DOI:10.1039/b410249e
Thisjournalis © TheRoyalSocietyofChemistry2004 3181 DaltonTrans .,2004,3181–3183
Dalton
www.rsc.org/dalton
COMMUNICATION
New route to a face-to-face biscorrole free-base and the
corresponding heterobimetallic copper(III)–silver(III) complex†
Ewa Pacholska,
a,b
Enrique Espinosa
a
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
b
Wydzial Chemii Uniwersystetu Wroclawskiego, ul. Joliot-Curie 14, 50-383, Wroclaw, Poland.
E-mail: pacholsk@wchuwr.chem.uni.wroc.pl; Fax: +48 71 3282348; Tel: +48 71 3757392
Received6thJuly2004,Accepted1stSeptember2004
FirstpublishedasanAdvanceArticleontheweb16thSeptember2004
A meso-aryl-substituted face-to-face biscorrole was
synthesised in a two-step reaction and the corresponding
homo-andheterobimetalliccomplexeswereobtainedandfully
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
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
H
6
-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.
Aside from the biscorrole H
6
-1, another corrole derivative is
detected in the reaction mixture. Indeed, the corrole–aldehyde
H
3
-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 H
3
-2 product,
but the formation of H
6
-1 is not favoured. Moreover, the
more drastic the conditions are the more “scrambling” effect
5
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.
Corrole–aldehyde H
3
-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 H
3
-2
is easy to separate from H
6
-1. In fact, the corrole–aldehyde
may be considered as an intermediate in the synthesis of the
symmetric biscorrole H
6
-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 CuH
3
-1 product (Scheme 2). The
great advantage of this asymmetric complex synthesis is an easy
purification process, as CuH
3
-1 is the only nonpolar reaction
product.
† Electronic supplementary information (ESI) available: Experimental
data. Fig. S1: UV-Vis spectra of Cu
2
-1, Ag
2
-1 and AgCu-1. Table S1:
Selected structural data for AgCu-1 and Cu
2
-1. See http://www.rsc.org/
suppdata/dt/b4/b410249e/
Scheme 1 Synthesis of biscorrole H
6
-1 and corrole–aldehyde H
3
-2.
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 Et
3
N, 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.
Scheme 2 Synthesis of CuH
3
-1.
Metallation reaction of biscorrole H
6
-1 and the corrole–
aldehyde H
3
-2 was carried out in mild conditions with copper
acetate in the presence of air. The nonpolar orange–brown
products Cu
2
-1 and Cu-2 were obtained from H
6
-1 and H
3
-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 H
6
-1 with one equivalent of metal salt was only
studied in the copper series. This reaction yielded (for two