Ferrocene labelled supported ionic liquid phase (SILP) containing organocatalytic anion for multi-component synthesis

Article abstract of DOI:10.1016/j.molcata.2009.10.013

Ferrocene labelled supported ionic liquid phase (SILP) catalyst containing l-prolinate anion has been synthesized by anion metathesis reactions of ionic liquid like unit grafted on Merrifield resin. The multi-component synthesis of 1-amidoalkyl-2-naphthol

Full text of DOI:10.1016/j.molcata.2009.10.013

Journal of Molecular Catalysis A: Chemical 316 (2010) 146–152
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Ferrocene labelled supported ionic liquid phase (SILP) containing
organocatalytic anion for multi-component synthesis
Gajanan Rashinkar, Rajashri Salunkhe∗
Department of Chemistry, Shivaji University, Kolhapur 416004, M.S., India
a r t i c l e i n f o
a b s t r a c t
Article history:
Ferrocene labelled supported ionic liquid phase (SILP) catalyst containing l-prolinate anion has been
synthesized by anion metathesis reactions of ionic liquid like unit grafted on Merrifield resin. The multi-
component synthesis of 1-amidoalkyl-2-naphthols from 2-naphthol, aryl aldehydes and amides has been
effectively achieved under solvent-free conditions using SILP catalyst. Additionally, the catalyst could be
reused for several cycles with slight loss of activity.
Received 1 September 2009
Received in revised form 8 October 2009
Accepted 8 October 2009
Available online 7 November 2009
© 2009 Elsevier B.V. All rights reserved.
Keywords:
Ferrocene
Supported ionic liquid phase
Merrifield resin
Amidoalkyl naphthols
Reusability
1. Introduction
circumvent the drawbacks associated with ILs. This new class of
advanced materials dramatically reduces the amount of ILs used,
Developments in the field of catalysis are being reported con-
stantly in the form of novel catalysts, new catalytic reactions and
alternative methodologies. Much of the pressure for this is driven
by the economic demands to develop systems in which easy separa-
tion of products and reuse of catalysts are possible along with high
reactivity and selectivity. As a part of this effort an ever increas-
ing degree has been focussed on ionic liquids (ILs) as an alternative
reaction media in synthetic chemistry [1]. The tempting proper-
ties of ILs such as negligible vapour pressure, large liquidus range,
high thermal stability, large electrochemical window and ability to
solvate compounds of varying polarity have made them an envi-
ronmentally attractive alternative to organic solvents. The almost
limitless combinations of cation–anion pairs allow the synthesis
of plethora of diverse ILs, catering to the needs of any particular
process [2]. However, despite their well reorganised advantages,
a series of drawbacks such as their high cost as compared to
traditional solvents, low biodegradability and (eco)toxicological
properties still exist [3]. This factor coupled with their recovery
that induces energy consumption via distillation [4] has been a
major obstacle in the preponderance of their use in industrial scale
applications. The new concept of supported ionic liquid phase (SILP)
catalysis involving immobilization of ILs onto a surface of a porous
high area support material [5] offers a highly attractive strategy to
retaining their properties. A number of benefits arise from the use
of SILP catalysts, chief of which are the ease of separation of cata-
lyst simply by filtration, as well as facilitating significant advances
in selectivity, recycling reproducibility and activity. The concept
of SILP catalysis has significantly progressed in the last few years,
resulting in new applications for various organic transformations
with the ionic liquid either containing a catalyst or being the cat-
alysts phase itself [6]. The bright prospects of the applications of
SILP catalysts in organic synthesis spurred us to investigate their
ability to catalyze multi-component reactions (MCRs).
The rapid assembly of molecular diversity utilizing multi-
component reactions has received a great deal of attention, most
notably for the speedy synthesis of novel molecular libraries [7].
These methodologies are of particularly great utility when they lead
to the formation of privileged medicinal scaffolds. 1-Amidoalkyl-
2-naphthol scaffolds are of significant medical relevance since
they can be converted into hypertensive and bradycardiac active
1-aminoalkyl-2-naphthols by amine hydrolysis reactions [8]. 1-
Amidoalkyl-2-naphthols are prepared by MCR of 2-naphthol with
aryl aldehydes and amides. Although the reaction has been inves-
tigated using number of Lewis or Bronsted acid catalysts [9–20],
there is still a scope for improvement especially towards develop-
ing a green protocol using highly efficient and reusable catalyst.
In continuation of our research devoted to the applications
of ferrocene in organic synthesis [21,22], we report herein an
improved strategy for the synthesis of a series of 1-amidoalkyl-
2-naphthols using ferrocene labelled supported ionic liquid phase
∗
Corresponding author. Tel.: +91 231 260 9169; fax: +91 231 269 2333.
E-mail address: gsrchemsuk@yahoo.co.in (R. Salunkhe).
1381-1169/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2009.10.013

G. Rashinkar, R. Salunkhe / Journal of Molecular Catalysis A: Chemical 316 (2010) 146–152
147
991, 897, 791, 463 cm−1; Elemental analysis observed: %C 66.26, %H
5.17, and %N 5.06. Loading: 0.9 mmol functional group g−1 resin.
(SILP) catalyst containing l-prolinate anion under solvent-free con-
ditions.
2.3. General method for the synthesis of
1-amidoalkyl-2-naphthols
2. Experimental
2.1. General remarks
A mixture of 2-naphthol (1 mmol), aromatic aldehyde (1 mmol),
amide (1.5 mmol) and [FemSILP]l-prolinate (50 mg) was stirred at
100 ◦C in an oil bath. After completion of the reaction as mon-
itored by the TLC, acetone (10 mL) was added and the reaction
mixture was filtered. The catalyst was washed with acetone (2×
10 mL). Evaporation of the solvent followed by column chromatog-
raphy over silica gel using ethyl acetate/petroleum ether (1:4, v/v)
afforded pure 1-amidoalkyl-2-naphthols, which were character-
ized by spectral methods.
1H NMR spectra were recorded on a Brucker Avon 300 MHz
spectrometer using DMSO-d6 as solvent using tetramethylsilane
(TMS) as an internal standard. Infrared spectra were recorded on
a PerkinElmer FTIR spectrometer. The samples were examined as
KBr discs ∼5% (w/w). Raman spectroscopy was done by means of
Brucker FT-Raman (MultiRAM) spectrometer. Mass spectra were
recorded on a Shimadzu QP2010 GCMS with an ion source temper-
ature of 280 ◦C. The materials were analysed by SEM using a JEOL
model JSM with 5 kV accelerating voltage. Elemental analyses were
performed on EURO EA3000 vectro model. For fluorescence studies,
the polymeric samples were suspended in methanolic solutions of
pyrene (0.01 M) and stirred for 4 h. After filtration and washing with
MeOH, the polymers were vacuum dried (60 ◦C). The samples were
introduced into fluorescence cells and excited at 338 nm (PC based
spectrofluorometer FP-750 JASCO, equipped with a 450 W xenon
lamp) and emitted light was recorded. The various aryl aldehydes
(Aldrich/BDH/Fluka), amides, 2-naphthol (sd Fine, India) and Mer-
rifield resin (2% cross-linked, 200–400 mesh, ca 2–3 mmol/g, Alfa
Aesar) were used as received. 1-N-Ferrocenylmethyl-1,2,4-triazole
was synthesized following the literature procedure [23].
Spectral
data
for
N-[(4-methyl-phenyl)-(2-hydroxy-
naphthalen-1-yl)-methyl] benzamide (Table 1, entry 6): 1H
NMR (300 MHz, DMSO-d6): ı 1.95 (s, 3H), 5.55 (bs, 1H), 6.93 (s,
1H), 7.02 (d, J = 7.5 Hz, 2H), 7.05 (s, 1H), 7.13–7.21 (m, 5H), 7.29
(d, J = 7.8 Hz, 2H), 7.62 (d, J = 9 Hz, 1H), 7.69 (d, J = 6 Hz, 1H), 7.89
(d, J = 7.9 Hz, 1H), 7.98 (s, 1H), 8.22 (d, J = 7.8 Hz, 1H), 9.78 (s, 1H);
IR (neat, thin film): ꢀ = 3401, 3062, 2922, 1641, 1560, 1514, 1480,
1438, 1380, 1274, 1180, 813, 739 cm−1; MS (EI): m/z 366 (M+−1);
anal. calcd. for C25H21NO2 C 81.72 H 5.76 N 3.81; found: C 81.68 H
5.82 N 3.79.
3. Results and discussion
3.1. Preparation of SILP catalyst
2.2. Preparation of SILP catalyst
SILP catalysts are prepared either by simple depositing or by
covalent attachment of ILs on the surface of high area support
like silica or polymeric based materials. We envisioned latter as
support for the preparation of SILP catalyst in the present work
since they provide reasonable stability to mechanical, chemical
and thermal demands under normal operating conditions. As these
materials are not able to adsorb ILs as films onto the surface [24],
our approach was based on the immobilization by covalent bond-
ing the IL like unit. In the preparation of SILP catalyst (Scheme 1),
the 1-N-ferrocenylmethyl-1,2,4-triazole (1) was reacted with Mer-
rifield resin to give the [FemSILP]Cl (2). The resulting compound
when treated with aqueous solution of ammonia underwent anion
metathesis reaction to form [FemSILP]OH (3). The substitution
of hydroxide anion by prolinate by the reaction of [FemSILP]OH
with l-proline afforded the ferrocene labelled SILP containing l-
prolinate anion, [FemSILP]l-prolinate (4).
The Raman and IR spectroscopy was used to monitor the
progress of the reactions involved in the synthesis of SILP catalyst.
The reaction of 1 with Merrifield resin was monitored by Raman
spectroscopy. The intensities of bands at 639 cm−1 (C–Cl stretch-
ing band) and 1266 cm−1 (wagging bands of CH2–Cl) diminished
significantly while the peaks at 459 cm−1 (Fe–Cp stretching band),
1383 cm−1, 1415 cm−1 and 1532 cm−1 (ring stretching modes of tri-
azole ring), 3135 cm−1 and 3186 cm−1 (C–H stretching of Cp rings)
increased in intensity after 72 h reflecting the substantial grafting of
1 onto Merrifield resin. Anion metathesis reactions were monitored
using IR spectroscopy. Appearance of a band of medium intensity at
3490 cm−1 (O–H stretch) in the IR spectrum of 3 clearly revealed the
considerable replacement of Cl by OH. The sharp band at 3397 cm−1
(N–H stretch) and 1633 cm−1 (C O stretch) in the IR spectrum of 4
confirmed the formation of [FemSILP]l-prolinate.
2.2.1. Preparation of [FemSILP]Cl (2)
A mixture of Merrifield resin (1.0 g) and 1-N-ferrocenylmethyl-
1,2,4-triazole (3 mmol) in 10 mL of toluene was heated at 80 ◦C
in an oil bath. After 72 h, the polymer was filtered, washed
with toluene (3× 20 mL), MeOH (3× 20 mL), CH2Cl2 (3× 20 mL)
and dried under vacuum at 50 ◦C for 48 h to afford [Fem-
SILP]Cl (2). IR (neat, thin film): ꢀ = 3111, 3014, 2923, 2847,
1601, 1556, 1490, 1450, 1390, 1259, 1187, 821, 699, 540 cm−1
Raman: ꢀ = 3186, 3135, 3007, 2891, 1532, 1415, 1383, 992,
;
792, 459 cm−1
; elemental analysis observed: %C 65.77, %H
4.68, and %N 4.44. Loading: 1.05 mmol functional group g−1
resin.
2.2.2. Preparation of [FemSILP]OH (3)
[FemSILP]Cl (1.0 g) was suspended in 10 mL of an aqueous solu-
tion of NH3. The system was stirred for 48 h at room temperature,
Afterwards the polymer was filtered and washed with MeOH (3×
20 mL), MeOH:H2O (1:1) (3× 20 mL), H2O (3× 20 mL) and MeOH
(3× 20 mL) and dried under vacuum at 50 ◦C for 48 h to afford
[FemSILP]OH (3). IR (neat, thin film): ꢀ = 3490, 3110, 3021, 2921,
2847, 1601, 1555, 1505, 1490, 1447, 1380, 1273, 1176, 818, 699,
543 cm−1; Raman: ꢀ = 3537, 3151, 3031, 2937, 2890, 1534, 1417,
1380, 991, 799, 460 cm−1; Elemental analysis observed: %C 66.06,
%H 4.93, and %N 5.01. Loading: 1.18 mmol functional group g−1
resin.
2.2.3. Preparation of [FemSILP]l-prolinate (4)
[FemSILP]OH (0.9 g) was suspended in 10 mL of a 1 M solution
of l-proline in MeOH:H2O (1:1). The system was heated at 60 ◦C
for 8 h. The filtration of the reaction mixture followed by wash-
ing with MeOH (3× 20 mL), MeOH:H2O (1:1) (3× 20 mL), H2O
(3× 20 mL) and MeOH (3× 20 mL) afforded [FemSILP]l-prolinate
(4). IR (neat, thin film): ꢀ = 3397, 3112, 3072, 2920, 2840, 1633,
1601, 1454, 1419, 1380, 1279, 1172, 818, 739, 551 cm−1; Raman:
ꢀ = 3380, 3185, 3137, 3008, 2890, 1610, 1531, 1416, 1382, 1049,
3.2. Morphology of SILP catalyst
An attempt was made to investigate the morphology of SILP
catalyst using scanning electron microscopy. The grafting of IL like

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Table 1
[FemSILP]l-prolinate catalyzed multi-component synthesis of 1-amidoalkyl-2-naphthols.a,b
Entry
Aryl aldehyde
Amide
Product
Yieldc (%)
TON
TOF h−1
1
Benzaldehyde
C6H5CONH2
82
1640
3.64
2
3
Benzaldehyde
Benzaldehyde
CH3CONH2
80
83
1600
1660
3.95
3.35
H2NCONH2
4
5
p-Methoxy benzaldehyde
p-Methoxy benzaldehyde
C6H5CONH2
69
71
1380
1420
2.04
2.25
CH3CONH2
6
7
8
p-Methyl benzaldehyde
p-Methyl benzaldehyde
p-Methyl benzaldehyde
PhCONH2
70
74
73
1400
1480
1460
2.59
2.98
2.70
H2NCONH2
CH3CONH2
9
p-Chloro benzaldehyde
PhCONH2
84
1680
4.14

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149
Table 1 (Continued )
Entry
Aryl aldehyde
Amide
Product
Yieldc (%)
TON
TOF h−1
10
m-Nitro benzaldehyde
PhCONH2
86
1720
3.82
11
m-Nitro benzaldehyde
CH3CONH2
87
1740
4.29
12
2-Furfuraldehyde
CH3CONH2
62
1240
1.62
a
All products were characterized by 1H NMR and IR spectroscopy as well as by mass spectrometry.
No chirality was observed.
Isolated yields after chromatography.
b
c
Fig. 1. Scanning electron micrographs (SEM images) of (A) Merrifield resin and (B) Fem[SILP]l-prolinate.
Fig. 2. Sketch of the tension suffered by the Merrifield resin beads (A) and high resolution SEM of totally destroyed beads in [FemSILP]l-prolinate (B).

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G. Rashinkar, R. Salunkhe / Journal of Molecular Catalysis A: Chemical 316 (2010) 146–152
Fig. 3. Fluorescence spectra of pyrene in Merrifield resin (A) and in [FemSILP]l-
prolinate (B).
Table 2
Fluorescence data of pyrene in Merrifield resin and [FemSILP]l-prolinate. Py values
(I1/I3) and positions of peaks I and III.
Entry
Polymer
I1/I3
ꢁ1 (nm)
ꢁ3 (nm)
1
2
Merrifield resin
Fem[SILP] l-prolinate
0.789
1.13
376
377
396
396
4 was evaluated by steady state fluorescence spectroscopy, using
pyrene as probe. In the fluorescence spectra of pyrene, the first band
v=0
corresponds to the transition S1 → Sv0=0, and its intensity (I1) is
dependent on the polarity of the medium, provided the existence
of vibronic coupling between S1 and S2 states while the third band
v=0
v=2
corresponds to the S1 → S0 transition and its intensity (I3) is
independent of the polarity. Hence, the ratio of I1/I3 (referred as
py value) has been used to estimate the polarity of several media
including SILPs [26]. The fluorescence spectra of pyrene adsorbed
on the Merrifield resin and 4 were measured (Fig. 3). The spectrum
of Merrifield resin showed the py value of 0.789 while that of 4
showed the py of 1.13 (Table 2). The increase in the py value clearly
reflects the increased polarity of 4 as compared to the Merrifield
resin. The substantially higher py value of SILP catalyst (ca 43%) as
compared to Merrifield resin can be attributed to the grafting of
ferrocene labelled triazolium unit in the matrix of Merrifield resin.
The presence of ferrocene leads to unsymmetrical charge distribu-
tion on the triazole ring resulting in the significant enhancement
of overall polarity of SILP catalyst.
Scheme 1. Synthesis of ferrocene labelled SILP catalyst containing l-prolinate anion,
[FemSILP]l-prolinate (4).
unit on Merrifield resin had a pronounced effect on its morphology.
The Merrifield resin beads in SILP catalyst did not appear spherical
like the original support beads (Fig. 1).
In fact the bead degradation was observed which may be plau-
sibly due to stress on the bead [25]. High ratios of grafted IL like
units mass to bead volume lead to a situation where most of the
beads experience enormous tension (Fig. 2A: graphic work has been
superimposed on high resolution SEM of Merrifield resin to show
points of tension due to grafting of IL like unit). These points of
tension evolve and give rise to stress in the bead which eventually
bursts (Fig. 2B). The bead degradation did not have any influence
on the catalytic activity of SILP catalyst.
3.4. Synthesis of 1-amidoalkyl-2-naphthols using SILP catalyst
3.3. Micropolarity of SILP catalyst
The synthesis of 1-amidoalkyl-2-naphthols was achieved by
multi-component condensation of 2-naphthol with aromatic alde-
hydes and amides in the presence of catalytic amount of 4
(Scheme 2). To find the optimum conditions, the reaction between
2-naphthol, benzaldehyde, and benzamide in the presence of SILP
catalyst (0.05 g) as a model was performed under solvent-free con-
The polarity of ILs is one of the fundamental parameters that
ascertain their final properties and this can also be a determinant
for SILPs. It has been suggested that the advanced properties of
SILP catalysts are, in part, directly related to the change of polar-
ity of SILPs as compared to their standard supports. The polarity of
Scheme 2. [FemSILP]l-prolinate promoted synthesis of 1-amidoalkyl-2-naphthols.

G. Rashinkar, R. Salunkhe / Journal of Molecular Catalysis A: Chemical 316 (2010) 146–152
151
Scheme 3. Mechanism of 1-amidoalkyl-2-naphthol synthesis using SILP catalyst.
Table 3
Optimization of the temperature in the preparation of 1-amidoalkyl-2-naphthols.a,b
Entry
Amount of catalyst (g)
Temp. (◦C)
Time (h)
Yieldc (%)
TON
TOF h−1
1
2
3
4
5
0.05
0.05
0.05
0.05
0.05
RT
40
60
80
100
5
5
5
5
5
32
40
42
68
82
640
800
840
1360
1640
1.42
1.77
1.86
3.02
3.64
a
The molar ratios of benzaldehyde/2-naphthol/benzamide is 1/1/1.5.
No chirality was observed.
Yields refer to pure isolated product.
b
c
ditions at different temperatures. As can be seen from Table 3,
the best results were achieved at 100 ◦C. Having established the
reaction conditions, a series of 1-amidoalkyl-2-naphthols were
synthesized by the reaction of 2-naphthol with various aromatic
aldehydes and amides in excellent yields with the TON in the range
of 1240–1740 and TOF in the range of 1.62–4.29 h−1. The results are
summarized in Table 1. In all cases amidoalkyl naphthols were the
sole products and no by-product was observed. For aryl aldehydes,
the effect of the electronic factor on the yield appeared to be greater
than that of steric effect. The aryl aldehydes with electron with-
drawing groups led to the higher yields as compared with those
having electron donating groups. This observation can be rational-
ized on the basis the mechanistic details of the reaction [12]. The
reaction involves in situ generation of ortho-quinone methides (o-
QMs) by the condensation of aromatic aldehyde with 2-naphthol.
The 1,4-nucleophilic addition of amides on o-QMs affords the syn-
thesis of 1-amidoalkyl-2-naphthols. Electron withdrawing groups
on aryl aldehyde in the o-QMs facilitates the rate of 1,4-nucleophilic
addition as the alkene LUMO is at lower energy in their presence
compared with electron donating groups. The identity of all the
compounds was ascertained on the basis of IR, 1H NMR and mass
spectroscopy data as well as on the basis of elemental analysis. The
physical and spectroscopic data were in full agreement with the lit-
erature data [9–20]. The plausible mechanism for the formation of
amidoalkyl naphthols using SILP catalyst is shown in Scheme 3. The
Fig. 4. Recyclic use of [FemSILP]l-prolinate in 1-amidoalkyl-2-naphthol synthesis.

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l-prolinate anion plays a vital role in the catalytic activity of SILP
catalyst. It initially facilitates the formation of o-QM from aryl alde-
hyde and 2-naphthol. The subsequent 1,4-nucleophilic addition
of amide on o-QM furnishes the corresponding 1-amidoalkyl-2-
naphthol.
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reaction simply by filtration and can be reused without any sig-
nificant loss in chemical yield of the products. The reusability of
the catalyst was investigated by the reaction of benzaldehyde, 2-
naphthol and benzamide. As shown in Fig. 4, the yield of the product
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4. Conclusion
In summary, we have developed an efficient method for multi-
component synthesis of 1-amidoalkyl-2-naphthols using ferrocene
labelled SILP catalyst containing l-prolinate anion under solvent-
free conditions. Short reaction times, high yields, clean reactions,
easy recovery and efficient reusability of catalyst not only make this
protocol an alternative to the existing methods but also become
significant under the roof of environmentally greener and safer
processes.
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