model Opti-
ma 3200 RL spectrometer under standard conditions. The iodine
analysis was performed by combustion of the sample in an oxygen
bomb (Calorimeter IKA 5012). The formed gases were absorbed by
a 0.25 M sodium hydroxide aqueous solution. The bomb was
rinsed twice with deionized water that was collected and added
to the sodium hydroxide aqueous solution. The combined solution
was diluted to an exact volume in a volumetric flask and analyzed
by HPLC (Waters 2690 model equipped with a Waters 996 photo-
diode array detector, IC-Pak Anion HR column). The corresponding
peak was interpreted based on the calibration curve obtained from
standard sodium iodide aqueous solutions. TGA analyses were per-
formed under an argon atmosphere at the Institut de Ciència dels
Materials de Barcelona using a NETZSCH STA 449 F1 instrument
(TGA/DSC).
Scheme 1. Catalytic cycle for PhI-catalyzed a-tosyloxylation of ketones.
inorganic network being built directly around the organic moieties.
Although the resulting catalytic systems often suffer from low
porosity and, thus, low surface areas, some recent reports demon-
strate excellent catalytic properties of such catalysts in different
organic transformations [19–23]. While two or more pendant
Si(OR)3 functional groups may allow for direct condensation, re-
lated hybrid silica can also be prepared from singly silylated pre-
cursors by their sol–gel co-gelification with tetraethyl
orthosilicate (TEOS) [24,25]. Regardless of the strategy employed
in the sol–gel formation, when applied as a catalyst, the supported
hybrid silica can easily be separated from the reaction mixture by a
simple filtration. The recovered material can then be reused, an
economically and environmentally relevant factor.
Following our interest in recyclable catalysts based on hybrid
silica materials [20–23,26–31], we present herein our results on
the synthesis and characterization of silica-immobilized iodoarenes
prepared by the sol–gel methodology and their catalytic perfor-
mance in the oxidative a-tosyloxylation of ketones using m-CPBA
as a stoichiometric oxidant.
2.3. Synthesis of silylated precursors
2.3.1. Preparation of (3-iodopropyl)triethoxysilane
This compound was prepared following a described procedure
[32]. A mixture of NaI (13.48 g, 89.9 mmol), (3-chloropropyl)trieth-
oxysilane (15.0 mL, 1.00 g/mL, 62.3 mmol) and anhydrous acetone
(50 mL) was stirred under reflux for 2 days under an argon atmo-
sphere. At this point, the mixture was filtered and the solvent from
the filtrate was evaporated under reduced pressure. The residue
was triturated with dry hexane (30 mL) and once again filtered.
After removal of hexane from the filtrate, the (3-iodopropyl)trieth-
oxysilane was obtained as a pale yellow liquid; yield: 18.63 g
(90%). 1H NMR (250 MHz, CDCl3) d (ppm): 3.82 (q, J = 7.0 Hz, 6 H,
OCH2), 3.22 (t, J = 7.0 Hz, 2 H, ACH2I), 1.99–1.87 (m, 2 H, ICH2CH2),
1.23 (t, J = 7.0 Hz, 9 H, CH3), 0.79–0.66 (m, 2 H, SiCH2). 13C NMR
2. Experimental
2.1. Reagents and methods
When required, experiments were carried out using standard
high vacuum and Schlenk techniques. Solvents were dried, distilled
and degassed shortly before use following standard procedures.
Ethanol was distilled from Mg/I2. Tetraethyl orthosilicate (TEOS)
98%, tetrabutylammonium fluoride (1 M solution in anhydrous
THF), m-chloroperbenzoic acid (m-CPBA) (approximately 65% pur-
ity), methanesulfonic acid (99% purity) and camphorsulfonic acid
(99% purity) were purchased from Aldrich and used without any
further treatment; p-toluenesulfonic acid (p-TsOHÁH2O) (98% pur-
ity) was purchased from Panreac and used as received. The silica
gel for flash chromatography was a Macherey–Nagel GmbH & Co.
KG silica gel with a particle size of 230–400 mesh and a pore vol-
ume of 0.9 mL/g. The silica gel used for purifying moisture-sensitive
organosilanes was dried under a nitrogen flow using a heat gun
just before use.
(100 MHz, CDCl3) d (ppm): 58.8, 27.8, 18.6, 12.6, 11.1. IR (ATR)
m
(cmÀ1): 2972, 2884, 1073, 784, 629.
2.3.2. Preparation of 1-iodo-3, 5-dimethoxybenzene 1
This compound was prepared following a described procedure
[33]. To stirred solution of 3,5-dimethoxyaniline (9.15 g,
a
59.7 mmol) in water (100 mL) maintained at À5 °C, concentrated
H2SO4 (9 mL) was added dropwise, followed by the addition of a
solution of NaNO2 (4.85 g, 70.3 mmol) in water (20 mL). Keeping
the temperature below 0 °C, the reaction mixture was stirred for
20 min, then diethyl ether was added (50 mL), followed by a drop-
wise addition of a solution of potassium iodide (30 g, 180.7 mmol)
in water (30 mL). After the mixture was stirred at room tempera-
ture for 6 h, the layers were separated and the aqueous phase
was extracted with additional diethyl ether (3 Â 100 mL). The
combined organic fraction was washed successively with 25% (w/
v) aqueous Na2S2O3Á5H2O (3 Â 50 mL), 1 M HCl (1 Â 100 mL) and
2 M NaOH (1 Â 100 mL), then dried over anhydrous MgSO4, filtered
and concentrated to a brown oil. The crude mixture was purified by
silica gel chromatography using hexane/ethyl acetate 95:5
(Rf = 0.56) as the eluent to yield 1-iodo-3,5-dimethoxybenzene, 1,
as a white solid; yield: 11.76 g (75%). 1H NMR (250 MHz, CDCl3)
2.2. Physicochemical characterization
IR data were obtained on a Bruker Tensor 27 with an ATR Gold-
en Gate. Liquid 1H and 13C NMR spectra were recorded on Bruker
DRX-250 MHz, DPX-360 MHz and AVANCE III 400 MHz instru-
ments, and CP-MAS 29Si solid state NMR spectra were recorded
on a Bruker AV400WB. All NMR experiments were performed at
the Servei de Ressonància Magnètica Nuclear of the Universitat Autò-
noma de Barcelona. 1H NMR chemical shifts (d, ppm) are referenced
to the residual protio signal of the deuterated solvent, and the 13C

194
W. Guo et al. / Reactive & Functional Polymers 73 (2013) 192–199
d (ppm): 6.85 (d, J = 2.2 Hz, 2 H, o-ArH), 6.40 (t, J = 2.2 Hz, 1 H, p-
ArH), 3.76 (s, 6 H, Me). 13C NMR (62.50 MHz, CDCl3) d (ppm):
164.4, 116.1, 100.9, 94.4, 55.8. IR (ATR)
1026, 1050, 615.
gelification was observed, and the material was aged at room tem-
perature for 6 days. The resulting gel was pulverized, separated by
filtration and washed successively with water (2 Â 6 mL), EtOH
(2 Â 6 mL) and acetone (2 Â 6 mL). The final solid was dried over-
night at 55 °C under vacuum (2.0 mbar) to afford M1 as a white so-
lid (1.005 g). 13C CP-MAS NMR (100.62 MHz) d (ppm): 159.5, 118.2,
113.2, 99.9, 93.7, 68.9, 57.4, 22.2, 17.6, 7.7. 29Si CP-MAS NMR
(79.5 MHz) d (ppm): À47.6 (T0, 2%), -55.0 (T1, 8%), À61.0 (T2,
m
(cmÀ1): 3069, 1258,
2.3.3. Preparation of 5-iodoresorcinol 2
This compound was prepared following a described procedure
[33]. mixture of 1-iodo-3,5-dimethoxybenzene (1) (6.60 g,
A
25.0 mmol) and hydroiodic acid (45 wt.%, 60 mL) was heated to re-
flux for 40 h. The solution was then cooled to room temperature
and diluted with water (deionized, 80 mL) and diethyl ether
(80 mL). The organic layer was separated and washed successively
with 1 M sodium thiosulfate (3 Â 60 mL) and distilled water
(1 Â 50 mL). The solution was dried with anhydrous MgSO4, and
the solvent was evaporated to afford an oil that spontaneously
solidified at room temperature to give 2 as a white solid; yield:
5.84 g (99%). 1H NMR (360 MHz, DMSO-d6) d (ppm): 9.52 (s, 2 H),
6.57 (d, J = 1.8 Hz, 2 H), 6.20 (br s, 1 H). 13C NMR (90 MHz,
20%), À68.6 (T3, 69%). IR (ATR)
m
(cmÀ1): 2929, 2880, 1590, 1567,
1433, 1260, 1014 (broad), 797, 676. BET surface area: <5 m2/g;
non-porous material. TGA: (argon, 20–700 °C) residual mass
47.9%. EA calculated for C12H15ISi2O5 (considering complete con-
densation): 34.13% C, 3.58% H, 13.30% Si, 30.05% I; found: 34.7%
C, 4.5% H, 11.5% Si, 13.5% I.
2.4.2. Preparation and characterization of hybrid silica material M2
Bis-silylated compound 3 (0.410 g, 0.636 mmol) and TEOS
(0.71 mL,
nol (3 mL). A solution of Milli-Q water (0.30 mL, 16.536 mmol)
and TBAF (50 L, commercial solution 1 M in anhydrous THF) in
q = 0.934 g/mL, 3.18 mmol) were dissolved in dry etha-
DMSO-d6) d (ppm): 159.3, 115.3, 102.4, 94.6. IR (ATR)
m
(cmÀ1):
3254, 1383, 1215, 610.
l
dry EtOH (0.80 mL) was then added to the first solution. The final
mixture was shaken vigorously for 10 s to obtain a homogenous
solution. After 10 min, a gel formed that was then aged at room
temperature for 6 days. The resulting gel was pulverized, filtered
and washed successively with water (2 Â 6 mL), EtOH (2 Â 6 mL)
and acetone (2 Â 6 mL). The final solid was dried overnight at
55 °C under vacuum (2.0 mbar) to afford M2 as a white solid
(0.410 g). 13C CP-MAS NMR (100.62 MHz) d (ppm): 160.7, 119.6,
101.7, 94.2, 69.8, 58.6, 22.8, 17.4, 8.5. 29Si CP-MAS NMR
(79.5 MHz) d: À59.3 (T2), À68.2 (T3), À93.3 (Q2), À102.3 (Q3),
2.3.4. Preparation of the bis-silylated iodoarene 3
Dry acetone (20 mL) was added to a mixture of compound 2
(2.360 g, 10 mmol), K2CO3 (6.90 g, 50 mmol) and (3-iodopropyl)tri-
ethoxysilane (10.801 g, 32.5 mmol) under a nitrogen atmosphere.
After refluxing for 27 h under nitrogen, the solvent was removed
under reduced pressure and the residue was extracted with dry
dichloromethane/hexane 1:4 (4 Â 10 mL), filtering the resulting
solution after each round of extraction. The volatile fraction was
removed under vacuum to afford a colorless oily residue, which
was purified by silica gel chromatography (hexane/ethyl acetate
25:1 as eluent). Rf = 0.22 (silica gel, hexane/ethyl acetate 95:5).
Yield of 3: 1.93 g, 30%. 1H NMR (250 MHz, CDCl3) d (ppm): 6.83
(d, J = 2.1 Hz, 2 H, o-ArH), 6.39 (m, 1 H, p-ArH), 3.93–3.77 (m, 16
H, AOCH2), 1.88 (m, 4 H), 1.23 (t, J = 7.0 Hz, 18 H, AMe), 0.79 –
0.69 (m, 4 H). 13C NMR (62.5 MHz, CDCl3) d (ppm): 160.3, 116.0,
À110.8 (Q4). IR (ATR)
m
(cmÀ1): 2944, 1592, 1438, 1050, 800, 679.
BET surface area: 255 m2/g; pore volume: 0.838 cm3/g. TGA: (argon,
20–700 °C) residual mass 59.8%. EA calculated for C12H15ISi2O5Á5SiO2
(considering complete condensation): 19.94% C, 2.09% H, 27.20% Si,
17.56% I; found: 17.8% C, 2.1% H, 24.2% Si, 8.2% I.
101.4, 93.6, 69.9, 58.1, 22.5, 18.1, 6.3. IR (ATR)
m
(cmÀ1): 2972,
2.4.3. Preparation and characterization of hybrid silica material M3
Monosilylated compound 4 (0.800 g, 1.887 mmol) and TEOS
2925, 2882, 1293, 1277, 1073, 628. HRMS (ESI): calculated for
[C24H45IO8Si2Na]+ (M++Na): 667.1595; found: 667.1600.
(2.10 mL,
(10 mL). Then, a solution of Milli-Q water (0.78 mL, 43.4 mmol)
and TBAF (113 L, commercial solution 1 M in anhydrous THF) in
q = 0.934 g/mL, 9.4 mmol) were dissolved in dry ethanol
2.3.5. Preparation of the monosilylated iodoarene 4
l
Dry acetone (20 mL) was added to a mixture of 3-iodophenol
(3.30 g, 15.0 mmol), K2CO3 (8.29 g, 60 mmol) and (3-iodopro-
pyl)triethoxysilane (4.984 g, 15.0 mmol) under nitrogen atmo-
sphere. The mixture was kept at reflux for 24 h under nitrogen.
The organic solvent was evaporated under vacuum and the residue
was extracted with dry hexane (4 Â 10 mL), filtering the resulting
solution after each round of extraction. The solvent was removed
under reduced pressure to afford 4 as a colorless oil (2.10 g, 33%
yield). 1H NMR (250 MHz, CDCl3) d (ppm): 7.25–7.12 (m, 2 H),
6.98 (t, J = 8.2 Hz, 1 H), 6.85 (d, J = 7.1 Hz, 1 H), 3.96–3.71 (m, 8
H), 1.88 (m, 2 H), 1.23 (t, J = 7.0 Hz, 9 H), 0.78–0.72 (t, J = 7.1 Hz,
2 H). 13C NMR (62.5 MHz, CDCl3) d (ppm): 160.0, 131.0, 129.9,
dry EtOH (1.3 mL) was added to the first solution. The final mixture
was shaken vigorously for 10 s to obtain a homogenous solution.
After 15 min, a gel formed that was then aged at room temperature
for 6 days. The gel obtained was pulverized, filtered off and washed
successively with water (2 Â 6 mL), EtOH (2 Â 6 mL) and acetone
(2 Â 6 mL). The final solid was dried overnight at 55 °C under vac-
uum (2.0 mbar) to afford M3 as a white solid (1.087 g). 13C CP-MAS
NMR (100.62 MHz) d (ppm): 159.8, 130.2, 123.8, 113.5, 94.5, 69.6,
60.2, 58.5, 30.8, 22.9, 19.8, 17.8, 13.7, 8.7. 29Si CP-MAS NMR
(79.5 MHz) d (ppm): À58.3 (T2), À69.2 (T3), À104.8 (Q3), À114.8
(Q4). IR (ATR)
m
(cmÀ1): 2942, 1584, 1050, 801, 680, 654. BET sur-
face area: 109 m2/g; pore volume: 0.711 cm3/g. TGA: (argon, 20–
700 °C) residual mass 67.1%. EA calculated for C9H10ISiO2.5Á5SiO2
(considering complete condensation): 17.62% C, 1.64% H, 27.46%
Si, 20.68% I; found: 17.3% C, 2.2% H, 27.3% Si, 6.3% I.
124.0, 114.5, 94.7, 70.4, 58.7, 23.0, 18.6, 6.8. IR (ATR)
m
(cmÀ1):
2967, 2883, 1584, 1259, 1075, 1015, 632. HRMS (ESI): calculated
for [C15H25IO4SiNa]+ (M++Na): 447.0465; found: 447.0467.
2.4. Preparation and characterization of hybrid silica materials
2.4.4. Preparation and characterization of hybrid silica material M4
Monosilylated compound 4 (0.400 g, 0.943 mmol) and TEOS
2.4.1. Preparation and characterization of hybrid silica material M1
The bis-silylated compound 3 (1.665 g, 2.583 mmol) was dis-
solved in dry ethanol (1.8 mL). To this solution, a solution of
(4.2 mL,
(15 mL). Then, a solution of Milli-Q water (1.4 mL, 77.8 mmol) and
TBAF (200 L, commercial solution 1 M in anhydrous THF) in dry
q = 0.934 g/mL, 18.9 mmol) were dissolved in dry ethanol
l
Milli-Q water (0.28 mL, 15.49 mmol) and TBAF (30
l
L, commercial
EtOH (4.8 mL) was added to the first solution. The final mixture
was shaken vigorously for 10 s to obtain a homogenous solution.
After 14 min, a gel formed that was then aged at room temperature
for 6 days. Then, the gel was pulverized, filtered off and washed
1 M in anhydrous THF) in dry EtOH (0.8 mL) was added. The final
mixture was shaken vigorously for 10 s to obtain a homogenous
solution and was then kept under static conditions. After 30 min,

W. Guo et al. / Reactive & Functional Polymers 73 (2013) 192–199
195
successively with water (2 Â 6 mL), EtOH (2 Â 6 mL) and acetone
(2 Â 6 mL). The final solid was dried overnight at 55 °C under vac-
uum (2.0 mbar) to afford M4 as a white solid (1.302 g). 29Si CP-MAS
NMR (79.5 MHz) d (ppm): À67.8 (T3), À104.8 (Q3), À113.0 (Q4). IR
pressure. The residue was further purified by flash column chro-
matography on silica gel.
2.5.2. a-Tosyloxypropiophenone, 5 [9]
(ATR)
m
(cmÀ1): 2971, 1584, 1050, 800, 681. BET surface area: 124
1H NMR (360 MHz, CDCl3) d (ppm): 7.93–7.84 (m, 2H), 7.73 (d,
J = 8.3 Hz, 2 H), 7.57 (t, J = 7.4 Hz, 1 H), 7.43 (t, J = 7.5 Hz, 2 H), 7.24
(t, J = 8.0 Hz, 2 H), 5.77 (q, J = 6.9 Hz, 1 H), 2.36 (s, 3 H), 1.57 (d,
J = 6.9 Hz, 3 H); 13C NMR (90 MHz, CDCl3) d (ppm): 194.9, 145.2,
134.0, 133.8, 133.5, 129.9, 128.9, 128.8, 128.0, 77.5, 21.7, 18.8; IR
m2/g; pore volume: 0.790 cm3/g. TGA: (argon, 20–700 °C) residual
mass 79.5%. EA calculated for C9H10ISiO2.5Á20SiO2 (considering
complete condensation): 7.91% C, 0.74% H, 43.17%Si, 9.29% I;
found: 10.1% C, 1.7% H, 44.0% Si, 3.9% I.
(ATR)
m
(cmÀ1): 2936, 1698 (C@O), 1577, 1356.
2.5. Catalysis
2.5.3. a-Tosyloxy-p-bromoacetophenone, 6 [34]
1H NMR (360 MHz, CDCl3) d (ppm): 7.83 (d, J = 8.2 Hz, 2 H), 7.70
(d, J = 8.5 Hz, 2 H), 7.60 (d, J = 8.5 Hz, 2 H), 7.34 (d, J = 8.1 Hz, 2 H),
5.20 (s, 2 H), 2.44 (s, 3 H); 13C NMR (90 MHz, CDCl3) d (ppm): 189.8,
2.5.1. General procedure for the catalytic oxidative
ketones
a-tosyloxylation of
All catalytic runs were performed in screw-top sealable tubes
(10 mL). To a solution of ketone (1 mmol) in CH3CN (5 mL), p-
toluenesulfonic acid (247 mg, 1.3 mmol), m-CPBA (65% purity,
397 mg, 2.3 mmol) and the supported catalyst (amount calculated
to give 0.1 mmol of I, 10 mol% I) were added. The tube was sealed,
and the mixture was stirred at 65 °C under a nitrogen atmosphere
for the time indicated in Table 3. For the catalyst recycling studies,
the reaction mixture was filtered and the recovered catalyst was
washed with acetonitrile (2 Â 3 mL), further washed with diethyl
ether (3 Â 3 mL), dried under a vacuum and directly used in the
next cycle. The IR spectra of the recovered M1 and M2 (see
Supporting information) suggested no sign of decomposition. The
filtrates were poured into a saturated aq. NaHCO3 solution and
extracted with CHCl3 (3 Â 15 mL). The combined organic layer
was dried over anhydrous Na2SO4 and concentrated under reduced
145.6, 132.6, 132.4, 130.1, 129.7, 128.3, 69.9, 21.8; IR (ATR)
m
(cmÀ1): 2918, 2852, 1699 (C@O), 1586, 1358, 1059.
2.5.4. a-Tosyloxy-p-nitroacetophenone, 7 [9]
1H NMR (360 MHz, CDCl3) d (ppm): 8.31 (d, J = 8.1 Hz, 2 H), 8.02
(d, J = 7.7 Hz, 2 H), 7.82 (d, J = 7.6 Hz, 2 H), 7.36 (d, J = 7.5 Hz, 2 H),
5.24 (s, 2 H), 2.46 (s, 3 H); 13C NMR (90 MHz, CDCl3) d (ppm): 189.9,
150.9, 145.8, 138.3, 132.4, 130.2, 129.5, 128.3, 124.2, 70.1, 21.8; IR
(ATR)
(NO2), 1320, 848.
m
(cmÀ1): 2950, 2858, 1708 (C@O), 1598, 1519 (NO2), 1341
2.5.5. a-Tosyloxy-3-pentanone, 8 [9]
1H NMR (360 MHz, CDCl3) d (ppm): 7.81 (d, J = 8.3 Hz, 2 H), 7.36
(d, J = 7.7 Hz, 2 H), 4.85–4.76 (m, 1 H), 2.59 (q, J = 7.1 Hz, 2 H), 2.46
Scheme 2. Synthesis of the bis- and monosilylated precursors 3 and 4 and of the hybrid silica materials M1–M4.
Table 1
Selected physical data for materials M1–M4.
c
Mat.
N2 sorption measurements
TGAb (%)
I
(mmol/g)
I/Sid
SBET (m2/g)
Uptake at saturationa cm3/g STP
Microporous contribution m2/g
Theor.
Exp.
M1
M2
M3
M4
<5
255
109
124
–
48
42
92
0
47
0
48
63
67
79
1.064
0.646
0.496
0.307
0.500
0.143
0.166
0.048
0.260
0.075
0.051
0.020
0
a
b
c
Amount of gas adsorbed at p/p° = 0.5.
Residual mass at 700 °C.
Determined by elemental analysis.
d
Based on the elemental analysis and ICP-OES results.

196
W. Guo et al. / Reactive & Functional Polymers 73 (2013) 192–199
(s, 3 H), 1.35 (d, J = 7.0 Hz, 3 H), 1.02 (t, J = 7.2 Hz, 3 H); 13C NMR
(90 MHz, CDCl3) d (ppm): 207.8, 145.4, 133.3, 130.1, 128.0, 80.8,
31.3, 21.8, 17.7, 7.1; IR (ATR)
907, 632.
m
(cmÀ1): 1724 (C@O), 1407, 1364,
2.5.6. a-Tosyloxyacetophenone, 9 [9]
1H NMR (250 MHz, CDCl3) d (ppm): 7.87–7.82 (m, 4 H), 7.61 (t,
J = 7.3 Hz, 1 H), 7.46 (t, J = 7.6 Hz, 2 H), 7.34 (d, J = 8.0 Hz, 2 H), 5.26
(s, 2 H), 2.44 (s, 3 H); 13C NMR (90 MHz, CDCl3) d (ppm): 190.4,
145.4, 134.3, 130.0, 129.0, 128.2, 128.1, 70.1, 21.8; IR (ATR)
m
(cmÀ1): 2933, 1712 (C@O), 1596, 1449, 1356.
2.5.7. a-Tosyloxy-p-methylacetophenone, 10 [9]
1H NMR (360 MHz, CDCl3) d (ppm): 7.84 (d, J = 8.2 Hz, 2 H), 7.73
(d, J = 8.1 Hz, 2 H), 7.34 (d, J = 8.1 Hz, 2 H), 7.25 (d, J = 7.5 Hz, 2 H),
5.23 (s, 2 H), 2.44 (s, 3 H), 2.40 (s, 3 H); 13C NMR (90 MHz, CDCl3) d
(ppm): 190.1, 145.6, 133.0, 131.6, 130.2, 129.9, 128.4, 70.2, 22.1; IR
(ATR)
m
(cmÀ1): 1699 (C@O), 1345, 1170.
2.5.8. a-Tosyloxy-p-chloroacetophenone, 11 [9]
1H NMR (360 MHz, CDCl3) d (ppm): 7.83 (d, J = 8.2 Hz, 2 H), 7.78
(d, J = 8.4 Hz, 2 H), 7.44 (d, J = 8.4 Hz, 2 H), 7.35 (d, J = 8.0 Hz, 2 H),
5.20 (s, 2 H), 2.45 (s, 3 H), 2.40 (s, 3 H); 13C NMR (90 MHz, CDCl3) d
(ppm): 189.6, 145.6, 140.9, 132.6, 132.2, 130.1, 129.6, 129.4, 128.3,
70.0, 21.8; IR (ATR)
m
(cmÀ1): 1699 (C@O), 1359, 1174, 660.
2.5.9. a-Tosyloxy-o-bromoacetophenone, 12 [34]
1H NMR (360 MHz, CDCl3) d (ppm): 7.80 (d, J = 7.5 Hz, 2 H), 7.60
(d, J = 7.0 Hz, 2 H), 7.38–7.33 (m, 4 H), 5.13 (s, 2 H), 2.45 (s, 3 H);
13C NMR (90 MHz, CDCl3) d (ppm): 194.8, 145.5, 137.6, 133.9,
133.0, 132.6, 130.0, 129.8, 128.2, 127.7, 119.3, 71.2, 21.8; IR
Fig. 1. 29Si CP-MAS solid state NMR spectra of M1–M4.
(ATR)
m
(cmÀ1): 1721 (C@O), 1176, 1040, 633.
Fig. 2. 13C CP-MAS solid state NMR spectra of M2 and M3 and the 13C NMR spectra of the corresponding precursors 3 and 4.

W. Guo et al. / Reactive & Functional Polymers 73 (2013) 192–199
197
2.5.10.
a
-(Camphorsulfonyloxy)acetophenone, 13 [9]
monosilylated precursor 4 was obtained by the alkylation of com-
mercial 3-iodophenol with (3-iodopropyl)triethoxysilane in reflux-
ing acetone in the presence of potassium carbonate. Precursor 3
could either be used directly in the sol–gel reaction to yield the
bridged silsesquioxane M1 or could be co-condensed with five
equiv of TEOS to yield M2. Similarly, the monosilane 4 was co-
condensed with TEOS at molar ratios of 1:5 and 1:20, providing
materials M3 and M4, respectively. In all cases, the sol–gel
reactions were performed in anhydrous ethanol with a stoichiom-
etric amount of water with respect to the ethoxy groups and under
nucleophilic catalysis (TBAF, 1 mol% with respect to Si) [23,31,35].
Materials M1–M4 were fully characterized by elemental analysis,
13C and 29Si solid state CP-MAS NMR, IR, thermogravimetric analy-
sis (TGA) and nitrogen-sorption measurements. Some physical
data of the materials are given in Table 1.
The TGA and DSC curves of M1–M4 (Supporting information)
showed a weight decrease of less than 5% below 250 °C, attributed
to the loss of the physisorbed water and remaining uncondensed
ethoxy groups. For all materials, a more significant weight loss
was found in the range of 250–700 °C, assigned to the decomposi-
tion of the organic constituent. As expected, M1 exhibited the
highest weight loss (52%) due to the higher content of organic mat-
ter in M1 compared with M2–M4. The covalent incorporation of
the organosilane in the hybrid silicas was ascertained by 29Si CP-
MAS solid state NMR. As shown in Fig. 1, the 29Si CP-MAS NMR
spectra of M1–M4 exhibit signals between À50 and À69 ppm cor-
responding mainly to T2 and T3 species (Table 1). For M1, despite
the presence of low intensity signals around À47 (T0) and
À54 ppm (T1), the condensation degree of the material is relatively
high (85%). Additionally, the spectra of M2–M4 showed signals
1H NMR (360 MHz, CDCl3) d (ppm): 7.91 (d, J = 7.3 Hz, 2 H), 7.63
(t, J = 7.4 Hz, 1 H), 7.50 (t, J = 7.6 Hz, 2 H), 5.53 (s, 2 H, CH2O), 3.80
(d, J = 15.1 Hz, 1 H, CHHSO2), 3.34 (d, J = 15.1 Hz, 1 H, CHHSO2),
2.48–2.36 (m, 2 H), 2.14–2.06 (m, 2 H), 1.95 (d, J = 18.5 Hz, 1 H),
1.82–1.76 (m, 1 H), 1.46 (ddd, J = 13.2, 9.4, 4.0 Hz 1 H), 1.12 (s, 3
H, CH3), 0.90 (s, 3 H, CH3); 13C NMR (90 MHz, CDCl3) d (ppm):
214.5, 190.9, 134.4, 133.8, 129.2, 128.0, 70.4, 48.6, 48.3, 42.9,
42.7, 27.1, 25.1, 19.9, 19.8; IR (ATR)
(C@O), 1171.
m
(cmÀ1): 1744 (C@O), 1707
2.5.11. a-(Methanesulfonyloxy)acetophenone, 14 [9]
1H NMR (360 MHz, CDCl3) d (ppm): 7.90 (d, J = 7.4 Hz, 2 H), 7.65
(t, J = 7.4 Hz, 1 H), 7.52 (t, J = 7.7 Hz, 2 H), 5.52 (s, 2 H), 3.29 (s, 3 H);
13C NMR (90 MHz, CDCl3) d (ppm): 191.2, 134.6, 133.5, 129.2,
127.9, 70.4, 39.3; IR (ATR)
m
(cmÀ1): 1703 (C@O), 1171, 966.
3. Results and discussion
3.1. Preparation and characterization of hybrid silica materials
In Scheme 2, we summarize the synthesis of bis- and monosily-
lated iodoarenes 3 and 4 and the materials M1–M2 and M3–M4
derived from these precursors. The bis-silylated monomer 3 was
prepared from the commercially available 3,5-dimethoxyaniline
through a three-step synthetic route involving a diazotization of
the aniline to the corresponding iodoarene 1 [33], followed by
the deprotection of the methoxy groups to give 5-iodoresorcinol
2 [33] and the subsequent alkylation of the phenolic OH groups
with (3-iodopropyl)triethoxysilane. In an analogous manner, the
Fig. 3. N2-sorption isotherms of M2–M4.
Table 2
Optimization of the reaction conditions with M2 as the catalyst.
b
Entrya
Solvent
m-CPBA (equiv)
M2 (mol%)
Temp. (°C)
Yield 5 (%)
1
2
3
4
5
6
7
8
9
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Chloroform
Toluene
1.1
1.1
1.1
2.3
3.0
2.3
2.3
2.3
2.3
10
10
10
10
10
10
10
5
50
65
70
65
65
65
65
65
65
25
37
37
69
68
0
4
15
70
Acetonitrile
Acetonitrile
15
a
[Substrate] = 0.2 M.
Corrected GC yield (Ph–Ph as int. standard).
b

198
W. Guo et al. / Reactive & Functional Polymers 73 (2013) 192–199
Table 3
typical of silica environments at around À105 and À115 ppm cor-
responding to Q3 and Q4 species, respectively. The incorporation of
a-Tosyloxylation of ketones using M1–M4 as catalysts under the optimized condi-
tions specified.
organic fragments in M2 and M3 was further evidenced by the 13
C
CP-MAS solid state NMR spectra, with a typical signal at around
10 ppm attributed to CH2ASi. The spectra of these materials and
their comparison with the 13C NMR solution spectra of the organic
precursors 3 and 4 are shown in Fig. 2. As expected, there is a high
degree of correlation between the position of the 13C signals of the
precursors and the corresponding hybrid silicas, with the presence
of aromatic CAI carbon atoms confirmed by the signal at 94 ppm.
However, the observation of additional smaller signals at ca. 11,
24, and 59 ppm in the aliphatic C region and the splitting of some
aromatic signals (101 and 116 ppm) in the case of M1 and M2 led
us to believe that the alkyl–aryl ether tethers were partially broken
during the sol–gel synthesis. The consequence of this partial cleav-
age in the case of the mono-ethers M3 and M4 would be a lower
iodine content than expected, as was indeed observed by elemen-
tal analysis. In the case of M1 and M2, the cleavage of both ether
functions linking the aromatic fragment to the siloxane network
is less probable, so the decrease in iodine content is less pro-
nounced, as observed in Table 1. For the catalytic runs, the catalyst
loading was based on the material’s % iodine as determined by ele-
mental analysis.
.
Entrya
Product
Cat.
Time (h)
Yieldb (%)
1
2
3
4
M1
M2
M3
M4
18
14
27
50
47
67
3
23
5
6
7
8
9
M1
M1
M2
M3
M4
21
13
14
19
19
60
62c
55
5
19
10
11
12
M1
M1
M2
21
13
14
35
51c
25
Nitrogen-sorption measurements are important for investigat-
ing the texture of materials. Material M1 displayed non-detectable
porosity, as was previously found for other bridged silsesquioxanes
prepared in the absence of TEOS under similar conditions [21]. As
shown in Fig. 3, materials M2–M4 exhibit type II isotherms
(according to IUPAC rules [36]) with a regular increase of nitrogen
uptake in the range of p/p° < 0.7 and without a sharp increase that
would come from a regular porous system. According to the t-plot,
a slight microporous contribution (47 m2 gÀ1) is detected in the
case of M2, whereas materials M3 and M4, obtained from the
monosilylated precursor 4, only display porosity arising from mes-
opores and external surfaces. In particular, the large amount of
nitrogen adsorbed at p/p° > 0.7 arises from nitrogen that condenses
in the voids between particles.
13
14
M1
M2
18
19
24
26
15
16
17
M1
M1
M2
18
13
19
43
36c
50
18
19
M1
M2
17
18
21
18
3.2. Catalytic activity of the silica-supported iodoarenes in the
tosyloxylation of ketones
a-
20
M1
16
54
The catalytic activity of materials M1–M4 in the
a-tosyloxyla-
tion of a range of ketones was then evaluated. As mentioned previ-
ously, the precedent for the use of supported ArI in oxidation
catalysis has been provided by Togo and coworkers, who used a
catalyst loading of 0.5–1.3 equiv of ArI [8–10].
Our initial catalytic tests were performed with propiophenone
as the substrate and in the presence of p-toluenesulfonic acid (p-
TsOH, 1.3 equiv), m-CPBA as the terminal oxidant and M2 as the
21
22
M1
M1
20
21
58
47c
catalyst to afford a-tosyloxypropiophenone (5) (Table 2). A screen-
ing of different reaction conditions was performed (solvent, cata-
lyst loading, amount of m-CPBA, temperature). The reaction using
10 mol% of M2 in the presence of 1.1 equiv of m-CPBA in acetoni-
trile gave moderate yields (25–37%) of 5 at 50 and 65 °C (Table 2,
entries 1–2), and no improvement was achieved by raising the
temperature to 70 °C (Table 2, entry 3). In the same solvent, the
yield could be improved to 69% by raising the amount of m-CPBA
to 2.3 equiv, although higher amounts of the oxidant (3.0 equiv)
had no beneficial effect (compare entries 4 and 5). Chloroform
and toluene were also tested as solvents and proved less effective
than acetonitrile (entries 6–7). The effect of catalyst loading was
also investigated (entries 8–9). As a result, the optimized reaction
conditions were as follows: 65 °C, 10 mol% of catalyst, acetonitrile
as solvent, 2.3 equiv of m-CPBA and 1.3 equiv of p-TsOH.
23
M1
17
42
24
25
26
M1
M1
M1
18
18
18
71
65c
42d
a
b
c
[Substrate] = 0.2 M.
Isolated yield.
Second cycle.
Third cycle.
This protocol was then extended to the oxidative
a-tosyloxyla-
d
tion of various ketones with the supported catalysts M1–M4

W. Guo et al. / Reactive & Functional Polymers 73 (2013) 192–199
199
(Table 3). The corresponding
a-tosyloxyketones 5–12 were iso-
Appendix A. Supplementary material
lated in yields of up to 67%. As expected, the activities of the
new silica-immobilized catalysts were lower than those shown
by homogenous iodoarenes for this type of transformation [8,14].
Nevertheless, it is worthwhile to mention a certain improvement
with respect to other systems [9], given the possibility of using just
10 mol% of the supported ArI. Materials M1–M4 were tested as
catalysts with propiophenone and p-bromoacetophenone as
substrates (Table 3, entries 1–9). Moderate to good isolated yields
of the tosylated ketones 5 and 6 were obtained for materials M1
and M2 derived from the bis-silylated monomer 3 (entries 1, 2, 5
and 7), whereas M4 displayed lower activity (23 and 19% isolated
yields of 5 and 6, respectively) (entries 4 and 9) and material M3
was essentially inactive under the reaction conditions (entries 3
and 8). The two best catalysts, M1 and M2, were also tested with
six other substrates: p-nitroacetophenone (entries 10–12),
3-pentanone (entries 13–14), acetophenone (entries 15–17), p-
methylacetophenone (entries 18–19), p-chloroacetophenone (entry
20) and 2-bromoacetophenone (entries 21–22). The corresponding
tosyloxyketones 7–12 were obtained in moderate isolated yields
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.reactfunctpolym.
2012.10.011.
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a
-tosyloxylation of ketones using m-
-tosyloxyketones
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We acknowledge financial support from the Ministerio de Cien-
cia e Innovación (MICINN) and the Ministerio de Educación y Ciencia
(MEC) of Spain (Project CTQ2009-07881/BQU, providing a Ramón y
Cajal contract to A.S. and a doctoral fellowship to A.M.-M.), Consol-
ider Ingenio 2010 (Project CSD2007-00006) and the Generalitat de
Catalunya (Project SGR2009-01441).