5-Methyl-5-aryldipyrromethanes: Synthesis, crystal structure and anion binding studies

Article abstract of DOI:10.1080/10610278.2013.794280

The eco-friendly and selective syntheses of 5-methyl-5-aryldipyrromethanes (1-4) in which aryl is FC₆H₄ 1, ClC₆H ₅ 2, CH₃OC₆H₅ 3 and CH ₃C₆H₅ 4,

Full text of DOI:10.1080/10610278.2013.794280

Supramolecular Chemistry, 2013
Vol. 25, No. 8, 474–480, http://dx.doi.org/10.1080/10610278.2013.794280
5-Methyl-5-aryldipyrromethanes: synthesis, crystal structure and anion binding studies
Aparna Sharmaa,b*, Sangeeta Obraib, Rakesh Kumarb, Amanpreet Kaurc and Geeta Hundalc*
b
aDepartment of Chemistry, Hans Raj Mahila Maha Vidyalaya, Jalandhar, India; Department of Chemistry, B. R. Ambedkar National
Institute of Technology, Jalandhar, Punjab, India; cGuru Nanak Dev University, Amritsar, India
(Received 9 February 2013; final version received 3 April 2013)
The eco-friendly and selective syntheses of 5-methyl-5-aryldipyrromethanes (1–4) in which aryl is FC6H4 1, ClC6H5 2,
CH3OC6H5 3 and CH3C6H5 4, have been reported in the presence of citric acid (weak organic acid) and characterised by IR,
1H NMR, 13C NMR and mass spectroscopy. The structures of 2–4 have been confirmed by X-ray crystallography. Anion
1
binding studies of 1–4 with different anions (e.g. F2, Cl2, CH3COO2, H2PO42 and HSO42) have been carried out by H
NMR titrations and binding constants have been evaluated using EQNMR program, revealing that they bind fluoride
selectively compared with other anions with 1:1 stoichiometry in CDCl3. The binding affinities of these compounds are
influenced by the nature of the substituent on the meso-carbon atom.
1
Keywords: methylaryldipyrromethanes; crystal structure; anion recognition; H NMR titrations
Introduction
and dihydrogen phosphate) forming 1:1 complexes (2a,b).
Dipyrromethanes interact with anions through H-bonding
because of acidic character of NH protons, although their
molecular recognition chemistry has been less explored as
compared with calix[4]pyrroles (1). Anion sensing and
neutral molecules sensing have been reported only for a
few dipyrromethanes and its derivatives (2). Charge-
transfer complex consisting of dihydroxymethyldi-(2-
pyrrolyl)methane and tetracyanoquinodimethane selec-
tively distinguishes cysteine from other amino acids which
also proved as a colorimetric probe for aniline. Similar
types of charge-transfer complexes have also been reported
to show excellent selectivity for other inorganic anions (3).
Introduction of electron-withdrawing compared with
that of electron-releasing groups in dipyrromethanes (4)
and calix[4]pyrroles (5) skeleton increases the acidity of
pyrrolic protons which in turn enhances their affinity and
selectivity towards anions. Introduction of bulky groups
such as admantane at meso-carbons also resulted in
enhanced association constants for anions (e.g. F2, Cl2,
Br2, HSO42 and H2PO24 ) because of hindered rotational
mobility of pyrrole moieties (2).
Molecular recognition of anions, cations and neutral
molecules by various receptors (7) are biomimetic
processes (8) and is a remarkable achievement in the
field of supramolecular chemistry.
Dipyrromethanes are the precursors for the synthesis
of porphyrins, calix[4]phyrins, corroles, calix[4]pyrroles
and phlorins (9) that have a wide variety of applications in
the fields of medicine, material science and optical sensors
(10). Dipyrromethanes are generally synthesised by acid-
catalysed condensation of aldehydes or ketones in the
presence of excess of pyrrole. Chemists are now trying to
develop more efficient and eco-friendly methods to
synthesise compounds by using milder acids as catalyst
and eco-friendly solvents as compared with traditional
acid-catalysed condensation reactions of aldehydes or
ketones with excess pyrrole as solvent (11).
The strength of our pathway is the use of non-
hazardous, inexpensive weak organic acid and green
solvent, i.e. water, leading to good yields of products by
recrystallisation. This method avoids excess use of
reactant, i.e. pyrrole, and also limits the formation of
oligomeric and polymeric products. To the best of our
knowledge, the chemistry of meso-methylaryldipyrro-
methanes is not well established, and they could be
potential receptors as well as good building blocks for the
synthesis of meso-functionalised calix[4]pyrroles. Among
methylaryldipyrromethanes, binding studies of only 5-
methyl-5(4-nitrophenyl)dipyrromethane and its further use
as precursor for the synthesis of meso-functionalised and
expanded calix[4]pyrroles have been reported in the
The binding constants (1:1) with fluoride ion for
various dipyrromethanes follow the order dimethyldipyr-
romethanes (6) . phenyldipyrromethanes (2a) .
diphenyldipyrromethanes (4a). The observed order may
be due to stronger repulsive interactions between the anion
and the two aryl rings. In general, dipyrromethanes are
more selective towards fluoride ion forming both 2:1
(host:fluoride) and 1:1 complexes rather than other anions
(e.g. chloride, bromide, acetate, nitrate, hydrogen sulphate
*Corresponding authors. Email: apparna_2007@yahoo.com; geetahundal@yahoo.com
q 2013 Taylor & Francis

Supramolecular Chemistry
475
literature (6). In this work, we report syntheses of 5-
methyl-5-aryldipyrromethanes 1–4, study of their anion
binding properties and crystal structure of 2–4. It is
anticipated that the presence of electron-withdrawing
group in 1 and 2 would enhance the anion binding ability
than electron-releasing groups in 3 and 4 at the para-
position of meso-phenyl substituents.
refluxed for 4.0 h in a round-bottomed flask. The reaction
was quenched by adding ammonia solution. Then, the
product separated out as sticky mass which was
thoroughly washed with water to remove any unreacted
pyrrole, ketone and weak acid. Finally, it was recrystal-
lised by dissolving in acetone/methanol. A single spot on
the TLC plate for each of these compounds confirmed the
presence of one compound in each case.
Synthesis of 6–8: Compounds 6–8 were also
synthesised using a similar procedure.
Experimental
General information
Melting points were determined on Gallenkamp electrically
heated apparatus in open capillaries and were uncorrected.
1H and 13C NMR were recorded in CDCl3 on the FT NMR
Spectrometer model Avance-II 400 (Bruker UK Limited,
Banner Lane, Coventry, CV4 9GH) using tetramethylsilane
as internal standard, and chemical shifts are expressed in
ppm. FT-IR spectra were recorded on the FT PerkinElmer
RX I-FTIR Spectrophotometer using KBr (solid) as medium
and expressed in cm21. Mass spectra were recorded on
Waters micromass Q_TOF MicroTM. X-ray crystallographic
data were collected on ‘Bruker APEX-II CCD’ area detector
diffractometer using graphite monochromated Mo Ka
Anion binding studies
1H NMR titrations: 1H NMR titrations were carried out by
the addition of Bu4NF (1 M) or Bu4NCl (1 M) to 0.0045 M
solution of 1–4 in CDCl3 solvent. After each addition,
NMR spectrum was recorded. The association constants
were determined by fitting the dependence of the chemical
shift of the NH signal (Dd) to the anion concentration,
using the EQNMR program.
Spectral data of 1–4
Compound 1: 55%; light brown solid, mp 838C; 1H NMR
˚
radiation (l ¼ 0.71073 A) source. The crystal structures
were solved by direct method using the SIR-97 program and
refined by full-matrix least-squares refinement methods
based on F 2, using SHELXLT-PC program (12d). All the
CH hydrogens were attached geometrically. Molecular
structures of compounds were drawn with the help of Oak
Ridge Thermal Ellipsoid Plot (ORTEP) program. Hydrogen
bonding was calculated using PARST (12). Pyrrole and
ketones were distilled immediately prior to use.
(CDCl3, 400 MHz, ppm) d 1.9 (s, 3H, CH3), 5.8 (m, 2H,
0
0
pyrrole-Ha ), 6.0 (m, 2H, pyrrole-Hb ), 6.5 (m, 2H, pyrrole-
Hb), 6.8 (m, 2H, Ph-H), 6.9 (m, 2H, Ph-H), 7.6 (br, s, 2H,
NH); 13C NMR (100 MHz, CDCl3) d 29.7 (C, CH3), 44.3
(C, meso), 106.5 (b0-C, pyrrole), 108.3 (b-C, pyrrole),
117.2 (a0-C, pyrrole), 137.2 (a-C, pyrrole), 129.1, 114.9
(Ph-C), 143.2 (Ph-C), 162.7 (Ph-C); IR (KBr): n 3416.5
(pyrrole NH), 3102.2 (b-pyrrole C–H), 2979.0, 1901.6,
1668.5, 1598.5, 1553.2, 1505.7, 1463.4, 1415.6, 1400.6,
1300.8, 1264.7, 1222.6, 1162.2, 842.5. 776.8 and
721.6 cm21; MS(EI) m/z: 254.1 (Mþ), 240.1 (Mþ-CH3),
188.1 (100%) (M-pyrrole), 121.0 (Mþ-2 pyrrole).
Representative experimental procedure for the synthesis
5-methyl-5-(4-fluorophenyl)dipyrromethane 1
4-Fluoroacetophenone, 1.21 ml (0.01 mol), and citric acid
(1%, w/v) were dissolved in distilled water (30 ml). Pyrrole,
1.38 ml (0.02mol), was added dropwise to this solution with
a constant stirring. The reaction mixture was refluxed till the
reaction was complete. The reaction was quenched by
adding 10 ml of 1 M ammonia solution leading to separation
of product as a sticky mass. The crude was thoroughly
washed with water to remove any unreacted reagents.
Finally, itwasrecrystallisedbydissolvinginmethanol:water
(1:1). A single spot on the Thin Layer Chromatography
(TLC) plate for each of these compounds confirmed the
presence of one compound in each case.
1
Compound 2: 65%; light brown solid, mp 858C; H
NMR (CDCl3, 400 MHz, ppm) d 2.0 (s, 3H, CH3), 5.9 (m,
0
0
2H, pyrrole-Ha ), 6.2 (m, 2H, pyrrole-Hb ), 6.7 (m, 2H,
pyrrole-Hb), 7.05–7.08 (m, 2H, Ph-H), 7.24–7.28 (m, 2H,
Ph-H), 7.8 (br, s, 2H, NH); 13C NMR (100 MHz, CDCl3) d
28.8 (C, CH3), 44.4 (C, meso), 106.5 (b0-C, pyrrole), 108.3
(b-C, pyrrole), 117.2 (a0-C, pyrrole), 136.9 (a-C, pyrrole),
129.8, 128.2 (Ph-C), 132.5 (Ph-C), 146.0 (Ph-C); IR
(KBr): n 3430.9 (pyrrole NH), 3099.8 (b-pyrrole C–H),
2980.09, 1664.78, 1572.3, 1553.39, 1485.68, 1303.3,
1128.04, 1090.1, 1026.5, 882.1, 837.5, 791.7 and
718.6 cm21; MS(EI) m/z: 269.1(Mþ 2 1), 204.1 (100%)
(Mþ-pyrrole), 137.0 (Mþ-2 C4H4N).
Synthesis of 2–4: Compounds 2–4 were also
synthesised using a similar procedure.
Compound 3: 55%; colourless crystals, mp 1258C; 1H
NMR (CDCl3, 400 MHz, ppm) d 2.0 (s, 3H, CH3), 3.78 (s,
0
3H0, OCH3), 5.9 (m, 2H, pyrrole-Ha ), 6.1 (m, 2H, pyrrole-
Hb ), 6.6 (m, 2H, pyrrole-Hb), 6.7–6.8 (m, 2H, Ph-H),
7.01–7.03 (m, 2H, Ph-H), 7.7 (br, s, 2H, NH); 13C NMR
(100 MHz, CDCl3) d 29.0 (CH3), 44.1 (meso, C), 55.32
Representative experimental procedure for the synthesis
tetra-cyclohexylcalix[4]pyrrole 5
A mixture of 5.8 ml of acetone (0.1 mol), 0.69 ml of
pyrrole (0.01 mol) and weak organic acid (10.0%) was

476
A. Sharma et al.
(OCH3, C), 106.2 (b0-C, pyrrole), 108.2 (b-C, pyrrole),
113.4 (a0-C, pyrrole), 137.8 (a-C, pyrrole), 128.5, 116.9
(Ph-C), 139.5 (Ph-C), 158.2 (Ph-C); IR (KBr): n 3410.4
(pyrrole NH), 3051.7 (b-pyrrole C–H), 3099.8, 2905.6,
2835.3 1602.9, 1580.9, 1557.4, 1457.7, 1373.9, 1242.7,
1115.3, 1066.3, 1025.0, 794.8, 772.7 and 713.2 cm21
;
MS(EI) m/z: 200.1(100%) (M-pyrrole), 185.1 (M-CH3-
pyrrole), 133.1 (M-2 pyrrole).
Scheme 1. Syntheses of 5-methyl-5-aryldipyrromethanes.
Compound 4: 58%; colourless crystals, mp 1208C; 1H
hazardous but also good catalysts; these can be easily
removed by washing with water.
NMR (CDCl3, 400 MHz, ppm) d 2.2 (s, 3H, CH3), 1.9 (s,
0
3H0, CH3), 5.8 (m, 2H, pyrrole-Ha ), 6.0 (m, 2H, pyrrole-
Hb ), 6.5 (m, 2H, pyrrole-Hb), 6.9 (m, 2H, Ph-H), 7.0 (m,
2H, Ph-H), 7.6 (br, s, 2H, NH); 13C NMR (100 MHz,
CDCl3): d 28.9 (CH3, C), 44.4 (meso, C), 20.9 (CH3, C),
106.1 (b0-C, pyrrole), 108.2 (b-C, pyrrole), 116.8 (a0-C,
pyrrole), 136.3 (Ph-C), 144.3 (Ph-C); IR (KBr): n 3422.5
(pyrrole NH), 3123.3 (b-pyrrole C–H), 2986.9, 2870.2,
1666.3, 1552.4, 1559.9, 1509.4, 1454.8, 1414.2, 1269.4,
1027.5, 882.8, 801.0, 777.2 and 725.5 cm21; MS(EI) m/z:
250.1 (Mþ), 249.2 (Mþ 2 1), 237 (Mþ-CH3), 184.1
(100%) (Mþ-pyrrole).
They catalyse the reaction of pyrrole with substituted
acetophenone in a selective and greener way giving
dipyrromethanes of high purity. Not many oligomeric and
polymeric products have been detected in workup even on
long exposure. Citric acid failed to catalyse the
condensation reaction of pyrrole with benzophenone
even on refluxing for extended periods. To extend the
scope of the reaction, calix[4]pyrroles (5–8) have also
been synthesised by condensation of pyrrole in the
presence of excess of ketone as solvent (cycohexanone,
acetone, methylethylketone and methyphenylketone)
using the same catalyst (Scheme 2).
Compound 5: 92%; light creamish solid, mp 2778C; 1H
NMR (CDCl3, 400 MHz) d 1.4 (m, 8H, C6H10), 1.48 (m,
16H, C6H10), 1.9 (m, 16H, C6H10), 5.89 (d, 8H, pyrrole), 7.0
(br, s, 4H, NH); IR (KBr): n 3433.9 (pyrrole NH), 3104.48
(b-pyrrole C–H), 2985.2, 2856.7, 1702.19, 1570.9, 1447
and 1215.3 cm21; MS(EI) m/z: 589.5 [Mþ þ 1].
Crystals of 2–4 suitable for X-ray crystallographic
analysis were obtained from ethanol–water mixture. All
the crystal systems are monoclinic with space group P21/c
for 2 and P21/n for 3 and 4 (Table 1). In crystal structures
of 2–4, meso-sp3 C atom is slightly deviated from
tetrahedral geometry as bulky aryl group leads to steric
crowding around it (Figures 1–3).
Compound 6: 95%; light creamish solid, mp 2988C; 1H
NMR (CDCl3, 400 MHz) d 1.5 (s, 24H, CH3), 5.90–5.89
(m, 8H, pyrrole-H), 7.01 (br, s, 4H, NH); IR (KBr): n
3441.8 (pyrrole NH), 3108.7 (b-pyrrole C–H), 2969.6,
2931.0, 1578.0, 1507.3, 1279.6, 775.1 and 760.1; MS(EI)
m/z: 429.2 [Mþ þ 1].
The pyrrolic NH protons are involved in intermole-
cular H-bonding interactions with the oxygen of anisole
group (Figure 2(b)) in 3. No significant hydrogen bonding
interactions have been observed in 2 and 4.
Compound 7: 82%; light creamish solid, mp 1458C; 1H
NMR (CDCl3, 400 MHz) d 0.75 (m, 12H, CH3, CH2CH3),
1.45 (s, 24H, CH3), 1.85 (m, 8H, CH2CH3), 5.8 (m, 8H,
pyrrole-H), 7.1 (br, s, 4H, NH); IR (KBr): n 3441.5
(pyrrole NH), 3106.5 (b-pyrrole C–H), 2969.1, 2931.0,
2870.4, 1640.1, 1578.0, 1414.0 (C–H bending), 1381.1,
964.0 and 725.1 cm21; MS(EI) m/z: 485.4 [Mþ þ 1].
Compound 8: 40%; light creamish solid, mp 2178C; 1H
NMR (CDCl3, 400 MHz) d 1.8 (s, 12H, CH3), 5.67–5.65 (d,
8H, pyrrole-H), 6.9–7.0 (m, 8H, phenyl-H), 7.1–7.2 (m,
12H, phenyl CH) 7.5 (br, s, 4H, NH); IR (KBr): n 3438.4
(pyrrole NH), 3105.0 (b-pyrrole C–H), 2975.0, 2873.4,
1596.7, 1575.0, 1491.3, 1444.9 1416.2, 1215.6, 1026.1,
769.9, 700.1 and 506.2 cm21; MS(EI) m/z: 677.5 [Mþ þ 1].
Anion binding studies
The anion binding properties of various substituted
methylaryldipyrromethanes 1–4 were investigated with
different anions (F2, Cl2, CH3COO2, H2PO42 and HSO24 )
by 1H NMR titrations in CDCl3 at room temperature.
Results and discussion
Compounds 1–4 were prepared in good yields by
refluxing pyrrole and substituted acetophenone in 2:1
ratio with weak organic acid (citric acid) as catalyst and
water as solvent till completion of the reaction (Scheme 1).
Weak organic acids are not only inexpensive and non-
Scheme 2. Syntheses of calix[4]pyrroles.

Supramolecular Chemistry
477
Table 1. Crystallographic data and structural refinement method for compounds 2–4.
2
3
4
Empirical formula
Formula weight
Crystal system
Crystal size (mm)
Colour
Shape
Space group
Unit cell dimensions
C16 H15 Cl N2
270.75
Monoclinic
0.16 £ 0.12 £ 0.11
Colourless
Needle
C17 H18 N2 O
266.34
Monoclinic
0.15 £ 0.11 £ 0.10
Colourless
Square
C17 H18 N2
250.33
Monoclinic
0.18 £ 0.16 £ 0.12
Colourless
Needle
P21/c
P21/n
P21/n
˚
˚
˚
˚
˚
a ¼ 16.400(4) A
a ¼ 11.1489(4) A
a ¼ 15.281(3) A
˚
˚
b ¼ 9.397(2) A
b ¼ 10.5641(4) A
b ¼ 6.4384(12) A
˚
˚
c ¼ 18.233(5) A
c ¼ 12.3010(4) A
c ¼ 15.508(3) A
a ¼ 90.008
a ¼ 90.008
a ¼ 90.008
b ¼ 112.135(7)8
g ¼ 90.008
1413.3(5), 4
1.176
b ¼ 93.815(12)8
g ¼ 90.008
b ¼ 91.169(2)8
g ¼ 90.008
3
Volume (A ), Z
˚
2803.9(11), 8
1.283
0.260
1448.49(9), 4
1.221
0.077
rcalc (g cm23
)
M (cm21
F(0 0 0)
Range of data collection, u
)
0.070
536
1136
1.24–28.59
220 # h # 21
2 12 # k # 11
2 24 # l # 24
26,538
568
2.44–32.48
216 # h # 16
2 15 # k # 14
2 18 # l # 17
20,872
1.59–31.35
222 # h # 22
2 5 # k # 9
2 22 # l # 20
17,372
Limiting frequency
Total reflections
Independent reflections
Completeness to u (%)
Refinement method
Goodness of fit on F 2
Final R indices [I . 2(I)]
R indices (all data)
Largest diff. peak
7016
97.8
5207
99.5
4616
99.3
Full matrix least squares on F 2
1.017
Full matrix least squares on F 2
1.024
Full matrix least squares on F 2
1.029
R1 ¼ 0.0522, wR2 ¼ 0.1263
R1 ¼ 0.1182, wR2 ¼ 0.1622
0.294 and 20.332
R1 ¼ 0.0491, wR2 ¼ 0.1306
R1 ¼ 0.0795, wR2 ¼ 0.1496
0.272 and 20.197
R1 ¼ 0.0506, wR2 ¼ 0.1338
R1 ¼ 0.0788, wR2 ¼ 0.1538
0.226 and 20.227
3
˚
and hole (e A )
Figure 1. (colour online) ORTEP diagram of 5-methyl-5-(4-chlorophenyl)dipyrromethane 2.

478
A. Sharma et al.
(a)
(b)
C8
C7
C6
C9
N1
C16
C15
C1
C14
C13
C10
C11
N2
C2
C3
C17
C5
C12
O1
C4
Figure 2. (colour online) (a) ORTEP diagram of 5-methyl-5-(4-methoxyphenyl)dipyrromethane 3 and (b) intermolecular H-bonding
interactions showing one-dimensional array.
Stability constants were determined using the EQNMR
(13) computer program for fitting the binding profiles to a
1:1 methylaryldipyrromethane–anion solution complex
model by observing the shifts of NH protons of pyrrole.
The anions were added in the form of tetrabutylammonium
salts and their concentrations ranged from 0.0011 to
0.036 M while the concentration of 1–4 was kept constant,
Table 2. The association constants of the complexes of 1–4
with anions determined by NMR titrations.a
F2
Cl2
CH3COO2
H2PO24
HSO24
1
2
3
4
2.23
2.51
2.26
2.13
1.65
2.01
1.85
1.35
1.78
2.00
1.64
1.70
1.84
1.78
1.39
1.46
1.44
1.24
1.78
1.24
1
0.0045 M, during the H NMR titration experiment. The
Note: K values are log10 values.
a Errors are ,6.0%.
results summarised (Table 2) revealed that compounds
1–4 bind strongly with fluoride ion as compared with
other anions with 1:1 stoichiometry. The titration profile
(Figure 4) showed pronounced changes observed in the
NMR spectra of 1 by the addition of fluoride ion. The
signal corresponding to the pyrrolic NH protons initially
11.0
10.5
10.0
9.5
9.0
8.5
8.0
7.5
Figure 4. 1H NMR spectra of 1 with varying concentration of
Bu4NF. The bottom spectrum corresponds to pure 1, whereas
other spectra correspond to 1 and the following fluoride ion
concentrations: 0.25, 0.50, 0.75, 1.0, 1.25, 1.50, 1.75, 2.0, 3.0,
4.0, 6.0 and 8.0 g equiv.
Figure 3. (colour online) ORTEP diagram of 5-methyl-5-(4-
methylphenyl)-dipyrromethane 4.

Supramolecular Chemistry
479
appeared at 7.71 ppm was deshielded to 8.78 ppm on
addition of 1.0 equiv. of fluoride ion, thus showing a
downfield shift of NH signal (Dd ¼ 1.07 ppm) along with
the splitting of signal at 1.25 equiv. which is the hallmark
of strong binding (14). It has been found that the signal
corresponding to NH proton in compound 1 does not
disappear even on addition of excess of tetrabutylammo-
nium fluoride (S 44). No signal is observed in the range of
15.0–16.0 ppm corresponding to [FHF]2, indicating that
deprotonation is not taking place (S 45). However, the
decrease in peak height corresponding to NH protons can
be attributed to H-bonding interactions. On addition of
1.0 equiv. of anion, a-CH proton of pyrrole near the
binding site experienced downfield shift from 6.62 to
6.71 ppm. At the same time, two b-CH protons and phenyl
CH protons underwent a reasonable downfield shift (0.03
and 0.09 ppm for pyrrolic CH; 0.02 and 0.07 ppm for
phenyl CH) (Supplementary data, available online). These
shifts showed that anion has induced electronic pertur-
bations in the receptor or host molecule.
catalyses the reactions in a selective and greener way,
giving products of high purity. 5-Methyl-5-aryldipyrro-
methanes 1–4 have been proved to be anion sensors using
1H NMR spectroscopic analysis. It has been observed that
introduction of electron-withdrawing groups enhanced the
binding ability of receptors as compared with electron-
releasing groups. All these receptors have more affinity
towards F2 ion than towards other anions as is evident
from their association constants (Table 2), yielding 1:1
complexes. The binding constants calculated for com-
pounds 1–4 with fluoride ion (reported in the present
work) are higher than those for 1:1 complex of fluoride
with diphenyldipyrromethane (4a). This may be attributed
to less steric crowding in methylaryldipyrromethane
compared with diphenyldipyrromethane at the meso-
position. Anion sensors with low value of binding constant
can be used as HPLC media for the separation of mixture
of compounds.
Supplementary data
Chloride, acetate, dihydrogen phosphate and hydrogen
sulphate ions have also induced downfield shift of NH
protons (Dd ¼ 0.21, 0.6637, 0.835 and 0.0685) in the same
receptor 1 due to their larger size, smaller basicity and
lesser nucleophilicity but to a smaller extent than fluoride
ion. Addition of 1 equiv. of fluoride ion to 2, 3 and 4
showed a downfield shift of NH signal Dd ¼ 1.43, 0.88,
0.64 ppm, respectively. The addition of other anions (Cl2,
CH3COO2, H2PO42 and HSO24 ) to the solutions of 2–4
also showed downfield shift of NH signal.
1
Supplementary data contain experimental procedures, H
NMR, mass spectra 1–8 and 13C NMR and binding
profiles for compounds 1–4. Crystal data for 2–4 are
presented in CIF format. Crystallographic data (excluding
structure factors) for the structure in this paper have been
deposited with the Cambridge Crystallographic Data
Centre, as supplementary publication number, CCDC Nos
923726, 898492 and 916187. Copies of data can be
obtained free of charge on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (Fax: þ44-(0) 1223-
336033 or email: deposit@ccdc.cam.ac.uk).
Compounds 1–4 are most selective towards fluoride as
compared with other anions and least selective towards
hydrogen sulphate ion with the exception of 3 having
methoxyphenyl group at meso-position. The latter is least
sensitive towards dihydrogen phosphate ion. The results
obtained from anion binding studies showed that the
compounds (Table 2) substituted with electron-withdraw-
ing group (1, 2) have higher binding constants than
compounds with electron-releasing group (3, 4). Com-
pound 2 with chlorophenyl substituent at meso-position
shows higher value of binding constant as than 1 with
fluorophenyl substituent at meso-position that may be
attributed to the presence of intermolecular hydrogen
bonding interactions between NH protons of one molecule
and the fluoro group present at the phenyl ring of another
molecule in 1. Similar interactions have also been reported
in the literature in case of b-monofluorocalix[4]pyrrole that
bound bromide, dihydrogen phosphate, hydrogen sulphate
less strongly than b-monochlorocalix[4]pyrrole (15).
Acknowledgements
The authors would like to thank Dr. B. R. Ambedkar National
Institute of Technology, Jalandhar, Punjab, India and Hans Raj
Mahila Maha Vidyalaya, Jalandhar, Punjab, India for their
support in carrying out the work. We gratefully acknowledge Mr.
Avtar Singh and Mr. Manish, NMR Lab, SAIF, Panjab
University, Chandigarh for recording NMR spectra.
References
(1) (a) Gale, P.A.; Sessler, J.L.; Kral, V.; Lynch, V. J. Am.
Chem. Soc. 1996, 118, 5140–5141; (b) Gale, P.A.;
Twyman, L.J.; Handlin, C.I.; Sessler, J.L. Chem. Commun.
1999, 18,1851–1852; (c) Nielsen, K.A.; Cho, W.S.;
Jeppesen, J.O.; Lynch, V.M.; Sessler, J.L.J. Am. Chem.
Soc. 2004, 126, 16296–16297; (d) Lee, C.H.; Lee, J.S.; Na,
H.K.; Yoon, D.W.; Miyaji H.; Cho, W.S.; Sessler, J.L.J. Org.
Chem. 2005, 70, 2067–2074; (e) Nishiyabu, R.; Anzenba-
cher Jr, P. J. Am. Chem. Soc. 2005, 127, 8270–8271.
Conclusion
(2) (a) Renic, M.; Basaric, N.; Majerski, K.M. Tetrahedron Lett.
2007, 48, 7873–7877; (b) Aleskovic, M.; Basaric, N.;
Majerski, K.M.; Molcanov, K.; Prodic, B.K.; Kesharwani,
M.K.; Ganguly, B. Tetrahedron 2010, 66, 689–1698; (c)
In summary, we have reported the synthesis of 5-methyl-5-
aryldipyrromethanes 1–4 and calix[4]pyrroles 4–8 in the
presence of milder, eco-friendly and versatile catalyst that

480
A. Sharma et al.
Piotrowski, T.; Radecka, H.; Radecki, J.; Depraetere, S.;
Dehaen, W. Mater. Sci. Eng. C 2001, 18, 223–228.
Hayakawa, J.; Ochi, T.; Masuda, R. Tetrahedron 1998, 54,
1407–1424; (f) Orlewska, C.; Maes, W.; Toppet, S.; Dehaen,
W. Tetrahedron Lett. 2005, 46, 6067–6070; (g) Turner, B.;
Botoshansky, M.; Eichen, Y. Angew. Chem. Int. Ed. 1998, 37,
2475–2478; (h) Hong, S.J.; Ka, J.W.; Won, D.H.; Lee, C.H.
Bull. Korean Chem. Soc. 2003, 24, 661–663; (i) Rohand, T.;
Dolusic, E.; Ngo, T.H.; Maes, W.; Dehaen, W. ARKIVOC,
2007, X, 307–324.
(3) (a) Guo, Y.; Shao, S.J.; Xu, J.; Shi, Y.P.; Jiang, S.X. Chin.
Chem. Lett. 2004, 15,1117–1119; (b) Guo, Y.; Shao, S.; Xu,
J.; Shi, Y.; Jiang, S. Tetrahedron Lett. 2004, 45, 6477–6480;
(c) Xu, J.; Guo, Y.; Shao, S.J. Chin. Chem. Lett. 2006, 17,
377–379; (d) Sessler, J.L.; Eller, L.R.; Cho, W.-S.;
Nicolaou, S.; Aguilar, A.; Lee, J.T.; Lynch, V.M.; Magda,
D.J. Angew. Chem. Int. Ed. 2005, 44, 5989–5992.
(4) (a) Sreedevi, K.C.G.; Thomas, A.P.; Salini, P.S.; Ramak-
rishnan, S.; Anju, K.S.; Holaday, M.G.D.; Reddy, M.L.P.;
Suresh, C.H.; Srinivasan, A. Tetrahedron Lett. 2011, 52,
5995–5999; (b) Chauhan, S.M.S.; Bisht, T.; Garg, B. Sens.
Actuators B 2009, 141, 116–123.
(5) (a) Gale, P.A.; Sessler, J.L.; Allen, W.E.; Tvermoes, N.A.;
Lynch, V. Chem. Commun. 1997, 665–666; (b) Anzenba-
cher Jr, P.; Try, A.C.; Miyazi, H.M.; Juriskova, K.; Lynch,
V.M.; Marquez, M.; Sessler, J.L.J. Am. Chem. Soc. 2000,
122, 10268–10272; (c) Anzenbacher, P.; Jurislorva, K;
Lynch, V.M.; Gale, P.A.; Sessler, J.L. J. Am. Chem. Soc.
1999, 121, 11020–11021; (d) Woods, C.J; Camiolo, S.;
Light, M.E.; Coles, S.J.; Hursthouse, M.B.; King, M.A;
Gale, P.A; Essex, J.W.J. Am. Chem. Soc. 2002, 124, 8644–
8652.
(10) (a) Sternberg, E.D.; Dolphin, D.; Bruckner, C. Tetrahedron
1998, 54, 4151–4202; (b) MacDonald, I.J.; Dougherty, T.J.
J. Porphyrins Phthalocyanines 2001, 5, 105–129; (c) Maes,
W.; Vanderhaeghen, J.; Smeets, S.; Asokan, C.V.; Renter-
ghem, L.M.V.; Du Prez, F.E.; Smet, M.; Dehaen, W. J. Org.
Chem. 2006, 71, 2987–2994; (d) Drain, C.M.; Hupp, J.T.;
Suslick, K.S.; Wasielewski, M.R.; Chen, X. J. Porphyrins
Phthalocyanines 2002, 6, 243–258; (e) Okura, I.
J. Porphyrins Phthalocyanines 2002, 6, 268-270.
(11) (a) Lee, C.H.; Lindsey, J.S. Tetrahedron 1994, 50, 11427–
11440; (b) Littler, B.J.; Miller, M.A.; Hung, C.H.; Wagner,
R.W.; O’Shea, D.F.; Boyle, P.D.; Lindsey, J.S.J. Org. Chem.
1999, 64, 1391–1396; (c) Kral, V.; Vasek, P.; Dolensky, B.
Collect. Czech. Chem. Commun. 2004, 69, 1126–1136; (d)
Okada, K.; Saburi, K.; Nomura, K.; Tanino, H. Tetrahedron
2001, 57, 2127–2131; (e) Naik, R.; Joshi, P.; Kaiwar, S.P.;
Deshpande, R.K. Tetrahedron 2003, 59, 2207–2213; (f)
Temelli, B.; Unaleroglu, C. Tetrahedron 2006, 62, 10130–
10135; (g) Gao, G.H.; Lu, L.; Gao, J.B.; Zhou, W.J.; Yang,
J.G.; Yu, X.Y.; He, M.Y. Chin. Chem. Lett. 2005, 16, 900–
902; (h) Zhang, Y.; Jun, L.; Zhicai, S. Chin. J. Chem. 2010,
28, 259–262; (i) Sobral, A.J.F.N.; Rebanda, N.G.C.L.; da
Silva, M.; Lampreia, S.H.; Silva, M.R.; Beja, A.M.; Paixao,
J.A.; Rocha Gonsalves, A.M.d’A. Tetrahedron Lett. 2003,
44, 3971–3973.
(12) (a) Sheldrick, G.M. Acta Crystallogr. 2008, A64, 112–122;
(b) Farrugia, L.J. J. Appl. Crystallogr. 1997, 30, 565–566;
(c) Altomare, A.; Burla, M.C.; Camalli, M.; Cascarano,
G.L.; Giacovazzo, C.; Guagliardi, A.; Moliterni, A.G.G.;
Polidori, G.; Spagna, R. J. Appl. Crystallogr. 1999, 32,
115–119; (d) Sheldrick, G.M.; SHELXTL/PC Siemens,
XCANS; Siemens Analytical X-ray Instruments: Madison,
WI, 1994; (e) Nardelli, M. Comput. Chem. 1983, 7, 95–97.
(13) Hynes, M.J. J. Chem. Soc. Dalton Trans. 1993, 2, 311–312.
(14) Nishiyabu, R.; Anzenbacher, Jr, P. Org. Lett. 2006, 8,
359–362.
(6) Bruno, G.; Cafeo, G.; Kohnke, F.H.; Nicolo, F. Tetrahedron
2007, 63, 10003–10010.
(7) (a) Schmidtchen, F.P.; Berger, M. Chem. Rev. 1997, 97,
1609–1646; (b) Antonisse, M.M.G.; Reinhoudt, D.N.
Chem. Commun. 1998, 443–448; (c) Allen, W.E.; Gale,
P.A.; Brown, C.T.; Lynch, V.M.; Sessler, J.L. J. Am. Chem.
Soc. 1996, 118, 12471–12472; (d) Sessler, J.L.; Maeda, H.;
Mizuno, T.; Lynch, V.M.; Furuta, H. Chem. Commun. 2002,
862–863; (e) Camiolo, S.; Coles, S.J.; Gale, P.A.;
Hursthouse, M.B.; Paver, M.A. Acta Crystallogr. Sect. E
2001, 57, 258–260; (f) Bachmann, J.; Nocera, D.G. J. Am.
Chem. Soc. 2005, 127, 4730–4743; (g) Bhattacharya, D.;
Dey, S.; Maji, S.; Pal, K.; Sarkar, S. Inorg. Chem. 2005, 44,
7699–7701.
(8) Chakrabarti, P.J. Mol. Biol. 1993, 234, 463–482.
(9) (a) Lee, C.H.; Li, F.; Iwamoto, K.; Dadok, J.; Bothnerby,
A.; Lindsey, J.S. Tetrahedron 1995, 51, 11645–11672;
(b) Shanmugathasan, S.; Edwards, C.; Boyle, R.W.
Tetrahedron 2000, 56, 1025–1046; (c) Lindsey, J.S.;
Schreiman, I.C.; Hsu, H.C.; Kearney, P.C.; Marguerettaz,
A.M. J. Org. Chem. 1987, 52, 827–836; (d) Hong, S.J.; Lee,
M.H.; Lee, C.H. Bull. Korean Chem. Soc. 2004, 25, 1545–
1550; (e) Setsune, J.; Hashimoto, M.; Shiozawa, K.;
(15) Miyaji, H.; An, D.; Sessler, J.L. Supramol. Chem. 2001, 13,
661–669.

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