Synthesis and crystal structure determination of Mn(II) Schiff base complexes and their performance in ethene polymerization

Article abstract of DOI:10.1016/j.poly.2013.03.063

Mn(II) complexes 1-10, of which eight are novel, were prepared in high yields by reacting MnCl₂ with bidentate N,N′-imine-pyridine and N,N′-imine-quinoline-type donor ligands having different kinds of chemical modifications. The complexes were fully characterized by elemental analysis, mass spectrometry and IR spectroscopy. Crystal structures of 6, 7 and 9 were determined by X-ray crystallography and the results showed that 6 has a dimeric square-pyramidal geometry, whereas 7 and 9 have distorted octahedral structures. Magnetic studies on the high spin complexes 6 and 9 showed that the former exhibits a weak intramolecular antiferromagnetic interaction through the chloride-bridging ligands with a magnetic exchange coupling J = -0.46(6) cm ^-1, whereas the latter, as expected for its mononuclear structure, only shows very weak intermolecular interactions and/or zero-field splitting effects. All the complexes were activated with methylaluminoxane and investigated under low pressure (5 bar) for ethene polymerization at 60 C. Complexes 1 and 6-10 showed catalytic activity. The prepared polyethenes exhibited high molar masses (296 000-399 000 g/mol) and high melting temperatures (133-140 C). The low molar mass distribution values of 2.15-2.55 indicated single-site polymerization behavior.

Full text of DOI:10.1016/j.poly.2013.03.063

Polyhedron 56 (2013) 221–229
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and crystal structure determination of Mn(II) Schiff base complexes
and their performance in ethene polymerization
Anjali Sood a,1, Minna T. Räisänen a, Erkki Aitola a, Ahlam Sibaouih a, Enrique Colacio b, Markku Ahlgren c,
Martin Nieger a, Timo Repo a, , Markku Leskelä a
⇑
a Laboratory of Inorganic Chemistry, Department of Chemistry, University of Helsinki, P.O. Box 55, FI-00014 Helsinki, Finland
b Departamento de Química Inorgánica, Facultad de Ciencias, Universidad de Granada, Avenida de Fuentenueva s/n, 18071 Granada, Spain
c Department of Chemistry, University of Eastern Finland, Joensuu Campus, P.O. Box 111, FI-80101 Joensuu, Finland
a r t i c l e i n f o
a b s t r a c t
Article history:
Mn(II) complexes 1–10, of which eight are novel, were prepared in high yields by reacting MnCl2 with
bidentate N,N0-imine-pyridine and N,N0-imine-quinoline-type donor ligands having different kinds of
chemical modifications. The complexes were fully characterized by elemental analysis, mass spectrome-
try and IR spectroscopy. Crystal structures of 6, 7 and 9 were determined by X-ray crystallography and
the results showed that 6 has a dimeric square-pyramidal geometry, whereas 7 and 9 have distorted octa-
hedral structures. Magnetic studies on the high spin complexes 6 and 9 showed that the former exhibits a
weak intramolecular antiferromagnetic interaction through the chloride-bridging ligands with a mag-
netic exchange coupling J = ꢀ0.46(6) cmꢀ1, whereas the latter, as expected for its mononuclear structure,
only shows very weak intermolecular interactions and/or zero-field splitting effects. All the complexes
were activated with methylaluminoxane and investigated under low pressure (5 bar) for ethene poly-
merization at 60 °C. Complexes 1 and 6–10 showed catalytic activity. The prepared polyethenes exhibited
high molar masses (296000–399000 g/mol) and high melting temperatures (133–140 °C). The low molar
mass distribution values of 2.15–2.55 indicated single-site polymerization behavior.
Received 21 January 2013
Accepted 26 March 2013
Available online 9 April 2013
Keywords:
Manganese
Schiff base
Crystal structure
Polymerization
Ethene
Molecular magnetism
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
study MnCl2 was reacted with a number of tridentate and tetra-
dentate nitrogen containing ligands and the complexes thus ob-
Manganese Schiff base complexes have been extensively
studied due to their catalytic [1–7], magnetic [8] and coordination
properties [9]. They catalyze various reactions effectively, such as
enantioselective olefin epoxidation [1], oxidation of sulfides [2],
hydrocarbons [3] and alcohols [4], as well as other asymmetric
reactions [5]. On the other hand, manganese catalysts in general
are still rarely used in olefin polymerization, though during the
past few years there has been a growing interest for their develop-
ment [6,7]. Manganese complexes are interesting particularly as
they are expected to have unique features differing both from early
and late transition metal catalysts [6e,7a].
tained
were
further
alkylated
and
activated
with
methylaluminoxane (MAO), and then studied as catalysts in eth-
ene polymerization [6a]. As an augmentation to this work, we
synthesized and fully characterized herein a series of Mn(II)
complexes with bidentate Schiff base ligands bearing nitrogen
donor atoms (Scheme 1). The catalytic activities of the prepared
complexes were demonstrated for low pressure ethene
polymerization.
2. Experimental
Manganese(II) complexes with coordinated bidentate nitrogen
containing ligands and two chlorine anions have so far only
been of limited interest, even though they have shown promis-
ing magnetic [10], photoluminescence [11], antibacterial and
antifungal [12], and catalytic [13] properties. In our previous
2.1. Materials and general procedures
All the complex preparations and polymerization experiments
were performed under argon using standard Schlenk techniques
or in a glove box. Solvents (HPLC grade) were dried over sodium
flakes and distilled before use. Anhydrous MnCl2 was purchased
from Aldrich and stored under an argon atmosphere. MAO (30%
in toluene) was obtained from Borealis Polymers Ltd. Other
reagents of high purity grade were purchased from commercial
sources and used as received.
⇑
Corresponding author. Tel.: +358 919150198.
E-mail address: timo.repo@helsinki.fi (T. Repo).
Present address: Department of Chemistry, School of chemical Technology, Aalto
1
University, P.O. Box 16100, FI-00076 Aalto, Finland.
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.03.063

222
A. Sood et al. / Polyhedron 56 (2013) 221–229
2.2. Polymerization procedure
spectrometer and the mass spectra of the ligands were measured
with a JEOL JMS-SX 102 EI+ instrument (70 eV), using a direct inlet
method. Infrared spectra were recorded with a Perkin–Elmer
Spectrum GX apparatus and elemental analyses were performed
with an EA 1110 CHNS-O CE instrument. NMR spectra were
recorded in CDCl3 at 25 °C on a Varian Gemini 2000 spectrometer
operating at 200 MHz (1H NMR) and 50 MHz (13C NMR). The field
dependence of the magnetization at different temperatures and
variable temperature (2–300 K) magnetic susceptibility measure-
ments on polycrystalline samples of 6 and 9 were carried out with
a Quantum Design SQUID MPMS XL-5 device operating at different
magnetic fields. The experimental susceptibilities were corrected
for the sample holder and diamagnetism of the constituent atoms
using Pascal’s tables.
Ethene polymerizations were done in a Büchi 1 L stainless steel
reactor under Ar. The reactor was loaded with the Mn(II) complex
(20 lmol), toluene (200 mL) and the cocatalyst (MAO 30%, cocata-
lyst:catalyst ratio 1000) and the autoclave was sealed. After
loading the reactor with ethene (5.0 bar), it was kept at room
temperature under stirring for 1 h, followed by overnight heating
at 60 °C. More details about the experimental procedure are given
elsewhere [6a].
2.3. Complex and polymer characterizations
The electrospray ionization time-of-flight (ESI-TOF) mass spec-
tra of the complexes were recorded with a Bruker Microtof mass
Scheme 1. A series of synthesized Mn(II) complexes (1–10).

A. Sood et al. / Polyhedron 56 (2013) 221–229
223
Table 1
Crystal data and structure refinement for 6, 7ꢂ0.5 C7H8, 7ꢂCH3OH and 9ꢂCH3OH.
6
7ꢂ0.5 C7H8
7ꢂCH3OH
9ꢂCH3OH
Empirical formula
Formula weight
T (K)
C
36H44Cl4Mn2N4
C24H20Cl2MnN4ꢂ0.5 C7H8
C24H20Cl2MnN4ꢂCH3OH
C26H24Cl2MnN4ꢂCH3OH
784.43
123
536.35
522.32
550.37
120
123
123
Crystal system
Space group
a (Å)
b (Å)
c (Å)
monoclinic
P21/n (no. 14)
9.767(2)
14.370(3)
14.422(3)
106.01(3)
1945.6(7)
2
monoclinic
P21/c (no. 14)
12.8347(2)
14.8466(3)
14.5287(3)
114.013(1)
2528.86(8)
4
monoclinic
P21/c (no. 14)
12.585(3)
14.907(3)
14.062(3)
111.78(3)
2449.7(8)
4
monoclinic
P21/c (no. 14)
13.436(1)
11.555(1)
17.447(2)
107.00(1)
2590.3(4)
4
b (°)
V (Å3)
Z
Dcal (g cmꢀ3
)
1.339
0.953
812
1.409
0.757
1104
1.416
0.782
1076
1.411
0.744
1140
Absorption coefficient (mmꢀ1
F(000)
)
Crystal dimensions (mm)
2hmax. (°)
0.28 ꢃ 0.15 ꢃ 0.12
0.20 ꢃ 0.20 ꢃ 0.08
0.16 ꢃ 0.16 ꢃ 0.06
0.40 ꢃ 0.25 ꢃ 0.15
55
55
55
55
No. of collected data
No. of unique data
Rint.
24,141
4447
0.074
31836
5808
0.089
50719
5622
0.046
53713
5930
0.025
No. of parameters/restraints
208/0
0.045
0.100
297/7
0.047
0.089
303/0
0.031
0.124
320/1
0.024
0.061
Ra [I > 2
r(I)]
b
wR2
Goodness-of-fit (GOF)
1.05
1.02
1.01
1.09
Largest difference peak and hole (e Aꢀ3
)
0.550 and ꢀ0.593
0.476 and ꢀ0.491
0.365 and ꢀ0.373
0.303 and ꢀ0.240
a
R =
wR2 = [
R
||Fo| ꢀ |Fc||/
R |Fo|.
b
2
R
[w(Fo ꢀ Fc2)2]/
R .
[w(Fo2)2]]1/2
Molar masses and molar mass distributions of polyethene
2.5. Syntheses of the ligands L1–L10
samples were determined with a Waters Alliance GPCV 2000 high
temperature gel permeation chromatograph device at 145 °C.
HMW7, 2ꢁHMWGE, and HMW2 Waters StyragelÒ columns were
used and molar mass calculations were carried out employing the
universal calibration method using narrow polystyrene standards.
The ligands L1 and L7 were prepared by literature procedures
[6,15]. The purities of all the ligands were verified by 1H NMR
and a full analysis of L1, L2, L4, L6, L7, L9 and L10 can be found
in the literature [6a,15,16].
2.4. Crystal structure determination
2.5.1. Synthesis of N-(quinolin-2-ylmethylene)aniline (L2)
L2 was synthesized by modifying a literature procedure [16a]. A
mixture of 2-quinolinecarboxaldehyde (1.00 g, 6.3 mmol) and
aniline (0.65 g, 6.9 mmol) was stirred overnight at 120 °C under
solvent-free conditions. The obtained crude product was dissolved
in n-pentane and L2 was collected as a yellow crystalline solid after
slow evaporation of the solvent. Yield 81% (1.21 g).
Single-crystal X-ray diffraction studies were carried out on a
Bruker-Nonius Kappa-CCD diffractometer at 123(2) K (L3ꢂMeOH,
6, 7ꢂCH3OH, 9ꢂCH3OH) or 120(2) K (7ꢂ0.5 C7H8) using Mo K
a
radiation (k = 0.71073 Å). Direct Methods (SHELXS-97) were used
for the structure solutions and refinements were carried out using
SHELXL-97 (full-matrix least-squares on F2) [14]. Semi-empirical
absorption corrections were applied and H atoms were localized
by difference electron density determination and refined using a
riding model (H(O, N) free). The crystallographic data are given
in Table 1. Complexes 6 and 9 were crystallized from methanol
with a few drops of n-hexane and complex 7 was crystallized both
from methanol (7ꢂCH3OH) and from methanol with a few drops of
toluene (7ꢂ0.5 C7H8). Crystals of L3ꢂMeOH were formed as a side
product2 when the ligand L3 was stored in a deep freezer for 2 days.
2.5.2. Synthesis of 2-benzyl-N-(quinolin-2-ylmethylene)aniline (L3)
For the synthesis of the novel ligand L3, ethanol (40 mL), 2-ben-
zylaniline (1.95 g, 10.1 mmol) and 2-quinolinecarboxaldehyde
(1.60 g, 10.1 mmol) were combined and refluxed for 20 min. Etha-
nol was removed and L3 was isolated as viscous yellow oil in 85%
yield (2.81 g). 1H NMR (200 MHz, CDCl3, TMS) dH (ppm): 4.24 (2H,
3
s, CH2), 7.03–7.36 (9H, m, H–Ar), 7.57 (1H, t, JHH = 8.0 Hz, H–Ar),
3
3
2
7.74 (1H, t, JHH = 7.5 Hz, H–Ar), 7.84 (1H, d, JHH = 7.8 Hz, H–Ar),
Side product L3ꢂMeOH was obtained as crystals when L3 reacted with methanol.
3
In the structure of L3ꢂMeOH, the imine bond is broken and the N(1) atom is
8.14–8.23 (2H, m, H–Ar), 8.35 (1H, d, JHH = 8.6 Hz, H–Ar), 8.70
(1H, s, CH@N). HRMS (m/z), Calc. for [C23H18N2+H]+: 323.1549.
protonated and
a methoxy group is covalently bonded to C(2). There is an
intramolecular N(1)–Hꢂ ꢂ ꢂN(2) H-bond with an N(1)ꢂ ꢂ ꢂN(2) distance of 2.646(3) Å.
Found: 323.1543 (error 1.91 ppm). FTIR (cmꢀ1):
m 1625 (s, imine
C
23H18N2ꢂCH3OH, M = 354.44, data collected at 123(2) K, crystal size
C@N).
ꢀ
0.30 ꢃ 0.15 ꢃ 0.10, triclinic, space group P1 (No. 2): a = 10.700(1) Å, b = 10.737(1) Å,
c = 74.99(1) Å,
(calc) = 1.292 Mg mꢀ3
(2hmax = 50°), 3194 unique [Rint = 0.054], 248 parameters,
(I > 2 (I)) = 0.057, wR2 (all data) = 0.180, GOF = 1.03, largest diff. peak and hole
a
= 74.99(1)°, b = 86.72(1)°,
c
l
= 81.26(1)°, V = 911.15(16) Å3, Z = 2,
= 0.079 mmꢀ1
10 974 reflections
restraint, R1
q
,
F(0 0 0) = 376,
,
1
2.5.3. Synthesis of 1-phenyl-N-(quinolin-2-ylmethylene)methanamine
(L4)
r
0.258/ꢀ0.341 e Åꢀ3. Selected bond lengths (Å) and angles (°) in L3ꢂMeOH: C(1)–O(1)
1.425(3), O(1)–C(2) 1.435(3), N(1)–C(12) 1.392(3), N(1)–C(2) 1.424(3), N(1)–H(1)
0.875(17), C(2)–C(3) 1.516(3), C(3)–N(2) 1.314(3), C(11)–N(2) 1.373(3), C(1)–O(1)–
C(2) 113.3(2), C(12)–N(1)–C(2) 123.2(2), C(12)–N(1)–H(1) 119.4(18), C(2)–N(1)–H(1)
113.4(18), N(1)–C(2)–O(1) 113.0(2), N(1)–C(2)–C(3) 110.3(2), O(1)–C(2)–C(3)
110.29(19), N(2)–C(3)–C(4) 123.4(2), N(2)–C(3)–C(2) 118.6(2), N(2)–C(11)–C(10)
119.2(2), N(2)–C(11)–C(6) 121.8(2), C(3)–N(2)–C(11) 118.3(2), N(1)–C(12)–C(13)
121.2(2), N(1)–C(12)–C(17) 119.6(2).
2-Quinolinecarboxaldehyde (1.5 g, 9.5 mmol), phenylmethan-
amine (1.10 g, 9.5 mmol) and a catalytic amount of formic acid
(2–3 drops) were stirred overnight at room temperature. L4 was
obtained in 88% yield (2.06 g). HRMS (m/z), Calc. for
[C17H14N2+H]+: 247.1230. Found: 247.1230 (error 1.16 ppm). FTIR
(cmꢀ1):
m 1669 (s, imine C@N).

224
A. Sood et al. / Polyhedron 56 (2013) 221–229
2.5.4. Synthesis of N-(quinolin-2-ylmethyl)propan-2-amine (L5)
2-Quinolinecarboxaldehyde (1.5 g, 9.5 mmol) and isopropyl-
amine (0.56 g, 9.5 mmol) were dissolved in methanol (5 mL) along
with a catalytic amount of formic acid (2–3 drops) and refluxed for
12 h. The novel ligand L5 was obtained as a yellow oil in 77% yield
(1.45 g) after solvent removal. 1H NMR (200 MHz, CDCl3, TMS) dH
2.6.2. Synthesis of 2-[(phenylimino)methyl]quinoline-Mn(II)Cl2 (2)
MnCl2 (0.30 g, 2.3 mmol) and N-(quinolin-2-ylmethylene)
aniline (L2; 0.55 g, 2.3 mmol) were stirred in THF (20 mL) for
48 h. 2 was isolated as a yellow powder in 81% yield (0.83 g). Anal.
Calc. for C20H20Cl2N2OMn (THF adduct): C, 55.79; H, 4.65; N, 6.51.
Found: C, 56.30; H, 4.48; N, 6.58%. HRMS (m/z), Calc. for [C16H12
ClN2Mn]+: 322.0064. Found: 322.0073 (error 2.84 ppm). FTIR
3
(ppm): 1.318 (6H, d, JHH = 6.2 Hz, CH3), 3.623–3.795 (1H, m,
3
N–CH), 7.542 (1H, q, JHH = 7.4 Hz, H–Ar), 7.671–7.847 (2H, m,
(cmꢀ1):
m 1639 (s, imine C@N).
H–Ar), 8.103–8.182 (3H, m, H–Ar), 8.57 (1H, s, CH@N). HRMS
(m/z), Calc. for [C13H13N2+H]+: 199.1230. Found: 199.1236 (error
2.6.3. Synthesis of 2-[2-benzyl(phenyl-imino)methyl]quinoline-
Mn(II)Cl2 (3)
2.96 ppm). FTIR (cmꢀ1):
m 1640 (s, imine C@N).
MnCl2 (0.50 g, 3.9 mmol) and 2-benzyl-N-(quinolin-2-ylmeth-
ylene)aniline (L3; 1.27 g, 3.9 mmol) were stirred in THF (20 mL)
for 48 h. 3 was obtained as a yellow powder in 74% yield
(1.26 g). Anal. Calc. for C23H18Cl2N2Mn: C, 60.69; H, 4.53; N, 5.24.
Found: C, 60.71; H, 4.90; N, 5.14%. HRMS (m/z), Calc. for [C23H18
ClN2Mn]+: 421.0534. Found: 421.053 (error 0.85 ppm). FTIR
2.5.5. Synthesis of 2,6-diisopropyl-N-(pyridine-2-ylmethylene)aniline
(L6)
The ligand L6 was prepared similarly to L4 by mixing 2-pyri-
dinecarboxaldehyde (1.00 g, 9.3 mmol) and 2,6-diisopropylaniline
(1.65 g, 9.3 mmol). The pure ligand was isolated as yellow block
crystals in 88% yield (1.78 g).
(cmꢀ1):
m 1628 (s, imine C@N).
2.6.4. Synthesis of bis{2-[2-
2.5.6. Synthesis of 2-benzyl-N-(pyridine-2-ylmethylene)aniline (L8)
The procedure is similar to that described above for L2. 2-Pyri-
dinecarboxaldehyde (1.50 g, 14.0 mmol) and 2-benzylaniline
(2.56 g, 14.0 mmol) were mixed and heated at 120 °C overnight
with stirring. L8 was obtained as a thick yellow oil in 80% yield
(2.06 g). 1H NMR (200 MHz, CDCl3, TMS) dH (ppm): 4.18 (2H, s,
(benzyl(phenylimino)methyl]quinoline}Mn(II)Cl2 (4)
MnCl2 (0.55 g. 4.4 mmol) and 1-phenyl-N-(quinolin-2-ylmeth-
ylene)methanamine (L4; 2.15 g, 8.7 mmol) were stirred in THF
(20 mL) for 48 h. 4 was isolated as a yellow powder in 87% yield
(2.43 g). Anal. Calc. for C34H30Cl2N4OMn (H2O adduct): C, 64.16;
H, 4.75; N, 8.80. Found: C, 64.61; H, 4.48; N, 8.65%. HRMS (m/z),
Calc. for [C34H28ClN4Mn]+: 582.1378. Found: 582.1379 (error
3
CH2), 7.02–7.28 (10H, m, H–Ar), 7.70 (1H, t, JHH = 7.0 Hz, H–Py),
3
8.19 (1H, d, JHH = 7.8 Hz, H–Py), 8.50 (1H, s, CH@N), 8.64 (1H, d,
0.33 ppm). FTIR (cmꢀ1):
m 1648 (s, imine C@N).
3JHH = 4.2 Hz, H–Py). HRMS (m/z), Calc. for [C19H16N2+Na]+:
295.1206. Found: 295.1215 (error ꢀ3.21 ppm) FTIR (cmꢀ1):
1629 (s, imine C@N).
m
2.6.5. Synthesis of 2-[isopropylimino)methyl]quinoline-Mn(II)Cl2 (5)
MnCl2 (0.50 g, 3.9 mmol) and N-(quinolin-2-ylmethylene)
propan-2-amine (L5; 0.78 g, 3.9 mmol) were stirred in THF
(20 mL) for 48 h. 5 was obtained as a yellow powder in 75% yield
(0.96 g). Anal. Calc. for C13H14Cl2N2Mn: C, 48.18; H, 4.35; N, 8.64.
Found: C, 48.32; H, 4.31; N, 8.63%. HRMS (m/z), Calc. for [C13H14
ClN2Mn]+: 288.0221. Found: 288.0210 (error 3.49 ppm). FTIR
2.5.7. Synthesis of 1-phenyl-N-(pyridine-2-ylmethylene)methanamine
(L9)
The procedure for L9 is similar to that described above for L4.
2-Pyridinecarboxaldehyde (1.50 g, 14.0 mmol) and phenylmethan-
amine (1.50 g, 14.0 mmol) were mixed. The product was isolated
as a yellow oily liquid in 80% yield (2.21 g).
(cmꢀ1):
m 1633 (s, imine C@N).
2.6.6. Synthesis of 2-[((2,6-diisopropylphenyl)imino)methyl]pyridine-
Mn(II)Cl2 (6)
2.5.8. Synthesis of 2-phenyl-N-(pyridine-2-ylmethylene)ethanamine
(L10)
L10 was prepared similarly to L4 by mixing 2-pyridinecarboxal-
dehyde (1.50 g, 14.0 mmol) and 2-phenylethanamine (1.70 g,
14.0 mmol). The pure ligand was isolated as a thick yellow oil in
77% yield (2.27 g).
MnCl2 (0.50 g, 3.9 mmol) and 2,6-diisopropyl-N-(pyridin-2-
ylmethylene)aniline (L6; 1.06 g, 3.9 mmol) were stirred in THF
(20 mL) for 48 h. 6 was isolated as a yellow powder in 80% yield
(1.25 g). Crystals suitable for X-ray studies were obtained from
methanol with a few drops of n-hexane. Anal. Calc. for C18H22Cl2N2
Mn: C, 55.12; H, 5.68; N, 7.14. Found: C, 55.38; H, 5.65; N, 7.30%.
HRMS (m/z), Calc. for [C18H22ClN2Mn]+: 356.0847. Found:
356.0856 (error ꢀ2.60 ppm). FTIR (cmꢀ1):
m 1632 (s, imine C@N).
2.6. Syntheses of complexes 1–10
2.6.7. Synthesis of bis{2-[(phenylimino)methyl]pyridine}Mn(II)Cl2 (7)
MnCl2 (0.50 g. 3.9 mmol) and N-(pyridine-2-ylmethylene)ani-
line (L7; 1.44 g, 7.9 mmol) were stirred in THF (20 mL) for 48 h. 7
was isolated as a yellow powder in 86% yield (1.68 g). Crystals suit-
able for X-ray structure determination were obtained both from
methanol and from methanol with a few drops of toluene. Anal.
Calc. for C24H20Cl2N4Mn: C, 58.79; H, 4.11; N, 11.43. Found: C,
58.35; H, 4.11; N 11.14%. HRMS (m/z), Calc. for [C24H20N4Cl2
Mn+Na]+: 512.0338. Found: 512.0316 (error 4.19 ppm). FTIR
Literature procedures [7b,7c] were modified for the preparation
of complexes 1–10. 2–10 were isolated and purified using the same
methods as described for 1. Complexes 1, 4, 7, 8, 9 and 10 are stable
with 1:2 stoichiometric ratios of Mn to ligand, while 2, 3, 5 and 6
are stable with a 1:1 ratio.
2.6.1. Synthesis of bis{2-[((2,6-
diisopropylphenyl)imino)methyl]quinoline}-Mn(II)Cl2 (1)
MnCl2 (0.19 g, 1.5 mmol) and 2,6-bis(1-methylethyl)-N-(2-
quinoline-2-methylene)-phenylamine (L1; 1.00 g, 3.1 mmol) were
stirred in toluene (20 mL). The solution slowly turned yellow and
stirring was continued for 48 h at room temperature. The yellow
product was filtered and washed with THF (2 ꢃ 10 mL) and Et2O
(2 ꢃ 10 mL), and then dried under vacuum. Yield 90% (1.03 g).
HRMS (m/z), Calc. for [C44H48 Cl2N4Mn+H]+: 758.2709. Found:
(cmꢀ1):
m 1632 (s, imine C@N).
2.6.8. Synthesis of bis{2-[(2-(phenyl-2-benzyl)
imino)methyl]pyridine}Mn(II)Cl2 (8)
MnCl2 (0.30 g. 2.3 mmol) and 2-benzyl-N-(pyridine-2-ylmeth-
ylene)aniline (L8; 1.30 g, 4.7 mmol) were stirred in THF (20 mL)
for 48 h. 8 was obtained as a yellow powder in 75% yield
(1.23 g). Anal. Calc. for C38H34Cl2N4OMn: C, 66.29; H, 4.98; N,
758.2686 (error 3.01 ppm). FTIR (cmꢀ1):
m 1633 (s, imine C@N).

A. Sood et al. / Polyhedron 56 (2013) 221–229
225
Table 2
8.14. Found: C, 66.71; H, 4.86; N, 7.62%. HRMS (m/z), Calc. for
[C38H32ClN4Mn]+: 634.1691. Found: 634.1705 (error 4.19 ppm).
FTIR (cmꢀ1):
1637 (s, imine C@N).
Selected bond lengths (Å) and angles (°) in 6.
m
Mn1–N2(pyridyl)
Mn1–N1(imino)
Mn1–Cl1
Mn1–Cl2
Mn1–Cl1A
2.237(2)
2.307(2)
2.462(9)
2.337(10)
2.531(9)
3.645(11)
Cl1–Mn1–ClA
N2–Mn1–N1
Mn1–Cl1–Mn1A
N2–Mn1–Cl2
N1–Mn1–Cl2
N2–Mn1–Cl1
86.2(3)
73.46(9)
93.77(3)
102.25(7)
104.82(7)
141.84(6)
90.30(6)
2.6.9. Synthesis of bis{2-[(2-(benzyl)imino)methyl]pyridine}Mn(II)Cl2
(9)
Mn1–Mn1A
MnCl2 (0.50 g. 3.9 mmol) and 1-phenyl-N-(pyridine-2-ylmethyl-
ene)methanamine (L9; 1.55 g, 7.9 mmol) were stirred in THF
(20 mL) for 48 h. 9 was isolated as a pale yellow powder in 84% yield
(1.73 g). Crystalssuitable for X-ray studies were obtained by dissolv-
ing the complex in methanol with a few drops of n-hexane. The solu-
tion was kept in a deep freezer for 24 h, resulting in the formation of
yellow transparent crystals. Anal. Calc. for C26H24Cl2N4Mn: C, 60.25;
H, 4.67; N, 10.80. Found: C, 59.87; H, 4.96; N, 10.58%. HRMS (m/z),
Calc. for [C26H24N4Cl2Mn+Na]+: 540.0656. Found: 540.0651 (error
N1–Mn1–Cl1
Cl2–Mn1–Cl1
N2–Mn1–Cl1A
N1–Mn1–Cl1A
Cl2–Mn1–Cl1A
N2–Mn1–Mn1A
N1–Mn1–Mn1A
Cl2–Mn1–Mn1A
Cl1–Mn1–Mn1A
Cl1A–Mn1–Mn1A
115.37(4)
88.76(7)
146.02(6)
107.18(4)
121.07(6)
125.41(6)
119.64(4)
43.86(2)
42.38(2)
3.51 ppm). FTIR (cmꢀ1):
m 1645 (s, imine C@N).
2.6.10. Synthesis of bis{2-[(2-
(phenylethyl)imino)methyl]pyridine}Mn(II)Cl2 (10)
distances of 2.463(9) and 2.532(9) Å. The noted distances are
similar to previously observed values [10].
MnCl2 (0.30 g, 2.3 mmol) and 1-phenyl-N-(pyridine-2-ylmeth-
ylene) ethanamine (L10; 0.99 g, 4.7 mmol) were stirred in THF
(20 mL) for 48 h. 10 was isolated as a yellow powder in 74% yield
(0.96 g). Anal. Calc. for C28H30Cl2N4OMn (H2O adduct): C, 59.58;
H, 5.36; N, 9.93. Found: C, 59.92; H, 5.03; N, 9.88%. HRMS (m/z),
Calc. for [C28H28ClN4Mn]+: 510.1378. Found: 510.1383 (error
The Mn(II) center has a distorted octahedral geometry in
complex 7. In Fig. 2 is shown only the structure of 7ꢂ0.5 C7H8, as
in the structure of 7ꢂCH3OH the only difference is the solvent
molecule. Atoms Cl2 and N1 (imino) are axially coordinated to
the Mn center and the Cl1, N2, N21 and N22 atoms occupy the
equatorial positions. The Mn atom deviates only slightly (0.20 Å)
from the equatorial plane. The structure is distorted, as indicated
by the N1–Mn1–Cl2 (158.50(5)°), N21–Mn1–Cl1 (158.45(5)°) and
N2–Mn1–N22 (157.23(7)°) bond angles. The benzyl substituents
are located on opposite sites of the equatorial plane.
1.11 ppm). FTIR (cmꢀ1):
m 1647 (s, imine C@N).
3. Results and discussion
3.1. Ligand and complex synthesis
Complex 9 was crystallized from methanol with a solvent
molecule hydrogen-bonded to one of the chlorine ligands (Fig. 3).
The hydrogen bond distance O1M–Hꢂ ꢂ ꢂCl1 is 2.204(2) Å, which
indicates a moderate interaction [17]. Similarly to complex 7, there
is a distorted octahedral coordination sphere around the Mn(II)
center. The pyridyl nitrogens (N1, N16), the imino nitrogen (N8)
and the Cl2 atom form an equatorial plane, leaving the Cl1 and
N23 atoms in the apical positions. The structure is distorted, as
indicated by the Cl2–Mn1–N8 (164.5(3)°), Cl1–Mn1–N23
(165.7(3)°) and N16–Mn1–N1 (155.4(4)°) bond angles. The benzyl
substituents are located on the opposite sites of the equatorial
plane and are bent towards the Mn center.
A series of nitrogen containing bidentate ligands (L1–L10) were
synthesized in good to high yields by the condensation of 8-quin-
oline carboxaldehyde or 2-pyridine carboxaldehyde with various
aromatic and aliphatic amines, typically under solvent-free condi-
tions. Steric and electronic diversities were also provided by
varying the substituents of the aromatic amines. Complexes 1–10
were synthesized under Ar in high yields by stirring anhydrous
MnCl2 and a ligand in the proper solvent for 48 h at room temper-
ature [11]. All the complexations were carried out with metal to
ligand ratios of 1:1 and 1:2, but with each ligand only one kind
of complex was obtained. In complexes 2, 3, 5 and 6 the Mn center
prefers to coordinate to one ligand, whereas in 1, 4 and 7–10 it
coordinates to two ligands.
3.3. Magnetic properties of complexes 6 and 9
3.2. Crystal structures
The temperature dependence of vM and vMT for complex 6 (vM
is the molar magnetic susceptibility per Mn2 unit) in an applied
Crystal structures were determined for complexes 6, 7 and 9
(Table 1) and for L3ꢂMeOH1. The structures of the complexes reveal
coordination arrangements typical of Mn(II) Schiff base complexes
[6f,15] and they are discussed below in more detail. In all the struc-
tures the Mn–N(pyridyl) (2.236(2)–2.271(2) Å) bond distances are
shorter than the Mn–N(imidyl) distances (2.307(2)–2.436(19) Å)
(Tables 2–4). The Mn–Cl (2.337(10)–2.484(4) Å) bond lengths are
within the typical range for Mn(II) complexes [6f,15].
Complex 6 was crystallized from methanol with a dimeric
structure (Fig. 1). The iminopyridyl ligands are coordinated in a
bidentate manner to the Mn(II) centers. Each five coordinated
Mn(II) has a distorted square pyramidal geometry where the Cl2
and Cl2A atoms occupy the apical positions. The equatorial posi-
tions are occupied by N1A, N2A, Cl1A and Cl1 as well as by N1,
N2, Cl1 and Cl1A atoms. The Mn centers, which are 3.646(11) Å
apart, are displaced by 0.72 Å from the planes formed by the atoms
in the equatorial positions. The two Mn centers and the bridging
Cl1 and Cl1A atoms form a square plane with Mn–Cl bond
magnetic field of 0.5 T is displayed in Fig. 4.
The value of
close to that expected for two uncoupled Mn2+ ions (g = 2, S =
5/2) of 8.75 cm3 K molꢀ1. The
MT value shows a slight decrease
v
MT at room temperature (9.20 cm3 K molꢀ1) is
v
with decreasing temperature in the 25–300 K range, followed by
a sharp decrease until 2 K to a value of 2.94 cm3 K molꢀ1. This indi-
cates presence of very weak antiferromagnetic interactions
between the Mn2+ ions through the chloride-bridging atoms. In
keeping with this, the thermal variation of vM shows a maximum
near 4 K. Simulation of the magnetic susceptibility data with the
Hamiltonian H = ꢀJ(SMnSMn) and using the MAGMUN program [18]
yielded an average g = 2.04(6) and J = ꢀ0.46(6) cmꢀ1. The intermo-
lecular interactions through Clꢂ ꢂ ꢂH contacts and the ZFS effects
were considered to be negligible and are included in the extracted
J value. The magnitude of the J value for 6 is not unexpected in
view of the results obtained for analogous compounds with similar
bridging angles, for which very weak magnetic couplings were also
observed [19].

226
A. Sood et al. / Polyhedron 56 (2013) 221–229
Table 3
Selected bond lengths (Å) and angles (°) in 7ꢂ0.5 C7H8 and 7ꢂCH3OH [in brackets].
Mn1–N2(pyridyl)
Mn1–N22(pyridyl)
Mn1–N1(imino)
Mn1–N21(imino)
Mn1–Cl1(equatorial)
Mn1–Cl2(axial)
2.265(2) [2.2647(18)]
2.271(2) [2.2656(15)]
2.436(19) [2.4143(15)]
2.346(2) [2.3563(18)]
2.418(7) [2.4094(10)]
2.444(7) [2.4640(7)]
N2–Mn1–N22
N2–Mn1–N21
N22–Mn1–N21
N2–Mn1–Cl1
N22–Mn1–Cl1
N21–Mn1–Cl1
N2–Mn1–N1
N22–Mn1–N1
N21–Mn1–N1
Cl1–Mn1–N1
N2–Mn1–Cl2
N22–Mn1–Cl2
N21–Mn1–Cl2
Cl1–Mn1–Cl2
N1–Mn1–Cl2
157.23(7) [155.31(6)]
91.91(7) [89.92(6)]
71.51(7) [71.48(7)]
98.89(5) [101.53(4)]
92.48(6) [95.23(4)]
158.45(5) [160.05(4)]
70.31(7) [70.58(5)]
89.64(7) [89.92(6)]
73.55(7) [73.98(5)]
92.54(5) [92.57(4)]
92.87(5) [95.23(4)]
103.61(5) [101.53(4)]
94.41(5) [94.45(4)]
103.55(3) [101.693(18)]
158.50(5) [162.57(4)]
Table 4
Selected bond lengths (Å) and angles (°) in 9ꢂCH3OH.
The magnetic properties of compound 9 in the form of the
temperature dependence of MT ( M is the molar magnetic suscep-
tibility per Mn2+ unit) under an applied magnetic field of 0.1 T are
v
v
Mn1–N1(pyridyl)
Mn1–N16(pyridyl)
Mn1–N23(imino)
Mn1–N8(imino)
Mn1–Cl1
2.268(11)
2.271(11)
2.339(11)
2.348(11)
2.484(4)
2.441(4)
N1–Mn1–N16
155.47(4)
94.91(4)
72.44(4)
71.75(4)
87.76(4)
93.43(4)
92.86(3)
106.73(3)
85.97(3)
164.51(3)
98.74(3)
93.34(3)
165.74(3)
86.97(3)
97.405(14)
shown in Fig. 6. The
v
MT value at room temperature (4.55 cm3 -
N1–Mn1–N23
N16–Mn1–N23
N1–Mn1–N8
N16–Mn1–N8
N23–Mn1–C8
N1–Mn1–Cl2
N16–Mn1–Cl2
N23–Mn1–Cl2
N8–Mn1–Cl2
N1–Mn1–Cl1
N16–Mn1–Cl1
N23–Mn1–Cl1
N8–Mn1–Cl1
Cl2–Mn1–Cl1
K molꢀ1) is close to the value of 4.375 cm3 K molꢀ1 expected for
an isolated Mn2+ ion with g = 2 and S = 5/2. When the temperature
is decreased, the
vMT value remains almost constant and follows
Mn1–Cl2
the Curie behavior between 300 and 20 K. Below 20 K, the
vMT
value undergoes an abrupt decrease, reaching a value of 3.69 cm3 -
K molꢀ1 at 2 K. This behavior is most likely due to the existence of
6
intermolecular interactions and/or ZFS effects of the A1g ground
state of the Mn2+ ion. The susceptibility data was fitted to the
theoretical equation for a mononuclear Mn2+ complex with zero-
6
field splitting of the A1g ground state [20]. A parameter (zJ0)
accounting for the intermolecular interactions in the molecular
field approximation was included in the theoretical equation. Two
types of fits of almost equal quality were performed with either
zJ0 or DMn fixed to zero, giving rise to the following parameters:
g = 2.027(3) and |DMn| = 2.7(1) cmꢀ1 with zJ0 = 0 and g = 2.031(3)
and zJ0 = ꢀ0.02(1) cmꢀ1 with DMn = 0. The DMn and zJ0 values can
be considered as the limiting values for these parameters, as zJ0
and DMn are strongly correlated. The calculated DMn value is clearly
overestimated as the Mn2+ ion is highly isotropic, thus indicating
that it must also contain an intermolecular contribution. It should
The field dependence of the magnetization at 2 K is given in
Fig. 5. The curve exhibits a sigmoidal shape at low field, which
agrees well with the existence of a weak antiferromagnetic
interaction between the Mn2+ ions. The 9.6 N
l
B value of the mag-
netization at the maximum applied field of 5 T is close to the
expected saturation value for two S = 5/2 metal ions (10 N B).
l
The magnetization data was perfectly simulated with parameters
extracted from the susceptibility data.
Fig. 1. Molecular structure of 6. Displacement parameters are drawn at 50% probability level. H-atoms are omitted for clarity.

A. Sood et al. / Polyhedron 56 (2013) 221–229
227
Fig. 2. Molecular structure of complex 7ꢂ0.5 C7H8. Displacement parameters are drawn at 50% probability level. H-atoms and toluene solvent molecule are omitted for clarity.
be noted that data simulations have demonstrated that small
changes in zJ0 have the same effect as significant changes in DMn
3.4. Ethene polymerization
.
The M versus H plot at 2 K for complex 9 is given in the inset of
Fig. 6. The magnetization data is below the Brillouin function,
which confirms the existence of antiferromagnetic interactions
and/or zero-field splitting effects of the ground state in this
compound. As expected, due to the weakness of the above interac-
tions, the 4.79 NlB magnetization value at the maximum applied
The catalytic properties of MAO activated complexes 1–10 were
studied for ethene polymerization (Table 5). The MAO activation
was performed at room temperature, as in our previous study it
was noticed that when the activation was done at an elevated tem-
perature the catalytic activities were significantly poorer [6a]. The
polymerizations were performed at 60 °C in toluene under 5 bar of
ethene pressure. Complexes 1 and 6–10 showed polymerization
field of 5 T is close to the saturation value (5 NlB).
Fig. 3. Molecular structure of complex 9ꢂCH3OH with a coordinated methanol solvent molecule. Displacement parameters are drawn at 50% probability level. H-atoms are
omitted for clarity.

228
A. Sood et al. / Polyhedron 56 (2013) 221–229
Table 5
Results of ethene polymerizations with MAO activated complexes 1–10.
a
d
e
f
Complex ncat
mol)
[Al]:[Mn]b Activityc
Mw
Mw/Mn
Tm
(
l
kgPE/(ncat ⁄ h) (g/mol)
(°C)
1
2
3
4
5
6
7
8
9
10
20
20
4
20
20
4
20
20
4
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
39
296 000 2.55
133
140
137
–
traces
traces
traces
traces
10
77
14
24
12
–
–
–
–
–
–
–
–
–
399 000 2.29
319 000 2.41
310 000 2.31
313 000 2.39
398 000 2.15
136
137
135
134
136
20
Polymerization conditions: toluene 100 mL, ethene pressure 5.0 bar, 60 °C,
overnight.
a
Amount of catalyst.
Cocatalyst:catalyst ratio with MAO.
Catalyst productivity, calculated as kg of polyethene per mole of catalyst in 1 h.
Weight average molar mass.
Polydispersity.
Peak melting temperature by DSC.
b
Fig. 4. Temperature dependence of
vMT for 6. Inset: Temperature dependence of
c
vM for 6 in the low temperature region. Solid lines represent the best fit to the
theoretical equation.
d
e
f
[6c,6f,7a–d] and therefore it can be concluded that most Mn
complexes have inherently relatively low activities for olefin poly-
merization. All the active catalysts produced a high molecular
weight polyethene (296000–399000 g/mol) with a typical peak
melting temperature (133–140 °C). In all cases the molar mass
distribution was very narrow (2.15–2.55), which indicates that
the complexes polymerize ethene with a single-site mechanism.
We also studied the tri-isobutylaluminum (TIBA)/N,N-dimethylan-
ilium tetrakis(pentafluorophenyl) borate activated complexes, but
they were not active for ethene polymerization.
4. Conclusions
Fig. 5. Field dependence of the magnetization at 2 K for 6. The solid line
corresponds to the curve simulated using the magnetic parameters of g = 2.04
An easy and convenient method to prepare scorpionate
Mn(II)Cl2 complexes with bidentate N,N0-imine-pyridine and
N,N0-imine-quinoline-type donor ligands was introduced. In the
ligand synthesis, a solvent-free method was typically employed,
whereas the complexes were successfully prepared in high yields
under mild reaction conditions (room temperature, 48 h). Complex
6 crystallized in a dimeric square-pyramidal geometry, whereas 7
and 9 have distorted octahedral crystal structures. Magnetic stud-
ies on the high spin complexes 6 and 9 showed that the former
and J = ꢀ0.46 cmꢀ1
.
exhibits
a weak intramolecular antiferromagnetic interaction
through the chloride-bridging ligands with a magnetic exchange
coupling J = ꢀ0.46(6) cmꢀ1, whereas the latter, as expected for its
mononuclear structure, only shows very weak intermolecular
interactions and/or zero-field splitting effects.
Mn complexes have only recently raised interest as catalysts in
ethene polymerization and consequently such studies are still
scarce. Six of the studied Mn(II) complexes (1, 6–10), when
activated with MAO, were able to catalyze low pressure ethene
polymerization to high molar mass polyethene. The complexes
catalyzed polymerization with a single-site mechanism. In accor-
dance with previous studies in the literature, the activities of the
complexes remained relatively low, but the obtained results clearly
show that the ligand has a significant effect on the activity of the
complex.
Fig. 6. Temperature dependence of
to the theoretical equation. Inset: Field dependence of the magnetization at 2 K. The
solid line corresponds to the Brillouin function for g = 2.03 and S = 5/2.
vMT for 9. The solid line represents the best fit
activity, 7 being the most active catalyst (77 kgPE/(ncat ⁄ h)). The
notable differences observed in the polymerization activities of
the complexes show that the ligand system has an evident effect
on the activity. Generally the active catalysts are the six coordi-
nated complexes with a metal to ligand ratio of 1:2 (1 and 7–10).
The only active catalyst with a 1:1 ligand/metal ratio is 6, having
a five coordinated dimeric structure. The observed catalytic activ-
ities are in accordance with results presented in the literature
Appendix A. Supplementary data
CCDC 761362, 761363, 761364, 761365 and 919665 contain the
supplementary crystallographic data for L3, 6, 7ꢂ0.5 C7H8, 9 and
7ꢂMeOH. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge

A. Sood et al. / Polyhedron 56 (2013) 221–229
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