Five-coordinate dinuclar cobalt (II), copper (II), zinc (II) and cadmium (II) complexes with 4-bromo-N-(2-pyridinylmethylene)benzenamine: Synthesis, characterisation and methyl methacrylate polymerization

Article abstract of DOI:10.1002/aoc.4766

A series of late transition metal complexes, [(bpma)Co(μ–Cl)Cl]₂, [(bpma)Cu(μ–Cl)Cl]₂, [(bpma)Zn(μ–Cl)Cl]₂ and [(bpma)Cd(μ–Br)Br]₂ (where bpma is 4-bromo-N-((pyridin-2-yl)methylene)benzenamine) have been synthes

Full text of DOI:10.1002/aoc.4766

Received: 12 October 2018
DOI: 10.1002/aoc.4766
Revised: 19 November 2018
Accepted: 23 November 2018
F U L L P A P E R
Five‐coordinate dinuclar cobalt (II), copper (II), zinc (II)
and cadmium (II) complexes with 4‐bromo‐N‐(2‐
pyridinylmethylene)benzenamine: Synthesis,
characterisation and methyl methacrylate polymerization
1
1
1
2
2
3
Suhyun Park | Jaegyeong Lee | Hyosun Lee
| Ah Rim Jeong | Kil Sik Min | Saira Nayab
1
Department of Chemistry and Green‐
A series of late transition metal complexes, [(bpma)Co(μ–Cl)Cl] , [(bpma)
Nano Materials Research Centre,
Kyungpook National University, 80
Daehakro, Buk‐gu, Daegu‐city 41566,
Republic of Korea
2
Cu(μ–Cl)Cl] , [(bpma)Zn(μ–Cl)Cl]2 and [(bpma)Cd(μ–Br)Br]2 (where
2
bpma is 4‐bromo‐N‐((pyridin‐2‐yl)methylene)benzenamine) have been synthe-
sized and structurally characterized. The X‐ray structures of dimeric complexes
2
Department of Educational Chemistry,
Kyungpook National University, 80
Daehakro, Buk‐gu, Daegu‐city 41566,
Republic of Korea
[(bpma)M(μ–X)X] (M = Co, Cu and Zn, X = Cl; M = Cd, X = Br) showed a
distorted 5‐coordinate trigonal bipyramidal geometry involving two nitrogen
atoms of N,N‐bidentate ligand, two bridged and one terminal halogen atoms.
2
3
Department of Chemistry, Shaheed
The complex [(bpma)Cu(μ–Cl)Cl] revealed the highest catalytic activity for
Benazir Bhutto University, Sheringal Dir
2
(
U), Khyber Pakhtunkhwa, Islamic
the polymerisation of methyl methacrylate in the presence of modified
Republic of Pakistan
4
methylaluminoxane with an activity of 9.14 × 10 g PMMA/mol·Cu·h at
Correspondence
60 °C and afforded syndiotactic poly (methylmethacrylate) (rr = 0.69).
Hyosun Lee, Department of Chemistry
and Green‐Nano Materials Research
Centre, Kyungpook National University,
KEYWORDS
4‐bromo‐N‐(2‐pyridinylmethylene) benzenamine, dinuclear transition metal complex, MMA
80 Daehakro, Buk‐gu, Daegu‐city, 41566,
polymerization, syndio‐enriched PMMA
Republic of Korea.
Email: hyosunlee@knu.ac.kr
Saira Nayab, Department of Chemistry,
Shaheed Benazir Bhutto University,
Sheringal Dir (U), Khyber Pakhtunkhwa,
Islamic Republic of Pakistan.
Email: sairanayab07@yahoo.com
Funding information
National Research Foundation (NRF) of
South Korea, funded by the Ministry of the
Education, Science, and Technology
(MEST), Grant/Award Number:
2017R1A2B4002100
1
| INTRODUCTION
Their structural stability and catalytic efficiency
made them useful mainly in the area of structural
[
7]
[8–10]
[11]
Schiff bases, such as pyridine‐3‐ylmethanimine gained
attention owing to their easy synthetic approach and
resultant stable coordination entities with a variety
of transition metals.
various coordination modes up to the tetradentate.
studies,
photoluminescence,
spectroscopy,
biological applica-
catalysts for alkene
[
12]
transfer hydrogenation reactions,
[
13]
[14]
tions,
oxidation catalyst,
[1–3]
[15]
[16]
[17,18]
These complexes showed
polymerization,
polymerizations.
epoxidation,
olefin
and MMA
[
4–6]
[19]
Appl Organometal Chem. 2019;33:e4766.
wileyonlinelibrary.com/journal/aoc
© 2018 John Wiley & Sons, Ltd.
1 of 11
https://doi.org/10.1002/aoc.4766

2
of 11
PARK ET AL.
Poly (methylmethacrylate) (PMMA), an acrylic poly-
weight aluminum of a toluene solution and used without
further purification. 4‐bromo‐N‐((pyridin‐2‐yl)methylene)
benzenamine (bpma) was prepared by previously
mer, is commonly used as a thermoplastic with enhanced
optical properties and wide range of industrial applica-
[20,21]
[32–36]
tions.
Obviously, the tacticity of the polymer is
reported procedure.
inherently important to its applications. Pure isotactic
PMMA have T about 51 °C, whereas for syndiotactic
g
2
.2 | Instrumentation
[22]
PMMA T is near 130 °C.
Thus, syndiotactic PMMA
g
1
13
via metal mediated polymerization is highly desirable
for improved optical applications. A great deal of atten-
tion has been directed recently toward the development
of late‐transition‐metal‐based complexes due to their
reduced oxophilicity and presumed better functional
group tolerance towards polar monomers. Yasuda and
H NMR (500 MHz) and C NMR (125 MHz) spectra
were recorded on a Bruker Avance Digital 500 NMR spec-
trometer; chemical shifts were reported in ppm units (δ)
relative to SiMe as the internal standard. Infrared (IR)
spectra were recorded on Bruker FT/IR‐Alpha (neat)
4
and the data are reported in reciprocal centimetres (cm
[23,24]
−
1
coworkers
reported that Cp *LnR (Ln = Sm or Yb)
2
). Elemental analysis (C, H, N) of the prepared com-
plexes were carried out on an elemental analyser (EA
108; Carlo‐Erba, Milan, Italy). The molecular weights
M ) and molecular weight distribution (MWD) of the
catalyzed highly syndiotactic PMMA, and Marks and
[25]
coworkers
showed that chiral ansa‐bridged
1
(
lanthanocenes give isotactic or syndiotactic PMMA based
n
on the ligand assembly. Alternatively, Ni (acac) catalyst
2
obtained poly (methylmethacrylate) (PMMA) were car-
ried out using gel permeation chromatography (GPC)
was found to be an effective catalyst for the nonspecific
polymerization of MMA in the presence of
(
in THF, Alliance e2695; Waters Corp., Milford, MA,
[26,27]
methylaluminoxane (MAO).
Schiff base derived late
USA). Glass transition temperature (T ) was determined
g
transition metal complexes, such as (α‐diimine)‐based
nickel complexes, pyridylbisimine‐based Fe (II) and Co
using a thermal analyser (DSC 4000; PerkinElmer).
(
II), iminopyridine‐ or aminopyridine‐based Fe (II)
2
2
.3 | Synthetic procedures
complexes polymerized MMA to give syndio‐enriched
PMMA.
were reported which polymerized MMA and yielded
syndiotactic‐rich PMMA with relatively wide PDIs.
[28]
Similarly, bis(β‐ketiminato) nickel complexes
.3.1 | [4‐bromo‐N‐((pyridin‐2‐yl)methy-
[
29]
lene)benzenamine] cobalt (II) chloride
([(bpma)co(μ–cl)cl]2)
We have recently used several late transition metals
with pyridineimine based ligands for PMMA
[30–32]
A solution of (bpma) (0.601 g, 2.30 mmol) in anhydrous
EtOH (40.0 ml) was added to a solution of CoCl ·6H O
precatalysts.
Thus, the current study demonstrate
2
2
the synthesis and structural studies of 4‐bromo‐N‐(2‐
pyridinylmethylene) benzenamine (bpma) based metal
(
0.547 g, 2.30 mmol) in anhydrous EtOH (40.0 ml) and
stirred at room temperature for 12 hr to give a dark green
precipitate. The solid was filtered and washed with cold
complexes [(bpma)M(μ–X)X] (M = Co, Cu and Zn,
2
X = Cl; M = Cd, X = Br). Further, we sought to investi-
gate the catalytic activity of synthesized metal complexes
for MMA polymerization in terms of metal centre varia-
tion and ligand effect.
EtOH (30.0 ml × 2), followed by washing with Et O
2
(
30.0 ml × 3). The product was dried under vacuum to
yield a final product (1.63 g, 90.6%). Analysis calculated
for C H Br Cl Co N (%): C, 36.87; H, 2.32; N, 7.17.
2
4
18
2
4
2 4
−
1
Found: C, 37.24; H, 2.33; N, 7.10. IR (solid neat; cm ):
067 (C‐H stretching), 1565 (N=C stretching), 1485
‐C=C aromatic) 1444 (‐C‐H bending) 690 (‐C‐Br).
3
(
2
2
| EXPERIMENTAL
.1 | General consideration
2
.3.2 | [4‐bromo‐N‐((pyridin‐2‐yl)methy-
CoCl ·6H O, CuCl ·2H O, ZnCl2, CdBr ·4H O, 2‐
lene)benzenamine] copper (II) chloride
([(bpma)cu(μ–cl)cl]2)
2
2
2
2
2
2
pyridinecarboxaldehyde, 4‐bromoaniline, magnesium
sulfate, and methyl methacrylate (MMA) were purchased
from Aldrich. Anhydrous solvents such as acetonitrile
[(bpma)Cu(μ‐Cl)Cl]2 was prepared by analogous
method as described for [(bpma)Co(μ‐Cl)Cl]2 except
utilizing (bpma) (0.601 g, 2.30 mmol) and CuCl ·2H O
(
CH CN), ethanol (EtOH), dimethylformamide (DMF),
3
diethyl ether (Et O) and dichloromethane (CH Cl ) were
2
2
2
2
2
purchased from Merck and used without further purifica-
tion. Modified methylaluminoxane (MMAO) was pur-
chased from Tosoh Finechem Corporation as 5.90%
(0.392 g, 2.30 mmol) to give a light green solid (1.70 g,
93.4%). Analysis calculated for C H Br Cl Cu N (%):
C, 36.44; H, 2.29; N, 7.08. Found: C, 36.58; H, 2.32; N,
24
18
2
4
2 4

PARK ET AL.
3 of 11
−
1
7
.23. IR (solid neat; cm ): 3079 (C‐H stretching), 1591 (‐
BrC H –), 140.01 (d, 1C, J = 168.94 Hz, –N=C–CH=CH–
6
4
N=C stretching), 1482 (‐C‐H bending), 1359 (‐C=C aro-
matic), 646 (‐C‐Br).
CH=CH–), 131.88 (d, 2C, J = 169.84 Hz, m‐BrC H –),
128.15 (d, 1C, J = 168.03 Hz, –N=C–CH=CH–CH=CH–),
6
4
1
1
28.05 (d, 1C, J = 169.84 Hz, –N=C–CH=CH–CH=CH–),
24.21 (d, 2C, J = 164.40 Hz, o‐BrC H –), 120.49 (s, 1C,
6
4
−1
2
.3.3 | [4‐bromo‐N‐((pyridin‐2‐yl)methy-
lene)benzenamine] zinc (II) chloride
[(bpma)Zn(μ–cl)cl]2)
ipso‐BrC H –). IR (solid neat; cm ): 3086 (C‐H
6
4
stretching), 3058 (w), 1592 (N=C stretching) (w), 1484
(
(‐C‐H bending) (s), 1438 (‐C=C aromatic), 600 (‐C‐Br).
[(bpma)Zn(μ–Cl)Cl]2 was prepared by analogous
method as described for [(bpma)Co(μ‐Cl)Cl] except uti-
2.4 | Catalytic activity for MMA
polymerization
2
lizing (bpma) (0.700 g, 2.68 mmol) and ZnCl (0.365 g,
2
2
.68 mmol) to give a white solid (2.03 g, 95.3%). Analysis
calculated for C H Br Cl N Zn (%): C, 36.27; H, 2.28;
In a Schlenk flask, the complex (15.0 μmol, 11.7 mg for
24
18
2
4
4
2
1
N, 7.05. Found: C, 36.61; H, 2.28; N, 7.20. H NMR
DMSO‐d , 500 MHz): δ 8.84 (d, 1H, J = 4.12 Hz, –N=C–
[(bpma)Co(μ–Cl)Cl] , 11.9 mg for [(bpma)Cu(μ–Cl)
2
(
Cl] , 11.9 mg for [(bpma)Zn(μ–Cl)Cl] , 16.0 mg for
6
2
2
CH=CH–CH=CH–), 8.68 (s, 1H, –N=CH–NC H –),
[(bpma)Cd(μ–Br)Br] was dissolved in dried toluene
5
4
2
8
1
.13–8.08 (m, 2H, –N=C–CH=CH–CH=CH–), 7.68 (br s,
H, –N=C–CH=CH–CH=CH–), 7.61 (d, 2H,
(10.0 ml) followed by the addition of modified methyl
aluminoxane (MMAO) (3.80 ml, 7.50 mmol) as a co‐
catalyst. The solution was stirred for 20 min at 60 °C.
The MMA (5.00 ml, 47.1 mmol) was added to the above
reaction mixture and stirred for 2 hr to get a viscous solu-
tion. MeOH (4.00 ml) was added to terminate polymeriza-
tion. The reaction mixture was poured into a large
quantity of MeOH (500 ml), and 35.0% HCl (5.00 ml)
was injected to remove the remaining co‐catalyst
(MMAO). The product was obtained by filtration and
washed with MeOH (250 ml × 2) to yield PMMA, and
dried under vacuum at 60 °C for 12 hr.
J = 8.54 Hz, –BrC H –), 7.33 (d, 2H, J = 7.93 Hz, –BrC
H –). C NMR (DMSO‐d , 125 MHz): δ 160.50 (d, 1C,
J = 171.66 Hz, –N=CH–NC H –), 150.13 (s, 1C, ipso‐
N=C–CH=CH–CH=CH–), 149.81 (d, 1C, J = 182.56 Hz,
–
1
1
6
4
6-
13
4
6
5
4
N=C–CH=CH–CH=CH–), 147.67 (s, 1C, ipso‐BrC H –),
6
4
39.36 (d, 1C, J = 168.03 Hz, –N=C–CH=CH–CH=CH–),
32.02 (d, 2C, J = 167.12 Hz, m‐BrC H –), 127.48 (d, 1C,
6
4
J = 168.94 Hz, –N=C–CH=CH–CH=CH–), 125.33 (d,
C, J = 170.75 Hz, –N=C–CH=CH–CH=CH–), 123.76
d, 2C, J = 163.49 Hz, o‐BrC H –), 120.09 (s, 1C, ipso‐
1
(
6
4
−
1
BrC H –). IR (solid neat; cm ): 3134 (C‐H stretching),
6
4
1
590 (N=C stretching), 1561 (‐C‐H bending), 1488–1446
2.5 | X‐ray crystallographic studies
(
‐C=C aromatic), 648 (‐C‐Br).
An X‐ray quality crystals of [(bpma)Co(μ–Cl)Cl] and
2
2
.3.4 | [4‐bromo‐N‐((pyridin‐2‐yl)methy-
lene)benzenamine] cadmium (II) bromide
[(bpma)cd(μ–Br)Br]2)
[(bpma)Cu(μ–Cl)Cl]
(10.0 ml) diffusion into an MeOH solution (5.00 ml) of
complexes. Similarly, the X‐ray quality single crystals of
2
were grown from
a
Et O
2
(
[
(bpma)Zn(μ–Cl)Cl] and [(bpma)Cd(μ–Br)Br] were
2
2
[
(bpma)Cd(μ–Br)Br]2 was prepared by analogous
grown from an IPA solution (10.0 ml) diffusion into
DMF solution (5.0 ml). An X‐ray‐quality single crystal
was mounted in a thin‐walled glass capillary on a Bruker
SMART CCD diffractometer equipped with a graphite‐
monochromated Mo Kα (λ = 0.71073 Å) radiation source
and a nitrogen cold stream (−100 °C). Data collection and
integration were performed with SMART (Bruker, 2000)
method as described for [(bpma)Co(μ‐Cl)Cl] except uti-
lizing (bpma) (0.601 g, 2.30 mmol) and CdBr·4H O
2
2
(0.791 g, 2.30 mmol) to give a beige solid (2.28 g, 92.9%).
Analysis calculated for C H Br Cd N (%): C, 27.02; H,
1
2
4
18
6
2 4
1
.70; N, 5.25. Found: C, 27.48; H, 1.71; N, 5.32. H NMR
(DMSO‐d , 500 MHz): δ 8.90 (d, 1H, J = 4.58 Hz, –N=C–
6
[36]
CH=CH–CH=CH–), 8.79 (s, 1H, –N=CH–NC H –), 8.17
and SAINT‐Plus (Bruker, 2001) software packages.
Semi‐empirical absorption corrections based on equiva-
5
4
(t, 1H, J = 7.63 Hz, –N=C–CH=CH–CH=CH–), 8.11 (d,
[
37]
1
H, J = 7.63 Hz, –N=C–CH=CH–CH=CH–), 7.77 (t, 1H,
lent reflections were applied by SADABS.
Structures
J = 6.26 Hz, –N=C–CH=CH–CH=CH–), 7.64 (d, 2H,
J = 8.54 Hz, –BrC H –), 7.44 (d, 2H, J = 8.54 Hz, –BrC
were solved by direct methods and refined using a full‐
matrix least‐squares method on F using SHELXTL.
All non‐hydrogen atoms were refined anisotropically.
Hydrogen atoms were added to their geometrically ideal
positions. Crystal and structure refinement data for all
structures are summarized in Table 1.
2
[38]
6
4
6-
13
H –). C NMR (DMSO‐d , 125 MHz): δ 160.03 (d, 1C,
4
6
J = 172.57 Hz, –N=CH–NC H –), 149.97 (d, 1C,
5
4
J = 184.38 Hz, –N=C–CH=CH–CH=CH–), 148.17 (s, 1C,
ipso‐N=C–CH=CH–CH=CH–), 147.08 (s, 1C, ipso‐

4
of 11
PARK ET AL.
[
33–36]
3
3
| RESULT AND DISCUSSION
.1 | Synthesis and properties
2‐pyridinecarboxaldehyde in MeOH as reported.
The complexation reaction progressed smoothly by
treating metal staring salts/precursors with ligand in
anhydrous EtOH and afforded [(bpma)Co(μ–Cl)Cl]2
Ligand (bpma) used in current study was obtained by the
(90.6%), [(bpma)Cu(μ–Cl)Cl] (93.4%), [(bpma)Zn(μ–
2
condensation reaction between the 4‐bromoaniline and
Cl)Cl] (95.3%) and [(bpma)Cd(μ–Br)Br] (92.9%) at
2
2
TABLE 1 Crystal data and structure refinement for [(bpma)M(μ–X)X]
2
(M = Co, Cu and Zn, X = Cl; M = Cd, X = Br)
[
(bpma)Co(μ–Cl)Cl]
2
[(bpma)Cu(μ–Cl)Cl]
Cl Cu
2
[(bpma)Zn(μ–Cl)Cl]
Cl Zn
2
[(bpma)Cd(μ–Br)Br]
Cd
2
Empirical formula
C
24
H
18Br
2
Cl Co
4
2
N
4
C
24
H
18Br
2
4
2
N
4
C
24
H
18Br
2
4
N
4
2
.
C
24
H
18Br
6
2 4
N
CHCl
3
Formula weight
Temperature/K
Wavelength/Å
Crystal system
Space group
a/Å
781.90
100(2)
0.610
791.12
200(2)
0.71073
794.78
100(2)
0.700
1066.68
100(2)
0.620
Monoclinic
P2(1)/n
7.5180(2)
13.994(3)
12.991(3)
90
Monoclinic
P2(1)/n
7.5294(1)
13.6544(2)
13.2348(2)
90
Monoclinic
P2(1)/n
7.5420(2)
14.260(3)
12.702(3)
90
Monoclinic
P2(1)/n
7.7090(2)
15.273(3)
12.474(3)
90
b/Å
c/Å
α/ °
β/ °
98.13(3)
90
98.001(3)
90
98.45(3)
90
96.09(3)
90
γ/ °
3
Volume/Å , Z
1353.0(5), 2
1347.4(3), 2
1.950
1351.2(5), 2
1.953
1460.4(5), 2
2.426
Density (calculated) /Mg m 1.919
−
3
Absorption coefficient/mm
3.038
4.963
4.941
6.770
−
1
F(000)
764
772
776
992
3
Crystal size/mm
0.10 × 0.06 × 0.03
1.846 to 27.996
0.23 × 0.21 × 0.13
2.15 to 28.37
0.08 × 0.06 × 0.03
2.128 to 33.319
0.20 × 0.15 × 0.10
2.327 to 25.993
Theta range for data
collection/deg
Index ranges
−11 ≤ h ≤ 11
−10 ≤ h ≤ 8
−18 ≤ k ≤ 16
−17 ≤ l ≤ 17
−11 ≤ h ≤ 11
−20 ≤ k ≤ 20
−19 ≤ l ≤ 19
−10 ≤ h ≤ 10
−21 ≤ k ≤ 21
−17 ≤ l ≤ 17
−
21 ≤ k ≤ 21
19 ≤ l ≤ 19
−
Reflections collected/unique 18164
9695
13401
15523
Independent reflections
5163 [R (int) = 0.0537]
100.0% (21.469°)
3334 [R (int) = 0.0384]
99.1% (28.37°)
4494 [R (int) = 0.0356]
97.3% (24.835°)
4325 [R (int) = 0.0302]
99.9% (21.839°)
Completeness to
theta = 28.30°
Refinement method
Full‐matrix least‐squares Full‐matrix least‐squares Full‐matrix least‐squares Full‐matrix least‐squares
2
2
2
2
on F
on F
on F
on F
Data/restraints/parameters
5163/0/163
0.950
3334/0/163
1.098
4494/0/164
1.063
4325/0/164
1.065
2
Goodness‐of‐fit on F
Final R indices
R
wR
1
= 0.0320
= 0.0728
R
1
= 0.0381
R
1
= 0.0335
R
1
= 0.0243
[I > 2sigma(I)]
2
wR = 0.0721
2
wR = 0.0899
2
wR = 0.0658
2
R indices (all data)
R
wR
1
= 0.0520
= 0.0774
R
1
= 0.0803
R
1
= 0.0392
R
1
= 0.0269
2
wR = 0.1168
2
wR = 0.0931
2
wR = 0.0670
2
Largest diff. Peak
and hole/e.Å
0.610 and − 1.518
1.090 and − 1.169
0.750 and − 1.290
1.343 and − 1.238
−
3

PARK ET AL.
5 of 11
1
13
ambient temperature. H NMR and C NMR along with
elemental analyses were consistent with the bpma and
3.2 | Crystal structure description
1
corresponding Zn (II) and Cd (II) formulation. H NMR
Dark green needle like crystals of [(bpma)Co(μ–Cl)Cl]
2
spectra of the Zn (II) and Cd (II) complexes were only
slightly shifted (δ 0.03–0.24) relative to those in the asso-
ciated ligands due to resonance effects of the nitrogen and
carbon atoms of the 4‐bromoaniline and pyridine. Owing
to the paramagnetic nature of Cu (II) and Co (II), we
and orange cubic crystals of [(bpma)Cu(μ–Cl)Cl] were
2
obtained from a Et O solution (10.0 ml) diffusion into an
2
MeOH (5.00 ml). The X‐ray quality single crystals of
[(bpma)Zn(μ–Cl)Cl] and [(bpma)Cd(μ–Br)Br] were
2
2
grown from an IPA solution (10.0 ml) diffusion into
DMF solution (5.0 ml). The ORTEP drawings of com-
plexes are shown in Figure 1 ([(bpma)Co(μ–Cl)Cl]2),
were unable to characterized [(bpma)Co(μ–Cl)Cl] and
2
1
13
[
(bpma)Cu(μ–Cl)Cl] by H NMR and C NMR spec-
2
troscopy. However, the characteristic absorption band
Figure 2 ([(bpma)Cu(μ–Cl)Cl] ), Figure 3 ([(bpma)
2
−
1
around 1590–1592 cm for the >C=N moiety was iden-
tified for synthesized complexes. Characteristic C–H
peaks in the IR spectra were also observed at 3067,
Zn(μ–Cl)Cl]
2
) and Figure 4 ([(bpma)Cd(μ–Br)Br] ).
2
All the synthesized complexes crystallized in monoclinic
system with P2(1)/n space groups. The selected bond
lengths and angles are recorded in Table 2.
X‐ray structures revealed chloro‐bridged dimeric spe-
cies with crystallographic inversion symmetry for
−
1
3
[
[
100, 3134 and 3086 cm for [(bpma)Co(μ–Cl)Cl]2,
(bpma)Cu(μ–Cl)Cl]2, [(bpma)Zn(μ–Cl)Cl]2 and
(bpma)Cd(μ–Br)Br] , respectively. Elemental analysis
2
of the synthesized complexes was consistent with the pro-
posed structures in Scheme 1 and confirmed the purity of
[(bpma)M(μ–Cl)Cl] (M = Co, Cu and Zn, X = Cl) com-
2
plexes, whereas a dimeric bromo‐bridged species for
([(bpma)Cd(μ–Br)Br]2) complex. The coordination
geometry around the M (II) centre in [(bpma)M(μ–X)
isolated complexes [(bpma)MX ] (M = Co, Cu and Zn,
2
X = Cl; M = Cd, X = Br). All the synthesized complexes
were stable towards oxygen and moisture and could be
stored for months at room temperature.
X]
(M = Co, Cu and Zn, X = Cl; M = Cd, X = Br) can
2
be best described as distorted trigonal bipyramidal
SCHEME 1 Synthesis of the bpma and
corresponding complexes, [(bpma)M(μ–
X)X]
2
(M = Co, Cu and Zn, X = Cl;
M = Cd, X = Br)

6
of 11
PARK ET AL.
FIGURE 1 ORTEP drawing of [(bpma)Co(μ–Cl)Cl]
2
with
thermal ellipsoids at 90% probability. All hydrogen atoms are
omitted for clarity
2
FIGURE 4 ORTEP drawing of [(bpma)Cd(μ–Br)Br] with
thermal ellipsoids at 90% probability. All hydrogen atoms are
omitted for clarity
consisting of two nitrogen atoms of 4‐bromoaniline and
pyridine moieties and two bridged halogen atoms along
with one terminal halogen atom.
The bond lengths of M–Npyridine (M = Co, Cu, Zn, and
Cd) and M–Nimine in [(bpma)M(μ–X)X] (M = Co, Cu
2
and Zn, X = Cl; M = Cd, X = Br) lie in 2.064(4) –
2.2886(2) Å and 2.038(4) – 2.4160(2) Å range, similar to
the M–N bond lengths of trigonal bipyramidal imine M
[
39–41]
(
II) complexes.
increased by approximately 0.015–0.200 Å, ranging in size
from ([(bpma)Cu(μ–Cl)Cl]2) ([(bpma)Co(μ–Cl)
Cl] ) < ([(bpma)Zn(μ–Cl)Cl] ) < ([(bpma)Cd(μ–Br)
The bond length of M–Nimine
<
2
2
Br] ). The M–Cl bond lengths ranged from 2.2333(7) –
2
[
42]
2
2
.6460(6) Å
while those of M–Br ranged from
.5298(5) – 2.8244(5) Å. The double imine N(2)–C(6) dis-
FIGURE 2 ORTEP drawing of [(bpma)Cu(μ–Cl)Cl]
thermal ellipsoids at 60% probability. All hydrogen atoms are
omitted for clarity
2
with
tances of 1.289(2) Å ([(bpma)Co(μ–Cl)Cl] ), 1.279(6) Å
2
([(bpma)Cu(μ–Cl)Cl] ), 1.282(2) Å ([(bpma)Zn(μ–Cl)
2
Cl] ) and 1.283(3) Å ([(bpma)Cd(μ–Br)Br] ) were in
2
2
accepted range of carbon‐nitrogen double bonds. The
C(5)–C(6) bond distances of the complexes ranged from
1.458(3) – 1.467(3) Å, reflecting delocalised π‐electrons.
The bond lengths were slightly affected by the central
metal variation.
The average Nimine–M–Npyridine bond angles for
[
(bpma)M(μ–Cl)Cl] (M = Co, Cu, Zn and Cd) ranged
2
from 70.07(6) – 80.92(2)°, whereas X–M–X angles ranged
from 118.59(6)‐ 125.42(2)° and were slightly affected by
metal center. The Npyridine–M(1)–Cl(1), Npyridine–M(1)–
Cl(2) and Cl(1)–M(1)–Cl(2) angles for the complexes
[
(bpma)M(μ–Cl)Cl] (M = Co, Cu and Zn) were nearly
2
120° in the range of 116.63(5)° – 122.98(3)°. Similarly, the
N(1)–Cd(1)–Br(3) and Br(2)–Cd(1)–Br(3) angles for
the complex [(bpma)Cd(μ–Br)Br] were nearly 120° in
FIGURE 3 ORTEP drawing of [(bpma)Zn(μ–Cl)Cl]
2
with
2
thermal ellipsoids at 50% probability. All hydrogen atoms are
omitted for clarity
the range of 124.85(5)° – 125.42(2)°, excluding the bond
angles of N(1)–M(1)–Br(2) which was 109.63(5)°. Nimine
–

PARK ET AL.
7 of 11
TABLE 2 The selected bond lengths (Å) and angles (°) of [(bpma)M(μ–X)X]
2
(M = Co, Cu and Zn, X = Cl; M = Cd, X = Br)
[(bpma)Cd(μ–Br)Br]
2
[(bpma)Co(μ–Cl)Cl]
2
[(bpma)Cu(μ–Cl)Cl]
2
[(bpma)Zn(μ–Cl)Cl]
2
Bond lengths
Co(1)–N(1)
Co(1)–N(2)
Co(1)–Cl(1)
Co(1)–Cl(2)
2.0671(2) Cu(1)–N(1)
2.1824(2) Cu(1)–N(2)
2.3258(7) Cu(1)–Cl(1)
2.2629(7) Cu(1)–Cl(2)
2.4721(6) Cu(1)–Cl(1)
1.352(2) N(1)–C(5)
1.289(2) N(2)–C(6)
1.428(2) N(2)–C(7)
1.458(3) C(5)–C(6)
2.064(4)
2.038(4)
2.4137(2)
2.2878(2)
2.3085(1)
1.346(6)
1.279(6)
1.444(6)
1.462(7)
Zn(1)–N(1)
Zn(1)–N(2)
Zn(1)–Cl(1)
Zn(1)–Cl(2)
Zn(1)–Cl(1)
N(1)–C(5)
N(2)–C(6)
N(2)–C(7)
C(5)–C(6)
2.0752(2)
2.2026(2)
2.2880(7)
2.2333(7)
2.6460(6)
1.354(2)
1.282(2)
1.426(2)
1.463(2)
Cd(1)–N(1)
Cd(1)–N(2)
Cd(1)–Br(3)
Cd(1)–Br(2)
Cd(1)–Br(2)
N(1)–C(5)
N(2)–C(6)
N(2)–C(7)
C(5)–C(6)
2.2886(2)
2.4160(2)
2.5298(5)
2.6166(6)
2.8244(5)
1.359(3)
1.283(3)
1.422(3)
1.467(3)
#1
#1
#1
#1
Co(1)–Cl(1)
N(1)–C(5)
N(2)–C(6)
N(2)–C(7)
C(5)–C(6)
Bond angles
N(1)–Co(1)–N(2)
N(1)–Co(1)–Cl(2)
N(2)–Co(1)–Cl(2)
N(1)–Co(1)–Cl(1)
N(2)–Co(1)–Cl(1)
N(1)–Co(1)–Cl(1)
N(2)–Co(1)–Cl(1)
78.39(6) N(1)–Cu(1)–N(2)
117.82(5) N(1)–Cu(1)–Cl(2)
95.99(5) N(2)–Cu(1)–Cl(2)
118.85(5) N(1)–Cu(1)–Cl(1)
89.36(5) N(2)–Cu(1)–Cl(1)
94.47(5) N(1)–Cu(1)–Cl(1)
169.55(4) N(2)–Cu(1)–Cl(1)
80.92(2)
119.81(1)
96.38(1)
121.52(1)
90.19(1)
93.22(1)
169.89(1)
118.59(6)
118.4(4)
112.7(3)
120.9(5)
119.2(5)
N(1)–Zn(1)–N(2)
N(1)–Zn(1)–Cl(2)
N(2)–Zn(1)–Cl(2)
N(1)–Zn(1)–Cl(1)
N(2)–Zn(1)–Cl(1)
N(1)–Zn(1)–Cl(1)
N(2)–Zn(1)–Cl(1)
78.39(6)
N(1)–Cd(1)–N(2)
N(1)–Cd(1)–Br(3)
N(2)–Cd(1)–Br(3)
N(1)–Cd(1)–Br(2)
N(2)–Cd(1)–Br(2)
N(1)–Cd(1)–Br(2)
N(2)–Cd(1)–Br(2)
70.07(6)
124.85(5)
102.39(5)
109.63(5)
90.19(5)
90.82(5)
161.79(4)
125.42(2)
119.47(2)
112.85(1)
122.7(2)
117.48(2)
120.44(5)
100.77(5)
116.63(5)
92.03(5)
#
#
1
1
#1
#1
#1
#1
#1
#1
90.78(5)
166.77(4)
122.89(3)
119.95(2)
111.23(1)
122.34(1)
117.68(2)
Cl(1)–Co(1)–Cl(2)
C(6)–N(2)–C(7)
C(6)–N(2)–Co(1)
C(8)–C(7)–N(2)
C(12)–C(7)–N(2)
122.98(3) Cl(1)–Cu(1)–Cl(2)
118.58(2) C(6)–N(2)–C(7)
111.54(1) C(6)–N(2)–Cu(1)
122.11(2) C(8)–C(7)–N(2)
118.02(2) C(12)–C(7)–N(2)
Cl(1)–Zn(1)–Cl(2)
C(6)–N(2)–C(7)
C(6)–N(2)–Zn(1)
C(8)–C(7)–N(2)
C(12)–C(7)–N(2)
Br(3)–Cd(1)–Br(2)
C(6)–N(2)–C(7)
C(6)–N(2)–Cd(1)
C(8)–C(7)–N(2)
C(12)–C(7)–N(2)
M(1)–Cl(1) and Nimine–M(1)–X(2) angles for Co (II) and
Cu (II) complexes were nearly 90 degrees in the range
of 89.36(5)° – 96.38(1)°, excluding Nimine–Zn(1)–Cl(2)
and Nimine–Cd(1)–Br(3) which were 100.77(5)° and
benzenamine (bpma)‐based complexes showed in the
order of [(bpma)Cu(μ–Cl)Cl]2 (0.806) > [(bpma)
Co(μ–Cl)Cl]2
(0.776)
>
[(bpma)Zn(μ–Cl)Cl]2
(0.731) > [(bpma)Cd(μ–Br)Br] (0.606), depending on
2
#
1
1
02.39(5)°, respectively. The N(2)–M(1)–X(1) angles
the bond angles around the metal centre. Among
[(bpma)M(μ–X)X]2 (M = Co, Cu and Zn, X = Cl;
M = Cd, X = Br), the geometry at copper centre is more
for the complexes [(bpma)M(μ–X)X]2 (M = Co, Cu
and Zn, X = Cl; M = Cd, X = Br) were 169.55(4)°,
1
69.89(1)°, 166.77(4)° and 161.79(4)°, respectively.
The comparison of bond angles and geometric param-
eter (τ) values it is evident that [(bpma)M(μ–X)X]2,
showed a distorted trigonal bipyramidal geometry with
N,N′‐bidentate iminopyridine, two bridged and one ter-
minal halogen ligand, achieving a 5‐coordinated com-
TABLE 3 Five‐coordinate geometry indices for [(bpma)M(μ–X)
2
X] (M = Co, Cu and Zn, X = Cl; M = Cd, X = Br) and represen-
tative examples from the literature
Complexes
Geometry
trigonal bipyramidal 1.00
trigonal bipyramidal 0.776 This work
τ
5
Reference
plexes (Table 3). τ are presented in Table 3 as improved
5
[43,44]
trigonal bipyramidal
simple metrics for quantitatively evaluating the geometry
[43,44]
of the five coordinate complexes.
The τ value of
[(bpma)Co(μ–Cl)Cl]
2
5
[(bpma)M(μ–X)X]2 (M = Co, Cu and Zn, X = Cl;
[(bpma)Cu(μ–Cl)Cl]2 trigonal bipyramidal 0.806 This work
M = Cd, X = Br) showed either square‐pyramidal or tri-
gonal bipyramidal distorted by 0.606–0.806 while an ideal
[
[
(bpma)Zn(μ–Cl)Cl]
2
trigonal bipyramidal 0.731 This work
(bpma)Cd(μ–Br)Br]
2
trigonal bipyramidal 0.606 This work
trigonal bipyramidal arrangement has the value of τ = 1.
5
[43,44]
Square‐pyramidal
square‐pyramidal
0.00
The τ values of the 4‐bromo‐N‐((pyridin‐2‐yl)methylene)
5

8
of 11
PARK ET AL.
(Table 2). Interestingly, the plane of the 4‐bromophenyl
current study with identical ligand architecture. Presum-
moiety and the plane of metal and pyridine were 20.95°
ably, the electron‐rich cloud around the Cu metal in
for [(bpma)Co(μ–Cl)Cl] , 20.65° for [(bpma)Cu(μ–Cl)
[(bpma)Cu(μ–Cl)Cl] provided increased activity com-
2
2
Cl] , 18.02° for [(bpma)Zn(μ–Cl)Cl]2 and 21.31° for
pared to the electronic effect of [(bpma)M(μ–X)X]2
(M = Co and Zn, X = Cl; M = Cd, X = Br).
2
[(bpma)Cd(μ–Br)Br]2.
To evaluate the total steric hindrance by bulky
ligands toward metal centre, it can be predicted and
quantitatively calculated by comparison through a topo-
graphic steric map of M (II) complexes by use of
3
.3 | Catalytic studies
[45]
The synthesized metal complexes could be activated with
MMAO to polymerise MMA, producing PMMA. The
obtained PMMA has the T in range of 122–129 °C, char-
acterized by DSC. The polymers were isolated as white
solids and characterised by GPC in THF using standard
polystyrene as the reference. (Table 4)
To confirm the catalytic activity of MMA polymerisa-
tion, metal salts/precursors such as CoCl ·6H O,
program ″SambVca″ (see supplementary materials).
Figure 1 in the supplementary material shows ball and
stick model, space‐filling model, and topographic steric
map of [(bpma)M(μ–X)X]2 (M = Co, Cu and Zn,
X = Cl; M = Cd, X = Br) for presenting steric bulk
ligands. Only considering total steric factor by topo-
graphic steric maps it is evident that more sterically hin-
dered complex displayed better catalytic performance.
For instance, Cu (II) complex despite of having more
sterically hindered with buried volume % is 36.2 showed
g
2
2
CuCl ·2H O, ZnCl , CdBr ·4H O and MMAO were tested
2
2
2
2
2
towards MMA under identical experimental conditions,
respectively. The synthesized metal complexes, [(bpma)
Cu(μ–Cl)Cl]2 and [(bpma)Zn(μ–Cl)Cl]2 exhibited
improved catalytic activities with better polymerization
control yielding high molecular weight PMMA with
narrower PDIs, whereas the Co and Cd complexes exhib-
ited lower activities compared to their corresponding
starting materials.
4
higher activity 9.14 × 10 g/molCu.h compared to rest of
its analogous under same conditions. These results are in
contrast to our previous results where more sterically
hindered environment negatively affect the catalytic
activity. Similarly the order of activity for [(bpma)
M(μ–X)X]2 (M = Co and Zn, X = Cl; M = Cd,
X = Br) was found to be [(bpma)Zn(μ–Cl)Cl] (buried
2
4
The catalytic activity of [(bpma)Cu(μ–Cl)Cl] was
volume
%
34.7, activity 3.24
×
10 g/molZn.
2
much higher compared to rest of complexes used in
h) > [(bpma)Co(μ–Cl)Cl]2 (buried volume % 34.7,
TABLE 4 Polymerization of MMA by M (II) complexes in the presence of MMAO
a
b
c
d
e
f
Entry
Catalyst
Yield
g)
Activity
T
g
Tacticity
%mr
Mn
w n
M /M
4
5
(
(g/mol‐Cat·h) × 10
(°C)
%mm
%rr
(g/mol) × 10
g
1
2
3
4
5
6
7
8
9
[CoCl
2
·6H
2
O]
30.3
11.1
11.1
18.2
8.97
19.8
58.6
20.8
15.5
4.73
1.74
1.73
2.85
1.40
3.08
9.14
3.24
2.48
133
136
129
131
120
125
128
129
122
6.30
8.80
9.20
6.20
37.2
10.5
11.4
10.3
11.0
23.9
23.7
24.2
29.0
10.9
20.5
20.3
21.2
19.9
69.8
67.5
66.6
64.8
51.9
69.0
68.3
68.5
69.1
10.7
13.4
1.33
9.42
6.78
8.53
9.12
8.32
9.05
1.49
1.93
1.58
1.84
2.09
2.61
1.97
2.58
2.56
g
[CuCl
2
2
·2H O]
g
[ZnCl
2
]
g
[CdBr
2
2
·4H O]
h
MMAO
[(bpma)Co(μ–Cl)Cl]
[(bpma)Cu(μ–Cl)Cl]
[(bpma)Zn(μ–Cl)Cl]
[(bpma)Cd(μ–Br)Br]
2
2
2
2
a
[M (II) catalyst]
0
= 15 μmol, and [MMA]
0 0 0
/[MMAO] /[M (II) catalyst] = 3100:500:1.
b
c
Yield defined a mass of dried polymer recovered/mass of monomer used.
Activity is (g PMMA)/(mol‐cat·h).
d
g
T is glass transition temperature which is determined by a thermal analyzer.
e
Determined using gel permeation chromatography (GPC) eluted with THF at room temperature by filtration with polystyrene calibration.
f
M
n
refers to the number average of molecular weights of PMMA.
g
It is a blank polymerization which was done solely by MMAO. It is a blank polymerization in which CoCl
2
·6H
2
O, CuCl
2
·2H
2
O, ZnCl
2
2 2
and CdBr .4H O were
also activated by MMAO.
h
It is a blank polymerization which was done solely by MMAO.

PARK ET AL.
9 of 11
4
activity 3.08 × 10 g/molCo.h) > [(bpma)Cd(μ–Br)Br]
(
polymerization with moderate activity and syndiotacticity.
2
4
buried volume % 30.8, activity 2.48 × 10 g/molCd.h).
Compared with our previous Co complexes with N, N‐
[
52]
Thus, it is revealed that the least sterically crowd around
the metal centre has detrimental effect on catalytic activ-
ity in the current system. Thus, the electronic effects of
catalysts are more pronounced compared to steric effect
in controlling the polymerization activity. The influence
of metal centre variation is also studied. It has been
observed that despite of having same buried volume %
bis(1‐pyrazolyl)methyl
the current Co complex exhib-
ited better activity and stereoselectivity and yielded PMMA
with high molecular weight. The MMA polymerisation
activity of complexes in the current study should be
considered as a function of the electron density around
the metal centre.
(
(
supplementary material, Figure S1) for Zn (II) and Co
II) complexes, Zn (II) complex showed higher activity
4
| CONCLUSIONS
compared to its Co (II) analogous. Thus, the activity of
these M (II) complexes with same ligand (bpma) toward
MMA polymerisation is influenced by both steric and
metal electronics. In addition, it is worth to note that
the solubility of complexes in polymerization media
showed an impact on polymerization activity in previous
research. Thus, the lower activity of [(bpma)Cd(μ–Br)
Br] and [(bpma)Co(μ–Cl)Cl] compared to metal pre-
In summary, we investigated the synthesis and X‐ray
crystallographic structures of [(bpma)Co(μ–Cl)Cl]2,
[(bpma)Cu(μ–Cl)Cl]2,
[(bpma)Zn(μ–Cl)Cl]2
and
[
(bpma)Cd(μ–Cl)Cl] complexes bearing 4‐bromo‐N‐(2‐
2
pyridinylmethylene) benzenamine ligand. The coordina-
tion geometry around the metal centres in [(bpma)
M(μ–X)X] (M = Co, Cu and Zn, X = Cl; M = Cd,
2
2
2
X = Br) complexes can be best described as distorted tri-
angular bipyramidal. The synthesized complexes
cursors CdBr ·4H O and CoCl ·6H O, respectively can
2
2
2
2
be attributed to its lower solubility in reaction media.
Moreover, the catalytic activity of [(bpma)Cu(μ–Cl)
Cl]2 was much higher than [(bpma)Co(μ–Cl)Cl]2,
[(bpma)M(μ–X)X]2 (M = Co, Cu and Zn, X = Cl;
M = Cd, X = Br) were investigated for their catalytic effi-
cacy in MMA polymerization. The catalytic activity of
[
(bpma)Zn(μ–Cl)Cl] and [(bpma)Cd(μ–Br)Br] . Pre-
2
2
[(bpma)Cu(μ–Cl)Cl]2 toward the polymerisation of
sumably, the electron‐rich cloud around the Cu metal in
(bpma)Cu(μ–Cl)Cl] provided increased activity com-
methyl methacrylate (MMA) in the presence of MMAO
[
2
4
resulted in an activity of 9.14 × 10 g PMMA/mol·Cu·h
pared to the electronic effect of [(bpma)M(μ–X)X]2
M = Co and Zn, X = Cl; M = Cd, X = Br). Thus, the
at 60 °C. All the complexes in the current investigation
afforded syndio‐enriched PMMA. The catalytic activity
in the present study can be considered as the function
of electronic density around the metal centre.
(
activity of these [(bpma)M(μ–X)X] (M = Co and Zn,
2
X = Cl; M = Cd, X = Br) complexes toward MMA poly-
merisation is influenced by metal electronics. No regular
trend for molecular weight and resultant PDIs can be
seen from polymerization in current data.
SUPPLEMENTARY MATERIAL
The tacticity of PMMA was determined in the range
around syndiotactic (δ 0.85), heterotactic (δ 1.02), and iso-
CCDC 1872375~1872378 contains the supplementary crys-
1
[46–48]
tactic (δ 1.21) based on H NMR.
of PMMA was around 69%, which was similar to all
(bpma)M(μ–X)X]2 (M = Co, Cu and Zn, X = Cl;
The syndiotacticity
tallographic data for [(bpma)Cu(μ–Cl)Cl]
2
, [(bpma)
and [(bpma)
, respectively. These data can be obtained
Zn(μ–Cl)Cl]
Cd(μ–Cl)Cl]
,
[(bpma)Co(μ–Cl)Cl]
2
2
[
2
M = Cd, X = Br) regardless of the polymerization cata-
lyst. However, the syndiotacticity was higher compared
to co‐catalyst, MMAO. Although syndiotacticity was not
sufficiently high to discuss a coordination polymerization
mechanism but was found to be in identical range for all
the synthesised complexes (rr = 0.69).
free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+44) 1223–336‐033; or e‐mail: deposit@ccdc.cam.ac.
uk. Additionally, steric maps of all [(bpma)M(μ–X)X]
2
(M = Co, Cu and Zn, X = Cl; M = Cd, X = Br) which is cal-
culated by the program ″SambVca″ was also presented in
the supplementary material.
Previously studied N,N‐di(2‐picolyl) cyclohexyl-
[49]
amine based Pd, Cu, Zn, and Cd complexes were found
to be active catalysts for the MMA polymerisation to yield
syndiotactic PMMA (rr = 0.73). Similarly, Cu (II) com-
plexes with ligand N‐(2‐furanylmethyl)‐N‐(1–3,5‐dimethyl‐
ACKNOWLEDGEMENT
[50]
1
H‐pyrazolylmethyl)‐N‐(phenylmethyl) amines
yielded
This research was supported by the National Research
Foundation (NRF) of South Korea, funded by the Minis-
try of the Education, Science, and Technology (MEST)
(Grant No. 2017R1A2B4002100).
syndiotactic PMMA (rr = 0.78) with only 30% conversion.
Copper (II) complex of 2‐(pyrazol‐3‐yl)‐6‐(pyrazolate) pyri-
[51]
dine and related ligand
reported catalyzed MMA

10 of 11
PARK ET AL.
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1993, 26, 7134.
[
[
25] M. A. Giardello, Y. Yamamoto, L. Brard, T. J. Marks, J. Am.
Chem. Soc. 1995, 117, 3276.
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