First synthesis of sterically hindered cofacial bis(corroles) and their bis(cobalt) complexes

Article abstract of DOI:10.1039/a805078c

Syntheses of face-to-face bis(corroles) exhibiting electronic interactions between the two chromophores.

Full text of DOI:10.1039/a805078c

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First synthesis of sterically hindered cofacial bis(corroles) and their bis(cobalt)
complexes
François Jérôme, Claude P. Gros, Catherine Tardieux, Jean-Michel Barbe and Roger Guilard*†
Laboratoire d’Ingénierie Moléculaire pour la Séparation et les Applications des Gaz (L.I.M.S.A.G.), U.M.R. 5633, Faculté des
Sciences ‘Gabriel’, 6, boulevard Gabriel, 21000 Dijon, France. E-mail: Roger.Guilard@u-bourgogne.fr
Syntheses of face-to-face bis(corroles) exhibiting electronic
R
H
interactions between the two chromophores.
R
R
NH
NH
NH
HN
HN
+
+
NH
MeOH
HBr
During the past few decades, numerous research has been
devoted to the synthesis of dimeric and higher order porphyrins
and, to a lesser extent, other macrocyclic tetrapyrroles cova-
lently linked by rigid linkers.1,2 Bis(porphyrins) with a gable or
face-to-face spatial arrangement are effective catalysts for the
four-electron reduction of dioxygen to water3 and the oxidation
of organic substrates.4 A few years ago, ‘Pacman’ porphyrins
achieved the microscopic reverse of dinitrogen fixation.5 As a
result of these significant data, many bisporphyrins and higher
oligomers have been prepared with a wide variety of linking
units.6 Except for a few examples,7 most of these rigidly linked
dimeric and higher order oligomeric systems have consisted of
porphyrin subunits. At the same time, corrole macrocycles were
gaining considerable attention due, in part, to their very rich
chemistry and to their ability, compared to porphyrins, to
stabilize higher oxidation states of certain coordinated metals.8
Very recently, symmetrical and unsymmetrical linear bis(cor-
role) and porphyrin–corrole dyads possessing para-phenyl
linking units have been described.7b Herein, we wish to report
the first synthesis of cofacial bis(corroles) H6BCA and
H6BCB9 as well as their bis(cobalt) complexes in order to study
metal–metal interactions.
H
R
Ar
Ar
R
R
H
R
R
NH
NH
NH
+
HN
HN
+
NH
H
CHO
N
H
H
R
2: R = Et
7: R = Ph
R
, 4 Br–
3a: R = Et
8a: R = Ph
1A : Ar = Anthracene bridge
R
R
NH
NH
N
HN
R
3a: R = Et
8a: R = Ph
R
R
1) NaHCO3
2) p-chloranil
3) N2H4 aq.
R
NH
NH
N
HN
R
R
3: R = Et
8: R = Ph
Scheme 1
unstable for a full characterization. Indeed, when left in solution
in the presence of air and light, 3 readily decomposed over a
period of a few minutes into a small amount of less-polar
compounds, along with a large amount of base-line materials
presumably due to the decomposition reaction with dioxygen of
the free-base bis(corrole) which acts as a sensitizer. Such an
instability has been pointed out for 10-monophenyl corrole 4
(Scheme 2).11b Indeed, compound 4 (as a free-base) was found
to be air-sensitive when left in solution and one of its
R
H6BCA : Ar = Anthracene bridge
R
R
N
N
N
N
M
M
3: M = 3H, R = Et
N
N
8: M = 3H, R = Ph
10: M = Co(py), R = Ph
11: M = Co, R = Ph
R
Ar
R
R
N
N
H6BCB : Ar = Biphenylene bridge
9: M = 3H, R = Ph
R
R
Ph
Me
Me
Ph
Me
Me
Me
Me
In the course of our work on the syntheses of cofacial
bis(porphyrins),10 it occurred to us that the conjugate addition
of a 3,4-disubstituted-2-formylpyrrole to a face-to-face bis(di-
pyrromethane) followed by a cyclization step should represent
a versatile method for new cofacial bis(corroles) formation.
Indeed, reaction of compound 1A10 with 4 equivalents of 2 in
methanol and in the presence of 30% hydrobromic acid in acetic
acid led in a first step to the bis(a,c-biladiene) salt 3a (Scheme
1), the progress of the reaction being monitored by UV–VIS
spectroscopy. In-situ addition of sodium hydrogencarbonate
and p-chloranil followed by addition of 50% hydrazine in water
gave 3 as a crude compound after solvent removal. Final
purification by chromatography on basic alumina afforded 3 in
5.5% yield. The proton NMR spectrum of the C2 symmetric
derivative 3 exhibits the characteristic patterns of two corrole
units cofacially linked by an anthracenyl bridge.11a Compound
3 displays a pseudo-molecular peak at m/z = 1163 [M + H]+, a
Soret band at 402 nm and three Q bands at 510, 548 and 598 nm.
Unfortunately, the free-base bis(corrole) 3 was found to be too
Me
Et
Me
NH HN
NH
HN
O2
NH
N
NH
O
N
Et
Et
Et
O
Et
Et
Et
Et
Et
Et
4
5
Me
Me
O2
NH HN
NH
N
Ph
Ph
Ph
6
Ph
Scheme 2
Chem. Commun., 1998
2007

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decomposition products was identified as an open chain
tetrapyrrole structure 5.11b To our knowledge, this is the first
example of molecular oxygen oxidation of a corrole macrocycle
to a biliverdin structure. Our data led to a possible reaction
mechanism involving addition of dioxygen at the 1,19-double
bond of the corrole derivative followed by bond cleavage giving
two amide groups as terminal functions. In order to prevent
oxidative attack of the corrole ring and cleavage of the
1,19-double bond, the four b-pyrrole positions (positions 2,3,17
and 18) were substituted by phenyl groups. As expected, free-
base corrole 611b,12 is far more stable than its alkyl-substituted
counterpart 4 as the presence of the bulky phenyl groups prevent
dioxygen oxidation of the 1,19-double-bond. Indeed, the
decomposition of 6 in solution in the presence of air and light
only occurred over a period of a few days.
According to these results, we were able to synthesize a stable
free-base bis(corrole) 8 (Scheme 1) by reacting first 1A10 with
7,13 and then by cyclizing the bis(a,c-biladiene) intermediate
8a, using p-chloranil as an oxidant. The free-base derivative 814
was isolated in 12.5% yield. Starting from 1,8-diformylbiphe-
nylene as a spacer and using the same experimental procedure,
compound 915 was obtained in 12% yield. LSIMS mass spectra
confirms the dimeric structure of 8 and 9 (m/z 1549 [M + H]+
and 1523 [M + H]+, respectively). Cofacial bis(corroles) 8 and
9, containing phenyl rings at eight b-pyrrole positions, are really
more stable than the unprotected one 3. Indeed, when 8 and 9
are exposed in solution to air and light, no major decomposition
is observed after a period of 48 h. Interestingly, the UV–VIS
absorptions of 8 and 9 show that the spectra are not simply
superpositions of the absorptions of the two corrole chromo-
phores. In particular, the Soret bands of 8 and 9 are red-shifted
with respect to those of the simple corrole possessing the same
substitution patterns due to the electronic interactions occurring
between the two corrole units in 8 and 9. It is also worthy to note
that no electronic interaction has been observed in the recently
published linear dimers.7b
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Kadish, Inorg. Chem., 1995, 34, 184.
9 H6BC for free-base biscorrole, A for anthracene bridge, B for
biphenylene bridge.
10 M. Lachkar, A. Tabard, S. Brandès, R. Guilard, A. Atmani, A. De Cian,
J. Fischer and R. Weiss, Inorg. Chem., 1997, 36, 4141; R. Guilard, S.
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11 (a) 1H NMR (CDCl3) for 3: d 8.84 (s, 4 H, meso H), [10.27 (s, 1 H), 8.40
(s, 1 H), 7.65 (d, 2 H), 7.54 (d, 2 H), 6.94 (dd, 2 H) anthracene H], 3.91
(m, 24 H, CH2CH3), 2.15 (s, 12 H, Me), 1.44 (m, 36 H, CH2CH3), 22.61
(s br, 6 H, NH); (b) C. Tardieux, C. P. Gros and R. Guilard,
J. Heterocycl. Chem., 1998, in press.
Standard procedures were employed to metallate the corrole
core with cobalt acetate.16 Compound 8 was heated at 80 °C in
pyridine with 2.5 equivalents of Co(OAc)2, the metallation
reaction being monitored by UV–VIS spectroscopy. Comple-
tion of the reaction occurring within 1–2 h was indicated by the
complete disappearance of the absorption at 607 nm and the
appearance of a Q band at 597 nm; the Soret band being
simultaneously slightly red-shifted (lmax 414 and 435 nm).
After purification, the homobimetallic BCA(Co)2(py)2 deriva-
tive 10 was isolated in 23% yield. Interestingly, the two axial
pyridine ligands can easily be removed under vacuum (20
mmHg, 50 °C) to yield quantitatively 11. The electronic
absorption spectra of 11 shows a 37 nm blue-shift of the Soret
12 Elemental analysis: Calc. for 6, C49H42N4: C, 85.68; H, 6.16; N, 8.16.
Found: C, 85.77; H, 6.21; N 7.80%. 1H NMR (CDCl3): d 9.76 (s, 2 H,
meso H5, H15), 9.50 (s, 1 H, meso H10), 7.88–6.96 (m, 20 H, Ph), 3.95
(q, 4 H, CH2CH3), 3.33 (s, 6 H, Me), 1.68 (t, 6 H, CH2CH3), 20.73 (s,
NH), 21.47 (s, NH). IR : n 3350 (NH), 2960 (CH), 2928 (CH), 2868
(CH) cm21. UV–VIS (CH2Cl2): lmax (e/dm3 mol21 cm21) 400 (83400),
413 (74700), 564 (19400), 599 nm (20 900); UV–VIS (after HCl
bubbling): lmax (e/dm3 mol21 cm21) 414 (95900), 475 (15000), 593
(39500). MS (EI): m/z (%) 686 (100) [M]+, 343 [M]2+
13 M. Friedman, J. Org. Chem., 1965, 30, 859.
.
14 Elemental analysis: Calc. for 8, C112H90N8·3H2O: C, 83.96; H, 6.04; N,
band [lmax (e/dm3 mol21 cm21
) = 377 (117000), 398
7.00. Found: C, 83.96; H, 6.00; N 6.78%. 1H NMR (C6D6): d 8.86 (s, 4
(144000), 529 (47 900) nm] compared to 10. In LSIMS mode,
the molecular peak for the BCA complex is observed at m/z =
1660 [M + H]+ (100%). It is also worthy to note that 11
decomposes rapidly in the absence of coordinated axial
ligands.
In conclusion, these cofacial bis(corroles) can be easily
prepared in four steps (starting from the bridging unit) and on a
large scale. Moreover, the synthesis of 8 and 9 described here
integrate well for the development of coordination chemistry of
cofacial bis(corroles) on a broad basis; work is currently
underway in these directions.
3
H, meso H), [8.79 (s, 1 H), 8.36 (d, JH–H = 6.5, 2 H), 7.98 (s, 1 H)
anthracene H], 7.80 (m, 8 H, Ph), [7.65 (d, 3JH–H = 6.5, 2 H), 7.57 (dd,
3JH–H = 6.5, 2 H) anthracene H], 7.52 (m, 8 H, Ph), 7.29 (m, 24 H, Ph),
3.27 (qd, 2JH–H = 14.7, 3JH–H = 7.5, 4 H, CHAHBCH3), 3.22 (qd, 2JH–H
= 14.7 Hz, 3JH–H = 7.5 Hz, 4 H, CHAHBCH3), 1.95 (s, 12 H, Me), 1.31
(t, 3JH–H = 7.5 Hz, 12 H, CH2CH3), 22.83 (s, 3 H, NH), 23.00 (s, 3 H,
NH). IR : n 3482 (NH), 3401 (NH), 2961 (CH), 2923 (CH), 2870 (CH)
cm21. UV–VIS (CH2Cl2): lmax (e/dm3 mol21 cm21) 406 (171000), 578
(44 500), 607 nm (37 000). MS (LSIMS): m/z 1549 [M + H]+.
15 Elemental analysis: Calc. for 9, C110H88N8·2H2O: C, 84.79; H, 5.96; N,
7.20. Found: C, 84.44; H, 5.98; N, 7.45%. 1H NMR (C6D6): d 9.59 (s,
4 H, meso H), [7.98 (d, 2 H), 7.61 (dd, 2 H), 7.47 (d, 2 H)] biphenylene
H], 7.10 (m, 40 H, Ph), 3.54 (m, 8 H, Et), 3.07 (s, 12 H, Me), 1.52 (t, 12
H, Et), 22.80 (s, 3 H, NH), 23.00 (s, 3 H, NH). UV–VIS (CH2Cl2):
lmax (e/dm3 mol21 cm21) 412 (142000), 572 (34000), 608 nm (33000).
MS (LSIMS): m/z 1523 [M + H]+.
Notes and References
1 L. R. Milgrom, in The Colours of Life, ed. L. R. Milgrom, Oxford
University Press, New York, 1997, p. 191.
2 J. L. Sessler and S. J. Weghorn, Expanded, Contracted and Isomeric
Porphyrins, Pergamon, Oxford, 1997.
16 M. Conlon, A. W. Johnson, W. R. Overend, D. Rajapaksa and C. M.
Elson, J. Chem. Soc., Perkin Trans. 1, 1973, 2281.
3 C. K. Chang, H.-Y. Liu and I. Abdalmuhdi, J. Am. Chem. Soc., 1984,
106, 2725; J. P. Collman, F. C. Anson, C. E. Barnes, C. S. Bencosme,
Received in Basel, Switzerland, 1st July 1998; 8/05078C
2008
Chem. Commun., 1998