Copper(II) complexes containing N′-aromatic group substituted N,N′,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)amines: Synthesis, structures, polymerization of methyl methacrylate and ring opening polymerization of rac-lactide

Article abstract of DOI:10.1016/j.poly.2020.114641

A series of Cu(II) complexes, [L_nCuCl₂] (L_n = L_A–L_F), supported by N′-aromatic-group-substituted N,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methylamine ligands have been synthesized. Variations of substitu

Full text of DOI:10.1016/j.poly.2020.114641

Journal Pre-proofs
Copper(II) Complexes Containing N′ -Aromatic Group Substituted N,N′ ,N-
bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)amines: Synthesis, Structures, Pol‐
ymerization of Methyl Methacrylate and Ring Opening Polymerization of
rac-Lactide
Hyungwoo Cho, Solhye Choe, Dongil Kim, Hyosun Lee, Saira Nayab
PII:
S0277-5387(20)30298-9
DOI:
Reference:
https://doi.org/10.1016/j.poly.2020.114641
POLY 114641
To appear in:
Polyhedron
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Revised Date:
Accepted Date:
18 April 2020
29 May 2020
31 May 2020
Please cite this article as: H. Cho, S. Choe, D. Kim, H. Lee, S. Nayab, Copper(II) Complexes Containing N′ -
Aromatic Group Substituted N,N′ ,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)amines: Synthesis, Structures,
Polymerization of Methyl Methacrylate and Ring Opening Polymerization of rac-Lactide, Polyhedron (2020),
doi: https://doi.org/10.1016/j.poly.2020.114641
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Revised
Copper(II) Complexes Containing N′-Aromatic Group Substituted N,N′,N-
bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)amines:
Synthesis,
Structures,
Polymerization of Methyl Methacrylate and Ring Opening Polymerization of rac-
Lactide
Hyungwoo Cho,a Solhye Choe,a Dongil Kim,a Hyosun Lee,a,* and Saira Nayabb,*
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
bDepartment of Chemistry, Shaheed Benazir Bhutto University, Sheringal Dir (U), Khyber
Pakhtunkhwa, Islamic Republic of Pakistan
*E-mail address: drnayab@sbbu.edu.pk, sairanayab07@yahoo.com
--------------------------------
*Corresponding authors. Tel: +82-53-950-5337; fax: +82-53-950-6330
E-mail address: hyosunlee@knu.ac.kr
Email address: drnayab@sbbu.edu.pk, sairanayab07@yahoo.com
1

Copper(II) Complexes Containing N′-Aromatic Group Substituted N,N′,N-
Bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)amines: Synthesis, Structures,
Polymerization of Methyl Methacrylate, and Ring-Opening Polymerization of
rac-Lactide
Abstract
A series of Cu(II) complexes, [LnCuCl2] (Ln = LA–LF), supported by N′-aromatic-group-
substituted N,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methylamine ligands have been synthesized.
Variations of substituents at the ortho position of the aniline moiety influenced the solid-state
structures of these complexes. The X-ray structures of [LnCuCl2] (Ln = LA–LC and LF) revealed that
ligands are coordinated in a N,N,N-tridentate fashion to Cu(II) center and adopted a distorted square-
pyramidal geometry, while [LDCuCl2] with N,N-bidentate coordination adopts distorted tetrahedral
geometry. These complexes were capable of polymerizing methyl methacrylate (MMA) in the
presence of modified methylaluminoxane (MMAO), with [LFCuCl2] displaying the highest activity
(2.81 × 104 g PMMA (mol Cu)−1 h−1). Regardless of ligand architecture, syndio-enriched PMMAs
have been furnished with a slightly broader polydispersity index (PDI). Additionally, the in situ
generated dimethyl derivatives, polymerized rac-LA and furnished PLA with mediocre
heterotacticities at room temperature. Importantly, the catalytic efficiencies of the Cu(II) complexes
studied have been found to be influenced by the steric and electronic properties of ligand.
Keywords: Pyrazolyl-methylamines; Copper complexes; Square-pyramidal geometry; Tetrahedral
geometry; Syndiotactic PMMA; Heterotactic PLA
2

1. Introduction
Pyrazole-based ligands have attracted a great deal of attention as a powerful chelating tool in
a wide array of transition-metal complexes [1-4]. The success of pyrazolyl-based ligands arise from
their easy synthetic approach and various modifications of their linker units composed of two or three
pyrazole moieties [5-7], which enables the construction of diverse coordination geometries and
significant nuclearities [8,9]. Since the pioneering work of Driessen in 1982 [10], a variety of N-
substituted bis-pyrazolyl ligands and their transition-metal complexes have been investigated
successfully in numerous catalytic transformations. For instance, they have been studied as
supramolecules for metal–organic frameworks (MOF) [6], catalysts for organic transformations
[11,7], and as bioinorganic materials in pharmaceutical preparations [12,13]. They have also been
utilized as metal-ion extractants [14], antibacterial agents [15,16], cancer sensors and oxidation agents
[17].
More recently, N-substituted pyrazolyl amines ligated to a variety of late transition metals
such as Pt(II), Pd(II), Ru(II), Rh(I), Ni(II), Zn(II), and Co(II) have demonstrated useful catalytic
properties in olefins [18-20] and in methyl methacrylate (MMA) polymerizations [21-23]. Early
transition-metal complexes generally cannot tolerate polar functional groups due to the highly
electron-deficient nature of the metal center. Late-transition-metal complexes overcome this
drawback and demonstrate better polymerization of polar monomers in a controlled fashion, owing
to their less-oxophilic nature [24-28]. Recently, our group has been involved in the synthesis of late
transition metal based initiators supported by the N,N-bis(1H-pyrazolyl-1-methyl)aniline ligand and
its derivatives for MMA and rac-LA polymerizations. These catalyst showed promising activities and
furnished polymers, PMMAs and PLAs, with moderate to high stereoselectivities [29-34]. Yu et al.
[35], Kang et al. [36] and Lian group [4] have reported similar results showing that pyrazolyl zinc
complexes are active initiators for the ring-opening polymerization (ROP) of LA because the pyrazole
3

motif offers highly electrophilic metal centers. However, thus far, Cu(II) complexes supported by bis-
pyrazolyl amine-based ligands have been less extensively investigated for MMA and rac-LA
polymerizations. Consequently, given the importance of bis-pyrazolyl-methylamine ligands and
taking into consideration the promising results obtained by our group [29-34], we herein studied the
synthesis of Cu(II) complexes based on N′-aromatic-group-substituted N,N′,N-bis((3,5-dimethyl-1H-
pyrazol-1-yl)methyl)amine ligands, and explored their catalytic efficacies toward MMA and rac-LA
polymerizations.
2. Experimental
2.1. Materials
The synthesis of all ligands and their corresponding Cu(II) complexes were carried out using
bench top techniques. The polymerization reactions were carried out using a high-vacuum Schlenk
line and glovebox. Copper(II) chloride dihydrate (CuCl2·2H2O), 3,5-dimethylpyrazole, para-
formaldehyde, aniline, 4-methoxyaniline, 4-fluoroaniline, 2,4,6-trimethylaniline, 2,6-diethylaniline,
4-isopropylaniline, magnesium sulfate (MgSO4), and molecular sieves (0.4 nm) were purchased from
Sigma-Aldrich. Anhydrous solvents such as ethanol (EtOH), acetonitrile (CH3CN), n-hexane (n-Hex),
diethyl ether (Et2O), and dimethylformamide (DMF) were purchased from Sigma-Aldrich and were
used without further purification. THF and toluene were dried over benzophenone ketyl radical,
whereas CH2Cl2 was dried over calcium hydride (CaH2); all of these solvents were deoxygenated by
distillation under argon before use. MMA dried over molecular sieves and was distilled under reduced
pressure before use. Modified methylaluminoxane (MMAO) was purchased from Tosoh Finechem
Corporation as 5.90 wt% aluminum in toluene solution and was used without further purification.
3,5-Dimethyl-1H-pyrazolyl-1-methanol was prepared as reported previously [37]. LA (N,N-Bis((3,5-
4

dimethyl-1H-pyrazol-1-yl)methyl)aniline) [29,30,38], LB (N,N-Bis((3,5-dimethyl-1H-pyrazol-1-
yl)methyl)-4-methoxyaniline) [31,39], LC N,N-Bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-4-
fluoroaniline [31,39], LD (N,N-Bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-2,4,6-trimethylaniline)
[31] and LE (N,N-Bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-2,6-diethylaniline) [30] were
synthesized according to the previously reported protocols.
2.2. Instrumentation
Elemental analysis (C, H, N) of the synthesized Cu(II) complexes was carried out using an
elemental analyzer (EA 1108; Carlo-Erba, Milan, Italy). The 1H NMR (500 MHz) and 13C NMR (125
MHz) spectra were recorded on a Bruker Avance digital NMR spectrometer. Chemical shifts are
reported in ppm relative to the signal of tetramethylsilane (SiMe4) as an internal standard; coupling
constants are reported in Hertz (Hz). Data are recorded as m = multiplet, br = broad, s = singlet, d =
doublet, t = triplet, and q = quartet. Fourier transform Infrared (FTIR) spectra were recorded on a
Bruker FT/IR-Alpha spectrometer (neat), and the data are reported in wavenumbers (cm1). The
number average molecular weights (Mn) and polydispersity index (PDI) values of the obtained
poly(methyl methacrylate) (PMMA) were measured using gel-permeation chromatography (GPC)
(THF, Alliance 1200S, Waters Corp., Milford, MA). The glass-transition temperature (Tg) of PMMA
was measured using a thermal analyzer (DSC 4000; Perkin-Elmer). The microstructural analysis of
PMMA as syndiotactic (rr, 0.85 ppm), heterotactic (mr, 1.02 ppm), or isotactic (mm, 1.21 ppm) was
carried out by 1H NMR (Figure S4) [40,41]. GPC analysis of PLA samples was performed at 25 °C
on a Waters Alliance GPCV2000 equipped with differential refractive index detectors and calibrated
using monodisperse polystyrene (PS) standards; THF was used as the eluent at a flow rate of 1.0
mL/min. Mn and PDI values of polymers are given relative to those of PS standards. The
5

1
stereochemistry of the PLA formed was determined by homodecoupled H NMR spectra of the
polymers (Figure S16) [42,43].
2.3. Synthetic procedures
2.3.1. N,N-Bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-4-isopropylaniline (LF)
The CH2Cl2 solution (50.0 mL) of 4-isopropylaniline (3.00 mL, 20.0 mmol) was added to a
CH2Cl2 solution (50.0 mL) of 3,5-dimethylpyrazole-1-methanol (5.05 g, 40.0 mmol), and the
resultant mixture was stirred at room temperature for 24 h. The mixture was dried over MgSO4 and
concentrated under reduced pressure. The crude liquid was subjected to vacuum distillation to give a
yellow oil as the final liquid (6.06 g, 76%). 1H NMR (CDCl3, 500 MHz): δ 7.09 (d, 2H, J = 8.39 Hz,
–C6H4–), 6.95 (d, 2H, J = 8.70 Hz, –C6H4–), 5.73 (s, 2H, –N–C(CH3))=CH–C(CH3)=N–), 5.46 (s,
4H, –N–CH2–N–), 2.85–2.80 (m, 1H, iso-C3H7–), 2.20 (s, 6H, –N–C(CH3))=CH–C(CH3)=N–), 2.01
(s, 6H, –N–C(CH3))=CH–C(CH3)=N–), 1.20 (d, 6H, J = 6.87, Hz iso-C3H7). 13C NMR (CDCl3, 125
MHz): δ 147.15 (s, 2C, –N–C(CH3))=CH–C(CH3)=N–), 143.93 (s, 1C, –C6H4–), 143.07 (s, 1C, –
C6H4–), 139.0 (s, 2C, –N–C(CH3))=CH–C(CH3)=N–), 126.5 (d, 2C, J = 156.2 Hz, –C6H4–), 120.9
(d, 2C, J = 164.39 Hz, –C6H4–) 105.2 (d, 2C, J =172.6 Hz, –N–C(CH3))=CH–C(CH3)=N–), 64.2 (t,
2C, J = 300.6 Hz, –N–CH2–N–), 32.9 (d, 1C, J = 138.9 Hz, iso-C3H7), 23.6 (q, 2C , J = 376.9 Hz,
iso-C3H7), 13.2 (q, 2C, J = 344.2 Hz, –N–C(CH3))=CH–C(CH3)=N–), 10.4 (q, 2C, J = 348.7 Hz, –
N–C(CH3))=CH–C(CH3)=N–). Analysis calculated for C21H29N5 (%): C, 71.7, H, 8.32, N, 19.9.
Found: C, 72.2, H, 8.43, N, 19.8. IR (oily liquid neat; cm−1): ν(C–H) 2961 w; ν(C = C) 1547 s; ν(C =
C) + ν (C = N) /pz ring, 1519 s, 1454 s; νbend(–C–H sp3) 1403 m; ν(N–C) 1225 s; νbend(C–H sp2) 809
w.
6

2.3.2 N,N-Bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)aniline copper(II) chloride ([LACuCl2])
A solution of LA (0.619 g, 2.00 mmol) in dried EtOH (20.0 mL) was treated with an EtOH
solution of CuCl2·2H2O (0.341 g, 2.00 mmol), and the resulting mixture was stirred at room
temperature for 12 h. The blue-green precipitate was filtered, washed with cold EtOH (50.0 mL × 2),
followed by subsequent washing with cold Et2O (50.0 mL × 2) to obtain [LACuCl2] as the final
product (0.719 g, 81%). The X-ray-quality single crystals were obtained by layering n-hexane over a
CH2Cl2 solution of [LACuCl2]. Analysis calculated for C19H25Cl2N5CuO (%): C, 48.7, H, 5.22, N,
15.8. Found: C, 48.7, H, 5.29, N, 15.8. IR (solid neat; cm−1): ν(C–H) 2921 w; ν(C=C) 1598 s; ν(C=C)
+ ν(C=N) /pz ring, 1549 s, 1506 s; νbend(–C–H sp3) 1454 m; ν(N–C) 1211 s; νbend(C–H sp2) 816 w.
2.3.3 N,N-Bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-4-methoxyaniline copper(II) chloride
([LBCuCl2])
A method analogous to that described for the preparation of [LACuCl2] was used to prepare
[LBCuCl2]; in this case, LB (0.677 g, 2.00 mmol) and CuCl2·2H2O (0.341 g, 2.00 mmol) were used
to obtain a blue solid (0.740 g, 78%). The X-ray-quality single crystals were obtained by layering n-
hexane over a CH2Cl2 solution of [LBCuCl2]. Analysis calculated for C19H25Cl2N5CuO (%): C, 48.1,
H, 5.32, N, 14.8. Found: C, 47.2, H, 5.28, N, 14.7. IR (solid neat; cm−1): ν(C–H) 2956 w; ν(C=C)
1554 s; ν(C=C) + ν(C=N) /pz ring, 1510 s, 1465 s; νbend(–C–H sp3) 1465 m; ν(N-C) 1249 s; νbend(C-
H sp2) 810 w.
2.3.4 N,N-Bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-4-fluoroaniline copper(II) chloride
([LCCuCl2])
A method analogous to that used to prepare [LACuCl2] was adopted for the synthesis of
[LCCuCl2]; in this case, LC (0.507 g, 2.00 mmol) and CuCl2·2H2O (0.341 g, 2.00 mmol) were used
7

to obtain a dark-green solid (0.636 g, 82%). The green crystals suitable for X-ray analysis were
obtained by layering n-hexane over a CH2Cl2 solution of [LCCuCl2]. Analysis calculated for
C18H22Cl2N5CuF (%): C, 46.8, H, 4.80, N, 15.2. Found: C, 46.4, H, 4.86, N, 15.3. IR (solid neat;
cm−1): ν(C–H) 3051 w; ν(C=C) 1553 s; ν(C=C) + ν(C=N) /pz ring, 1510 s, 1465 s; νbend(–C–H sp3)
1399 m; ν(N–C) 1214 s; νbend(C–H sp2) 859 w.
2.3.5 N,N-Bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-2,4,6-trimethylaniline copper(II) chloride
([LDCuCl2])
A method analogous to that described for [LACuCl2] was used to synthesize [LDCuCl2]; in
this case, utilizing LD (0.703 g, 2.00 mmol) and CuCl2·2H2O (0.341 g, 2.00 mmol) to get pale green
solid (0.729 g, 75%). The green cubic X-ray-quality single crystals were obtained by layering n-
hexane over a CH2Cl2 solution of [LDCuCl2]. Analysis calculated for C22H31Cl4N5Cu (%): C, 46.3,
H, 5.47, N, 12.3. Found: C, 46.2, H, 5.46, N, 12.6. IR (solid neat; cm-1): ν(C‐H) 2913 w; ν(C = C)
1552 s; ν(C = C) + ν (C = N) /pz ring, 1486 s, 1459 s; νbend(‐C‐H sp3) 1418 m; ν(N-C) 1221 s; νbend(C-H
sp2) 827 w.
2.3.6 N,N-Bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-2,6-diethylaniline copper(II) chloride
([LECuCl2])
A method analogous to that described for [LACuCl2] was adopted for the synthesis of
[LECuCl2]; in this case, LE (0.731 g, 2.00 mmol) and CuCl2·2H2O (0.341 g, 2.00 mmol) were used
to obtain a green solid as the final product (0.700 g, 70%). Analysis calculated for C21H29Cl2N5Cu
(%): C, 52.9, H, 6.25, N, 14.0. Found: C, 53.0, H, 6.37, N, 14.6. IR (solid neat; cm−1): ν(C–H) 3195
w; ν(C=C) 1568 s; ν(C=C) + ν(C=N) /pz ring, 1512 s, 1470 s; νbend(–C–H sp3) 1411 m; ν(N-C) 1278
s; νbend(C-H sp2) 818 w.
8

2.3.7 N,N-Bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-4-isopropylaniline copper(II) chloride
([LFCuCl2])
A method analogous to that described for [LACuCl2] was adopted for the synthesis of
[LFCuCl2]; in this case, LF (0.507 g, 2.00 mmol) and CuCl2·2H2O (0.341 g, 2.00 mmol) were used
to obtain a green solid as the final product (0.636 g, 82%). The X-ray-quality single crystals were
obtained by layering n-hexane over a CH2Cl2 solution of [LFCuCl2]. Analysis calculated for
C21H29Cl2N5Cu (%): C, 51.9, H, 6.02, N, 14.4. Found: C, 51.4, H, 6.22, N, 13.8. IR (solid neat; cm−1):
ν(C–H) 2959 w; ν(C=C) 1552 s; ν(C=C) + ν(C=N) /pz ring, 1509 s, 1462 s; νbend(–C–H sp3) 1391 m;
ν(N–C) 1210 s; νbend(C–H sp2) 808 w.
2.4. MMA polymerization
In a Schlenk flask (100 mL), [LACuCl2] (6.66 mg, 15.0 μmol), [LBCuCl2] (7.11 mg, 15.0
μmol), [LCCuCl2] (6.93 mg, 15.0 μmol), [LDCuCl2] (7.29 mg, 15.0 μmol), [LECuCl2] (7.50 mg, 15.0
μmol), or [LFCuCl2] (7.29 mg, 15.0 μmol) was dissolved in toluene (10.0 mL). MMAO (5.90 wt%
in toluene, 3.80 mL, [MMAO]0/[Cu(II) catalyst]0 = 500) under a dry argon atmosphere was
transferred to the aforementioned mentioned solution. After the mixture had been stirred at 60 °C for
20 min, it was transferred into an MMA (5.00 mL, 47.1 mmol, [MMA]0/[M(II) catalyst]0 = 3100)
solution. The reaction flask was immersed in an oil bath at 60 °C, and the mixture was stirred for 2
h. The resulting polymer was precipitated in MeOH (500 mL) and HCl (5.00 mL) with stirring for 1
h. The polymer was filtered and subsequently washed with MeOH (100 mL × 3) to give PMMA,
which was dried under vacuum at 60 °C.
2.5. rac-Lactide polymerization
9

In a general polymerization reaction for rac-LA with the dimethyl copper initiators, the active
catalytic species were generated as follows. Dichloro Cu(II) complexes, i.e., [LACuCl2] (0.222 g,
0.50 mmol), [LBCuCl2] (0.237 g, 0.50 mmol), [LCCuCl2] (0.231 g, 0.50 mmol), [LDCuCl2] (0.243
g, 0.50 mmol), [LECuCl2] (0.250 g, 0.50 mmol), or [LFCuCl2] (0.243 g, 0.50 mmol), and dried THF
(7.35 mL) were added to a 100 mL Schlenk flask under an argon atmosphere. To this solution was
added MeLi (1.00 mmol, 0.65 mL of a 1.6 M solution in Et2O) dropwise to generate in situ dimethyl
Cu(II) species. After the mixture was stirred for 2 h at room temperature, the resulting THF solution
of a dimethyl Cu(II) complex, i.e. [LnCuMe2] (Ln = LA–LF), was used as an initiator for the 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 5.00 mL of dried
CH2Cl2 was added to completely solubilize the monomer. The polymerization was initiated by slow
addition of the catalyst solution (1.0 mL, 0.0625 mmol) via a syringe under argon at 25 °C into
monomer solution. The reaction mixture was stirred for the specified time and the polymerization
reactions were quenched by using H2O (1.0 mL) followed by the addition of n-hexane (2.0 mL) and
the solvent was evaporated directly to give sticky polymeric material. The resultant polymeric residue
was subjected to monomer conversion determination, which was monitored by integrating monomer
1
1
versus polymer methine resonances in H NMR spectrum; H NMR (CDCl3, 500 MHz) for the
obtained polymer: δ 5.13-5.20 (m, 1H), 1.50-1.62 (m, 3H). The precipitates collected from the bulk
mixture were again dissolved with CH2Cl2, and sequentially precipitated into n-hexane. Solvents were
decanted and the white solids were dried in vacuo at 40 °C for 12 h.
2.6. X-ray crystallographic studies
10

X-ray-quality single crystals of [LnCuCl2] (Ln = LA–LD and LF) were coated with Paratone-
N oil, and the diffraction data were collected at 100(2) K using synchrotron radiation ( = 0.700 Å)
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 PAL BL2D-SMDC program [44]
was used for data collection (the detector distance was 63 mm, omega scan; ∆ω = 1°, exposure time
was 1 sec per frame); HKL3000sm (Ver. 703r) [45] was used for cell refinement, reduction, and
absorption correction. A green cubic-shaped crystal of the complexes were picked up with Paratone-N
oil and mounted onto a Bruker SMART CCD diffractometer equipped with a graphite-
monochromated Mo-Kα (λ = 0.71073 Å) radiation source; data were collected with the samples under
a N2 cold stream (200(2) K) at the Western Seoul Center of Korea Basic Science Institute. Data
collection and integration were performed with the SMART (Bruker, 2000) and SAINT-Plus (Bruker,
2001) software packages [46]. Semi-empirical absorption corrections based on equivalent reflections
were applied by SADABS [47]. All measured structures were solved by dual-space algorism related
with intrinsic phasing using the SHELXT-2018/2 [48] program and were refined by full-matrix least-
squares refinement using the SHELXL-2018/3 [49] program. 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 the positions of their parent atoms using
the appropriate HFIX command in the SHELXL-2018/3 program. The crystallographic refinements
and structural data are summarized in Table S1.
3. Results and Discussion
3.1. Synthesis and physical parameters
The ligands were obtained via a single-step condensation reaction of the aniline derivatives
and 3,5-dimethyl-1H-pyrazolyl-1-methanol in CH2Cl2 (Scheme 1). In the 1H NMR spectrum of LF,
11

the protons of the –CH2– linker units of 3,5-dimethylpyrazole and aniline were observed at δ 5.46
ppm (Figure S1). The meta and ortho protons of 4-isopropylaniline appeared at δ 7.09 and 6.95 ppm,
respectively. The –CH– protons of the isopropyl group and –CH3 groups appeared at δ 2.80 and 2.20
ppm, respectively. Similarly, the 13C NMR spectrum (Figure S2) of LF shows representative peaks
consistent with the ligand formulation. The Cu(II) complexes were synthesized via coordination of
ligands (Ln = LA–LF) with CuCl2·2H2O in a 1:1 molar ratio in anhydrous EtOH in facile yields and
purity (Scheme 1).
Spectroscopic characterization by FTIR confirmed the synthesis of the Cu(II) complexes.
The characteristic peaks observed in the FTIR spectra of [LnCuCl2] (Ln = LA–LF) lie in the expected
range. For instance, the common absorption bands for v(C=C) + v(C=N) of the pyrazole rings appread
at ~1512 and ~1479 cm−1, whereas the aromatic C–H and C=C stretching bands appeared at ~3207–
2961 and ~1579–1552 cm−1, respectively [50]. In addition, typical sp3 and sp2 C–H bending bands
appeared at frequencies consistent with those reported in the literature. The FTIR spectra of the
complexes showed that the peaks corresponding to aromatic C=C stretching and aromatic C–H bands
shifted from lower wavenumbers to higher wavenumbers compared with the peaks of their
corresponding ligands. The effect of ring substituents on N-C and symCH3 is observed to be small.
However, the symCH3 stretching frequencies increases as ring substituents become more electron
donating particularly at ortho position, as evident from the perturbed N-C (1221 to 1278 cm-1) and

symCH3 frequencies. The bulkier alkyl group results in vibrations occurred at slightly higher
frequencies (3138-3219 cm-1 for 2,6-diethyl substituent in [LECuCl2]) compared to less bulkier
groups (2718-2913 cm-1, for 2,6-dimethyl substituents in [LDCuCl2]). Additionally, the presence of
2,6-dimethyl substituents on the aniline ring perturbed the binding of the ligand to metal centre and
resulted in bidentate instead of tridentate. At same time the anticipated increase in the perturbed N-C
12

(1278 cm-1) and symCH3 (3138-3219 cm-1) for 2,6-diethyl substituents at aniline moiety in [LECuCl2]
might reflect the bidentate coordination mode.
The elemental analysis results for the synthesized complexes are consistent with the formula proposed
in Scheme 1 and confirm the purity of the isolated complexes. All of the synthesized Cu(II)
complexes [LnCuCl2] (Ln = LA–LF) were found to be stable and can be stored at room temperature
for months without appreciable degradation.
3.2. Molecular structures of Cu(II) complexes
Single-crystal X-ray diffraction studies were performed to determine the geometries of Cu(II)
complexes. The ORTEP diagrams of [LnCuCl2] (Ln = LA–LD and LF) are shown in Figs. 1–5, and
selected bond lengths and angles are listed in Table 1. Complexes, [LACuCl2], [LBCuCl2],
[LCCuCl2], [LDCuCl2], and [LFCuCl2] crystallized in monoclinic systems with P212121, P21/c, C2/c,
P-1, and P21/n space groups, respectively.
Cu(II) complexes [LnCuCl2] (Ln = LA–LC and LF) exhibited distorted square-pyramidal
geometries around a Cu(II) center via tridentate coordination to an N-substituted bis-pyrazolyl ligand,
along with monodentate coordination to two chloro ligands. The M–Npyrazole and Cu–Cl lengths in
[LnCuCl2] (Ln = LA–LC and LF) lie in 2.257(9)–2.383(9) Å and 1.981(4)–2.011(3) Å ranges and are
not strongly affected by the para substituents of the aniline moieties. These structural parameters
agreed well with the expected values based on the parameters of similar complexes [3]. The length
of Cu–Namine bond increase in the order: 2.222(2) Å [LFCuCl2] < 2.367(3) Å [LACuCl2] < 2.368(3)
Å [LBCuCl2] < 2.4458(1) Å [LCCuCl2]. Substituents at the para position of the aniline moiety exert
electronic effects on the Cu–Namine bond lengths in [LnCuCl2] (Ln = LA–LC and LF).
13

The Npyrazole–Cu–Npyrazole angles are 155.32(1) [LACuCl2], 155.94(5) [LBCuCl2],
154.77(5) [LCCuCl2], and 159.64(9) [LFCuCl2]. These angles are slightly affected by the steric
bulk of the aniline substituents. The Npyrazole–Cu–Npyrazole angles increase according to the increasing
para substituents in the order H < F < OMe < CH(CH3)2. The Cl–Cu–Cl, Namine–Cu–Npyrazole, and
Npyrazole–Cu–Cl angles lie in the ranges 124.43(3)–143.91(2), 77.59(5)–79.93(8), and 92.83(4)–
96.85(7), respectively. These values do not substantially vary from the expected values. Furthermore,
the angles between the aromatic substituent plane and the bis-pyrazole plane are 42.78° for
[LACuCl2], 47.22° for [LBCuCl2], 43.12° for [LCCuCl2], and 35.5° for [LFCuCl2].
By contrast, [LDCuCl2] exhibited four-coordination geometry involving two nitrogen atoms
of pyrazole moieties and two chloro ligands, resulting in an eight-membered chelate ring (Fig. 4)
[36]. In [LDCuCl2], the Cu(II) center in ligated to N,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-
2,4,6-trimethylaniline and adopted a distorted tetrahedral geometry. These results suggest that the
presence of methyl substituents at the ortho position steers the coordination mode and resultant
geometries of the synthesized Cu(II) complexes. The average Cu–Npyrazole and Cu–Cl bond lengths
are 2.002(2) and 2.243(8) Å, respectively, whereas the Namine···Cu distance is 2.954 Å. The bond
angles of Npyrazole–Cu–Npyrazole and Cl–Cu–Cl are 145.27(8)° and 139.96(3)° in [LDCuCl2],
respectively.
The τ5 values provide useful information about the geometry of five-coordinate
complexes, i.e., complexes with an ideal square pyramidal geometry are characterized by a value for
τ5 of zero, on the other hand the value of τ5 is equal to one in the case of an ideal trigonal bipyramidal
geometry [51]. A comparison of the τ5 parameter of the Cu(II) complexes synthesized in the present
study are listed in Table 2. Based on the τ5 values the geometry around the Cu(II) center in [LnCuCl2]
(Ln = LA–LC and LF), can be described as distorted square-pyramidal consisting of three nitrogen
atoms of pyrazolyl-methylamine framework and two Cl atoms. The plane angles between N2–Cu1–
14

N5 and Cl1–N3–Cl2 and between N2–Cu1–N4 and Cl1–N3–Cl2 in [LBCuCl2] and [LCCuCl2] are
distorted by approximately 89.50° and 89.60°, respectively.
The new geometric parameters for the four‐coordinate compounds (τ4) as improved simple
metrics for quantitatively evaluating the geometry are presented in Table 3 [52]. The τ4 values for a
perfect tetrahedron and perfect square-planar geometry are 1.00 and zero, respectively. The degrees
of distortion based on bond angles around the Cu(II) centers of the complexes prepared in the present
work were evaluated using these structural indexes. The τ4 value of [LDCuCl2] is 0.531, which is
closer to 1 than to zero. Thus, the geometry of [LDCuCl2] is best described as a distorted tetrahedron
geometry. The plane angle between the Cl2–Cu1–Cl1 and Npyrazole–Cu1–Npyrazole planes in [LDCuCl2]
is calculated as 51.37°. Thus, variation in the steric bulk at the ortho position of the aniline moiety
strongly affects the resultant geometry of these Cu(II) complexes.
3.3. MMA polymerization
In our continuing effort to design effective and stereoselective bis(pyrazolyl amine)-based
PMMA catalysts, we assessed the catalytic performance of the Cu(II) complexes supported by
bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)amines in MMA polymerization. Representative
polymerization results are listed in Table 4. Polymerization data indicate that all synthesized Cu(II)
complexes polymerized MMA, yielding PMMA with a Tg between 122 and 128 °C. The polymers
were isolated as white powders and were characterized by GPC using polystyrene standards as a
reference and THF as the eluent.
Notably, [LFCuCl2] exhibited the highest catalytic activity (2.81 × 104 g (mol Cu)−1 h−1) and
produced PMMA with molecular weight (2.27 × 105 g mol−1) compared to rest of its analogous. The
steric bulk of the substituents at the ortho position of the aniline moiety influenced the catalytic
performance of the Cu(II) complexes. For instance, when the ethyl (–CH2CH3) group attached at the
15

ortho position of the aniline moiety in [LECuCl2] changed to –CH3 (in [LDCuCl2]) and –H (in
[LCCuCl2]) groups, an increase in MMA activity was observed (Table 4). A trivial tendency between
the steric bulk and catalytic capabilities in complexes bearing alkyl groups attached at the ortho
position of the aniline moiety was observed to be in the order of –CH2CH3 < –CH3 < –H (Table 4).
The presence of an ethyl group at the ortho position increases the steric demand of the ligand, thus
decreasing the size of the possible reaction site. However, the electron-donating character of the alkyl
moieties lowers the Lewis acidity of the metal center. The metal is thus less activating and thereby
hinders the polymerization. As evident from our previous report, bulky substituents attached to amine
or pyrazole moieties negatively affect MMA activation; in this case, the steric clashes between the
attached ligands and the incoming monomer likely impede the monomer’s approach to the metal site
[53]. These results are in contrast to our previous results, which indicated that an increase in steric
bulk at pyrazole and aniline moieties corresponded to greater polymerization activities [32]. However,
despite of the lower steric bulk at ortho positions, [LACuCl2] and [LBCuCl2] exhibited lower
activities. These surprising results with respect to steric bulk and the observed activities are difficult
to explain. It is evident from polymerization data that [LFCuCl2] exhibited the highest catalytic
activity compared to rest of its analogous. The presence of fluoro substituent at para position of
aniline moiety in [LFCuCl2] might impend the electron withdrawing effect enhancing Lewis acid
strength of metal centre. Additionally, the presence of less sterically bulky substituent (-H) at ortho
position and better solubility of [LFCuCl2] can also be attributed to its better performance in term of
activity. The PDI values of PMMA obtained with the Cu(II) complexes ranged from 1.42 to 1.61 at
60 °C. The molecular weights of the resultant PMMAs were not significantly affected by steric bulk
of the substituents of the aniline moieties. Furthermore, the mediocre activities of our current system
can be ascribed to their low solubility in the polymerization media.
16

In comparison with our previously reported five-coordinated Cu(II) complexes bearing N,N-
bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)cyclopentanamine [54] and N-methyl-N-((pyridine-2-
yl)methyl)benzeneamine [56], the current catalytic system exhibits slightly higher activities and
stereoselectivities, yielding PMMA with lower molecular weights. Similarly, compared with
previously reported four-coordinated Zn(II) and Co(II) complexes with N,N′,N-bis((1H-pyrazol-1-
yl)methyl)amine derivatives [54], [LDCuCl2] with a four-coordination structure exhibits lower
activity and yields PMMA with identical stereoselectivity.
The blank polymerization of MMA was carried out using starting materials, i.e.,
CuCl2·2H2O/MMAO or solely MMAO, under identical experimental conditions to evaluate the
ligand effect on the central metal atom. The polymerization data clearly show that the
CuCl2·2H2O/MMAO system exhibited lower activities and stereoselectivities and yielded PMMA
with comparable molecular weights. Similarly, in the case of MMAO, the activity and
stereoselectivity were lower than [LnCuCl2]/MMAO systems. Attempts to induce polymerization
with dichloro Cu(II) complexes in the absence of MMAO were unsuccessful.
Isotactic PMMA, which is produced through radical processes commercially, has a Tg value
of approximately 65 C [56]. Recent advancements have been focused on preparing PMMA with a
high Tg and improved properties via non-radical MMA polymerization catalyzed by coordination
complexes. The syndiotactic enchainment ranged from 0.66 to 0.68 in almost all cases, irrespective
of the catalysts’ coordination modes and activities. The syndiotacticity of the resultant PMMA was
not strongly affected by variation of the aniline substituents. Importantly, the resultant syndiotactic
enchainment was not sufficiently high to enable us to predict the mechanism of coordination
polymerization for the catalytic species in the present work. Future work will be focused on ligand
modification to improve the catalytic performance and the resultant stereocontrol of the MMA
polymerization.
17

3.4. rac-Lactide polymerization
ROP in a controlled and selective manner is a useful approach towards the synthesis of
biodegradable polymers [57]. In this regard the in situ generated dimethyl Cu(II) species were
investigated for their catalytic efficacies in the ROP of rac-LA at 25 C. All the dimethyl Cu(II)
species effectively catalyzed rac-LA polymerization, and the complete conversion of rac-LA to PLA
1
was confirmed by the absence of the monomer signal in the H NMR spectrum (Figure S15).
Representative polymerization results are summarized in Table 5.
The experimental Mn values (corrected using a Mark–Houwink factor of 0.58) [58,59]
determined with GPC were in agreement with theoretical values, suggesting polymerization at a
single reaction site provided by the dimethyl Cu(II) complexes. Polymerization data indicate that
PLAs obtained with [LnCuMe2] (Ln = LA–LF) have broader PDIs, which might be a consequence of
backbiting or transesterification side reactions, resulting in the formation of macrocycles with a wide
molecular-weight distributions (MWD). When dichloro Co(II) complexes, [LnCuCl2] (Ln = LA – LF),
were utilized as catalysts under the same experimental conditions; rac-LA polymerization was not
1
initiated. Inspecting the H NMR spectra of the an isolated PLAs we were able to infer that the
polymers are end-capped, with an –C(=O)CH3 group at one terminus overlapped with those of PLA
backbones and a hydroxyl group –CHMe–(OH) at the other (Figure S17). The coordination insertion
mechanism [60,61] can be invoked for the ROP of rac-LA by these initiators. With this mechanism,
rac-LA initially coordinates to the M(II) centre, yielding a penta-coordinated intermediate, followed
by cleavage of the acyl-oxygen bond to open the monomer ring. Another molecule of rac-LA gets
opened by attaching to the M(II) centre in a similar manner. The successive addition of monomer
produces a hetero-enriched PLA.
18

Variation of the substituents at the ortho position of the aniline moiety did not affect the
activity of the Cu(II) complexes at room temperature. However, the preliminary polymerization data
o
obtained at -25 C using dimethyl Cu(II) species showed that LD containing complex exhibited the
highest activity (Table S2; entry 5). The order of activity with respect to ortho substituents follow
o
the order; [LDCuCl2] > [LECuCl2] > [LFCuCl2] at -25 C (Table S2; entries 5-7). It is presumed
that the electron-donating character of the methyl moieties increases the electronic density around the
metal center. Therefore, the metal is more activated, thereby promoting the polymerization. More
detailed investigation is underway that is aimed at improving the Cu(II) complexes’ catalytic activity
and stereoselectivity through modification of the ligand framework at low temperatures.
On the basis of comparisons with previously reported values, the PLA produced by [LnCuMe2]
(Ln = LA–LF) was concluded to be predominantly heterotactic. The polymerization temperature
apparently influenced the alternative insertion of rac-LA and the resultant microstructures of the PLA.
The probability of heterotactic enchainment (Pr values) ranged from 0.72 to 0.78 at 25 °C. However,
a decrease in temperature from 25 to −25 °C resulted in increased heterotacticity (0.84 ≤ Pr ≤ 0.90)
(Table S2). These results are consistent with our previous findings. No regular trend in heterotacticity
was observed, suggesting that substituents at the para and ortho positions of the aniline less
significantly affected the heterotacticity in the ROP of rac-LA.
The activities of the current system toward rac-LA at 25 °C are higher that the activities of
our previously reported dimethyl complexes with comparable heterotacticity [62,63].
NacnacBnCuOiPr, a recently reported, highly active catalyst for the ROP of LA, produced PLA with
almost no stereocontrol [64]. Compared with the highly effective Cu(II) initiators based on N-
(pyridin-2-ylmethyl)amine [36], the current Cu(II) systems exhibit lower catalytic efficacy but
produce PLA with better heterotacticity and PDIs.
19

4. Conclusions
In summary, we demonstrated the synthesis and X-ray crystallographic structures of
[LnCuCl2] (Ln = LA–LF) supported by bis((3,5-dimethyl-1H-pyrazol-1-yl)methylamine derived
ligands. In [LnCuCl2] (Ln = LA–LC and LF), the Cu(II) center is coordinated to pyrazole and amine
nitrogen atoms along with two chloro ligands, displaying a five-coordinated distorted square-
pyramidal geometry. However, the [LDCuCl2] with four-coordination mode adopted a distorted
tetrahedron geometry. Investigation of the catalytic efficacy of synthesized Cu(II) complexes in
MMA polymerization revealed [LFCuCl2] (2.81 × 104 g PMMA/mol Cu h) to display promising
catalytic activity and furnished syndio-enriched PMMA. The activities of the studied Cu(II)
complexes varied with respect the substituents of the aniline moiety. Additionally, in situ generated
dimethyl Cu(II) complexes demonstrated high activities toward rac-LA, and furnished PLAs with
mediocre heterotacticity with slightly higher PDI values. Notably, the activities of the catalyst for
MMA and rac-LA polymerization was observed to be influenced by the steric and electronic
properties of the ligand attached to metal center.
Supplementary Materials
CCDC 1903792 – 1903796 contains the supplementary crystallographic data for [LACuCl2],
[LBCuCl2], [LCCuCl2], [LDCuCl2]·CH2Cl2 and [LFCuCl2]·3CH2Cl2, 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.
Conflicts of Interests
20

There are no conflicts to declare.
Acknowledgments
This research was supported by the National Research Foundation (NRF) of South Korea, funded by
the Ministry of the Education, Science, and Technology (MEST) (Grant No. 2019R1A2C1088654).
X-ray crystallography with PLS-II 2D-SMC beamline was supported by MSIP and POSTECH.
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23

R2
R2
OH
N
2
N
R1
R1
R1
R1
CuCl2 . 2H2O
CH2Cl2
N
N
RT / 72 h
EtOH / RT / 12 h
N
N
N
N
R2
N
N
N
N
Cu
Cl
Cl
LA:
LB:
LC:
LD:
LE:
LF:
(R1 = -H, R2 = -H)
(R1 = -H, R2 = -OCH3)
(R1 = -H, R2 = -F)
(R1 = -CH3, R2 = -CH3)
(R1 = -CH2CH3, R2 = -H)
(R1 = -H, R2 = -CH(CH3)2)
R1
R1
[LnCuCl2] (Ln = LA - LF)
NH2
Scheme 1. Schematic representation of the synthesis of ligands (Ln = LA–LF) and their
corresponding Cu(II) complexes, [LnCuCl2] (Ln = LA–LF).
24

Table 1. The selected bond lengths (Å) and angles (°) of [LnCuCl2] (Ln = LA–LD and LF).
[LACuCl2]
[LBCuCl2]
[LCCuCl2]
[LDCuCl2]·CH2Cl2
[LFCuCl2]·3CH2Cl2
Bond lengths (Å)
Cu(1)-N(5)
Cu(1)-N(1)
Cu(1)-Cl(1)
Cu(1)-Cl(2)
Cu(1)-N(5)
Cu(1)-N(3)
N(1)-N(2)
1.981(4)
2.011(3)
2.2703(1)
2.3052(1)
1.981(4)
2.367(3)
1.371(4)
Cu(1)-N(5)
1.9898(2)
1.9965(2)
2.2742(6)
2.2931(5)
1.9898(2)
2.3680(1)
1.3657(2)
Cu(1)-N(4)
Cu(1)-N(2)
Cu(1)-Cl(2)
Cu(1)-Cl(1)
N(1)-C(6)
1.9927(1)
Cu(1)-N(2)
Cu(1)-N(4)
Cu(1)-Cl(1)
Cu(1)-Cl(2)
N(3)-C(7)
N(1)-C(3)
N(1)-N(2)
2.001(2)
Cu(1)-N(5)
Cu(1)-N(1)
Cu(1)-N(3)
Cu(1)-Cl(1)
N(3)-C(1)
1.996(2)
Cu(1)-N(2)
Cu(1)-Cl(1)
Cu(1)-Cl(2)
Cu(1)-N(5)
Cu(1)-N(3)
N(1)-N(2)
2.0077(1)
2.2652(5)
2.2902(6)
1.4543(2)
2.4458(1)
1.3546(2)
2.003(2)
2.2405(8)
2.2453(9)
1.444(3)
1.350(3)
1.372(2)
2.006(2)
2.222(2)
2.2568(9)
1.464(3)
2.3827(8)
1.372(3)
Cu(1)-N(3)
N(1)-C(3)
Cu(1)-Cl(2)
N(1)-N(2)
Bond angles (°)
N(5)-Cu(1)-N(1)
N(5)-Cu(1)-Cl(1)
N(1)-Cu(1)-Cl(1)
N(5)-Cu(1)-Cl(2)
N(1)-Cu(1)-Cl(2)
Cl(1)-Cu(1)-Cl(2)
N(5)-Cu(1)-N(3)
N(1)-Cu(1)-N(3)
155.32(1)
N(5)-Cu(1)-N(2)
155.94(5)
95.97(4)
94.91(4)
92.89(4)
93.38(4)
133.72(2)
77.99(5)
78.03(5)
N(4)-Cu(1)-N(2)
N(4)-Cu(1)-Cl(2)
N(2)-Cu(1)-Cl(2)
N(4)-Cu(1)-Cl(1)
N(2)-Cu(1)-Cl(1)
Cl(2)-Cu(1)-Cl(1)
N(4)-Cu(1)-N(3)
N(2)-Cu(1)-N(3)
154.77(5)
95.66(4)
94.83(4)
92.10(5)
92.83(5)
143.905(2)
77.84(5)
76.98(5)
N(2)-Cu(1)-N(4)
N(2)-Cu(1)-Cl(1)
N(4)-Cu(1)-Cl(1)
N(2)-Cu(1)-Cl(2)
N(4)-Cu(1)-Cl(2)
145.27(8)
96.53(6)
96.35(6)
94.97(6)
95.59(6)
N(5)-Cu(1)-N(1)
N(5)-Cu(1)-N(3)
N(1)-Cu(1)-N(3)
N(5)-Cu(1)-Cl(1)
N(1)-Cu(1)-Cl(1)
N(3)-Cu(1)-Cl(1)
N(5)-Cu(1)-Cl(2)
N(1)-Cu(1)-Cl(2)
159.64(9)
79.73(8)
79.93(8)
97.65(7)
96.58(7)
136.81(6)
91.83(7)
92.06(7)
95.64(1)
96.85(1)
91.10(1)
95.24(1)
134.32(4)
77.83(1)
77.59(1)
N(5)-Cu(1)-Cl(1)
N(2)-Cu(1)-Cl(1)
N(5)-Cu(1)-Cl(2)
N(2)-Cu(1)-Cl(2)
Cl(1)-Cu(1)-Cl(2)
N(5)-Cu(1)-N(3)
N(2)-Cu(1)-N(3)
Cl(1)-Cu(1)-Cl(2) 139.96(3)
C(3)-N(1)-N(2)
C(3)-N(1)-C(6)
111.05(2)
127.80(2)
25

Cl(2)-Cu(1)-N(3)
C(2)-N(1)-N(2)
C(2)-N(1)-Cu(1)
99.99(8)
105.4(3)
140.0 (3)
Cl(1)-Cu(1)-N(3)
Cl(2)-Cu(1)-N(3)
C(3)-N(1)-N(2)
121.94(3)
100.34(4)
111.65(1)
Cl(2)-Cu(1)-N(3)
Cl(1)-Cu(1)-N(3)
C(3)-N(1)-N(2)
118.17(4)
97.92(3)
111.50(1)
N(2)-N(1)-C(6)
C(1)-N(2)-N(1)
C(1)-N(2)-Cu(1)
119.77(2)
106.01(2)
134.38(2)
N(3)-Cu(1)-Cl(2)
Cl(1)-Cu(1)-Cl(2)
C(2)-N(1)-N(2)
98.77(6)
124.43(3)
106.0(2)
26

Table 2. Five-coordinate geometry indices (τ5) for [LnCuCl2] (Ln = LA–LC and LF) and
representative examples from the literature.
Complexes
Geometry
Trigonal bipyramidal
Square pyramidal
Square pyramidal
Square pyramidal
Square pyramidal
Square pyramidal
τ5
1.000
0.350
0.370
0.180
0.381
0.000
Reference
[51]
Trigonal bipyramidal (D3h)
[[LACuCl2]
This work
This work
This work
This work
[51]
[LBCuCl2]
[LCCuCl2]
[LFCuCl2]
Square pyramidal (C4v) a
See reference [51]
27

Table 3. Four-coordinate geometry indices (τ4) for [LDCuCl2] and representative examples
from the literature.
Complexes
Geometry
Square planar
Tetrahedral
Tetrahedral
τ4
Reference
[52]
Square planar (D4h)a
[LDCuCl2]
0.00
0.531
1.00
This work
[52]
Tetrahedral (Td) a
See reference [52]
28

Table 4. Polymerization of MMA by [LnCuCl2] (Ln = LA–LF) complexes in the presence of
MMAO.
d
f
f
Entry
Catalysta
Yieldb
(g)
Activityc
Tg
Tacticitye
%mr
23.9
Mw
Mw/Mn
(g (mol-Cat)−1 h−1)
%mm
7.20
37.2
7.53
7.76
7.53
6.51
7.36
7.55
%rr
67.5
51.9
68.4
66.5
68.9
68.7
68.5
68.6
(g mol−1)
×105
2.73
(C)
129
120
127
128
128
125
123
122
× 104
1.73
1
2
3
4
5
6
7
8
CuCl2·2H2Og
MMAOh
10.8
6.83
13.6
14.7
16.0
16.2
15.9
18.0
1.49
1.37
1.61
1.57
1.55
1.51
1.42
1.48
1.07
2.13
2.30
2.53
2.50
2.48
2.81
10.9
1.75
3.08
2.35
2.48
2.20
1.78
2.27
[LACuCl2]
[LBCuCl2]
[LCCuCl2]
[LDCuCl2]
[LECuCl2]
[LFCuCl2]
24.0
24.6
24.9
24.8
25.3
23.9
a [Cu(II) catalyst]0 = 15 μmol, and [MMA]0/[MMAO]0/[Cu(II) catalyst]0 = 3100:500:1, polymerization temp. = 60 C, time = 2 h.
b Yield defined a mass of dried polymer recovered/mass of monomer used.
c Activity is calculated (g of PMMA)/(mol Cu·h).
d Tg is the glass-transition temperature, which was determined using a thermal analyzer.
e The microstructural analysis of PMMA as syndiotactic (rr, 0.85 ppm), heterotactic (mr, 1.02 ppm), or isotactic (mm, 1.21 ppm) was carried
out by 1H NMR [40,41].
f Determined by gel-permeation chromatography (GPC) eluted with THF at room temperature by filtration, with polystyrene calibration; Mn
refers the number average molecular weights of PMMA.
g Blank polymerization using CuCl2·2H2O, also activated by MMAO.
h Blank polymerization carried out solely with MMAO.
29