Intermolecular C–O Coupling Using Hemicucurbituril Supported Ionic Liquid Phase Catalyst

Article abstract of DOI:10.1007/s10562-016-1871-x

Abstract: Hemicucurbituril supported ionic liquid phase catalyst (HmCucSILP) has been synthesized by anchoring multilayer of ionic liquid ([Bmim]Cl) containing Pd(OAc)₂ and X-phos on the surface of hemicucurbit[6]uril. The HmCucSILP was effectively employed in intermolecular C–O coupling of aryl halides with sodium alkoxides for the synthesis of alkyl aryl ethers. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-016-1871-x

Catal Lett (2016) 146:2485–2494
DOI 10.1007/s10562-016-1871-x
Intermolecular C–O Coupling Using Hemicucurbituril Supported
Ionic Liquid Phase Catalyst
1
1
1
Rajanikant Kurane · Prakash Bansode · Sharanabasappa Khanapure ·
1
1
1
Dolly Kale · Rajashri Salunkhe · Gajanan Rashinkar
Received: 23 June 2016 / Accepted: 20 September 2016 / Published online: 19 October 2016
Springer Science+Business Media New York 2016
©
Abstract Hemicucurbituril supported ionic liquid phase
catalyst (HmCucSILP) has been synthesized by anchoring
multilayer of ionic liquid ([Bmim]Cl) containing Pd(OAc)2
and X-phos on the surface of hemicucurbit[6]uril. The
HmCucSILP was effectively employed in intermolecular
C–O coupling of aryl halides with sodium alkoxides for the
synthesis of alkyl aryl ethers.
at a fast pace since the last decade 1[ –3]. Much of the interest
in SILP catalysts stems from their superior performance over
traditional ionic liquids (ILs) that enables their application in
fixed-bed technology [4]. The use of these advanced materi-
als is particularly advantageous because of unique benefits
such as ease of separation of catalyst simply by filtration,
as well as facilitating significant advances in selectivity and
recycling reproducibility [ 5]. The scrutiny of the recent lit -
erature reveals an explosion of interest in the development
of novel SILP catalysts for achieving efficient organic trans-
formations [6–11]. The SILP catalysts are usually prepared
by depositing ILs on the surface of high area support mate -
rial either by covalent bonding or impregnation method. The
most common supports used for synthesis of SILP catalysts
are silica or polymer based materials [ 12–16]. In addition,
carbon nanotubes, [ 17] active carbon cloth, [ 18] chitosan,
Graphical Abstract
[19] magnetic nanoparticles [ 20] etc. have also been occa -
sionally employed as supports. In expanding the catalytic
properties of SILPs, it is highly desirable to search new
support materials for their synthesis since the performance
of SILP catalysts is strongly dependent upon the choice of
support material. The scrutiny of a suitable support is often
governed by the process conditions at which a SILP catalyst
has to operate. Nevertheless, the key features of a support
material are to possess insolubility in common solvents and
chemical inertness. With this regard, we sought to explore
compatibility of hemicucurbiturils [ 21] as a support for the
Keywords Hemicucurbituril · Intermolecular C–O
coupling · Alkyl aryl ethers · X-Phos · Reusability
1
Introduction
The contemporary concept of supported ionic liquid phase
SILP) catalysis involving the use of covalently anchored
(
film of ionic liquid (IL) on a high area porous material to cat-
alyze variety of organic and inorganic reactions is evolving
synthesis of SILP catalyst. Hemicucurbiturils are macro
-
cycles consisting of alternating methylene and N-substituted
ethylene urea units that closely resemble a family of cucur -
biturils [ 22] with a mimic chemistry. These macrocycles
can be constructed in two sizes viz; hemicucurbit[6]uril and
hemicucurbit[12]uril. Recent developments in the chemistry
ꢀ
Gajanan Rashinkar
gsr_chem@unishivaji.ac.in
1
of hemicucurbiturils reveal that their cavities are particu
larly useful for the applications in supramolecular chemistry
-
Department of Chemistry, Shivaji University,
Kolhapur 416004, Maharashtra, India
1
3

2
486
R. Kurane et al.
as hosts for guests like uranyl and transition metal cations
and certain anions [23, 24]. The contemporary studies have
unveiled the catalytic potential of these cavitands [ 25]. We
envisioned that their insolubility in most solvents and chem-i
cal inertness are extremely well-suitable to serve as a robust
support material for synthesis of SILPs.
Alkyl aryl ethers are important structural motifs found
in large number of pharmaceuticals, agrochemicals, natu -
ral products, fine chemicals and functional materials [26].
In addition, many of their derivatives are deliberately uti -
lized in skin protecting products as UV absorbers 2[ 7]. Due
to intriguing structural features and diverse properties, the
synthesis of these privileged scaffolds has received consid-
erable attention in recent years. The metal-free access to
these compounds is achieved by Williamson ether synthe-
sis, [28] Mitsunobu reactions, [29] Nucleophilic aromatic
substitution [30] and reactions via benzyne intermediates
Raman spectroscopy was done by using Bruker FT-
Raman (MultiRAM) spectrometer. H NMR and 13C
1
NMR spectra were recorded on a Bruker AC (300 MHz
1
13
for H NMR and 75 MHz for C NMR) spectrometer
using CDCl as solvent and tetramethylsilane (TMS)
3
as an internal standard. Chemical shifts are expressed
in δ parts per million (ppm) values and coupling con-
stants are expressed in hertz (Hz). Mass spectra were
recorded on a Shimadzu QP2010 GCMS. The materials
were analyzed by SEM using a JEOL model JSM with
5 and 20 kV accelerating voltage. Elemental analyses
were performed on EURO EA3000 vectro model. Melt-
ing points were determined on MEL-TEMP capillary
melting point apparatus and are uncorrected. Hemicu -
curbituril and [Bmim]Cl were synthesized following
the literature procedure [ 22, 46]. The X-phos (Sigma–
Aldrich) and all other chemicals (Spectrochem) were
used as received.
[
31, 32]. In addition, approaches involving stoichiometric
use of diaryliodonium salts [ 33] and hypervalent iodine
compounds [ 34, 35] have also been employed for their
synthesis. The synthesis of alkyl aryl ethers received a
decisive impetus as different research groups reported on
intermolecular C–O cross-coupling chemistry employ
ing transition metal catalysis [ 36–41]. Amongst these,
Pd mediated intermolecular C–O bond formation process
by cross coupling of aryl halides and alkoxides is most
attractive method due to high functional group tolerance
especially with the application to unactivated aryl halide
2.1 Preparation of HmCucSILP
A mixture of Pd(OAc) (224mg), X-phos (476mg), [Bmim]
2
-
Cl (1 gm) and hemicucurbituril (5 gm) in methanol (25 mL)
was stirred at room temperature. After 24 h, solvent was
removed under rotary evaporator to get desired HmCuc
-
SILP catalyst. FT-IR (KBr, thin film): υ=3283, 2944, 1665,
1484, 1443, 1402, 1371, 1286, 1213, 1131, 1011, 929, 851,
−
1
793 cm ; FT-Raman (KBr): υ=3055, 3005, 2906, 1613,
−1
substrates, compatibility with common and ecobenign sol-
vents, and easy binding ability to the variety of ligands.
Various elegant catalytic protocols have been reported
for the synthesis of alkyl aryl ethers using this procedure
1429, 1268, 1183, 1030, 1003, 835, 679, 641cm ; elemen-
tal analysis observed: %C 17.57, %O 11.92, %N 16.26, %P
−1
0.14, %Pd 0.13; loading: 0.006 mmol g matrix.
[
42–44]. Although impressive progress has been made in
2.2 General Procedure for the Synthesis of Alkyl Aryl
Ethers
the Pd catalyzed intermolecular C–O bond formation pro-
cess for the synthesis of alkyl aryl ethers, there is a still
scope for improvement especially towards development of
environmentally benign protocol using highly efficient and
reusable catalyst.
A mixture of aryl halide (1 mmol) and sodium alkoxide
(3.0 mmol) was refluxed in the presence of 200 mg of
HmCucSILP catalyst in toluene (5 mL) for an appropri -
ate time as indicated in Table 2. After completion of the
reaction, the reaction mixture was filtered and solvent was
evaporated in vacuo to give the crude product, which was
purified by column chromatography over silica gel using
hexane/EtOAc as the eluent.
As part of our program aimed at exploiting the applica -
tions of SILP catalysis in synthesis of bioactive molecules,
[45] we report herein the preparation of hemicucurbitu
-
ril supported ionic liquid phase catalyst (acronymed as
HmCucSILP) for the synthesis of alkyl aryl ethers using
intermolecular C–O cross-coupling between aryl halides
and sodium alkoxides.
2.3 Spectral Data of Representative Compounds
2
.3.1 Methoxybenzene (Table2, entry 1)
2
Experimental Section
Clear liquid, bp 156°C; FT-IR (neat): υ=2916, 2875,
All reactions were carried out under air atmosphere
in dried glasswares. Infrared spectra were measured
with a Perkin-Elmer one FT-IR spectrophotometer.
1640, 1568, 1420, 1402, 1317, 1298, 1108, 1068, 1012,
−1 1
980, 785 cm ; H NMR (CDCl , 300 MHz): δ 7.20–7.28
3
1
3
(m, 2H), 6.65–6.69 (m, 3H), 3.66 (s, 3H) ppm;
C NMR
The samples were examined as KBr discs ~5 % (w/w).
(CDCl , 75 MHz): δ 162.1, 128.8, 120.7, 114.2, 54.8 ppm;
3
1
3

Intermolecular C–O Coupling Using Hemicucurbituril Supported Ionic Liquid Phase Catalyst
24873
+
13
mass (EI) m/z: 108 [M] ; Anal. Calcd. for C H O: %C
3.40 (s, 2H), 1.37 (d, 6H) ppm; C NMR (CDCl , 75 MHz):
7
8
3
7
7.74, %H 7.47, observed: %C 77.46, %H 7.22.
δ 150.7, 140.2, 117.8, 116.4, 71.0, 22.2 ppm; mass (EI) m/z:
+
1
51 [M] ; Anal. Calcd. for C H NO: %C 71.48, %H 8.56,
9
13
2
.3.2 Ethoxybenzene (Table2, entry 5)
%N 9.13, observed %C 70.96, %H 8.65%N 9.09.
Clear liquid, bp 169°C; FT-IR (neat): υ=2984, 1601, 1476,
2.3.7 4-Methoxybenzaldehyde (Table2, entry 10)
1
7
2
496, 1390, 1301, 1242, 1173, 1115, 1079, 1046, 921, 883,
−1 1
96 cm ; H NMR (CDCl , 300 MHz): δ 7.42–7.48 (m,
Dark brown liquid, bp 250°C; FT-IR (neat): υ=2940, 2910,
3
H), 7.05–7.14 (m, 3H), 4.13 (q, J=6 Hz, 2H), 1.54–1.59
2850, 2710, 1710, 1625, 1595, 1535, 1480, 1412, 1390,
1
3
−1 1
(
d, 3H) ppm; C NMR (CDCl , 75 MHz): δ 159.1, 129.5,
1275, 1177, 1101, 1030, 825, 780 cm ; H NMR (CDCl ,
3
3
+
1
20.6, 114.5, 63.3, 14.9 ppm; mass (EI) m/z: 122 [M]
;
300 MHz): δ 9.91 (s, 1H), 7.83 (d, J=8.8 Hz, 2H), 7.04
1
3
Anal. Calcd. for C H O: %C 78.66, %H 8.24, observed:
(d, J=8.9 Hz, 2H), 3.77 (s, 3H) ppm;
C NMR (CDCl ,
3
8
10
%C 78.41, %H 8.22.
75 MHz): δ 190.5, 164.5, 131.09, 129.84, 114.64, 55.14 ppm;
mass (EI) m/z: 136[M] ; Anal. Calcd. for C H O : %C
+
8
8
2
2
.3.3 Isopropoxybenzene (Table2, entry 9)
70.47, %H 5.46, observed %C 70.12, %H 5.22.
Clear brown liquid, bp 176°C; FTIR (neat): υ=2965, 1602,
2.3.8 4-Ethoxybenzaldehyde (Table2, entry 14)
1
7
2
465, 1352, 1290, 1179, 1135, 1069, 1019, 945, 876, 769,
−1 1
45 cm ; H NMR (CDCl , 300 MHz): δ 6.91–6.97 (m,
Dark brown liquid, bp 252°C; FT-IR (neat): υ=2985, 2889,
3
H), 6.71–6.73 (m, 3H), 4.39–4.45 (m, 1H), 1.37 (d, 6H)
2827, 1682, 1598, 1576, 1509, 1476, 1425, 1396, 1312,
1
3
−1 1
ppm; C NMR (CDCl , 75 MHz): δ 158.2, 128.7, 119.6,
1251, 1214, 1156, 1114, 1038, 921, 828, 781cm ; H NMR
3
+
1
15.2, 73.2, 22.7 ppm; mass (EI) m/z: 136 [M]
; Anal.
(CDCl , 300 MHz): δ 9.89 (s, 1H), 7.87 (d, J=8.8 Hz, 2H),
3
Calcd. for C H O: %C 79.47, %H 8.65, observed %C
7.02 (d, J=8.8 Hz, 2H), 4.18 (q, 2H), 1.47 (t, J=12 Hz,
9
12
1
3
7
9.14, %H 8.15.
3H) ppm; C NMR (CDCl , 75 MHz): δ 190.85, 164.07,
3
1
32.01, 129.78, 114.72, 6.92, 14.63 ppm; mass (EI) m/z:
+
2
.3.4 4-Methoxyaniline (Table2, entry 19)
150 [M] ; Anal. Calcd. for C H O %C 71.77, %H 6.59,
9
10
2
observed %C 71.42, %H 6.46.
Dark brown solid, mp 154°C; FT-IR (KBr, thin film):
υ=3316, 3256, 1593, 1540, 1440, 1352, 1235, 1210, 1150,
2.3.9 4-Isopropoxybenzaldehyde (Table2, entry 18)
−1 1
1
035, 981, 893, 695 cm ; H NMR (CDCl , 300 MHz):
3
δ 6.71 (d, J=8.1 Hz, 2H), 6.52 (d, J=8.2 Hz, 2H), 3.32
Dark yellow liquid, bp 111°C; FT-IR (neat): υ=2981, 2939,
1
3
(
s, 2H), 3.92 (s, 3H) ppm;
C NMR (CDCl , 75 MHz):
2733, 1688, 1597, 1574, 1507, 1467, 1428, 1386, 1310,
3
−1 1
δ 151.5, 140.1, 117.2, 115.5, 55.0 ppm; mass (EI) m/z:
1253, 1216, 1157, 1102, 1007, 947, 866 cm ; H NMR
+
1
23[M] ; Anal. Calcd. for C H NO: %C 79.47, %H 8.65,
(CDCl , 300 MHz): δ 9.85 (s, 1H), 7.82 (d, J=7.5 Hz, 2H),
7
9
3
%N 11.15, observed %C 79.14, %H 8.15, %N 11.03.
6.96 (d, J=7.5 Hz, 2H), 4.63–4.69 (m, 1H), 1.37 (d, 6H)
1
3
ppm; C NMR (CDCl , 75 MHz): δ 190.8, 163.1, 132.04,
3
+
2
.3.5 4-Ethoxyaniline (Table2, entry 23)
129.4, 115.5, 70.2, 21.8 ppm; mass (EI) m/z: 164 [M]
Anal. Calcd. for C H O : %C 72.97, %H 7.27, observed
;
1
0
12
2
Dark brown liquid, bp 251°C; FT-IR (neat): υ=3430, 2979,
%C 72.62, %H 7.16.
1
1
626, 1507, 1479, 1395, 1328, 1294, 1227, 1173, 1114,
−
1 1
044, 921, 819 cm ; H NMR (CDCl , 300 MHz): δ 6.78
3
(
3
d, J=7.9 Hz, 2H), 6.67 (d, J=7.9 Hz, 2H), 3.97 (q, 2H),
3 Results and Discussion
1
3
.36 (s, 2H), 1.40 (t, 3H) ppm; C NMR (CDCl , 75 MHz):
3
δ 152.0, 140.0, 116.4, 115.6, 64.0, 15.0 ppm; mass (EI) m/z:
Amongst the various approaches used for the synthesis of
+
1
37 [M] ; Anal. Calcd. for C H NO: %C 69.97, %H 8.01,
SILP catalysts, the impregnation method is the most attrac -
tive since it is simple and no further treatment of the support
is needed. In the SILP catalysts prepared by this method, the
IL containing catalytic system is deposited on the support
as a multilayer which acts as an immobilizing medium for
the catalyst. The van der Waals forces are strong enough to
hold the entire system sufficiently stringent in the catalytic
8
11
%N 10.11 observed %C 70.02, %H 7.96%N 9.96.
2
.3.6 4-Isopropoxyaniline (Table2, entry 27)
Yellow liquid, bp 93°C; FT-IR (neat): υ=3354, 2976,
1
9
625, 1505, 1383, 1335, 1290, 1224, 1180, 1112, 1009,
−1 1
51, 821 cm ; H NMR (CDCl , 300 MHz): δ 6.76 (d,
process. These interesting properties prompted us to syn
thesize HmCucSILP by using impregnation method. In the
-
3
J=8.7 Hz, 2H), 6.62 (d,J=8.7 Hz, 2H), 4.33–4.45 (m, 1H),
1
3

4
2488
R. Kurane et al.
−
1
preparation of HmCucSILP, a mixture of hemicucurbit[6]
uril, ionic liquid (1-butyl-3-methylimidazolium chloride,
hemicucurbituril ring at 3283, 1664cm and the [Bmim]Cl
−
1
−1
bands at 2944 cm (aliphatic C–H stretch) and 1484 cm
(in-plane C–C and C–N stretching vibrations of imidazo
[Bmim]Cl), ligand (X-phos) and catalyst [Pd(OAc) 2] was
-
stirred in methanol at ambient temperature for 24 h. The
removal of solvent under vacuo afforded desired HmCuc -
SILP in the form of dry powder that was used without any
further treatment for further studies.
lium ring). In addition, the characteristic peak of Pd(OAc)
2
−
1
at 1443 cm (C–H bending vibration of C–O–O and CH
3
−1
in Pd(OAc) ) and X-phos at 793cm (weak bending vibra-
2
tion indicate the presence of P–C bond) confirmed the
confinement of ionic liquid along with catalyst and ligand
without any obvious changes in the structures. The FT-
Raman spectrum of HmCucSILP showed vibrational bands
The confinement of [Bmim]Cl, Pd(OAc) and XPhos
2
in hemicucurbituril matrix was investigated by FT-IR
and FT-Raman spectroscopy. The FT-IR spectrum of
HmCucSILP displayed characteristic vibrational bands of
−
1
of imidazolium ring at 3055, 2906, 1268, and 1183 cm
−1
and characteristics C =O stretching mode at 1613 cm .
−1
The wagging vibrational bands at 641 and 1030 cm for
O–C–O bond of Pd(OAc) and Ar–P bond of X-phos con -
2
firmed the formation of HmCucSILP.
The amount of Pd(OAc) 2 and X-phos in HmCucSILP
catalyst was quantified by mapping palladium and phos-
phorus using energy dispersive X-ray (EDX) analysis. The
analysis revealed presence of 0.13 % of Pd and 0.14 % of P
in the HmCucSILP catalyst confirming almost 1:1 metal to
ligand stoichiometry.
The size and morphology of the HmCucSILP catalyst
was studied by scanning electron microscopy (SEM). A
typical SEM image is presented in Fig. 1. The SEM image
showed that HmCucSILP catalyst particles are spherical in
shape.
Fig. 1 SEM of HmCucSILP catalyst
Fig. 2 TGA curve of HmCucSILP catalyst
1
3

Intermolecular C–O Coupling Using Hemicucurbituril Supported Ionic Liquid Phase Catalyst
24895
Table 1 Optimization of reac-
tion conditions in intermolecu-
lar C–O cross coupling reaction
between diverse aryl halides
I
O
HmCucSILP
Solvent, Reflux
with sodium ethoxide
CH CH ONa
+
3
2
Entry
Solvent
Catalyst (mg)
Time (h) Temp (°C) Yielda
%)
(
1
2
3
4
5
6
7
8
9
Methanol
Ethanol
100 (0.0006 mmol)
100 (0.0006 mmol)
100 (0.0006 mmol)
100 (0.0006 mmol)
100 (0.0006 mmol)
150 (0.0009 mmol)
200 (0.0012 mmol)
300 (0.0018 mmol)
100 (0.0006 mmol)
100 (0.0006 mmol)
100 (0.0006 mmol)
100 (0.0006 mmol)
–
25
28
23
48
12
10
9
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
30
20
30
Trace
60
71
83
85
40
15
–
Isopropanol
1,4-Dioxane
Toluene
Toluene
Toluene
Toluene
8
DMSO
24
28
30
35
30
24
1
0
THF
11
Water
1
1
1
2
3b
DMF
42
–
Hemicucurbituril
[Bmim]Cl
4
Pd-X phos (1:1)
30
2
.5 (0.012 mmol)–5.71
0.012 mmol)
2.5 (0.012 mmol)–5.71
0.012 mmol)
Hemicucurbituril- Pd-X phos Hemicucurbituril 100 mg
1:1) and Pd-X phos 2.5
(
1
1
5b
6b
Pd-X phos (1:1)
28
25
Reflux
Reflux
40
56
(
(
(
(
0.012 mmol)–5.71
0.012 mmol)
aIsolated yields after column chromatography
bToluene was used as solvent
The thermal stability of HmCucSILP catalyst was stud -
ied by using TGA analysis in the temperature range of
between iodobenzene with sodium ethoxide was chosen as
a model reaction for the optimization of reaction param
eters (Table 1). Initially, the effect of various solvents on
the model reaction was studied. The model reaction was
performed under reflux conditions in various solvents that
include nonpolar toluene and 1,4-dioxane, polar aprotic ace-
tonitrile, THF, DMF and DMSO and polar protic methanol,
-
2
5–1000°C. The TGA profile is shown in Fig. 2. The ini-
tial weight loss of 5.2% observed in the thermogram can be
attributed to loss of physisorbed water. The further weight
loss of 14.2 % could be due to collective loss of water of
crystallization and any other water molecules associated
with ionic liquid matrix and decomposition of X-phos. The
steep weight loss (52.92 %) in the range 250–350 °C can be
reasonably assigned to allied decomposition of hemicucur -
bituril and [Bmim]Cl. The last weight loss of 25.95 % can
be plausibly due to decomposition of carbonaceous interme-
diates formed during previous decomposition steps. Finally,
the small residual weight of around 0.8 % retained in the
thermogram corresponds to the formation of non volatile
ethanol, isopropanol and water. The experimental proce
-
dure for reaction was simple and straightforward. A mixture
of iodobenzene (1 mmol) and sodium ethoxide (3 mmol)
in solvent (5 mL) was heated to reflux in the presence of
HmCucSILP (200 mg) till the completion of reaction as
monitored by TLC. The reaction was sluggish in ethanol,
methanol, isopropanol, DMSO and DMF as the correspond-
ing ethoxy benzene was formed in low yield (Table
entries 2, 1, 3, 9, 12). The use of 1,4-dioxane, THF, and
1,
metal oxide (PdO) from Pd(OAc) . The thermal profile is in
2
good agreement with the individual TGAprofiles of [Bmim]
water, (Table 1, entries 4, 10, 11) gave anticipated product
in trace amount. It was observed that toluene was the most
effective in providing highest conversion (Table 1, entry 8).
Next, the effect of catalyst loading on the model reaction
Cl, and Pd(OAc) reported in the literature [47, 48].
2
Next, we turned our attention toward assessing cata
-
lytic potential of HmCucSILP catalyst. The C–O coupling
1
3

2
R. Kurane et al.
Table 2 HmCucSILP catalyzed
synthesis of alkyl aryl ethers
R'
X
O
HmCucSILP
Toluene
R'-ONa
2
+
R
R
1
3
3 2 3 3 2
R' ; a = -CH , b = -CH CH , c = -CH(CH )
Entry
X
–R
1
–R′
2
Product
3
Time (h) Yielda
(%)
1
2
3
4
5
6
7
8
9
–Cl
–Cl
–Cl
–Br
–Br
–Br
–I
–H
–CH3
3a
3b
3c
3a
3b
3c
3a
3b
3c
3d
3e
3f
9
9
82
82
80
78
80
75
85
84
80
75
72
75
78
76
72
78
78
76
75
77
71
78
75
73
77
80
74
–H
–CH CH
3
2
–H
–CH(CH3)2
–CH3
10
9
–H
–H
–CH CH
9
3
2
–H
–CH(CH3)2
–CH3
10
8
–H
–I
–H
–CH CH
9
3
2
–I
–H
–CH(CH3)2
–CH3
9
1
0
4-Cl
4-Cl
4-Cl
4-Br
4-Br
4-Br
4-I
–CHO
–CHO
–CHO
–CHO
–CHO
–CHO
–CHO
–CHO
–CHO
–NH2
–NH2
–NH2
–NH2
–NH2
–NH2
–NH2
–NH2
–NH2
10
10
10
10
9
11
–CH CH
3
2
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
–CH(CH3)2
–CH3
3d
3e
3f
–CH CH
3
2
–CH(CH3)2
–CH3
10
8
3d
3e
3f
4-I
–CH CH
8
3
2
4-I
–CH(CH3)2
–CH3
8
4-Cl
4-Cl
4-Cl
4-Br
4-Br
4-Br
4-I
3g
3h
3i
9
–CH CH
9
3
2
–CH(CH3)2
–CH3
10
10
10
9
3g
3h
3i
–CH CH
3
2
–CH(CH3)2
–CH3
3g
3h
3i
9
4-I
–CH CH
10
10
3
2
4-I
–CH(CH3)2
Optimal reaction conditions: 1 (1 mmol), R′ONa (3 mmol), Toluene (5 mL) and HmCucSILP (200 mg)
aIsolated yields after column chromatography
was investigated. As shown in Table 1, the yield of ethoxy-
benzene increased by increasing quantity of catalyst from
well for electron-withdrawing as well as electron-donat -
ing substituents on aryl halides to afford the correspond-
ing ethers in good to excellent yields (71–75 % yield;
Table 2, entries 10–27). In addition, the tolerance for
the alkoxide reagent was also investigated. As shown in
Table 2, several alkyl alkoxides such as sodium methox -
ide and isopropoxide underwent smooth C–O coupling
with aryl halides forming the corresponding ethers in sat-
isfactory yields.
1
00 to 200 mg (Table 1, entries 5–7). However, further
increase in the amount of the catalyst did not have a signifi-
cant effect on the product yield and reaction time (Table 1,
entries 8).
Using the optimal reaction conditions, the general
ity of this protocol was studied. Firstly, a wide range of
aryl halides including iodides, bromides and chlorides
were studied (Table 2). In all cases, the reactions gave
the corresponding products in good to excellent yields
-
It is noteworthy to mention that in control experiments
when hemicucurbituril, [Bmim]Cl and Pd(OAc) 2-X-phos
(1:1) were used as only catalysts, all the reactions were
(
Table 2). The reactions proceeded smoothly and equally
1
3

Intermolecular C–O Coupling Using Hemicucurbituril Supported Ionic Liquid Phase Catalyst
24917
Fig. 3 1H NMR spectrum of
hemicucurbit[6]uril
Fig. 4 1H NMR spectrum of
HmCucSILP catalyst
incomplete and <60% yields were obtained (Table
1,
to the formation of host guest inclusion complex in case
entries 13–15). These results suggest that hemicucurbituril
in combination with palladium acetate-XPhos and [Bmim]
Cl exhibit synergistic effect in catalysis. The enhanced
reactivity of HmCucSILP in the synthesis of alkyl aryl
ethers can be attributed to the ability of hemicucurbit[6]
uril to form stable host guest complex as evidenced from
of hemicucurbit[6]uril. Seen in this light, the HmCucSILP
is a host–guest type complex. This has been further sup
ported by the changes observed in the FT-IR spectra. The
-
FT-IR absorption of carbonyl groups on hemicucurbit[6]uril
−
1
exhibits split bands at 1681 and 1644 cm while only one
−1
band at 1644 cm in the FT-IR spectrum of HmCucSILP
reveals the probability of formation of inclusion complex
with X-phos in presence of [Bmim]Cl. We believe that the
resultant inclusion complex acts as a strong ligand for sta -
1
H NMR and FT-IR spectroscopic studies. The comparison
1
of H NMR spectra of hemicucurbit[6]uril and HmCucSILP
shown in Figs. 3 and 4 clearly indicates that the shapes
of proton resonances of hemicucurbit[6]uril (δ 3.37 and δ
bilization of Pd(OAc) . The collective effect increases the
2
4
.68) get broaden in HmCucSILP. It has been demonstrated
catalytic activity of Pd as seen from the high yields obtained
in the presence of hemicucurbituril to that in its absence.
by Xiang et al. [ 22, 49] that such a broadening results due
1
3

8
2492
R. Kurane et al.
Scheme 1 Proposed mecha-
nism for synthesis of alkyl aryl
ethers
Cy
Cy
P
OAc
OAc
Pd
iPr
Ln-Pd
Pri
X
iPr
Ln-Pd
R
X = Cl, Br, I
R
OR'
Oxidative Addition
Reductive Elimination
R
R
Ln Pd
O-R'
Ln Pd
X
NaX
Transmetallation
Support is removed for simplicity
NaOR'
R' = Me, Et, iPr
8
4%
formed X-phos-Pd species enters into the catalytic cycle
by reacting with aryl halide to produce X-phos-Pd-Ar-X
adduct via oxidative addition. In next step, transmetala
tion occurs subsequent to the oxidative addition in which
Pd-alkoxide complex is formed from Pd-halide adduct. In
the conclusive step, expected alkyl aryl ether is produced
by reductive elimination process which readily occurs due
to cis-interaction of Pd-arene to phosphorous center along
with the regeneration of Ln-Pd active center.
7
9%
8
6
4
2
0
0
0
0
0
-
6
7%
5
5%
In order to ascertain whether the catalyst is truly het
erogeneous, we have performed a number of heterogene
ity tests. Initially, leaching of Pd and phosphorous from
HmCucSILP was studied by ICP-AES. Only a small
-
-
0
1
2
3
amount of Pd (<1.2 ppb) as well as phosphorous ( <1 ppb)
was leached into the solvent indicating that most of IL along
with catalyst remains tethered to the support. This indicates
that IL containing catalyst is significantly embedded in the
No. of Cycles
Fig. 5 Reusability of HmCucSILP catalyst in synthesis of alkyl aryl
ethers
hemicucurbituril matrix thus making HmCucSILP leach
ing resistant for a good retrieval and reusability. Using the
-
The comprehensive studies involving nature of interac
-
tions responsible for existence and stabilization of inclusion
complexes wherein hemicucurbiturils act as a host for bet -
ter understanding of its role in organic transformations is
underway in our laboratory.
A proposed mechanism for the synthesis of alkyl aryl
ethers from aryl halides and sodium alkoxides using
HmCucSILP catalyst is illustrated in Scheme1. The initially
same amount of Pd and phosphorous as that leached out, the
model reaction could not be initiated even after prolonged
reaction time (36 h). The heterogeneity of HmCucSILP
was also assessed by hot filtration test for the model reac-
tion. After 50 % completion of reaction (GC), the HmCuc -
SILP was quickly removed by filtration and the reaction
was continued with filtrate for additional 4 h. No further
1
3

Intermolecular C–O Coupling Using Hemicucurbituril Supported Ionic Liquid Phase Catalyst
24939
increase in the product yield beyond 50 % was observed
GC). This result confirmed the heterogeneous nature of the
halides with different sodium alkoxides. The efficiency of
protocol is represented by efficient C–O bond formation
(
HmCucSILP.
using electron rich aryl chlorides and bromides. In addi
-
Recovery and reusability of SILP catalysts with mini
mal effort is an important issue that must be addressed
before endorsing it for industrial scale. The reusability of
-
tion, this procedure displays number of significant key fea-
tures such as high product yields, shorter reaction times,
clean and easy work-up procedure and easy recovery and
reuse of catalyst.
the HmCucSILP catalyst was tested for model reaction. The
catalyst was easily recovered after each run simply by fil-
tration, washed three times with toluene, dried in an oven
at 110 °C for 12 h and tested in the subsequent runs. The
catalyst showed unprivileged recycling performance as
there was significant decrease in the product yield with the
prolonged reaction time during each successive run. The
decline in catalytic potential was elucidated on the basis of
inflation of reactant and product molecules that might be
hooked up the catalyst sites. Therefore, we attempted reus -
ability studies after reactivation at each cycle. The reacti -
vation involved vacuum treatment of HmCucSILP after
filtering and washing with toluene, so as to remove cap-
tivated reactant and product moieties on the surface. The
reactivation resulted in improved catalytic performance as
the corresponding yields started at 84 % and reached 55 %
at the third run without extended reaction time (Fig. 5). The
decline in the yields of the products even after reactivation
is probably due to agglomeration of support particles into
larger crystallites which limits accessing of reacting mol -
ecules to the active catalytic sites. Another striking feature
of HmCucSILP was its stability. The catalytic activity of
HmCucSILP did not change after 1 week of air exposure
at room temperature indicating its exceptional stability.
The FT-IR spectrum of reused catalyst displayed the char -
Acknowledgments The authors GSR, PAB, SGK, DPK, RSS
and RMK thank UGC, New Delhi for financial assistance [F. No.
4
0–96/2011 (SR)].
References
1
2
. Riisager A, Fehrmann R, Haumannand M, Wasserscheid P (2006)
Top Catal 40:91
. Van Doorslaer C, Wahlen J, Mertens P, Binnemans K, De Vos D
(2010) Dalton Trans 39:8377
3
4
. Mehnert CP (2005) Chem Eur J 11:50
. Werner S, Szesni N, Fischer RW, Haumann M, Wasserscheid P
(2009) Phys Chem Chem Phys 11:10817
5
. Smith K (1992) Solid supports and catalysts in organic synthesis.
PTR Prentice Hall, New York, pp 302–326
6
7
. Rashinkar G, Salunkhe R (2010) J Mol Cat A Chem 316:146
. Gao L, Kojima K, Nagashima H (2015) Tetrahedron 71:6414
8. Hong Y, Jiao Q, Zhang Y, Zhang J, Wu Q, Zhao Y, Neerunjun S,
Li H (2016) Catal Lett 146:951
9
. Gago S, Bruno SM, Queiros DC, Valente AA, Gonc¸alves IS,
Pillinger M (2011) Catal Lett 141:1009
1
0. Song KM, Gao HY, Liu FS, Pan J, Guo LH, Zai SB, Wu Q (2009)
Catal Lett 131:566
11. Riisager A, Eriksen KM, Wasserscheid P, Fehrmann R (2003)
Catal Lett 90:149
1
2. Elhamifar D, Kazempoor S, Karimi B (2016) Catal Sci Tech
6
:4318
−1
acteristic bands at 3279, 1675 cm (vibrational bands of
13. Li H, Bhadury PS, Song B, Yang S (2012) RSC Adv 2:12525
14. Burguete MI, Erythropel H, Garcia-Verdugo E, Luis SV, Sans V
(2008) Green Chem 10:401
−1
hemicucurbituril ring), 2959 cm (aliphatic C–H stretch of
−
1
[
Bmim]Cl), 1479 cm (in-plane C–C and C–N stretching
1
5. Gelesky MA, Chiaro SSX, Pavan FA, dos Santos JHZ, Dupont J
2007) Dalton Trans 5549
−1
vibrations of imidazolium ring), 1456 cm [C–H bending
vibration of C–O–O and CH 3 in Pd(OAc) ] and 784 cm
(
−
1
16. Sans V, Karbass N, Burguete MI, Compan V, Garcia-Verdugo E,
Luis SV, Pawlak M (2011) Chem Eur J 17:1894
2
(P–C bond stretching vibration of X-phos) whereas EDX
1
1
1
2
7. Rodríguez-Pérez L, Teuma E, Falqui A, Gómez M, Serp P (2008)
Chem Commun 35:4201
8. Mikkola J, Virtanen P, Karhu H, Salmia T, Murzin DY (2006)
Green Chem 8:197
analysis indicated the presence of 0.12 % Pd and 0.11 % P
revealing that the basic structure of the catalyst is retained
even after the third catalytic cycle.
9. Clousier N, Moucel R, Naik P, Madec PJ, Gaumont AC, Dez I
(2011) C R Chim 14:680
0. Qiao Y, Li H, Hua L, Orzechowski L, Yan K, Feng B, Pan Z,
Theyssen N, Leitner W, Hou Z (2012) Chem Plus Chem 77:1128
1. Khaleel IA, Werner MN (2015) Chem Soc Rev 44:394
4
Conclusion
2
2
2. Miyahara Y, Goto K, Oka M, Inazu T (2004) Angew Chem Int Ed
In conclusion, we have demonstrated a novel catalytic pro-
tocol in which supramolecular catalysis is encouraged by
inducing hemicucurbituril in the field of supported ionic
liquid phase catalysis. In this regards, we have engineered
4
3:5019
2
3. Buschmann HJ, Zielesyn A, Schollimeyer E (2006) J Incl Phe
nom Macro Chem 154:181
-
24. Buschmann HJ, Schollmeyer E (2005) Inorg Chem Commun
:125
5. Cong H, Yamato T, Feng X, Tao Z (2012) J Mol Cat A Chem
65:181
8
hemicucurbituril supported ionic liquid phase (HmCuc
SILP) catalyst by supporting metal–ligand system of
-
2
3
Pd(OAc) and X-phos with the help of ionic liquid, [Bmim]
2
26. Milton EJ, Fuentes JA, Clarke ML (2009) Org Biomol Chem
7:2645
Cl. The catalyst displayed ingenious effect in intermo
lecular C–O cross coupling reaction between diverse aryl
-
2
7. Fuhrmann E, Talbiersky JR (2005) Org Process Res Dev 9:206
1
3

1
20494
R. Kurane et al.
40. Mann G, Hartwig JF (1997) Tetrahedron Lett 38:8005
41. Parrish CA, Buchwald SL (2001) J Org Chem 66:2498
42. Wu X, Fors BP, Buchwald SL (2011) Angew Chem Int Ed
50:9943
43. Landeros FB, Carrow BP, Hartwig JF (2009) J Am Chem Soc
131:8141
44. Marquard SL, Hartwig JF (2011) Angew Chem Int Ed 50:7119
45. Kurane R, Jadhav J, Khanapure S, Salunkhe R, Rashinkar G
(2013) Green Chem 15:1849
2
8. Barluenga J, Tomas-Gamasa M, Aznar F, Valdes C (2010) Angew
Chem Int Ed 49:4993
2
3
9. Lepore SD, He Y (2003) J Org Chem 68:8261
0. Anderson KW, Ikawa T, Tundel RE, Buchwald SL (2006) J Am
Chem Soc 128:10694
3
3
3
1. Cano R, Ramon DJ, Yus MJ (2011) J Org Chem 76:654
2. Xu B, Xue J, Zhu J, Li Y (2008) Chem Lett 37:202
3. Ghosh R, Lindstedt E, Jalalian N, Olofsson B (2014) Chemis
tryOpen 3:54
-
3
3
3
4. Yusubov MS, Maskaev AV, Zhdankin VV (2011) ARKIVOC (i):370
5. Merritt EA, Olofsson B (2009) Angew Chem Int Ed 121:9214
6. Gowrisankar S, Sergeev AG, Anbarasan P, Spannenberg A, Neu -
mann H, Beller M (2010) J Am Chem Soc 132:11592
7. Bhadra S, Matheis C, Katayev D, Gooßen LJ (2013) Angew
Chem Int Ed 52:9279
8. Stambuli JP, Weng Z, Incarvito CD, Hartwig JF (2007) Angew
Chem Int Ed 46:7674
9. Altman RA, Shafir A, Choi A, Lichtor PA, Buchwald SL (2008) J
Org Chem 73:284
46. Dharaskar SA, Varma MN, Shende DZ, Yoo CK, Wasewar KL
(2013) Sci World J 2013:1
47. Bianchini D, Butler IS, Barsan MM, Martens W, Frost RL, Gal -
land GB, dos Santos JHZ (2008) Spectrochim Acta Mol Biomol
Spectrosc 71:45
48. Gallagher PK, Gross ME (1986) J Therm Anal Calorim 31:1231
49. Xiang DD, Geng QX, Cong H, Tao Z, Yamato T (2015) Supramol
Chem 27:37
3
3
3
1
3