Synthesis and structure of amine-bridged bis(phenolate) lanthanide complexes and their application in the polymerization of ε-caprolactone

Article abstract of DOI:10.1016/j.jorganchem.2013.10.031

A series of lanthanide complexes 1-8 were afforded by the amine elimination reactions of amine-bridged bis(phenols) H₂L_1-3 [L _1-3 = Et₂NCH₂CH₂N{CH ₂-(2-O-C₆H₂-R₂-3-R ₁-5)₂, R₁ = ^tBu, R₂ = ^tBu (L₁); R₁ = Me, R₂ = ^tBu (L₂); R₁ = Me, R₂ = Me (L ₃)] and H₂L_4-6 [L_4-6 = CH ₃CH₂CH₂N{CH₂-(2-O-C ₆H₂-R₂-3-R₁-5)}₂, R ₁ = ^tBu, R₂ = ^tBu (L₄); R₁ = Me, R₂ = ^tBu (L₅); R ₁ = Me, R₂ = Me (L₆)] with Ln[N(SiMe ₃)₂]₃ (Ln = La, Gd). The bis(phenolate) lanthanide amides L_1-6La[N(SiMe₃)₂] (1-6) were given by the reactions of La[N(SiMe₃)₂]₃ with H₂L_1-6 in 1:1 M ration in THF. The bis(phenolate) lanthanide complexes Ln₂[L₆]₃ (Ln = La (7), Ln = Gd (8)) were given by the reactions of Ln[N(SiMe₃) ₂]₃(Ln = La, Ga) with H₂L₆ in 2:3 M ratio in THF. Complexes 3 and 8 have been characterized by X-ray crystal structural analysis. The structure of complexes 3 reveals that it has unsolvated centrosymmetric dimer, built around a central, planar La₂O ₂ ring. Complex 8 possesses a THF-solvated unsymmetric dimer. The coordination geometry in complexes 3 and 8 around each of the lanthanide metal atoms can be described as a distorted octahedron. The catalytic properties of complexes 1-6 on the ring-opening polymerization of ε-caprolactone have been studied. The results show that lanthanide amides complexes 1-6 are efficient catalysts for the ring-opening polymerization of ε-caprolactone.

Full text of DOI:10.1016/j.jorganchem.2013.10.031

Journal of Organometallic Chemistry 749 (2014) 356e363
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and structure of amine-bridged bis(phenolate) lanthanide
complexes and their application in the polymerization of
ε-caprolactone
,
a
a
a
Le-Qing Deng a, Yan-Xu Zhou a, Xian Tao b , Yu-Long Wang , Qing-Song Hu , Pan Jin ,
**
,
Ying-Zhong Shen a
*
a Applied Chemistry Department, School of Material Science & Engineering, Nanjing University of Aeronautics & Astronautics, Nanjing 210016, PR China
b Jiangsu MO Opto-Electronic Material Co., Ltd., Tonggang Road 7, Zhenjiang New District, Zhenjiang 212132, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of lanthanide complexes 1e8 were afforded by the amine elimination reactions of amine-
bridged bis(phenols) H2L1e3 [L1e3 ¼ Et2NCH2CH2N{CH2e(2-OeC6H2eR2-3eR1-5)2, R1
¼
tBu, R2
¼
tBu
Received 25 September 2013
Received in revised form
15 October 2013
(L1); R1 ¼ Me, R2 ¼ tBu (L2); R1 ¼ Me, R2 ¼ Me (L3)] and H2L4e6 [L4e6 ¼ CH3CH2CH2N{CH2e(2-OeC6H2
eR2-3eR1-5)}2, R1
¼
tBu, R2
¼
tBu (L4); R1 ¼ Me, R2
¼
tBu (L5); R1 ¼ Me, R2 ¼ Me (L6)] with Ln
Accepted 18 October 2013
[N(SiMe3)2]3 (Ln ¼ La, Gd). The bis(phenolate) lanthanide amides L1e6La[N(SiMe3)2] (1e6) were given by
the reactions of La[N(SiMe3)2]3 with H2L1e6 in 1:1 M ration in THF. The bis(phenolate) lanthanide
complexes Ln2[L6]3 (Ln ¼ La (7), Ln ¼ Gd (8)) were given by the reactions of Ln[N(SiMe3)2]3(Ln ¼ La, Ga)
with H2L6 in 2:3 M ratio in THF. Complexes 3 and 8 have been characterized by X-ray crystal structural
analysis. The structure of complexes 3 reveals that it has unsolvated centrosymmetric dimer, built around
a central, planar La2O2 ring. Complex 8 possesses a THF-solvated unsymmetric dimer. The coordination
geometry in complexes 3 and 8 around each of the lanthanide metal atoms can be described as a dis-
torted octahedron. The catalytic properties of complexes 1e6 on the ring-opening polymerization of
ε-caprolactone have been studied. The results show that lanthanide amides complexes 1e6 are efficient
catalysts for the ring-opening polymerization of ε-caprolactone.
Keywords:
Structure
Amine-bridged bis(phenolate) lanthanide
complexes
Polymerization
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
lactones [19,20]. In the literature, they paid attention to the tetra-
dentate amine-bis(phenolate) ligands: a type of [ONXO]2ꢀ (X ¼ N, O).
Aliphatic polyesters are an important class of polymers because
of their biodegradability, biocompatibility and permeability [1,2].
Organometallic catalytic polymerization reactions have commonly
been employed in the preparation of polylactide and polylactones
[3]. Numerous of catalysts like alkali metals [4], alkaline earth metals
[5e7], transition metals [8e11], and rare earth metals [12e16] have
been explored for the ring-opening polymerization (ROP) of lac-
tones. Among them, organolanthanide catalysts have got a great
interest due to their high activities and capabilities of preparing
polymers with high molecular weights in narrow polydispersity.
Amine-bridged bis(phenolate) lanthanide derivatives showed
high activity for the polymerization of cyclic esters. Shen and co-
workers have demonstrated that bridged bis(phenolate) lanthanide
amides can serve as catalysts for the ROP of lactide [17,18] and
In order to generate more reactive catalysts, yet still maintain
the robust nature of the catalyst precursor, we turned our attention
to related amine-bis(phenolate) ligands: three tetra-dentate
H2[ONNO] ligands H2L1eH2L3 and three tridentate H2[ONO] li-
gands H2L4eH2L6. Herein, we report the synthesis and structure of
a series of lanthanide complexes (1e8) supported by amine-
bridged bis(phenolate) ligands via the convenient protonolysis re-
action. The catalytic properties of the complexes (1e6) have also
been studied in the polymerization of ε-caprolactone under mild
conditions. Compounds were fully characterized by nuclear mag-
netic resonance (NMR) spectroscopy, elemental analysis (EA), and
X-ray single crystal diffraction analysis.
2. Experimental
2.1. General procedures
* Corresponding author. Tel.: þ86 25 52112906x84765; fax: þ86 25 52112626.
** Corresponding author. Tel.: þ86 511 85575222; fax: þ86 511 85575111.
E-mail addresses: 18651656012@163.com (X. Tao), yz_shen@nuaa.edu.cn
(Y.-Z. Shen).
The complexes described below are sensitive to air and mois-
ture. Therefore, all manipulations were performed under pure
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.10.031

L.-Q. Deng et al. / Journal of Organometallic Chemistry 749 (2014) 356e363
357
nitrogen with rigorous exclusion of air and moisture using Schlenk
techniques and glovebox. THF, toluene, and hexane were distilled
from sodium benzophenone ketyl before use. HN(TMS)2, ε-Capro-
lactone, and nBuLi are commercially available. HN(TMS)2 and
ε-Caprolactone was dried over CaH2 for 3 days and distilled before
use. The starting complexes La[N(TMS)2]3/Gd[N(TMS)2]3 [21] and
H2L1wH2L6 [22] were synthesized according to published methods.
Lanthanide analyses were performed by EDTA titration with a
xylenol orange indicator and hexamine buffer. Elemental analysis
was performed on a PerkineElmer 240C elemental analyzer. NMR
spectra were recorded on a Bruker Advance 400 spectrometer at
resonant frequencies of 400 MHz for 1H and 101 MHz for 13C nuclei
using C6D6 or d6-DMSO as the solvent. Melting points were
observed in sealed capillaries and were uncorrected. The weight
average molecular weight (Mw) and the number average molecular
weight (Mn) were determined by GPC on a Water GPC system
equipped with four Waters Ultrastyragel columns (300 ꢁ 7.5 mm,
guarded and packed with 1 ꢁ105,1 ꢁ104, 1 ꢁ103, and 500 A gels) in
series. Tetrahydrofuran (THF, 1 mL minꢀ1) was used as the eluent
and the signal was monitored by a differential refractive index
detector. Monodispersed polystyrene was used as the molecular
weight standard.
days. Complex 3 was soluble in THF, little soluble in toluene and
hexane. M.p.: 309 ꢂCe311 ꢂC. 1H NMR (400 MHz, d6-DMSO):
d
¼ 6.90 (s, ArH, 1H), 6.79e6.61 (m, ArH, 4H), 6.59 (s, ArH, 2H), 6.44
(s, ArH, 1H), 3.31 (s, ArCH2, 4H), 2.36 (s, NCH2, 2H), 2.09e1.96 (m,
ArCH3, NCH2, 30H), 0.79 (s, CH2CH3, 6H), 0.64 (t, J ¼ 6.7 Hz, CH2CH3,
6H), 0.01 (s, Si(CH3)3, 36H). 13C NMR (101 MHz, d6-DMSO)
d 164.1
(Ar), 129.2 (Ar), 128.8 (Ar), 125.8 (Ar), 123.9 (Ar), 118.2 (Ar), 67.49
(ArCH2), 31.42 (NCH2), 31.15 (NCH2), 25.60 (NCH2), 22.53 (ArCH3),
18.14 (ArCH3), 12.73 (CH2CH3), 3.16 (Si(CH3)3). Anal. Calcd for
C60H104La2N6O4Si4: C, 52.80; H, 7.63; N, 6.16; La, 20.37. Found: C,
52.71; H, 7.83; N, 6.04; La, 20.18.
2.1.4. Syntheses of [CH3CH2CH2N{CH2-(2-OeC6H2e3,5-tBu2)}2]La
[N(TMS)2](THF), L4La[N(TMS)2](THF)2 (4)
The synthesis of 4 was carried out by the same way as that for
the synthesis of 1, but H2L4 (0.78 g, 1.58 mmol) and La[N(TMS)2]3
(0.98 g, 1.58 mmol) was used and subsequent work to afford 4 as a
yellow power (1.15 g, 78%). M.p.: 213 ꢂCe215 ꢂC. 1H NMR (400 MHz,
C6D6):
d
¼ 7.57 (s, ArH, 2H), 7.14 (s, ArH, 2H), 3.65 (s, THF, 8H), 3.55
(d, J ¼ 5.2 Hz, ArCH2, 4H), 2.52 (d, J ¼ 6.9 Hz, NCH2CH2, 2H), 1.69 (s,
C(CH3)3, 18H), 1.41 (s, C(CH3)3, 18H), 1.35 (s, NCH2CH2, 2H), 1.30 (s,
THF, 8H), 0.61 (t, J ¼ 6.6 Hz, CH2CH3, 3H), 0.35 (s, Si(CH3)3, 18H). 13
C
NMR (101 MHz, C6D6):
d
¼ 161.8 (Ar), 137.5 (Ar), 135.4 (Ar), 126.4
2.1.1. Syntheses of [Et2NCH2CH2N{CH2e(2-OeC6H2e3,5-tBu2)}2]La
[N(TMS)2], L1La[N(TMS)2] (1)
(Ar), 124.3 (Ar), 124.1 (Ar), 69.3 (THFeC), 59.4 (ArCH2), 52.1 (NCH2),
35.5 (C(CH3)3), 34.3 (C(CH3)3), 32.2 (C(CH3)3), 30.7 (C(CH3)3), 25.5
(THF-C), 15.3 (CH3CH2), 11.7 (CH2CH3), 4.9 (Si(CH3)3). Anal. Calcd for
La[N(TMS)2]3 (1.30 g, 2.09 mmol) dissolved in 10 mL of THF was
added to H2L1 (1.16 g, 2.09 mmol) dissolved in 10 mL THF. The re-
action mixture was stirred for 3 h at 60 ꢂC, and then the solvent was
removed under oil pump vacuum. The residue was extracted with
mixture of THF and hexane, and recrystallized to afford a pale
yellow solid (1.25 g, 70%). M.p.: 245 ꢂCe248 ꢂC. 1H NMR (400 MHz,
C47H85LaN2O4Si2: C, 60.17; H, 9.07; N, 2.99; La, 14.82. Found: C,
60.05; H, 9.17; N, 2.86; La, 14.68.
2.1.5. Syntheses of [CH3CH2CH2N{CH2-(2-OeC6H2etBu-3eMe-5)}2]
La[N(TMS)2](THF), L5La[N(TMS)2](THF) (5)
C6D6):
d
¼ 7.59 (s, ArH, 2H), 7.12 (s, ArH, 2H), 3.76 (s, ArCH2, 4H),
The synthesis of 5 was carried out by the same way as that for
the synthesis of 1, but H2L5 (0.56 g, 1.37 mmol) and La[N(TMS)2]3
(0.85 g, 1.37 mmol) was used and subsequent work to afford 5 as a
yellow power (0.75 g, 75%). M.p.: 209 ꢂCe211 ꢂC. 1H NMR (400 MHz,
2.82 (s, NCH2, 2H), 2.12 (s, NCH2, 2H), 1.66 (s, C(CH3)3, 18H), 1.40 (s,
C(CH3)3, 18H), 1.28 (s, NCH2CH3, 4H), 0.74 (s, 6H), 0.51 (s, Si(CH3)3,
18H). 13C NMR (101 MHz, C6D6):
d
¼ 162.1 (Ar),137.2 (Ar),135.7 (Ar),
126.3 (Ar), 124.3 (Ar), 124.3 (Ar), 69.6 (ArCH2), 60.7 (NCH2), 51.7
(NCH2), 47.4 (NCH2), 35.5 (C(CH3)3), 34.25 (C(CH3)3), 32.2 (C(CH3)3),
30.7 (C(CH3)3), 25.4 (CH2CH3), 5.8 (Si(CH3)3). Anal. Calcd for
C6D6):
d
¼ 7.27 (s, ArH, 2H), 6.82 (s, ArH, 2H), 3.76 (s, THF, 4H), 3.48
(s, ArCH2, 4H), 2.54 (d, J ¼ 6.8 Hz, NCH2CH2, 2H), 2.33 (s, ArCH3, 6H),
1.65 (s, C(CH3)3, 18 H, THF, 4H), 1.28 (s, NCH2CH2, 2H), 0.57 (t,
J ¼ 6.7 Hz, CH2CH3, 3H), 0.36 (s, Si(CH3)3, 18H). 13C NMR (101 MHz,
C
42H76LaN3O2Si2: C, 59.28; H, 8.94; N, 4.94; La, 16.34. Found: C,
59.04; H, 9.07; N, 4.79; La, 16.11.
C6D6):
d
¼ 161.9 (Ar), 135.9 (Ar), 130.3 (Ar), 124.8 (Ar), 124.1 (Ar),
59.1 (ArCH2), 35.1 (C(CH3)3), 30.6 (C(CH3)3), 25.1 (NCH2CH2), 23.1
(NCH2CH2), 21.1 (ArCH3), 11.7 (CH2CH3), 4.9 (Si(CH3)3). Anal. Calcd
for C37H65LaN2O3Si2: C, 56.85; H, 8.32; N, 3.59; La, 17.78. Found: C,
56.73; H, 8.16; N, 3.45; La, 17.70.
2.1.2. Syntheses of [Et2NCH2CH2N{CH2e(2-OeC6H2etBu-3eMe-
5)}2]La[N(TMS)2](THF), L2La[N(TMS)2](THF) (2)
The synthesis of 2 was carried out by the same way as that for
the synthesis of 1, but H2L2 (0.59 g, 1.26 mmol) and La[N(TMS)2]3
(0.78 g, 1.26 mmol) was used and subsequent work to afford 2 as a
yellow power (0.82 g, 85%). M.p.: 211 ꢂCe213 ꢂC. 1H NMR (400 MHz,
2.1.6. Syntheses of [CH3CH2CH2N{CH2-(2-OeC6H2e3,5-Me2)}2]La
[N(TMS)2], L6La[N(TMS)2] (6)
C6D6):
d
¼ 7.29 (s, ArH, 2H), 6.76 (s, ArH, 2H), 3.72 (s, ArCH2, 4H, THF,
The synthesis of 6 was carried out by the same way as that for
the synthesis of 1, but H2L6 (0.48 g, 1.45 mmol) and La[N(TMS)2]3
(0.90 g, 1.45 mmol) was used and subsequent work to afford 6 as a
yellow power (0.74 g, 82%). M.p.: 260 ꢂCe262 ꢂC. 1H NMR
4H), 2.88 (d, J ¼ 2.8 Hz, NCH2, 4H), 2.35 (s, ArCH3, 6H), 1.62 (s,
C(CH3)3,18H),1.36 (s, NCH2, 4H, THF, 4H), 0.78 (t, J ¼ 6.6 Hz, CH2CH3,
6H), 0.51 (s, Si(CH3)3,18H). 13C NMR (101 MHz, C6D6):
d
¼ 162.3 (Ar),
136.2 (Ar), 130.3 (Ar), 129.3 (Ar), 124.8 (Ar), 123.5 (Ar), 68.8 (THFe
CH2), 60.1 (ArCH2), 51.6 (NCH2), 47.3 (NCH2), 35.1 (C(CH3)3), 30.6
(C(CH3)3), 25.6 (ArCH3), 21.0 (CH2CH3), 5.9 (Si(CH3)3). Anal. Calcd
for C40H72LaN3O3Si2: C, 57.27; H, 8.59; N, 5.01; La, 16.57. Found: C,
57.01; H, 8.63; N, 4.89; La, 16.42.
(400 MHz, C6D6):
d
¼ 6.90 (s, ArH, 2H), 6.72 (s, ArH, 2H), 3.57 (s,
ArCH2, 4H), 2.44 (s, NCH2, 2H), 2.31 (s, CH2CH3, 2H), 2.21 (s, ArCH3,
6H), 1.38 (s, ArCH3, 6H), 0.46 (t, J ¼ 6.5 Hz, CH2CH3, 3H), 0.20 (s,
Si(CH3)3, 18H). 13C NMR (101 MHz, C6D6)
d
¼ 161.6 (Ar), 133.1 (Ar),
129.3 (Ar), 128.6 (Ar), 127.4 (Ar), 125.7 (Ar), 68.03 (ArCH2), 31.9
(NCH2), 25.7 (NCH2), 23.1 (ArCH3), 20.7 (ArCH3), 14.4 (CH2CH3), 11.6
(CH2CH3), 4.5 (Si(CH3)3). Anal. Calcd for C27H45LaN2O2Si2: C, 51.86;
H, 7.20; N, 4.48; La, 22.23. Found: C, 51.73; H, 7.36; N, 4.41; La, 22.31.
2.1.3. Syntheses of {[Et2NCH2CH2N{CH2-(2-OeC6H2e3,5-Me2)}2]La
[N(TMS)2]}2, {L3La[N(TMS)2]}2 (3)
La[N(TMS)2]3 (1.17 g, 1.89 mmol) dissolved in 10 mL THF was
added to H2L3 (0.73 g, 1.89 mmol) dissolved in 10 mL THF. The re-
action mixture was stirred for 3 h at 60 ꢂC, and then the solvent was
removed under oil pump vacuum to afford a pale yellow solid (1.04,
82%). The residue was extracted with mixture of THF and hexane
(1:3), from which 3 was obtained as colorless crystals in several
2.1.7. Syntheses of [CH3CH2CH2N{CH2-(2-OeC6H2e3,5-
Me2)}2]3La2(THF), (L6)3La2(THF) (7)
To a THF solution of La[N(TMS)2]3 (0.88 g, 1.42 mmol) was added
a THF solution of H2L6 (0.70 g, 2.13 mmol). The reaction mixture
was stirred for 3 h at 60 ꢂC, and then the solvent was removed

358
L.-Q. Deng et al. / Journal of Organometallic Chemistry 749 (2014) 356e363
Table 1
25.1 (ArCH3), 20.3 (ArCH3), 20.3 (ArCH3), 17.3 (ArCH3), 17.2 (ArCH3),
13.9 (CH2CH3), 13.4 (CH2CH3), 12.0(CH2CH3), 11.7 (CH2CH3). Anal.
Calcd for C67H89La2N3O7: C, 60.62; H, 6.71; N, 3.17; La, 20.95. Found:
C, 60.57; H, 6.84; N, 3.26; La, 21.02.
Crystal and data collection parameters of complexes 3 and 8.
3
8$0.5C6H14
Formula
C60H104La2N6O4Si4
1363.67
Monoclinic
P21/n
12.1448(9)
16.2868(10)
17.5273(15)
90
101.064(8)
90
3402.5(5)
2
C70H96Gd2N3O7
1406.00
Triclinic
P-1
13.2206(3)
14.3852(5)
20.4636(6)
85.527(2)
72.852(2)
66.446(3)
3405.42(17)
2
Formula weight
Crystal system
Space group
2.1.8. Syntheses of [CH3CH2CH2N{CH2-(2-OeC6H2e3,5-
Me2)}2]3Gd2(THF), (L6)3Gd2(THF) (8)
ꢀ
a/A
To a THF solution of Gd[N(TMS)2]3 (1.31 g, 2.05 mmol) was
added a THF solution of H2L6 (1.01 g, 6.76 mmol). The reaction
mixture was stirred for 3 h at 60 ꢂC, and then the solvent was
removed under vacuum to afford a pale yellow solid (1.17, 89%). The
residue was extracted with mixture of THF and hexane, from which
8 was obtained as colorless crystals in several days. M.p.: 319 ꢂCe
321 ꢂC. Anal. Calcd for C67H89Gd2N3O7: C, 58.99; H, 6.53; N, 3.08;
Gd, 23.07. Found: C, 59.04; H, 6.71; N, 3.16; Gd, 23.13.
ꢀ
b/A
ꢀ
c/A
ꢂ
ꢂ
a
/
b
/
ꢂ
g
/
3
ꢀ
V/A
Z
Dc/Mg mꢀ3
F(000)
1.331
1416
1.35
1.371
1442
1.98
m
/mmꢀ1
Cryst size (mm)
Temp/K
q
0.22 ꢁ 0.20 ꢁ 0.18
0.22 ꢁ 0.20 ꢁ 0.18
2.2. Experimental for ε-caprolactone ring-opening polymerization
223
223
range (ꢂ)
3.1e24.0
4161
0.047
3.2e28.3
14,185
0.033
Reflections
R1a
The procedures for the ring-opening polymerization of ε-cap-
rolactone initiated by complexes 1e6 were similar, and a typical
polymerization procedure is given below.
In the glovebox, a 100 mL Schlenk flask, equipped with a mag-
netic stirring bar, was charged with a solution of initiator in
toluene. Then the desired ε-caprolactone was added to this solution
by syringe. The mixture was stirred vigorously for the desired time
and then exposed to air. A couple drops of 1 M HCl and ethanol
solution were added to fully quench and the polymer was precip-
itated, which was dried under vacuum and weighed.
wR2b
0.097
0.071
ꢀꢀ3
Drmin, max/e A
ꢀ0.53, 1.07
ꢀ0.67, 1.27
Goodness of fitc
1.032
1.04
P
P
P
P
a
R1
w3
¼
(jjFoj ꢀ jFcjj)/ jFoj; wR2 ¼ [ (w(F2o ꢀ Fc2)2)/ (wFo4)]1/2
.
b
¼
1/[
s
2(F2o)
þ
(0.0318P)2],
P
¼
(F2o
þ
2F2c)/3. w8
¼
1/
[
s
2(F2o) þ (0.0209P)2 þ 1.5203P], P ¼ (Fo2 þ 2F2c)/3.
P
S ¼ [ w(F2o ꢀ F2c)2]/(n ꢀ p)1/2, n ¼ number of reflections, p ¼ parameters used.
c
under vacuum to afford a pale yellow solid (0.80, 91%). M.p.:
290 ꢂCe294 ꢂC. 1H NMR (400 MHz, d6-DMSO)
For product analyses, 0.0300 g of poly(CL) was dissolved in 4 mL
of THF overnight. After centrifugation, the clear solution was
measured by GPC with THF (1 mL minꢀ1) as the eluent. The weights
of poly(CL) were calculated with monodispersed polystyrene as the
molecular weight standard.
d
¼ 6.68 (s, ArH, 2H),
6.62 (s, ArH, 4H), 6.54 (s, ArH, 6H), 3.60 (t, J ¼ 5.8 Hz, ArCH2, 4H, THF,
4H), 3.33 (s, ArCH2, 2H), 3.25 (s, ArCH2, 2H), 2.11 (s, ArCH3, 6H), 2.08
(s, ArCH3, 6H), 2.06 (s, ArCH3, 12H), 2.02 (s, ArCH3, 12H), 1.76 (t,
J ¼ 5.9 Hz, THF, 4H), 1.61e1.48 (m, CH2CH3, 2H), 1.40 (dd, J ¼ 14.4,
7.0 Hz, CH2CH3, 4H), 0.63 (t, J ¼ 7.1 Hz, CH2CH3, 3H), 0.43 (t,
2.3. X-ray data collection and refinement of crystal structure
J ¼ 7.0 Hz, CH2CH3, 6H). 13C NMR (101 MHz, DMSO)
d
¼ 163.1 (Ar),
161.7 (Ar), 130.1 (Ar), 130.0 (Ar), 129.8 (Ar), 128.9 (Ar), 128.7 (Ar),
124.0 (Ar), 123.9 (Ar), 123.6 (Ar), 123.5 (Ar), 119.2 (Ar), 117.7 (Ar),
67.00 (THF), 57.2 (ArCH2), 57.0 (ArCH2), 54.3 (ArCH2), 49.6 (NCH2),
The crystals of the complexes were mounted on a glass fiber for
X-ray measurement. Diffraction data were collected on a Rigaku
Mercury CCD area detector in the
u scan mode using MoKa
Scheme 1. Synthesis of the ligands.

L.-Q. Deng et al. / Journal of Organometallic Chemistry 749 (2014) 356e363
359
Scheme 2. Synthesis of the complexes 1e3.
Scheme 3. Synthesis of the complexes 4e6.
C250C270 with occupancies of 31.9 (7) and 68.1(7)%, respectively. In
complex 8, the disorder carbon atom C17 and THF were split into
C17/C64C65C66C67 and C170/C640C650C660C670 with occupancies
of 79.7(23) and 20.3(23)%, respectively. The disorder n-hexane
solvent was split into C68C69C70 and C680C690C700 with occu-
pancies of 82.6(11) and 17.4(11)%, respectively. The crystallographic
data and experimental details of the data collection, as well as the
structure refinement are given in Table 1. Diagrams were made
ꢀ
radiation (
reflections (I > 2
l
¼ 0.71073 A) at 223(2) K. All measured independent
(I)) were used in the structural analyses and semi-
s
empirical absorption corrections were applied using SADABS [23].
The structure was solved and refined using SHELXL-97 [24]. All
hydrogen atoms were positioned geometrically and refined using a
riding model. The non-hydrogen atoms were refined with aniso-
tropic thermal parameters. In complex 3, the disorder ethyl and
silicon methyl were split into C21C22/C25C27 and C210C220/
Scheme 4. Synthesis of the complexes 7 and 8.

360
L.-Q. Deng et al. / Journal of Organometallic Chemistry 749 (2014) 356e363
Fig. 1. Molecular structure of complex
3
showing the atom-numbering scheme.
Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms are omitted
for clarity.
Fig. 3. Molecular structure of complex
8 showing the atom-numbering scheme.
Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms are omitted
for clarity.
Fig. 2. ORTEP drawing of the molecular core of 3.
with SHELXL-97 as well and all calculations were performed on a
Pentium 4 computer.
3. Results and discussion
Fig. 4. ORTEP drawing of the molecular core of 8.
3.1. Synthesis and characterization of lanthanide complexes 1e8
complexes (1e6), given by the reaction of the Ln[N(TMS)2]3 with
H2Ln (n ¼ 1e6) in 1:1 M ratio, demonstrated that the phenolate
lanthanide amides was formed.
The ligand H2L1eH2L6 was prepared according to the literature
procedure in Scheme 1 [22]. An amine elimination reaction was
used to synthesize the lanthanide complexes here. Slow addition of
a THF solution of H2L into the THF solution of Ln[N(TMS)2]3
(Ln ¼ La, Gd) at room temperature, stirred for 3 h at 60 ꢂC. After
workup, the desired complexes 1e8 were isolated from a concen-
trated mixture of THF and hexane, as shown in Schemes 2e4.
3.2. Crystal structures
Crystals suitable for an X-ray structure determination of com-
plexes 3 and 8 were obtained from a hexane/THF mixed (3:1) so-
lution at room temperature. The molecular structure diagrams of
complex 3, which is unsolvated and centrosymmetric, are shown in
Disappearance of the phenolate OeH signal (
d
¼ 13e14) in the
1H NMR spectra of lanthanide complexes confirms the occurrence
of protonolysis. The chemical shifts of the LnLaeN(SiCH3)2 in the
Table 2
ꢂ
ꢀ
Selected bond lengths (A) and bond angles ( ) for 3.
ꢀ
Bond lengths (A)
La(1)eO(1)
La(1)eN(1)
2.495(3)
2.784(3)
La(1)eO2)
La(1)eN2)
2.240(3)
2.972(4)
La(1)eO(1A)
La(1)eN(3)
2.488(3)
2.428 (4)
Bond angles (ꢂ)
O(1)eLa(1)eN(1)
O(1)eLa(1)eO(1A)
N(1)eLa(1)eN(2)
La(1)eO(2)eC(3)
La(1)eN(2)eC(20)
75.36(10)
65.70(11)
63.28 (11)
145.1(3)
O(1)eLa(1)eN(3)
O(1AeLa(1)eN(2)
N(1)eLa(1)eN(3)
La(1)eO(1)eLa(1A)
N(1)eC(19)eC(20)
99.94(11)
162.94(10)
159.85(12)
114.30(11)
113.4 (4)
O(1)eLa(1)eO(2)
O(2)eLa(1)eN(1)
N(2)eLa(1)eN(3)
La(1)eN(1)eC(19)
N(2)eC(20)eC(19)
138.91(10)
72.78(11)
96.91(12)
116.3 (3)
113.1 (4)
102.6 (3)

L.-Q. Deng et al. / Journal of Organometallic Chemistry 749 (2014) 356e363
361
Table 3
ꢂ
ꢀ
Selected bond lengths (A) and bond angles ( ) for 8.
ꢀ
Bond lengths (A)
Gd(1)eO(1)
Gd(1)eO(4)
Gd(2)eO(1)
Gd(2)eO(6)
2.332(2)
2.348(2)
2.284(2)
2.159(2)
Gd(1)eO(2)
Gd(1)eN(1)
Gd(2)eO(4)
Gd(2)eO(7)
2.139(2)
2.576(3)
2.277(2)
2.413(2)
Gd(1eO(3)
Gd(1eN(2)
Gd(2eO(5)
Gd(2eN(3)
2.130(2)
2.584(3)
2.172(2)
2.597(3)
Bond angles (ꢂ)
N(1)eGd(1)eO(1)
N(2)eGd(1)eO(2)
O(1)eGd(1)eO(3)
Gd(1)eO(1)eGd(2)
O(1)eGd(2)eO(6)
O(5)eGd(2)eO(6)
78.73 (8)
101.17 (8)
93.42 (9)
106.85 (9)
103.91 (8)
153.36 (9)
N(1)eGd(1)eO(2)
N(2)eGd(1)eO(3)
O(2)eGd(1)eO(3)
O(1)eGd(2)eO(4)
O(1)eGd(2)eO(7)
O(5)eGd(2)eO(7)
76.32 (9)
76.54 (9)
114.46(10)
74.23 (8)
85.26 (9)
87.18 (9)
N(2)eGd(1)eO(1)
O(1)eGd(1)eO(2)
O(3)eGd(1)eO(4)
O(1)eGd(2)eO(5)
O(1)eGd(2)eN(3)
O(6)eGd(2)eN(3)
106.41(8)
144.63(8)
147.15(8)
101.44(8)
176.48(8)
77.36(8)
Table 4
Polymerization of ε-CL initiated by 1e6a.
metal atom is six-coordinated by three oxygen atoms and two ni-
trogen atoms from a dianionic bis(phenolate) ligand (L3), and one
nitrogen atom from eN(TMS)2 group. One oxygen atom in this
bis(phenolate) ligand (L3) is monodentate to lanthanide and
another is as a m2-O-bridge between metals. The coordination ge-
ometry around the metal center can be best described as a slightly
distorted octahedron, in which O(1), O(2), N(1), and N(3) occupied
equatorial positions and O(1A) and N(2) occupied axial positions.
Entry
Initiator
[M]0/[I]0
Time (min)
Yieldb (%)
Mnc (104)
PDIc
1
2
3
4
5
6
7
8
1
1
2
2
3
3
4
4
5
5
6
6
100
250
100
250
100
250
100
250
100
250
100
250
1
1
1
1
1
1
1
1
1
1
1
1
62
53
57
66
35
20
60
70
73
97
100
74
2.5
1.8
3.7
2.7
0.85
0.63
5.4
2.0
1.2
1.39
1.65
1.15
1.02
1.48
1.63
1.20
1.67
1.57
1.61
1.35
1.53
ꢀ
The La(1)eO(2) bond length (2.240(3) A) is shorter than those in
ꢀ
[ONNO]LaCp (2.291(2) A) [ONNO]Me2NCH2CH2N{CH2e(2-Oe
C6H2etBu-3eMe-5)}2] [25]. The La(1)eO-m2 bond length of
9
10
11
12
1.3
0.81
0.72
ꢀ
ꢀ
ꢀ
2.495(3) A and 2.488 A, respectively, and the average 2.491(3) A, are
ꢀ
closed to those in [La(OAr)3(THF)3]2$5THF (2.494 A) [26]. The Lae
N(TMS)2 bond length (2.428(4) A) is longer than those in {[ON]La
ꢀ
a
General polymerization conditions: [M]0 ¼ 0.5 M, solvent ¼ toluene, T ¼ 20 ꢂC.
Yield: weight of polymer obtained/weight of monomer used.
Measured by GPC relative to monodispersed polystyrene.
t
ꢀ
[N(TMS)2]2 (2.392(9) A) [ON ¼ 3,5- Bu2-2-(OH)eC6H2CH2NHC6H4e
b
c
ꢀ
ꢀ
o-OCH3] [27]. The LaeNamine bond (2.784(3) A and 2.972(4) A) were
longer comparable to the literature [25]. The bite angle O(1)e
La(1)eO(2) of 138.91(10)00 for the bis(pheno1ate) ligands is appar-
ently smaller than the corresponding angles found in amine-
bis(pheno1ate) lanthanide alkane [28] and amides [29].
Figs. 1 and 2, with selected bond distances and angles listed in
Table 2. The structure shows a dimeric feature containing an Ln2O2
core bridging through the oxygen atoms of the two OAr groups. The
two bridging oxygen atoms and two lanthanide atoms are exactly
coplanar as required by the crystallographic symmetry. The central
Single-crystal X-ray diffraction shows that complex 8 possess a
THF-solvated dimeric structure with half a hexane in a unit cell
(Figs. 3 and 4). The structure contains an Ln2O2 core bridging
Fig. 5. 1H NMR spectrum of PCL.

362
L.-Q. Deng et al. / Journal of Organometallic Chemistry 749 (2014) 356e363
Scheme 5. Possible Mechanism for the ROP of ε-CL.
through the oxygen atoms of the two OAr groups, adopting a
twisted octahedral geometry. The selected bond distances and
angles are listed in Table 3. Each of the Gd atoms is six-coordinated
but their bonding environment are different, and there are two
different coordination modes in the bis(phenolate) ligand (L6). The
Gd1 atom is coordinated to two single coordinate oxygen atoms (O2
and O3), two m2-bridge oxygen atoms (O1 and O4) and two nitrogen
atoms(N1 and N2). The Gd2 atom is coordinated to one oxygen
atom (O7) from THF, two single coordinate oxygen atoms (O5, O6),
two m2-bridge oxygen atoms (O1 and O4) and one nitrogen
atom(N3). The GdeO(Ar) bond length is comparable to that formed
in the Gd4(Cat)6(THF)6 (Cat ¼ 3,5-di-tert-butyl-catecholate) [30].
The O1eGd1eO2, O3eGd1eO4 and O5eGd2eO6 bond angles are
144.63(8)ꢂ, 147.15(8)ꢂ and 153.36(9)ꢂ, respectively.
4. Conclusion
In summary, a series of lanthanide (La/Gd) complexes stabilized
by amine-bridged bis(phenolate) ligands were synthesized via
amine elimination reactions, and the structural features of com-
plexes (3 and 8) were determined by X-ray diffraction study. It was
found that the bis(phenolate) lanthanide amides (1e6) were effi-
cient initiators for the ring-opening polymerization of ε-CL. NMR
spectrum of PCL revealed that the ring-opening polymerization of
ε-CL proceeded via a coordination-insertion mechanism.
Acknowledgment
This work was supported by National Science and Technology of
Major Project (2009ZX02039-002), and State Key Laboratory of
ASIC & System, Fudan University (12KF007).
3.3. Catalytic activity studies
Appendix A. Supplementary material
Their performance of complexes 1e6 as catalysts for the ROP of
ε-CL was examined in a toluene solution at 20 ꢂC, and the pre-
liminary results are listed in Table 4. It can be seen that all com-
plexes are efficient initiators of the polymerization of ε-CL in
toluene. All polymerizations proceeded fast and completed within
1 min to give polymers with relatively narrow molecular weight
distributions (PDIs) (1.02e1.63).
For the complexes 1e6, the influence of the substituent
groups, located ortho- and para-position to the binding oxygen
atoms, and the presence of side arm donor were studied. The data
shows that the polymerization yields of complex 4e6 with tri-
dentate [ONO] ligands are higher than those of complexes 1e3
with an extra side arm nitrogen donor (average yields: 56.5 (for
1) < 65 (for 4), 61.5 (for 2) < 85 (for 5), 27.5 (for 3) < 87 (for 6)).
The bulky t-Bu substituents may have a good effect on the
polymerization, with a higher molecular weight (Mn (104): 2.5 for
1, 3.7 for 2, 0.85 for 3).
CCDC 941929 and 941930 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
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