Zinc complexes supported by N,O-bidentate amino-alkoxyl ligands: Synthesis, characterization and catalytic property for the ring-opening polymerization of L-lactide

Article abstract of DOI:10.1016/j.poly.2017.10.038

A series of new zinc complexes based on the amino-alkoxyl ligands 1-HOC(R¹R²)-2-NMe₂C₆H₄ [R¹ = H, R² = Ph (L¹H), R¹ = Et, R² = Ph (L²H), R¹ = H, R² = 2-FPh (L³H), R¹ = H, R² = 2-BrPh (L⁴H)] were synthesized. The zinc complexes were characterized by NMR spectroscopy and elemental analysis, as well as by an X-ray diffraction study. The solid-state structures of 2 and 3 reveal that the Zn centers adopt four-coordinated distorted tetrahedral geometries. These complexes show high activities in the ring-opening polymerization of L-lactide in the presence of benzyl alcohol in a living fashion. Complex 3 (R¹ = H, R² = 2-FPh) shows the highest activity among complexes 1–4.

Full text of DOI:10.1016/j.poly.2017.10.038

Accepted Manuscript
Zinc complexes supported by N,O-bidentate amino-alkoxyl ligands: synthesis,
characterization and catalytic property for the ring-opening polymerization of
L-lactide
Yancheng Han, Aihong Gao, Yongfang Zhang, Wei Yao, Haibin Guan
PII:
S0277-5387(17)30703-9
https://doi.org/10.1016/j.poly.2017.10.038
POLY 12905
DOI:
Reference:
Polyhedron
To appear in:
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Accepted Date:
3 August 2017
27 October 2017
Please cite this article as: Y. Han, A. Gao, Y. Zhang, W. Yao, H. Guan, Zinc complexes supported by N,O-bidentate
amino-alkoxyl ligands: synthesis, characterization and catalytic property for the ring-opening polymerization of L-
lactide, Polyhedron (2017), doi: https://doi.org/10.1016/j.poly.2017.10.038
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Zinc complexes supported by N,O-bidentate amino-alkoxyl ligands:
synthesis, characterization and catalytic property for the
ring-opening polymerization of L-lactide
Yancheng Hana1, Aihong Gaoa1, Yongfang Zhanga, Wei Yaoa*, Haibin Guanb*
a School of Resources and Environment, University of Jinan, Shandong Provincial Engineering
Technology Research Center for Ecological Carbon Sink and Capture Utilization, Jinan 250022, P.
R. China
b Energy Research Institute of Shandong Academy of Sciences, Jinan 250014, China
* Corresponding author. Tel./fax: +86-531-82769233. E-mail address: yaoweiujn@aliyun.com (W.
Yao); guanhb@sderi.cn (H. Guan)
1 These authors contributed equally.

Abstract
A series of new zinc complexes based on the amino-alkoxyl ligands
[1-HOC(R1R2)-2-NMe2C6H4 [R1 = H, R2 = Ph (L1H), R1 = Et, R2 = Ph (L2H), R1 = H,
R2 = 2-FPh (L3H), R1 = H, R2 = 2-BrPh (L4H)] were synthesized. The zinc complexes
were characterized by NMR spectroscopy and elemental analysis, as well as by an
X-ray diffraction study. The solid-state structures of 2 and 3 reveal that the Zn centers
adopt four-coordinated distorted tetrahedral geometries. These complexes show high
activities in the ring-opening polymerization of L-lactide in the presence of benzyl
alcohol in a living fashion. Complex 3 (R1 = H, R2 = 2-FPh) shows the highest
activity among complexes 1-4.
Keywords:
Catalyst
Zinc complex
Lactide
Ring-opening polymerization
Amino-alkoxyl ligands
1. Introduction
Over the past few decades, there has been a great increase in the development of
polylactide (PLA) because of its biodegradability and biocompatibility. PLAs are
being exploited for a wide range of applications, such as packaging materials,
bio-absorbable implants, drug delivery and tissue engineering scaffolds [1]. The
ring-opening polymerization (ROP) of lactide (LA) is the most efficient method to
prepare PLA, owing to the advantage of achieving well controlled molecular weights
and a narrow molecular weight distribution [2]. Metal complexes, such as lithium [3],

aluminum [4], magnesium [5], titanium [6], zinc [7] and others [8] with ancillary
ligands, have been proven to be powerful catalysts for the ROP of LA. Among the
reported catalysts, zinc complexes have been intensively studied due to their excellent
catalytic properties for the ROP of LA. Recently, zinc complexes bearing
N,O-bidentate, N,N,O-tridentate or N,N,N,O-tetradentate ligands were efficient
catalysts for the ROP of LA [7]. Carpentier’s group reported an efficient system for
the ROP of LA using fluorous alkoxide-imino zinc complexes [7a]. A series of
N,N,O-chelate zinc complexes reported by Wang’s group efficiently catalyzed the
ROP of rac-LA in a controlled fashion [7b]. Ma’s group reported that aminophenolate
N,N,O-zinc complexes showed moderate catalytic activities for the ROP of LA [7c].
Recently, the same group found that N,N,N,O-Zn complexes are efficient initiators
for the ROP of rac-LA at ambient temperature [7d].
In the search for new polymerization catalysts, amino-alkoxy zinc complexes have
been prepared. In this paper, we report the synthesis and full characterization of these
complexes, which, in the presence of benzyl alcohol (BnOH), catalyze the ROP of
L-LA with high activities. It was found that the ligand architecture and the reaction
conditions significantly influence the polymerization activity.
2. Experimental
2.1. General considerations
All reactions and manipulations which related to the preparation of the metal
complexes were carried out under nitrogen with standard Schlenk-line or glovebox
techniques. All solvents were refluxed over the appropriate drying agent and distilled
prior to use. Ligand 1 (Scheme 1) was prepared according to a literature procedure [9].
1H and 13C NMR spectra were measured using a Varian Mercury-300 NMR
spectrometer, a Bruker AVANCE-400 NMR spectrometer or a Bruker AVANCE-600
NMR spectrometer. The elemental analyses were performed on a Perkin-Elmer 2400
analyzer. The molecular weight and molecular weight distribution of the polymers
o
were measured on a TOSOH HLC 8220 GPC at 40 C using THF as the eluent
against polystyrene as a standard.

2.2. Synthesis of L2H
A dry 250 mL two-necked flask was filled with 5.00 g (41 mmol) of
N,N-dimethylaniline, 50 mL of anhydrous diethyl ether and 5 mL of TMEDA, and the
solution was stirred under a nitrogen atmosphere. n-BuLi (20.5 mL, 2.0 M in hexane)
was added at –78 oC. The solution was allowed to warm to room temperature, stirred
for 12 hrs, then propiophenone (5.50 mL, 41 mmol) in 30 mL of anhydrous diethyl
ether was added dropwise to the reaction mixture. The resulting mixture was stirred
for an additional 5 hrs. The precipitate was collected and washed with dry hexane (20
mL). The solid was poured into a water/diethyl ether solution (1/5, 30 mL). The
organic extract was dried over anhydrous MgSO4 and evaporated to yield a yellow
solid product (0.73 g, 89%). Anal. Calc. for C17H21NO (255.16): C, 79.96; H, 8.29; N,
5.49. Found: C, 79.90; H, 8.31; N, 5.40%. 1H NMR (400 MHz, CDCl3, 293 K) δ, ppm:
7.51 (d, J = 6.8 Hz, 1H, Ar–H), 7.40 (t, J = 6.6 Hz, 2H, Ar–H), 7.30 (d, J = 6.8 Hz, 2H,
Ar–H), 7.27–7.21 (m, 3H, Ar–H), 7.15 (m, 1H, Ar–H), 2.74 (s, 6H, NCH3), 2.27 (q, J
= 7.3 Hz, 2H, CH2CH3), 0.95 (t, J = 7.3 Hz, 3H, CH2CH3). 13C NMR (100 MHz,
CDCl3, 293 K) δ, ppm: 151.6, 149.2, 141.8, 128.0, 127.7, 127.7, 126.0, 125.9, 125.8,
123.3, 79.2, 46.5, 35.7, 8.2.
2.3. Synthesis of L3H
The reaction was carried out by a similar procedure as described for L2H, except
that 4.40 mL (41 mmol) of 2-flurobenzaldehyde was used instead of propiophenone.
The product, as yellow solid, was obtained in 75% yield. Anal. Calc. for C15H16FNO
1
(245.12): C, 73.45; H, 6.57; N, 5.71. Found: C, 73.51; H, 6.62; N, 5.78%. H NMR
(300 MHz, CDCl3, 293 K) δ, ppm: 7.54 (t, J = 7.1 Hz, 1H, Ar–H), 7.33–7.29 (m, 3H,
Ar–H), 7.18 (t, J = 6.9 Hz, 1H, Ar–H), 7.09 (m, 2H, Ar–H), 6.98 (d, J = 7.1 Hz, 1H,
Ar–H), 6.39 (s, 1H, PhCHOH), 2.74 (s, 6H, NCH3). 13C NMR (75MHz, CDCl3, 293
K) δ, ppm: 153.4, 146.7, 132.4, 132.6, 123.3, 123.2, 123.1, 120.2, 119.0, 116.5, 110.5,
109.8, 64.3, 40.5.
2.4. Synthesis of L4H
The reaction was carried out by a similar procedure as described for L2H, except
that 4.90 mL (41 mmol) of 2-bromobenzaldehyde was used instead of propiophenone.

The product, as yellow solid, was obtained in 80% yield. Anal. Calc. for C15H16BrNO
1
(305.04): C, 58.84; H, 5.27; N, 4.57. Found: C, 58.76; H, 5.31; N, 4.625%. H NMR
(600 MHz, CDCl3, 293 K) δ, ppm: 7.59 (dd, J = 12.8, 4.8 Hz, 2H, Ar–H), 7.38 (t, J =
7.5 Hz, 1H, Ar–H), 7.35–7.31 (m, 1H, Ar–H), 7.31–7.25 (m, 1H, Ar–H), 7.20 (td, J =
7.8, 1.7 Hz, 2H, Ar–H), 7.06–6.96 (m, 1H, Ar–H), 6.64 (s, 1H, PhCHOH), 2.81 (s, 6H,
NCH3). 13C NMR (100 MHz, CDCl3, 293 K) δ, ppm: 152.0, 141.8, 137.3, 132.5,
129.4, 129.0, 128.6, 128.1, 127.8, 125.2, 123.6, 121.1, 73.3, 45.4.
2.5. Synthesis of (L1ZnEt)2 (1)
ZnEt2 (0.8 mL, 0.8 mmol, 1.0 M in hexane) was added to a solution of L1H (0.18 g,
o
0.8 mmol) in toluene (10 mL) at 0 C with stirring. The reaction mixture was gently
heated to 80 oC for 12 hrs. After removal of the solvent, the product was recrystallized
using hexane to give the desired complex as a colorless solid (0.22 g, 88%). Anal.
Calc. for C34H42N2O2Zn2 (638.18): C, 63.66; H, 6.60; N, 4.37. Found: C, 63.61; H,
1
6.57; N, 4.32%. H NMR (300 MHz, C6D6, 293 K) δ, ppm: 7.45 (m, 4H, Ar–H),
7.33–6.98 (m, 14H, Ar–H), 6.17 (s, 2H, PhCHO), 2.29 (s, 12H, NCH3), 1.32 (q, J =
13
6.7 Hz, 6H, CH2CH3), 0.19 (t, J = 6.7 Hz, 4H, CH2CH3). C NMR (75 MHz, CDCl3,
293 K) δ, ppm: 149.8, 147.6, 140.7, 131.8, 127.9, 127.4, 126.5, 125.1, 120.6, 119.4,
80.2, 47.0, 13.0, –3.2.
2.6. Synthesis of (L2ZnEt)2 (2)
The reaction was carried out by a similar procedure as described for 1, except that
0.23 g (0.9 mmol) of L2H was used instead of L1H. The product, as colorless solid,
was obtained in 90% yield. Anal. Calc. for C38H50N2O2Zn2 (694.25): C, 65.43; H,
1
7.22; N, 4.02. Found: C, 65.50; H, 7.25; N, 4.12%. H NMR (400 MHz, CDCl3, 293
K) δ, ppm: 7.52 (m, 4H, Ar–H), 7.47–7.27 (m, 10H, Ar–H), 7.10 (m, 4H, Ar–H), 2.85
(s, 12H, NCH3), 2.23 (m, 6H, CH2CH3),1.37 (m, 4H, ZnCH2CH3), 1.04 (m, 6H,
CH2CH3), 0.21 (m, 4H, ZnCH2CH3). 13C NMR (100 MHz, CDCl3, 293 K) δ, ppm:
150.2, 147.2, 142.8, 128.4, 127.9, 127.5, 126.3, 126.2, 126.1, 125.3, 125.0, 123.2,
77.3, 45.3, 33.4, 13.3, 8.2, –3.2.
2.7. Synthesis of (L3ZnEt)2 (3)
The reaction was carried out by a similar procedure as described for 1, except that

0.24 g (1.0 mmol) of L3H was used instead of L1H. The product, as colorless solid,
was obtained in 87% yield. Anal. Calc. for C34H40F2N2O2Zn2 (674.16): C, 60.28; H,
5.95; N, 4.13. Found: C, 60.31; H, 5.99; N, 4.08%. 1H NMR (300 MHz, C6D6, 293 K)
δ, ppm: 7.78 (m, 2H, Ar–H), 7.49 (m, 4H, Ar–H), 7.13–7.01 (m, 10H, Ar–H), 6.99 (s,
2H, PhCHO), 2.94 (s, 12H, NCH3), 1.39 (t, J = 7.0 Hz, 6H, ZnCH2CH3), 0.22 (q, J =
7.0 Hz, 4H, ZnCH2CH3). 13C NMR (75 MHz, CDCl3, 293 K) δ, ppm: 149.5, 145.7,
138.7, 132.1, 130.0, 129.0, 128.3, 128.0, 127.3, 124.8, 123.4, 118.7, 76.1, 45.9, 13.0,
–3.3.
2.8. Synthesis of (L4ZnEt)2 (4)
The reaction was carried out by a similar procedure as described for 1, except that
0.34 g (1.0 mmol) of L4H was used instead of L1H. The product, as colorless solid,
was obtained in 88% yield. Anal. Calc. for C34H40Br2N2O2Zn2 (794.00): C, 51.09; H,
1
5.04; N, 3.50. Found: C, 51.00; H, 5.07; N, 3.54%. H NMR (400 MHz, CDCl3, 293
K) δ, ppm: 7.63–7.51 (m, 4H, Ar–H), 7.39–7.36 (m, 4H, Ar–H), 7.20–7.13 (m, 4H,
Ar–H), 6.49 (s, 2H, PhCHO), 2.83 (s, 6H, NCH3), 2.81 (s, 6H, NCH3), 1.36 (t, J = 8.1
Hz, 6H, ZnCH2CH3), 0.21 (q, J = 8.1 Hz, 4H, ZnCH2CH3). 13C NMR (100 MHz,
CDCl3, 293 K) δ, ppm: 149.6, 145.8, 138.8, 132.2, 130.1, 129.1, 128.3, 128.1, 127.4,
123.5, 121.1, 118.8, 76.1, 45.3, 13.1, –3.3.
2.9. ROP of L-LA
In a typical polymerization experiment, the zinc complex, the required amount of
L-LA and BnOH in toluene were loaded in a flame-dried vessel containing a magnetic
bar. The vessel was placed in an oil bath. After a certain reaction time, the polymer
was isolated by precipitation with cold methanol. The precipitate was collected and
o
dried under vacuum at 40 C for 24 hrs. For some polymerization reactions, samples
1
were taken to determine the monomer conversion by H NMR spectroscopy during
the reaction.
2.10. X-ray crystallography
Diffraction data of 2 and 3 were collected at 120 K with a Xcalibur, Eos, Gemini
diffractometer equipped with graphite-monochromated Mo-Kα radiation (λ = 0.71073

Å). Using OLEX2 [10], the structures were solved with the SHELXS [11] structure
solution program using direct methods and refined with the SHELXL [11] refinement
package using least squares minimization. Further crystal data details for complexes 2
and 3 are found in Table S1.
3. Results and discussion
3.1. Synthesis and characterization of the zinc complexes
New ligands and Zn complexes 1-4 were synthesized as described in Scheme 1.
The ligands [1-HOC(R1R2)-2-NMe2C6H4 [R1 = H, R2 = Ph (L1H), R1 = Et, R2 = Ph
(L2H), R1 = H, R2 = 2-FPh (L3H), R1 = H, R2 = 2-BrPh (L4H)] were synthesized by
the reaction of 2-NMe2C6H4Li with the corresponding ketone or aldehyde in high
yield (75-89%) [9].
Treatment of L1H–L4H with an equivalent of ZnEt2 in toluene with the release of
ethane gave the zinc complexes ((L1ZnEt)2 (1), (L2ZnEt)2 (2) (L3ZnEt)2 (3) and
(L4ZnEt)2 (4)). When the ligand 1-HOC(Ph)2-2-NMe2C6H4, containing bulky
substituents, was chosen to react with ZnEt2, an unknown complex was obtained. The
complex was insoluble in organic solvents, even in DMSO or DMF. Complexes 1-4
were characterized by 1H and 13C NMR spectra and elemental analysis.
The molecular structures of 2 and 3 were determined by single crystal X-ray
diffraction studies. Crystals of 2 and 3 suitable for the X-ray diffraction studies were
o
obtained from a solution of toluene and n-hexane at 4 C overnight. The molecular
structures of 2 and 3 are illustrated in Figs. 1 and 2, and the crystal data are given in
Table S1. The solid-state structures of 2 and 3 reveal that the Zn centers adopt
four-coordinated distorted tetrahedral geometries. Complexes 2 and 3 exist as dimers
with coordination of the ethyl residue, nitrogen atoms of the ligands and the O atom,
which bridges between the two Zn centers; All complexes are C2 symmetric,
generating a Zn2O2 planar core in the center of each molecule, which have previously
been observed in other zinc compounds that contain, for example, thiolate-oxo [12a],
alkoxide-imino [12b], aryloxide [12c], aminoalcoholate [12d], aminophenoxide [12e]
or pyrazolyl-alkoxide [12f] ligands. The Zn–O distances (1.996(1) and 2.034(1) Å in
2, and 1.999(1) and 1.994(1) Å in 3) are shorter than those of ethylzinc complexes

bearing aminophenoxo ligands [2.055(2)-2.084(2) Å in ref. 12e], but longer than
those of mononuclear zinc complex with two aminophenoxo ligands [1.911(1) and
1.918(1) Å in ref. 12e]. The Zn–N bonds (2.207(2) Å in 2, and 2.174(1) Å in 3) are
comparable with those of dimeric zinc complexes with aminoalcoholate ligands
[ 2.180(9) and 2.185(2) Å in ref. 12d]
3.2. Ring-opening polymerization of L-LA
Complexes 1-4 were examined for the ROP of L-LA under different conditions. As
shown in Table 1, 1-4 showed moderate catalytic activities toward the polymerization,
yielding PLA with broad molecular weight distributions in the absence of BnOH
(Entries 1-4). By contrast, 1-4 were efficient catalysts in the presence of BnOH,
yielding PLA with narrow molecular weight distributions (Entries 5-8). Their
activities are higher than those of the fluorous alkoxide-imino zinc complexes [7a]. 1,
bearing a bulky substituted group bound to the alkoxyl function (R1 = H, R2 = Ph),
has a high catalytic activity for L-LA polymerization. An increase in steric bulk results
in a slight increase of the turnover frequency (TOF) from 1380 h−1 for 1 to 1500 h−1
for 2 (R1 = Et, R2 = Ph). The replacement of the aryl group at the ortho-position with
a halogen atom causes an increase of activity for complexes 3 and 4. The value of the
TOF increases to 2000 and 1880 h−1, respectively. For 1000 equiv. of L-LA ([LA]0 =
0.25 M), in the presence of 1 equiv. of BnOH, the polymerization initiated by
complex 3 proceeded fast to 95% within 5 mins (TOF = 11400 h−1), yielding PLA
with Mn =1.22×105 g mol−1 and a narrow PDI of 1.26 in a controlled fashion (entry
17). Fast polymerization could also be initiated by complexes 1, 2 and 4, when 1000
equiv. of L-LA were used. The different catalytic performances suggest that the
change of substituents influences the polymerization activities, as reported in other
metal catalyst systems [14].
The influences of the Zn/BnOH molar ratio and the reaction temperature on
the polymerization were investigated in detail with complex
3 (Entries 7, 9-11).
Variations of the Zn/BnOH molar ratio affected the polymerization activities,
and the highest polymerization activity was observed at a Zn/BnOH molar ratio

of 1. In general, complex
3 shows remarkably higher catalytic activity at higher
temperature. Meanwhile, a decrease of the reaction temperature to 20 °C
significantly reduces the activity.
To further investigate the performance of complex
3, polymerization
experiments for different times with a monomer/ /BnOH = 300/1/1 system
3
were performed. A linear relationship between the number-averaged molecular
weight (Mn) and the monomer conversion, as shown in Fig. 3, implies the
“living” character of the polymerization process catalyzed by
3/BnOH.
For studying the mechanism of the polymerization, the end group of a typical
1
1
polymer sample was analyzed by its H NMR spectrum (Fig. S1). The H NMR
spectrum shows prominent peaks of the PLA main chain at δ 1.48-1.60 and 5.00-5.25
ppm. Two peaks at δ 5.00-5.25 and 7.31-7.36 ppm were attributed to the benzyl
protons on the benzyloxycarbonyl end. The peak at δ 4.35 ppm was attributed to the
methenyl proton connected to the hydroxyl end. The results demonstrate that the PLA
chain is capped by one benzyl and one hydroxyl end. The ROP of L-LA follows a
coordination insertion mechanism [15].
4. Conclusion
In conclusion, four zinc complexes based on amino-alkoxy ligands are
reported. All of complexes
polymerization of -LA in the presence of BnOH. The polymerization reactions
of -LA catalyzed by these catalyst systems take place in a living fashion with
1-4 are efficient catalysts for the ring-opening
L
L
narrow molecular weight distributions. Overall, those performances compare
well with those of related efficient N,O-bidentate zinc systems [7a].
Acknowledgments
We are grateful for financial support from the National Natural Science Foundation of
China (No. 21104026), China Scholarship Council (No. 2015020000004).
Appendix A. Supplementary data

CCDC 949036 and 949037 contain the supplementary crystallographic data for 2 and 3.
These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge
Crystallographic Data Center, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Reference
[1] (a) G. Swift, Acc. Chem. Res. 26 (1993) 105;
(b) J.J. Marler, J. Upton, R. Langer, J.P. Vacanti, Adv. Drug Delivery Rev. 33 (1998)
165.
[2] (a) J. Wu, T.L. Yu, C.T. Chen, C.C. Lin, Coord. Chem. Rev. 250 (2006) 602;
(b) J.A. Galbis, M.d.G. García-Martín, M.V. de Paz, E. Galbis, Chem. Rev. 116 (2016)
1600;
(c) D.J.A. Cameron, M.P. Shaver, Chem. Soc. Rev. 40 (2011) 1761;
(d) M.K. Kiesewetter, E.J. Shin, J.L. Hedrick, R.M. Waymouth, Macromolecules 43
(2010) 2093;
(e) M.J. Stanford, A.P. Dove, Chem. Soc. Rev. 39 (2010) 486;
(f) Y. Sarazin, J.F. Carpentier, Chem. Rev. 115 (2015) 3564.
[3] (a) M.W. Drover, J.N. Murphy, J.C. Flogeras, C.M. Schneider, L.N. Dawe, F.M.
Kerton, Polyhedron 108 (2016) 50;
(b) H.Y. Chen, L. Mialon, K.A. Abboud, S.A. Miller, Organometallics 31 (2012)
5252;
(c) E. Kober, R. Petrus, P. Kocięcka, Z. Janas, P. Sobota, Polyhedron 85 (2015) 814;
(d) M.W. Drover, J.N. Murphy, J.C. Flogeras, C.M. Schneider, L.N. Dawe, F.M.
Kerton, Polyhedron 102 (2015) 60;
(e) D. Alhashmialameer, N. Ikpo, J. Collins, L.N. Dawe, K, Hattenhauer, F.M. Kerton,
Dalton Trans. 2015, 44 (2015) 20216;
(f) Y. Sun, L. Wang, D. Yu, N. Tang, J. Wu, J. Mol. Catal. A: Chem. 2014, 393 (2014)
175;
(g) B.T. Ko, C.C. Lin, J. Am. Chem. Soc. 123 (2001) 7973;
(h) M.L. Hsueh, B.H. Huang, J. Wu, C.C. Lin, Macromolecules 38 (2005) 9482;

(i) Y. Huang, Y.H Tsai, W.C. Hung, C.S. Lin, W Wang, J.H. Huang, S. Dutta, C.C. Lin,
Inorg. Chem. 49 (2010) 9416;
(j) F.M. García-Valle, R. Estivill, C. Gallegos, T. Cuenca, M.E.G. Mosquera, V.
Tabernero, J. Cano, Organometallics 34 (2015) 477.
[4] (a) N. Nomura, R. Ishii, Y. Yamamoto, T. Kondo, Chem. Eur. J. 13 (2007) 4433;
(b) T.M. Ovitt, G.W. Coates, J. Am. Chem. Soc. 124 (2002) 1316;
(c) N. Spassky, M. Wisniewski, C. Pluta, A. LeBorgne, Macromol. Chem. Phys. 197
(1996) 2627;
(d) N. Nomura, R. Ishii, M. Akakura, K. Aoi, J. Am. Chem. Soc. 124 (2002) 5938;
(e) T.M. Ovitt, G.W. Coates, J. Polym. Sci., Part A: Polym. Chem. 38 (2000) 4686;
(f) P. Hormnirun, E.L. Marshall, V.C. Gibson, A.J. White, D.J. Williams, J. Am. Chem.
Soc. 126 (2004) 2688;
(g) N. Maudoux, T. Roisnel, J.F. Carpentier, Y. Sarazin, Organometallics 33 (2014)
5740;
(h) Z. Zhong, P.J. Dijkstra, J. Feijen, Angew. Chem. Int. Ed. 114 (2002) 4692.
[5] (a) Y. Yang, H. Wang, H. Ma, Polyhedron 117 (2016) 569;
(b) K. Devaine-Pressing, J.H. Lehr, M.E. Pratt, L.N. Dawe, A.A. Sarjeant, C. M.
Kozak, Dalton Trans. 44 (2015) 12365;
(c) M.H. Chisholm, J. Gallucci, K. Phomphrai, Chem. Comm. (2003) 48-49;
(d) J. Wu, B.H. Huang, M.L. Hsueh, S.L. Lai, C.C. Lin, Polymer 46 (2005), 9784;
(e) L. Wang, H. Ma, Macromolecules 43 (2010) 6535;
(f) C.A. Wheaton, P.G. Hayes, B.J. Ireland, Dalton Trans. (2009) 4832;
(g) H.Y. Tang, H.Y. Chen, J.H. Huang, C.C. Lin, Macromolecules 40 (2007), 8855;
(h) M.H. Chisholm, N.W. Eilerts, J.C. Huffman, S.S. Iyer, M. Pacold, K. Phomphrai, J.
Am. Chem. Soc. 122 (2000) 11845;
(i) C.Y. Sung, C.Y. Li, J.K. Su, T.Y. Chen, C.H. Lin, B.T. Ko, Dalton Trans. 41 (2012)
953.
[6] (a) S. Gendler, A.L. Zelikoff, J. Kopilov, I. Goldberg, M. Kol, J. Am. Chem. Soc.
130 (2008) 2144;
(b) Y. Kim, G.K. Jnaneshwara, J.G. Verkade, Inorg. Chem. 42 (2003) 1437;

(c) S. Gendler, S. Segal, I. Goldberg, Z. Goldschmidt, M. Kol, Inorg. Chem. 45 (2006)
4783;
(d) H.C. Tseng, H.Y. Chen, Y.T. Huang, W.Y. Lu, Y.L. Chang, M.Y. Chiang, Y.C. Lai,
H.Y. Chen, Inorg. Chem. 55 (2016) 1642;
[7] (a) E. Grunova, T. Roisnel, J.F. Carpentier, Dalton Trans. (2009) 9010;
(b) X. Yu, C. Zhang, Z.X. Wang, Organometallics 32 (2013) 3262;
(c) H. Wang, Y. Yang, H. Ma, Macromolecules 47 (2014) 7750;
(d) Y. Yang, H. Wang, H. Ma, Inorg. Chem. 54 (2015) 5839;
(e) A. Otero, J. Fernández-Baeza, L.F. Sánchez-Barba, J. Tejeda, M. Honrado, A.
Garcés, A. Lara-Sánchez, A.M. Rodríguez, Organometallics 31 (2012) 4191;
(f) H. Wang, H. Ma, Chem. Commun. 49 (2013) 8686;
(g) M. Huang, C. Pan, H. Ma, Dalton Trans. 44 (2015) 12420;
(h) C. Bakewell, G. Fateh-Iravani, D.W. Beh, D. Myers, S. Tabthong, P. Hormnirun,
A.J.P. White, N. Long, C.K. Williams, Dalton Trans. 44 (2015), 12326;
(i) M. Honrado, A. Otero, J. Fernández-Baeza, L.F. Sánchez-Barba, A. Garcés, A.
Lara-Sáncheza, A.M. Rodrígueza, Dalton Trans. 43 (2014) 17090;
(j) A. Gao, W. Yao, Y. Xiao, M Zhang, G. Zhu, N. Zhang, S. Wang, D. Wang, Y. Zhang,
Y. Gao, Z. Xu, P. Lu, Z. Zhang, Polyhedron 85 (2015) 537;
(k) Y. Han. Q. Feng, Y. Zhang, Y. Zhang, W. Yao, Polyhedron 121 (2017) 206;
(l) K.S. Kwon, S. Nayab, H. Lee, J.H. Jeong, Polyhedron 126 (2017) 127;
(m) F. Drouin, P.O. Oguadinma, T.J.J. Whitehorne, R.E. Prud’homme, F. Schaper,
Organometallics 29 (2010) 2139;
(n) B.M. Chamberlain, M. Cheng, D.R. Moore, T.M. Ovitt, E.B. Lobkovsky, G.W.
Coates, J. Am. Chem. Soc. 123 (2001) 3229;
(o) C.K. Williams, L.E. Breyfogle, S.K. Choi, W. Nam, Jr.V.G. Young, M.A. Hillmyer,
W.B. Tolman, J. Am. Chem. Soc. 125 (2003) 11350;
(p) M. Cheng, A.B. Attygalle, E.B. Lobkovsky, G.W. Coates, J. Am. Chem. Soc. 121
(1999) 11583;
(q) K.S. Kwon, S. Nayab, J. H. Jeong, Polyhedron 85 (2015) 615;
(r) D.J. Darensbourg, O. Karroonnirun, Macromolecules 43 (2010), 8880;

(s) L.R. Collins, L.A. Moffat, M.F. Mahon, M.D. Jones, M.K. Whittlesey, Polyhedron
103 (2016) 121;
(t) E.D. Akpan, S.O. Ojwach, B. Omondi, V.O. Nyamori, Polyhedron 110 (2016) 63;
(u) T. Rosen, Y. Popowski, I. Goldberg, M. Kol, Chem. Eur. J. 22 (2016), 11533;
(v) C. Bakewell, G. Fateh-Iravani, D.W. Beh, D. Myers, S. Tabthong, P. Hormnirun,
C.K. Williams, Dalton Trans. 44 (2015) 12326;
(w) T. Ebrahimi, E. Mamleeva, I. Yu, S.G. Hatzikiriakos, P. Mehrkhodavandi, Inorg.
Chem. 55 (2016) 9445;
(x) Y. Yang, H. Wang, H. Ma, Inorg. Chem. 54 (2015) 5839.
[8] (a) J. Cho, S. Nayab, J.H. Jeong, Polyhedron 113 (2016) 81;
(b) S.H. Ahn, M.K. Chun, E. Kim, J.H. Jeong, S. Nayab, H. Lee, Polyhedron 127
(2017) 51;
(c) H. Ma, J Okuda, Macromolecules 38 (2005) 2665;
(d) W. Gu, P. Xu, Y. Wang, Y. Yao, D. Yuan, Q. Shen, Organometallics 34 (2015)
2907;
(e) H. Ma, T.P. Spaniol, J. Okuda, Inorg. Chem. 47 (2008) 3328;
(f) K.C. Hultzsch, T.P. Spaniol, J. Okuda, Angew. Chem. Int. Ed. 38 (1999) 227;
(g) A. Routaray, S. Mantri, N. Nath, A.K. Sutar, T. Maharana, Polyhedron 119 (2016)
335;
(h) K.S. Kwon, S. Nayab, J.H. Jeong, Polyhedron 130 (2017) 23;
[9] D.J. Peterson, J. Am. Chem. Soc. 93 (1971) 4027.
[10] O.V. Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschmann,
OLEX2. J. Appl. Cryst. 42 (2009) 339.
[11] G.M. Sheldrick, Acta. Cryst. A64 (2008) 112.
[12] (a) T.J. Boyle, H.D. Pratt, T.M. Alam, T. Headley, M.A. Rodriguez, Eur. J. Inorg.
Chem. (2009) 855;
(b) E. Grunova, T. Roisnel, J.-F. Carpentier, Dalton Trans. (2009) 9010;
(c) V. Poirier, T. Roisnel, J.-F. Carpentier, Y. Sarazin, Dalton Trans. (2009) 9820;
(d) A.L. Johnson, N. Hollingsworth, G. Kociok-Köhn, K.C. Molloy, Inorg. Chem. 47
(2008) 12040;

(e) J.D. Farwell, P.B. Hitchcock, M.F. Lappert, G.A. Luinstra, A.V. Protchenko, X.-H.
Wei, J. Organomet. Chem. 693 (2008) 1861;
(f) M. Honrado, A. Otero, J. Fernańdez-Baeza, L.F. Sańchez-Barba, A. Garceś, A.
Lara-Sańchez, A.M. Rodrıǵuez, Organometallics 33 (2014) 1859.
[13] (a) I. Barakat, P. Dubois, R. Jerome, P. Teyssie, J. Polym. Sci. A: Polym. Chem.
31 (1993) 505;
(b) H. Ma, J. Okuda, Macromolecules 38 (2005) 2665.
[14] L. Bourget-Merle, M.F. Lappert, J.R. Severn, Chem. Rev. 102 (2002) 3031.
[15] (a) W. Yao, Y. Mu, A. Gao, W. Gao, L. Ye, Dalton Trans. 24 (2008) 3199;
(b) Y. Zhang, A. Gao, Y. Zhang, Z. Xu, W. Yao, Polyhedron 112 (2016) 27;
(c) Y.H. Tsai, C.H. Lin, C.C. Lin, B.T. Ko, J. Polym. Sci., Part A: Polym. Chem. 47
(2009) 4927;
(d) H.R. Kricheldorf, S.R. Lee, S. Bush, Macromolecules 29 (1996) 1375.

O
N
R2
N
N
R1
R1
Et2O
R2
Et2Zn
n-BuLi
Zn
O
toluene
O
Zn
TMEDA
OH
R1
R1
R2
N
R2
R1 = H, R2 = Ph (1)
R1 = Et, R2 = Ph (2)
R1 = H, R2 = Ph (L1H)
R1 = Et, R2 = Ph (L2H)
R1 = H, R2 = 2-FPh (3)
R1 = H, R2 = 2-BrPh (4)
R1 = H, R2 = 2-FPh (L3H)
R1 = H, R2 = 2-BrPh (L4H)
Scheme 1. Synthesis of complexes 1-4.

Fig. 1. The molecular structure of complex 2. Thermal ellipsoids are shown at the
30% probability level. Hydrogen atoms and solvent molecules are omitted for clarity.
Selected bond lengths (Å) and angles (o): Zn(1)–N(1) 2.207(2), Zn(1)–O(1) 1.996(1),
Zn(1)–C(1) 1.986(2), Zn(1)–O(1A) 2.034(1), N(1)–Zn(1)–O(1) 91.09(6),
O(1)–Zn(1)–O(1A) 84.90(6), C(1)–Zn(1)–O(1) 130.97(7), C(1)–Zn(1)–O(1A)
129.51(8), C(1)–Zn(1)–N(1) 91.09(6), N(1)–Zn(1)–O(1A) 97.59(6).

Fig. 2. The molecular structure of complex 3. Thermal ellipsoids are shown at the
30% probability level. Hydrogen atoms and solvent molecules are omitted for clarity.
Selected bond lengths (Å) and angles (o): Zn(1)–N(1) 2.174(1), Zn(1)–O(1) 1.999(1),
Zn(1)–C(1) 1.976(2), Zn(1)–O(1A) 1.994(1), N(1)–Zn(1)–O(1) 99.52(5),
O(1)–Zn(1)–O(1A) 83.97(5), C(1)–Zn(1)–O(1) 127.27(6), C(1)–Zn(1)–O(1A)
127.62(6), C(1)–Zn(1)–N(1) 119.88(6), N(1)–Zn(1)–O(1A) 87.69(5).

Fig. 3. Linear relationship between Mn and L-LA conversion initiated by 3
([L-LA]0/[3]0/[BnOH]0 = 300/1/1, T = 60 oC, toluene).

Table 1. ROP of L-LA catalyzed by 1-4a.
d
e
Entry
Cat. [LA]0/[Zn]0/[BnOH]0
Time
(min)
30
30
30
30
4
Yield
(%)b
88
T
(oC)
60
60
60
60
60
60
60
60
40
20
60
60
60
60
60
60
60
60
TOFc
Mn.calcd
Mn
PDIe
(×103)
12.9
13.2
13.6
13.3
13.4
14.5
14.5
13.6
14.1
13.5
6.7
(×103)
12.3
12.7
13.1
13.1
13.0
13.1
13.2
12.4
13.4
12.9
6.7
1
100:1:0
100:1:0
100:1:0
100:1:0
100:1:1
100:1:1
100:1:1
100:1:1
100:1:1
100:1:1
100:1:2
150:1:1
200:1:1
250:1:1
1000:1:1
1000:1:1
1000:1:1
1000:1:1
176
180
1.24
1.20
1.25
1.27
1.15
1.14
1.18
1.17
1.10
1.07
1.24
1.15
1.24
1.20
1.18
1.22
1.26
1.24
1
2
3
4
1
2
3
4
3
3
3
3
3
3
1
2
3
4
2
90
3
93
186
4
90
180
5
92
1380
1500
2000
1880
1582
112
6
4
100
100
94
7
3
8
3
9
10
50
12
7
97
10
11
12
13
14
15
16
17
18
93
92
460
96
1234
950
21.7
27.6
34.7
131.0
132.5
136.8
129.6
20.7
26.1
34.0
114.2
118.7
122.4
111.2
12
17
7
95
96
847
91
7800
9200
11400
10800
6
92
5
95
5
90
aPolymerization conditions: catalyst, 30 µmol, [L-LA]0 = 0.25 M in toluene, N2 atmosphere.
bDetermined by 1H NMR spectroscopy.
cMole of LA consumed per mol of catalyst per hour.
d Calculated from ([L-LA]0/[Zn]0) × conversion × 144.13 or ([L-LA]0/[BnOH]0) × conversion × 144.13 + 108.
e Determined by GPC against polystyrene standards in THF, multiplied by 0.58 [13].

A series of new zinc complexes based on amino-alkoxyl ligands have been
synthesized and fully characterized. These zinc complexes show high activities for the
ring-opening polymerization of L-lactide in the presence of benzyl alcohol in a living
fashion.