A mononuclear nickel(II) complex and a dinuclear manganese(III) complex derived from N,N'-bis(5-methoxysalicylidene)-1,2-ethanediamine: Synthesis, crystal structures and catalytic epoxidation property

Article abstract of DOI:10.1134/S1070328416010073

Synthesis and characterization of a mononuclear nickel(II) complex [NiL] · CH₃OH (I) and a dinuclear manganese(III) complex [Mn₂L₂(NCS)₂] (II) derived from the bis-Schiff base N,N'-bis(5-methoxysalicylidene)-1,2

Full text of DOI:10.1134/S1070328416010073

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2016, Vol. 42, No. 1, pp. 44–49. © Pleiades Publishing, Ltd., 2016.
A Mononuclear Nickel(II) Complex and a Dinuclear Manganese(III)
Complex Derived from N,N'-bis(5-methoxysalicylidene)-1,2-
Ethanediamine: Synthesis, Crystal Structures and Catalytic
Epoxidation Property1
F. Y. Wei
Department of Chemistry and Chemical Engineering, Baoji University of Arts and Sciences, Baoji, 721013 P.R. China
e-mail: weifenyan78@163.com
Received March 31, 2015
Abstract—Synthesis and characterization of a mononuclear nickel(II) complex [NiL] ⋅ CH3OH (I) and a
dinuclear manganese(III) complex [Mn2L2(NCS)2] (II) derived from the bis-Schiff base N,N'-bis(5-
methoxysalicylidene)-1,2-ethanediamine (H2L) are reported. The complexes were characterized by elemen-
tal analyses, IR spectra and molar conductivity. Single crystal X-ray structures of the complexes have been
determined (CIF files CCDC nos. 1056778 (I) and 1056688 (II)). The Ni atom in I is in a square planar coor-
dination, and the Mn atom in II is in an octahedral coordination. Catalytic property for epoxidation of sty-
rene by the complexes using PhIO and NaOCl as oxidant has been studied. As a result, complex II is efficient
for the styrene epoxidation.
DOI: 10.1134/S1070328416010073
INTRODUCTION
ate oxo-metallic species to the olefin as well as the spin
state of the intermediate oxo-metallic species, which
exists possibly in a higher oxidation state, are still
debatable issues [17]. Mohanta and coworkers
reported the efficient catalyst for styrene epoxidation
with Schiff base manganese(III) complexes and found
that complexes with chloride ligand is better than
those with methanol or azide ligand [18]. Pseudoha-
lides, especially azide, thiocyanate or dicyanamide,
have long been known for their versatile coordination
modes. As a further study of the catalytic epoxidation
of Schiff base complexes, in this study, the synthesis,
characterization, and crystal structures of a new
nickel(II) complex [NiL] · CH3OH (I) and a dinuclear
manganese(III) complex [Mn2L2(NCS)2] (II),
derived from the bis-Schiff base N,N'-bis(5-methox-
Schiff bases are very popular ligands because they
efficiently act as chelates generating a rich variety of
coordination compounds, ranging from mononuclear
to polynuclear species. In recent years, a great number
of complexes with Schiff bases have been reported,
showing interesting structures and excellent proper-
ties, such as catalytic [1–3], magnetic [4–6], lumines-
cent [7–9] and biological [10–12]. Manganese com-
plexes with Schiff bases are often described as good
epoxidation catalysts, due to their high activity and
selectivity [13–15]. The method is mild and is an envi-
ronment friendly process. Epoxidation of olefins cata-
lyzed by manganese(III) salen complexes has been
studied extensively since Kochi and coworkers
described in 1986 that they are highly effective, che-
moselective, and stereoselective catalysts [16].
Numerous salen type ligands have been prepared and
utilized to investigate steric, electronic, and overall
structural effects on the catalytic activity of manga-
nese(III) center. Thus, manganese(III) complexes
derived from salen type ligands can be used as labora-
tory and industrial homogeneous catalysts in the
epoxidation of unfunctionalised alkenes using iodos-
ylbenzene, sodium hypochlorite, hydrogen peroxide
and alkyl hydroperoxides as the oxygen source. The
mechanism of the oxygen transfer from the intermedi-
ysalicylidene)-1,2-ethanediamine
reported.
(H2L),
are
N
N
MeO
OH HO
(H2L)
OMe
1
The article is published in the original.
44

A MONONUCLEAR NICKEL(II) COMPLEX AND A DINUCLEAR MANGANESE(III)
45
EXPERIMENTAL
shaped X-ray diffraction quality single crystals sepa-
rated out. They were filtered, washed with methanol
and dried in vacuo over anhydrous CaCl2.
Material and measurements. All chemicals and
solvents used for the synthesis were of analytical grade.
5-Methoxysalicylaldehyde,
ethane-1,2-diamine,
For C38H36N6O8S2Mn2
ammonium thiocyanate, styrene and styrene oxide
were purchased from Aldrich and used without further anal. calcd., %:
C, 51.9;
C, 51.7;
H, 4.1;
H, 4.2;
N, 9.6.
N, 9.5.
purification. Iodosylbenzene (PhIO) was prepared by
the hydrolysis of iodobenzene diacetate. Nickel per-
chlorate hexahydrate and manganese perchlorate
hexahydrate were prepared by the treatment of per-
chloric acid with nickel carbonate and manganese car-
bonate, respectively, followed by slow evaporation on
a steam bath. They were then filtered through a fine
glass-frit and preserved in an anhydrous CaCl2 desic-
cator. The Schiff base compound H2L was prepared by
2 : 1 condensation of 5-methoxysalicylaldehyde and
ethane-1,2-diamine in methanol, according to the lit-
erature method [19].
Found, %:
X-ray structure determination. Intensity data of the
complexes were collected at 298(2) K on a Bruker
Smart 1000 CCD diffractometer with graphite-mono-
chromated MoKα radiation (λ = 0.71073 Å). Suitable
crystals were affixed to the end of glass fibers using sil-
icone grease and transferred to the goniostat. The unit
cell parameters were obtained from SAINT; absorp-
tion corrections were performed with SADABS [20].
Structures of the complexes were solved by direct
method and refined by full-matrix least-squares
method on F2 using SHELXTL crystallographic soft-
ware package [21]. All the non-hydrogen atoms are
refined anisotropically. All hydrogen atoms were
included in fixed calculated positions. Crystal data for
the complexes are summarized in Table 1. Selected
bond lengths and angles of the complexes are given in
Table 2.
Infrared spectra were recorded as KBr pellets on a
JASCO FT-IR 4100 spectrophotometer. Elemental
analyses (C, H, N) were carried out using a Perkin-
Elmer 2400 II elemental analyser. GC analysis was
performed with Agilent 6890N Network GC systems.
Molar conductivity of the complexes in acetonitrile
was measured with a DDS-11A molar conductivity
meter.
Supplementary material for structure I has been
deposited with the Cambridge Crystallographic Data
Centre (CCDC nos. 1056778 (I) and 1056688 (II);
Caution! Although no problem was encountered in
this work, perchlorate salts are potentially explosive
and should be used in small quantity with much care.
deposit@ccdc.cam.ac.uk
cam.ac.uk).
or
http://www.ccdc.
Synthesis of complex I. The appropriate quantity of
solid Schiff base ligand H2L (0.328 g, 1 mmol) was dis-
solved in dry methanol (20 mL). A solution of
nickel(II) perchlorate hexahydrate (0.366 g, 1 mmol)
in dry methanol (10 mL) was added to this solution
followed by the addition of ammonium thiocyanate
(0.076 g, 1.00 mmol) in dry methanol (10 mL). The
mixture was refluxed for 1 h. The resulting red solution
was then filtered off and the filtrate was left undis-
turbed. After a week fine red needle shaped X-ray dif-
fraction quality single crystals separated out. They
were filtered, washed with methanol and dried in
vacuo over anhydrous CaCl2.
General method for styrene epoxidation. The epox-
idation reactions were carried out at room temperature
in acetonitrile under nitrogen atmosphere with con-
stant stirring. The composition of the reaction mixture
was 2.00 mmol of styrene, 2.00 mmol of chloroben-
zene (internal standard), 0.10 mmol of the complexes
(catalyst) and 2.00 mmol iodosylbenzene or sodium
hypochlorite (oxidant) in 5.00 mL acetonitrile. When
the oxidant was sodium hypochlorite, the solution was
buffered to pH 11.2 with NaH2PO4 and NaOH. The
composition of reaction medium was determined by
GC with styrene and styrene epoxide quantified by the
internal standard method (chlorobenzene). Styrene
oxide was used as standard sample in GC analysis. All
other products detected by GC were mentioned as
others. For the complexes the reaction time for maxi-
mum epoxide yield was determined by withdrawing
periodically 0.10 mL aliquots from the reaction mix-
For C19H22N2O5Ni
anal. calcd., %:
Found, %:
C, 54.7;
C, 54.5;
H, 5.3;
H, 5.4;
N, 6.7.
N, 6.9.
Synthesis of complex II. The appropriate quantity ture and this time was used to monitor the efficiency of
of solid Schiff base ligand H2L (0.328 g, 1 mmol) was the catalyst on performing at least two independent
experiments. Blank experiments with each oxidant
and using the same experimental conditions except
catalyst were also performed.
dissolved in dry methanol (20 mL). A solution of man-
ganese(II) perchlorate hexahydrate (0.362 g, 1 mmol)
in dry methanol (10 mL) was added to this solution
followed by the addition of ammonium thiocyanate
(0.076 g, 1.00 mmol) in dry methanol (10 mL). The
mixture was refluxed for 1 h. The resulting brown
solution was then filtered off and the filtrate was left
RESULTS AND DISCUSSION
The tetradentate bis-Schiff base H2L was easily
undisturbed. After a week fine deep brown block prepared from the reaction between 5-methoxysalicy-
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46
WEI
Table 1. Crystallographic data and experimental details for complexes I and II
Value
Parameter
I
II
Formula weight
Crystal size, mm
Crystal system
Space group
a, Å
417.1
0.17 × 0.15 × 0.12
Monoclinic
P21/n
878.7
0.23 × 0.22 × 0.18
Triclinic
P1
11.406(1)
7.413(1)
7.856(2)
9.577(2)
b, Å
c, Å
α, deg
β, deg
γ, deg
21.622(2)
90
92.079(2)
90
13.989(2)
92.008(2)
102.001(2)
105.989(2)
984.9(3)
V, Å3
1827.0(3)
Z
4
1
ρcalcd, g cm–3
1.516
1.482
μ(MoKα), mm–1
1.096
0.806
F(000)
872
16048
3390
2658
246
452
4884
2766
2160
255
Number of measured reflections
Number of observations (I > 2σ(I))
Unique reflections
Parameters
Number of restraints
R1, wR2 (I > 2σ(I))*
R1, wR2 (all data)*
13
0
0.0512, 0.1366
0.0688, 0.1492
1.046
0.0642, 0.1323
0.0866, 0.1487
1.105
Goodness of fit of F2
Largest difference peak/hole, e Å–3
0.905/–0.645
0.511/–0.485
2
2 2
1/2
*R = ∑||F | – |F ||/∑|F |, wR = [∑w
2 2/∑w
]
.
(Fo − Fc )
(Fo )
1
o
c
o
2
400 cm–1 region. The strong sharp bands around
1615–1623 cm–1 in the spectra of the complexes are
characteristic of ν(C=N). The band centered at 3327
cm–1 in the spectrum of complex I is due to the meth-
anol molecule of crystallization. The intense absorp-
tion at 2113 cm–1 is due to the thiocyante ligand in II.
laldehyde and ethane-1,2-diamine in methanol with
2 : 1 stoichiometric ratio. Reaction of H2L and ammo-
nium thiocyanate with nickel perchlorate hexahydrate
and manganese perchlorate hexahydrate, respectively,
in a molar ratio of 1 : 1 : 1 in methanol, followed by
slow evaporation, afforded the single crystals of com-
plexes I and II, respectively. The thiocyanate ligand
coordinated to the Mn atom of the manganese com-
plex, while not coordinated to the Ni atom of the
nickel complex. During the synthesis performed under
aerobic conditions, the reaction system of complex II
exhibited an obvious color change from light to deep
brown. This suggest the occurrence of oxidation pro-
cess (Mn(II) → Mn(III)) induced by the oxygen in air.
Crystals of the complexes are stable in air. The molar
conductivities of the complexes I and II in acetonitrile
are 25 and 18 Ω–1 cm2 mol–1, respectively, indicating
the non-electronic nature [22]. The infrared spectra of
An ORTEP representation of complex I with atom
numbering scheme is depicted in Fig. 1. The complex
contains a mononuclear [NiL] complex molecule and
a methanol molecule of crystallization. The Ni centre
is four coordinated by four donor atoms (N2O2) of the
coordinated Schiff base ligand L. The coordination
environment of the Ni atom is slightly distorted, as
evidenced from the bond lengths and angles. The
metal–ligand bond distances involving the imine
nitrogens (Ni(1)–N(1) 1.846(3), Ni(1)–N(2)
1.851(3) Å) are comparable to the bond lengths involv-
ing phenolate oxygens (Ni(1)–O(1) 1.847(3), Ni(1)–
the complexes were recorded within the 4000– O(2) 1.848(3) Å). The trans angles (178.9(1)° and
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A MONONUCLEAR NICKEL(II) COMPLEX AND A DINUCLEAR MANGANESE(III)
47
Table 2. Selected bond lengths (Å) and angles (deg) for complexes I and II*
Bond
d, Å
Bond
d, Å
I
Ni(1)−O(1)
Ni(1)−N(1)
1.847(3)
1.846(3)
Ni(1)−O(2)
1.848(3)
1.851(3)
Ni(1)−N(2)
II
Mn(1)−O(1)
Mn(1)−N(1)
Mn(1)−N(3)
1.873(3)
1.989(4)
2.193(6)
Mn(1)−O(2)
Mn(1)−N(2)
Mn(1)−O(2)i
1.905(3)
1.977(4)
2.594(6)
Angle
ω, deg
Angle
ω, deg
I
O(1)Mn(1)O(2)
O(2)Mn(1)N(2)
O(2)Mn(1)N(1)
O(1)Mn(1)N(3)
N(2)Mn(1)N(3)
O(1)Mn(1)O(2)i
N(1)Mn(1)O(2)i
N(3)Mn(1)O(2)i
95.9(1)
88.8(2)
165.0(2)
95.3(2)
93.0(2)
89.6(2)
O(1)Mn(1)N(2)
O(1)Mn(1)N(1)
N(2)Mn(1)N(1)
O(2)Mn(1)N(3)
N(1)Mn(1)N(3)
O(2)Mn(1)O(2)i
N(2)Mn(1)O(2)i
169.8(2)
91.4(2)
82.0(2)
97.0(2)
95.3(2)
81.5(2)
85.4(2)
82.2(2)
175.0(2)
II
N(1)Ni(1)O(1)
O(1)Ni(1)O(2)
O(1)Ni(1)N(2)
94.5(1)
84.9(1)
178.6(1)
N(1)Ni(1)O(2)
N(1)Ni(1)N(2)
O(2)Ni(1)N(2)
178.9(1)
86.1(2)
94.5(1)
i
* Symmetry code: –x, 1 – y, –z.
178.6(1)°) and the cis angles (84.9(1)–94.5(1)°) devi- four donor atoms (N2O2) of the coordinated Schiff
ate slightly from the ideal values. The coordinate bond
values are in agreement with those observed in
nickel(II) complexes with Schiff bases [23, 24]. The
average deviation (0.017(1) Å) of the donor atoms and
base ligand L, one phenolate oxygen atom of another
Schiff base ligand, and one thiocyanate nitrogen atom.
In the octahedral coordination, O(2A) and N(3) are
the axial ligand atoms, and O(1), O(2), N(1) and N(2)
the displacement (0.003(1) Å) of the metal center from form the equatorial plane. The coordination environ-
ment of the Mn atom is slightly distorted, as evidenced
from the bond lengths and angles. In the equatorial
plane, the metal–ligand bond distances involving the
imine nitrogens (Mn(1)–N(1) 1.989(4), Mn(1)–N(2)
1.977(4) Å) are slightly longer than the bond lengths
involving phenolate oxygens (Mn(1)–O(1) 1.877(3),
Mn(1)–O(2) 1.905(3) Å). As expected due to Jahn–
Teller distortion of high spin manganese(III), the
bond distances involving the axial donor atoms
(Mn(1)–O(2A) 2.594(6), Mn(1)–N(3) 2.193(6) Å)
significantly longer than the bond lengths involving
the equatorial atoms. The trans angles (169.8(2)°,
165.0(2)°, and 175.0(2)°) and the cis angles (81.5(2)°–
97.0(2)°) deviate slightly from the ideal values. The
the least-squares plane defined by the donor atoms
indicates that the N2O2 cavity affords an almost per-
fect plane to the metal center. The Schiff base ligand is
approximate planar with dihedral angel between the
two benzene rings of 2.6(3)°. The methanol molecule
is linked to the [NiL] complex molecule through inter-
molecular O(5)–H(5A)⋅⋅⋅O(2) hydrogen bond (O(5)–
H(5A) 0.82, H(5A)⋅⋅⋅O(2) 2.00(2) Å, O(5)⋅⋅⋅O(2)
2.819(7) Å, O(5)–H(5A)⋅⋅⋅O(2) = 178(3)°).
An ORTEP representation of complex II with atom
numbering scheme is depicted in Fig. 2. The dinuclear
manganese complex possesses a crystallographic
inversion center symmetry, with the Mn⋅⋅⋅Mn separa-
tion of 3.437(2) Å. The Mn centre is six coordinated by coordinate bond values are in agreement with those
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 42 No. 1 2016

48
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C(8)
C(9)
C(10)
C(7)
N(2)
N(1)
C(1)
C(11)
C(6)
C(4)
C(16)
C(5)
O(3)
C(12)
O(2)
C(18)
C(17)
Ni(1)
C(2) O(1)
C(15)
O(4)
C(13)
C(3)
C(14)
O(5)
C(19)
Fig. 1. A perspective view of the molecular structure of complex I with atom labeling scheme. Thermal ellipsoids are drawn at the
30% probability level. Hydrogen bond is shown as a dashed line.
S(1)
C(19)
N(3)
C(8)
N(1)
C(18)
C(9)
N(2)
C(16)
C(10)
C(7)
C(1)
C(6)
C(4)
Mn(1)
C(17)
C(11)
O(4)
C(15)
C(14)
C(5)
O(1)
C(12)
C(13)
C(2)
O(2)
O(2A)
O(3)
C(3)
O(1A)
N(1A)
Mn(1A)
N(2A)
N(3A)
Fig. 2. A perspective view of the molecular structure of complex II with atom labeling scheme. Thermal ellipsoids are drawn at
the 30% probability level. Atoms with the suffix A are at the symmetry position –x, 1 – y, –z.
observed in manganese(III) complexes with Schiff
bases [25, 26]. The average deviation (0.036(2) Å) of
the equatorial donor atoms and the displacement
(0.176(2) Å) of the metal center from the least-squares
plane defined by the equatorial donor atoms indicates
that the N2O2 cavity affords an almost perfect plane to
the metal center. The Schiff base ligand is approximate
planar with dihedral angel between the two benzene
rings of 9.1(3)°.
Epoxidation of styrene was carried out at room
temperature with the complexes as the catalyst and
PhIO or NaOCl as the oxidant. For the reaction sys-
tem with complex I as the catalyst, the red color was
not changed. While the brown solution containing
complex II and the substrate was intensified after the
addition of oxidant indicating the formation of oxo-
metallic intermediates of the catalyst. After comple-
tion of oxidation reaction of the alkene, the solution
with complex II as the catalyst regains its initial color
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A MONONUCLEAR NICKEL(II) COMPLEX AND A DINUCLEAR MANGANESE(III)
49
7. Marinescu, G., Madalan, A.M., and Andruh, M., J.
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Time,
h
Conversion, Epoxide
Oxidant
%
yield, %
еpoxide оther
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vol. 1079, p. 423.
2.5 PhIO
3.0 NaOCl
94
79
81
62
85
78
15
22
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of styrene epoxide despite of the formation of by-
products which have been identified by GC-MS as
benzaldehyde, phenylacetaldehyde, styrene epoxide
derivative, alcohols, etc. When the reactions were car-
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NaOCl as oxidant, styrene conversion dropped to
79%. It is evident that PhIO acts as a better oxidant
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ACKNOWLEDGMENTS
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20. Sheldrick, G.M., SAINT (version 6.02), SADABS (ver-
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We acknowledge the Education Office of Shanxi
Province (project no. 11JK0601) and the Natural Sci-
ence Foundation of China (project no. 21173003) for
supporting this work.
21. Sheldrick, G.M., SHELXL-9, A Program for Crystal
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