Molybdenum (VI) Complexes Containing Pyridylimine Ligands: Effect of the Imine Nitrogen Substituent in the Epoxidation Reaction

Article abstract of DOI:10.1002/ejic.202000790

A series of pyridylimine ligands with variations of the substituent at the imine nitrogen were synthesized and coordinated to the [MoCl₂O₂] core. The novel molecular structures of the complexes were fully characterized by ¹H and ¹³C NMR, FT-IR, ESI, EA, and X-ray crystallography, and their catalytic activity was studied for the epoxidation of alkenes using tert-butyl hydroperoxide (TBHP) as the oxidant. The new complexes showed excellent catalytic activity and fine selectivity in the epoxidation reaction compared with similar homogeneous molybdenum complexes. The results demonstrated that there is a significant change in the catalytic performance, depending on the alkyl arm on the structure of the pyridilimine ligand. The catalytic results indicated that complex [MoCl₂O₂(L)] (L: N-(2-Pyridinylmethylene)-1-tert-butylimine) C₅ is the best catalytic precursor in the epoxidation of cyclohexene (TON: 92920 and TOF: 30974 h^?1).

Full text of DOI:10.1002/ejic.202000790

European Journal of Inorganic Chemistry
Accepted Article
Title: Molybdenum (VI) Complexes Containing Pyridylimine Ligands:
Effect of the Imine Nitrogen Substituent in the Epoxidation
Reaction
Authors: Daniel Martínez-Martínez, Mayra León Santiago, Rubén A.
Toscano, and Manuel Jose Amezquita Valencia
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.202000790
Link to VoR: https://doi.org/10.1002/ejic.202000790
0
1/2020

European Journal of Inorganic Chemistry
10.1002/ejic.202000790
FULL PAPER
Molybdenum (VI) Complexes Containing Pyridylimine Ligands:
Effect of the Imine Nitrogen Substituent in the Epoxidation
Reaction
[
a]
[a]
[a]
Daniel Martínez-Martínez, M. León Santiago, Rubén A. Toscano, and Manuel Amézquita-
Valencia*[a]
[
a]
Daniel Martínez Martínez, M. Sc. Mayra León Santiago, Dr. Rubén A. Toscano, Dr. Manuel Amézquita Valencia
Department of inorganic Chemistry
Universidad Nacional Autónoma de México, Instituto de Química
Ciudad Universitaria, Ciudad de México, 04510, México
E-mail: manuel.amezquita@iquimica.unam.mx
https://iquimica.unam.mx/dr-manuel-jose-amezquita-valencia
Supporting information for this article is given via a link at the end of the document.
-1 [14-15]
Abstract: A series of pyridylimine ligands with variations of the
its predecessor [turnover frequency (TOF), 174 h ].
In the
substituent at the imine nitrogen were synthesized and coordinated to
same way, the analogous MoCl complexes using bipyridine
2 2
O
the [MoCl
2
O
2
] core. The novel molecular structures of the complexes
ligands were synthesized, giving promising results in the
1
13
-1 [16]
were fully characterized by H and C NMR, FT-IR, ESI, EA, and X-
ray crystallography, and their catalytic activity was studied for the
epoxidation of alkenes using tert-butyl hydroperoxide (TBHP) as the
oxidant. The new complexes showed excellent catalytic activity and
fine selectivity in the epoxidation reaction compared with similar
homogeneous molybdenum complexes. The results demonstrated
that there is a significant change in the catalytic performance,
depending on the alkyl arm on the structure of the pyridilimine ligand.
epoxidation of olefins (TOF around 1150 h ).
The authors
found that catalytic activity was influenced by the donor capability
of the substituent on the bipyridine ring. The solubility of the
[MoCl O (N-N)] complexes in an organic solvent is an important
2 2
factor to consider, which may be responsible in some cases of
poor catalytic activity. Hence, replacing the solvent could increase
the reactivity. For example, a Mo complex with 5,5´-bis-
methoxycarbonyl-2-2´-bipyridine ligand showed a high activity in
-1
The catalytic results indicated that complex [MoCl
Pyridinylmethylene)-1-tert-butylimine) is the best catalytic
precursor in the epoxidation of cyclohexene (TON: 92920 and TOF:
2
O
2
(L)] (L: N-(2-
the epoxidation of cis-cyclooctene (TOF 8000 h ) in ionic liquids;
this excellent result was attributed to the Mo complex’s high
solubility.[
C
5
17]
-1
3
0974 h ).
Pyrazolylpyridines are another class of diimine ligands that
have been used to generated coordination compounds of Mo(VI).
The catalytic behaviors of these complexes resulted in the
production of the desired epoxide in excellent selectivity with
Introduction
-1 [18-19]
moderate TOF (347 h ).
In seeking to broaden the utility of
this class of catalysts, the use of pyrazole monohydrate as the
monodentate ligand in the Mo-catalyzed epoxidation of cyclic
Epoxides are important compounds that participate in useful
organic syntheses and their reactivity permits the preparation of a
diverse array of intermediates that play a crucial role in fine
-1
olefins led to a yield of 90% with a good TOF of 1800 h after 5
[20]
min. An alternative class of ligand that can be used in the
[
1,2]
chemistry.
In general, different heterogeneous and
epoxidation reaction are the pyridylimines, which have presented
similar properties to bipyridines (N-N donor set), yet are much
easier to prepare and modify. Despite these advantages, there
are only a handful of reports describing the Mo-catalyzed
epoxidation employing pyridylimine ligands. In this regard, Gomes
homogeneous catalysts have been used in the epoxidation
reaction, but homogeneous systems are the most widely applied
industrial process for oxidation of olefins.[2,3] As expected, various
metal complexes have been employed in oxygen atom transfer
[4-9]
reactions,
however, the molybdenum complexes have always
et al. reported the synthesis of a complex [Mo(CO)
4
(pyim)] (pyim:
been an alternative for epoxidation of olefins, on account of their
high activity.[10] It is well known that the use of nitrogen-containing
ligands leads to an increase in both catalytic activity and the
N-(n-propyl)-2-pyridylmethanimine)
immobilization on MCM-41.
and
its subsequent
[21]
Later, the same group
demonstrated the utility of the ligand previously synthesized in the
[11,12]
selectivity in these types of processes.
These improvements
preparation of [MoCl
2
O
2
(pyim)]. The new complex showed a
are attributed to the possibility of modifying the steric and
electronic properties on the ligand.
Considerable efforts have been devoted to developing
catalysts with high catalytic performance containing bidentate
nitrogen donor ligands. In this context, Kühn´s group synthesized
-1
relevant catalytic activity (TOF of 1855 h ) in the epoxidation of
[22]
various olefins.
Recently, a series of allyl molybdenum
complexes supported by these kinds of ligands were studied.
However, the presence of different substituents (H, Me, Ph) at the
[23]
imine-carbon did not significantly change the activity. Despite
2 2
a series of molybdenum complexes of the type [MoX O (N-N)] (X:
the outcome, we consider that the selection of the appropriate
substituent present at the nitrogen of the imine moiety could
change the catalytic activity.
Cl, Br) using various bidentate N-ligands, where 1,4-diaza-1,3-
butadiene-bearing aryl groups on the nitrogen atoms showed
good activity in the epoxidation of cis-cyclooctene with tert-butyl
hydroperoxide (TBHP) as the oxidant.[13] Gonçalves et al.
reported an interesting modification replacing X from Cl to Me,
with the new complex presenting similar results in comparison to
Herein, we aimed to expand the range of molybdenum
2 2
complexes of the type [MoCl O (pyridylimine)] used in the
epoxidation of olefins. For purposes of comparison, we studied
9
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.202000790
FULL PAPER
the influence of the substituent on the imine nitrogen, considering
both their size and electron-donating properties.
are shown in Figures 1 and 2, with data collection and general
parameters summarized in Table 1.[
24]
Results and Discussion
Synthesis and Characterizations of Molybdenum
Complexes
1 9
Pyridylimine ligands (L -L ) were obtained in quantitative yields
by the condensation reaction between 2-pyridinecarboxadehyde
and the corresponding amine and the products obtained were
used without purification. Coordination tests were performed
using MoCl
temperature, affording the expected monomeric coordination
entity of formula [MoCl (L)] (Scheme 1). The different
2
O
2
(MeCN)
2
in acetonitrile solution at room
2
O
2
complexes were obtained in good yields and purified by washes
with diethyl ether, and finally by co-precipitation using methylene
chloride and hexane. The new complexes C -C showed good
1 9
solubility in methylene chloride, acetone, and dimethyl sulfoxide.
These complexes were partially soluble in acetonitrile and
methanol, but poor solubility in chloroform and insoluble in diethyl
ether and hexanes.
1 6
Figure 1. Crystal structures of complexes C and C , with 50% thermal ellipsoids.
Hydrogen atoms are omitted for clarity.
1 9
Scheme 1. Molybdenum complexes synthesized (C -C )
The complexes were characterized by FTIR, elemental
analysis, ESI, H, 13C NMR, and X-ray crystallography. The FTIR
spectra of all nine complexes (See experimental section, Table
1
S1) are in agreement with the coordination of the pyridylimine
21-23]
ligand to the MoCl
2
O
2
core through the nitrogen atoms.[
The
-1

C=N stretching frequencies are observed around 1647 cm and
-1
-1
1
597 cm . The strong band at 903 cm (average) and medium
band at 937 (average) were assigned to the asymmetric and
symmetric stretching vibrations, respectively, of the cis-[MoO
2
]
[22]
unit.
The H and 13C NMR spectra of the different complexes (C
1
-
1
C
9
) revealed a variation between the chemical shifts of the free
ligand and the bound ligand, with the proton signal of all
complexes being shifted to lower field after complexation. In all
cases, there was a notable rearrangement of hydrogens near the
imine and pyridine nitrogens. Furthermore, one set of resonances
for the iminopyridine ligand was observed, which corresponded to
8 9
Figure 2. Crystal structures of complexes C and C , with 50% thermal ellipsoids.
Hydrogen atoms are omitted for clarity.
[21-22]
a mononuclear complex.
Elemental analyses of newly made
complexes were consistent with the proposed structures shown
in Scheme 1.
The structures of some molybdenum compounds were
unambiguously determined with X-ray crystallographic analysis.
The complexes (C
1
, C
6 8 9
, C and C ) are isostructural and
crystallized with
environment, which can be explained mainly by cis-oxo-trans-
Cl-cis-N-N rearrangement.[ Thus, the metal center is bonded to
a
distorted octahedral coordination
[
25]
Crystals of complexes C
diffraction were obtained by slow diffusion of hexane or diethyl
ether into their concentrated CH Cl solution. Molecular structures
1 6 8 9
, C , C , and C suitable for X-ray
26]
1
two terminal cis-oxo groups [Mo=O, 1.6865(19)-1.6940(17) C ,
2
2
9
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.202000790
FULL PAPER
1
.6830(2)-16910(2) C
6
, 1.6831(2)-1.686(2), C
8
and 1.6830(6)-
coordinated Cl atoms [2.3870(7)-2.3369(7) C , 2.3646-2.3673 C
1
6
,
1
.6880(6), C , Å]. The N-N-chelated moiety is positioned trans- to
9
2.3603-2.3714(9) C , 2.3680(2)-2.3380(2) C , Å].
8
9
the oxygen atom [2.3483-2.3256 (Average), Å] and two axially
1 6 8 9
Table 1. Crystallographic data for compounds C , C , C and C .
C
1
C
6
C
8
C
9
Empirical formula
Formula weight
Temperature
λ (Å)
C
8
H
10Cl
2
MoN
2
O
2
C
12
H
16Cl
2
MoN
2
O
2
C
13
H
12Cl
2
MoN
2
O
2
C
14 2 2 2
H14Cl MoN O
333.02
298
387.11
303(2)
395.09
304(2)
409.11
298
0.71073
Triclinic
P-1
0.71073
0.71073
0.7173
Crystal system
Space group
a (Å)
Monoclinic
Orthorhombic
P b c a
11.2803(4)
12.8812(4)
20.6749(6)
90
Monoclinic
P 21
P2 /c
1
8.0504(6)
8.7834(7)
8.9280(7)
83.953(1)
84.288(1)
74.143(1)
602.24(8)
2
13.350(4)
8.4616 (14)
8.7904(13)
11.629(2)
90
b (Å)
6.8217(13)
17.265(4)
90
c (Å)





108.048(6)
90
90
110.789(5)
90

90
V (Å3)
Z
1495.0(6)
4
3004.14(17)
8
808.7(2)
2
Dcal (mg/cm3)
1.837
1.720
1.747
1.680
-
1
µ (mm )
1.514
1.233
1.230
1.145
Reflections collected
Independent reflections
11362
32913
4188
56057
4213
4683
3484
4683
R
int
0.0369
0.0312
0.0661
1.026
0.0571
0.0408
0.0709
1.054
0.0550
0.0380
0.0840
1.094
0.0421
0.0646
0.0796
1.203
R1 [I>2(I)]
wR [all data]
Goodness-of-fit
2
For the complexes C1,
lengths were longer than those of Mo-Nimine due to the different
basicity for the pyridine with respect to the imine. In the C
C
8
and C
9
, the Mo-Npyridine bond
different oxygen sources were tested. For this purpose, the
reactions were performed using 3.0 mol% of catalyst, 1.5
equivalent of oxidant [H O (30% in water), t-BuOOH (80% in
2 2
6
complex, Mo-Nimine bond length was larger, which is associated
with a steric effect. The N-Mo-N angle in the complexes were
approximately 69.9° (Average). The molecular structure of
water) and t-BuOOH (5.5 M in decane)] in methylene chloride as
a solvent, at reflux temperature for 15 h.
complex C
in the same plane while in the case of C
parallel (89.87°). In contrast, the alkyl moiety from the C
complexes were hinged and the angles between the planes were
6.1° and 18.9°, respectively. These different angles relate to the
flexibility of the substituent on the imine-nitrogen.
1
had both the pyridine fragment and the alkyl moiety
these groups were
and C
Although the epoxidation reactions in all cases were
effective, our results showed that t-BuOOH in decane was the
best option, giving 100% of conversion and 96% of selectivity for
6
8
9
8
the epoxide using the C complex (See supporting information,
6
Table S2). In the case of the oxidants in an aqueous medium, the
selectivity toward the epoxide was affected severely. We
observed that the formations of 2-cyclohexenol and 2-
cyclohexenone were favored. Continuing with the optimization of
the reaction, the combinations of different solvents, oxidants, and
temperatures were evaluated by using the C8 complex and
cyclohexene as a substrate; the results are displayed in Table 2.
Catalytic Activities of Molybdenum Complexes (C
1 9
-C ) in
Epoxidation of Olefins
To optimize the reaction conditions, we started our catalytic study
using the C , C and C complexes in combination with
cyclohexene as a model substrate and an oxidant. Initially,
4
6
8
9
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.202000790
FULL PAPER
First, we optimized the solvent and the temperature of the
reaction. The results showed that the highest conversions were
obtained at 40 °C in dichloromethane, with excellent selectivities
The effect of different oxidants was evaluated in the
epoxidation of cyclohexene at 40 °C (Entries 9-14). These results
indicate that the presence of water in the oxidant had a negative
effect on the reaction. The high conversion and low selectivity
toward epoxide can be explained by the formation of 1,2-diol,
through the epoxide ring-opening process in the presence of
water. Also, we found that elevating the temperature of the
(Tabla 2, entry 1). In contrast, Employing other solvents such as
acetonitrile, tetrahydrofuran, chloroform, or ethanol led to poor
conversions (entries 2-4). Similar results were observed in the
cyclooctene epoxidation reaction, where the complexes
containing the cis-[MoO
2
] core were inactive under these
reaction caused an increase in the ring-opening reaction and the
[27-30]
[34]
conditions.
These conversions could be associated with the
over oxidation of the substrate. (Entries 15-18).
Finally, the
tendencies of the solvents to coordinate strongly with Mo (VI) ion,
competing directly with the oxidant. In contrast, noncoordinating
solvents such as dichloromethane and dichloroethane facilitated
the epoxidation reaction (Entries 1 and 5). The increase in the
temperature to 80 °C did not improve substantially the catalytic
activity (Entries 6-7). The use of a chlorinated solvent afforded
excellent conversion with good selectivity to the corresponding
epoxide (Entry 8). Similar results have been reported in the
literature, where chlorinated solvents presented an excellent
performance in the epoxidation of olefins.[32-33]
influence of the amounts of oxidant was evaluated. Using 1.0
equivalent of TBHP the conversion was slightly affected (Entry 19).
With 2.0 equivalent of TBHP, no change in the catalytic behavior
was observed (Entry 20). For subsequent epoxidation reactions,
we chose 1.5 equivalent of TBHP, 40 °C in dichloromethane as a
solvent.
[31]
Next, the reaction time was optimized (Figure 3), as
exemplified by the kinetic curve obtained for the complex C . First,
8
3.0 mol % of catalyst was used and the results indicated 34% of
conversion in the first hour; after 3 hours the conversion tended
to converge to 100%, with 1,2-epoxycyclohexane being the only
reaction product observed.
Table 2. Screening of reaction conditions.[a]
Entry
1
Oxidant
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
Solvent
DCM
ACN
THF
Conversion (%)[b]
Selectivity (%)[b]
100
20
96
100
99
99
98
99
97
96
17
18
16
24
15
14
10
11
14
10
90
94
2
3
45
4
EtOH
DCE
ACN
THF
18
5
83
6[c]
7[c]
8[c]
9
28
78
DCE
ACN
EtOH
DCM
ACN
EtOH
DCM
ACN
EtOH
DCM
DCM
DCM
DCM
96
H
2
H
2
H
2
O
2(aq)
O
2(aq)
O
2(aq)
97
10
11
12
13
14
100
100
98
Figure 3. Time-dependent conversion of cyclohexene epoxidation at 40 °C
using TBHP and different concentrations of complex C in 5 mL of CH Cl . 3.0
8
2 2
mol% (■, black), 1.0 mol% (●, red), 0.1 mol% (▲, blue) and 0.01 mol% (♦, light
green), average of selectivity (◄, green). Conversion and selectivity determined
by GC-MS.
TBHP(aq)
TBHP(aq)
TBHP(aq)
TBHP(aq)
96
100
100
98
Continuing with the optimization of the reaction, the catalyst
loading was changed over the range of 1.0% to 0.01%. The
variation of the amount of catalyst did not have a remarkable
effect on the performance of the reaction (Figure 3, 1.0 mol% (●,
red), 0.1 mol% (▲, blue) and 0.01 mol% (♦, light green). Even
when the reaction was carried out at 0.01 mol% of catalyst, high
conversion (98%) and excellent selectivity (95%) was obtained. In
general, epoxidation of cyclohexene was almost the same in the
different catalyst loadings, showing an overall conversion
between 36% to 42% after the first hour of reaction. Then, the
conversion increased significantly, being almost quantitative in
approximately 3 h. This indicates that the catalyst has a notable
catalytic activity and a high selectivity at low concentration.
1 [
5
c]
c]
c]
c]
d]
e]
1 [
6
2 2(aq)
H O
1 [
1 [
1 [
2 [
7
TBHP(aq)
99
8
H
2
O
2(aq)
100
97
9
TBHP
TBHP
0
100
[
a] Reaction conditions: Cyclohexene (2.0 mmol), TBHP (1.5 equivalent, 5.5 M,
decane), 40 °C, 15 h, 5 mL of solvent. [b] Determined by GC-MS. [c]
Temperature of reaction 80 °C. [d] 1.0 equivalent of TBHP (5.5 M, decane) was
used. [e] 2.0 equivalent of TBHP (5.5 M, decane) was used.
With the optimal reaction conditions in hand, we compared
the catalytic activity of the other complexes synthesized. In
9
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.202000790
FULL PAPER
1 9
general, the efficiency of complexes C -C for the epoxidation of
cyclohexene and n-hexene was satisfactory, affording the
corresponding epoxides in good conversion with excellent
selectivity (72%-100%) within 3 hours of reaction (Table 3).
All examined complexes displayed quite high catalytic
activity (turnover number (TON) up to 9752 and turnover
-1
3
frequency (TOF) up to 3208 h , C ). It is worth noting that all
catalysts led epoxidation of the alkene irrespective of the
substituent on the imine-nitrogen, although there were subtle
1 9
Scheme 2. Epoxidation of different olefins using C -C .
differences between catalysts. Using the complex C
alkenes, the desired product was obtained in excellent conversion
Entry 5, TON over 9000 and TOF over 3000 for both alkenes).
Similar results employing the C , C , and C complexes were
found (Entries 6 and 7). Interestingly, when using the complexes
-C and C -C with an extended methylene chain on the imine,
the epoxidation performance of the linear olefin was affected by
chain length (Entries 1-4, 8 and 9). Hence, it is possible that the
degree of the selectivity in the reaction is dependent on the
bulkiness of the ligand used. The general tendency showed better
activity with tert-butyl, cyclohexyl, and cycloheptyl groups present
on the imine-nitrogen. This behavior could be associated with the
ability of the ligand to donate electrons, affording the formation of
more reactive Mo species.[35]
5
for both
As shown in the Table 4, the epoxidation of styrene and -
methyl styrene occurred to a lesser degree with respect to
aliphatic olefins, and the selectivity was affected by the exclusive
(
6
7
9
formation
methylphenylacetaldehyde, respectively. As reported in the
literature,[18,36] the complexes with the structure MoCl
(N-N)
have presented low reactivity and selectivity with these kinds of
alkenes. It is important to note that the complexes C , C , and C
9
of
benzaldehyde,
acetophenone,
and
-
C
1
4
8
9
2 2
O
1
5
were more active, confirming the influence of the substituent.
Interestingly, in the case of more sterically hindered olefins, our
results point once again to the strong influence of the substituent
at the imine nitrogen on the catalytic activity. The family of
complexes C
1
to C
4
showed a low conversion, but a good
which
selectivity toward the desired epoxide. The complex C
5
.[a]
contains the tert-butyl group at the nitrogen of the imine moiety
was the best catalyst of the series, affording 62% of conversion
and 88% of selectivity in the epoxidation of limonene, with p-
mentha-2,8-dien-1-ol as a byproduct. However, the performance
in the epoxidation of citral was a critical result. Complexes
containing ligands with substituents that were sterically more-
demanding such as C and C showed a minor catalytic activity
1 9
Table 3. Epoxidation of cyclohexene and n-hexene using C -C
Entry
1
Complex
Substrate
Conv./Sel.(%)[b]
TON[c]
TOF (h-1)[d]
C
1
C
2
C
3
C
4
C
5
C
6
C
7
C
8
C
9
cyclohexene
100/96
78/99
9625
7814
3208
2605
1-hexene
2
3
4
5
6
7
8
9
cyclohexene
-hexene
100/92
81/72
9244
5846
3081
1949
6
7
1
with respect to C
than C in the epoxidation of limonene, but C
transformation of citral.
5
. Meanwhile, the complex C
8
was more active
was better in the
9
9
cyclohexene
-hexene
100/98
84/100
9752
8440
3251
2813
1
cyclohexene
-hexene
100/83
77/81
8291
6216
2764
2072
Table 4. Epoxidation of aromatic and aliphatic olefins using C
1
-C
9
.[a]
TOF (h-1)[d]
1
Conv./Sel.(%)[b]
TON[c]
cyclohexene
-hexene
100/93
92/100
9280
9148
3093
3049
Complex
Substrate
1
styrene
Me-styrene
limonene
citral
11/76
32/85
53/89
21/90
803
268
900
1568
628
cyclohexene
-hexene
98/89
88/100
8751
8800
2917
2933
C
1
C
2
C
3
C
4
C
5
2700
4703
1884
1
cyclohexene
-hexene
99/93
89/100
9225
8900
3075
2967
1
styrene
Me-styrene
limonene
citral
2/35
8/70
40/90
19/99
64
558
3625
1868
22
186
1208
623
cyclohexene
-hexene
98/95
51/100
8520
5051
2840
1684
1
cyclohexene
-hexene
100/96
82/100
9568
8161
3189
2720
styrene
Me-styrene
limonene
citral
8/94
14/90
39/90
19/99
748
249
411
1170
628
1
1234
3510
1885
[
a] Conditions: Substrate (2.0 mmol), TBHP (1.5 equivalent, 5.5 M, decane),
catalyst (0.01 mol%, C -C ), 40 °C, CH Cl (5 mL), 3 h. [b] Conversion and
selectivity were determined by GC-MS. [c] TON calculated per molecules of
catalyst. [d] TOF after of 3 hours.
1
9
2
2
styrene
Me-styrene
limonene
citral
8/81
5/54
8/93
613
279
721
204
93
241
808
24/99
2423
The catalytic activity of the different molybdenum
complexes was next investigated in the epoxidation of
representative olefins such as styrene, -methylstyrene (Me-
styrene), S-limonene, and citral (Scheme 2).
Styrene
Me-styrene
Limonene
citral
14/77
26/83
62/88
26/99
1080
2193
5495
2568
360
731
1832
856
styrene
Me-styrene
9/83
29/91
774
2625
258
875
9
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.202000790
FULL PAPER
C
6
limonene
citral
49/92
16/99
4475
1586
1492
529
once again, but the performance was poor (33% of conversion
and 100% of selectivity at 12 hours). The results achieved above
demonstrated the superiority of the ligand containing the tert-butyl
group compared to previously used ligands.
styrene
Me-styrene
limonene
citral
8/78
8/69
46/94
8/99
648
538
4369
804
216
179
1456
268
C
7
styrene
Me-styrene
limonene
citral
2/66
5/62
34/99
6/99
155
288
3392
592
52
96
1131
197
Conclusion
C
8
9
Nine new mononuclear molybdenum complexes containing
pyridylimine ligands have been synthesized and structurally
characterized. The ligand adopt a bidentate coordination mode to
give distorted octahedral molybdenum complexes. The catalytic
activities of the Mo (VI) complexes were tested in the epoxidation
of aliphatic and aromatic olefins by using tert-butyl hydroperoxide
as the oxidant. The results demonstrated that the nature of the
substituents on the imine-nitrogen have an important influence on
the catalytic activity. A long carbon chain on the ligand generated
low stability on the complex, impairing the oxidation of the double
bond, resulting in lower activity. Epoxidation was favored when
bulky substituents such as tert-butyl, cyclohexyl, and cycloheptyl
were present on the nitrogen of the imine, as was the case for
styrene
Me-styrene
limonene
citral
6/70
22/78
23/86
24/92
451
150
571
655
752
C
1713
1965
2257
[
a] Same conditions as in table 3 were used. [b] Conversion and selectivity were
determined by GC-MS. [c] TON calculated per molecules of catalyst. [d] TOF
after of 3 hours.
To demonstrate the importance of the ligand bearing the
tert-butyl substituent, we examined the complexes C , C , and C ,
5 6 9
which had similar backbones and presented comparable activity.
To improve the reaction, the effect of the catalytic loading was
evaluated (Table 5). Our test commenced with cyclohexene under
previously optimized conditions using the C
). Notably, by decreasing the catalyst loading to 0.001 mol%, we
obtained the corresponding epoxide in >99% of conversion and
5 7 5
complexes C -C . It is interesting to note that complex C exhibits
the best catalytic activity in the epoxidation reaction. Therefore,
the design of new ligands based on these classes of substituents
is relevant to insights into the chemistry of these systems.
5
complex (See Table
3
-1
excellent selectivity 93% (TON: 92920 and TOF: 30974 h ).
Applying C and C gave the desired product in moderate
Experimental Section
6
9
selectivities of 63% and 58%, respectively. In comparison to
previously reported Mo(VI) complexes bearing a nitrogen-
Material and reagents
chelating ligand, the current system C
5
exhibited a notable
All solvents were dried and distilled under nitrogen prior to use.
Molybdenum precursor and other reagents were obtained from Strem
Chemical or Aldrich Chemical Co. Column chromatography was
undertaken with silica gel (60, 230-400 mesh). 1H NMR and 13C {1H}
catalytic activity in the reaction of epoxidation under similar
[22,29,37]
conditions.
3
NMR spectra were measured in CDCl on a BRUKER Advance 300 MHz
spectrometer. Chemical shifts are reported in ppm with the solvent signal
as a reference, and coupling constants (J) are given in Hertz (Hz). Melting
Table 5. Effect of the catalyst amount on the epoxidation of cyclohexene using
, C and C
C
5
6
9
.
Complex[a]
Conv./Sel. (%)[b]
100/93
TON[c]
92920
63472
58262
TOF[d]
30974
21157
19421
points were determined on a Fischer-Johns apparatus and are
uncorrected. The infrared spectra were recorded on an Alpha ATR
spectrometer from Bruker Optics and analysed with OPUS soft-ware.
Elemental analyses were carried out with an Exeter Analytical. X-ray
determination was collected on a Bruker SMART APEX CCD area
diffractometer by the -scan method. The reaction was monitored using a
GC-MS Agitent technologies 7890B-5977A-MSD and a HP-5-MS column.
The product identifications were performance on the base of commercial
mass spectroscopy database (NIST14). Mass spectra were obtained using
a JEOL the ACCUTOF JMS-T100LC (DART method) and Bruker Esquire
C
5
C
6
C
9
100/63
100/58
[
a] 0.001 mol% of catalyst was used. [b] Conversion and selectivity were
determined by GC-MS. [c] TON calculated per molecules of catalyst. [d] TOF
after of 3 hours.
6
000 for ESI.
Synthesis of ligand, L
-Pyridinecarboxaldehyde (0.10 mol) was added in a solution of 10 mL of
It was necessary to increase the catalyst loading and the
reaction time to obtain the best outcome with styrene and -
methyl styrene. Using 0.1 mol% of C with styrene, the best
5
results were obtained at 12 hours of reaction, achieving 60% of
yield and 92% of selectivity to obtain the specific epoxide. In the
[
38]
1
2
a 40% aqueous ethylamine solution (0.1 mol) at 0 °C. The reaction was
stirred for 1 h, after that time, the mixture was extracted four times with 30
mL of methylene chloride each. Finally, organic layers were combined,
presence of C
was obtained. For epoxidation of -methyl styrene, C
best performance with 61% of conversion and 90% of selectivity.
Various attempts to increase the conversion using C and C were
fruitless. Finally, the epoxidation of limonene was carried out with
the three complexes. Notably, the C complex displayed the best
activity. In the presence of this complex, the conversion and
selectivity could be improved to 86% and 90% (1,2-epoxylinonen), mmol), corresponding amine (2.1 mmol), and Na
respectively. For citral, the C complex displayed the best results
dissolved in dry THF (10 mL). The reaction was stirred at room
6
and C9, less than 20% of styrene oxide product
6
gave the
2 4
dried (Na SO ) and the solvent was removed under reduced pressure,
affording the desired product in excellent yield.
5
9
2 9
Synthesis of ligands, L -L
5
A 50 mL bottom flask was loaded with 2-Pyridinecarboxaldehyde (2.1
SO , the mixture was
2
4
5
9
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.202000790
FULL PAPER
temperature overnight, then the solution was filtered and the solvent was
removed. The oil residue was used without prior purification (Quantitative
yield).
136.49 (C
3 2 4 7 8
), 124.44 (C ), 121.37 (C ), 72.25 (C ), 36.17 (C ), 28.49 (C10),
-1
24.66 (C ). IR (ATR-FTIR, cm ): 1644 C=N (Imine) y 1586-1566 C=N (Py).
9
+
MS (DART, m/z): [M+1] 203.
N-(2-Pyridinylmethylene)-1-ethanamine (L
1H NMR (300 MHz, CDCl
-d, δ ppm): 8.62–8.52 (d, 1H, H1), 8.33 (s, 1H,
), 7.91 (d, J = 7.9 Hz, 1H, H ), 7.74–7.61 (t, 1H, H ), 7.30–7.17 (t, 1H,
), 3.65 (q, J = 7.2, 1.7 Hz, 2H, H ), 1.26 (t, J = 7.2 Hz, 3H, H ). 13C {1H}
), 154.5 (C ), 149.3 (C ), 136.4
), 16.0 (C ). IR (ATR-FTIR, cm-1),
648 C=N (Imine) y 1585-1566 C=N (Py). MS (DART, m/z): [M+1]+ 135.
1
): Yellow oil (98%), C
8
H
10
N
2
.
8
N-(2-Pyridinylmethylene)-1-Benzylamine (L ): Dark yellow oil (84%),
. 1H NMR (300 MHz, CDCl
-d, δ ppm): 8.68 (dd, J = 4.8, 0.9 Hz,
), 8.09 (d, J = 7.9 Hz, 1H, H ), 7.76 (td, J = 7.8, 1.7
), 7.42–7.25 (m, 6H, H2, 9-11), 4.90 (s, 2H, H
MHz, CDCl -d, δ ppm): 162.84 (C ), 154.52 (C ), 149.41 (C
136.58 (C ), 128.58 (C10), 128.19 (C ), 127.18 (C11), 124.86 (C
(C ), 64.95 (C
3
C
1H, H
Hz, 1H, H
13
H
12
N
2
3
H
H
6
4
3
1
), 8.52 (s, 1H, H
6
4
). 13C { H} NMR (75
), 138.68 (C ),
), 121.37
1
2
7
8
3
7
RMN (75 MHz, CDCl3-d, δ ppm): 161.2 (C
), 124.5 (C ), 121.1 (C ), 55.5 (C
6
5
1
3
6
5
1
8
(
C
3
2
4
7
8
3
9
2
-1
1
4
7
). IR (ATR-FTIR, cm ): 1645 C=N (Imine) y 1585-1566 C=N
+
(
Py). MS (DART, m/z): [M+1] 197.
N-(2-Pyridinylmethylene)-1-butanamine (L
1H NMR (300 MHz, CDCl
-d, δ ppm): 8.56 (d, J = 4.8 Hz, 1H, H
H, H ), 7.91 (d, J = 7.9 Hz,1H, H ), 7.66 (t, J = 7.7 Hz, 1H, H ), 7.22 (t, J
7.5, 4.9 Hz, 1H, H ), 3.60 (t, J = 7.0 Hz, 2H, H
), 1.41–1.23 (m, 2H, H
-d, δ ppm): 161.65 (C
), 121.15 (C ), 61.24 (C
2
): Brown oil (93%), C10
14 2
H N .
3
1
), 8.30 (s,
N-(2-Pyridinylmethylene)-1-benzeneethanamina (L
(99%), C14 -d, δ ppm): 8.53 (d, J = 4.8 Hz,
. 1H NMR (300 MHz, CDCl
1H, H ), 8.21 (s, 1H, H ), 7.89 (d, J = 7.9 Hz, 1H, H ), 7.63 (td, J = 7.7, 1.7
Hz, 1H, H ), 7.24–7.07 (m, 6H, H2, 10-12), 3.84 (td, J = 7.6, 1.3 Hz, 2H, H ),
2.95 (t, J = 7.5 Hz, 2H, H -d, δ ppm):
). 13C {1H} NMR (75 MHz, CDCl
162.33 (C ), 154.48 (C ), 149.44 (C ), 136.56 (C ), 128.95
), 62.92 (C ),
9
): Dark yellow oil
1
=
H
6
4
3
H
14
N
2
3
2
7
), 1.64 (p, J = 7.1 Hz, 2H,
1
6
4
), 0.87 (t, J = 7.3 Hz, 3H, H10). 13C { H} NMR (75
1
8
9
3
8
MHz, CDCl
24.56 (C
3
6
), 154.65 (C
), 32.75 (C
5
), 149.37 (C
), 20.41 (C
1
), 136.50 (C
), 13.85 (C10).
3
),
7
3
1
2
4
7
8
9
6
5
1
), 139.69 (C
9
3
-1
IR (ATR-FTIR, cm ): 1648 C=N (Imine) y 1586-1566 C=N (Py). MS (DART,
(C11), 128.40 (C10), 126.21 (C12), 124.71 (C
2
), 121.27 (C
4
7
+
-1
m/z): [M+1] 163.
37.33 (C
8
). IR (ATR-FTIR, cm ): 1647 C=N (Imine) y 1585-1566 C=N (Py).
+
MS (DART, m/z): [M+1] 211.
N-(2-Pyridinylmethylene)-1-hexanamine (L
3
): Brown oil (99%),
-d, δ ppm): 8.64 (d, J = 4.5 Hz, 1H,
), 7.98 (d, J = 7.9 Hz, 1H, H ), 7.73 (td, J = 7.7, 1.5 Hz,
), 7.33–7.25 (m, 1H, H ), 3.67 (t, J = 7.0 Hz, 2H, H
Hz, 2H, H
NMR (75 MHz, CDCl
C
H
12
H
18
N
2
. 1H NMR (300 MHz, CDCl
), 8.37 (s, 1H, H
3
Synthesis of [MoCl (L -L )] complexes, C -C
2
O
2
1
9
1
9
1
6
4
1H, H
3
2
7
), 1.72 (p, J = 7.1
In
MoCl
equivalent of the pyridylimine ligand corresponding (L
hour under nitrogen at room temperature. The solvent was removed
a
Schlenk tube under nitrogen atmosphere,
(CH CN) ] (0.5 mmol) in acetonitrile (10 mL) was added 1.0
-L ) and stirred for
a solution of
), 1.44–1.23 (m, 6H, H9-11), 0.91–0.85 (m, 3H, H12). 13C { H}
1
8
[
2
O
2
3
2
3
-d, δ ppm): 161.66 (C
), 124.58 (C ), 121.18 (C ), 61.61 (C
), 22.61 (C11), 14.07 (C12). IR (ATR-FTIR, cm ): 1648 C=N
6
), 154.67 (C
5
), 149.39 (C
1
),
1
9
1
2
36.53 (C
7.02 (C
3
2
4
7
), 31.64 (C
8
-1
), 30.67 (C10),
1
9
under vacuum and the crude obtained was washed with diethyl ether and
hexane, then solid was dissolved in methylene chloride and precipitated
used hexane, affording the desired complex (C -C ).
1 9
+
(
Imine) y 1586-1566 C=N (Py). MS (DART m/z): [M+1] 191.
N-(2-Pyridinylmethylene)-1-decanamine (L
. 1H NMR (300 MHz, CDCl
-d, δ ppm): 8.56 (dt, J = 4.9, 1.3 Hz,
), 8.30 (d, J = 1.4 Hz, 1H, H ), 7.91 (d, J = 7.9 Hz, 1H, H ), 7.66 (td,
J = 7.7, 1.8 Hz, 1H, H ), 7.23 (ddd, J = 7.3, 4.8, 1.2 Hz, 1H, H ), 3.59 (td,
J = 7.0, 1.4 Hz, 2H, H ), 1.31–1.12 (m, 18H,
-d, δ ppm):
), 124.57 (C ), 121.17
), 30.70 (C14), 29.58 (C10-11), 29.43 (C12), 29.32
4
): Dark yellow oil (90%),
C
16
H
26
N
2
3
Epoxidation
1H, H
1
6
1
3
2
The analytic activity of all complexes toward different olefins epoxidation
was examined by treating a solution of the corresponding complex in
methylene chloride by using tert-butyl hydroperoxide in decane (5.5 M) as
an oxidant. The catalytic reaction was carried out at 40 °C. The oxygenated
product was identified by an Agilent technologies GC-MS instrument
equipped with the 7890B GC system and 5977A MSD using the HP-5MS
capillary column. Catalytic epoxidation: The epoxidation reaction of
olefins was carried out at 40 °C for 3h, in a flask with magnetic stirred. The
7
), 1.65 (p, J = 7.1 Hz, 2H, H
8
9-15), 0.83–0.76 (m, 4H, H16). 13C { H} NMR (75 MHz, CDCl
1
H
1
3
61.65 (C
), 61.61 (C
13), 27.34 (C
Imine) y 1586-1567 C=N (pyr). MS (DART, m/z): [M+1] 247.
5
), 154.67 (C
), 31.89 (C
), 22.68 (C15), 14.11 (C16). IR (ATR-FTIR, cm ): 1649 C=N
6
), 149.38 (C
1
), 136.51 (C
3
2
(
(
(
C
4
7
8
-1
C
9
+
N-(2-Pyridinylmethylene)-1-tert-butylimine (L
. 1H NMR (300 MHz, CDCl
-d, δ ppm): 8.56 (ddd, J = 5.0, 1.8, 0.9
Hz, 1H, H ), 8.30 (s, 1H, H ), 7.95 (dt, J = 8.0, 1.1 Hz, 1H, H ), 7.65 (td, J
7.6, 1.5 Hz, 1H, H ), 7.33–7.06 (m, 1H, H ), 1.25 (s, 9H, H
NMR (76 MHz, CDCl -d, δ ppm): 156.41 (C ), 155.50 (C ), 149.24 (C
36.52 (C ), 124.40 (C ), 120.97 (C ), 57.83 (C ), 29.58 (C ). IR (ATR-
5
): Dark yellow oil (92%),
2 2
flask was loaded with olefin (2.0 mmol), complex [MoCl O (L)] (0.01%
relation catalyst/substrate), tert-butyl hydroperoxide (1.5 equivalent) and
methylene chloride (5 mL) as a solvent.
C
10
H
14
N
2
3
1
6
4
1
=
3
2
8
). 13C { H}
3
6
5
1
),
[
MoCl
2
O
2
(L
H NMR [300 MHz, CDCl
H, H ), 8.13 (t, J = 6.4 Hz, 1H, H
m, 1H, H ), 4.34 (q, J = 7.0 Hz, 2H, H
1H} NMR [75 MHz, CDCl
-d, δ ppm]: 158.63 (C
40.83 (C ), 128.42 (C ), 128.12 (C ), 56.47 (C
FTIR, cm ]: 1647 C=N (Imine), 1597-1569 C=N (Py), 904 (Mo=O). MS
1
)] (C
1
): Gray solid (92%), m.p. 125-127 °C, C
-d, δ ppm]: 9.39 (d, J = 4.7 Hz, 1H, H
), 7.84 (d, J = 6.7 Hz, 1H, H
), 1.64 (t, J = 7.1 Hz, 3H, H
), 152.53 (C
), 14.79 (C
8
H
10Cl
2
MoN
), 8.38 (s,
2 2
O .
1
3
1
2
4
7
8
1
3
1
-
FTIR, cm ): 1644 C=N (Imine) y 1587-1567 C=N (Py). MS (DART, m/z):
1
(
{
1
6
3
4
), 7.77–7.69
+
[
M+1] 163.
). 13
2
7
8
C
5
),
3
6
1
), 147.97 (C
N-(2-Pyridinylmethylene)-1-Cyclohexanamine (L
93%), C12 -d, δ ppm): 8.65–8.50 (m, 1H,
. 1H NMR (300 MHz, CDCl
), 8.33 (s, 1H H )), 7.92 (d, J = 7.9 Hz, 1H, H ), 7.65 (td, J = 7.7, 1.6 Hz,
H, H ), 7.22 (ddd, J = 7.4, 4.9, 1.2 Hz, 1H, H ), 3.37–3.08 (m, 1H, H ),
.92–1.45 (m, 8H, H8-9), 1.38–1.24 (m, 2H, H10). 13C { H} NMR (75 MHz,
6
): Dark yellow oil
3
2
4
7
8
). IR [ATR-
(
H
16
N
2
3
-1
H
1
6
4
ESI, m/z): [M-Cl]+ 298. Anal. Calcd. for C
(
H10Cl MoN O : C, 28.85; N,
8 2 2 2
1
1
3
2
7
8.41; H, 3.03. Found: C, 27.28; N, 7.65; H, 3.12.
1
CDCl
3
-d, δ ppm): 159.49 (C
6
), 154.93 (C
5
), 149.37 (C
), 25.62 (C10), 24.71 (C
1
), 136.48 (C
3
),
).
[
MoCl
2
O
2
(L
H NMR [300 MHz, CDCl
H, H ), 8.13 (t, J = 7.4 Hz, 1H, H
J = 7.6, 5.0 Hz, 1H, H ), 4.25 (t, J = 7.2 Hz, 2H, H
.48–1.33 (m, 2H, H
CDCl -d, δ ppm]: 159.21 (C
28.44 (C
2
)] (C
2
): Gray solid (82%), m.p. 94-96 °C, C10
-d, δ ppm]: 9.38 (d, J = 4.9 Hz, 1H, H
), 7.83 (d, J = 7.5 Hz, 1H, H ), 7.73 (dd,
H
14Cl
2
MoN
), 8.33 (s,
2 2
O .
124.48 (C
2
), 121.38 (C ), 69.64 (C
4
7
), 34.17 (C
8
9
1
3
1
-1
IR (ATR-FTIR, cm ): 1646 C=N (Imine) y 1587-1566 C=N (Py). MS (DART,
m/z): [M+1] 189.
1
6
3
4
+
2
7
), 2.17–2.00 (m, 2H, H
8
),
), 0.93 (t, J = 7.3 Hz, 3H, H10).13C { H} NMR [75 MHz,
1
1
9
N-(2-Pyridinylmethylene)-1-Cycloheptanamine (L
93%), C13 -d, δ ppm): 8.63 (dt, J = 4.9,
. 1H NMR (300 MHz, CDCl
), 8.34 (s, 1H, H ), 7.99 (d, J = 8.0 Hz, 1H, H ), 7.72 (td, J =
.7, 1.7 Hz, 1H, H ), 7.28 (ddd, J = 7.5, 4.8, 1.2 Hz, 1H, H ), 3.46 (m, J =
.4 Hz, 1H, H ), 1.83–1.74 (m, 6H, H
), 1.65–1.52 (m, 6H, H10). 13C { H}
-d, δ ppm): 158.72 (C ), 155.05 (C ), 149.38 (C ),
7
): Dark yellow oil
3
6
), 152.54 (C
), 62.12 (C ), 30.81 (C
1
), 147.90 (C
8
), 20.22 (C
5
), 140.83 (C
9
), 13.70 (C10).
3
),
(
H
18
N
2
3
1
2
), 128.13 (C
4
7
1
7
6
.3 Hz, 1H, H
1
6
4
-1
IR [ATR-FTIR, cm ]: 1597 C=N (Py), 904 (Mo=O). MS [ESI, m/z]:
M+4Na]+ 453. Anal. Calcd. for C10
3
2
[
H14Cl MoN O : C, 33.26; N, 7.76; H,
2 2 2
1
7
9
3
.91. Found: C, 33.98; N, 7.31; H, 3.99.
NMR (75 MHz, CDCl
3
6
5
1
9
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.202000790
FULL PAPER
[
MoCl
2
O
2
(L
H NMR [300 MHz, CDCl
H, H ), 8.12 (td, J = 7.7, 1.6 Hz, 1H, H
dd, J = 7.7, 5.2 Hz, 1H, H ), 4.24 (t, J = 7.3 Hz, 2H, H
Hz, 2H, H
NMR [75 MHz, CDCl
3
)] (C
3
): Gray solid (76%), m.p. 122-123 °C, C12
-d, δ ppm]: 9.39 (d, J = 5.0 Hz, 1H, H
), 7.82 (d, J = 7.6 Hz, 1H, H
H
18Cl
2
MoN
), 8.32 (s,
), 7.72
2
O
2
.
[MoCl
2
O
2
(L9)] (C9): Brown solid (79%), m.p. 121-124 °C,
1
. 1H NMR (300 MHz, CDCl
3
1
C
H
H
14
H
14Cl
2
2
MoN O
2
3
-d, δ ppm): 9.52–9.42 (d, 1H,
), 7.97 (s, 1H, H ), 7.83–7.74 (m, 1H,
1
(
6
3
4
1
4
), 8.15 (td, J = 7.7, 1.6 Hz, 1H, H
), 7.71 (d, J = 7.6 Hz, 1H, H
3
6
2
7
), 2.10 (p, J = 7.3
2
), 7.40–7.23 (m, 5H, H10-12), 4.57 (t, J = 7.0
), 1.37–1.24 (m, 6H, H9-11), 0.82 (t, J = 6.9 Hz, 3H, H12). 13C { H}
-d, δ ppm]: 159.0 (C
), 128.35 (C ), 127.98 (C ), 62.39 (C
1
Hz, 2H, H
δ ppm]: 159.67 (C
129.28 (C11), 128.76 (C10), 128.49 (C12), 128.02 (C
), 3.46 (t, J = 7.1 Hz, 2H, H
), 152.54 (C ), 147.68 (C
). 13C { H} NMR [75 MHz, CDCl
1
-d,
), 137.83 (C ),
), 126.94 (C ), 63.28
8
8
7
3
3
6
), 152.52 (C
1
), 147.89 (C
5
),
6
1
5
), 140.75 (C
3
9
1
2
40.73 (C
6.67 (C
3
2
4
7
), 31.35 (C
8
), 28.78 (C10),
2
4
-1
-1
9
), 22.53 (C11), 14.03 (C12). IR [ATR-FTIR, cm ]: 1647 C=N
(C
7
), 35.09 (C
8
). IR [ATR-FTIR, cm ]: 1645 C=N (Imine), 1598-1567 C=N
+
+
(
4
Imine), 1597-1568 C=N (Py), 901 (Mo=O). MS (ESI, m/z): [M+K+2Na]
92. Anal. Calcd. for C12 MoN
C, 37.39; N, 7.42; H, 4.97.
(Py), 901 (Mo=O). MS [ESI, m/z]: [M+3K+Na] 548. Anal. Calcd. for
C H14Cl MoN O : C, 41.10; N, 6.85; H, 3.45. Found: C, 40.48; N, 6.27; H,
14 2 2 2
3.54.
H18Cl
2
2
O
2
: C, 37.04; N, 7.20; H, 4.66. Found:
[
MoCl
2
O
2
(L
H NMR [300 MHz, CDCl
.41 (s, 1H, H ), 8.21 (td, J = 7.7, 1.6 Hz, 1H, H
), 7.82 (dd, J = 7.7, 5.2 Hz, 1H, H ), 4.33 (t, J = 7.3 Hz, 2H, H
H, H
75 MHz, CDCl
28.4 (C ), 128.1 (C
11), 29.20 (C12), 28.8 (C13), 27.0 (C
4
)] (C
4
): Gray solid (76%), m.p. 122-123 °C, C16
-d, δ ppm]: 9.49 (dd, J = 5.1, 1.5 Hz, 1H, H
), 7.90 (d, J = 7.6 Hz, 1H,
H
26Cl
2
MoN
2
O
1
),
2
.
Acknowledgments
1
3
8
H
2
[
1
(
6
3
We gratefully acknowledge the financial support from DGAPA-
UNAM (PAPIIT IA-203820) and CONACyT (626716 grant to D.
M-M). We also thank M. Paz Orta, R. Patiño, S. Hernández-
Ortega, J. Pérez, M. C. García, C. Márquez, L. Rios, E. García,
G. Cortés (UCTIC), H. Rios, E. Huerta, M. A. Peña, M. Reyes
Lezama, E. Tapia Mendoza (LANCIC-IQ-UNAM), B. Quiroz and
N. Esturau (LURMN-IQ-UNAM) for the excellent technical support.
4
2
7
), 2.19 (m,
1
), 1.55–1.15 (m, 14H, H9-15), 1.00–0.73 (m, 3H, H16). 13C { H} NMR
8
3
-d, δ ppm]: 159.1 (C
6
1 5 3
), 152.5 (C ), 147.9 (C ), 140.8 (C ),
2
4
), 62.4 (C ), 31.8 (C
7
8
), 29.5 (C14), 29.5 (C10), 29.2
C
9
), 22.6 (C15), 14.1 (C16). IR [ATR-
-
1
+
FTIR, cm ]: 1597-1568 (C=N), 901 (Mo=O). MS [ESI, m/z]: [M+4K] 604.
Anal. Calcd. for C12
4
2 2 2
H26Cl MoN O : C, 43.16; N, 6.26; H, 5.89. Found: C,
2.81; N, 6.67; H, 6.06.
Keywords: Molybdenum • Epoxidation • 2-Pyridylimino •
Turnover frequency • Homogeneous catalysis
[
C
MoCl
2
O
2
(L
MoN
5
)] (C
5
): Gray solid (86%), m.p. 137 °C (Desc.).
. 1H NMR [300 MHz, CDCl
10
H14Cl
2
2
O
2
3
-d, δ ppm]: 9.42 (d, J = 4.7
), 7.82 (d, J = 7.6
), 1.94 (s, 2H, H ), 1.70 (s,
), 152.40 (C ),
), 65.03 (C ), 29.43 (C ).
Hz, 1H, H
Hz, 1H, H
7
1
1 6 3
), 8.37 (s, 1H, H ), 8.12 (t, J = 7.7 Hz, 1H, H
4
), 7.72 (dd, J = 7.6, 5.3 Hz, 1H, H
1
2
8
[1]
[2]
J. E. Bäckvall, Modern Oxidation Methods, Wiley-VCH, 2011, pp 1–79.
S. T. Oyama, Mechanisms in Homogeneous and Heterogeneous
Epoxidation Catalysis, Elsevier, Amsterdam, 2008, pp. 4–57.
K. A. Joergensen, Chem. Rev. 1989, 89 431–458.
T. Punniyamurthy, S. Velusamy, J. Iqbal, Chem. Rev. 2005, 105, 2329–
2364.
H, H
48.55 (C
8
).13C { H} NMR [75 MHz, CDCl
3
-d, δ ppm]: 155.87 (C
), 128.20 (C
6
1
5
), 140.62 (C
3
), 128.49 (C
2
4
7
8
-1
IR [ATR-FTIR, cm ]: 1634 C=N (Imine), 1597 C=N (Py), 908 (Mo=O). MS
ESI, m/z]: [M+2K]+ 436. Anal. Calcd. for C10
MoN : C, 33.26; N,
.76; H, 3.91. Found: C, 33.86; N, 8.09; H, 6.01.
[3]
[4]
[
7
H14Cl
2
2 2
O
[
[
5]
6]
F. G. Gelalcha, Adv. Synth & Catal. 2014, 356, 261–299.
P. Liu, E. L.-M. Wong, A.W.-H. Yuen, C.-M. Che, Org. Lett. 2008, 10,
3275–3278.
[
C
MoCl
2
O
2
(L
MoN
6
)] (C
6
): Gray solid (74%), m.p. 160 °C (Desc.).
. 1H NMR [300 MHz, CDCl
12
H16Cl
2
2
O
2
3
-d, δ ppm]: 9.49 (d, J = 4.8
), 7.79 (d, J = 7.5
), 4.26–4.18 (m, 1H, H ), 2.28-
-d, δ ppm]: 157.5 (C ),
), 128.0 (C ), 71.5 (C ), 33.0
[
7]
I. Garcia-Bosch, X. Ribas, M. Costas, Adv. Synth. & Catal. 2009, 351,
Hz, 1H, H
Hz, 1H, H
1
1
(
1 6 3
), 8.39 (s, 1H, H ), 8.11 (t, J = 7.4 Hz, 1H, H
348–352.
4
), 7.71 (dd, J = 7.7, 5.1 Hz, 1H, H
2
7
.19 (m, 10H, H8-10). 13C { H} NMR [75 MHz, CDCl
52.4 (C
1
[8]
9]
E. M. McGarrigle, D. G. Gilheany, Chem. Rev. 2005, 105, 1563–1602.
P. Saisaha, J. W. de Boer, W. R. Browne, Chem. Soc. Rev. 2013, 42,
2059–2074.
3
6
[
1
), 148.3 (C
5
), 140.6 (C
3
), 128.2 (C
2
4
7
-
1
C
8
), 25.4 (C10), 25.2 (C
9
). IR [ATR-FTIR, cm ]: 1637 C=N (Imine), 1524
+
[10] Q. H. Xia, H. Q. Ge, C. P. Ye, Z. M. Li, K. X. Su. Chem. Rev. 2005, 105,
603–1662.
C=N (Py), 905 (Mo=O). MS [ESI, m/z]: [M+2K+Na] 488. Anal. Calcd. for
C H16Cl MoN O : C, 37.22; N, 7.24; H, 4.17. Found: C, 36.96; N, 6.80; H,
12 2 2 2
1
[
[
11] A. Syamal, M. R. Maurya. Coord. Chem. Rev. 1989, 95, 183-238.
12] F. Fache, E. Schulz, M. L. Tommasino, M. Lemaire. Chem. Rev. 2000,
4.44.
1
00, 2159–2232.
[
C
MoCl
2
O
2
(L
MoN
Hz, 1H, H ), 8.42 (s, 1H, H
Hz, 1H, H
7
)] (C
. 1H NMR [300 MHz, CDCl
), 8.11 (t, J = 7.7 Hz, 1H, H
3
7
): Gray solid (91%), m.p. 170 °C (Desc.),
-d, δ ppm]: 9.38 (d, J = 4.9
), 7.81 (d, J = 7.6
), 4.35 (td, J = 10.4, 3.8 Hz, 1H, H ),
-d, δ ppm]: 157.58
), 128.11 (C ), 74.56
[
[
[
[
[
[
13] F. E. Kühn, A. D. Lopes, A. M. Santos, E. Herdtweck, J. J. Haider, C. C.
Romão, A. Gil Santos, J. Mol. Catal. A: Chem. 2000, 151, 147–160.
14] A. Valente, J. Moreira, A. D. Lopes, M. Pillinger, C. D. Nunes, C. C.
Romão, F. E. Kühn, I. S. Gonçalves. New J. Chem. 2004, 28, 308–313.
15] F. E. Kühn, A. M. Santos, I. S. Gonçalves, C. C. Romão, A. D. Lopes.
Appl. Organometal. Chem., 2001, 15, 43–50.
13
H18Cl
2
2
O
2
3
1
6
4
), 7.74–7.67 (m, 1H, H
2
7
.36–1.50 (m, 12H, H8-10).13C { H} NMR [75 MHz, CDCl
1
2
3
(
(
(
C
6
), 152.32 (C
1
), 148.42 (C
5
), 140.70 (C
3
), 128.24 (C
2
4
-1
C
7
), 35.09 (C ), 27.16 (C10), 25.05 (C
8
9
). IR [ATR-FTIR, cm ]: 1639 C=N
16] A. Günyar, M.-D. Zhou, M. Drees, P. N. W. Baxter, G. Bassioni, E.
Herdtweck, F. E. Kühn. Dalton Trans. 2009, 8746–8754.
+
Imine), 1595 C=N (Py), 910 (Mo=O). MS [ESI, m/z]: [M+3K] 518. Anal.
Calcd. for C13
N, 6.81; H, 4.86.
2 2 2
H18Cl MoN O : C, 38.92; N, 6.98; H, 4.52. Found: C, 38.26;
17] A. Gunyara, D. Betzb, M. Dreesb, E. Herdtweckb, F. Ebruno. J. Mol.
Catal. A: Chem. 2010, 331, 117–124.
18] S. M. Bruno, C. C. L. Pereira, M. S. Balula, M. Nolasco, A. A. Valente, A.
Hazell, M. Pillinger, P. Ribeiro-Claro, I. S. Gonçalves. J. Mol. Catal. A:
Chem. 2007, 261, 79–87.
[
C
MoCl
2
O
2
(L
MoN
Hz, 1H, H ), 8.05 (td, J = 7.7, 1.5 Hz, 1H, H
.73–7.67 (m, 1H, H
8
)] (C8): Brown solid (80%), m.p. 128 °C (Desc.).
. 1H NMR [300 MHz, CDCl
-d, δ ppm]: 9.42 (d, J = 4.6
), 7.88 (t, J = 2.0 Hz, 1H, H ),
), 7.44–7.35 (m, 5H, H9-
-d, δ ppm]:
), 133.08 (C ), 130.64
), 63.07 (C ). IR
13
H12Cl
2
2
O
2
3
1
3
6
[
19] A. C. Coelho, M. Nolasco, S. S. Balula, M. M. Antunes, C. C. L. Pereira,
F. A. Almeida Paz, A. A. Valente, M. Pillinger, P. Ribeiro-Claro, J.
Klinowski, I. S. Gonçalves. Inorg. Chem. 2011, 50, 525–538.
20] C. C. L. Pereira, S. S. Balula, F. A. A. Paz, A. A. Valente, M. Pillinger, J.
Klinowski, I. S. Gonçalves. Inorg. Chem. 2007, 46, 8508–8510.
21] A. C. Gomes, S. M. Bruno, S. Gago, R. P. Lopes, D. A. Machado, A. P.
Carminatti, A. A. Valente, M. Pillinger, I. S. Gonçalves. J. Organomet.
Chem. 2011, 696, 3543–3550.
7
4
), 7.64 (d, J = 7.6 Hz, 1H, H
2
), 5.56 (d, J = 2.0 Hz, 2H, H
58.68 (C ), 152.62 (C ), 148.04 (C
10), 129.50 (C ), 129.29 (C11), 128.28 (C
7
). 13C { H} NMR [75 MHz, CDCl
1
3
1
1
1
(
6
1
5
), 140.63 (C
3
8
[
[
C
9
2
), 128.24 (C
4
7
-1
[
[
7
ATR-FTIR, cm ]: 1642 C=N (Imine), 1598 C=N (Py), 910 (Mo=O). MS
ESI, m/z]: [M+K]+ 434. Anal. Calcd. for C13
MoN : C, 39.52; N,
.09; H, 3.06. Found: C, 40.18; N, 7.13; H, 3.29.
H12Cl
2
2 2
O
9
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.202000790
FULL PAPER
[
22] S. S. Balula, S. M. Bruno, A. C. Gomes, A. A. Valente, M. Pillinger, I. S.
Gonçalves, D. J. Macquarrie, J. H. Clark. Inorg. Chim. Acta, 2012, 387,
234–239.
[
[
23] M. Vasconcellos-Dias, J. Marreiros, R. Sales, V. Félix, P. Brandão, C. D.
Nunes, M. J. Calhorda. Molecules, 2019, 24, 578.
1 6 8 9
24] CCDC 2022764 (C ), 2022765 (C ), 2022763 (C ), 2022762 (C ); these
data can be obtained free of charge from The Cambridge
Crystallographic Data Centre.
[
[
25] S. R. Gilani, Z. Mahmood. J. Chem. Soc. Pak. 2003, 25, 41–43.
26] G. Barea, A. Lledos, F. Maseras, Y. Jean. Inorg. Chem. 1998, 37, 3321–
3325.
[
27] R. Bikas, V. Lippolis, N. Noshiranzadeh, H. Farzaneh-Bonab, A. J. Blake,
M. Siczek, H. Hosseini-Monfared, T. Lis. Eur. J. Inorg. Chem. 2017, 999–
1
006.
28] M. Mirzaee, B. Bahramian, A. Amoli, Appl. Organometal. Chem. 2015,
9, 593–600.
[
[
[
2
29] M. Bagherzadeh, S. Ataie, H. Mahmoudi, J. Janczak, Inorg. Chem.
Commun. 2017, 84, 63–67.
30] R. Bikas, V. Lippolis, N. Noshiranzadeh, H. Farzaneh‐Bonab, A. J. Blake,
M. Siczek, H. Hosseini‐Monfared, H. T. Lis. Eur. J. Inorg. Chem. 2017,
9
99–1006.
31] M. Ghorbanloo, A. Mohamadi, M. Amini, J. Tao. Transition Met. Chem.
015, 40, 321–331.
[
[
[
[
[
2
32] M. Bagherzadeh, R. Latifi, L. Tahsini, V. AMani, A. Ellern, L. K. Woo.
Polyhedron 2009, 28, 2517–2521.
33] A. Rezaeifard, I. Sheikhshoaie, N. Monadi, H. Stoeckli-Evans. Eur. J.
Inorg. Chem. 2010, 2010, 799–806.
34] T-U. Yoon, S. Ahn, A-R. Kim, J. M. Notestein, O. Farha, Y-S. Bae. Catal.
Sci. Technol, 2020, 10, 4580–4585.
35] A. Al-Ajlouni, A. A. Valente, C. D. Nunes, M. Pillinger, A. M. Santos, J.
Zhao, C. C. Romao, I. S. Gonçalves, F.E. Kuhn. Eur. J. Inorg. Chem.
2005, 1716–1723.
[
[
[
36] F. E. Kühn, A. M. Santos, A. D. Lopes, I. S. Gonçalves, E. Herdtweck, C.
C. Romão, J. Mol. Catal A: Chem. 2000, 164, 25–38.
37] L. M. Peschel, F. Belaj, J. A. Schachner, N. C. Mösch‐Zanetti, Eur. J.
Inorg. Chem., 2017, 2808-2817.
38] M. Schulz, M. Klopfleisch, H. Görls, M. Kahnes, M. Westerhausen, Inorg.
Chim. Acta, 2009, 362, 4706–4712.
9
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.202000790
FULL PAPER
Entry for the Table of Contents
Dioxomolybdenum (VI) complexes with the general formula [MoCl
2
O
2
(pyridilimine)] were applied as homogeneous catalysts for the
epoxidation of olefins. The new compounds showed high catalytic activity. The performance of the complexes in the reaction can be
attributed to the substituent at the imine fragment.
9
This article is protected by copyright. All rights reserved.