Novel Cobalt(II) complexes containing N,N-di(2-picolyl)amine based ligands; Synthesis, characterization and application towards methyl methacrylate polymerisation

Article abstract of DOI:10.1016/j.molstruc.2016.02.022

The reaction of [CoCl₂·6H₂O] with N′-substituted N,N-di(2-picolyl)amine ligands such as 1-cyclohexyl-N,N-bis(pyridin-2-ylmethyl)methanamine (L_A), 2-methoxy-N,N-bis(pyridin-2-ylmethyl)ethan-1-amine (L_B), and 3-methoxy-N,N-bis(pyridin-2-ylmethyl)propan-1-amine (L_C), yielded [L_nCoCl₂] (L_n = L_A, L_B and L_C), respectively. The Co(II) centre in [L_nCoCl₂] (L_n = L_A, and L_C) adopted distorted bipyramidal geometries through coordination of nitrogen atoms of di(2-picolyl)amine moiety to the Co(II) centre along with two chloro ligands. The 6-coordinated [L_BCoCl₂] showed a distorted octahedral geometry, achieved through coordination of the two pyridyl units, two chloro units, and bidentate coordination of nitrogen and oxygen in the N′-methoxyethylamine to the Co(II) centre. [L_CCoCl₂] (6.70 × 10⁴ gPMMA/molCo h) exhibited higher catalytic activity for the polymerisation of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) compared to rest of Co(II) complexes. The catalytic activity was considered as a function of steric properties of ligand architecture and increased steric bulk around the metal centre resulted in the decrease catalytic activity. All Co(II) initiators yielded syndiotactic poly(methylmethacrylate) (PMMA).

Full text of DOI:10.1016/j.molstruc.2016.02.022

Journal of Molecular Structure 1113 (2016) 24e31
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Novel Cobalt(II) complexes containing N,N-di(2-picolyl)amine based
ligands; Synthesis, characterization and application towards methyl
methacrylate polymerisation
,
, *
Seoung Hyun Ahn a, Sang-Il Choi a, Maeng Joon Jung a, Saira Nayab b **, Hyosun Lee a
a Department of Chemistry and Green-Nano Materials Research Center, Kyungpook National University, 1370 Sankyuk-dong, Buk-gu, Daegu-city, 702-701,
Republic of Korea
b Department of Chemistry, Shaheed Benazir Bhutto University, Sheringal Dir (U), Khyber Pakhtunkhwa, Pakistan
a r t i c l e i n f o
a b s t r a c t
The reaction of [CoCl2$6H2O] with N0-substituted N,N-di(2-picolyl)amine ligands such as 1-cyclohexyl-
N,N-bis(pyridin-2-ylmethyl)methanamine (LA), 2-methoxy-N,N-bis(pyridin-2-ylmethyl)ethan-1-amine
(LB), and 3-methoxy-N,N-bis(pyridin-2-ylmethyl)propan-1-amine (LC), yielded [LnCoCl2] (Ln ¼ LA, LB
and LC), respectively. The Co(II) centre in [LnCoCl2] (Ln ¼ LA, and LC) adopted distorted bipyramidal ge-
ometries through coordination of nitrogen atoms of di(2-picolyl)amine moiety to the Co(II) centre along
with two chloro ligands. The 6-coordinated [LBCoCl2] showed a distorted octahedral geometry, achieved
through coordination of the two pyridyl units, two chloro units, and bidentate coordination of nitrogen
and oxygen in the N0-methoxyethylamine to the Co(II) centre. [LCCoCl2] (6.70 ꢀ 104 gPMMA/molCo h)
exhibited higher catalytic activity for the polymerisation of methyl methacrylate (MMA) in the presence
of modified methylaluminoxane (MMAO) compared to rest of Co(II) complexes. The catalytic activity was
considered as a function of steric properties of ligand architecture and increased steric bulk around the
metal centre resulted in the decrease catalytic activity. All Co(II) initiators yielded syndiotactic poly(-
methylmethacrylate) (PMMA).
Article history:
Received 22 December 2015
Received in revised form
5 February 2016
Accepted 5 February 2016
Available online 11 February 2016
Keywords:
Cobalt(II) complexes
N0-substituted N,N-di(2-picolyl)amine
MMA polymerisation
Syndiotactic PMMA
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
initiation, propagation and termination [4e8]. Late transition metal
complexes, due to their less oxophilic nature makes them likely
Metal-catalysed coordination polymerisation of methyl meth-
acrylate (MMA) have gained much attention recently due to the
ability (of coordinationeaddition polymerisation) to rapidly pro-
targets for the development of catalysts for the polymerisation of
polar monomers such as methyl methacrylate (MMA) [9e14].
Syndiotactic PMMA (rr ¼ 0.72) produced via late transition metal
catalysts was first described with Cp2NieMAO [15]. Since then,
important research has been conducted with late transition metal
complexes such as (a-diimine)nickel, (pyridyl bisimine)iron(II), and
(pyridyl bisimine)cobalt(II) complexes activated with MAO that
resulted in PMMA with moderate syndiotacticity [16].
Recently reported by our group are Pd(II), Zn(II), Cu(II) and Pt(II)
based catalytic systems with N0-substituted N,N-di(2-picolyl)amine
ligands that yielded PMMA with moderate syndiotacticity [17e19].
Ligand architecture having N,N-di(2-picolyl)amine moiety and its
various N0-substituted derivatives are known to form diverse co-
ordination geometries from mononuclear to poly-nuclear with
transition metals [20e34]. Furthermore the stereo-electronic
properties of these ligands can be easily tuned by appropriate
choice of substituents on pyridine ring or amine residue or on both
moieties [35e42]. Thus keeping in view the importance and
duce high molecular weight (MW) poly(methylmethacrylate)
(PMMA) with controlled stereoregularity [1]. The optical properties
of PMMA are far improved with high glass transition temperature
(Tg) which in turn depend on tacticity of PMMA (Tg of isotactic
PMMA is about 65 ꢁC, whereas syndiotactic PMMA exhibits Tg
around 140 ꢁC). That is why many attempts aiming to increase the
syndiotacticity of PMMA were planned [2,3]. Transition metal
complexes with appropriate ancillary ligand are crucial for
achieving high degree of control over polymerisation as these
metal complexes influence all steps of polymerisation such as
* Corresponding author.
** Corresponding author.
E-mail address: hyosunlee@knu.ac.kr (H. Lee).
http://dx.doi.org/10.1016/j.molstruc.2016.02.022
0022-2860/© 2016 Elsevier B.V. All rights reserved.

S.H. Ahn et al. / Journal of Molecular Structure 1113 (2016) 24e31
25
versatility of these architectures we explored several structural
variations of N0-substituted N,N-di(2-picolyl)amine based com-
plexes and their effect on MMA polymerisation [43].
and CoCl2$6H2O (0.119 g, 0.500 mmol). The purple solid was ob-
tained as final product (0.174 g, 89.7%). X-ray quality crystals were
obtained by diffusion of methylene chloride into hexane solution of
[LBCoCl2]. Analysis calculated for C15H19Cl2CoN3O: C, 46.53; H,
4.95; N, 10.85. Found: C, 45.80; H, 4.98; N, 10.80%. IR (Solid neat;
cmꢂ1): 3016 (w), 2994 (w), 2971 (w), 1602 (s), 1558 (w), 1473 (m),
1435 (s), 1289 (m), 1147 (m), 1118 (s), 1086 (m), 1019 (s), 850 (m),
835 (m), 766 (s).
In a continuation of our research work which has been synthesis
and structure determination of transition metal complexes as a pre-
catalyst towards MMA polymerisation, the current work has been
focused on synthesis of Co(II) complexes bearing tridentate N0-
substituted N,N-di(2-picolyl)amine with various steric and elec-
tronic properties and their X-ray structure analysis. Additionally
[LnCoCl2] (Ln ¼ LA, LB, and LC) complexes as a catalysts are evaluated
for their catalytic activities in MMA polymerisation as a function of
steric bulk around the metal centre.
2.2.3. [3-Methoxy-N,N-bis(pyridin-2-ylmethyl)propan-1amine]
cobalt(II) chloride ([LCCoCl2])
Synthesis of [LCCoCl2] was carried out using same manner as
described for [LACoCl2], except utilizing LC (0.135 g, 0.500 mmol)
and CoCl2$6H2O (0.119 g, 0.500 mmol). The purple solid was filtered
and washed with EtOH (25.0 mL ꢀ 2), followed by washing with
Et2O (25.0 mL ꢀ 2) (0.177 g, 88.8%). X-ray quality crystals were
obtained by diffusion of diethyl ether into dimethylformamide
solution of [LCCoCl2]. Analysis calculated for C16H21Cl2CoN3O: C,
47.90; H, 5.28; N, 10.47. Found: C, 48.16; H, 5.37; N, 10.48%. IR (Solid
neat; cmꢂ1): 3029 (w), 2936 (w), 2927 (w), 2913 (w),1605 (m),1570
(w), 1479 (m), 1445 (m), 1393 (m), 1310 (w), 1114 (s), 1053 (m), 1024
(m), 963 (m), 864 (m), 777 (s).
2. Experimental
2.1. Physical measurements
CoCl2$6H2O,
2-picolylchloride
hydrochloride,
cyclo-
hexylmethylamine, 2-methoxyethanamine, 3-methoxypropan-1-
amine, KOH, and methylmethacrylate (MMA) were purchased
from SigmaeAldrich (St. Louis, MO) and anhydrous solvents such as
C2H5OH, DMF, Et2O, and CH2Cl2 were purchased from Merck
(Darmstadt, Germany) and used without further purification. The
deionized water was prepared using a Millipore Milli-Q water
system (Bedford, MA). Modified methylaluminoxane (MMAO) was
purchased from Tosoh Finechem Corporation (Tokyo, Japan) as 6.9%
aluminium (by weight) in a toluene solution and used without
2.3. X-ray crystallographic studies
further purification. Synthesis
of N,N-di(2-picolyl)cyclo-
An X-ray-quality single crystal was coated with paratone-N oil
and the diffraction data measured at 100(2) K with synchrotron
hexylmethylamine (LA) [44], 2-methoxy-N,N-bis(pyridin-2-
ylmethyl)ethanamine (LB) and 3-methoxy-N,N-bis(pyridin-2-
ylmethyl)propan-1-amine (LC) [45], was carried out utilizing pre-
viously reported procedures. Elemental analyses (C, H, N) of the
prepared complexes were performed on an elemental analyzer (EA
1108; Carlo-Erba, Milan, Italy). 1H NMR (operating at 400 MHz) and
13C NMR (operating at 100 MHz) spectra of ligands were recorded
on an Advance Digital 400 NMR spectrometer (Bruker, Billerica,
radiation (
l
¼ 0.71073 Å) for [LACoCl2] and ( ¼ 0.63000 Å) for
l
[LBCoCl2] and [LCCoCl2], respectively on an ADSC Quantum-210
detector at 2D SMC with a silicon (111) double crystal mono-
chromator (DCM) at the Pohang Accelerator Laboratory, South
Korea. The ADSC Q210 ADX program [46] was used for data
collection (detector distance is 63 mm, omega scan; Du ¼ 1ꢁ,
exposure time is 1 s per frame) and HKL3000sm (Ver. 703r) [47]
was used for cell refinement, reduction and absorption correction
(Tmin ¼ 0.868, Tmax ¼ 0.962). Structures were solved by direct
methods, and refined by full-matrix least-squares refinement using
the SHELXL-2014 [48] computer program. The positions of all non-
hydrogen atoms were refined with anisotropic displacement fac-
tors. All hydrogen atoms were placed using a riding model, and
their positions were constrained relative to their parent atoms
using the appropriate HFIX command in SHELXL-2014.
MA); chemical shifts were recorded in ppm units (d) relative to
SiMe4 as the internal standard. Infrared (IR) spectra were recorded
on a Bruker FT/IR-Alpha (neat) and the absorbance frequencies are
reported in reciprocal centimetres (cmꢂ1). The molecular weights
and molecular weight distribution of the obtained poly(-
methylmethacrylate) (PMMA) were determined using gel perme-
ation chromatography (GPC) (CHCl3, Alliance e2695; Waters Corp.,
Milford, MA). Glass transition temperature (Tg) was determined
using a thermal analyzer (Q2000; TA Instruments, New Castle, DE).
2.2. Synthesis of Co(II) complexes
2.4. MMA polymerisation studies
2.2.1. [N,N-di(2-picolyl)cyclohexylmethylamine]cobalt(II) chloride
([LACoCl2])
The methyl methacrylate (MMA) was extracted with 10% NaOH,
washed with water, dried over MgSO4 and distilled over CaH2 un-
der reduced pressure before use. In a Schlenk line, complex
Ethanolic solution of LA (0.148 g, 0.500 mmol) was treated with
ethanolic solution of CoCl2$6H2O (0.119 g, 0.500 mol) and stirred for
12 h at ambient temperature. The purple precipitate was filtered
and washed with EtOH (25.0 mL ꢀ 2), followed by washing with
Et2O (25.0 mL ꢀ 2) to get final product (0.185 g, 85.0%). X-ray quality
crystals were obtained by diffusion of diethyl ether into acetone
solution of [LACoCl2]. Analysis calculated for C19H25Cl2CoN3: C,
53.66; H, 5.93; N, 9.88. Found: C, 53.74; H, 5.96; N, 9.77%. IR (Solid
neat; cmꢂ1): 2916 (w), 2850 (w), 1606 (m), 1560 (s), 1481 (w), 1441
(m), 1303 (m), 1099 (m), 1025 (m), 981 (m), 772 (s).
(15.0 mmol, 8.20 mg for [LACoCl2]; 7.90 mg for [LBCoCl2]; 8.20 mg
for [LCCoCl2] was dissolved in dried toluene (10.0 mL) followed by
the addition of modified MMAO (6.90 wt% in toluene, 3.25 mL,
7.50 mmol, and [MMAO]0/[Co(II) catalyst]0 ¼ 500) as a co-catalyst.
The solution was stirred at 60 ꢁC for 20 min. The MMA (5.00 mL,
47.1 mmol, [MMA]0/[Co(II) catalyst]0 ¼ 3100) was added to the
above reaction mixture and stirred at 60 ꢁC for 2 h to obtain a
viscous solution. MeOH (2.00 mL) was added to terminate the
polymerisation. The reaction mixture was poured into a large
quantity of MeOH (500 mL), and 35% HCl (5.00 mL) was injected to
remove the remaining co-catalyst (MMAO). The resulting polymer
was filtered and washed with MeOH (250 mL ꢀ 2) to yield poly(-
methyl methacrylate) (PMMA), which was vacuum-dried at 60 ꢁC.
2.2.2. [2-Methoxy-N,N-bis(pyridin-2-ylmethyl)ethanamine]
cobalt(II) chloride ([LBCoCl2])
Synthesis of [LBCoCl2] was carried out using same manner as
described for [LACoCl2], except utilizing LB (0.129 g, 0.500 mmol)

26
S.H. Ahn et al. / Journal of Molecular Structure 1113 (2016) 24e31
Scheme 1. Synthetic route for Co(II) complexes.
3. Results and discussion
controlled polymerisation. In this regards N,N-di(2-picolyl)amine
based precursors with various N0-substituents are promising li-
gands in organometallic catalysis. These ligands were easily ob-
tained via the condensation of 2-picoline amine and primary amine
with various R groups in single straightforward step in facile yield
[44,45]. The complexation reactions are performed in EtOH at room
3.1. Synthetic and spectral aspects
The design of new ligands with diverse coordination modes
with transition metals is a current challenge in the field of
Table 1
Crystal data and structural refinement for synthesized Co(II) complexes.
[LACoCl2]
[LBCoCl2]
[LCCoCl2]
Empirical formula
Formula weight
C19H25Cl2CoN3
425.25
C15H19Cl2CoN3O
387.16
C16H21Cl2CoN3O
401.19
Temperature K
200(2)
100(2)
100(2)
Wavelength (Å)
Crystal system
Space group
0.71073
Monoclinic
P21/c
0.630
Orthorhombic
Pna21
0.630
Monoclinic
P21/c
Unit cell dimensions
a (Å)
9.0133(8)
14.034(3)
8.101(2)
b (Å)
40.854(5)
8.452(2)
13.832(3)
c (Å)
16.289(2)
90
95.435(2)
90
5971.1(9), 12
1.419
1.137
13.979(3)
90
90
90
1658.1(6), 4
1.551
0.971
796
0.15 ꢀ 0.10 ꢀ 0.04
2.808 to 33.486
ꢂ22 ꢃ h ꢃ 22, ꢂ13 ꢃ k ꢃ 13,
ꢂ24 ꢃ l ꢃ 24
25871
15.960(3)
90
95.67(3)
90
1779.6(6), 4
1.497
0.907
828
0.50 ꢀ 0.15 ꢀ 0.10
1.731 to 29.486
ꢂ12 ꢃ h ꢃ 12, ꢂ21 ꢃ k ꢃ 21
ꢂ24 ꢃ l ꢃ 24
25381
aꢁ
bꢁ
gꢁ
Volume (Å3), Z
Density (calculated) (g/cm3)
Absorption coefficient (mmꢂ1
F(000)
)
2652
Crystal size (mm3)
0.21 ꢀ 0.10 ꢀ 0.05
1.00 to 28.32
ꢂ11 ꢃ h ꢃ 12, ꢂ24 ꢃ k ꢃ 54
ꢂ21 ꢃ l ꢃ 21
42850
q
range for data collection
Index ranges
Reflections collected
Independent reflections
14818 [R(int) ¼ 0.0593]
8137 [R(int) ¼ 0.0299]
7028 [R(int) ¼ 0.0426]
Completeness to
q
99.7%
98.5%
99.5%
Refinement method
Full-matrix least-squares on F2
14818/0/676
1.069
R1 ¼ 0.0547; wR2 ¼ 0.0976
R1 ¼ 0.1121; wR2 ¼ 0.1344
0.846 and ꢂ0.847
Full-matrix least-squares on F2
8137/1/200
1.091
R1 ¼ 0.0200; wR2 ¼ 0.0593
R1 ¼ 0.0204; wR2 ¼ 0.0595
0.491 and ꢂ0.871
Full-matrix least-squares on F2
7028/0/209
1.077
R1 ¼ 0.0283; wR2 ¼ 0.0762
R1 ¼ 0.0310; wR2 ¼ 0.0775
0.457 and ꢂ1.195
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2sigma(I)]
R indices (all data)
Largest diff. peak and hole (e.Åꢂ3
)

S.H. Ahn et al. / Journal of Molecular Structure 1113 (2016) 24e31
27
Fig. 1. ORTEP drawing of [LACoCl2] with thermal ellipsoids at 50% probability. All hydrogen atoms are omitted for clarity.
temperature by treating CoCl2$6H2O with ligands (Ln ¼ LA, LB, and
LC) in 1:1 ratio and yielded corresponding complexes in quantita-
tive yields (85e90%) as illustrated in (Scheme 1). Complexes are
stable toward oxygen and moisture, and readily soluble in DMF and
DMSO but insoluble in MeOH, EtOH, and MeCN.
The elemental analysis is consistent with the chemical formula.
In the IR spectrum of complexes, the bands in range of 2944e3029
and 1699e1567 cmꢂ1 are assigned to CeH and C]C stretching
frequencies, respectively, characteristics of aromatic groups.
distorted octahedral geometry around the metal centre, achieved
through coordination of the two pyridyl units, two chlorides and
the N0,O-bidentate of nitrogen and oxygen in the N0-methoxyethyl
moiety to the Co(II) centre. Such variable coordination modes of 2-
methoxy-N,N-bis(pyridin-2-ylmethyl)etanamine (LB) and 3-
methoxy-N,N-bis(pyridin-2-ylmethyl)propan-1-amine (LC) to the
metal centre are consistent with the previous reports [45,50e53].
The bond lengths of CoeNamine and CoeNpyridine for Co(II)
complexes ranged from 2.193(3)
ꢂ
2.307(3)
Å
and
2.072(3) ꢂ 2.247(1) Å, respectively. There exist a difference of
0.08e0.235 Å in lengths of CoeNamine and CoeNpyridine in com-
plexes [LnCoCl2] (Ln ¼ LA, LB, and LC) and this might be due to dif-
ference in hybridization and basicity of nitrogen atoms. The more
basic Namine atom has sp3 hybridization while Npyridine has sp2 hy-
bridization with weak basic character. Moreover, the Namine atom
3.2. Molecular structures
Single crystals suitable for X-ray crystallographic studies are
obtained from Et2O or acetone diffusion into DMF or DMSO. Crystal
data and structural refinements for the synthesized Co(II) com-
plexes are summarized in Table 1. The ORTEP drawings and of
[LACoCl2], [LBCoCl2], and [LCCoCl2] are shown in Figs. 1e3,
respectively. The selected bond lengths and angles are listed in
Table 2. The 5-coordinate monomeric [LACoCl2] and [LCCoCl2] had a
trigonal bipyramidal geometries obtained via coordination of the
two pyridyl units and nitrogen in the N0-substituted amine moiety
was coordinated to Co(II) centre solely through a
s-bond, but the
Npyridine atoms were coordinated by both a -bond and a weak p-
s
to the Co(II) centre. Specifically, Tau (t) values of [LACoCl2] and
[LCCoCl2] were 0.59 and 0.60, respectively, indicating trigonal
bipyramidal (tbp) geometry [49]. However, [LBCoCl2] exhibited a
Fig. 2. ORTEP drawing of [LBCoCl2] with thermal ellipsoids at 50% probability.
Fig. 3. ORTEP drawing of [LCCoCl2] with thermal ellipsoids at 50% probability.

28
S.H. Ahn et al. / Journal of Molecular Structure 1113 (2016) 24e31
Table 2
Selected bond lengths (Å) and angles (ꢁ) of Co(II) complexes.
[LACoCl2]
[LBCoCl2]
[LCCoCl2]
Bond lengths (Å)
Co(1)-N(1)
Co(1)-N(3)
Co(1)-Cl(1)
Co(1)-N(2)
Co(1)-Cl(2)
N(1)-C(1)
N(1)-C(5)
N(2)-C(6)
2.072(3)
2.078(3)
2.288(1)
2.307(3)
2.309(1)
1.337(5)
1.354(5)
1.475(5)
1.477(5)
1.490(5)
Co(1)-N(3)
Co(1)-N(1)
Co(1)-N(2)
Co(1)-Cl(1)
Co(1)-O(1)
Co(1)-Cl(2)
N(1)-C(1)
N(1)-C(5)
N(2)-C(7)
N(2)-C(6)
2.111(1)
2.113(1)
2.193(1)
2.3263(5)
2.350(1)
2.3991(4)
1.341(2)
1.345(2)
1.471(2)
1.473(2)
Co(1)-N(1)
Co(1)-N(3)
Co(1)-N(2)
Co(1)-Cl(2)
Co(1)-Cl(1)
N(1)-C(5)
N(1)-C(1)
N(2)-C(6)
N(2)-C(7)
N(2)-C(13)
2.0725(8)
2.0906(8)
2.2476(8)
2.3124(7)
2.3202(5)
1.348(1)
1.348(1)
1.473(1)
1.479(1)
1.486(1)
N(2)-C(7)
N(2)-C(13)
Bond Angles (ꢁ)
N(1)-Co(1)-N(3)
N(1)-Co(1)-Cl(1)
N(3)-Co(1)-Cl(1)
N(1)-Co(1)-N(2)
N(3)-Co(1)-N(2)
Cl(1)-Co(1)-N(2)
N(1)-Co(1)-Cl(2)
N(3)-Co(1)-Cl(2)
Cl(1)-Co(1)-Cl(2)
N(2)-Co(1)-Cl(2)
106.7(1)
133.5(1)
113.1(1)
77.0(1)
76.7(1)
89.64(9)
97.2(1)
98.1(1)
99.81(5)
170.45(9)
N(3)-Co(1)-N(1)
N(3)-Co(1)-N(2)
N(1)-Co(1)-N(2)
N(3)-Co(1)-Cl(1)
N(1)-Co(1)-Cl(1)
N(2)-Co(1)-Cl(1)
N(3)-Co(1)-O(1)
N(1)-Co(1)-O(1)
N(2)-Co(1)-O(1)
Cl(1)-Co(1)-O(1)
155.17(4)
79.41(4)
76.26(4)
100.58(3)
102.12(3)
167.60(3)
81.04(4)
88.55(4)
76.60(4)
91.11(3)
N(1)-Co(1)-N(3)
N(1)-Co(1)-N(2)
N(3)-Co(1)-N(2)
N(1)-Co(1)-Cl(2)
N(3)-Co(1)-Cl(2)
N(2)-Co(1)-Cl(2)
N(1)-Co(1)-Cl(1)
N(3)-Co(1)-Cl(1)
N(2)-Co(1)-Cl(1)
Cl(2)-Co(1)-Cl(1)
112.07(3)
77.73(3)
77.15(3)
104.75(3)
136.41(2)
89.03(3)
100.18(3)
94.97(3)
170.13(2)
100.82(2)
Fig. 4. Perspective view for non-covalent hydrogen bonding interaction of [LACoCl2] (dot line; C(4)-H(4)-Cl(4), short dash line; C(9)-H(9)Cl(3), and long dash line; C(47)-H(47)-
Cl(6)).
Fig. 5. Perspective view for non-covalent hydrogen bonding interaction of [LBCoCl2].
back bond to Co(II) centre. In addition, the difference in CoeNamine
and CoeNpyridine for Co(II) complexes might also be attributed to
the variable steric environment around the metal centre provided
by the different N0-substituted moieties at amine unit.
The average NpyridineeCoeNpyridine bond angles for 5-coordinate
complexes i.e. [LACoCl2] and [LCCoCl2], are 106.7(1)ꢁ and
112.07(3)ꢁ, respectively. Similarly two NamineeCoeNpyridine angles
in [LACoCl2] are [77.0(1)ꢁ and 76.7(1)]; [LCCoCl2] [77.73(3)ꢁ and
77.15(3)ꢁ] indicative of 5-memebered fused ring. Additionally, the
bond angles of NamineeCoeCl(1) are [89.64(9)ꢁ and 89.03(3)], while
amineeCoeCl(2) angles are [170.45(9)ꢁ and 170.13(2)] in [LACoCl2]
N
and [LCCoCl2], indicated that the geometry around the Co center is
a distorted 5-coordinated trigonal bipyramidal involving coordi-
nation of the nitrogen of pyridyl units, amine moiety and the metal
center, thus forming two 5-membered chelate rings. The bond
angles Cl(1)eCoeCl(2) in 5-coordinated [LACoCl2] and [LCCoCl2]
are 99.81(5)ꢁ and 100.82(2)ꢁ, respectively. In a 6-coordinate
[LBCoCl2],
NpyridineeCoeNpyridine and two NamineeCoeNpyridine

S.H. Ahn et al. / Journal of Molecular Structure 1113 (2016) 24e31
29
Fig. 6. Perspective view for non-covalent hydrogen bonding interaction of [LCCoCl2].
angles are 155.17(4)ꢁ, 79.41(4)ꢁ and 76.26(4)ꢁ, respectively. There
exists a difference of 3.15ꢁ in two 5-membered fused rings in
[LBCoCl2] which might be due to the steric encumbrance provided
by coordination of oxygen atom of 2-methoxyethyl moiety to the Co
centre. Similarly N(1)eCoeO(1) and N(3)eCoeO(1) angles in
[LBCoCl2] are 81.04(4)ꢁ and 88.55(4)ꢁ, respectively and this differ-
ence might be representative of the steric adjustment between
pyridine moieties and 2-methoxyethyl unit.
channel by extending 1D channel of Co1 and Co2 along axis a to
arises b and c (2D channel, Fig. 4) with combination of Co3. Non-
covalent interaction, such as bond distances of CeH .......X (X ¼ Cl,
O) and CHX angles in the complexes was calculated and presented
as Table 3. Non-covalent interaction bond lengths of CeH .......X in
[LACoCl2] and [LBCoCl2] ranged from 3.517(1) Å to 3.655(5) Å
[54e58]. Specifically, hydrogen bond length of CeH .......O in
[LCCoCl2] was calculated as 3.26l(1) Å because eOCH3 group is
known to be good proton acceptor (Fig. 6).
Perspective view for non-covalent hydrogen bonding interac-
tion of [LnCoCl2] (Ln ¼ LA, LB and LC) was shown in Figs. 4e5,
respectively. Interestingly, [LACoCl2] forms three dimensional (3D)
3.3. Methyl methacrylate (MMA) polymerisation
The synthesized complexes were assessed towards MMA
polymerisation at 60 ꢁC. It has been observed that these com-
plexes act as effective initiators in presence of MMAO and poly-
Table 3
Selected CeH .......X (X ¼ Cl, O) bond distances (Å) and CHX angles (ꢁ).
merise
methyl
methacrylate
(MMA)
to
yield
CeH.......
X
d(CeH) d(H.......X) d(C.......X) <(CHX)
poly(methylmethacrylate) (PMMA) with Tg ranging from 129 ꢁC to
131 ꢁC. As mentioned earlier that non-radical mediated polymer-
isation of MMA is used to achieve syndiotacticity and hence high
Tg of PMMA with improved optical properties. The resultant
PMMA were isolated as white solids and characterized by gel
permeation chromatography (GPC) in THF using standard poly-
styrene as a reference. No catalytic activities have been observed
for these complexes in the absence of MMAO. The molecular
weight Mw ranged from 9.71 ꢀ 105 g/mol to 14.2 ꢀ 105 g/mol, with
a polydispersity index (PDI) value in range of 1.43e1.99. The re-
sults of polymerisation are summarized in Table 4.
.......
.......
[LACoCl2]a C(4)-H(4)
C(9)-H(9)
Cl(4)
Cl(3)
0.95
0.95
0.95
0.95
2.70
2.78
2.62
2.72
2.65
2.58
3.583(5) 154.7
3.655(5) 153.4
3.517(1) 157.3
3.637(5) 162.5
3.618(1) 165.1
3.261(1) 126
.......
C(10)-H(10)
C(47)-H(47)
Cl(4)
Cl(6)
.......
[LBCoCl2]b C(14)eH(14B)
Cl(1) 0.99
O(1) 0.99
.......
.......
[LCCoCl2]c C(7)eH(7A)
a
Symmetry transformations used to generate equivalent atoms: 1-x,-y,1-z
x,y,1 þ z 2-x,-y,1-z x,1/2-y,-1/2 þ z.
b
Symmetry transformations used to generate equivalent atoms: x-1/2,-y-1/2,z.
c
Symmetry transformations used to generate equivalent atoms: 1-x,y,z.
Table 4
MMA Polymerisation by Co(II) complexes in the presence of MMAO.a
Entry
Catalyst
Yieldb
(%)
Activityc
Tg
Tacticity
%mm
Mw
Mw/Mn
d
e
f
(g/molcat$h) ꢀ 104
(ꢁC)
%mr
%rr
(g/mol) ꢀ 105
1
2
3
4
5
[CoCl2$6H2O]g
MMAOh
[LACoCl2]
[LBCoCl2]
[LCCoCl2]
30.3
8.97
46.0
47.9
49.34
4.73
1.40
7.17
7.47
9.34
133
120
131
129
129
6.30
37.2
5.90
6.30
5.70
23.9
10.9
24.1
23.4
22.0
69.8
51.9
70.0
70.3
72.3
10.7
0.61
9.71
10.6
14.2
1.49
2.20
1.99
1.92
1.43
a
[Cd(II) catalyst]0 ¼ 15
m
mol, [MMA]0/[MMAO]0/[Cd(II) catalyst]0 ¼ 3100:500:1, Temp ¼ 60 ꢁC, and time ¼ 2 h.
b
c
Yield defined as mass of dried polymer recovered/mass of monomer used.
Activity is gPMMA/(molCo h).
d
e
f
Tg is glass transition temperature determined using a thermal analyzer.
Determined using gel permeation chromatography (GPC) eluted with THF at room temperature by filtration with polystyrene calibration.
Mn refers to the number average of molecular weights of PMMA.
It is a blank polymerisation in which [CoCl2.6H2O] was also activated by MMAO.
It is a blank polymerisation which was done solely by MMAO.
g
h

30
S.H. Ahn et al. / Journal of Molecular Structure 1113 (2016) 24e31
It
has
been
found
that
monomeric
[LCCoCl2]
Supplementary materials
(9.34 ꢀ 104 gPMMA/molCo h) exhibited highest activity and pro-
vided PMMA with the PDI value of 1.43 and molecular weight of
14.2 ꢀ 105 g/mol at 60 ꢁC. It is clear from polymerisation results that
PDIs decreased with increasing molecular weights of the resultant
PMMA [59,60]. However, the molecular weights of the polymers
isolated did not increase as the yield increased, which might be due
to the fact that the chain growth would completed at the beginning
of the polymerisation.
CCDC 1412224e1412226 contains the supplementary crystallo-
graphic data for complexes [LACoCl2], [LBCoCl2], and [LCCoCl2],
respectively. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (þ44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.
uk.
The decrease catalytic activity of Co(II) centre in 5-coordinated
[LACoCl2] and 6-coordinated [LBCoCl2] might be due to the steric
encumbrance provided by N0-substituted cyclohexyl and 2-
methoxyethyl substituents at amine moiety (Figs. 1 and 2). How-
ever in case of [LCCoCl2] the pendent 3-methoxypropyl group lies
away from metal centre and thus resulted in open reactive site for
monomer approach. Experiments were carried out using starting
materials CoCl2$6H2O, or MMAO alone at a specific temperature
towards MMA polymerisation. It has been found that PDI and tac-
ticity is almost unchanged particularly in case of CoCl2$6H2O.
The tacticity of PMMA, was identified in the range around
Acknowledgements
This research was supported by the National Research Founda-
tion of Korea (NRF), funded by the Ministry of the Education, Sci-
ence, and Technology (MEST) (Grant No. 2014-R1A1A3049750). X-
ray crystallography with PLS-II 2D-SMC beamline was supported by
MSIP and POSTECH.
References
[1] E.Y.-X. Chen, Chem. Rev. 109 (2009) 5157.
syndiotactic (rr,
d
d 0.85), heterotactic (mr, d 1.02) and isotactic (mm,
[2] J. Gromada, J.F. Carpentier, A. Mortreux, Coord. Chem. Rev. 248 (2004) 397.
[3] D. Barbier-Baudry, F. Bouyer, A.S. Madureira Bruno, M. Visseaux, Appl. Orga-
nometal. Chem. 20 (2006) 24.
[4] D.F. Grishin, L.L. Semenycheva, Russ. Chem. Rev. 70 (2001) 425.
[5] A.V. Yakimanskii, Polym. Sci. Ser. C 47 (2005) 1.
[6] R.M. Islamova, G.R. Sadykova, I.A. Ionova, Ya Z. Voloshin, Yu N. Bubnov,
I.S. Makarov, Yu B. Monakov, Polym. Sci. Ser. B 51 (2009) 219.
[7] R.M. Islamova, O.I. Golovochesova, Yu B. Monakov, I.A. Utepova,
A.A. Musikhina, O.N. Chupakhin, Polym. Sci. Ser. B 52 (2010) 637.
[8] Yu B. Monakov, R.M. Islamova, I.A. Ionova, S.A. Syrbu, T.A. Ageeva,
O.I. Koifman, Mendeleev Commun. 20 (2010) 33.
[9] G.J.P. Britovsek, V.C. Gibson, D.F. Wass, Angew. Chem. Int. Ed. 38 (1999) 428.
[10] S.D. Ittel, L.K. Johnson, M. Brookhart, Chem. Rev. 100 (2000) 1169.
[11] V.C. Gibson, S.K. Spitzmesser, Chem. Rev. 130 (2003) 283.
[12] L.S. Boffa, B.M. Novak, Chem. Rev. 100 (2000) 1479.
1.21) based on 1H NMR spectroscopy [61,62]. The syndiotacticity
of PMMA by monomeric [LCCoCl2] was found to be 0.72, which was
slightly higher compared to rest of complexes [LACoCl2], and
[LBCoCl2] and even the reference material i.e. CoCl2$6H2O. How-
ever, there was a significant difference of the syndiotacticity of
PMMA compared to the co-catalyst, MMAO. Despite of lower ac-
tivities observed for [LACoCl2], and [LBCoCl2] the syndiotacticity
was not affected much. Furthermore, it has been observed that the
current system resulted PMMA with higher molecular weights,
higher Tg, and better syndiotacticity compared to our previous re-
ported Co(II) complexes [63].
It has been observed that catalytic activity of complexes was
affected by steric encumbrance provided by N0-substitution at the
amine moiety, as determined by the amount of resultant PMMA.
The polymerization activity and resultant molecular weights of
PMMA should be considered as a function of steric bulk around the
metal centre. MMA polymerisation achieved via coordination
complexes resulted in syndiotacticity enchainment, which resulted
in Tg up to 140 ꢁC. The syndiotacticity of resultant PMMA was
around 70%, which was similar to all the synthesized complexes
and was not much affected by the steric encumbrance provided by
ligand architecture. Thus, the observed moderate syndiotacticity of
PMMA was not sufficient to confer a coordination polymerisation
mechanism for these complexes.
[13] F. Speiser, P. Braunstein, L. Saussine, Acc. Chem. Res. 38 (2005) 784.
[14] J. Zhang, X. Wang, G.X. Jin, Coord. Chem. Rev. 250 (2006) 95.
[15] K. Endo, A. Inukai, Macromol. Rapid Commun. 21 (2000) 785.
[16] I. Kim, J. Hwang, J.K. Lee, C.S. Ha, S.I. Woo, Macromol. Rapid Commun. 24
(2003) 508.
[17] D. Kim, S. Kim, E. Kim, H.-J. Lee, H. Lee, Polyhedron 63 (2013) 139.
[18] S. Kim, D. Kim, Y. Song, H.-J. Lee, H. Lee, Aust. J. Chem. 67 (2014) 953.
[19] Y. Song, D. Kim, H.-J. Lee, H. Lee, Inorg. Chem. Commun. 45 (2014) 66.
[20] L. You, S.R. Long, V.M. Lynch, E.V. Anslyn, Chem. Eur. J. 17 (2011) 11017.
[21] L. Zhang, R.J. Clark, L. Zhu, Chem. Eur. J. 14 (2008) 2894.
[22] A. Beitat, S.P. Foxon, C.-C. Brombach, H. Hausmann, F.W. Heinemann,
F. Hampel, U. Monkowius, C. Hirtenlehner, G. KnVor, S. Schindler, Dalton
Trans. 40 (2011) 5090.
[23] C. Gwizdala, C.V. Singh, T.R. Friss, J.C. MacDonald, S.C. Burdette, Dalton Trans.
41 (2012) 8162.
[24] F.B. Johansson, A.D. Bond, C.J. McKenzie, Inorg. Chem. 45 (2007) 2224.
[25] S.A. de Silva, A. Zavaleta, D.E. Baron, O. Allam, E.V. Isidor, N. Kasbimura,
J.M. Percarpio, Tetrahedron Lett. 38 (1997) 2237.
[26] J. Qian, L. Wang, W. Gu, X. Liu, J. Tian, S. Yan, Dalton Trans. 40 (2011) 5617.
[27] D.C. Bebout, S.W. Stokes, R.J. Butcher, Inorg. Chem. 38 (1999) 1126.
[28] N. Niklas, F.W. Heinemann, F. Hampel, R. Alsfasser, Angew. Chem. Int. Ed. 41
(2002) 3386.
[29] D.C. Bebout, E.V. Bowers, R.E. Freer, M.E. Kastner, D.A. Parrish, R.J. Butcher,
J. Chem. Crystallogr. 43 (2013) 108.
4. Conclusion
In the work presented here, we demonstrated the synthesis and
X-ray crystallographic studies of mononuclear [LnCoCl2] (Ln ¼ LA,
LB, LC) complexes. These novel Co(II) complexes exhibited diverse
structural variations on amine moiety of N,N-di(2-picolyl)amine
architecture. The Co(II) centre in [LnCoCl2] (Ln ¼ LA, and LC) is 5-
coordinated and adopted a distorted trigonal bipyramidal geome-
try while [LBCoCl2] exhibited 6-coordinated distorted octahedral
geometry. The complex [LCCoCl2] showed better catalytic activity
for MMA polymerisation at 60 ꢁC compared to its counter parts
containing LA and LB. The catalytic activity in the current study can
be explain as a function of steric encumbrance that hinder the
monomer approach to the active centre. It is anticipated that new
N,N-di(2-picolyl)amine based architecture may be applied to afford
other pyridyl-amine based Co(II) complexes with better catalytic
activities. Studies in these respects are under way in our laboratory.
[30] G.H. Eom, J.H. Kim, Y.D. Jo, E.Y. Kim, J.M. Bae, C. Kim, S.-J. Kim, Y. Kim, Inorg.
Chim. Acta 387 (2012) 106.
[31] H. Lee, H.-S. Lee, J.H. Reibenspies, R.D. Hancock, Inorg. Chem. 51 (2012) 10904.
[32] K. Grubel, B.J. Laughlin, T.R. Maltais, R.C. Smith, A.M. Arifc, L.M. Berreau, Chem.
Commun. 47 (2011) 10431.
[33] K. Eubert, D. BVohme, J. KVosters, W.-Z. Shen, E. Freisinger, J. Müller, Z. Anorg,
Allg. Chem. 638 (2012) 1761.
[34] P. Das, S. Bhattacharya, S. Mishra, A. Das, Chem. Commun. 47 (2011) 8118.
[35] H. Ohtsu, Y. Shimazaki, A. Odania, O. Yamauchi, Chem. Commun. (1999) 2393.
[36] N. Niklas, O. Walter, R. Alsfasser, Eur. J. Inorg. Chem. (2000) 1723.
[37] A. Hazell, C.J. McKenzie, L.P. Nielsen, J. Chem. Soc. Dalton Trans. (1998) 1751.
[38] S.S. Massoud, E. Taylor, Y. Liu, J. Grebowicz, R. Vicente, R. Lalancette,
U. Mukhopadhyay, I. Bernalf, S.F. Watkins, Cryst. Eng. Comm. 16 (2014) 175.
[39] Y.-H. Ho, M.-C. Chang, K.-H. Yu, Y.-H. Liu, Y. Wang, Y.-C. Cheng, J.-T. Chen,
Dalton Trans. 43 (2014) 6287.
[40] T. Li, J. Du, T. Li, Z. Wu, W. He, J. Zhu, Z. Guo, Chem. Biodivers. 5 (2008) 1495.
[41] Y. Zhao, J. Zhu, W. He, Z. Yang, Y. Zhu, Y. Li, J. Zhang, Z. Guo, Chem. Eur. J. 12
(2006) 6621.
[42] A. Panja, M. Shyamal, A. Sahab, T.K. Mandal, Dalton Trans. 43 (2014) 5443.

S.H. Ahn et al. / Journal of Molecular Structure 1113 (2016) 24e31
31
[43] Y. Song, S. Nayab, J. Jeon, S.H. Park, H. Lee, J. Organomet. Chem. 783 (2015) 55.
[44] B. Antonioli, B. Büchner, J.K. Clegg, K.n Gloe, K. Gloe, L. Gotzke, A. Heine,
[52] Q.-Y. Li, X.-Y. Tang, W.-H. Zhang, J. Wang, Z.-G. Ren, H.-X. Li, Y. Zhang, J.-
P. Lang, J. Mol. Struct. 879 (2008) 119.
€
A. Jager, K.A. Jolliffe, O. Kataeva, V. Kataev, R. Klingeler, T. Krause, L.F. Lindoy,
A. Popa, W. Seichter, M. Wenzel, Dalton Trans. (2009) 4795.
[45] J.-Z. Wu, E. Bouwman, A.M. Mills, A.L. Spek, J. Reedijk, Inorg. Chim. Acta 357
(2004) 2694.
[46] A.J. Arvai, C. Nielsen, ADSC Quantum-210 ADX Program, Area Detector System
Corporation, Poway, CA, USA, 1983.
[47] Z. Otwinowski, W. Minor, in: C.W. Carter Jr., R.M. Sweet (Eds.), Methods in
Enzymology, vol. 276, Academic Press, New York, 1997 part A, p. 307.
[48] G.M. Sheldrick, Acta Crystallogr. Sect. A 64 (2008) 112.
[49] A.W. Addison, T.N. Rao, J. Reedijk, J. van Rijn, G.C. Verschoor, J. Chem. Soc.
Dalton Trans. (1984) 1349.
[53] G.J.P. Britovsek, M. Bruce, V.C. Gibson, B.S. Kimberley, P.J. Maddox,
€
S. Mastroianni, S.J. McTavish, C. Redshaw, G.A. Solan, S. Stromberg,
A.J.P. White, D.J. Williams, J. Am. Chem. Soc. 121 (1999) 8728.
[54] D.M. Roe, P.M. Bailey, K. Moseley, P.M. Maitlis, J. Chem. Soc. Chem. Comm. 23
(1972) 1273.
[55] M. Brookhart, M.L.H. Green, Organomet. Chem. 250 (1983) 395.
[56] A. Albinati, P.S. Pregosin, F. Wombacher, Inorg. Chem. 29 (1990) 1812.
[57] A. Mukhopadhyay, S. Pal, Eur. J. Inorg. Chem. (2006) 4879.
[58] M. Brookhart, M.L.H. Green, G. Parkin, PNAS 104 (2007) 6908.
[59] J. Llorens, E. Rude, R.M. Marcos, Polymer 44 (2003) 1741.
[60] G.T. Lewis, V. Nguyen, Y. Cohen, J. Polym, Sci. A Poly. Chem. 45 (2007) 5748.
[61] Y. Mikata, T. Fujimoto, Y. Sugai, S. Yano, Eur. J. Inorg. Chem. (2007) 1143.
[62] T. Kitaura, T. Kitayama, Macromol. Rapid Commun. 28 (2007) 1889.
[63] M. Yang, W.J. Park, K.B. Yoon, J.H. Jeong, H. Lee, Inorg. Chem. Commun. 14
(2011) 189.
[50] Y. Mikata, T. Fujimoto, T.i Fujiwara, S.-i Kondo, Inorg. Chim. Acta 370 (2011)
420.
[51] S.I. Kirin, C.M. Happel, S. Hrubanova, T. Weyhermüller, C.K. Klein, N. Metzler-
Nolte, Dalton Trans. (2004) 1201.