Facile synthesis and supramolecular network of a Zn(II)-octaesterporphyrin

Article abstract of DOI:10.1016/S0040-4039(02)01377-1

The present work reports the synthesis of an octaester porphyrin and its Zn(II) complex which shows an unusual two-dimensional supramolecular coordination network structure.

Full text of DOI:10.1016/S0040-4039(02)01377-1

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 6427–6429
Facile synthesis and supramolecular network of a
Zn(II)–octaesterporphyrin
P. Bhyrappa,* G. Vaijayanthimala and B. Verghese
Department of Chemistry, Indian Institute of Technology–Madras, Chennai 600 036, India
Received 17 April 2002; revised 26 June 2002; accepted 4 July 2002
Abstract—The present work reports the synthesis of an octaester porphyrin and its Zn(II) complex which shows an unusual
two-dimensional supramolecular coordination network structure. © 2002 Elsevier Science Ltd. All rights reserved.
Functionalised porphyrins are of considerable interest
owing to their use as model compounds1,2 and also for
their interesting physico-chemical properties.3 Further-
more, these multifunctionalized porphyrins are useful
compounds for generation of materials with interesting
properties.4 A wide variety of meso-tetraphenylpor-
phyrins with varying substituents at the meso-positions
have been explored for the control of molecular self-
assembly processes to generate functional materials
with specific properties.4 It has been shown that the
effect of the carboxy group enhances the thermal stabil-
ity of the resultant self-assembly in the solid state.5
Further, the synthesis of porphyrins with appropriate
functional groups at the meta or ortho positions are
potentially attractive due to their three-dimensional
disposition of substituents. Such molecular building
blocks provide intermolecular interactions in three
dimensions for the construction of robust solid net-
works with interesting properties. Herein, we present
the facile synthesis of a multi-functionalized porphyrin
5,10,15,20 - tetrakis(3%,5% - dicarboxyethylesterphenyl)-
porphyrin, H2T(3%,5%-DCEP)P and examined the inter-
esting X-ray structure of the ZnT(3%,5%-DCEP)P com-
plex.
free base porphyrin, H2T(3%,5%-DCEP)P (3) was synthe-
sized by the condensation of pyrrole with 5-
formylisophthalic acid diethylester (2) in dichloro-
methane under mild conditions (Scheme 1).10 Its Zn(II)
complex was prepared using the reported procedure.11
The compounds synthesized were characterized by UV–
1
vis, H NMR, mass spectroscopic and elemental analy-
sis. MT(3%,5%-DCEP)P complexes show a marginal red
The precursor 5-formylisophthalic acid diethylester6 (2)
was synthesized via oxidation of 5-hydroxymethyl
isophthalic acid diethylester7 (1) using chromium(VI)
quinolinate8 in CH2Cl2 or ceric(VI) ammonium nitrate
in an acetic acid medium.9 The dicarboxydiethyl ester
* Corresponding author. E-mail: bhyrappa@iitm.ac.in
Scheme 1.
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)01377-1

6428
P. Bhyrappa et al. / Tetrahedron Letters 43 (2002) 6427–6429
shift in electronic transitions relative to the correspond-
ing MTPPs. The 1H NMR spectra of the octaester
porphyrin exhibited down-field ortho- (8.60 ppm) and
para-phenyl (9.20 ppm) proton resonances relative to the
corresponding
resonances
of
meso-tetraphenyl-
porphyrin, (H2TPP), 8.20 and 7.60 ppm, respectively.
The downfield shift of the resonances is possibly due to
the electron withdrawing effect of the ester groups.
The X-ray structure of the ZnT(3%,5%-DCEP)P12 was
examined to determine the role of the octaester groups
on the self-assembly process. The crystals of ZnT(3%,5%-
DCEP)P were grown by diffusing methanol into a
CHCl3 solution of the porphyrin. The ORTEP structure
of the Zn(II) complex is shown in Fig. 1. The molecule
crystallizes free of any solvent in the lattice and there are
two molecules in the unit cell. Surprisingly, the Zn(II) ion
is in a six coordinate geometry with the two axially
ligated ester groups bonded through keto-functionalities
from the two neighboring porphyrins. The ligated ester
groups are from the phenyl rings positioned trans to one
another and the bound ester groups are from opposite
faces of the porphyrin. The porphyrins are arranged
alternately in a slip-stack orientation to give a two-
dimensional array (Fig. 2). In this orientation, the
adjacent molecules show an offset orientation to induce
a coordinative interaction between the Zn(II) center and
the peripheral ester groups. The alternative array showed
a two-dimensional coordination polymeric network with
Figure 2. The coordination mode of the Zn(II) centre showing
the ester groups from the neighbouring molecules. Symmetry
related neighbouring molecular units are shown.
,
the closest inter-layer distance of 3.432 A indicating the
absence of any strong inter-layer interactions. The closest
distance between the adjacent Zn(II) centers of the
core are not significantly different from those of the
ZnTPP complex.13
,
adjacent two-dimensional layers is 24.12 (3) A. In this
structure, the average dihedral angle formed by the
phenyl groups with the porphyrin core is 75.4(2)°. The
Zn(II) ion is situated almost in the plane of four nitrogen
The synthesis of an octaester porphyrin has been pre-
sented. The crystal structure shows an interesting two-
dimensional coordination polymeric structure in the
solid state. The de-esterification of the octaester and its
use in the construction of solid networks is being actively
investigated. The octacarboxy porphyrin would be of
interest for its strong complementary hydrogen bonding
interactions and may lead to robust network solids.
,
atoms with an average Zn–N distance of 2.039(3) A. The
axially ligated oxygen of the ester groups and the Zn(II)
,
center are situated at a distance of 2.500(8) A apart. The
observed bond lengths and bond angles of the 24 atom
Acknowledgements
This work was supported by grants from the Department
of Science and Technology, DST (No. SP/S1/F09/98)
and Council of Scientific and Industrial Research, CSIR
(No. 01(1550)/98/EMRII), India to Dr. P. Bhyrappa.
References
1. Morgan, D.; Dolphin, D. Struct. Bonding (Berlin) 1987, 64,
115.
2. Momenteau, M.; Reed, C. A. Chem. Rev. 1994, 94, 659.
3. Senge, M. O. In The Porphyrin Handbook; Kadish, K. M.;
Smith, K. M.; Guilard, R., Eds. Highly substituted por-
phyrins; Academic Press: San Diego, 2000; Vol. 1, pp.
239–347 and references cited therein.
Figure 1. ORTEP structure of the complex ZnT(3%,5%-
DCEP)P. Only the Zn(II), pyrrolic nitrogen and ester groups
are labelled for clarity.

P. Bhyrappa et al. / Tetrahedron Letters 43 (2002) 6427–6429
6429
4. Chou, J.-H.; Kosal, M. E.; Nalwa, H. S.; Rakow, N. A.;
Suslick, K. S. In The Porphyrin Handbook; Kadish, K.
M.; Smith, K. M.; Guilard, R., Eds. Applications of
porphyrins and metalloporphyrins to materials chemistry;
Academic Press: New York, 2000; Vol. 6, pp. 43–131 and
references cited therein.
g) was added slowly in the solid form and the solution
was stirred for a further 45 min. The solution was con-
centrated to a small volume (ꢀ50 ml) using a rotary
evaporator. To this solution, dry silica gel (40 g, 100–200
mesh) was added and the slurry was evaporated to give a
dry black powder, which was loaded onto a silica gel
column using CHCl3 as the eluant. The desired free-base
porphyrin was eluted with (8:1, v/v) CHCl3/ethyl acetate.
The product was recrystallized from CH3OH/CHCl3 mix-
ture and dried under vacuum at 110°C for 12 h. The yield
of the product was found to be 2.1 g (25%). H2T(3%,5%-
DCEP)P: UV–vis in toluene: umax (log m): 424 (5.46), 515
(4.36), 556 (3.88), 591 (3.85), 647 (3.80). 1H NMR (400
MHz, CDCl3): l 9.21 (s, 4H, phenyl-p-H), 9.05 (s, 8H,
pyrrrole-H), 8.76 (s, 8H, phenyl-o-H), 4.42 (q, 16H,
J=7.11 Hz, -OCH2), 1.35 (t, 24H, J=7.13 Hz, -CH3),
-2.81 (s, 2H, NH). Anal. calcd for C68H62N4O16: C, 68.56;
H, 5.25; N, 4.70%. Found: C, 68.30; H, 5.32; N, 4.47%.
FAB mass spectrum (m/z)=1192.10 (calcd 1191.26).
H2TPP umax (log m): 419 (5.71), 515 (4.30), 550 (4.05), 591
(3.93), 651 (3.88). ZnT (3%,5%-DCEP)P: umax (log m) : 429
(5.74), 552 (4.43), 591 (3.58). 1H NMR (400 MHz, in
CDCl3): l 9.10 (s, 4H, phenyl-p-H), 8.95 (s, 8H, l-
pyrrole-H), 8.50 (s, 8H, phenyl-o-H), 4.46 (q, 16H, J=
7.12 Hz, -OCH2), 1.30 (t, 24H, J=7.14 Hz, -CH3).
ZnTPP: umax (log m): 423 (5.86), 550 (4.51), 589 (3.78).
11. Adler, A. D.; Longo, R. R.; Kampas, F.; Kim, J. J.
Inorg. Nucl. Chem. 1970, 32, 2443.
5. Diskin-Posner, Y.; Dahal, S.; Goldberg, I. Angew. Chem.,
Int. Ed. Engl. 2000, 39, 1288.
6. 5-(Hydroxymethyl)isophthalic acid diethylester (1) (5 g,
20 mmol) was dissolved in CH2Cl2 (300 ml). To this
solution, quinolinium chlorochromate (7.0 g, 35 mmol)
was added slowly in the solid form. The reaction mixture
was stirred and refluxed for 15 h. At the end of this
period, the solvent was evaporated and the residue was
dissolved in CHCl3 (20 ml) and chromatographed on a
silica gel column. The first fraction was eluted with 10%
ethyl acetate in CHCl3. The desired aldehyde (2) was
vacuum dried at room temperature for a period of 12 h
(yield: 4 g (80%)). Melting point, 67°C. 1H NMR (400
MHz, CDCl3): l 10.15 (s, 1H, CHO), 8.80 (s, 1H, p-H),
8.65 (d, 2H, o-H), 4.43 (q, 4H, J=7.12 Hz, -OCH2), 1.41
(t, 6H, J=7.14 Hz, CH3). Anal. calcd for C13H14O5: C,
62.39; H, 5.64%. Found: C, 62.52; H, 5.42%.
7. Leon, J. W.; Kawa, M.; Frechet, M. J. J. Am. Chem. Soc.
1996, 118, 8847.
8. (a) Srinivasan, R.; Ramesh, C. V.; Madhulatha, W.;
Balabubramanian, K. Indian J. Chem. B. 1996, 35, 480;
(b) Ozgun, B.; Degrimenbasi, N. Synth. Commun. 1996,
26, 3601.
12. Crystal structure data was collected on a CAD-4, Enraf–
Nonius diffractometer at 293 K. Monoclinic, space
9. Antonio, J. M.-V.; Inmaculada, R.; Jose, G. F.-G.; Jose,
F. Tetrahedron Lett. 1998, 39, 9271.
,
group, C2/c, a=15.13(5), b=27.83(14), c=15.620(6) A,
3
,
h=k=90.00, i=105.90(3)°, v=6325(40) A , Z=4.
10. The free-base porphyrin was synthesized using the
modified procedure: Wagner, R.; Lindsey, J. S. J. Org.
Chem. 1989, 54, 828. To anhydrous CH2Cl2 (1600 ml)
containing pyrrole (2.0 ml, 27 mmol) and 5-formyl isoph-
thalic acid ester (2) (7.25 g, 29 mol) (purged with N2 gas
for 20 min). BF3·etherate (1.75 ml (1 mol)) was added at
once and the mixture was stirred for 45 min under an N2
atmosphere at room temperature. Then, p-chloranil (4.72
3
,
d
calcd=1.317 g/m , (Cu Ka)=0.71073 A, 2qmax=30°, R
(all ata)=0.0900 WR=0.1545 for 5767, 3595 unique,
refinement on F2. Structure refinement was performed
using SHELX-97 software.
13. Scheidt, W. R.; Mondal, J. U.; Eigenbrot, C. W.; Adler,
A.; Radonavich, L. J.; Hoard, J. L. Inorg. Chem. 1986,
25, 795.