Synthesis, characterization, and catalytic application of aluminum anilido-oxazolinate complexes

Article abstract of DOI:10.1002/ejic.200900064

A family of aluminum complexes containing anilido-oxazol-inate ligands are described. Reactions of five anilido-oxazol-inate ligand precursors, HNPh ^TRiMeOxa, HNPh^DiiPrOxa, HNPh^OMeOxa, HNPh ^SMeOxa, or HNPhOxa, w

Full text of DOI:10.1002/ejic.200900064

FULL PAPER
DOI: 10.1002/ejic.200900064
Synthesis, Characterization, and Catalytic Application of Aluminum
Anilido-Oxazolinate Complexes
Chi-Tien Chen,*[a] Han-Jade Weng,[a] Ming-Tsz Chen,[a] Chi-An Huang,[a] and
Kuo-Fu Peng[a]
Keywords: Aluminum / Anilido-oxazolinate ligands / Ring-opening polymerization / Biodegradable polymers
A family of aluminum complexes containing anilido-oxazol-
inate ligands are described. Reactions of five anilido-oxazol-
inate ligand precursors, HNPhTriMeOxa, HNPhDiiPrOxa,
HNPhOMeOxa, HNPhSMeOxa, or HNPhOxa, with 1 molar
equiv. of AlMe3 in toluene give the aluminum dimethyl com-
Ar = =
2-methylthiophenyl, (NPhSMeOxa)AlMe2 (4); Ar
phenyl, (NPhOxa)AlMe2 (5), respectively]. The molecular
structures are reported for compounds 1–4. Their catalytic ac-
tivities toward the ring-opening polymerization reactions of
L-lactide or ε-caprolactone in the presence of BnOH are also
plexes (NArOxa)AlMe2 [Ar = 2,4,6-trimethylphenyl, (NPhTriMe
-
under investigation.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
Oxa)AlMe2 (1); Ar = 2,6-diisopropylphenyl, (NPhDiiPrOxa)-
AlMe2 (2); Ar = 2-methoxyphenyl, (NPhOMeOxa)AlMe2 (3);
dimethyl complexes have been synthesized. Their catalytic
activities in ring-opening polymerization are also investi-
gated.
Introduction
Poly(ε-caprolactone) (PCL) and poly(lactide) (PLA), as
well as their copolymers, are interesting candidates in both
biocompatible and biodegradable polymers, which have a
wide range of applications, such as tissue engineering, drug
delivery, and environmentally friendly wrapping materials.[1]
One of the promising methodologies for the syntheses of
these polymers is ring-opening polymerization that employs
metal-based initiator/catalysts. Therefore metal complexes
bearing auxiliary ligands as initiators/catalysts for ring-
opening polymerization have attracted great interest, mainly
because of their promising activities and great success in
preparing the well-defined polyesters.[1,2]
β-Diketiminate ligands, which normally act as hard
monoanionic ancillary ligands,[3] have received increasing
attention for their successful application in ring-opening
polymerization reactions.[1,2,4] Therefore some metal com-
plexes bearing structurally related ligands with similar che-
lating systems and isoelectronic features were synthesized
and some of their catalytic activities in ring-opening poly-
merization have been examined.[5] According to our pre-
vious catalytic studies on the zinc anilido-oxazolinate com-
plexes[5k] and the catalytic activities demonstrated by some
aluminum complexes bearing β-diketiminate or anilido-
imino ligands in ring-opening polymerization,[4,5k–5m] alu-
minum anilido-oxazolinate complexes are expected to be ef-
ficient initiators/catalysts in ring-opening polymerization.
In this paper, several ligand precursors and their aluminum
Results and Discussion
Synthesis and Characterization
Preparation of ligand precursors HNPhSMeOxa and
HNPhOxa was straightforward, using palladium-catalyzed
amination[6] of 2-(2-bromophenyl)-4,4-dimethyl-2-oxazol-
ine[7a] (for HNPhSMeOxa) or 2-(4,4-dimethy-4,5-dihydro-
oxazo-2-yl)-phenylamine[7b] (for HNPhOxa) with 2-methyl-
thioaniline (for HNPhSMeOxa) or iodobenzene (for
HNPhOxa) in the presence of Pd(OAc)2, bis[2-(diphenyl-
phosphanyl)phenyl] ether (DPEPhos), and sodium tert-bu-
toxide in refluxing toluene to afford the target compounds
in high yield.[8] Compounds HNPhSMeOxa and HNPhOxa
are characterized by NMR spectroscopy as well as elemen-
tal analyses.
Complexes 1–5 were synthesized by an alkane elimi-
nation reaction in moderate to high yields. Treatment of
ligand precursors HNPhTriMeOxa,[5k] HNPhDiiPrOxa,[5k]
HNPhOMeOxa,[5k] HNPhSMeOxa, or HNPhOxa with
AlMe3 in toluene yields the desired anilido-oxazolinate alu-
minum dimethyl complexes 1–5. Complexes 1–5 were all
characterized by NMR spectroscopy and elemental analy-
ses. The disappearance of the N–H signal of the ligand pre-
cursors and the appearance of the resonance for protons of
methyl groups in the high-field region are consistent with
the structures proposed in Scheme 1. Because of the sym-
metric environment around the metal center, one singlet
corresponding to two methyl groups on the metal center
[a] Department of Chemistry, National Chung Hsing University,
Taichung 402, Taiwan
E-mail: ctchen@dragon.nchu.edu.tw
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C.-T. Chen, H.-J. Weng, M.-T. Chen, C.-A. Huang, K.-F. Peng
FULL PAPER
and two singlets corresponding to two methyl groups and quite similar with different substituents on the anilido
two protons of the methylene group on the oxazolinate part groups. The Al–Namido bond lengths [1.8868(19) Å for 1;
were observed for 1, 2, and 5. Splitting peaks were found 1.8904(17) Å for 2; 1.8864(18) Å for 3; 1.8937(16) Å for 4]
around these regions because of the lower symmetry re- are shorter than the Al–Noxazoline bond lengths [1.923(2) Å
sulting from the substituents on the anilido groups of the for 1; 1.9369(18) Å for 2; 1.9370(16) Å for 3; 1.9348(16) Å
ligands for 3 and 4. However, only one singlet for the for 4], which might result from the π-donation ability of the
methyl group on the metal center was observed for 3.
anionic amido nitrogen.[9] The bond lengths of Al–Namido
and Al–Noxazoline are comparable to those [1.870(4)–
1.890(3) Å for Al–Namido; 1.917(5)–1.963(1) Å for Al–
Scheme 1.
Suitable crystals for structural determination of 1–4 were
obtained from concentrated hexane solution. Their molecu-
lar structures are depicted in Figures 1, 2, 3, and 4. The
structures of 1–4 reveal that the Al centers adopt a distorted
tetrahedral geometry with the metal center chelated by two
nitrogen donor atoms of the anilido-oxazolinate ligands
and two methyl groups, even though the ligands bear poten-
tially dative functionalities. Basically, compounds 1–4 are
Figure 2. Molecular structure of 2. Selected bond lengths [Å] and
bond angles [°]: Al–N(2), 1.8904(17); Al–N(1), 1.9369(18); Al–
C(24), 1.950(2); Al–C(25), 1.972(2); N(1)–C(19), 1.297(3); N(1)–
C(21), 1.498(3); N(2)–C(1), 1.367(2); N(2)–C(7), 1.442(2); N(2)–
Al–N(1), 92.65(8); N(2)–Al–C(24), 111.14(9); N(1)–Al–C(24),
113.67(10); N(2)–Al–C(25), 115.59(10); N(1)–Al–C(25), 104.54(10);
C(24)–Al–C(25), 116.59(12). Hydrogen atoms on carbon atoms
omitted for clarity.
Figure 1. Molecular structure of 1. Selected bond lengths [Å] and
bond angles [°]: Al–N(2), 1.8868(19); Al–N(1), 1.923(2); Al–C(21),
1.963(3); Al–C(22), 1.961(3); N(1)–C(16), 1.298(3); N(1)–C(18),
Figure 3. Molecular structure of 3. Selected bond lengths [Å] and
bond angles [°]: Al–N(2), 1.8864(18); Al–N(1), 1.9370(16); Al–
C(19), 1.974(2); Al–C(20), 1.958(3); N(1)–C(14), 1.307(2); N(1)–
1.516(3); N(2)–C(1), 1.362(3); N(2)–C(7), 1.452(3); N(2)–Al–N(1), C(16), 1.502(3); N(2)–C(1), 1.365(2); N(2)–C(7), 1.449(2); N(2)–
93.66(8); N(2)–Al–C(22), 113.97(11); N(1)–Al–C(22), 109.13(13); Al–N(1), 93.85(7); N(2)–Al–C(20), 111.70(12); N(1)–Al–C(20),
N(2)–Al–C(21), 115.25(13); N(1)–Al–C(21), 110.06(13); C(22)–Al– 111.06(9); N(2)–Al–C(19), 112.46(10); N(1)–Al–C(19), 110.33(11);
C(21), 112.95(17). Hydrogen atoms on carbon atoms omitted for
clarity.
C(20)–Al–C(19), 115.43(13). Hydrogen atoms on carbon atoms
omitted for clarity.
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Aluminum Anilido-Oxazolinate Complexes
Nimine] found in aluminum anilido-imine complexes.[5m,9] ing polymerization of -lactide employing 1–5 as catalysts
The N–Al–N angles [93.66(8)° for 1; 92.65(8)° for 2; is examined under dry nitrogen. Representative results are
93.85(7)° for 3; 93.88(7)° for 4] in these complexes are close collected in Table 1. The optimal conditions were found to
to those [93.79(5)–95.51(18)°] found in aluminum anilido- be toluene (10 mL) at 80 °C in the presence of benzyl
imine complexes.[5m,9]
alcohol after several trials on running polymerization with
CH2Cl2, THF, and toluene using 3 as the catalyst (entries
1–5). The same conditions were applied to examine the
catalytic activities of 1, 2, 4, and 5 (entries 6–10). Experi-
mental results show compounds 3–5 are efficient catalysts
for the polymerization of -lactide. However, only a trace
amount of polymer can be isolated using 1 or 2 as a cata-
lyst, implying the steric effect resulting from the anilido
group prevents the metal center from the coordination of
monomers. The linear relationship between the number-
average molecular weight (Mn) and the monomer-to-initia-
tor ratio ([M]0/[I]0) exhibited by 3 (entries 8, 11–13) implies
the “living” character of the polymerization process. Repre-
sentative results initiated by 3 are demonstrated in Figure 5
(entries 8, 11–13). This controlled behavior is further con-
firmed by the resumption experiment (entry 14). The “im-
mortal” character was examined using four equivalent ra-
tios (on [M]o/[Al]o) of benzyl alcohol as the chain transfer
agent (entry 15). The Mn of the polymer in each case be-
came half of that found in the reaction with the addition
of two equivalent ratios of benzyl alcohol. The end-group
Figure 4. Molecular structure of 4. Selected bond lengths [Å] and
bond angles [°]: Al–N(2), 1.8937(16); Al–N(1), 1.9348(16); Al–
C(19), 1.962(2); Al–C(20), 1.957(2); N(1)–C(14), 1.294(2); N(1)–
C(16), 1.500(2); N(2)–C(1), 1.363(3); N(2)–C(7), 1.441(2); N(2)–
Al–N(1), 93.88(7); N(2)–Al–C(20), 111.44(9); N(1)–Al–C(20),
110.82(9); N(2)–Al–C(19), 113.27(8); N(1)–Al–C(19), 109.95(9);
C(20)–Al–C(19), 115.43(10). Hydrogen atoms on carbon atoms
omitted for clarity.
1
analysis is demonstrated by the H NMR spectrum of the
polymer produced from -lactide and 3 ([M]o/[Al]o = 50),
as shown in Figure 6. Peaks are similar to those found on
1
the H NMR spectra of polymers produced by [Li]/BnOH
initiator[10] and are assignable to the corresponding protons
in the proposed structure. Compound 3 also demonstrates
catalytic activity using isopropyl alcohol (IPA) as initiator
under the same conditions (entry 16).
Polymerization Studies
Several aluminum anilido-imino[5l,5m] or aluminum β-di-
Complexes 1–5 were also investigated regarding their
ketiminate[4] complexes are known as efficient initiators/cat- catalytic behavior in the ROP of ε-caprolactone. Represen-
alysts in ring-opening polymerization (ROP); the structur- tative results are collected in Table 2. The catalytic activities
ally related aluminum complexes 1–5 were expected to work were proved to be affected by the steric effect of the substit-
as catalysts toward the ROP of cyclic esters. The ring-open- uents on the 2,6-position of the anilido group again by
Table 1. Polymerization of -lactide using compounds 1–5 as catalysts in toluene at 80 °C if not otherwise stated.[a]
Entry
Catalyst {[M]0:[Al]0}:[BnOH]
Time [h]
Mn (obsd.)[b] Mn (calcd.)[c]
% Conv.[d]
% Yield[e]
Mw/Mn[b]
1
3
3
3
3
3
1
2
3
4
5
3
3
3
3
3
3
100:0
100:2
100:2
100:2
100:2
100:2
100:2
100:2
100:2
100:2
200:2
300:2
400:2
24
44
24
48
48
24
24
24
24
24
24
24
24
24 (24)
24
24
–
–
–
–
–
–
–
–
–
–
–
–
–
–
trace
trace
trace
17
–
–
–
–
–
–
–
76
76
71
83
81
87
53
62
80
–
–
–
–
–
–
–
1.07
1.07
1.30
1.13
1.04
1.10
1.08
1.04
1.15
2[f]
3[g]
4[g]
5[h]
6
29
trace
trace
95
88
95
98
92
94
95 (66)
97
7
8
9
10
11
12
13
14
15
16
13000
11900
13000
25300
42300
52800
14500
9900
13800
6900
6400
6900
14200
20000
27200
9600
7100
6900
100 (100):2
200:4
100:2 (IPA)
95
[a] In 10 mL. [b] Obtained from GPC analysis. [c] Calculated from [M(lactide)ϫ[M]0/[Al]0 ϫconversion yield/([BnOH]eq)] + M(BnOH).
1
[d] Obtained from H NMR analysis. [e] Isolated yield. [f] Dichloromethane, T = 26 °C. [g] THF, T = 50 °C. [h] T = 50 °C.
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C.-T. Chen, H.-J. Weng, M.-T. Chen, C.-A. Huang, K.-F. Peng
FULL PAPER
using complexes 1–2 as catalysts (entries 1–2). Experimental
results indicate that complexes 3–5 have higher activities in
catalyzing ROP of ε-caprolactone than in catalyzing ROP
of -lactide (entries 3–6). This might result from the chelate
effect caused by the opened monomer.[11] Compound 3 also
demonstrates better activities than the other two at 50 °C
and 80 °C. The plot of Mn versus ([M]0/[I]0) demonstrated
by those data initiated by 3 exhibits a linear relationship
indicating the “living” character of the polymerization pro-
cess, as shown in Figure 7 (entries 3, 7–9). A similar “liv-
ing” character is seen in the polymerization reactions initi-
ated by 3 (entries 4, 12–14) at 80 °C within 40 min, as
shown in Figure 8. Compound 3 also demonstrates “im-
mortal” character by using four equivalent ratios (on [M]o/
[Al]o) of benzyl alcohol as the chain transfer agent at 50 °C
and 80 °C (entries 10 and 15). The Mn of the polymer in
each case became half of that found in the reaction with
the addition of two equivalent ratios of benzyl alcohol. The
1H NMR spectrum of PCL-50 prepared from ε-caprolac-
tone and 3 ([M]o/[Al]o = 50) for the chain-end studies is
shown in Figure 9. Peaks are assignable to the correspond-
ing protons in the proposed structure,[5l,12] indicating the
metal benzyl oxide complex might form first, followed by
the ring cleavage of the acyl-oxygen bond to form a metal
alkoxide intermediate, which further reacts with excess lac-
tones to yield polyesters.[5l,12] Poor activity was observed by
using isopropyl alcohol (IPA) as initiator under the same
conditions (entry 11).
Figure 5. Polymerization of -lactide initiated by 3 in toluene at
80 °C.
In conclusion, a family of aluminum dimethyl complexes
containing anilido-oxazolinate ligands have been prepared
and fully characterized. Complexes 3–5 were employed as
catalysts for the ring-opening polymerization of -lactide
and ε-caprolactone in the presence of benzyl alcohol. They
all demonstrate efficient activities for the controlled poly-
merization of -lactide and ε-caprolactone with both living
and immortal characters. However, the poor performance
of complexes 1–2 indicates bulky substituents on the 2,6-
position of the anilido group might strongly affect the cata-
1
Figure 6. H NMR spectrum of PLA-50 initiated by 3 in toluene.
Table 2. Polymerization of ε-caprolactone using compounds 1–5 as catalysts at 50 °C.[a]
Entry
Catalyst {[M]0:[Al]0}:[BnOH] Time [min] Mn (obsd.)[b] Mn (calcd.)[c]
% Conv.[d]
% Yield[e]
Mw/Mn[b]
1
2
3
1
2
3
3
4
5
3
3
3
3
3
3
3
3
3
100:2
100:2
100:2
100:2
100:2
100:2
200:2
300:2
400:2
200:4
100:2(IPA)
200:2
300:2
400:2
120
120
120
9
–
–
–
–
trace
trace
96
98
99
95
96
97
97
95
14
95
96
96
97
–
–
–
–
9200
13500
11600
13000
16800
26600
31300
8200
–
23300
31200
45900
11200
5500
5500
5500
5500
11000
16700
22200
5400
–
10900
16500
22500
5600
88
97
98
94
96
87
87
77
–
95
89
95
89
1.06
1.08
1.09
1.06
1.07
1.12
1.13
1.05
–
1.08
1.11
1.16
1.07
4[f]
5[f]
6
75
120
240
330
420
120
120
12
15
40
10
7
8
9
10
11
12[f]
13[f]
14[f]
15[f]
200:4
[a] In toluene (15 mL). [b] Obtained from GPC analysis. [c] Calculated from [M(caprolactone)ϫ[M]0/[Al]0 ϫconversion yield/([BnOH]
1
eq)] + M(BnOH). [d] Obtained from H NMR analysis. [e] Isolated yield. [f] T = 80 °C.
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Aluminum Anilido-Oxazolinate Complexes
Experimental Section
General: All manipulations were carried out under dinitrogen using
standard Schlenk-line or drybox techniques. Solvents were refluxed
over the appropriate drying agent and distilled prior to use. Deuter-
ated solvents were dried with molecular sieves.
1H and 13C{1H} NMR spectra were recorded with either Varian
Mercury-400 (400 MHz) or Varian Inova-600 (600 MHz) spec-
trometers in [D]chloroform at ambient temperature unless stated
otherwise, referenced internally to the residual solvent peak, and
reported as parts per million relative to tetramethylsilane. Elemen-
tal analyses were performed by an Elementar Vario ELIV instru-
ment. The GPC measurements were performed in THF at 35 °C
with a Waters 1515 isocratic HPLC pump, a Waters 2414 refractive
index detector, and Waters styragel column (HR4E). Molecular
weights and molecular weight distributions were calculated using
polystyrene as standard. Melting points were measured under dry
dinitrogen using a MEL-TEMP II instrument and were not cor-
rected.
Figure 7. Polymerization of ε-caprolactone initiated by 3 in toluene
at 50 °C.
Pd(OAc)2 (Acros), AlMe3 (Aldrich, 2.0  in toluene), NaOtBu
(TCI), 2-methylthioaniline (Lancaster), -proline (Lancaster),
K3PO4 (Alfa), iodobenzene (Acros), and bis[2-(diphenylphos-
phanyl)phenyl] ether (DPEPhos, Strem) were used as supplied. 2-
(2-Bromophenyl)-4,4-dimethyl-2-oxazoline,[7a] 2-(4,4-dimethyl-4,5-
dihydro-oxazol-2-yl)-phenylamine,[7b] HNPhTriMeOxa,[5k] HNPhDiiPr
-
Oxa,[5k] and HNPhOMeOxa[5k] were prepared according to the lit-
erature. Benzyl alcohol was dried with magnesium sulfate and dis-
tilled before use. ε-Caprolactone was dried with magnesium sulfate
and distilled under reduced pressure. -Lactide was recrystallized
from toluene prior to use.
Preparations
HNPhSMeOxa: Toluene (3 mL) was added to a flask containing 2-
(2-bromophenyl)-4,4-dimethyl-2-oxazoline (0.61 g, 2.4 mmol), Na-
OtBu (0.27 g, 3.4 mmol), bis[2-(diphenylphosphanyl)phenyl] ether
(DPEPhos, 0.065 g, 0.072 mmol), Pd(OAc)2 (0.018 g, 0.08 mmol),
and 2-methylthioaniline (0.26 mL, 3.0 mmol) at room temperature.
The reaction mixture was refluxed for five days. All the volatiles
were pumped off and the residue was extracted with ethyl acetate
(5 mL). Crude product was purified by column chromatography
(hexane/ethyl acetate, 5:1) to afford a yellow solid; yield 0.52 g,
Figure 8. Polymerization of ε-caprolactone initiated by 3 in toluene
at 80 °C.
1
69%. H NMR (600 MHz): δ = 1.40 [s, 6 H, C(CH3)2], 2.43 (s, 3
H, SCH3), 4.04 (s, 2 H, CH2), 6.76 (m, 1 H, CH-Ph), 7.08 (m, 1
H, CH-Ph), 7.19 (m, CH-Ph, 2H overlap), 7.24 (m, 1 H, CH-Ph),
7.36 (m, 1 H, CH-Ph), 7.47 (m, 1 H, CH-Ph), 7.81 (m, 1 H, CH-
Ph), 10.54 (br., 1 H, NH) ppm. 13C{1H} NMR (150 MHz): δ =
16.1 (s, SCH3), 28.5 [s, C(CH3)2], 67.9 [s, C(CH3)2], 77.4 (s, CH2),
113.1, 117.0, 122.3, 123.7, 126.0, 128.6, 129.7, 131.6 (s, CH-Ph),
110.9, 132.1, 139.9, 145.5, 161.8 (Cquat
) ppm. C18H20N2OS
(312.43): calcd. C 69.20, H 6.45, N 8.97; found C 69.57, H 6.59, N
8.77.
HNPhOxa: Toluene (10 mL) was added to a flask containing 2-
(4,4-dimethy-4,5-dihydro-oxazo-2-yl)-phenylamine (0.95 g, 5.0
mmol), NaOtBu (0.67 g, 7.0 mmol), bis[2-(diphenylphosphanyl)-
phenyl] ether (DPEPhos, 0.081 g, 0.1 mmol), Pd(OAc)2 (0.022 g,
0.1 mmol), and 0.61 mL iodobenzene (5.5 mmol) at room tempera-
ture. The reaction mixture was refluxed for six days. All the vola-
tiles were pumped off and the residue was extracted with CH2Cl2.
(25 mL). Crude product was purified by column chromatography
(hexane/ethyl acetate, 40:1) to afford a white solid; yield 1.20 g,
1
Figure 9. H NMR spectrum of PCL-50 initiated by 3 in toluene.
lytic activities of ring-opening polymerization in this sys-
tem. Preliminary studies on fine-tuning of ligand precursors
and further application of metal complexes to the catalytic
reactions are currently underway.
1
90%. H NMR (400 MHz): δ = 1.38 (s, 6 H, CH3), 4.02 (s, 2 H,
CH2), 6.74 (m, 1 H, Ph), 7.07 (m, 1 H, Ph), 7.22–7.36 (m, 6 H,
Ph), 7.78 (m, 1 H, Ph), 10.44 (s, 1 H, NH) ppm. 13C{1H} NMR
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C.-T. Chen, H.-J. Weng, M.-T. Chen, C.-A. Huang, K.-F. Peng
FULL PAPER
(100 MHz): δ = 28.7 (s, CH3), 67.9 (s, Cquat), 77.4 (s, CH2), 110.5
(s, Cquat), 113.0, 116.8, 122.0, 122.8, 129.2, 129.8, 131.8 (s, C6H5),
141.5, 145.7, 162.1 (s, Cquat) ppm. C17H18N2O (266.34): calcd. C
76.66, H 6.81, N 10.52; found C 77.02, H 6.88, N 10.58.
lowish-green solid; yield 0.15 g, 73%. Suitable crystals of 4 for
structural determination were recrystallized from a concentrated
hexane solution; m.p. 184.0–186.0 °C. 1H NMR (600 MHz): δ =
–0.91 (s, 3 H, Al-CH3), –0.81 (s, 3 H, Al-CH3), 1.53 [s, 3 H, C(CH3)
2], 1.54 [s, 3 H, C(CH3)2], 2.30 (s, 3 H, SCH3), 4.26 (d, J = 8.4 Hz,
1 H, CH2), 4.30 (s, J = 8.4 Hz, 1 H, CH2), 6.17 (d, J = 8.4 Hz, 1
H, CH-Ph), 6.49 (t, J = 7.2 Hz, 1 H, CH-Ph), 7.05 (d, J = 7.8 Hz,
1 H, CH-Ph), 7.11 (m, 1 H, CH-Ph), 7.17 (m, 1 H, CH-Ph), 7.22
(m, CH-Ph, 2H overlap), 7.72 (m, 1 H, CH-Ph) ppm. 13C{1H}
NMR (150 MHz): δ = –9.2 (s, Al-CH3), –6.9 (s, Al-CH3), 14.9 (s,
SCH3), 27.3 [s, C(CH3)2], 27.7 [s, C(CH3)2], 66.4 [s, C(CH3)2], 79.2
(s, CH2), 114.0, 116.6, 125.5 (two C intensities), 125.7, 128.9, 130.5,
135.1 (s, CH-Ph), 105.2, 138.2, 143.3, 156.0, 168.8 (Cquat) ppm.
C20H25AlN2OS (368.47): calcd. C 65.19, H 6.84, N 7.60; found C
64.71, H 7.08, N 7.76.
(NPhTriMeOxa)AlMe2 (1): AlMe3 (0.35 mL, 2.0  in toluene,
0.7 mmol) was added to a flask containing HNPhTriMeOxa (0.15 g,
0.5 mmol) and toluene (20 mL) at 0 °C. The reaction mixture was
warmed to room temperature and reacted overnight. After 13 h of
stirring, all the volatiles were removed under reduced pressure to
afford a yellowish-green solid; yield 0.09 g, 49%; m.p. 149.5–
151.1 °C. 1H NMR (600 MHz): δ = –0.89 (s, 6 H, Al-CH3), 1.53 [s,
6 H, C(CH3)2], 2.05 (s, 6 H, 2,6-CH3), 2.30 (s, 3 H, 4-CH3), 4.28
(s, 2 H, CH2), 6.07 (d, J = 8.4 Hz, 1 H, CH-Ph), 6.43 (m, 1 H, CH-
Ph), 6.93 (s, 2 H, 3,5-C6H2), 7.06 (m, 1 H, CH-Ph), 7.71 (m, 1 H,
CH-Ph) ppm. 13C{1H} NMR (150 MHz): δ = –7.5 (s, Al-CH3),
18.3 (s, 2,6-CH3), 20.9 (s, 4-CH3), 27.5 [s, C(CH3)2], 66.2 [s,
C(CH3)2], 79.2 (s, CH2), 113.2, 116.0, 129.3, 130.6, 135.4 (s, CH-
(NPhOxa)AlMe2 (5): AlMe3 (0.70 mL, 2.0  in toluene, 1.4 mmol)
was added to a flask containing HNPhOxa (0.27 g, 1.0 mmol) and
toluene (20 mL) at 0 °C. The reaction mixture was warmed to room
temperature and reacted overnight. After 14 h of stirring, all the
volatiles were removed under reduced pressure. The crude product
was washed with hexane (5 mL) to afford a yellowish-green solid;
Ph), 104.6, 134.3, 136.2, 140.3, 156.1, 168.8 (Cquat
) ppm.
C22H29AlN2O (364.46): calcd. C 72.50, H 8.02, N 7.69; found C
72.84, H 8.44, N 7.56.
(NPhDiiPrOxa)AlMe2 (2): AlMe3 (1.4 mL, 2.0  in toluene,
2.8 mmol) was added to a flask containing HNPhDiiPrOxa (0.71 g,
2 mmol) and toluene (15 mL) at 0 °C. The reaction mixture was
warmed to room temperature and reacted for 2.5 h. All the volatiles
were removed under reduced pressure to afford a yellowish-green
solid; yield 0.66 g, 81%. Suitable crystals of 2 for structural deter-
mination were recrystallized from concentrated hexane solution;
1
yield 0.25 g, 76%; m.p. 130.5–132.5 °C. H NMR (600 MHz): δ =
–0.87 (s, 6 H, Al-CH3), 1.53 [s, 6 H, C(CH3)2], 4.27 (s, 2 H, CH2),
6.40 (d, J = 8.4 Hz, 1 H, CH-Ph), 6.44 (m, 1 H, CH-Ph), 7.07–7.11
(m, 3 H, CH-Ph), 7.18 (t, J = 7.8 Hz, 1 H, CH-Ph), 7.38 (m, 2 H,
CH-Ph), 7.69 (m, 1 H, CH-Ph) ppm. 13C{1H} NMR (150 MHz): δ
= –7.6 (s, Al-CH3), 27.5 [s, C(CH3)2], 66.3 [s, C(CH3)2], 79.2 (s,
CH2), 113.5, 116.9, 124.6, 128.2, 129.6, 130.5, 135.1 (s, CH-Ph),
104.9, 146.8, 156.9, 168.8 (Cquat) ppm. C19H23AlN2O (322.38):
calcd. C 70.79, H 7.19, N 8.69; found C 70.05, H 6.55, N 8.11.
1
m.p. 189.0–191.0 °C. H NMR (600 MHz): δ = –0.92 (s, 6 H, Al-
CH3), 0.95 [d, J = 7.2 Hz, 6 H, CH(CH3)2], 1.16 [d, J = 6.6 Hz, 6
H, CH(CH3)2], 1.54 [s, 6 H, C(CH3)2], 3.12 [septet, J = 7.2 Hz, 2
H, CH(CH3)2], 4.32 (s, 2 H, CH2), 6.17 (d, J = 8.4 Hz, 1 H, CH-
Ph), 6.47 (m, 1 H, CH-Ph), 7.07 (m, 1 H, CH-Ph), 7.19 (m, 1 H,
CH-Ph), 7.22–7.26 (m, 2 H, CH-Ph), 7.70 (m, 1 H, CH-Ph) ppm.
Polymerization Procedure of L-Lactide or ε-Caprolactone: Typically,
toluene (10 mL containing 0.1 mmol benzyl alcohol for -lactide
or 15 mL containing 0.25 mmol benzyl alcohol for ε-caprolactone)
was added to a flask containing a prescribed amount of monomers
(-lactide or ε-caprolactone) and catalyst (0.05 mmol for -lactide,
0.125 mmol for ε-caprolactone). The reaction mixture was stirred
at the prescribed temperature for the prescribed time. After the
reaction was quenched by the addition of acetic acid solution
(10 mL, 0.35 ), the resulting mixture was poured into n-heptane
(50 mL) to precipitate polymers. Crude products were recrystallized
from THF/hexane and dried in vacuo up to a constant weight.
13C{1H} NMR (150 MHz):
δ = –8.7 (s, Al-CH3), 24.4 [s,
CH(CH3)2], 25.1 [s, CH(CH3)2], 27.5 [s, C(CH3)2], 27.7 [s,
CH(CH3)2], 66.0 [s, C(CH3)2], 79.4 (s, CH2), 113.8, 119.0, 124.0,
125.7, 130.4, 134.5 (s, CH-Ph), 105.6, 141.5, 146.6, 157.5, 168.6
(Cquat) ppm. C25H35AlN2O (406.54): calcd. C 73.86, H 8.68, N
6.89; found C 73.62, H 8.90, N 7.00.
(NPhOMeOxa)AlMe2 (3): AlMe3 (2.1 mL, 2.0  in toluene,
4.2 mmol) was added to a flask containing HNPhOMeOxa (0.89 g,
3 mmol) and toluene (30 mL) at 0 °C. The reaction mixture was
warmed to room temperature and reacted overnight. After 13 h of
stirring, all the volatiles were removed under reduced pressure to
afford a yellow solid; yield 0.92 g, 87%. Suitable crystals of 3 for
structural determination were recrystallized from a concentrated
hexane solution; m.p. 138.5–140.5 °C. 1H NMR (600 MHz): δ =
–0.92 (s, 6 H, Al-CH3), 1.45 [s, 3 H, C(CH3)2], 1.57 [s, 3 H,
C(CH3)2], 3.78 (s, 3 H, OCH3), 4.19 (d, J = 8.4 Hz, 1 H, CH2),
4.28 (d, J = 8.4 Hz, 1 H, CH2), 6.53 (m, 1 H, CH-Ph), 6.85 (d, J
= 8.4 Hz, 1 H, CH-Ph), 6.91 (m, CH-Ph, 2H overlap), 7.03 (m, 1
H, CH-Ph), 7.14 (m, CH-Ph, 2H overlap), 7.70 (m, 1 H, CH-Ph)
ppm. 13C{1H} NMR (150 MHz): δ = –9.4 (s, Al-CH3), –8.2 (s, Al-
CH3), 26.8 [s, C(CH3)2], 28.1 [s, C(CH3)2], 54.7 (s, OCH3), 66.4 [s,
C(CH3)2], 79.4 (s, CH2), 111.0, 114.6, 118.3, 121.2, 123.3, 125.7,
Crystal Structure Data: Crystals were grown from concentrated
hexane solution (for 1–4) and isolated by filtration. Suitable crys-
tals of 1–4 were sealed in thin-walled glass capillaries under nitro-
gen and mounted on a Bruker CCD Smart-1000 diffractometer.
The absorption correction was based on the symmetry equivalent
reflections using the SADABS program.[13] The space group deter-
mination was based on a check of the Laue symmetry and system-
atic absences and was confirmed using the structure solution. The
structure was solved by direct methods using a SHELXTL pack-
age.[14] All non-hydrogen atoms were located from successive Fou-
rier maps and hydrogen atoms were refined using a riding model.
Anisotropic thermal parameters were used for all non-hydrogen
atoms and fixed isotropic parameters were used for hydrogen
atoms. Some details of the data collection and refinement are given
in Table 3.
130.2, 134.3 (s, CH-Ph), 107.4, 137.2, 153.6, 155.9, 167.8 (Cquat
)
ppm. C20H25AlN2O2 (352.41): calcd. C 68.16, H 7.15, N 7.95;
found C 67.75, H 7.43, N 8.05.
CCDC-701925 (for 1), -701926 (for 2), -701927 (for 3), and -701928
(for 4) contain the supplementary crystallographic data for this pa-
per. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
(NPhSMeOxa)AlMe2 (4): AlMe3 (0.45 mL, 2.0  in toluene,
1.2 mmol) was added to a flask containing HNPhSMeOxa (0.18 g,
0.56 mmol) and toluene (15 mL) at 0 °C. After 13 h of stirring, all
the volatiles were removed under reduced pressure to afford a yel-
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 2129–2135

Aluminum Anilido-Oxazolinate Complexes
Table 3. Summary of crystal data for compounds 1–4.
1
2
3
4
Empirical formula
Formula mass
T [K]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
C22H29AlN2O
364.45
293(2)
monoclinic
P21/c
10.4262(12)
8.1808(10)
25.597(3)
90
C25H35AlN2O
406.53
293(2)
monoclinic
P21/n
10.0961(8)
12.0705(10)
20.2512(16)
90
C20H25AlN2O2
352.40
293(2)
orthorhombic
Pca21
16.9986(14)
8.3598(7)
13.6445(12)
90
C20H25AlN2OS
368.46
293(2)
orthorhombic
Pca21
16.8403(9)
8.1689(4)
14.0728(8)
90
β [°]
95.933(2)
90
2171.6(4)
4
1.115
0.105
11879
265
0.057
0.1635
1.086
101.105(2)
90
2421.7(3)
4
1.115
0.101
13554
262
0.0428
0.1170
0.807
90
90
1939.0(3)
4
1.207
0.119
10455
226
90
90
γ [°]
V [Å3]
1935.95(18)
4
1.264
0.223
10362
Z
ρcalcd [Mg/m3]
µ(Mo-Kα) [mm–1]
Reflections collected
Number of parameters
226
[a]
R1
0.0305
0.0854
1.034
0.0296
0.0752
1.022
[a]
wR2
Gof[b]
[a] R1 = [Σ|Fo| – |Fc|]/Σ|Fo|; wR2 = [Σw(Fo – Fc ) /Σw(Fo2)2]1/2; w = 0.10. [b] Gof = [Σw(Fo – Fc ) /(Nrflns – Nparams)]1/2
.
2
2 2
2
2 2
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Received: January 19, 2009
Published Online: March 31, 2009
Eur. J. Inorg. Chem. 2009, 2129–2135
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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