Towards a global greener process: from solvent-less synthesis of molybdenum(vi) ONO Schiff base complexes to catalyzed olefin epoxidation under organic-solvent-free conditions

Article abstract of DOI:10.1039/c6nj03174a

Nine Schiff base ligands derived from o-hydroxyaldehydes (2-hydroxybenzaldehyde, 2-hydroxy-3-methoxybenzaldehyde, 2-hydroxy- 1-naphthaldehyde) and nine corresponding dioxomolybdenum(vi) complexes, cis-[MoO₂L(CH₃OH)] or cis-[MoO₂L(CH₃OH)]·CH₃OH and dinuclear [MoO₂L]₂, have been prepared using the conventional solution-based method as well as mechanochemically, by liquid assisted grinding (LAG). All products have been characterised by means of IR spectroscopy, thermal analyses and also by powder and five molybdenum complexes by single crystal X-ray diffraction. The crystal structure analysis of mononuclear complexes reveal distorted octahedral Mo(vi) coordination by ONO donor atoms from a dianionic tridentate Schiff base ligand, two oxido oxygen atoms from the MoO₂²⁺ moiety and an oxygen atom from the MeOH molecule trans to the oxido oxygen atom. Due to the trans effect of the oxido oxygen atom, Mo-O(MeOH) is the longest bond distance within the Mo coordination sphere and it expected to be the point of maximum reactivity of the complexes. All complexes have been studied as pre(catalysts) for the epoxidation of cis-cyclooctene, cyclohexene and (R)-limonene using aqueous tert-butyl peroxide (TBHP) as the oxidant and in the absence of an organic solvent.

Full text of DOI:10.1039/c6nj03174a

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Towards a global greener process: from solvent-
less synthesis of molybdenum(VI) ONO Schiff base
complexes to catalyzed olefin epoxidation under
organic-solvent-free conditions†
Cite this:DOI: 10.1039/c6nj03174a
Marina Cindric,*a Gordana Pavlovic,b Robert Katavaabcd and Dominique Agustin*cd
´
´
Nine Schiff base ligands derived from o-hydroxyaldehydes (2-hydroxybenzaldehyde, 2-hydroxy-3-
methoxybenzaldehyde, 2-hydroxy- 1-naphthaldehyde) and nine corresponding dioxomolybdenum(VI)
complexes, cis-[MoO2L(CH3OH)] or cis-[MoO2L(CH3OH)]ÁCH3OH and dinuclear [MoO2L]2, have been
prepared using the conventional solution-based method as well as mechanochemically, by liquid
assisted grinding (LAG). All products have been characterised by means of IR spectroscopy, thermal
analyses and also by powder and five molybdenum complexes by single crystal X-ray diffraction. The crystal
structure analysis of mononuclear complexes reveal distorted octahedral Mo(VI) coordination by ONO donor
2+
atoms from a dianionic tridentate Schiff base ligand, two oxido oxygen atoms from the MoO2 moiety and
Received (in Victoria, Australia)
10th October 2016,
Accepted 6th December 2016
an oxygen atom from the MeOH molecule trans to the oxido oxygen atom. Due to the trans effect of the
oxido oxygen atom, Mo–O(MeOH) is the longest bond distance within the Mo coordination sphere and it
expected to be the point of maximum reactivity of the complexes. All complexes have been studied as
pre(catalysts) for the epoxidation of cis-cyclooctene, cyclohexene and (R)-limonene using aqueous tert-
butyl peroxide (TBHP) as the oxidant and in the absence of an organic solvent.
DOI: 10.1039/c6nj03174a
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and the development of synthetic procedures such as metal-
catalyzed oxidation processes provide new insights into ecologically
Introduction
The development of sustainable and environmentally friendly and economically more acceptable path in catalysis. The synthesis,
chemical processes integrating the twelve principles of green structure and different properties of various high-valent metal
chemistry is a challenging quest for chemists.1 The most complexes are described in a large number of articles and most
important principles are diminishing the use of organic solvent, of these complexes have shown to be very effective catalysts in
especially toxic, and increasing the use of catalysts in order to epoxidation.2 Molybdenum is one of the most used elements,
obtain selective and quick processes. The chemical transforma- especially within industrial processes.3 The molybdenum(VI)
tions including (ep)oxidation are interesting since epoxides are [MoO2(acac)2] complex used in many substitution reactions, was
key starting materials for a wide variety of products in organic described as one of the best molecular (pre)catalysts for the
chemistry. The most commonly used efficient non-catalyzed homogeneous catalytic epoxidation of olefins with TBHP/decane
(ep)oxidation processes are not green. The new approaches in organic solvents.4 Among the high number of molybdenum(VI)
complexes tested in the epoxidation of alkenes, [MoO2L(ROH)]
a University of Zagreb, Faculty of Science, Department of Chemistry,
Horvatovac 102a, HR-10000 Zagreb, Croatia. E-mail: marina@chem.pmf.hr;
Fax: +385 1 4606 341
complexes of Schiff base ligands have proven to be active catalysts.
Due to the ease of change of their steric and/or electronic
properties by the appropriate choice of the corresponding
aldehyde and amine components, Schiff bases have been used
extensively.5 Most of those catalyzed reactions are performed in
an organic solvent.6 Carrying out research in accordance with
the principles of green chemistry is still a challenge for many
laboratories.7
We have recently developed an organic-solvent free procedure
for the epoxidation of alkenes, using molybdenum(VI) complexes
as catalysts, coordinated with ONO or ONS ligands.8 The catalysts
are very often synthesized via classical methods, using a significant
b University of Zagreb, Faculty of Textile Technology, Department of Applied
´
Chemistry, Prilaz Baruna Filipovica 28a, HR-10000 Zagreb, Croatia
c CNRS, LCC (Laboratoire de Chimie de Coordination), 205 route de Narbonne,
BP 44099, F-31077 Toulouse Cedex 4, France. E-mail: dominique.agustin@iut-tlse3.fr;
Fax: +335 63 351 910; Tel: +335 63 621 172
d
´
Universite de Toulouse, UPS, INPT, Institut Universitaire de Technologie Paul
´
Sabatier, Departement de Chimie, Av. Georges Pompidou, CS 20258,
F-81104 Castres Cedex, France
† Electronic supplementary information (ESI) available. CCDC 1508023–1508027
(compounds 2a, 3, 6, 7 and 9). For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c6nj03174a
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amount of organic solvents. In order to increase the ‘‘green’’
The required time for grinding in the agate mortar was
contribution to a catalytic process, i.e. considering not only determined empirically when the colour of the reaction mixture
catalyzed transformation but also catalyst synthesis, one of the stopped changing. All products were obtained as solid powders.
most promising additional approaches used is the preparation The IR spectra, analytical data and results of PXRD experiments
of a catalyst using a greener method.9 The latest reports have for all ligands obtained using both methods matched well
shown that solvent-free synthesis and mechanochemistry have (Table S1 and Fig. S1–S6, ESI†). The obtained results were in
been developed as effective and rapid, ecological procedures for agreement with the literature data12 for solvent free syntheses
a wide range of different ligands and their corresponding metal of Schiff base ligands derived from 2-amino-5-methylphenol
complexes.10
and 2-hydroxybenzaldehyde (H2L3) and 3-methoxy-2-hydroxy-
Based on our previous investigations11 on this topic we have benzaldehyde (H2L6) respectivelly, or from 2-amino-4-methyl-
been interested in exploring (a) a comparison between mechano- phenol and 2-hydroxybenzaldehyde (H2L2).
chemical and solvent-based synthetic methods for preparing
Dioxomolybdenum(VI) complexes, 1–9 (Table 1) have also been
Schiff base ligands and their molybdenum(VI) complexes; (b) obtained using both methods. In the synthesis of all complexes, a
influence of Schiff base ligands substitutuents on the crystal very suitable, easily accessible precursor [MoO2(acac)2] was used.
structure and the catalytic properties of the corresponding metal Herein, we report for the first time liquid-assisted mechanosynthesis
complexes; and (c) the catalytic activity of the complexes in the of nine dioxomolybdenum complexes containing Schiff base
epoxidation of olefins with aqueous TBHP as the oxidant under derivatives of 2-hydroxybenzaldehyde (H2L1–3), 3-methoxo-2-
organic solvent free conditions.
hydroxybenzaldehyde (H2L4–6) and 2-hydroxy-1-naphthaldehyde
(H2L7–9) with 2-aminophenol and its 4-methyl- and 5-methyl
derivatives (Scheme 1).
Five complexes, mononuclear [MoO2L1(CH3OH)] (1), [MoO2L2-
(CH3OH)] (2) [MoO2L2(CH3OH)]ÁCH3OH (2a), [MoO2L5(CH3OH)]
(5) and dinuclear [MoO2L8]2 (8), were prepared using the classical
solution-based method reported in the literature.11 Complex 2a of
the general formula [MoO2L2(CH3OH)]ÁCH3OH is unstable; a
red solvatomorph of the orange complex 2 has been previously
reported by us.11 Similar synthetic conditions are used in the
synthesis of five new complexes [MoO2L3(CH3OH)]ÁCH3OH (3),
[MoO2L4(CH3OH)] (4), [MoO2L6(CH3OH)]ÁCH3OH (6), [MoO2L7-
(CH3OH)] (7) and [MoO2L9(CH3OH)]ÁCH3OH (9).
Results and discussion
Ligands and complexes: synthesis and characterization
The Schiff base ligands, H2L1–9 were obtained using a classical
solution-based method (a) or by liquid-assisted mechanosynthesis
by using an agate mortar or ball milling (b), via a typical
condensation reaction between the appropriate substituted
aldehyde and 2-aminophenol or its 4- and 5-methyl derivatives
(Scheme 1 and Table 1). Due to the different colours and in
some cases different aggregation states of the reactants, the
progress of the liquid-assisted mechanosynthesis can be readily
monitored using a camera.
Applying the classical solution-based method and liquid-
assisted mechanosynthesis, the replacement of the acetylacetonate
ligands with a tridentate ligand L2À produced mononuclear and/or
dinuclear octahedrally coordinated molybdenum(VI) complexes.
During the milling of the mixture of [MoO2(acac)2] and H2L8 and
formation of complexes 8 the colour of the reaction mixtures
changed from orange to orange-green. Addition of a few drops of
methanol changed the colour of the mixture back to orange. This
behaviour is probably caused due to the important role of solvent
molecules in the stability of the intermediate during the formation
of these binuclear complexes. This behaviour is not observed
during the preparation of any other complex (Fig. S7–S15, ESI†).
The [MoO2L1(D)] complexes derived from 2-hydroxybenz-
aldehyde and 2-aminophenol (H2L1), coordinated with different
solvent molecules (D = water, DMSO, alcohol, THF, imidazole,
pyridine-N-oxide), have been reported in the literature so far.13–15
To examine the thermal stabilities of the prepared com-
plexes, they are heated in an oxygen atmosphere from 25 1C to
600 1C. All complexes display very similar thermal behavior and
small differences could be coupled with the observed structural
differences. Thermal analysis data for complexes obtained
using a solution based method, cis-[MoO2L1,2,4,5,7(CH3OH)] and
[MoO2L2a,3,6,9(CH3OH)]ÁCH3OH, reveal a well-defined endothermic
step in the range from 38 to 232 1C, corresponding to the loss
of only coordinated methanol molecules in 1 (64–158 1C), 2
(42–110 1C), 4 (60–123 1C), 5 (43–154 1C), and 7 (48–125 1C) or
Scheme 1 Two synthetic paths of molybdenum(VI) complexes and ligands.
Table 1 Schiff base ligands and related complexes
H2L1–9
R1
R2
R3
Complexes, 1–9
H2L1
H2L2
H2L3
H2L4
H2L5
H2L6
H
H
H
OMe
OMe
OMe
H
Me
H
H
Me
H
H
H
Me
H
H
[MoO2L1(CH3OH)] 1
[MoO2L2(CH3OH)]a
2
[MoO2L3(CH3OH)]ÁCH3OH 3
[MoO2L4CH3OH] 4
[MoO2L5(CH3OH)] 5
Me
[MoO2L6(CH3OH)]ÁCH3OH 6
H2L7
H2L8
H2L9
H
H
H
H
Me
H
H
H
Me
[MoO2L7(CH3OH)] 7
[MoO2L8]2
8
[MoO2L9(CH3OH)]ÁCH3OH 9
a
[MoO2L2(CH3OH)]ÁCH3OH 2a unstable solvatomorph of 2 prepared
and characterized.
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solvated and coordinated in 2a (53–117 1C), 3 (38–169 1C), 6 deviation from the ideal value approximately around 1701 in all
(52–143 1C), and 9 (50–132 1C). The relatively labile binding of complexes (Table S6, ESI†). The deformation of the octahedral
methanol molecules in the solid state is evident. The second cis angle values around the metal center is determined by the
step, in the temperature range of 200 to 580 1C is followed by ligand planarity, the bicyclic system of two chelate rings which
the decomposition of [MoO2L]. This stage includes highly are slightly folded along the axis of the molybdenum–imino
exothermic oxidative reactions and the complete loss of organic bond and by the offset of the metal centre apart from the
matter, with MoO3 being the final residue. Thermal analysis chelate planes towards the terminal oxygen atom. The latter
data for the [MoO2L8]2 complex correspond to a one-step increases misalignment of the planes defined by the chelate
decomposition process in the range 266–514 1C. The thermal ring atoms from coplanarity with the planes of the peripheral
behavior of complexes prepared using the LAG method showed aromatic systems (phenyl or naphthyl rings) (Table S5, ESI†).
differences relative to the complexes obtained from the solution, The Mo(VI) is shifted from the equatorial plane of the octahedron
certainly due to the fact that complexes prepared using the LAG towards the terminal oxygen atom and the calculated dihedral
method do not contain solvent of crystallization or some of them angles exhibit that the largest deviation from coplanarity occurs
are polymers. The data for complexes obtained using the LAG in complexes 3, 6 and 9 which contain solvent of crystallization
method are given in Table S2 (ESI†) and compared with those or the –OCH3 group (vs. –CH3 group). These conformational
obtained using the solution-based method.
discrepancies are caused by intermolecular interactions, formed
The infrared spectra of all the prepared complexes (by both by a methoxy group which is known to have formation capability
methods) exhibit bands characteristic of these types of complexes as a proton acceptor. Namely, complex 6 is the only one contain-
and all data are in accordance with the literature data.13,14 The IR ing both methanol solvent of crystallization and a methoxy
spectra of cis-[MoO2L1,2,5,7(CH3OH)] and [MoO2L2a,3,6,9(CH3OH)]Á group.In contrast, complex 7 does not contain methanol solvent
CH3OH complexes exhibit strong vibrations between 960 and of crystallization or a methoxy group and its chelate and aromatic
890 cmÀ1. The appearance of two (or three) bands in this region ring systems are almost coplanar.
is characteristic of cis-MoO2 species. The presence of only a single
The crystal structures of complexes 2a, 3, 6, 7 and 9 are
stretch at about 930 cmÀ1 in the spectra of some complexes dominated by two types of hydrogen bonds: O–HÁ Á ÁO and
prepared using method (a) (e.g. [MoO2L8]2) or (b) (e.g. complexes C–HÁ Á ÁO. The main supramolecular motif (Fig. 1) made by
4, 7 and 8) instead the usual doublet of MoO2 suggests poly- the methanol molecule of crystallization is the infinite chain
merisation via oxo bridging between molybdenum centres. The shaped by the O–HÁ Á ÁO types of hydrogen bonds with the
presence of stretching vibrations at about 870 and 750 cmÀ1 coordinated methanol –OH group and the oxido oxygen atom
confirms the presence of oxo bridging, Mo–OÁÁÁMo. Several (Fig. 1b, c and e) for complexes 2a, 6 and 9, respectively. In all
medium to weak bands in the region 550–650 cmÀ1 are three structures the crystallized MeOH molecule acts as a proton
assigned to Mo–O(PhO) stretching vibrations. The strong to donor and acceptor simultaneously; with the oxido oxygen atom
medium bands in the region 1625–1160 and 1440–1300 cmÀ1 as the proton donor and with coordinated MeOH as the proton
are assigned to CQN and phenolic C–O stretching vibrations, acceptor bridging complex molecules in the crystal.
respectively (Table S3, ESI†).
These 1D infinite chains are usually transversally supported
by rings formed via C–HÁ Á ÁO types of hydrogen bonds and
consequently infinite ribbons of alternating condensed rings
Molecular and crystal structure of complexes 2a, 3, 6, 7 and 9
The aim of the work was to find out the possible correlation are formed. The main supramolecular pattern found in 3 and 7
between the crystal structure and the catalytic activity of com- is a centrosymmetric dimer formed by two molecules of solvent
plexes. Complexes 2a, 3, 6 and 9 (general and crystallographic CH3OH, which are joined by the O–HÁ Á ÁO intermolecular
data are given in Table S4, ESI†) contain one methanol solvent hydrogen bond and further with two complex molecules via
molecule per complex molecule in the asymmetric unit, the phenolate O4 oxygen atom (Fig. 1a). Since complex 7 does
while complex 7 crystallizes without solvent of crystallization. not contain solvent molecule of crystallization, the main supra-
The metal center is ligated by two terminal oxygen atoms and molecular synthon formed via the O–HÁ Á ÁO hydrogen bond is a
one tridentate dianionic Schiff base ligand coordinating via the centrosymmetric dimer between the –OH group of coordinated
phenolic oxygen atom, the imine N atom and the hydroxyl methanol and the O3 donor atom of the five-membered chelate
oxygen atom to the metal center (Fig. S16(a)–(e), ESI†). The ring of another complex molecule (Fig. 1d). Detailed descriptions
sixth coordination site is occupied by the oxygen atom from the of these supramolecular architectures are given in the ESI†
coordinated methanol molecule (Table S5, ESI†). The molybdenum (Fig. S21 and Table S7). The preliminary data of the molecular
2+
oxido groups of the MoO2 moiety show the expected mutual and crystal structure of the [MoO2L4(CH3OH)] complex were
cis configuration and are located trans to the imine N atom and accomplished using the PXRD method (Table S4, ESI†).
the coordinated MeOH molecule. The longest bond distance
within the Mo coordination sphere is Mo–O(MeOH), due to the
Catalytic activity of molybdenum complexes
trans effect of the oxido oxygen atom, and it is expected to be The catalytic activity of all molybdenum complexes, prepared
the point of maximum reactivity of the complex. The axial using the solution based method, was evaluated for the epox-
octahedral angle around Mo(VI), which is constrained by the idation of three substrates: cis-cyclooctene, cyclohexene and
stereochemical rigidity of the ligand itself, exhibits the largest (R)-limonene. The influence of the ligand substitution was the
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Scheme 2 Epoxidation of cis-cyclooctene catalysed by molybdenum
complexes.
studied parameter. The prominence in these investigations was
given to low Mo/alkene ratio (0.5%), all alkenes were (ep)oxidized
by aqueous TBHP in the absence of organic solvent.
The complexes are moderately soluble in substrates and
insoluble in water at room temperature, but dissolve in the
organic phase after the addition of aqueous TBHP at 80 1C. The
coloured organic phase suggests that, as previously observed
with similar complexes, the catalyst is mostly confined in the
organic phase. Catalysts containing a 3-methoxy substituent
(4–6) showed best solubility and were dissolved within 10 min
after the addition of TBHP. Catalyst 8 (binuclear complex)
remained poorly dissolved in reactions with all three sub-
strates, even after 4 h. As was previously described, coordinated
methanol is released during catalysis. Catalysts 7 and 9 started
to precipitate as the reaction advanced, certainly due to the
release of coordinating methanol and formation of dimers.
Epoxidation reactions of cyclooctene, cyclohexene and
limonene
Cyclooctene. Cyclooctene (CO) is considered in the literature
as a model olefin for the epoxidation (Scheme 2). This substrate
is a good indicator of epoxidation since few by-products are
observed and the corresponding epoxide (COE) is sufficiently
stable in the presence of water, as previously shown. A blank
reaction without the catalyst showed very low conversion after
4 hours, exhibiting the activity of the complexes. Catalyzed
epoxidation of cis-cyclooctene with all complexes led to conversion
of CO between 68 and 86% with selectivity towards COE between
90 and 97%. A small portion of organic compounds are observed
in the water phase since the mass balance in the organic phase
(substrate + epoxide) is between 91 and 98%.
The comparisons can be made starting from the simple
2-hydroxybenzaldehydato backbone (L1). Introduction of methyl
in the R2 or R3 position did not change the catalytic results
dramatically, with a slightly better conversion with complex 3
(R3 = Me) and a better activity. When R2 = Me (complex 2), the
compound seemed to be less active with a lower TOF.
Introduction of the methoxy group or the naphthyl group on
the ligand backbone was noticeable in the catalytic results. For
both changes, the conversion was higher than their corres-
ponding methylated complexes on SAP backbones.
The most efficient catalyst was the complex possessing a
naphthyl backbone substituted by one methyl in the X-position
with 86% of CO conversion and 97% selectivity towards COE
(and the highest TOF of 200) (Table 2).
Fig. 1 Main supramolecular interactions shaped by the O–HÁ Á ÁO types of
hydrogen bonds with the coordinated methanol oxygen atom. (a) Infinite
1D chain formation along the a axis in 2a via O1M–H1OMÁ Á ÁO1A and O5A–
H5OÁ Á ÁO1M intermolecular hydrogen bonds. The methanol solvent mole-
cule acts as a proton donor in hydrogen bond formation with the terminal
oxido O1A atom and as a proton acceptor in hydrogen bond formation
with a coordinated methanol molecule. (b) Formation of a supramolecular
8-membered hydrogen bonded ring via the O–HÁ Á ÁO type of hydrogen
bond in 3. Further supramolecular linking between the complex and the
solvent molecule by the O–HÁ Á ÁO type of hydrogen bond. (c) Linking of
the complex and solvent molecules in 6 into one-dimensional infinite
chains spreading along the b axis via O7–H7Á Á ÁO2 and O5–H5Á Á ÁO7
intermolecular hydrogen bonds. (d) Formation of the centrosymmetric
dimers via the O–HÁ Á ÁO hydrogen bond between –the OH group of
coordinated methanol and the O3 donor atom of the five-membered chelate
ring of another complex molecule in 7. (e) Infinite one-dimensional chains
formation spreading along the a axis in 9 by solvent molecules of crystal-
lization which act as a proton donor and aa proton acceptor via O5–H5ÁÁÁO6
(proton acceptor) and O6–H6ÁÁÁO2 (proton donor) intermolecular hydrogen
bonds.
During the catalytic process, complexes 4–6 (derived from
3-methoxy-2-hydroxybenzaldehyde) were soluble while complexes
7–9 (derived from 2-hydroxy-1-naphthaldehyde) were poorly soluble.
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Table 2 The epoxidation of cyclooctene with TBHP using Mo(VI) complexes
Table
3
The epoxidation of cyclohexene with TBHP using Mo(VI)
complexes
Selectivity towards
Mo cat.a CO conversionb (%)
COE (%)
TOFc/hÀ1 TONd
Conversionb (%) Selectivity after 4 h (%)
Mo cat.a
CH
CHO
CHD
TOFc/hÀ1 TONd
No cat.
2
23
92
91
91
1
2
3
68
68
75
117
74
158
135
135
148
No cat.
15
70
54
58
o1
20
26
23
31
33
39
1
2
3
77
43
59
140
108
115
32
4
5
6
83
74
80
94
94
92
164
138
153
165
147
157
4
5
6
62
57
55
20
28
29
35
30
35
56
50
64
124
107
110
7
8
9
80
72
86
93
90
97
105
51
200
160
142
170
7
8
9
56
37
54
19
5
20
39
71
41
53
17
55
110
74
112
a
Reaction conditions: time, 4 h; temperature, 80 1C; [Mo]/CO/TBHP
b
c
molar ratio: 0.5/100/200. Calculated after 4 h. n(CO transformed)/
n(catalyst)/time at 30 min. n(CO transformed)/n(catalyst) at 4 h.
d
a
Reaction conditions: time, 4 h; temperature, 80 1C; [Mo]/CH/TBHP
b
c
molar ratio: 0.5/100/200. Calculated after 4 h. n(CH transformed)/
n(catalyst)/time at 30 min. n(CH transformed)/n(catalyst) at 4 h.
d
The low solubility does not seem to be a problem for the
catalysis. It is probable that those complexes are slightly soluble
and it is enough to be extremely active.
depending on the nature of the catalyst. Since CHD is soluble
in water, the diol, consecutive to the CHO ring opening can be
observed in all cases. The mass balance in the organic phase
indicates that cyclohexanediol (CHD) is transferred into the water
phase. [MoO2(L1)(MeOH)] was the best catalyst in terms of CH
conversion. The trend showed that the presence of the naphthyl
backbone gave slightly worse results but the influence of methyl
and/or methoxy substitution was not very significant.
Limonene. Limonene (Lim) is an interesting substrate to
study. Indeed, the intrinsic geometry around the double bond
and the presence of isopropenyl can have an influence on the
epoxidation, giving cis and trans 1,2-limonene epoxide (cis- and
trans-LimO) (Scheme 4). The subsequent epoxide ring opening
with water leads mainly to the trans-diaxial limonene-1,2-diol
(LimD). This diol is also water-soluble. The analysis of the
content of the organic phase was performed and the results are
given in Table 4.
The analyses of all experiments at the end of the reaction
show that epoxidation of (R)-limonene yielded cis and trans-
LimO, and LimD for all complexes. The calculated mass
balance in the organic phase at the end of the reaction showed
that around 80% of the compounds (Lim + LimO (cis + trans) +
LimD) are present in the organic phase. It has been shown in
several articles that limonene diol (LimD) can be obtained
In accordance with the literature data15 it has been observed
that Lewis acidity of the catalyst helps in the ring opening
process for small rings. The use of ligands with a methyl group
in the R2 position make the dioxomolybdenum(VI) complex
(2, 5 and 8) a weaker Lewis acid and showed worse results.
Cyclohexene. Cyclohexene (CH) showed to be an interesting
model substrate for epoxidation tests under solvent free con-
ditions. Indeed, without using a catalyst and using TBHP in
water only, CH was poorly converted (7%) and the corres-
ponding expected epoxide (CHO) was detected in very low
quantity (Scheme 3). When the catalyst was added, conversions
were observed and the presence of epoxide (CHO) and sub-
sequent ring opening in the presence of water (i.e. the cyclo-
hexanediol, CHD) could be observed in the organic phase. We
have shown recently that a part of the diol is transferred in the
aqueous phase (water being present because of the nature of
the oxidant, i.e. TBHP in water). A GC analysis of the water
phase showed that only diol was present, justifying this
assumption. The control of the mass balance at the end of
the reaction as for cyclooctene showed that between 60 and
80% of compounds (CH + CHO + CHD) are maintained in the
organic phase (Table 3). All reactions in the presence of complexes
exhibited higher conversion of cyclohexene, indicating their
catalytic role.
The conversion values were between 54 and 70% (and 37%
for complex 5), depending on the nature the catalyst. As observed
previously with similar complexes, the selectivity towards epoxide
(CHO) lay between 19 and 32% (5% for the dimeric complex 8),
Scheme 3 Epoxidation of cyclohexene catalysed by molybdenum com-
Scheme 4 Epoxidation of limonene catalysed by molybdenum complexes
plexes using TBHP in water.
using TBHP in water.
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Table 4 The epoxidation of limonene with TBHP using Mo(VI) complexes
best catalyst in terms of cyclohexene conversion; (b) the presence
of a naphthyl and methyl and/or methoxy group on the ligand
backbone does not affect the catalytic results. Introduction of the
methoxy and naphthyl groups on the ligand backbone is notice-
able on the conversion of cyclooctene to the corresponding
epoxide; and (c) the epoxidation of (R)-limonene yield cis and
trans 1,2-limonene epoxide and trans diaxial limonene-1,2-diol
for all complexes, present mostly in the organic phase.
Selectivity (%)
Mo Lim
Max
cat.a conversionb (%) cis-LimO trans-LimO LimD TOFc (hÀ1) TONd
No
1
2
8
67
49
63
17
9
28
14
nd
28
14
25
31
35
33
45
41
79
134
98
126
3
4
5
6
62
59
66
8
19
8
31
34
31
30
22
30
76
64
84
124
116
132
Experimental
Materials and methods
7
9
52
55
6
8
29
32
30
29
39
55
103
108
Ligands H2L1–9 were prepared by Schiff’s base condensation
and by neat grinding according to the procedures described in
the literature.11b,12 The molybdenum precursor [MoO2(acac)2]
was prepared according to the literature procedure.16 Methanol
was dried using magnesium turnings and iodine and then
distilled. For the catalytic investigations cis-cyclooctene (98%
Aldrich), cyclooctene oxide (Aldrich), limonene (Aldrich), limonene
oxide (Aldrich), cyclohexene (Aldrich) cyclohexene oxide (Aldrich)
TBHP (70% in water, Aldrich), H2O2 (35% in water, Aldrich) and
diethyl ether (ACROS) were commercially available and used as
received.
Catalytic reactions were followed by gas chromatography on
an Agilent 6890A chromatograph equipped with an FID detec-
tor, a HP5-MS capillary column (30 m  0.25 mm  0.25 mm)
and automatic sampling, or on a Fisons GC 8000 chromato-
graph equipped with an FID detector and with a SPB-5 capillary
column (30 m  0.32 mm  0.25 mm). The GC parameters were
quantified with authentic samples of the reactants and the
products. The conversion of olefins and the formation of the
corresponding oxides or diols were calculated from calibration
curves (r2 = 0.999) relatively to an internal standard.
a
Reaction conditions: time, 4 h; temperature, 80 1C; [Mo]/Lim/TBHP
b
c
molar ratio: 0.5/100/200. Calculated after 4 h. n(Lim transformed)/
n(cat.)/time at 30 min. n(Lim transformed)/n(cat.) at 4 h.
d
mainly from cis-epoxide (LimO) in the presence of a molybdenum
catalyst, or under acidic conditions. At the first few hours of the
reaction the proportion of cis and trans is close, not showing
selectivity between both stereoisomers. This phenomenon was
also observed in our case with all the catalyst by a kinetic
experiment. The plateau of 50% of each isomer was not reached
showing that both epoxides are sensitive to water and are opened.
However, the quantity of cis-LimO decreases very fast in contrast
to trans-LimO, while the quantity of trans-diol increases at the
same time.
Conclusions
LAG method can be used for the synthesis of molybdenum
Schiff base complexes
A comparison between liquid-assisted grinding and solvent-
based synthetic methods for preparing Schiff base ligands and
their molybdenum(VI) complexes was explored. The complexes
prepared using the LAG method showed differences in the
properties and structures relative to the complexes obtained
from the solution, certainly due to the fact that complexes
prepared using the LAG method do not contain methanol
solvent of crystallization.
Crystallography
Selected crystallographic and refinement data for structures
corresponding to compounds 2a, 3, 6, 7 and 9 obtained by the
single-crystal X-ray diffraction experiment are summarized in
Table S4 (ESI†). Selected geometries including valence bonds
and angles, hydrogen bond geometry and pÁ Á Áp interactions are
given in Tables S5 and S6 (ESI†), respectively. Data collection
was performed on an Oxford Xcalibur diffractometer equipped
with a CCD detector under graphite-monochromated MoKa
radiation (l = 0.71703 Å) at room temperature (296(2) K) by
employing the o-scan technique. Programs CrysAlis CCD
and CrysAlis RED (Versions 1.171.33.55 and 1.171.34.4)17 were
employed for data collection, cell refinement and data
reduction. The intensity data were corrected for Lorentz and
polarization factors as well as for absorption effects using a
multi-scanning method.
Influence of substituents and solvent molecules on Schiff base
ligands on the crystal structure of complexes
Conformational discrepancies caused by intermolecular inter-
actions are observed only in the complexes which contain
solvent of crystallization or the –OCH3 group (vs. –CH3 group)
on the Schiff base backbone. These hydrogen bonds are formed
between the methoxy group, which is known to have formation
capability as a proton acceptor, and the solvent molecule.
Electronic influence of substituents on the Schiff base
backbone alters Lewis acidity of the catalyst, which is crucial
for its activity
(a) The molybdenum(VI) complex coordinated with Schiff’s base all unique data. Programs SHELXL201418 and SHELXL201419
derived from 2-hydroxybenzaldehyde and 2-aminophenol is the integrated in the WinGX (v. 1.80.05)20 software system were
The structures (2a, 3, 6, 7 and 9) were solved using direct
methods and successive Difference Fourier maps and refined
by weighted full-matrix least-squares based on F2 by using
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used to solve and refine structures. All non-hydrogen atoms
In continuation are given analytical data for six new complexes
were refined with anisotropic displacement parameters. The (3, 4, 6, 7, 9) obtained using both methods, solvatomorphic form
hydrogen atoms, except those from the coordinated or solvent 2a obtained using method (a) and four complexes (1, 2, 5 and 8)
methanol molecules, were treated by a riding model as they known from the literature obtained using method (b).
were placed on the basis of the conformation of the preceding
carbon or nitrogen atoms with assigned isotropic displacement solution-based method according to the literature data.11
parameters. The hydrogen atoms belonging to the oxygen
Method (b) [MoO2(L1)(MeOH)] yield ( yellow powder):
methanol molecule was firstly found in the difference Fourier 52.8 mg (46.4%). C, 44.7; H, 3.2; N, 3.6; Mo, 25.6%. Calc. for
1: method (a) complex 1 has been prepared using the
map at the final stages of the refinement procedure and then
C14H13MoNO5 (Mr = 371.22): C, 45.3; H, 3.5; N, 3.8; Mo, 24.7%.
refined by SHELXL2014 DFIX instruction at the O–H distance of IR(KBr, cmÀ1): 1611n(CQN); 935 and 907n(MoO )
.
2
0.82(2) Å with assigned isotropic displacement parameters
being 1.2 times larger than the equivalent isotropic displace- crystals): 19.8 mg (31%). C, 45.9; H, 4.6; N, 3.3; Mo, 22.9%. Calc.
2:Ámethod (a) [MoO2(L2)(MeOH)]ÁMeOH: yield (unstable red
ment parameters of the parent oxygen atom. The positional for C16H19MoNO6 (Mr = 417.26): C, 46.1; H, 4.6; N, 3.4; Mo,
disorder of the complex molecule in 3 has been resolved and 23.0%. IR(KBr, cmÀ1): 1605n(CQN); 933 and 912n(MoO )
.
2
fixed at major (A) and minor (B) component abundance in the
final ratio of 57 : 43.
Method (b) [MoO2(L2)(MeOH)]: yield (orange powder):
35.4 mg (60%). Found: C, 46.7; H, 3.8; N, 3.6; Mo, 24.8%. Calc.
Due to the lack of a satisfactory parameter-to-data ratio for C15H15MoNO5 (Mr = 385.26): C, 46.8; H, 3.9; N, 3.6; Mo,
(not to be less than 10) the non-hydrogen atoms of both 24.9%. IR(KBr, cmÀ1): 1606n(CQN); 935 and 907n(MoO )
components A and B have been refined anisotropically by
.
2
3: method (a) [MoO2(L3)(MeOH)]ÁMeOH: yield (red crystals):
applying a SHELXL2014 RIGU restraint on each of the two 75 mg (27.4%). Found: C, 45.9; H, 4.6; N, 3.3; Mo, 22.8%. Calc.
parts as well as ISOR instruction for O3A, O3B, O4A, O4B, O5A for C16H19MoNO6 (Mr = 417.26): C, 46.0; H, 4.6; N, 3.4; Mo,
and O5B atoms.
23.0%. IR (KBr, cmÀ1): 1614 n(CQN); 946 and 911 n(MoO )
.
2
The molecular geometry calculations especially including
Method (b) [MoO2(L3)(MeOH)]: yield (red powder): 22 mg
H-bonding and non-covalent interactions were performed using (29.9%). Found: C, 45.9; H, 3.8; N, 3.7; Mo, 22.96%. Calc. for
programmes PLATON and PARST95 integrated in the WinGX
C15H15MoNO5 (Mr = 385.26): C, 46.7; H, 4.2; N, 3.6; Mo, 24.91%.
software system.21 Program ORTEP-3,22 also part of the WinGX IR (KBr, cmÀ1): 1613 n(CQN); 934 and 896 n(MoO )
.
2
software system, was used for molecular visualization. Packing
diagrams were generated using Mercury.
4: method (a) [MoO2(L4)(MeOH)]: yield (yellow crystals):
100 mg (40.6%). C, 50.3; H, 3.5; N, 3.2; Mo, 23.5%. Calc. for
The powder X-ray diffraction data were collected using a
C15H15MoNO6 (Mr = 401.2): C, 44.9; H, 3.8; N, 3.5; Mo, 23.7%.
Panalytical X’Change powder diffractometer in the Bragg-Brentano IR(KBr, cmÀ1): 1609n(CQN); 949 and 926n(MoO )
.
2
geometry using CuKa radiation. The sample was contained on a Si
sample holder. Patterns were collected in the range of 2y = 5–501 (33.6%). C, 50.3; H, 3.5; N, 3.2; Mo, 23.0%. Calc. for
Method (b) [MoO2(L4)]2: yield (dark yellow powder): 38 mg
with the step size of 0.031 and at 1.5 s per step. The data were
C
28H22Mo2N2O10 (Mr = 738.4): C, 45.5; H, 3.0; N, 3.8; Mo,
collected and visualized using the X’Pert program Suite.23
26.0%. IR(KBr, cmÀ1): 1625n(CQN); 816 and 750n(Mo O )
.
2
2
5: method (a) complex 5 has been prepared using the
solution-based method according to the literature data.11
Method (b) [MoO2(L5)(MeOH)]: yield (orange powder):
44.6 mg (35.0%). C, 45.9; H, 4.3; N, 3.1; Mo, 21.4%. C16H17MoNO6
(Mr = 415.25): C, 46.3; H, 4.1; N, 3.4; Mo, 23.1%. IR(KBr, cmÀ1):
General procedure for the synthesis of complexes 1–9
Synthesis of the mononuclear complexes [MoO2(L1,2,4,5 or 7)-
(MeOH)], [MoO2(L2a,3,6 or 9)(MeOH)]ÁMeOH and the binuclear
complex [MoO2(L8)]2.
1617n(CQN); 931 and 899n(MoO )
.
(a) General method: solution-based synthesis for complexes. A
mixture of [MoO2(acac)2] (0.61 mmol) and the appropriate
ligand H2L1–9 (0.61 mmol) was refluxed for 4 hours in dry
methanol (30 mL). The solution was left at room temperature
for three days and the obtained crystalline precipitate was
filtered off, rinsed with cold methanol and dried in air. The
same products were obtained if the reactions were performed
in situ without previous isolation of Schiff base ligands.
2
6: method (a) [MoO2(L6)(MeOH)]ÁMeOH: yield (orange-red
crystals): 190 mg (69.3%). Found: C, 44.9; H, 4.6; N, 3.0; Mo,
21.7%. Calc. for C17H21MoNO7 (Mr = 447.26): C, 45.7; H, 4.7; N,
3.2; Mo, 21.5%. IR(KBr, cmÀ1): 1624n(CQN); 899 and 882n(MoO )
.
2
Method (b) [MoO2(L6)(MeOH)]: yield (orange-red powder):
56.4 mg (44.3%). Found: C, 45.9; H, 4.6; N, 3.3; Mo, 23.6%. Calc.
for C16H17MoNO6 (Mr = 415.25): C, 46.3; H, 4.1; N, 3.4; Mo,
23.1%. IR(KBr, cmÀ1): 1614n(CQN); 935 and 902n(MoO )
.
2
(b) General method: liquid-assisted mechanosynthesis (LAG) of
7: method (a) [MoO2(L7)(MeOH)]: yield (red crystals):
complexes. All complexes were synthesized by liquid-assisted 40.31 mg (62.5%). C, 51.3; H, 3.6; N, 3.0; Mo, 22.6%. Calc. for
grinding together with equimolar quantities of the appropriate
C18H15MoNO5 (Mr = 421.3): C, 51.4; H, 3.4; N, 3.3; Mo, 22.8%.
Schiff base ligand (0.15 mmol) and [MoO2(acac)2] (0.15 mmol) IR(KBr, cmÀ1): 1609n(CQN); 934 and 910n(MoO )
.
2
in the presence of 30 mL of methanol. Grinding was performed
Method (b) [MoO2(L7)]2: yield (red powder): 50.0 mg (77.6%).
in a stainless steel jar of 10 mL volume. A Retsch MM200 C, 52.0; H, 3.0; N, 3.2; Mo, 23.7%. Calc. for C34H22Mo2N2O8
grinder mill operating at 25 Hz frequency was used for the (Mr = 784.4): C, 52.5; H, 2.8; N, 3.6; Mo, 24.5%. IR(KBr, cmÀ1):
synthesis.
1609n(CQN); 812 and 742n(Mo O ).
2 2
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270, 225; ( f ) M. R. Maurya, A. Arya, P. Adao and
J. C. Pessoa, Appl. Catal., A, 2008, 351, 239; (g) G. Grivani,
A. D. Khalaji, V. Tahmasebi, K. Gotoh and H. Ishida, Poly-
hedron, 2012, 31, 265; (h) S. Rayati, M. Koliaei, F. Ashouri,
S. Mohebbi, A. Wojtczak and A. Kozakiewicz, Appl. Catal., A,
2008, 346, 65.
8: method (a) complex 8 has been prepared using the
solution-based method according to the literature data.11
Method (b) [MoO2(L8)]2: yield: 48.8 mg (dark brown powder)
(79.2%). C, 51.3; H, 4.5; N, 3.0; Mo, 22.9%. Calc. for
C
36H26Mo2N2O8 (Mr = 806.48): C, 53.6; H, 3.2; N, 3.5; Mo,
23.8%. IR(KBr, cmÀ1): 1619n(CQN); 824(MoO ) and 742n(Mo O )
.
t
2 2
9: method (a) [MoO2(L9)(MeOH)]ÁMeOH: yield (orange crystals):
110 mg (38.6%). C, 51.3; H, 4.5; N, 3.0; Mo, 19.9%. Calc. for
C20H19MoNO6 (Mr = 465.32): C, 51.6; H, 4.1; N, 3.0; Mo, 20.5%.
3 (a) J. Kollar, US Pat., 3350422, Halcon International, 1967;
(b) J. Kollar, US Pat., 3351635, Halcon International, 1967;
(c) J. Kollar, US Pat., 3507809, Halcon International, 1970;
(d) J. Kollar, US Pat., 3625981, Halcon International, 1971;
(e) M. N. Sheng and G. J. Zajaczek, GB 1.136.923, 1968;
( f ) K. A. Jorgensen, Chem. Rev., 1989, 89, 431; (g) B. S. Lane
and K. Burgess, Chem. Rev., 2003, 103, 2457; (h) F. E. Ku¨hn,
A. M. Santos and M. Abrantes, Chem. Rev., 2016, 106, 2455.
4 (a) R. Martos Calvente, J. M. Campos-Martin and J. L. G.
Fierro, Catal. Commun., 2002, 3, 247; (b) K. Dallmann,
R. Buffon and W. Loh, J. Mol. Catal. A: Chem., 2002, 178, 43.
5 (a) K. Nakayima, K. Yokoyama, T. Kano and M. Kojima,
Inorg. Chim. Acta, 1998, 282, 209; (b) C. P. Rao, A. Sreedhara,
P. V. Rao, N. K. Lokanath, M. A. Sridhar, J. S. Prasad and
K. Rissanen, Polyhedron, 1999, 18, 289; (c) C. A. Mcauliffe,
F. P. Mc Cullough, M. J. Parrott, C. A. Rice, B. J. Sayle and
W. Levanson, J. Chem. Soc., Dalton Trans., 1977, 1762;
(d) E. C. Alyea and A. Malek, Can. J. Chem., 1975, 53, 939;
(e) A. Elmali and Y. Elerman, J. Mol. Struct., 1998, 442, 31;
( f ) A. Elmali, Y. Elerman and C. T. Zeyrek, J. Mol. Struct.,
1998, 443, 123; (g) M. Kabak, A. Elmali and Y. Elerman,
J. Mol. Struct., 1999, 477, 151; (h) A. Elmali, M. Kabak and
Y. Elerman, J. Mol. Struct., 1999, 484, 229; (i) V. Barba,
IR(KBr, cmÀ1): 1631n(CQN); 900 and 885n(MoO )
.
2
Method (b) [MoO2(L9)(MeOH)]: yield (orange brown powder):
59.3 mg (22.3%). C, 51.3; H, 4.5; N, 3.0; Mo, 24.2%. Calc. for
C19H15MoNO5 (Mr = 433.30): C, 51.4; H, 4.5; N, 3.0; Mo, 22.1%.
IR(KBr, cmÀ1): 1619n(CQN); 942 and 900n(MoO )
.
2
Ligands: all experimental details, IR spectra, PXRD data for
ligands H2Ln (n = 1, 4, 5, 7, 8 and 9) are given in Table S1 and
Fig. S1–S6 (ESI†).
General procedure for the epoxidation of olefins by aqueous
TBHP
For cyclooctene and limonene. A mixture of cis-cyclooctene
(2.00 mL, 15.4 mmol) or (R)-limonene (2.5 mL, 15.4 mmol),
0.1 mL acetophenone (internal reference) and Mo (pre)catalyst
(0.5% catalyst loading, 0.077 mmol) was stirred and heated up
to 80 1C before adding aqueous TBHP (70 wt%, 4.25 mL,
30.8 mmol).
For cyclohexene. A mixture of cyclohexene (1.6 mL, 15.8 mmol),
dodecane (internal reference) and Mo (pre)catalyst (0.5% catalyst
loading, 0.079 mmol) was stirred and heated up to 80 1C before
adding aqueous TBHP (70 wt%, 4.38 mL, 31.6 mmol).
´
D. Cuahutle, R. Santillan and N. Farfan, Can. J. Chem.,
2001, 79, 1229; ( j) P. G. Lacroix, F. Averseng, I. Malfant
and K. Nakatani, Inorg. Chim. Acta, 2004, 357, 3825;
The catalytic experiments were performed with a 0.5/200/100
Mo/TBHP/alkene molar proportion. All the reactions were
performed for 4 h. Aliquots (0.1 mL) of organic phase were
taken at required times from the reaction media, mixed with
2 mL of Et2O and a small quantity of MnO2 was added. The
mixture was then filtered through silica and analyzed by GC.
¨
(k) V. T. Kasumov, S. Ozal-Yaman and E. Tas, Spectrochim.
Acta, Part A, 2005, 62, 716; (l) R. Kannappan, D. M. Tooke,
A. L. Spek and J. Reedijk, Inorg. Chim. Acta, 2006, 359, 334;
´
´
´
(m) M. Rodrıguez, R. Santillan, Y. Lopez, N. Farfan, V. Barba,
´
´
´
K. Nakatani, E. V. Garcıa Baez and I. I. Padilla-Martınez,
Supramol. Chem., 2007, 19, 641.
Acknowledgements
´
6 (a) J. M. Bregeault, J. Chem. Soc., Dalton Trans., 2003, 3289;
(b) Z. Dawoodi and R. L. Kelly, Polyhedron, 1986, 5, 271;
(c) D. D. Agarwal and S. Shrivastava, Polyhedron, 1988,
7, 2569; (d) D. D. Agarwal, J. Mol. Catal., 1988, 44, 65;
(e) J. M. Sobczak and J. J. Ziolkowski, Appl. Catal. A Chem.,
2003, 248, 261; ( f ) M. Bagherzadeh and S. G. Esfahani, Sci.
Iran., Trans. C, 2010, 17, 131; (g) J. Zhao, X. Zhou,
ˇ
Prof. Visnja Vrdoljak is acknowledged for useful discussions
during the writing of the article. This research was supported
by the Ministry of Science, Education and Sports of the
Republic of Croatia.
˜
A. M. Santos, E. Herdtweck, C. C. Romao and F. E. Ku¨hn,
References
Dalton Trans., 2003, 3736; (h) S. L. Pandhare, R. R. Jadhao,
V. G. Puranik, P. V. Joshi, F. Capet, M. K. Dongare,
S. B. Umbarkar, C. Michon and F. Agbossou-Niedercorn,
J. Organomet. Chem., 2014, 772–773, 271.
7 I. P. Beleteskaya and L. M. Kustov, Russ. Chem. Rev., 2010,
79, 441.
8 (a) J. Morlot, N. Uyttebroeck, D. Agustin and R. Poli, Chem-
CatChem, 2013, 5, 601; (b) W. Wang, T. Vanderbeeken,
D. Agustin and R. Poli, Catal. Commun., 2015, 63, 26;
(c) J. Pisk, D. Agustin, J. C. Daran, V. Vrdoljak and R. Poli,
1 R. A. Sheldon, Green Chem., 2007, 9, 1273.
2 (a) C. Wang, X. Wu, S. Tu and B. Jiang, Synth. React. Inorg.,
Met.-Org., Nano-Met. Chem., 2009, 39, 78; (b) P. Panneerselvam,
R. R. Nair, G. Vijayalakshmi, E. H. Subramanian and S. K.
Sridhar, Eur. J. Med. Chem., 2005, 40, 225; (c) W. Lu, Y. H.
Huang, S. I. Lo and H. H. Wei, Inorg. Chem. Commun., 2007,
10, 1210; (d) N. C. Gianneschi, S. T. Nguyen and C. A. Mirkin,
J. Am. Chem. Soc., 2005, 127, 1644; (e) M. R. Maurya, A. K.
Chandrakar and S. Chand, J. Mol. Catal. A: Chem., 2007,
New J. Chem.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2016

View Article Online
NJC
Adv. Synth. Catal., 2011, 353, 2910; (d) J. Pisk, B. Prugovecki,
Paper
ˇ
(c) C. Zhang, G. Rheinwald, V. Lozan, B. Wu, P.-G.
Lassahn, H. Lang and C. Janiak, Z. Anorg. Allg. Chem.,
2002, 628, 1259; (d) P. K. Nath and K. C. Dash, Transition
Met. Chem., 1985, 10, 262; (e) J. M. Sobczak, T. Glowiak and
J. J. Ziolkowski, Transition Met. Chem., 1990, 15, 208.
ˇ
´
´
D. Matkovic-Calogovic, R. Poli, D. Agustin and V. Vrdoljak,
ˇ
Polyhedron, 2012, 33, 441; (e) J. Pisk, B. Prugovecki,
ˇ
´
´
ˇ
D. Matkovic-Calogovic, T. Jednacak, P. Novak, D. Agustin
and V. Vrdoljak, RSC Adv., 2014, 4, 39000; ( f ) V. Vrdoljak,
´
J. Pisk, D. Agustin, P. Novak, J. Parlov Vukovic and 14 (a) P. K. Nath and K. C. Dash, Transition Met. Chem., 1985,
ˇ
´
´
D. Matkovic-Calogovic, New J. Chem., 2014, 38, 6176;
10, 262; (b) J. M. Sobczak, T. Glowiak and J. J. Ziolkowski,
Transition Met. Chem., 1990, 15, 2008; (c) W.-S. Jung, H.-Y.
Moon and Y.-Y. Park, Polyhedron, 1997, 16, 2169; (d) J. Topich,
Inorg. Chim. Acta, 1981, 20, 3704.
(g) C. Cordelle, D. Agustin, J. C. Daran and R. Poli, Inorg.
Chim. Acta, 2010, 364, 144; (h) B. Guerin, D. Mesquita
Fernandes, J.-C. Daran, D. Agustin and R. Poli, New
´
J. Chem., 2013, 37, 3466; (i) W. Wang, T. Guerrero, 15 M. Minelli, F. Namuswe, D. Jeffrey, A. L. Morrow, I. A. Guzei,
´
S. R. Merecias, H. Garcıa-Ortega, R. Santillan, J.-C. Daran,
D. Swenson, E. Bothe and T. Weyhermu¨ller, Inorg. Chem.,
2006, 45, 5455.
´
N. Farfan, D. Agustin and R. Poli, Inorg. Chim. Acta, 2015,
431, 176; ( j) J. Pisk, J.-C. Daran, R. Poli and D. Agustin, J. Mol. 16 G. J. J. Chen, J. W. McDonald and W. E. Newton, Inorg.
Catal. A: Chem., 2015, 403, 52; (k) W. Wang, J.-C. Daran, Chem., 1976, 15, 2612.
R. Poli and D. Agustin, J. Mol. Catal. A: Chem., 2016, 416, 117. 17 Oxford Diffraction Ltd, Xcalibur CCD system, CrysAlis
9 (a) K. Yamaguchi, K. Kamata, S. Yamaguchi, M. Kotani and
N. Mizuno, J. Catal., 2008, 258, 121; (b) J. Kasai,
Software system, Versions 1.171.32.24 and 1.171.33.41.
Abingdon; Oxfordshire, England, 2008.
Y. Nakagawa, S. Uchida, K. Yamaguchi and N. Mizuno, 18 G. M. Sheldrick, A short history of SHELX., Acta Crystallogr.,
Chem. – Eur. J., 2006, 12, 4176. Sect. A: Found. Crystallogr., 2008, A64, 112.
10 (a) A. V. Trask, W. D. S. Motherwell and W. Jones, Chem. 19 L. J. Farrugia, WinGX (Ver. 1.80.05) suite for small-molecule
Commun., 2004, 890; (b) N. Shan, F. Toda and W. Jones,
Chem. Commun., 2002, 2372; (c) D. Braga, S. L. Giaffreda,
single-crystal crystallography, J. Appl. Crystallogr., 1999,
32, 837.
F. Grepioni, A. Pettersen, L. Maini, M. Curzi and M. Polito, 20 L. Spek, A Multipurpose Crystallographic Tool, J. Appl.
Dalton Trans., 2006, 1249. Crystallogr., 2003, 36, 7.
11 (a) M. Cindric, N. Strukan, V. Vrdoljak, T. Kajfeˇz and 21 L. J. Farrugia, Ortep-3 for Windows (v. 2.02) – a version of
´
B. Kamenar, Z. Anorg. Allg. Chem., 2002, 628, 2113;
(b) D. Agustin, C. Bibal, B. Neveux, J.-C. Daran and R. Poli,
the current release of ORTEP-III, which incorporates a
Graphical User Interface (GUI), J. Appl. Crystallogr., 1997,
30, 565.
´
Z. Anorg. Allg. Chem., 2009, 635, 2120; (c) M. Cindric,
N. Strukan, V. Vrdoljak and B. Kamenar, Z. Anorg. Allg. Chem., 22 C. F. Macrae, I. J. Bruno, J. A. Chisholm, P. R. Edgington,
2004, 630, 585.
P. McCabe, E. Pidcock, L. Rodriguez-Monge, R. Taylor,
M. Towler, J. Van der Streek and P. A. Wood, J. Appl.
Crystallogr., 2008, 41, 466.
ˇ
12 B. Kaitner and M. Zbacnik, Acta Chim. Slov., 2012, 59, 670.
13 (a) O. A. Rajan and A. Chakravorty, Inorg. Chem., 1981,
20, 660; (b) T. Glowiak, L. Jerzykiewicz, J. M. Sobczak and 23 X’Pert Software Suite, Version 1.3e, Panalytical B. V., Almelo,
J. J. Ziolkowski, Inorg. Chim. Acta, 2003, 356, 387; The Netherlands, 2001.
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