Synthesis and structural characterization of aluminum complexes supported by NNO-tridentate ketiminate ligands: Efficient catalysts for ring-opening polymerization of l-lactide

Article abstract of DOI:10.1016/j.inoche.2012.01.004

Four NNO-tridentate ketiminate derivatives (^HL-H, ^FL-H, ^OMeL-H and ^tBuL-H) were prepared through the condensation reaction of 1-(4-chlorophenyl)-4-(4-X-benzoyl)-3-methyl-1H- pyrazol-5(4H)-one (X = H, F, OMe, ^tBu) with N,N-dimethylenediamine (1.1 molar equiv) under reflux condition. Further reaction of AlMe₃ (1.2 molar equiv) with ^HL-H, ^FL-H, ^OMeL-H and ^tBuL-H, respectively, affords penta-coordinated mono-adduct aluminum complexes [(^HL)AlMe₂] (1), [(^FL)AlMe ₂] (2), [(^OMeL)AlMe₂] (3), and [( ^tBuL)AlMe₂] (4) in high yield. Experimental results indicate complexes 1-4 are active catalysts for ring-opening polymerization of l-lactide (l-LA) in the presence of benzyl alcohol (BnOH). Al complex 2 catalyzes efficiently not only in a "living" fashion but also an "immortal" manner, giving polymers with the expected molecular weights and narrow PDIs.

Full text of DOI:10.1016/j.inoche.2012.01.004

Inorganic Chemistry Communications 18 (2012) 38–42
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Synthesis and structural characterization of aluminum complexes supported by
NNO-tridentate ketiminate ligands: Efficient catalysts for ring-opening
polymerization of l-lactide
Hui-Ju Chuang a, Yu-Chu Su a, Bao-Tsan Ko b, Chu-Chieh Lin a,
⁎
a
Department of Chemistry, National Chung Hsing University, Taichung 402, Taiwan, R.O.C.
b
Department of Chemistry, Chung Yuan Christian University, Chung-Li 320, Taiwan, R.O.C.
a r t i c l e i n f o
a b s t r a c t
Four NNO-tridentate ketiminate derivatives (HL-H, FL-H, OMeL-H and tBuL-H) were prepared through the conden-
sation reaction of 1-(4-chlorophenyl)-4-(4-X-benzoyl)-3-methyl-1H-pyrazol-5(4H)-one (X=H, F, OMe, Bu)
Article history:
t
Received 8 December 2011
Accepted 5 January 2012
Available online 12 January 2012
with N,N-dimethylenediamine (1.1 molar equiv) under reflux condition. Further reaction of AlMe3 (1.2 molar
equiv) with HL-H, FL-H, OMeL-H and tBuL-H, respectively, affords penta-coordinated mono-adduct aluminum
complexes [(HL)AlMe2] (1), [(FL)AlMe2] (2), [(OMeL)AlMe2] (3), and [(tBuL)AlMe2] (4) in high yield. Exper-
imental results indicate complexes 1–4 are active catalysts for ring-opening polymerization of L-lactide (L-LA) in
the presence of benzyl alcohol (BnOH). Al complex 2 catalyzes efficiently not only in a “living” fashion but also an
“immortal” manner, giving polymers with the expected molecular weights and narrow PDIs.
© 2012 Elsevier B.V. All rights reserved.
Keywords:
Aluminum complex
Catalyst
NNO-tridentate
Ring-opening polymerization
L-lactide
Over the past two decades, there has been considerable attention
focused on the development of catalytic systems for ring-opening
polymerization (ROP). ROP using metal complexes provides a prom-
ising method to prepare biodegradable polymers, such as poly(ε-
caprolactone) (PCL) and poly(lactide) (PLA) as well as their copolymers.
These metal complexes have been mainly designed to realize the single
active site for minimizing the side reaction, and a variety of catalytic
systems supported by various ancillary ligands such as β-diketiminate,
Schiff base, amino-bis(phenolate), bisphenolate [1], anilido-aldiminate
[2], and benzotriazole phenolate [3] have been reported to achieve
great catalytic activities with living properties. For instance, NNO-
tridentate Schiff-base zinc alkoxides demonstrated the excellent
catalytic activity (0 °C, 6 min) and the greater controlled manner
(PDI≦1.10) toward the polymerization of L-lactide (L-LA), and their
activities are dramatically affected by the substituents on the imine
carbon of the NNO-ligands [4].
Encouraged by the excellent catalytic systems derived from NNO-
tridentate ligands, our current interest has been to design and to
prepare NNO-tridentate ketiminate ligands bearing aluminum, mag-
nesium and zinc alkoxides and to apply these complexes as initiators
for ROP of L-LA [5]. Most recently, the pyrazole containing ketiminate de-
rivative, (4Z)-4-{[(2-(dimethylamino) ethylamino](phenyl)methylene}-
3-methyl-1-phenyl-1H-pyrazol-5(4H)-one was successfully synthesized
via one-step condensation, and magnesium and zinc benzylalkoxides
incorporating such a ligand catalyzes the ROP of LA with not only good
catalytic activities in a controlled character but also the excellent stereo-
selectivity (Pr=0.87) [6]. However, no aluminum complex of NNO-
tridentate ketiminate ligands has been isolated to date, and the electronic
effect of the substituents on the NNO-tridentate ketiminate derivatives
might result in dramatic differences of polymerization activity and con-
trolled character. Herein, we report the synthesis, crystal structure and
ROP catalytic studies of novel aluminum derivatives based on NNO-
tridentate ketiminate ligands of this kind.
The synthetic routes of NNO-tridentate ketiminate ligands (L-H)
and their Al complexes (1–4) are outlined in Scheme 1. According
to the previous literatures [7], pyrazole containing ketiminate ligands
can be prepared via two-step synthesis starting from 1-phenyl-pyrazol-
5-one and benzoyl chloride derivatives as shown in Scheme 1(a). Four
NNO-ketiminate derivatives with 4-substitutited phenyl group (HL-
H, FL-H, OMeL-H, and tBuL-H) were prepared in moderate to high yield
(≧70%) on condensation of diketone (L') with N,N-dimethylenediamine
under refluxing absolute ethanol. These ligands were isolated as pale
yellow solids and were characterized by 1H, 13 C NMR and mass
spectra as well as microanalyses. For instances, the 1H NMR spectra
of OMeL-H displayed resonances at δ 3.24 ppm for the methylene
protons of –NHCH2CH2, and signals of methylene (δ=2.47 ppm) or
methyl (δ=2.21 ppm) protons of –CH2CH2N(CH3)2, indicating the
formation of the desired NNO-tridentate ketiminate ligand. The
broad N–H signal at the down field of ~11.2 ppm indicates a hydro-
gen bond between N–H and O(carbonyl), which was further con-
firmed by X-ray structural determination. Single crystals suitable
for X-ray determination of compound OMeL-H were obtained from a
⁎
Corresponding author. Tel.: +886 4 22840411 718; fax: +886 4 22862547.
E-mail address: cchlin@mail.nchu.edu.tw (C.-C. Lin).
1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2012.01.004

H.-J. Chuang et al. / Inorganic Chemistry Communications 18 (2012) 38–42
39
Scheme 1. Synthetic routes of ligands L–H and complexes (1)–(4).
saturated EtOH solution. The solid-state structure of OMeL-H [8]
(Fig. 1) shows an intramolecular hydrogen bond of N―H…O between
the amine and amide groups. The distance of O…H (1.994(4) Å) is sub-
stantially shorter than the Van der Waals distance of 2.72 Å for the O
and H atom. The six-membered ring (O(1), C(14), C(13), C(5), N(3),
H(3A)) formed from the N―H…O hydrogen-bond is almost coplanar
with mean deviation of 0.0454 Å. Complexes 1–4 were further synthe-
sized via alkane elimination in toluene. Treatment of the ligand (L-H)
with AlMe3 (1.2 molar equiv) yields the mono-adduct aluminum
complex (1: [(HL)AlMe2] [9]; 2: [(FL)AlMe2] [10]; 3: [(OMeL)AlMe2]
[11]; 4: [(tBuL)AlMe2] [12]) in high yield, respectively. The formation
of expected complexes 1–4 were demonstrated by the disappear-
ance of the N-H signal of the L-H group at ~11.2 ppm and the ap-
pearance of the resonance for methyl protons of Al-Me in the
region of −0.78 ppm for 1, −0.79 ppm for 2 and 3 in NMR spectra.
All these compounds were isolated as white crystalline solids and
were characterized by spectroscopic studies as well as microanaly-
ses. The structures of complexes 2 and 3 were further verified with
X-ray single crystal measurements.
Suitable crystals of complexes 2 and 3 suitable for X-ray structural
determinations were grown from their toluene/hexane solutions.
Oak Ridge thermal-ellipsoid plots (ORTEP) display selected bond
lengths and angles of the molecular structures of 2 [13] and 3 [14]
in Figs. 2 and 3, respectively. The molecular structures of compounds
2 and 3 are isostructural, except either a fluoro (−F) or a methoxy
(−OMe) substituent at the 4-position of the phenyl group. Both
complexes exhibit a monomeric feature with a penta-coordinated
Al center, containing one six- and one five-membered chelating
ring. The geometry around Al atom is distorted from trigonal–bipy-
ramidal environment with one oxygen atom, two nitrogen atoms
from the NNO-tridentate ketiminate ligand, and two C atoms from
two methyl groups. Their principal structural features include keti-
minate nitrogen atom N(2) and carbon atoms C(1), C(2) occupying
the equatorial plane; the angles (O(1)―Al(1)―N(1)) formed by
the axial bonds are 166.76(7)° for 2 and 166.13(5)° for 3, respec-
tively. The distances between the Al atom and atoms O(1), N(1),
N(2), C(1) and C(2) are 1.9152(15), 2.2232(18), 2.0405(17),
1.970(2) and 1.976(2) Å for 2, which are all longer than bond
lengths observed for the four-coordinated aluminum complex bear-
ing a NO-bidentate ketiminate derivative [15]. In comparison, the
Al-containing bond distances of Al(1)―O(1)=1.8942(12) Å, Al(1)―
N(1)=2.1896(14) Å, Al(1)―N(2)=2.0403(13) Å, Al(1)―C(1)=
Fig. 1. ORTEP drawing of OMeL–H with probability ellipsoids drawn at level 50%. Selected
bond lengths/Å and angles/deg: N(3)–C(5) 1.321(2), C(5)–C(13) 1.403(3), C(13)–C(14)
1.443(2), O(1)–C(14) 1.245(2), N(2)–C(14) 1.382(2), N(1)–N(2) 1.411(2), N(1)–C(15)
1.310(2), C(13)–C(15) 1.431(3), O(1) …H(3A) 1.994(4), N(3)–H(3A) …O(1) 138.8(3).

40
H.-J. Chuang et al. / Inorganic Chemistry Communications 18 (2012) 38–42
Fig. 2. ORTEP drawing of complex 2 with probability ellipsoids drawn at level 50%.
Selected bond lengths/Å and angles/deg: Al(1)–O(1) 1.9152(15), Al(1)–N(1) 2.2232(18),
Al(1)–N(2) 2.0405(17), Al(1)–C(1) 1.970(2), Al(1)–C(2) 1.976(2), O(1)–Al(1)–N(1)
166.76(7), O(1)–Al(1)–N(2) 89.09(6), N(1)–Al(1)–N(2) 77.95(7), O(1)–Al(1)–C(1)
93.05(9), O(1)–Al(1)–C(2) 91.66(9), N(1)–Al(1)–C(1) 95.10(8), N(1)–Al(1)–C(2)
92.70(8), N(2)–Al(1)–C(1) 116.17(9), N(2)–Al(1)–C(2) 120.96(9), C(1)–Al(1)–C(2)
122.71(10).
Fig. 3. ORTEP drawing of complex 3 with probability ellipsoids drawn at level 50%.
Selected bond lengths/Å and angles/deg: Al(1)–O(1) 1.8942(12), Al(1)–N(1) 2.1896(14),
Al(1)–N(2) 2.0403(13), Al(1)–C(1) 1.9826(16), Al(1)–C(2) 1.9923(16), O(1)–Al(1)–N(1)
166.13(5), O(1)–Al(1)–N(2) 89.45(5), N(1)–Al(1)–N(2) 79.26(5), O(1)–Al(1)–C(1)
96.60(6), O(1)–Al(1)–C(2) 89.16(6), N(1)–Al(1)–C(1) 94.90(6), N(1)–Al(1)–C(2)
91.55(6), N(2)–Al(1)–C(1) 110.55(6), N(2)–Al(1)–C(2) 128.28(7), C(1)–Al(1)–C(2)
120.96(7).
1.9826(16) Å and Al(1)―C(2)=1.9923(16) Å in 3 are all similar to those
found in complex 2 and other aluminum complexes [16–18]. The six-
membered rings, Al(1)O(1)C(15)C(14)C(7)N(2), consisting of an Al
center coordinated by the oxygen atom O(1) and nitrogen atom N(2)
of the ketiminate ligand are nearly coplanar with mean deviation of
0.0840 Å for 2 and 0.0202 Å for 3. It is interesting to note that the
torsion angles between the six-membered chelating ring and the
aromatic ring attached to the carbon atom C(7) are 91.2° for 2
and 88.3° for 3, respectively.
and [L-LA]0/[BnOH]0, and the PDIs of PLLAs catalyzed by 2 range
from 1.13 to 1.23, which indicate that polymerizations proceed in
a “living” fashion. The 1H NMR spectrum of PLLA-25 (25 indicate
Table 1
Ring-opening polymerization of L-lactide (L-LA) catalyzed by complexes 1–4 in the
presence of BnOH.
On the basis of lactone polymerizations catalyzed with O,O-bidentate
dipyrazolate aluminum complex [16], dimethyl aluminum anilido-
oxazolinate [17] or anilido-pyrazolate complexes [18], mono-adduct
Al methyl complexes 1–4 have the potential to perform as catalysts
toward the ROP of L-lactide (L-LA) in the presence of benzyl alcohol
(BnOH). Similar conditions following our previous studies [2c] were
first utilized to examine the catalytic activities of L-LA polymerizations
using 1–4 as catalyst precursors under dry N2. Representative results
of L-LA polymerizations under varied conditions are listed in Table 1.
It was found that a great catalytic activity and a “controlled” character
were achieved with a Al:BnOH molar ratio of 1:2 in toluene at 110 °C.
Experimental results indicated that complexes 1–4 exhibited good
activities and is somewhat higher than the activity of [(MMPEP)
Al(μ-OBn)]2, which required 48 h to reach 87% conversion [19]. Among
them, complex 2 showed the greater “controlled” character than
other complexes. As a result, polymerizations catalyzed by 2 were
systematically investigated the “living” character (Table 1, entries
2, 5–7). The monomer conversion attained ≧91% in toluene within
14 h with [L-LA]0/[BnOH]0 ratio in a range 25–150. As depicted in
Fig. 4, a linear relationship was demonstrated between actual mo-
lecular weight Mn (Mn(GPC) value corrected by a factor of 0.58)
Entry Cat. [L-LA]0/[Cat.]0/
[BnOH]0
t
Conv. Mn
Mn
Mn
PDIe
(h) (%)a
(calcd.)b (obsd.)c (NMR)d
1f
1
2
3
4
2
2
2
2
2
2
100/1/2
100/1/2
100/1/2
100/1/2
50/1/2
200/1/2
300/1/2
200/1/10
400/1/20
1000/1/50
14 93
14 91
14 91
14 90
14 91
14 93
14 92
6800
6600
6700
6600
3400
13500
20000
2800
2800
2800
7700
7100
6000
6300
3500
15100
18800
2100
2300
2400
7400
6300
6200
6100
3200
11000
14400
2900
2900
2700
1.16
1.16
1.20
1.15
1.23
1.22
1.13
1.17
1.14
1.13
2f
3f
4f
5f
6f
7f
8g
9g
10h
9
8
92
93
12 92
a
Obtained from 1H NMR determination.
Calculated from the molecular weight of L-LA times [L-LA]0/[BnOH]0 times conver-
b
sion yield plus the molecular weight of BnOH.
c
Obtained from GPC analysis times 0.58 [20].
d
Obtained from 1H NMR analysis.
e
Obtained from GPC analysis.
0.1 mmol complexes, 10 mL toluene, 110 °C.
0.05 mmol complexes, 10 mL toluene, 110 °C.
0.05 mmol complexes, 20 mL toluene, 110 °C.
f
g
h

H.-J. Chuang et al. / Inorganic Chemistry Communications 18 (2012) 38–42
41
provides an efficient way by using only small amounts of catalyst to
synthesize PLLA with a narrow PDI, and the metal residues are eventu-
ally reduced in the isolated polymer.
In conclusion, three novel aluminum complexes bearing NNO-
tridentate ketiminate ligands have been synthesized and structurally
characterized by spectroscopic studies as well as X-ray single crystal
determinations. Experimental results indicate that Al complex 2 cata-
lyzes the ROP of L-LA in the presence of BnOH with the “living” and
“immortal” characters. The “immortal” manner of 2 has paved a
way to synthesize as much as 50-fold polymer chains of PLLA with a
narrow PDI in the presence of small amounts of catalyst.
Acknowledgments
Financial support from the National Science Council of the Republic
of China (NSC-98-2113-M-005-001-MY3) is gratefully appreciated.
Fig. 4. Polymerization of L-LA catalyzed by 2 in toluene at 110 οC. The relationship between
Mn(■)(PDI(●)) of polymer and the initial molar ratio [L-LA]0/[BnOH]0 is shown.
Appendix A. Supplementary data
Supplementary data to this article can be found online at doi:10.
1016/j.inoche.2012.01.004.
the [L-LA]0/[BnOH]0 ratio, Fig. 5) displays that the PLLA chain is
capped by one benzyl ester and one hydroxyl chain end with the
integration ratio ~5:1 between Ha and Hd. Based on the 1H NMR
spectrum of PLLA, it was believed that the [(L)AlMe2]/BnOH system
could result in situ formation of a metal-benzylalkoxy species, and
the insertion of an benzylalkoxy group into L-LA occurred to initiate
the polymerization. Complex 2 catalyzes the ROP of L-LA in not only
a “living” fashion but also an “immortal” manner. The “immortal”
character was further investigated using excess equiv. ratios of
BnOH (up to 50 equiv.) as the chain transfer agent (entry 8–10).
For instance, 50-fold BnOH can be added to [L−LA]0/[Al]0 =1000
for 12 h, producing a narrow PDI polymer with Mn only ~1/5 that
for the addition of [L−LA]0/[Al]0/[BnOH]0=200/1/2 (Table 1, entry
10 vs 6). It is worthy of note that complex 2 in the presence of excess
amounts of BnOH (>10 equiv.) showed the improved catalytic activity
(conv. ≧92%; t≦12 h) and the better controlled behavior (PDIb1.20) at
110 °C (Table 1, entries 8–10). The “immortal” character of complex 2
References
[1] (a) B.J. O'Keefe, M.A. Hillmyer, W.B. Tolman, Polymerization of lactide and related
cyclic esters by discrete metal complexes, J. Chem. Soc. Dalton Trans. 1 (2001)
2215–2224;
(b) A.C. Albertsson, I.K. Varma, Recent developments in ring opening polymeri-
zation of lactones for biomedical applications, Biomacromolecules 4 (2003)
1466–1486;
(c) O. Dechy-Cabaret, B. Martin-Vaca, D. Bourissou, Controlled ring-opening
polymerization of lactide and glycolide, Chem. Rev. 104 (2004) 6147–6176;
(d) J. Wu, T.-L. Yu, C.-T. Chen, C.-C. Lin, Recent developments in main group
metal complexes catalyzed/initiated polymerization of lactides and related
cyclic esters, Coord. Chem. Rev. 250 (2006) 602–626;
(e) C.A. Wheaton, P.G. Hayes, B.J. Ireland, Complexes of Mg, Ca and Zn as
homogeneous catalysts for lactide polymerization, Dalton Trans. (2009)
4832–4846;
(f) D.J. Darensbourg, O. Karroonnirun, S.J. Wilson, Ring-opening polymerization
of cyclic esters and trimethylene carbonate catalyzed by aluminum half-
salen complexes, Inorg. Chem. 50 (2011) 6775–6787.
Fig. 5. 1H NMR spectrum of PLLA-25 (Table 1, entry 4) in CDCl3.

42
H.-J. Chuang et al. / Inorganic Chemistry Communications 18 (2012) 38–42
[2] (a) W. Gao, D. Cui, X. Liu, Y. Zhang, Y. Mu, Rare-earth metal bis(alkyl)s supported
3.17 (2H, t, J=6.8 Hz, NCH2CH2), 2.68 (2H, t, J=6.8 Hz, NCH2CH2), 2.27 (6H,
s, N(CH3)2), 1.39 (3H, s, CH3C=N), -0.79 (6H, s, Al(CH3)2). 13C NMR (CDCl3,
by a quinolinyl anilido-imine ligand: synthesis and catalysis on living poly-
merization of ε-caprolactone, Organometallics 27 (2008) 5889–5893;
(b) W. Yao, Y. Mu, A. Gao, W. Gao, L. Ye, Bimetallic anilido-aldimine Al or Zn
complexes for efficient ring-opening polymerization of ε-caprolactone,
Dalton Trans. 1 (2008) 3199–3206;
ppm):
δ 173.71, 164.30, 161.81, 160.84, 148.55, 137.28, 132.21, 130.16,
128.76, 127.86, 121.00, 116.78, 116.57 (Ar and Py), 101.65 (C=C-NH), 55.21
(NHCH2CH2), 46.78 (NHCH2CH2), 45.52 (N(CH3)2), 14.97 (N=C-CH3), -8.56
(Al(CH3)2).
(c) Y.-H. Tsai, C.-H. Lin, C.-C. Lin, B.-T. Ko, Tridentate anilido-aldimine magne-
sium and zinc complexes as efficient catalysts for ring-opening polymeriza-
tion of ε-caprolactone and L-lactide, J. Polym. Sci. Part A: Polym. Chem. 47
(2009) 4927–4936;
(d) Y.-C. Liu, C.-H. Lin, B.-T. Ko, R.-M. Ho, Ring-opening polymerization of β-
butyrolactone catalyzed by efficient magnesium and zinc complexes derived
from tridentate anilido-aldimine ligand, J. Polym. Sci. Part A: Polym. Chem.
48 (2010) 5339–5347.
[11] [(OMeL)AlMe2] (3): Yield: 0.73 g (78 %). Anal. calc. for C24H30AlClN4O2: N, 11.95;
C, 61.47; H, 6.45. Found: N, 11.76; C, 61.50; H, 6.85%. 1H NMR (CDCl3, ppm): δ
7.94 (2H, d, J=8.8 Hz, ArH), 7.34 (2H, d, J=8.8 Hz, ArH), 7.13 (2H, d, J=8.4
Hz, ArH), 7.04 (2H, d, J=8.4 Hz, ArH), 3.88 (3H, s, ArOCH3), 3.21 (2H, t, J=6.8
Hz, NCH2CH2), 2.67 (2H, t, J=6.8 Hz, NCH2CH2), 2.27 (6H, s, N(CH3)2), 1.41
(3H, s, CH3C=N), -0.79 (6H, s, Al(CH3)2). 13C NMR (CDCl3, ppm): δ 174.82,
160.74, 160.10, 149.00, 137.36, 129.80, 128.65, 128.34, 127.06, 120.84, 114.62
(Arand Py), 101.76 (C=C-NH), 55.30 (NHCH2CH2), 55.04 (OCH3), 46.56 (NHCH2CH2),
44.84 (N(CH3)2),14.93 (N=C-CH3), -8.54 (Al(CH3)2).
[3] (a) C.-Y. Li, C.-Y. Tsai, C.-H. Lin, B.-T. Ko, Synthesis, structural characterization
and reactivity of aluminium complexes supported by benzotriazole phenox-
ide ligands: air-stable alumoxane as an efficient catalyst for ring-opening
polymerization of L-lactide, Dalton Trans. 1 (2011) 1880–1887;
[12] [(tBuL)AlMe2] (4): Yield: 0.80 g (81 %). Anal. calc. for C27H36AlClN4O: N, 11.32;
C, 65.51; H, 7.33. Found: N, 11.21; C, 66.25; H, 7.75%. 1H NMR(CDCl3, ppm):
δ7.95 (2H, d, J =8.8Hz, ArH), 7.54 (2H, d, J =8.4Hz ArH), 7.35 (2H, d, J =9.2Hz,
ArH), 7.13 (2H, d, J =8.6Hz, ArH), 3.21 (2H, t, J =13.6Hz, NCH2CH2), 2.67 (2H,
(b) Y.-E. Tai, C.-Y. Li, C.-H. Lin, Y.-C. Liu, B.-T. Ko, Y.-S. Sun, Efficient catalysts for
ring-opening polymerization of ε-caprolactone and β-butyrolactone: syn-
thesis and characterization of zinc complexes based on benzotriazole phen-
oxide ligands, J. Polym. Sci. Part A: Polym. Chem. 49 (2011) 4027–4036;
(c) J.-Y. Li, C.-Y. Li, W.-J. Tai, C.-H. Lin, B.-T. Ko, Synthesis and structural charac-
terization of zinc complexes supported by amino-benzotriazole phenoxide
ligands: efficient catalysts for ring-opening polymerization of ε-caprolactone
and β-butyrolactone, Inorg. Chem. Commun. 14 (2011) 1140–1144.
[4] H.-Y. Chen, H.-Y. Tang, C.-C. Lin, Ring-opening polymerization of lactides initiated
by zinc alkoxides derived from NNO-tridentate ligands, Macromolecules 39 (2006)
3745–3752;
t,
J =13.2Hz, NCH2CH2), 2.26 (6H, s, N(CH3)2), 1.37 (9H, s, CH3C=N),
1.33(3H, s, ArC(CH3)3), -0.79 (6H, s, Al(CH3)2). 13C NMR(CDCl3, ppm):
δ175.13, 160.78, 152.79, 149.00, 137.41, 133.29, 129.98, 128.72, 126.13, 125.28,
121.00 (Ar and Py), 101.65 (C=C-NH), 55.28 (NHCH2CH2), 46.68 (NHCH2CH2), 44.92
(N(CH3)2), 34.87 (C(CH3)3), 31.29(C(CH3)3), 14.58 (N=C-CH3), -8.58 (Al(CH3)2) ppm.
[13] Crystal data for complex 2: C23H27AlClFN4O, M=456.92, triclinic, space group
P-1, a=10.2603(4) Å, b=10.5288(3) Å, c=12.3331(5) Å, α=101.806(3)°
β=113.387(4)° γ=99.609(3)° V=1150.44(7) Å3, T=110(2)K, Z=2, Dc=1.319
Mg/m3, F(000)=480, 2θmax=58.50° 12583 reflections collected, 5427 unique
[R(int)=0.0279], no. of observed reflections 3575 (I >2σ(I)); R1=0.0450,
wR2=0.1250.
(b) W.-C. Hung, Y. Huang, C.-C. Lin, Efficient initiators for the ring-opening poly-
merization of L-lactide: synthesis and characterization of NNO-tridentate
Schiff-base zinc complexes, J. Polym. Sci. Part A: Polym. Chem. 46 (2008)
6466–6476.
[14] Crystal data for complex 3: C24H30AlClN4O2, M=468.95, triclinic, space group
P-1, a=9.6850(5) Å, b=10.9437(5) Å, c=12.1709(5) Å, α=107.185(4)°
β=91.980(4)° γ=103.589(4)° V=1190.37(10) Å3, T=110(2)K, Z=2,
Dc=1.308 Mg/m3, F(000)=496, 2θmax=58.88° 16126 reflections collected,
5741 unique [R(int)=0.0182], no. of observed reflections 4670 (I >2σ(I));
R1=0.0389, wR2=0.1321.
[15] R.-C. Yu, C.-H. Hung, J.-H. Huang, H.-Y. Lee, J.-T. Chen, Four- and five-coordinate
aluminum ketiminate complexes: synthesis, characterization, and ring-opening
polymerization, Inorg. Chem. 41 (2002) 6450–6455.
[16] C.-Y. Tsai, C.-Y. Li, C.-H. Lin, B.-H. Huang, B.-T. Ko, Reactions of 4-methylidene-
bis(1-phenyl-3-methylpyrazol-5-one) with trimethylaluminum: synthesis, struc-
ture and catalysis for the ring-opening polymerization of ε-caprolactone, Inorg.
Chem. Comm. 14 (2011) 271–275.
[5] H.-Y. Tang, H.-Y. Chen, J.-H. Huang, C.-C. Lin, Synthesis and structural characteri-
zation of magnesium ketiminate complexes: efficient initiators for the ring-
opening polymerization of L-lactide, Macromolecules 40 (2007) 8855–8860.
[6] Y. Huang, W.-C. Hung, M.-Y. Liao, T.-E. Tsai, Y.-L. Peng, C.-C. Lin, Ring-opening
polymerization of lactides initiated by magnesium and zinc complexes based
on NNO-tridentate ketiminate ligands: activity and stereoselectivity studies, J.
Polym. Sci. Part A: Polym. Chem. 47 (2009) 318–2329.
[7] H.-S. Lee, S.-Y. Ahn, H.-S. Huh, Y. Ha, Introduction of new ancillary ligands to the
iridium complexes having 2,3-diphenylquinolinato ligands for OLED, J. Ogano-
met. Chem. 694 (2009) 3325–3330.
[8] Crystal data for OMeL-H: C22H25ClN4O2, M=412.91, Monoclinic, space group
C2/c, a=21.6291(4) Å, b=16.5309(3) Å, c=11.8297(2) Å, α=90.00°
β=101.407(2)° γ=90.00° V=4146.14(13) Å3, T=110(2)K, Z=8, Dc=1.323
Mg/m3, F(000)=1744, 2θmax=58.68° 18209 reflections collected, 5096 unique
[R(int)=0.0241], no. of observed reflections 3853 (I >2σ(I)); R1=0.0524,
wR2=0.1536.
[17] C.-T. Chen, H.-J. Weng, M.-T. Chen, C.-A. Huang, K.-F. Peng, Synthesis, characteri-
zation, and catalytic application of aluminum anilido-oxazolinate complexes, Eur.
J. Inorg. Chem. (2009) 2129–2135.
[18] K.-F. Peng, C.-T. Chen, Synthesis and catalytic application of aluminium anilido-
pyrazolate complexes, Dalton Trans. (2009) 9800–9806.
[19] Y.-C. Liu, B.-T. Ko, C.-C. Lin, A highly efficient catalyst for the “Living” and “Immor-
tal” polymerization of ε-caprolactone and L-lactide, Macromolecules 34 (2001)
6196–6201.
[20] The Mn (GPC) value is multiplied by a factor of 0.58, giving the actual Mn of the
polylactide, see: (a). J. Baran, A. Duda, A. Kowalski, R. Szymanski, S. Penczek,
Intermolecular chain transfer to polymer with chain scission. General treatment
and determination of kp/ktr in L, L-lactide polymerization, Macromol. Rapid Com-
mun. 18 (1997) 325–333;
[9] [(HL)AlMe2] (1): Yield: 0.67 g (76 %). Anal. calc. for C23H28AlClN4O: N, 12.76; C,
62.94; H, 6.43. Found: N, 12.30; C, 64.77; H, 6.99%. 1H NMR (CDCl3, ppm): δ 7.96
(2H, d, J=8.8 Hz, ArH), 7.53 (3H, m, ArH), 7.35 (2H, d, J=8.8 Hz, ArH), 7.22 (2H,
d, J=6.4 Hz, ArH), 3.18 (2H, t, J=6.8 Hz, NCH2CH2), 2.67 (2H, t, J=6.8 Hz,
NCH2CH2), 2.26 (6H, s, N(CH3)2), 1.35 (3H, s, CH3C=N), -0.78 (6H, s, Al(CH3)2).
13C NMR (CDCl3, ppm): δ 174.69, 160.86, 148.83, 137.38, 136.28, 129.38, 129.04,
128.74, 128.22, 125.77, 121.00 (Ar and Py), 101.50 (C=C-NH), 55.28 (NHCH2CH2),
44.93 (NHCH2CH2), 46.72 (N(CH3)2), 14.72 (N=C-CH3), -8.58 (Al(CH3)2).
[10] [(FL)AlMe2] (2): Yield: 0.73 g (80 %). Anal. calc. for C23H27AlClFN4O: N, 12.66;
C, 60.46; H, 5.96. Found: N, 12.22; C, 60.35; H, 5.53%. 1H NMR (CDCl3, ppm): δ
7.94 (2H, d, J=8.8 Hz, ArH), 7.36 (2H, d, J=8.8 Hz, ArH), 7.25 (4H, m, ArH),
(b) T. Biela, A. Duda, S. Penczek, Control of Mn, Mw/Mn, end-groups, and kinetics
in living polymerization of cyclic esters, Macromol. Symp. 183 (2002) 1–10.