Coordination and structural studies of crowned-porphyrins

Article abstract of DOI:10.1039/b701889d

Simple chelating agents have been synthesized using a porphyrin and a covalently linked crown-ether. Depending on the relative spatial arrangement of both motifs, the resulting ligands, either a macrotricycle or bis-macrocycles, differ one from another by

Full text of DOI:10.1039/b701889d

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PAPER
www.rsc.org/dalton | Dalton Transactions
Coordination and structural studies of crowned-porphyrins†‡§
Zakaria Halime,a,c Mohammed Lachkar,c Lo¨ıc Toupet,d Athanassios G. Coutsolelosb and Bernard Boitrel*a
Received 7th February 2007, Accepted 1st June 2007
First published as an Advance Article on the web 3rd July 2007
DOI: 10.1039/b701889d
Simple chelating agents have been synthesized using a porphyrin and a covalently linked crown-ether.
Depending on the relative spatial arrangement of both motifs, the resulting ligands, either a
macrotricycle or bis-macrocycles, differ one from another by their flexibility or their aptitude to chelate
bivalent or trivalent cations. The coordination chemistry as well as the structural study of these ligands
and complexes are reported. In the particular case of the macrotricycle, the crown-ether motif,
perpendicular to the porphyrin induces a side selectivity for the coordination of lead(II) outside the
cavity. Furthermore, the coordination of zinc(II) implies a change of conformation of the ligand in
which the crown-ether is parallel to the porphyrin.
was obtained by means of ‘two-point’ recognition.3 Moreover,
metalloporphyrins were found to be efficient for multi-point
Introduction
recognition.4 Regarding the role of water coordination in bi-
ological systems,5 zinc strapped porphyrins were also studied
as water molecule multi-point binding systems.6 Furthermore,
cofacial tetraazamacrocycles maintained in a cofacial geometry
on a porphyrin are adequate ligands for studying the possible
interactions between two transition metals.7 Accordingly, it was
reasoned that for larger elements such as those of Groups 13–15 or
lanthanides, such assemblies could be suitable for the binding of a
cation if each element—the porphyrin and the crown-ether—were
maintained in a geometry such that each macrocycle could interact
with the cation for binding purposes. Indeed, such complexes
are expected to be attractive in the domains of imaging and
therapy.8
Thus, the possible synthesis of various macromolecules in a
simple reaction mixing a porphyrin and 1,4,10,13-tetraoxa-7,16-
diaza-cyclooctadecane (Kryptofix-2,2) was recently investigated.9
Four different macromolecules were purified and identified as a
macrotricycle, a bis-macrocycle, a tris-macrocycle and a cryptand.
Two major products—macrotricycle 1 and bis-macrocycle 2
(Scheme 1)—were obtained in ratios dependent on the reaction
conditions. In this work, the study of these ligands in the
coordination of several cations (Zn, Pb, Bi, La) as well as the
structural characterisation of 1, 1Zn and 1Pb are reported.
The design and synthesis of macrocyclic ligand frameworks for
the sequestration of various elements has been investigated for
several decades and still remains an active area of research.1
Within this field, ligands of different types could exhibit a
synergy for the recognition of host molecules. For instance,
in crown-ether porphyrin molecules,2 it has been shown that
the stability of a supramolecular porphyrin–fullerene conjugate
aSciences Chimiques de Rennes, UMR CNRS 6226, Inge´nierie Chimique et
Mole´cules pour le Vivant, 35042, Rennes Cedex, France. E-mail: bernard.
boitrel@univ-rennes1.fr; Fax: +33(2)2323 5637; Tel: +33(2)2323 5856
bUniversity of Crete, Chemistry Department, Laboratory of BioInorganic
Chemistry, PO Box 1470, 714 09 Heraklion, Crete, Greece. E-mail:
coutsole@chemistry.uoc.gr
cUniversite´ Sidi Mohammed Ben Abdellah, Faculte´ des Sciences Dhar
El Mehraz, Laboratoire d’Inge´nierie des Mate´riaux Organome´talliques et
Mole´culaires (LIMOM), B.P. 1796 (Atlas), 30000, Fe`s, Morocco. E-mail:
mlachkar@caramail.com
dUniversite´ de Rennes1, Groupe Matie`re Condense´e et Mate´riaux, UMR
CNRS 6626, 35042, Rennes Cedex, France
† The HTML version of this article has been enhanced with colour images.
‡ CCDC reference numbers 292378, 296454 and 628337. For crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/b701889d
§ Electronic supplementary information (ESI) available: NMR and mass
spectrometry data for all new compounds. See DOI: 10.1039/b701889d
Scheme 1 Syntheses of crown-porphyrins. Ar1 = 3,5-dimethoxyphenyl, Ar2 = 2,4,6-trimethylphenyl. (i) Zn(OAc)2, THF, RT, overnight or Pb(OAc)2,
pyridine, 50 ◦C, 1 h; (ii) succinic anhydride, aluminium oxide, CH2Cl2, RT.
3684 | Dalton Trans., 2007, 3684–3689
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resolution of the free-base porphyrin 1. Indeed, crystals suitable
for X-ray analysis were obtained from slow diffusion of methanol
in a chloroform solution of 1.¶ Unexpectedly, and in contrast to
the structure in solution, the crown-ether residue in 1 is orthogonal
to the mean porphyrin plane (Fig. 1, Table 1) with an angle of 89◦
between the two planes.* This specific orientation is maintained
by two hydrogen bonds between O5 and N8 and O4 and N5 with
Results and discussion
Synthesis of ligand precursors
Two different methods to optimize the yield of either 1 or 2
independently of the nature of Ar (Scheme 1) were reported.9
For this study, the univocal reaction of Kryptofix-2,2 with a single
ortho-amino phenyl porphyrin (Ar2 = 2,4,6-trimethylphenyl) to
obtain bis-macrocycle 2 with a yield of 88% was chosen. Opposite
to 1, in which the crown-ether cycle cannot escape from its apical
position to the porphyrin, 2 can be considered as a freely hinged
ligand in which the distance between the two macrocycles may
change. Therefore, 2 is expected to be more flexible than 1.
Additionally, the remaining secondary amine function of 2 can
be further functionalised to obtain a new ligand 3 which possesses
a carboxylic pendant arm. Indeed, this simple strategy proved to
be efficient to increase the kinetics of metallation of bismuth in
tetra-aryl porphyrins.10 The succinic motif was selected on the
basis of its length which appears sufficient to allow the terminal
carboxylic acid to coordinate a large cation inside the porphyrin.
Thus, 2 reacts easily at room temperature with succinic anhydride
leading to 3 in 81% yield. Where 1 or 2 are expected to stabilize
bivalent metals with the dianionic porphyrin ligand, this new
ligand 3 can supply intramolecularly a third counter-anion to a
trivalent element such as bismuth or a lanthanide. From the proton
NMR data of 1 and 2, as expected, in solution, the crown-ether
macrocycle is less shielded in 2 than in 1. Moreover, in the latter,
the mean planes of the two macrocycles are on average parallel as
revealed by the three singlets of the crown-ether integrating for 8
protons each at 2.56, 1.94 and 0.49 ppm. The study of the new
bis-macrocycle 3 could supply additional information about the
effective pre-organisation of the bis-macrocylic scaffold common
in 2 and 3. For instance, the proton NMR crown-ether signature
in 2 is composed of 3 broad singlets at 2.88, 2.38 and 1.97. In 3,
it appears roughly as the same 3 broad signals at 2.80, 2.75 and
2.42 ppm. The shift to lower field for one signal can be attributed to
the change of the secondary amine of 2 to the withdrawing electron
amide group of 3. The pendant succinamic residue of 3 leads to
two poorly resolved triplets at 2.39 and 2.26 ppm. These chemical
shifts can be compared with those of the analogous compound in
which the succinamic acid is tethered directly on the meso aromatic
group of the porphyrin at 1.99 and 1.64 ppm.11 From this light
deshielding, it can be concluded that the pendant succinamic acid
is located further away with no specific orientation towards the
porphyrin. However, the basic concept of this type of ligand was
to probe the possibility of an effect of the crown-ether via an
interaction of its oxygen donor atoms on the insertion of large
cations into the ligand. In such an eventuality, the crown-ether as
well as the pendant arm would move closer to the porphyrin.
˚
˚
respective bond lengths of 2.98 A and 3.00 A. The distances from
˚
˚
the porphyrinic mean plane to O4 and O5 are 3.10 A and 2.95 A,
respectively. Knowing that the average out-of-plane distance for a
BiIII atom in a porphyrin is 1.2 A,13 this specific geometry of 1 could
˚
rationalize why the metallation process is disfavoured for bismuth.
Additionally, the distortion of the porphyrin plane observed in 1
is almost a pure ruffled distortion with a torsion angle Ca–N4–
N2–Ca = 11.5◦. This distortion is not compatible with the domed
distortion required for a bismuth porphyrin.14 Indeed, the two
meso carbon atoms C10 and C20 are pulled outside the plane
of the porphyrin towards the crown-ether and the four nitrogen
atoms are located below the plane of the porphyrin. With such a
Fig. 1 X-Ray structure of 1 (black spheres depict atoms above the mean
porphyrin plane, the four nitrogen atoms are located below this plane.
˚
Vertical positions relative to the plane in A: C5: −0.19, C10: 0.26, C15:
−0.17, C20: 0.18).
¶ This structural study was rather difficult to solve and refine due to a
poor diffracting sample, presence of solvents and disorder in a chain.
Furthermore it appears that this structure is not really centrosymmetrical
(C2/c) but Cc. Considering the Ccspace group, two porphyrins are found
in the asymmetric unit with disorder in only one molecule. However, as
we are very close to centrosymmetry, correlations exist in the refinement
matrix, hence a poor quality of the geometry for the two moieties and non-
positive definite atoms. This pseudo centrosymmetry also explains illogical
intermolecular distances for a solvent molecule.
* The mean porphyrin plane is composed of the 24 atoms of the macrocycle.
For the metalloporphyrins, the coordinated metal is not considered. In the
case of the crown-ether, the mean plane was calculated only considering
the six heteroatoms of the macrocycle but not the carbon atoms.
Structural studies
It has been previously reported that a bis-crown-ether porphyrin
was not able to cooordinate bismuth. This observation was
explained by the strength applied on each side of the porphyrin by
the linked crown-ether.12 This is, in part, why the coordination
of bismuth on a mono-crown-ether porphyrin such as 1 was
also investigated. Unfortunately, the metallation process, using
bismuth nitrate or bismuth chloride, even at 100 ◦C, was not
more successful. Some explanations are supplied by the structural
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Table 1 Details of data collection, structure solution and refinement for 1, 1Zn, 1Pb (refinement method: full-matrix least squares (F2))
Compound
1
1Zn
1Pb
Empirical formula
C62H62N8O10·0.5C5H12·C2H5OH
1161.35
100(1)
292378
0.71073
2(C62H60N8O10Zn·H2O)·CH2Cl2
C62H60N8O10Pb·2CHCl3·(0.5H2O)2
Mr
2406.12
1541.16
T/K
120(1)
296454
0.71073
120(1)
628337
0.71073
CCDC n◦
˚
k/A
Crystal system
Space group
Monoclinic
C2/c
14.8938(7)
22.5940(7)
35.296(2)
—
101.776(4)
—
11628(1)
Monoclinic
P2/a
23.755(1)
8.6928(4)
30.912(1)
—
108.134(1)
—
6066.2(4)
1.401
Monoclinic
P21/n
17.2553(4)
20.8665(5)
18.5943(5)
—
101.284(2)
—
6566.2(3)
1.559
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
Dc/Mg m−3
1.327
8
0.91
Z
2
6.05
4
l/cm−1
28.79
F(000)
4936
2664
3104
Crystal size/mm
0.25 × 0.12 × 0.12
2.53–26.00
0 to 18, 0 to 27, −43 to 43
80307
11076 (0.0555)
96.8
None
11076/0/762
1.145
R1 = 0.1098
wR2 = 0.3292
R1 = 0.1682
wR2 = 0.3518
2.385, −1.015
0.35 × 0.20 × 0.16
2.53–26.00
0 to 29, 0 to 10, −38 to 38
41065
11877 (0.0612)
99.4
None
11877/0/777
0.861
R1 = 0.0430
wR2 = 0.0996
R1 = 0.0995
wR2 = 0.0.1073
1.388, −0.670
0.25 × 0.15 × 0.08
2.91–32.22
−22 to 25, −31 to 27, −25 to 26
60218
20640 (0.0545)
88.9
None
20640/0/820
0.998
R1 = 0.0483
wR2 = 0.1351
R1 = 0.0917
wR2 = 0.1417
2.692, −1.959
h Range/◦
Index ranges hkl
Reflections collected
Independant reflections (Rint
Completeness to hmax (%)
Absorption correction
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
)
R Indices (all data)
−3
˚
Dqmax, min/e A
distortion, bismuth cannot be coordinated inside the cavity of the
macrotricycle in as much as bismuth would require an additional
nitrato residue as counter-anion.
Conversely, in macrotricycle 1, the steric hindrance—
particularly emphasized by the possible conformation of the
crown-ether found in the X-ray structure—is possibly the crucial
factor that explains why no coordination of bismuth(III) occurs.
This behaviour could be different for bivalent cations such as
zinc(II) or lead(II), which is isoelectronic with bismuth(III). Obvi-
ously, zinc(II), known to be usually five-coordinate in porphyrins,
is much smaller than bismuth(III) with an EIR = 68 pm. Lead(II),
which also exhibits a similar lone-pair character to bismuth(III),
also has a smaller EIR = 98 pm with a CN = 4 in porphyrins.
Thus, zinc insertion was sucessfully performed at room tem-
perature according to well established methods.17 In solution, by
proton NMR spectroscopy, the chemicals shifts of the signals from
the methylene groups of the crown-ether in 1Zn were shown to be
2.17, 1.66 and 1.07 ppm. The difference between the most shielded
and the least shielded protons is 1.1 ppm where this difference
in the free-base compound is 2.1 ppm. In light of the known
structure of 1, this observation is consistent with a crown-ether
more parallel with the porphyrin in 1Zn than it is in 1. Crystals
suitable for X-ray analysis were obtained by slow diffusion of
methanol into a solution of 1Zn in chloroform and revealed two
different porphyrins in the structure (Fig. 2, Table 1). The first
striking difference with 1 is the parallel arrangement of the crown-
ether with the porphyrin. Indeed, in both motifs (A) and (B), the
angles between the porphyrin and the crown-ether are 0.0◦ and
3.4◦, respectively. This geometry is the result of the coordination of
a water molecule on the zinc atom. This water molecule is stabilized
by two hydrogen bonds with two oxygen atoms diametrically
These results prompted us to investigate the possible coordi-
nation of bismuth by ligands 2 and 3. As ligand 1 appears to be
sterically over-crowded, 2 and 3 are more freely hinged and less
congested bis-macrocycles, 3 further exhibiting an intramolecular
counter-anion for bismuth inside the porphyrin. Thus, bismuth
insertion was investigated in 2 and 3 with either Bi(NO3)3 or BiCl3
(10 equiv.) in pyridine at various temperatures from 50 ◦C up
◦
to 100 C overnight. Higher temperatures were not tested as the
structural integrity of the ligands would be affected by atropiso-
merisation of the meso nitro-phenyl group. The failure of bismuth
insertion at 100 ◦C is in favour of a lack of interaction of the crown-
ether motif. Therefore, it is logical that bismuth insertion requires
higher temperatures than 100 ◦C just as in unfunctionalized
porphyrins.15 To confirm this result, the insertion of lanthanum
was also studied. Indeed, with a coordination number of 8,
which would be expected in 3, BiIII and LaIII exhibit the same
effective ionic radius (EIR) of 116 pm.16 Unfortunately, with
La(CF3SO3)3·H2O (10 equiv.) in pyridine, lanthanum insertion in
◦
3 remained unsuccessful too, even at 100 C overnight. As LaIII
usually exhibits coordination numbers (CN) from 6 to 12, and as
ligand 3 can formally allow a CN = 9, this result indicates that
bis-macrocycles such as 3 are not suitable for the coordination of
large trivalent cations such as BiIII or LaIII, presumably because of
a too large distance between the two building blocks, namely the
porphyrin and the crown-ether.
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Fig. 2 X-Ray structure of the aqua complex of 1Zn. The two independent zinc complexes each have crystallographically imposed twofold symmetry, with
˚
the Zn1–O4 and Zn2–O44 bonds on the two fold axes (MP: mean porphyrinic plane, distances in A; O43–O44 = 2.959, Zn2–O44 = 2.143, Zn2–MP =
−0.355, O4–O2 = 2.723, Zn1–O4 = 2.064, Zn1–MP = 0.189, Zn1–Zn2 = 16.757).
located in the crown-ether. In motif (B), the axial water molecule
(O4) is coordinated inside the macrotricyclic cavity with hydrogen
bonds to O2 atoms. In porphyrin (A), the axial water molecule
(O44) is coordinated outside the macrotricyclic pocket and is held
by two hydrogen bonds to O43 atoms from the crown-ether of
another molecule. Both Zn–O and hydrogen bonds are shorter in
motif (B) than in motif (A) (Fig. 2 caption). In motif (A) in which
the intermolecular hydrogen bonds form a wire in the crystal, it
˚
is worth noting that Zn2 is −0.355 A below the mean porphyrin
˚
plane. This distance is much shorter in motif (B) (0.189 A) in which
the hydrogen bonds are intramolecular. It should be underlined
that in both motifs (A) and (B), the polyhedron of coordination of
zinc with the weakly bound axial water molecule induces a parallel
conformation of the system at least in the solid state.
The same experiment was carried out with lead using lead
acetate in pyridine at 50 ◦C for the metallation reaction. After
1 h, the metallation was complete. On one hand, in solution, the
proton NMR chemical shifts of the methylene groups from the
crown-ether in 1Pb are observed at 2.57, 1.83 and 0.91 ppm. They
are almost the same as those of the free-base compound (2.56,
1.94 and 0.49) with the exception of the most shielded signal.
Thus, this similitude is in favour of a position of the crown-ether
perpendicular to the porphyrin in 1Pb. On the other hand, in the
solid state, it is known from previous X-ray studies that lead(II)
in porphyrins remains four-coordinate out of the plane of the
porphyrin.18
As for 1 and 1Zn, crystals suitable for X-ray analysis by slow
diffusion of methanol into a chloroform solution of 1Pb were
obtained (Fig. 3, Table 1). The same spatial arrangement of the
crown-ether present in 1 is found in 1Pb, with the crown-ether
orthogonal to the mean porphyrin plane (88◦) and the existence of
two hydrogen bonds between two adjacent oxygen atoms O2 and
O3 of the crown-ether and the two nitrogen atoms N5 and N8 from
the amide groups of the porphyrin. As expected, lead(II) is four-
Fig. 3 X-Ray structure of 1Pb (MP: mean porphyrinic plane, distances
˚
in A; Pb–MP = 1.417, N5–O2 = 2.916, N8–O3 = 2.905, N1–Pb = 2.409,
N2–Pb = 2.386, N3–Pb = 2.394, N4–Pb = 2398).
atoms as well as the nitrogen atoms on the side of lead. Therefore,
the perpendicular conformation of the crown-ether excludes the
“inside” coordination of lead. This observation is consistent with
an interaction of the lone pair of lead with those of O2 and O3 or
directly with the scaffold of the crown-ether.19 It is also possible
that the linkage of the crown-ether induces a distortion—as seen
in 1—which is favourable to a coordination of lead outside the
cavity of the macrotricycle.
Experimental
˚
coordinate, 1.417 A out of the plane of the porphyrin but outside
(i) General considerations
the macrotricyclic cavity. The lengths of nitrogen-to-lead bonds are
comparable with those reported for the “roof” porphyrin.18a The
porphyrin adopts a domed distortion with the b pyrrolic carbon
atoms on the side of the crown-ether and the a pyrrolic carbon
1H (500.13 MHz, 300.13 MHz) and 13C (125 MHz, 75 MHz)
NMR spectra were recorded on Bruker Avance spectrometers
and referenced to the residual protonated solvent. Mass spectra
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were performed on a MS/MS ZABSpec TOF spectrometer at
the University of Rennes I (C.R.M.P.O.). UV-visible spectra were
recorded on an Uvikon XL spectrometer. Infrared spectra were
recorded on Bruker IFS28 spectrometer. All solvents (ACS for
analysis) were purchased from Carlo Erba. THF was distilled over
potassium metal whereas methanol was distilled over magnesium
turnings. CH2Cl2 was used as received. Triethylamine was distilled
over CaH2. The starting materials were generally used as received
(Acros, Aldrich) without any further purification. All reactions
were performed under an argon atmosphere and monitored by
TLC (silica, CH2Cl2–MeOH). Column flash chromatography was
performed on silica gel (Merck TLC-Kieselgel 60 H, 15 lm).
1.07 (8H, br s, CH2). 13C NMR (CDCl3, 298K, 75 MHz): d =
158.8, 150.0, 140.9, 132.8, 131.6, 129.3, 121.8, 121.3, 114.9, 113.3,
99.5, 77.2, 69.2, 56.6, 48.6. ESI-HRMS: calcd m/z = 1140.3724
•
[M]+ for C62H60N8O10Zn, found 1140.3743. UV-vis (CH2Cl2): k,
nm (10−3e, dm3 mol−1 cm−1): 427 (440.1), 559 (16.6), 591 (5.6),
601 (6.4).
1Pb. In a 50 mL flask, 16 mg (14.8 lmol) of 1 were◦dissolved
in 4 mL pyridine. The solution was warmed up to 50 C before
6.2 mg (16.3 lmol) of Pb(OAc)2·3H2O were added. After 1 h of
heating, the solvent was evaporated and dissolved in a minimum
of CHCl3 to be poured onto a silica gel chromatography column.
Complex 1Pb was eluted with a 0.5% CH3OH–CHCl3 mixture
and obtained in 84% yield (16 mg, 12.5 lmol). 1H NMR (CDCl3,
298 K, 500 MHz): d = 9.11 (4H, d, J = 4.0 Hz, bpyr), 8.92 (4H,
d, J = 4.0 Hz, bpyr), 8.54 (2H, br s, aro), 7.95 (2H, d, J = 7.5 Hz,
aro), 7.77 (2H, t, J = 7.5 Hz, aro), 7.56 (2H, br s, aro), 7.39
(4H, br s, aro), 6.92 (2H, br s, aro), 5.67 (2H, s, NHCO), 4.00
(12H, s, OCH3), 2.57 (8H, s, CH2), 1.83 (8H, br s, CH2), 0.91
(8H, br s, CH2). 13C NMR (CDCl3, 298K, 125 MHz): d = 158.9,
158.7, 149.1, 140.6, 134.3, 132.4, 131.8, 129.2, 121.2, 114.2, 99.8,
68.6, 55.6, 49.6. ESI-HRMS: calcd m/z = 1285.4277 [M + H]+ for
C62H61N8O10Pb, found 1285.4287. UV-vis (CH2Cl2): k, nm (10−3e,
dm3 mol−1 cm−1): 354 (20.4), 468 (156.3), 606 (6.2), 654 (8.1).
(ii) Ligand precursors
Ligands 1 and 2 were synthesized as previously described.9
4-(16-{2-[a-15-(2-Nitro-phenyl)-10,20-bis-(2,4,6-trimethyl-phe-
nyl)-porphyrin-a-5-yl]-phenylcarbamoyl}-1,4,10,13-tetraoxa-7,16-
diaza-cyclooctadec-7-yl)-4-oxo-butyric acid 3. In a 50 mL flask,
2 (24 mg, 22.9 lmol) and aluminium oxide (2.3 mg, 22.9 lmol)
were dissolved in 10 mL of dry CH2Cl2. Then succinic anhydride
(3.4 mg, 34.4 lmol) was added and the reaction was stirred at room
temperature. After 3 h, the solution was evaporated to dryness and
the residue dissolved in a minimum of CHCl3 to be poured onto
a silica gel chromatography column. Product 3 was eluted with a
0.1 : 12 : 87.9 acetic acid–CH3OH–CHCl3 mixture and obtained
(iv) Crystallographic method
1
The samples were studied on an Oxford Diffraction Xcalibur
Saphir 3 diffractometer with graphite monochromatized Mo-Ka
radiation. The data collections were performed with CrysAlis.20
The structures were solved with SIR-9721 which revealed the non-
hydrogen atoms of the molecule. After anisotropic refinement,
many hydrogen atoms may be found with a Fourier Difference.
Atomic scattering factors were taken from ref. 22, ball and stick
views were realised with PLATON9823 and Pov-RAY. The whole
structures were refined with SHELXL9724 by the full-matrix least-
squares techniques (use of F2 magnitude, x, y, z, bij for C, Cl, N,
O, Pb and Zn atoms, x, y, z in riding mode for H atoms).
in 81% yield (21 mg, 18.5 lmol). H NMR (500 MHz, CDCl3):
d = 8.86 (d, J = 4.5 Hz, 2H, bpyr), 8.72–8.70 (m, 4H, bpyr), 8.62
(m, 3H, bpyr + aro), 8.45 (d, J = 8.5 Hz, 1H, aro), 8.23 (d, J =
8.2 Hz, 1H, aro), 8.02 (t, J = 8.0 Hz, 1H, aro), 7.97 (t, J = 8.0 Hz,
2H, aro), 7.83 (bs, 1H, NH), 7.76 (t, J = 7.8 Hz, 1H, aro), 7.37 (t,
J = 7.8 Hz, 2H, aro), 7.31 (bs, 4H), 3.10 (bs, 4H, –CH2–), 3.00–
2.00 (bs, 12H, –CH2–), 2.74 (bs, 4H, –CH2–), 2.65 (s, 6H, –CH3),
2.43 (bs, 4H, –CH2–), 2.40 (m, 2H, –CH2–), 2.26 (bs, 2H, –CH2–),
1.86 (s, 6H, –CH3), 1.83 (s, 6H, –CH3), −2.56 (s, 2H, NHpyr). 13
C
NMR (125 MHz, CDCl3): d = 136.9, 135.1, 131.1, 129.7, 129.5,
127.9, 123.9, 120.3, 119.1, 48.4, 30.5, 27.7, 21.6, 21.5, 21.4. ESI-
HRMS: calcd m/z = 1169.5113 [M + Na]+ for C67H70N8O10Na,
found 1169.5112. FTIR (KBr, cm−1): 1710 (CO)acide, 1670 (CO)amide
1660 (CO)urea, UV-vis (CH2Cl2) k, nm (10−3e, dm3 mol−1 cm−1): 421
,
Conclusions
In this work, the coordination properties of a macrotricycle and
two different bis-macrocycles towards the possible chelation of
various elements such as bivalent cations (Zn, Pb) and trivalent
cations (Bi, La) were studied. Although the structure of both bis-
macrocycles is expected to be more flexible, none of them is able
to coordinate bismuth(III) or lanthanum(III). In contrast to tetra-
aryl porphyrins, a pendant-armed succinamic acid attached to the
crown-ether does not improve the coordination of large trivalent
cations. It is plausible that the urea linkage between the two
macrocycles represents a too rigid hinge and that the crown-ether
motif cannot interact together with the porphyrin in the metalation
process. On the other hand, the rigid macrotricycle exhibits an
interesting behavior towards the chelation of bivalent cations.
Indeed, it has been shown that, relative to the porphyrin plane,
the crown-ether can switch from an orthogonal conformation to a
parallel position. Accordingly, the coordination of lead(II) occurs
outside the macrotricycle in which the orthogonal conformation
of the crown-ether is locked by two hydrogen bonds with the amide
groups of the porphyrin as in the free-base compound. In contrast,
(202.8), 515 (10.2), 550 (5.1), 592 (5.1), 647 (4.1).
(iii) Complex syntheses
1Zn. To a solution of porphyrin 1 (23.2 lmol, 25 mg) in THF
(10 mL) was added zinc acetate (0.185 mmol, 41 mg) and sodium
acetate (0.185 mmol, 15.2 mg). The mixture was stirred overnight
at room temperature, then solvent was removed under vacuum.
The resulting powder was dissolved in chloroform and washed
with water, dried over MgSO4 and concentrated under vacuum.
The resulting powder was dissolved in chloroform and directly
loaded onto a silica gel chromatography column. The expected
compound eluted with 4% MeOH–CHCl3 was obtained in 82%
yield (22 mg). 1H NMR (CDCl3, 298 K, 300 MHz): d = 8.98 (4H,
d, J = 4.5 Hz, bpyr), 8.85 (4H, d, J = 4.5 Hz, bpyr), 8.46 (2H, d,
J = 7.2 Hz, aro), 7.98 (2H, d, J = 8.1 Hz, aro), 7.72 (2H, t, J =
7.5 Hz, aro), 7.54 (2H, t, J = 7.5 Hz, aro), 7.41 (2H, s, aro), 7.20
(2H, s, aro), 6.92 (2H, br s, aro), 5.69 (2H, s, NHCO), 4.01 (6H, s,
OCH3), 3.88 (6H, s, OCH3), 2.17 (8H, s, CH2), 1.66 (8H, s, CH2),
3688 | Dalton Trans., 2007, 3684–3689
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the coordination of zinc(II) implies a change of conformation of
the ligand in which the crown-ether is parallel to the porphyrin.
This phenomenon is due to an axially coordinated water molecule
twice hydrogen-bound to two diametrically located oxygen atoms
of the crown-ether.
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Acknowledgements
We acknowledge Platon bilateral program for financial support,
also part of the project is co-funded by the European Social Fund
and National resources (GC). We gratefully acknowledge La Ligue
contre le cancer, Re´gion Bretagne, and the Agence Universitaire
pour la Francophonie. We are particularly indebted to the Comite´
des Coˆtes-d’Armor de La Ligue contre le cancer for his generous
help to ZH.
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