Comparative study of ring-opening polymerization of L-lactide and ε-caprolactone using zirconium hexadentate bis(aminophenolate) complexes as catalysts

Article abstract of DOI:10.1039/c4ra13236j

A series of zirconium bis(aminophenolate) complexes as catalysts for the ring opening polymerization of l-lactide (LA) and ε-caprolactone (CL) were investigated. Ligands bearing various chelating groups have a profound influence on the catalysis results. Among them, the thiophen-2-yl methyl group showed the greatest activity while the pyridine-2-yl methyl group showed the worst performance with regard to the rate of CL polymerization. However, the trend was reversed for the rate of LA polymerization. The kinetic results indicated a first-order dependency on [CL] and [LA]. However, the order of the catalyst concentration was different. Polymerization proceeded with second-order dependence on [L^OMeZr(OBn)₂] for CL but with first-order dependence on [L^OMeZr(OBn)₂] for LA.

Full text of DOI:10.1039/c4ra13236j

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Comparative study of ring-opening polymerization
of L-lactide and 3-caprolactone using zirconium
hexadentate bis(aminophenolate) complexes as
catalysts†
Cite this: RSC Adv., 2015, 5, 477
Hsiu-Wei Ou,a Michael Y. Chiang,ab Jaya Kishore Vandavasi,a Wei-Yi Lu,a
a
a
a
a
*
Yen-Jen Chen, Hsi-Ching Tseng, Yi-Chun Lai and Hsuan-Ying Chen
A series of zirconium bis(aminophenolate) complexes as catalysts for the ring opening polymerization of
L-lactide (LA) and 3-caprolactone (CL) were investigated. Ligands bearing various chelating groups have a
profound influence on the catalysis results. Among them, the thiophen-2-yl methyl group showed the
greatest activity while the pyridine-2-yl methyl group showed the worst performance with regard to the
rate of CL polymerization. However, the trend was reversed for the rate of LA polymerization. The kinetic
results indicated a first-order dependency on [CL] and [LA]. However, the order of the catalyst
concentration was different. Polymerization proceeded with second-order dependence on
[LOMeZr(OBn)2] for CL but with first-order dependence on [LOMeZr(OBn)2] for LA.
Received 27th October 2014
Accepted 20th November 2014
DOI: 10.1039/c4ra13236j
www.rsc.org/advances
In 2010 and 2012, Sun3e and Okuda3k reported zirconium
complexes with an eight-coordinate metal center that included
Introduction
two tetradentate ligands and two OSSO bis(phenolate) ligands,
respectively, which demonstrated outstanding polymerization
activity for meso-lactide. These ndings inspired us to design a
series LZr(OR)2 complexes bearing hexadentate salan ligands
for catalytic studies. ROP catalysis is favored by reducing the
bond strength of Zr–OR bond which is usually strong due to the
high oxidation state of Zr(IV) ion. Multi-dentate ligands can
donate electrons to metal through coordination, thereby
weakening the metal–alkoxide bond.5 On the other hand,
however, the pendant atoms on the hexadentate ligands is in
direct competition with monomers which may result in a
decreased polymerization rate. The difficulty is in identifying
suitable pendant atoms that are capable of minimizing the
competition with monomers by forming a labile coordination
with Zr center. Herein, we report the syntheses of a series of
hexadentate salan ligands, their associated kinetic studies, and
their applications in ROP catalysis.
Poly(lactide) (PLA), poly(3-caprolactone) (PCL), and their
copolymers are applied in a wide range of elds1 due to their
biodegradability, biocompatibility, and permeability. The most
common method used for the synthesis of PLA and PCL is ring-
opening polymerization (ROP). Most metal complexes2 have
been used as catalysts for the ROP of cycloesters. However, the
use of catalysts of low cytotoxicity is essential for materials
with medicinal applications. Zirconium complexes are also
commonly used as catalysts for ROP due to the inexpensive
precursors and high oxidation state associated with polyanionic
ligands. Fig. 1 presents a series of multi-dentate ligands of
zirconium complexes used for ROP of cycloesters.
Among these, salen,3g salan3c,d and salalen3h,i type (i.e. bis-
(iminophenol)) ligands are the most commonly used due to the
ease of diverse modication on the moiety between the two
nitrogen atoms.4 The previous studies usually involved up to
three or four dentate ligands around the metal. Never has
hexadentate ligand been applied to the synthesis of zirconium
complex.
Results and discussion
Synthesis and characterization of Zr complexes
aDepartment of Medicinal and Applied Chemistry, Kaohsiung Medical University,
Kaohsiung 80708, Taiwan, Republic of China. E-mail: hchen@kmu.edu.tw; Fax: Arylaldehydes and ethyldiamine were condensed to produce
+886-7-3125339; Tel: +886-7-3121101-2585
bDepartment of Chemistry, National Sun Yat-sen University, Kaohsiung, Taiwan,
diimines. Further reduction using NaBH4 followed by reaction
with 2,4-di-tert-butyl-6-(chloromethyl)phenol offered a series of
hexadentate salan ligands. All ligands were reacted with two
equivalents of n-butyllithium in THF to produce a moderate
80424, Republic of China
† Electronic supplementary information (ESI) available: Polymer characterization
data and details of the kinetic study are available. CCDC 1019661, 1019662 and
yield of lithium compounds. These lithium complexes were
then reacted with ZrCl4 to form zirconium dichloride
1019663. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c4ra13236j
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Fig. 1 Multi-dentate ligands applied to the synthesis of zirconium complexes.
complexes. Subsequent reaction with sodium benzyl alkoxide and oxygen of benzyl alkoxide, which can be attributed to
gave zirconium dibenzyl alkoxide complexes (Fig. 2). The reduced bonding distance between the zirconium and oxygen of
structures of the nal complexes were conrmed according to benzyl alkoxide. The X-ray structure of LFZr(OBn)2 (Fig. 4) and
1
their H and 13C NMR spectra, elemental analyses, and X-ray LThZr(OBn)2 (Fig. 5) present a geometry similar to that of
crystallographic analyses. The X-ray structure of LBnZr(OBn)2 LBnZr(OBn)2. In LFZr(OBn)2, the axial angles of O(1)–Zr–O(1A) is
(Fig. 3) reveals that the zirconium complex is neutral, displaying 165.64(15)o and the equatorial angles for N(1)–Zr–N(1A),
two cis benzyl alkoxide and two trans phenolate groups (a-cis O(2)–Zr–N(1), and O(2)–Zr–O(2A) are 72.28(14), 95.88(10), and
form). The axial angle of O(1)–Zr–O(1A) is 165.50(8)ꢀ and the 106.61(16)ꢀ, respectively. The distances between the Zr atom
˚
equatorial angles between N(1)–Zr–N(1A), O(2)–Zr–N(1), and and O(1), O(2), and N(1) are 2.039(2), 1.942(2), and 2.472(3) A,
O(2)–Zr–O(2A) are 71.85(8), 91.87(6), and 105.88(9)ꢀ, respec- respectively, conrming that the structure was distorted from
tively. The distances between the Zr atom and O(1), O(2), and an ideal octahedral geometry. The angles of C(24)–O(2)–Zr is
N(1) are 2.0401(13), 1.9379(15), and 2.4684(17) A, respectively, 168.8(3)ꢀ. In LThZr(OBn)2, the axial angles of O(1)–Zr–O(1A) is
˚
conrming that the structure is distorted from an ideal octa- 164.69(8)ꢀ and the equatorial angles for N(1)–Zr–N(1A), O(2)–Zr–
hedral geometry. Moreover, the angles of C(24)–O(2)–Zr was N(1), and O(2)–Zr–O(2A) are 72.41(8), 91.56(6), and 105.84(9)ꢀ,
168.36(15)ꢀ with a strong p characteristic between zirconium respectively. The distances between the Zr atom and O(1), O(2),
Fig. 2 Synthesis of bis(aminophenol) ligands and their Zr complexes.
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Fig. 3 Molecular structure of complex LBnZr(OBn)2 shown with 20% probability ellipsoids. CCDC deposition number: 1019663 (all of the
hydrogen atoms were omitted for clarity).
Fig. 4 Molecular structure of complex LFZr(OBn)2 shown with 20% probability ellipsoids. CCDC deposition number: 1019661 (all of the
hydrogen atoms were omitted for clarity).
and N(1) are 2.0408(14), 1.9391(14), and 2.4644(17) A, respec- polymerization ([CL]/[Cat.] ¼ 200), LFZr(OBn)2, LThZr(OBn)2,
˚
tively. Finally, the angles for C(22)–O(2)–Zr is 167.71(15)ꢀ.
and LBnZr(OBn)2, (entries 1–3) showed greater activity than
others and LPyZr(OBn)2 (entry 7) was least efficient. Their ability
of polymer control was efficient with a limited polydispersity
index (PDI) (PDI ¼ 1.09–1.21) and anticipated molecular weight
Polymerization of 3-caprolactone and L-lactide
We investigated the polymerizations of 3-caprolactone (CL) and when two benzyl alkoxide were used as initiators. As shown in
L-lactide (LA) using zirconium complexes as initiators in toluene Table 1 (entries 8–14) for LA polymerization ([LA]/[Cat.] ¼ 200),
under nitrogen at 100 ꢀC (Table 1). In Table 1, entries 1–7 for CL LFuZr(OBn)2, LOMeZr(OBn)2, and LPyZr(OBn)2 (entries 8–10)
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Fig. 5 Molecular structure of complex LThZr(OBn)2 shown with 20% probability ellipsoids. CCDC deposition number: 1019662 (all of the
hydrogen atoms were omitted for clarity).
Table 1 Polymerization of CL and LA using each of the Zr complexes as an initiator at 100 ꢀC
b
a
c
Entry
Catalyst LZr(OBn)2
Time (h)
Conva
Mn(Cal)
Mn(NMR)
Mn(GPC)
PDIc
1d
LF
4
4
4
4
4
99%
99%
99%
82%
74%
54%
42%
89%
84%
85%
75%
74%
69%
53%
11 400
10 600
11 400
9500
8500
6300
4900
12 900
9700
9800
9600
11 000
11 800
10 900
11 200
11 200
10 400
6700
12 500
9600
15 400
9800
11 300
11 200
15 600
9300
9100
9000
4900
5200
8000
7300
1.17
1.12
1.18
1.09
1.16
1.21
1.12
1.42
1.02
1.12
1.07
1.03
1.06
1.03
2d
LTh
3d
LFu
4d
LBn
LNMe2
LOMe
LPy
5d
6d
4
4
7d
8e
LFu
48
48
48
48
48
48
48
9e
LOMe
LPy
10e
11e
12e
13e
14e
LNMe2
7500
LF
8500
8000
7700
11 000
8300
8400
12 700
13 000
10 400
LBn
LTh
a
b
Obtained from 1H NMR analysis. Calculated from the molecular weight of monomer ꢁ [monomer]0/2[Cat]0 ꢁ conversion yield + Mw(OBn).
c
Obtained from GPC analysis and calibration based on the polystyrene standard. Values in parentheses are the values obtained from GPC
d
e
times 0.58 for PLA and 0.56 for PCL. Reaction condition: toluene (2 mL), [CL] ¼ 5.0 M, [CL] : [Cat] ¼ 200 : 1. Reaction condition: toluene (2
mL), [LA] ¼ 5.0 M, [LA] : [Cat] ¼ 200 : 1.
showed the greater activity and LThZr(OBn)2 (entry 14) was the
To elucidate the catalytic behavior of these zirconium
least active catalyst. The Mn(NMR) of PLA catalyzed using complexes involved in the polymerization of CL and LA, we
LFuZr(OBn)2, LPyZr(OBn)2, and LBnZr(OBn)2 was inconsistent conducted kinetic studies to determine the kobs (Table 2, Fig. S1
with Mn(GPC), perhaps due to the fact that transesterication and S2, and Tables S1 andS2†). In Table 2, the trend of the
was initiated by the catalysts for LA polymerization. activity of zirconium complexes with regard to polymerization
Moreover, these Zr complexes appeared more active in the in CDCl3 are similar to the trends observed in the polymeriza-
polymerization of CL than in the polymerization of LA. This tion activity in Table 1. However, the zirconium complexes used
trend is opposite to that of our previous ndings related to Ti for polymerization in CL and LA presented precisely the oppo-
complexes.4
site results. For example, the order of CL polymerization is
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Table 2 Kinetic study of polymerization of 3-caprolactone and L-
lactide using each of the Zr complexes as an initiator in a sealed NMR
tube in CDCl3
LA polymerization, this would imply the mononuclear form
of LOMeZr(OBn)2. In addition, CL and LA polymerizations
using zirconium complexes as catalysts requires no induc-
tion period, unlike the previously reported case with titanium
complexes.4 One reason for this may be that the zirconium
complexes with a six-coordinate metal center do not have to
transform into other species in order to be coordinated with
CL or LA since the maximum coordination number of Zr ion
is eight.
CDCl3
Catalyst LZr(OBn)2
CL
LA
Entry
kobs
Ranking kobs
Ranking
LTh
0.1162 (35)
0.0989 (67)
0.0916 (73)
0.0662 (18)
0.0424 (16)
0.0282 (10)
0.0202 (3)
1
2
3
4
5
6
7
0.0265 (12)
7
6
3
5
4
2
1
LF
0.0281 (17)
0.3238 (153)
0.0297 (15)
0.0337 (15)
0.3264 (85)
1.1741 (363)
LFu
LBn
LNMe2
LOMe
LPy
Conclusions
This study synthesized a series of zirconium complexes
bearing salan ligands to catalyze the polymerization of CL
and LA. The polymerization rate of CL and LA showed
opposing trends, according to the pendent group. Among the
zirconium complexes, the thiophen-2-yl methyl group was
most effective in enhancing the polymerization rate of CL,
whereas the pyridine-2-ylmethyl group was most effective in
polymerization of LA. Kinetic studies indicated a rst-order
dependency on [CL] and [LA] respectively. Polymerization
proceeded with second-order dependence on [LOMeZr(OBn)2]
for CL but with rst-order dependence on [LOMeZr(OBn)2] for
LA. These results revealed that the chelating groups inu-
enced the polymerization activity of zirconium complexes.
However, the effect of chelation differ between CL and LA
polymerization.
LThZr(OBn)2 > LFZr(OBn)2 S LFuZr(OBn)2 > LBnZr(OBn)2
>
LNMe2Zr(OBn)2 > LOMeZr(OBn)2 S LPyZr(OBn)2, whereas the
order of LA polymerization is LPyZr(OBn)2 > LOMeZr(OBn)2
LFuZr(OBn)2 > LNMe2Zr(OBn)2 > LBnZr(OBn)2 > LFZr(OBn)2
>
>
LThZr(OBn)2. The differences between CL and LA are that the
size of LA exceeds that of CL and the dipole moment of CL
exceeds that of LA. Nevertheless it is difficult to explain the
results according to these properties of CL and LA.
Kinetic study of the polymerization of CL and LA catalyzed
using LOMeZr(OBn)2
To rationalize our results related to the catalytic activity of these
zirconium complexes in the polymerization of CL and LA, we
conducted kinetic studies to establish the reaction order for
monomer and catalysts. The experiments were performed using
a ratio of [M]0/[LOMeZr(OBn)2] ([CL] ¼ 0.2 M in 5 mL CH2Cl2 at
room temperature and [LA] ¼ 1.25 M in 1 mL CDCl3 at 100 ꢀC)
as shown in Tables S5, S6 and Fig. S5–S8.† Preliminary results
indicate a rst-order dependency on monomer ([CL] or [LA])
(Fig. S5 and S7†). By plotting ln kobs vs. ln [LOMeZr(OBn)2], we
obtained an order of 2.17 for [LOMeZr(OBn)2], kp (propagation)
values of 0.0015 for CL polymerization (Fig. S6†). By plotting
kobs vs. [LOMeZr(OBn)2] under the assumption that the order of
[LOMeZr(OBn)2] was 1, we obtained kp values of 1.6632 for LA
polymerization (Fig. S6†). The polymerization of CL and LA
using LOMeZr(OBn)2 demonstrated the following rate law:
Experimental section
Standard Schlenk techniques and a N2-lled glovebox were
used throughout the isolation and treatment of all
compounds. Solvents, 3-caprolactone, L-lactide, and deuter-
ated solvents were puried prior to use. 2,4-Di-tert-butyl-
phenol, sodium borohydride, formaldehyde (37 wt% sol. in
water), triethylamine, thionyl chloride, ethylenediamine
anhydrous, benzaldehyde, picolinaldehyde, 2-methoxy-
benzaldehyde, 2-uorobenzaldehyde, thiophene-2-carbal-
dehyde, furan-2-carbaldehyde, titanium(IV) isopropoxide,
sodium hydride, deuterated chloroform, L-lactide, and
3-caprolactone were purchased from Acros. Benzyl alcohol
was purchased from Alfa. 1H and 13C NMR spectra were
1
recorded on a Varian Gemini2000-200 (200 MHz for H and
d[CL]/dt ¼ 0.0015 ꢁ [LOMeZr(OiPr)2]2.17[CL]1
d[LA]/dt ¼ 1.6632 ꢁ [LOMeZr(OiPr)2]1[LA]1
50 MHz for 13C) spectrometer with chemical shis given in
ppm from the internal TMS or center line of CDCl3. Micro-
analyses were performed using a Heraeus CHN-O-RAPID
instrument. GPC measurements were performed on a Jasco
Formulating an appropriate mechanism to explain the PU-2080 PLUS HPLC pump system equipped with a differ-
polymerization of CL and LA in accordance with the above ential Jasco RI-2031 PLUS refractive index detector using THF
kinetic data was challenging. It was necessary to rationalize (HPLC grade) as an eluent (ow rate 1.0 mL minꢂ1, at 40 ꢀC).
˚
the mechanism on the basis of the results observed during The chromatographic column was JORDI Gel DVB 103 A, and
the catalytic activity of zirconium complexes in the poly- the calibration curve was made by primary polystyrene
merization of CL and LA. The order of [LOMeZr(OBn)2] is 2.17 standards to calculate Mn(GPC). 2,4-Di-tert-butyl-6-(chloro-
for CL and 1 for LA. Therefore, one possible mechanism methyl)phenol,6 LBn-H2,4 LOMe-H2, LF-H2, LFu-H2, LTh-H2, and
underlying CL polymerization would entail dinucleon8 from 2-(dimethylamino)benzaldehyde7 were prepared following
LOMeZr(OBn)2 aggregation acting as the real active species. In literature procedures.
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Synthesis of N,N0-bis(2-dimethylaminobenzyl)-N,N0-bis[(3,5-
di-tert-butyl-2-hydroxyphenyl)-methylene]-1,2-diaminoethane
(LNMe2-H2)
(2.29 g 10 mmol) dissolved in THF (40 mL) was added. Aer
stirring for one day, the mixture was reacted with sodium benzyl
alkoxide that was synthesized from sodium hydride (0.48 g, 20
mmol) and benzyl alcohol (2.16 g, 20 mmol) for another day.
Volatile materials were removed under vacuum again and
toluene (20 mL) was added to form a suspension. The sodium
and lithium salts were removed by ltration and yellow powder
was obtained under vacuum. It was washed with hexane (30 mL)
to afford nal product as light yellow powder. Yield: 6.17 g
A mixture of ethylenediamine (6.01 g, 100 mmol) and 2-(dimethyl-
amino)benzaldehyde (24.80 g, 200 mmol) was reuxed for one
day in ethanol (150 mL). The reaction solution was cooled down
in ice bath and sodium borohydride (7.57 g, 200 mmol) was
transferred to the solution slowly. Aer 1 h, the solution was
reuxed again for a day. Volatile materials were removed under
vacuum to yield yellow oil. The oil was dissolved in CH2Cl2
(200 mL) and the solution was washed with water (2/200 mL).
Aer solvent removal under reduced pressure, white powder
was obtained. The white powder was set with 2,4-di-tert-butyl-6-
(chloromethyl)phenol (53.55 g, 210 mmol) and NEt3 (28 mL, 200
mmol) in 400 mL ethanol and reuxed for one month. Volatile
materials were removed under vacuum to yield yellow oil. The
oil was dissolved in CH2Cl2 (200 mL) and the solution was
washed with water (2/200 mL) and several drops of HCl (37%).
The yellow oil was obtained when CH2Cl2 was removed and
ethanol (250 mL) was added to dissolve the oil. The white
powder was obtained and ltered aer 10 day at ꢂ20 ꢀC. Yield:
48.84 g (64%). 1H NMR (CDCl3, 200 MHz): d 10.84 (2H, s, ArOH),
7.23–6.78 (12H, m, ArH), 3.60 (4H, s, NCH2PhN(CH3)2), 3.59 (4H,
s, NCH2Ar), 2.63 (4H, s, NCH2CH2N), 2.50 (12H, PhN(CH3)2),
1.39 (18H, s, ArC(CH3)3), 1.24 (18H, s, ArC(CH3)3). 13C NMR
(CDCl3, 50 MHz): d 154.08, 153.58, 140.18, 135.36, 131.77,
130.91, 128.17, 123.50, 123.48, 122.68, 121.41, 119.57 (Ar), 58.98
(NCH2PhN(CH3)2), 53.74 (NCH2Ar), 50.32 (NCH2CH2N), 45.16
(PhN(CH3)2), 34.81 (ArC(CH3)3), 34.06 (ArC(CH3)3), 31.70
1
(63%). H NMR (CDCl3, 200 MHz): d 7.44–6.01 (24H, m, ArH),
5.29 (4H, s, OCH2Ph), 4.22 (2H, dd, J ¼ 14.2 Hz, NCH2Ph), 4.06
(2H, dd, J ¼ 13.4 Hz, NCH2Ar), 4.22 (2H, dd, J ¼ 14.2 Hz,
NCH2Ph), 3.91 (2H, dd, J ¼ 14.2 Hz, NCH2Ph), 3.32 (2H, dd, J ¼
13.4 Hz, NCH2Ar), 2.70 (2H, dd, J ¼ 9.8 Hz, NCH2CH2N), 2.38
(2H, dd, J ¼ 9.8 Hz, NCH2CH2N), 1.50 (18H, s, ArC(CH3)3), 1.26
(18H, s, ArC(CH3)3). 13C NMR (CDCl3, 50 MHz): d 158.04, 143.80,
138.89, 136.59, 132.35, 131.40, 128.17, 127.97, 126.44, 126.34,
126.22, 124.71, 124.05, 123.42 (Ar), 72.25 (OCH2Ph), 59.13
(NCH2Ar), 58.33 (NCH2Ph), 45.93 (NCH2CH2N), 35.19
(ArC(CH3)3), 34.13 (ArC(CH3)3), 31.79 (ArC(CH3)3), 30.13
(ArC(CH3)3). Elemental analysis (C61H79N2O4Zr) found: N,
2.87%; C, 73.58%; H, 8.05%. Anal. calcd: N, 2.86%; C, 73.50%;
ꢀ
H, 7.81%. Mp: 224 C.
Synthesis of LOMeZr(OBn)2
Synthetic procedures were similar to that for LBnZr(OBn)2 except
LOMe-H2 was used in place of LBn-H2. Yield: 8.84 g (85%). 1H
NMR (CDCl3, 200 MHz): d 7.47–6.62 (22H, m, ArH), 5.34 (4H, s,
OCH2Ph), 4.45 (2H, dd, J ¼ 13.8 Hz, NCH2PhOMe), 4.27 (2H, dd,
J ¼ 13.0 Hz, NCH2Ar), 3.97 (2H, dd, J ¼ 13.8 Hz, NCH2PhOMe),
3.39 (2H, dd, J ¼ 13.0 Hz, NCH2Ar), 3.22 (6H, s, NCH2PhOCH3),
3.15 (2H, dd, J ¼ 9.2 Hz, NCH2CH2N), 1.96 (2H, dd, J ¼ 9.2 Hz,
NCH2CH2N), 1.48 (18H, s, ArC(CH3)3), 1.22 (18H, s, ArC(CH3)3).
13C NMR (CDCl3, 50 MHz): d 189.86, 159.36, 157.96, 144.21,
138.34, 136.61, 134.85, 129.72, 127.86, 126.19, 125.98, 124.65,
123.95, 123.65, 120.77, 120.36, 120.25, 111.46 (Ar), 71.96
(OCH2Ph), 59.35 (NCH2PhOMe), 55.32 (OCH3), 51.43 (NCH2-
PhOMe), 45.22 (NCH2CH2N), 35.13 (ArC(CH3)3), 34.08
(ArC(CH3)3), 31.84 (ArC(CH3)3), 30.10 (ArC(CH3)3). Elemental
analysis (C63H83N2O6Zr) found: N, 2.95%; C, 72.03%; H, 7.80%.
(ArC(CH3)3),
29.55
(ArC(CH3)3).
Elemental
analysis
(C50H74N4O2) found: N, 7.55%; C, 78.39%; H, 9.44%. Anal.
calcd: N, 7.34%; C, 78.69%; H, 9.77%. ESI-MS(+) m/z calcd ¼
763.15. Found: 763.49.
Synthesis of N,N0-bis(pyridin-2-methylbenzyl)-N,N0-bis[(3,5-di-
tert-butyl-2-hydroxyphenyl)-methylene]-1,2-diaminoethane
(LPy-H2)
Synthetic procedures were similar to that of LNMe2-H2 except
pyridine-2-methylbenzaldehyde was used in place of 2-(dime-
thylamino)benzaldehyde. 1H NMR (CDCl3, 200 MHz): d 10.46
(2H, s, ArOH), 8.50 (2H, d, J ¼ 4.8 Hz, PyrH), 7.59–6.79 (10H, m,
ArH, PyrH), 3.70 (8H, s, NCH2Pyr), 3.59 (4H, s, NCH2Ar), 2.81
(4H, s, NCH2CH2N), 1.39 (18H, s, ArC(CH3)3), 1.25 (18H, s,
ArC(CH3)3). 13C NMR (CDCl3, 50 MHz): d 157.47, 153.82, 149.01,
140.53, 136.52, 135.60, 123.92, 123.62, 122.98, 122.26, 121.17
(Ar), 59.43 (NCH2Pyr), 59.01 (NCH2Ar), 50.47 (NCH2CH2N),
34.85 (ArC(CH3)3), 34.09 (ArC(CH3)3), 31.67 (ArC(CH3)3), 29.56
(ArC(CH3)3). Elemental analysis (C44H62N4O2) found: N, 3.21%;
C, 77.59%; H, 9.29%. Anal. calcd: N, 8.25%; C, 77.83%; H,
9.20%. ESI-MS(+) m/z calcd ¼ 678.49. Found: 679.31.
ꢀ
Anal. calcd: N, 2.69%; C, 71.57%; H, 7.75%. Mp: 207 C.
Synthesis of LFZr(OBn)2
Synthetic procedures were similar to that for LBnZr(OBn)2 except
LF-H2 was used in place of LBn-H2. Yield: 7.01 g (69%). 1H NMR
(CDCl3, 200 MHz): d 7.43–6.60 (22H, m, ArH), 5.31 (4H, s,
OCH2Ph), 4.31 (2H, dd, J ¼ 10.0 Hz, OCH2PhF), 4.21 (2H, dd, J ¼
13.0 Hz, NCH2Ar), 4.15 (2H, dd, J ¼ 10.0 Hz, NCH2PhF), 3.22
(2H, dd, J ¼ 13.0 Hz, NCH2Ar), 2.96 (2H, dd, J ¼ 10.6 Hz,
NCH2CH2N), 2.24 (2H, dd, J ¼ 10.6 Hz, NCH2CH2N), 1.50 (18H,
s, ArC(CH3)3), 1.24 (18H, s, ArC(CH3)3). 13C NMR (CDCl3, 50
MHz): d 157.68, 143.79, 138.90, 136.90, 136.45, 134.84, 130.56,
130.39, 127.92, 126.34, 126.16, 124.78, 123.91, 123.15, 118.95,
Synthesis of LBnZr(OBn)2
A mixture of LBn-H2 (6.77 g, 10 mmol) and n-butyllithium (8.00 118.60, 116.90, 115.63 (Ar), 72.21 (OCH2Ph), 59.27 (NCH2PhF),
mL, 2.5 M) in THF (40 mL) was stirred for 3 h. Volatile materials 51.20 (NCH2PhF), 45.73 (NCH2CH2N), 35.11 (ArC(CH3)3), 34.08
were removed under vacuum and then zirconium(IV) chloride (ArC(CH3)3), 31.73 (ArC(CH3)3), 30.09 (ArC(CH3)3). Elemental
482 | RSC Adv., 2015, 5, 477–484
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Synthesis of LFuZr(OBn)2
analysis (C61H77N2F2O4Zr) found: N, 2.60%; C, 71.13%; H,
7.35%. Anal. calcd: N, 2.76%; C, 70.90%; H, 7.34%. Mp: 218 ꢀC.
Synthetic procedures were similar to that for LBnZr(OBn)2 except
except LFu-H2 was used in place of LBn-H2. Yield: 3.45 g (36%).
1H NMR (CDCl3, 200 MHz): d 7.37–7.14 (14H, m, ArH), 6.70,
6.32, 6.03 (6H, m, FuH), 5.20 (4H, s, OCH2Ph), 4.26 (2H, dd, J ¼
15.8 Hz, NCH2Fu), 4.06 (2H, dd, J ¼ 13.2 Hz, NCH2Ar), 4.00 (2H,
dd, J ¼ 15.8 Hz, NCH2Fu), 3.45 (2H, dd, J ¼ 13.2 Hz, NCH2Ar),
2.84 (2H, dd, J ¼ 10.2 Hz, NCH2CH2N), 2.45 (2H, dd, J ¼ 10.2 Hz,
NCH2CH2N), 1.50 (18H, s, ArC(CH3)3), 1.29 (18H, s, ArC(CH3)3).
13C NMR (CDCl3, 50 MHz): d 157.85, 148.18, 143.60, 143.29,
138.90, 136.52, 127.92, 126.30, 126.17, 124.88, 123.94, 123.15,
112.71, 110.32 (Ar, Ph, Furan), 72.13 (OCH2Ph), 59.37 (NCH2-
Furan), 50.24 (NCH2 Ar), 46.81 (NCH2CH2N), 35.14 (ArC(CH3)3),
34.13 (ArC(CH3)3), 31.79 (ArC(CH3)3), 30.06 (ArC(CH3)3).
Elemental analysis (C57H75N2O6Zr) found: 2.76%; C, 69.91%; H,
7.74%. Anal. calcd: N, 2.92%; C, 70.03%; H, 7.56%. Mp: 122 ꢀC.
Synthesis of LNMe2Zr(OBn)2
Synthetic procedures were similar to that for LBnZr(OBn)2 except
1
LNMe2-H2 was used in place of LBn-H2. Yield: 8.74 g (82%). H
NMR (CDCl3, 400 MHz): d 7.48–6.58 (22H, m, ArH), 5.36 (4H, s,
OCH2Ph), 4.52 (2H, dd, J ¼ 14.0 Hz, NCH2PhNMe2), 4.22 (2H,
dd, J ¼ 12.8 Hz, NCH2Ar), 3.97 (2H, dd, J ¼ 14.0 Hz, NCH2-
PhNMe2), 3.39 (2H, dd, J ¼ 12.8 Hz, NCH2Ar), 3.15 (2H, dd, J ¼
9.2 Hz, NCH2CH2N), 1.98 (12H, s, NCH2PhN(CH3)2), 1.96 (2H,
dd, J ¼ 9.2 Hz, NCH2CH2N), 1.48 (18H, s, ArC(CH3)3), 1.22 (18H,
s, ArC(CH3)3). 13C NMR (CDCl3, 50 MHz): d 157.94, 155.74,
144.22, 138.53, 136.40, 135.29, 129.40, 127.87, 127.20, 126.21,
126.07, 126.03, 124.94, 124.24, 123.65, 123.59, 120.93 (Ar, Ph),
71.99 (OCH2Ph), 58.95 (NCH2 BnN(CH3)2), 52.25 (NCH2 Ar),
44.78 (NCH2CH2N), 44.46 (BnN(CH3)2),35.16 (ArC(CH3)3), 34.07
(ArC(CH3)3), 31.82 (ArC(CH3)3), 30.08 (ArC(CH3)3). Elemental
analysis (C65H89N4O4Zr) found: N, 3.57%; C, 72.27%; H, 7.84%.
General procedures for the polymerization of CL
A typical polymerization procedure was exemplied by the
synthesis of entry 6 (Table 1) using complex LOMeZr(OBn)2 as a
catalyst. The polymerization conversion was analyzed by 1H
NMR spectroscopic studies. Toluene (2.0 mL) was added to a
mixture of complex LOMeZr(OBn)2 (0.05 mmol) and 3-capro-
lactone (1.14 g, 10 mmol) at 100 ꢀC. Aer the solution was
stirred for 4 h, the reaction was quenched by adding a drop of
ethanol. Then the polymer was precipitated as white solid by
pouring into n-hexane (30.0 mL). The white solid was redis-
solved in CH2Cl2 (5.0 mL) and then n-hexane (70.0 mL) added to
give white crystalline solid. Yield: 0.62 g (54%).
ꢀ
Anal. calcd: N, 5.25%; C, 72.07%; H, 8.13%. Mp: 178 C.
Synthesis of LPyZr(OBn)2
Synthetic procedures were similar to that for LBnZr(OBn)2 except
LPy-H2 was used in place of LBn-H2. Yield: 7.27 g (74%). 1H NMR
(CDCl3, 400 MHz): d 9.03 (PyrH), 7.60–6.60 (20H, m, ArH), 5.46
(4H, d, J ¼ 4 Hz, OCH2Ph), 4.61 (2H, dd, J ¼ 14.8 Hz, NCH2Py),
4.38 (2H, dd, J ¼ 13.2 Hz, NCH2Ar), 3.57 (2H, dd, J ¼ 14.8 Hz,
NCH2Py), 3.43 (2H, dd, J ¼ 13.2 Hz, NCH2Ar), 3.11 (2H, dd, J ¼
13.2 Hz, NCH2CH2N), 2.40 (2H, dd, J ¼ 13.2 Hz, NCH2CH2N),
1.29 (18H, s, ArC(CH3)3), 1.24 (18H, s, ArC(CH3)3). 13C NMR
(CDCl3, 100 MHz): d 156.57, 150.54, 145.58, 138.48, 137.10,
136.80, 127.63, 127.60, 126.34, 126.23, 126.13, 125.51, 125.45,
124.74, 123.83, 123.25, 122.43 (Ar, Pyr), 71.18 (OCH2Ph), 59.85
(NCH2Pyr), 50.29 (NCH2Ar), 48.24 (NCH2CH2N), 34.80
(ArC(CH3)3), 34.02 (ArC(CH3)3), 30.52 (ArC(CH3)3), 29.81
(ArC(CH3)3). Elemental analysis (C59H77N4O4Zr) found: 5.60%;
C, 69.60%; H, 8.03%. Anal. calcd: N, 5.70%; C, 70.91%; H,
Acknowledgements
This study is supported by Kaohsiung Medical University “Aim
for the top 500 universities grant” under Grant no. KMU-
DT103007, NSYSU-KMU JOINT RESEARCH PROJECT (NSYSU
KMU 103-I004), and the Ministry of Science and Technology
(Grant NSC 101-2113-M-037 -009). We thank Center for
Research Resources and Development at Kaohsiung Medical
University for the instrumentation and equipment support.
ꢀ
7.59%. Mp: 168 C.
Synthesis of LThZr(OBn)2
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484 | RSC Adv., 2015, 5, 477–484
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