Aluminium complexes containing pyrazolyl-phenolate ligands as catalysts for ring opening polymerization of ε-caprolactone

Article abstract of DOI:10.1016/j.jorganchem.2012.12.003

A series of pyrazolyl-phenolate ligand precursors has been described. Reactions of five pyrazolyl-phenolate ligand precursors, HOPh ^MePz^Me, HOPh^MePz^tBu, HOPh^MePz^Ph, HOPh^MePz

Full text of DOI:10.1016/j.jorganchem.2012.12.003

Journal of Organometallic Chemistry 725 (2013) 15e21
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Aluminium complexes containing pyrazolylephenolate ligands as
catalysts for ring opening polymerization of ε-caprolactone
*
Tzu-Lun Huang, Chi-Tien Chen
Department of Chemistry, National Chung Hsing University, 250 Kuo Kuang Rd., Taichung 402, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of pyrazolylephenolate ligand precursors has been described. Reactions of five pyrazolyl-
phenolate ligand precursors, HOPhMePzMe, HOPhMePztBu, HOPhMePzPh, HOPhMePzF-Ph or HOPhHPztBu
,
)
Received 29 August 2012
Received in revised form
28 November 2012
with one molar equivalent of AlMe3 in THF gave the aluminium dimethyl complexes, Me2Al(OPhR1PzR2
[R1 ¼ methyl, R2 ¼ methyl, Me2Al(OPhMePzMe) (1); R1 ¼ methyl, R2 ¼ tert-butyl, Me2Al(OPhMePztBu) (2);
Accepted 4 December 2012
R1 ¼ methyl, R2 ¼ phenyl, Me2Al(OPhMePzPh) (3); R1 ¼ methyl, R2 ¼ 4-fluorophenyl, Me2Al(OPhMePzF-Ph
)
(4); R1 ¼ H, R2 ¼ tert-butyl, Me2Al(OPhHPztBu) (5)], respectively. The molecular structures are reported
for compounds 3 and 5. Their catalytic activities towards the ring opening polymerization reaction of
ε-caprolactone in the presence of benzyl alcohol are also under investigation.
Ó 2012 Elsevier B.V. All rights reserved.
Keywords:
Aluminium
Pyrazolylephenolate ligand
Ring opening polymerization
ε-Caprolactone
1. Introduction
cyclic esters recently [47e52]. These achievements encouraged us
to prepare metal complexes bearing ligands with combination of
Environmentally friendly polyesters such as poly(caprolactone)
and polylactide as well as their co-polymers have been leading
candidates in biomedical and pharmaceutical industries due to
their biocompatible and biodegradable properties [1]. Up to date,
a diversity of main group and transition metal complexes worked
as initiators/catalysts for ring opening polymerization to produce
well-controlled polymers has been reported and reviewed [2e10].
In those reports, introduction of suitable auxiliary ligands could
prevent polymers from trans-esterifications which always occur as
side reactions during the ring opening polymerization. Aluminium-
catalyzed polymerization of cyclic esters demonstrated by using
complexes containing ligands with N,O-coordination modes has
been a focus of interest, mainly due to the great success of those
complexes bearing salen or salan [11e24], imino-phenolate [25e
37] or ketiminate [38e43] ligands in ring opening polymeriza-
tion. Some of them exhibit significant advances in stereo-controlled
polymerization. Pyrazole-containing metal complexes seem to be
another attractive focus since Chisholm reported tris(pyrazolyl)
hydroborate metal complexes exhibited efficient activities and
controlled characters [44e46]. Several aluminium complexes
bearing ligands with pendant pyrazolyl functionalities have been
reported and applied in catalyzing ring opening polymerization of
chelating systems with pyrazolyl and phenolate features for
examination of their catalytic activities in ring opening polymeri-
zation. In this paper, several phenolate ligand precursors bearing
pyrazolyl functionalities and their aluminium dimethyl complexes
have been synthesized. Their catalytic activities in ring opening
polymerization are also investigated.
2. Results and discussion
2.1. Syntheses and characterization of aluminium complexes
Ligand precursor, HOPhMePzMe, was prepared by methylation of
3-(2-hydroxy-5-methyl-phenyl)(5-phenyl)pyrazole using NaH and
methyl iodide in tetrahydrofuran. Preparation of ligand precursors,
HOPhMePztBu, HOPhMePzPh or HOPhMePzF-Ph, was straightforward
via the condensation reaction of related diketone with tert-butyl
hydrazine (for HOPhMePztBu), phenylhydrazine (for HOPhMePzPh
)
or para-flurophenylhydrazine (for HOPhMePzF-Ph). Ligand
precursor, HOPhHPztBu, was prepared from condensation of related
diketone with tert-butyl hydrazine, as shown in (Scheme 1). All of
the compounds were characterized by NMR spectroscopy as well as
elemental analyses.
Complexes 1e5 were synthesized by alkane elimination reac-
tions in moderate to high yields. Treatment of ligand precursors,
HOPhMePzMe
, , ,
HOPhMePztBu HOPhMePzPh HOPhMePzF-Ph or
* Corresponding author. Tel.: þ886 4 22840411; fax: þ886 4 22862547.
E-mail address: ctchen@dragon.nchu.edu.tw (C.-T. Chen).
HOPhHPztBu, with one equivalent of AlMe3 in tetrahydrofuran
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.12.003

16
T.-L. Huang, C.-T. Chen / Journal of Organometallic Chemistry 725 (2013) 15e21
Scheme 1. Synthesis of aluminium pyrazolylephenolate complexes 1e5.
ꢀ
yielded the desired aluminium dimethyl complexes 1e5.
Complexes 1e5 were all characterized by NMR spectroscopy and
elemental analyses. The disappearance of the OeH signal of the
ligand precursors 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). Singlets corresponding to two
methyl groups on metal centre, methyl or tert-butyl groups on
nitrogen atom of pyrazolyl group, proton on pyrazolyl ring, or
methyl on phenyl ring might result from the symmetric environ-
ment around the metal centre.
groups. The bond distances of AleNpyrazole 1.9697(12) A for 3;
ꢀ
ꢀ
2.0049(13) A for 5 are in the normal range 1.890(2)e2.037(18) A
found in aluminium pyrazolyl-containing complexes [47,48,50e
ꢀ
55]. The bond distances of AleOphenoxide 1.7737(11) A for 3;
ꢀ
1.7814(12) A for 5 are slightly longer than those found in the
literature 1.748(3)e1.7673(15) A [47,51]. The bond distances of Ale
for 3; 1.9521(17) and
1.9637(16) A for 5 are between those found in the literature
ꢀ
ꢀ
Cmethyl 1.9584(16) and 1.9595(15)
A
ꢀ
ꢀ
1.933(4)e1.98(1) A [47,48,50e55].
Suitable crystals for structural determination of 3 or 5 were
obtained from concentrated hexane solutions. Their molecular
structures are depicted in Figs. 1 and 2 The structures of 3 or 5
reveal that the aluminium centres adopt a distorted tetrahedral
geometry with the metal centres chelated by one nitrogen donor
atom of pyrazolyl ring, one oxygen donor atom of phenolate group
and two methyl groups. Basically, compounds 3 and 5 are quite
similar with different substituents on the phenolate and pyrazolyl
2.2. Polymerization studies
Due to the successful application of aluminium complexes
bearing N,O-coordination modes ligands in the ring opening poly-
merization (ROP) [11e43,47e52], the structurally-related
aluminium complexes 1e5 were expected to work as catalysts
ꢀ
ꢀ
ꢀ
ꢀ
Fig. 1. Molecular structure of 3. Select bond lengths (A) and bond angles ( ): AleN(1)
1.9697(12), AleO 1.7737(11), AleC(23) 1.9584(16), AleC(24) 1.9595(15), N(1)eN(2)
1.3691(16), OeC(1) 1.3328(17); OeAleC(23) 111.17(7), C(23)eAleC(24) 117.79(7), Oe
AleN(1) 91.96(5), C(23)eAleN(1) 110.95(6), C(24)eAleN(1) 108.83(6), C(1)eOeAl
129.64(9). Hydrogen atoms on carbon atoms omitted for clarity.
Fig. 2. Molecular structure of 5. Select bond lengths (A) and bond angles ( ): AleN(1)
2.0049(13), AleO 1.7814(12), AleC(20) 1.9521(17), AleC(21) 1.9637(16), N(1)eN(2)
1.3778(17), OeC(1) 1.3397(18); OeAleC(20) 105.03(7), C(20)eAleC(21) 122.46(7), Oe
AleN(1) 94.66(5), C(20)eAleN(1) 115.12(7), C(21)eAleN(1) 108.12(7), C(1)eOeAl
121.62(10). Hydrogen atoms on carbon atoms omitted for clarity.

T.-L. Huang, C.-T. Chen / Journal of Organometallic Chemistry 725 (2013) 15e21
17
Table 1
Polymerization of ε-Caprolactone using compounds 1e5 as catalysts in toluene if not otherwise stated.a
Mn (obsd)b
Mn (calcd)c
Conv. (%)d
Yield (%)e
Mw/Mn
b
Entry
Catalyst
[M]0:[Al]0:[BnOH]
T (ꢀC)
t (min)
1f
2
2
2
2
2
1
3
4
5
2
2
2
2
2
2
2
100:1:2
100:1:2
100:1:2
100:1:2
100:1:2
100:1:2
100:1:2
100:1:2
200:1:2
300:1:2
400:1:2
200:1:2
300:1:2
400:1:2
200:1:4
25
25
50
50
50
50
50
50
50
50
50
25
25
25
25
60
60
20
20
60
60
60
20
40
60
80
120
420
540
240
e
e
27
93
49
95
95
91
91
97
96
97
97
90
97
93
93
e
e
5000
e
5400
e
73
e
1.10
e
3g
4
6200
4800
4600
4500
7100
11,500
15,500
18,500
11,100
16,300
18,700
5100
5500
5500
5300
5300
5500
11,100
16,700
22,300
10,400
16,700
21,300
5400
79
37
70
73
81
84
93
96
91
98
90
90
1.11
1.20
1.21
1.17
1.11
1.21
1.27
1.30
1.14
1.16
1.21
1.07
5
6
7
8
9
10
11
12
13
14
15
a
In 15 mL.
b
c
d
e
f
Obtained from GPC analysis times 0.56.
Calculated from [M(monomer) ꢁ [M]0/[Al]0 ꢁ conversion yield/([BnOH]eq)] þ M(BnOH).
Obtained from 1H NMR analysis.
Isolated yield.
In 15 mL CH2Cl2.
In 15 mL THF.
g
towards the ROP of cyclic esters. The ring opening polymerization
of ε-caprolactone employing 1e5 as catalysts in the presence of
benzyl alcohol has been systematically investigated under a dry
nitrogen atmosphere. Representative results are shown in Table 1.
Experimental conditions were found to be 15 mL toluene at 50 ꢀC in
the presence of benzyl alcohol after several trials on running the
polymerization with dichloromethane, tetrahydrofuran or toluene
at 25 ꢀC or 50 ꢀC using 2 as pre-catalyst (entries 1e4). The opti-
mized conditions were applied to examine the catalytic activities of
1, 3, 4 and 5 (entries 5e8). Catalytic results show compounds 2 and
5 can reach similar activities within the same period (entries 4 and
8), whereas compounds 1, 3 and 4 exhibit poor catalytic activities
with time up to 1 h. The catalytic results exhibited by compounds 1
and 2 show the steric effect caused by tert-butyl group on the
nitrogen atom of the pyrazolyl ring might enhance the catalytic
activity of the ROP of ε-caprolactone. Poor conversions demon-
strated by 3 and 4 might result from the presence of phenyl rings
interfering with the coordination of monomer to the aluminium
centre during ROP. Based on those results, electron-donating
groups on the nitrogen atom of the pyrazolyl ring could enhance
the catalytic activities; however, the electron-withdrawing phenyl
substituents in 3 and 4 showed diminished ROP activity resulting
from steric and electronic effects. No significant differences of
catalytic activities were observed upon changing the substituents
on phenolate-part (entries 2 and 8). The linear relationship
between the number-average molecular weight (Mn) and the
monomer-to-initiator ratio ([M]0/[I]0) exhibited by 2 at different
temperatures implies the “living” character of the polymerization
process. Representative results are demonstrated in Fig. 3 (at 50 ꢀC;
entries 4, 9e11) and Fig. 4 (at 25 ꢀC; entries 2, 12e14). The
“immortal” character was examined using four equiv. ratios (on
[M]0/[Al]0) of benzyl alcohol as the chain transfer agent (entry 15).
The Mn of the polymer created from this polymerization reaction
became half of those found in the reactions with the addition of two
equiv. ratios of benzyl alcohol (entries 9 and 12). The end group
analysis is demonstrated by the 1H NMR spectrum of the polymer
produced from ε-caprolactone and 2 ([M]0/[BnOH] ¼ 50; Table 1,
entry 2), as shown in Fig. 5. Peaks are assignable to the corre-
sponding protons in the proposed structure, indicating the ROP
might be initiated with metal benzyl oxide complex first, followed
by the ring cleavage of the acyleoxygen bond to form a metal
alkoxide intermediate, which further reacts with excess lactones to
yield polyesters [30].
Fig. 3. Polymerization of ε-caprolactone initiated by 2 in toluene at 50 ꢀC.
Fig. 4. Polymerization of ε-caprolactone initiated by 2 in toluene at 25 ꢀC.

18
T.-L. Huang, C.-T. Chen / Journal of Organometallic Chemistry 725 (2013) 15e21
1
Fig. 5. H NMR spectrum of PCL-50 initiated by 2 in toluene at 25 ꢀC (Table 1, entry 2).
3. Conclusion
peak and reported as parts per million relative to tetramethylsilane.
Elemental analyses were performed using an Elementar Vario ELIV
instrument. 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. High-resolution mass
spectra (EI-HRMS) were recorded with a Finnigan/Thermo Quest
MAT 95XL spectrometer.
Methyl iodide (Showa), NaH (Fluka, 55e65% gas-volumetric),
hydrazine monohydrate (Alfa), tert-butyl hydrazine hydrochlo-
ride (TCI), phenylhydrazine (Alfa), 4-flurophenylhydrazine hydro-
chloride (Acros), 1-(2-hydroxy-5-methylphenyl)-3-phenyl-1,3-
propanedione (Acros), 1-(2-hydroxyphenyl)-3-phenyl-1,3-prop-
anedione (Alfa) and AlMe3 (Aldrich, 2.0 M in toluene) were used
as supplied. 4-Methyl-2-(5-phenyl-1H-pyrazol-3-yl)phenol [56],
3-(2-hydroxy-5-methyl-phenyl)(5-phenyl)(1-methyl)pyrazole [57]
were prepared by the literature’s method. Benzyl alcohol was
dried over magnesium sulphate and distilled before use. NEt3 was
dried with CaH2 and distilled before use. ε-Caprolactone was dried
over magnesium sulphate and distilled under reduced pressure.
In conclusion, a family of aluminium dimethyl complexes con-
taining pyrazolylephenolate ligands has been prepared and fully
characterized. They all show catalytic activities in the ring opening
polymerization of ε-caprolactone in the presence of benzyl alcohol.
Under optimized conditions, compound 2 demonstrates efficient
activities for the controlled polymerization of ε-caprolactone with
both living and immortal characters. According to the catalytic
results, bulkier aliphatic substituent on the nitrogen atom of pyr-
azolyl ring seems suitable for the enhancement of catalytic activi-
ties. Poor activities demonstrated by complexes bearing ligands
with phenyl groups on the nitrogen atom of pyrazolyl ring might
result from the electronic effect of aromaticity leading to affect the
Lewis acidity of metal centre.
4. Experimental
4.1. General
All manipulations were carried out under an atmosphere of
dinitrogen using standard Schlenk-line or dry box techniques.
Solvents were refluxed over the appropriate drying agent and
distilled prior to use. Deuterated solvents were dried over molec-
ular sieves. 1H and 13C{1H} NMR spectra were recorded either on
Varian Mercury-400 (400 MHz) or Varian Inova-600 (600 MHz)
spectrometers in chloroform-d at ambient temperature unless
stated otherwise and referenced internally to the residual solvent
4.2. Synthesis of HOPhMePzMe
A solution of HOPhMePz (1.45 g, 5.8 mmol) in 25 mL dry THF was
added slowly with NaH (0.46 g of 55e65%, 11.6 mmol) at 0 ꢀC. The
reaction mixture was warmed up to room temperature and stirred
for a further 3 h until hydrogen evolution ceased. To this solution,

T.-L. Huang, C.-T. Chen / Journal of Organometallic Chemistry 725 (2013) 15e21
19
0.36 mL of methyl iodide (5.8 mmol) was added dropwise and
resulting mixture was stirred for 12 h at room temperature. The
solvent was removed in vacuum and 25 mL of a 1 M solution of
NaHCO3 were added to the residue. The aqueous solution was
extracted three times with 20 mL diethylether, the organic layer
was dried over Na2SO4 and filtered. All volatiles were removed
under reduced pressure to yield a white solid. The crude product
was purified by flash column chromatography on silica gel (ethyl
acetate:hexane ¼ 1:5) afforded a white solid (0.69 g, 45%). Anal.
Calc. for C17H16N2O: C, 77.25; H, 6.10; N, 10.60. Found: C, 77.25; H,
purified by flash column chromatography on silica gel (ethyl
acetate:hexane ¼ 1:5) afforded a brown solid (0.92 g, 45%). Anal.
Calc. for C22H17FN2O: C, 76.73; H, 4.98; N, 8.13. Found: C, 76.73; H,
5.18; N, 7.86. 1H NMR (400 MHz, CDCl3):
d (ppm) 10.54 (s, 1H, OH),
3
7.43 (d, JHH ¼ 1.6 Hz, 1H, ArH), 7.26e7.37 (m, 7H, ArH), 7.01e7.07
3
(m, 3H, ArH), 6.95 (d, JHH ¼ 1.6 Hz, 1H, ArH), 6.87 (s, 1H, PzH),
2.34 (s, 3H, ArCH3). 13C NMR (100 MHz, CDCl3):
d (ppm) 153.8,152.0,
143.9, 135.5, 129.6, 128.8, 128.2, 115.6 (C), 130.3, 128.8, 128.6, 126.7,
126.6, 116.9, 116.0, 115.7, 104.5 (ArCH or PzCH), 20.5 (ArCH3).
6.47; N, 10.23. 1H NMR (400 MHz, CDCl3):
d
(ppm) 10.69 (s, 1H, OH),
4.6. Synthesis of HOPhHPztBu
3
7.33e7.50 (br, 6H, ArH), 7.02 (d, JHH ¼ 8 Hz, 1H, ArH), 6.93 (d,
3JHH ¼ 8.4 Hz, 1H, ArH), 6.65 (s, 1H, PzH), 3.90 (s, 3H, PzCH3), 2.32 (s,
To
a flask containing benzoyl(2-hydroxybenzoyl) methane
3H, ArCH3). 13C NMR (100 MHz, CDCl3):
d
(ppm) 153.6, 150.2, 144.4,
(1.44 g, 6.0 mmol), tert-butyl hydrazine hydrochloride (0.90 g,
7.2 mmol) and triethylamine (1.25 mL, 9.0 mmol), 40 mL methanol
was added. The reaction mixture was refluxed for 12 h and cooled
to room temperature. All volatiles were removed under reduced
pressure and the residue was extracted with 20 mL toluene to
afford brown solid. The crude product was purified by flash column
chromatography on silica gel (ethyl acetate:hexane ¼ 1:10) affor-
ded a yellow solid (1.00 g, 57%). Anal. Calc. for C19H20N2O: C, 78.05;
129.7, 128.0, 116.0 (C), 129.6, 128.7,128.63, 128.60, 126.4, 116.6,102.2
(ArCH or PzCH), 37.2 (PzCH3), 20.4 (ArCH3).
4.3. Synthesis of HOPhMePztBu
To a flask containing 1-(2-hydroxy-5-methylphenyl)-3-phenyl-
1,3-propanedione (1.52 g, 6.0 mmol), tert-butyl hydrazine hydro-
chloride (0.90 g, 7.2 mmol) and triethylamine (1.25 mL, 9.0 mmol),
30 mL methanol was added. The reaction mixture was refluxed for
12 h and cooled to room temperature. All volatiles were removed
under reduced pressure and the residue was extracted with 20 mL
toluene to afford brown solid. The crude product was purified by
H, 6.89; N, 9.58. Found: C, 78.30; H, 7.08; N, 9.35. 1H NMR (400 MHz,
3
CDCl3):
d
(ppm) 11.23 (s, 1H, OH), 7.52 (dd, J1HH ¼ 7.8 Hz,
3J2HH ¼ 2 Hz, 1H, ArH), 7.38e7.47 (m, 5H, ArH), 7.19 (t, 3JHH ¼ 7.6 Hz,
1H, ArH), 7.02 (dd, 3J1HH ¼ 8.4 Hz, 3J2HH ¼ 1.2 Hz, 1H, ArH), 6.88 (t,
3JHH ¼ 7.6 Hz, 1H, ArH), 6.53 (s, 1H, PzH), 1.50 (s, 9H, PzC(CH3)3). 13
C
flash
column
chromatography
on
silica
gel
(ethyl
NMR (100 MHz, CDCl3): d (ppm) 155.9, 148.0, 143.8, 143.8, 133.1,
acetate:hexane ¼ 1:10) afforded a brown solid (0.82 g, 45%). Anal.
116.6 (C), 133.1, 130.3, 128.7, 127.9, 125.9, 119.1, 116.7, 105.8 (ArCH or
PzCH), 61.5 (PzC(CH3)3), 30.8 (PzC(CH3)3).
Calc. for C20H22N2O: C, 78.40; H, 7.24; N, 9.14. Found: C, 78.22; H,
7.44; N, 8.99. 1H NMR (400 MHz, CDCl3):
d (ppm) 11.03 (s, 1H, OH),
3
7.37e7.46 (m, 5H, ArH), 7.31 (d, JHH ¼ 0.8 Hz, 1H, ArH), 7.00 (dd,
4.7. Synthesis of (Me2AlOPhMePzMe) (1)
3
3
3J1HH ¼ 8.4 Hz, J2HH ¼ 2 Hz, 1H, ArH), 6.92 (d, JHH ¼ 8.4 Hz, 1H,
ArH), 6.53 (s, 1H, PzH), 2.29 (s, 3H, ArCH3), 1.50 (s, 9H, PzC(CH3)3).
To a flask containing HOPhMePzMe (0.36 g, 1.3 mmol) and 25 mL
13C NMR (100 MHz, CDCl3):
d
(ppm) 153.7, 148.1, 143.8, 133.2, 128.0,
THF, 0.66 mL AlMe3 (2.0 M in toluene, 1.32 mmol) was added at
116.2 (C), 130.3, 129.5, 128.7, 127.9, 126.3, 116.5, 105.8 (ArCH or
PzCH), 61.5 (PzC(CH3)3), 30.8 (PzC(CH3)3), 20.5 (ArCH3).
0
ꢀC. The reaction mixture was allowed to warm to room temper-
ature and reacted overnight. After 12 h of stirring, the volatiles were
removed under reduced pressure. The residue was washed with
15 mL hexane to afford white solid (0.25 g, 57%). Suitable crystals of
1 for structural determination were recrystallized from concen-
trated hexane solution. Anal. Calc. for C19H21N2OAl: C, 71.23; H,
6.61; N, 8.74. Found: C, 71.03; H, 6.77; N, 8.70. 1H NMR (600 MHz,
4.4. Synthesis of HOPhMePzPh
To a flask containing 1-(2-hydroxy-5-methylphenyl)-3-phenyl-
1,3-propanedione (1.52 g, 6.0 mmol) and phenylhydrazine
(0.708 mL, 7.2 mmol), 40 mL methanol was added. The reaction
mixture was refluxed for 12 h and cooled to room temperature. The
formed precipitates were successively collected and dried under
reduced pressure to yield pink solid. The crude product was puri-
fied by flash column chromatography on silica gel (ethyl
acetate:hexane ¼ 1:15) afforded a pink solid (1.50 g, 71%). Anal.
Calc. for C22H18N2O: C, 80.96; H, 5.56; N, 8.58. Found: C, 81.19; H,
CDCl3):
d (ppm) 7.54 (m, 3H, ArH), 7.48 (m, 2H, ArH), 7.36 (d,
3JHH ¼ 2.4 Hz, 1H, ArH), 7.06 (dd, 3J1HH ¼ 8.1 Hz, 3J2HH ¼ 2.4 Hz, 1H,
ArH), 6.86 (d, 3JHH ¼ 8.4 Hz, 1H, ArH), 6.75 (s, 1H, PzH), 3.94 (s, 3H,
PzCH3), 2.28 (s, 3H, ArCH3), -0.65 (s, 6H, AlCH3). 13C NMR (150 MHz,
CDCl3):
d (ppm) 156.3, 151.0, 147.5, 128.7, 126.2, 115.2 (C), 132.5,
130.2, 129.1, 129.0, 127.0, 121.1, 103.1 (ArCH or PzCH), 36.1 (PzCH3),
20.4 (ArCH3), ꢂ8.7 (AlCH3).
5.89; N, 8.35. 1H NMR (400 MHz, CDCl3):
d (ppm) 10.66 (s, 1H, OH),
7.44 (dd, 3J1HH ¼ 1.6 Hz, 3J2HH ¼ 0.4 Hz, 1H, ArH), 7.27e7.38 (m, 10H,
4.8. Synthesis of (Me2AlOPhMePztBu) (2)
3
3
ArH), 7.06 (dd, J1HH ¼ 8 Hz, J2HH ¼ 2.4 Hz, 1H, ArH), 6.95 (d,
3JHH ¼ 8.4 Hz, 1H, ArH), 6.88 (s, 1H, PzH), 2.34 (s, 3H, ArCH3). 13C
To a flask containing HOPhMePztBu (0.46 g, 1.5 mmol) and 25 mL
THF, 0.75 mL AlMe3 (2.0 M in toluene, 1.5 mmol) was added at 0 ꢀC.
The reaction mixture was allowed to warm to room temperature
and reacted overnight. After 12 h of stirring, the volatiles were
removed under reduced pressure. The residue was washed with
15 mL hexane to afford white solid (0.35 g, 73%). Anal. Calc. for
C22H27AlN2O: C, 72.90; H, 7.51; N, 7.73. Found: C, 73.33; H, 7.41; N,
NMR (100 MHz, CDCl3):
d (ppm) 153.9, 151.9, 143.8, 139.3, 129.8,
128.2, 115.7 (C), 130.2, 128.89, 128.77, 128.7, 128.5, 127.6, 126.7,
124.8, 116.9, 104.6 (ArCH or PzCH), 20.57 (ArCH3).
4.5. Synthesis of HOPhMePzF-Ph
To a flask containing 1-(2-hydroxy-5-methylphenyl)-3-phenyl-
1,3-propanedione (1.52 g, 6.0 mmol), 4-fluorophenylhydrazine
hydrochloride (1.17 g, 7.2 mmol) and triethylamine (1.25 mL,
9.0 mmol), 40 mL methanol was added. The reaction mixture was
refluxed for 12 h and cooled to room temperature. All volatiles were
removed under reduced pressure and the residue was washed with
20 mL toluene to afford brown solid. The crude product was
7.32. 1H NMR (600 MHz, CDCl3):
7.40 (m, 2H, ArH), 7.08 (d, JHH ¼ 8.4 Hz, 1H, ArH), 6.88 (d,
3JHH ¼ 7.8 Hz, 1H, ArH), 6.56 (s, 1H, PzH), 2.27 (s, 3H, ArCH3), 1.62 (s,
9H, PzC(CH3)3), -0.59 (s, 6H, AlCH3). 13C NMR (150 MHz, CDCl3):
d
(ppm) 7.45e7.49 (m, 4H, ArH),
3
d
(ppm) 156.1, 152.2, 148.7, 132.5, 129.5, 126.5, 116.7 (C), 132.6, 129.4,
128.4, 127.7, 120.4, 109.0 (ArCH or PzCH), 63.9 (PzC(CH3)3), 32.3,
(PzC(CH3)3), 20.5 (ArCH3), ꢂ7.3 (AlCH3).

20
T.-L. Huang, C.-T. Chen / Journal of Organometallic Chemistry 725 (2013) 15e21
4.9. Synthesis of (Me2AlOPhMePzPh) (3)
Table 2
Summary of crystal data for compounds 3 and 5.
To a flask containing HOPhMePzPh (0.37 g, 1.1 mmol) and 25 mL
THF, 0.57 mL AlMe3 (2.0 M in toluene, 1.1 mmol) was added at 0 ꢀC.
The reaction mixture was allowed to warm to room temperature
and reacted overnight. After 12 h of stirring, the volatiles were
removed under reduced pressure. The residue was washed with
15 mL hexane to afford white solid (0.32 g, 74%). Anal. Calc. for
C24H23N2OAl: C, 75.37; H, 6.06; N, 7.33. Found: C, 74.96; H, 6.35; N,
3
5
Empirical formula
Formula mass
T, K
AlC24H23N2O
382.42
100(2)
Monoclinic
P21/n
10.7074(3)
9.0691(2)
21.3827(5)
90
95.887(2)
90
2065.45(9)
4
1.230
0.114
9303
253
0.0403
0.1350
1.006
AlC21H25N2O
348.41
100(2)
Monoclinic
C2/c
22.8072(7)
9.2707(3)
18.2968(6)
90
96.984(3)
90
3839.9(2)
8
1.205
0.116
9954
226
0.0425
0.1177
1.001
Crystal system
Space group
ꢀ
a, [A]
ꢀ
b, [A]
6.93. 1H NMR (600 MHz, CDCl3):
d
(ppm) 7.51 (t, 3JHH ¼ 7.2 Hz, 1H,
ꢀ
c, [A]
a
b
g
[ꢀ]
[ꢀ]
[ꢀ]
ArH), 7.46 (t, 3JHH ¼ 7.8 Hz, 2H, ArH), 7.42 (s, 1H, ArH), 7.36 (m, 3H,
ArH), 7.31 (t, 3JHH ¼ 7.2 Hz, 2H, ArH), 7.25 (d, 3JHH ¼ 7.8 Hz, 2H, ArH),
7.09 (dd, 3J1HH ¼ 8.4 Hz, 3J2HH ¼ 1.8 Hz, 1H, ArH), 6.99 (s, 1H, PzH),
3
ꢀ
V, [A ]
3
Z
6.87 (d, JHH ¼ 8.4 Hz, 1H, ArH), 2.32 (s, 3H, ArCH3), ꢂ1.07 (s, 6H,
rcalc, [Mg/m3]
AlCH3). 13C NMR (150 MHz, CDCl3):
d (ppm) 156.8, 152.2, 147.3,
m
(Mo Ka), [mmꢂ1
]
132.9, 127.6, 126.2, 115.2 (C), 136.4, 130.7, 129.7, 129.6, 128.7, 128.4,
127.2, 121.2, 103.7 (ArCH or PzCH), 20.5 (ArCH3), ꢂ9.3 (AlCH3).
Reflections collected
No. of parameters
a
R1
a
wR2
4.10. Synthesis of (Me2AlOPhMePzF-Ph) (4)
GoFb
a
R1 ¼ [SjF0j ꢂ jFcj]/SjF0j]; wR2 ¼ [Sw(F20 ꢂ Fc2)2/Sw(F02)2]1/2, w ¼ 0.10.
To a flask containing HOPhMePzF-Ph (0.51 g, 1.5 mmol) and 25 mL
THF, 0.75 mL AlMe3 (2.0 M in toluene, 1.5 mmol) was added at 0 ꢀC.
The reaction mixture was allowed to warm to room temperature
and reacted overnight. After 12 h of stirring, the volatiles were
removed under reduced pressure. The residue was washed with
15 mL hexane to afford brown solid (0.29 g, 48%). Anal. Calc. for
C24H22FN2OAl: C, 71.99; H, 5.54; N, 7.00. Found: C, 71.48; H, 6.03; N,
b
GoF ¼ [Sw(F20 ꢂ F2c)2/(Nrflns ꢂ Nparams)]1/2
.
4.13. X-ray crystallography
Crystals 3 and 5 were grown from concentrated hexane solu-
tions and isolated by filtration. Suitable crystals of 3 or 5 were
mounted onto a glass fibre using perfluoropolyether oil and cooled
rapidly in a stream of cold nitrogen gas using an Oxford Cry-
osystems Cryostream unit. Diffraction data were collected at 100 K
using Oxford Gemini S diffractometer. The absorption correction
was based on the symmetry equivalent reflections using the
SADABS program [58]. The space group determination was based
on a check of the Laue symmetry and systematic absences and was
confirmed using the structure solution. The structure was solved by
direct methods using a SHELXTL package [59]. All non-H atoms
were located from successive Fourier maps, and hydrogen atoms
were refined using a riding model. Anisotropic thermal parameters
were used for all non-H atoms, and fixed isotropic parameters were
used for H atoms. Some details of the data collection and refine-
ment are given in Table 2.
6.65. 1H NMR (600 MHz, CDCl3):
d (ppm) 7.33e7.42 (m, 6H, ArH),
7.26 (d, 3JHH ¼ 7.2 Hz, 2H, ArH), 7.15 (t, 3JHH ¼ 7.8 Hz, 2H, ArH), 7.11
(d, 3JHH ¼ 7.8 Hz, 1H, ArH), 6.99 (s, 1H, PzH), 6.87 (d, 3JHH ¼ 7.8 Hz,
1H, ArH), 2.32 (s, 3H, ArCH3), ꢂ1.06 (s, 6H, AlCH3). 13C NMR
(150 MHz, CDCl3):
d (ppm) 162.6, 156.8, 152.3, 147.6, 132.4, 127.4,
126.3, 115.0 (C), 133.1, 130.6, 130.5, 129.9, 128.9, 128.7, 127.2, 121.2,
116.9, 116.7, 103.8 (ArCH or PzCH), 20.5 (ArCH3), ꢂ9.2 (AlCH3).
4.11. Synthesis of (Me2AlOPhHPztBu) (5)
To a flask containing HOPhHPztBu (0.29 g, 1 mmol) and 25 mL
THF, 0.50 mL AlMe3 (2.0 M in toluene, 1.0 mmol) was added at 0 ꢀC.
The reaction mixture was allowed to warm to room temperature
and reacted overnight. After 12 h of stirring, the volatiles were
removed under reduced pressure. The residue was washed with
15 mL hexane to afford white solid (0.19 g, 55%). Anal. Calc. for
C21H25AlN2O: C, 72.39; H, 7.23; N, 8.04. Found: C, 71.92; H, 7.12; N,
Acknowledgements
We would like to thank the National Science Council of the
Republic of China for financial support (grant number NSC 98-2113-
M-005-002-MY3 and NSC 101-2113-M-005-012-MY3).
8.04. 1H NMR (600 MHz, CDCl3):
d (ppm) 7.45e7.49 (m, 4H, ArH),
3
7.39e7.40 (m, 2H, ArH), 7.26 (t, JHH ¼ 7.2 Hz, 1H, ArH), 6.97 (d,
3JHH ¼ 8.4 Hz, 1H, ArH), 6.78 (t, 3JHH ¼ 7.2 Hz, 1H, ArH), 6.56 (s, 1H,
PzH), 1.63 (s, 9H, PzC(CH3)3), ꢂ0.58 (s, 6H, AlCH3). 13C NMR
Appendix A. Supplementary material
(150 MHz, CDCl3): d (ppm) 158.4, 152.2, 148.8, 132.4, 117.2 (C), 131.7,
CCDC-875010 (for 3) and 875011 (for 5) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
129.5, 129.4, 128.4, 127.6, 120.7, 117.7, 109.1 (ArCH or PzCH), 64.0
(PzC(CH3)3), 32.3 (PzC(CH3)3), ꢂ7.2 (AlCH3).
4.12. General procedure for ε-caprolactone polymerization
References
Typically, to a flask containing prescribed amount of catalysts
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(0.35 N), the resulting mixture was poured into 50 mL n-heptane to
precipitate polymers. Crude products were recrystallized from THF/
hexane and dried in vacuo up to a constant weight.
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