New route to a face-to-face biscorrole free-base and the corresponding heterobimetallic copper(III)-silver(III) complex

Article abstract of DOI:10.1039/b410249e

A meso-aryl-substituted face-to-face biscorrole was synthesised in a two-step reaction and the corresponding homo- and heterobimetallic complexes were obtained and fully characterised.

Full text of DOI:10.1039/b410249e

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C O M M U N I C A T I O N
New route to a face-to-face biscorrole free-base and the
corresponding heterobimetallic copper(III)–silver(III) complex†
Ewa Pacholska,a,b Enrique Espinosaa and Roger Guilard*a
a
LIMSAG, UMR 5633, Faculté des Sciences Gabriel, Université de Bourgogne,
6 Boulevard Gabriel, 21000, Dijon, France. E-mail: roger.guilard@u-bourgogne.fr;
Fax: +33 380 396117; Tel: +33 380 396111
Wydzial Chemii Uniwersystetu Wroclawskiego, ul. Joliot-Curie 14, 50-383, Wroclaw, Poland.
b
E-mail: pacholsk@wchuwr.chem.uni.wroc.pl; Fax: +48 71 3282348; Tel: +48 71 3757392
Received 6th July 2004, Accepted 1st September 2004
First published as an Advance Article on the web 16th September 2004
Aside from the biscorrole H6-1, another corrole derivative is
detected in the reaction mixture. Indeed, the corrole–aldehyde
H3-2 (7%) results from the condensation of only one aldehyde
group with dipyrromethane (Scheme 1) (2 = 4-[10-(5,15-
dimesitylcorrolato)]-6-formyldibenzothiophene trianion).
The condensation of dipyrromethane with a second aldehyde
group seems to be more difficult and probably produces an inter-
mediate which is not very stable in the reaction conditions.
Prolongation of the reaction time or increase of either acid
catalyst or substrate concentration consumes the H3-2 product,
but the formation of H6-1 is not favoured. Moreover, the
more drastic the conditions are the more “scrambling” effect5
occurs, even for the case of the sterically encumbered mesityl-
substituted dipyrromethane, which is known to minimize
this effect. Therefore, milder conditions were used to reduce
formation of side products.
A
meso-aryl-substituted
face-to-face
biscorrole
was
synthesised in a two-step reaction and the corresponding
homo- and heterobimetallic complexes were obtained and fully
characterised.
Metal complexes of face-to-face bismacrocycles containing
porphyrins and/or corroles are stimulating continuous endeavor
due to their potential applications such as fixation/activation
of dioxygen, dinitrogen or dihydrogen.1,2 The properties of
bisporphyrins are altered by changing the bridge and/or the
peripheral substituents. Changing the oxidation state of the
central metal atom by replacing a porphyrin by a corrole ring
gives another freedom degree for tuning the properties of face-
to-face systems. Unfortunately, the synthesis of face-to-face
biscorroles, especially for the case of asymmetric dimers, is
multistep and time consuming.3
Corrole–aldehyde H3-2, regarded as a side product, may serve
as a starting material for asymmetric bismacrocycle synthesis.
This compound is easily available since the synthesis does
not require any protection of the aldehyde group and H3-2
is easy to separate from H6-1. In fact, the corrole–aldehyde
may be considered as an intermediate in the synthesis of the
symmetric biscorrole H6-1, but the reaction of this compound
with dipyrromethane did not give the expected bismacrocycle.
However, when the corresponding copper complex Cu-2 is used
(see below), the second corrole moiety formation takes place
in 16% yield, leading to the CuH3-1 product (Scheme 2). The
great advantage of this asymmetric complex synthesis is an easy
purification process, as CuH3-1 is the only nonpolar reaction
product.
Here we report a new method for face-to-face biscorrole
synthesis, which allows to decrease significantly the number of
the reaction steps. Stable monocopper-, biscopper- and bissilver-
biscorrole complexes having the metal centers in high oxidation
state were obtained and a simplified route to a pure hetero-
bimetallic copper(III)–silver(III) biscorrole was afforded.
The two-step synthesis (starting from easily available and
stable compounds) of meso-mesityl substituted biscorrole
H6-1 (1 = 4,6-bis[10-(5,15-dimesitylcorrolato)]dibenzothiophene
hexaanion) is described in Scheme 1. The synthesis is based on
the methods previously reported by Gryko and our group for
monocorroles and, in one case, for linear biscorrole.4 The use of
a dibenzothiophene moiety as a rigid spacer is more convenient
than for instance the anthracene group which is synthesised
according to a multistep reaction.
Scheme 1 Synthesis of biscorrole H6-1 and corrole–aldehyde H3-2.
Scheme 2 Synthesis of CuH3-1.
The first step of the synthesis is the acid-catalysed conden-
sation of 4,6-diformyldibenzothiophene with four equivalents
of 5-mesityldipyrromethane in the presence of TFA. After
neutralisation by Et3N, the second step—i.e. oxidation by DDQ
(2,3-dichloro-5,6-dicyano-p-benzoquinone)—is performed. The
biscorrole is obtained in 3% yield. The free base is moderately
stable and decomposes more rapidly when exposed to light.
Metallation reaction of biscorrole H6-1 and the corrole–
aldehyde H3-2 was carried out in mild conditions with copper
acetate in the presence of air. The nonpolar orange–brown
products Cu2-1 and Cu-2 were obtained from H6-1 and H3-2,
respectively, in good yields (about 80%). Unlike the free-base
corroles, the complexes are stable and can be also obtained by
the condensation reaction of dialdehyde with dipyrromethane
in the presence of copper acetate, followed by DDQ oxidation,
as already described for free-base corroles. The metallation
reaction of H6-1 with one equivalent of metal salt was only
studied in the copper series. This reaction yielded (for two
† Electronic supplementary information (ESI) available: Experimental
data. Fig. S1: UV-Vis spectra of Cu2-1, Ag2-1 and AgCu-1. Table S1:
Selected structural data for AgCu-1 and Cu2-1. See http://www.rsc.org/
suppdata/dt/b4/b410249e/
T h i s j o u r n a l i s
©
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
D a l t o n T r a n s . , 2 0 0 4 , 3 1 8 1 – 3 1 8 3
3 1 8 1

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different conditions) an inseparable mixture of Cu2-1, CuH3-1
and unreacted ligand H6-1.
The copper complexes of the studied corroles, which are
regarded as very difficult to demetallate even in the presence
of strong acids, may be demetallated in the reaction with
concentrated HCl and zinc powder. However, this is only
achieved in a moderate yield due to the fragile character of the
respective free-bases, which lead to non-identified decomposi-
tion products.
The free base biscorrole H6-1 was refluxed under argon
in pyridine with 7 equivalents (3.5 per corrole ring) of silver
acetate to give Ag2-1. These reaction conditions are those
followed by Brückner for the preparation of meso-(triaryl-
corrolato)silver.6 The asymmetric complex AgCu-1 was
obtained starting from a monocopper biscorrole CuH3-1 in
a similar way (Scheme 3). Both silver complexes are bright
red–pink, nonpolar and stable.
Fig. 1 ORTEP drawing of Cu2-1 (top) and AgCu-1 (bottom) showing
thermal ellipsoids at 50% probability level. Hydrogen atoms have been
omitted for clarity.
Scheme 3 Synthesis of AgCu-1.
All the complexes (Cu2-1, Ag2-1, Cu-2, CuH3-1 and AgCu-1)
were characterised by MALDI-TOF mass spectrometry, UV-vis
spectroscopy and 1H NMR (see ESI†).
were obtained. A simple route to asymmetric complexes is also
described in this paper.
The heterobimetallic copper–silver biscorrole AgCu-1 has
both cofacially oriented metal centers in rare high oxidation
states, namely +3 for each of them. The UV-Vis spectrum
of this complex shows features which are close to the super-
position of the respective spectra of Ag2-1 and Cu2-1. This is
in accordance with the very poor interaction between both
Notes and references
‡ X-Ray crystallography: single crystals of Cu2-1 and AgCu-1
complexes were obtained in the presence of dichloromethane–ethanol.
In both cases, all X-ray data were used for direct methods structure
determination and full-matrix least-squares refinements on F2.9
Hydrogens were placed at calculated idealized positions and refined
with a global isotropic thermal factor as riding atoms.
1
metallocorrole moieties. Similar additivity is shown in the H
Crystal data for Cu2-1·2.5CH2Cl2·1.5C2H6O: M = 1652.03, tetragonal,
a = 28.0568(6), c = 20.8677(5) Å, V = 16426.7(6) Å3, T = 110(2) K, space
group I 4 , Z = 8, l(Mo-Ka) = 0.759 mm−1, 15540 reflections measured
(all of them unique). Except for CH2Cl2, the other solvent molecules were
found disordered exhibiting partial site occupation factors. The final
R(F) was 0.0683 (I > 2r(I) and 0.1294 (all data). A refinement of
racemic twinning was performed, the estimated Flack parameter being
0.47(1). Crystal data for AgCu-1·CH2Cl2·1.5C2H6O: M = 1568.97,
tetragonal, a = 28.1479(4), c = 20.8620(4) Å, V = 16529.1(5) Å3,
T = 110(2) K, space group I 4 , Z = 8, l(Mo-Ka) = 0.635 mm−1, 44411
reflections measured, 15026 reflections unique (Rint = 0.1171). The
metals were found disordered between both coordination sites sharing
their positions (sofs = 0.578(5)/0.422(5)). The solvent molecules were
also found disordered exhibiting partial site occupation factors. The
final R(F) was 0.0658 (I > 2r(I)) and 0.1263 (all data). At convergence,
the Flack parameter was −0.02(2). Two accessible voids of 297 Å3 each
and two others of 422 Å3 were respectively found in the unit cells of
Cu2-1 and AgCu-1, but residuals did not indicate the presence of further
solvent molecules. In both cases the disorder of some CH2Cl2 or C2H6O
molecules was unclear. CCDC reference numbers 213082 and 243876.
See http://www.rsc.org/suppdata/dt/b4/b410249e/ for crystallographic
data in CIF or other electronic format.
NMR spectra. For the copper–silver complex AgCu-1, two sets
of b-pyrrolic peaks are easily distinguishable for each metallo-
corrole at room temperature. Those assigned to the silver moiety
are narrow and located downfield (9.0–8.4 ppm) compared to
Ag2-1 (8.9–8.3 ppm). The copper–corrole part of the AgCu-1
complex is marked by broadened and relatively upfield-shifted
peaks (7.7–6.8 ppm), as observed for Cu2-1 (7.9–6.9 ppm). As
a consequence, the diamagnetic character and high oxidation
states of both metals are confirmed, as well as the mainly non-
interacting character of both cofacial metallocorroles.
Single-crystal X-ray studies of Cu2-1 and AgCu-1 revealed the
isostructural crystal structures of these complexes.‡ Their very
similar molecular conformations are shown in Fig. 1 (selected
structural data are gathered in the ESI†).
For Cu2-1, the eight Cu–N coordination distances range from
1.883(6) to 1.905(6) Å. They are shorter than those observed
for 5,10,15,20-tetraphenylporphyrinatocopper(II), Cu(II)TPP
(Cu–N 1.981 Å)7 and exhibit a similar range of values found
in Cu(III) complexes (Cu–N 1.804–1.907 Å).8 For AgCu-1, the
M–N coordination distances range from 1.899(6) to 1.923(6) Å.
In both molecular structures it is noteworthy the position of two
methyl groups lying inside of the complex cavity. They belong to
two different mesityl groups and point to the metal center which
is coordinated by the other corrole moiety. The hydrogen-metal
distances are 2.72 and 2.85 Å, and 2.58 and 2.66 Å, for AgCu-1
and Cu2-1, respectively.
1 R. Paolesse, in The Porphyrin Handbook, ed. K. M. Kadish,
K. M. Smith and R. Guilard, New York, 2000, vol. 2; pp. 201–232;
C. Erben, S. Will and K. M. Kadish, in The Porphyrin Handbook, ed.
K. M. Kadish, K. M. Smith and R. Guilard, New York, 2000, vol. 2;
pp. 233–300; R. Guilard, J.-M. Barbe, C. Stern and K. M. Kadish,
in The Porphyrin Handbook, ed. K. M. Kadish, K. M. Smith and
R. Guilard, San Diego, CA, 2003, vol. 18; pp. 303–349.
2 C. J. Chang, Y. Deng, C. Shi, C. K. Chang, F. C. Anson and D. G.
Nocera, Chem. Commun., 2000, 1355; K. M. Kadish, Z. Ou,
J. Shao, C. P. Gros, J.-M. Barbe, F. Jerome, F. Bolze, F. Burdet and
R. Guilard, Inorg. Chem., 2002, 41, 3990; F. Jérôme, C. P. Gros,
In conclusion, a biscorrole was synthesized according to a
very convenient two-step procedure and the corresponding
copper and silver complexes stabilizing high oxidation states
3 1 8 2
D a l t o n T r a n s . , 2 0 0 4 , 3 1 8 1 – 3 1 8 3

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D a l t o n T r a n s . , 2 0 0 4 , 3 1 8 1 – 3 1 8 3
3 1 8 3