Methylaluminium 8-quinolinolates: Synthesis, characterization and use in ring-opening polymerization (ROP) of ε-caprolactone

Article abstract of DOI:10.1039/c0dt01207f

The stoichiometric reactions of 2-(2,6-R-phenylimino)quinolin-8-ol (L1-L5, L1: R = Me, L2: R = Et, L3: R = ⁱPr, L4: R = Cl, L5: R = F) with Me₃Al afforded the dimeric aluminium complexes [Me ₂AlL]₂ (1-5) in good yields. By contrast, stoichiometric reactions of 2-(1-(2,6-R-phenylimino)propyl) quinolin-8-ol (L6-L10, L6: R = Me, L7: R = Et, L8: R = ⁱPr, L9: R = Cl, L10: R = F)) with Me ₃Al gave the mononuclear aluminium complexes Me₂AlL (6-10) accompanied with by-products of the form Me₂AlL·Me ₃Al (11-15). All methylaluminium complexes were characterized by NMR spectroscopy, elemental analysis, and the molecular structures of complexes 3, 6 and 8 were determined by single-crystal X-ray diffraction. Aluminium compounds 1-5 possessed negligible activity towards the ring-opening polymerization of ε-caprolactone either in the presence or absence of BnOH. In contrast, in the presence of BnOH, the mononuclear aluminium compounds 6-10 could efficiently initiate the ring-opening polymerization of ε-caprolactone; the polymerization proceeded in a living manner.

Full text of DOI:10.1039/c0dt01207f

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PAPER
Methylaluminium 8-quinolinolates: synthesis, characterization and use in
ring-opening polymerization (ROP) of e-caprolactone†
Wen-Hua Sun,*a Miao Shen,a Wenjuan Zhang,a Wei Huang,a Shaofeng Liua and Carl Redshaw*b
Received 10th September 2010, Accepted 23rd December 2010
DOI: 10.1039/c0dt01207f
The stoichiometric reactions of 2-(2,6-R-phenylimino)quinolin-8-ol (L1–L5, L1: R = Me, L2: R = Et,
i
L3: R = Pr, L4: R = Cl, L5: R = F) with Me3Al afforded the dimeric aluminium complexes [Me2AlL]2
(1–5) in good yields. By contrast, stoichiometric reactions of 2-(1-(2,6-R-phenylimino)propyl)
i
quinolin-8-ol (L6–L10, L6: R = Me, L7: R = Et, L8: R = Pr, L9: R = Cl, L10: R = F)) with Me3Al gave
the mononuclear aluminium complexes Me2AlL (6–10) accompanied with by-products of the form
Me2AlL·Me3Al (11–15). All methylaluminium complexes were characterized by NMR spectroscopy,
elemental analysis, and the molecular structures of complexes 3, 6 and 8 were determined by
single-crystal X-ray diffraction. Aluminium compounds 1–5 possessed negligible activity towards the
ring-opening polymerization of e-caprolactone either in the presence or absence of BnOH. In contrast,
in the presence of BnOH, the mononuclear aluminium compounds 6–10 could efficiently initiate the
ring-opening polymerization of e-caprolactone; the polymerization proceeded in a living manner.
disfavor the initiation of the ROP of e-CL.9–11 With this in mind,
1. Introduction
we have embarked upon a programme to explore the scope of
Recent environmental concerns call for developing environmen-
aluminium compounds bearing ligands derived from bulky 2-
tally friendly materials.1 Poly(e-caprolactone) (PCL) is considered
a topical material due to its practical biocompatibility, allowing
for its potential applications in the medical, pharmaceutical and
tissue engineering arenas.2 Ring-opening polymerization (ROP)
of e-caprolactone (CL) catalyzed by metal complexes permits
excellent controllability over the molecular weight and distribution
of the resultant polymer.2 Thus far, a wide range of metal
(arylimino)quinolin-8-ols (L). The steric hindrance associated
with the 2-(arylimino) quinolin-8-ols (L) can be controlled through
judicious choice of arylimino groups and can thus be used to
prevent the formation of AlL3 type complexes, instead favoring
mononuclear Me2AlL or dimeric [Me2AlL]2 complexes. The new
mononuclear compounds Me2AlL are highly active for the ROP
of e-CL acting in a living fashion in the presence of BnOH.
catalysts or initiators have been developed by combination of
Herein, the synthesis and characterization of the title aluminium
various ligands with a range of metals, which include magnesium,
compounds bearing 2-(arylimino)quinolin-8-olates are reported
calcium, aluminium, titanium, iron, zinc, tin, and rare earth
metals.1–5 Among the reported catalysts, aluminium complexes are
promising candidates for industrial application due to their high
activity and low toxicity.3 Although aluminium complexes bearing
in detail, as well as the catalytic behavior of the mononuclear
aluminium compounds 6–10 in the ROP of e-CL.
8-quinolinolato(Q) derivatives are well known as the emissive and
electron transporting material in organic light-emitting devices
2. Results and discussion
(OLEDs),6–8 the catalytic behavior of such species is rather limited.
This is primarily because the reaction of 8-quinolinolato(Q)
derivatives with R3Al usually affords either AlQ3-type complexes
or dimeric aluminium complexes [Al(R)2Q]2, both of which
2.1 Synthesis and characterization of aluminium compounds 1–10
The ligands (L1–L5) were prepared by the condensation reaction
of 8-hydroxyquinoline-2-carbaldehyde with the corresponding
substituted anilines (Scheme 1).12 All organic compounds L1–L5
were isolated as yellow powders by column chromatography, and
fully characterized by IR, 1H NMR, 13C NMR spectroscopy and
elemental analysis.
The dimeric aluminium compounds 1–5 were synthesized in
good yields by the stoichiometric reaction of Me3Al with the
corresponding ligands L1–L5 in n-heptane (Scheme 1) according
to the previous procedure.9–11 Resultant aluminium compounds
were precipitated from the reaction solutions as yellow powders.
After being filtered and washed twice with n-heptane, they were
aKey Laboratory of Engineering Plastics and Beijing National Laboratory for
Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences,
Beijing, 100190, China. E-mail: whsun@iccas.ac.cn; Fax: +86 10 62618239;
Tel: +86 10 62557955
bSchool of Chemistry, University of East Anglia, Norwich, UK NR4 7TJ.
E-mail: carl.redshaw@uea.ac.uk; Fax: +44 (0)1603 592003; Tel: +44
(0)1603 593137
† Electronic supplementary information (ESI) available. CCDC reference
numbers 783402–783405. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c0dt01207f
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atoms. The two methyl groups bonded to the same Al center
are on the opposite side from the lozenge plane. The Al(1)–O(1)
and Al(1a)–O(1) bond lengths are approximately the same as
those of Al(1a)–O(1a) and Al(1)–O(1a), respectively. The O(1)–
Al(1)–O(1a), O(1)–Al(1a)–O(1a), Al(1)–O(1a)–Al(1a) and Al(1)–
O(1)–Al(1a) bond angles are 72.99(15), 73.80(13), 105.97(17) and
107.19(18)◦, respectively. The non-ligating imino nitrogen atoms
[N(2), N(2a)] adopt an anti geometry with respect to the quinoline
nitrogen atoms [N(1), N(1a)], placing it in a distal relationship
to the aluminium centre. The coordination geometry and bond
lengths around the Al centers are similar to the reported dimeric
compound [Et2Al(quinolin-8-olate)]2.9 The Al–O distances for
Al(1)–O(1), Al(1a)–O(1a), Al(1a)–O(1) and Al(1)–O(1a) [1.882(3),
˚
1.890(3), 2.001(3) and 2.029(3) A] are very close to those in
previously reported structure [Et2Al(quinolin-8-olate)]2 [1.882(3),
9
˚
1.868(3), 2.003(4) and 2.009(4) A, respectively]. The Al–N bond
˚
distances [Al(1)–N(1) 2.181(3) and Al(1a)–N(1a) 2.208(4) A] in
Scheme 1 Synthesis of ligands L1–L5 and dimeric aluminium com-
pounds 1–5.
3, however, are somewhat longer than those in the analogue
[Et2Al(quinolin-8-olate)]2 [2.132(5) A], due to the steric repulsion
˚
confirmed to be the expected complexes by 1H NMR spectra
and elemental analysis. Comparison of the 1H NMR spectra
with those of the corresponding ligand L1–L5, showed additional
resonances in the high field region (-0.60 to -0.40 ppm), which are
attributed to the methyl groups attached to the aluminium centers,
while the O–H signals (broad single peak around 8.17 ppm) of
the free ligands had, as expected, disappeared. These aluminium
compounds 1–5 are insoluble inn-heptane and only slightly soluble
in toluene, THF, CH2Cl2 and CHCl3.
The molecular structure of aluminium compound 3 was de-
termined by single-crystal X-ray crystallography. The ORTEP
diagram is shown in Fig. 1; selected bond lengths and angles
are given in the caption. Compound 3 has a dimeric structure
with a lozenge plane occupying Al(1), Al(1a), O(1), and O(1a)
of the arylimino groups.
The ligands (L6–L10) were prepared in moderate (acceptable)
yields by the condensation reaction of 1-(8-hydroxyquinolin-2-
yl)propan-1-one with the corresponding anilines. The stoichio-
metric reactions of L6–L10 (for which an ethyl group has been
introduced at the imino-carbon) with Me3Al in toluene gave
the mononuclear compounds Me2AlL (6–10) as major products
(yields > 90%) and minor by-products Me2AlL·AlMe3 (11–15),
the structures of which were confirmed by 1H NMR spectroscopy
(Scheme 2). The steric hindrance enhanced the bonding between
the metal center with the nearby N-atom and reduced further pos-
sible aggregation, as reported within alkylaluminium bis(2-methyl-
8-quinolinolate)9 and scandium complexes.13 In these reactions,
the formation of binuclear compounds 11–15 seems unavoidable,
and they are obtained as yellow powders precipitated from chilled
toluene solutions. Compounds 11–15 were insoluble in saturated
hydrocarbons and only slightly soluble in toluene, THF, CH2Cl2
and CHCl3. Using saturated hydrocarbons as reaction solvents can
increase the yield of the binuclear compounds. Analytically pure
samples of 6–10 were collected from the concentrated toluene–n-
hexane solutions containing the Al complexes cooled in a freezer
◦
1
(-30 C). Comparing their H NMR spectra, there is no signal
Fig.
1 ORTEP drawing of 3 with thermal ellipsoids drawn at
the 30% probability level. Hydrogen atoms are omitted for clarity.
Selected bond lengths (A) and angles (◦): Al(1)–O(1) 1.882(3),
˚
Al(1)–C(32) 1.963(5), Al(1)–C(31) 1.989(6), Al(1)–O(1A) 2.029(3),
Al(1)–N(1) 2.181(3), Al(1A)–O(1A) 1.890(3), Al(1A)–C(31A) 1.975(6),
Al(1A)–O(1) 2.001(3), Al(1A)–C(32A) 2.065(5), Al(1A)–N(1A)
2.208(4), O(1)–Al(1)–O(1A) 72.99(15), C(31)–Al(1)–O(1A) 96.7(2),
C(32)–Al(1)–O(1A) 96.3(2), O(1)–Al(1)–N(1) 79.13(16), C(31)–Al(1)–
N(1) 95.9(2), C(32)–Al(1)–N(1) 96.3(2), O(1A)–Al(1)–N(1) 152.12(16),
O(1)–Al(1)–C(31) 117.2(3), O(1)–Al(1)–C(32) 116.9(2), C(31)–Al(1)–
C(32) 125.8(3), C(1A)–O(1A)–Al(1A) 121.5(3), C(1A)–O(1A)–Al(1)
132.3(3), Al(1A)–O(1A)–Al(1) 105.97(17), O(1A)–Al(1A)–O(1) 73.80(13),
C(31A)–Al(1A)–C(32A) 125.5(2), O(1)–Al(1A)–C(32A) 97.96(18),
O(1A)–Al(1A)–N(1A) 78.77(14), C(31A)–Al(1A)–N(1A) 96.09(19),
O(1)–Al(1A)–N(1A) 152.57(14), C(32A)–Al(1A)–N(1A) 93.85(18).
Scheme 2 Synthesis of ligands L6–L10 and aluminium compounds 6–15.
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attributable to the proton of O–H in the ligands, whilst at high field
one or two sets of signals for the groups (CH3)2Al and (CH3)3Al
occur in the range d -0.49 to -0.70 ppm.
Single crystals of compounds 6 and 8 were obtained from
toluene/n-heptane solutions at -30 ◦C. Their molecular structures
were determined by single-crystal X-ray diffraction. The molecular
structure of 6 is shown in Fig. 2, with selected bond lengths
and angles given in the caption. The geometry around the Al
metal center can be described as a distorted trigonal pyramid.
The quinoline nitrogen atom and the two methyl carbon atoms
form an equatorial plane. The deviation of the aluminium
˚
atom from the equatorial plane is 0.158 A. The phenyl ring is
almost perpendicularly oriented (85.9◦) to the coordination plane
containing the ligand backbone and the aluminium atom. The
Fig.
3
ORTEP drawing of
8
with thermal ellipsoids drawn at
4–9
˚
˚
Al–C bond distances in 6 [1.971(5) A, 1.975(5) A] are typical,
the 30% probability level. Hydrogen atoms◦ are omitted for clar-
˚
˚
ity. Selected bond lengths (A) and angles ( ): Al(1)–O(1) 1.881(2),
while the Al(1)–O(1) bond length at 1.891(3) A is characteristic
Al(1)–C(31) 1.955(3), Al(1)–C(32) 1.981(3), Al(1)–N(1) 1.991(3),
N(2)–C(10) 1.287(4), O(1)–Al(1)–N(1) 82.54(11), O(1)–Al(1)–C(31)
100.55(14), O(1)–Al(1)–C(32) 103.15(13), C(31)–Al(1)–C(32) 122.68(16),
C(31)–Al(1)–N(1) 132.69(14), C(32)–Al(1)–N(1) 101.80(14), N(2)–C(10)–
C(8) 114.4(3).
for an oxygen atom of a s–bond, which is a little longer than
that found in C7 (1.777(2) A). The Al(1)–N(1) (nitrogen of
14a
˚
˚
quinoline) bond length is 2.010(4) A, which is longer than that
found in C7 (1.987(2)).14a It is noted that the Al(1)–N(2)(imino)
˚
bond length (2.389(4) A) is substantially longer than typical Al–N
14
˚
coordination bond distances (about 2.0 A), which indicates the
weak interaction between the Al and imino nitrogen atom in 6.
for this nitrogen and the quinoline nitrogen to adopt an anti-
form relationship in 3, it is believed that a weak interaction is
present. Similar to that of 6, the phenyl ring of the imino group is
oriented orthogonally (88.6◦) to the coordination rings. The Al–C
4–9
˚
˚
bond distances in 8 [1.995(3) A, 1.981(3) A] are also typical,
˚
while the Al(1)–O(1) bond length at 1.881(2) A is characteristic
for an oxygen atom of a s–bond, and the Al(1)–N(1) bond length
˚
is 1.991(3) A, characteristic of a quinoline nitrogen atom with
donating coordination.15
1
The H NMR resonances of 11–15 corresponding to protons
of Al–Me were observed as a combination of AlMe3 (s, ca.
-0.6 ppm, 9H) and product L–AlMe2 (s, -0.7 ppm, 6H) that was
identified by the integration ratios. Combined with the elemental
analyses and previous reports,16 the structure could be identified
as Me2AlL·Me3Al with two Al atoms bridged by O atom. The
molecular structure of 12 was also confirmed by single crystal
X-ray diffraction,17 but the R value is high due to poor crystal
quality.
As the results showed above, the stoichiometric reactions
of analogues’ (L1–L10) with Me3Al resulted in different types
of mononuclear or dimeric methylaluminium compounds. The
sterically bulky ethyl group present in the organic ligands L6–L10
caused congestion and led to the arylimino nitrogen adopting a
syn-geometry with the quinoline. Meanwhile, the strong interac-
tion between the imino group and the aluminium center results in
the formation of mononuclear compounds (6–10). The monomeric
aluminium compounds 6–10 exhibited high catalytic activity in the
ROP of e-CL.
Fig. 2 ORTEP drawing of 6 with thermal ellipsoids drawn at the
30% probability level. Hydrogen atoms are omitted for clarity. Selected
◦
˚
bond lengths (A) and angles ( ): Al(1)–O(1) 1.891(3), Al(1)–C(32)
1.971(5), Al(1)–C(31) 1.975(5), Al(1)–N(1) 2.010(4), Al(1)–N(2) 2.389(4),
N(2)–C(10) 1.282(5), O(1)–Al(1)–C(32) 99.10(17), O(1)–Al(1)–C(31)
103.54(18), C(32)–Al(1)–C(31) 119.2(2), O(1)–Al(1)–N(1) 81.46(14),
C(32)–Al(1)–N(1) 129.06(18), C(31)–Al(1)–N(1) 109.87(18), O(1)–Al(1)–
N(2) 150.45(14), C(32)–Al(1)–N(2) 92.75(16), C(31)–Al(1)–N(2)
93.90(17), N(1)–Al(1)–N(2) 70.15(13), N(2)–C(10)–C(8) 114.2(4).
The molecular structure of 8 is illustrated in Fig. 3, together
with selected bond lengths and angles. The molecular structure of
8 shows the O(1)-quinoline–C(10)–N(2) portion of the ligand to be
˚
coplanar to within 0.03 A, a geometry very similar to 6. Here, the
2.2 Ring-opening polymerization (ROP) of e-CL by aluminium
compounds 6–10
˚
aluminium atom lies 0.37 A out of the plane and adopts a severely
distorted tetrahedral geometry with angles at aluminium ranging
between 82.54(1) and 132.69(14)◦. The imino nitrogen N(2) points
into the flattened ‘basal’ face of the tetrahedron; the aluminium
Ring-opening polymerizations (ROP) of e-caprolactone (CL)
using 1–10 were conducted both in the presence and absence of
BnOH. The aluminium compounds 1–5 exhibited very low activity
in the ROP of e-CL, and are therefore not discussed further.
For the catalytic systems of the aluminium compounds 6–10, the
˚
atom lies only 0.189 A out of the N(1)–C(31)–C(32) plane, but lies
˚
between 0.658 and 0.994 A out of the other tetrahedral faces. The
˚
distance of N(2)–Al(1) is long at 2.458 A, but given the potential
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Table 1 The ROP of e-CL by 6–10/BnOHa
T/◦C
t/min
mg/yield (%)
Mn ¥ 10-4
Mw/Mn
Mn ¥ 10-4
b
b
cal.
Entry
Cat.
CL : Al : BuOH
1
2
3
4
5
6
7
8
6
7
8
9
10
8
8
8
8
8
8
8
8
8
8
8
250 : 1 : 1
250 : 1 : 1
250 : 1 : 1
250 : 1 : 1
250 : 1 : 1
250 : 1 : 1
250 : 1 : 1
250 : 1 : 1
250 : 1 : 1
250 : 1 : 1
125 : 1 : 1
500 : 1 : 1
750 : 1 : 1
1000 : 1 : 1
250 : 1 : 1
250 : 1 : 1
90
90
90
90
90
60
90
90
90
90
90
90
90
90
40
20
30
30
30
30
30
60
10
20
40
50
30
30
30
30
360
720
503 (87.6)
515 (89.7)
483(84.1)
530 (92.3)
537(93.6)
528 (92.0)
266(46.4)
399(69.5)
523(91.1)
545(94.9)
236 (82.3)
978 (85.2)
1482 (86.1)
1975 (86.0)
464(80.8)
536(93.4)
2.98
3.02
2.77
3.60
3.52
3.05
1.29
2.19
3.10
3.24
1.45
4.93
7.59
10.03
2.98
3.24
1.21
1.26
1.13
1.46
1.36
1.15
1.07
1.08
1.20
1.34
1.14
1.19
1.29
1.32
1.21
1.31
2.51
2.57
2.41
2.64
2.68
2.64
1.33
1.99
2.61
2.71
1.43
4.87
7.38
9.92
2.32
2.67
9
10
11
12
13
14
15
16
a Conditions: 20 mmol Al, 1.0 M e-CL toluene solution. b GPC data in THF vs. polystyrene standards, using a correcting factor 0.56.18
polymerization did not take place without adding BnOH. In the
presence of BnOH, the aluminium compounds 6–10 can efficiently
initiate the ROP of e-CL, suggesting the formation of Al–alkoxide
species, which can act as the initiator via a coordination insertion
Table 1]. The results strongly suggest that a certain degree of
transesterification accompanied the propagation in the ROP of
e-CL. The degree of the transesterification seemed to increase in
the order with 8 < 7 < 6 < 9, 10 consistent with a decrease in the
bulk of the ortho-substituent in the imino groups. It is assumed
that the bulkier substituent would be required to prohibit the
transesterification process from accompanying the propagation
in the ROP, probably via a protection effect acting on the active
propagating species.14a
In addition, the Mn values of the polymers obtained increased
linearly along with the molar ratios of CL/Al (Fig. 5), see runs
3, 11–14 in Table 1. Moreover, shown within entries 3, 7–10 in
Table 1, the polymerization rate of the ROPs was first-order-
dependent upon the monomer concentration (Fig. 6), suggesting
no deactivation of active species during the ROP of CL. Taking
all results into account, it is clear that the ROP herein proceeds in
a living manner.
1
mechanism,14–16 which is also in agreement with the H NMR of
resultant polymer. The high yields are observed within 30 min,
results for which are summarized in Table 1.
All the PCLs obtained possessed a narrow distribution
[Mw/Mn = 1.07–1.46] with unimodal characteristics (Table 1,
entries 1–5), indicating single-site catalysis. Compound 8 was used
to investigate the influence of the reaction parameters on the ROP
in detail.
According to entries 3, 7–10 in Table 1, the linear relationship
between the monomer conversions and Mn values, was observed
with narrow molecular weight distributions [1.07–1.34], indicating
the classical feature of a living polymerization process (Fig. 4).
The molecular weight distributions (Mw/Mn values) of the resul-
tant polymers became a little broader with increased monomer
conversions [e.g., PDI: 1.07 (conversion 46.4%), 1.08 (conversion
69.5%), 1.21 (conversion 91.1%), and 1.34 (conversion 94.9%) in
Fig. 5 Plots of Mn values vs. CL/Al molar ratio in the ROP of e-CL
initiated by 8/PhCH2OH (entries 3, 11–14, Table 1).
Reflected by the data in Table 1 (entries 3, 6, 15 and 16), the
observed activities decreased upon lowering the polymerization
temperature, and conversely, elevating the reaction temperature
resulted in higher conversion, which was reflected by the ratio of
Fig. 4 Mn and Mw/Mn vs. monomer conversion in the ROP of e-CL
initiated by 8/PhCH2OH (entries 3, 7–10, Table 1).
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4.2 Synthesis and characterization of
2-(1-(phenylimino)methyl)quinoline-8-ols (L1–L5) and
2-(1-(phenylimino)propyl)quinoline-8-ols (L6–L10)
Synthesis of 2-((2,6-dimethylphenylimino)methyl)quinolin-8-ol
(L1). The starting material 8-hydroxyquinoline-2-carbaldehyde
was prepared according to the literature.12 A mixture of
8-hydroxyquinoline-2-carbaldehyde (0.35 g, 2.0 mmol), 2,6-
dimethylaniline (0.24 g, 2.0 mmol) and a few drops of acetic acid
was refluxed in ethanol (20 mL) for 4 h. The reaction mixture was
concentrated, purified by column chromatography on silica gel and
then recrystallized from chilled petrol ether solutions to provide
the desired product L1 (0.42 g, 76% yield) as a yellow powder. 1H
NMR (CDCl3): d 8.47 (s, 1H), 8.42 (d, 1H, J = 8.5 Hz), 8.27 (d,
1H, J = 8.6 Hz), 8.16 (bs, 1H), 7.53 (t, 1H, J = 7.9 Hz), 7.40 (d, 1H,
J = 8.0 Hz), 7.23 (d, 1H, J = 7.7 Hz), 7.11 (d, J = 7.40 Hz, 2H), 7.00
(t, 1H, J = 7.5 Hz), 2.20 (s, 6H). 13C NMR (CDCl3): d 163.3, 152.7,
152.4, 148.6, 137.9, 137.3, 136.9, 129.5, 129.4, 128.3, 127.0, 124.4,
118.9, 118.1, 110.8, 18.5. Mp: 78–80 ◦C. FT-IR (KBr, cm-1): 3424
(m), 3049 (m), 2952 (m), 2919 (m), 1630 (s), 1593 (m), 1567 (m),
1508 (m), 1466 (s), 1435 (m), 1397 (w), 1371 (m), 1321 (m), 1278
(m), 1249 (m), 1228 (m), 1192 (m), 1165 (m), 1087 (m), 1039 (w),
972 (w), 841 (m), 741 (m), 721 (m). Anal. Calcd for C18H16N2O:
C, 78.24; H, 5.84; N, 10.14. Found: C, 78.19; H, 5.77; N, 10.41%.
Fig. 6 Plots of Ln[[CL]/[CL]0] vs. time in the ROP of e-CL initiated by
the catalytic system of 8/PhCH2OH (entries 3, 7–10, Table 1).
Mncal/Mn. At higher reaction temperature, the molecular weights
are closer to the calculated values.
3. Conclusion
A series of ligands 2-(arylimino)quinolin-8-ols (L1–L10) and
aluminium compounds (1–15) were synthesized and characterized
by NMR spectroscopy, and elemental analysis. The molecular
structures of compounds 3, 6 and 8 were confirmed by X-
ray crystallography. The introduction of an imino group at the
8-quinolinolato(Q) prevents the formation of common AlQ3-
type compounds and allows for the isolation of the monomeric
Me2AlL or dimeric [Me2AlL]2 compounds. Dimeric [Me2AlL]2
(1–5) showed negligible activity in the ROP of e-CL, whereas
mononuclear complexes 6–10 exhibit high activity towards the
ROP of e-CL in the presence of BnOH; the polymerization
proceeding in a living manner.
Synthesis of 2-((2,6-diethylphenylimino)methyl)quinolin-8-ol
(L2). The synthesis of L2 was carried out by the same procedure
as that of L1, except that 2,6-diethylaniline was used. Yield: 0.49 g
(81%). 1H NMR (CDCl3): d 8.47 (s, 1H), 8.40 (d, 1H, J = 8.6 Hz),
8.27 (d, 1H, J = 8.7 Hz), 8.17 (br, 1H), 7.53 (t, 1H, J = 7.8 Hz),
7.40 (d, 1H, J = 8.1 Hz), 7.16–7.23 (m, 4H), 2.58–2.53 (m, 4H),
1.17 (t, J = 7.2 Hz, 6H). 13C NMR (CDCl3): d 163.0, 152.8, 152.3,
149.7, 137.9, 137.0, 132.9, 129.5, 129.4, 126.6, 126.2, 124.7, 119.0,
118.1, 110.9, 24.9, 14.8. Mp: 56–58 ◦C. FT-IR (KBr, cm-1): 3409
(m), 3053 (m), 2963 (m), 2930 (m), 2871 (m), 1630 (s), 1590 (m),
1567 (m), 1505 (s), 1469 (s), 1449 (s), 1370 (m), 1327 (m), 1282
(m), 1250 (m), 1234 (m), 1185 (m), 1162 (w), 1084 (m), 1059 (w),
973 (w), 840 (m), 751 (m), 720 (m). Anal. Calcd for C20H20N2O:
C, 78.92; H, 6.62; N, 9.20. Found: C, 79.03; H, 6.48; N, 9.39%.
4. Experimental
4.1 General procedures
All reactions were performed using standard Schlenk techniques
in an atmosphere of high purity nitrogen or glove-box techniques.
Toluene, n-heptane and THF were dried by refluxing over sodium
and benzophenone, distilled under nitrogen and stored over
Synthesis of 2-((2,6-diisopropylphenylimino)methyl)quinolin-8-ol
(L3). The synthesis of L3 was carried out by the same procedure
as that of L1, except that 2,6-diisopropylaniline was used. Yield:
0.58 g (88%). 1H NMR (CDCl3): d 8.45 (s, 1H), 8.42 (d, 1H, J =
8.6 Hz), 8.28 (d, 1H, J = 8.6 Hz), 8.17 (s, 1H), 7.54 (t, 1H, J =
7.9 Hz), 7.40 (d, 1H, J = 8.2 Hz), 7.17–7.24 (m, 4H), 3.00 (sept,
J = 6.8 Hz, 2H), 1.20 (d, J = 6.8 Hz, 12H). 13C NMR (CDCl3): d
162.9, 152.3, 148.6, 137.9, 137.3, 137.0, 129.5, 129.4, 124.8, 123.3,
119.0, 118.1, 110.9, 128.2, 28.2, 23.6. Mp: 126–128 ◦C. FT-IR
(KBr, cm-1): 3341 (m), 3069 (w), 2960 (m), 2870 (m), 1640 (s),
1588 (w), 1567 (m), 1504 (s), 1461 (s), 1433 (m), 1381 (m), 1369
(m), 1328 (m), 1280 (w), 1251 (m), 1222 (m), 1183 (m), 1158 (m),
1085 (w), 1045 (m), 934 (w), 848 (m), 755 (m), 723 (m). Anal.
Calcd for C22H24N2O: C, 79.48; H, 7.28; N, 8.43. Found: C, 79.12;
H, 7.37; N, 8.62%.
˚
activated molecular sieves (4 A) for 24 h in a glovebox prior to
˚
use. C6D6 was dried over activated 4 A molecular sieves. CH2Cl2
and CDCl3 were dried over CaH2 for 48 h, distilled under nitrogen
˚
and stored over activated molecular sieves (4 A) in a glovebox prior
to use. Me3Al was purchased from Aldrich and used as received.
Elemental analyses were performed using a PE2400II Series
1
(Perkin–Elmer Co.). H, 13C NMR spectra were recorded on a
Bruker DMX-400 (400 MHz for 1H, 100 MHz for 13C) instrument.
All spectra were obtained in the solvent indicated at 25 ◦C unless
otherwise noted and chemical shifts are given in ppm and are
1
referenced to SiMe4 (d 0.00, H, 13C). The GPC measurements
were performed on a set of Water-515 HPLC pump, a Waters
2414 refractive index detector, and a combination of Styragel HT-
2, HT-3 and HT-4, the effective molar mass ranges of which are
100–10 000, 500–30 000 and 5000–600 000, respectively. THF was
used as the eluent (flow rate: 1 mL min-1, at 40 ◦C). Molecular
weights and molecular weight distributions were calculated using
polystyrenes as standard.
Synthesis of 2-((2,6-dichlorophenylimino)methyl)quinolin-8-ol
(L4). The synthesis of L4 was carried out by the same procedure
as that of L1, except that 2,6-dichloroaniline was used. Yield:
1
0.29 g (46%). H NMR (CDCl3): d 8.63 (s, 1H), 8.44 (d, 1H,
J = 8.6 Hz), 8.29 (d, 1H, J = 8.6 Hz), 8.16 (s, 1H), 7.55 (t, 1H,
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The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 2645–2653 | 2649
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J = 8.0 Hz), 7.42–7.39 (m, 3H), 7.25–7.23 (m, 1H), 7.05 (t, 1H, J =
8.1 Hz). 13C NMR (CDCl3): d 167.1, 152.8, 151.6, 146.6, 137.9,
137.0, 129.8, 129.7, 128.6, 125.8, 125.7, 119.2, 118.1, 110.9. Mp:
950 (s), 853 (s). 792 (m), 755 (s), 721 (s), 673 (w), 553 (w). Mp:
83–84 ◦C. Anal. Calcd. for C22H24N2O: C, 79.48; H, 7.28; N, 8.43.
Found: C, 79.24; H, 7.47; N, 8.22%.
◦
128–130 C. FT-IR (KBr, cm-1): 3386 (m), 3049 (w), 2917 (w),
Synthesis of 2-(1-(2,6-diisopropylphenylimino)propyl)quinoline-
8-ol (L8). Using the same procedure, 2-(1-(2,6-diisopropylphe-
nylimino)propyl)quinoline-8-ol was obtained as a yellow green
solid in 25% yield. 1H NMR (CDCl3): d 8.47 (d, 1H, J = 8.7 Hz),
8.27 (d, 1H, J = 8.3 Hz), 8.16 (s, 1H), 7.52 (t, 1H, J = 7.8 Hz),
7.41 (d, 1H, J = 8.1 Hz), 7.24 (d, 1H, J = 7.4 Hz), 7.19 (d, 2H, J =
7.8 Hz), 7.03 (d, 1H, J = 7.5 Hz), 2.85–2.81 (m, 2H), 2.77–2.72 (m,
2H), 1.23 (d, 6H, J = 7.6 Hz), 1.15 (d, 6H, J = 7.4 Hz), 1.11 (t, 3H,
J = 7.1 Hz). 13C NMR (CDCl3): d 170.3, 153.3, 152.5, 146.2, 137.1,
136.7, 130.8, 129.0, 128.9, 126.7, 123.0, 120.6, 118.0, 110.4, 28.5,
23.6, 13.7, 11.4. FT-IR (KBr, cm-1): 3436 (m), 3066 (m), 2964 (w),
2930 (m), 2865 (s), 1633 (s), 1567 (m), 1505 (m), 1455 (m), 1432
(s), 1333 (m), 1309 (s), 1237 (s), 1188 (s), 1164 (m), 1089 (m), 1060
(m), 951 (m), 873 (s), 789 (m), 761 (w), 749 (m), 721 (m), 678 (w),
551 (w). Mp: 147–148 ◦C. Anal. Calcd. For C24H28N2O: C, 79.96;
H, 7.83; N, 7.77. Found: C, 79.73; H, 7.67; N, 7.91%.
1640 (s), 1627 (s), 1569 (m), 1558 (m), 1505 (s), 1471 (s), 1432 (s),
1371 (m), 1320 (m), 1285 (m), 1253 (m), 1240 (m), 1195 (m), 1167
(w), 1081 (s), 976 (w), 839 (s), 751 (m), 719 (m). Anal. Calcd for
C16H10Cl2N2O: C, 60.59; H, 3.18; N, 8.83. Found: C, 60.47; H,
3.46; N, 8.58%.
Synthesis of 2-((2,6-difluorophenylimino)methyl)quinolin-8-ol
(L5). The synthesis of L5 was carried out by the same procedure
as that of L1, except that 2,6-difluoroaniline was used. Yield: 0.38 g
(67%). 1H NMR (CDCl3): d 8.89 (s, 1H), 8.40 (d, 1H, J = 8.6 Hz),
8.24 (d, 1H, J = 8.6 Hz), 8.20–8.16 (m, 1H), 7.53 (t, 1H, J = 7.9 Hz),
7.38 (d, 1H, J = 8.2 Hz), 7.24 (t, 1H, J = 7.6 Hz), 7.18–7.14 (m, 1H),
7.01 (t, 2H, J = 7.9 Hz). 13C NMR (CDCl3): d 165.8, 156.7, 154.2,
152.8, 152.2, 137.9, 136.8, 129.6, 128.2, 126.5, 119.1, 118.1, 112.2,
◦
110.8. Mp: 128–130 C. FT-IR (KBr, cm-1): 3435 (s), 3056 (w),
3011 (w), 1621 (s), 1585 (m), 1567 (m), 1508 (s), 1463 (s), 1397 (w),
1373 (m), 1329 (m), 1286 (m), 1237 (m), 1195 (m), 1167 (m), 1087
(m), 1012 (m), 966 (m), 839 (m), 755 (m), 716 (m). Anal. Calcd
for C16H10F2N2O: C, 67.60; H, 3.55; N, 9.85. Found: C, 67.54; H,
3.76; N, 10.03%.
Synthesis of 2-(1-(2,6-dichlorophenylimino)propyl)quinoline-8-
ol (L9). Using the same procedure, 2-(1-(2,6-dichlorophe-
nylimino)propyl)quinoline-8-ol was obtained as a yellow green
solid in 17% yield. 1H NMR (CDCl3): d 8.55 (d, 1H, J = 8.4 Hz),
8.31 (d, 1H, J = 8.6 Hz), 8.15 (s, 1H), 7.56 (t, 1H, J = 7.5 Hz),
7.44 (d, 1H, J = 7.5 Hz), 7.25 (d, 1H, J = 7.4 Hz), 7.06 (d, 2H,
J = 8.0 Hz), 7.02 (t, 1H, J = 7.6 Hz), 2.94–2.89 (m, 2H), 1.18 (t,
3H, J = 7.4 Hz). 13C NMR (CDCl3): d 174.9, 152.7, 152.5, 145.6,
137.2, 136.9, 129.3, 128.4, 124.5, 124.4, 120.8, 118.0, 110.6, 112.4,
24.7, 11.5. FT-IR (KBr, cm-1): 3430 (w), 2973 (m), 1638 (s), 1502
(s), 1466 (m), 1224 (m), 1191 (m), 1084 (s), 1023 (w), 844 (s), 794
(m), 755 (s), 729 (m), 573 (w). Mp: 136–137 ◦C. Anal. Calcd. For
C18H14Cl2N2O: C, 62.62; H, 4.09; N, 8.11. Found: C, 62.18; H,
4.11; N, 7.83%.
Synthesis of 2-(1-(2,6-dimethylphenylimino)propyl)quinoline-8-ol
(L6). A solution of 2,6-dimethylaniline (0.290 g, 2.4 mmol), 1-
(8-hydroxyquinoline-2-yl)propan-1-one (0.374 g, 2 mmol), and
a catalytic amount of p-toluenesulfonic acid (0.1 g) in toluene
was refluxed for 24 h, then the solvent was removed in-vacuo.
The product, 2-(1-(2,6-dimethylphenylimino)propyl), was purified
by column chromatography (silica gel, petroleum ether/ethyl
acetate = 20 : 1), the second part to elute was collected and
concentrated to give a yellow green solid in 50% yield (0.308 g).
1H NMR (CDCl3): d 8.51 (d, 1H, J = 8.6 Hz), 8.26 (d, 1H, J =
8.3 Hz), 8.14 (s, 1H), 7.54 (t, 1H, J = 7.9 Hz), 7.41 (d, 1H, J =
8.2 Hz), 7.24 (d, 1H, J = 7.8 Hz), 7.10 (d, 2H, J = 7.5 Hz), 6.98 (t,
1H, J = 7.5 Hz), 2.83–2.79 (m, 2H), 2.08 (s, 6H), 1.09 (t, 3H, J =
7.4 Hz). 13C NMR (CDCl3): d 170.9, 153.1, 152.4, 148.4, 137.0,
136.7, 129.0, 128.8, 128.0, 125.2, 123.2, 120.3, 118.0, 110.4, 23.1,
18.2, 11.6. FT-IR (KBr, cm-1): 3394 (w), 2962 (m), 1637.5 (m), 1505
(m), 1467 (m), 1258 (s), 1199 (m), 1028 (m), 1012 (s), 860 (m), 792
(s), 755 (m), 720 (m), 584 (m). Mp: 78–79 ◦C. Anal. Calcd. for
C20H20N2O: C, 78.92; H, 6.62; N, 9.20. Found: C, 79.12; H, 6.73;
N, 9.09%.
Synthesis of 2-(1-((2,6-difluorophenyl)imino)propyl)quinolin-8-
ol (L10). Using the same procedure, 2-(1-((2,6-difluorophe-
nyl)imino)propyl)quinolin-8-ol was obtained as a yellow green
solid in 15% yield. 1H NMR (CDCl3): d 8.46 (d, 1H, J = 8.4 Hz),
8.26 (d, 1H, J = 8.6 Hz), 8.11 (s, 1H), 7.53 (t, 1H, J = 7.5 Hz),
7.40 (d, 1H, J = 7.5 Hz), 7.23 (d, 1H, J = 7.4 Hz), 7.07 (d, 2H,
J = 8.0 Hz), 6.99 (t, 1H, J = 7.6 Hz), 2.94–2.89 (m, 2H), 1.18 (t,
3H, J = 7.3 Hz). 13C NMR (CDCl3): d 176.9, 153.7, 152.4, 145.5,
137.7, 136.2, 129.4, 128.1, 124.8, 124.4, 120.8, 118.1, 110.5, 112.7,
24.9, 11.6. FT-IR (KBr, cm-1): 3425 (w), 2965 (m), 1642 (s), 1509
(s), 1464 (m), 1230 (m), 1191 (m), 1085 (s), 1031 (w), 840 (s), 795
(m), 752 (s), 728 (m), 570 (w). Mp: 130–131 ◦C. Anal. Calcd. For
C18H14F2N2O: C, 69.22; H, 4.52; N, 8.97. Found: C, 69.18; H, 4.41;
N, 8.83%.
Synthesis of 2-(1-(2,6-diethylphenylimino)propyl)quinoline-8-
ol (L7). Using the above procedure, but 2,6-diethylaniline
was used instead of 2,6-dimethylaniline, the 2-(1-(2,6-
diethylphenylimino)propyl)quinoline-8-ol was obtained as a yel-
1
low green solid in 24% yield. H NMR (CDCl3): d 8.49 (d, 1H,
4.3 Synthesis of aluminium complexes 1–15
J = 8.6 Hz), 8.26 (d, 1H, J = 8.3 Hz), 8.14 (s, 1H), 7.54 (t, 1H, J =
7.9 Hz), 7.41 (d, 1H, J = 8.2 Hz), 7.22 (d, 1H, J = 7.8 Hz), 7.14
(d, 2H, J = 7.5 Hz), 7.07 (t, 1H, J = 7.5 Hz), 2.82–2.77 (m, 2H),
2.48–2.42 (m, 2H), 2.36–2.32 (m, 2H), 1.20 (t, 6H, J = 7.5 Hz),
1.10 (t, 3H, J = 7.4 Hz). 13C NMR (CDCl3): d 170.5, 153.3, 152.5,
147.5, 137.1, 136.7, 130.9, 129.0, 128.9, 125.9, 123.5, 120.4, 118.0,
110.4, 24.7, 23.4, 13.6, 11.6. FT-IR (KBr, cm-1): 3443 (m), 3066
(w), 2962 (m), 2929 (m), 2869 (m), 1624 (s), 1566 (s), 1504 (s),
1431 (m), 1333 (s), 1309 (m), 1231 (s), 1191 (s), 1162 (s), 1086 (m),
Synthesis of 1. Into
dimethylphenylimino)methyl)quinolin-8-ol
a
stirred solution of 2-((2,6-
(L1) (0.28 g,
1.0 mmol) in toluene (25.0 mL), 1.0 mL (1.0 mmol) AlMe3
solution (1.0 M solution in n-hexane) was added dropwise at
-30 ◦C. The solution was allowed to warm slowly to room
temperature and was stirred overnight. The mixture was filtered
and washed with n-heptane. The yellow solid was dried and
collected. Yield: 0.29 g (86%). 1H NMR (CDCl3): d 8.88 (br, 2H),
2650 | Dalton Trans., 2011, 40, 2645–2653
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8.63–8.59 (m, 2H), 8.45 (d, 2H, J = 8.4 Hz), 7.60 (t, 2H, J =
7.8 Hz), 7.41 (d, 2H, J = 7.8 Hz), 7.15–7.28 (m, 8H), 2.07 (s, 12H),
-0.59 (s, 12H). Calcd for C40H42Al2F4N4O2: C, 72.27; H, 6.37; N,
8.43. Found: C, 72.08; H, 6.28; N, 8.23%.
-0.61 (s, 6H), -0.73 (s, 9H). Anal. Calcd for C25H34Al2N2O: C,
69.42; H, 7.92; N, 6.48. Found: C, 69.29; H, 7.96; N, 6.40%.
Synthesis of 7 and 12. The synthesis of 7 and 12 was carried
out by the same procedure as that of 6 and 11, except that 2-(1-
(2,6-diethylphenylimino)propyl)quinolin-8-ol was used. Data for
7: yield 0.32 g (83%). 1H NMR (CDCl3): d 8.60 (d, 1H, J = 8.5 Hz),
7.98 (d, 1H, J = 8.5 Hz), 7.67 (t, 1H, J = 8.1 Hz), 7.13–7.28 (m,
5H), 2.71–2.68 (m, 2H), 2.57–2.54 (m, 2H), 2.18–2.14 (m, 2H),
1.18–1.27 (m, 9H), -0.82 (s, 6H). 13C NMR (CDCl3): d 168.4,
160.8, 144.1, 143.7, 141.5, 140.6, 133.7, 132.8, 130.2, 125.7, 125.6,
119.8, 113.4, 110.6, 23.9, 23.7, 13.9, 11.5, -9.6. Anal. Calcd for
C24H29AlN2O: C, 74.20; H, 7.52; N, 7.21. Found: C, 74.28; H,
Synthesis of 2. The synthesis of
2 was carried out
by the same procedure as that of 1, except that 2-((2,6-
diethylphenylimino)methyl)quinolin-8-ol (L2) was used. Yield:
1
0.27 g (78%). H NMR (CDCl3): d 8.89 (br, 2H), 8.61–8.59 (m,
2H), 8.44 (d, 2H, J = 8.1 Hz), 7.60 (t, 2H, J = 7.8 Hz), 7.40 (d, 2H,
J = 7.7 Hz), 7.15–7.28 (m, 8H), 2.59–2.51 (m, 8H), 1.17 (t, 12H,
J = 7.2 Hz), -0.59 (s, 12H). Calcd for C44H50Al2N4O2: C, 73.31; H,
6.99; N, 7.77. Found: C, 73.53; H, 6.72; N, 8.08%.
1
7.48; N, 7.44%. Data for 12: 0.028 g (6%). H NMR (CDCl3): d
Synthesis of 3. The synthesis of
3 was carried out
8.72 (d, 1H, J = 8.5 Hz), 8.10 (d, 1H, J = 8.6 Hz), 7.85 (t, 1H, J =
7.9 Hz), 7.77 (d, 1H, J = 8.1 Hz), 7.52 (d, 1H, J = 7.9 Hz), 7.16–
7.28 (m, 3H), 2.72–2.68 (m, 2H), 2.56–2.53 (m, 2H), 2.18–2.15 (m,
2H), 1.18–1.27 (m, 9H), -0.64 (s, 6H), -0.73 (s, 9H). Anal. Calcd
for C27H38Al2N2O: C, 70.41; H, 8.32; N, 6.08. Found: C, 70.75; H,
7.98; N, 6.32%.
by the same procedure as that of 1, except that 2-((2,6-
diisopropylphenylimino)methyl)quinolin-8-ol was used. Yield:
1
0.29 g (75%). H NMR (CDCl3): d 8.90 (br, 2H), 8.64–8.60 (m,
2H), 8.44 (d, 2H, J = 8.3 Hz), 7.60 (t, 2H, J = 7.8 Hz), 7.41 (d,
2H, J = 7.8 Hz), 7.33 (d, 2H, J = 7.5 Hz), 7.15–7.28 (m, 6H),
3.02–2.98 (m, 4H), 1.21 (d, 12H, J = 6.8 Hz), -0.59 (s, 12H). Calcd
for C48H58Al2N4O2: C, 74.20; H, 7.52; N, 7.21. Found: C, 74.53;
H, 7.62; N, 7.09%.
Synthesis of 8 and 13. The synthesis of 8 and 13 was carried
out by the same procedure as that of 6 and 11, except that 2-(1-
(2,6-diisopropylphenylimino)propyl)quinolin-8-ol was used. Data
1
Synthesis of 4. The synthesis of
4 was carried out
for 8: yield 0.31 g (74%). H NMR (CDCl3): d 8.59 (d, 1H, J =
by the same procedure as that of 1, except that 2-((2,6-
8.5 Hz), 7.98 (d, 1H, J = 8.6 Hz), 7.67 (t, 1H, J = 8.1 Hz), 7.13–7.28
(m, 5H), 2.61–2.78 (m, 4H), 1.35 (t, 3H, J = 7.7 Hz), 1.23 (d, 1H,
J = 6.6 Hz), 1.07 (d, 1H, J = 6.8 Hz), -0.78 (s, 6H). 13C NMR
(CDCl3): d 168.7, 160.5, 144.4, 142.6, 141.5, 140.5, 138.6, 133.5,
130.1, 126.0, 124.2, 120.3, 113.5, 111.0, 28.2, 24.9, 24.8, 24.7, 12.3,
-9.2. Anal. Calcd for C26H33AlN2O: C, 74.97; H, 7.99; N, 6.73.
Found: C, 75.12; H, 7.65; N, 6.88%. Data for 13: yield: 0.44 g
(9%). 1H NMR (CDCl3): d 8.71 (d, 1H, J = 8.6 Hz), 8.10 (d, 1H,
J = 8.5 Hz), 7.84 (t, 1H, J = 7.9 Hz), 7.75 (d, 1H, J = 8.1 Hz),
7.52 (d, 1H, J = 8.0 Hz), 7.15–7.28 (m, 3H), 2.61–2.78 (m, 4H),
1.35 (t, 3H, J = 7.7 Hz), 1.23 (d, 1H, J = 6.7 Hz), 1.07 (d, 1H, J =
6.8), -0.59 (s, 6H),-0.72 (s, 9H). Anal. Calcd for C29H42Al2N2O:
C, 71.28; H, 8.66; N, 5.73. Found: C, 71.43; H, 8.91; N, 5.46%.
dichlorophenylimino)methyl)quinolin-8-ol was used. Yield: 0.23 g
1
(66.8%). H NMR (CDCl3): d 8.90 (br, 2H), 8.63–8.58 (m, 2H),
8.44 (d, 2H, J = 8.3 Hz), 7.60 (t, 2H, J = 7.7 Hz), 7.15–7.35 (m,
10H), -0.60 (s, 12H). Calcd for C36H30Al2Cl4N4O22: C, 57.93; H,
4.05; N, 7.51. Found: C, 58.03; H, 4.12; N, 7.92%.
Synthesis of 5. The synthesis of
5 was carried out
by the same procedure as that of 1, except that 2-((2,6-
difluorophenylimino)methyl)quinolin-8-ol was used. Yield: 0.23 g
1
(66.8%). H NMR (CDCl3): d 8.90 (br, 2H), 8.61–8.58 (m, 2H),
8.44 (d, 2H, J = 8.3 Hz), 7.60 (t, 2H, J = 7.8 Hz), 7.41 (d, 2H,
J = 7.8 Hz), 7.33 (d, 2H, J = 7.5 Hz), 7.13–7.28 (m, 6H), -0.53
(s, 12H). Anal. Calcd for C36H30Al2F4N4O2: C, 63.53; H, 4.44; N,
8.23. Found: C, 63.28; H, 4.82; N, 8.49%.
Synthesis of 9 and 14. The synthesis of 9 and 14 was carried out
by the same procedure as that of 6 and 11, except that 2-(1-(2,6-
dichlorophenylimino)propyl)quinolin-8-ol was used. Data for 9:
yield: 0.28 g (70%). 1H NMR (CDCl3): d 8.59 (d, 1H, J = 8.5 Hz),
7.97 (d, 1H, J = 8.5 Hz), 7.67 (t, 1H, J = 8.0 Hz), 7.11–7.24 (m,
Synthesis of 6 and 11. Into a stirred solution of 2-(1-(2,6-
dimethylphenylimino)propyl)quinolin-8-ol (0.30 g, 1.0 mmol) in
toluene (10.0 mL), 1.0 mL (1.0 mmol) AlMe3 solution (1.0 M
solution in n-hexane) was added dropwise at -30 ◦C. The solution
was allowed to warm slowly to room temperature and was stirred
for 3 h. The reaction mixture was filtered and the yellow solid 11
was washed with n-heptane and dried (0.035 g, 8% yield). While
the filtrate was concentrated in vacuo, the chilled-concentrated
toluene–n-hexane solution was placed in the freezer (-30 ◦C) and
afforded the aluminium compound 6 (0.29 g, 81% yield) as red
5H), 2.77–2.75 (m, 2H), 1.28 (t, 3H, J = 7.8 Hz), -0.80 (s, 6H). 13
C
NMR (CDCl3): d 172.1, 161.1, 152.0, 143.3, 141.3, 134.3, 130.4,
129.2, 128.4, 126.7, 125.4, 119.5, 113.5, 112.4, 112.2, 110.6, 24.4,
11.6,-10.1. Anal. Calcd for C20H19AlCl2N2O: C, 59.86; H, 4.77; N,
6.98. Found: C, 60.02; H, 4.49; N, 6.63%. Data for 14: yield 6%.
1H NMR (CDCl3): d 8.43 (d, 1H, J = 8.5 Hz), 8.18 (d, 1H, J =
8.4 Hz), 7.51 (t, 1H, J = 8.0 Hz), 7.44 (d, 1H, J = 8.1 Hz), 7.38
(d, 1H, J = 8.0 Hz), 7.15–7.18 (m, 2H), 6.99 (t, 1H, J = 8.1 Hz),
2.68–2.64 (m, 2H), 1.56 (t, 3H, J = 7.5 Hz), -0.32 (s, 6H),-0.72 (s,
9H). Anal. Calcd for C23H28Al2Cl2N2O: C, 58.36; H, 5.96; N, 5.92.
Found: C, 58.28; H, 6.07; N, 5.67%.
1
crystals. H NMR (CDCl3): d 8.60 (d, 1H, J = 8.5 Hz), 7.98 (d,
1H, J = 8.5 Hz), 7.67 (t, 1H, J = 8.1 Hz), 7.06–7.18 (m, 5H),
2.70–2.67 (m, 2H), 2.06 (s, 6H), 1.25 (t, 3H, J = 7.6 Hz), -0.79 (s,
6H). 13C NMR (CDCl3): d 168.3, 160.8, 144.8, 144.0, 141.5, 133.8,
130.2, 128.7, 127.3, 125.3, 119.7, 113.3, 110.5, 23.5, 18.7, 11.4.
Anal. Calcd for C22H25AlN2O: C, 73.78; H, 7.46; N, 7.40. Found:
Synthesis of 10 and 15. The synthesis of 10 and 15 was carried
out by the same procedure as that of 6 and 11, except that 2-
(1-(2,6-difluorophenylimino)propyl)quinolin-8-ol was used. Data
for 10: yield: 0.30 g (82%). 1H NMR (CDCl3): d 8.62 (d, 1H, J =
8.5 Hz), 8.03 (d, 1H, J = 8.5 Hz), 7.69 (t, 1H, J = 8.0 Hz), 7.44
1
C, 73.62; H, 7.81; N, 7.78%. Data for 11: H NMR (CDCl3): d
8.77 (d, 1H, J = 8.4 Hz), 8.11 (d, 1H, J = 8.5 Hz), 7.86 (t, 1H, J =
7.9 Hz), 7.78 (d, 1H, J = 8.1 Hz), 7.53 (d, 1H, J = 7.9 Hz), 7.16–7.18
(m, 3H), 2.76–2.74 (m, 2H), 2.07 (s, 6H), 1.28 (t, 3H, J = 7.6 Hz),
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Table 2 Crystal data and refinement details for 3, 6 and 8
3
6
8
Empirical formula
Formula weight
Crystal color
T/K
C48H58N4Al2O2
776.94
Yellow
173(2)
C22H25N2AlO
360.42
Red
173(2)
0.71073
C26H33N2AlO
416.52
Red
173(2)
0.71073
˚
Wavelength/A
0.71073
Crystal system
Space group
Monoclinic
P21
14.338(3)
14.612(3)
15.122(3)
90.0
103.05(3)
90.0
3086.6(11)
2
0.836
0.077
832
0.23 ¥ 0.21 ¥ 0.10
1.38–27.33
-18 £ h £ 18
- 18 £ k £ 17
- 19 £ l £ 19
24 947
13 265
0.0613
99.0 (q = 27.33)
0.985
R1 = 0.0939
wR2 = 0.2407
R1 = 0.1245
wR2 = 0.2638
0.338,-0.349
Monoclinic
P21/n
14.043(3)
9.4295(19)
15.913(3)
90.0
110.56 (3)
90.0
1972.9(7)
4
1.213
0.115
768
0.16 ¥ 0.13 ¥ 0.05
1.67–25.00
-16 £ h £ 16
- 10 £ k £ 11
- 18 £ l £ 18
13 031
3461
0.0670
99.6 (q = 25.00)
1.300
R1 = 0.1086
wR2 = 0.1950
R1 = 0.1225
wR2 = 0.2022
0.340,-0.255
Monoclinic
P21/n
10.237(2)
15.701(3)
14.671(3)
90.0
95.25(3)
90.0
2348.2(8)
4
1.178
0.106
896
0.29 ¥ 0.20 ¥ 0.10
1.90–27.52
-12 £ h £ 13
- 19 £ k £ 20
- 18 £ k £ 19
18 916
5364
0.0495
99.1 (q = 27.52)
1.274
R1 = 0.0960
wR2 = 0.2285
R1 = 0.1066
wR2 = 0.2351
0.414,-0.494
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
Volume/A
Z
D
calc/Mg m-3
m/mm-1
F(000)
Crystal size/mm
q range/◦
Limiting indices
No. of rflns collected
No. of unique rflns
Rint
Completeness to q (%)
Goodness-of-fit on F2
Final R indices [I > 2s(I)]
R indices (all data)
-3
˚
Largest diff. peak, hole/e A
(d, 2H, J = 8.1 Hz), 7.11–7.24 (m, 3H), 2.77–2.71 (m, 2H), 1.36 (t,
3H, J = 7.8 Hz), -0.73 (s, 6H). 13C NMR (CDCl3): d 171.3, 160.8,
143.7, 142.5, 141.4, 140.7, 134.1, 130.5, 128.9, 126.6, 126.0, 120.0,
113.7, 111.8, 24.8, 11.6, -9.7. Anal. Calcd for C20H19AlF2N2O: C,
65.21; H, 5.20; N, 7.60. Found: C, 65.07; H, 5.58; N, 7.68%. Data
for 15: yield 0.031 g (7%). 1H NMR (CDCl3): d 8.43 (d, 1H, J =
8.5 Hz), 8.18 (d, 1H, J = 8.4 Hz), 7.51 (t, 1H, J = 8.0 Hz), 7.44 (d,
1H, J = 8.1 Hz), 7.38 (d, 1H, J = 8.0 Hz), 7.15–7.18 (m, 2H), 6.99
(t, 1H, J = 8.1 Hz), 2.66–2.62 (m, 2H), 1.56 (t, 3H, J = 7.5 Hz),
-0.32 (s, 6H), -0.72 (s, 9H). Anal. Calcd for C23H28Al2F2N2O: C,
62.72; H, 6.41; N, 6.36. Found: C, 62.56; H, 6.19; N, 6.78%.
4.5 Crystal structure determinations†
Single crystals of 3, 6 and 8 suitable for X-ray diffraction
analysis were obtained from chilled toluene/n-heptane
or dichloromethane/n-heptane solutions. With graphite-
˚
monochromated Mo-Ka radiation (l
=
0.71073 A), cell
parameters were obtained by global refinement of the positions of
all collected reflections. Intensities were corrected for Lorentz and
polarization effects and empirical absorption. The structures were
solved by direct methods and refined by full-matrix least squares
on F2. All hydrogen atoms were placed in calculated positions.
Structure solution and refinement were performed by using the
SHELXL-97 package.19 In solving 3, the inverted structures is
employed for refinement, however, the Flack parameter is even
worse, so a racemic twin is concluded. Details of the X-ray
structure determinations and refinements are provided in Table 2.
4.4 The ROP of e-CL
Typical polymerization procedures in the presence of benzyl
alcohol (Table 1, run 3) are as follows. A toluene solution of 8
(0.020 mmol, 1.0 mL toluene) and BnOH (0.020 mmol) were added
into a Schlenk tube in the glove-box at room temperature. The
solution was stirred for 2 min, and then e-caprolactone (5.0 mmol)
along with 3.44 mL toluene was added to the solution. The
reaction mixture was then placed into an oil bath preheated at
90 ◦C, and the solution was stirred for the prescribed time (30 min).
The polymerization mixture was then quenched by addition of an
excess of glacial acetic acid (0.2 mL) into the solution, and the
resultant solution was then poured into methanol (200 mL). The
resultant polymer was then collected on filter paper and was dried
in vacuo.
Acknowledgements
This work was supported by National Natural Science Foun-
dation of China (No. 20874105) and MOST 863 program No.
2009AA033601. CR wishes to thank the EPSRC for an overseas
travel grant (EP/H031855/1).
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This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 2645–2653 | 2653
©