Polymerizations of methyl methacrylate and rac-lactide by zinc(II) precatalyst containing N-substituted 2-iminomethylpyridine and 2-iminomethylquinoline

Article abstract of DOI:10.1080/00958972.2017.1416106

The reaction of [ZnCl₂] with N-cyclopentyl-1-(quinolin-2-yl)methanimine (L_A), N-cyclohexyl-1-(quinolin-2-yl)methanimine (L_B), N-cyclohexyl-1-(pyridin-2-yl)methanimine (L_C), 2,6-diethyl-N-(pyridin-2-ylmethylene)a

Full text of DOI:10.1080/00958972.2017.1416106

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Polymerizations of methyl methacrylate and
rac-lactide by zinc(II) precatalyst containing
N-substituted 2-iminomethylpyridine and 2-
iminomethylquinoline
Joung Heo, Hyosun Lee & Saira Nayab
To cite this article: Joung Heo, Hyosun Lee & Saira Nayab (2017): Polymerizations of
methyl methacrylate and rac-lactide by zinc(II) precatalyst containing N-substituted 2-
iminomethylpyridine and 2-iminomethylquinoline, Journal of Coordination Chemistry, DOI:
10.1080/00958972.2017.1416106
To link to this article: https://doi.org/10.1080/00958972.2017.1416106
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Dec 2017.
Published online: 27 Dec 2017.
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Date: 03 January 2018, At: 00:07

Journal of Coordination Chemistry, 2017
ꢁꢁpꢂ://ꢃꢄꢅ.ꢄꢆg/10.1080/00958972.2017.1416106
ꢀ
Polymerizations of methyl methacrylate and rac-
lactide by zinc(II) precatalyst containing N-substituted
2-iminomethylpyridine and 2-iminomethylquinoline
a
a
b
Joung Heo , Hyosun Lee and Saira Nayab
ꢇ
dꢈpꢇꢆꢁꢉꢈꢊꢁ ꢄꢋ Cꢀꢈꢉꢅꢂꢁꢆꢌ ꢇꢊꢃ Gꢆꢈꢈꢊ-nꢇꢊꢄ mꢇꢁꢈꢆꢅꢇꢍꢂ rꢈꢂꢈꢇꢆcꢀ Cꢈꢊꢁꢆꢈ, Kꢌꢎꢊgpꢄꢄk nꢇꢁꢅꢄꢊꢇꢍ uꢊꢅvꢈꢆꢂꢅꢁꢌ,
b
dꢇꢈgꢎ, rꢈpꢎbꢍꢅc ꢄꢋ Kꢄꢆꢈꢇ; dꢈpꢇꢆꢁꢉꢈꢊꢁ ꢄꢋ Cꢀꢈꢉꢅꢂꢁꢆꢌ, sꢀꢇꢀꢈꢈꢃ Bꢈꢊꢇzꢅꢆ Bꢀꢎꢁꢁꢄ uꢊꢅvꢈꢆꢂꢅꢁꢌ, sꢀꢈꢆꢅꢊgꢇꢍ dꢅꢆ (u),
iꢂꢍꢇꢉꢅc rꢈpꢎbꢍꢅc ꢄꢋ Pꢇkꢅꢂꢁꢇꢊ
ABSTRACT
ARTICLE HISTORY
The reaction of [ZnCl ] with N-cyclopentyl-1-(quinolin-2-yl)
rꢈcꢈꢅvꢈꢃ 8 ocꢁꢄbꢈꢆ 2017
accꢈpꢁꢈꢃ 30 nꢄvꢈꢉbꢈꢆ 2017
2
methanimine (L ), N-cyclohexyl-1-(quinolin-2-yl)methanimine (L ),
A
B
N-cyclohexyl-1-(pyridin-2-yl)methanimine (L ), 2,6-diethyl-N-(pyridin-
C
KEYWORDS
2
-ylmethylene)aniline (L ), N-cyclopentyl-1-(pyridin-2-yl)methanimine
D
2-ꢅꢉꢅꢊꢄꢉꢈꢁꢀꢌꢍpꢌꢆꢅꢃꢅꢊꢈ;
2-ꢅꢉꢅꢊꢄꢉꢈꢁꢀꢌꢍqꢎꢅꢊꢄꢍꢅꢊꢈ;
Zꢅꢊc(ii) cꢄꢉpꢍꢈxꢈꢂ;
ꢂꢌꢊꢃꢅꢄꢁꢇcꢁꢅc Pmma;
ꢀꢈꢁꢈꢆꢄꢁꢇcꢁꢅc Pla
(
L ), and N-phenyl-(pyridin-2-yl)methanimine (L ) in ethanol produced
E
F
the bidentate [(NN′)ZnCl ] complexes, [L ZnCl ], [L ZnCl ], [L ZnCl ],
2
A
2
B
2
C
2
[
L ZnCl ], [L ZnCl ]and [L ZnCl ], respectively.The molecular structures
D 2 E 2 F 2
revealed that the zinc in [L ZnCl ] (L = L − L ) showed a distorted
n
2
n
A
D
tetrahedral geometry involving two nitrogens of N,N’-bidentate ligands
and two chloride ligands. Most of these initiators were effective for
polymerization of methyl methacrylate (MMA) and polymerization
of rac-lactide (rac-LA). [L ZnCl ] (with N-cyclohexyl substituted at
C
2
imine-pyridine moiety) exhibited the highest catalytic activity for
MMA polymerization in the presence of modified methylaluminoxane
4
(
MMAO) with an activity of 3.33 × 10 g PMMA/mol·Zn·h at 60 °C,
giving moderate syndiotactic poly methyl methacrylate (PMMA) with
5
high molecular weight (9.62 × 10 g/mol). The dimethyl derivatives
[
L ZnMe ] (L = L − L ), generated in situ, polymerized rac-LA with
n 2 n A F
moderate activity and yielded a polylactide (PLA) with good number-
average molecular weights and narrower polydispersity indices (PDIs).
[
L ZnMe ] effectively initiates the ring-opening polymerization (ROP)
of rac-LA to attain heterotactic PLA (P = 0.91).
A 2
r
CONTACT hꢌꢄꢂꢎꢊ lꢈꢈ
ꢀꢌꢄꢂꢎꢊꢍꢈꢈ@kꢊꢎ.ꢇc.kꢆ; sꢇꢅꢆꢇ nꢇꢌꢇb
ꢂꢇꢅꢆꢇꢊꢇꢌꢇb07@ꢌꢇꢀꢄꢄ.cꢄꢉ
sꢎppꢍꢈꢉꢈꢊꢁꢇꢍ ꢃꢇꢁꢇ ꢋꢄꢆ ꢁꢀꢅꢂ ꢇꢆꢁꢅcꢍꢈ cꢇꢊ bꢈ ꢇccꢈꢂꢂꢈꢃ ꢇꢁ ꢀꢁꢁpꢂ://ꢃꢄꢅ.ꢄꢆg/10.1080/00958972.2017.1416106.
©
2017 iꢊꢋꢄꢆꢉꢇ uK lꢅꢉꢅꢁꢈꢃ, ꢁꢆꢇꢃꢅꢊg ꢇꢂ tꢇꢌꢍꢄꢆ & fꢆꢇꢊcꢅꢂ Gꢆꢄꢎp

2
J. HEO ET AL.
1
. Introduction
Schiff base compounds are popular nitrogen-donor ligands. The convenient synthetic
approach and thermal stability of Schiff base ligands have contributed significantly for their
applications as supporting ligands for metal-based initiators. Additionally, they are diverse
and have the potential to fine-tune the steric and electronic properties by varying the sub-
stituents. For example, a variety of transition metal complexes including Schiff base ligands
such as α- and β-diimine, 2,6-bis(imino)pyridines, pyridyl-imines and N-substituted 2-imi-
noalkylpyridines have various applications. Transition metal complexes having simple
pyridyl-imines and N-substituted 2-iminoalkylpyridines have been applied to catalysts for
organic transformations [1–18], bioinorganic chemistry [19–25], electrochemistry [26–31],
supramolecular materials chemistry [32–35] and α-olefins polymerization [36–38].
Metal complexes with suitable ligand architecture are vital for achieving a high degree
of polymerization control as these metal complexes influence all steps of polymerization
such as initiation, propagation, and termination [39–43]. Especially, late transition metal
complexes proved to be better candidates for polymerization of polar monomer in controlled
fashion due to their less oxophilic nature [44, 45]. Schiff base derived late transition metal
complexes, for example, sterically bulky diimine (a-diimine)-based nickel complexes,
pyridylbisimine-based iron(II) and cobalt(II), iminopyridine- or aminopyridine-based iron(II)
complexes, were used for α-olefin polymerization, specifically, polymerized methylmeth-
acrylate (MMA) in combination with modified aluminoxane (MAO) to give syndiotactic-rich
polymethylmethacrylate (PMMA) [46]. Wu and co-workers reported bis(β-ketiminato)nickel
complexes to polymerize MMA and yielded syndiotactic-rich PMMA with relatively wide
molecular weight distribution [47]. Similarly a variety of Zn(II) complexes [48–55] supported
by Schiff base ligands demonstrated their potential toward ring opening polymerization
(
ROP) of lactic acid (LA) with excellent catalytic performance owing to the fact that Schiff
base ligands provide electrophilic metal centers for initiators to efficiently coordinate to
monomers [56, 57].
Our group recently synthesized late transition metal complexes such as Zn(II), Cu(II), Pd(II),
Pt(II), Cd(II), and Co(II) complexes with N-substituted 2-iminoalkylpyridines for MMA [58–60]
and LA [61–63] polymerization. In our continuing effort toward the development of effective
and stereoselective catalysts for MMA and rac-LA polymerizations, herein we describe the
synthesis and structural characterization of Zn(II) complexes bearing 2-iminomethylpyridine-
and 2-iminomethylquinoline-based ligands. The effect of steric bulk of substituents attached
to imine moiety on the activity and stereoselectivity are herein discussed.
2
. Experimental
2
.1. General consideration and materials
The syntheses of methyl derivatives of the zinc complexes and all polymerizations were
carried out by the use of standard Schlenk techniques, high vacuum, and glove box under
argon unless otherwise specified. An anhydrous [ZnCl ], 2-pyridinecarboxaldehyde, 2-quin-
2
olinecarboxaldehyde, aniline, cyclopentanamine, cyclohexanamine, 2,6-diethylaniline and
methyl methacrylate (MMA) were purchased from Aldrich, TCI and anhydrous solvents such
as ethanol (C H OH), isopropyl alcohol (IPA), dimethylformamide (DMF), diethyl ether (Et O),
2
5
2
dichloromethane (CH Cl ), and n-hexane were purchased from Merck. THF and toluene were
2
2

JOURNAL OF COORDINATION CHEMISTRY
3
dried over Na/benzophenone ketyl radical, while CH Cl was dried over CaH . These solvents
2
2
2
were deoxygenated by distillation under argon prior to use. Modified methylaluminoxane
MMAO) was purchased from Tosoh Finechem Corporation as 5.90% weight aluminum of a
(
toluene solution and used without purification. 3,6-Dimethyl-1-dioxane-2,5-dione (rac-LA)
was purchased from Aldrich and stored in a glove box.
Elemental analyses (C, H, N) of the prepared complexes were carried out on an elemental
1
13
analyzer (EA 1108; Carlo-Erba, Milan, Italy). H NMR (400 MHz, 500 MHz) and C NMR
100 MHz, 125 MHz) spectra were recorded on a Bruker Avance Digital NMR spectrometer;
chemical shifts were reported in ppm units relative to SiMe as the internal standard. Infrared
(
4
(
IR) spectra were recorded on a Bruker FT/IR-Alpha (neat) and the data are reported in recip-
−1
rocal centimeters (cm ). The molecular weights and molecular weight distributions of the
obtained PMMAs and PLAs were carried out using gel permeation chromatography (GPC)
(
THF, Alliance e2695; Waters Corp., Milford, MA). Glass transition temperature (T ) was deter-
g
mined using a thermal analyzer (DSC 4000; Perkin Elmer).
2
.2. Preparation of ligands and Zn (II) complexes
Ligands L (L = L − L ) were obtained by literature methods at high yields (70 – 98%) from
n
n
A
F
the condensation reaction between the appropriate X-amine (X = cyclopentyl, cyclohexyl,
phenyl, 2,6-diethyl-phenyl) and 2-pyridinecarboxaldehyde or 2-quinolinecarboxaldehyde
in CH Cl [58, 64–74]. The syntheses of [L ZnCl ] and [L ZnCl ] were carried out as previously
2
2
E
2
F
2
reported [8, 20, 60, 75].
2
.2.1. N-cyclopentyl-1-(quinolin-2-yl)methanimine(dichloro)zinc(II), [L ZnCl ]
A
2
A solution of L (1.23 g, 5.50 mmol) in ethanol (150 mL) was added to a solution of [ZnCl ]
A
2
(0.750 g, 5.50 mmol) in ethanol (150 mL) at room temperature. Precipitation of a white mate-
rial occurred while stirring at room temperature for 12 h. The white powder was filtered and
washed with cold ethanol (50.0 mL), followed by washing with diethyl ether (50.0 mL) to
give a final white product (1.79 g, 90.3%). X-ray crystals of [L ZnCl ] were obtained within
A
2
three days from Et O solution (10.0 mL) diffusion into a DMF solution (10.0 mL) of [L ZnCl ].
2
A
2
Analysis calculated for C H Cl N Zn (%): C, 49.96; H, 4.47; N, 7.77. Found: C, 49.92; H, 4.48;
1
5
16
2
2
1
N, 7.74. H NMR (CDCl , 500 MHz) δ: 8.66 (d, 1H, J = 8.20 Hz, –NC H –), 8.61 (s, 1H, –N = CH–
3
9
6
NC H –), 8.59 (d, 1H, J = 9.30 Hz, –NC H –), 8.04–8.01 (m, 2H, –NC H –), 7.85–7.80 (m, 2H, –
9
6
9
6
9
6
NC H –), 4.42–4.36 (m, 1H, ipso–C H –), 2.35–2.27 (m, 2H, –NC H –), 2.23–2.16 (m, 2H, -C H –),
9
6
5
9
5
9
5
9
1
3
2
.14–2.06 (m, 2H, –C H –), 1.81–1.75 (m, 2H, –C H –). C NMR (CDCl , 100 MHz) δ: 159.31 (s,
5 9 5 9 3
1
C, –N = CH–NC H –), 146.34 (s, 1C, ipso-NC H –), 145.17 (s, 1C, –NC H –), 142.28 (s, 1C,
9
6
9
6
9
6
-
NC H –), 134.23 (s, 1C, –NC H –), 130.73 (s, 1C, –NC H –), 130.41 (s, 1C, -NC H –), 128.23 (s,
9 6 9 6 9 6 9 6
1
C, –NC H –), 128.14 (s, 1C, –NC H –), 122.00 (s, 1C, –NC H –), 70.59 (s, 1C, ipso-C H –), 34.56
9 6 9 6 9 6 5 9
−1
(
s, 2C, –C H –), 24.98 (s, 2C, –C H –). IR (solid neat; cm ): 3047 (w), 2956 (w), 2875 (w), 2313
5 9 5 9
(
7
w), 1695 (s), 1647 (s), 1518 (s), 1456 (s), 1390 (s), 1326 (s), 1222 (w), 1081 (w), 940 (w), 838 (s),
59 (s), 637 (s).
2
.2.2. N-cyclohexyl-1-(quinolin-2-yl)methanimine(dichloro)zinc(II), [L ZnCl ]
B 2
Following a procedure similar to that described for [L ZnCl ], L (0.715 g, 3.00 mmol) and
A
2
B
[
ZnCl ] (0.409 g, 3.00 mmol) were used to give a white powder as a final product (0.951 g,
2
8
4.6%). X-ray crystals of [L ZnCl ] were obtained within three days from Et O (10.0 mL)
B
2
2

4
J. HEO ET AL.
diffusion into a DMF solution (10.0 mL) of [L ZnCl ]. Analysis calculated for C H Cl N Zn
B
2
16 18
2
2
1
(
%): C, 51.30; H, 4.84; N, 7.48. Found: C, 51.29; H, 4.85; N, 7.45. H NMR (CDCl , 400 MHz) δ:
3
8
.66 (d, 1H, J = 7.60 Hz, –NC H –), 8.62 (s, 1H, –N = CH–NC H –), 8.58 (d, 1H, J = 7.60 Hz, –
9 6 9 6
NC H –), 8.02 (t, 2H, J = 6.80 Hz, –NC H –), 7.82 (t, 2H, J = 8.00 Hz, –NC H –), 3.87 (q, 1H,
9
6
9
6
9
6
J = 10.8 Hz, ipso-C H –), 2.15–2.11 (m, 2H, p-C H –), 2.03–1.95 (m, 4H, o-C H –), 1.76–1.73
6
11
6
11
3
6
11
1
(
m, 1H, m-C H –), 1.43–1.32 (m, 3H, –C H –). C NMR (CDCl , 100 MHz) δ: 159.45 (s, 1C,
6
11
6
11
3
-
N = CH–NC H –), 150.47 (s, 1C, ipso-NC H –), 145.64 (s, 1C, –NC H –), 134.63 (s, 1C, -NC H –),
9 6 9 6 9 6 9 6
1
31.90 (s, 1C, –NC H –), 130.83 (s, 1C, –NC H –), 128.75 (s, 1C, –NC H –), 128.51 (s, 1C, –
9 6 9 6 9 6
NC H –), 127.90 (s, 1C, –NC H –), 122.45 (s, 1C, –NC H –), 68.79 (s, 1C, ipso-C H –), 34.56 (s,
9
6
9
6
9
6
6
11
−
1
2
2
1
C, o-C H –), 25.09 (s, 1C, p-C H –), 25.06 (s, 2C, m-C H –). IR (solid neat; cm ): 3115 (w),
6 11 6 11 6 11
925 (s), 2853 (w), 2374 (w), 2314 (w), 1693 (s), 1651 (s), 1523 (s), 1460 (s), 1215 (s), 1153 (s),
088 (s), 965 (w), 890 (s), 827 (s), 761 (s).
2
.2.3. N-cyclohexyl-1-(pyridin-2-yl)methanimine(dichloro)zinc(II), [L ZnCl ]
C 2
Following a procedure similar to that described for [L ZnCl ], L (2.00 g, 10.6 mmol) and
A
2
C
[
ZnCl ] (1.44 g, 10.6 mmol) were used to give a white powder as a final product (2.45 g,
2
7
1.2%). X-ray crystals of [L ZnCl ] were obtained within three days from Et O solution
C
2
2
(
10.0 mL) diffusion into a CH Cl (10.0 mL) solution of [L ZnCl ]. Analysis calculated for
2 2 C 2
1
C H Cl N Zn (%): C, 44.41; H, 4.97; N, 8.63. Found: C, 44.43; H, 5.00; N, 8.65. H NMR (DMSO-d ,
12
16
2
2
6
500 MHz) δ: 8.80 (d, 1H, J = 4.40 Hz, –NC H –), 8.65 (s, 1H, –N = CH–NC H –), 8.20 (t, 1H,
5 4 5 4
J = 9.20 Hz, –NC H –), 8.04 (d, 1H, J = 7.80 Hz, –NC H –), 7.77 (t, 1H, J = 7.50 Hz, –NC H –),
5
4
5
4
5
4
3
.57–3.43 (m, 1H, ipso-C H –), 1.78–1.72 (m, 4H, o-C H –), 1.61–1.04 (m, 6H, m, p-C H –).
6 11 6 11 6 11
1
3
C NMR (DMSO-d , 125 MHz) δ: 159.79 (d, 1C, J = 170 Hz, –N = CH–NC H –), 149.39 (d, 1C,
6
5
4
J = 182 Hz, -NC H -), 148.41 (s, 1C, ipso-NC H –), 140.94 (d, 1C, J = 167 Hz, –NC H –), 128.20
5
4
5
4
5
4
(
d, 1C, J = 169 Hz, –NC H –), 126.73 (d, 1C, J = 181 Hz, –C H –), 65.86 (d, 1C, J = 141 Hz, ipso-
5 4 5 4
C H –), 33.05 (t, 2C, J = 129 Hz, o-C H –), 24.94 (t, 1C, J = 126 Hz, p-C H –), 24.44 (t, 2C,
6
11
6
11
6
11
−
1
J = 125 Hz, m-C H –). IR (solid neat; cm ): 3019 (w), 2372 (w), 2314 (w), 1692 (s), 1529 (s),
6
11
1215 (s), 1030 (s), 970 (s), 878 (s), 771 (s).
2
.2.4. 2,6-Diethyl-N-(pyridin-2-ylmethylene)aniline(dichloro)zinc(II), [L ZnCl ]
D
2
Following a procedure similar to that described for [L ZnCl ], isopropyl alcohol solution of
A
2
L (0.875 g, 3.67 mmol) and [ZnCl ] (0.500 g, 3.67 mmol) were used to give a white powder
D
2
as a final product (1.10 g, 80.0%). X-ray crystals of [L ZnCl ] were obtained within three days
D
2
from Et O solution (10.0 mL) diffusion in a CH Cl (10.0 mL) solution of [L ZnCl ]. Analysis
2
2
2
D
2
calculated for C H Cl N Zn (%): C, 51.30; H, 4.84; N, 7.48. Found: C, 51.33; H, 4.81; N, 7.47.
1
6
18
2
2
1
H NMR (DMSO-d , 500 MHz) δ: 8.74 (d, 1H, J = 4.90 Hz, –NC H –), 8.37 (s, 1H, –N = CH–NC H –
6
5
4
5 4
)
, 8.19 (t, 1H, J = 9.30 Hz, –NC H –), 8.05 (d, 1H, J = 7.60 Hz, –NC H –), 7.63 (t, 1H, J = 7.80 Hz,
5 4 5 4
–
NC H –), 7.12–7.04 (m, 3H, –(CH CH ) C H –), 2.43 (q, 4H, J = 15.1 Hz, -(CH CH ) C H –), 1.06
5 4 2 3 2 6 3 2 3 2 6 3
13
(t, 6H, J = 7.50 Hz, –(CH CH ) C H –). C NMR (DMSO-d , 125 MHz) δ: 163.92 (d, 1C, J = 172 Hz,
2 3 2 6 3 6
–
1
1
N = CH–NC H –), 152.53 (s, 1C, ipso-(CH CH ) C H –), 149.64 (d, 1C, J = 182 Hz, –NC H –),
5 4 2 3 2 6 3 5 4
48.43 (s, 1C, ipso-NC H –), 138.37 (d, 1C, J = 134 Hz, –NC H –), 132.80 (s, 2C, –(CH CH ) C H –),
5
4
5
4
2
3 2 6 3
26.90 (d, 1C, J = 166 Hz, -NC H –), 126.19 (d, C, J = 159 Hz, –(CH CH ) C H –), 124.82 (d, 1C,
5
4
2
3 2
6
3
J = 163 Hz, -(CH CH ) C H –), 122.41 (d, 1C, J = 130 Hz –NC H –), 24.03 (t, 2C, J = 127 Hz,
2
3 2
6
3
5
4
−1
-
(CH CH ) C H –), 14.57 (q, 2C, J = 253 Hz, –(CH CH ) C H –). IR (solid neat; cm ): 3067 (w),
2 3 2 6 3 2 3 2 6 3
2962 (w), 2876 (w), 2343 (w), 1633 (w), 1588 (s), 1446 (s), 1369 (w), 1300 (s), 1218 (w), 1169
(
s), 1101 (s), 1020 (s), 908 (s), 865 (w), 774 (s), 642 (s).

JOURNAL OF COORDINATION CHEMISTRY
5
2
.2.5. N-cyclopentyl-1-(pyridin-2-yl)methanimine(dichloro)zinc(II), [L ZnCl ] [60]
E
2
Following a procedure similar to that described for [L ZnCl ], L (2.00 g, 11.5 mmol) and
A
2
E
[
ZnCl ] (1.57 g, 11.5 mmol) were used to give a white powder as a final product (3.05 g,
2
8
5.4%). X-ray crystals of [L ZnCl ] were obtained within three days from Et O solution
E
2
2
(
10.0 mL) diffusion into a CH Cl (10.0 mL) solution of [L ZnCl ]. Analysis calculated for
2 2 E 2
1
C H Cl N Zn (%): C, 42.55; H, 4.54; N, 9.02. Found: C, 42.12; H, 4.54; N, 8.86. H NMR (DMSO-d ,
11
14
2
2
6
400 MHz) δ: 8.79 (d, 1H, J = 3.60 Hz, –NC H –), 8.59 (s, 1H, –N = CH-NC H –), 8.15 (t, 1H,
5 4 5 4
J = 3.80 Hz, –NC H –), 8.03 (d, 1H, J = 7.60 Hz, –NC H –), 7.72 (t, 1H, J = 7.40 Hz, –NC H –),
5
4
5
4
5
4
13
4
.07 (m, 1H, –C H –), 1.87–1.84 (m, 4H, –C H –), 1.72–1.63 (m, 4H, –C H –). C NMR (DMSO-d ,
5 9 5 9 5 9 6
1
00 MHz) δ: 160.41 (s, 1C, –N = CH–NC H –), 149.85 (s, 1C, ipso-NC H –), 141.30 (s, 1C, –
5
4
5
4
NC H –), 128.61 (s, 1C, –NC H –), 126.80 (s, 1C, –NC H –), 110.77 (s, 1C, –NC H –), 69.24 (s,
5
4
5
4
5
4
5
4
−1
1
C, ipso-C H –), 33.42 (s, 2C, –C H –), 24.54 (s, 2C, –C H –). IR (solid neat; cm ): 3102 (w), 3024
5 9 5 9 5 9
(
(
w), 2376 (s), 2313 (s), 2178 (w), 1750 (s), 1694 (s), 1649 (s), 1525 (s), 1217 (w), 1091 (s), 1023
s), 944 (w), 775 (s), 713 (w), 643 (s).
2
.2.6. N-phenyl-1-(pyridin-2-yl)methanimine(dichloro)zinc(II), [L ZnCl ] [8, 20]
F 2
Following a procedure similar to that described for [L ZnCl ], L (2.00 g, 11.0 mmol) and
A
2
F
[
ZnCl ] (1.50 g, 11.0 mmol) were used to give a white powder as a final product (3.12 g,
2
8
9.1%). X-ray crystals of [L ZnCl ] were obtained within three days from Et O solution
F
2
2
1
(
10.0 mL) diffusion into a DMF (10.0 mL) solution of [L ZnCl ]. H NMR (DMSO-d , 500 MHz)
F 2 6
δ: 8.81 (d, 1H, J = 4.43 Hz, –NC H –), 8.66 (s, 1H, –N = CH–NC H –), 8.13 (d, 1H, J = 7.78 Hz,
5
4
5
4
–
NC H –), 8.07 (t, 1H, J = 7.78 Hz, –NC H –), 7.65 (t, 1H, J = 7.78 Hz, –NC H –), 7.43 (t, 2H,
5 4 5 4 5 4
J = 7.78 Hz, -C H –), 7.36–7.29 (m, 3H, –C H –).
6
5
6
5
2
.3. X-ray crystallographic studies
An X-ray-quality single crystal was coated with paratone-N oil and the diffraction data meas-
ured at 193(2) K with synchrotron radiation (λ = 0.71073 Å) for [L ZnCl ] and 200(2) K with
A
2
synchrotron radiation (λ = 0.71073 Å) for [L ZnCl ] and [L ZnCl ] while for [L ZnCl ] data
B
2
C
2
D
2
are measured at 100(2) K with synchrotron radiation (λ = 0.61000 Å), respectively, on an ADSC
Quantum-210 detector at 2D SMC with a silicon (111) double crystal monochromator (DCM)
at the Pohang Accelerator Laboratory, South Korea. The ADSC Q210 ADX program [76] was
used for data collection (detector distance is 63 mm, omega scan; ∆ω = 1º, exposure time
is 1 s per frame) and HKL3000sm (Ver. 703r) [77] was used for cell refinement, reduction and
absorption correction (Tmin = 0.868, Tmax = 0.962). Structures were solved by direct methods
and refined by full-matrix least-squares using the SHELXL-2014 [78] computer program. The
positions of all non-hydrogen atoms were refined with anisotropic displacement factors. All
hydrogens were placed using a riding model, and their positions constrained relative to their
parent atoms using the appropriate HFIX command in SHELXL-2014. X-ray crystallography
with PLS-II 2D-SMC beamline was supported by MSIP and POSTECH. The crystal and structure
refinement data for all structures including [L ZnCl ] and [L ZnCl ] are summarized in Table
E
2
F
2
1
. The final cycle of refinement converged with R [I > 2σ(I)] = 0.0303, wR [I > 2σ(I)] = 0.0711
1
2
for [L ZnCl ], R [I > 2σ(I)] = 0.0452, wR [I > 2σ(I)] = 0.0943 for [L ZnCl ], R [I > 2σ(I)] = 0.0571,
A
2
1
2
B
2
1
wR [I > 2σ(I)] = 0.1321 for [L ZnCl ] and R [I > 2σ(I)] = 0.0263, wR [I > 2σ(I)] = 0.0719 for
2
C
2
1
2
[
L ZnCl ], respectively.
D
2

6
J. HEO ET AL.

JOURNAL OF COORDINATION CHEMISTRY
7
2
.4. Catalytic activity for MMA polymerization
Methyl methacrylate (MMA) was dried over molecular sieves and distilled under reduced
pressure before use. To a 100 mL Schlenk flask containing [L ZnCl ] (5.40 mg, 15.0 μmol),
A
2
[
L ZnCl ] (5.60 mg, 15.0 μmol), [L ZnCl ] (4.90 mg, 15.0 μmol), [L ZnCl ] (5.60 mg, 15.0 μmol),
B 2 C 2 D 2
[
L ZnCl ] (4.70 mg, 15.0 μmol) and [L ZnCl ] (4.80 mg, 15.0 μmol) in toluene (10.0 mL) was
E
2
F
2
added MMAO (modified methylaluminoxane, 5.90 wt% in toluene, 3.80 mL, [MMAO] /[Zn(II)
0
catalyst] = 500) under a dry argon atmosphere. After the mixture had been stirred at 60 °C
0
for 20 min, it was transferred into MMA (5.00 mL, 47.1 mmol, [MMA] /[M(II) catalyst] = 3100).
0
0
The reaction flask was immersed in an oil bath at 60 °C and stirred for 2 h. The resulting
polymer was precipitated into methanol (500 mL) and HCl (5.00 mL) was added with stirring
overnight. The polymer was filtered and washed with methanol (500 mL × 3) to give polym-
ethylmethacrylate (PMMA), which was vacuum-dried at 60 °C.
2
.5. Ring opening polymerization of rac-lactide
Polymerization for rac-LA with dimethyl zinc initiators, the catalyst species were generated
as follows. Dichloro Zn(II) complexes (0.50 mmol) and dried THF (7.30 mL) were added to a
Schlenk flask (100 mL) under argon. To this solution was added MeLi (0.63 mL of 1.60 M
solution in diethyl ether, 1.00 mmol) dropwise. After stirring for 2 h at room temperature,
the resulting THF solution was used as an initiator for ROP of rac-LA. The general procedure
for the polymerization reaction was as follows. A Schlenk flask (100 mL) was charged with
rac-LA (0.901 g, 6.25 mmol) under argon and dried CH Cl (5.00 mL) was added. The polym-
2
2
erization was initiated by slow addition of the catalyst solution (1.00 mL, 0.0625 mmol) via
a syringe under argon and the resulting mixture was stirred for the allotted time at −50 °C.
The polymerization reactions were quenched using H O (1.00 mL) followed by addition of
2
1
hexane (2.00 mL) to precipitate the polymer. The monomer conversion was measured by H
NMR spectroscopy. H NMR (CDCl ) for the obtained PLA (polylactide): δ = 5.13–5.20 (m, 1H),
1
3
1.51–1.63 (m, 3H).
3
. Results and discussion
3
.1. Synthesis and chemical properties
Scheme 1 shows the synthesis of ligands and their corresponding dichloro Zn(II) complexes.
The reaction of 2-iminomethylpyridine- and 2-iminomethylquinoline-based ligands (L = L
n
A
−
L ) with [ZnCl ] in 1:1 M ratio afforded white air stable dichloro Zn(II) complexes in yields
D 2
of [L ZnCl ] (90.3%), [L ZnCl ] (84.6%), [L ZnCl ] (71.2%) and [L ZnCl ] (80.0%) after wash-
A
2
B
2
C
2
D
2
1
13
ing with cold EtOH and Et O. H NMR, C NMR, and IR analyses were consistent with ligands
and Zn(II) complexes formulation. The representative H NMR and C NMR spectrum of
L ZnCl ] are shown in Figures 1 and 2, respectively. Comparison of the IR spectra of ligands
2
1
13
[
C
2
with that of complexes was also performed. A considerable difference in IR stretching band
for > C=N- group is observed due to Zn(II) complex formation. New absorption bands at 637
−1
–
771 cm are due to formation of Zn–N bonds in [L ZnCl ] (L = L − L ). Elemental analyses
n 2 n A D
of newly synthesized complexes were consistent with the proposed structures in Scheme 1
and confirmed the purity of the isolated complexes [L ZnCl ] (L = L − L ).
n
2
n
A
D

8
J. HEO ET AL.
Scheme 1. sꢌꢊꢁꢀꢈꢂꢅꢂ ꢄꢋ L (l = l − l ) ꢇꢊꢃ [L ZnCl ] (l = l − l ).
n
ꢊ
a
f
n
2
ꢊ
a
f
0
0
0
0
0
0
0
0
.8
.7
.6
.5
.4
.3
.2
.1
water
e
g
DMSO
c
h i
a
0
d
b
f
-
0.1
9
8
7
6
5
4
3
2
1
0
Chemical Shift (ppm)
1
Figure 1. h nmr ꢂpꢈcꢁꢆꢎꢉ ꢄꢋ [L ] (ꢎppꢈꢆ ꢆꢈꢃ pꢈꢇkꢂ) ꢇꢊꢃ [L ZnCl ] (ꢍꢄwꢈꢆ bꢍꢇck pꢈꢇkꢂ).
C
C
2
3
.2. Description of molecular structures
Single crystal X-ay diffraction studies were carried out to elucidate the precise structures of
L ZnCl ] (L = L − L ). ORTEP drawings of the complexes are shown in Figure 3 ([L ZnCl ]),
[
n
2
n
A
D
A
2
Figure 4 ([L ZnCl ]), Figure 5 ([L ZnCl ]), Figure 6 ([L ZnCl ]), Figure 7 ([L ZnCl ]) and Figure 8
B
2
C
2
D
2
E
2
(
[L ZnCl ]). Selected bond lengths and angles are listed in Table 2. Molecular structures of
F
2
[
L ZnCl ] and [L ZnCl ] were previously reported [8, 20, 60]. The coordination geometry
E 2 F 2
around Zn(II) can be described as a slightly distorted tetrahedron, consisting of the two
nitrogens of bidentate chelating ligand and chlorides.
The bond lengths of Zn-Nquinoline, pyridine in [L ZnCl ] (L = L − L ) were 2.061(9) – 2.102(4)
n
2
n
A
D
Å, while that of Zn–Nimine are 2.063(2) – 2.094(1) Å, similar to the Zn–N bond length of tetra-
hedral imine Zn(II) complexes [12, 20, 50, 55, 60, 79–83]. The bond length of Zn-Nimine
increased by 0.02 – 0.03 Å with increase in size of substituent attached to amine moiety in

JOURNAL OF COORDINATION CHEMISTRY
9
DMSO
i
h
0
0
0
0
0
0
.30
.25
.20
.15
.10
.05
j
a
g
f
c
d
b
e
1
60
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Chemical Shift (ppm)
1
3
Figure 2. C nmr ꢂpꢈcꢁꢆꢎꢉ ꢄꢋ [L ZnCl ].
C
2
Figure 3. orteP ꢃꢆꢇwꢅꢊg ꢄꢋ [L ZnCl ] wꢅꢁꢀ ꢁꢀꢈꢆꢉꢇꢍ ꢈꢍꢍꢅpꢂꢄꢅꢃꢂ ꢇꢁ 50% pꢆꢄbꢇbꢅꢍꢅꢁꢌ. aꢍꢍ ꢀꢌꢃꢆꢄgꢈꢊꢂ ꢇꢆꢈ ꢄꢉꢅꢁꢁꢈꢃ
A
2
ꢋꢄꢆ cꢍꢇꢆꢅꢁꢌ.
order of cyclopentyl ([L ZnCl ]) = cyclohexyl ([L ZnCl ]) < cyclohexyl ([L ZnCl ]) < 2,6-dieth-
A
2
C
2
B
2
ylphenyl ([L ZnCl ]). The bond lengths of Zn–N were shorter than those of Zn-Nquinoline,
D
2
imine
due to the different basicity for imine, quinoline and pyridine nitrogen. The Zn-Cl bond
pyridine
lengths are 2.198(2) – 2.217(2) Å, in the accepted range of reported Zn(II) imine complexes.
The double imine N(2)=C(10) distances of 1.276(3) Å ([L ZnCl ]), 1.256(7) Å ([L ZnCl ]), and
A
2
B
2
the corresponding N(2)=C(6) imine distances of 1.269(1) Å ([L ZnCl ]) and 1.277(1) Å
C
2
(
[L ZnCl ]) were in the range of accepted carbon–nitrogen double bonds. The C(9)-C(10)
D 2
bond distances are 1.467(8) Å ([L ZnCl ]) and 1.482(4) Å ([L ZnCl ]), reflecting delocalized
B
2
A
2

10
J. HEO ET AL.
Figure 4. orteP ꢃꢆꢇwꢅꢊg ꢄꢋ [L ZnCl ] wꢅꢁꢀ ꢁꢀꢈꢆꢉꢇꢍ ꢈꢍꢍꢅpꢂꢄꢅꢃꢂ ꢇꢁ 50% pꢆꢄbꢇbꢅꢍꢅꢁꢌ. aꢍꢍ ꢀꢌꢃꢆꢄgꢈꢊꢂ ꢇꢆꢈ ꢄꢉꢅꢁꢁꢈꢃ
B
2
ꢋꢄꢆ cꢍꢇꢆꢅꢁꢌ.
Figure 5. orteP ꢃꢆꢇwꢅꢊg ꢄꢋ [L ZnCl ] wꢅꢁꢀ ꢁꢀꢈꢆꢉꢇꢍ ꢈꢍꢍꢅpꢂꢄꢅꢃꢂ ꢇꢁ 50% pꢆꢄbꢇbꢅꢍꢅꢁꢌ. aꢍꢍ ꢀꢌꢃꢆꢄgꢈꢊꢂ ꢇꢆꢈ ꢄꢉꢅꢁꢁꢈꢃ
C
2
ꢋꢄꢆ cꢍꢇꢆꢅꢁꢌ.
π-electrons. The bond lengths of the synthesized Zn(II) complexes [L ZnCl ] (L = L − L )
n
2
n
A
D
were slightly affected by the N-cycloalkyl substituent group. The N(1)-Zn(1)-Cl(2) and N(2)-
Zn(1)-Cl(1) angles for the quinoline-based complexes [L ZnCl ] (L = L , L ) were 111.21(7)
n
2
n
A
B
–
118.75(7)° while these angles were 112.46(2) – 118.24(3)° for pyridine-based [L ZnCl ] and
C 2
[
L ZnCl ] complexes.
D 2
The average N(1)-Zn(1)-N(2) bond angle of five-membered chelate rings was 80.41(3) –
8
0.90(9)° and slightly affected by substituted rings. The Cl(1)-Zn(1)-Cl(2) angles in [L ZnCl ]
n
2
(
L = L and L ) were almost 116°, but 113.56(7)° and 119.06(2)° for [L ZnCl ] and [L ZnCl ],
n A C B 2 D 2
respectively. This trend was observed in related quinolinyl-imine zinc systems [25, 84]. The
plane of the N-cyclopentyl and 2,6-diethyl-phenyl pendent groups, tetrahedral Zn(II) centers

JOURNAL OF COORDINATION CHEMISTRY
11
Figure 6. orteP ꢃꢆꢇwꢅꢊg ꢄꢋ [L ZnCl ] wꢅꢁꢀ ꢁꢀꢈꢆꢉꢇꢍ ꢈꢍꢍꢅpꢂꢄꢅꢃꢂ ꢇꢁ 90% pꢆꢄbꢇbꢅꢍꢅꢁꢌ. aꢍꢍ ꢀꢌꢃꢆꢄgꢈꢊꢂ ꢇꢆꢈ ꢄꢉꢅꢁꢁꢈꢃ
D
2
ꢋꢄꢆ cꢍꢇꢆꢅꢁꢌ.
Figure 7. orteP ꢃꢆꢇwꢅꢊg ꢄꢋ [L ZnCl ] wꢅꢁꢀ ꢁꢀꢈꢆꢉꢇꢍ ꢈꢍꢍꢅpꢂꢄꢅꢃꢂ ꢇꢁ 50% pꢆꢄbꢇbꢅꢍꢅꢁꢌ. aꢍꢍ ꢀꢌꢃꢆꢄgꢈꢊꢂ ꢇꢆꢈ ꢄꢉꢅꢁꢁꢈꢃ
E
2
ꢋꢄꢆ cꢍꢇꢆꢅꢁꢌ (ꢆꢈpꢆꢄꢃꢎcꢈꢃ ꢋꢆꢄꢉ ꢁꢀꢈ Cif fiꢍꢈ ꢄꢋ ꢆꢈꢋꢈꢆꢈꢊcꢈ [60]).
Figure 8. orteP ꢃꢆꢇwꢅꢊg ꢄꢋ [L ZnCl ] wꢅꢁꢀ ꢁꢀꢈꢆꢉꢇꢍ ꢈꢍꢍꢅpꢂꢄꢅꢃꢂ ꢇꢁ 70% pꢆꢄbꢇbꢅꢍꢅꢁꢌ. aꢍꢍ ꢀꢌꢃꢆꢄgꢈꢊꢂ ꢇꢆꢈ ꢄꢉꢅꢁꢁꢈꢃ
F
2
ꢋꢄꢆ cꢍꢇꢆꢅꢁꢌ (ꢆꢈpꢆꢄꢃꢎcꢈꢃ ꢋꢆꢄꢉ ꢁꢀꢈ Cif fiꢍꢈ ꢄꢋ ꢆꢈꢋꢈꢆꢈꢊcꢈꢂ [8] ꢇꢊꢃ [20]).

12
J. HEO ET AL.

JOURNAL OF COORDINATION CHEMISTRY
13
and pyridine/quinoline moieties were perpendicular in [L ZnCl ] and [L ZnCl ]. Moreover,
A
2
D
2
the N-cyclohexyl groups in [L ZnCl ] and [L ZnCl ] were in the stable chair formation i.e.
B
2
C
2
N-cyclohexyl group, zinc and quinoline/pyridine moieties were located in the same plane.
3
.3. MMA polymerization
It is evident that T is mainly dependent on tacticity of PMMA and higher T resulted in
g
g
improved optical properties. Thus, MMA polymerization through coordination complexes
is used to achieve PMMA with high syndiotacticity, resulting in T up to 140 °C [85–88]. The
g
catalytic capabilities of our Zn(II) complexes were evaluated for MMA polymerization in the
presence of modified MMAO at 60 °C. All complexes efficiently initiate polymerization of
MMA yielding PMMA with T ranging from 120 to 137 °C. The main polymerization results
g
are summarized in Table 3. The polymers were isolated as white solids and characterized by
GPC in THF using standard polystyrene as the reference.
Blank polymerization was performed with [ZnCl ]/MMAO at 60 °C to verify if some activity
2
can be addressed to these components. No appreciable amount of PMMA was obtained
with MMAO alone and complexes showed higher activities compared to starting metal mate-
rials. Similarly, no polymer resulted with dichloro Zn(II) complexes in the absence of MMAO.
The 2-iminomethylpyridine-based Zn(II) complexes exhibited higher activities compared to
complexes bearing 2-iminomethylquinoline ligands (Table 3, entry 3 vs entry 7; entry 4 vs
Table 3. Pꢄꢍꢌꢉꢈꢆꢅzꢇꢁꢅꢄꢊ ꢄꢋ mma bꢌ [L ZnCl ] (l = l − l ) ꢅꢊ ꢁꢀꢈ pꢆꢈꢂꢈꢊcꢈ ꢄꢋ mmao.
n
2
ꢊ
a
f
Catalysta
Yieldb
%)
Activityc
Tgd
Tacticity
Mwe
(g/ꢉꢄꢍ) × 105
M /Mn
f
Entry
w
(
(g/ꢉꢄꢍ-
Cꢇꢁ·ꢀ) × 10
1.73
(℃)
%ꢉꢉ
%ꢉꢆ
%ꢆꢆ
4
1
2
3
4
5
6
7
8
[ZnCl2]g
11.1
8.97
16.4
18.0
21.4
14.7
17.8
12.3
129
120
130
137
124
134
125
134
9.20
37.2
11.6
10.3
8.33
7.69
10.7
11.1
24.2
10.9
21.2
20.7
22.2
23.1
21.4
22.2
66.6
51.9
67.3
69.0
69.4
69.2
68.0
66.7
1.33
0.61
9.90
9.89
9.62
8.89
9.78
9.62
1.58
2.20
2.53
2.44
2.50
2.53
2.52
2.56
ꢀ
mmao
1.40
2.55
2.81
3.33
2.30
2.78
1.91
[L ZnCl ]
A
2
[L ZnCl ]
B
2
[L ZnCl ]
C
2
[L ZnCl ]
D
2
ꢅ
j
[L ZnCl ]
E
2
[L ZnCl ]
F
2
ꢇ
[
Zꢊ(ii) cꢇꢁꢇꢍꢌꢂꢁ] = 15 μꢉꢄꢍ, [mma] /[mmao] /[Zꢊ(ii) cꢇꢁꢇꢍꢌꢂꢁ] = 3100:500:1, pꢄꢍꢌꢉꢈꢆꢅzꢇꢁꢅꢄꢊ tꢈꢉp. = 60 °C ꢇꢊꢃ ꢁꢅꢉꢈ = 2 ꢀ.
0 0 0 0
b
yꢅꢈꢍꢃ ꢃꢈfiꢊꢈꢃ (ꢇ ꢉꢇꢂꢂ ꢄꢋ ꢃꢆꢅꢈꢃ pꢄꢍꢌꢉꢈꢆ ꢆꢈcꢄvꢈꢆꢈꢃ)/(ꢇ ꢉꢇꢂꢂ ꢄꢋ ꢉꢄꢊꢄꢉꢈꢆ ꢎꢂꢈꢃ).
acꢁꢅvꢅꢁꢌ ꢅꢂ g ꢄꢋ Pmma/(ꢉꢄꢍ-Zꢊ·ꢀ).
c
ꢃ
ꢈ
tg ꢅꢂ gꢍꢇꢂꢂ ꢁꢆꢇꢊꢂꢅꢁꢅꢄꢊ ꢁꢈꢉpꢈꢆꢇꢁꢎꢆꢈ wꢀꢅcꢀ ꢅꢂ ꢃꢈꢁꢈꢆꢉꢅꢊꢈꢃ bꢌ ꢇ ꢁꢀꢈꢆꢉꢇꢍ ꢇꢊꢇꢍꢌzꢈꢆ.
dꢈꢁꢈꢆꢉꢅꢊꢈꢃ bꢌ gꢈꢍ pꢈꢆꢉꢈꢇꢁꢅꢄꢊ cꢀꢆꢄꢉꢇꢁꢄgꢆꢇpꢀꢌ (GPC) ꢈꢍꢎꢁꢈꢃ wꢅꢁꢀ thf ꢇꢁ ꢆꢄꢄꢉ ꢁꢈꢉpꢈꢆꢇꢁꢎꢆꢈ bꢌ fiꢍꢁꢆꢇꢁꢅꢄꢊ wꢅꢁꢀ pꢄꢍꢌꢂꢁꢌꢆꢈꢊꢈ
cꢇꢍꢅbꢆꢇꢁꢅꢄꢊ.
ꢋ
m ꢆꢈꢋꢈꢆꢂ ꢁꢄ ꢁꢀꢈ ꢊꢎꢉbꢈꢆ ꢇvꢈꢆꢇgꢈ ꢄꢋ ꢉꢄꢍꢈcꢎꢍꢇꢆ wꢈꢅgꢀꢁꢂ ꢄꢋ Pmma.
ꢊ
g
ꢀ
ꢅ
iꢁ ꢅꢂ ꢇ bꢍꢇꢊk pꢄꢍꢌꢉꢈꢆꢅzꢇꢁꢅꢄꢊ wꢀꢅcꢀ [ZnCl ] wꢇꢂ ꢇꢍꢂꢄ ꢇcꢁꢅvꢇꢁꢈꢃ bꢌ mmao.
iꢁ ꢅꢂ ꢇ bꢍꢇꢊk pꢄꢍꢌꢉꢈꢆꢅzꢇꢁꢅꢄꢊ wꢀꢅcꢀ wꢇꢂ ꢃꢄꢊꢈ ꢂꢄꢍꢈꢍꢌ bꢌ mmao.
2
Cꢄꢉpꢍꢈx [L ZnCl ] ꢅꢂ ꢆꢈpꢄꢆꢁꢈꢃ ꢅꢊ ꢄꢎꢆ ꢈꢇꢆꢍꢅꢈꢆ wꢄꢆk [60], ꢀꢄwꢈvꢈꢆ ꢃꢇꢁꢇ ꢅꢊ tꢇbꢍꢈ 3 cꢄꢉꢈꢂ ꢋꢆꢄꢉ ꢁꢀꢅꢂ wꢄꢆk.
E
2
j
Cꢄꢉpꢍꢈx [L ZnCl ] ꢅꢂ ꢆꢈpꢄꢆꢁꢈꢃ ꢅꢊ ꢁꢀꢈ ꢍꢅꢁꢈꢆꢇꢁꢎꢆꢈ [8,20].
F
2

14
J. HEO ET AL.
entry 5) in case of cyclopentyl or cyclohexyl substituents at imine-quinoline or imine-pyridine
moieties. Less sterically hindered imine-pyridine-based Zn(II) complexes have higher polym-
erization activity compared to imine-quinoline-based Zn(II) complexes bearing more steri-
cally demanding substituents under the same circumstances with cyclopentyl or cyclohexyl
substituents at imine-quinoline or imine-pyridine moieties. Steric hindrance of the substit-
uents on imine-quinoline or imine-pyridine moieties played a dominant role in determining
the activity of these complexes for MMA polymerization. Comparing 2-iminomethylquino-
line-based Zn(II) complexes ([L ZnCl ] and [L ZnCl ]), and 2-iminomethylpyridine-based
A
2
B
2
Zn(II) complexes ([L ZnCl ], [L ZnCl ], [L ZnCl ] and [L ZnCl ]), complexes [L ZnCl ] and
C
2
D
2
E
2
F
2
B
2
[
L ZnCl ] (both complexes have sterically demanding cyclohexyl moiety at imine-quinoline
C 2
and imine-pyridine residue, respectively) exhibited highest catalytic activity compared to
the other complexes under the same experimental conditions. We assumed that in less
sterically hindered complexes, the monomer could easily coordinate to the metal center.
The presence of sterically demanding substituents around the metal center negatively affects
MMA activation probably from the steric bulk depressing the monomer approach to the
metal sites. However, polymerization results in the series of 2-iminomethylpyridine-based
Zn(II) complexes ([L ZnCl ], [L ZnCl ], [L ZnCl ] and [L ZnCl ]) demonstrated that ease of
C
2
D
2
E
2
F
2
monomer insertion does not give higher polymerization activity. For instance [L ZnMe ]
D
2
bearing 2,6-diethylphenyl substituent at imine-pyridine moiety, which is believed to have
more steric hindrance than [L ZnMe ], exhibited higher activity than [L ZnMe ]. The 2-imi-
F
2
F
2
nomethylpyridine-based complexes showed activities [L ZnCl ] > [L ZnCl ] > [L ZnCl ] >
C
2
E
2
D
2
[
L ZnCl ] depending upon the steric bulk as well as the orientation of imine substituents to
F 2
the xy-plane of the pyridine ring and metal center.
However, catalytic activities of 2-iminomethylquinoline-based Zn(II) complexes increased with
increasing ring size of N-substituted cycloalkyl group (cyclopentyl < cyclohexyl) at 60 °C. Further,
[
L ZnCl ] with a perpendicular and slightly twisted N-cyclopentyl group toward the xy plane of
A 2
the 2-iminomethylquinoline-Zn residue by 76.8° causes steric hindrance around the Zn(II) metal
center during the MMA polymerization and hence showed lower activity compared to [L ZnCl ],
B
2
in which the distortion angle of N-cyclohexyl group toward the xy plane of the 2-iminomethylquin-
oline-Zn residue was 90.0°. Furthermore, the similar trend in activity was observed in 2-imi-
nomethylpyridine system to show higher activity for N-cyclohexyl group substituted on the
2
-iminomethylpyridine-based Zn(II) complex [L ZnCl ] (distortion angle of N-cyclohexyl ring
C 2
toward the xy plane of the 2-iminomethylpyridine-Zn residue was 84.5°) than N-cyclopentyl
group substituted on the 2-iminomethylpyridine-based Zn(II) complex [L ZnCl ] (distortion
E
2
angle of N-cyclopentyl ring toward the xy plane of the 2-iminomethylpyridine-Zn residue was
5.0°). Further, [L ZnCl ] bearing 2,6-diethylphenyl substituent at imine moiety exhibited a
7
D
2
higher activity than [L ZnCl ] bearing phenyl substituent at imine moiety. An ortho ethyl sub-
F
2
stituents on phenyl ring bestow some degree of steric hindrance compared to unsubstituted
phenyl ring (see the steric map in Figure 9).The distortion angle of phenyl substituent ring toward
the xy plane of the 2-iminomethylpyridine-Zn residue was 3.6° in [L ZnCl ]; thus both phenyl
F
2
substituent ring and metallacyclic ring are almost parallel. On the other hand, the distortion
angle of 2,6-diethylphenyl substituent ring toward the xy plane of the 2-iminomethylpyridine-Zn
o
residue was 80.8 in [L ZnCl ]; thus both 2,6-diethylphenyl substituent ring and metallacyclic
D
2
ring are almost perpendicular. Further, the C(15)-Zn(1) and C(13)-Zn(1) distances in [L ZnCl ]
D
2
were calculated as 3.840 Å and 4.205 Å to give more steric hindrance of 2,6-diethylphenyl sub-
stituent ring than phenyl substituent ring in the 2-iminomethylpyridine-Zn(II) complexes.

JOURNAL OF COORDINATION CHEMISTRY
15
To evaluate the total steric hindrance by bulky ligands toward metal center, it can be
predicted and quantitatively calculated by comparison through a topographic steric map of
Zn(II) complexes by use of program “SambVca” [89]. Figure 9 shows ball and stick model,
space-filling model, and topographic steric map of [L ZnCl ] (L = L − L ) for presenting bulky
n
2
n
A
F
ligands. Only considering total steric factor by topographic steric map of [L ZnCl ] (L = L
n
2
n
A
-
L ), less sterically hindered [L ZnCl ] (buried volume % is 39.6) has slightly higher polymer-
F
B
2
4
.
ization activity (2.81 × 10 g/molZn h) compared to more sterically demanding [L ZnCl ]
A
2
4
.
(buried volume % is 40.8 and MMA activity is 2.55 × 10 g/molZn h) in imine-quinoline-based
[
L ZnCl ] %V 40.8
[L ZnCl ] %V 39.6
[L ZnCl ] %V 38.0
C 2 Bur
A
2
Bur
B
2
Bur
Zn
Zn
Zn
[
L ZnCl ] %V 38.3
[L ZnCl ] %V 37.6
[L ZnCl ] %V 36.9
F 2 Bur
D
2
Bur
E
2
Bur
Zn
Zn
Zn
Figure 9. Bꢇꢍꢍ ꢇꢊꢃ ꢂꢁꢅck ꢉꢄꢃꢈꢍ, ꢂpꢇcꢈ-fiꢍꢍꢅꢊg ꢉꢄꢃꢈꢍ, ꢇꢊꢃ ꢁꢄpꢄgꢆꢇpꢀꢅc ꢂꢁꢈꢆꢅc ꢉꢇp ꢄꢋ [L ZnCl ] (l = l − l )
n
2
ꢊ
a
f
ꢋꢄꢆ pꢆꢈꢂꢈꢊꢁꢅꢊg ꢂꢁꢈꢆꢅc bꢎꢍk.

16
J. HEO ET AL.
Zn(II) complexes system. However, the opposite trend was found in the system of imine-
pyridine-based Zn(II) complexes, less sterically hindered [L ZnCl ] (buried volume % is 36.8)
F
2
4
.
has lower polymerization activity (1.91 × 10 g/molZn h) compared to more sterically demand-
ing [L ZnCl ] (buried volume % is 38.3 and MMA activity is 2.30 × 10 g/molZn h). Thus, both
4
.
D
2
steric and electronic effects of catalysts are needed to correlate the polymerization activity
and structure of complexes. Further, the solubility of complexes or active species in polym-
erization solvent also influences polymerization activity.
These results are in contrast to previously reported Zn(II) complexes where electronic
density around the metal center resulted in higher activities [60, 90]. In comparison with
reported N,N′,N-bis((1H-pyrazol-1-yl)methyl)amine-based Zn(II) complexes, the current sys-
tem showed higher activities with better molecular weights and T but slightly lower stere-
g
oselectivity [91, 92]. These catalytic systems are faster than our previously reported Pd(II)
complexes, which also contain 2-iminomethylpyridine- and 2-iminomethylquinoline-based
5
ligands, and yielded PMMA with higher molecular weights (9.90 × 10 g/mol), T (137 °C)
g
and comparable stereoselectivities [58, 59]. The molecular weights of 2-iminomethylpyri-
dine-based Zn(II) complexes were slightly lower compared to 2-iminomethylquinoline bear-
ing Zn(II) complexes (Table 3).
The tacticity of PMMA was determined in the range around syndiotactic (δ 0.850), het-
1
erotactic (δ 1.02), and isotactic (δ 1.21) based on H NMR [87]. The syndiotacticity of PMMA
was 70%, similar to all [L ZnCl ] (L = L − L ) regardless of the imine substituents. However,
n
2
n
A
F
the syndiotacticity was higher compared to co-catalyst, MMAO. Cu(II) complexes with ligand
N-(2-furanylmethyl)-N-(1–3,5-dimethyl-1H-pyrazolylmethyl)-N-(phenylmethyl)amines [93]
reported were found to be active catalysts for the MMA polymerization to yield syndiotactic
PMMA (rr = 0.78) with only 30% conversion. Similarly, Fe(II) complexes with pyridylmethyl-
amine [94] were also used as catalysts for MMA polymerization with moderate activity and
syndiotacticity. Recentlylanthanidemetalorganosamarium(II)complexwithbispyrrolylaldimi-
nato ligand produces isotactic PMMA with an mm value of 98% [95]. The moderate syndio-
tacticity in the current study was not sufficient to confer a mechanism of coordination
polymerization, but clearly showed the steric effect in [L ZnCl ] (L = L − L ) during MMA
n
2
n
A
F
polymerization. The syndiotacticity and PDIs were not strongly affected by the substituents
of the ligand around the metal center. However, increased molecular weights of the resultant
PMMAs have been observed with decrease in the steric bulk of imine substituents (Table 3).
3
.4. rac-LA polymerization
Dimethyl derivatives [L ZnMe ] (L = L − L ), generated in situ, by treating dichloro zinc
n
2
n
A
F
complexes with two equiv. of MeLi in THF, were evaluated for ROP of rac-LA in CH Cl at
2
2
-50 °C. Representative polymerization data are tabulated in Table 4. Dimethyl Zn(II) com-
plexes efficiently catalyzed ROP of rac-LA yielding PLAs with high molecular weights and
narrower molecular weight distributions (M /M = 1.09−1.24). Completion of the reaction
w
n
1
was confirmed by the absence of monomer signals in the H NMR spectra. The number
average molecular weights (M ) were determined based on end-group analysis with H NMR
1
n
spectra and by GPC inTHF relative to the polystyrene standards. The number-average molec-
1
ular weight (M ) determined from H NMR spectra of the obtained PLA and those determined
n
with GPC were almost identical (corrected using the Mark–Howink factor of 0.58) [96–98]
value obtained from [monomer]/[initiator] molar ratio. The narrower polydispersities

JOURNAL OF COORDINATION CHEMISTRY
17
Table 4. Pꢄꢍꢌꢉꢈꢆꢅzꢇꢁꢅꢄꢊ ꢄꢋ rac-ꢍꢇcꢁꢅꢃꢈ wꢅꢁꢀ in situ gꢈꢊꢈꢆꢇꢁꢈꢃ [L ZnMe ] (l = l − l ) ꢋꢆꢄꢉ ꢁꢀꢈ ꢆꢈꢇcꢁꢅꢄꢊ
n
2
ꢊ
a
f
[
L ZnCl ] (l = l − l ) ꢇꢊꢃ mꢈlꢅ ꢅꢊ Ch Cꢍ .
n 2 ꢊ a f 2 2
Catalysta
Conv. (%)
b
Mnc (g/mol) × 10 (calcd.)
3
Mnd (g/mol) × 10 (GPC)
3
PDId
Pre
Entry
1
2
3
4
5
6
7
mꢈlꢅ
85
100
53
85
85
80
63
12.25
14.41
7.64
12.25
12.25
11.53
9.08
3.88
11.00
6.94
13.40
11.58
10.35
8.80
1.14
1.24
1.09
1.23
1.17
1.12
1.10
0.67
0.91
0.91
0.91
0.85
0.87
0.86
[L ZnMe ]
A
2
[L ZnMe ]
B
2
[L ZnMe ]
C
2
[L ZnMe ]
D
2
[L ZnMe ]
E
2
[L ZnMe ]
F
2
ꢇ
Cꢄꢊꢃꢅꢁꢅꢄꢊꢂ: [iꢊꢅꢁꢅꢇꢁꢄꢆ] = 0.0625 ꢉꢉꢄꢍ; [rac-la]/[iꢊꢅꢁꢅꢇꢁꢄꢆ] = 100; 5.00 ꢉl ꢄꢋ Ch Cꢍ ꢇꢂ pꢄꢍꢌꢉꢈꢆꢅzꢇꢁꢅꢄꢊ ꢂꢄꢍvꢈꢊꢁ; pꢄꢍꢌꢉꢈꢆꢅzꢇ-
2
2
ꢁ
ꢅꢄꢊ ꢁꢅꢉꢈ = 12 ꢀ; ꢁꢈꢉp = −50 °C.
b
c
1
mꢄꢊꢄꢉꢈꢆ cꢄꢊvꢈꢆꢂꢅꢄꢊ (%) ꢃꢈꢁꢈꢆꢉꢅꢊꢈꢃ bꢌ h nmr ꢂpꢈcꢁꢆꢄꢂcꢄpꢌ.
Cꢇꢍcꢎꢍꢇꢁꢈꢃ ꢋꢆꢄꢉ [ꢉꢄꢍꢈcꢎꢍꢇꢆ wꢈꢅgꢀꢁ ꢄꢋ rac-la] × [rac-la]/[iꢊꢅꢁꢅꢇꢁꢄꢆ] × cꢄꢊvꢈꢆꢂꢅꢄꢊ %.
dꢈꢁꢈꢆꢉꢅꢊꢈꢃ bꢌ gꢈꢍ pꢈꢆꢉꢈꢇꢁꢅꢄꢊ cꢀꢆꢄꢉꢇꢁꢄgꢆꢇpꢀꢌ (GPC) ꢅꢊ thf, ꢆꢈꢍꢇꢁꢅvꢈ ꢁꢄ pꢄꢍꢌꢂꢁꢌꢆꢈꢊꢈ ꢂꢁꢇꢊꢃꢇꢆꢃ (cꢄꢆꢆꢈcꢁꢈꢃ ꢎꢂꢅꢊg ꢁꢀꢈ mꢇꢆk−
hꢄꢎwꢅꢊk ꢋꢇcꢁꢄꢆ ꢄꢋ 0.58) [96–98].
Pꢆꢄbꢇbꢅꢍꢅꢁꢌ ꢄꢋ ꢀꢈꢁꢈꢆꢄꢁꢇcꢁꢅc ꢈꢊcꢀꢇꢅꢊꢉꢈꢊꢁ (P ) wꢈꢆꢈ cꢇꢍcꢎꢍꢇꢁꢈꢃ ꢄꢊ ꢁꢀꢈ bꢇꢂꢅꢂ ꢄꢋ ꢀꢄꢉꢄꢊꢎcꢍꢈꢇꢆ ꢃꢈcꢄꢎpꢍꢈꢃ h nmr ꢂpꢈcꢁꢆꢇ ꢇc-
ꢃ
ꢈ
1
ꢆ
cꢄꢆꢃꢅꢊg ꢁꢄ ꢍꢅꢁꢈꢆꢇꢁꢎꢆꢈ [108–110].
(1.09–1.24) indicate that the polymerization occurred through a living polymerization mech-
anism with a single reaction site provided by these dimethyl zinc complexes. Dichloro com-
plexes [L ZnCl ] (L = L − L ) screened for ROP of rac-LA under the same experimental
n
2
n
A
F
conditions exhibited no activity.
1
H NMR spectra showed peaks for methane protons of –CH(CH )(OH) at δ 2.90 ppm and
3
the signals for –C(=O)CH at the other terminus overlapped with those of PLA backbones.
3
A coordination insertion mechanism [99–101] for the ROP of rac-LA can be predicted where
initially LA is coordinated to Zn(II) to yield a five-coordinate intermediate, followed by cleav-
age of acyl-oxygen bond to open the monomer ring. Another molecule of LA gets ring
opening by coordinating to Zn(II) center in a similar manner. The subsequent addition of LA
produces hetero-enriched PLA.
The polymerization data revealed that 2-iminomethylquinoline-based Zn(II) complexes
exhibit higher activities (Table 4, entries 2 and 3). In the case of 2-iminomethylpyridine-based
complexes the steric bulk around the metal center played a significant role in controlling
the catalytic activities toward ROP of rac-LA. Complexes with more sterically demanding
ligands are more active toward lactide polymerization which might be due to enhanced
electron density on the metal center. The presence of (-CH CH ) substituents at ortho position
2
3
in [L ZnMe ] compared to –H in [L ZnMe ] might provide greater electronic density around
D
2
F
2
the metal center and hence showed greater activity. These investigations are in contrast to
our previous reports where complexes with flexible and less sterically demanding ligands

18
J. HEO ET AL.
provide better activities and heteroselectivities [61, 62, 102–104]. In comparison to the highly
effective zinc initiators, based on phenolate diamines/diimines [105–107], the catalytic effi-
cacy of Zn(II) complexes in the current study are lower but produce PLA with better stereo-
selectivity (Table 4).
The stereo-selectivity of PLA is not much influenced by the structure of the ancillary
ligands attached to the metal during the polymerization process. Microstructural analyses
of the obtained PLA were performed by inspecting the methane proton region of homode-
1
coupled H NMR spectra and P values were calculated with equation P = 2I /(I + I ), where
r
r
1
1
2
I = (sis + sii) and I = (iis + iii + isi) [108–110]. It is clear from the polymerization data that all
1
2
the complexes exhibited a strong preference for heterotactic enchainment (Table 4).
L ZnMe ] (L = L − L ) produced PLA with a high degree of heterotacticity (P = 0.91, Figure 10,
[
n
2
n
A
C
r
entries2–4)comparedtoitsanalogsunderthe same experimental conditions. These results are
superior to our previously reported Zn(II) complexes in terms of heterotactic enchainment.
However, the monomer conversion was lower for the current catalytic system. Among the
2-iminomethylpyridine-based dimethyl Zn(II) complexes enhancing the steric hindrance on
imine moiety lead to decrease heterotacticity i.e. [L ZnMe ] (P = 0.85, Table 4, entry 5)
D
2
r
compared to [L ZnMe ] (P = 0.91, Table 4, entry 4), indicating that the larger steric hindrance
C
2
r
might impede the regularity of monomer insertion [102, 111].
Polymerization results show that the catalytic activities of these dimethyl complexes were
affected by steric hindrance of the substituents attached to the imine moiety around the
metal center. The increase in steric bulk around the metal center results in better activities
toward ROP of rac-LA whereas the stereoselectivities are negatively affected. Heterotactic-
enriched PLA resulted from all the dimethyl Zn(II) complexes of the current study via chain-
end-control mechanism, as previously demonstrated by the Darensbourg group for Zn(II)
sis
isi
iii
sii/iis
iis/sii
1
Figure 10. hꢄꢉꢄꢊꢎcꢍꢈꢇꢆ ꢃꢈcꢄꢎpꢍꢈꢃ h nmr ꢂpꢈcꢁꢆꢎꢉ ꢄꢋ pꢄꢍꢌꢍꢇcꢁꢅꢃꢈ (ꢋꢄꢆ ꢁꢀꢈ pꢆꢈpꢇꢆꢇꢁꢅꢄꢊ cꢄꢊꢃꢅꢁꢅꢄꢊꢂ, ꢂꢈꢈ
ꢈꢊꢁꢆꢌ 2 ꢅꢊ tꢇbꢍꢈ 4); P = 2 I /[I I ] = 2 (7.24 + 1.41)/[(7.24 + 1.41) + (1.17 + 1.48 + 7.76)] ≈ 0.91.
r
1
1+ 2

JOURNAL OF COORDINATION CHEMISTRY
19
complexes with Schiff bases [112]. More investigations are ongoing to fully describe the role
of current catalytic system and mechanism of ROP of rac-LA.
4
. Conclusion
We investigated the syntheses and structures of [L ZnCl ] (L = L − L ), which were prepared
n
2
n
A
F
by direct ligation of [ZnCl ] with the corresponding 2-iminomethylpyridine and 2-imi-
2
nomethylquinoline ligands. The coordination geometry around the Zn(II) centers in [L ZnCl ]
n
2
(
L = L − L ) were distorted tetrahedral. [L ZnCl ] exhibited higher activity for MMA polym-
n A F C 2
erization with moderate syndiotacticity compared to the rest of its analogs. The catalytic
activities of [L ZnCl ] (L = L − L ) toward MMA polymerization can be considered as a
n
2
n
A
F
function of steric bulk, provided by the substituents attached to imine moiety, around the
metal center. The dimethyl derivatives, generated in situ, effectively polymerized ROP of
rac-LA. [L ZnMe ] polymerized rac-LA and yielded heterotactic PLA with P = 0.91 at -50 °C.
A
2
r
This enhanced heterotactic enchainment was found with these dimethyl Zn(II) initiators
bearing the proper complexity of the substituents at the nitrogens of the imine moiety.
Supplementary material
CCDC 1573913–1573916 contains the supplementary crystallographic data for [L ZnCl ], [L ZnCl ],
B
2
C
2
[
L ZnCl ] and [L ZnCl ], respectively. CCDC 98541 and CCDC 717945 contain the supplementary crys-
A 2 D 2
tallographic data for [L ZnCl ] and [L ZnCl ], respectively. These data can be obtained free of charge via
E
2
E
2
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Center,
2 Union Road, Cambridge CB2 1EZ, UK; Fax: (+44) 1223–336-033; or E-mail: deposit@ccdc.cam.ac.uk.
1
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This research was supported by the National Research Foundation of Korea (NRF), funded by the
Ministry of the Education, Science, and Technology (MEST) [grant number 2017R1A2B4002100].
References
[1] D. Carmona, C. Vega, F.J. Lahoz, S. Elipe, L.A. Oro, M.P. Lamata, F. Viguri, R. García-Correas,
C. Cativiela, M.P.L.-R. de Víu. Organometallics, 18, 3364 (1999).
[
[
[
[
[
[
[
2] J.G. Hinman, C.R. Baar, M.C. Jennings, R.J. Puddephatt. Organometallics, 19, 563 (2000).
3] B.P. Buffin, P.J. Squattrito, A.O. Ojewole. Inorg. Chem. Commun., 7, 14 (2004).
4] K. Nienkemper, V.V. Kotov, G. Kehr, G. Erker, R. Fröhlich. Eur. J. Inorg. Chem., 366 (2006).
5] A. Ouali, J.-F. Spindler, A. Jutand, M. Taillefer. Adv. Synth. Catal., 349, 1906 (2007).
6] W. Massa, S. Dehghanpour, K. Jahani. Inorg. Chim. Acta, 362, 2872 (2009).
7] C.-J. Qiu, Y.-C. Zhang, Y. Gao, J.-Q. Zhao. J. Organomet. Chem., 694, 3418 (2009).
8] M. Schulz, M. Klopfleisch, H. Görls, M. Kahnes, M. Westerhausen. Inorg. Chim. Acta, 362, 4706
(2009).
[9] P. Shejwalkar, N.P. Rath, E.B. Bauer. Dalton Trans., 40, 7617 (2011).
[10] B.C.E. Makhubela, A. Jardine, G.S. Smith. Green Chem., 14, 338 (2012).

20
J. HEO ET AL.
[11] M.D. Serio, G. Carotenuto, M.E. Cucciolito, M. Lega, F. Ruffo, R. Tesser, M. Trifuoggi. J. Mol. Catal.
A: Chem., 353, 106 (2012).
[
[
[
[
[
12] L. Wang, Y. Zhang, X. Yu, H. He. J. Zhang. Synth. Met., 162, 2138 (2012).
13] Y. Abedia, A. Biffisa, R. Gavaa, C. Tubaroa. Appl. Organomet. Chem., 28, 512 (2014).
14] G.S. Nyamato, S.O. Ojwach, M.P. Akerman. Organometallics, 34, 5647 (2015).
15] S. Menati, H.A. Rudbari, B. Askari, M.R. Farsani, F. Jalilian, G. Dini. C. R. Chimie, 19, 347 (2016).
16] X. Song, M.H. Lim, D.K.B. Mohamed, S.M. Wong, J. Zhao, T.S.A. Hor. J. Organomet. Chem., 814, 1
(2016).
[
[
[
[
17] J.M. Gichumbi, H.B. Friedrich, B. Omondi. Inorg. Chim. Acta, 456, 55 (2017).
18] J.H. Docherty, J. Peng, A.P. Dominey, S.P. Thomas. Nature Chem., 9, 595 (2017).
19] Z.-L. You, X. Han, G.-N. Zhang. Z. Anorg. Allg. Chem., 634, 142 (2008).
20] J.J. Braymer, J.-S. Choi, A.S. DeToma, C. Wang, K. Nam, J.W. Kampf, A. Ramamoorthy, M.H. Lim.
Inorg. Chem., 50, 10724 (2011).
[
[
21] C.M. Álvarez, R. García-Rodríguez, D. Miguel. Inorg. Chem., 51, 2984 (2012).
22] T.S.B. Baul, S. Kundu, A. Linden, N. Raviprakash, S.K. Manna, M.F.C. Guedes da Silva. Dalton Trans.,
4
3, 1191 (2014).
[
[
[
23] T.S. Basu Baul, S. Kundu, P. Singh, Shaveta, M.F.C. Guedes da Silva. Dalton Trans., 44, 2359 (2015).
24] B.A. Miles, A.E. Patterson, C.M. Vogels, A. Decken, J.C. Waller. Polyhedron, 108, 23 (2016).
25] A. Wang, R. Fan, Y. Dong, Y. Song, Y. Zhou, J. Zheng, X. Du, K. Xing, Y. Yang. ACS Appl. Mater.
Interfaces, 9, 15744 (2017).
[
[
26] S. Roy, T.K. Mondal, P. Mitra, E.L. Torres, C. Sinha. Polyhedron, 30, 913 (2011).
27] J. Schnödt, J. Manzur, A.-M. García, I. Hartenbach, C. Yong Su, J. Fiedler. W. Kaim, Eur. J. Inorg.
Chem., 1436, (2011).
[28] A. Saha Roy, P. Saha, P. Mitra, S. Sundar Maity, S. Ghosh, P. Ghosh. Dalton Trans., 40, 7375 (2011).
[29] C.W. Machan, S.A. Chabolla, C.P. Kubiak. Organometallics, 34, 4678 (2015).
[30] X.-M. Wang, S. Chen, R.-Q. Fan, F.-Q. Zhang, Y.-L. Yang. Dalton Trans., 44, 8107 (2015).
[31] A. Ayadi, D.G. Branzea, M. Allain, D. Canevet, H. Dinçalp, A. El-Ghayoury. Polyhedron, 135, 86 (2017).
[32] J. Zhang, W. Li, W. Bu, L. Wu, L. Ye, G. Yang. Inorg. Chim. Acta, 358, 964 (2005).
[33] C. Yu, Z. Zhang, L. Liu, H. Li, Y. He, X. Lü, W.-K. Wong, R.A. Jones. New J. Chem., 39, 3698 (2015).
[34] Y.-W. Dong, R.-Q. Fan, W. Chen, H.-J. Zhang, Y. Song, X. Du, P. Wang, L.-G. Wei, Y.-L. Yang. Dalton
Trans., 46, 1266 (2017).
[35] A. Wang, R. Fan, Y. Dong, W. Chen, Y. Song, P. Wang, S. Hao, Z. Liu, Y. Yang. Dalton Trans., 46, 71
(2017).
[
[
[
[
[
[
[
36] C. Bianchini, G. Mantovani, A. Meli, F. Migliacci, F. Laschi. Organometallics, 22, 2545 (2003).
37] J. Cloete, S.F. Mapolie. J. Mol. Catal. A: Chem., 243, 221 (2006).
38] C.-Y. Hsiao, H.-A. Han, G.-H. Lee, C.-H. Peng. Eur. Polym. J., 51, 12 (2014).
39] D.F. Grishin, L.L. Semenycheva. Russ. Chem. Rev., 70, 425 (2001).
40] V.C. Gibson, R.K. O’Reilly, D.F. Wass, A.J.P. White, D.J. Williams. Dalton Trans., 2824, (2003).
41] A.V. Yakimanskii. Polym. Sci. Ser. C, 47, 1 (2005).
42] R.M. Islamova, G.R. Sadykova, I.A. Ionova, Ya Z. Voloshin, YuN Bubnov, I.S. Makarov, YuB Monakov.
Polym. Sci. Ser. B, 51, 219 (2009).
[43] YuB Monakov, R.M. Islamova, I.A. Ionova, S.A. Syrbu, T.A. Ageeva, O.I. Koifman. Mendeleev
Commun., 20, 33 (2010).
44] L.S. Boffa, B.M. Novak. Chem. Rev., 100, 1479 (2000).
[
[
[
[
[
[
[
[
[
[
[
45] X. He, Y. Yao, X. Luo, J. Zhang, Y. Liu, L. Zhang, Q. Wu. Organometallics, 22, 4952 (2003).
46] I. Kim, J.-M. Hwang, J.K. Lee, C.S. Ha, S.I. Woo. Macromol. Rapid Commun., 24, 508 (2003).
47] X. He, Q. Wu. Appl. Organomet. Chem., 20, 264 (2006).
48] H.-Y. Chen, H.-Y. Tang, C.-C. Lin. Macromolecules, 39, 3745 (2006).
49] W.-C. Hung, Y. Huang, C.-C. Lin. J. Polym. Sci. A: Polym. Chem., 46, 6466 (2008).
50] J. Borner, U. Florke, K. Huber, A. Doring, D. Kuckling, S. Herres-Pawli. Chem. Eur. J., 15, 2362 (2009).
51] Z. Liu, W. Gao, J. Zhang, D. Cui, Q. Wu, Y. Mu. Organometallics, 29, 5783 (2010).
52] L. Yao, L. Wang, J. Zhang, N. Tang, J. Wu. J. Mol. Catal. A: Chem., 352, 57 (2012).
53] Y. Sun, Y. Cui, J. Xiong, Z. Dai, N. Tang, J. Wu. Dalton Trans., 44, 16383 (2015).
54] M. Huang, C. Pan, H.Y. Ma. Dalton Trans., 44, 12420 (2015).

JOURNAL OF COORDINATION CHEMISTRY
21
[
[
[
55] K.S. Kwon, S. Nayab, J.H. Jeong. Polyhedron, 85, 615 (2015).
56] A. Arbaoui, C. Redshaw, D.L. Hughes. Chem. Commun., 4717, (2008).
57] H.-W. Ou, K.-H. Lo, W.-T. Du, W.-Y. Lu, W.-J. Chuang, B.-H. Huang, H.-Y. Chen, C.-C. Lin. Inorg. Chem.,
5, 1423 (2016).
1
[
[
[
[
[
[
[
[
58] S. Kim, E. Kim, H.-J. Lee, H. Lee. Polyhedron, 69, 149 (2014).
59] D. Kim, Y. Song, S. Kim, H.-J. Lee, H. Lee. J. Coord. Chem., 67, 2312 (2014).
60] Y. Song, D. Kim, H.-J. Lee, H. Lee. Bull. Korean Chem. Soc., 35, 2929 (2014).
61] J. Jeong, Y. An, Y. Kang, Q.T. Nguyen, H. Lee, B.M. Novak. Polyhedron, 27, 319 (2008).
62] S. Nayab, H. Lee, J. Jeong. Polyhedron, 43, 55 (2012).
63] S.H. Ahn, M.K. Chun, E. Kim, J.H. Jeong, S. Nayab, H. Lee. Polyhedron, 127, 51 (2017).
64] A.J. Deeming, I.P. Rothwell, M.B. Hursthouse, K.M.A. Malik. J. Chem. Soc., Dalton Trans., 1899, (1979).
65] G.J.P. Britovsek, S.P.D. Baugh, O. Hoarau, V.C. Gibson, S.K. Spitzmesser, D.F. Wass, A.J.P. White, D.J.
Williams. Inorg. Chim. Acta, 345, 279 (2003).
[66] M.L. Conrad, J.E. Enman, S.J. Scales, H. Zhang, C.M. Vogels, M.T. Saleh, A. Decken, S.A. Westcott.
Inorg. Chim. Acta, 358, 63 (2005).
[
[
[
[
[
[
[
67] Y. Song, Z. Xu, Q. Sun, B. Su, Q. Gao, H. Liu, J. Zhao. J. Coord. Chem., 60, 2351 (2007).
68] G.A. Ardizzoia, S. Brenna, F. Castelli, S. Galli. Inorg. Chim. Acta, 362, 3507 (2009).
69] S. Song, Y. Li, C. Redshaw, F. Wang, W.-H. Sun. J. Organomet. Chem., 696, 3772 (2011).
70] S. Song, W. Zhao, L. Wang, C. Redshaw, F. Wang, W.-H. Sun. J. Organomet. Chem., 696, 3029 (2011).
71] S. Song, T. Xiao, L. Wang, C. Redshaw, F. Wang, W.-H. Sun. J. Organomet. Chem., 699, 18 (2012).
72] B. Zhang, S.-F. Zhu, Q.-L. Zhou. Tetrahedron, 69, 2033 (2013).
73] Y.-W. Dong, R.-Q. Fan, X.M. Wang, P. Wang, H.-J. Zhang, L.-G. Wei, Y. Song, X. Du, W. Chen, Y.-L.
Yang. Eur. J. Inorg. Chem., 3598 (2016).
[
74] Y.-W. Dong, R.-Q. Fan, X.M. Wang, P. Wang, H.-J. Zhang, L.-G. Wei, W. Chen, Y.-L. Yang. Cryst. Growth
Des., 16, 3366 (2016).
[
[
75] F. Capitan, A. La Iglesia, F. Salinas, L.F. Capitan-Vallvey. An. Quim., 73, 226 (1977).
76] A.J. Arvai, C. Nielsen. ADSC Quantum-210 ADX Program., Area Detector System Corporation,
Poway, CA, USA (1983).
[77] Z. Otwinowski, W. Minor, Methods in Enzymology, C.W. Carter, Jr., R.M. Sweet (Eds.), Vol. 276, Part
A, p. 307, Academic Press, New York (1997).
[
[
[
[
[
[
[
[
78] G.M. Sheldrick. Acta Crystallogr., Sect. A, 64, 112 (2008).
79] M. Khalaj, S. Dehghanpour, A. Mahmoudi, S. Seyedidarzam. Acta Cryst., E65, m890 (2009).
80] M.R.T.B. Olyai, V.R. Fard, J.S. Far, A. Mahmoudi. Z. Kristallogr., 225, 169 (2010).
81] Y.W. Ding, X.L. Wang, L.L. Ni. Acta Cryst., E67, m261 (2011).
82] S. Dehghanpour, A. Mahmoudi. Acta Cryst., E68, m1113 (2012).
83] S. Salehzadeh, M. Khalaj, S. Dehghanpour, I. Tarmoradi. Acta Cryst., E67, m1556 (2011).
84] D. Prema, A.V. Wiznycia, B.M.T. Scott, J. Hilborn, J. Desper, C.J. Levy. Dalton Trans., 42, 4788 (2007).
85] W. Wang, P.A. Stenson, A. Marin-Becerra, J. McMaster, M. Schroder, D.J. Irvine, D. Freeman, S.M.
Howdle. Macromolecules, 37, 6667 (2004).
[86] B. Lian, C.M. Thomas, O.L. Casagrande, C.W. Lehmann Jr, T. Roisnel, J.F. Carpentier. Inorg. Chem.,
4
6, 328 (2007).
[
[
[
87] T. Kitaura, T. Kitayama. Macromol. Rapid Commun., 28, 1889 (2007).
88] B.K. Bahuleyan, D. Chandran, C.H. Kwak, C.-S. Ha, I. Kim. Macromol. Res., 18, 745 (2008).
89] L. Falivene, R. Credendino, A. Poater, A. Petta, L. Serra, R. Oliva, V. Scarano, L. Cavallo.
Organometallics, 35, 2286 (2016). For online program, see https://www.molnac.unisa.it/OMtools/
sambvca2.0/index.html.
[
[
[
[
[
90] S. Ahn, J. Shin, S. Nayab, H. Lee. Bull. Korean Chem. Soc., 36, 763 (2016).
91] E. Kim, H.Y. Woo, S. Kim, H. Lee, D. Kim, H. Lee. Polyhedron, 42, 135 (2012).
92] S. Shin, S.H. Ahn, M.J. Jung, S. Nayab, H. Lee. J. Coord. Chem., 69, 2391 (2016).
93] C. Lansalot-Matras, F. Bonnette, E. Mignard, O. Lavastre. J. Organomet. Chem., 693, 393 (2008).
94] T.V. Laine, U. Piironen, K. Lappalainen, M. Klinga, E. Aitola, M. Leskela. J. Organomet. Chem., 606,
112 (2000).
[
[
95] C. Cui, A. Shafir, C.L. Reeder, J. Arnold. Organometallics, 22, 3357 (2003).
96] J. Baran, A. Duda, A. Kowalski, R. Szymanski, S. Penczek. Macromol. Rapid Commun., 18, 325 (1997).

22
J. HEO ET AL.
[
[
[
97] M. Sava, M. Schappacher, A. Soum. Macromol. Chem. Phys., 203, 889 (2002).
98] J.C. Wu, B.H. Huang, M.L. Hsueh, S.L. Lai, C.C. Lin. Polymer, 46, 9784 (2005).
99] T.J.J. Whitehorne, F. Schaper. Inorg. Chem., 52, 13612 (2013).
[
[
[
[
[
[
100] T.J.J. Whitehorne, F. Schaper. Can. J. Chem., 92, 206 (2014).
101] K.S. Kwon, J. Cho, S. Nayab, J.H. Jeong. Inorg. Chem. Commun., 55, 36 (2015).
102] Y. Kang, J. Jeong, N. Lee, Y. Lee, H. Lee. Polyhedron, 29, 2404 (2010).
103] S. Nayab, H. Lee, J. Jeong. Polyhedron, 30, 405 (2011).
104] S. Nayab, H. Lee, J. Jeong. Polyhedron, 31, 682 (2012).
105] C.K. Williams, L.E. Breyfogle, S.K. Choi, W. Nam, V.G. Young, M.A. Hillmyer, W.B. Tolman. J. Am.
Chem. Soc., 125, 11350 (2003).
[
[
[
[
106] C.M. Silvernail, L.J. Yao, L.M.R. Hill, M.A. Hillmyer, W.B. Tolman. Inorg. Chem., 46, 6565 (2007).
107] H.Y. Chen, H.Y. Tang, C.C. Lin. Macromolecules, 39, 3745 (2016).
108] M. Cheng, A.B. Attygalle, E.B. Lobkovsky, G.W. Coates. J. Am. Chem. Soc., 121, 11583 (1999).
109] B.M. Chamberlain, M. Cheng, D.R. Moore, T.M. Ovitt, E.B. Lobkovsky, G.W. Coates. J. Am. Chem.
Soc., 123, 3229 (2001).
[110] M.T. Zell, B.E. Padden, A.J. Paterick, K.A.M. Thakur, R.T. Kean, M.A. Hillmyer, E.J. Munson.
Macromolecules, 35, 7700 (2002).
111] H. Wang, J. Guo, Y. Yang, H. Ma. Dalton Trans., 45, 10942 (2016).
112] D.J. Darensbourg, O. Karroonnirun. Inorg. Chem., 49, 2360 (2010).
[
[