Synthesis of meso-polyphosphorylporphyrins and example of self-assembling

Article abstract of DOI:10.1021/ol901421e

Pd-catalyzed coupling reactions have been used to prepare meso-phosphorylporphyrins. A 2D metal-organic network formed via P=O-Zn axial supramolecular coordination of 5, 15-bis(diethoxyphosphoryl)-10,20- diphenylporphyrin is the first example of a 2D fram

Full text of DOI:10.1021/ol901421e

ORGANIC
LETTERS
2009
Vol. 11, No. 17
3842-3845
Synthesis of
meso-Polyphosphorylporphyrins and
Example of Self-Assembling
Yulia Y. Enakieva,† Alla G. Bessmertnykh,‡ Yulia G. Gorbunova,*,†
Christine Stern,‡ Yoann Rousselin,‡ Aslan Y. Tsivadze,† and Roger Guilard*,‡
Russian Academy of Science, Frumkin Institute of Physical Chemistry and
Electrochemistry, Leninsky pr., 31, GSP-1, 119991, Moscow, Russia, and UniVersite´ de
Bourgogne - ICMUB UMR CNRS 5260, 9 aVenue Alain SaVary - BP 47870,
21078 Dijon, France
yulia@igic.ras.ru; roger.guilard@u-bourgogne.fr
Received June 23, 2009
ABSTRACT
Pd-catalyzed coupling reactions have been used to prepare meso-phosphorylporphyrins. A 2D metal-organic network formed via PdO···Zn
axial supramolecular coordination of 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrin is the first example of a 2D framework based on
phosphorylporphyrin derivatives.
The design of coordination networks formed upon a mutual
interconnection between organic ligands and a metal center is
a rapidly developing field.1-7 The strategy of formation of
these molecular architectures takes place under self-assembly
conditions and exploits ionic interactions, hydrogen bonding,
coordination bonds, and dispersion forces. For example, the
self-organization of porphyrins is of particular interest.8-10
This robust ligand can be metalated by a very large number
of metallic elements and may be functionalized with various
coordinating groups at the periphery of the macrocycle.
Porphyrin-based architectures have been used to fabricate
photonic materials, for fundamental studies of biological
systems or the generation of molecular solids displaying
chemical and catalytic properties.11 Owing to these features,
pyridyl, imidazolyl, carboxylate, amino, hydroxyl, nitro,
cyano, aryl, sylfonyl, and alkyl porphyrins have been used
as precursors in the synthesis of noncovalent architec-
tures.12-23 The key role of metallophosphonates in the
fabrication of molecular assemblies is also well-known,24-27
but surprisingly very few studies have been dedicated to the
design of porphyrin derivatives containing phosphonate
groups at the periphery of the macrocyclic ligand. The
interest of these synthons has been demonstrated a long time
ago by the studies on grafting phosphonated porphyrins at
† Frumkin Institute of Physical Chemistry and Electrochemistry.
‡ Universite´ de Bourgogne.
(1) Kitagawa, S.; Kitaura, R.; Noro, S.-i. Angew. Chem., Int. Ed. 2004,
43, 2334
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(8) Chambron, J.-C.; Heitz, V.; Sauvage, J.-P. The Porphyrin Handbook;
Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic Press: San Diego,
2000; Vol. 6, p 1.
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O. M. J. Am. Chem. Soc. 2005, 127, 1504
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(9) Harvey, P. D. The Porphyrin Handbook; Kadish, K. M., Smith,
K. M., Guilard, R., Eds.; Academic Press: San Diego, 2003; Vol. 18, p 63.
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(11) Chou, J.-H.; Nalwa, H. S.; Kosal, M. E.; Rakow, N. A.; Suslick,
K. S. The Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R.,
Eds.; Academic Press: San Diego, 2000; Vol. 6, p 43.
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10.1021/ol901421e CCC: $40.75
Published on Web 07/31/2009
 2009 American Chemical Society

the surface of zirconium oxide or incorporating these
derivatives in isomorphous matrices.28-31 Very recently, it
was proven that an appropriate choice of a porphyrin
backbone makes possible the assembly of phosphonate
porphyrins in extended 1D chains.32,33 Due to the nonplanar
character of the phosphonate group, it is clear that the
fabrication of phosphonate porphyrin-based 2D and 3D
architectures is a priori more difficult than the elaboration
of such materials using carboxylic or pyridyl porphyrins as
a precursor. In this work, we describe the first example of a
meso-phosphorylporphyrin-based polymer exhibiting a 2D structure
and the self-organization of such a porphyrin ligand in solution.
One of the major challenges that still lies ahead to fabricate
materials containing phosphonato-substituted porphyrins is the
finding of an efficient synthetic method for these precursors.
Only a multistep synthesis developed by Lindsey’s group,34 or
a Pd-catalyzed phosphorylation according to Hirao’s condi-
tions,35,36 gives porphyrins possessing (4-dialkoxyphospho-
rylaryl) groups at the periphery of the macrocycle. Two
monosubstituted meso-phosphoryl porphyrin derivatives have
been recently obtained via a Cu-catalyzed phosphorylation
reaction.37 The widely applicable transition-metal-catalyzed
cross-coupling methodology is a powerful tool in porphyrin
series synthesis. For example, the formation of carbon-carbon
bonds is obtained by Suzuki or Sonogashira reactions, and
more recently hetero-cross-coupling reactions (C-N, C-O,
C-S, C-B, C-P) have been successfully realized.38-40
However, compared to regular classical methods used for
common aryl halide derivatives, particular experimental
conditions should be found to allow the catalytic transforma-
tions due to the electronic structure of the porphyrins or their
solubility. We have probed a catalytic methodology to
prepare polyphosphoryl-substituted porphyrins which are
suitable precursors to elaborate 2D- or 3D-ordered architec-
tures (Scheme 1).
Scheme 1
.
Pd-Catalyzed Coupling of meso-Bromoporphyrins
with Diethylphosphite
(12) Goldberg, I. Chem.sEur. J. 2000, 6, 3863
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4, 633
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(16) Muniappan, S.; Lipstman, S.; Goldberg, I. Acta Crystallogr., Sect.
The results are summarized in Table 1.41 When classical
Hirao’s conditions are applied for the diphosphorylation of 5,15-
C: Cryst. Struct. Commun. 2006, C62, m495
(17) Taniguchi, M.; Ptaszek, M.; McDowell, B. E.; Boyle, P. D.;
Lindsey, J. S. Tetrahedron 2007, 63, 3850
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Fukuda, T.; Kobayashi, N.; Fukuzumi, S. Angew. Chem., Int. Ed. 2008,
Table 1. Synthesis of meso-Polyphosphorylporphyrins
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bromide
derivative
Pd(OAc)2/
3PPh3 equiv
HOP(OEt)2
equiv
.
product
yield %
.
1H2
1H2
1Zn
3Zn
5Zn
0.1
1.0
0.1
0.1
0.3
2.4
24
2.4
14
2H2
2H2
2Zn
4Zn
6Zn
<5
32
51
68
50
.
.
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14
420
.
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dibromo-10,20-diphenylporphyrin 1Zn, the target product 2Zn
was obtained as traces. Our attempts to optimize the synthesis
have shown that the nature of the solvent is a key parameter
on the reaction pathway. A high yield of the product 2Zn (51%)
was obtained in the presence of 10 mol % of catalytic precursor
Pd(OAc)2/3PPh3 when ethanol was used as a solvent. The
phosphorylation of 1Zn was more efficient and gave a higher
yield of the target product compared to the reaction involving
the free base 1H2. Indeed, only traces of product 2H2 were
observed under catalytic conditions (10 mol % Pd(OAc)2/
3PPh3). 2H2 has been obtained only in the presence of a
stoichiometric amount of palladium precursors and a large
excess (24 equiv) of diethylphosphite using 1H2 as starting
.
F.; Talham, D. R. J. Am. Chem. Soc. 2002, 124, 4363
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Lysenko, A. B.; Mathur, G.; Li, Q.; Bocian, D. F.; Misra, V.; Lindsey,
J. S. J. Org. Chem. 2004, 69, 1453.
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2004, 69, 1444.
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Org. Lett., Vol. 11, No. 17, 2009
3843

compound. The formation of a catalytically nonefficient
Pd-porphyrin complex cannot be excluded, but such a complex
has never been observed by MALDI-TOF analysis of the
reaction mixtures. It is remarkable to note that the polyphos-
phorylation of the meso-tetra(4-bromoaryl)-substituted porphyrin
3Zn can be carried out under the same conditions. Four
consecutive catalytic cycles were carried out in a one-pot
reaction in the presence of 10 mol % of the catalyst precursor
(2.5 mol % for each bromide). The yield of the porphyrin
phosphonate 4Zn was much higher (68%) than the yield in the
phosphorylation of the corresponding free base of 3Zn in a
toluene/THF mixture (28%).35 Thus, the palladium-catalyzed
polyphosphorylation of the studied porphyrin bromides in
ethanol have produced a wide variety of novel polyphosphoryl
porphyrins. In particular, the Pd-catalyzed polyphosphorylation
methodology allows the phosphorylation of the compound 5Zn
where two bromide atoms are directly linked to the macrocyclic
ring and two bromides are located at the para position of the
meso-phenyl substituents. The target tetrasubstituted porphyrin
6Zn was isolated in 50% yield. Polyphosphoryl-substituted
compounds 2Zn, 4Zn, and 6Zn prepared according to this route
are suitable precursors for the elaboration of well-ordered
porphyrin assemblies due to their symmetry and the presence
of appropriate ligands at the periphery of the macrocycle.
Compound 2Zn gives violet monocrystals by slow evapora-
tion from a chloroform or chloroform-ethanol mixture. It is
interesting to note that upon slow diffusion of a solution of
Zn(OAc)2 in MeOH into a solution of 2H2 in CHCl3 the same
violet monocrystals have been obtained. The three isomorphous
crystals (monoclinic, Z ) 2, space group P21/a) are formed of
2Zn units without any solvent molecules. The porphyrin core
of 2Zn is almost planar. The zinc atom located exactly in the
center of the ring exhibits a six-coordinate square bipyramidal
stereochemistry as shown in Figure 1.41,42 The two apical
equatorial Zn-N distance is 2.061(3) Å. The axial Zn-O1
bond distance is equal to 2.465(2) Å. This coordination
configuration propagates along two axes to produce a 2D
coordination polymer, as illustrated in Figure 2. The 2D
Figure 2. 2D network structure of 2Zn in monocrystal. The meso-aryl
substituents, hydrogen atoms, and ethyl groups are omitted for clarity.
sheets are composed by slightly deformed square mesh
formed by four zinc porphyrins. This arrangement contributes
to create cavities which are in fact not accessible due to the bulky
ethyl groups of phosphonates located onto the meso-position of
the porphyrin macrocycle and pointing into the cavity.
The degree of ordering of complex 2Zn in the solid state
can be efficiently estimated using infrared spectroscopy.41 The
PdO stretching vibrations (1250-1300 cm-1) in aryl phos-
phonates are sensitive to the environment variation, and a
bathochromic shift of 30-80 cm-1 occurs when this bond is
involved in a hydrogen-bond formation or coordinated to the
metal ion.43 Only one ν(PdO) band at 1233 cm-1 was observed
in the IR spectrum of the monocrystal of complex 2Zn (Figure
3, red curve). Indeed, a molecular self-assembling via PdO···Zn
interactions in the monocrystal leads to the appearance in the
spectrum of a band corresponding to the vibrations of the
coordinated phosphoryl group. On the contrary, two strong PdO
stretching bands at 1259 and 1235 cm-1 are observed in the
spectrum of polycrystalline compound 2Zn (Figure 3, blue
curve). The relative intensity of these bands depends on the method
of sample preparation (pure, KBr pellet or thin film prepared by
the evaporation of a chloroform/ethanol solution on the surface of
a KBr plate). The second band at 1259 cm-1 can be assigned to
the vibrations of an uncoordinated phosphoryl group.
(40) Atefi, F.; Arnold, D. P. J. Porphyrins Phthalocyanines 2008, 12,
801.
Figure 1. ORTEP view of the molecular structure of 2Zn. 50%
(41) See the Supporting Information.
probability ellipsoids. Disordered parts of ethyl groups are omitted for
(42) Crystal data for 2Zn: C40H38N4O6P2Zn, Mr ) 798.05, monoclinic,
space group P21/a, a ) 12.1377(5) Å, b ) 11.4995(4) Å, c ) 12.4813(4) Å,
ꢀ ) 91.668(2)°, V ) 1741.37(11) Å3, Z ) 2, Fcalcd ) 1.522 Mg/m3, T ) 115(2)
K, Mo KR radiation (λ ) 0.71073 Å), µ ) 0.854 mm-1, 6730 measured
reflections, 3970 [R(int) ) 0.0424] independent reflections, R1 ) 0.0593 (I >
2σ(I)), wR2 ) 0.1208 (all data), GOF ) 1.134 (I > 2σ(I)). Structure information
is given in the Supporting Information. CCDC-730343 contains the supple-
mentary crystallographic data for this paper. These data can be obtained free
of charge from the Cambridge Crystallographic Data Centre at www.ccdc.ca-
m.ac.uk/data_request/cif.
clarity.42
coordination sites are occupied by O1 oxygen atoms belong-
ing to the diethoxyphosphoryl substituents of two adjacent
complexes, and the Zn-O bond is slightly tilted from the
vertical to the four nitrogen plane with angles N2-Zn-O1#3
) 92.07(9)° and N1-Zn-O1#3 ) 82.84(10)°. The average
(43) Bellamy, L. J. The Infrared Spectra of Complex Molecules; John
Wiley & Sons: New York, 1962.
3844
Org. Lett., Vol. 11, No. 17, 2009

the PdO···Zn coordination bond occurs.37,46 The PdO···Zn bond
in 2Zn assembly is weaker compared to the intermolecular
bonds of Zn-phosphoryl porphyrin dimers.37,46
UV-vis absorption spectroscopy can be used to estimate
more precisely the range of concentration where the self-
assembling of compound 2Zn takes place. We have shown that
no evolution of the UV-vis spectrum of 2Zn in chloroform
occurs in the range 10-7 to 2 × 10-5 M. A further increase of
the concentration leads to a bathochromic shift (2-3 nm) of
all the bands (Figure 4). Such spectral changes indicate the
Figure 3. Infrared data of 2Zn and PdO stretching bands for the
monocrystalline (red curve) and the powder forms (blue curve).
The influence of the molecular aggregation in solution on
the crystal growth is a topic of special interest for crystal
engineering.20,21,44,45 For this purpose, we have studied the
aggregation of 2Zn in solution by using different spectro-
scopic techniques. Chloroform was chosen as an appropriate
solvent due to the low solubility of 2Zn in dichloromethane,
toluene, and other nonpolar solvents.
Figure 4. UV-vis absorption spectra of 2Zn in chloroform at
various concentrations and the normalized spectra in the range
The 1H NMR spectrum of 2Zn in CDCl3 (10-3-10-2 M) at
room temperature exhibits very broad signals.41 It is interesting
to note that a narrowing and a downfield shift of the signals in
more diluted solutions suggest that the aggregation is responsible
for signals broadening. The aggregates already exist in a 8.7 ×
10-5 M solution where distinct signals of all proton resonances
expected for the molecule 2Zn are observed, but some signals
are still broad.41 The low intensity of signals in more diluted
solutions does not allow us to determine the precise limit of
the concentration where the compound 2Zn exists only as a
monomer. A more strong coordinating solvent (MeOH-d4, 25%
v/v) was added to confirm the aggregation phenomenon.41
Under these conditions, distinct and sharp signals for all the
protons were observed. Moreover, the 1H NMR titration of the
compound 2Zn was carried out in CDCl3 by methanol-d4 and
trifluoroethanol, a less coordinating alcohol.41 Sharp signals of
all protons were observed after addition of 20 µL of methanol-
d4, while 120 µL of trifluoroethanol is needed to observe a well-
resolved spectrum. Similar changing was observed in the 31P
NMR spectrum where narrowing of a broad signal (δ ) 23.5
ppm) was observed after the addition of 20 µL of methanol-d4
or 120 µL of trifluoroethanol. These data allow us to conclude
that the molecular aggregates are formed in the chloroform
solution through the coordination of the diethoxyphosphoryl
group to the zinc atom as observed by X-ray study in the solid
state. The chemical shifts of pyrrolic protons as well as the
protons of the diethoxyphosphoryl group are less pronounced
than for Zn-porphyrins having intramolecularly connected
diethoxyphosphoryl groups or for Zn-porphyrin dimers where
500-650 nm (inset).
formation of extended supramolecular aggregates with brickwall
structure.47 Considering deviation from the Beer-Lambert law
of Soret-band (λ ) 420 nm), the self-organization of compound
2Zn via PdO···Zn bonds occurs when the concentration of the
compound in chloroform is higher than 2 × 10-5 M.
To prove the coordination of phosphoryl groups to the Zn
center in the chloroform solutions, we have also monitored the
spectral changing induced by diethylphosphite addition to 2 ×
10-5 M solution of compound 2Zn where only a monomer form
exists.41 The bathochromic shifts of the bands (3 nm) induced
by diethylphosphite coordination to Zn were similar to those
observed for the aggregation phenomenon.
In summary, we have successfully applied a transition-metal-
catalyzed cross-coupling methodology for the synthesis of a
series of novel meso-polyphosphorylporphyrins which are
suitable building blocks to give new 2D and 3D coordination
networks.Astablephosphonateporphyrinbased2Dmetal-organic
framework was fabricated via a supramolecular self-assembling
involving PdO···Zn axial bond formation. These aggregates are
also observed in chloroform solution. The properties of this new
and novel phosphonato porphyrin-based network are studied
to develop photonic materials and to mimic biological deriva-
tives.
Acknowledgment. This work was supported by ARCUS
2007 Burgundy-Russia project, Russian Foundation for Basic
Research (grant#07-03-92212), the CNRS, and European
Research Association “Suprachem”.
Supporting Information Available: Experimental details
and characterization data. This material is available free of
charge via the Internet at http://pubs.acs.org.
OL901421E
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