Pillared salicylaldehyde derivatives as building blocks for the design of cofacial salen-type ligands

Article abstract of DOI:10.1016/j.tetlet.2005.02.092

The syntheses of pillared salicylaldehyde derivatives on a naphthalene block are reported. These compounds can be considered as building blocks for the elaboration of cofacial salen-typed ligands. The X-ray structure of a dinuclear manganese(III) complex is described, supporting our strategy to build topologically controlled multinuclear metal complexes.

Full text of DOI:10.1016/j.tetlet.2005.02.092

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 2923–2926
Pillared salicylaldehyde derivatives as building blocks for the
design of cofacial salen-type ligands
Laurent Sabater,a Regis Guillotb and Ally Aukaulooa,*
a
ˆ
´
Laboratoire de Chimie Inorganique, UMR 8613, Bat. 420, Universite Paris Sud, 91405 Orsay, France
ˆ
b
´ ´ ´
Institut de Chimie Moleculaire et des Materiaux d’Orsay, Bat. 420, Universite Paris Sud, 91405 Orsay, France
Received 9 February 2005; revised 15 February 2005; accepted 16 February 2005
Abstract—The syntheses of pillared salicylaldehyde derivatives on a naphthalene block are reported. These compounds can be con-
sidered as building blocks for the elaboration of cofacial salen-typed ligands. The X-ray structure of a dinuclear manganese(III)
complex is described, supporting our strategy to build topologically controlled multinuclear metal complexes.
Ó 2005 Elsevier Ltd. All rights reserved.
1. Introduction
an excellent example.5 Different families of ligand have
also been elaborated in the aim to gain a synergistic
effect between the two metal centres. He and Lippard6
have designed biscompartmental ligands based on the
1,8-naphtyridine skeleton as bridging unit. These ligands
have been used to devise Hemerytrin models7 among
others. The originality of these ligands is to maintain
two metal centres in a given disposition without any
common shared intraligand atom. Whereas ligands
developed by Gavrilova and Bosnich8 to study chemical
cooperativity between two metal ions contain common
coordinating atoms, oxygen atom of phenol group. In
these systems, the coordinating environment of the
two metal ions are not similar. One site is composed
of a hexadentate coordinating environment and the
other site is 4- or 5-coordinated. The unsaturation for
the coordination sphere of the second metal centre is
the privilege site for activation of small molecules such
as dioxygen and the second metal centre acting as a
redox relay.
Often nature makes use of di- or polynuclear metallic
centres at their active sites for the proper functioning
of enzymes. For instance, the active site of catalase,1 en-
zyme responsible for the dismutation of H2O2, consists
of two Mn ions held in close proximity by the polypep-
tide skeleton. In PSII, four Mn ions are present in the
oxygen evolving complex (OEC).2 The actual X-ray data
for this enzyme indicates a cubane-type structure for
these ions.3 In the field of bioinorganic chemistry, chem-
ists devote a particular effort in the preparation of
simple low-molecular-weight models for the active
di(poly)nuclear sites of enzymes. The transfer of the first
coordination spheres, disposition and topologies of the
metal centres within the active sites into synthetic low-
molecular-weight models are the main parameters that
the chemist must take into account in the design of the
ligand. The aim is to reproduce as close as possible the
3D structure and the electronic behaviour of the active
sites.4
These examples illustrate the fact that ligand design
remain the tour de force in the modelization of dinuclear
enzymatic sites.
At the forefront of this research, is the design of specific
ligands that can hold metallic ions into a predefined dis-
position and in a given environment. The pioneering
work of Collman groupin the modelization of C cO is
2. Discussion
In our laboratory, polydentate ligands containing
amine, pyridine and phenol groups have been exten-
sively used in the study of redox active manganese9
and iron10 chemistry. In many cases, starting with a
mononuclear compound, resulted in the formation of
Keywords: Suzuki coupling; Duff reaction; Cofacial salen-type ligand;
Dinuclear manganese(III) complex.
*
Corresponding author. Tel.: +33 01 69 15 47 56; fax: +33 01 69 15 47
54; e-mail: aukauloo@icmo.u-psud.fr
0040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.02.092

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L. Sabater et al. / Tetrahedron Letters 46 (2005) 2923–2926
interdinuclear compounds, which can be considered as
thermodynamic products. In the aim to prevent the
uncontrolled formation of these stable dimers and to ex-
pect a cooperative effect between metal ions, we have
launched a project for the synthesis of multidentate
dinucleating ligands whereby after metallation, the me-
tal centres will be settled in a face to face fashion sepa-
rated by a well defined distance. As, already proposed in
the literature, such synthetic approach requires the use
of a rigid molecular brick to hold the coordinating
cavities in a given topology.
coupling reaction, we have preferred to realise the cou-
pling reaction on 2 using a monoboronic derivative 4
and 7 leading to the formation of 5 and 6, respectively.
The 4-methoxyphenyl boronic acid 4 was synthesized
starting from 3 following literature procedure,14 while
compound 7 is commercially available. Typical Suzuki
cross coupling reaction was performed15–17 with com-
pounds 2 and 4 in a mixture of toluene/ethanol/
water (2/2/1) using Na2CO3 as base and Pd(PPh3)4
(10 mol %) as catalyst. The reaction mixture was first de-
gassed and put under an argon atmosphere before heat-
ing to reflux for 18 h. The bis(4-methoxyphenyl)-1,8-
naphthalene 5 was obtained after purification by column
chromatography (CH2Cl2/hexane 1/1, silica gel) in good
yield (65%). While compound 6 was isolated after puri-
fication by column chromatography (CH2Cl2/MeOH 98/
2, silica gel) in a 60% yield. Deprotection of the phenol
We report herein the synthesis and characterization of
pillared salicylaldehyde derivatives, which can be con-
sidered as the building block in the elaboration of cofa-
cial salen-type ligands. In this study, naphthalene was
chosen as the rigid molecular basement to hold the
salicylaldehyde motifs.
18
groups upon treatment with BBr3 gave compound 8
quantitatively. Hence, following this synthetic sequence,
we have found that the crucial step, that is, Suzuki cross
coupling reaction, works best.
A similar synthetic strategy was developed precedently
by McAuliffe and co-workers.11 However, the poor yield
reported has lead us to conceive different reaction path-
ways leading to the target compounds with more conve-
nient yields. The synthetic route leading to the
salicylaldehyde derivatives is shown in Scheme 1.12 1,8-
Diiodonaphthalene 2 has been synthesized as described
by House et al.13 Although the starting diamino 1 com-
pound was purified by distillation under reduced pres-
sure, in our hands, the yield of this reaction has never
exceeded 35–40% when the reaction was carried on a
50 g scale. Contrary to what has been previously de-
scribed, where compound 2 was converted to the 1,8-
naphthalene diboronic acid to undergo a Suzuki cross
Demethylation of compound 5 following the same pro-
cedure as above gave the bisphenol derivative 9. This
compound was then formylated at the ortho positions
following a modified Duff reaction19,20 to give the tetra-
formyl derivative 10. To the best of our knowledge, this
is the first time that such a face to face diformylated phe-
nol compound is described. This compound thus opens
the way to prepare biscompartmental ligands arranged
in a cofacial manner. Indeed, tetranucleating ligands
can be easily prepared by Schiff-base condensation reac-
tion of 10 with primary amine derivatives.
HO
OH
HO
OH
Br
O
B
B
ii
3
4
1
2
7
O
NH2 NH2
O
O
i
5
6
iii
iii
I
I
O
O
O
O
O
O
iv
iv
9
10
8
v
O
O
O
O
HO
OH
HO
OH
HO
OH
O
O
Scheme 1. Reagents and conditions: (i) NaNO2/KI at À20 °C in H2SO4; (ii) n-BuLi/B(OMe)3 at À78 °C; (iii) NaCO3, Pd(PPh3)4 (5 mol %) in toluene/
EtOH/H2O (2/2/1) reflux 24 h; (iv) BBr3 in CH2Cl2 at À10 °C; (v) HMTA in TFA 5 days.

L. Sabater et al. / Tetrahedron Letters 46 (2005) 2923–2926
2925
O
O
3. Summary and conclusions
11
8
OH
As benchworks in our laboratory we are studying the
spectroelectrochemical properties of the dinuclear man-
ganese complex. Also, the tetraformyl derivative
described hereby is now being used to prepare tetra-
nucleating ligands.
H2N
N
N
2 eq.
N
OH
N
N
N
12
Acknowledgements
N
N
OH
This work was supported by the CNRS (Programme
Energie, PRI4), the CEA for the LRC project (LRC-
CEA no. 33V) and the European Commission (NEST
STRP SOLAR-H contract 516510). The authors wish
to thank Professor J.-J. Girerd for fruitful discussions.
OH
N
N
N
Scheme 2. Condensation of primary amine 11 in MeOH for 24 h.
Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tetlet.
2005.02.092.
References and notes
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´ `
9. Hureau, C.; Sabater, L.; Anxolabehere-Mallart, E.; Nier-
Figure 1. Ortepview of complex 13 (ellipsoid 50%).
`
lich, M.; Charlot, M.-F.; Gonnet, F.; Riviere, E.; Blondin,
G. Chem. Eur. J. 2004, 10.
Hereby, we report an example on the propensity to pre-
pare dinucleating ligands from 8. As shown in Scheme 2,
treatment of 8 with 2 equiv of amine 11 gave 12, which
was isolated as a yellow solid. The dinuclear manga-
nese(III) complexes has been prepared upon metallation
of 12 with 2 equiv of MnII(H2O)4Cl2 to give compound
13. Oxidation of Mn(II) to Mn(III) occurs upon reac-
tion in air. Slow evaporation of a methanolic solution
gives suitable monocrystal for X-ray analysis. The X-
ray structure of the dinuclear manganese(III) complex
is represented in Figure 1. The hydrogen atoms have
been omitted for clarity. Each pentadentate ligand
(N4O coordinating cavity) wraps a manganese ion and
its coordination sphere is completed with a bound chlo-
ride ion. Two other chloride ions are outside the coordi-
nation spheres for electroneurality. The intrametallic
´ `
`
10. Balland, V.; Anxolabehere-Mallart, E.; Banse, F.; Riviere,
E.; Bourcier, S.; Nierlich, M.; Girerd, J.-J. Eur. J. Inorg.
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12. See supplementary material.
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Chem. 1972, 37, 1003–1011.
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´
17. Hassan, J.; Sevignon, M.; Gozzi, C.; Schulz, E.; Lemaire,
˚
distance between two manganese ions is 6.4 A. It is
worth noticing that there is no bridging atom between
the two manganese ions.21
M. Chem. Rev. 2002, 102, 1359–1469.
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L. Sabater et al. / Tetrahedron Letters 46 (2005) 2923–2926
19. Lindoy, L. F.; Meehan, G. V.; Svenstrup, N. Synthesis
1998, 1029–1032.
20. Asato, E.; Chinen, M.; Yoshino, A.; Sakata, Y.; Sugiura,
K.-I. Chem. Lett. 2000, 29, 678–679.
21. Crystal data of the compound 13: chemical for-
mula C52H46Cl4Mn2N8O14, M = 1258.65, monoclinic,
C2/c. See also supplementary material. Crystallo-
graphic data (excluding structure factors) for the struc-
ture in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supple-
mentary number CCDC 261270. Copies of the data
can be obtained, free of charge, on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
[fax: +44(0) 1223 336033 or e-mail: deposit@ccdc.cam.
ac.uk].
˚
a = 29.29(1), b = 13.68(1), c = 17.83(1) A, b = 120.21(1)°,
V = 6174(3) A , Z = 4, qcalcd = 1.354 g cmÀ3, l (MoKa) =
3
˚
0.647 mmÀ1
, F(000) = 2576, T = 293 K, space group