Heteroleptic lanthanide amide complexes bearing carbon-bridged bis(phenolate) ligands: Synthesis, structure and their application in the polymerization of ε-caprolactone

Article abstract of DOI:10.1039/c5ra23520k

A convenient method for the synthesis of anionic lanthanide amide complexes bearing carbon-bridged bis(phenolate) ligands H₂L [L = (o-CH₃)PhCH(C₆H₂-3-^tBu-5-R-2-O)₂; R = Me, L = L₁ and R = ^tBu, L = L₂] is described. The bis(phenolato)lanthanide complexes LLnN(SiMe₃) [L = L₁, Ln = La (1), Ln = Gd (2) and L = L₂, Ln = La (3), Ln = Gd (4)] were synthesized in nearly quantitative yields by the reaction of Ln[N(SiMe₃)₂]₃ (Ln = La or Gd) with H₂L in a 1 : 1 molar ratio in THF at 60 °C. The bis(phenolato)lanthanide pyrazolato complexes LLnPzMe₂(THF)₃ [L = L₁, Ln = La (5), Ln = Gd (6) and L = L₂, Ln = La (7), Ln = Gd (8)] were obtained in high yields by further reacting the obtained LLnN(SiMe₃) with another 1 equiv. of 3,5-dimethylpyrazole (Me₂PzH). Meanwhile, the complexes LLnPzMe₂ can also be synthesized by the direct reaction of Ln[N(SiMe₃)₂]₃ with H₂L and Me₂PzH in 1 : 1 : 1 molar ratio in situ in THF. Complexes 5-8 have been characterized by X-ray crystal structural analysis. The central lanthanide metal atom is seven-coordinated by one bis(phenolate) ligand, one pyrazole ligand and three THF molecules in a distorted pentagonal bipyramid. The catalytic activity of compounds 1-8 in the ring-opening polymerization of ε-caprolactone was studied. The catalytic mechanism was studied and discussed as well.

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Heteroleptic lanthanide amides complexes bearing carbon-
bridged bis(phenolate) ligands: synthesis, structure and their
application in the polymerization of ε-caprolactone
Received 00th January 20xx,
Accepted 00th January 20xx
Yan-Xu Zhou1, Jing Zhao1, Ling Peng1, Yu-Long Wang1, Xian Tao1, Ying-Zhong Shen1*
A convenient method for the synthesis of anionic lanthanide amides complexes bearing carbon-bridged bis(phenolate)
ligands H2L [L = (o-CH3)PhCH(C6H2-3-tBu-5-R-2-O)2, R = Me, L = L1; R = tBu, L = L2 ] is described. The bis(phenolato)lanthanide
complexes LLnN(SiMe3) [L = L1, Ln = La (1); Ln = Gd (2); L = L2, Ln = La (3); Ln = Gd (4) ] were synthesized by the reaction of
Ln[N(SiMe3)2]3 (Ln = La, Gd) with H2L in a 1:1 molar ratio in THF at 60 °C in nearly quantitative yields. The
bis(phenolato)lanthanide pyrazolato complexes LLnPzMe2⋅(THF)3 [L = L1, Ln = La (5); Ln = Gd (6); L = L2, Ln = La (7); Ln = Gd
(8) ] was obtained by using LLnN(SiMe3) obtained further reacting with another 1 equiv of 3,5-dimethylpyrazole (Me2PzH)
in high yields. Meanwhile, the complexes LLnPzMe2 can also be synthesized by the direct reaction of Ln[N(SiMe3)2]3 with
H2L and Me2PzH in 1:1:1 molar ratio in situ in THF. Complexes 5 - 8 have been characterized by X-ray crystal structural
analysis. The central lanthanide metal atom is seven-coordinated by one bis(phenolate) ligand, one pyrazole ligand and
three THF molecules in a distorted pentagonal bipyramid. The catalyst activity of compounds 1 - 8 to the ring-opening
polymerization of ε-caprolactone was studied. The catalyst mechanism was studied and discussed as well.
DOI: 10.1039/x0xx00000x
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reaction during polymerization. Carbon-bridged bis(phenolate)
lanthanide derivatives showed higher activity for the
polymerization of cyclic esters. Shen and co-workers have
Introduction
Aliphatic polyesters are a prefered choice for potential commodity
plastic of environmentally-friendly because of their biodegradability,
biocompatibility and potential availability from renewable
resources.1-3 The polymerization mechanism could be defined as
demonstrated that bridged bis(phenolate) lanthanide complexes
can serve as catalysts for the ROP of lactide29 and lactones.30
However, most of them paid attention to bis(phenolate)lanthanide
alkoxides.31,32 Meanwhile, The structural chemistry of anionic five-
membered nitrogen heterocyclic ligands, especially pyrazolate and
1,2,4-triazolate ligands, has received much attention because of the
structural diversity and variety of the coordination modes of these
compounds.33 Pyrazolate ligands are among the most versatile of
ligands, with 20 different coordination modes identified so far.34-36
To the best of our knowledge, the application of the heteroleptic
pyrazolato lanthanide complexes bearing carbon-bridged
bis(phenolate) ligands in ring-opening polymerization has not been
reported.
enzymatic
polymerization,4-6
polycondenzation,7
polymerization,10,11
anionic
or
polymerization,8,9
cationic
coordination/insertion
polymerization.12,13
Ring
opening
polymerization of cyclic esters, however, is currently a topical
research field with metal complex-induced coordination/insertion
type polymerization. A wide range of metals have been explored for
the ring-opening (ROP) polymerization of lactones through the
coordination/insertion mechanism; typically alkali metals,14 alkaline
earth metals,15-17 transition metals,18-20 and rare earth metals.21-23
Among them, organolanthanide based system seems to be active
and suitable in preparing the well-defined polymers with high
molecular weights in narrow polydispersity due to their high
activities and capabilities.24,25 Recently, bulky carbon-bridged
bis(phenolate) ligands have attracted increasing attention in
organolanthanide chemistry.26-28 Not only have they attractive
features, such as being easily available and tunable, but it can also
provide O,O-bidentate chelating to stabilize the metal center to
realize the single active site complex and limit back-biting side
In order to develop the new lanthanide containing
organometallic complexes which could be used as catalyst in the
polymerization of polyesters, we turned our attention to related
carbon-bis(phenolate) ligands with two O,O-bidentate ligands (H2L1
-
H2L2). We report here the synthesis
a
series of
bis(phenolato)lanthanide complexes (1 4) and heteroleptic
–
pyrazolato lanthanide complexes (5 - 8) bearing carbon-bridged
bis(phenolate) ligands for the first time. The complexes obtained
were characterized by nuclear magnetic resonance (NMR)
spectroscopy and elemental analysis, respectively. The single
crystals of complexes 5 - 8 have been determined by X-ray
diffraction. The catalytic properties of the complexes (1 - 8) have
also been studied in the polymerization of ε-caprolactone under
mild conditions.
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R
O
tBu
Results and discussion
O
OH
OH
OH
=
OH
Ln
N(TMS)2
2HN(TMS)
+
Ln[N(TMS) ]
+
2
2 3
60
℃
O
tBu
Synthesis and Characterization of Lanthanide Complexes 1 – 8.
Ln La(a), Gd(b)
=
R
Me Ln La(1), Gd(2)
=
=
=
R
t
3
4
R
Bu Ln La( ), Gd( )
=
Ligands (H2L1 and H2L2) were prepared according to the literature
procedure (scheme 1).37 A series of lanthanide complexes can be
R
R
Me, H2L1
=
tBu, H L2
B
=
2
d
o
H
N
h
t
H
N
e
M
synthesized
by
amine
elimination
reaction.
N
N
Bis(phenolato)lanthanide complexes (1 – 4) could be prepared by
the reaction of Ln[N(SiMe3)2]3 (Ln = La, Gd) with H2L (H2L1 and H2L2)
in a 1:1 molar ratio in THF at 60 °C in nearly quantitative yields.
Complexes 5 – 8 (LLnPzMe2(THF)3 [L = L1, Ln = La (5); Ln = Gd (6); L =
L2, Ln = La (7); Ln = Gd (8) ] could be synthesized by using complex 1
- 4 further reacting with 1 equiv of Me2PzH in THF in high yields
(Scheme 2). Complexes 5 - 8 can also be synthesized by the direct
reaction of Ln[N(SiMe3)2]3 with H2L1/H2L2 and Me2PzH in a 1:1:1
molar ratio in situ in THF. (Scheme 2)
O
O
N
+
HN(TMS)2
N
Ln
(THF)3
R
R
Me Ln La(5), Gd(6)
t
=
=
=
7
8
Bu Ln La( ), Gd( )
=
Scheme 2. Synthesis of the complexes 1 – 8
Meanwhile ， we had tried another way for synthesis of
complexes 5 - 8. First of all, Ln[N(SiMe3)2]3 reacted with Me2PzH in a
OH
H
N
N
O
O
1
:
1
molar ratio in THF to produce complexes
N
OH
1:1
N
La
Ln[N(TMS)2]3
Me2PzLn[N(TMS)2]2(THF)2
Me2PzLn[N(TMS)2]2(THF)2, which can be used as a precursor to
synthesize the corresponding heteroleptic pyrazolato lanthanide
complexes 5 - 8 by a further reaction with 1 equiv of H2Ln (n = 1, 2).
(Scheme 3)
1:1
(THF)3
5
8
Complexes
-
Ln=La(c), Gd(d)
Due to the strong paramagnetism of the central metal ions (Gd),
complexes 2, 4, 6 and 8 did not provide any resolvable 1H NMR
spectra. In the 1H NMR spectrum of complex 1 and 3, except for the
resonances of the L2− groups, Si(CH3)- group and THF molecules，no
resonance of the hydroxyl proton of the bridged bis(phenol) was
observed, indicating that the phenolate lanthanide amides was
formed. Disappearance of the Si(CH3)- group signal (δ = 0.4 ~ 0.5) in
the 1H NMR spectra of lanthanide complexes 5 and 7, indicating
that the substitution reaction had been achieved. In the FT-IR
pectrogram, we find the absorption peak of complexes 1 - 8 are
very similar to the corresponding ligands ,and the absorption of
active hydrogen of ligands H2L and Me2PzH are disappeared，which
can also indicate that the substitution reaction had indeed occurred.
It was unsuccessful to determine definitive structures of
complexes 1 – 4, due to solvent loss and the deterioration in crystal
quality. By single-crystal structure analysis, the definitive structures
of complexes 5 - 8 were determined (see below). The definitive
molecular structures determined by X-ray crystal structural analysis
are consistent with the 1H NMR results.
Scheme 3. Synthesis of the complexes 5 and 7 (Method C)
Crystal structures
Crystals suitable for X-ray structure determination of complexes 5
- 8 were obtained from a hexane/THF mixed solution at room
temperature. The crystallographic data and experimental details of
the data collection, as well as the structure refinement are given in
table 1. The molecular structures of molecules 5 and 6 are depicted
in Fig. 1 and Fig. 2.
R1
tBu
R1
CHO
O
OH
OH
O
PhSO3H
H2O
+
+
2
tBu
hexane, heat
OH
R1
tBu
Figure 1. Molecular structure of complex 5 showing the atom-
numbering scheme. Thermal ellipsoids are drawn at the 30%
probability level. Hydrogen atoms are omitted for clarity.
H2L1 R Me
=
R
tBu
H2L2
=
Scheme 1. Synthesis of the ligands.
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Table 1. Crystallographic data for 5 - 8.
5
6
7
8
formula
formula weight
crystal system
Space group
a/Å
b/Å
c/Å
α/deg
β/deg
C47H67LaN2O6
894.94
Triclinic
P-1
13.336 (2)
14.166 (3)
16.340 (3)
75.288 (2)
70.091 (2)
63.392 (2)
2576.1 (8)
2
C47H67GdN2O6
913.28
Triclinic
P-1
13.348 (2)
14.064 (3)
16.293 (3)
75.129 (2)
69.752 (2)
62.759 (2)
2533.6 (8)
2
C53H79LaN2O6
979.09
Monoclinic
P21/c
13.629 (3)
19.851 (4)
19.143 (4)
90
96.50 (3)
90
5145.8 (19)
4
C53H79GdN2O6
997.43
Monoclinic
P21/c
13.740 (2)
20.389 (4)
18.914 (3)
90
97.246 (2)
90
5256.2 (15)
4
γ/deg
V/Å3
Z
Dc/Mg m-3
F(000)
1.154
936
0.87
1.197
950
1.35
1.264
2064
0.88
1.260
2092
1.31
µ/mm-1
Cryst size (mm)
temp/K
0.20×0.20× 0.20
296
0.20×0.20× 0.20
296
0.20×0.20× 0.20
173
0.20×0.20× 0.20
296
θ range (°)
reflections
R1
1.3-25
8990
0.064
1.3-25
8764
0.059
3.2-25
9034
0.030
1.5-25
9257
0.031
wR2
0.221
0.205
0.076
−0.39, 0.60
1.05
0.080
−0.40, 0.54
1.03
Δρmin, max/e Å-3
goodness of fit
−0.59，1.82
1.12
−1.19，1.89
1.05
a) R1 =
∑(||Fo|-|Fc||)/
∑
|Fo|; wR2 = [
∑
(w(Fo2-Fc ) )/
∑
(wFo4)]1/2
.
2 2
b) w5 = 1 / [σ2(Fo2) + (0.159 P)2], P = (Fo2+2Fc )/3.
2
w6 = 1 / [σ2(Fo2) + (0.1414 P)2], P = (Fo2+2Fc )/3.
2
w7 = 1 / [σ2(Fo2) + (0.0351P)2], P = (Fo2+2Fc )/3.
2
w8 = 1 / [σ2(Fo2) + (0.0405P)2 + 1.2726P], P = (Fo2+2Fc )/3.
2
c) S = [∑w(Fo2-Fc )2]/(n-p)1/2, n = number of reflections, p = parameters used.
2
Complex 5 and 6 are isostructural, they have a monomeric
Compared with the neutral pyrazole, the C-C bond lengths and C-
N bond lengths of the anionic pyrazole have some obvious
structure; the lanthanide atom are seven-coordinated by two
nitrogen atoms from pyrazolato group, two oxygen atoms from one difference. In [La(Ph2Pz)3(Ph2PzH)2],41 the C-C bond lengths of the
L12− group, and three oxygen atoms from three THF molecules. The neutral pyrazole are 1.372 Å and 1.410 Å, the C-N bond lengths are
coordination geometry at the lanthanide atom can be best 1.343 Å and 1.354 Å, respectively. While in complex 5, the C-C bond
described as a distorted pentagonal bipyramid. The average La-O(Ar) lengths of the anionic pyrazole are 1.368 Å and 1. 374 Å, the C-N
bond lengths of 5 (2.272 (6) Å) is comparable with Gd-O(Ar) bond bond lengths are 1.333 Å and 1.339 Å, respectively. So, it’s very
lengths of 6 (2.18 (3) Å) taking into account the difference in ionic difficult to distinguish between C-C single bond and C=C double
radii is considered. The average La-O(Ar) bond lengths (for 5) is bond from the bond length, as also is unable to distinguish between
comparable with those in (C5H5)La(MBMP)(THF)3 (2.256 Å) (MBMP2- C-N single bond and C=N double bond. The chemical shift of C-H
=
2,2-methylene-bis(6-tert-butyl-4-methyl-phenoxo))38
and protons for neutral pyrazole ligand Me2PzH is 5.73 ppm, however
[ONNO]LaCp (2.291 Å) [ONNO = Me2NCH2CH2N{CH2-(2-O- C6H2)- the chemical shift of C-H protons for anionic pyrazole ligand Me2Pz-
tBu-3-Me-5)}2],39 but slightly longer than those in [(MBMP)La(μ- （complexes 5 and 7）is 5.76 ppm，it is clearly that there is a
OCH2Ph)(THF)2]2 (2.226 Å)40 and L’2La(TMS)2 (2.227 Å) (L’ = 3,5-But2- slight difference between neutral and anionic pyrazole ligand，
2-(O)-C6H2CH=N-2,6-Pri2-C6H3).13 The average C-O bond lengths of which could be attributed to the anionic pyrazole ligand undergo
the phenolate ligands in complexes 5 and 6 are 1.335(7) Å and delocalization.
1.351(8) Å, respectively, which are apparently shorter than the
single C-O bond length, reflecting substantial electron delocalization 4, with their selected bond lengths and bond angles listed in Table 2.
from the oxygen into the aromatic rings. Complexes 7 and 8 are isostructural, they have a monomeric
The molecular structures of 7 and 8 are depicted in Fig. 3 and Fig.
In complexes 5 and 6, the two nitrogen atoms of pyrazolato structure; the central metal atom is seven-coordinated by one
group are also coordinated to the lanthanide atom, the Ln-N (1) bis(phenolate) ligand, one pyrazole groups, and three THF
bond lengths is comparable with Ln-N (2) bond lengths. The average molecules in a distorted pentagonal bipyramid. The average La-O(Ar)
La-N bond lengths of 5 (2.512(6) Å) is comparable with Gd-N bond bond lengths of 7 (2.304 (17) Å ) is comparable with Gd-O(Ar) bond
lengths of 6 (2.415 (7) Å) when the difference in ionic radii is lengths of 8 (2.195 (2) Å) considering the difference in ionic radii.
considered.
The molecular structure analysis of complexes 7 and 8 are
consistent with the complex 5 and 6.
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Figure 4. 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.
Figure 2. Molecular structure of complex 6 showing the atom-
numbering scheme. Thermal ellipsoids are drawn at the 30 %
probability level. Hydrogen atoms are omitted for clarity.
activity for the polymerization in comparison with the
corresponding gadolinium amides complexes. For example, using
complex 1 as the initiator, the yield reaches 95% (Mn: 6.43×104)and
77% (Mn: 8.73×104) when the molar ratio of monomer to initiator
are respectively 100 and 500 (Entry 1, 3); whereas the yield is 92%
(Mn: 7.85×104) and 83% (Mn: 5.84×104) using the complex 2 as the
initiator (Entry 5, 7), which isn’t consistent with the active trend for
the polymerization of cyclic esters initiated by the lanthanide-based
complexes.43,44 All of the same kind of amido lanthanide complexes
show a similar catalytic behavior.
The amides groups has a significant effect on the polymerization.
Complexes 1 - 4 showed higher activity for polymerization than the
complexes 5 - 8. Using 1 as the initiator, the yield reaches 95% in 1
min at room temperature when the molar ratio of monomer to
initiator ([M0]/[I0]) is 250, whereas the yield is 81% in 30 min using 5
as the initiator under the same polymerization conditions (Entries 1,
17). Using 1 - 4 as the initiator, even for [M]0/[I]0 = 750, the
polymerization still can proceed, while it wasn’t completed after
several days when using complexes 5 – 8 as the initiator under the
same polymerization conditions，which was attributed to the
different molecular structures of the lanthanide amides, the bulky –
PzMe2 groups may have a bad effect on the polymerization.
However, the effect of the bis(phenolato) groups in these
complexes on the polymerization was not observed.
Figure 3. Molecular structure of complex 7 showing the atom-
numbering scheme. Thermal ellipsoids are drawn at the 30 %
probability level. Hydrogen atoms are omitted for clarity.
Catalytic activity studies
Their performance of complexes 1 - 8 as catalysts for the ROP of ε-
CL was examined in a toluene solution at 20 °C, and the preliminary
results are listed in table 2. It can be seen that all complexes are
efficient initiators of the polymerization of ε-CL in toluene. All
polymerizations proceeded fast and completed within 1 h to give
polymers with relatively narrow molecular weight distributions
(PDIs) (≤1.53). These initiators showed high activity (even for
The microstructure of PCL was determined by 1H NMR
experiments using initiator 1 and a 10 :1 monomer to initiator ratio,
as shown in Figure 5.
O
O
O
O
O
O
O
O
O
M
O
O
[M]0/[I1 - 4
]
0
= 750), the polymerization still can proceed smoothly)
insertion to the Ln-M
O
M
LnM
Ln
(CH2)5
and produced PCL with a molecular weight of 8.73×104 and a PDI of
1.18. In comparison with carbon-bridged Bis(phenolato)lanthanide
alkoxides reported by Yao and co-workers (time of polymerization 1
h, temperature 17 °C, yield 31–100%, Mn 0.68×104- 4.56×104, PDI
1.14–1.29), 42 complexes 1 - 4 exhibit higher catalytic activity.
The ionic radii of the lanthanide metals have a profound effect on
the polymerization activity of the corresponding lanthanide
complexes.36 However, these lanthanum amides showed similar
Ln
coordination
M
= N(TMS)2
n CL
O
O
O
H+ EtOH
OH
O
M
M
Ln
O
(CH2)5
n
n
O
O
Scheme 4. Possible Mechanism for the ROP of ε-CL.
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Figure 5. 1H NMR spectrum of PCL (CDCl3)
a-position to terminal hydroxy group. One possible polymerization
mechanism is via the coordination/insertion (shown in Scheme 4),
which is similar to the literature.45,46
Table 2. Polymerization of ε-CL initiated by 1 – 8a
c
entry
initiator
[M
]0/[
I
]
Time
(min)
Yieldb
（%）
95
Mn
PDIc
0
(104)
1
2
3
4
5
6
7
8
1
1
1
1
2
2
2
2
3
3
3
3
4
4
4
4
5
5
6
6
7
7
8
8
a
a
b
b
100
250
500
750
100
250
500
750
100
250
500
750
100
250
500
750
100
250
100
250
100
250
100
250
100
250
100
250
1
1
10
60
1
6.43
6.78
8.73
5.63
7.85
6.73
5.84
5.36
6.21
5.83
6.81
5.72
6.29
7.34
5.47
4.85
3.42
3.53
3.31
3.78
4.32
4.68
3.67
4.57
5.61
6.42
6.70
5.84
1.47
1.39
1.18
1.42
1.41
1.53
Experimental section
93
77
46
92
90
83
50
97
100
80
54
88
96
83
44
81
82
83
77
82
87
88
79
86
98
HN(TMS)2 (TMS=SiMe3), ε-Caprolactone, and nBuLi are commercially
available. All manipulations were performed under pure nitrogen
1
10
60
1
1.30 with rigorous exclusion of air and moisture using Schlenk
1.28
1.37
1.21
1.45
1.33
1.27
1.29
1.18
1.23
1.41
1.39
techniques and glovebox. THF, toluene, and hexane were distilled
from sodium benzophenone ketyl before use. ε-Caprolactone was
dried over CaH2 for 3 days，and distilled under reduced pressure.
HN(TMS)2 was dried with small amount of sodium and distilled
before use. The starting complexes La[N(TMS)2]3/Gd[N(TMS)2]3,47
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
1
10
60
1
38
H2L1~H2L2 and Me2PzH48 were synthesized according to published
1
procedures. Lanthanide analysis were performed by EDTA titration
with a xylenol orange indicator and hexamine buffer. 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
10
60
10
30
10
30
10
30
10
30
1
1.34 C6D6 or d6-DMSO as the solvent. Elemental analysis was performed
1.37
1.28
1.31
1.26
1.39
2.03
2.24
2.15
2.38
on a Perkin-Elmer 240C elemental analyzer. 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 min-1) 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.
10
1
10
89
96
a General polymerization conditions: [
M]0/[I]0: the ratio of monomer
to Ln (Gd or La), solvent = toluene, T = 20 °C.
b Yield: weight of polymer obtained/weight of monomer used.
c Measured by GPC in THF calibrated with polystyrene standard.
X-ray data collection and refinement of crystal structure
1
The H NMR spectrum of the polymer clearly shown that only the -
N(SiMe3)2 group was observed, according to the resonance at -0.01
ppm. No resonance signal was observed for the phenolate ligand.
The crystals of the complexes were mounted on a glass fiber for X-
ray measurement. Diffraction data were collected on a Rigaku
The signal at 3.64 ppm can be assigned to the methylene protons at Mercury CCD area detector in the ω scan mode using MoKα
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radiation (λ = 0.71073 Å) at 223(2) K. All measured independent Synthesis
RSC Advance
of [(o-OCH3)PhCH(C6H2-3,5-tBu2-2-O)2]La[N(TMS)2],
reflections (I > 2σ(I)) were used in the structural analysis and semi- [L2La[N(TMS)2] (3). The synthesis of complex 3 was carried out in
empirical absorption corrections were applied using SADABS.49 The the same way as the described for the synthesis of complex 1, but
structure was solved and refined using SHELXL-97.50 All hydrogen H2L2 (0.99 g, 1.86 mmol) was used instead of H2L1. The following
atoms were positioned geometrically and refined using a riding procedure is similar to that described for complex 1, and complex 3
model. The non-hydrogen atoms were refined with anisotropic was isolated as orange-yellow crystals (1.45 g, 92 %). mp. 241-
thermal parameters.
243 °C. 1H NMR (400 MHz, C6D6, 25°C): δ = 7.43 (d, J = 7.6 Hz, Ar
H), 7.40 (d, J = 2.0 Hz, Ar , 2 H), 7.12 (d, J = 7.9 Hz, Ar , 1 H), 6.76 (t,
J = 7.4 Hz, Ar , 1 H ), 6.59 (d, J = 2.4 Hz, Ar , 1 H ), 5.79 (s, C , 1 H),
3.00 (s, OC 3, 3 H), 2.20 (s, C 3, 6 H), 1.36 (s, C(CH3)3, 18 H), 1.29 (s,
H, 2
H
H
H
H
H
Ring-Opening Polymerization for ε-Caprolactone
H
H
C(CH3)3, 18 H), 0.47 (s, Si(CH3)3, 18 H). 13C NMR (101 MHz, C6D6,
25°C): δ = 158.6 (Ar), 158.3 (Ar), 137.8 (Ar), 137.3 (Ar), 135.9 (Ar),
132.1 (Ar), 129.8 (Ar), 127.2 (Ar), 126.0 (Ar), 121.6 (Ar), 121.1 (Ar),
The procedures for the ring-opening polymerization of ε-
Caprolactone initiated by complexes 1 - 8 were similar, and a typical
polymerization procedure is given below. In the glovebox, a 100 mL
Schlenk flask, equipped with a magnetic stirring bar, was charged
with a solution of initiator in toluene. To this solution was added
desired amount of ε-Caprolactone by syringe. The mixture was
stirred vigorously for the desired time. Then，a couple drops of 1
M HCl - ethanol solution were added to fully quench and the
polymer was precipitated, which was dried under vacuum and
weighed.
113.5 (Ar), 56.3 (O
CH3), 42.1 (CH), 35.8 (C(CH3)3), 34.4 (C(CH3)3),
32.1 (C( H3)3), 30.7 (C(
C
C
H3)3), 5.4 (Si(CH3)3). Anal. Calcd for
C42H66LaNO3Si2: C, 60.92; H, 8.03; N, 1.69; La, 16.77. Found: C, 60.98;
H, 8.14; N, 1.52; La, 16.84. IR (KBr, cm-1): 2957 (s), 2905 (m),
2871(m), 1595 (w), 1462 (m), 1440 (m), 1359 (m), 1246 (w), 1022
(w), 831 (w), 751 (w).
Synthesis of [(o-OCH3)PhCH(C6H2-3,5-tBu2-2-O)2]Gd[N(TMS)2],
[L2Gd[N(TMS)2] (4). Synthesis of complex 4 was carried out in the
same way as that described for complex 1, but H2L2 (0.99 g, 1.86
mmol) and Gd[N(TMS)2]3 (1.19 g, 1.86 mmol) was used and
subsequent work to afford 4 as orange-yellow microcrystals (1.46 g,
93 % based on Gd). mp. 248-251 °C. Anal. Calcd for C42H66GdNO3Si2:
C, 59.60; H, 7.86; N, 1.65; Gd, 18.58. Found: C, 59.54; H, 7.94; N,
1.53; Gd, 18.64. IR (KBr, cm-1): 2960 (s), 2895 (m), 2868 (m), 1603
(w), 1458 (m), 1442 (m), 1360 (m), 1251 (w), 1025 (w), 829 (w), 754
(w).
General procedure
Synthesis of [(o-OCH3)PhCH(C6H2-3-tBu-5-Me-2-O)2]La[N(TMS)2],
[L1La[N(TMS)2] (1). H2L1 (0.92 g, 2.06 mmol) dissolved in 15 mL of
THF was slowly added to La[N(TMS)2]3 (1.28 g, 2.06 mmol) dissolved
in 25 mL of THF. The reaction mixture was stirred for 3 h at 60 °C,
and all volatiles were removed under oil pump vacuum. 10 mL of
toluene was added to extract the product, and orange-yellow
microcrystals were obtained in a nearly quantitative yield by cooling
the toluene solution (1.41 g, 92 % based on La). mp. 236-238 °C. 1H
Synthesis of [(o-OCH3)PhCH(C6H2-3-tBu-5-Me-2-O)2]La(PzMe2)
(THF)3, [L1Gd(Me2Pz)(THF)3] (5). Method A. Complex 1 (1.16 g,
1.56 mmol) dissolved in 10 mL of THF was added to Me2PzH (0.15 g,
1.56 mmol) dissolved in 10 mL of THF. The reaction mixture was
stirred for 6 h at 60 °C, and then the all volatiles was removed
under oil pump vacuum. Toluene was added to extract the product,
and pale-blue microcrystals were obtained from the concentrated
toluene solution at -30 °C (1.20 g, 86 % base on La). mp. 256-258 °C.
NMR (400 MHz, C6D6, 25°C): δ = 7.21 (s, Ar
7.01 (d, J = 7.4 Hz, Ar , 2 H), 6.74 (d, J = 7.9 Hz, Ar
= 2.0 Hz, Ar , 1 H ), 5.84 (s, C , 1 H), 3.00 (s, OCH3, 3 H), 2.20 (s, CH3,
H
, 2 H), 7.13 (s, Ar
H, 2 H),
H
H
, 1 H ), 6.56 (d, J
H
H
6 H), 1.29 (s, C(CH3)3, 18 H), 0.48 (s, Si(CH3)3, 18 H). 13C NMR (101
MHz, C6D6, 25°C): δ = 158.7 (Ar), 158.1 (Ar), 136.8 (Ar), 132.5 (Ar),
130.2 (Ar), 129.4 (Ar), 129.3 (Ar), 127.3 (Ar), 125.8 (Ar), 124.1 (Ar),
121.5 (Ar), 113.1 (Ar), 55.9 (O
CH3), 41.7 (CH), 35.5 (C(CH3)3), 30.7
1H NMR (400 MHz, d6-DMSO, 25°C): δ = 7.25 (t, J = 7.5 Hz, Ar
H
, 1 H),
, 1 H ),
, 1 H), 5.75 (s, PzH,
(C
(CH3)3), 25.5 ( H3), 5.4 (Si(CH3)3). Anal. Calcd for C36H54LaNO3Si2: C,
C
7.16 (s, ArH, 1 H), 7.08 (m, Ar
, 2 H ), 6.51 (s, Ar
H
, 1 H), 6.77 (d, J = 7.9 Hz, Ar
H
58.12; H, 7.32; N, 1.88; La, 18.67. Found: C, 57.94; H, 7.54; N, 1.72;
La, 18.51. IR (KBr, cm-1): 2961 (s), 2899 (m), 2871 (m), 1601 (w),
1460 (m), 1437 (m), 1362 (m), 1248 (w), 1024 (w), 833 (w), 752 (w).
6.60 (s, Ar
H
H
, 2 H ), 6.39 (s, C
H
1 H), 3.60 (t, J = 5.8 Hz, THF, 12 H), 3.34 (s, OCH3, 3 H), 2.12 (s,
Pz(CH3)2, 6 H), 2.02 (s, ArCH3, 6 H), 1.76 (t, J = 5.9 Hz , THF, 12 H),
1.37 (s, C(CH3)3, 18 H). 13C NMR (101 MHz, d6-DMSO, 25°C): δ =
162.7 (Ar), 161.2 (Ar), 157.9 (C(Pz), 137.1 (Ar), 134.2 (Ar), 133.9 (Ar),
129.7 (Ar), 128.2 (Ar), 127.3 (Ar), 125.3 (Ar), 122.8 (Ar), 121.5 (Ar),
112.2 (Ar), 103.1 (C(Pz)), 67.5 (THF), 56.4 (OCH3), 55.5 (CH), 35.0
(C(CH3)3), 31.4 (C(CH3)3), 31.2 (ArCH3), 25.6 (THF), 21.5 (CH3). Anal.
Calcd for C47H67LaN2O6: C, 63.08; H, 7.55; N, 3.13; La, 15.22. Found:
C, 62.92; H, 7.67; N, 3.04; La, 15.13. IR (KBr, cm-1): 2960 (s), 2920
(m), 2868 (m), 1590 (w), 1465 (m), 1442 (m), 1397 (w), 1285 (w),
1250 (m), 1178 (w), 1034 (w), 864 (w), 754 (m), 692 (w).
Synthesis of [(o-OCH3)PhCH(C6H2-3-tBu-5-Me-2-O)2]Gd[N(TMS)2],
[L1Gd[N(TMS)2] (2). The synthesis of complex 2 was carried out in
the same way as the described for the synthesis of complex 1, but
Gd[N(TMS)2]3 (1.32 g, 2.07mmol) was used instead of La[N(TMS)2]3.
Orange-yellow microcrystals were obtained from subsequent work
(1.47 g, 93 % based on Gd). mp. 242-245 °C. Anal. Calcd for
C36H54GdNO3Si2: C, 56.73; H, 7.14; N, 1.84; Gd, 20.63. Found: C,
56.58; H, 7.37; N, 1.75; Gd, 20.49. IR (KBr, cm-1): 2960 (s), 2902 (m),
2870 (m), 1599 (w), 1460 (m), 1439 (m), 1361 (m), 1245 (w), 1018
(w), 834 (w), 750 (w).
Method B. H2L1 (0.92 g, 2.06 mmol) dissolved in 15 mL of THF was
slowly added to La[N(TMS)2]3 (1.28 g, 2.06 mmol) dissolved in 25 mL
6 | RSC Advance.
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of THF at 60 °C. After the solution was stirred for 3 h at 60 °C, (m), 2870 (m), 1594 (w), 1460 (m), 1438 (m), 1360 (m), 1288 (w),
Me2PzH (0.20 g, 2.06 mmol) was added. The reaction mixture was 1251 (w), 1049 (w), 1030 (w), 835 (w), 756 (m), 691 (w).
stirred for 6 h at 60 °C, and then the all volatiles were removed
under oil pump vacuum. Toluene was added to extract the product,
Syntheses of [(o-OCH3)PhCH(C6H2-3,5-tBu2-2-O)2]Gd(PzMe2)(THF)3,
and pale-blue microcrystals were obtained by cooling the toluene
[L2Gd(PzMe2)(THF)3] (8). The synthesis of complex 8 was carried out
solution (1.56 g, 85% base on La).
in the samilar way as that described for complex 5 (method B), but
Method C. Me2PzH (0.84 g, 1.35 mmol) dissolved in 15 mL of THF
H2L2 (1.04 g, 1.95 mmol) and Gd[N(TMS)2]3 (1.24 g, 1.95 mmol)
was slowly added to La[N(TMS)2]3 (0.13 g, 1.35 mmol) dissolved in
was used and subsequent work to afford
8 as pale-blue
25 mL of THF at -30 °C. After the solution was stirred for 12 h at
60 °C, H2L1 (0.60 g, 1.35 mmol) was added. The reaction mixture
was stirred for 6 h at 60 °C, and then the all volatiles were removed
under oil pump vacuum. Toluene was added to extract the product,
and pale-blue microcrystals were obtained by cooling the toluene
solution (0.86 g, 85% base on La).
microcrystals (1.64 g, 84 %, base on Gd). mp. 272-274 °C. Anal.
Calcd for C53H79GdN2O6: C, 63.82; H, 7.98; N, 2.81; Gd, 15.77. Found:
C, 63.68; H, 7.86; N, 2.97; Gd, 15.63. IR (KBr, cm-1): 2960 (s), 2904
(m), 2866 (m), 1600 (w), 1461 (m), 1436 (m), 1361 (m), 1292 (w),
1254 (w), 1054 (w), 1029 (w), 833 (w), 756 (m), 692 (w).
Complex c｛Me2PzLa[N(TMS)2]2(THF)2｝：mp. 187-189 °C. 1H NMR
(400 MHz, C6D6): δ 6.17 (s, 1H, Pz-H), 3.68 (m, 8H, THF), 2.29 (s, 6H,
CH3), 1.34 (m, 8H, THF), 0.34 (s, 36H, SiMe3). 13C NMR (101 MHz,
C6D6): δ 145.2(C=N), 109.4(C=C), 68.5(THF), 24.9(THF), 13.0(CH3),
3.6(Si(CH3)3). Anal. calcd. for C25H57LaN4O2Si4: La, 19.93; C, 43.08; H,
8.24; N, 8.04. Found: La, 19.73; C, 43.24; H, 8.02; N, 8.19.
Conclusion
In summary, a series of new heteroleptic lanthanide amides
complexes bearing carbon-bridged bis(phenolate) ligands have
been synthesized via simple protonolysis exchange reactions using
Complex d｛Me2PzGd[N(TMS)2]2(THF)2｝：mp. 194-196 °C. Anal.
calcd. for C25H57GdN4O2Si4: Gd, 21.92; C, 41.86; H, 8.29; N, 7.81.
Found: La, 21.71; C, 42.03; H, 8.13; N, 8.02.
Ln[N(TMS)2]3(Ln
= La, Gd) as the starting material. At frist,
Ln[N(TMS)2]3 reacted with H2Ln (n = 1, 2) to produce complexes 1 –
4, which can further react with 1 equiv of Me2PzH in THF to yield
heteroleptic pyrazolato lanthanide complexes 5 – 8 in high yield.
Meanwhile, Ln[N(TMS)2]3(Ln = La, Gd) reacted with Me2PzH to form
Synthesis of [(o-OCH3)PhCH(C6H2-3-tBu-5-Me-2-O)2]Gd(PzMe2)
(THF)3, [L1Gd(Me2Pz)(THF)3] (6). The synthesis of complex 6 was
carried out in the samilar way as that described for complex 5
(method B), but Gd[N(TMS)2]3 (1.12 g, 1.75 mmol) was used instead
of La[N(TMS)2]3. Amount of pale-blue microcrystals were obtained
from the concentrated tolune solution (1.39 g, 87 %, base on Gd).
mp. 267-269 °C. Anal. Calcd for C47H67GdN2O6: C, 61.81; H, 7.39; N,
3.07; Gd, 17.22. Found: C, 61.72; H, 7.51; N, 3.14; Gd, 17.11. IR (KBr,
cm-1): 2958 (s), 2919 (m), 2871 (m), 1587 (w), 1467 (m), 1442 (m),
1394 (w), 1288 (w), 1246 (m), 1180 (w), 1030 (w), 866 (w), 756 (m),
691 (w).
complex Me2PzLn[N(TMS)2]2(THF)2, which can be used as
a
precursor to synthesize the corresponding heteroleptic pyrazolato
lanthanide complexes by a further reaction with 1 equiv of H2Ln (n =
1, 2). Moreover, the complexes LLnPzMe2 can also be synthesized
by the direct reaction of Ln[N(SiMe3)2]3 with H2L and Me2PzH in
1:1:1 molar ratio in situ in THF, all of these syntheses are quite
straight forward and easy to access. These aminolanthanide
complexes are well-characterized, and 5 – 8 of them are structurally
characterized. The coordination geometries around the central
metals in these complexes are similar. Furthermore, it was found
that these complexes can catalyze the controlled polymerization ε-
CL via a coordination-insertion mode, and the amides groups has a
significant effect on the polymerization.
Synthesis of [(o-OCH3)PhCH(C6H2-3,5-tBu2-2-O)2]La(PzMe2)(THF)3,
[L2La(PzMe2)(THF)3] (7). The synthesis of complex 7 was carried out
in the samilar way as that described for complex 5 (method B), but
H2L2 (1.15 g, 2.16 mmol) was used instead of H2L1. Pale-blue
microcrystals were obtained from the concentrated tolune solution
(1.84 g, 87%, base on La). mp. 264-266 °C. 1H NMR (400 MHz, d6-
Acknowledgment
DMSO, 25°C) : δ = 7.25 (m, Ar
7.06 (m, Ar , 1 H) , 6.99 (d, J = 6.3 Hz, Ar
Ar , 2 H ), 6.65 (m, Ar , 1 H), 6.27 (s, C
H
, 1 H), 7.18 (d, J = 7.1 Hz, Ar
, 2 H ), 6.76 (d, J = 5.8 Hz,
, 1 H), 5.76 (s, Pz , 1 H),
H, 1 H),
This work was supported by State Key Laboratory of ASIC & System,
Fudan University (12KF007), and A Project Funded by the Priority
Academic Program Development of Jiangsu Higher Education
Institutions.
H
H
H
H
H
H
3.60 (t, J = 5.8 Hz, THF, 12 H), 3.19 (s, OCH3, 3 H), 2.13 (s, Pz(CH3)2, 6
H), 1.76 (t, J = 5.9 Hz, THF, 12 H), 1.39 (s, C(CH3)3, 18 H), 1.13 (s,
C(CH3)3, 18 H). 13C NMR (101 MHz, d6-DMSO, 25°C): δ = 162.71 (Ar),
161.9 (Ar), 159.1 (C(Pz), 139.8 (Ar), 133.6 (Ar), 133.5 (Ar), 133.0 (Ar),
132.6 (Ar), 130.4 (Ar), 129.4 (Ar), 128.7 (Ar), 124.5 (Ar), 112.9 (Ar),
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DOI: 10.1039/C5RA23520K
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Heteroleptic lanthanide amides complexes bearing carbonꢀbridged bis(phenolate) ligands:
synthesis, structure and their application in the polymerization of εꢀcaprolactone
YanꢀXu Zhou1, Jing Zhao 1, Ling Peng1, YuꢀLong Wang1, Xian Tao1, YingꢀZhong Shen1*
The bis(phenolato)lanthanide complexes LLnN(SiMe3) [L = L1, Ln = La (1); Ln = Gd (2); L = L2, Ln = La (3); Ln = Gd
(4) ] were synthesized by the reaction of Ln[N(SiMe3)2]3 (Ln = La, Gd) with H2L in a 1:1 molar ratio in THF. Complexes
5 – 8 can also be synthesized by the direct reaction of Ln[N(SiMe3)2]3 with H2L and Me2PzH in 1:1:1 molar ratio in situ
in THF. Complexes 5 ꢀ 8 have been characterized by Xꢀray crystal structural analysis. The catalyst activity of compounds
1 ꢀ 8 to the ringꢀopening polymerization of εꢀcaprolactone was studied.