Bimetallic anilido-aldimine Al or Zn complexes for efficient ring-opening polymerization of ε-caprolactone

Article abstract of DOI:10.1039/b719017d

Four bimetallic Al or Zn complexes supported by anilido-aldimine ligands (o-C₆H₄(NHAr)-CH=N)₂CH₂CH ₂ (Ar = 2,6-Me₂C₆H₃, L ¹H₂; Ar = 2,6-ⁱPr₂C ₆H₃, L²H₂) have been synthesized and characterized. Treatment of L¹H₂ or L²H ₂ with two equiv. of AlMe₃ gives bimetallic complex L ¹(AlMe₂)₂1 or L²(AlMe ₂)₂2, respectively. Reaction of L¹H₂ or L²H₂ with two equiv. of ZnEt₂ leads to bimetallic complex L¹(ZnEt)₂3 or L²(ZnEt) ₂4, respectively. All of the complexes 1-4 are efficient catalysts for ring-opening polymerization of ε-caprolactone (CL) in the presence of benzyl alcohol and catalyze the polymerization of CL in living fashion yielding polymers with a narrow polydispersity index. The activity of bimetallic Zn complexes 3 and 4 is higher than bimetallic Al complexes 1 and 2. The Royal Society of Chemistry 2008.

Full text of DOI:10.1039/b719017d

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www.rsc.org/dalton | Dalton Transactions
Bimetallic anilido-aldimine Al or Zn complexes for efficient ring-opening
polymerization of e-caprolactone†
Wei Yao, Ying Mu,* Aihong Gao, Wei Gao and Ling Ye
Received 10th December 2007, Accepted 14th March 2008
First published as an Advance Article on the web 17th April 2008
DOI: 10.1039/b719017d
Four bimetallic Al or Zn complexes supported by anilido-aldimine ligands
1
i
2
=
(o-C6H4(NHAr)–CH N)2CH2CH2 (Ar = 2,6-Me2C6H3, L H2; Ar = 2,6- Pr2C6H3, L H2) have been
synthesized and characterized. Treatment of L1H2 or L2H2 with two equiv. of AlMe3 gives bimetallic
complex L1(AlMe2)2 1 or L2(AlMe2)2 2, respectively. Reaction of L1H2 or L2H2 with two equiv. of ZnEt2
leads to bimetallic complex L1(ZnEt)2 3 or L2(ZnEt)2 4, respectively. All of the complexes 1–4 are
efficient catalysts for ring-opening polymerization of e-caprolactone (CL) in the presence of benzyl
alcohol and catalyze the polymerization of CL in living fashion yielding polymers with a narrow
polydispersity index. The activity of bimetallic Zn complexes 3 and 4 is higher than bimetallic Al
complexes 1 and 2.
Introduction
Results and discussion
There has been a growing research interest in the synthesis of
poly(e-caprolactone) (PCL) due to its potential applications in
medicine, pharmaceuticals, and tissue engineering such as delivery
media for the controlled release of drugs, scaffolds, and the
delivery of antibodies and genes.1 Metal complex-catalyzed ring-
opening polymerization (ROP) of e-caprolactone (CL) is the most
promising method for synthesis of PCL because of its good control
over the molecular weight and distribution of the polymerization
product.2 So far, a lot of metal catalysts or initiators have been
reported, including magnesium,3 calcium,4 aluminium,5 titanium,6
iron,7 zinc,8 tin,9 and rare earth metal10 complexes supported by
various ligands. Among the reported catalysts, aluminium and
zinc-containing catalysts are the most promising candidates for
industrial application. Recently Nomura and coworkers reported
a number of highly efficient salicylaldimine–aluminium catalysts
for the ROP of CL in the presence of benzyl alcohol (BnOH).5o To
explore more efficient catalysts for the ROP of CL, and considering
that the steric effect of the substituents at the ortho position of the
phenoxy group in the salicylaldimine complexes may be smaller
than that of the substituents on the coordinating atoms of the
ligand, we have synthesized a family of new anilido-aldimine
ligands and their bimetallic Al or Zn complexes. It was found
that the new bimetallic anilido-aldimine Al or Zn complexes are
highly active catalysts for the ROP of CL, producing PCL with
living fashion and controllable molecular weight in the presence
of BnOH. Herein we report the synthesis, structures and catalytic
property of these new complexes 1–4 for the ROP of CL.
Synthesis and characterization
New ligands and their bimetallic Al or Zn complexes 1–4 were
synthesized as described in Scheme 1. Ligands (L1H2, L2H2) were
prepared by condensation of ethylenediamine with two equiv. of
2-fluorobenzaldehyde in methanol, followed by reaction with two
equiv. of the lithium salt of substituted aniline in THF. L1H2 and
L2H2 were characterized by 1H and 13C NMR spectroscopy along
with elemental analyses. 1H NMR spectra of both ligands exhibit
=
resonances at about d 8.4 for the imino N CH proton, with the
corresponding 13C NMR resonance at around d 165.3. The NH
resonance appears characteristically low field at about d 10.48 for
both L1H2 and L2H2.
Scheme 1 Synthetic procedure of ligands L1H2, L2H2 and complexes 1–4.
Compounds 1–4 were all synthesized in toluene by alkane
elimination reaction in high yields (>90%). Treatment of the
ligand L1H2 or L2H2 with two equiv. of AlMe3 gives the bimetallic
complex L1(AlMe2)2 1 or L2(AlMe2)2 2, respectively. Reaction of
L1H2 or L2H2 with two equiv. of ZnEt2 leads to the formation
of bimetallic complex L1(ZnEt)2 3 or L2(ZnEt)2 4, respectively.
Complexes 1–4 were all characterized by elemental analyses and
1H and 13C NMR spectroscopy. The disappearance of the N–H
signal of the ligands and the appearance of the resonance for
protons of AlMe2 or ZnEt in the high-field region (d −0.84–0.20)
demonstrate the formation of the desired complexes.
State Key Laboratory for Supramolecular Structure and Materials, School
of Chemistry, Jilin University, 2699 Qianjin Street, Changchun, 130012,
People’s Republic of China. E-mail: ymu@mail.jlu.edu.cn; Fax: +86 431-
85193421; Tel: +86 431-85168376
† Electronic supplementary information (ESI) available: NMR spectra and
GPC elution curves. CCDC reference numbers 661121–661123. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/b719017d
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Crystals of complexes 1–3 suitable for X-ray crystal structure
determination were grown from a mixture of CH2Cl2–hexane at
−20 ◦C. Their molecular structures are shown in Fig. 1, 2 and 3.
Selected bond lengths and angles for 1–3 are given in Table 1. X-
Ray analysis reveals that the Al centres of complexes 1 and 2 adopt
a distorted tetrahedral geometry and the zinc centres of complex 3
adopt a trigonal planar geometry with the metal center chelated by
imine and amido nitrogen atoms of the bidentate ligand. In these
three complexes, the six-membered chelating ring is nearly planar,
˚
˚
with the metal atom lying out of the plane by 0.0387 A for 1, 0 A for
˚
2, and 0.0709 and 0.0985 A for 3. The torsion angles between the
six-membered chelating ring and the aromatic ring attached to the
amido nitrogen atom are 89.2(1)◦ for 1, 90(2)◦ for 2, and 89.3(3)◦
and 74.2(2)◦ for 3. The imino C N bonds within the chelating
=
˚
rings retain their double bond character, being 1.287(6) A for 1,
˚
1.285(4) and 1.292(4) A for 3, while those in complex 2 do not
retain their double bond character, being 1.351(7) A due to the
˚
ethylenediamine unit in complex 2 being disordered. The Al–N
Fig. 1 X-Ray structure of complex 1, with all non-hydrogen atoms shown
as 30% thermal ellipsoids.
˚
˚
(amido) distances (1.870(4) A for 1, 1.890(4) A for 2) and the Zn–
˚
N (amido) distances (1.926(3) and 1.935(3) A for 3) are shorter
˚
˚
than the Al–N (imine) distances (1.917(5) A for 1, 1.962(5) A for
˚
2) and the Zn–N (imine) distances (1.995(2) and 1.979(3) A for 3),
which is similar to the case in the reported Al and Zn complexe◦s
with bidentate anilido-imine ligands.11 The N–Al–N angles (94.2
for 1, 95.5◦ for 2) and the N–Zn–N angles (96.4 and 95.9◦ for 3)
in these complexes are also close to those in the known Al and
◦
˚
Table 1 Selected bond lengths (A) and angles ( )
Complex 1
Al–N(1)
Al–N(2)
Al–C(33)
Al–C(34)
N(1)–C(9)
N(2)–C(15)
N(1)–Al–N(2)
N(1)–Al–C(33)
1.870(4)
1.917(5)
1.943(6)
1.953(6)
1.355(6)
1.287(6)
94.25(19)
116.3(2)
N(1)–Al–C(34)
N(2)–Al–C(33)
N(2)–Al–C(34)
C(33)–Al–C(34)
C(1)–N(1)–Al
C(9)–N(1)–Al
C(15)–N(2)–Al
C(16)–N(2)–Al
114.8(2)
109.3(2)
108.7(2)
111.8(3)
113.9(3)
128.6(3)
124.4(3)
119.2(4)
Fig. 2 X-Ray structure of complex 2, with all non-hydrogen atoms shown
as 30% thermal ellipsoids (the ethylenediamine unit is disordered and only
one set of thermal ellipsoids for N2, C15A, C15C and N2B are plotted for
clarity).
Complex 2
Al–N(1)
Al–N(2)
Al–C(16)
Al–C(16)A
N(1)–C(1)
N(2)–C(7)
N(1)–Al–N(2)
N(1)–Al–C(16)
1.890(4)
1.962(5)
1.956(6)
1.956(6)
1.353(5)
1.351(7)
95.51(18)
116.2(2)
N(1)–Al–C(16)A
N(2)–Al–C(16)
N(2)–Al–C(16)A
C(16)–Al–C(16)A
C(1)–N(1)–Al
C(8)–N(1)–Al
C(7)–N(2)–Al
116.2(2)
98.4(2)
117.0(2)
111.6(2)
126.3(3)
116.6(3)
118.5(3)
122.7(4)
C(15)–N(2)–Al
Complex 3
Zn(1)–N(1)
Zn(1)–N(2)
Zn(2)–N(3)
Zn(2)–N(4)
Zn(1)–C(33)
Zn(2)–C(35)
N(1)–C(9)
N(2)–C(15)
N(3)–C(18)
N(4)–C(24)
N(1)–Zn(1)–N(2)
N(3)–Zn(2)–N(4)
1.926(3)
1.995(2)
1.979(3)
1.935(3)
1.949(4)
1.938(4)
1.363(4)
1.285(4)
1.292(4)
1.354(4)
96.35(11)
95.89(10)
N(1)–Zn(1)–C(33)
N(2)–Zn(1)–C(33)
N(3)–Zn(2)–C(35)
N(4)–Zn(2)–C(35)
C(1)–N(1)–Zn(1)
C(9)–N(1)–Zn(1)
C(15)–N(2)–Zn(1)
C(16)–N(2)–Zn(1)
C(17)–N(3)–Zn(2)
C(18)–N(3)–Zn(2)
C(24)–N(4)–Zn(2)
C(25)–N(4)–Zn(2)
130.92(13)
132.68(14)
132.65(17)
131.36(17)
116.09(19)
126.1(2)
120.4(2)
122.5(2)
122.0(2)
120.6(2)
Fig. 3 X-Ray structure of complex 3, with all non-hydrogen atoms shown
as 30% thermal ellipsoids.
Zn complexes.11 It should be noted that the ethylenediamine unit
in complex 2 is disordered, while the same phenomenon does not
occur in complexes 1 and 3.
125.8(2)
114.53(19)
3200 | Dalton Trans., 2008, 3199–3206
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Polymerization studies
found that the number-averaged degree of polymerization (DPn)
of the obtained polymers (calculated from 1H NMR) is close
to the monomer : BnOH molar ratio and the number-averaged
molecular weight (Mn) of the polymers produced by complexes 1
and 3 (determined by gel permeation chromatography, GPC) is
proportional to the monomer : BnOH molar ratio (Fig. 5 and 6).
The Mn determined by GPC is much greater than the predicted
value due to the difference in hydrodynamic volume of the
poly(caprolactone) and poly(styrene) standards used to calibrate
the GPC. The most probable molecular weight Mp [2871.1 − 23
(Na+) = 2848.1 or 2985.4 − 23 (Na+) = 2962.4] from the MALDI-
The polymerization reaction of CL under different conditions
was studied in toluene in the presence of complexes 1–4 together
with BnOH. The polymerization results are listed in Table 2.
1
The H NMR spectrum of a typical polymer sample is shown
in Fig. 4. Complexes 1–4 all show high catalytic activity for the
ROP of CL in the presence of BnOH, while no reaction takes
place in the absence of BnOH (Table 2, entries 1–4). Complexes
1 and 3 were used to study the effect of reaction conditions
on the performance of these new catalysts in detail since they
were found to show higher catalytic activity than their analogous
complexes 2 and 4. The effect of the amount of BnOH was
first tested and it was found that the highest catalytic activity
can be obtained with the Al : BnOH molar ratio being 2 : 1
for complex 1, while for complex 3 a Zn : BnOH molar ratio
of 1 : 1 gives the highest catalytic activity. The reason why the
Al : BnOH molar ratio of 2 : 1, instead of 1 : 1, for complex 1
shows the highest catalytic activity is not clear. In all cases, it was
Fig. 5 Plot of Mn versus [CL]/[BnOH] for the polymerization of CL
catalyzed by complex 1 and BnOH in toluene at 70 ◦C. (A) Mn calculated
from GPC. (B) Mn calculated from 1H NMR.
Fig. 4 1H NMR spectrum of a typical polymer sample (Table 2, entry 5).
Table 2 Ring-opening polymerization of e-CL initiated by complexes 1–4a
T/◦C
Yieldb (%)
DPn
Mn ×103
PDId
c
d
Entry
Catalyst
BnOH : M : CL
t
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
1
2
3
4
1
1
1
1
1
1
1
1
1
2
3
3
3
3
3
3
3
3
3
4
0 : 2 : 100
0 : 2 : 100
0 : 2 : 100
0 : 2 : 100
4 : 2 : 100
2 : 2 : 100
1 : 2 : 100
1 : 2 : 100
1 : 2 : 100
1 : 2 : 200
1 : 2 : 400
1 : 2 : 600
1 : 2 : 800
1 : 2 : 100
4 : 2 : 100
2 : 2 : 100
1 : 2 : 100
2 : 2 : 100
2 : 2 : 100
2 : 2 : 200
2 : 2 : 400
2 : 2 : 600
2 : 2 : 800
2 : 2 : 100
24 h
24 h
24 h
24 h
70
70
70
70
70
70
70
50
20
70
70
70
70
70
70
70
70
50
20
70
70
70
70
70
0
0
0
0
—
—
—
—
26
56
94
105
90
190
410
590
807
102
30
64
92
54
60
—
—
—
—
—
—
—
—
1.5 h
89.0
91.5
96.5
93.0
82.1
97.0
96.4
95.6
95.0
97.2
96.0
98.0
91.2
97.6
93.0
95.7
96.2
93.8
97.1
96.4
7.3
1.12
1.26
1.53
1.37
1.16
1.19
1.46
1.57
1.74
1.23
1.07
1.18
1.66
1.14
1.42
1.24
1.66
1.47
1.58
1.14
20 min
10 min
25 min
8 h
22 min
50 min
1.5 h
13.8
19.7
21.2
17.7
49.8
82.6
116
149
20.8
7.99
14.4
18.5
10.3
12.8
26.0
57.5
82.3
107
10.2
2 h
11 min
20 min
1 min
6 min
2.5 min
4 min
2.5 min
5.5 min
10 min
15 min
1.5 min
99
213
302
392
51
a Polymerization conditions: catalyst, 0. 19 mmol; CL, 3.0 mol L−1 in toluene; N2 atmosphere. b Isolated yield. c The number-average degree of
polymerization by 1H NMR. d Obtained from GPC analysis.
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Scheme 2 The proposed mechanism for polymerization by Zn complexes
with BnOH.
(or a short-chain PCL molecule) to form the PCL molecule and a
new benzyloxyzinc (or alkoxyzinc) species that will initiate a new
PCL chain. In the whole polymerization procedure, BnOH acts as
a chain initiator as well as a chain transfer reagent by forming the
benzyloxyzinc complex. According to such a mechanism, the PCL
molecule should be capped with a benzyl group and a CH2OH
group, which has been confirmed by the MALDI-TOF MS study
that shows the molecular weights of the PCL molecules being close
to M = n × MCL + MBnOH. The mechanism for the Al catalyst
system should be similar to the one for the Zn catalyst system.
To prove the formation of the benzyloxymetal species in the
reaction, the reaction of complex 3 with BnOH in 1 : 1 Zn : BnOH
molar ratio was monitored by 1H NMR in CDCl3 at room
Fig. 6 Plot of Mn versus [CL]/[BnOH] for the polymerization of CL
catalyzed by complex 3 and BnOH in toluene at 70 ◦C. (A) Mn calculated
from GPC. (B) Mn calculated from 1H NMR.
TOF MS spectrum (Fig. S1, ESI†) for a typical polymer sample
(Table 2, entry 5) is quite consistent with the predicted Mn value
based on the monomer : BnOH molar ratio (monomer : BnOH ×
MCL + MBnOH = 25 × 114.14 + 108.14 = 2961.7). These results
demonstrate the “living” character of the polymerization process
with BnOH as a kind of initiator. The polydispersity index (PDI)
of the polymers produced by complexes 1–4 ranges from 1.07 to
1.74. The narrow molecular weight distribution is a well-known
feature of coordination polymerization reactions. Similar results
1
temperature. The H NMR spectrum of the reaction mixture is
shown in Fig. 7. The disappearance of the resonances for protons
of ZnEt in the high-field region and the appearance of broad
PhCH2OZn signal in the region of 4.0–4.5 ppm demonstrate the
formation of a benzyloxy complex. The broad signal implies that
the benzyloxy complex may exist in polymeric form through weak
coordination of the oxygen atom in the benzyloxy group to the
Zn metal center in another benzyloxy complex. The reaction
of complex 1 with BnOH in 1 : 1 Al : BnOH molar ratio was
also monitored by 1H NMR in CDCl3 at room temperature,
and complex 1 was found to be converted to the corresponding
benzyloxy complex quantitatively (Fig. S2, ESI†). To confirm that
the benzyloxy–Zn complex can catalyze the ROP of CL, a solution
of CL in CDCl3 was added to the above reaction mixture at room
have been reported using bis(phenolate)aluminium catalysts5i,l–n
,
and salicylaldimine–aluminium catalysts.5o The catalytic perfor-
mance of our new aluminium catalysts is similar to that of the
salicylaldimine–aluminium catalysts and better than that of the
bis(phenolate)aluminium catalysts, while the catalytic activity of
our bimetallic zinc catalysts is relatively high in comparison with
that of known zinc catalysts.8 The catalytic activity of all complexes
1–4 are dependent on the reaction temperature and increase upon
elevating the reaction temperature from 20 to 70 ◦C. The catalytic
activity of the bimetallic Zn complexes 3 and 4 is higher than
the bimetallic Al complexes 1 and 2 in the order: 3 > 4 >
1 > 2, probably because the bond dissociation energy of Zn–O
(284 kJ mol−1) is much lower than that of Al–O (512 kJ mol−1)12
and the four coordinate aluminium centers in complexes 1 and
2 are more crowded than the three coordinate zinc centers in
complexes 3 and 4. High catalytic activity of the bimetallic Zn
complexes may also be a result of the cooperative effect of the two
metal centers.13
=
temperature and the formation of the Zn[O(CH2)5C O]nOCH2Ph
intermediates was detected by H NMR spectroscopy (shown in
1
According to the above results and referring to the generally
accepted mechanisms for the ROP of cyclic esters mediated by
metal alkoxides,5i,14,15 a mechanism for the Zn catalyst system can
be proposed as shown in Scheme 2. First, BnOH reacts with the
alkyl–Zn complex to form the catalytically active benzyloxyzinc
species. The coordination of the lactone molecule to the metal
center, followed by ring cleavage at the acyl-oxygen bond and
insertion into the Zn–O bond of the benzyloxyzinc species then
occurs to form a new alkoxyzinc intermediate. Repetition of the
same procedure forms the PCL chain on the Zn center. The PCL
chain can be removed from the Zn center by reacting with BnOH
Fig. 7 1H NMR spectrum of the reaction mixture of complex 3 and
BnOH in CDCl3 at room temperature.
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Fig. 8), in which the polymer chain shows similar resonances to
those in the spectrum of the PCL sample shown in Fig. 4.
MALDI/TOF (matrix assisted laser desorption ionization/time-
of-flight) MS (COMPACT).
Synthesis of compound A
A mixture of 2-fluorobenzaldehyde (5.0 mL, 47.20 mmol), and
ethylenediamine (1.6 mL, 23.60 mmol) in absolute MeOH (20 mL)
was stirred for 12 h. The mixture was then cooled to 0 ◦C for 12 h.
The product was collected by vacuum filtration and washed with
cool MeOH (5 mL) to give a white solid (3.80 g, 59%). Anal.
calcd for C16H14F2N2 (272.29): C 70.58, H 5.18, N 10.29; found:
1
C 70.54, H 5.21, N 10.32%. H NMR (500 MHz, CDCl3, 293
K): d 4.03 (s, 4H, NCH2), 7.07 (t, 2H, J = 9.5 Hz, Ph–H), 7.18
(t, 2H, J = 7.5 Hz, Ph–H), 7.39–7.98 (m, 4H, Ph–H), 8.63 (s,
2H, CH NAr) ppm. 13C {1H} NMR (125 MHz, CDCl3, 293 K):
=
d 61.88, 115.64, 115.81, 124.33, 127.77, 132.16, 132.23, 156.03,
Fig. 8 1H NMR spectrum of the reaction mixture of complex 3, BnOH
and CL in CDCl3 at room temperature.
156.06, 161.23, 163.23 ppm.
Synthesis of ligand L1H2
Conclusion
A solution of nBuLi (28.9 mL, 31.8 mmol) in hexanes was added
to a solution of 2,6-dimethylaniline (3.9 mL, 31.8 mmol) in THF
(30 mL) at −78 C. The mixture was allowed to warm to room
In conclusion, four bimetallic Al or Zn complexes supported
by anilido-aldimine ligands have been synthesized and fully
characterized. All of the complexes 1–4 are efficient catalysts for
the ring-opening polymerization of e-caprolactone in the presence
of benzyl alcohol. The polymerization reaction of e-caprolactone
catalyzed by these catalyst systems takes place in living fashion
with narrow PDIs. The catalytic activity of the bimetallic Zn
complexes 3 and 4 is higher than that of the bimetallic Al
complexes 1 and 2. The DPn of the obtained polymers is close
to the monomer : BnOH molar ratio in the polymerization. By
forming the benzyloxy complex, BnOH acts as a chain initiator as
well as a chain transfer reagent in the polymerization procedure.
The formation of the benzyloxy complexes of Al or Zn during the
polymerization was confirmed by 1H NMR spectroscopy and the
structure of the produced PCL was determined by both 1H NMR
spectroscopy and MALDI-TOF MS study.
◦
temperature and stirred for 12 h. The resulting solution was
transf◦erred into a solution of A (4.33 g, 15.9 mmol) in THF (40 mL)
at 25 C. After stirring for 12 h, the reaction was quenched with
H2O (25 mL), extracted with CHCl3, and the organic phase was
evaporated to dryness in vacuo to give the crude product as a
yellow solid. Pure product was obtained by recrystallization from
MeOH at −20 ◦C as a yellow solid (4.83 g, 64%). Anal. calcd for
C32H34N4 (474.64): C 80.98, H 7.22, N 11.80; found: C 80.96, H
1
7.25, N 11.79%. H NMR (300 MHz, CDCl3, 293 K): d 2.12 (s,
12H, CH3), 3.95 (s, 4H, NCH2), 6.17 (d, 2H, J = 8.7 Hz, Ph–
H), 6.59 (d, 2H, J = 7.0 Hz, Ph–H), 7.02–7.26 (m, 10H, Ph–H),
1
8.40 (s, 2H, CH NAr), 10.48 (s, 2H, NH) ppm. 13C { H} NMR
=
(75 MHz, CDCl3, 293 K): d 18.24, 62.16, 111.26, 115.11, 116.85,
125.86, 128.14, 130.92, 133.49, 136.40, 137.88, 147.68, 165.29 ppm.
Synthesis of ligand L2H2
Experimental section
n
A solution of BuLi (20 mL, 22 mmol) in hexanes was added
General
to a solution of 2,6-isopropylaniline (4.1 mL, 22 mmol) in THF
◦
All reactions were performed using standard Schlenk techniques
in an atmosphere of high-purity nitrogen or glove-box techniques.
Toluene, hexane and THF were dried by refluxing over sodium and
benzophenone, and distilled under nitrogen prior to use. C6D6 was
(30 mL) at −78 C. The mixture was allowed to warm to room
temperature and stirred for 12 h. The resulting solution was
transf◦erred into a solution of A (3.00 g, 11 mmol) in THF (40 mL)
at 25 C. After stirring for 12 h, the reaction was quenched with
H2O (25 mL), extracted with CHCl3, and the organic phase was
evaporated to dryness in vacuo to give the crude product as a
yellow solid. Pure product was obtained by recrystallization from
MeOH at −20 ◦C as a yellow solid (2.78 g, 43%). Anal. calcd for
C40H50N4 (586.85): C 81.86,; H 8.59, N 9.55; found: C 81.78, H
˚
dried over activated 4 A molecular sieves and vacuum-transferred
to a sodium-mirrored air-free flask. CDCl3 and CH2Cl2 were dried
over CaH2 for 48 h and vacuum-transferred to an air-free flask.
AlMe3, ZnEt2 and nBuLi were purchased from Aldrich and used as
received. 1H NMR and 13C NMR spectra were measured using a
Varian Mercury-300 NMR spectrometer and a Bruker AVANCE-
500 NMR spectrometer. The elemental analysis was performed
on a Perkin-Elmer 2400 analyzer. The GPC measurements were
performed on a Water-410 system using THF as the eluent (flow
1
8.63, N 9.59%. H NMR (300 MHz, CDCl3, 293 K): d 1.11 (s,
24H, CH3), 3.06 (m, 4H, J = 7.0 Hz, CH3CHCH3), 3.91 (s, 4H,
NCH2), 6.19 (d, 2H, J = 8.4 Hz, Ph–H), 6.57 (t, 2H, J = 7.4 Hz,
Ph–H), 7.03 (t, 2H, J = 7.8 Hz, Ph–H), 7.10 (d, 2H, J = 7.5 Hz,
◦
rate: 1 mL min−1, at 35 C) or using CH2Cl2 as the eluent (flow
Ph–H), 7.22–7.32 (m, 6H, Ph–H), 8.41 (s, 2H, CH NAr) 10.49 (s,
=
rate: 1 mL min−1, at 25 ◦C). Molecular weights and molecular
weight distributions were calculated using polystyrene as standard.
MS spectra were performed on 1100MS series and AXIMA CFR
2H, NH) ppm. 13C{ H} NMR (75 MHz, CDCl3, 293 K): d 22.77,
1
24.74, 28.34, 62.21, 111.49, 114.84, 116.36, 123.61, 127.08, 130.97,
133.42, 135.06, 147.34, 149.31, 165.40 ppm.
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Table 3 Crystal data and structural refinements details for 1, 2 and 3
Compound
Formula
Fw
1
2
3
C36H44Al2N4
586.71
Triclinic
C44H60Al2N4
698.92
C36H42N4Zn2
661.48
Cryst. syst.
Tetragonal
P42(1)m
15.200(2)
15.200(2)
9.0022(18)
90
90
90
2079.9(6)
2
1.116
Monoclinic
P2(1)/c
11.059(2)
15.168(3)
19.787(4)
90
95.93(3)
90
3301.2(11)
4
¯
¯
Space group
P1
˚
a/A
7.1734(14)
9.0776(18)
13.563(3)
96.84(3)
92.58(3)
103.15(3)
851.5(3)
1
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
Z
D
calcd/g cm−3
1.144
314
1.331
1384
F(000)
756
h range for data collection/◦
Limiting indices
1.52–27.48
0 ≤ h ≤ 9
−11 ≤ k ≤ 11
−17 ≤ l ≤ 17
3564/0/191
0.993
3.00–27.46
−19 ≤ h ≤ 19
−19 ≤ k ≤ 19
−11 ≤ l ≤ 10
1417/6/142
1.050
3.21–27.46
−19 ≤ h ≤ 19
−19 ≤ k ≤ 17
−25 ≤ l ≤ 25
7465/0/379
1.000
No. of data/restraints/params
Goodness-of-fit on F2
Final R indices I > 2r(I)
a
a
a
R1 = 0.0837
R1 = 0.0627
R1 = 0.0471
b
b
b
wR2 = 0.2163
wR2 = 0.1753
wR2 = 0.0927
a
a
a
R indices (all data)
R1 = 0.1971
R1 = 0.0696
R1 = 0.1089
b
b
b
wR2 = 0.2658
wR2 = 0.1821
wR2 = 0.1113
Rint
0.0872
0.0496
0.0695
ꢀ
ꢀ
ꢀ
ꢀ
a R1 = ꢀFo| − |Fcꢀ/ |Fo|. b wR2 = { w(Fo − Fc2)2/ w(Fo2)2}
.
2
1/2
Synthesis of complex 1
4H, J = 6.7 Hz, CH3CHCH3), 3.92 (s, 4H, NCH2), 6.16 (d, 2H,
J = 9.0 Hz, Ph–H), 6.44 (t, 2H, J = 7.4 Hz, Ph–H), 7.057–7.32
AlMe3 (4.22 mL, 1.0 M in toluene, 4.22 mmol) was added to
a solution of L1H2 (1.00 g, 2.11 mmol) in 20 mL of toluene at
−10 ◦C with stirring, gently heating to 80 ◦C for 2 d, during which
a clear yellow solution was formed. After removal of the solvent,
the product was precipitated with 10 mL hexane. The precipitate
was removed by filtration over a Celite plug. Removal of solvent
in vacuo gave a yellow powder that crystallized from a mixture of
CH2Cl2–hexane to give the desired complex as a yellow crystalline
solid (1.14 g, 92% yield). Anal. calcd for C36H44Al2N4 (586.72): C
73.69, H 7.56, N 9.55; found: C 73.68, H 7.58, N 9.56%. 1H NMR
(300 MHz, CDCl3, 293 K): d −0.79 (s, 12H, AlCH3), 2.13 (s, 12H,
CH3), 3.92 (s, 4H, NCH2), 6.07 (d, 2H, J = 9.0 Hz, Ph–H), 6.44
(t, 2H, J = 7.5 Hz, Ph–H), 7.00–7.26 (m, 10H, Ph–H), 8.03 (s,
1
(m, 10H, Ph–H), 8.04 (s, 2H, CH NAr) ppm. 13C{ H} NMR
=
(75 MHz, CDCl3, 293 K): d −9.14, 24.34, 25.32, 27.86, 56.58,
114.67, 115.22, 118.48, 124.44, 126.42, 135.52, 136.37, 139.97,
146.20, 157.22, 170.86, 171.05 ppm.
Synthesis of complex 3
ZnEt2 (4.22 mL, 1.0 M in toluene, 4.22 mmol) was added to a
solution of L1H2 (1.00 g, 2.11 mmol) in 20 mL of toluene at
−10 ◦C with stirring, gently heating to 80 ◦C for 2 d, during
which a clear yellow solution was formed. After removal of the
solvent, the product was precipitated with 10 mL hexane. The
precipitate was removed by filtration over a Celite plug. Removal
of solvent in vacuo gave a yellow powder that crystallized from a
mixture of CH2Cl2–hexane to give the desired complex as a yellow
crystalline solid (1.27 g, 91% yield). Anal. calcd for C36H42N4Zn2
(661.56): C 65.36, H 6.40, N 8.47; found: C 65.40, H 6.38, N,
2H, CH NAr) ppm. 13C{1H} NMR (75 MHz, CDCl3, 293 K): d
=
−8.24, 18.67, 56.84, 114.73, 115.01, 116.01, 125.80, 129.06, 136.14,
136.79, 136.86, 142.46, 156.03, 171.89 ppm.
1
8.43%. H NMR (300 MHz, CDCl3, 293 K): d 0.26 (q, 4H, J =
Synthesis of complex 2
8.1 Hz, ZnCH2), 0.90 (t, 6H, J = 8.1 Hz, ZnCH2CH3), 2.01 (s,
12H, CH3), 4.14 (s, 4H, NCH2), 6.16 (d, 2H, J = 8.7 Hz, Ph–H),
AlMe3 (3.4 mL, 1.0 M in toluene, 3.40 mmol) was added to a
solution of L2H2 (1.00 g, 1.70 mmol) in 20 mL of toluene at −10 ◦C
with stirring, gently heating to 80 ◦C for 2 d, during which a clear
yellow solution was formed. After removal of the solvent, the
product was precipitated with 10 mL hexane. The precipitate was
removed by filtration over a Celite plug. Removal of solvent in
vacuo gave a yellow powder that crystallized from a mixture of
CH2Cl2–hexane to give the desired complex as a yellow crystalline
solid (1.11 g, 93% yield). Anal. calcd for C44H60Al2N4 (698.94): C
75.61, H 8.65, N 8.02; found: C 75.55, H 8.67, N, 8.06%. 1H NMR
(300 MHz, CDCl3, 293 K): d −0.80 (s, 12H, AlCH3), 0.97 (d,
12H, J = 6.9 Hz, CH3), 1.23 (d, 12H, J = 6.9 Hz, CH3), 3.13 (m,
6.42 (t, 2H, J = 7.4 Hz, Ph–H), 7.00–7.15 (m, 10H, Ph–H), 8.24
1
(s, 2H, CH NAr) ppm. 13C{ H} NMR (75 MHz, CDCl3, 293
=
K): d −1.22, 12.11, 18.52, 18.67, 62.64, 113.11, 114.08, 114.85,
124.21, 128.59, 128.68, 128.73, 133.44, 134.59, 134.70, 137.50,
137.66, 147.62, 156.34, 170.29, 170.47 ppm.
Synthesis of complex 4
ZnEt2 (3.4 mL, 1.0 M in toluene, 3.40 mmol) was added to a
solution of L2H2 (1.0 g, 1.70 mmol) in 20 mL of toluene at −10 ◦C
with stirring, gently heating to 80 ◦C for 2 d, during which a
3204 | Dalton Trans., 2008, 3199–3206
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clear yellow solution was formed. After removal of the solvent,
the product was precipitated with 10 mL hexane. The precipitate
was removed by filtration over a Celite plug. Removal of solvent
in vacuo gave a yellow powder that crystallized from a mixture of
CH2Cl2–hexane to give the desired complex as a yellow crystalline
solid (1.20 g, 91% yield). Anal. calcd for C44H58N4Zn2 (773.78): C
68.30, H 7.56, N 7.24; found: C 68.25, H 7.60, N 7.20%. 1H NMR
(500 MHz, C6D6, 293 K): d 0.46 (q, 4H, J = 8.0 Hz, ZnCH2),
0.79 (t, 6H, J = 6.2 Hz, ZnCH2CH3), 1.02 (d, 12H, J = 6.5 Hz,
CH3), 1.14 (d, 12H, J = 7.5 Hz, CH3), 3.09 (m, 4H, J = 6.5 Hz,
CH3CHCH3), 3.33 (s, 4H, NCH2), 6.37 (t, 2H, J = 7.0 Hz, Ph–H),
6.46 (d, 2H, J = 9.0 Hz, Ph–H), 6.88 (t, 2H, J = 7.8 Hz, Ph–H),
2 (a) A. C. Albertsson and I. K. Varma, Biomacromolecules, 2003, 4,
1466; (b) B. J. O’Keefe, M. A. Hillmyer and W. B. Tolman, J. Chem.
Soc., Dalton Trans., 2001, 2215; (c) J. Wu, T. L. Yu, C. T. Chen and
C. C. Lin, Coord. Chem. Rev., 2006, 250, 602.
3 Recent studies of Mg: (a) M. H. Chisholm, J. C. Huffman and K.
Phomphrai, J. Chem. Soc., Dalton Trans., 2001, 222; (b) M. L. Shueh,
Y. S. Wang, B. H. Huang, C. Y. Kuo and C. C. Lin, Macromolecules,
2004, 37, 5155; (c) L. F. Sa´nchez-Barba, D. L. Hughes, S. M. Humphrey
and M. Bochmann, Organometallics, 2006, 25, 1012; (d) L. E. Breyfogle,
C. K. Williams, V. G. Young, M. A. Hillmyer and W. B. Tolman, Dalton
Trans., 2006, 928; (e) Y. Sarazin, R. H. Howard, D. L. Hughes, S. M.
Humphrey and M. Bochmann, Dalton Trans., 2006, 340; (f) W. Y. Lee,
H. H. Hsieh, C. C. Hsieh, H. M. Lee, G. H. Lee, J. H. Huang, T. C. Wu
and S. H. Chuang, J. Organomet. Chem., 2007, 692, 1131; (g) T. L. Yu,
C. C. Wu, C. C. Chen, B. H. Huang, J. C. Wu and C. C. Lin, Polymer,
2005, 46, 5909.
4 Recent studies of Ca: (a) Z. Y. Zhong, P. J. Dijkstra, C. Birg, M.
Westerhausen and J. Feijen, Macromolecules, 2001, 34, 3863; (b) Z. Y.
Zhong, M. J. K. Ankone´, P. J. Dijkstra, C. Birg, M. Westerhausen
and J. Feijen, Polym. Bull. (Berlin), 2001, 46, 51; (c) Z. Y. Zhong, S.
Schneiderbauer, P. J. Dijkstra and J. Feijen, Polym. Bull. (Berlin), 2003,
51, 175.
6.94 (d, 2H, J = 8.0 Hz, Ph–H), 7.29 (s, 6H, Ph–H), 7.66 (s, 2H,
1
CH NAr) ppm. 13C{ H} NMR (75 MHz, C6D6, 293 K): d −0.98,
=
12.51, 24.25, 24.46, 28.40, 62.14, 113.38, 114.22, 116.58, 124.32,
125.85, 134.47, 137.54, 143.74, 144.91 158.07, 170.48, 170.52 ppm.
Polymerization of CL
5 Recent studies of Al: (a) S. Liu, M. A. Munoz-Hernandez and D. A.
Atwood, J. Organomet. Chem., 2000, 596, 109; (b) M. H. Chisholm,
D. Navarro-Llobet and W. J. Simonsick, Jr., Macromolecules, 2001, 34,
8851; (c) B. Antelmann, M. H. Chisholm, S. S. Iyer, J. C. Huffman,
D. Navarro-Llobet, W. J. Simonsick and W. Zhong, Macromolecules,
2001, 34, 3159; (d) D. Chakradorty and E. Y. X. Chen, Macromolecules,
2002, 35, 13; (e) R. C. Yu, C. H. Hung, J. H. Huang, H. Y. Lee and J. T.
Chen, Inorg. Chem., 2002, 41, 6450; (f) S. Dagorne, L. Lavanant, R.
Welter, C. Haquette, P. Chassenieux and G. Jaouen, Organometallics,
2003, 22, 3732; (g) C. H. Huang, F. C. Wang, B. T. Ko, T. L. Yu and
C. C. Lin, Macromolecules, 2001, 34, 356; (h) G. Zheng and H. D. H.
Stover, Macromolecules, 2003, 36, 7439; (i) C. T. Chen, C. A. Huang
and B. H. Huang, Macromolecules, 2004, 37, 7968; (j) L. M. Alcazar-
Roman, B. J. O’Keefe, M. A. Hillmyer and W. B. Tolman, Dalton Trans.,
2003, 3082; (k) J. Lewin´ski, P. Horeglad, E. Tratkiewicz, W. Grzenda,
J. Lipkowski and E. Kolodziejczyk, Macromol. Rapid Commun., 2004,
25, 1939; (l) M. L. Hsueh, B. H. Huang and C. C. Lin, Macromolecules,
2002, 35, 5763; (m) C. T. Chen, C. A. Hung and B. H. Huang, Dalton
Trans., 2003, 3799; (n) H. L. Chen, B. T. Ko, B. H. Huang and C. C. Lin,
Organometallics, 2001, 20, 5076; (o) N. Nomura, T. Aoyama, R. Ishii
and T. Kondo, Macromolecules, 2005, 38, 5363; (p) D. Chakradorty
and E. Y. X. Chen, Organometallics, 2002, 21, 1438; (q) S. Milione,
F. Grisi, R. Centore and A. Tuzi, Organometallics, 2006, 25, 266;
(r) A. Amgoune, L. Lavanant, C. M. Thomas, Y. Chi, R. Welter, S.
Dagorne and J. F. Carpentier, Organometallics, 2005, 24, 6279; (s) D.
Chakraborty and E. Y. X. Chen, Organometallics, 2003, 22, 769; (t) J.
Lewin´ski, P. Wo´jcik, K. Horeglad and I. Justyniak, Organometallics,
2005, 24, 4588; (u) M. R Tenbreteler, Z. Y. Zhong, P. J. Dijkstar, A. A.
Palmans, J. S. Peeters and J. Feijen, J. Polym. Sci., Part A: Polym.
Chem., 2007, 45, 429; (v) S. Dagorne, F. L. Bideau, R. Welter, S.
Bellemin-Laponnaz and A. Maisse-Franc¸ois, Chem.–Eur. J., 2007, 13,
3202; (w) L. Dosta´l, R. Jambor, I. C´ısarˇova´, J. Merna and J. Holecˇek,
Appl. Organomet. Chem., 2007, 21, 688; (x) J. Lewin´ski, P. Horeglad,
M. Dranka and I. Justyniak, Inorg. Chem., 2004, 43, 5789.
6 Recent studies of Ti: (a) D. Takeuchi, T. Nakamura and T. Aida,
Macromolecules, 2002, 33, 729; (b) V. V. Burlakov, A. V. Letov, P. Arndt,
W. Baumann, A. Spannenberg, C. Fischer, L. I. Strunkina, M. K.
Minacheva, Y. S. Vygodskii, U. Rosenthal and V. B. Shur, J. Mol.
Catal. A: Chem., 2003, 46, 51; (c) Y. Takashima, Y. Nakayama, T.
Hirao, H. Yasuda and A. Harada, J. Organomet. Chem., 2004, 689,
612; (d) J. Cayuela, V. Bounor-Legate´, P. Cassagnau and A. Michel,
Macromolecules, 2006, 39, 1338; (e) M. G. Davidson, M. D. Jones,
M. D. Lunn and M. F. Mahon, Inorg. Chem., 2006, 45, 2282; (f) A. J.
Chmura, M. G. Davidson, M. D. Jones, M. D. Lunn, M. F. Mahon,
A. F. Johnson, P. Khunkamchoo, S. L. Roberts and S. S. F. Wong,
Macromolecules, 2006, 39, 7250; (g) H. Wang, H. S. Chan, J. Okuda
and Z. W. Xie, Organometallics, 2005, 24, 3118; (h) F. Gornshtein,
M. Kapon, M. Botoshansky and M. S. Eisen, Organometallics, 2007,
26, 497; (i) L. I. Strunkina, M. K. Minacheva, K. A. Lyssenko, V. V.
Burlakov, W. Baumann, P. Atndt, B. N. Strunin and V. B. Shur,
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M. D. Jones, M. D. Lunn and M. F. Mahon, Dalton Trans., 2006,
887.
The polymerization reaction of CL was carried out in toluene
using catalysts 1–4 in the presence of BnOH. CL (3.0 mol L−1)
was added to a rapidly stirred solution of catalyst (0.19 mmol)
and BnOH, and the reaction mixture was stirred at the proposed
temperature for the prescribed time, during which an increase in
the viscosity of the solution was observed. After the reaction was
quenched by the addition of an excess of 1.0 M aqueous acetic
acid solution, the polymer was precipitated into MeOH. Crude
product was washed with cool MeOH three times (10 mL) and
dried in vacuo to a constant weight. 1H NMR spectra of the PCL
were measured using a Bruker AVANCE-500 NMR spectrometer.
Crystal structure data
Single crystals of 1, 2 and 3 suitable for X-ray structural analysis
were obtained from CH2Cl2–hexane. Diffraction data of 1 were
collected at 293 K with a Bruker SMART-CCD diffractometer
equipped with graphite-monochromated Mo-Ka radiation (k =
˚
0.71073 A). Diffraction data of 2 and 3 were collected at 293 K
on a Rigaku R-AXIS RAPID IP diffractometer equipped with
˚
graphite-monochromated Mo-Ka radiation (k = 0.71073 A). De-
tails of the crystal data, data collections, and structure refinements
are summarized in Table 3. The structures were solved by direct
methods and refined by full-matrix least-squares on F2. All non-
hydrogen atoms were refined anisotropically and the hydrogen
atoms were included in idealized position. All calculations were
performed using the SHELXTL16 crystallographic software pack-
ages.
CCDC reference numbers 661121–661123. For crystallographic
data in CIF or other electronic format see DOI: 10.1039/b719017d
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (Nos 20674024 and 20374023).
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