Synthesis and crystal structure of a novel phthalocyanine-calixarene conjugate

Article abstract of DOI:10.1142/S1088424611003628

We report the synthesis and crystal structure of a novel phthalocyanine-calixarene conjugate (Pc-Calix) derived from a calixarene-based phthalonitrile (Pn-Calix). Crystal structures confirm the retention of the full cone configuration of the calixarene un

Full text of DOI:10.1142/S1088424611003628

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2011; 15: 686–690
DOI: 10.1142/S1088424611003628
Published at http://www.worldscinet.com/jpp/
Synthesis and crystal structure of a novel phthalocyanine-
calixarene conjugate
C. Grazia Bezzua, Madeleine Helliwellb, Benson M. Kariukia and Neil B. McKeowna*
a School of Chemistry, Cardiff University, Cardiff CF10 3AT, United Kingdom
b School of Chemistry, University of Manchester, Manchester M13 9PL, United Kingdom
Dedicated to Professor Karl M. Kadish on the occasion of his 65th birthday
Received 18 May 2011
Accepted 27 May 2011
AbsTRACT: We report the synthesis and crystal structure of a novel phthalocyanine-calixarene
conjugate (Pc-Calix) derived from a calixarene-based phthalonitrile (Pn-Calix). Crystal structures
confirm the retention of the full cone configuration of the calixarene unit, which is thus suitable for the
binding of appropriate chemical species. This new conjugate may find application as a molecular sensor
in which the calixarene acts as the binding site and the perturbations of the optical properties of the
phthalocyanine reports the presence of the binding species.
keywORDs: phthalocyanine, calixarene, synthesis.
their cavity and complexation properties for different
INTRODUCTION
applications [13].
Phthalocyanines have been widely studied as molecu-
Due to the interest in both classes of organic materials,
lar materials because of their outstanding electronic and
it is desirable to prepare synthetic conjugates of phtha-
optical properties [1–3]. Apart from their extensive use
locyanines and calixarenes in which the functionality
as blue and green colorants, they have applications as the
of both partners are preserved. With this aim in mind,
active component in organic electronic devices [3], in
Nolan and coworkers [14] reported the synthesis of an
optical data storage [4], in photodynamic cancer therapy
[5], in solar energy conversion [6, 7], in sensors [8], in
catalysis [9], as liquid crystals [10, 11], and furthermore,
asymmetrical phthalocyanine that contained a single
dimethoxy-4-t-butylcalix[4]arene substituent. Due to the
partial cone conformation obtained for the phthalonitrile
they are excellent building blocks for supramolecular
precursor to this conjugate, one of the benzo units of the
chemistry [3]. Calixarenes are also a class of functional
resulting phthalocyanine fills the cavity of the calixarene.
organic molecules which have attracted much attention
Although this conformation blocks the binding func-
due to their ability to act as host molecules for both neu-
tionality of the calixarene, the remarkable ability of the
tral and charged species [12, 13]. They are a synthetically
calixarene substituent to prohibit self-association of the
versatile class of macrocyclic compound with a unique
phthalocyanine was demonstrated. Phthalocyanine dim-
bowl-like structure, which offers countless opportunities
ers bridged by one [15] or more [16–18] calixarene units
for functionalization on both their hydrophobic upper
have also been reported and various sensing, and spectro-
rim and hydrophilic lower rim. Much work has been
electrochemical properties examined.
devoted to the synthesis of calixarenes in order to tailor
Here we report the synthesis and crystal structure of an
asymmetrical octa-substituted phthalocyanine (Pc-Ca-
lix) in which a single 4-t-butylcalix[4]arene is introduced
onto the periphery. Of note is the full cone conformation
of the calixarene, which allows binding within its cav-
ity as demonstrated by the inclusion of the axial acetone
*Correspondence to: Neil B. McKeown, email: mckeownnb@
cardiff.ac.uk, tel: +44 (0)292-087-5851, fax: +44 (0)292-087-
4030
Copyright © 2011 World Scientific Publishing Company

SyntheSIS anD CryStal StruCture Of a nOvel PhthalOCyanIne-CalIxarene COnJugate
687
ligand of a neighboring Pc-Calix within its crystal struc-
with the chlorine substituent pointing toward the hydro-
philic lower rim (Figs 1a and 1b). The cone conformation
of Pn-Calix is in contrast to the partial cone configuration
obtained by Nolan and coworkers [14] for the products
formed between the analogous nucleophilic aromatic sub-
stitution reaction between 3- or 4-nitrophthalonitrile with
distal dimethoxy-4-t-butylcalix[4]arene. In order to obtain
the partial cone configuration, the phthalonitrile needs to
react with a calixarene phenol group from within the cav-
ity of the calixarene and it appears that the relatively large
chlorine atom next to the site of substitution on 4,5-di-
chlorophthalonitrile disfavors its approach via the cavity.
The retention of the full cone configuration has important
consequences for the potential functionality of the resul-
tant Pc-Calix in that the calixarene unit is free to engage
in the binding of suitable molecules. The packing arrange-
ment of the Pn-Calix molecules is composed of two
molecular layers with the upper rims of the calixarenes
facing each other to form capsule-like units that contain
two methanol molecules. This arrangement maximizes
hydrophobic and hydrophilic intermolecular interactions.
The pendant phthalonitrile substituents are positioned to
the side of the capsules and nitrile-nitrile close interac-
tions occur between two nitrile groups on neighboring
molecules (Fig. 1c), with the other nitrile interacting with
the hydroxyl groups within the same molecule.
The unsymmetrical Pc-Calix, derived from three
4,5-bis(2′,6′-di-i-propylphenoxy)phthalonitrile units and a
single Pn-Calix, is obtained from the Zn2+ mediated reac-
tion in NMP using a ratio of 9:1 of the two phthalonitrile
precursors, respectively (Scheme 1). Pc-Calix was iso-
lated in 12% yield from the complex product mixture by
column chromatography. The structure of Pc-Calix was
confirmed by Matrix Assisted Laser Desorption Ionisation
mass Spectrometry (MALDI MS), which showed a clus-
ter of peaks corresponding to the mass of the molecule.
1H NMR is also consistent with the structure of Pc-Calix
ture. Therefore, Pc-Calix might act as a molecular sensor
with the calixarene acting as the binding site with result-
ing perturbations of the optical properties of the phthalo-
cyanine reporting the presence of the bound species.
ResULTs AND DIsCUssION
The key intermediate for the synthesis of the phtha-
locyanine-calixarene conjugate (Pc-Calix) is the phtha-
lonitrile substituted calixarene (Pn-Calix), which is
obtained from the aromatic nucleophilic substitution
reaction between 4-t-butylcalix[4]arene and 4,5-dichlo-
rophthalonitrile in DMF using K2CO3 as base (Scheme 1).
Potential multiple substitution of the calixarene by phtha-
lonitrile is avoided by the use of a 1:1 stoichiometric ratio
of the two starting materials. Interestingly, only one of the
two activated chlorines of the phthalonitrile unit is sub-
stituted despite the possibility of a further intramolecu-
lar reaction with either the adjacent or opposite phenolic
groups on the calixarene. Indeed, attempts to force such
a reaction by heating pure Pn-Calix with K2CO3 in DMF
at higher temperatures (>150 °C) failed presumably due
to the highly constrained nature of both of the potential
products (Scheme 1). Mass spectrometry, NMR and a sin-
gle crystal X-ray diffraction (XRD) study confirmed the
structure of Pn-Calix. The pattern of the methylene proton
signals in the 1H NMR spectrum in CDCl3 indicates that it
adopts a cone conformation [21], and this conclusion was
confirmed by the single crystal XRD analysis. Pn-Calix
¯
forms crystals of triclinic symmetry belonging to the P1
space group by slow diffusion of methanol into CHCl3
solution. The crystals are clathrates with four Pn-Calix
molecules per unit cell and a single methanol molecule
situated inside the cavity of each calixarene. The phtha-
lonitrile substituent is placed almost perpendicularly to
the phenoxyl group of the calixarene to which it is bound,
iPr
iPr
iPr
N
O
O
i
iPr
OH
OH
OH
OH
HO
OH
OH
O
CN
CN
ii
iPr
iPr
iPr
iPr
N
N
N
Zn
N
OH
OH
OH
O
O
O
Cl
N
Cl
N
N
iPr
iPr
iPr
O
O
OH OH
OH
O
OH
O
O
O
iPr
CN
CN
NC
NC
scheme 1. Synthesis of Pn-Calix and Pc-Calix. Reagents and conditions: (i) K2CO3, 70 °C, 72 h. (ii) Zn(II)acetate, NMP, 165 °C
Copyright © 2011 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2011; 15: 687–690

688
C.g. Bezzu et al.
Fig. 1. (a) Face-on and (b) edge-on depictions of the molecular structure of Pn-Calix and (c) its packing arrangement from a single
crystal XRD study
and its UV-vis spectrum showed a distinct Q-band at λmax
=
cofacial association of the phthalocyanine macrocycles,
which is of interest for retaining the optical properties of
the phthlocyanine molecule within the solid state [22–24].
We anticipate that the functionalities of both partners will
be preserved within this new conjugate and that it may find
application as a molecular sensor in which the calixarene
acts as the binding site and the perturbations of the opti-
cal properties of the phthalocyanine reports the presence
of the binding species. Studies to realize this potential are
planned.
684 nm typical for a metal-containing phthalocyanine. No
shift or broadening of this band was observed for more
concentrated solutions demonstrating that the bulky sub-
stituents efficiently prevent aggregation. Ultimate confir-
mation of the structure of Pc-Calix was obtained from a
single-crystal XRD study using crystals grown by slow
diffusion of acetone into CHCl3 solution. The crystal
proved to be a clathrate with monoclinic unit cell belong-
ing to the P21/n space group with 4 phthalocyanine mol-
ecules and 16 acetone and 8 chloroform molecules, some
of which are at partial occupancy, per unit cell. A further
acetone molecule is axially bonded to the central Zn2+ cat-
ion. Analysis of the molecular structure (Fig. 2) reveals
that both the di-i-propylphenoxyl and the 4-t-butylcalix[4]
arene substituents are oriented perpendicular to the mac-
rocyclic plane of the phthalocyanine core, which is only
slightly distorted from planarity. Importantly, the calix-
arene retains its full cone conformation and its capacity to
engage in supramolecular binding is demonstrated by the
inclusion of the axial acetone ligand from a neighboring
Pc-Calix molecule (Fig. 3). The packing arrangement also
shows the efficiency of the bulky substituents to prohibit
eXPeRIMeNTAL
General
Infra-redspectrawererecordedintherange4000–6000
cm-1 using a Perkin-Elmer 1600 series FTIR instrument.
Elemental analysis was carried out with a Carlo Erba
EA1101 elemental analyzer. UV-vis absorption spectra
were recorded in the range 200–800 nm using a Jasco
1
V-570 UV-vis/NIR spectrophotometer. H NMR spectra
were recorded in CDCl3 using anAvance Bruker DPX 400
Fig. 2. (a) Face-on and (b) edge-on depictions of the molecular structure of Pc-Calix from the single crystal XRD analysis
Copyright © 2011 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2011; 15: 688–690

SyntheSIS anD CryStal StruCture Of a nOvel PhthalOCyanIne-CalIxarene COnJugate
689
Fig. 3. (a) Packing arrangement of Pc-Calix along the c axis with all substituents removed for clarity to illustrate the isolation of
the phthalocyanine cores within the crystal. (b) Depiction of the supramolecular binding of the axial acetone ligand of one Pc-Calix
molecule within the calixarene unit of its neighbor (phenoxyl substituents removed for clarity)
instrument (400 MHz) with 13C NMR spectra recorded at
100 MHz respectively. MALDI-TOF mass spectroscopic
analysis was performed with a Waters MALDI Micro
MX spectrometer. The precursor 4,5-bis(2′,6′-di-iso-
propylphenoxy)phthalonitrile was prepared as reported
previously [19, 20] from commercially available 2,6-di-
i-propyl phenol and 4,5-dichlorophthalonitrile.
124.8, 117.6, 115.2, 114.7, 114.2, 109.2, 34.5, 34.0,
33.8, 32.2, 31.4, 31.1. LRMS (EI): m/z 808.42 ([M]•+,
100%). HRMS calcd. for C52H57O4N2Cl 808.4007, found
808.4000.
Crystals were prepared by the slow diffusion of
MeOH into a CHCl3 solution of Pn-Calix. Data were
collected at 100 K (nitrogen cryogen), using synchro-
tron radiation at the CCLRC Daresbury Laboratory
on a Bruker APEX CCD diffractometer. Crystal data
(calix): crystal size 0.3 × 0.07 × 0.02 mm, triclinic,
synthesis
¯
Preparation of 4-chloro-5-(4-t-butylcalix[4]arenyl)-
phthalonitrile (Pn-Calix). Anhydrous potassium car-
bonate (2.1 g, 15.2 mmol) was added to a solution of
t-butylcalix[4]arene (1.65 g, 2.5 mmol) and 4,5-dichlo-
rophthalonitrile (0.50 g, 2.5 mmol) in anhydrous dim-
ethylformamide (20 mL). The mixture was stirred under
nitrogen atmosphere for 72 h at 70 °C. After cooling, the
reaction mixture was poured into water (200 mL) and
the aqueous solution was neutralized with hydrochloric
acid (2N). The resulting solid was filtered and washed
with water. Purification by column chromatography on
SiO2, eluting with hexane-ethyl acetate (8:2), gave the
title compound as a white solid . Yield: 1.50 g (73%), mp
185–186 °C. IR (nujol): ν, cm-1 3461, 3288, 2234, 1585,
space group P1, a = 1.5385(12) nm, b = 1.7110(13) nm,
c = 2.0965(16) nm, α = 91.613(10), β = 109.176(10),
γ = 112.248(10), V = 4.750(6) nm3, Z = 2, μ(0.67100) =
0.131 μm-1, 21653 reflections measured, 13414 unique
reflections (Rint = 0.2575), 5784 reflections with I >
2σ(I), R = 0.1156 and ωR2 = 0.2842 (observed data),
R = 0.2004 and ωR2 = 0.3336 (all data). The asym-
metric unit contains two molecules together with some
solvent methanol and H2O molecules, the latter at par-
tial occupancy.
Preparation of 2,3,9,10,16,17-hexakis(2′,6′-di-
i-propylphenoxy)-23-(4-t-butylcalyx[4]arenyl)-24-
chloro phthalocyaninato zinc (Pc-Calix). A mixture of
4,5-bis(2′,6′-di-iso-propylphenoxy)phthalonitrile (1.60 g,
3.35 mmol), Pn-Calix (0.30 g, 0.37 mmol) and zinc(II)
acetate (0.55 g, 2.96 mmol) in dry N-methylpyrrolidone
(5 mL) was heated at 150 °C for 20 h. The reaction
mixture was cooled to room temperature, poured into
20 mL of distilled water and then collected by filtration.
Purification by column chromatography on SiO2, elut-
ing with toluene, gave 0.68 g of 2,3,9,10,16,17,23,24-
octaakis(2′,6′-di-i-propylphenoxy)phthalocyaninato zinc
1
1302, 1269, 1202, 1012, 897, 872, 740. H NMR (400
MHz; CDCl3): , ppm 9.19 (br s, 1H), 7.72 (br s, 3H),
7.28 (s, 2H), 7.09 (s, 2H), 7.05 (d, 2H, J = 2.4 Hz), 6.79
(s, 1H), 6.74 (br s, 2H), 3.99 (d, 2H, J = 13.4 Hz), 3.72
(m, 4H), 3.61 (d, 2H, J = 14.4 Hz), 1.29 (s, 9H), 1.25 (s,
9H), 1.15 (s, 18H). 13C NMR (100 MHz; CDCl3): , ppm
156.7, 151.1, 148.4, 147.2, 144.0, 143.4, 135.3, 131.9,
128.7, 128.0, 127.9, 127.6, 127.1, 126.2, 125.9, 125.4,
Copyright © 2011 World Scientific Publishing Company
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690
C.g. Bezzu et al.
(62%) and the desired Pc-Calix as a green solid. Yield:
0.10 g (12%), mp > 300 °C. UV-vis (DCM): λmax, nm
684, 615, 348, 292, 230. IR (DCM): ν, cm-1 3387, 2963,
2869, 1609, 1440, 1397, 1269, 1183, 1095, 1025, 893,
794, 724. 1H NMR (400 MHz; CDCl3): , ppm 9.53 (br
s, 2H), 8.43 (s, 1H), 8.27 (s, 2H), 8.20 (s, 2H), 8.14 (s,
2H), 7.53 (m, 20H), 7.02 (br m, 6H), 3.54 (br m, 20H),
1.25 (br m, 108H). MS (MALDI-TOF): cluster centered at
m/z 2316.662, ([M]+, 100%). Anal. calcd. for C148H165Cl-
N8O10Zn: C, 76.73; H, 7.18; Cl, 1.53; N, 4.84%. Found C,
76.20; H, 7.38; N 4.71%.
Crystals were prepared by the slow diffusion of ace-
tone into a CHCl3 solution of Pc-Calix. Single-crystal
XRD data were collected at 150 K using graphite mono-
chromated MoKα radiation on a Bruker-Nonius Kappa
CCD diffractometer with an Oxford Cryosystems cool-
ing apparatus. The structure was solved from these data
by direct methods and refined using SHELX-97. Crystal
size 0.8 × 0.5 × 0.4 mm, monoclinic, space group P21/n,
a = 2.60440(3) nm, b = 1.98390(2) nm, c = 3.08170(4)
nm, β = 101.8030(10), V =15.5861(3) nm3, Z = 4, μ =
0.249 μm-1, 38603 reflections measured, 22265 unique
reflections (Rint = 0.0484), 15622 reflections with I >
2σ(I), R = 0.0884 and ωR2 = 0.2345 (observed data),
R = 0.1274 and ωR2 = 0.2681 (all data).
3. de la Torre G, Claessens CG and Torres T. Chem.
Commun. 2007; 2000–2015.
4. Emmelius M, Pawlowski G and Vollmann HW.
Angew. Chem. 1989; 101: 1475–1502.
5. Ben-Hur E and Chan W-S. In The Porphyrin Hand-
book, Vol. 19, Kadish KM, Smith KM and Guilard
R. (Eds.) Academic Press: 2003; pp 1–35.
6. Rostalski J and Meissner D. Sol. Energy Mater. Sol.
Cells 2000; 63: 37–47.
7. Nazeeruddin MK, Humphry-Baker R, Gratzel M
and Murrer BA. Chem. Commun. 1998; 719–720.
8. Guillaud G, Simon J and Germain JP. Coord. Chem.
Rev. 1998; 178–180: 1433–1484.
9. Meunier B and Sorokin A. Acc. Chem. Res. 1997;
30: 470–476.
10. Duro JA, de la Torre G, Barbera J, Serrano JL and
Torres T. Chem. Mater. 1996; 8: 1061–1066.
11. Cammidge AN and Gopee H. Chem. Commun.
2002; 966–967.
12. Gutsche CD and Editor. Calixarenes: An Introduc-
tion, 2nd Edition, RSC: 2008.
13. Gutsche CD. Calixarenes Revisited, RSC: 1998.
14. O’Malley S, Alhashimy N, O’Mahony J, Kieran A,
Pryce M and Nolan K. Tetrahedron Lett. 2007; 48:
681–684.
15. O’Malley S, Schazmann B, Diamond D and Nolan
K. Tetrahedron Lett. 2007; 48: 9003–9007.
16. Ceyhan T, Altindal A, Oezkaya AR, Celikbicak O,
Salih B, Kemal Erbil M and Bekaroglu O. Polyhe-
dron 2007; 26: 4239–4249.
Acknowledgements
We thank the EPSRC (Grants EP/F019114/1 and EP/
H024034/1) for funding.
17. Ceyhan T, Altindal A, Oezkaya AR, Erbil MK and
Bekaroglu O. Polyhedron 2007; 26: 73–84.
18. Koca A, Ceyhan T, Erbil MK, Ozkaya AR and
Bekaroglu O. Chem. Phys. 2007; 340: 283–292.
19. McKeown NB, Makhseed S, Msayib KJ, Ooi L-L,
Helliwell M and Warren JE. Angew. Chem., Int. Ed.
2005; 44: 7546–7549.
20. Bezzu CG, Warren JE, Helliwell M, Allan DR and
McKeown NB. Science 2010; 327: 1627–1630.
21. Chowdhury S and Georghiou PE. J. Org. Chem.
2001; 66: 6257–6262.
supporting information
Crystallographic data for Calix-Pn and Calix-Pc
have been deposited at the Cambridge Crystallographic
Data Centre (CCDC) under numbers CCDC 825909
and 825910. Copies can be obtained on request, free of
charge, via www.ccdc.cam.ac.uk/conts/retrieving.html
or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK (fax: +44 1223-
336-033 or email: deposit@ccdc.cam.ac.uk).
22. Brewis M, Hassan BM, Li H, Makhseed S,
McKeown NB and Thompson N. J. Porphyrins
Phthalocyanines 2000; 4: 460–464.
23. Hassan BM, Li H and McKeown NB. J. Mater.
Chem. 2000; 10: 39–45.
ReFeReNCes
1. Leznoff CC, Lever ABP and Editors. Phthalocya-
nines: Properties and Applications, Vol. 1–4, Wiley:
1989–1995.
2. McKeown NB. Phthalocyanine Materials: Struc-
ture, Synthesis and Function, Cambridge University
Press: 1998.
24. Brewis M, Helliwell M and McKeown NB. Tetrahe-
dron 2003; 59: 3863–3872.
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