Bis(amido)titanium complexes having chelating diaryloxo ligands bridged by sulfur or methylene and their catalytic behaviors for ring-opening polymerization of cyclic esters

Article abstract of DOI:10.1016/j.jorganchem.2003.10.042

A series of bis(dialkylamido) titanium complexes coordinated by O-E-O (E=S, CH₂) chelating bis(aryloxo) ligands, Ti[E(4-Me-6-^tBuC₆H₂O)₂] (NR₂)₂ (1: E=S, R=Me; 2: E=S, R=Et; 3: E=CH₂, R=Me; 4: E=CH₂, R=Et), were synthesized by the reaction of Ti(NR₂) ₄ (R=Me, Et) with 2,2^′-E(4-Me-6- ^tBuC₆H₂OH)₂ (E=S, CH₂). The crystal structures of complexes 2 and 4 were determined by X-ray diffraction study. Complex 2 has a trigonal bipyramidal structure with the sulfur and nitrogen atom in trans positions and complex 4 has a tetrahedral structure. The complex 2 was found to initiate the controlled polymerization of E-caprolactone in toluene at 100 °C affording poly(E-caprolactone) and poly(l-lactide) with relatively narrow molecular weight distributions. The complex 4 showed higher activity for the polymerization of E-caprolactone to give a polymer with a broader molecular weight distribution in comparison with complex 2.

Full text of DOI:10.1016/j.jorganchem.2003.10.042

Journal of Organometallic Chemistry 689 (2004) 612–619
www.elsevier.com/locate/jorganchem
Bis(amido)titanium complexes having chelating diaryloxo
ligands bridged by sulfur or methylene and their catalytic
behaviors for ring-opening polymerization of cyclic esters
a
Yoshinori Takashima , Yuushou Nakayama , Toshikazu Hirao ,
b
a
b
Hajime Yasuda , Akira Harada
c,
*
a
Department of Materials Chemistry, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan
b
c
Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
Received 29 August 2003; accepted 27 October 2003
Abstract
A series of bis(dialkylamido) titanium complexes coordinated by O–E–O (E ¼ S, CH2) chelating bis(aryloxo) ligands, Ti[E(4-Me-
6-tBuC6H2O)2](NR2)2 (1: E ¼ S, R ¼ Me; 2: E ¼ S, R ¼ Et; 3: E ¼ CH2, R ¼ Me; 4: E ¼ CH2, R ¼ Et), were synthesized by the re-
action of Ti(NR2)4 (R ¼ Me, Et) with 2,20-E(4-Me-6-tBuC6H2OH)2 (E ¼ S, CH2). The crystal structures of complexes 2 and 4 were
determined by X-ray diffraction study. Complex 2 has a trigonal bipyramidal structure with the sulfur and nitrogen atom in trans
positions and complex 4 has a tetrahedral structure. The complex 2 was found to initiate the controlled polymerization of e-cap-
rolactone in toluene at 100 °C affording poly(e-caprolactone) and poly(
L-lactide) with relatively narrow molecular weight distri-
butions. The complex 4 showed higher activity for the polymerization of e-caprolactone to give a polymer with a broader molecular
weight distribution in comparison with complex 2.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Titanium complexes; Sulfur- or methylene-bridged bis(aryloxo) ligands; Dialkylamido ligand; Cyclic esters; Ring-opening polymerization
1. Introduction
minoxane [7]. These dianionic ligand contribute not only
to stabilization of the active species but also to raising the
activity of the catalyst system, and the coordination of
the bridging sulfur atom to the metal is the key feature for
the high activity of the bis(aryloxo) titanium complexes
[8]. Titanium complexes bearing a methylene-bridged
bis(aryloxo) ligand, [Ti(mbp)X2]2 (mbp ¼ 2,20-CH2(4-
Me-6-tBuC6H2O)2, X ¼ Cl and OiPr), have been known
to initiate controlled polymerization of e-CL in the pres-
ence of some cocatalysts such as propylene oxide and
oxetane [9], in sharp contrast to the uncontrolled poly-
merization of cyclic esters with Ti(OnBu)4 [10]. Our group
has reported the syntheses and structures of titanium
complexes having a tellurium-bridged chelating diaryloxo
ligand, (TeBP)TiX2 (X ¼ Cl and OiPr, TeBP ¼ 2,20-
tellurobis(4-methyl-6-tert-butylphenoxo)) and (C5R5)
TiCl(TeBP) (R ¼ H and Me), and their catalytic behav-
iors for polymerization of ethylene and cyclic esters [11].
However, these complexes were hardly soluble in toluene
Early transition metal complexes with various chelat-
ing bis(aryloxo) ligands have recently been noticed as
catalyst precursors for the polymerization of ethylene
[1,2], a-olefins [1,2] and cyclic esters [3,4], and for ring-
opening metathesis polymerization [5,6]. Kakugo and
Miyatake reported that a titanium complex having a
sulfur-bridged bis(aryloxo) ligand, Ti(tBu2tbp)Cl2
(tBu2tbp ¼ 2,20-thiobis(4-methyl-6-tert-butylphenoxo))
and Ti(tBu2tbp)(OiPr)2, which had shown distinctively
high activity for the polymerization of ethylene, propyl-
ene, styrene and dienes, as well as for copolymerization of
ethylene with styrene, upon activation with methylalu-
* Corresponding author. Fax: +81-6-6850-5446.
E-mail address: harada@chem.sci.osaka-u.ac.jp (A. Harada).
0022-328X/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2003.10.042

Y. Takashima et al. / Journal of Organometallic Chemistry 689 (2004) 612–619
613
and gave poly(e-caprolactone) with rather broad molec-
NR2
Ti
tBu
OH
CH2
OH
tBu
ular weight distribution in toluene. In order to improve
the solubility of these complexes, we studied about their
bis(dialkylamido) derivatives. To the best of our knowl-
edge, no group 4 bis(dialkylamido) complex having sul-
fur- or methylene-bridged bis(aryloxo) ligand has been
known, while a series of their dichloro and diisopropoxo
derivatives has been reported [12–15]. Here we report the
synthesis and structures of the bis(dialkylamido)titanium
complexes with sulfur- or methylene-bridged chelating
bis(aryloxo) ligands and the catalytic behavior of these
bis(amido)titanium complexes for ring-opening poly-
tBu
tBu
Me
Me
Me
NR2
O
-78 ~ 25 ˚C
THF
O
Ti(NR2)4
+
CH2
R = Me, Et
Me
R = Me (3)
R = Et (4)
Scheme 2.
methyl substituents, while the aromatic protons at 3-
and 5-positions appeared as two doublets. The signals
for the methylene protons of the methylene-bridged
bis(aryloxo) ligand in 3 and 4 appeared as two doublets
merization of e-caprolactone and L-lactide.
2
2
(3: JHH ¼ 13:7 Hz, 4: JHH ¼ 14:1 Hz). The protons at
dialkyl amido ligands appeared as two singlet for the
protons of dimethyl amido substituents in 1 and 3 and
two quartet and two triplets for the protons of diethyl
amido substituents in 2 and 4 (Fig. 1). The two amido
groups are inequivalent even in the mbp complexes 3
and 4, suggesting that the flipping of the mbp ligand is
restricted.
2. Results and discussion
2.1. Preparation and characterization of bis(dialkylam-
ido)titanium complexes 1–4
The reaction of Ti(NMe2)4 with 1 equivalent of 2,20-
CH2(4-Me-6-tBuC6H2OH)2 was reported by Chisholm
et al. [16] to give an amide-free bis(mbp) complex,
Ti(mbp)2, at 0 °C in toluene. In order to obtain
bis(dialkylamido)titanium complexes, we investigated
similar reactions at lower temperature in THF.
Ti(NR2)4 (R ¼ Me, Et) were reacted with 1 equivalent of
2,20-S(4-Me-6-tBuC6H2OH)2 in THF at )78 °C to afford
bis(dialkylamido)titanium complexes, Ti(tBu2tbp) (NR2)2
(1: R ¼ Me, 2: R ¼ Et) (Scheme 1). The corresponding
mbp complexes, Ti(mbp)(NR2)2 (3: R ¼ Me, 4: R ¼ Et),
were also synthesized in a similar manner (Scheme 2).
Slow addition of the solution of the bis(aryloxo) ligand
to Ti(NR2)4 solution at low temperature ()78 °C) is very
important to obtain the bis(dialkylamido)titanium
complexes. In fact, the quick addition of the ligand so-
lution to the Ti(NMe2)4 solution at 25 °C only gave
Ti[E(4-Me-6-tBuC6H2O)2]2 in low yield instead of 1 and
3. All of these bis(dialkylamido)titanium complexes
were highly air-sensitive.
2.2. Molecular structures of bis(diethylamido)titanium
complexes 2 and 4 by X-ray analyses
The single crystals of the bis(diethylamido)titanium
complexes 2 and 4 were grown by slow crystallization
from n-pentane. Figs. 2 and 3 demonstrate the molecu-
lar structures of 2 and 4 elucidated by X-ray crystallo-
graphic analyses and Table 1 summarizes the selected
1
The H NMR spectra of the complexes 1–4 showed
one singlet for the protons of the two tert-butyl sub-
stituents and one singlet for the protons of the two
tBu
NR2
tBu
Me
Me
OH
O
Ti NR2
-78 ~ 25 ˚C
THF
tBu
O
Ti(NR2)4
S
+
S
OH
tBu
Me
R = Me, Et
Me
R = Me (1)
R = Et (2)
Fig. 1. 1H NMR spectra of (a) Ti(tBu2tbp)(NEt2)2 (2) and (b)
Ti(mbp)(NEt2)2 (4).
Scheme 1.

614
Y. Takashima et al. / Journal of Organometallic Chemistry 689 (2004) 612–619
Table 1
ꢀ
Selected bond distances (A) and angles (°) for 2 and 4
Complex 2
Complex 4
Bond distances
Ti–N1
Ti–N2
1.892(3)
1.863(3)
2.783(1)
1.886(2)
1.887(2)
–
1.895(2)
1.869(2)
–
Ti–S
Ti–O1
1.8341(19)
1.826(2)
3.267(3)
2.564
Ti–O2
Tiꢀ ꢀ ꢀC1
Tiꢀ ꢀ ꢀH1A
–
Bond angles
O–Ti–O
110.20(10)
103.3(1)
100.6(1)
107.74(9)
114.2(2)
C–E–C (E ¼ S, CH2)
N1–Ti–N2
Ti–O–C
105.10(11)
148.73(18) (O1)
142.57(17) (O2)
135.1(2) (O1)
131.9(2) (O2)
127.87
Tiꢀ ꢀ ꢀH1A–C1
bond distances and angles. Both 2 and 4 were obtained
as mononuclear complexes, in sharp contrast to the di-
nuclear structures of the corresponding chloro and al-
t
koxo complexes having Bu2tbp ligand, {Ti(tBu2tbp)
Cl2}2 (5) [11a] and {Ti(tBu2tbp)(OiPr)2}2 (6) [17]. The
coordination geometry around the titanium center in 2
can be described as pseudo Cs symmetric trigonal bi-
pyramidal in which one of the two diethylamido ligands
and the sulfur atom of the Bu2tbp ligand occupy the
apical positions. The complex 4 has a pseudo Cs sym-
metric tetrahedral structure. The Ti–S bond length in 2
Fig. 2. ORTEP drawing of Ti(tBu2tbp)(NEt2)2 (2) with numbering
scheme. All hydrogen atoms are omitted for clarity.
t
ꢀ
(2.783(1) A) is longer than those in the corresponding
ꢀ
dichloro complex 5 (2.664(2) A) [11a], diisopropoxo
ꢀ
(2.719(1) A) [17], and aryl complex
complex
t
6
ꢀ
Ti( Bu2tbp)(o-CH2NMe2C6H4)Cl (7: 2.704(1) A) [17],
and shorter than that in a cyclopentadienyl (Cp) com-
t
ꢀ
plex, Ti( Bu2tbp)CpCl (8: 2.907(1) A) [18]. The Ti–O
ꢀ
distances in the sulfur-bridged complex 2 (av. 1.887 A) is
longer than that in methylene-bridged complex 4 (av.
ꢀ
1.830 A), due to the decreased p-donation from oxygen
atoms by coordination of the sulfur-bridging atom to
titanium metal center. The Ti–O distances in 2 are
ꢀ
comparable to the diisopropoxo complex 6 (1.892 A)
[17], and longer than those in the corresponding chloride
ꢀ
complex 5 (1.846 A) [17], aryl complex 7 (1.855 A) [9a]
ꢀ
ꢀ
and Cp complex (1.827 A) 8 in the titanium complex
with the tbp ligand. The Ti–O distances in the methy-
lene-bridged complex 4 are longer than that of the a
series of titanium complexes with methylene-bridged
ꢀ
bis(aryloxo) ligand (1.751–1.788 A) [19–21] and the
other titanium complex with monodentate aryloxo or
alkoxo ligands [22–27], due to the p-donation from the
nitrogen atoms to the metal center [28]. The axial Ti–N
ꢀ
bond distance in the sulfur-bridged complex 2 is 0.03 A
longer than the equatorial one in 2. The Ti–N1 distance
farther from the bridging methylene group in 4 was also
Fig. 3. ORTEP drawing of Ti(mbp)(NEt2)2 (4) with numbering
scheme. All hydrogen atoms except for H1A and H1B are omitted for
clarity.
ꢀ
longer by 0.03 A than that closer to the methylene

Y. Takashima et al. / Journal of Organometallic Chemistry 689 (2004) 612–619
615
ꢀ
group. Although the Tiꢀ ꢀ ꢀC1 distance (3.267(3) A) in 4 is
much longer than those of agostic Tiꢀ ꢀ ꢀH–C interaction,
the Tiꢀ ꢀ ꢀH1A (one of the two hydrogen atoms on C1)
broader molecular weight distribution (Mw=Mn ¼ 1:60).
The molecular weight of the polymers obtained by 2 and
4 systems were higher than that calculated from the
initial molar ratio of e-CL to catalysts. In comparison
between the sulfur-bridged complex 2 system and the
methylene-bridged complex 4 system, the reaction rate
at the initial stage in sulfur-bridged complex 2 system is
faster than that in methylene-bridged complex 4 system
at the polymerization time of 4 h, while the polymer
yield of the methylene-bridged complex 4 grew higher
than that in the sulfur-bridged complex 2 at the poly-
merization time of 8 h. At this stage, the polymer ob-
tained with 2 had lower molecular weight and narrower
molecular weight distribution than those obtained with
4. This suggests that the sulfur-bridged complex 2 sys-
tem would be more effective for the initiation than the
methylene-bridged complex 4 system, while the propa-
gation in the complex 2 system would be slower than
that in the complex 4 system.
ꢀ
distance (2.58 A) in 4 is only slightly longer than typical
Tiꢀ ꢀ ꢀH distances of agostic Tiꢀ ꢀ ꢀH–C interaction (2.06–
ꢀ
2.45 A) [29]. Thus, the complex 4 could have a weak
Tiꢀ ꢀ ꢀH–C interaction. This could be the reason for the
restricted flipping of the mbp ligand in 3 and 4 (vide
supra).
2.3. Polymerization of e-caprolactone and
and 4
L
-lactide by 2
Recently, Aida and coworkers reported that a diiso-
propoxo analogue of 4, Ti(mbp)(OiPr)2, initiated living
polymerization of lactones [9c]. The dichloro complex
Ti(mbp)Cl2 was inactive without addition of propylene
oxide [9c], while the corresponding dichloride complex
having the sulfur-bridged ligands Ti(tbp)Cl2 catalyzed
the polymerization of e-caprolactone (e-CL) without any
cocatalysts at 100 °C to give the polymers in good yield,
although the resulting poly(e-CL) had a relatively broad
molecular weight distribution [11b]. In contrast, the
corresponding bis(diethylamido) complexes having the
sulfur- or methylene-bridged ligands 2 and 4 polymer-
ized e-CL in toluene at 100 °C without any cocatalyst to
give poly(e-CL) with relatively narrow molecular weight
distribution (Table 2). The complex 2 catalyzed poly-
merization of e-CL in 90.3% yield within 32 h to afford
poly(e-CL) with Mn of 18,800 and Mw=Mn of 1.31. The
molecular weight distribution of the polymer obtained
with the amido complex 2 was narrower than that ob-
tained with the corresponding chloro complex 5 in tol-
uene, though the activity of 2 is lower than that of 5
[11b]. The basisity of the amido group of 2 should
suppress the side reactions such as back-biting. The
polymerization of e-CL with complex 4 proceeded to
reach to 91.0% yield within 8 h to afford a polymer with
higher molecular weight (Mn ¼ 56; 200) and relatively
In the 1H NMR spectrum of the poly(e-CL) obtained
by 2 (run 4 in Table 2), resonances for –CH2OH, –
NCH2CH3 and –NCH2CH3 end-groups appeared at
3.63, 3.35 and 1.17 ppm, respectively (Fig. 4). Thus, the
Fig. 4. 1H NMR spectrum (400 MHz, CDCl3, 30 °C) of the poly(e-
caprolactone) obtained by 2. *: side band.
Table 2
Polymerization of e-caprolactone by 2 and 4
a
Mn=103a
Run
Complex
Time (h)
Yield (%)
Mw=Mn
Calculateda
Observedb
1
2
3
4
5
6
7
8
2
2
2
2
4
4
4
4
4
8
56.9
80.2
89.3
90.3
23.5
52.9
83.5
91.0
13.0
18.3
20.4
20.6
5.4
8.2
13.1
14.8
18.8
15.3
21.8
39.2
56.2
1.09
1.13
1.14
1.31
1.16
1.17
1.47
1.60
16
32
2
4
12.1
19.1
20.8
5
8
In toluene, at 100 °C, [e-CL]0/[Ti] ¼ 200.
a Mn(calcd) ¼ (MW of e-CL) ꢁ [e-CL]0/[Ti] ꢁ (polymer yield).
b Determined by GPC analysis in THF calibrated with standard poly(styrene).

616
Y. Takashima et al. / Journal of Organometallic Chemistry 689 (2004) 612–619
Table 3
Polymerization of
L
-lactide by 2
a
Mn=103a
Run
Time (h)
Yield (%)
Mw=Mn
Calculateda
Observedb
1
2
3
4
36
48
24.4
54.2
82.1
90.3
7.0
15.6
23.7
26.0
7.6
13.6
18.1
20.4
1.08
1.13
1.19
1.23
86
120
In toluene, at 100 °C, [
L
-LA]0/[Ti] ¼ 200.
a Mn(calcd) ¼ (MW of
L
-LA) ꢁ [ -LA]0/[Ti] ꢁ (polymer yield).
L
b Determined by GPC analysis in THF calibrated with standard poly(styrene).
initiation in these systems would be formal migratory
insertion of the monomer into Ti–NEt2 bond to gener-
ate titanium alkoxide species, and repeated monomer
insertion and quenching with MeOH would give poly-
mers with hydroxy and amide end groups. The Mn of
this polymer can be calculated to be 1.8 ꢁ 104 based on
4. Experimental
4.1. General considerations
All manipulations involving air- and moisture-sensi-
tive organometallic compounds were carried out by the
use of standard Schlenk techniques under an argon at-
mosphere. THF, toluene and n-pentane were dried and
deoxygenated by distillation over sodium benzophenone
ketyl under argon. C6D6 was dried over Na/K alloy and
thoroughly degassed by trap-to-trap distillation before
use. 2,20-Thiobis(4-methyl-6-tert-butylphenol) was sup-
plied by Ciba-Geigy AG. e-Caprolactone and 2,20-
1
the H NMR spectrum, which is almost equal to that
estimated by GPC calibrated with standard poly(sty-
rene).
The sulfur-bridged complex 2 system was also applied
to the polymerization of
are summarized in Table 3. The polymer yield reached
to 96.2% within 120 h to afford poly( -LA) with Mn of
L-lactide (L-LA) and the results
L
20,400 and Mw=Mn of 1.23. The molecular weight of
the polymer increased linearly to the polymer yield,
indicating living nature of this polymerization system,
although, the molecular weight distribution was also
increasing with the polymer yield. Some side reaction
such as back-biting could be accompanying the
polymerization.
methylenebis(4-methyl-6-tert-butylphenol)
purchased
from Nacarai Tesque Co. Ti(NMe2)4 and Ti(NEt2)4
were prepared according to the literature [30].
1
The H (500 and 400 MHz), and 13C (125 and 100
MHz) NMR spectra in C6D6 was measured on JEOL
JNM-LA500 and JEOL JNM-GSX400 spectrometers.
Assignments for 1H and 13C NMR peaks for some
1
complexes were aided by 2D H–1H NOESY, 2D 1H–
1H COSY, 2D, 2D HMQC and 2D HMBC spectra.
Mass spectra were recorded on a JEOL SX-102 spec-
trometer. All melting points of the complexes were
measured in sealed tubes under an argon atmosphere
and were not corrected.
3. Conclusion
A series of bis(dialkylamido)titanium complexes con-
taining sulfur- or methylene-bridged chelating bis(aryl-
oxo) ligands, Ti[E(4-Me-6-tBuC6H2O)2](NR2)2 (1: E¼S,
R ¼ Me; 2: E ¼ S, R ¼ Et; 3: E ¼ CH2, R ¼ Me; 4:
E ¼ CH2, R ¼ Et), was prepared and the complexes 2 and
4 were determined to have mononuclear pseudo Cs
symmetric structures by X-ray diffraction study. In their
catalytic behavior for ring-opening polymerization of e-
4.2. Preparation of Ti[S(4-Me-6-tBuC6H2O)2](NMe2)2
(1)
A solution of 2,20-S(4-Me-6-tBuC6H2OH)2 (0.35 g,
0.97 mmol) in THF (5 ml) was slowly added to a solu-
tion of Ti(NMe2)4 (0.33 g, 0.97 mmol) in THF (35 ml) at
)78 °C. The reaction mixture was stirred for 10 min and
then allowed to warm to ambient temperature followed
by stirring for 2 h. The color of the solution changed
from yellow to orange. All volatiles were removed under
reduced pressure to give microcrystals. Recrystallization
from n-pentane gave Ti[S(4-Me-6-tBuC6H2O)2](NMe2)2
(1) (0.32 g, 59%) as orange crystals, m.p. 98–102 °C
caprolactone and L-lactide, the sulfur-bridged complex 2
produced poly(e-CL) with controlled molecular weight
and relatively narrow molecular weight distribution in
toluene without any cocatalyst. The ring-opening poly-
merization of e-CL by 4 gave poly(e-CL) with higher
molecular weight and broader molecular weight distri-
bution for those for complex 2, while the corresponding
dichloride complex, Ti[CH2(4-Me-6-tBuC6H2O)2]Cl2,
was inactive for the polymerization of e-caprolactone
without cocatalyst.
1
(dec.). H NMR (C6D6, 30 °C, 400 MHz): d 7.52 (d,
4
4JHH ¼ 2:1 Hz, 2H, 3-C6H2O), 7.15 (d, JHH ¼ 2:1 Hz,
2H, 5-C6H2O), 3.45 (s, 6H, –NMe2), 3.32 (s, 6H,

Y. Takashima et al. / Journal of Organometallic Chemistry 689 (2004) 612–619
617
–N0Me2), 2.11 (s, 6H, 4-Me), 1.58 (s, 18H, 6-tBu). 13C
NMR (C6D6, 30 °C, 100 MHz): d 165.2 (1-C6H2O),
137.9 (6-C6H2O), 132.2 (4-C6H2O), 129.7 (5-C6H2O),
128.8 (3-C6H2O), 124.6 (2-C6H2O), 35.6 (6-CMe3), 29.7
(6-CMe3), 29.7 (–N0CH3), 26.1 (–NCH3), 20.9 (4-Me).
HRMS (EI): Calc. for C26H40O2N2Ti1S1 492.2293.
Found 492.2277.
(t, JHH ¼ 7:1 Hz, 6H, –CH2Me0). 13C NMR (C6D6, 30
°C, 125 MHz): d 159.9 (1-C6H2O), 136.6 (6-C6H2O),
133.3 (4-C6H2O), 129.4 (3-C6H2O), 128.3 (2-C6H2O),
125.9 (5-C6H2O), 47.6 (–N0CH2–), 47.4 (–NCH2–), 35.3
(–CH2–), 34.2 (6-CMe3), 30.6 (6-CMe3), 21.1 (4-Me),
15.5 (–N0CH2CH3), 15.2 (–NCH2CH3). HRMS (EI):
Calc. for C31H50O2N2Ti1 530.3355. Found 530.3336.
3
4.3. Preparation of Ti[S(4-Me-6-tBuC6H2O)2](NEt2)2
(2)
4.6. Polymerization of cyclic esters
To a solution of monomer (1 mmol) in toluene (0.90
ml) was added a toluene solution (0.10 ml) of complex 2
or 4 (5 lmol). The reaction mixture became a orange-
clear solution. The reaction tube was sealed under an
argon atmosphere and kept at 100 °C with stirring.
After the prescribed reaction time, the polymerization
was terminated by adding a large amount of methanol.
The resulting white polymer was collected by centrifu-
gation and dried in vacuo.
The complex 2 was synthesized and isolated as orange
crystals in 64% yield in a similar manner to 1, m.p.; 123–
1
128 °C. H NMR (C6D6, 30 °C, 500 MHz): d 7.55 (d,
4JHH ¼ 1:6 Hz, 2H, 3-C6H2O), 7.14 (d, 4JHH ¼ 1:6 Hz, 2H,
3
5-C6H2O), 3.96 (q, 4H, JHH ¼ 6:9 Hz, –N(CH2Me)2),
3.64 (q, 4H, 3JHH ¼ 7:1 Hz, –N0(CH2Me)2), 2.12 (s, 6H,
3
4-Me), 1.57 (s, 18H, 6-tBu), 1.26 (t, JHH ¼ 6:9 Hz, 6H,
3
–CH2Me), 1.23 (t, JHH ¼ 7:1 Hz, 6H, –CH2Me0).
13C NMR (C6D6, 30 °C, 125 MHz): d 166.0 (1-C6H2O),
137.9 (6-C6H2O), 133.0 (4-C6H2O), 130.0 (5-C6H2O),
128.8 (3-C6H2O), 125.7 (2-C6H2O), 48.8 (–NCH2–),
47.7 (–N0CH2–), 35.5 (6-CMe3), 30.0 (6-CMe3), 20.7
(4-Me), 15.5 (–NCH2CH3), 15.1 (–N0CH2CH3). HRMS
(EI): Calc. for C30H48O2N2Ti1S1 548.2919. Found
548.2932.
4.7. GPC analysis of the polymers
Gel permeation chromatographic (GPC) analyses
were carried out at 40 °C using a Tosoh TSKgel
G2000HXL and G3000HXL columns connected to a
Tosoh RI-8012 detector. THF was used as a eluent at a
flow rate of 0.8 ml/min. Samples were prepared in THF
(0.5 mg/ml) and were filtered through a Advantec DIS-
MIC-25JP filter in order to remove particulates before
injection. The GPC column was calibrated versus
poly(styrene) standards (Aldrich).
4.4. Preparation of Ti[CH2(4-Me-6-tBuC6H2O)2]
(NMe2)2 (3)
The complex 3 was synthesized and isolated as yellow
crystals in 56% yield in a similar manner to 1, m.p. 124–
1
128 °C (dec.). H NMR (CD2Cl2, 30 °C, 400 MHz): d
7.05 (s, 2H, 5-C6H2O), 6.87 (s, 2H, 3-C6H2O), 3.82 (d,
2JH2H1 ¼ 13:7 Hz, 1H, CH2H1), 3.45 (s, 6H, –N0Me2),
4.8. Crystallographic data collections and structure
determination of 2 and 4
2
3.31 (d, JH1H2 ¼ 13:7 Hz, 1H, CH1H2), 2.87 (s, 6H,
–NMe2), 2.20 (s, 6H, 4-Me), 1.37 (s, 18H, 6-tBu). 13C
NMR (CD2Cl2, 30 °C, 100 MHz): d 158.5 (1-C6H2O),
137.2 (6-C6H2O), 131.5 (4-C6H2O), 129.4 (5-C6H2O),
128.9 (3-C6H2O), 125.8 (2-C6H2O), 45.0 (–CH2–), 33.1
(6-CMe3), 33.1 (–N0CH3), 30.6 (–NCH3), 30.3 (6-
CMe3), 21.2 (4-Me). HRMS (EI): Calc. for
C27H42O2N2Ti1 474.2729. Found 474.2748.
A crystal of 2 was sealed in a glass capillary under
argon. The measurement of 2 was made on a Rigaku
AFC-5R four-circle diffractometer for data collection
using Mo Ka radiation. Relevant crystal and data sta-
tistics are summarized in Table 4. Three standard re-
flections were chosen and monitored every 150
reflections. Empirical absorption correction was carried
out on the basis of an azimuthal scan. The unit cell
parameters at 23 °C were determined by a least-squares
fit to 2h values of 25 strong higher reflections for com-
plex 2. Complex 2 showed no significant intensity decay
during the data collection. The structures of complex 2
was solved by direct methods (SHELXS-86) [31] and
expanded using Fourier techniques (DIRDIF 94) [32]
and refined by the full-matrix least square method. Mea-
sured non-equivalent reflections with I > 2:0rðIÞ were
used for the structure determination. In the subsequent
4.5. Preparation of Ti[CH2(4-Me-6-tBuC6H2O)2]
(NEt2)2 (4)
The complex 4 was synthesized and isolated as yellow
crystals in 74% yield in a similar manner to 1, m.p. 143–
148 °C (dec.). 1H NMR (C6D6, 30 °C, 500 MHz): d 7.22
4
4
(d, JHH ¼ 2:1 Hz, 2H, 3-C6H2O), 7.11 (d, JHH ¼ 2:1
2
Hz, 2H, 5-C6H2O), 4.21 (d, JH1H2 ¼ 14:1 Hz, 1H,
CH2H1), 3.73 (q, 4H, 3JHH ¼ 7:1 Hz, –N0CH2–), 3.57 (q,
P
2
3
2
4H, JHH ¼ 6:9 Hz, –NCH2–), 3.55 (d, JH2H1 ¼ 14:1
refinement the function
mized, where jFoj and jFcj are the observed and calcu-
xðjFoj ꢂ jFcjÞ was mini-
Hz, 1H, –CH2H1–), 2.24 (s, 6H, 4-Me), 1.62 (s, 18H,
6-tBu), 1.18 (t, JHH ¼ 6:9 Hz, 6H, –CH2Me), 1.07
3
lated structure factors amplitudes, respectively. The

618
Y. Takashima et al. / Journal of Organometallic Chemistry 689 (2004) 612–619
Table 4
Crystal data and collection parameters
Complex 2
Complex 4
Formula
C30H48N2O2S1Ti1
548.68
C31H50N2O2Ti1
530.63
Formula weight
Crystal system
Space group
Monoclinic
P21=c (#14)
15.498(4)
21.770(8)
9.396(4)
–
Monoclinic
P21=c (#14)
16.355(3)
12.160(3)
16.725(5)
–
ꢀ
a (A)
ꢀ
b (A)
ꢀ
c (A)
a (°)
b (°)
c (°)
93.35(3)
–
111.541(12)
–
3
ꢀ
V (A )
3164(1)
4
3093.7(13)
4
Z
Number of reflections for cell determination (2h range)
25 (25.0–29.0)
1.151
744.00
13074 (2.7–54.8)
1.139
1152
Dcalcd (g/cm3)
F ð000Þ
l [Mo Ka] (cmꢂ1
Diffractometer
Temperature (K)
)
3.63
3.04
R-AXIS-RAPID
193(2)
AFC-5R
296(2)
16.0
Scan speed (deg/min)
–
Scan width (°)
0:74 þ 0:3 tan h
–
–
222.0
Total oscillation angles (°)
Exposure time (min per deg)
2hmax (°)
–
55.0
5.0
54.8
Number of reflections measured (total)
Number of reflections measured (unique) (Rint
Number of variables
R1; wR2 (all data)
8928
7257 (0.109)
325
27135
7011 (0.1090)
337
)
0.113, 0.1430
0.0494
1.246
0.1254, 0.1495
0.0632
0.983
R ðI > 2:0rÞðIÞ
GOF on F 2
ꢂ3
ꢀ
D (e A
)
0.55, )1.27
0.614, )0.362
P
P
P
P
2
agreement indices are defined as R ¼ jjFoj ꢂ jFcjj=
jFoj and Rw ¼ ½ xðFo2 ꢂ Fc2Þ = xðFo2Þ2ꢃ1=2. The
positions of all non-hydrogen atoms for complex were
found from a difference Fourier electron density maps
and refined anisotoropically. All hydrogen atoms were
P
P
P
2
2 1=2
jFoj
and
Rw ¼ ½ xðjFoj ꢂ jFcjÞ = xðjFojÞ ꢃ
where xꢂ1 ¼ r2ðFoÞ ¼ ½rc2ðFoÞ þ p2=4ðFo2Þꢃ. The posi-
tions of all non-hydrogen atoms for complex 2 were
found from a difference Fourier electron density map
and refined anisotropically. All hydrogen atoms were
ꢀ
placed in calculated positions (C–H ¼ 0.95 A) and kept
fixed.
ꢀ
All calculations were performed using the TEXSAN
crystallographic software package, and illustrations
were drawn with ORTEP.
placed in calculated positions (C–H ¼ 0.95 A) and
constrained to ride on their respective carbon atoms.
A crystal of 4 suitable for X-ray diffraction study was
mounted on a cryoloop. The measurement of 4 was
made on a Rigaku R-AXIS-RAPID Imaging Plate dif-
fractometer with graphite monochromated Mo Ka ra-
diation (k ¼ 0:71069). Relevant crystal and data
statistics are summarized in Table 4. Indexing was per-
formed from one oscillation, which was exposed for 5.0
min. The camera radius was 127.40 mm. Readout was
performed in the 0.100 mm pixel mode. The data was
corrected for Lorentz and polarization effects. The
structures of complex 4 was solved by direct methods
(SIR-92) [33] and expanded using Fourier techniques
(DIRDIF 94) [32] and refined by full-matrix least
squares refinement (SHELXL-97) [34]. In the subsequent
Crystallographic data for the structural analysis of 2
and 4 have been deposited with the Cambridge Crys-
tallographic Data Centre, CCDC no. 218168 and
218167, respectively. Copies of this information may be
obtained free of charge from the Director, CCDC, 12
Union Road Cambridge CB2 1EZ, UK (Fax: +44-1223-
336-033 or e-mail: deposit@ccdc.cam.ac.uk or http://
www.ccdc.cam.ac.uk).
Acknowledgements
P
2
refinement the function
mized, where jFoj and jFcj are the observed and calcu-
xðjFoj ꢂ jFcjÞ was mini-
We are indebted to a Grant-in-Aid for Scientific
Research (Grant no. 14044072 and 14350488) from the
Ministry of Education, Culture, Sports, Science and
Technology. This work was carried out financed by the
lated structure factors amplitudes, respectively. The
agreement indices are defined as R ¼ jjFoj ꢂ jFcjj=
P

Y. Takashima et al. / Journal of Organometallic Chemistry 689 (2004) 612–619
619
(c) J. Okuda, S. Fokken, T. Kleinhenn, T.P. Spaniol, Eur. J.
Inorg. Chem. (2000) 1321.
NEDO International Joint Research Grant Program
(Biodegradable Copolymers). Y.T. is a research fellow
of the Japan Society for the Promotion of Science, 2000–
2002.
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