Imidazolidine Ring Cleavage upon Complexation with First-Row Transition Metals

Article abstract of DOI:10.1002/ejic.201700605

The reaction of a cyclic diaminal ligand, obtained from the reaction of N,N′-bis(2-pyridylmethyl)ethane-1,2-diamine, as a secondary diamine, and isophthalaldehyde, with different first-row transition-metal ions, such as Fe^III, Zn^II,

Full text of DOI:10.1002/ejic.201700605

A Journal of
Accepted Article
Title: Imidazolidine Ring Cleavage upon Complexation with First Row
Transition Metals
Authors: Khaled Cheaib, Christian Herrero, Regis Guillot, Frederic
Banse, Jean-Pierre Mahy, and frederic Avenier
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201700605
Link to VoR: http://dx.doi.org/10.1002/ejic.201700605

European Journal of Inorganic Chemistry
10.1002/ejic.201700605
FULL PAPER
Imidazolidine Ring Cleavage upon Complexation with First Row
Transition Metals
Khaled Cheaib, Christian Herrero, Régis Guillot, Frédéric Banse,* Jean-Pierre Mahy,* Frédéric
Avenier*
Abstract: The reaction of a cyclic di-aminal ligand, obtained from
the reaction of N,N′-bis(2-pyridylmethyl) ethane-1,2-diamine as a
secondary diamine and isophthalaldehyde, with different first row
transition metal ions such as Fe(III), Zn(II), Cu(II) and Cu(I) was
explored using UV-visible kinetic studies, and cyclic voltammetry.
The 3D structure of the resulting metal complexes were determined
by X-Ray diffraction analysis. We demonstrate that the ring cleavage
reaction of the imidazolidine ligand upon complexation with various
metal ions depends on the Lewis acidity of the metal ions, as well as
on the coordinative requirements of the metal centers. With a soft
acid such as Cu(I), the di-aminal ligand was unmodified and
stabilized tricoordinated planar cuprous ions. In contrast, in the
presence of harder acids, such as Fe(III), Zn(II) and Cu(II), the di-
aminal ligand undergoes hydrolysis/cleavage to yield complexes of
the tetradentate N,N′-bis(2-pyridylmethyl) ethane-1,2-diamine ligand.
Interestingly, it was also observed that the ring cleavage reaction in
The principal method of synthesis of imidazolidines
involves the reaction of aldehydes with aliphatic 1,2-diamines in
which both amine groups are secondary. If the polyamine
contains primary and secondary amine groups, the
condensation products are either exclusively imidazolidines, or
mixtures of imidazolidines and of the corresponding isomeric
acyclic Schiff base, with relative ratios depending on the
aldehyde and diamine substituents.1
Upon complexation with metal ions, both imidazolidine ring
formation and opening have been observed in several systems
(Scheme 1). The template effect of metal ions in the opening of
the imidazolidine ring was investigated with ligands issued from
the condensation of one primary and one secondary amine with
an aldehyde by two different research groups. Boča et al. (L1,
Scheme 1) first reported that imidazolidine ring-closing and ring-
opening were related to the competition that exists between the
2
presence of Fe(III) led to the formation of Fe(II) complexes. However, Lewis acidity of the metal ion and that of the sp -hybridized
we demonstrate that these two events are independent from each
other.
imine carbon site.12 The complete opening of the aminal ring
could be induced by hard Lewis acids (e. g. Fe(III)) whereas an
only partial ring opening could be observed with softer Lewis
acids (e. g. Cu(II)).12 In contrast, Tuchagues et al. (L2, Scheme
1
) postulated that the size of the metal ion played an important
Introduction
role in shifting the equilibrium toward one tautomeric form or the
other.13 They showed that low spin Fe(II) was small enough to
induce a template effect resulting in the opening of the ring,
while Ni(II) was too large to be coordinated by the pentadentate
open form, therefore stabilizing the tetradentate aminal ring
isomer.
In 2009, on the basis of electrochemical data and UV-
Visible spectroscopy studies, Sosa-Torres et al. (L3, Scheme 1)
detailed the oxidative dehydrogenation of the aminal ring
Imidazolidines,
also
known
as
aminals
or
1
tetrahydroimidazoles, have attracted much attention due to their
usefulness in diverse applications. They have indeed proven
their importance in biological systems and pharmaceutical
2-6
processes, and their potential as protective groups in organic
synthesis7 as well as sacrificial chiral ligands in asymmetric
catalysis.8 In these latter cases, their attractiveness is largely
due to their dynamic behavior in solution. Indeed, while they are
stable under basic conditions, they can be hydrolyzed under
(
obtained from a secondary diamine) upon complexation with
14,15
Fe(III).
In this case, in addition to the ring opening, the ferric
9
acidic ones and these properties involving reversible formation
ion was reduced to Fe(II) and the secondary amine located on
the ligand skeleton was oxidized to the corresponding imine.
Similar ligands, synthesized from secondary diamines as
starting material, (L4, Scheme 1) were extensively studied in
order to build metal complexes with specific magnetic
properties.16-23 In the presence of metal ions, cleavage was
of aminals have been nicely exploited in dynamic combinatorial
chemistry for the controlled release of bioactive volatiles.10,11
Studying the reactivity of this class of compounds is thus of
great interest in order to control their fate and improve their use
in various applications.
observed instead of ring opening,21-23 but this ligand hydrolysis
could be inhibited in the presence of exogenous bridging
ligands.17,21
[
a]
Khaled Cheaib, Christian Herrero, Régis Guillot, Frédéric Banse,
Jean-Pierre Mahy, Frédéric Avenier
In the course of our research on dinuclear complexes,24-26
the synthesis of new polydentate nitrogen ligands led us to
explore the reaction of the cyclic di-aminal ligand L (obtained
from the reaction of a dialdehyde, isophthalaldehyde, and a
Institut de Chimie Moléculaire et des Matériaux d'Orsay (UMR
CNRS 8182)
Univ. Paris Sud, Université Paris Saclay
91405 Orsay Cedex, France.
E-mail: frederic.banse@u-psud.fr; jean-pierre.mahy@u-psud.fr;
frederic.avenier@u-psud.fr
secondary
diamine,
N,N'-bis(2-pyridylmethyl)-ethane-1,2-
diamine) with different first row transition metal ions such as
Fe(III), Zn(II), Cu(II) and Cu(I).
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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European Journal of Inorganic Chemistry
10.1002/ejic.201700605
FULL PAPER
Scheme 1. Imidazolidine ring opening and ring cleavage reactions reported in the literature.12-23 Counter anions and exogenous ligands are omitted for clarity
In this paper, we demonstrate that the ring cleavage
reaction of the imidazolidine ligand upon complexation with
various metal ions depends on the Lewis acidity and on the
coordination requirements of the metal ions. Interestingly, we
also observe that the ring cleavage reaction in presence of
Fe(III) leads to the formation of Fe(II) complexes. However, we
demonstrate that these two events are independent from each
other.
ion in a distorted octahedral geometry (Figure 1). As shown in
Figure 1, H L’ acts as a tetradentate neutral ligand in cis-
coordination mode (Scheme S2). The pyridyl nitrogens
(N and N ) occupy the axial coordination positions whereas the
secondary amine nitrogens (N and N ) are in the equatorial
plane. The octahedral environment of the ferrous ion is
completed by the coordination of two CH CN molecules and two
ClO -
anions balancing the charge of the cation. The short Fe-N
2
1
2
3
4
3
4
bond distances (average distance of 1.971(2) Å) obtained from
the diffraction data are in accordance with a low-spin electronic
configuration (S=0) for this complex in the solid state, in
agreement with crystallographic data reported by Ray et al.27
Results and Discussion
Complexation of Fe(III), Cu(II) and Zn(II) ions with ring
cleavage of the aminal group
The bis-ring imidazolidine ligand L was synthesized by
condensation of isophthalaldehyde with two equivalents of N,N'-
2
bis(2-pyridylmethyl)-ethane-1,2-diamine (H L') (Scheme S1,
Figures S1 to S3). Its reaction with two equivalents of
III
Fe (ClO
4
)
36
H
2
O in acetonitrile under aerobic conditions,
induced a progressive color change from red to purple. Slow
diffusion of diethyl ether into this solution led to the formation of
a red powder in good yield (58%, see Supporting Information,
synthesis of C1 method A, Scheme S1). After recrystallization,
Scheme 2. Reduction/cleavage reaction of L in the presence of 2 equiv. FeIII
(hydrolysis of the L promoted by FeIII).
X-ray diffraction analysis indicated the formation of
Upon dissolution in acetonitrile, the UV-Vis spectrum of C1
II
[
Fe (H
2
L’)(CH
3
CN)
2
](ClO
4
)
2
revealing that the iron center of
(Figure 2A, black trace) shows a charge transfer band at 315 nm
-
1
-1
-
complex C1 was in its reduced form (Figure 1 and Scheme 2).
The reduction of iron(III) into iron(II) was accompanied by ring
cleavage of the aminal rings. Interestingly, C1 could also be
( ca. 7000 M cm ) with a shoulder at 360 nm ( ca. 4500 M
1
-1
-1
-1
cm ) and a low intensity band at 490 nm ( ca. 500 M cm ).
This spectrum slowly evolves over 20 hours to give a new
charge transfer band at 360 nm that develops at the expense of
the band at 315 nm, together with the appearance of a broad
absorption at 530 nm. During this slow process, an isosbestic
point appears at 335 nm suggesting the existence of two
species in equilibrium. This observation is supported by
electrochemical studies that reveals the presence of two
reversible redox waves with very close potential E1/2 values of
obtained with a similar yield (51%) by the direct reaction of H
2
L'
II
with an Fe salt (Supporting Information, synthesis of C1,
method B, Scheme S4). The fact that the yields of C1 formation
following the two methods are similar indicates that C1 formation
from L and an FeIII salt is not a parasite reaction.
Complex C1 crystallized in the centrosymmetric monoclinic
II
space group C2/c as a mononuclear Fe species with the ferrous
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European Journal of Inorganic Chemistry
10.1002/ejic.201700605
FULL PAPER
of C1 after time evolution (corresponding to the red trace on panel A); 1mM in
0
.975 V and 1.135 V vs SCE (Figure 2B). Tetraazadentate
-
1
6 3
0.1 M TBAPF / CH CN, 100 mV.s
ligands can coordinate to an octahedral iron center in three
different topologies, cis-, cis-, and trans forms (Scheme S2).28
Similar tetradentate ligands, the cyclohexyl derivatives BPMCN
and BQCN, have been shown to give Fe(II) complexes with
either a cis- or cis- geometry, depending on the synthetic
In order to better understand why complex C1 was formed
III
when the ligand L was mixed with 2 equivalents of Fe (ClO
4
)
36
2
H O in acetonitrile, the reaction was followed by UV-Visible
29-31
route used.
Additionally, it was also demonstrated that the
spectroscopy (Figure 3A). The initial mixture of L + 2 equiv.
Fe(III) did not exhibit any feature in the visible, except for tails of
intense UV absorptions (Figure 3A, black trace). Then, the
characteristic absorption band of C1 at 530 nm increased
gradually during the course of the reaction (Figure 3A and 3B,
red traces). Interestingly, the reaction seemed to proceed in two
stages, as suggested by the time evolution of the spectra in the
UV region (Figure 3B, black trace). One may assign the first
phase of the evolution to the redox/cleavage reaction of Fe(III)
and L to yield C1. This irreversible reaction proceeds without
any isosbestic point (from bold black to blue trace; Figure 3A).
The second stage would correspond to the equilibrium between
the different isomers of C1 in solution (from blue to red), which is
clearly evidenced by the isosbestic point observed at 335 nm.
The final spectrum (Figure 3A, red trace), is identical to that
observed for the isolated complex C1 in solution (Figure 2A, red
trace). The characteristic 530 nm absorption band in the final
spectrum (red trace) displayed an electronic extinction
structure observed in the solid-state did not represent the only
Figure 1. Structure of the molecular cation of C1 determined by X-ray
diffraction analysis.
-1
-1
coefficient (ca. 2000 M .cm ) that matches the absorptivity of
C1 in its steady state equilibrium. This indicates that the reaction
geometry in solution, as dynamic equilibria between complexes
with different geometries (cis-, cis-, and trans) were observed
3
2,33
in solution.
In the case of C1, Britovsek et al. have reported
1
H NMR evidences of rearrangements between geometrical
isomers.28 This fluxional behaviour may be related to the low
0.8
0.65
0.6
A
B
0
.6
.4
0.55
spin (S=0) to high spin (S=2) spin crossover observed in
acetonitrile solution.28 Therefore, one can assume that the final
UV-Vis spectrum (Figure 2A, red trace) corresponds either to the
trans or the cis- isomer, whereas the initial one (Figure 2A,
black trace) is characteristic of the cis- complex characterized
by X-ray crystallography. By analogy with electronic absorption
spectra of similar amine/pyridine Fe(II) complexes, the two sets
of bands observed can be assigned to ligand-centred *
transitions (max < 270 nm) and to metal-to-ligand charge
0
.5
0
.45
0
0
0
.2
.1
0
0.2
0
300
400
500
600
700
0
50
100
150
200
250
300
350
400
Wavelength (nm)
Time (min)
Figure 3. (A) Evolution of the cleavage/reduction reaction of L promoted by
III
Fe(III) (0.05 mM L and 0.1 mM Fe (ClO
4
)
36 H
2
O in CH
3
CN) monitored by UV-
-1
-1
transfer transitions (MLCT, max= 368 nm,  ca. 6500 M cm
Visible spectroscopy. Black trace: initial spectrum, blue to red trace:
equilibrium between both forms of C1 evidenced by the isosbestic point
observed at 335 nm. (B) Time traces at 320 nm (black trace) and 530 nm red
trace).
-
1
-1 34
and 530 nm  ca. 2000 M cm ). The MLCT extinction
coefficient values are intermediate between low spin (S=0) and
high spin (S=2) Fe complexes,35 which supports the existence
of a spin state equilibrium for C1 in solution.
II
-
-
-
5
5
6
was almost quantitative, i.e. L was quantitatively transformed
into H L' while Fe(III) was completely reduced to Fe(II). Control
2
2
.5
1
1.5 10
A
B
1
5
10
10
1
experiments confirmed that light and dioxygen had no effect on
the redox/ring cleavage process. Once evolution of the
absorption spectrum stopped, the solution was filtered off on
silica and the structure of the organic compound remaining in
solution was found to be that of isophthalaldehyde, as shown by
1H NMR (Figure S4). This confirmed that the interaction of the
bis-imidazolidine (L) with iron led to its hydrolysis, yielding C1
and the starting isophthalaldehyde fragment (Scheme 2). In
contrast, in the absence of a metal salt, L was stable in
acetonitrile, methanol or chloroform as no trace of
0
0.5
-
6
-
5 10
1 10
0
-
-5
300
400
500
600
700
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Wavelength (nm)
E (V vs SCE)
Figure 2. (A) Evolution as a function of time of the UV-Visible spectrum of C1
.2 mM in CH CN (black trace, t=0; red trace, t= 20 h). (B) Cyclic voltammetry
0
3
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European Journal of Inorganic Chemistry
10.1002/ejic.201700605
FULL PAPER
decomposition could be observed both by 1H and 13C NMR
spectroscopy as well as ESI MS analysis (Figures S1 to S3).
Complexation of Cu(I) ions with retention of ligand integrity
When Cu(I) was used as a metal precursor, the bis-
imidazolidine ligand (L) remained stable and did not undergo
any ring cleavage. The reaction of one equivalent of L with two
Concerning ligand hydrolysis and the effect of different
metal ions.
I
equivalents of Cu (OTf) under argon atmosphere, resulted in
In order to understand the ring cleavage reaction of L
promoted by Fe(III), different first row transition metals were
the formation of
a
colourless compound (Figure 5A).
Recrystallization of this compound led to the formation of single
crystals suitable for X-Ray diffraction analysis. The resulting
structure displayed in Figure 5B shows the formation of complex
used, such as Zn(II) as redox inactive and Cu(II) and Cu(I) as
II
redox active metal ions. Addition of two equivalents of M (OTf)
2
(
M= Zn or Cu) in acetonitrile or methanol solution to one
C4 ([Cu
2
(L)](OTf)
2
)
that bears two crystallographically
equivalent of L induced the hydrolytic cleavage of the aminal
independent cuprous ions.
II
ring and the formation of M (H
2
L’) complexes (C2 M=Zn, and C3
M=Cu, Scheme S3). The isophthalaldehyde fragment and the
monotopic tetradentate protonated ligand (H L’) were thus
2
A
2
2
OTf
generated in a similar way to that described above with Fe(III).
In addition, the yield in isolated C2 (65%) and C3 (55%) were
similar or better than that in C1 indicating that these two
complexes were obtained as main products. The structures of
C2 and C3 are shown in Figure 4. Zinc complex C2 adopts a
similar geometry to that of the ferrous complex C1. The Zn(II)
N
N
N
N
N
CuI
N
N
N
1 equiv. [Cu
I(OTf)]2; C6H5CH3
N
N
N
N
N
Toluene, Ar, rt, 24 h
N
N
N
CuI
C4
cation is in
a
distorted octahedral [ZnN
4 2
O ] environment,
surrounded by H
mode. The coordination sphere is completed by two water
molecules (Figure 4, left).
2
L' acting as a tetradentate ligand in a cis-
Figure 5. (A) Synthesis and schematic representation of the formation of C4.
B) Structure of the molecular cation of C4 determined by X-ray diffraction
analysis.
(
Alternatively, by adding Cu(II) to ligand L, a different
geometry of H
It adopted a trans coordination mode around the metal center
Figure 4, right) with the cupric ion coordinated by four N atoms
2
L’ was stabilized for complex C3 in the solid state.
Each Cu(I) is three fold coordinated to two pyridyl
(
nitrogens (N1, N2 for Cu1 and N5, N6 for Cu2) and one
imidazolidine nitrogen (N3 for Cu1 and N4 for Cu2) in a distorted
trigonal planar geometry. In contrast, N7 and N8 are not
coordinated to a copper center, as shown by Cu1—N8 and
Cu2—N7 distances of 3.714(4) and 3.609(4) Å, respectively. Cu-
Nimidazolidine bond lengths (Cu1―N3 2.213(4) Å and Cu2—N4
2
.210(4) Å) fall in the range of Cu-Namine distances for which
copper adopts the same trigonal geometry.37,38 Consequently,
C27—N4 (1.499(6) Å) and C30—N3 (1.480(6) Å) are
significantly elongated compared to C-Nimidazolidine in which the N
atom is uncoordinated (C30—N7 1.454(6) Å and C27—N8
1.461(6) Å). These structural data reveal a weakening of the
C27—N4 and C30—N3 bonds induced by coordination to the
metal center, in agreement with their elongation.
In light of these observations, the cleavage of the
imidazolidine rings during complexation may be discussed in
terms of the Lewis acidity of the metal ion and stability of the
Figure 4. Structure of the molecular cations of C2 (left) and C3 (right)
determined by X-ray diffraction analysis.
z+
final complexes with respect to that of the starting (L + 2 M )
compounds. Upon coordination to the metal center, L chelates
the metal center as observed in complex C4. This results in an
elongation of two of the C-Nimidazolidine bonds revealing
a
of the ancillary ligand and two trans triflate anions in the axial
positions. The resulting molecular complex had an octahedral
coordination geometry with the main tetragonal distortion
departing from an ideal geometry due to a strong Jahn–Teller
effect. Apical bond lengths (Cu1–O6, 2.46 Å, and Cu1–O2, 2.53
Å) were very long by comparison to the equatorial Cu-N bond
lengths (ca. 2 Å). The mean Cu(II)–O (triflate) bond length
polarization of these and an increased electrophilic character of
3
δ+
the sp -hybridized imidazolidine carbon atoms. These C atoms
become more prone to nucleophilic attack by adventitious water
molecules, which leads to the hydrolysis of the aminal ring. Thus,
it is likely that a soft Lewis acid, such as Cu(I), does not induce a
strong enough polarization and does not promote hydrolysis of
the imidazolidine rings whereas harder Lewis acids, such as
Fe(III), Cu(II) and Zn(II), readily do it. Additionally, the
coordinative requirements of Cu(I) allow the stabilization of the
computed from 128 hits in the CSD was approximately 2.55 Å,
which confirmed that triflate ions were weakly bonded in C3.36
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European Journal of Inorganic Chemistry
10.1002/ejic.201700605
FULL PAPER
closed form of the ligand (L). In contrast, hydrolysis/cleavage
from L to H L' leads to a stronger Lewis base due to a gain of
2
denticity of the ligand, for which Fe(III), Cu(II) and Zn(II) have
higher affinity. Furthermore, the chelation of the metal ion by
led to the formation of C1 after one night, as revealed by UV-
visible measurements. This was confirmed by X-ray diffraction
analysis after isolation and recrystallization of the complex
(Scheme S5). Thus, these observations indicate that reduction
of FeIII into Fe is not dependent on any oxidative transformation
II
H
2
L' leads to three five membered metallocycles and thus,
III
additional stabilization of the final species, while coordination by
L, with only one five membered metallocycle, provides a much
weaker chelate effect (Scheme 3).
of H
2
L’. While the Fe (H
2
L') complexes are stable in the
presence of chloride as exogenous ligands, they are unstable in
their absence. This is consistent with the redox properties
observed for both C5, and a stoichiometric mixture of H
2
L’ and
Concerning the reduction of FeIII into FeII during the
imidazolidine ring cleavage.
Control experiments (under argon atmosphere and
protected from light) confirmed that there was no effect of light
and/or dioxygen on the redox/ring cleavage process. In order to
better understand the reduction of Fe(III) and its possible
Fe(ClO O, when investigated by cyclic voltammetry
4 2
)36H
(Figure 6). Besides the characteristic irreversible anodic wave of
the chloride counter ions at high potential, the Fe(III) complex
C5 presents a reversible wave at 0.270 V vs SCE. This value is
similar to the one reported for [Fe(BPMEN)Cl
(0.18 V vs SCE).46 Regarding the H
L’/Fe(III) stoichiometric
2
]+ by Girerd et al
2
relation to the ring cleavage process, complexation of one
mixture, it displays, after the time evolution discussed above,
two reversible redox signals with high positive E1/2 values (1.197
V and 1.095 V vs SCE) which are characteristic of complex C1
(Figure 2B and Figure 6). These values are in agreement with a
good stabilization of the Fe(II) center in C1 and suggest the
facile reduction of Fe(III) in the absence of chlorides.
III
equivalent of Fe (ClO
4
)
36H
2
O with the tetradentate ligand H
2
L'
was carried out under aerobic conditions (Scheme S5). In this
case, spontaneous reduction took place and the ferrous complex
C1 was obtained. It is worth noting that water molecules present
in solution were not oxidized to dioxygen. Indeed, no evolution of
dioxygen could be detected when the reaction was followed
using a Clark electrode, and no ligand oxidation could be
observed as well. In C1, both the C-Namine average bond lengths
To get insight into the reduction of FeIII when complexed to
2
H L’, we performed additional experiments in MeOH. Similarly to
what happened in acetonitrile, slow evolution into a ferrous
purple complex with spectral features similar to C1 was
observed by UV-visible spectrocopy, indicating that the nature of
the solvent was not a critical parameter. In order to determine if
the reduction of Fe(III) happened via a radical mechanism, EPR
experiments using PBN as a spin trap were carried out in
(
1.484(3) Å) and the C-C bond length of the ethylenediamine
fragment (1.511(4) Å) are consistent with
character.
a
single bond
N
N
3
CH CN/EtOH as solvent (Scheme S6). No conclusive radical
M
trapping information could be obtained, but interestingly, a small
amount of a dinuclear Fe(III) complex bridged by an acetate ion
was isolated as single crystals (C6, Figure S6). This result
indicated that EtOH was oxidized into its corresponding acid
during the process, which suggested that solvent could serve as
H
H
N
N
N
N
N
N
M
N
N
M
N
N
H₂L'
monotopic, tetradentate and
L
electron
donor
for
Fe(III)
reduction
during
the
forming three five membered rings
bitopic, tridentate for each metal and
hydrolysis/cleavage of L to yield the stable complex C1.
Additionally, considering that C1 was formed starting from L and
chelating the metal by one five membered ring
2
a ferric salt, or from H L’ and a ferric salt one can conclude that
the hydrolysis/cleavage of L and the reduction of Fe(III) are most
likely independent from each other.
2
Scheme 3. Chelating characteristics of the ligands H L’ and L
Spontaneous reduction of the Fe(III) under aerobic
conditions is quite rare in iron coordination chemistry. A few
examples of spontaneous reduction of a ferric ion chelated with
bis(methylimidazolyl)ketone,39 salicyloyl hydrazonodithiolane,40
hydrazide,41 or Schiff base ligands42-44 have been identified in the
literature, but the mechanism of the reduction has not been
reported. Nevertheless, Sosa-Torres et al. reported that
oxidative dehydrogenation of polyamine ligands in the presence
of FeIII led to the FeII complexes of the corresponding imine
ligands.14,45 In our case, we were unable to isolate any Fe(III)
-
5
1
10
-6
5 10
0
-6
-
-
5 10
1 10
-5
intermediate complex using Fe(ClO
(
4
)
36H
2
O
as metal salt
Scheme S5). However, the stoichiometric addition of FeCl to
L' afforded a high spin ferric complex
3
-
5
-
1.5 10
methanolic solutions of H
2
0
0.5
1
1.5
2
III
C5 [Fe (H
2
L’)Cl
2
]Cl (Figure S5 and Scheme S5) in high yield (ca.
E (V vs SCE)
80 %). Addition of 3 equivalents of silver perchlorate to an
acetonitrile solution of C5 allowed to remove chloride ions which
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European Journal of Inorganic Chemistry
10.1002/ejic.201700605
FULL PAPER
III
Figure 6. Cyclic voltammograms of 0.25 mM H
2
L’ + 0.5 mM Fe (ClO
mM C5 (red). The cyclic
voltammogram of 1 mM C1 after time evolution is shown as the blue trace.
4
)
36H
2
O
Electronic absorption spectroscopy. All experiments were carried out
with a Varian Cary 300-bio or a Cary 60 spectrophotometer in quartz
cuvette with one cm optical path length.
after complete reduction (green) and of
1
-
1
6 3
Room temperature, 0.1 M TBAPF / CH CN, 100 mV.s .
Electrochemistry. All electrochemical experiments were run under an
argon atmosphere. Cyclic voltammetry measurements were recorded
using an Autolab potentiostat controlled with a Nova 1.10 software
package. The counter electrode used was a Pt wire and the working
electrode was a glassy carbon disk carefully polished before each
voltammogram with 1 μm diamond paste, sonicated in an ethanol bath,
and washed with ethanol. The reference electrode used was a SCE
electrode isolated from the rest of the solution by a fritted bridge.
Experiments were run in acetonitrile using 0.1 M tetrabutylammonium
hexafluorophosphate as supporting electrolyte.
The in-depth understanding of the formation of C6 is out of
the scope of this paper. It is indeed a slow process that implies
oxidation of the solvent into products that we have not been able
to identify yet, except in the case of EtOH. However, one may
III
suggest that upon the reduction of formally four Fe , one EtOH
molecule was oxidized to the corresponding acetate (Scheme
S6). Owing to the bridging character of acetate, such process
would give rise to the formation of dinuclear iron(II) species,
which are known to readily react with O
2
,47-49 and then would
X-ray diffraction. X-ray diffraction data for compounds C1 and C6 were
collected by using a Kappa X8 APPEX II Bruker diffractometer with
graphite-monochromated MoKα radiation. X-ray diffraction data for
compounds C2, C3, C4 and C5 were collected by using a Kappa
VENTURE PHOTON 100 Bruker diffractometer with IµS microfocus
graphite-monochromated MoKα radiation (λ = 0.71073 Å). Crystals were
mounted on a CryoLoop (Hampton Research) with Paratone-N (Hampton
Research) as cryoprotectant and then flash frozen in a nitrogen-gas
stream at 100 K. The temperature of the crystal was maintained at the
selected value (100 K) by means of a 700 series Cryostream cooling
device to within an accuracy of ±1 K. The data were corrected for Lorentz
polarization, and absorption effects. The structures were solved by direct
methods using SHELXS-971 and refined against F2 by full-matrix least-
squares techniques using SHELXL-2014 or 20162 with anisotropic
displacement parameters for all non-hydrogen atoms. Hydrogen atoms
were located on a difference Fourier map and introduced into the
calculations as a riding model with isotropic thermal parameters. All
calculations were performed by using the Crystal Structure
crystallographic software package WINGX. CCDC 1530705-1530710
contains the supplementary crystallographic data for this paper. These
data can be obtained free of charge from the Cambridge Crystallographic
lead to the formation of the dinuclear ferric complex C6.
Conclusions
The fate of the complexes obtained by coordination of
metal ions to the imidazolidine ligand L depends on the nature of
the metal and its coordinative preference. With a soft Lewis acid
such as Cu(I), L is preserved and acts as a tridentate bitopic
ligand, even though two of the C-N bonds of the imidazolidine
moeties appear weakened upon coordination to the metal cation.
When using harder Lewis acids such as Fe(III), Zn(II), and Cu(II),
L
undergoes hydrolysis/cleavage to yield the tetradentate
amine/pyridine ligand H L'. This reaction on the L ligand can be
2
seen as the result of both a stronger polarization, and thus an
increased weakening of the C-N bond upon coordination to a
harder acid, and to the formation of more stable complexes
between H
cleavage of the aminal, the Fe (H
2
L' and Fe(III), Zn(II), or Cu(II). Independently to ring
III
Data
Centre
via
2
L') complex is slowly reduced,
http://www.ccdc.cam.ac.uk/Community/Requestastructure.
most probably by the solvent, leading to the formation of its
Fe(II) counterpart which exhibits a strong redox stability, as
determined by cyclic voltametry.
1
,3-bis(1,3-bis(pyridin-2-ylmethyl)imidazolidin-2-yl)benzene (L). N,N′-
4
bis(2pyridylmethyl) ethane-1,2-diamine (H
2
L’) (2 g, 8.25 mmol) was
dissolved in 35 mL of diethyl ether. To this solution was added
isophthaladehyde (553 mg, 4.126 mmol) dissolved in 15 mL of diethyl
ether. The mixture was allowed to react overnight. The product (L) was
precipitated as a white powder and was then filtered on a fritted glass
and washed with diethyl ether. The filtrate was concentrated and
recrystallized in a minimum amount of diethyl ether. L: 2.2 g, 91% yield.
Experimental Section
abbreviations: BPMCN, N,N′-bis(2-pyridylmethyl)-N,N′-dimethyl-trans-
1
1
,2-diaminocyclohexane; BQCN, N,N′-bis(8-quinolyl)-N,N′-dimethyl-trans-
,2-diaminocyclohexane; PBN (Phenyl N-t-butylnitrone); BPMEN, N,N′-
1H NMR (250 MHz, CDCl
3
) δ 8.41 (d, 4H, J= 4.2 Hz, Py-H); δ 7.88 (s, 1H,
dimethyl-N,N′-bis(pyridylmethyl)ethylenediamine)
phenyl-H); δ 7.58 (d, 2H, J= 4.2 Hz, phenyl-H); δ 7.48 (t, 4H, J= 7.5 Hz,
Py-H); δ 7.32 (broad, 5H, phenyl-H and Py-H); δ 7.03 (t, 4H, J= 6.2 Hz,
Py-H); δ 4.05 (s, 2H, N-CH-N); δ 3.86 (d, 4H, 2J=14.4Hz, Py-CH2) δ
Chemicals were purchased from Aldrich and TCI and were used without
purification. All solvents except for DCM, CH CN and MeOH were
3
2
3
(
1
[
.51 (d, 4H, J=14.4Hz, Py-CH2); δ 3.31 (m, 4H, N-CH2-CH2-N); δ 2.68
m, 4H, N-CH2-CH2-N). 13C NMR (75 MHz, CDCl
36.2, 130.6, 129.8, 128.2, 122.7, 121.7, 88.9, 58.8, 51.2. HRMS (ESI ),
M+H] = 583.3298. Calculated for C36
) 159.4, 148.6, 140,
3
purchased from Aldrich or VWR and were used as received. NMR
spectra were taken either on a Brucker AV 250 MHz or on a Brucker 300
MHz spectrometer using the residual protonated solvent as internal
standard. Chemical shifts (δ) are given in parts per million (ppm) and
coupling constants (J) are reported in hertz (Hz). Splitting patterns are
designated as singlet (s), doublet (d), triplet (t), doublet of doublet (dd),
and doublet of doublet of doublet (ddd). Splitting patterns that could not
be interpreted or easily visualized are designated as multiplet (m).
Electrospray mass spectra were taken on a Thermo Scientific TSQ, or a
Bruker microTOF in the positive mode of detection (ESI+).
+
+
H N
39 8
= 583.3219.
II
[Fe (H
2
L’)(CH
3
CN)](ClO
4
)
2
(C1) has been synthesised via two different
III
methods. Method A. A solution of Fe (ClO
4
)
2
36 H O (80 mg, 0.17 mmol)
in 2 mL of acetonitrile was slowly added to L (50 mg, 0.085 mmol) and
stirred for 6 hours at room temperature under aerobic conditions. The
color of the solution changed from red to purple. The solvent was
evaporated under reduced pressure and the resulting pasty complex was
dissolved in small amount of CH
3
CN/DCM (0.1 mL / 2 mL) and
precipitated with Et O. The red solid was filtered, washed with diethyl
2
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European Journal of Inorganic Chemistry
10.1002/ejic.201700605
FULL PAPER
ether and dried under vacuum. C1: 57 mg, Yield: 58 %. Crystals of C1
that were suitable for X-Ray diffraction were grown by diffusing diethyl
ether into an acetonitrile solution of C1. Method B. In a glovebox, a
homogeneous solution was then stirred overnight. Crystals of C6 were
obtained by slow evaporation of the solution mixture. The quantity of
crystals obtained was not enough to determine the yield of product
formation.
II
solution of Fe Cl
2
(34.5 mg, 0.27 mmol) in acetonitrile (2 mL) was added
L’ (66 mg, 0.27 mmol) in acetonitrile (2 mL).
After stirring for 15 min, the mixture was then treated with 2 mL of an
acetonitrile solution of AgClO (112 mg, 0.54 mmol), resulting in the
to a stirred solution of H
2
Supporting Information, including schemes S1 to S6, figures S1 to S6
and tables S1 to S2, is available from the link on the first page of this
paper.
4
formation of a white precipitate of AgCl, which was filtered away after
allowing the mixture to stir. The filtrate was then dried under vacuum,
3 2
redissolved in CH CN/DCM (0.1 mL / 2 mL) and precipitated with Et O,
yielding the desired complex as a red powder. C1: 80 mg, Yield 51%.
HRMS (ESI+), m/z [Fe (H
II
L’)(OH)]+= 333.056. Calculated for
Acknowledgements
2
C
14
H
21FeN = 333.10. Crystals of C1 that were suitable for X-Ray
4 2
O
diffraction were grown by diffusing diethyl ether into an acetonitrile
solution of C1. Caution! Perchlorate salts are potentially explosive and
should be handled with care.
The authors thank the Labex CHARMMMAT as well as the
Agence Nationale de la Recherche (ANR BIOXICAT; 12-JS07-
0007-01) for financial support. This work was also supported by
the ECOSTBio Action CM1305.
2 2 2 2
2 2
[Zn(H L’)(H O) ](OTf) (C2). A solution of Zn(OTf) ; 6H O (31 mg, 0.085
mmol) in 2 mL of acetonitrile was slowly added to L (25 mg, 0.043 mmol)
and stirred for 2 hours at room temperature under aerobic conditions.
The solvent was evaporated under reduced pressure and the resulting
light yellow powder was redissolved in 0.5 mL of DCM and precipitated
Keywords: Imidazolidine • Ring cleavage • Iron • Reduction •
Copper
with Et
2
O. The light yellow solid was filtered, washed with diethyl ether
+
and dried in vacuum. C2: 44 mg, Yield: 65%. HRMS (ESI ), m/z
[
[
[
1]
2]
3]
R. J. Ferm and J. L. Riebsomer, Chem. Rev., 1954, 54, 593–613.
V. Sharma and M. Khan, Eur J Med Chem, 2001, 36, 651–658.
M. C. Caterina, I. A. Perillo, L. Boiani, H. Pezaroglo, H. Cerecetto, M.
González and A. Salerno, Bioorg. Med. Chem., 2008, 16, 2226–2234.
G. Crank, D. Harding and S. S. Szinai, J. Med. Chem., 1970, 13, 1212–
&.
II
L’)(OTf)]+= 455.01. Calculated for ZnC15
[
Zn (H
2
18 3 4 3
H F N O S
455.03.
Crystals of C2 that were suitable for X-Ray diffraction were grown by
slow evaporation of a DCM/Et O (1/1) solution of C2.
2
[
4]
Cu(H
of acetonitrile was slowly added to L (30 mg, 0.05 mmol) and stirred for
6 hours at room temperature under aerobic conditions. The solution was
2 2
2
L’)(OTf) (C3). A solution of Cu(OTf) (37.2 mg, 0.1 mmol) in 2 mL
[5]
[6]
[7]
J. K. de A. L. Neves, S. P. S. Botelho, C. M. L. de Melo, V. R. A.
Pereira, M. D. C. A. de Lima, I. da Rocha Pitta, M. C. P. de Azevedo
Albuquerque and S. Lins Galdino, Parasitol Res, 2010, 107, 531–538.
S. P. Swain, Y.-C. Shih, S.-C. Tsay, J. Jacob, C.-C. Lin, K. C. Hwang,
J.-C. Horng and J. R. Hwu, Angew. Chem. Intl. Ed., 2015, 127, 10064–
10068.
3
filtered through a filter paper and the solvent was removed under
reduced pressure. The blue powder of the desired complex was filtered,
washed with Et
2
O and dried under vacuum. C3: 34.1 mg, yield: 55 %
HRMS (ESI+), m/z [Cu (H
II
L’)(OTf)]+= 454.035. Calculated for
2
15 3
C H18CuF N
4 3
O S = 454.04 Crystals of C3 that were suitable for X-Ray
M. Koepf, S. H. Lee, B. J. Brennan, D. D. Méndez-Hernández, V. S.
Batista, G. W. Brudvig and R. H. Crabtree, J. Org. Chem., 2015, 80,
9881–9888.
3
diffraction were grown by diffusing diethyl ether into a DCM/CH CN
solution of C3.
[
8]
A. Alexakis, P. Mangeney, N. Lensen, J. P. Tranchier, R. Gosmini and
S. Raussou, Pure and Applied Chemistry, 1996, 68, 531–534.
T. H. Fife and A. M. Pellino, J. Am. Chem. Soc., 1980, 102, 3062–3071.
I
2
[Cu (L)](OTf)
2
(C4). The ligand
L
and [Cu (OTf)]
;C H CH
2 6 5 3
being
insoluble in acetonitrile, the synthesis has been carried out in
toluene/DCM (1/1 v/v) mixture. Note that attempts to synthesize C4 in
a
[9]
[10] G. Godin, B. Levrand, A. Trachsel, J.-M. Lehn and A. Herrmann, Chem.
Commun., 2010, 46, 3125–3127.
I
II
MeOH led to Cu oxidation into Cu . In a glovebox, a brown solution of
I
[
Cu (OTf)]
; C H CH
2 6 5 3
(26.6 mg, 0.051 mmol) in toluene (2 mL) was
[11] B. Buchs née Levrand, G. Godin, A. Trachsel, J.-Y. de Saint Laumer,
J.-M. Lehn and A. Herrmann, Eur. J. Org. Chem., 2011, 681–695.
[12] M. Boča, P. Baran, R. Boča, H. Fuess, G. Kickelbick, W. Linert, F. Renz
and I. Svoboda, Inorg. Chem., 2000, 39, 3205–3212.
added dropwise to a light yellow stirred solution of L (30 mg, 0.051 mmol)
in DCM (2 mL). After stirring for three hours the desired complex was
precipitated as
a silver crystalline powder C4. After 30 min of
centrifugation the filtrate was removed, the silver powder was washed
with diethyl ether and dried under vacuum. C4: 36 mg, Yield: 70%.
Crystals of C4 that were suitable for X-Ray diffraction were grown by
diffusion of diethyl ether into an acetone solution of C4.
[13] N. Bréfuel, C. Lepetit, S. Shova, F. Dahan and J.-P. Tuchagues, Inorg.
Chem., 2005, 44, 8916–8928.
[14] V. M. Ugalde-Saldívar, H. Höpfl, N. Farfán, A. R. Toscano and M. E.
Sosa-Torres, Inorg. Chim. Acta, 2005, 358, 3545–3558.
[
[
[
[
[
[
15] J. P. Saucedo-Vázquez, V. M. Ugalde-Saldívar, A. R. Toscano, P. M. H.
Kroneck and M. E. Sosa-Torres, Inorg. Chem., 2009, 48, 1214–1222.
16] M. Fondo, N. Ocampo, A. M. García-Deibe and J. Sanmartín, Inorg.
Chem., 2009, 48, 4971–4979.
III
[
Fe (H
2
L’)(Cl)
2
]Cl (C5). A solution of FeCl
3
(9.9 mg, 0.061 mmol) in 2
L’ (15 mg, 0.061 mmol)
mL of MeOH was slowly added to a solution of H
2
in MeOH (1mL) and stirred for 2 hours at room temperature under
aerobic conditions. C5 was isolated as a yellow crystals suitable for X-
Ray diffraction by slow evaporation of the previous solution. C5: 19 mg,
17] M. Fondo, N. Ocampo, A. M. García-Deibe, E. Ruíz, J. Tercero and J.
Sanmartín, Inorg. Chem., 2009, 48, 9861–9873.
18] M. Bera, K. Biradha and D. Ray, Inorg. Chim. Acta, 2004, 357, 3556–
2
yield: 80%. Crystals were washed with Et O and dried under vacuum.
3
562.
19] M. Bera, U. Mukhopadhyay and D. Ray, Inorg. Chim. Acta, 2005, 358,
37–443.
FeIII
22.1 mg, 0.048 mmol) in 3 mL of EtOH was slowly added to a solution of
L’ (11.6 mg, 0.048 mmol) and N-tert-Butyl-α-phenylnitrone (22.8 mg,
.144 mmol) in 2 mL of EtOH. A precipitation took place. 2 mL of
acetonitrile were added in order to solubilize the mixture and the resulting
III
[
(
H
0
2 2 4 3
4 2
(-O)(-OAc)(H L’)](ClO ) (C6). A solution of Fe (ClO )36H O
4
20] K. Pramanik, P. Malpaharia, A. J. Mota, E. Colacio, B. Das, F. Lloret
2
and S. K. Chandra, Inorg. Chem., 2013, 52, 3995–4001.
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700605
FULL PAPER
[
21] A. R. Paital, W.-T. Wong, G. Aromí and D. Ray, Inorg. Chem., 2007, 46,
727–5733.
[37] K. D. Karlin, Y. Gultneh, J. P. Hutchinson and J. Zubieta, J. Am. Chem.
Soc., 1982, 104, 5240–5242.
5
[
[
22] P. K. Nanda, D. Mandal and D. Ray, Polyhedron, 2006, 25, 702–710.
23] S. Paul, W.-T. Wong and D. Ray, Inorg. Chim. Acta, 2011, 372, 160–
[38] T. N. Sorrell, M. R. Malachowski and D. L. Jameson, Inorg. Chem.,
1982, 21, 3250–3252.
1
67.
[39] P. C. A. Bruijnincx, I. L. C. Buurmans, Y. Huang, G. Juhász, M. Viciano-
Chumillas, M. Quesada, J. Reedijk, M. Lutz, A. L. Spek, E. Münck, E. L.
Bominaar and R. J. M. Klein Gebbink, Inorg. Chem., 2011, 50, 9243–
9255.
[
[
[
[
24] F. Avenier, L. Dubois, P. Dubourdeaux and J.-M. Latour, Chem.
Commun., 2005, 480.
25] A. Trehoux, Y. Roux, R. Guillot, J.-P. Mahy and F. Avenier, J. Mol.
Catal. A, 2015, 396, 40–46.
[40] N. Bouslimani, N. Clément, G. Rogez, P. Turek, M. Bernard, S.
Dagorne, D. Martel, H. N. Cong and R. Welter, Inorg. Chem., 2008, 47,
7623–7630.
26] F. Avenier, C. Herrero, W. Leibl, A. Desbois, R. Guillot, J.-P. Mahy and
A. Aukauloo, Angew. Chem. Int. Ed., 2013, 52, 3634–3637.
27] S. Kundu, E. Matito, S. Walleck, F. F. Pfaff, F. Heims, B. Rábay, J. M.
Luis, A. Company, B. Braun, T. Glaser and K. Ray, Chem. Eur. J., 2012,
[41] N. Bouslimani, N. Clément, C. Toussaint, S. Hameury, P. Turek, S.
Choua, S. Dagorne, D. Martel and R. Welter, Eur. J. Inorg. Chem.,
2009, 2009, 3734–3741.
18, 2787–2791.
[
[
[
[
[
[
[
[
28] M. Grau, A. Kyriacou, F. C. Martinez, I. M. de Wispelaere, A. J. P.
White and G. J. P. Britovsek, Dalton Trans., 2014, 43, 17108–17119.
29] M. Costas, J.-U. Rohde, A. Stubna, R. Y. N. Ho, L. Quaroni, E. Münck
and L. Que, J. Am. Chem. Soc., 2001, 123, 12931–12932.
[42] K. Ghosh, N. Tyagi, A. Kumar Dhara and U. P. Singh, Chem. Asian J.,
2014, 10, 350–361.
[43] M. Martinho, F. Banse, J.-F. Bartoli, T. A. Mattioli, P. Battioni, O. Horner,
S. Bourcier and J.-J. Girerd, Inorg. Chem., 2005, 44, 9592–9596.
[44] A. K. Patra, M. M. Olmstead and P. K. Mascharak, Inorg. Chem., 2002,
41, 5403–5409.
30] M. Costas, A. K. Tipton, K. Chen, D.-H. Jo and L. Que, J. Am. Chem.
Soc., 2001, 123, 6722–6723.
31] S. Hong, Y.-M. Lee, K.-B. Cho, K. Sundaravel, J. Cho, M. J. Kim, W.
Shin and W. Nam, J. Am. Chem. Soc., 2011, 133, 11876–11879.
32] J. England, G. J. P. Britovsek, N. Rabadia and A. J. P. White, Inorg.
Chem., 2007, 46, 3752–3767.
[45] V. M. Ugalde-Saldívar, M. E. Sosa-Torres, L. Ortiz-Frade, S. Bernès
and H. Höpfl, J. Chem. Soc., Dalton Trans., 2001, 3099–9.
[46] N. Raffard, V. Balland, J. Simaan, S. Létard, F. Banse, E.
Anxolabéhère-Mallart and J.-J. Girerd, C. R. Chimie, 2002, 5, 99–109.
[47] M. Costas, C. W. Cady, S. V. Kryatov, M. Ray, M. J. Ryan, E. V. Rybak-
Akimova and L. Que, Inorg. Chem., 2003, 42, 7519–7530.
[48] D. Lee, B. Pierce, C. Krebs, M. P. Hendrich, B. H. Huynh and S. J.
Lippard, J. Am. Chem. Soc., 2002, 124, 3993–4007.
33] J. England, C. R. Davies, M. Banaru, A. J. P. White and G. J. P.
Britovsek, Adv. Synth. Catal., 2008, 350, 883–897.
34] J. England, R. Gondhia, L. Bigorra-Lopez, A. R. Petersen, A. J. P.
White and G. J. P. Britovsek, Dalton Trans., 2009, 5319–5334.
35] N. Ségaud, J.-N. Rebilly, K. Sénéchal-David, R. Guillot, L. Billon, J.-P.
Baltaze, J. Farjon, O. Reinaud and F. Banse, Inorg. Chem., 2013, 52,
[49] J. R. Frisch, R. McDonnell, E. V. Rybak-Akimova and L. Que Jr., Inorg.
Chem., 2013, 52, 2627–2636.
691–700.
[36] T. Pandiyan, H. J. Guadalupe, J. Cruz, S. Bernès, V. M. Ugalde
Salvdivar and I. González, Eur. J. Inorg. Chem., 2008, 2008, 3274–
3285.
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European Journal of Inorganic Chemistry
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FULL PAPER
Reaction of the imidazolidine ligand
upon complexation with various first
row transition metals (Fe(III), Zn(II),
Cu(II) and Cu(I)) depends on the
Lewis acidity of the metal ions, as
well as on the coordinative
Imidazolidine complexation
Khaled Cheaib, Christian Herrero,
Régis Guillot, Frédéric Banse, Jean-
Pierre Mahy, Frédéric Avenier
Page No. – Page No.
requirements of the metal centers.
Imidazolidine Ring Cleavage upon
Complexation with First Row
Transition Metals
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