Synthesis and structural characterization of a dichloro zinc complex of N,N′-bis-(2,6-dichloro-benzyl)-(R,R)-1,2-diaminocyclohexane: Application to ring opening polymerization of rac-lactide

Article abstract of DOI:10.1016/j.poly.2011.10.035

A novel dichloro zinc complex (L¹)ZnCl₂, where L ¹ is N,N′-bis-(2,6-dichloro-benzyl)-(R,R)-1,2- diaminocyclohexane, has been synthesized and characterized. The dimethyl derivatives, generated in situ from the well characte

Full text of DOI:10.1016/j.poly.2011.10.035

Polyhedron 31 (2012) 682–687
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Polyhedron
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Synthesis and structural characterization of a dichloro zinc complex
of N,N0-bis-(2,6-dichloro-benzyl)-(R,R)-1,2-diaminocyclohexane:
Application to ring opening polymerization of rac-lactide
⇑
Saira Nayab, Hyosun Lee, Jong Hwa Jeong
Department of Chemistry and Green-Nano Materials Research Center, Kyungpook National University, 1370 Sankyuk-dong, Taegu 702-701, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
A novel dichloro zinc complex (L1)ZnCl2, where L1 is N,N0-bis-(2,6-dichloro-benzyl)-(R,R)-1,2-diaminocy-
clohexane, has been synthesized and characterized. The dimethyl derivatives, generated in situ from
the well characterized dichloro zinc complexes (L1)ZnCl2 and (L2)ZnCl2, where L2 is N,N0-bis-(benzyl)-
(R,R)-1,2-diaminocyclohexane, were employed as initiators for the ring opening polymerization (ROP)
of rac-lactide (rac-LA). The complexes were found to be highly efficient initiators yielding the polylactide
(PLA) with a narrow molecular weight distribution. The catalytic activity and heterotactic selectivity of
the Zn(II) complexes were affected by the substituents on the phenyl groups of benzyl moieties in
(R,R)-1,2-diaminocyclohexane. The dimethyl derivative of (L2)ZnCl2 produced highly stereocontrolled
PLA with Pr = 0.75 at ꢀ25 °C.
Article history:
Received 10 August 2011
Accepted 24 October 2011
Available online 10 November 2011
Keywords:
Polylactide
(R,R)-1,2-Diaminocyclohexane
Zinc complex
Ring opening polymerization
Heterotacticity
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
polycondensation route [8]. The use of a single site homogenous
metal catalyst is the most effective and versatile approach towards
Polylactide (PLA), a biorenewable, biocompatible and biode-
gradable polymer, has been a subject of considerable attention in
academic as well as in industrial research over the past few dec-
ades [1]. The physical features, such as gas permeability, low haze,
transparency, flavor-resistance, high mechanical strength and easy
processibility, make PLA a practical alternative to traditional petro-
chemical based polymeric materials [2]. The synthesis of PLA can
be accomplished either by polycondensation of lactic acid or ROP
of lactide (LA). LA, the cyclic dimer of lactic acid, can be derived
from inexpensive and annually renewable resources, such as corn,
molasses, starch, sugars as well as dairy products, and hence this
reduces the environmental load on the fossil fuel required to pro-
duce PLA. Furthermore, PLA is degradable to carbon dioxide and
water, and thus emerges as an environmentally friendly material
[3]. Furthermore, PLA based bioplastics have been increasing its
utility in a wide range of pharmaceutical, biomedical [4,5], agricul-
ture [6] as well as industrial and microelectronic fields [7].
the synthesis of PLA via ROP, as their steric and electronic environ-
ments and Lewis acidity can be tuned effectively. Many metal spe-
cies, such as calcium [9], magnesium [10], zinc [11,12], aluminum
[13], tin [14], lead and bismuth [15], lanthanides [16], group 4 ele-
ments [17], iron [18], germanium [19] and indium [20], have been
utilized extensively for the ROP of rac-LA. However, zinc based ini-
tiators are much preferred for PLA synthesis, especially for resorb-
able biomaterials [21], food packaging [22] and pharmaceutical
applications [23] due to their biocompatibility, coupled with
their lower toxicity. Representative zinc complexes, comprising
mostly of achiral supporting ligand specimens including
b-diketiminate [24], tris(pyrazolyl)hydroborate [25], amidinate
[26], phenolates [27], amino-bis(pyrazolyl) [28], oxazolinate [29],
salen type ligand [30], Schiff’s bases [31] and recently neutral
N-heterocyclic carbenes [32], oxabispidine [33] and guanidine
[34], have been synthesized and their successful application
towards the ROP of rac-LA has been extensively reviewed recently
[35]. Especially, zinc acetate in the presence of BnOH, reported by
the Chakraborty group, has shown the highest catalytic activity
and no stereoregularity for the obtained PLA using rac-LA [36].
The research results showed that the mechanical and physical
properties, as well as biological degradation behaviors, of polymers
rely dramatically on the tacticity of the obtained polymers, which
in turn is influenced by the initiator’s architecture. Therefore, chiral
catalysts are considered to be highly versatile in terms of stereo-
regularity and increased tacticities [37,38]. The most important
ROP is undeniably, the most desirable and convenient method
to produce PLA in terms of its greater degree of control over the
molecular parameters of the subsequent polymeric materials. This
significant regulatory effect of the polymerization process leads to
polymers being obtained with lower polydispersities, higher
molecular weights and high stereoregularity compared to the
⇑
Corresponding author. Tel.: +82 53 950 6343; fax: +82 53 950 6330.
E-mail address: jeongjh@knu.ac.kr (J.H. Jeong).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.10.035

S. Nayab et al. / Polyhedron 31 (2012) 682–687
683
breakthrough, reported by Spassky, was for chiral salen-based alu-
minum initiators, resulting in excellent isotactic stereospecificity
for the ROP of rac-LA [39–43]. However, these catalytic systems
suffered from inherently low activities and the polymerization
runs had to be carried out at high temperatures over a relatively
long period of time to obtain affordable conversions. Achiral zinc
complexes supported by b-diiminates are found to be highly active
and heterospecific (Pr = 0.94) towards the ROP of rac-LA [44]. Chiral
zinc catalysts for rac-LA polymerization are rare [45–47]. Recently,
the C2 symmetric chiral ligands (R,R)-1,2-diaminocyclohexane
derivatives are arising as attractive auxiliaries to serve as a power-
ful stereoregulating system for the ROP of LA [48,49]. Herein, we
reported the synthesis and characterization of a dichloro zinc
complex incorporating N,N0-bis-(2,6-dichloro-benzyl)-(R,R)-1,2-
diaminocyclohexane. The dimethyl derivatives of (L1)ZnCl2 and
(L2)ZnCl2 [50], generated in situ, were evaluated as initiators for
the ROP of rac-LA.
2.3. Polymerization of rac-LA with the in situ generated dimethyl zinc
complexes
The active catalyst, the dimethyl zinc complex, was prepared as
follows. (L1)ZnCl2 (0.28 g, 0.50 mmol) and dried THF (7.30 mL)
were added to a 100 mL Schlenk flask under argon to make a
homogenous solution. To this solution was added MeLi (0.65 mL
of a 1.6 M solution in diethyl ether, 1 mmol) dropwise at ꢀ78 °C.
After being stirred for 2 h at room temperature, the resulting solu-
tion of (L1)ZnMe2 was used as a catalyst for the polymerization
reaction. The general procedure for the polymerization reaction
was as follows. A 100 mL Schlenk flask was charged with rac-LA
(0.901 g, 6.25 mmol) in a glove box. Dried CH2Cl2 (5 mL) was trans-
ferred to the flask via a syringe and stirred to make a homogenous
solution. The polymerization reaction was initiated by slowly add-
ing the catalyst solution (1 mL, 0.0625 mmol) via a gas tight syr-
inge under argon at 25 °C. The reaction mixture was stirred at 25
and then ꢀ25 °C for 12 h. All the volatiles were removed and the
obtained crude polymeric material was dissolved in CH2Cl2
(5 mL), followed by the addition of water (1 mL) and then hexane
(2 mL) to yield the resultant sticky polymeric material, which
was then washed with Et2O (5 mL ꢁ 2). The polymer was dried
completely in vacuo for 12 h at 40 °C. A white solid was obtained
as the final polymeric material (0.89 g, 98.7%). 1H NMR
(400 MHz, CDCl3): d 5.14–5.25 (m, 1H), 1.54–1.63 (m, 3H).
2. Experimental
2.1. General considerations
All manipulations involved in the synthesis of the ligands and
the complexes were carried out by the use of bench top techniques
in air, unless otherwise specified. All polymerizations were carried
out using standard Schlenk techniques, high vacuum and a glove
box under argon. THF was dried over Na/benzophenone ketyl,
while CH2Cl2 was dried over CaH2. These solvents were deoxygen-
ated by distillation under argon prior to use. The starting materials,
( )-trans-1,2-diaminocyclohexane, L-(+)-tartaric acid, 2,6-chloro-
benzaldehyde (98%), NaBH4, ZnCl2, methyl lithium (MeLi) (1.6 M
in diethyl ether) and 3,6-dimethyl-1-dioxane-2,5-dione (rac-LA),
were purchased from Aldrich and were used without further puri-
fication. L1 [51] and (L2)ZnCl2 [50] were prepared by the reported
procedure.
2.4. X-ray crystallography
An X-ray quality single crystal, which was obtained from a hot
EtOH solution, was mounted in a thin-walled glass capillary on an
Enraf-Noius CAD-4 diffractometer with MoK
a
radiation
(k = 0.71073 Å). Unit cell parameters were determined by least-
squares analysis of 25 reflections (10° < h < 13°). Intensity data
were collected with a h range of 1.59–25.47° in the
x/2h scan
mode. Three standard reflections were monitored every 1 h during
the data collection. The data were corrected for Lorentz-polariza-
tion effects and decay. Empirical absorption corrections with
1H NMR (400 MHz) spectra were recorded on a Bruker Advance
Digital 400-NMR spectrometer and chemical shifts were recorded
in ppm units using SiMe4 as an internal standard. Coupling con-
stants are reported in Hertz (Hz). Infrared (IR) spectra were re-
corded on a Bruker FT/IR-Alpha (neat) and the data are reported
in reciprocal centimeters. Elemental analyses were determined
using an EA 1108-Elemental Analyzer at the Chemical Analysis.
Gel permeation chromatography (GPC) analyses were carried out
on a Waters Alliance GPCV2000, equipped with differential refrac-
tive index detectors. The GPC columns were eluted using THF with
a 1 ml/min rate at 25 °C and were calibrated with monodisperse
polystyrene standards.
w
-scans were applied to the data. The structure was solved using
the direct method and refined by full-matrix least-squares tech-
niques on F2 using SHELXL-97 and SHELXS-97 program packages [52].
All non hydrogen atoms were refined anisotropically, except for
the disordered Cl atoms on the phenyl groups of the benzyl moie-
ties and all non hydrogen atoms of solvated EtOH, which were re-
fined isotropically. All hydrogen atoms were refined positioned
geometrically using the riding model with fixed isotropic thermal
factors. The final cycle of the refinement converged with
R1 = 0.045 and wR2 = 0.125.
2.2. Synthesis
3. Results and discussion
2.2.1. Dichloro [N,N-bis-(2,6-dichloro-benzyl)-(R,R)-1,2-
3.1. Synthesis and characterization
diaminocyclohexane] Zn(II) complex, (L1)ZnCl2
An EtOH (7 mL) solution of L1 (1.48 g, 3.42 mmol) was treated
with ZnCl2 (0.46 g, 3.42 mmol) in EtOH (5 mL) at ambient temper-
ature overnight to give a solid precipitation. Washing the precipi-
tate after filtration with Et2O afforded a white solid as the final
product (1.67 g, 87%). Anal. Calc. for C20H20Cl6N2Zn: C, 42.40; H,
3.56; N, 4.95. Found: C, 42.36; H, 3.60; N, 5.00%. 1H NMR
(400 Hz, CDCl3) d: 7.37 (m, 4H, ArH), 7.29 (m, 2H, ArH), 4.45 (m,
4H, N(CH2)2), 2.85 (m, 2H, CHA), 1.98 (m, 2H, (NH)2CHA), 1.71
(m, 2H, CHA), 1.22 (m, 2H, CHA), 1.11 (m, 2H, CHA). IR (solid neat;
cmꢀ1): 2931 (m), 2860 (m), 2360 (m), 2341 (w), 1580 (m), 1560
(m), 1435 (s), 1191 (m), 1156 (w), 1089 (s), 1042 (w), 1004 (w),
960 (m), 935 (m), 841 (w), 818 (w), 779 (s), 764 (s), 725 (m), 701
(m), 636 (m), 619 (w), 566 (w).
The synthesis of the ligand involved the use of the (R,R)-1,2-
diaminecyclohexane-L-tartrate salt to resolve free pure (R,R)-1,2-
diaminocyclohexane, which in turn undergoes a condensation
reaction with 2,6-dichlorobenzaldehyde to produce the diimine
product. The diimine moiety was further reduced using NaBH4 in
MeOH at ambient temperature to obtain the N,N0-disubstituted
C2 symmetric diamine. The corresponding dichloro Zn(II) complex
was synthesized via the reaction of the ligand precursor with ZnCl2
in a 1:1 molar ratio in dried EtOH at ambient temperature (Scheme
1). The white analytically pure dichloro zinc complex was obtained
in 85–87% yield after washing the solid with cold EtOH and Et2O
followed by drying in vacuo. The newly synthesized ligand and zinc
complex were characterized by 1H NMR, IR and elemental analysis.

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S. Nayab et al. / Polyhedron 31 (2012) 682–687
Cl
Cl
Cl
Cl
O
H
+ 2
N
NH
NH
Cl
Cl
NaBH4
NH3
CO2
Cl
Cl
H3N
O2C
Cl
2 N NaOH / MC / RT
MeOH / RT
N
HO
OH
(R,R)-
Cl
L1
Cl
Cl
NH
Cl
NH
Cl
ZnCl2
Zn
Cl
EtOH / RT
Cl
(L1)ZnCl2
Scheme 1. Synthesis of the L1 supported mononuclear dichloro zinc complex.
The crystal structure of (L1)ZnCl2 was determined by X-ray
crystallography.
ical parameters are very similar to those in (L2)ZnCl2 [50]. The data
reflect that a much smaller bite angle is observed for N1–Zn–N2
compared to Cl1–Zn–Cl2. This is a common structural feature for
(L)ZnX2 type complexes, where L is a bidentate ligand forming a
five-membered ring with Zn and X is a halide, with the ligands
forming a distorted tetrahedral geometry around the zinc centre.
The crystal structure of (L1)ZnCl2 revealed a relatively rigid
framework, where the chloro substituted phenyl groups of the
benzyl moieties are arranged in a ‘‘back and forth’’ manner to the
five-membered ring comprising the Zn atom (Fig. 2a) and this lead
to less bulk around the metal center. However, the two unsubsti-
tuted phenyl groups of the benzyl moieties in (L2)ZnCl2 lie above
and below the plane of corresponding five-membered ring and re-
sulted in bulkiness in either side of the metal center (Fig. 2b).
Moreover, (L1)ZnCl2 has two chiral centers, RC and RC, derived
from the (R,R)-1,2-diaminocyclohexane fragment, while the hydro-
gen atoms of the chiral carbon and nitrogen are found to be in
head-to-tail conformation (Fig. 1). The resulting X-ray structure
also shows that the two stereogenic nitrogen atoms are RN and
RN. Furthermore, the chelate formation by the homochiral biden-
tate diaminocyclohexane ligand leads to stabilization of the diva-
lent zinc centre and the resultant five-membered chelate ring
made up of N1–C1–C6–N2 atoms with Zn is found to be in the
k-conformation.
The crystallographic data and the results of the refinement for
(L1)ZnCl2 are summarized in Table 1. Selected bond angles and
lengths for (L1)ZnCl2 are tabulated in Table 2. An ORTEP drawing
of (L1)ZnCl2 with the atomic labeling is shown in Fig. 1. The X-
ray structure revealed that the zinc atom is coordinated by two
nitrogen atoms of a bidentate chiral ligand and two chloro ligands
adopting a nearly tetrahedral geometry. The Zn–N bond lengths for
(L1)ZnCl2 are 2.102(5) Å for Zn–N1 and 2.081(5) Å for Zn–N2. The
bond distances for Zn–Cl are 2.186(2) and 2.239(2) Å for Zn–Cl1
and Zn–Cl2, respectively. The bond angles for Cl1–Zn–Cl2 and
N1–Zn–N2 are 122.31(9)° and 85.5(2)°, respectively. These numer-
Table 1
Crystallographic data of (L1)ZnCl2ꢂCH3CH2OH.
Empirical formula
Formula weight
Crystal system
Space group
Unit cell dimensions
a (Å)
C20H22 Cl6 N2 ZnꢂCH3CH2OH
614.53
Orthorhombic
P21212
16.914(1)
b (Å)
19.552(2)
c (Å)
8.3217(6)
2752.0(7)
V (Å3)
Z
4
Dcalc (mg/m3)
Absorption coefficient (mmꢀ1
F(000)
1.483
1.493
1256
3.2. Ring opening polymerization of rac-LA using the dimethyl zinc
complexes
)
h range for data collection (°)
Index ranges
1.59–25.47
ꢀ20 6 h 6 0,
The synthesis of a high molecular weight polymer generally de-
pends upon the controlled ROP of rac-LA using well-defined metal
0 6 k 6 23,
0 6 l 6 10
Reflections collected
3006
Table 2
Independent reflections (Rint
Reflections observed (>2d)
Data completeness
)
2911 (0.0087)
2077
1.000
Selected bond lengths (Å) and bond angles (°) of (L1)ZnCl2ꢂCH3CH2OH.
Zn–N1
Zn–N2
Zn–Cl1
Zn–Cl2
2.102(5)
2.081(5)
2.186(2)
2.239(2)
N1–C1
N1–C14
N2–C6
N2–C7
1.474(8)
1.480(8)
1.500(8)
1.473(8)
Refinement method
Full-matrix least-squares on F2
2911/0/286
1.099
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0452, wR2 = 0.1247
R1 = 0.0741, wR2 = 0.1337
0.00 (3)
0.543 and ꢀ0.545
N1–Zn–N2
N2–Zn–Cl2
N2–Zn–Cl1
85.5(2)
105.3(2)
122.6(2)
N1–Zn–Cl2
N1–Zn–Cl1
Cl1–Zn–Cl2
102.2(2)
111.1(1)
122.3(9)
Absolute structure parameter
Largest difference peak and hole (e/Å3)

S. Nayab et al. / Polyhedron 31 (2012) 682–687
685
C4
C3
Cl3
C5
Cl6
C2
C19
C9
C20
C1
C6
C18
C10
C7
N1
C15
C8
C14
N2
C17
C11
C16
C13
Cl4
Zn
C12
Cl5
Cl2
Cl1
Fig. 1. An ORTEP drawing of (L1)ZnCl2 with the atomic numbering scheme; ellipsoids are drawn at the 40% probability level.
Fig. 2. Comparative views of the X-ray structures (a) (L1)ZnCl2 and (b) (L2)ZnCl2, which demonstrates the imparted coordination sphere around the Zn atoms by the
substituted and unsubstituted phenyl groups of the benzyl moieties.
complexes. The dichloro Zn(II) complexes did not show any activ-
ity towards the polymerization of rac-LA at room temperature or
ꢀ25 °C. The active dimethyl derivatives of the complexes (L1)ZnCl2
and (L2)ZnCl2 have been generated in situ by treating these dichloro
complexes with two equivalents of MeLi in THF. The THF solutions
of the dimethyl complexes were systematically examined under
argon atmosphere for their catalytic activities toward the ROP of
rac-LA, and the results are summerized in Table 3. Conversion of
the rac-LA monomer to PLA has been determined on the basis of
1H NMR spectroscopic studies. These dimethyl derivatives of the
zinc complexes, (L1)ZnMe2 and (L2)ZnMe2, were found to be highly
efficient initaitors for the ROP of rac-LA at room temperature as
well as at low temperature in CH2Cl2. The monomer was quantita-
tively (697%) converted to the polymeric species within 12 h by
using the dimethyl zinc complexes as initiators. The active catalyst
species formation was confirmed by 1H NMR analysis, with the

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S. Nayab et al. / Polyhedron 31 (2012) 682–687
corresponding peaks for the methyl groups appearing at d ꢀ0.57
and ꢀ0.62 ppm in CDCl3 for (L1)ZnMe2 and (L2)ZnMe2, respectively.
The Mn and molecular weight distribution (Mw/Mn) of the obtained
polymers are given in Table 3. The well controlled living polymer-
ization is evidenced by the narrow PDIs and the linear relationship
between the measured Mn values, % conversion and monomer/ini-
tiator ratio (Table 3).
ments of the transition states associated with the polymerization
process, as is evident from the crystal structure of (L2)ZnCl2
(Fig. 2b) [50]. The decrease in heterotacticity of the PLA obtained
using the chloro substituted complex (L1)ZnCl2 might be the result
of the rigidity of the chloro substituted benzyl moieties in coma-
prison to the flexible free benzyl units in (L2)ZnCl2 (Fig. 2a).
Furthermore, the experimental results demonstrate that tem-
perature has no major influence on the tacticity of the obtained
PLAs, as lowering the temperature from 25 to ꢀ25 °C resulted in
a Pr value increase from 70% to 75% for (L2)ZnCl2 under same exper-
imental conditions. The high heterotactic PLA could be obtained
mainly by a chain end control mechanism [56] using (L1)ZnMe2
and (L2)ZnMe2 as initiators. As stated earlier, the chirality of the
ancillary ligand bound to the metal atom is also crucial in deter-
mining the stereochemical selectivity [45]. However, recent stud-
ies have highlighted some complex aspects, namely the nature of
metal, size of ancillary ligand, chirality of the ligand framework,
the chirality of the end group of the growing polymer chain as well
as solvent seem to play unpredictable roles for chiral complexes in
influencing the stereo-preference in a racemic monomer mixture
[57].
The experimental results indicate that the chloro substituents
on the phenyl groups of benzyl moieties of the (R,R)-1,2-diamino-
cyclohexane fragment in the complex (L1)ZnCl2 play a major role in
tuning the tacticity of the the obtained polymer. The heterotactic-
ities of the PLAs obtained at two different temperatures (Table 3)
were assigned using the methine proton region of the homodecou-
pled 1H NMR spectra, as described by Hillmyer and co-workers
[53,54]. Fig. 3 represents a homodecoupled 1H NMR spectrum of
the obtained PLA from polymerization of rac-LA using (L2)ZnMe2.
The microstructures of PLA derived from rac-LA can exhibit five
tetrad sequences, i.e. sis, sii, iis, iii, isi, for describing its tacticites.
The degree of heterotactic PLA can be represented by the parame-
ter Pr, which represents the probability of forming new racemic
diad [35]. Pr values were calculated using the equation Pr = 2I1/
[I1 + I2] from the homodecoupled 1H NMR spectra, where
I1 = (sis + sii/iis) and I2 = (iis/sii + iii + isi) [45,55]. As illustrated from
the polymerization data (Table 3), the unsubstituted (L2)ZnCl2
complex gives a high heterotactic preference compared to the
chloro substituted complex (L1)ZnCl2. The beneficial effect on
sterocontrol can be attributed to the greater flexibility imparted
by the unsubstituted benzyl moiety to the metal coordination
sphere and improved accommodation of the geometric requir-
4. Conclusion
In conclusion, the present investigation has demonstrated that
dimethyl zinc complexes supported by the homochiral ligands L1
and L2, which were generated in situ, were found to be highly effi-
cient initiators for the ROP of rac-LA. The polymerization of rac-LA
catalyzed by these zinc initiators is demonstrated in a living fash-
ion with narrow PDIs. The Mn of the obtained PLAs is close to the
monomer/initiator molar ratio in the polymerization process.
Moreover, the decrease in stereoregularity of the PLA obtained
using the dimethyl zinc complex bearing the ligand with chloro
substituents on the phenyl groups of the benzyl moieties towards
the ROP of rac-LA may be explained by the lack of flexibility of the
substituted benzyl units, which would either hamper the mono-
mer attack or create a significant transition state associated with
the polymerization process around the coordination sphere of
the zinc center.
Table 3
ROP of rac-LA initiated by the in situ generated dimethyl zinc complexes supported by
homochiral (R,R)-1,2-diaminocyclohexane based ligands.
Catalyst
Temp.
(°C)
aConversion
(%)
bMn ꢁ 103
bMw ꢁ 103
bPDI
cPr
(L1)ZnMe2
(L1)ZnMe2
(L2)ZnMe2
(L2)ZnMe2
25
98.7
98.3
97
14.98
14.32
15.07
14.27
18.47
18.26
18.22
18.27
1.2
1.2
1.2
1.2
0.63
0.67
0.70
0.75
ꢀ25
25
ꢀ25
97
The monomer/catalyst ratio was fixed at 100 in all cases. Solvent for polymeriza-
tion = 5 mL CH2Cl2. Time = 12 h.
Acknowledgement
a
Determined by 1H NMR.
b
Determined by gel permeation chromatography (GPC) in THF, relative to a
This research was supported by the Kyungpook National Uni-
versity Research Fund, 2010.
polystyrene standard.
c
Probability of heterotactic enchainment Pr values were calculated on the basis
of homonuclear decoupled 1H NMR spectra according to the literature [45,55].
Appendix A. Supplementary data
CCDC 838450 contains the supplementary crystallographic
data for compound (L1)ZnCl2. 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.
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