Calix[4]arene Schiff bases-potential ligands for fluorescent studies

Article abstract of DOI:10.1016/j.tet.2008.09.091

A series of novel double-armed calix[4]arene derivatives incorporating imine substituents were synthesised from the Schiff-base reaction of 25,27-bis[2-[(1-formyl-2-phenyl)oxy]ethyl]-p-tert-butylcalix[4]arene (1) with the appropriate amine or hydrazone. All compounds were characterised by various spectroscopic and analytical techniques, and in three cases, by X-ray crystallographic studies. In the case of compound 2, inclusion compounds were synthesised with both m-xylene and dimethylformamide and their X-ray structures revealed these inclusion sites-between the pendant arms and in the upper cavity, respectively. In all cases, the pendant arms are bent away from each rather than adopting a face-to-face conformation.

Full text of DOI:10.1016/j.tet.2008.09.091

Tetrahedron 64 (2008) 11058–11066
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Calix[4]arene Schiff basesdpotential ligands for fluorescent studies
,
b
b
Mary F. Mahon a, John McGinley b , A. Denise Rooney , John M.D. Walsh
*
a X-ray Crystallographic Unit, Department of Chemistry, University of Bath, Bath BA2 7AY, United Kingdom
b Chemistry Department, National University of Ireland Maynooth, Maynooth, Co. Kildare, Ireland
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel double-armed calix[4]arene derivatives incorporating imine substituents were syn-
thesised from the Schiff-base reaction of 25,27-bis[2-[(1-formyl-2-phenyl)oxy]ethyl]-p-tert-butylca-
lix[4]arene (1) with the appropriate amine or hydrazone. All compounds were characterised by various
spectroscopic and analytical techniques, and in three cases, by X-ray crystallographic studies. In the case
of compound 2, inclusion compounds were synthesised with both m-xylene and dimethylformamide and
their X-ray structures revealed these inclusion sitesdbetween the pendant arms and in the upper cavity,
respectively. In all cases, the pendant arms are bent away from each rather than adopting a face-to-face
conformation.
Received 30 June 2008
Received in revised form 11 September
2008
Accepted 25 September 2008
Available online 8 October 2008
Keywords:
Calix[4]arene
Schiff bases
X-ray structure
NMR spectroscopy
Inclusion
Ó 2008 Elsevier Ltd. All rights reserved.
Synthesis
1. Introduction
incorporated onto both the upper and the lower rims of calix[4]-
arenes and their ability to complex transition metals assessed.2a,c,4
Calix[4]arenes, containing three-dimensional cavities, are pop-
ular building blocks in supramolecular chemistry, especially in
molecular recognition.1 Their controlled synthetic functionalisation
allows the use of these compounds in supramolecular chemistry as
molecular scaffolds for the construction of various receptors.
Modified calix[4]arene derivatives, having additional binding sites
at the lower rim, enhance the binding ability of the parent cal-
ix[4]arene. They are frequently employed as platforms that permit
functional groups to be orientated to provide well-organised cavi-
ties. Their development as a force within supramolecular chemistry
has resulted from their synthetic availability and their relative ease
of modification, coupled with the presence of various cavities,
which are capable of binding cationic, anionic or neutral species,
which becomes apparent from the number of review articles and
books available.1
Recently, a number of papers have appeared in the literature
concerned with the synthesis and characterisation of Schiff-base
derivatives of calix[4]arenes and their application in either photo-
chromic studies or as ion-selective extractants.2 Schiff bases offer
potential as optical switches resulting from their intramolecular
hydrogen transfer ability from the hydroxyl oxygen to the imine
nitrogen, in both solution and solid state.2b,3 They have been
As part of a broad study of the interactions of various functional
groups at both the wide and the narrow rims, we have prepared
and characterised various calix[4]arene derivatives and their metal
complexes.5 Part of our current investigations into calix[4]arene
compounds involves the investigation of their potential use as
fluorescent sensors. As a part of that study, this paper describes the
calix[4]arene lower rim functionalisation with a variety of Schiff-
base ligands (Scheme 1), their syntheses and characterisation and
a discussion of their subsequent structures. Our goal is to study the
binding properties of transition metal ions with these Schiff-base
calix[4]arene compounds and to investigate any interesting prop-
erties resulting from these complexation reactions. The comparison
of any X-ray crystal structures of metal complexes of the pendant
Schiff-base calix[4]arenes with the X-ray structures of the
calix[4]arene derivates described in this paper will be very in-
formative. Binding studies on metal complexes will be reported in
due course.6
2. Results and discussion
2.1. Synthesis
The synthesis of the starting calix[4]arene, p-tert-
butylcalix[4]arene aldehyde 1, was carried out according to
the reported literature procedure,7 involving the reaction of
* Corresponding author. Tel.: þ353 1 708 4615; fax: þ353 1 708 3815.
E-mail address: john.mcginley@nuim.ie (J. McGinley).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.09.091

M.F. Mahon et al. / Tetrahedron 64 (2008) 11058–11066
11059
O
O
OH
O
O
OH
O
O
OH
O
O
OH
N
i
OH
NC
N
CN
HO
N
CN
N
NC
N
N
NH2
H2N
2
7
vii
vi
ii
O
OH
O
O
O
O
O
OH
OH
OH
O
O
O
O
OH
OH
N
N
O
NH2
N
O
N
N
H2N
N
N
CHO
N
CHO
6
3
1
iv
iii
v
O
O
O
O
OH
OH
O
O
OH
OH
N
OMe
OH
5
MeO
O
O
N
N
N
N
4
HO
N
Scheme 1. Reaction conditions: (i) salicylaldehyde hydrazone, acetic acid, abs ethanol, rt, 24 h; (ii) hydrazine hydrate, acetonitrile, rt, 12 h; (iii) hydrazine hydrate, ethanol,
(iv) ethanol, , 24 h; (v) o-vanillin hydrazone, abs ethanol, , 1 h; (vi) 2-pyridine hydrazone, ethanol, rt, 96 h; (vii) diaminomaleonitrile, acetic acid, abs ethanol, rt, 24 h.
D
, 21⁄2 h;
D
D
2-(20-bromoethoxy)benzaldehyde with p-tert-butylcalix[4]arene.
Compounds o-vanillin hydrazone8 and pyridine hydrazone9 have
been previously reported and were synthesised here using a modi-
fied procedure. The Schiff-base reactions of 1 with the various
hydrazones or amine compounds were carried out at room tem-
perature togive the products shown in Scheme 1 in highyield. When
a reaction mixturewas heated, as in the case of 3 going to4, wefound
that the cyclic system was obtained. This intramolecular reaction
occurred, presumably, because of the presence of water in our sol-
vent system, thereby causing one pendant imine to decompose to
the original aldehyde, which would subsequently react with the
remaining amine to give the cyclic system, as shown in 4. We have
previously observed this type of behaviour involving amide bonds
rather than amine bonds,5b,10 while other groups have observed
similar reactions with other Schiff-base compounds.11 All the com-
pounds were characterised by CHN analyses and by 1H and 13C NMR
spectroscopy.
The cone conformation for 1–7 was derived from the bridging
methylene proton signals. In all cases, a pair of doublets in the 1H
NMR spectra were observed between
d
3.1 and 4.4 with J¼12.7–
13 Hz. The 1,3-disubstitution of the lower rim was confirmed by the
appearance of two singlet resonances for both the aromatic protons
of the calix[4]arenes and the methyl protons of the tert-butyl
groups, with the actual positions of the signals dependant on the
substituent attached. The formation of the imine compounds 2–7
was determined by the loss of the signals due to the aldehyde group
of 1 at
spectra and the appearance of signals at w
spectra and at w
d
10.50 in the 1H NMR spectra and at
d
190.2 in the 13C NMR
8–9.3 in the 1H NMR
d
d
150–160 in the 13C NMR spectra, depending on
the substituent attached to the imine nitrogen atom. These values
Table 1
1H NMR chemical shifts of calix[4]arenes 1–7 (300 MHz)
No. Solvent
Lower rim
Calixarene core
Upper rim
OCH2 OH –HCN– –CH2– –CH2– Ar–H Ar–H t-Bu t-Bu
2.2. NMR data
1
2
3
4
5
6
7
CDCl3
CDCl3
CDCl3
CDCl3
CDCl3
CDCl3
4.40 7.49
d
4.30
4.33
4.39
4.31
4.31
4.36
4.25
3.31
3.27
3.33
3.11
3.12
3.28
3.38
7.00 6.88 1.25 1.02
6.96 6.85 1.17 1.00
7.06 6.85 1.27 1.00
6.94 6.78 1.23 0.92
6.93 6.78 1.23 0.93
6.97 6.87 1.21 1.01
4.40 7.46 8.64
4.24 7.77 8.21
4.45 7.28 9.02
4.44 7.35 8.71
The structures of 1–7 were fully characterised using 1H and 13
C
NMR spectroscopy. Table 1 shows the 1H NMR values for the tert-
butyl, aromatic protons, bridging methylene proton and chain
methylene proton signals for 1–7 as well as the imine proton sig-
nals for 2–7.
4.37
7.67 8.62
DMSO-d6 4.36 8.33 8.76
7.13
7.08 1.22 1.15

11060
M.F. Mahon et al. / Tetrahedron 64 (2008) 11058–11066
compare favourably with those previously reported for other lower
rim calix[4]arene Schiff-base compounds.2c,d,4b–e,7,12 The unreacted
hydroxyl proton signal appears in the 1H NMR spectra of all the
sharp band is observed at 3534 and 3460 cmꢀ1, respectively, which
is due to the presence of a free NH2 group in both of these com-
pounds. Because of the complexity of compounds 1–7 and also
their resulting IR spectra, it is impossible to assign other bands with
confidence.
compounds as a sharp singlet between wd 7.3 and 7.9, with the
variation in the position being an indication of the strength of the
intramolecular hydrogen bond to the oxygen atom of the neigh-
bouring ring of the calix[4]arene. The bridging ethylene protons of
the linker chain appear in the 1H NMR spectra of compounds, 1–7,
2.4. X-ray crystallographic studies
as a multiplet centred at w
d 4.4, except in the case of 3 where the
Table 2 gives the crystal data and refinement parameters for the
four structures and Table 3 gives the intramolecular hydrogen
bonds in each of the four structures.
multiplet is found at 4.24.
d
The four aromatic proton signals of the phenyl ring appear as
multiplets in the 1H NMR spectra of compounds 1–7, some of which
are overlapping. In the case of compounds 2 and 5, it is difficult to
distinguish between the two phenyl rings, which are present in the
pendant arm attached to the lower rim. However, in the cases of 3,
4, 6 and 7, the four signals are easily discernable and differ signif-
icantly from the starting calix[4]arene dialdehyde compound 1.
Again, the position of the four signals was dependant on the sub-
stituent attached to the imine nitrogen atom.
The asymmetric unit of 2a contains one functionalised cal-
ix[4]arene molecule, which has trapped one molecule of m-xylene.
The final molecular structure is shown in Figure 1. The asymmetric
unit of 2b contains the same functionalised calix[4]arene molecule
as in 2a, but this time the calix[4]arene contains one molecule of
dimethylformamide (DMF), which is trapped in the upper cavity.
The molecular structure is shown in Figure 2. The asymmetric unit
of 4 contains one functionalised calix[4]arene molecule, with one
molecule of DMF trapped within the upper cavity, similar to that
observed in 2b. The final molecular structure is shown in Figure 3.
The asymmetric unit of 7 consists of two derivatised calix[4]arene
molecules and three ethyl acetate solvent molecules. The molecular
structure of the functionalised calix[4]arene is shown in Figure 4.
The calix[4]arene is present in all cases in a symmetrical cone
conformation, except in the case of 7 where the calix[4]arene is
present in a slightly flattened cone conformation. The cone con-
formation in all cases is stabilised by two intramolecular H-bonds
between the hydroxyl oxygens and the substituted oxygens, given
in Table 3. These values are within the range of previously pub-
lished values for the intramolecular H-bonds between the hydroxyl
oxygens and the substituted oxygens at the lower rim of a cal-
ix[4]arene.2c,5f,14 The only other intramolecular H-bonds observed
in 2a and 2b are between the Schiff-base hydroxyl hydrogens and
the imine nitrogens, again within the range of previously published
values for the intramolecular H-bonds between the hydroxyl oxy-
gens and imine nitrogen atoms.15 In the case of 4, one intra-
molecular H-bond is observed between the ether oxygen (O5) and
the imine nitrogen (N3) (O5/N3 2.741(2) Å, respectively). Only one
intramolecular bond is observed as a result of the trans nature of
the two C]N double bonds. This results from the lone pair situated
The various substituents attached to the imine group are also
easily distinguishable in both the 1H and the 13C NMR spectra of
compounds 2–7. In 2, the additional imino-phenol group is clearly
observed by a second imine singlet at
singlet for the phenolic OH group at 11.71. In 3, the primary amine
appears as a broad singlet at 4.95. In 5, the imino-o-vanillin group
can be seen by the second imine singlet at 8.71, a broad singlet for
the phenolic OH group at 11.57 and a singlet for the methoxy
group at 3.94. The presence of the pyridyl group in 6 is clearly
d 8.64 as well as a broad
d
d
d
d
d
observed as a well-defined series of doublets and triplets, as
expected for a 2-pyridyl group.5c,e,13
2.3. IR data
The major difference in the IR spectrum of 1 compared to those
of 2–7 is the presence of an aldehyde peak at 1682 cmꢀ1 in 1 and
the absence of this peak in the Schiff-base compounds 2–7. In the
case of 7, two bands at 2232 and 2205 cmꢀ1 are observed, which are
indicative of the presence of the nitrile groups. The 3200–
3600 cmꢀ1 region of the spectra of 1–7 contains a broad band with
a peak at w3350 cmꢀ1, which is due to the several OH groups
present in all the compounds. In the case of 3 and 7, an additional
Table 2
Crystal data and refinement parameters for 2a, 2b, 4 and 7
2a
2b
4
7
Empirical formula
Formula weight
Crystal system
Space group
C84H94N4O8
1287.63
Triclinic
Pꢀ1
C79H91N5O9
1254.57
Monoclinic
P21/c
C65H79N3O7
1014.31
Monoclinic
P21/c
C152H174N16O18
2513.07
Triclinic
Pꢀ1
Dimensions
a¼10.8820(1) Å,
b¼15.1550(1) Å,
c¼22.8020(1) Å,
U¼3687.41(5) Å3
Z¼2
a
¼101.083(1)ꢁ
a¼17.1160(2) Å,
a
¼90ꢁ
a¼12.6560(1) Å,
b¼35.8240(3) Å,
c¼13.2220(1) Å,
a
b
¼90ꢁ
a¼17.8530(1) Å,
b¼20.9960(2) Å,
c¼21.7370(2) Å,
a
¼100.136(1)ꢁ
b
¼91.568(1)ꢁ
b¼13.4260(1) Å,
c¼30.6690(4) Å,
b
¼94.738(1)ꢁ
¼90ꢁ
¼95.486(1)ꢁ
b
¼103.846(1)ꢁ
g
¼91.306(1)ꢁ
g
g
¼90ꢁ
g
¼109.330(1)ꢁ
U¼7023.63(13) Å3
U¼5967.25(8) Å3
U¼7169.76(10) Å3
Z¼4
Z¼4
Z¼2
Density (calcd)
m
1.160 mg mꢀ3
0.074 mmꢀ1
1380
1.186 mg mꢀ3
0.077 mmꢀ1
2688
1.129 mg mꢀ3
0.073 mmꢀ1
2184
1.164 mg mꢀ3
0.077 mmꢀ1
2684
F(000)
Crystal size
Range for data
0.60ꢂ0.50ꢂ0.50 mm
0.25ꢂ0.20ꢂ0.10 mm
0.35ꢂ0.20ꢂ0.10 mm
0.30ꢂ0.30ꢂ0.25 mm
3.51–27.65ꢁ
3.56–27.49ꢁ
3.53–27.44ꢁ
3.86–27.48ꢁ
collection (q)
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit
56,708
16,861
16,861/0/863
1.026
101,843
16,068
16,068/12/863
1.013
82,356
13,578
13,578/0/692
1.017
136,944
32,677
32,677/3/1731
1.016
Final R indices [I>2
R indices (all data)
Largest diff.
s
(I)]
R1¼0.0639, wR2¼0.1668
R1¼0.0860, wR2¼0.1864
1.093 and ꢀ0.562 e Åꢀ3
R1¼0.0646, wR2¼0.1336
R1¼0.1375, wR2¼0.1630
0.343 and ꢀ0.376 e Åꢀ3
R1¼0.0554, wR2¼0.1134
R1¼0.1104, wR2¼0.1355
0.400 and ꢀ0.331 e Åꢀ3
R1¼0.0715, wR2¼0.1760
R1¼0.1207, wR2¼0.2085
1.031 and ꢀ0.476 e Åꢀ3
peak and hole
Deposition number
CCDC 692925
CCDC 692926
CCDC 692927
CCDC 692928

M.F. Mahon et al. / Tetrahedron 64 (2008) 11058–11066
11061
Table 3
one of the N-methyl groups points directly into the cavity while the
C]O group is pointing away from the cavity, as Takemura and co-
workers had observed in the DMF inclusion complexes of homo-
Intramolecular hydrogen bond distances for structures 2a, 2b, 4 and 7
O/O (Å)
O/N (Å)
azacalix[4]arenes.17b A CH/
p interaction between an N–Me group
2a
2b
4
2.809(2), 2.797(2)
2.706(2), 2.747(2)
2.673(2), 2.740(2)
2.797(2), 2.991(2)
2.641(2), 2.642(2)
2.678(3), 2.564(6)
2.741(2)
of the DMF and the benzene ring of the calix[4]arene was clearly
observed, as indicated by the short contacts between the N–Me
carbon (C79) and its protons and the aromatic rings. Table 4 sum-
marises these short contacts. Furthermore, although the solvent is
now included in a different position, compared to that of the m-
xylene molecule, the same folding of the pendant arms is observed.
The CH/p interaction between an N–Me group of the DMF and the
benzene ring of the calix[4]arene in 4 was again clearly observed,
and is summarised in Table 4.
7
d
on the second nitrogen of the double bond pointing away from the
other ether oxygen atom (O2). A similar situation was reported by
Sukwattanasinitt and co-workers in their study of azobenzene-
bridged crown ether calix[4]arenes.16
An interesting feature of the crystal structures 2a, 2b and 7 is
that the two pendant arms do not exist in a face-to-face orientation,
but instead are bent away from each other. This type of orientation
has been previously observed by Kim and co-workers18 in their
papers on pyrene-containing calix[4]arene derivatives and by Beer
and co-workers.19 However, their functionalised calix[4]arenes are
attached to the lower rim by means of an amide bond. The hy-
drogen atom of this amide bond formed an intramolecular H-bond
with the oxygen atom of the phenolic hydroxyl group in the cal-
ix[4]arene ring. This H-bond, along with the H-bonds formed be-
tween the phenolic hydrogens and the phenol ethers to give the
cone conformation, combined to orient both the pyrene groups18
and the ferrocene groups19 away from each other in both cases. This
cannot be the reason in our cases as there are no amide bonds
present in either of the three structures. Furthermore, the effect of
Inclusion solvent molecules are observed in 2a, 2b and 4. The
average distance between the centroid of the m-xylene fragments
and the centroids of the two calix[4]arene phenyl rings is 4.9 Å. The
position of the m-xylene molecule led us to believe that this was
responsible for the bending away of the pendant arms of the cal-
ix[4]arene derivative in the manner shown in Figure 1. In order to
observe the role played by the solvent in the structural conforma-
tion, we decided to change the solvent to DMF and see if this new
host–guest interaction would result in a different conformation of
the pendant arms.
The cone conformation of 2b helps in the formation of an
intercavity inclusion complex with a molecule of DMF. Several in-
clusion complexes of DMF in calix[4]arene derivatives have been
reported previously.17 The DMF molecule, in this case, is positioned
inside the upper cavity of the calix[4]arene in such a manner that
Figure 1. Molecular structure of 2a showing selected labels. Hydrogens from functionalities that do not contribute to hydrogen bonding with the asymmetric unit are omitted for
clarity. Ellipsoids are displayed at the 30% probability level.

11062
M.F. Mahon et al. / Tetrahedron 64 (2008) 11058–11066
Figure 2. Molecular structure of 2b showing selected labels. Hydrogens from functionalities that do not contribute to hydrogen bonding with the asymmetric unit are omitted for
clarity. Ellipsoids are displayed at the 30% probability level.
Figure 3. Molecular structure of 4 showing selected labels. Hydrogens from functionalities that do not contribute to hydrogen bonding with the asymmetric unit are omitted for
clarity. Ellipsoids are displayed at the 30% probability level.

M.F. Mahon et al. / Tetrahedron 64 (2008) 11058–11066
11063
Figure 4. Molecular structure of 7 showing selected labels. Hydrogens from functionalities that do not contribute to hydrogen bonding with the asymmetric unit are omitted for
clarity. Ellipsoids are displayed at the 30% probability level.
included solvent molecules can be excluded as the X-ray crystal
structures of 2 containing m-xylene and DMF were obtained, and
although the solvent was found in two different inclusion sites, the
folding away of the pendant arms resulted in both cases. One
possible explanation is steric interactions. The pendant arms are
bent away from each other since if they were in a face-to-face
conformation then the arms would be in very close proximity and
would probably collide with each other. However, a possible an-
swer for this orientation can be found when the space-filled dia-
grams are considered. Figure 5 shows the space-filled diagram for
structure 2a as viewed from beneath. The m-xylene molecule is
shown in orange while the carbon, nitrogen and oxygen atoms are
in green, blue and red, respectively. This view shows that the two
oxygen atoms (O5 and O6), which are connected by two methylene
units, are in close proximity to each other with a distance of 2.91 Å
separating the two atoms. Where hydrogen bonding is possible
within the pendant groups, it is exploited in the solid-state
structure and the resulting conformation utilises it. Analysis of the
supramolecular arrays in all cases does not afford additional insight
in the pendant orientations. The molecules pack in a way that gives
low energy solid-state structures, with no obvious p–p stacking. A
second feature of the crystal structures 2a, 2b and 7 is that if the
methylene groups are ignored, the pendant arms are almost planar.
This planarity suggests that there is extended
p-conjugation
throughout the functionalised arm. This type of -conjugation has
p
been previously reported for calix[4]arenes at both the upper and
the lower rims.20
Table 4
Distances between N–Me and benzene rings (Å), shown to two decimal places
Me(DMF)/
p
plane 1
3.73 and 3.91
Me(DMF)/p plane 2
2b
4
C(79)
C(79)
x.x
2.78
x.x
H(79C)
C(65)
H(65C)
2.76
3.84 and 3.92
2.88
H(79A)
C(65)
H(65A)
2.86
Plane 1 of 2b: C(1)–C(2)–C(3)–C(4)–C(5)–C(6).
Plane 2 of 2b: C(34)–C(35)–C(36)–C(37)–C(38)–C(39).
Plane 1 of 4: C(1)–C(2)–C(3)–C(4)–C(5)–C(6).
Plane 2 of 4: C(34)–C(35)–C(36)–C(37)–C(38)–C(39).
Figure 5. Space-filled view of 2a showing proximity of oxygen atoms (shown in red).

11064
M.F. Mahon et al. / Tetrahedron 64 (2008) 11058–11066
3. Conclusion
required product (0.58 g, 91%); nmax (KBr)/cmꢀ1 3368, 3181, 1583,
1565, 1473, 1389, 1150, 993, 776, 622; dH (300 MHz, CDCl3, Me4Si)
5.83 (2H, br s, NH2), 7.17 (1H, m, Ar–H), 7.65 (1H, m, Ar–H), 7.77 (1H,
m, Ar–H), 7.83 (1H, s, HC]N), 8.54 (1H, m, Ar–H); dC (75 MHz,
CDCl3, Me4Si) 119.7, 122.8, 136.3, 142.6, 149.2, 154.3.
The Schiff-base reactions between 1 and various amines or
hydrazones resulted in a series of pendant Schiff-base calix[4]arene
derivatives. X-ray crystallographic studies of three of these con-
firmed both the cone conformation of the calix[4]arene and the
imine formation. They also showed that the pendant arms did not
adopt a face-to-face conformation but instead were bent away from
each other. These conformations were brought about by steric
constrictions, as well as the formation of additional intramolecular
interactions between hydroxyl groups on the pendant arms and an
aromatic ring of the calix[4]arene.
4.2.4. Compound 2
The ortho-substituted dialdehyde calix[4]arene
1
(2.0 g,
2.1 mmol) in absolute ethanol (50 mL) and acetic acid (2 mL) and
salicylaldehyde hydrazone (0.69 g, 5.1 mmol) in absolute ethanol
(100 mL) were stirred at room temperature for 24 h. The resulting
yellow precipitate was removed by filtration, washed with ethanol
and dried in the oven to give 2$hemihydrate (2.18 g, 87%) as
a yellow solid, mp 166–168 ꢁC. (Found: C, 76.80; H, 6.94; N, 4.66.
(C76H84N8O8)2$H2O requires: C, 76.67; H, 7.20; N, 4.71%.) nmax (KBr)/
cmꢀ1 3457, 3354, 2956, 2887, 1624, 1603, 1576, 1486, 1274, 1056,
750; dH (300 MHz, CDCl3, Me4Si) 1.00 (18H, s, t-Bu), 1.17 (18H, s,
t-Bu), 3.27 (4H, d, J¼13.0, ArCH2Ar), 4.33 (4H, d, J¼13.0, ArCH2Ar),
4.40 (8H, m, OCH2CH2O), 6.85 (4H, s, Ar–H), 6.91 (2H, m, Ar–H), 6.96
(4H, s, Ar–H), 7.02 (6H, m, Ar–H), 7.27 (2H, m, Ar–H), 7.33 (2H, m,
Ar–H), 7.42 (2H, m, Ar–H), 7.46 (2H, s, calix-OH), 8.08 (2H, m, Ar–H),
8.64 (2H, s, HC]N), 9.12 (2H, s, HC]N), 11.71 (2H, s, Ar–OH); dC
(75 MHz, CDCl3, Me4Si) 31.0, 31.6, 31.7, 33.7, 34.0, 67.2, 73.6, 112.0,
116.9, 117.8, 119.2, 121.1, 122.6, 125.1, 125.7, 127.5, 127.7, 132.2, 132.6,
132.8, 132.9, 141.5, 147.2, 149.6, 150.3, 158.2, 158.4, 159.9, 164.1.
4. Experimental
4.1. General
1H and 13C NMR (
d ppm, J Hz) spectra were recorded on a Bruker
Avance 300 MHz NMR spectrometer using saturated CDCl3 solu-
tions with Me4Si reference, unless indicated otherwise, with reso-
lutions of 0.18 Hz and 0.01 ppm, respectively. Infrared spectra
(cmꢀ1) were recorded as KBr discs or liquid films between KBr
plates using a Perkin Elmer System 2000 FT-IR spectrometer.
Melting point analyses were carried out using a Stewart Scientific
SMP 1 melting point apparatus and are uncorrected. Microanalysis
was carried out at the Microanalytical Laboratory of either Uni-
versity College, Dublin or the National University of Ireland Cork.
Standard Schlenk techniques were used throughout. Starting ma-
terials were commercially obtained and used without further
purification.
4.2.5. Compound 3
A solution of dialdehyde calix[4]arene 1 (0.5 g, 0.5 mmol) in
acetonitrile (50 mL) was added dropwise, over 20 min, to hydrazine
hydrate (0.53 g, 10.6 mmol). The resulting pale yellow solution was
stirred for 12 h. After this time, the solvent was removed under
reduced pressure and the residue was treated with ethanol (20 mL)
from which a white solid precipitated. This solid was removed by
filtration, washed with ethanol and dried in the oven to give 3
(0.40 g, 76%) as a white solid, mp 218–220 ꢁC. (Found: C, 76.52; H,
7.87; N, 5.94. C62H76N4O6 requires: C, 76.51; H, 7.87; N, 5.75%.) nmax
(KBr)/cmꢀ1 3534, 3378, 2961, 1687, 1600, 1485, 1289, 1058, 924,
756; dH (300 MHz, CDCl3, Me4Si) 1.00 (18H, s, t-Bu), 1.27 (18H, s,
t-Bu), 3.33 (4H, d, J¼13.0, ArCH2Ar), 4.24 (8H, m, OCH2CH2O), 4.39
(4H, d, J¼13.0, ArCH2Ar), 4.95 (4H, br s, NH2), 6.72 (2H, m, Ar–H),
6.85 (4H, s, Ar–H), 6.93 (2H, m, Ar–H), 7.06 (4H, s, Ar–H), 7.17 (2H,
m, Ar–H), 7.75 (2H, m, Ar–H), 7.77 (2H, s, calix-OH), 8.21 (2H, s,
HC]N); dC (75 MHz, CDCl3, Me4Si) 31.1, 31.7, 33.9, 34.0, 66.8, 74.2,
111.7, 121.1, 124.2, 125.3, 125.6, 125.7, 127.6, 129.6, 132.6, 139.7, 141.7,
147.2, 149.6, 150.7, 155.8.
4.2. Synthetic procedures
The synthesis of compounds 1,7 o-vanillin hydrazone8 and pyr-
idine hydrazone9 has been described in the literature previously.
4.2.1. Compound 1
The ortho-substituted dialdehyde calix[4]arene 1 was prepared
as described in the literature;7 dH (300 MHz, CDCl3, Me4Si) 1.02
(18H, s, t-Bu), 1.25 (18H, s, t-Bu), 3.31 (4H, d, J¼12.9, ArCH2Ar), 4.30
(4H, d, J¼12.9, ArCH2Ar), 4.40 (8H, m, OCH2CH2O), 6.88 (4H, s, Ar–
H), 7.0 (4H, m, Ar–H), 7.02 (4H, s, Ar–H), 7.49 (2H, s, calix-OH), 7.50
(2H, m, Ar–H), 7.83 (2H, m, Ar–H), 10.50 (2H, s, HC]O); dC (75 MHz,
CDCl3, Me4Si) 31.1, 31.7, 31.8, 33.8, 34.0, 67.5, 73.6,112.4,121.0,125.2,
125.8, 127.8, 128.3, 132.7, 135.8, 141.8, 147.4, 149.8, 150.3, 160.8,
190.2.
4.2.6. Compound 4
4.2.2. o-Vanillin hydrazone
A solution of dialdehyde calix[4]arene 1 (1.0 g, 1.06 mmol) and
salicylaldehyde hydrazone (0.6 g, 4.43 mmol) was heated to reflux
in ethanol (60 mL) for 3 h. On cooling, a yellow solid precipitated,
which was removed by filtration, washed with ethanol and dried in
the oven to give 4$hydrate (0.45 g, 46%) as a yellow solid, mp 210–
212 ꢁC (Found: C, 77.67; H, 7.59; N, 2.69. C62H74N2O7 requires: C,
77.63; H, 7.78; N, 2.92%.) nmax (KBr)/cmꢀ1 3435, 2960, 1621, 1601,
1485,1253,1161,1052, 751; dH (300 MHz, CDCl3, Me4Si) 0.92 (18H, s,
t-Bu), 1.23 (18H, s, t-Bu), 3.11 (4H, d, J¼12.9, ArCH2Ar), 4.31 (4H, d,
J¼12.9, ArCH2Ar), 4.45 (8H, m, OCH2CH2O), 6.78 (4H, s, Ar–H), 6.88
(2H, m, Ar–H), 6.94 (4H, s, Ar–H), 7.01 (2H, m, Ar–H), 7.28 (2H, s,
calix-OH), 7.36 (2H, m, Ar–H), 7.82 (2H, m, Ar–H), 9.02 (2H, s,
HC]N); dC (75 MHz, CDCl3, Me4Si) 31.0, 31.1, 31.7, 33.7, 38.9, 65.7,
73.6, 111.6, 120.9, 123.7, 124.8, 125.5, 127.7, 130.9, 131.5, 133.0, 141.0,
146.9, 149.0, 150.6, 157.2, 157.3.
o-Vanillin (1.0 g, 6.57 mmol) in ethanol (40 mL) was added
dropwise, over 20 min, to hydrazine hydrate (1.64 g, 32.86 mmol)
in ethanol (10 mL). The yellow solution was stirred for 1 h, after
which time the solvent was removed under reduced pressure to
leave a yellow oil. On standing, the oil crystallised into a yellow
solid, which was analysed as the required product (1.07 g, 88%), mp
168–170 ꢁC; nmax (KBr)/cmꢀ1 3380, 1620, 1576, 1468, 1320, 1246,
1090, 964, 838, 776, 625; dH (300 MHz, CDCl3, Me4Si) 3.90 (3H, s,
OCH3), 5.46 (2H, s, NH2), 6.87–6.72 (3H, m, Ar–H), 7.86 (1H, s,
HC]N), 11.20 (1H, s, OH); dC (75 MHz, CDCl3, Me4Si) 56.1, 112.3,
118.6, 118.8, 121.2, 146.6, 147.3, 148.1.
4.2.3. 2-Pyridine hydrazone
2-Pyridinecarboxaldehyde (0.5 g, 4.67 mmol) in ethanol (30 mL)
was added dropwise, over 20 min, to hydrazine hydrate (0.7 g,
14.0 mmol) in ethanol (10 mL). The yellow solution was stirred for
12 h, after which time the solvent was removed under reduced
pressure to leave a yellow/brown oil, which was analysed as the
A solution of 3 (50 mg, 0.05 mmol) was heated to reflux, under
nitrogen, in ethanol (8 mL) for 12 h, which resulted in a yellow
suspension. On cooling, the suspension was removed by filtration,
washed with ethanol and dried in the oven to give 4$hydrate

M.F. Mahon et al. / Tetrahedron 64 (2008) 11058–11066
11065
(45 mg, 88%) as a yellow solid, which gave identical IR and NMR
spectroscopic data to that outlined already.
evaporation. Crystallographic data were collected on a Nonius
KappaCCD area detector diffractometer using Mo K radiation
a
(
l
¼0.71073 Å) at a temperature of 150(2) K, and all structures were
4.2.7. Compound 5
solved by direct methods and refined on all F2 data using the
SHELXL-97 suite of programs.21 Hydrogen atoms not involved in
hydrogen bonding were included in idealised positions and refined
using the riding model. Absorption corrections were applied on
merit.
A solution of dialdehyde calix[4]arene 1 (0.36 g, 0.38 mmol) and
o-vanillin hydrazone (0.18 g, 0.98 mmol) in ethanol (20 mL) was
heated to reflux, under nitrogen, for 1 h. The pale yellow suspen-
sion was allowed to cool and the resulting solid was removed by
filtration, washed with ethanol and dried in the oven to give
5$dihydrate (0.31 g, 64%) as a yellow solid, mp 226–228 ꢁC. (Found:
C, 73.45; H, 7.08; N, 4.61. C78H88N4O10 requires: C, 73.32; H, 7.26; N,
4.39%.) nmax (KBr)/cmꢀ1 3376, 2961, 1682, 1560, 1459, 1394, 1248,
1075, 923, 756; dH (300 MHz, CDCl3, Me4Si) 0.93 (18H, s, t-Bu), 1.23
(18H, s, t-Bu), 3.12 (4H, d, J¼12.8, ArCH2Ar), 3.94 (6H, s, OCH3), 4.31
(4H, d, J¼12.8, ArCH2Ar), 4.44 (8H, m, OCH2CH2O), 6.78 (4H, s, Ar–
H), 6.91 (4H, m, Ar–H), 6.93 (4H, s, Ar–H), 7.03 (4H, m, Ar–H), 7.35
(2H, s, calix-OH), 7.37 (2H, m, Ar–H), 7.83 (2H, m, Ar–H), 8.71 (2H, s,
HC]N), 9.03 (2H, s, HC]N), 11.57 (2H, s, OH); dC (75 MHz, CDCl3,
Me4Si) 31.0, 31.1, 31.7, 33.7, 33.9, 56.2, 65.7, 73.6, 111.6, 115.1, 117.3,
119.4, 120.9, 123.7, 124.0, 124.8, 125.5, 127.6, 131.0, 131.5, 133.0,
140.9, 146.9, 148.3, 149.0, 150.6, 157.2, 157.3, 164.8.
A number of noteworthy points pertain to the refinements. In
particular, the asymmetric unit in 2a contains one molecule of the
calix[4]arene, which has trapped one molecule of m-xylene. This
solvent is disordered, and optimal modelling of this region of the
electron density map was achieved by isotropic refinement as two
fragments in a 60:40 ratio. The aromatic rings in both xylene
fragments were treated as rigid hexagons. C30–C40 also exhibited
disorder (55:45 ratio), which was readily modelled. In 2b, the
asymmetric units comprises one calix[4]arene molecule and one
molecule of DMF, the latter occupying the calix[4]arene pore. Dis-
order was also evident in this structure, with C70–76 and O8 being
equally disordered over two sites. In addition, the b-carbons in the
t-Bu group based on C18 are fragmented over two positions in an
85:15 occupancy ratio. One DMF solvent molecule is present in the
motif of compound 4, while the equivalent motif in 7 consists of
two derivatised calix[4]arene molecules and three solvent mole-
cules. One tertiary butyl group in each calix[4]arene (based on C7
and C99, respectively) exhibited disorder 65:35 of the methyl
groups. These partial carbons were treated isotropically. The ethyl
acetate molecule (containing O5S and O6S) also exhibited disorder
in a 65:35 ratio. The larger occupancy fragment was modelled an-
isotropically, while the minor portion was isotropically treated as
non-bonded, fragment atoms approximating to 0.35% of a mole-
cule. Although the partial hydrogen atoms could not be meaning-
fully included in the refinement for this latter moiety, they have
been included in the unit cell contents. To aid convergence, three
distance similarity restraints were applied to C–C, O–C and C/C
distance in the solvent. This latter structure was refined using full
matrix least squares. Since the number of parameters (1731) for this
structure exceeds the SHELXL21 array, SHELXH21 was used in the
final refinement cycles.
4.2.8. Compound 6
A solution of calix[4]arene 3 (0.54 g, 0.57 mmol) and 2-pyridine
hydrazone (0.43 g, 3.1 mmol) was stirred in ethanol (40 mL) for 4
days at room temperature. The resulting yellow suspension was
removed by filtration, washed with ethanol and dried in an oven to
give 6 (0.42 g, 63%) as a yellow solid, mp 166–168 ꢁC. (Found: C,
76.88; H, 7.09; N, 6.99. C74H82N6O6 requires: C, 77.17; H, 7.18; N,
7.29%.) nmax (KBr)/cmꢀ1 3348, 2959, 1690, 1602, 1485, 1450, 1250,
1058, 752; dH (300 MHz, CDCl3, Me4Si) 1.01 (18H, s, t-Bu), 1.21 (18H,
s, t-Bu), 3.28 (4H, d, J¼12.9, ArCH2Ar), 4.36 (4H, d, J¼12.9, ArCH2Ar),
4.37 (8H, m, OCH2CH2O), 6.87 (4H, s, Ar–H), 6.92 (2H, m, Ar–H), 6.97
(4H, s, Ar–H), 7.03 (2H, m, Ar–H), 7.29 (2H, m, Ar–H), 7.40 (2H, dt,
J¼7.7 and 1.7, Ar–H), 7.66 (2H, m, Ar–H), 7.67 (2H, s, calix-OH), 7.93
(2H, m, Ar–H), 8.14 (2H, dd, J¼7.7 and 1.7, Ar–H), 8.62 (2H, s, HC]N),
8.66 (2H, m, Ar–H), 9.24 (2H, s, HC]N); dC (75 MHz, CDCl3, Me4Si)
31.1, 31.6, 32.0, 33.8, 34.0, 67.2, 73.7, 112.1, 121.2, 122.0, 124.6, 125.1,
125.7,127.7,127.8,132.8,132.9,136.3,141.4,149.7,149.8,150.5,153.5,
158.2, 159.0, 160.9.
Table 2 summarises crystallographic parameters of all four
structures. CCDC 692925–692928 contain the supplementary
crystallographic data for this paper. This data can be obtained free
of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data on request.
4.2.9. Compound 7
A solution of dialdehyde calix[4]arene 1 (1.0 g, 1.05 mmol) and
diaminomaleonitrile (0.27 g, 2.55 mmol) was stirred together in
absolute ethanol (80 mL) and acetic acid (1 mL) for 24 h. The
resulting pale yellow solid was removed by filtration, washed with
ethanol and dried in the oven. The solvent of the filtrate was re-
moved under reduced pressure, the residue was taken up in
methanol and the insoluble yellow material removed by filtration.
The combined yellow materials was analysed as 7$(acetic acid)1.5
(1.15 g, 97%), mp 290–292 ꢁC (decomp.). (Found: C, 71.88; H, 6.49;
N, 9.43. C146H164N16O18 requires: C, 72.13; H, 6.80; N, 9.22%). nmax
(KBr)/cmꢀ1 3455, 3337, 2956, 2233, 2205, 1603, 1485, 1364, 1162,
924, 755; dH (300 MHz, DMSO-d6, Me4Si) 1.15 (18H, s, t-Bu), 1.22
(18H, s, t-Bu), 3.38 (4H, d, J¼12.7, ArCH2Ar), 4.25 (4H, d, J¼12.7,
ArCH2Ar), 4.36 (8H, m, OCH2CH2O), 7.08 (4H, s, Ar–H), 7.12 (2H, m,
Ar–H), 7.13 (4H, s, Ar–H), 7.20 (2H, m, Ar–H), 7.61 (2H, m, Ar–H), 7.74
(4H, s, NH2), 8.30 (2H, m, Ar–H), 8.33 (2H, s, calix-OH), 8.76 (2H, s,
HC]N); dC (75 MHz, CDCl3, Me4Si) 30.8, 31.3, 31.5, 33.5, 33.9, 67.2,
73.4, 103.7, 112.4, 113.5, 114.4, 120.8, 123.9, 125.0, 125.6, 126.2, 127.3,
128.0, 133.1, 133.2, 140.9, 146.9, 149.4, 150.0, 150.8, 158.0.
Acknowledgements
The authors would like to thank Dr. J. C. Stephens for useful and
helpful discussions. J.M.D.W. would like to thank North Tipperary
County Council and the National University of Ireland Maynooth for
financial assistance.
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