Structural characterisation of the first mononuclear bismuth porphyrin

Article abstract of DOI:10.1039/b309615g

A single carboxylate picket bismuth porphyrin has been characterised in the solid state as the first instance of a non-dimeric structure; the carboxylate picket, bent over the macrocycle, is coordinated to the bismuth, inducing a significant distortion of

Full text of DOI:10.1039/b309615g

Structural characterisation of the first mononuclear bismuth porphyrin
Bernard Boitrel,*a Zakaria Halime,a Lydie Michaudet,a Mohamed Lachkarb and Loïc Toupetc
a Université de Rennes1, Institut de Chimie, UMR CNRS 6509, 35042 Rennes Cedex, France.
E-mail: Bernard.Boitrel@univ-rennes1.fr; Fax: 02 2323 5637; Tel: 02 2323 6372
b Université Sidi Mohammed Ben Abdellah, Faculté des Sciences Dhar El Mehraz, Département de Chimie,
B. P. 1796 (Atlas), 30 000 Fes, Morocco. E-mail: mlachkar@hotmail.com; Tel: 055 7331071; Fax: 055
7331071
c
Université de Rennes1, Groupe Matière Condensée et Matériaux, UMR CNRS 6626, 35042 Rennes Cedex,
France
Received (in Cambridge, UK) 12th August 2003, Accepted 12th September 2003
First published as an Advance Article on the web 30th September 2003
A single carboxylate picket bismuth porphyrin has been
characterised in the solid state as the first instance of a non-
dimeric structure; the carboxylate picket, bent over the
macrocycle, is coordinated to the bismuth, inducing a
significant distortion of the porphyrin core.
is as stable as its four pickets counterpart 4ESBi(NO3)
previously described.6 No demetallation was observed either
during the purification process or over long periods of time. We
were able to obtain crystals‡ suitable for X-ray study by
diffusion of water onto a solution of 1Bi in pyridine.
Obviously, as depicted in Fig. 1, the main difference with all
bismuth porphyrins reported to date, for which X-ray data were
obtained, is the mononuclear structure with the counter-anion
delivered by the unique arm of the ligand. Indeed, the two
oxygen atoms of the carboxylate group (O4 and O5) bound to
the metal centre are stabilised by two hydrogen bonds with the
neighbouring nitrogen from the amide linkage, N7 and N8
respectively. The two other coordination sites are occupied by
two water molecules (O7 and O8), the bismuth being eight-
coordinate and lying 1.145 Å above the N4 plane. The mean Bi–
N bond length is 2.343(2) Å, the same value as 2.340(2) Å in
4ESBi(NO3).6 The two coordinated water molecules are also
included in a hydrogen bonding net. The first one, O7 is
hydrogen bonded to O5 from the carboxylate group and to N5
The coordination chemistry of bismuth with different types of
ligands has recently regained interest both at the fundamental
and application levels.1 In the latter case, this can be explained
by the 212 and 213 isotope of bismuth that could be applied in
a radio-immunotherapy.2 Of particular interest among these
ligands is the porphyrin core. Indeed, until the early nineties,
only two reports of bismuth porphyrins were known in the
literature.3 More recently, several studies of new bismuth
porphyrins4 have been published including the X-ray structure
of the metal complexes.5 Owing to these solid state structures,
the out-of-plane coordination of the bismuth cation was
confirmed. Additionally, all the complexes crystallise as dimers
with either bridging halide or nitrate ions, or solvents mole-
cules.
In 2000, we reported the synthesis and the characterisation of
a bismuth porphyrin bearing four ester pendant arms.6 We had
designed this new ligand with potentially oxygen-atom donors
around the metallic cation. We had chosen an aliphatic and
flexible group such as the ethyl succinyl residue to allow an
eventual folding of the pickets over the coordination site.
Actually, the X-ray structure revealed that the coordination of
the ester carbonyl group occurs through the formation of a
centrosymmetric dimer and for only one picket. Indeed, the
bismuth atom was found to be eight-coordinate with a bidentate
nitrato ligand and a water molecule. Thus, it appeared that the
three other pickets were not in direct interaction with the
bismuth itself.
These observations prompted us to synthesise a related
porphyrinoid ligand with only one picket of the same length and
flexibility than the previously used motif. On the other hand, we
decided to investigate the possible coordination of a carboxylate
group in lieu of the ester function. Indeed, this group could
eventually represent the counter-anion of the bismuth cation in
the porphyrin core and therefore, satisfy its coordination
sphere.
Scheme 1 Reagents and conditions: i, CH3COCl (3 eq.), NEt3, THF; ii,
ClCO(CH2)2CO2Et (1.1 eq.), NEt3, THF; iii, KOH, EtOH, 55 °C; iv,
Bi(NO3)3·5H2O (3 eq.), 50 °C, pyridine.
The preparation of the succinic acid (SA) picket porphyrin
1Bi is outlined in Scheme 1. The first step of the synthesis
requires the protection of three amino groups of the meso(tetra-
o-aminophenyl)porphyrin (atropisomer aaaa, TAPP) with
acetyl chloride in dry THF. The optimisation of the yield (55%)
towards the three-protected porphyrin 2 requires the use of 3 eq.
of the acylation reagent and the separation of undesired
compounds such as the tetra- and di-acylated porphyrins was
performed on a silica-gel chromatography. The remaining
amino group was functionalised with 1.1 eq. of ethyl succinyl
chloride to obtain 3 (89%) whose ester group was hydrolysed
with KOH, leading to 1.† The metal insertion was achieved by
heating at 50 °C the free-base porphyrin in pyridine with
bismuth nitrate. It is worth noting that the bismuth complex 1Bi
Fig. 1 ORTEP diagram (30% thermal ellipsoids) of 3Ac1SABi 1Bi.
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This journal is © The Royal Society of Chemistry 2003

from an acetamide residue. The second one, O8 is hydrogen
bonded to N10 of a solvated pyridine molecule and to another
water molecule (O9) itself hydrogen bonded to N6, also from an
acetamide residue.
We gratefully acknowledge La Ligue contre le cancer as well
as Région Bretagne for financial support.
Notes and references
The bismuth atom is coordinated in a distorted antiprismatic
geometry as shown in Fig. 2. This distortion is particularly
appreciable with the O7–Bi–O8 and O4–Bi–O8 angles which
are 76.87 ° and 76.31° respectively, where the O4–Bi–O5 and
O5–Bi–O7 are 46.97 ° and 58.30°. It is reasonable to correlate
this distortion to the deformation of the porphyrin plane which
adopt a “saddle-shaped” and ruffled conformation (Fig. 3).7 To
the best of our knowledge, this type of deformation of the
macrocycle has never been reported for bismuth porphyrins.
Indeed, the carbon atoms in the opposite meso positions (5,15
and 10, 20) are not located in the 24-atom least-squares plane
but above or below. More precisely, the deviations (Cm) from
the mean porphyrin plane of the four meso carbons are 0.297 Å,
20.150 Å, 0.243 Å and 20.164 Å, leading to an average value
of 0.213 Å, smaller than that observed for highly distorted
nickel porphyrins.8 Furthermore, the dihedral angles between
the two opposite pyrrole planes – e.g. C7–C8 and C17–C18 or
C2–C3 and C12–C13 – are 15.5 ° and 12.8 ° respectively. These
two major distortions seem to be the result of a too short length
of the coordinating arm as the latter has to pull the meso carbon
on which it is tethered to be able to coordinate the metal.
However, this hypothesis could be simply probed by the
substitution of the succinate by the glutarate motif which
possesses one more carbon.
In conclusion, this is the second example of a picket
porphyrin able to stabilise a metal such as bismuth. We have
been able to demonstrate that a suitable group located around
the metal can dramatically change the structure – and pre-
sumably the properties – of the complex. Thus, in the case of a
carboxylate residue, the bismuth does not require an ‘external’
counter-anion and the complex exhibits a mononuclear struc-
ture. On the other hand, the present study reminds us of the
importance of the steric factor as revealed by the significant
distortion of the porphyrinic core.
† Selected data for 3Ac1ES 3: HR-MS (FAB): m/z 929.3763 [(M + H)+,
100%]. dH(300 MHz, CDCl3, 300 K): 8.87 (s, 8H, b-pyr), 8.71 (br s, 4H,
aro), 7.8 (br s, 8H, aro), 7.55 (br s, 4H, aro), 6.97 (s, 4H, –NHCO), 3.55 (q,
J = 6.4 Hz, 2H, –CH2CH3), 2.19 (br s, 2H, –CH2CH2–), 1.60 (br s, 2H,
–CH2CH2–), 1.30 (br s, 9H, –CH3), 0.87 (t, J = 6.4 Hz, 3H, –CH2CH3),
22.71 (s, 2H, –NH pyr). For 3Ac1SA 1: HR-MS (ESI): m/z 939.3017 [(M
+ K)+, 100%]. dH(500 MHz, DMSO-d6, 298 K): 11.85 (s, 1H, –COOH),
8.81 (br s, 2H, –NHCO), 8.78 (br s, 2H, –NHCO), 8.70 (s, 8H, b-pyr), 8.14
(d, J = 7.5 Hz, 4H, aro), 8.10 (d, J = 7.5 Hz, 2H, aro), 7.94 (d, J = 7.0 Hz,
4H, aro), 7.83 (t, J = 8 Hz, 4H, aro), 7.57 (t, J = 6,5 Hz, 4H, aro), 1.99 (t,
J = 5 Hz, 2H, –CH2CH2–), 1.64 (br s, 2H, –CH2CH2–), 1.24 (s, 3H, –CH3),
1.22 (s, 6H, –CH3), 22.72 (s, 2H, –NH pyr). For 3Ac1SABi 1Bi: HR-MS
(ESI): m/z 1129.2863 [(M + Na)+, 100%].UV-VIS (CH2Cl2): lmax/nm (log
e/dm2 mol21cm21): 350 (4.8), 472 (13.5), 598 (1.7), 646 (1.5). FTIR (of
crystals, KBr, cm21): 1670 (CO); 990 r(Bi–Np). dH(500 MHz, DMSO-d6,
300 K): 9.03 (d, J = 4.5 Hz, 2H, b-pyr), 9.03 (d, J = 4.5 Hz, 2H, b-pyr),
8.99 (d, J = 8 Hz, 6H, Pyr), 8.97 (d, J = 5 Hz, 2H, b-pyr), 8.89 (d, J = 5
Hz, 2H, b-pyr), 8.72 (br s, 4H, aro), 8.55 (t, J = 7 Hz, 3H, Pyr), 8.33 (br s,
1H, aro), 8.33–8.26 (m, 2H, aro), 8.07 (t, J = 6.6, 1H, aro), 7.99 (t, J = 7.8
Hz, 6H, Pyr), 7.90 (m, 3H, aro), 7.73 (br s, 1H, aro), 7.45 (br s, 4H,
–NHCO), 7.36 (t, J = 7 Hz, 2H, aro), 7.16 (m, 2H, aro), 1.87 (br s, 2H,
–CH2–), 1.63 (br s, 2H, –CH2–), 1.49 (s, 9H, –CH3).
‡ Crystal data: C54H41BiN8O6·3H2O·1.5(C5H5N) : M = 2664.31, triclinic,
¯
space group P1, a = 12.7605(1), b = 13.8671(2), c = 15.7654(2) Å, a =
78.693(1), b = 89.696(1), g = 77.096(1)°, V = 2664.31(6) Å3, Z = 2, Dx
= 1.595 Mg m23, l(MoKa) = 0.71073 Å, m = 33.79 cm21, F(000) =
1290, T = 120 K. The sample (0.32*0.32*0.12 mm) is studied on a
NONIUS Kappa CCD with graphite monochromatized MoKa radiation.
The cell parameters are obtained with Denzo and Scalepack9 with 10 frames
(psi rotation : 1° per frame). The data collection (Nonius, 1999) ( 2qmax
=
60°, 310 frames via 2.0° omega rotation and 30 s per frame, range HKL : H
0,16 K 218,18 L 220,20) gives 71226 reflections. The data reduction with
Denzo and Scalepack9 leads to 12259 independent reflections from which
11368 with I > 2.0s(I). The structure was solved with SIR-200210 which
reveals the non hydrogen atoms of structure. After anisotropic refinement,
many hydrogen atoms may be found with a Fourier Difference. The whole
structure was refined with SHELXH11 by the full-matrix least-square
techniques ( use of F square magnitude ; x, y, z, bij for Bi, O, N and C atoms,
x, y, z in riding mode for H atoms ; 707 variables and 11368 observations
2
with I > 2.0s(I) ; calc w = 1/[s (Fo2) + (0.036P)2 + 6.55P] where P = (Fo2
+ 2Fc2)/3 with the resulting R = 0.033, Rw = 0.082 and Sw = 1.077, Dr <
2.17 eÅ23. Atomic scattering factors from International Tables for X-ray
Crystallography.12 Ortep views created with POV-Ray. CCDC 215678. See
http://www.rsc.org/suppdata/cc/b3/b309615g/ for crystallographic data in
.cif or other electronic format.
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Fig. 2 Coordination geometry of bismuth in 1Bi.
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Fig. 3 Side view of 1Bi looking along the N2–Bi–N4 axis. For the sake of
clarity, the hydrogen bonding net has been omitted.
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C. Wilson, Kluwer Academic Publishers, Dordrecht.
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