Synthesis and structural characterization of [(dpca)MX2] (M = Cu, X = Cl; M = Cd, X = Br and M = Zn, X = NO3) complexes containing N,N-di(2-picolyl)cyclohexylamine (dpca) and their application to methyl methacrylate polymerization

Article abstract of DOI:10.1016/j.inoche.2014.04.005

A novel series of [(dpca)MX₂] (M = Cu, X = Cl; M = Cd, X = Br and M = Zn, X = NO₃) complexes were synthesized through the reaction of N,N-di(2-picolyl)cyclohexylamine (dpca) with the corresponding metal starting materials. X-ray crystallographic analysis determined that the metal center in complexes [(dpca)CuCl₂], [(dpca)CdBr₂] and [(dpca)Zn(NO₃)₂] showed a distorted 5-coordinated square pyramidal, trigonal bipyramidal, and 7-coordinated pentagonal bipyramidal geometry, respectively, involving coordination of the nitrogen atom of the cyclohexylamine moiety with the metal center. Specifically, the catalytic activity of [(dpca)Zn(NO₃)₂] (1.04 × 10⁵ g PMMA/mol Zn·h) for the polymerization of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) at 60 °C was six-fold higher than the reference complex [ZnCl₂] (1.73 × 10 ⁴ g PMMA/mol Zn·h).

Full text of DOI:10.1016/j.inoche.2014.04.005

Inorganic Chemistry Communications 45 (2014) 66–70
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Synthesis and structural characterization of [(dpca)MX2] (M = Cu,
X = Cl; M = Cd, X = Br and M = Zn, X = NO3) complexes containing N,
N-di(2-picolyl)cyclohexylamine (dpca) and their application to methyl
methacrylate polymerization
Yujin Song a, Dongil Kim a, Ha-Jin Lee b,c, Hyosun Lee a,
⁎
a
Department of Chemistry and Green-Nano Materials Research Center, Kyungpook National University, 1370 Sankyuk-dong, Buk-gu, Daegu, 702-701, Republic of Korea
Jeonju Center, Korea Basic Science Institute (KBSI), 634-18 Keumam-dong, Dukjin-gu, Jeonju, 561-180, Republic of Korea
Department of Chemistry, Chonbuk National University, Dukjin-gu, Jeonju, 561-756, Republic of Korea
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel series of [(dpca)MX2] (M = Cu, X = Cl; M = Cd, X = Br and M = Zn, X = NO3) complexes were
synthesized through the reaction of N,N-di(2-picolyl)cyclohexylamine (dpca) with the corresponding metal
starting materials. X-ray crystallographic analysis determined that the metal center in complexes [(dpca)CuCl2],
[(dpca)CdBr2] and [(dpca)Zn(NO3)2] showed a distorted 5-coordinated square pyramidal, trigonal bipyramidal,
and 7-coordinated pentagonal bipyramidal geometry, respectively, involving coordination of the nitrogen atom
of the cyclohexylamine moiety with the metal center. Specifically, the catalytic activity of [(dpca)Zn(NO3)2]
(1.04 × 105 g PMMA/mol Zn·h) for the polymerization of methyl methacrylate (MMA) in the presence of modified
Received 11 February 2014
Accepted 2 April 2014
Available online 18 April 2014
Keywords:
Copper(II) complex
Cadmium(II) complex
Zinc(II) complex
N,N-di(2-picolyl)cyclohexylmethylamine
Methyl methacrylate polymerization
Syndiotacity
methylaluminoxane (MMAO) at 60 °C was six-fold higher than the reference complex [ZnCl2] (1.73 × 104
PMMA/mol Zn·h).
g
© 2014 Elsevier B.V. All rights reserved.
Copper, cadmium and zinc metal complexes containing N,N-di(2-
picolyl)amine and its derivatives have been investigated extensively
due to their diverse structural variations in coordination modes from
N,N-bidentate and N,N,X-tridentate to N,N,X,X′-tetradentate [1–30].
These complexes can be applied for synthetic, kinetic and spectro-
scopic applications [1–14], as photoluminescent and supramolecular
materials [15–20], for biological enzymatic applications [21–28] and
for catalysis of organic transformation [28–30]. In contrast, isotactic
polymethylmethacrylate (PMMA), which is produced commercially
using radical processes, has a glass transition temperature (Tg) around
65 °C [31]. However, non-radical-mediated polymerization of methyl
methacrylate (MMA) can be used to increase the Tg for syndiotatic
PMMA. Thus, studies of non-radical-mediated MMA polymerization
have been performed, and some transition metal complexes have
been applied successfully to this process [31–39]. In previous studies,
we reported Pd(II) and Pt(II) complexes with N,N-di(2-picolyl)cyclo-
hexylamine (dpca) and observed a high activity of [(dpca)PdCl]ClO4
for MMA polymerization [40]. Accordingly, we explored several struc-
tural variations of cadmium, copper and zinc metal complexes with
[dpca], where the tridentate N-donor ligand and metal complexes
show different steric and electronic properties, and finally investigated
the “transition metal effect” under the same ligand system on MMA
polymerization.
The ligand [dpca] [41] and its complexes [(dpca)CuCl2], [(dpca)
CdBr2] and [(dpca)Zn(NO3)2] were prepared using the synthetic proce-
dure illustrated in Scheme 1.
The results of 1H-NMR, 13C-NMR and elemental analyses were con-
sistent with [(dpca)CuCl2], [(dpca)CdBr2] and [(dpca)Zn(NO3)2] com-
plex formulation. Note that 1H-NMR for N–CH2–pyridine of [dpca]
showed a singlet peak at δ 3.78. However, the proton peaks of N–CH2–
pyridine for all complexes appeared as two doublet peaks; e.g., [(dpca)
CdBr2] at δ 4.28 (2JH–H = 15.6 Hz) and δ 3.84 (2JH-H = 16.0 Hz) and
[(dpca)Zn(NO3)2] at δ 4.37 (2JH–H = 16.8 Hz) and δ 3.89 (2JH–H
=
16.4 Hz), indicating that 1H-NMR peaks for N–CH2–pyridine were
affected by the asymmetric location of the N–cyclohexyl group with
respect to the plane of the metal center. The electronic absorption spec-
tra of [dpca] in DMF showed one absorption band at λmax = 266 nm
with molar absorption coefficients of 425 cm−1 M−1, which were
attributed to π–π* interactions of the pyridine. Specifically, the UV–
vis spectra of [(dpca)CuCl2] showed two bands at λ1 = 273 nm and
λ2 = 763 nm (d–d transition) with molar absorption coefficients
of 1268 cm−1 M−1 and 48 cm−1 M−1, respectively (Fig. 1). Crystallo-
graphic and structural data for [(dpca)MX2] are summarized in
⁎
Corresponding author. Tel.: +82 53 950 5337; fax: +82 53 950 6330.
E-mail address: hyosunlee@knu.ac.kr (H. Lee).
http://dx.doi.org/10.1016/j.inoche.2014.04.005
1387-7003/© 2014 Elsevier B.V. All rights reserved.

Y. Song et al. / Inorganic Chemistry Communications 45 (2014) 66–70
67
Scheme 1. Synthesis of [(dpca)MX2] (M = Cu, X = Cl; M = Cd, X = Br and M = Zn, X = NO3) complexes.
Table 1. The selected bond lengths and angles are listed in Table 2.
ORTEP drawings of the complexes are shown in Fig. 2 ([(dpca)CuCl2]),
Fig. 3 ([(dpca)CdBr2]) and Fig. 4 ([(dpca)Zn(NO3)2]). The bond lengths
of M–Namine for [(dpca)CuCl2], [(dpca)CdBr2] and [(dpca)Zn(NO3)2]
were 2.103(4), 2.466(6) and 2.278(4) Å, respectively.
angles for [(dpca)CuCl2] were 81.79(15)° and 81.68(16)°. The coor-
dination geometry around the metal center in [(dpca)CuCl2] can be
described as a 5-coordinated square pyramid geometry, indicative of
the Jahn–Teller effect based on bonds angle of Namine–Cu–Cl(1)
[159.04(12)°], Namine–Cu–Cl(2) [93.96(11)°] and Npyridine–Cu–Npyridine
[162.80(12)°] for [(dpca)CuCl2]. Two Namine–Cd–Npyridine bond angles
for [(dpca)CdBr2] were 72.7(2)° and 73.3(2)°, indicative of 5-
membered fused ring strain, which had a major effect on [(dpca)
CdBr2]. Additionally, the bond angle of Namine–Cd–Br(1) [163.11(14)°],
The bond lengths of M–Npyridine in [(dpca)CuCl2] were 1.989(4) and
1.999(4) Å, in [(dpca)CdBr2] were 2.294(6) and 2.290(6) Å, and in
[(dpca)Zn(NO3)2] were 2.062(4) and 2.072(4) Å. The bond length
of M–Namine in [(dpca)CuCl2] was 2.103(4), in [(dpca)CdBr2] was
2.466(6), and in [(dpca)Zn(NO3)2] was 2.278(4). Since the Namine
atom of the sp3 hybrid orbital was connected by three carbon atoms,
and a metal atom is a stronger base than Npyridine of the sp2 hybrid or-
bital, the M–Namine bond lengths were ca. 0.1–0.2 Å longer than those
of M–Npyridine. Moreover, the Namine atom was coordinated to metal
solely through a σ-bond, but the Npyridine atoms were coordinated by
both a σ-bond and a weak π-back bond. The xz plane of the cyclohexyl
group in [(dpca)CuCl2] and its yz plane in [(dpca)Zn(NO3)2] were per-
pendicular with respect to the xy plane of the metal and two pyridine
rings in a chair form. However, the yz plane of the cyclohexyl group
and the two pyridine rings in [(dpca)CdBr2] appeared as the back of
a chair and elbow rests, respectively. Two Namine–M–Npyridine bond
Namine–Cd–Br(2) [91.48(14)°] and NpyridineCd–Npyridine [103.6(2)°] for
[(dpca)CdBr2] indicated that the coordination around the cadmium
center in [(dpca)CdBr2] was a distorted 5-coordinated trigonal bipyra-
midal geometry involving coordination of the nitrogen atom of the
cyclohexylamine moiety and the metal center, thus forming two 5-
membered chelate rings. In addition, the bond angles Cl(1)–Cu–Cl(2)
in square pyramidal [(dpca)CuCl2] and Br(1)–Cd–Br(2) in trigonal bipy-
ramidal [(dpca)CdBr2] were 107.00(6) and 105.14(3)°, respectively. Two
Namine–M–Npyridine bond angles for [(dpca)Zn(NO3)2] were 78.56(15)°
and 78.67(14)°. In addition, the corresponding O(1)–Zn–O(4) in
[(dpca)Zn(NO3)2] was 79.19(17)°, which was indicative of a more
distorted trigonal bipyramid geometry. However, compared to covalent
bonds of Zn–O(1) [2.107(4) Å] and Zn–O(4) [2.128(5) Å], bond lengths
of Zn–O(2) and Zn–O(5) were extended by ca. 0.5 Å, namely, about
2.597 Å and 2.614 Å, respectively. Thus, bonds of Zn–O(2) and Zn–
O(5) can be considered a non-bonding interaction between oxygen
and zinc metal. Alternatively, [(dpca)Zn(NO3)2] is 7-coordinated and
can be best described as a distorted pentagonal bipyramid with the
N(1) and N(2) pyridine nitrogen atoms occupying the axial positions
at normal distances. The plane is defined by four oxygen atoms from
two nitrate anions and the amine nitrogen atom N(3) connected to
the cyclohexyl group. This semi-coordination is most likely due to
the small bite angle of the bidentate nitrate ligand (the bond angle of
O(2)–Zn–O(1) was calculated as 53.20°), which also induces distortion
in the pentagonal bipyramid geometry.
[(dpca)CuCl2], [(dpca)CdBr2] and [(dpca)Zn(NO3)2] could be acti-
vated with co-catalyst modified methylaluminoxane (MMAO) to
polymerize methyl methacrylate (MMA) (Scheme 2 and Table 3). For
comparison, the reference complexes, anhydrous [CuCl2], [CdCl2], and
[ZnCl2], were used for MMA polymerization [42–44].
The activity of [(dpca)Zn(NO3)2] (1.03 × 105 g PMMA/mol Zn·h) in-
creased six-fold compared to [ZnCl2] (1.73 × 104 g PMMA/mol Zn·h) at
60 °C. However, [(dpca)CuCl2] (6.40 × 104 g PMMA/mol Cu·h) and
[(dpca)CdBr2] (6.22 × 104 g PMMA/mol Cd·h) showed only three-fold
Fig. 1. UV–vis absorption spectra of [dpca] and [(dpca)MX2] (M = Cu, X = Cl; M = Cd,
X = Br and M = Zn, X = NO3) complexes.

68
Y. Song et al. / Inorganic Chemistry Communications 45 (2014) 66–70
Table 1
Crystal data and structural refinement for [(dpca)MX2] (M = Cu, X = Cl; M = Cd, X = Br and M = Zn, X = NO3) complexes.
[(dpca)CuCl2]
18H23Cl2CuN3
500.79
200(2)K
[(dpca)CdBr2]
[(dpca)Zn(NO3)2]
Empirical formula
Formula weight
Temperature
C
C18H23Br2CdN3
553.61
200(2)K
C18H23N5O6Zn
470.78
200(2)K
Wavelength
0.71073 Å
0.71073 Å
0.71073 Å
Crystal system
Space group
Monoclinic
C2/c
Monoclinic
P2(1)/c
Monoclinic
P2(1)/n
Unit cell dimensions
a = 24.3497(10) Å
b = 11.4808(5) Å
c = 16.6790(7) Å
α = 90°
a = 8.5186(5) Å
b = 14.2767(9) Å
c = 16.0859(9) Å
α = 90°
a = 8.578(2) Å
b = 15.379(4) Å
c = 15.268(4) Å
α = 90°
β = 114.1220(10)°
γ = 90°
β = 90.2700(10)°.
γ = 90°
β = 99.951(5)°
γ = 90°
Volume, Z
4255.5(3) Å3, 8
1.563 g/cm3
1956.3(2) Å3, 4
1.880 g/cm3
1983.8(9) Å3, 4
1.576 Mg/m3
1.285 mm−1
976
Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Index ranges
1.539 mm−1
2056
5.206 mm−1
1080
0.18 × 0.17 × 0.11 mm3
1.89 to 28.30°
−32 ≤ h ≤ 16
−14 ≤ k ≤ 15
−19 ≤ l ≤ 22
15,588
0.34 × 0.25 × 0.25 mm3
1.91 to 26.02°
−10 ≤ h ≤ 7
−17 ≤ k ≤ 17
−19 ≤ l ≤ 19
11,934
0.33 × 0.14 × 0.12 mm3
1.89 to 28.28°
−11 ≤ h ≤ 11
−15 ≤ k ≤ 20
−20 ≤ l ≤ 20
14,603
Reflections collected
Independent reflections
Completeness to θ = 28.27°
Refinement method
5273 [R(int) = 0.0763]
99.7%
3846 [R(int) = 0.0429]
99.2%
4917 [R(int) = 0.0527]
99.6%
Full-matrix least-squares on F2
5273/0/244
Full-matrix least-squares on F2
3846/0/217
Full-matrix least-squares on F2
4917/0/272
Data/restraints/parameters
Goodness-of-fit on F2
0.914
1.209
1.111
Final R indices [I N 2σ(I)]
R1 = 0.05559
wR2 = 0.1186
R1 = 0.1308
wR2 = 0.1630
0.954 and −0.933 e⋅Å−3
R1 = 0.0407
wR2 = 0.1008
R1 = 0.0569
wR2 = 0.1639
1.202 and −1.780 e⋅Å−3
R1 = 0.0533
wR2 = 0.1071
R1 = 0.1111
wR2 = 0.1647
1.018 and −1.447 e⋅Å−3
R indices (all data)
Largest diff. peak and hole
and two-fold increases in activity compared to the corresponding
[CuCl2] (1.90 × 104 g PMMA/mol Cu·h) and [CdCl2] (3.53 × 104
metal than copper and cadmium metals to facilitate MMA polymeriza-
tion. On the other hand, the microstructure of PMMA was determined
using 1H-NMR spectroscopy as syndiotactic (rr, δ 0.85), heterotactic
(mr, δ 1.02) and isotactic (mm, δ 1.21) [43,45]. Since higher optical
quality of PMMA represents a higher glass transition temperature (Tg)
up to 140 °C, non-radical-mediated MMA polymerization by complex
catalysts increased PMMA syndiotacticity. The syndiotacticity of
g
PMMA/mol Cd·h), respectively. Previously reported [(dpca)PdCl]ClO4
(1.28 × 105 g PMMA/mol Pd·h) showed over six-fold higher activity
than the corresponding reference material [PdCl2] (1.97 × 104
g
PMMA/mol Pd·h). Since all complexes contained a 5-coordinated ge-
ometry, [dpca] may induce more steric and electronic effects on zinc
Table 2
Selected bond lengths (Å) and angles (°) of [(dpca)MX2] (M = Cu, X = Cl; M = Cd, X = Br and M = Zn, X = NO3) complexes.
[(dpca)CuCl2]
[(dpca)CdBr2]
[(dpca)Zn(NO3)2]
Bond lengths
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–N(3)
Cu(1)–Cl(1)
Cu(1)–Cl(2)
N(1)–C(1)
N(1)–C(5)
N(2)–C(12)
N(2)–C(8)
N(3)–C(7)
1.989(4)
1.999(4)
2.103(4)
2.2719(15)
2.5348(14)
1.338(6)
1.348(6)
1.346(6)
1.356(6)
1.488(6)
Cd(1) –N(2)
Cd(1)–N(1)
Cd(1)–N(3)
Cd(1)–Br(2)
Cd(1)–Br(1)
N(1)–C(5)
N(1)–C(1)
N(2)–C(8)
N(2)–C(12)
N(3)–C(7)
2.290(6)
2.294(6)
2.466(6)
2.5871(10)
2.6016(9)
1.330(9)
1.360(10)
1.334(10)
1.355(10)
1.467(10)
Zn(1)–N(1)
Zn(1)–N(2)
Zn(1)–O(1)
Zn(1)–O(4)
Zn(1)–N(3)
N(1)–C(1)
N(1)–C(5)
N(2)–C(12)
N(2)–C(8)
N(3)–C(6)
2.062(4)
2.072(4)
2.107(4)
2.128(5)
2.278(4)
1.340(6)
1.340(6)
1.332(6)
1.350(6)
1.479(6)
Bond angles
N(1)–Cu(1)–N(2)
N(1)–Cu(1)–N(3)
N(2)–Cu(1)–N(3)
N(1)–Cu(1)–Cl(1)
N(2)–Cu(1)–Cl(1)
N(3)–Cu(1)–Cl(1)
N(1)–Cu(1)–Cl(2)
N(2)–Cu(1)–Cl(2)
N(3)–Cu(1)–Cl(2)
Cl(1)–Cu(1)–Cl(2)
162.80(17)
81.79(15)
81.68(16)
97.14(12)
96.59(13)
159.04(12)
91.92(12)
93.93(12)
93.96(11)
107.00(6)
N(2)–Cd(1)–N(1)
N(2)–Cd(1)–N(3)
N(1)–Cd(1)–N(3)
N(2)–Cd(1)–Br(2)
N(1)–Cd(1)–Br(2)
N(3)–Cd(1)–Br(2)
N(2)–Cd(1)–Br(1)
N(1)–Cd(1)–Br(1)
N(3)–Cd(1)–Br(1)
Br(2)–Cd(1)–Br(1)
103.6(2)
72.7(2)
73.3(2)
109.06(16)
137.80(15)
91.48(14)
98.41(16)
95.58(15)
163.11(14)
105.14(3)
N(1)–Zn(1)–N(2)
N(1)–Zn(1)–O(1)
N(2)–Zn(1)–O(1)
N(1)–Zn(1)–O(4)
N(2)–Zn(1)–O(4)
O(1)–Zn(1)–O(4)
N(1)–Zn(1)–N(3)
N(2)–Zn(1)–N(3)
O(1)–Zn(1)–N(3)
O(4)–Zn(1)–N(3)
156.66(16)
98.35(15)
94.94(15)
103.39(18)
97.87(18)
79.19(17)
78.57(15)
78.67(14)
137.54(15)
143.09(17)

Y. Song et al. / Inorganic Chemistry Communications 45 (2014) 66–70
69
Fig. 2. ORTEP drawing of [(dpca)CuCl2] with thermal ellipsoids at 50% probability. All
hydrogen atoms are omitted for clarity.
Fig. 4. ORTEP drawing of [(dpca)Zn(NO3)2] with thermal ellipsoids at 50% probability. All
hydrogen atoms are omitted for clarity.
PMMA by [(dpca)Zn(NO3)2] was ca. 72%, which was similar to the other
complexes [(dpca)CuCl2], [(dpca)CdBr2] and [(dpca)PdCl]ClO4. In
addition, all complexes yielded PMMA with Tg ranging from 132
to 135 °C. Although the moderate syndiotacticity was not sufficient
to confer a coordination polymerization mechanism for all complexes,
we clearly observed stronger steric or electronic effects of [dpca]
on the zinc metal in [(dpca)Zn(NO3)2] than on copper and cadmium
metals in [(dpca)CuCl2] and [(dpca)CdBr2], respectively, for MMA
polymerization.
Appendix A. Supplementary materials
CCDC 985692 ~ 985694 contains the supplementary crystallo-
graphic data for complexes [(dpca)CuCl2], [(dpca)CdBr2] and [(dpca)
Zn(NO3)2], respectively. These data can be obtained 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.
Supplementary data to this article can be found online at http://dx.doi.
org/10.1016/j.inoche.2014.04.005.
Acknowledgments
This research was supported by the National Research Foundation of
Korea (NRF), funded by the Ministry of the Education, Science, and
Technology (MEST) (Grant No. 2012-R1A2A2A01045730).
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hydrogen atoms are omitted for clarity.

70
Y. Song et al. / Inorganic Chemistry Communications 45 (2014) 66–70
Scheme 2. Representative methyl methacrylate (MMA) polymerization.
Table 3
Polymerization of MMA by [(dpca)MX2] (M = Cu, X = Cl; M = Cd, X = Br and M = Zn, X = NO3) complexes in the presence of MMAO.
Catalysta
Temp. (time)
°C (h)
Yieldb
(g)
Activityc
Tg
Tacticity
%mm
Mw
Mw/Mn
d
e
f
Entry
(g/molcat·h) × 104
(°C)
%mr
%rr
(g/mol) × 105
1
2
3
4
5
6
7
8
9
10
[CuCl2]g
[CdCl2]g
[ZnCl2]g
MMAOh
[PdCl2]i
[(dpca)PdCl]ClO4
[(dpca)PtCl]ClO4
[(dpca)CuCl2]
[(dpca)CdBr2]
[(dpca)Zn(NO3)2]
60(2 h)
60(2 h)
60(2 h)
60(2 h)
60(2 h)
60(0.5 h)
60(2 h)
60(2 h)
60(2 h)
60(2 h)
0.57
1.06
0.52
0.42
0.59
0.96
0.40
1.92
1.87
3.88
1.90
3.53
1.73
1.40
1.97
12.8
1.3
6.40
6.22
10.3
132
123
129
120
129
130
127
132
135
133
6.90
5.60
9.20
37.2
10.2
6.75
9.53
7.00
6.62
6.1
24.3
30.3
24.2
10.9
23.5
20.11
24.83
22.5
23.2
21.8
68.8
64.1
66.6
51.9
66.3
73.14
65.64
70.5
70.2
72.1
6.29
4.72
1.33
8.15
7.52
0.80
6.31
6.37
7.28
7.28
2.13
1.49
1.58
1.97
1.63
1.59
1.64
2.14
1.98
1.98
i
i
a
[M(II) catalyst]0 = 15 μmol, and [MMA]0/[MMAO]0/[M(II) catalyst]0 = 3100:500:1.
Yield defined as mass of dried polymer recovered.
Activity is g of PMMA/(mol M·h).
Tg is glass transition temperature determined using a thermal analyzer.
Determined using gel permeation chromatography (GPC) eluted with THF at room temperature by filtration with polystyrene calibration.
Mn refers to the number average of molecular weights of PMMA.
Blank polymerization, in which anhydrous [CuCl2], [CdCl2] and [ZnCl2] and metal starting complexes [CdBr2·4H2O] and [Zn(NO3)2·6H2O] were also activated by MMAO.
Blank polymerization accomplished solely by MMAO.
Reference [40].
b
c
d
e
f
g
h
i
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