Preparation and characterization of copper(ii) and nickel(ii) complexes of a new chiral salen ligand derived from (+)-usnic acid

Article abstract of DOI:10.1039/b811589c

Chiral copper(ii) and nickel(ii) complexes were obtained after reaction of diacetate salts with a new chiral salen ligand derived from (+)-usnic acid.

Full text of DOI:10.1039/b811589c

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Preparation and characterization of copper(II) and nickel(II) complexes of a
new chiral salen ligand derived from (+)-usnic acid†
Maryle`ne Chollet-Krugler,a Sophie Tomasi,*a Philippe Uriac,a Loic Toupetb and Pierre van de Weghe*a
Received 8th July 2008, Accepted 7th October 2008
First published as an Advance Article on the web 20th October 2008
DOI: 10.1039/b811589c
Chiral copper(II) and nickel(II) complexes were obtained after
reaction of diacetate salts with a new chiral salen ligand
derived from (+)-usnic acid.
Complexes of diimino functionalized ligands are often used as
catalysts for a wide variety of reactions. Salen ligands are prepared
by the condensation of two equivalents of a salicylaldehyde
derivatives with diamines. Chiral versions of such ligands are
usually accessed using chiral 1,2-diamines.1 However it could
be possible to prepare chiral salen ligands from enantiopure
salicylaldehyde derivatives. As a continuation of our ongoing work
on enhancing the use of lichen substances,2 we recently developed
an efficient and rapid parallel synthesis of polyamine usnic acid
derivatives.3 Due to their structures, this class of products possesses
all the characteristics of salen ligands.
(+)-Usnic acid 1, a polyfunctionalized compound, exhibited
several biological activities4 and also metal binding properties.
The preparation of copper(II) and palladium(II) complexes from
(+)-usnic acid, acetyl and enamine derivatives has been already
reported.5 The metal coordination abilities of this abundant lichen
substance indicate that lichens could be considered as biomonitors
of environmental metal ions. On the basis of the above observation
we decided to explore for the first time the metal binding capacity
of chiral salen ligand derived from (+)-usnic acid 1. Thus this
communication deals with the synthesis of a new chiral salen
ligand and its use for the preparation of copper(II) and nickel(II)
complexes.
The chiral salen ligand 2 was prepared by condensation of
one equivalent of ethylene diamine with two equivalents of 1 in
refluxing EtOH-THF (Scheme 1). After removing of unreacted
Scheme 1 Synthesis of complexes 3, 4, 7 and 8.
diamine by washing with water, the excess of 1, tedious to
eliminate using conventional column chromatography, was finally
scavenged by aminomethyl resin. Such 2 was isolated as pure form
after recrystallization in high yield (84%). NMR spectroscopic
analysis (Table 1) and X-ray crystal structure analysis‡ (Fig. 1
and 3) show that 2 was obtained in its ketoenamine form rather
than enolimine tautomer. This observation is in accordance with
previous works reported by us3 and others.5,6 This is supported
6b
˚
bond length of 0.861 A, in agreement with Albrecht et al. The
C10–O6 bond length and the value of the C17N1C19 bond angle
(128.48◦) are also in accordance with calculated bond lengths
◦
˚
(about 1.246 A) and interplanar angles (124.554–128.64 ) in
N-salicylidene anilines in their ketoenamine forms.7
We here report the complexation of 2 with copper(II) and
nickel(II). Metal complexes were quickly formed by adding to
a solution of 2 in dichloromethane one equivalent of diacetate
salt dissolved in a little amount of methanol. Slow evaporation
of solvents gave violet and orange microcrystalline solids of
copper(II) 3 and nickel(II) 4† respectively in almost quantitative
yields. All attempts to obtain a single-crystal suitable for X-ray
structure analysis have failed so far. We however confirmed the
˚
by a short C10–O6 bond with a length of 1.244 A and a N1–H1
aEA “Substances licheniques et photoprotection”, Faculte´ de Pharmacie,
2 Avenue du Professeur Le´on Bernard, 35043, Rennes Cedex, France.
E-mail: sophie.tomasi@univ-rennes1.fr; Fax: + 33 (0)2 23 23 47 04;
Tel: + 33 (0)2 23 23 48 17. E-mail: pierre.van-de-weghe@univ-rennes1.fr;
Fax: + 33 (0)2 23 23 44 25; Tel: + 33 (0)2 23 23 38 03
bGMCM, CNRS, UMR 6509, Universite´ de Rennes 1, Campus de Beaulieu,
F-35042, Rennes Cedex
† Electronic supplementary information (ESI) available: Experimental
details. CCDC reference numbers 627762 & 670706. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/b811589c
formation of complexes 3 and 4 by HRMS. The Ni(II) complex
4 is diamagnetic and its structure was determined by H and 13
C
1
NMR (Table 1). Signals of the methylene and the CH3-12 groups
6524 | Dalton Trans., 2008, 6524–6526
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a
Table 1 Selected 1H and 13C NMR data of 2, 4, 6 and 8 in CDCl3
1H NMR
13C NMR
Nucleus
2
4
6
8
2
4
6
8
CH3-12
CH2
CO-3
2.66
3.86
2.45
3.26
2.40
3.70
2.21
3.18
18.16
42.58
191.03
21.37
54.01
183.46
16.30
42.67
190.18
20.00
53.99
179.13
a
d in ppm.
Fig. 1 ORTEP drawing of the molecular structure of 2.
1
have respectively an upfield and a downfield shift in the H and
13C NMR spectra, in comparison to the salen ligand 2. On the
other hand, the CO-3 signal is shifted to lower value with respect
to that of 2 (Table 1). Finally, no signal of the amine proton (NH)
of the keto-enamine tautomer was found in the 1H spectrum of 4.
Moreover the IR spectra of 4 showed the disappearance of NH
bands and the shift of the CO-3 band from 1550 cm-1 to 1450 and
1410 cm-1. All these observations support the coordination of Ni
ion to the nitrogen and oxygen atoms of the enolimine form.
To obtain crystals suitable for X-ray structure analysis, we
prepared (+)-7,9-di-O-benzylusnic acid 5. Thus, (+)-usnic acid
1 was treated with tetramethylammonium hydroxide in hexam-
ethylphosphoramide (HMPA) at 0 ◦C, and the resulting phenoxide
ion alkylated with benzylbromide to provide the dialkylated
derivative 5 in 26% yield.8 A new ligand 6 was synthesized after
condensation of 5 with diaminoethane. The lack of selectivity
of carbonyl groups C13 and C11 gave a complex mixture of
compounds from which 6 was isolated in low yield (15%). The
Fig. 2 ORTEP drawing of the molecular structure of the complex 8.
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Cu(II) and Ni(II) complexes 7 and 8 were prepared from 6 following
the above method (Scheme 1). IR data of 8 are similar to those
reported for 4 with the disappearance of NH band at 3368 cm-1,
Acknowledgements
We gratefully acknowledge Dr. Olivier Lavastre (UMR 6226-
CNRS-Universite´ de Rennes, 1 Avenue du ge´ne´ral Leclerc, 35042,
Rennes Cedex, France) for fruitful discussions and the CRMPO
scientists for mass measurements. This work was supported by
Universite´ de Rennes 1 and Rennes Me´tropole.
the appearance of C N band at 1546 cm-1 and the shift of the CO-3
=
band from 1569 cm-1 to 1451 and 1400 cm-1. NMR studies of 8 also
show similar shifts for CH3-12, methylene and CO-3 groups than
those observed for 4 (Table 1) indicating the similar structure of
these Ni(II) complexes. Recrystallisation from CH2Cl2-methanol
of 8 results in crystals suitable for single X-ray structure analysis
(Fig. 2). The selected bond lengths and angles are summarized in
Fig. 3. The elongation and the shortening of certain bonds, and the
decrease of the value of the C–N–C angle suggests the transition
from a ketoenamine in 2 (C17–N1–C19 128.4(2)◦) towards an
enolimine form in 8 (C15–N2–C16 119.1(4)◦). To our knowledge,
the nature of complex 8 is scarce6c,9 and no crystal structure of
Ni(II) complex has been reported. However, the Ni–N and Ni–
O bond lengths in the complex 8 are comparable with those
reported for Ni(II)-N,N¢-bis(3¢,5¢-di-tertbutylsalicylidene ethylene
Notes and references
‡ Crystal data for 2: C38H36N2O12, M = 712.69, triclinic, P-1, a = 7.5006(6),
˚
b = 10.1555(7), c = 11.3793(9) A, a = 72.374(6), b = 88.638(6), g =
◦
˚
3
-3
˚
90.841(5) , V = 825.64(11) A , Z = 1, Dx = 1.433 Mg.m , l(MoKa) =
-1
0.71069 A, m = 0.108 mm , F(000) = 374, T = 295(2) K. Z = 1, 7721
refelections collected, 5566 independent reflections (Rint = 0.06221) which
were used in all calculations. The final wR2 was 0.1245 (all data). Crystal
data for 8: C134H118Cl6N4Ni2O24, M = 2498.44, monoclinic, P21, a =
˚
15.912(2), b = 23.792(4), c = 17.535(2) A, a = 90, b = 113.5190(1), g =
◦
3
-3
˚
˚
90 , V = 6087.0(15) A , Z = 2, Dx = 1.363 Mg.m , l(MoKa) = 0.71069 A,
m = 0.515 mm-1, F(000) = 2600, T = 110(2) K. Z = 1, 96611 reflections
collected, 36765 independent reflections (Rint = 0.0361) which were used
in all calculations. The final wR was 0.081 (all data). The CIF files have
been deposit at Cambridge Crystallographic Deposit Center with registry
number for 2 CCDC 627762 and for 8 CCDC 670706. For crystallographic
data in CIF or other electronic format see DOI: 10.1039/b811589c
˚
diamine) (Ni–N = 1.843(4) and 1.846(2) A, Ni–O = 1.841(4) and
10
˚
1.846(2) A, respectively). In addition the value of C–N–C angle
(119.1(4)◦) in 8 compares well with that described by Shimazaki
(119.88◦).10 Ni(II) ion coordinates thus two imine nitrogen atoms
and two oxygen atoms in a square planar geometry as classical
metal salen complexes with a pseudo C2-symmetry. The structures
of complexes 3, 4 and 7 were supposed by analogy with complex 8.
1 (a) T. R. J. Achard, L. A. Clutterbuck and M. North, Synlett, 2005,
1828; (b) P. G. Cozzi, Chem. Soc. Rev., 2004, 33, 410; (c) E. N. Jacobsen,
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N. Skert and P. L. Nimis, Naturwissenschaften, 2002, 89, 137.
5 (a) M. Takani, T. Yajima, H. Masuda and O. Yamauchi, J. Inorg.
Biochem., 2002, 91, 139; (b) M. Takani, T. Takeda, T. Yajima and O.
Yamauchi, Inorg. Chem., 2006, 45, 5938.
6 (a) J. P. Kutney and I. H. Sanchez, Can. J. Chem., 1976, 54, 2795;
(b) M. Albrecht, I. Janser, S. Kamptmann, P. Weis, B. Wibbeling and
R. Fro¨hlich, Dalton Trans., 2004, 37; (c) K. C. Moss and F. P. Robinson,
J. Can. Chem., 1973, 51, 505.
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T. M. Krygwski and R. Kauppinen, J. Org. Chem., 2007, 72,
5598.
◦
˚
Fig. 3 Selected bond lengths (A) and angles ( ) of 2 and 8.
8 J. P. Kutney and I. H. Sanchez, Can. J. Chem., 1977, 55, 1085.
9 W. S. Durfee and C. G. Pierpont, Inorg. Chem., 1993, 32, 493.
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and O. Yamauchi, J. Am. Chem. Soc., 2007, 129, 2559 and references
cited herein.
In conclusion, we have developed the preparation of copper(II)
and nickel(II) complexes based on a new chiral salen ligand derived
from (+)-usnic acid. Formation of the metal complexes enhances
the enolimine character of the salen-type ligand 2 significantly.
6526 | Dalton Trans., 2008, 6524–6526
This journal is
The Royal Society of Chemistry 2008
©