Dinuclear aluminum complexes supported by amino- or imino-phenolate ligands: Synthesis, structures, and ring-opening polymerization catalysis of rac-lactide

Article abstract of DOI:10.1039/c2dt32520a

Two series of ligand precursors [2-OH-3-(CH₂NR ₂)-5-MeC₆H₂]₂CH₂ (1: NR₂ = NMe₂; 2: NR₂ = N(CH₂) ₄; 3: NR₂ = N(CH₂)₅; 4: NR ₂ = N(Me)Ph) and [2-OH-3-(CHNR)-5-MeC₆H₂] ₂CH₂ (10: R = 2,6-Pri2C₆H₃; 11: R = p-MeC₆H₄; 12: R = p-ClC₆H₄; 13: R = p-MeOC₆H₄; 14: R = Bu^t) were prepared. These compounds reacted with AlMe₃ to afford corresponding dinuclear aluminum complexes [AlMe₂{2-O-3-(CH₂NR₂)-5- MeC₆H₂}]₂CH₂ (6: NR₂ = NMe₂; 7: NR₂ = N(CH₂)₄; 8: NR ₂ = N(CH₂)₅; 9: NR₂ = N(Me)Ph) and [AlMe₂{2-O-3-(CHNR)-5-MeC₆H₂}] ₂CH₂ (15: R = 2,6-Pri2C₆H₃; 16: R = p-MeC₆H₄; 17: R = p-ClC₆H₄; 18: R = p-MeOC₆H₄; 19: R = Bu^t). All the compounds were characterized by ¹H and ¹³C NMR spectroscopy and elemental analyses. Complexes 6 and 16 were additionally characterized by single crystal X-ray diffraction techniques. Catalysis of the aluminum complexes towards the ring-opening polymerization of rac-lactide was evaluated in the presence of benzyl alcohol. All the polymerization reactions proceed in a controlled manner.

Full text of DOI:10.1039/c2dt32520a

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Dinuclear aluminum complexes supported by amino-
or imino-phenolate ligands: synthesis, structures, and
ring-opening polymerization catalysis of rac-lactide†
Cite this: Dalton Trans., 2013, 42, 3860
Xiao-Feng Yu and Zhong-Xia Wang*
Two series of ligand precursors [2-OH-3-(CH2NR2)-5-MeC6H2]2CH2 (1: NR2 = NMe2; 2: NR2 = N(CH2)4; 3:
NR2 = N(CH2)5; 4: NR2 = N(Me)Ph) and [2-OH-3-(CHvNR)-5-MeC6H2]2CH2 (10: R = 2,6-Pri2C6H3; 11: R =
p-MeC6H4; 12: R = p-ClC6H4; 13: R = p-MeOC6H4; 14: R = But) were prepared. These compounds reacted
with AlMe3 to afford corresponding dinuclear aluminum complexes [AlMe2{2-O-3-(CH2NR2)-
5-MeC6H2}]2CH2 (6: NR2 = NMe2; 7: NR2 = N(CH2)4; 8: NR2 = N(CH2)5; 9: NR2 = N(Me)Ph) and [AlMe2{2-O-
3-(CHvNR)-5-MeC6H2}]2CH2 (15: R = 2,6-Pri2C6H3; 16: R = p-MeC6H4; 17: R = p-ClC6H4; 18: R = p-MeOC6H4;
19: R = But). All the compounds were characterized by 1H and 13C NMR spectroscopy and elemental ana-
lyses. Complexes 6 and 16 were additionally characterized by single crystal X-ray diffraction techniques.
Catalysis of the aluminum complexes towards the ring-opening polymerization of rac-lactide was evalu-
ated in the presence of benzyl alcohol. All the polymerization reactions proceed in a controlled manner.
Received 22nd October 2012,
Accepted 12th December 2012
DOI: 10.1039/c2dt32520a
www.rsc.org/dalton
Introduction
Polylactides (PLA) have attracted great interest over the past
decades due to their biodegradable and biocompatible proper-
ties.1 The ring-opening polymerization (ROP) of lactides using
metal complexes as the catalysts or initiators is the most
effective method for the synthesis of PLA. So far, a great many
complexes of metals such as magnesium,2 aluminum,3 zinc,4,5
and tin6 have been reported to be effective for the ROP of lac-
tides. Among these catalysts or initiators, bimetallic complexes
are relatively scarce although several examples have been
reported. For example, Tolman et al. reported a dizinc-monoalk-
oxide complex supported by a dinucleating ligand (I, Chart 1) to
be a highly active catalyst for the controlled polymerization of
lactides.7a Carpentier et al. showed that a dinuclear complex of
zinc bearing an amino-bis(pyrazolyl) ligand (II, Chart 1) initiates
polymerization of rac-lactide at 20 °C to yield atactic polymers
with controlled molecular masses and relatively narrow polydis-
persities.7b Thibault and Fontaine proved that bimetallic alumi-
num complexes supported by functionalized trisamido ligands
(III, Chart 1) are active in the polymerization of ε-caprolactone
and rac-lactide.7c In some systems bimetallic complexes exhibit
Chart 1 Examples of bimetallic catalysts for the ring-opening polymerization
of cyclic esters.
higher catalytic activity than corresponding mononuclear ones
for the ROP of cyclic esters and this is ascribed to cooperative
effects.8 For example, Redshaw et al. confirmed that two remote
dialkylaluminum centers supported by a macrocyclic Schiff base
ligand exhibit beneficial cooperative effects in catalyzing the
ROP of ε-caprolactone.8a In order to learn more about the cata-
lysis of bimetallic systems, we initiated a study on the ROP of
cyclic esters using bimetallic complexes as the catalysts. Herein
we report synthesis and characterization of bimetallic aluminum
complexes supported by N,O-chelate ligands and catalysis of the
complexes in the ROP of rac-lactide.
CAS Key Laboratory of Soft Matter Chemistry and Department of Chemistry,
University of Science and Technology of China, Hefei, Anhui 230026, People’s
Republic of China. E-mail: zxwang@ustc.edu.cn; Fax: +86 551 3601592;
Results and discussion
Tel: +86 551 3603043
Synthesis and characterization of compounds
†Electronic supplementary information (ESI) available. CCDC 906746 and
906747. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c2dt32520a
Synthesis of compounds 1–4 and their aluminum complexes
6–9 is shown in Scheme 1. Compounds 1–3 were prepared by
3860 | Dalton Trans., 2013, 42, 3860–3868
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of 117.9(2)° is wider than that of C(23)–Al(2)–C(24) [112.9(3)°],
and the former is close to that in Me2Al[O-2-But-6-{Me2NCH2}-
C6H3] [118.13(7)°].9 The angles of C–Al–O and C–Al–N in
complex 6 are comparable to corresponding ones in Me2Al-
[O-2-But-6-{Me2NCH2}C6H3].9
Synthesis of compounds 10–19 is shown in Scheme 2. The
bis(imine-phenols) 10–14 were prepared through condensation
of 2,2′-methylene bis(4-methyl-6-formylphenol) with two equiv.
of primary amines in refluxing ethanol. Compounds 10 and 14
were purified by removing ethanol and then washing with
hexane. Compounds 11–13 formed precipitates in ethanol and
were purified by recrystallizing from toluene. Treatment of
10–14 with excess AlMe3 in toluene afforded dinuclear alumi-
num complexes 15–19. Each of 10–19 gave a satisfactory
elemental analytical result. The 1H and 13C NMR spectra are
consistent with their respective structure. The NMR spectra of
Scheme 1 Synthesis of compounds 1–4 and 6–9.
the Mannich reaction from 2-[(2-hydroxy-5-methylphenyl)-
methyl]-4-methylphenol, HCHO and corresponding secondary
amines. However, a similar procedure was unsuccessful for the
synthesis of compound 4. Alternatively, compound 4 was syn-
thesized from PhNH(Me) and corresponding benzyl chloride
derivative, 5. Treatment of compounds 1–4 with excess AlMe3
in toluene afforded dinuclear aluminum complexes 6–9. It
should be indicated that the reactions between 1–4 and AlMe3
require an elevated temperature, otherwise the reactions can
not go to completion.
Compounds 1–4 were characterized by 1H and 13C NMR
spectroscopy and elemental analyses. The analytical results
match the calculated values very well. The NMR spectra are
consistent with the respective structure of the compounds.
Complexes 6–9 gave also satisfactory elemental analytical
results. The 1H NMR spectrum of each complex exhibits single
Al–Me signal, showing all the four methyl groups to be chemi-
cally equivalent and the two aluminum atoms have the same
coordination environments in each molecule. In addition, the
1H NMR spectra of complexes 6–9 do not display the signals of
the OH group. This implies that the OH groups in 1–4 have
been transformed to OAlMe2 through the reactions. The
coordination mode of the aluminum atom in complex 6 has
been confirmed by single crystal X-ray diffraction. The ORTEP
drawing is presented in Fig. 1, along with selected bond
lengths and angles. In the molecule, each aluminum atom is
four coordinate and has a distorted tetrahedral coordination
geometry. The Al–O distance of an average of 1.759 Å is very
close to that in the mononuclear aluminum complex Me2Al-
[O-2-But-6-{Me2NCH2}C6H3] (1.758(1) Å).9 The Al–N distances
of 2.027(4) Å and 1.996(4) Å, respectively, are slightly shorter
than that in Me2Al[O-2-But-6-{Me2NCH2}C6H3] [2.036(1) Å].9
The Al–C distances ranging from 1.935(5) Å to 1.952(4) Å are
comparable to corresponding ones in Me2Al[O-2-But-
Fig. 1 The ORTEP diagram of complex 6 (30% probability thermal ellipsoids).
Selected bond lengths (Å) and angles (°): Al(1)–O(1) 1.760(3), Al(1)–N(1)
2.027(4), Al(1)–C(21) 1.948(5), Al(1)–C(22) 1.952(4), Al(2)–O(2) 1.758(3), Al(2)–
N(2) 1.996(4), Al(2)–C(23) 1.949(5), Al(2)–C(24) 1.935(5), O(1)–Al(1)–C(21)
113.55(18), O(1)–Al(1)–C(22) 110.95(18), C(21)–Al(1)–C(22) 117.9(2), O(1)–Al(1)–
N(1) 96.45(14), C(21)–Al(1)–N(1) 108.64(19), C(22)–Al(1)–N(1) 106.85(19),
O(2)–Al(2)–C(23) 114.0(2), O(2)–Al(2)–C(24) 112.8(2), C(24)–Al(2)–C(23) 112.9(3),
O(2)–Al(2)–N(2) 96.88(17), C(23)–Al(2)–N(2) 109.6(2), C(24)–Al(2)–N(2) 109.5(2).
6-{Me2NCH2}C6H3].9 In complex 6, the C(21)–Al(1)–C(22) angle Scheme 2 Synthesis of compounds 10–19.
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complexes 15–19 also exhibit a single Al–Me signal for each corresponding ones in Me2Al[O-2-But-6-{(2,4,6-Me3C6H2)-
complex, implying that two aluminum atoms in a molecule NvCH}C6H3] (1.7748(19) and 1.965(2) Å, respectively).10 In
have the same coordination environments and the methyl addition, the nitrogen atoms in complex 16 show approxi-
groups are chemically equivalent.
mately planar geometry, sum of the angles around the nitro-
Complex 16 was further characterized by single crystal X-ray gen atoms being 359.96° (for N1) and 359.63° (for N2),
diffraction. The ORTEP drawing is shown in Fig. 2, along with respectively. The C2–N1 and C10–N2 distances are 1.292(4) Å
selected bond lengths and angles. The skeletal structure of 16 and 1.297(4) Å, respectively, which are indicative of C–N
is similar to that of 6. Thus, each of the central aluminum double bonds.
atoms is four coordinate and displays distorted tetrahedral
geometry. However, some differences of bond lengths and
bond angles between the two complexes are noted. For
Ring-opening polymerization of rac-lactide
The ROP of rac-lactide using 6–9 and 15–19 as catalysts was
studied and the results are listed in Table 1. The experimental
results show that all the dinuclear aluminum complexes are
active in the ROP of rac-lactide in the presence or absence of
BnOH. However, in the absence of BnOH, the catalytic activi-
ties are lower and lead to higher PDI in comparison with the
catalytic systems using BnOH (entries 1 and 8). It was also
noted that in the absence of BnOH the catalytic polymerization
with complex 15 leads to a higher molecular weight of PLA
than the calculated value. It seems only one active site is in
action in the catalyst molecule (entry 8). In the presence of two
equiv. of BnOH, complex 6 drives 93% conversion of rac-LA in
21 h at 70 °C when the monomer-to-catalyst ratio ([LA]0–[6]0) is
100 : 1. The molecular weight of the PLA measured by GPC is
close to the theoretical value calculated from the monomer :
BnOH molar ratio and shows low polydispersity, which imply
the polymerization is well controlled (entry 2). In the case of
the 400 : 1 : 2 ratio of lactide : 6 : BnOH, the polymerization
reaction still proceeds smoothly and is also well controlled
(entry 3). When the ratio of lactide : 6 : BnOH was changed to
400 : 1 : 4, the molecular weight of the polymer was still pro-
portional to the monomer : BnOH molar ratio and the molecu-
lar weight distribution of the polymer was narrow. These are
the characteristics of immortal polymerization.11 Complexes 7
and 8 exhibit similar catalytic activity to complex 6 in the pres-
ence of BnOH (entries 5 and 6). However, the molecular weight
example, the Al–O distance (av. 1.767 Å) in complex 16 is
slightly longer than that in complex 6 (av. 1.759 Å). The Al–N
distance of an average of 1.9665 Å in complex 16 is shorter
than that in complex 6 (av. 2.0115 Å). This results from
different hybrids of the nitrogen atoms in two complexes. The
Al–O and Al–N distances in complex 16 are comparable to
Fig. 2 The ORTEP diagram of complex 16 (30% probability thermal ellipsoids.
The toluene molecule is omitted.). Selected bond lengths (Å) and angles (°):
Al(1)–O(1) 1.772(3), Al(1)–C(32) 1.942(4), Al(1)–C(33) 1.965(4), Al(1)–N(1)
1.970(3), Al(2)–O(2) 1.762(3), Al(2)–C(34) 1.949(4), Al(2)–C(35) 1.954(4), Al(2)–
N(2) 1.963(3), O(1)–Al(1)–C(32) 112.55(16) O(1)–Al(1)–C(33) 111.28(18), C(32)–
Al(1)–C(33) 119.36(17), O(1)–Al(1)–N(1) 94.45(14), C(32)–Al(1)–N(1) 108.57(17),
C(33)–Al(1)–N(1) 107.53(17), O(2)–Al(2)–C(34) 110.61(18), O(2)–Al(2)–C(35)
112.69(16), C(34)–Al(2)–C(35) 118.14(19), O(2)–Al(2)–N(2) 94.59(13), C(34)–
Al(2)–N(2) 111.68(16), C(35)–Al(2)–N(2) 106.55(17).
Table 1 The ROP of rac-LA catalyzed by complexes 6–9 and 15–19a
Entry
Cat.
[Cat]0 : [BnOH]0 : [LA]0
Time (h)
Conv.b (%)
Mc c (10−3
)
Mn d (10−3
)
PDId
1
2
3
4
5
6
7
8
6
6
6
6
7
8
9
15
15
15
15
16
17
18
19
1 : 0 : 100
1 : 2 : 100
1 : 2 : 400
1 : 4 : 400
1 : 2 : 100
1 : 2 : 100
1 : 2 : 100
1 : 0 : 100
1 : 2 : 100
1 : 2 : 400
1 : 4 : 400
1 : 2 : 100
1 : 2 : 100
1 : 2 : 100
1 : 2 : 100
24
21
45
45
25
25
33
24
16
60
60
24
24
24
24
44
93
47
61
94
90
50
74
93
54
75
79
91
95
91
3.3
6.8
13.8
8.9
6.9
6.6
3.7
5.4
6.8
15.7
10.9
5.8
6.7
7.0
3.3
6.4
13.4
6.4
9.9
6.5
2.9
10.5
7.0
11.3
10.4
4.7
1.86
1.20
1.20
1.16
1.27
1.21
1.14
1.33
1.16
1.11
1.09
1.11
1.08
1.20
1.11
9
10
11
12
13
14
15
5.5
7.1
5.6
6.7
a All polymerizations were carried out in toluene at 70 °C, [LA]0 = 0.5 M. b Measured by 1H NMR spectra. c Mc = 144.13 × ([LA]0/[BnOH]0) × conv.%
+ 108.13. In the absence of BnOH (entries 2 and 9), Mc = 144.13 × ([LA]0/[Cat.]0)/2 × conv.%. d Determined by GPC using polystyrene as the
standard, multiplied by 0.58.12
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of the polymer catalyzed by 7/BnOH is higher than the calcu- weight distribution is narrow (entries 9 and 12–15). When the
lated value. Complex 9 shows lower catalytic activity than 6–8, ratio of lactide : 15 : BnOH is 400 : 1 : 2, the polymerization
but the molecular weights of the polymers determined by GPC reaction proceeds slower and the determined molecular weight
are close to a theoretical value calculated according to the of the polymer is lower than the calculated value. However,
monomer : BnOH molar ratio (entry 7). The lower activity of when the ratio of lactide : 15 : BnOH is 400 : 1 : 4, the reaction
complex 9 compared to complexes 6–8 may be because of the proceeds faster and the molecular weight of the polymer
presence of phenyl groups on the nitrogen atoms in 9, which matches the calculated value very well (entries 10 and 11).
leads to weaker electron donor ability of the nitrogen atoms. Under comparable conditions, complexes 7 and 8 show similar
Among complexes 15–19 complex 15/BnOH system displays catalytic activity to complexes 17–19.
highest activity and complex 16/BnOH shows the lowest activity
The 1H NMR spectrum of the resulting polymer (Fig. 3)
when the ratio of lactide : catalyst : BnOH is 100 : 1 : 2. Under shows no ligand signals or terminal methyl signals. This
the same conditions, complexes 17, 18 and 19 exhibit similar means that the polymerization is not initiated by the Al–O
catalytic activity. The high activity of complex 15 is probably bonds of the ligand or Al–Me bonds. Alternatively, the polymer
related to the steric hindrance of the aryl groups on the nitro- chain is capped with one benzyl ester and one hydroxyl end.
gen atoms. In each case the determined molecular weight by The molecular weights determined by GPC are close to the cal-
GPC matches the calculated value very well and the molecular culated values based on the monomer : BnOH molar ratio in
most cases as mentioned above. These results are consistent
with an insertion mechanism of a benzyl alkoxy group into the
lactide.
Homonuclear decoupled 1H NMR spectra in the methine
range of PLA (see Fig. S1 in ESI†) showed that slightly prevail-
ing isotactic PLAs were obtained using complexes 6 and 15 as
the catalysts.13
The catalytic activities of the dinuclear aluminum com-
plexes 15, 16 and 19 were compared with those of correspond-
ing mononuclear aluminum complexes A1–A3 (Chart 2)
reported previously10 and the results are presented in Table 2.
A1 has the same N-substituent as complex 15. In the presence
of BunOH A1 drives polymerization of rac-LA in 23% yield in
24 h at 80 °C when the ratio of lactide : A1 : BunOH is 100 : 1 : 1.
Complex 15 shows higher activity. It leads to 75% yield of PLA
in 24 h at 80 °C when the ratio of lactide : 15 : BunOH is
200 : 1 : 2. Complex A2 has a similar N-substituent (Ph) as 16
Fig. 3 The 1H NMR spectrum of PLA initiated by 6-BnOH (entry 2, Table 1).
(p-MeC6H4) and complex A3 has the same N-substituent as 19.
Under the same conditions, 16 and 19 also display higher
activity than A2 and A3, respectively. The higher activity of the
dinuclear complexes is probably due to a cooperative effect. In
the catalytic process, one aluminum atom serves as the Lewis
acid, and an alkoxy group bound to the second aluminum
center attacks the carbonyl group of the incoming lactide. But
other factors such as the effect of substituents on 2-position of
aromatic rings cannot be ruled out.
Kinetic studies of rac-lactide polymerization catalyzed by
Chart 2
the dinuclear aluminum complexes in the presence of BnOH
Table 2 The ROP of rac-LA catalyzed by complexes 15, 16, 19 and mononuclear aluminum complexes A1–A3a
Entry
Cat.
[Cat.]0 : [BuOH]0 : [LA]0
Yieldb (%)
TOF (h−1
)
Mn c (×10−3
)
PDIc
1
2
3
4
5
6
A1
15
A2
16
A3
19
1 : 1 : 100
1 : 2 : 200
1 : 1 : 100
1 : 2 : 200
1 : 1 : 100
1 : 2 : 200
23
75
19
39
4
0.96
3.13
0.79
1.63
0.17
2.83
13.5
16.7
10.8
9.0
—
12.1
1.10
1.06
1.11
1.11
—
68
1.08
a All polymerizations were run in toluene at 80 °C for 24 h in the presence of BunOH, [LA]0 = 1.0 mol cm−3
in THF using polystyrene as the standard.
.
b Isolated yield. c Determined by GPC
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■
▲
( GPC) and polydispersity ( , Mw/Mn) as a function of
Fig. 7 Plots of PLA Mn
Fig. 4 Plots of ln([M]0/[M]) versus time for the polymerization of rac-LA cata-
lyzed by 6–9. [M]0–[Al]–[BnOH]0 = 100 : 1 : 2, [M]0 = 0.5 M; solvent: toluene;
polymerization temperature: 70 °C.
rac-LA conversion using complex 15 at 70 °C. [M]0 : [Al]0 : [BnOH]0 = 100 : 1 : 2,
[M]0 = 0.5 M; solvent: toluene.
This also implies that the polymerizations are controllable. A
further indicator of controlled polymerization is the linear
relationship between number-average molecular weight and
conversion throughout the reaction process in the polymeriz-
ation using complexes 6 and 15, respectively, as catalysts,
along with low polydispersity (Fig. 6 and 7). These facts also
show that the polymerizations have the “living” character.
Conclusions
We have synthesized and characterized two classes of dinuc-
lear aluminum complexes supported by N,O-chelate ligands.
In the presence of BnOH, the complexes are efficient catalysts
for the ROP of rac-lactide and the reactions lead to polymers
with good molecular weight control and narrow molecular
weight distribution. The catalytic activity of the complexes is
affected by the substituents on the coordinated N atoms. Two
aluminum centers in the dinuclear aluminum complexes may
have a cooperative effect in the catalytic process.
Fig. 5 Plots of ln([M]0/[M]) versus time for the polymerization of rac-LA cata-
lyzed by 15–19. [M]0–[Al]–[BnOH]0 = 100 : 1 : 2, [M]0 = 0.5 M; solvent: toluene;
polymerization temperature: 70 °C.
Experimental
General
All air or moisture sensitive manipulations were performed
under dry N2 using standard Schlenk techniques. Solvents
were distilled under nitrogen over sodium (toluene) or sodium/
benzophenone (n-hexane and diethyl ether). 2-[(2-Hydroxy-
5-methylphenyl)-methyl]-4-methylphenol,14 2-(chloromethyl)-
6-[[3-(chloromethyl)-2-hydroxy-5-methylphenyl]-methyl]-
4-methylphenol15 and 2,2′-methylene bis(4-methyl-6-formyl-
phenol)16 were prepared according to reported methods. AlMe3
(2 M in toluene) was purchased from Acros Organics and used
as received. CDCl3 and C6D6 were purchased from Cambridge
Isotope Laboratories and stored over activated molecular sieves
(CDCl3) or Na/K alloy (C6D6). Other chemicals and solvents
were purchased from commercial venders. NMR spectra were
recorded on a Bruker av300 spectrometer at ambient tempera-
ture. The chemical shifts of 1H and 13C NMR spectra were
■
▲
( GPC) and polydispersity ( , Mw/Mn) as a function of
Fig. 6 Plots of PLA Mn
rac-LA conversion using complex 6 at 70 °C. [M]0 : [Al]0 : [BnOH]0 = 100 : 1 : 2,
[M]0 = 0.5 M; solvent: toluene.
were also carried out. Plots of ln([LA]0/[LA]t) versus time using
each catalyst exhibit a good linear relationship (Fig. 4 and 5).
This indicates that the polymerization proceeds with first-
order dependence on monomer concentration in each case.
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referenced to TMS or internal solvent resonances. Elemental 128.41, 129.81, 153.62. Anal. calcd for C27H38N2O2: C, 76.74;
analyses were performed by the Analytical Center of the Uni- H, 9.06; N, 6.63%. Found: C, 76.50; H, 8.83; N, 6.52%.
versity of Science and Technology of China. Gel permeation
Synthesis of [2-OH-3-{CH2N(Me)Ph}-5-MeC6H2]2CH2 (4)
chromatography (GPC) measurements were performed on a
Waters 150C instrument equipped with UltraStyragel columns A mixture of 2-(chloromethyl)-6-[[3-(chloromethyl)-2-hydroxy-
(103, 104, and 105 Å) and a 410 refractive index detector, using 5-methyl-phenyl]methyl]-4-methylphenol (1.50 g, 4.61 mmol),
monodispersed polystyrene as the calibration standard. THF N-methylaniline (1.20 g, 11.20 mmol), NaHCO3 (1.50 g,
(HPLC grade) was used as an eluent at a flow rate of 1 cm3 17.86 mmol), and THF (50 cm3) was refluxed for 12 h and then
min−1
.
cooled to room temperature. The solvent was removed under
vacuum. CH2Cl2 (100 cm3) and H2O (100 cm3) were added to
the residue. The resulting mixture was stirred for 30 min. The
organic layer was separated and dried over MgSO4, filtered,
and concentrated under vacuum to give a crude product. The
crude product was washed with n-hexane three times to give a
white powder of 4 (1.30 g, 67%), mp 120–122 °C. 1H NMR
(CDCl3, 300 MHz): δ 2.23 (s, 6H, NMe), 2.89 (s, 6H, ArMe), 3.90
(s, 2H, ArCH2Ar), 4.39 (s, 4H, NCH2Ar), 6.75 (s, 2H, Ar-H), 6.93
(m, 2H, Ar-H), 7.00 (m, 4H, Ar-H), 7.04 (s, 2H, Ar-H), 7.30 (d, J =
9 Hz, 4H, Ar-H), 9.57 (b, 2H, OH). 13C NMR (CDCl3, 75 MHz):
δ 20.78, 30.36, 39.98, 57.16, 116.86, 120.51, 123.11, 127.06,
127.39, 127.46, 129.34, 130.11, 150.55, 150.97. Anal. calcd for
C31H34N2O2·0.06CH2Cl2: C, 79.10; H, 7.29; N, 5.94%. Found:
C, 79.03; H, 7.45; N, 5.81%.
Synthesis of [2-OH-3-(CH2NMe2)-5-MeC6H2]2CH2 (1)
A mixture of 2-[(2-hydroxy-5-methylphenyl)methyl]-4-methyl-
phenol (3.00 g, 13.14 mmol), dimethylamine (33% w/w
aqueous solution, 4.80 g), formaldehyde (37%–40% w/w
aqueous solution, 5.20 g), and ethanol (50 cm3) was refluxed
for 12 h and then cooled to room temperature. Hydrobromic
acid (48% w/w aqueous solution, 6.0 cm3) was added to the
solution. The resulting mixture was stirred for 30 min. The
solvent was removed from the mixture under vacuum. The
residue was washed using THF and then neutralized with satu-
rated NaHCO3 solution (100 cm3). The resulting mixture was
extracted with CH2Cl2 (3 × 30 cm3). The organic layer was dried
over MgSO4, filtered, and concentrated under vacuum to give a
white powder of 1 (2.50 g, 56%), mp 106–108 °C. 1H NMR
(CDCl3, 300 MHz): δ 2.20 (s, 6H, ArMe), 2.33 (s, 12H, NMe),
3.61 (s, 4H, NCH2), 3.95 (s, 2H, ArCH2Ar), 6.66 (s, 2H, Ar-H),
6.82 (s, 2H, Ar-H), 10.33 (b, 2H, OH). 13C NMR (CDCl3,
75 MHz): δ 20.71, 28.99, 44.53, 62.91, 121.20, 126.93, 127.53,
127.58, 130.05, 153.55. Anal. calcd for C21H30N2O2·0.06CH2Cl2:
C, 72.78; H, 8.73; N, 8.06%. Found: C, 72.78; H, 8.63;
N, 7.82%.
Synthesis of [2-(OAlMe2)-3-(CH2NMe2)-5-MeC6H2]2CH2 (6)
AlMe3 (1.00 cm3, 2.0 M solution in toluene, 2.00 mmol) was
added to a stirred solution of 1 (0.30 g, 0.88 mmol) in toluene
(20 cm3) at about −80 °C. The mixture was warmed to room
temperature, stirred for 12 h at room temperature and for
another 12 h at 80 °C. The resulting mixture was cooled to
room temperature. The solvent was removed under vacuum.
The residue was dissolved in diethyl ether (20 cm3) and then
filtered. The filtrate was concentrated in vacuo to give colorless
crystals of 6 (0.23 g, 57%), mp 181–183 °C. 1H NMR (C6D6,
300 MHz): δ −0.46 (s, 12H, AlMe), 1.55 (s, 12H, NMe), 2.32 (s,
6H, ArMe), 3.04 (s, 4H, NCH2Ar), 4.56 (s, 2H, ArCH2Ar), 6.38 (s,
2H, Ar-H), 7.53(s, 2H, Ar-H). 13C NMR (C6D6, 75 MHz): δ
−10.79, 20.88, 30.37, 44.48, 62.89, 120.09, 125.40, 127.60,
128.07, 132.74, 133.01. Anal. calcd for C25H40Al2N2O2: C, 66.06;
H, 8.87; N, 6.16%. Found: C, 66.24; H, 8.65; N, 6.02%.
Synthesis of [2-OH-3-{CH2N(CH2)4}-5-MeC6H2]2CH2 (2)
Compound 2 was synthesized according to the same procedure
as for that of 1, but pyrrolidine (1.89 g, 26.57 mmol) was used
instead of dimethylamine. After similar work-up, compound 2
was obtained as a white powder (3.60 g, 69%), mp 124–126 °C.
1H NMR (CDCl3, 300 MHz): δ 1.85 (m, 8H, CH2), 2.18 (s, 6H,
ArMe), 2.67 (m, 8H, CH2), 3.81 (s, 4H, NCH2Ar), 3.91 (s, 2H,
ArCH2Ar), 6.69 (s, 2H, Ar-H), 6.81 (s, 2H, Ar-H), 9.80 (b, 2H,
OH). 13C NMR (CDCl3, 75 MHz): δ 20.71, 23.74, 29.40, 53.44, Synthesis of [2-(OAlMe2)-3-{CH2N(CH2)4}-5-MeC6H2]2CH2 (7)
58.52, 121.42, 126.90, 127.50, 127.64, 130.11, 153.35. Anal.
AlMe3 (0.92 cm3, 2.0 M solution in toluene, 1.84 mmol) was
calcd for C25H34N2O2: C, 76.10; H, 8.69; N, 7.10%. Found:
C, 76.32; H, 8.67; N, 6.83%.
added to a stirred solution of 2 (0.30 g, 0.76 mmol) in toluene
(20 cm3) at about −80 °C. The mixture was warmed to room
temperature, stirred for 12 h at room temperature and for
another 12 h at 80 °C. The resulting mixture was cooled to
Synthesis of [2-OH-3-{CH2N(CH2)5}-5-MeC6H2]2CH2 (3)
Compound 3 was synthesized using the same procedure as for room temperature. The solvent was removed from the mixture
that of 1, but piperidine (2.34 g, 27.48 mmol) was used instead under vacuum. The residue was dissolved in diethyl ether
of dimethylamine. After similar work-up, compound 3 was (20 cm3) and filtered. The filtrate was concentrated and cooled
1
obtained as a white powder (3.70 g, 67%), mp 116–118 °C. H to about −80 °C to afford colorless crystals (0.22 g, 57%), mp
1
NMR (CDCl3, 300 MHz): δ 1.51 (m, 4H, CH2), 1.64 (m, 8H, 201–203 °C. H NMR (C6D6, 300 MHz): δ −0.41 (s, 12H, AlMe),
CH2), 2.18 (s, 6H, ArMe), 2.52 (m, 8H, CH2), 3.64 (s, 4H, 1.12 (m, 8H, NCH2CH2), 2.02–2.35 (m, 8H, NCH2CH2), 2.35 (s,
NCH2Ar), 3.95 (s, 2H, ArCH2Ar), 6.65 (s, 2H, Ar-H), 6.79 (s, 2H, 6H, ArMe), 3.21 (s, 4H, NCH2Ar), 4.60 (s, 2H, ArCH2Ar), 6.42 (s,
Ar-H), 11.06 (b, 2H, OH). 13C NMR (CDCl3, 75 MHz): δ 20.69, 2H, Ar-H), 7.57 (s, 2H, Ar-H). 13C NMR (C6D6, 75 MHz): δ
24.18, 25.89, 29.01, 53.93, 62.34, 120.89, 127.02, 127.46, −10.35, 15.59, 22.40, 30.40, 53.81, 59.56, 120.72, 125.17,
This journal is © The Royal Society of Chemistry 2013
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Dalton Transactions
129.34, 132.42, 133.09, 156.38 ppm. Anal. calcd for 7.17 (s, 2H, Ar-H),7.46 (m, 8H, Ar-H), 8.59 (s, 2H, NvCH),
C29H44Al2N2O2: C, 68.75; H, 8.75; N, 5.53%. Found: C, 68.61; 13.55 (b, 2H, OH). 13C NMR (CDCl3, 75 MHz): δ 20.65, 21.19,
H, 8.48; N, 5.52%.
28.26, 118.63, 121.11, 127.76, 128.40, 130.09, 130.45, 135.03,
136.74, 146.17, 157.14, 162.01. Anal. calcd for C31H30N2O2:
C, 80.49; H, 6.54; N, 6.06. Found: C, 80.31; H, 6.53; N, 5.98%.
Synthesis of [2-(OAlMe2)-3-{CH2N(CH2)5}-5-MeC6H2]2CH2 (8)
The same procedure as for that of 6 was used, but 3 was used
instead of 2. Thus, reaction of 3 (0.30 g, 0.71 mmol) with
Synthesis of [2-OH-3-{CHvN(p-ClC6H4)}-5-MeC6H2]2CH2 (12)
AlMe3 (0.85 cm3, 1.70 mmol) afforded, after similar workup, The same procedure as for that of 10 was used, but 4-chloro-
1
colorless crystals of 7 (0.24 g, 63%), mp 160–162 °C. H NMR aniline (1.35 g, 10.58 mmol) was employed instead of 2,6-diiso-
(C6D6, 300 MHz): δ −0.36 (s, 12H, AlMe), 0.89 (m, 4H, CH2), propylaniline. The crude product was further purified by
1.03–1.05 (m, 8H, CH2), 2.10–2.35 (m, 8H, CH2), 2.36 (s, 6H, recrystallization from toluene to give a yellow powder of 12
ArMe), 3.32 (s, 4H, NCH2Ar), 4.57 (s, 2H, ArCH2Ar), 6.46 (s, 2H, (2.0 g, 75%), mp 222–224 °C. 1H NMR (CDCl3, 300 MHz): δ
Ar-H), 7.60(s, 2H, Ar-H). 13C NMR (C6D6, 75 MHz): δ −8.93, 2.28 (s, 6H, ArMe), 4.09 (s, 2H, ArCH2Ar), 7.14 (s, 2H, Ar-H),
15.60, 20.73, 22.99, 30.27, 52.61, 58.75, 119.35, 125.35, 129.33, 7.06 (s, 2H, Ar-H), 7.24 (d, J = 9 Hz, 4H, Ar-H), 7.38 (d, J = 9 Hz,
132.22, 133.22, 156.36. Anal. calcd for C31H48Al2N2O2·0.5Et2O: 4H, Ar-H), 8.55 (s, 2H, NvCH), 13.20 (b, 2H, OH). 13C NMR
C, 69.32; H, 9.34; N, 4.90%. Found: C, 69.51; H, 9.08; (CDCl3, 75 MHz): δ 20.63, 28.70, 118.42, 122.56, 128.23,
N, 4.82%.
128.43, 129.63, 130.74, 132.37, 135.59, 147.30, 157.17, 163.25.
Anal. calcd for C29H24Cl2N2O2: C, 69.19; H, 4.81; N, 5.56%.
Found: C, 69.26; H, 4.88; N, 5.55%.
Synthesis of [2-(OAlMe2)-3-{CH2N(Me)Ph}-5-MeC6H2]2CH2 (9)
The same procedure as for that of 5 was used, but 4 was used
instead of 1. Thus, treatment of 4 (0.30 g, 0.64 mmol) with
AlMe3 (0.80 cm3, 2.0 M solution in toluene, 1.60 mmol)
Synthesis of [2-OH-3-{CHvN(p-MeOC6H4)}-5-MeC6H2]2CH2
(13)
afforded, after similar workup, colorless crystals of 8 (0.27 g, The same procedure as for that of 10 was used, but 4-methoxy-
73%), mp 250–252 °C. 1H NMR (C6D6, 300 MHz): δ −0.29 (s, aniline (1.30 g, 10.56 mmol) was used instead of 2,6-diisopro-
12H, AlMe), 2.19 (s, 6H, ArMe), 2.42 (s, 6H, NMe), 4.30–4.60 (b, pylaniline. The crude product was further purified by
6H, NCH2Ar + ArCH2Ar), 6.74 (s, 2H, Ar), 6.83–6.91 (m, 6H, Ar), recrystallization from toluene to give a yellow powder of 12
7.09–7.14 (m, 4H, Ar-H), 7.22 (s, 2H, Ar-H). 13C NMR (C6D6, (1.9 g, 73%), mp 185–187 °C. 1H NMR (CDCl3, 300 MHz): δ
75 MHz): δ −9.01, 20.81, 20.83, 33.39, 55.87, 117.14, 122.03, 2.26 (s, 6H, ArMe), 3.82 (s, 6H, OMe), 4.10 (s, 2H, ArCH2Ar),
125.25, 128.13, 129.53, 129.57, 129.61, 129.63, 129.65, 129.70, 6.93 (d, J = 9 Hz, 4H, Ar-H), 7.03 (s, 2H, Ar-H), 7.10 (s, 2H, Ar-
131.71, 148.98 ppm. Anal. calcd for C35H44Al2N2O2: C, 72.64; H), 7.25 (d, J = 9 Hz, 4H, Ar-H), 8.55 (s, 2H, NvCH), 13.52 (b,
H, 7.66; N, 4.84%. Found: C, 72.36; H, 7.63; N, 4.60%.
2H, OH). 13C NMR (CDCl3, 75 MHz): δ 20.64, 28.60, 55.64,
114.70, 118.72, 122.36, 127.73, 128.39, 130.30, 134.80, 141.72,
157.03, 158.77, 160.78. Anal. calcd for C31H30N2O4: C, 75.28;
H, 6.11; N, 5.66%. Found: C, 75.45; H, 6.41; N, 5.66%.
Synthesis of [2-OH-3-{CHvN(2,6-Pri2C6H3)}-5-MeC6H2]2CH2
(10)
A
mixture of 2,2′-methylene bis(4-methyl-6-formylphenol)
Synthesis of [2-OH-3-(CHvNCMe3)-5-MeC6H2]2CH2 (14)
(1.50 g, 5.28 mmol), 2,6-diisopropylaniline (1.87 g,
10.55 mmol) and ethanol (50 cm3) was refluxed for 12 h and The same procedure as for that of 10 was used, but tert-butyl-
then cooled to room temperature. The solvent was removed amine (0.78 g, 10.66 mmol) was employed instead of 2,6-diiso-
from the mixture under vacuum. The residue was washed propylaniline. After similar workup, compound 14 was
1
using n-hexane three times to give a yellow powder of 10 obtained as a yellow powder (1.8 g, 86%), mp 118–120 °C. H
(1.70 g, 53%), mp 160–162 °C. 1H NMR (CDCl3, 300 MHz): δ NMR (CDCl3, 300 MHz): δ 1.33 (s, 18H, CMe3), 2.23 (s, 6H,
1.18 (d, J = 9 Hz, 24H, CHMe2), 2.29 (s, 6H, ArMe), 3.00 (m, 4H, ArMe), 4.04 (s, 2H, ArCH2Ar), 6.94 (s, 2H, Ar-H), 6.95 (s, 2H, Ar-
CHMe2), 4.17 (s, 2H, ArCH2Ar), 7.04 (s, 2H, Ar-H), 7.15–7.18 H), 8.42 (s, 2H, NvCH), 14.35 (b, 2H, OH). 13C NMR (CDCl3,
(m, 8H, Ar-H), 8.27 (s, 2H, NvCH), 13.15 (b, 2H, OH). 13C 75 MHz): δ 20.61, 28.22, 29.78, 56.90, 118.09, 126.77, 128.50,
NMR (CDCl3, 75 MHz): δ 20.60, 23.73, 28.24, 28.61, 118.05, 129.53, 133.87, 157.94, 159.88. Anal. calcd for C25H34N2O2:
123.37, 125.43, 127.92, 128.41, 130.57, 135.31, 138.96, 146.63, C, 76.10; H, 8.69; N, 7.10%. Found: C, 76.24; H, 8.48; N, 6.98%.
157.32, 166.94. Anal. calcd for C41H50N2O2: C, 81.69; H, 8.36;
Synthesis of [2-(OAlMe2)-3-{CHvN(2,6-Pri2C6H3)}-
5-MeC6H2]2CH2 (15)
N, 4.65%. Found: C, 81.41; H, 8.19; N, 4.75%.
Synthesis of [2-OH-3-{CHvN(p-MeC6H4)}-5-MeC6H2]2CH2 (11)
The same procedure as for that of 6 was used, but compound
A
mixture of 2,2′-methylene bis(4-methyl-6-formylphenol) 10 was employed instead of 1. Thus, reaction of 10 (0.50 g,
(1.50 g, 5.28 mmol), p-toluidine (1.14 g, 10.64 mmol) and 0.83 mmol) with AlMe3 (1.30 cm3, 2.60 mmol) in toluene gen-
ethanol (50 cm3) was refluxed for 12 h. The mixture was fil- erated, after similar workup, yellow crystals of 15 (0.32 g, 54%),
tered to afford a yellow powder of 11 (1.9 g, 78%), mp mp 260–262 °C. 1H NMR (C6D6, 300 MHz): δ −0.23 (s, 12H,
1
212–214 °C. H NMR (CDCl3, 300 MHz): δ 2.28 (s, 6H, ArMe), AlMe), 0.86 (d, J = 6 Hz, 12H, CHMe2), 1.27 (d, J = 6 Hz, 12H,
2.38 (s, 6H, ArMe), 4.12 (s, 2H, ArCH2Ar), 7.06 (s, 2H, Ar-H), CHMe2), 2.21 (s, 6H, MeAr), 3.15 (m, 4H, CHMe2), 4.37 (s, 2H,
3866 | Dalton Trans., 2013, 42, 3860–3868
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ArCH2Ar), 6.50 (s, 2H, Ar-H), 7.08–7.14 (m, 6H, Ar-H), 7.76 (s, Synthesis of [2-(OAlMe2)-3-(CHvNCMe3)-5-MeC6H2]2CH2 (19)
2H, NvCH), 7.81 (s, 2H, Ar). 13C NMR (C6D6, 75 MHz): δ
AlMe3 (0.90 cm3, 2.0 M solution in toluene, 1.80 mmol) was
−8.61, 20.34, 22.67, 25.97, 28.45, 30.77, 119.13, 124.46, 126.74,
added to a stirred solution of 14 (0.30 g, 0.76 mmol) in toluene
128.43, 132.79, 133.22, 141.66, 142.61, 142.87, 162.24, 173.74.
(20 cm3) at about −80 °C. The mixture was warmed to room
temperature and stirred for 12 h. The solvent was removed
Anal. calcd for C45H60Al2N2O2: C, 75.60; H, 8.46; N, 3.92%.
Found: C, 75.48; H, 8.56; N, 3.89%.
from the mixture under vacuum. The residue was dissolved in
diethyl ether (20 cm3) and filtered. The filtrate was concen-
Synthesis of [2-(OAlMe2)-3-{CHvN(p-MeC6H4)}-
5-MeC6H2]2CH2 (16)
trated and cooled to about −80 °C to afford colorless crystals
of 19 (0.19 g, 49%), mp 185–187 °C. 1H NMR (C6D6, 300 MHz):
δ −0.19 (s, 12H, AlMe), 1.00 (s, 18H, CMe3), 2.22 (s, 6H, ArMe),
4.27 (s, 2H, ArCH2Ar), 6.36 (s, 2H, Ar-H), 7.59 (s, 2H, NvCH),
7.70 (s, 2H, Ar-H). 13C NMR (C6D6, 75 MHz): δ −5.93, 20.40,
29.79, 30.58, 59.26, 118.43, 125.74, 132.77, 132.85, 140.27,
160.83, 168.42. Anal. calcd for C29H44Al2N2O2: C, 68.75;
H, 8.75; N, 5.53%. Found: C, 68.54; H, 9.05; N, 5.77%.
AlMe3 (1.00 cm3, 2.0 M solution in toluene, 2.00 mmol) was
added to a stirred solution of 11 (0.30 g, 0.65 mmol) in toluene
(20 cm3) at about −80 °C. The mixture was warmed to room
temperature and stirred for 12 h. The solvent was removed
under vacuum. The residue was washed with n-hexane
(30 cm3) and then dissolved in toluene (5 cm3). n-Hexane
(30 cm3) was added to the solution to give light yellow crystals
of 16 (0.18 g, 48%), mp 180–182 °C. 1H NMR (C6D6, 300 MHz):
δ −0.10 (s, 12H, AlMe), 2.00 (s, 6H, ArMe), 2.21 (s, 6H, ArMe),
4.33 (s, 2H, ArCH2Ar), 6.30 (s, 2H, Ar-H), 6.81 (d, J = 6 Hz, 4H,
Ar-H), 6.92 (d, J = 6 Hz, 4H, Ar-H, 7.42 (s, 2H, Ar-H), 7.77(s, 2H,
NvCH). 13C NMR (C6D6, 75 MHz): δ −8.33, 20.35, 20.82, 30.76,
118.89, 122.29, 126.29, 130.42, 133.24, 136.60, 137.60, 141.23,
144.93, 161.88, 169.61. Anal. calcd for C35H40Al2N2O2: C, 73.15;
H, 7.02; N, 4.87%. Found: C, 73.39; H, 7.13; N, 4.62%.
X-ray crystallography
Single crystals of complexes 6 and 16 were respectively
mounted in Lindemann capillaries under nitrogen. Diffraction
data were collected at 298(2) K on a Bruker Smart CCD area-
detector with graphite-monochromated Mo Kα radiation (λ =
0.71073 Å). The structures were solved by direct methods using
SHELXS-9717 and refined against F2 by full-matrix least-
squares using SHELXL-97.18 Hydrogen atoms were placed in
calculated positions. Crystal data and experimental details of
the structure determinations are listed in Table 3.
Synthesis of [2-(OAlMe2)-3-{CHvN(p-ClC6H4)}-5-MeC6H2]2CH2
(17)
Polymerization of rac-LA
Complex 17 was synthesized using the same procedure as for
that of 6, but compound 12 was employed instead of 1. Thus,
treatment of 12 (0.30 g, 0.60 mmol) with AlMe3 (0.90 cm3,
1.80 mmol) produced, after similar workup, yellow crystals of
A typical polymerization procedure is exemplified by the syn-
thesis of PLA using complex 6 as a catalyst in the presence of
1
17 (0.20 g, 54%), mp 187–189 °C. H NMR (C6D6, 300 MHz): δ
Table 3 Details of the X-ray structure determinations of complexes 6 and 16
−0.22 (s, 12H, AlMe), 2.21 (s, 6H, ArMe), 4.25 (s, 2H, ArCH2Ar),
6.33 (s, 2H, Ar-H), 6.65 (d, J = 9 Hz, 4H, Ar-H), 6.93 (d, J = 9 Hz,
4H, Ar-H), 7.23 (s, 2H, Ar-H), 7.70 (s, 2H, NvCH). 13C NMR
(C6D6, 75 MHz): δ −8.47, 20.34, 30.87, 118.72, 123.74, 126.51,
129.97, 132.98, 133.35, 133.65, 141.70, 145.57, 162.14, 170.66.
Anal. calcd for C33H24Al2N2O2: C, 64.39; H, 5.57; N, 4.55%.
Found: C, 64.61; H, 5.58; N, 4.44%.
6
16·0.5C6H5Me
Empirical formula
Fw
C25H40Al2N2O2
454.55
C38.5H44Al2N2O2
620.72
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Monoclinic
P21/c
16.1331(15)
9.5710(8)
22.699(2)
90
128.290(2)
90.00
2751.0(4)
4
Triclinic
P1
ˉ
9.1161(8)
13.6920(11)
15.7135(13)
104.683(2)
91.7960(10)
103.913(2)
1832.7(3)
2
α (°)
β (°)
γ (°)
Synthesis of [2-(OAlMe2)-3-[CHvN(p-MeOC6H4)]-
5-MeC6H2]2CH2 (18)
V (Å3)
Z
Complex 18 was synthesized employing the same procedure as
for that of 6, but compound 13 was used instead of 1. Thus,
treatment of 13 (0.50 g, 1.01 mmol) with AlMe3 (1.50 cm3,
3.00 mmol) afforded, after similar workup, yellow crystals of
Dcalcd (g cm−3
F (000)
)
1.098
984
0.127
1.125
662
0.113
μ (mm−1
)
θ range for data collecn (°)
No. of reflns collected
2.29 to 25.02
13 616
2.34 to25.02
9701
1
18 (0.30 g, 49%), mp 220–222 °C. H NMR (C6D6, 300 MHz): δ
No. of indep reflns (Rint
)
4850(0.0678)
4850/0/290
1.029
R1 = 0.0673,
wR2 = 0.1509
R1 = 0.1572,
wR2 = 0.1751
0.607 and −0.392
6382(0.0471)
6382/0/441
1.012
R1 = 0.0597,
wR2 = 0.0911
R1 = 0.1700,
wR2 = 0.1049
0.179 and −0.140
−0.21 (s, 12H, AlMe), 2.21 (s, 6H, ArMe), 3.23 (s, 6H, OMe), 4.37
(s, 2H, ArCH2Ar), 6.36 (s, 2H, Ar-H), 6.59 (d, J = 6 Hz, 4H, Ar-H),
6.90 (d, J = 6 Hz, 4H, Ar-H), 7.40 (s, 2H, Ar-H), 7.77(s, 2H,
NvCH). 13C NMR (C6D6, 75 MHz): δ −8.62, 20.39, 31.35, 55.68,
115.54, 119.68, 123.51, 124.50, 127.43, 127.74, 127.84, 133.14,
140.33, 141.04, 168.87. Anal. calcd for C35H40Al2N2O4: C, 69.29;
H, 6.65; N, 4.62%. Found: C, 69.40; H, 6.85; N, 4.43%.
No. of data/restraints/params
Goodness of fit on F2
Final R indices [I > 2σ(I)]
R indices (all data)
Largest diff peak and hole
[e Å−3
]
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Dalton Transactions
two equiv. of benzyl alcohol. To a Schlenk tube was charged
with rac-LA (0.495 g, 3.43 mmol), BnOH (0.69 cm3, 0.1 M solu-
tion in toluene, 0.069 mmol) and toluene (4.2 cm3). The
mixture was heated to 70 °C. To the stirred mixture a solution
of complex 6 in toluene (2.0 cm3, 0.01715 M, 0.0343 mmol)
was added via a syringe. After the solution was stirred at 70 °C
for 21 h, the polymerization reaction was terminated by
addition of several drops of glacial acetic acid. After stirring
for 0.5 h at room temperature, the resulting solution was
dropped into n-hexane to give a white precipitate. The precipi-
tate was collected by filtration, and dried under vacuum to give
a white solid.
For the GPC analysis, the sample was dissolved in dichloro-
methane, passed through a short neutral aluminum oxide
column, precipitated in methanol and dried under vacuum.
For the kinetic studies, samples were taken from the reac-
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Acknowledgements
We thank the National Natural Science Foundation of China
(Grant no. 20972146) and the Foundation for Talents of Anhui
Province (Grant no. 2008Z011) for financial support. We also
thank Professor D.-Q. Wang for the crystal structure determi-
nations and Professor S.-Y. Liu for the GPC analyses.
9 S. Dagorne, L. Lavanant, R. Welter, C. Chassenieux,
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3868 | Dalton Trans., 2013, 42, 3860–3868
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