Synthesis and characterization of benzoxazine-functionalized amine bridged bis(phenolate) lanthanide complexes and their application in the ring-opening polymerization of cyclic esters

Article abstract of DOI:10.1039/c2dt11736c

The synthesis and structures of lanthanide complexes supported by benzoxazine-functionalized amine bridged bis(phenolate) ligand 6,6′-(2-(8-tert-butyl-6-methyl-2H-benzo[e][1,3]oxazin-3(4H)-yl) ethylazanediyl)bis(methylene)bis(2-tert-butyl-4-methylphenolato) (L ^2-) are described. Salt metathesis reaction between lanthanide trichloride and 2 eq of LNa₂ in THF at room temperature afforded the corresponding "ate" complexes [L₂LnNa(THF)₂] (LnY (1), Nd (2), Er (3), Yb (4)). Further treatment of the product with 18-crown-6 afforded discrete ion-pair complexes [L₂Ln][(18-crown-6) Na(THF)₂] (LnY (5), Yb (6)). The single-crystal structural analyses of 1 and 3-6 revealed that the lanthanide cation and the sodium cation were bridged by two phenolate oxygen atoms in complexes 1, 3 and 4, while in complexes 5 and 6, the anion comprises a lanthanide cation coordinated by two L^2- and the cation is comprised of a sodium cation surrounded by an 18-crown-6 and two THF molecules. These complexes were found to exhibit distinct activities towards the ring-opening polymerization of ε-caprolactone and l-lactide. The Royal Society of Chemistry 2012.

Full text of DOI:10.1039/c2dt11736c

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PAPER
Synthesis and characterization of benzoxazine-functionalized amine bridged
bis(phenolate) lanthanide complexes and their application in the ring-opening
polymerization of cyclic esters†
Zhenhua Liang, Xufeng Ni,* Xue Li and Zhiquan Shen*
Received 14th September 2011, Accepted 1st December 2011
DOI: 10.1039/c2dt11736c
The synthesis and structures of lanthanide complexes supported by benzoxazine-functionalized amine
bridged bis(phenolate) ligand 6,6′-(2-(8-tert-butyl-6-methyl-2H-benzo[e][1,3]oxazin-3(4H)-yl)
ethylazanediyl)bis(methylene)bis(2-tert-butyl-4-methylphenolato) (L2−) are described. Salt metathesis
reaction between lanthanide trichloride and 2 eq of LNa2 in THF at room temperature afforded the
corresponding “ate” complexes [L2LnNa(THF)2] (LnvY (1), Nd (2), Er (3), Yb (4)). Further treatment of
the product with 18-crown-6 afforded discrete ion-pair complexes [L2Ln][(18-crown-6)Na(THF)2]
(LnvY (5), Yb (6)). The single-crystal structural analyses of 1 and 3–6 revealed that the lanthanide
cation and the sodium cation were bridged by two phenolate oxygen atoms in complexes 1, 3 and 4,
while in complexes 5 and 6, the anion comprises a lanthanide cation coordinated by two L2− and the
cation is comprised of a sodium cation surrounded by an 18-crown-6 and two THF molecules. These
complexes were found to exhibit distinct activities towards the ring-opening polymerization of
ε-caprolactone and L-lactide.
advantages: economical and easy preparation and relative ease of
Introduction
manipulation of coordination number, as well as the “tunability”
of the steric factors.4 The previous studies have shown that the
Organolanthanide complexes are useful catalysts for many
polymerization reactions1 and organic synthesis.2 The catalytic
choice of bis(phenolate) framework and its combination with
behavior of the complexes is greatly affected by the steric and
electronic environment around the metal center provided by the
ligand.3 Hence, the designation of new ligands plays a significant
role in exploring new complexes with novel structure and new
reaction properties. Recently, many researchers are interested in
amine bis(phenolate) ligands (Chart 1A) because of their
extra sidearm nitrogen/oxygen donors incorporated in the bis
(phenolate) scaffolds are critical for the activity and stereocontrol
ability of the catalysts.4f,4i
Polybenzoxazine, a newly developed high performance ther-
mosetting resin system, has attracted considerable interest for its
interesting features and capability to overcome several shortcom-
ings of conventional novolac and resole type phenolic resins.5
Benzoxazine monomers are synthesized by condensation reac-
tion of primary amines with formaldehyde and substituted
phenols. The “hard” nitrogen and oxygen donor atoms in ben-
zoxazine ring (Chart 1B) have the potential to coordinate with
the metal center during the formation of metal complex, if it has
been incorporated in the ligand. Various types of benzoxazine
monomer have been synthesized using phenols and amines with
different substitution groups attached.5 However, in spite of few
Cu6 and Ag7 complexes bearing benzoxazine as anionic ligands,
to our best knowledge, no research on the synthesis of metal
complexes bearing ligands containing benzoxazine monomer as
a neutral pendant has been reported before this work. Herein we
report the synthesis of an amine bridged bis(phenolate) ligand
with a benzoxazine group on the sidearm of the amine bridge
(Chart 1C) and its lanthanide “ate” complexes containing a Na
cation. The “ate” complexes were further reacted with 18-crown-
6 to form discrete ion-pair lanthanide complexes. In addition,
these complexes were used to initiate the ring-opening polymer-
ization of ε-caprolactone and L-lactide.
Chart 1
MOE Key Laboratory of Macromolecular Synthesis and
Functionalization, Department of Polymer Science and Engineering,
Zhejiang University, Hangzhou, 310027, China. E-mail: xufengni@zju.
edu.cn, zhiqaun_shen@163.com; Fax: 86 571 87951773; Tel: 86 571
87953739
†Electronic supplementary information (ESI) available: CCDC reference
numbers 837472–837476. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c2dt11736c
2812 | Dalton Trans., 2012, 41, 2812–2819
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Scheme 2 Synthesis of [L2LnNa(THF)2].
Scheme 1 Synthesis of H2L.
Results and discussion
Synthesis and characterization of lanthanide complexes (1–6)
Dibenzoxazine was prepared by the Mannich condensation of
2-tert-butyl-4-methylphenol, ethane-1,2-diamine and paraformal-
dehyde in a molar ratio 2 : 1 : 6 (Scheme 1).8 Subsequent treat-
ment of this product with two equivalents of 2-tert-butyl-4-
methylphenol in benzene provided the benzoxazine-functiona-
lized amine-bis(phenol) H2L in high yield. Their structures were
confirmed by NMR studies. Treatment of H2L with excess
sodium metal in THF affords [LNa2(THF)] with high yield. The
isolated sodium salt was characterized by NMR analysis.
Lanthanide chloride complexes of amine-bis(phenolate)
ligands have been synthesized by the salt metathesis reaction
between LnCl3 and one equivalent of corresponding lithium or
sodium salt in THF.4e,4j We tried to synthesize lanthanide chlor-
ide complexes supported by benzoxazine-functionalized amine-
bis(phenolate) ligand (L) by the reaction of LnCl3 (LnvSc, Y,
Nd, Gd) with one equivalent of corresponding lithium or sodium
salt in THF. After the reaction, the product was extracted by
toluene, however, our attempts failed in isolating a crystalline
product from several solvents (toluene, hexane, diethyl ether).
The solute should be lanthanide complexes bearing L, since
LnCl3(THF)x is insoluble in toluene and the EDTA titration
results showed that the conversions of the lanthanides are more
than 90%. The difficulty of the isolation of crystalline product
might be due to two reasons: (a) if the benzoxazine group can
coordinate with the metal center like the amino sidearm in
lanthanide amine-bis(phenolate) complexes, there might be two
enantiomers in the solution as the two sides of the nitrogen atom
in benzoxazine group are not symmetric; (b) if the benzoxazine
group is too large to coordinate with the metal, the nitrogen and
oxygen atoms in the benzoxazine ring might compete with the
intermolecular coordinated THF for coordinating sites and this
may cause the formation of oligomer. Our attempt to isolate this
product will go on.
Fig. 1 X-Ray structure of 4 with thermal ellipsoids at the 50% prob-
ability level. Hydrogen atoms are omitted for clarity.
room temperature. They are isostructures. The X-ray structure of
4 is shown in Fig. 1, and selected bond angles and lengths of 1,
3 and 4 are listed in Table 1. Complex 4 has a C2 symmetrical
dinuclear structure which comprises a six-coordinated rare-earth
metal center coordinated by four oxygen atoms and two nitrogen
atoms from two amine bis(phenolate) ligands in a distorted octa-
hedron, and a four-coordinated sodium cation. Unlike those in
the lanthanide complexes bearing a mono amine bis(phenolate)
ligand,4a–c,4d–m the pendant nitrogen atom in benzoxazine group
does not coordinate to the central metal. It is reasonable to
ascribe this difference to the increased steric hindrance in com-
plexes due to the coordination of two bulky amine bis(phenol-
ate) groups to one rare-earth metal atom. This structure is similar
to the lanthanide “ate” complex [(Me2NCH2CH2N{CH2-(2-O-
C6H2-But2-2,4)}2)2YbNa(THF)2].4d The bridging Yb–O(Ar) and
Yb–N bond lengths are comparable with the previously reported
values.4d The average bridging Ln–O(Ar) bond lengths are about
0.07 Å longer than that of the terminal one, which is comparable
with that observed in [(Me2NCH2CH2N{CH2-(2-O-C6H2-But2-
2,4)}2)2YbNa(THF)2].4d The bite angle O1–Yb–O2 of 154.297°
in complex 4 is apparently larger than those found in carbon
bridged bis(phenolate) complexes.9 The bite angle O1–Y–O2 of
152.649° in complex 1 is smaller than that in complex 4 as the
radii of the rare-earth metal cation is smaller.
The reaction of LnCl3 with two equivalents of LNa2 in THF
afforded
the
expected
lanthanide
“ate”
complexes
[L2LnNa(THF)2] (LnvY (1), Nd (2) , Er (3), Yb (4)) in high
yields. These complexes gave satisfactory elemental analyses (C,
H, N, Ln). Further single crystal X-ray diffraction studies of
complexes 1, 3 and 4 revealed that the new lanthanide “ate”
complexes were formed: a Na atom is connected to one oxygen
atom from each of the amine bis(phenolate) ligands as shown in
Scheme 2. The structure of 1 was also confirmed by NMR
spectroscopy.
Crown ethers exhibit an extremely versatile range of inter-
actions with alkali metal cations in the solid state.10 The reaction
of [L2LnNa(THF)2] (LnvY (1), Yb (4)) with 3 equivalents of
18-crown-6 in toluene at 80 °C for 3 h afforded the discrete ion-
pair complexes [L2Ln][(18-crown-6)Na(THF)2] (LnvY (5), Yb
(6)) which were confirmed by elemental analyses, single crystal
X-ray diffraction analyses and NMR in the case of 5 (Scheme 3).
Crystals of complexes 1, 3 and 4 suitable for an X-ray diffrac-
tion study were grown from concentrated toluene solution at
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Table 1 Selected bond lengths (Å) and bond angles (°) for 1, 3 and 4
angles of 5 and 6 are provided in Table 2. Complex 5 is com-
posed of a discrete six-coordinate [L2Y]− anion and an [(18-
crown-6)Na(THF)2]+ cation. In the anion, the yttrium atom is
located in the centre of an octahedron comprised of four phenol-
ate oxygen atoms and two nitrogen atoms from two amine-
bisphenolate ligands. Two phenolate oxygen atoms from one
ligand and two nitrogen atoms from two ligands can be con-
sidered to occupy equatorial positions within the octahedron
about yttrium center and the other two oxygen atoms from the
other ligand can be considered to occupy axial positions. The
average Yb–O(Ar) bond length in complex 6 is 2.140 Å, which
falls in the range between the terminal and bridging Yb–O(Ar)
bond lengths in complex 4. The bite angles O1–Yb–O2 and O4–
Yb–O5 of 157.158° and 157.508° are larger than that observed
in complex 4 and larger than that of the discrete ion-pair carbon
bridged bis(phenolate) lanthanide complexes.13 In the cation, the
18-crown-6 macrocycle adopts an approximately planar arrange-
ment of oxygen atoms in which the Na+ is centrally located with
the six oxygen atoms alternating above and below the plane and
two THF molecules coordinated to Na+ below and above the
planar. This is the standard crown configuration for Na+ or K+.10
The coordination geometry of the sodium cation may be
described as an axially bicapped trigonal antiprism with two
THF oxygen occupying the two axial coordination sites. The
Na–O distances in the macrocycle complex are in the range
2.516–3.021 Å, with an average distance of 2.701 Å. The Na–O
distances to the two axial THF molecules are much shorter at
2.363 Å and 2.321 Å. These values are comparable with values
reported in the previous literature.14
Bond length
1
3
4
Ln–O(1)
Ln–O(2)
Ln–N(1)
Na–O(2)
2.136(2)
2.212(3)
2.564(3)
2.356(3)
2.320(4)
2.133(2)
2.196(2)
2.539(2)
2.338(2)
2.306(2)
2.114(2)
2.185(2)
2.525(2)
2.338(2)
2.309(2)
Na–O(4)
Bond angle
O1–Ln–O2
O1–Ln–N1
O2–Ln–N1
O2–Ln–O2A
O1–Ln–O1A
O2–Na–O2A
152.64(9)
76.64(9)
77.35(9)
83.21(13)
98.99(15)
83.21(13)
152.96(6)
76.75(6)
77.43(6)
83.25(9)
98.59(9)
77.21(9)
154.29(7)
77.43(7)
78.04(7)
83.52(9)
98.37(10)
76.97(10)
Scheme 3 Synthesis of [L2Ln][(18-crown-6)Na(THF)2].
These complexes (1–6) are moderately air- and moisture-sen-
sitive. Although their solutions changed gradually to dark green
in a few minutes, the crystals can be exposed to air for three
hours without apparent decomposition. These complexes are
freely soluble in THF, slightly soluble in toluene but insoluble in
hexane.
Although there are examples shown that crown ethers coordinate
with a lanthanide cation to form novel neutral11 or cationic
lanthanide complexes,12 in this reaction the excess crown ether
did not coordinate with a lanthanide atom. There were some dis-
crete ion-pair anionic lanthanide complexes reported in the pre-
vious literature,9,13 but these complexes are the first examples
consisting of a crown ether.
Crystals of complexes 5 and 6 suitable for an X-ray diffraction
study were obtained from a toluene solution at room temperature.
They are isostructural. The structure of 5 with the atom-number-
ing scheme is shown in Fig. 2 and the selected bond lengths and
Ring-opening polymerization of ε-caprolactone and L-lactide
Poly(ε-caprolactone) (PCL) and Poly(lactide) (PLA) are promis-
ing biomaterials for their widely recognized biocompatibility15
and biodegradability16 Ring-opening polymerization (ROP) of
ε-caprolactone (CL) and L-lactide (L-LA) is the most important
method to prepare PCL and PLLA with well controlled molecu-
lar weight and narrow molecular weight distribution. Recently,
alkali metals,17 poor metals,18 transition metals,18c,18e,19 and
lanthanide20,21 metal-based catalysts were used to initiate the
ROP of CL and L-LA.
All these complexes (1–6) can initiate the ROP of CL in
toluene at 70 °C. The polymerization results are listed in
Table 3. For complexes 1, 2 and 4, high conversions (>90%) was
reached after 24 h. A comparison study of the activities of these
complexes revealed that the activities of the discrete ion-pair
complexes (entry 9 and 10) are lower than their “contact” com-
plexes counterparts (entry 1 and 4, conversion < 50%). All the
number average molecular weight (Mn) values of the PCLs with
different initiators at different monomer/initiator molar ratio
1
determined by SEC and H-NMR were in overall good agree-
Fig. 2 X-Ray structure of 5 with thermal ellipsoids at the 50% prob-
ability level. Hydrogen atoms are omitted for clarity.
ment with the calculated values (Mn cal in Table 3) based on the
2814 | Dalton Trans., 2012, 41, 2812–2819
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Table 2 Selected bond lengths (Å) and bond angles (°) for 5 and 6
Complex
5
6
5
6
Ln–O1
Ln–O2
Ln–O4
Ln–O5
Ln–N1
Ln–N3
Na–O7
Na–O8
Na–O9
Na–O10
Na–O11
2.168(2)
2.180(2)
2.167(2)
2.156(2)
2.558(2)
2.563(2)
3.021
2.140(2)
2.146(2)
2.136(2)
2.137(2)
2.516(2)
2.520(3)
3.01
Na–O12
Na–O13
Na–O14
2.744(3)
2.363(3)
2.327(3)
154.27(7)
154.91(7)
75.51(7)
79.00(7)
78.98(7)
75.93(7)
178.67(7)
163.84(9)
2.732(3)
2.363(3)
2.321(3)
157.15(8)
157.50(8)
77.00(8)
80.37(3)
80.26(8)
77.24(8)
178.90(8)
163.63(9)
O1–Ln–O2
O4–Ln–O5
O1–Ln–N1
O2–Ln–N1
O4–Ln–N3
O5–Ln–N3
N1–Ln–N3
O13–Na–O14
2.744
2.7596
2.516(3)
2.608(3)
2.609(3)
2.500(3)
2.604(3)
2.601(3)
Table 3 Polymerization of CL initiated by complexes 1–6a
e
Entry
Initiator
[CL]/[I]b
Conversion (%)
Mn cal (103)c
MnNMR (103)d
MnSEC (103)e
7.2
Mw/Mn
1
2
3
4
5
6
7
8
9
1
1
1
4
4
4
2
3
5
6
100
200
400
100
200
400
100
100
100
100
91
90
47
95
82
49
>99
66
40
39
5.2
5.0
8.5
7.5
4.6
7.5
7.9
5.3
3.7
2.1
1.9
1.49
1.47
1.30
1.56
1.68
1.15
1.39
1.44
1.17
1.13
10.2
10.7
5.4
9.4
11.2
5.7
3.8
2.3
2.2
12.4
9.8
6.2
10.9
9.2
8.9
3.9
2.7
2.4
10
c
1
a Conditions: [CL]0 = 1 mol L−1, 70 °C in toluene for 24 h. b CL/initiator molar ratio. Mn cal = ([CL]0/[I])×Mw(CL)×(conv./100)/2. d By H-NMR
analysis. e Measured by SEC at 40 °C in THF relative to polystyrene standards using a correcting factor of 0.56 for Mn.22
Table 4 Polymerization of L-LA initiated by complexes 1 and 2a
d
Entry
Initiator
T/°C
Time (h)
[L-LA]/[I]b
Conversion (%)
MnNMR (103)c
MnSEC(103)d
Mw/Mn
1
2
3
4
5
6
1
1
2
2
2
2
20
50
20
20
20
20
24
24
6
6
24
24
100
100
100
200
300
400
—
3
99
95
86
13
—
—
3.90
6.15
8.18
3.18
—
—
1.46
1.51
1.40
1.10
1.58
2.64
3.78
4.78
3.0
a Conditions: [L-LA]0 = 1 mol L−1, THF as solvent. b L-LA/initiator molar ratio. c By 1H-NMR analysis. d Measured by SEC at 40 °C in THF relative
to polystyrene standards using a correcting factor of 0.58 for Mn.22
growth of two polymer chains per Ln cation, and the molecular
weight distributions were moderately narrow (Mw/Mn
The preliminary results are listed in Table 4. Complex 2 can
initiate the ROP of L-LA in THF at 20 °C. The MnSEC of the
PLLAs obtained by complex 2 increases from 3.9 × 103 to 8.2 ×
103 g mol−1 (entries 3–5 in Table 4) as the [L-LA]/[I] molar
ratio increase from 100 to 300. In contrast to complex 2,
complex 1 cannot initiate the ROP of L-LA at the same con-
dition (entry 1 in Table 4) and the conversion is only 3% even at
higher temperature (50 °C) for 24 h (entry 2 in Table 4).
=
1.13∼1.68). These phenomena can probably be explained by the
structures of these complexes. In complexes 1–4, each complex
has four ArO groups which have the potential to initiate the ring-
opening polymerization of CL, but the two bridging ArO–Ln
bonds are longer and weaker than the corresponding terminal
ArO–Ln bonds in complexes 1–4 and the corresponding
ArO–Ln bonds in the anion part of the discrete ion-pair com-
plexes, so the two bridging ArO groups are more active than the
nonbridging ArO groups for the initiation of CL polymerization.
As a result, the “contact” complexes are more active than their
discrete ion-pairs and each Ln cation initiates two PCL chains.
Because complex 2 showed relatively higher activity for ROP
of CL, its catalytic character for ROP of L-LA was also studied.
The end groups and the Mns (MnNMR in Table 3 and Table 4)
1
of these PCLs and PLAs are analyzed by H-NMR spectra. The
1H-NMR analysis (supported in the ESI†) reveal that these poly-
mers are capped by a methyl ester at one end and a hydroxyl
group at the other. The formation of the methyl ester may be
ascribed to the replacement of the phenolate (ArO) ester bond by
methanol during termination. The presence of the end groups
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indicated that the ROP of CL and L-LA initiated by these com-
plexes are preceded by an acyl-oxygen bond cleavage and
cooperated coordination–insertion mechanism.20a,20b
1H NMR (400 MHz, CDCl3, 25 °C): δ 9.01 (2H, s, OH) 7.02
(2H, s, ArH), 6.91 (1H, s, ArH), 6.74 (2H, s, ArH), 6.53 (1H, s,
ArH), 4.93 (2H, s, NCH2O benzoxazine ring), 4.03 (2H, s,
ArCH2N benzoxazine ring), 3.63 (2H, s, NCH2Ar), 3.03 (2H, t,
J = 6 Hz, NCH2CH2- benzoxazine ring), 2.66 (2H, t, J = 6 Hz,
NCH2CH2- benzoxazine ring), 2.25 (6H, s, CH3Ar), 2.23 (3H, s,
CH3Ar), 1.42 (18H, s, C(CH3)3), 1.34 (9H, s, C(CH3)3)); 13C
NMR (100 MHz, CDCl3, 25 °C): δ 153.3, 150.3, 137.7, 137.1,
129.6, 129.1, 127.6, 127.5, 126.0, 122.5, 119.0 (Ar-C), 81.5
(NCH2O), 56.6 (ArCH2NCH2Ar), 49.4 (NCH2CH2-benzoxazin),
49.3 (NCH2CH2-benzoxazin), 47.9 (NCH2Ar benzoxazin), 35.1
(C(CH3)3), 34.8 (C(CH3)3), 29.9 (C(CH3)3), 21.2 (ArCH3), 21.1
(ArCH3), 21.1(ArCH3).
Conclusion
Lanthanide “ate” complexes containing sodium cation were syn-
thesized and further treatment of the product with 18-crown-6
afforded discrete ion-pair complexes. These complexes are
employed to initiate the controlled ring-opening polymerization
of CL and L-LA, and the experimental results showed that the
contact “ate” complexes are more active than their discrete ion-
pair counterpart in ring-opening polymerization of CL.
[LNa2(THF)]. H2L (1.2 g, 2 mmol) was dissolved in 20 mL
THF and then sodium metal (0.55 g, 24 mmol) was added at
room temperature. After stirring at room temperature for 12 h,
the reaction mixture was filtered and the solvent was removed
under vacuum. The residue was dissolved by 20 mL hexane and
then the solution was concentrated to about 5 mL. White powder
formed in the solution at room temperature after 1 day. (1.27 g,
89%).1H NMR (400 MHz, CDCl3, 25 °C): δ 7.00 (2H, s, ArH),
6.92 (1H, s, ArH), 6.71 (2H, s, ArH), 6.51 (1H, s, ArH), 4.9
(2H, s, NCH2O benzoxazine ring), 4.01 (2H, s, ArCH2N ben-
zoxazine ring), 3.74 (4H, t, J = 6.4 Hz α-CH2 THF), 3.60 (4H,
s, NCH2Ar), 3.00 (2H, br, NCH2CH2N-benzoxin ring), 2.65
(2H, br, NCH2CH2benzoxin ring), 2.23 (12H, s, CH3Ar), 2.20
(3H, s, CH3Ar), 1.85 (4H, t, J = 6.4 Hz, β-CH2 THF), 1.39
(18H, s, C(CH3)3), 1.31 (9H, s, C(CH3)3)); 13C NMR
(100 MHz, CDCl3, 25 °C): δ153.0, 150.9, 150.26, 137.6, 137.4,
136.9, 129.5, 129.05, 129.00, 127.5, 126.0, 125.9, 125.8, 122.3,
119.7,118.9 (Ar-C), 82.1, 81.4 (NCH2O), 68.2 (α-CH2 THF),
56.4 (ArCH2NCH2Ar), 51.2, 49.7 (NCH2CH2-benzoxazine),
49.2 (NCH2CH2-benzoxazine), 47.8 (NCH2Ar benzoxazine),
34.9 (C(CH3)3), 34.8 (C(CH3)3), 31.8 (C(CH3)3), 29.9
(C(CH3)3), 29.8 (C(CH3)3), 25.9 (β-CH2 THF), 22.9 (ArCH3),
21.1(ArCH3), 21.0(ArCH3).
Experimental Section
General Procedures
All manipulations were performed under argon using standard
Schlenk techniques. THF, hexane and toluene were distilled from
sodium benzophenone ketyl before use. Anhydrous lanthanide
trichloride was prepared according to the literature procedures.23
The other reagents are commercially available and used without
further purification. Lanthanide analyses were performed by
EDTA titration with xylenol orange indicator and hexamine
buffer. Carbon, hydrogen and nitrogen analyses were performed
by direct combustion with a Flash EA-1112 instrument. NMR
spectra were recorded on a Bruker Avance DMX 400 spec-
trometer. Molecular weight (Mn) and molecular weight distri-
bution (MWD = Mw/Mn) were measured by size exclusion
chromatograph (SEC) equipped with RI (Waters 2414) detector
and a Waters 1525 isocratic high performance liquid chromato-
graphy pump at 40 °C with THF as the eluent at a flow rate of
1.0 mL min−1
.
Synthesis
1,2-Bis(8-tert-butyl-6-methyl-2H-benzo[e][1,3]oxazin-3(4H)-yl)
ethane (dibenzoxazine). 2-tert-Butyl-4-methylphenol (4.12 g,
20.0 mmol), aqueous formaldehyde solution (4.11 mL,
50.0 mmol) and ethylenediamine (0.67 mL, 10.0 mmol) were
mixed in 20 mL methanol. The mixture was refluxed overnight
with stirring, and a white precipitate appeared. After the reaction
mixture was cooled to room temperature, the precipitate product
was collected by filtration and finally recrystallized from a THF–
[YL2Na(THF)2] (1)·2toluene. H2L (2.4 g, 4 mmol) was dis-
solved in 40 mL THF and then sodium metal (0.55 g, 24 mmol)
was added at room temperature. After stirring at room tempera-
ture for 12 h, the reaction mixture was filtered and the solution
was added dropwise to the slurry of YCl3 (0.39 g, 2.0 mmol) in
THF (40 mL) at room temperature. After this mixture was stirred
for another 12 h at room temperature, the solvent was removed
under vacuum and a light yellow oil was obtained. The oil was
extracted with 40 mL hot toluene and then filtered; the solution
was concentrated until crystallization occurred, and colorless
crystals were obtained at room temperature in a few days (2.09 g,
72%). Found: C, 74.43; H, 8.70; N, 3.36; Y, 5.32.
1
hexane mixed solvent (3.31 g, 76%). H NMR (400 Hz, CDCl3,
25 °C): δ 6.94 (d, 2H, J = 2 Hz, Ph), 6.63 (d, 2H, J = 2 Hz, Ph),
4.94 (s, 4H, NCH2O benzoxazine ring), 4.08 (s, 4H, NCH2Ar
benzoxazine ring), 3.05 (s, 4H, NCH2CH2N), 2.25 (s, 6H,
ArCH3), 1.35 (s, 18H, tBu).
C
100H140N4NaO8Y requires C, 73.32; H, 8.61; N, 3.42;
1
6,6′-(2-(8-tert-Butyl-6-methyl-2H-benzo[e][1,3]oxazin-3(4H)-
yl)ethylazanediyl)bis(methylene)bis(2-tert-butyl-4-methylphenol)
(H2L). Dibenzoxazine (3.31 g, 7.6 mmol) and 2-tert-butyl-4-
methylphenol (2.5 g, 15.2 mmol) were mixed in 20 mL benzene.
The mixture was stirred and refluxed for 3 days and then the
solvent was removed and 40 mL methanol was added. White
powder was formed in methanol, and it was collected by fil-
tration and finally recrystallized from THF. (3.19 g, 70%)
Y, 5.43%); H NMR (400 MHz, CDCl3, 25 °C): δ 7.00 (4H, s,
ArH), 6.90 (2H, s, ArH), 6.72 (4H, s, ArH), 6.51 (2H, s, ArH),
4.9 (4H, s, NCH2O benzoxazine ring), 4.01 (4H, s, ArCH2N
benzoxazine ring), 3.75 (8H, t, J = 6.4 Hz α-CH2 THF), 3.61
(8H, s, NCH2Ar), 3.01 (4H, t, J = 6.4 Hz, NCH2CH2N-benzoxin
ring), 2.65 (4H, t, J = 6.4 Hz, NCH2CH2benzoxin ring), 2.23
(12H, s, CH3Ar), 2.21 (6H, s, CH3Ar), 1.86 (8H, t, J = 6.4 Hz,
β-CH2 THF), 1.40 (36H, s, C(CH3)3), 1.32 (36H, s, C(CH3)3));
2816 | Dalton Trans., 2012, 41, 2812–2819
This journal is © The Royal Society of Chemistry 2012

View Article Online
13C NMR (100 MHz, CDCl3, 25 °C): δ 162.4, 161.1, 151.5,
138.2, 137.53, 137.50, 136.6, 129.8, 129.4, 129.2, 128.65,
128.6, 128.2, 127.5, 126.2, 125.7, 124.75, 123.8, 123.2, 121.4,
120.8 (Ar-C), 82.7 (NCH2O), 68.3 (α-CH2 THF), 60.3, 59.7
yellow block crystals were isolated from the concentrated
toluene solution at room temperature. (2.5 g, 78%). Found: C,
70.76; H, 8.31; N, 3.16; Yd, 10.25. C100H140N4NaO8Yb requires
C, 69.74; H, 8.19; N, 3.25; Yb, 10.05%).
(ArCH2NCH2Ar),
52.2
(NCH2CH2-benzoxazine),
45.1
(NCH2CH2-benzoxazine), 43.0 (NCH2Ar benzoxazine), 35.2 (C
(CH3)3), 35 (C(CH3)3), 34.8 (C(CH3)3), 30.7 (C(CH3)3), 30.2
(C(CH3)3), 30.1 (C(CH3)3), 30.0 (C(CH3)3), 29.8 (C(CH3)3),
25.7 (β-CH2 THF), 21.8 (ArCH3), 21.3(ArCH3), 21.1(ArCH3).
[Y(L)2][(18-Crown-6)Na(THF)2]
(5)·toluene. Complex
1
(1.00 g, 0.7 mmol) was dissolved in 40mL toluene and to this
solution 18-crown-6 (0.55 g, 20 mmol) was added at room temp-
erature. The mixture was heated to 80 °C and stirred for 12 h.
The reaction mixture was cooled to room temperature and the
solvent was removed under vacuum until a light yellow oil
formed. Then, 50 mL hexane was added and the mixture was
sonicated for 30 min and a white precipitate fell out. The hexane
was removed by syringe and the precipitate was washed by
20 mL×2 hexane. The precipitate was dissolved in 30 mL hot
toluene and colorless block crystals were obtained at room temp-
erature in a few days (0.9 g, 80%). Found: C, 69.71; H, 8.65;
N, 3.21. Y, 4.94. C105H156N4NaO14Y requires C, 69.66; H, 8.69;
N, 3.09; Y, 4.91%); 1H NMR (400 MHz, CDCl3, 25 °C):
δ 6.5–7.0 (12H, m, ArH), 4.4–4.6 (8H, m, NCH2O, ArCH2N
benzoxazine ring), 3.75 (8H, m, α-CH2 THF), 3.60 (8H, s,
NCH2Ar), 3.65 (24H, s, crown ether), 2.6–3.2 (8H, m,
NCH2CH2N-benzoxin ring), 2.25 (3H, s, CH3Ar), 2.22 (3H, s,
CH3Ar), 2.16 (6H, s, CH3Ar), 2.11 (6H, s, CH3Ar), 1.85
(8H, m, β-CH2 THF), 1.44 (18H, s, C(CH3)3), 1.39 (9H, s,
C(CH3)3)), 1.37 (18H, s, C(CH3)3), 1.10 (9H, s, C(CH3)3)); 13C
NMR (400 MHz, CDCl3, 25 °C): δ 164.0, 163.9, 163.8,163.7,
151.5, 138.2, 137.3, 136.6, 136.0, 129.4, 128.65, 128.6, 128.5,
[Nd(L)2Na(THF)2] (2)·2toluene. The synthesis of complex 2
was carried out in the same way as that described for complex 1,
but NdCl3 (0.654 g, 2.62 mmol) was used instead of YCl3. Blue
block crystals were isolated from the concentrated toluene sol-
ution at room temperature. (3.6 g, 82%). Found: C, 71.06; H,
8.16; N, 3.47; Nd, 8.54. C100H140N4NaNdO8 requires C, 70.93;
H, 8.33; N, 3.31; Nd, 8.52%).
[Er(L)2Na(THF)2](3)·2toluene. The synthesis of complex 4
was carried out in the same way as that described for complex 1,
but ErCl3 (0.66 g, 2.42 mmol) was used instead of YCl3. Pink
block crystals were isolated from the concentrated toluene sol-
ution at room temperature. (2.86 g, 69%). Found: C, 70.17; H,
8.09; N, 3.20; Er, 9.46. C100H140ErN4NaO8 requires C, 69.97;
H, 8.22; N, 3.26; Er, 9.74%).
[Yb(L)2Na(THF)2] (4)·2toluene. The synthesis of complex 3
was carried out in the same way as that described for complex 1,
but YbCl3 (0.52 g, 1.86 mmol) was used instead of YCl3. Pale
Table 5 Crystallographic data for complexes 1 and 3–6
Compound reference
1
3
4
5
6
Chemical formula
Formula Mass
Crystal system
a/Å
C86H124N4NaO8Y C86H124ErN4NaO8 C86H124N4NaO8Yb C78H108N4O6Y˙C20H40NaO8 C78H108N4O6Yb˙C20H40NaO8
1453.79
1532.14
Monoclinic
32.2263(9)
12.5493(2)
27.4684(8)
90.00
117.893(4)
90.00
9818.2(4)
100(2)
1537.92
Monoclinic
32.2724(8)
12.5414(2)
27.4732(6)
90.00
117.684(3)
90.00
9846.6(4)
100(2)
1718.10
Triclinic
1802.23
Triclinic
Monoclinic
32.5870(14)
12.7586(5)
27.7173(13)
90.00
117.313(6)
90.00
16.6199(5)
18.4971(6)
19.0982(7)
88.399(3)
81.357(3)
75.770(2)
5626.1(3)
110(2)
16.5630(4)
18.4928(4)
19.0775(5)
88.251(2)
81.427(2)
75.735(2)
5599.8(2)
110(2)
b/Å
c/Å
α (°)
β (°)
γ (°)
Unit cell volume/Å3 10239.1(8)
T/K
293(2)
C2/c
4
ˉ
P1
2
ˉ
P1
2
Space group
No. of formula units
per unit cell, Z
Absorption
C2/c
4
C2/c
4
0.618
24944
9350
0.905
30978
8963
1.000
26085
9001
0.575
37049
20542
0.892
64784
20442
coefficient, μ/mm−1
No. of reflections
measured
No. of independent
reflections
Rint
0.0560
0.0702
0.0295
0.0271
0.0327
0.0283
0.0388
0.0545
0.0479
0.0385
Final R1 values
(I > 2σ(I))
Final wR(F2) values 0.1875
(I > 2σ(I))
0.0817
0.0298
0.0831
1.134
0.0790
0.0325
0.0813
1.097
0.1554
0.0781
0.1701
1.042
0.1004
0.0492
0.1071
1.113
Final R1 values (all
0.1094
data)
Final wR(F2) values 0.2080
(all data)
Goodness of fit on
0.980
F2
CCDC number
837472
837474
837473
837475
837476
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 2812–2819 | 2817

View Article Online
126.9, 126.2, 125.7, 124.5, 124.5, 123.6, 121.2, 119.6, 119.1
(Ar-C), 82.8 (NCH2O), 68.9 (crown ether), 68.3 (α-CH2 THF),
59.8, 59.5 (ArCH2NCH2Ar), 51.9 (NCH2CH2-N), 44.3
(NCH2CH2-N), 43.4 (NCH2Ar benzoxazine), 35.0 (C(CH3)3),
35 (C(CH3)3), 34.9 (C(CH3)3), 30.4 (C(CH3)3), 30.15
(C(CH3)3), 25.9 (β-CH2 THF), 21.8 (ArCH3), 21.4(ArCH3),
21.3(ArCH3), 21.2(ArCH3).
21174121), and the Special Funds for Major Basic Research Pro-
jects (G2011CB606001).
Notes and references
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C
105H156N4NaO14Yb requires C, 66.57; H, 8.30; N, 2.96; Yb,
9.13%).
Additional experimental data
Attempted synthesis of [LLnCl(THF)n] LnvY, La, Nd,
Lu. The attempted synthesis of these complexes was carried out
in the same way as that described for complex 1, but
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hexane, diethyl ester and DME.
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Acknowledgements
The authors gratefully acknowledge the financial supports of the
National Natural Science Foundation of China (20874083,
2818 | Dalton Trans., 2012, 41, 2812–2819
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Dalton Trans., 2012, 41, 2812–2819 | 2819