Copper(II) complexes containing N,N′-bidentate N-substituted N-(pyridin-2-ylmethyl)amine: Synthesis, structure and application towards polymerization of rac-lactide

Article abstract of DOI:10.1016/j.poly.2017.01.050

The reaction between [CuCl₂·2H₂O] and N,N′-bidentate N-(pyridin-2-ylmethyl)amines (L_n= L_A–L_E) in methanol yielded new Cu(II) complexes; namely mononuclear [L_ACuCl₂] and dinuclear

Full text of DOI:10.1016/j.poly.2017.01.050

Accepted Manuscript
Copper(II) complexes containing N,N ′-bidentate N-substituted N-(pyridin-2-
ylmethyl)amine: synthesis, structure and application towards polymerisation of
rac-Lactide
Seoung Hyun Ahn, Min Kyung Chun, Eunhee Kim, Jong Hwa Jeong, Saira
Nayab, Hyosun Lee
PII:
S0277-5387(17)30087-6
DOI:
http://dx.doi.org/10.1016/j.poly.2017.01.050
POLY 12454
Reference:
Polyhedron
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27 December 2016
25 January 2017
25 January 2017
Please cite this article as: S.H. Ahn, M.K. Chun, E. Kim, J.H. Jeong, S. Nayab, H. Lee, Copper(II) complexes
containing N,N ′-bidentate N-substituted N-(pyridin-2-ylmethyl)amine: synthesis, structure and application towards
polymerisation of rac-Lactide, Polyhedron (2017), doi: http://dx.doi.org/10.1016/j.poly.2017.01.050
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Copper(II) complexes containing N,N′-bidentate N-substituted N-(pyridin-
2-ylmethyl)amine: synthesis, structure and application towards
polymerisation of rac-Lactide
Seoung Hyun Ahna, Min Kyung Chuna, Eunhee Kima, Jong Hwa Jeonga, Saira Nayabb,*
and Hyosun Leea,*
aDepartment of Chemistry and Green-Nano Materials Research Center, Kyungpook National
University, 80 Daehakro, Bukgu, Daegu, 41566, Republic of Korea
*E-mail address: hyosunlee@knu.ac.kr (H. Lee)
bDepartment of Chemistry, Shaheed Benazir Bhutto University, Sheringal Dir (U), Khyber
Pakhtunkhwa, Islamic Republic of Pakistan
Tel. (82)-53-950-5337
Fax: (82)-53-950-6330
E-mail: hyosunlee@knu.ac.kr
Copper(II) complexes containing N,N′-bidentate N-substituted N-(pyridin-
2-ylmethyl)amine: synthesis, structure and application towards
polymerisation of rac-Lactide

Seoung Hyun Ahna, Min Kyung Chuna, Eunhee Kima, Jong Hwa Jeonga, Saira Nayabb,*
and Hyosun Leea,*
Abstract
.
The reaction between [CuCl2 2H2O] and N,N′-bidentate N-(pyridin-2-ylmethyl)amines (Ln =
LA–LE) in methanol yielded new Cu(II) complexes; namely mononuclear [LACuCl2] and
dinuclear [LnCu(-Cl)Cl]2 (Ln = LB–LE) complexes, respectively. Monomeric [LACuCl2]
showed a distorted square planar geometry around copper metal based on x-ray
crystallography. The dimeric [LnCu(-Cl)Cl]2 (Ln = LB–LE) had a chloro-bridged 5-
coordinated and a distorted square pyramidal geometry around the Cu(II) center. The range of
Cu∙∙∙Cu´ distance was 3.3238(6)–3.593(2) Å in [LnCu(-Cl)Cl]2 (Ln = LB–LE). The Cu(II)-
alkoxy derivatives, generated in situ, of these synthesized Cu(II) complexes have shown
moderate activity towards the polymerization of rac-lactide (rac-LA) and yielded hetero-
enriched PLA. The steric hindrance and electronic effects has a great influence on the
catalytic activity and stereoselectivity of initiators.
Keywords: Dinuclear copper(II) complex / Molecular structure / rac-lactide / ring opening
polymerization / heterotacticity

1. Introduction
Poly(lactic acid) (PLA) [1], produced by the ring-opening polymerization (ROP) of lactide
(LA), is a prominent biodegradable and biocompatible polyester. PLA has been recognized as
suitable alternative to the petroleum-based polymers since it is derived from renewable
resources and is environmentally friendly as it degrades to nontoxic components i.e. water
and carbon dioxide. As a result PLA has found very useful applications in biomedical,
pharmaceutical and packing industries [2]. A variety of metal based initiators have been
utilized for controlled ROP of lactide (LA), such as aluminum [3-6], tin [7], calcium [8]
lithium [9], magnesium [10], iron [11], zinc [12-15], titanium [16], and zirconium [17]. It is
known that metallic residues in polymers were difficult to remove. Therefore, nontoxic and
biocompatible metal complexes such as Zn, Cu and alkali metals [18] have been widely used
in ROP. In this regard copper complexes with high electron transfer ability, moderate Lewis
acidity and stability associated with reactive intermediates made them ideal for biomedical
applications of PLA, such as stents and scaffolds for tissue engineering applications
[19].Copper is a biocompatible metal associated with the survival of life and till date few
reports are documented on copper initiators for LA polymerization. Recently Cu(II)
complexes based on pyrazole [20], phenoxy-ketimine [21], salicylaldimine [22] and
diketiminate [23] have been documented to achieve moderate to high activities and
stereoslectivities in controlled manner.
The electronic and steric properties of the ligand affects the coordination mode around
the metal centers, and has large impacts on the control of PLA microstructures. Thus a
careful design of the ligand motif could result in controlled ROP of lactide [24,25]. Recently,
we have embarked on the study of the ROP of lactide using highly effective nitrogen donors
Zn(II) and Cu(II) complexes [26] that polymerized LA in stereoselective manner yielded

hetero-enriched PLA. In our continues search for the effective and stereoselective catalysts
for ROP of rac-LA, we herein reported the synthesis and structural characterization of novel
monomeric and dimeric Cu(II) complexes ligated to N,N-bidentate N-(pyridin-2-
ylmethyl)amine based ligands with two sterically and electronically differentiated nitrogen
donors. A detailed structural study of the synthesized Cu(II) complexes and polymer tacticity
of these ROP reactions have been performed and are herein discussed.
2. Experimental
2.1. Materials and Instrumentation
.
[CuCl2 2H2O], 2,6-diisopropylaniline, 2,4-diethylaniline, cyclopentylamine,
cyclohexylamine, furfurylamine, 2-pyridinecarboxaldehyde, sodium borohydride, magnesium
sulfate, and LiOCHMe2 (2.0 M in THF) were purchased from Aldrich and anhydrous
solvents such as methanol (CH3OH), diethyl ether (Et2O), chloroform (CH3Cl),
dichloromethane (CH2Cl2), tetrahydrofuran (THF) were purchased from Merck and used
without further purification. CH2Cl2 and THF for polymerization reactions were dried over
CaH2 or Na/benzophenone ketyl by distillation under argon prior to use. Elemental analyses
(C, H, N) of the prepared complexes were carried out on an elemental analyzer (EA 1108;
Carlo-Erba, Milan, Italy). Gel permeation chromatography (GPC) analyses of polymer
samples were carried out at 25 °C using THF as the eluent on a Waters Alliance GPCV2000,
equipped with differential refractive index detectors, and calibrated using monodisperse
polystyrene standards at a flow rate of 1.0 mL/min. 1H-NMR (operating at 400 MHz) spectra
were recorded on a Bruker Advance Digital 400 NMR spectrometer; chemical shifts were
recorded in ppm units (relative to SiMe4 as the internal standard. Infrared (IR) spectra were
recorded on Bruker FT/IR-Alpha as neat used and the data are reported in reciprocal

centimeters (cm-1). Ligands, N-(2,6-diisopropylphenyl)-N-(pyridin-2-ylmethyl)amine (LA),
N-(2,6-diethylphenyl)-N-(pyridin-2-ylmethyl)amine (LB), N-cyclopentyl-N-(pyridin-2-
ylmethyl)amine (LC) N-cyclohexyl-N-(pyridin-2-ylmethyl)amine (LD) and N-(furan-2-
ylmethyl)-N-(pyridin-2-ylmethyl)amine), and (LE) have been synthesized using previously
reported methods [27-35].
2.2. Synthesis of Cu(II) complexes
2.2.1. [N-(2,6-diisopropylphenyl)-N-(pyridin-2-ylmethyl)aminedichlorocopper(II)]
([LACuCl2])
MeOH solution (10.0 mL) of CuCl2·2H2O (0.150 g, 0.879 mmol) was added dropwise a
MeOH solution (10.0 mL) of LA (0.235 g, 0.879 mmol) to get dark green solution. Green
crystals of complex were obtained by diffusion of Et2O into the dark green solution for 30
min, and were collected by filtration and washed with Et2O and dried in air. Yield: 0.165 g
(41%). Anal Calcd for C18H24Cl2CuN2: C, 53.7; H, 6.00; N, 6.95; Found: C,53.5; H,5.98; N,
7.01. IR (solid neat; cm-1): 3275 (s), 3079 (w), 2967 (m), 2924 (w), 2866 (w), 1627 (w), 1595
(m), 1479 (m), 1175 (w), 1055 (w), 811 (s), 768 (s), 540 (m).
2.2.2. [N-(2,6-diethylphenyl)-N-(pyridin-2-ylmethyl)aminedichlorocopper(II)]2 ([LBCu(-
Cl)Cl]2)
[LBCu(-Cl)Cl]2 was synthesized by analogous method as that for [LACuCl2] except
utillizing CuCl2·2H2O (0.150 g, 0.879 mmol) and LB (0.211 g, 0.879 mmol) in MeOH. The
final product was get as dark green crystalline solid. Yield: 0.255 g (34%). Anal Calcd for
C32H40Cl4Cu2N4: C, 51.3; H, 5.38; N, 7.47; Found: C,51.2; H,5.32; N, 7.44. IR (solid neat;

cm-1): 3296 (m), 3102 (w), 3045 (w), 2956 (w), 1604 (m), 1475 (m), 1396 (w), 1284 (m),
1050 (m), 1028 (m), 942 (m), 812 (m), 568 (m).
2.2.3. [N-(2,6-diethylphenyl)-N-(pyridin-2-ylmethyl)aminedichlorocopper(II)]2 ([LCCu(-
Cl)Cl]2)
[LCCu(-Cl)Cl]2 was synthesized by analogous method as that for [LACuCl2] except
utillizing CuCl2·2H2O (0.150 g, 0.879 mmol) and LC (0.155 g, 0.879 mmol) to get blue
crystals as final product. Yield: 0.214 g (34%). Anal Calcd for C22H32Cl4Cu2N4: C, 42.5; H,
5.19; N, 9.02 Found: C, 42.5; H,5.17; N,8.92. IR (solid neat; cm-1): 3200 (m), 3105 (w), 3044
(w), 2949 (m), 1604(m), 1475 (m), 1283 (m), 1159(w), 1004 (m), 934 (m), 777 (s), 545 (m).
2.2.4. [N-cyclohexyl-N-(pyridin-2-ylmethyl)amine(μ-chloro)chlorocopper(II)]2 ([LDCu(-
Cl)Cl]2)
[LDCu(-Cl)Cl]2 was synthesized by analogous method as that for [LACuCl2] except
utillizing CuCl2·2H2O (0.150 g, 0.879 mmol) and LD (0.167 g, 0.879 mmol) to get green
crystalline solid as final product. Yield: 0.194 g, (30%). Anal Calcd for C24H36Cl4Cu2N4: C,
44.4; H, 5.59; N, 8.63 Found: C, 44.4; H,5.57; N,8.57. IR (solid neat; cm-1): 3195 (m), 3104
(w), 3068 (w), 3024 (w), 2921 (m), 2844 (m), 1607 (m), 1480 (w), 1449 (m), 1088 (m), 771
(s), 554 (m).
2.2.5. [N-(furan-2-ylmethyl)-N-(pyridin-2-ylmethyl)amine(μ-chloro)chlorocopper(II)]2
([LECu(-Cl)Cl]2)
[LECu(-Cl)Cl]2 was synthesized by analogous method as that for [LACuCl2] except
utillizing CuCl2·2H2O (0.150 g, 0.879 mmol) and LE (0.165 g, 0.879 mmol) to get green

colour crystalline product. Yield: 0.172 g (27%). Anal Calcd for C22H24Cl4Cu2N4O2: C, 40.9;
H, 3.75; N, 8.68 Found: C, 41.0; H,3.74; N,8.63. IR (solid neat; cm-1): 3182 (m), 3110 (w),
2947 (w), 2915 (w), 1608 (m), 1572 (s), 1486 (m), 1421 (m), 1144 (m), 1000 (w), 730 (s),
554 (m).
2.3. Ring opening polymerization of rac-lactide
In a general polymerization reaction for rac-LA with the diisopropoxide copper
initiators, the active catalytic species were generated as follows. 0.50 mmol of dichloro Cu(II)
complexes and dried THF (7.00 mL) were added to a 100 mL Schlenk flask under argon
atmosphere. To this solution was added LiOCHMe2 (1.0 mL of 2.0 M solution in THF, 2.0
mmol) drop wise for the dimeric complexes at -78 ºC. In the case of momeric complex,
[LACuCl2], 0.50 mmol of copper complex and dried THF (7.50 mL) were added to a 100 mL
Schlenk flask under argon atmosphere and to this solution was added LiOCHMe2 (0.5 mL of
2.0 M solution in THF, 1.0 mmol) drop wise at -78 ºC. After being stirred for 2 h at room
temperature, the resulting THF solutions of both monomeric and dimeric diisopropoxide
complexes were was used as 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 atmosphere and 5.0 mL of dried CH2Cl2 was added. The
desired amount of catalysts solution was injected slowly to the monomer solution under
argon at room temperature, as presented for various runs in Table 3. The reaction mixture
was stirred for the allotted time and the polymerisation reactions were quenched by using
H2O (1.00 mL). CH2Cl2 (5.00 mL) was added to the resultant residue and then hexane (2.00
mL) was added to precipitate the polymer. The monomer conversion was measured by 1H-
NMR spectroscopy. 1H-NMR (CDCl3) for the obtained PLA: δ = 5.13-5.20 (m, 1H), 1.51-
1.63 (m, 3H).

2.4. X-ray crystallographic analysis
The X-ray-quality single crystal was coated with paratone-N oil and the diffraction
data measured at 100(2) K with synchrotron radiation ( = 0.63000 Å) on an ADSC
Quantum-210 detector at 2D SMC with a silicon (111) double crystal monochromator (DCM)
at the Pohang Accelerator Laboratory, Korea. The BL2D-SMDC program [36] was used for
data collection (detector distance is 63 mm, omega scan; ∆ω = 1º, exposure time is 1 sec per
frame) and HKL3000sm (Ver. 703r) [37] was used for cell refinement, reduction and
absorption correction. Structures were solved by direct methods [38], and refined by full-
matrix least-squares refinement using the SHELXL-2014 computer program [39]. The
positions of all non-hydrogen atoms were refined with anisotropic displacement factors. All
hydrogen atoms were placed using a riding model, and their positions were constrained
relative to their parent atoms using the appropriate HFIX command in SHELXL-2014.
3. Results and Discussion
3.1. Synthesis and characterization
Reaction of N,N′-bidentate N-(pyridin-2-ylmethyl)amines (Ln = LA–LE) with
equimolar amount of [CuCl2.2H2O] afforded mononuclear [LACuCl2] and dinuclear
[LnCu(μ-Cl)Cl]2 (Ln = LB-LE) complexes in MeOH at ambient temperature in yields (27-
41%). Owing to the paramagnetic nature of Cu(II) complexes, we were unable to study
structural aspect of these complexes via NMR spectroscopy. However, comparison of the IR
spectra of ligand with that of synthesized Cu(II) complexes was performed, in the N-H
region. The characteristic N-H peaks for ligands in the IR spectra were observed in range
3321– 3395 cm-1, while the N-H stretching band appeared in range 3182 and 3297 cm-1 for

corresponding dichloro Cu(II) complexes. In addition, new absorption bands in 540 -568 cm-1
range has been observed for Cu–N bonds in synthesized Cu(II) complexes.
The molecular structures of synthesized complexes were determined using X-ray
crystallography. Single crystal of complexes suitable for the structural characterization was
grown at ambient temperature from a saturated CH2Cl2/n-hexane solution. Crystal data and
structural refinement of Cu(II) complexes, monomeric [LACuCl2] and dimeric [LnCu(-
Cl)Cl]2 (Ln = LB–LE), were listed in the Table 1. The selected bond lengths (Å) and selected
bond angles (º) are summarized in Table 2. The molecular structures Cu(II) complexes have
been shown in Fig. 1-5.
X-ray diffraction analysis revealed that complex [LACuCl2] crystallized in the
monoclinic system with space group P21/n and existed as monomeric and solvent-free
complex (Fig. 1). The central metal atom in [LACuCl2] was four-coordinated and adopted
somewhat distorted square planer geometry. The Cu-Npyridine and Cu-Namine bond distances
were 1.988(1) and 2.070(2) Å, respectively. This difference of 0.082 Å in Cu-N lengths
might be due to difference in hybridization and basicity of two nitrogen atoms. Similarly, Cu-
Cl bond distances were found to be in expected range 2.2203(9)–2.2117(9) Å. Much larger
Cl1-Cu-Cl2 angle [99.36(2)°] was observed compared to N1-Cu-N2 [81.31(6)°] for
[LACuCl2].
By contrast, the molecular structure of dimeric [LnCu(μ-Cl)Cl]2 (Ln = LB–LE)
complexes showed that the Cu(II) ion adopts a distorted square pyramidal geometry with the
chloro-bridged ligands (Fig. 2–5). In dimeric complexes Cu(II) ion is 5-coordinated with the
secondary nitrogen and pyridyl moiety of ligands, as well as three chlorido ligands containing
a bridged chlorido ligand. The Cu-Npyridine and Cu-Namine bond distances were in 2.002(1)–
2041(5) Å, and 2013(6)–2069(1) Å, respectively. For the coordinated chloride anion in
[LnCu(μ-Cl)Cl]2 (Ln = LB–LE), Cu-Cl bond distance were 2.2364(9), 2.2667(2), 2.294(2) and

2.260(2) Å respectively. Similarly the Cu-Clbridged lengths were found to be in range
2.260(6)–2.691(2) Å. In addition Cu∙∙∙Clnonbridged length was found to be 3.500(1) Å and that
of Cu∙∙∙Cu was 3.915(1) Å.
3.3. Ring Opening Polymerization of rac-LA
All the synthesized Cu(II) complexes were investigated as catalytic precursors
towards ROP of rac-LA at ambient temperature. The active species were generated in situ by
treating dichloro Cu(II) complexes with two equivalents of LiOCHMe2 in THF. The resulting
alkoxy derivatives efficiently polymerized ROP of rac-LA. The Mn were determined using
end-group analysis with the 1H-NMR spectra, and by GPC in THF, compared to polystyrene
standards. The polymerization results are listed in Table 4. It is evident that all runs
represent efficient initiators towards ROP of rac-LA. The half values of Mn (corrected using
the Mark–Houwink factor of 0.58) [40] observed compared to theoretical values suggests two
growing polymer chain at Cu(II) center. The narrower PDIs reveal that polymerization is well
controlled. The dichloro Cu(II) complexes failed to initiate ROP of rac-LA under same
experimental conditions.
The 1H-NMR spectra of the isolated PLAs showed that the polymer is end-capped
with an isopropoxide [–C(O)CH(CH3)2] group at one end and a hydroxyl group [–CHMe–
(OH)] at the other. Considering the experimental findings for the ROP of rac-LA, under the
conditions mentioned, the polymerization proceeds by the mechanism as outlined in (Scheme
2). A coordination insertion mechanism [41-43] for the ROP of LA can be predicted where
the pre-coordination of the LA monomer to the Cu(II) centre yields a monomeric 5-
coordinated intermediate. The two alkoxy group then acts as a nucleophile and cleavage of
acyl-oxygen bond opens the LA ring. The subsequent addition of LA produced hetero-
enriched PLA. Mandal et al. reported imino phenoxide ligands supported copper complexes

that polymerized ROP of lactide in presence of BnOH and yielded PLA with moderate
molecular weights with conversion rate about 90 % with low stereoselectivity [46]. For
comparison N,N’-bis(2-hydroxy-3- methoxybenzaldehyde) benzene-1,2-diamine based
copper complexes are reported here that efficiently produce PLA but yielded PLA with low
molecular weight [47]. Similarly NacnacBnCuOiPr proved to be one of the most active
catalysts for ROP of lactide was found to be atatcic with almost no stereocontrol [48].
Blank polymerization with Li(OCHMe2)2 (Entries 1 and 2; Table 3) under same
experimental condition yielded appreciable amount of PLA with almost no level of
stereocontrol (Pr = 0.52). The catalytic activities were not much affected by the substituents
attached to the nitrogen of amine moiety and were almost similar to that found with
LiOCHMe2. However, the stereoselectivity was affected in the resultant PLA by the
variability of R group substituents attached to amine nitrogen. The lower degree of
heterotacticity was obtained with diisoproxide of monomeric [LACuCl2] (Pr = 0.65). Among
the dimeric complexes, [LCCu(-Cl)Cl]2 with less steric bulk, provided better activity and
stereoselectivity. The higher degree of heterotacticity with diisoproxide of dimeric
[LBCuCl2]2, [LCCuCl2]2, [LECuCl2]2, (Pr = 0.75 ~0.78) by the proper complexity of the
substituents at the nitrogen atoms. The result imply that the polymerization progresses by the
chain-end mechanism. However, the alkoxy derivative of [LDCuCl2]2 was unexpectablely
unstable that leads to failure of ROP of rac-LA. Further investigations to improve the
catalytic activities in term of ligand architecture variations and resultant tacticities are
underway in our laboratory.
4. Conclusion
Novel Cu(II) complexes, mononuclear [LACuCl2] and dinuclear [LnCu(-Cl)Cl]2 (Ln
= LB–LE), were synthesized and structurally characterized using X-ray diffraction analysis.

The geometry around the mononuclear [LACuCl2] can be best described as distorted square
planar involving the Cu(II) center. The dimeric complexes [LnCu(-Cl)Cl]2 (Ln = LB–LE)
had a chloro-bridged 5-coordinated distorted square pyramidal geometry around the Cu(II)
center. The copper alkoxides, generated in situ, towards the ROP of rac-LA were not
enhanced using LiOCHMe2. The improvement of heterotactic selectivity was found when
alkoxide initiators of dimeric [LBCuCl2]2, [LCCuCl2]2, [LECuCl2]2 bearing the proper
complexity of the substituents at the nitrogen atoms. The 13C-{1H} NMR spectra indicate the
stereochemistry of PLA is heterotactic.
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. 2014-
R1A1A3049750). X-ray crystallography with PLS-II 2D-SMC beamline was supported by
MSIP and POSTECH.
Appendix A. Supplementary material
CCDC 1524526 - 1524530 contains the supplementary crystallographic data for [LACuCl2]
and [LnCu(-Cl)Cl]2 (Ln = LB–LE) 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.
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Scheme 1. Synthesis of ligands (Ln = LA–LE) and their corresponding Cu(II) complexes, [LACuCl2] and [LnCu(-Cl)Cl]2 (Ln = LB–LE).

Scheme 2. Proposed mechanism for ROP of rac-LA catalyzed by N-(pyridin-2-ylmethyl)amine based Cu(II) complexes.

Table 1. Crystal data and structural refinement of [LACuCl2] and [LnCu(-Cl)Cl]2 (Ln = LB–LE).
[LACuCl2]
[LBCu(-Cl)Cl]2
[LCCu(-Cl)Cl]2
[LDCu(-Cl)Cl]2
[LECu(-Cl)Cl]2
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
C18H24Cl2CuN2
402.83
102(2)
0.63000
Monoclinic
P21/n
C32H40Cl4Cu2N4
749.56
100(2)
0.63000
Triclinic
P-1
C22H32Cl4Cu2N4
621.40
200(2)
0.71073
Monoclinic
C2/c
C24H36Cl4Cu2N4(C3H7O)
722.54
200(2)
0.71073
Monoclinic
P21/c
C22H24Cl4Cu2N4O2
645.33
200(2)
0.71073
Monoclinic
P21/n
Unit cell dimensions
a (Å)
b (Å)
c (Å)
α (°)
12.733(3)
9.876(2)
14.639(3)
90
9.3690(2)
9.515(2)
10.524(2)
67.36(3)
10.863(1)
12.645(2)
18.588(2)
90
12.528(2)
13.061(3)
19.582(4)
90
9.978(1)
10.670(1)
12.705(2)
90
β (°)
γ (°)
105.14(3)
90
1777.0(7), 4
1.506
1.097
836
0.10 x 0.07 x 0.05
1.676 to 25.998
-17  h  17
-13  k  13
-20  l  20
16073
70.94(3)
75.03(3)
808.9(4), 1
1.539
1.199
97.242(3)
90
2532.9(5), 4
1.630
2.120
1272
0.25 x 0.16 x 0.12
2.21 to 28.33
-14  h  9
-16  k  15
-24  l  24
9149
92.327(4)
90
3201.4(1), 4
1.499
1.692
1496
0.36 x 0.34 x 0.27
1.87 to 28.32
-16  h  15
-17  k  15
-26  l  25
23040
107.399(3)
90
1290.7(3), 2
1.661
2.089
652
0.31 x 0.22 x 0.21
2.29 to 28.34
-13  h  10
-13  k  14
-16  l  16
9099
Volume (Å3), Z
Density (calculated) (Mg/m3)
Absorption coefficient (mm-1)
F(000)
386
Crystal size (mm3)
θ range for data collection (°)
Index ranges
0.10 x 0.08 x 0.06
2.698 to 25.998
-13  h  13
-13  k  13
-14  l  14
9009
Reflections collected
4930 [R(int) = 0.0398]
98.8
Empirical
4523 [R(int) = 0.0350]
99.0
Empirical
3140 [R(int) = 0.0387]
99.5
Semi-empirical
7922 [R(int) = 0.0543]
99.3
None
3174 [R(int) = 0.0222]
98.4
Semi-empirical
Independent reflections
Completeness to θ = 22.21°
Absorption correction
Full-matrix least-squares on F2 Full-matrix least-squares on F2 Full-matrix least-squares on F2 Full-matrix least-squares on F2 Full-matrix least-squares on F2
Refinement method
4930 / 0 / 212
1.059
4523 / 0 / 192
1.095
3140 / 0 / 145
1.170
7922 / 12 / 354
1.209
3174 / 0 / 154
1.229
Data / restraints / parameters
Goodness-of-fit on F2
R1 = 0.0353, wR2 = 0.0932
R1 = 0.0448, wR2 = 0.0969
0.452 and -1.234
R1 = 0.0247, wR2 = 0.0716
R1 = 0.0257, wR2 = 0.0722
0.505 and -1.019
R1 = 0.0441, wR2 = 0.0796
R1 = 0.0907, wR2 = 0.1423
1.192 and -1.369
R1 = 0.0785, wR2 = 0.2131
R1 = 0.1285, wR2 = 0.3350
2.975 and -2.506
R1 = 0.0401, wR2 = 0.0813
R1 = 0.0722, wR2 = 0.1460
1.011 and -1.619
Final R indices [I>2sigma(I)]
R indices (all data)
Largest diff. peak/hole (e.Å-3)

Table 2. Selected bond lengths (Å) and angles (o) of [LACuCl2] and [LnCu(-Cl)Cl]2 (Ln = LB–LE).
[LACuCl2]
[LBCu(-Cl)Cl]2
[LCCu(-Cl)Cl]2
[LDCu(-Cl)Cl]2
[LECu(-Cl)Cl]2
Bond lengths (Å)
Cu(1)-N(1)
Cu(1)-N(2)
Cu(1)-Cl(1)
Cu(1)-Cl(2)
N(1)-C(1)
N(1)-C(5)
N(2)-C(6)
N(2)-C(7)
C(1)-C(2)
C(2)-C(3)
1.988(1)
2.070(2)
2.223(6)
2.245(9)
1.342(2)
1.343(2)
1.458(2)
1.463(2)
1.388(2)
1.380(3)
Cu(1)-Cl(1)
Cu(1)-Cl(2)
Cu(1)-N(1)
Cu(1)-N(2)
N(1)-C(1)
N(1)-C(5)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
2.236(9)
2.260(6)
2.000(1)
2.069(1)
1.345(2)
1.344(2)
1.389(2)
1.389(2)
1.389(2)
1.390(2)
Cu(1)-N(1)
Cu(1)-N(2)
Cu(1)-C(1)
Cu(1)-C(2)
N(1)-C(1)
N(1)-C(5)
C(1)-N(2)
C(2)-N(3)
C(3)-C(4)
C(4)-C(5)
2.010(5)
2.040(4)
2.267(2)
2.279(2)
1.347(7)
1.345(7)
1.371(8)
1.388(9)
1.383(9)
1.373(8)
Cu(1)-N(1)
Cu(1)-N(2)
Cu(1)-Cl(1)
Cu(1)-Cl(2)
Cu(1)-Cl(3)
Cu(2)-N(3)
Cu(2)-N(4)
Cu(2)-Cl(2)
Cu(2)-Cl(4)
N(1)-C(1)
2.041(5)
2.013(6)
2.294(2)
2.691(2)
2.287(2)
2.047(5)
2.008(6)
2.304(2)
2.256(2)
1.484(9)
Cu(1)-N(1)
Cu(1)-N(2)
Cu(1)-Cl(1)
Cu(1)-Cl(2)
N(1)-C(1)
N(1)-C(5)
N(2)-C(6)
N(2)-C(7)
C(1)-C(2)
C(2)-C(3)
2.007(4)
2.034(5)
2.260(2)
2.267(1)
1.345(7)
1.349(7)
1.489(7)
1.494(7)
1.379(8)
1.367(1)
Bond angles (o)
N(1)-Cu(1)-N(2)
N(1)-Cu(1)-Cl(1)
N(2)-Cu(1)-Cl(1)
N(1)-Cu(1)-Cl(2)
N(2)-Cu(1)-Cl(2)
Cl(1)-Cu(1)-Cl(2)
C(1)-N(1)-C(5)
C(1)-N(1)-Cu(1)
C(5)-N(1)-Cu(1)
C(6)-N(2)-C(7)
81.31(6)
159.64(5)
92.20(4)
95.10(4)
152.22(5)
99.36(2)
119.44(1)
123.19(1)
116.79(1)
110.68(1)
N(1)-Cu(1)-N(2)
N(1)-Cu(1)-Cl(1)
N(1)-Cu(1)-Cl(2)
N(2)-Cu(1)-Cl(1)
N(2)-Cu(1)-Cl(2)
Cl(1)-Cu(1)-Cl(2)
C(1)-N(1)-Cu(1)
C(5)-N(1)-Cu(1)
C(6)-N(2)-Cu(1)
C(7)-N(2)-Cu(1)
83.00(5)
97.64(4)
166.59(3)
159.33(3)
87.99(4)
94.29(2)
124.60(8)
115.76(8)
110.98(8)
116.52(8)
N(1)-Cu(1)-N(2)
N(1)-Cu(1)-Cl(1)
N(1)-Cu(1)-Cl(2)
N(2)-Cu(1)-Cl(1)
N(2)-Cu(1)-Cl(2)
Cl(1)-Cu(1)-Cl(2)
C(1)-N(1)-Cu(1)
C(5)-N(1)-Cu(1)
C(5)-N(1)-C(1)
N(1)-C(1)-C(2)
81.98(2)
95.08(1)
159.60(1)
175.37(2)
91.22(1)
92.73(6)
126.3(4)
114.6(4)
118.9(5)
112.2(5)
N(1)-Cu(1)-N(2)
N(1)-Cu(1)-Cl(1)
N(1)-Cu(1)-Cl(2)
N(1)-Cu(1)-Cl(3)
N(2)-Cu(1)-Cl(1)
N(2)-Cu(1)-Cl(2)
N(2)-Cu(1)-Cl(3)
Cl(1)-Cu(1)-Cl(2)
Cl(1)-Cu(1)-Cl(3)
Cl(2)-Cu(1)-Cl(3)
83.2(2)
N(1)-Cu(1)-N(2)
N(1)-Cu(1)-Cl(1)
N(1)-Cu(1)-Cl(2)
N(2)-Cu(1)-Cl(1)
N(2)-Cu(1)-Cl(2)
Cl(1)-Cu(1)-Cl(2)
C(1)-N(1)-Cu(1)
C(5)-N(1)-Cu(1)
C(1)-N(1)-C(5)
C(6)-N(2)-C(7)
82.29(2)
95.06(1)
165.82(1)
175.42(1)
89.9(1)
89.67(2)
86.34(2)
177.56(2)
166.10(2)
92.28(2)
94.42(2)
99.19(6)
92.51(7)
94.38(6)
93.42(6)
126.2(4)
113.8(4)
120.0(5)
112.5(5)

Table 3. Polymerization of rac-lactide with in situ generated [(LA)Cu(OCHMe2)2] and
[(Ln)Cu(OCHMe2)2] (Ln = LB–LE).
b
c
d
Mn
Mn
Mn
(g/mol)
× 103
(g/mol) ×
(g/mol) ×
Run Catalyst
Rx(min)a
PDI
Pre
103
103
(calcd)
(NMR)
(GPC)
1
2
3
4
LiOCHMe2 (1 mol%)
10
5
14.41
13.38
7.20
7.51
8.01
12.96
7.25
7.66
8.61
1.43
1.35
1.41
1.43
0.54
0.55
0.65
0.78
LiOCHMe2 (2 mol%)
[(LA)Cu(OCHMe2)]
7.21
10
7
14.41
28.82
[(LB)Cu(-Cl(OCHMe2)]2
5
6
5
-
28.82
-
8.11
-
8.51
-
1.36
-
0.80
-
[(LC)Cu(-Cl(OCHMe2)]2
[(LD)Cu(-Cl(OCHMe2)]2
f
7
7
28.82
8.20
7.95
1.39
0.75
[(LE)Cu(-Cl)(OCHMe2)]2
Reaction conditions: 0.0625 mmol of initiator, [rac-LA]/[Initiator] = 100, CH2Cl2 = 5 mL for run-1; 0.1250 mmol
of initiator = 0.1250 mmol, [rac-LA]/[Initiator] = 50, CH2Cl2 = 5 mL for run-2; 0.0625 mmol of initiator, [rac-
LA]/[Initiator] = 100, CH2Cl2 = 5 mL for run-3; 0.0316 mmol initiator, [rac-LA]/[Initiator] = 200, CH2Cl2 = 5 mL
for run-4,5,7. a Reaction time for 100 % conversion determined by 1H-NMR. bCalculated from [molecular weight
of rac-LA] × [rac-LA]/[Initiator] × conversion %. c Experimental molecular weight determined by the relative
intensities of the main chain and terminal resonances from 1H-NMR spectra. d Experimental values (corrected
using the Mark-Houwink factor of 0.58) [40] were determined by gel permeation chromatography (GPC) in THF
relative to polystyrene standard. e Probability of heterotactic enchainment (Pr) were calculated on the basis of
homonuclear decoupled 1H NMR spectra according to literature [44,45]. f catalytic precursor [LnCu(-Cl)Cl]2
decomposed when treated with co-catalyst LiOCHMe2 during in situ alkoxide species formation and failed to
polymerized rac-LA.

Figure 1. Molecular structure of [LACuCl2].

Figure 2. Molecular structure of [LBCu(-Cl)Cl]2.

Figure 3. Molecular structure of [LCCu(-Cl)Cl]2.

Figure 4. Molecular structure of [LDCu(-Cl)Cl]2.

Figure 5. Molecular structure of [LECu(-Cl)Cl]2.

Graphical Abstract (Pictorial)
Novel monomeric and dimeric Cu(II) complexes based on N-substituted N-(pyridin-2-ylmethyl)amine
ligands have been synthesized and characterized. Cu(II)-alkoxy derivatives, generated in situ,
polymerized ROP of rac-LA in controlled fashion yielding hetero-enriched PLA (Pr = 0.80).