Group 3 metal initiators with an [OSSO]-type bis(phenolate) ligand for the stereoselective polymerization of lactide monomers

Article abstract of DOI:10.1002/asia.201100826

A series of 1,Iω-dithiaalkanediyl-bridged bis(phenols) of the general type [OSSO]H₂ with variable steric properties and various bridges were prepared. The stoichiometric reaction of the bis(phenols) 1,3-dithiapropanediyl-2,2'-bis(4,6-di-tert-bu

Full text of DOI:10.1002/asia.201100826

DOI: 10.1002/asia.201100826
Group 3 Metal Initiators with an [OSSO]-Type Bis(phenolate) Ligand for the
Stereoselective Polymerization of Lactide Monomers
Andreas Kapelski,[a] Jean-Charles Buffet,[a, b] Thomas P. Spaniol,[a] and Jun Okuda*[a]
Abstract: A series of 1,w-dithiaalkane-
diyl-bridged bis(phenols) of the general
type [OSSO]H2 with variable steric
properties and various bridges were
prepared. The stoichiometric reaction
phenyl-2-propyl)phenol], 1,3-dithiapro-
panediyl-2,2’-bis[6-(1-methylcyclohex-
yl)-4-methylphenol] (C1, R=1-methyl-
cyclohexyl), and 1,4-dithiabutanediyl-
2,2’-bis[6-(1-methylcyclohexyl)-4-meth-
ylphenol] with rare-earth metal silyla-
s(phenolate) silylamido complexes [Ln-
(OSSO){N(SiHMe2)2}(thf)] in moder-
G
E
E
ACHTUNGTRENNUNG
ate to good yields. The monomeric
nature of these complexes was shown
by an X-ray diffraction study of one of
the yttrium complexes. The complexes
efficiently initiated the ring-opening
polymerization of rac- and meso-lactide
to give heterotactic-biased poly(rac-lac-
tides) and highly syndiotactic poly(me-
so-lactides). Variation of the ligand
backbone and the steric properties of
the ortho substituents affected the level
of tacticity in the polylactides.
of the bis
diyl-2,2’-bis(4,6-di-tert-butylphenol),
1,3-dithiapropanediyl-2,2’-bis[4,6-di(2-
ACHTUNGTRENNUNG(phenols) 1,3-dithiapropane-
mido precursors [Ln{N
ACHTUNGTRNE(NUNG SiHMe2)2}3
R
ACHTUNGERTN(NUNG thf)x] (Ln=Sc, x=1 or Ln=Y, x=2;
thf=tetrahydrofuran) afforded the cor-
responding scandium and yttrium bi-
phenyl-2-propyl)phenol], rac-2,3-trans-
propanediyl-1,4-dithiabutanediyl-2,2’-
bis
rac-2,3-trans-butanediyl-1,4-dithiabu-
tane diyl-2,2’-bis[4,6-di(2-phenyl-2-pro-
pyl)phenol], rac-2,3-trans-hexanediyl-
1,4-dithiabutanediyl-2,2’-bis[4,6-di(2-
ACHTUNGTRENNUNG[4,6-di(2-phenyl-2-propyl)phenol],
Keywords: lactides · lanthanides ·
polymers · ring-opening polymeri-
zation · stereoselectivity
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
Introduction
Polylactide (PLA) is currently attracting interest as a biode-
gradable thermoplastic derived from “carbon-neutral” bio-
mass feedstocks.[1] The production of isotactic poly(l-lac-
tide) has been commercialized with an annual production
capacity exceeding 105 metric tons. The monomer l-lactide
(l-LA) is produced by thermolysis of oligo(l-lactide).[2] Be-
cause there are two stereogenic centers in one lactide mole-
cule, three stereoisomers—(S,S)-LA, (R,R)-LA, and meso-
LA—can be distinguished. A racemic mixture of (S,S)-LA
and (R,R)-LA is called rac-lactide (rac-LA; Scheme 1).
The physical and mechanical properties of a polymeric
material are dependent on many factors, such as molecular
weight, molecular weight distribution, and stereochemistry.
Polymers that have stereocenters in the repeating unit can
exhibit two structures of maximum order: isotactic and syn-
diotactic. Due to their stereoregularity, isotactic (Tm >
Scheme 1. Lactide monomers with the stereochemistry of the stereogenic
centers indicated.
1808C) and syndiotactic polymers (Tm =1528C) are typically
crystalline; an important feature for many applications. Het-
erotactic PLAs are amorphous and no melting temperatures
have been reported to date.
Molecularly defined single-site initiators for the ring-
opening polymerization (ROP) of lactide monomers are
based on Lewis acidic di-,[3] tri-,[4] and tetravalent[5] metals.
Polymerization of l-lactide leads to isotactic poly(l-lactide),
whereas polymerization of rac-lactide can lead to atactic,
heterotactic, stereoblock, or stereocomplex PLA. Stereocon-
trolled polymerization of meso-lactide, which is a byproduct
during the production of l-lactide, can give syndiotactic and
heterotactic poly(meso-lactides). To date, only a limited
number of polymerization initiators for meso-lactide are
known.[6] We previously reported the use of trivalent metal
complexes with an [OSSO]-type bis(phenolate) ligand for
the ROP of rac-lactide to form heterotactic poly(rac-lacti-
des) and meso-lactide to form highly syndiotactic poly(me-
so-lactides) (Scheme 2).[4g,h,7]
[a] Dipl.-Chem. A. Kapelski, Dr. J.-C. Buffet, Dr. T. P. Spaniol,
Prof. J. Okuda
Institute of Inorganic Chemistry, RWTH Aachen
Landoltweg 1, 52056 Aachen (Germany)
Fax : (+49)241 80 92 644
E-mail: jun.okuda@ac.rwth-aachen.de
[b] Dr. J.-C. Buffet
Present address:
Chemistry Research Laboratory
Department of Chemistry
University of Oxford
Mansfield Road, Oxford OX1 3TA (UK)
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FULL PAPERS
tyl)benzyl alcohol in toluene,
followed by the addition of 1,2-
ethylenedithiol (Scheme 4).
After workup, proACHTUNGTRENNlUNG iACTHUNGRTENgNUNG and 3 was
obtained as a colorless solid in
63% yield.
We have introduced various
chiral backbones with different
ring sizes. Proligands 4 and 6
were synthesized by following a
modification of a procedure by
Scheme 2. Synthesis of heterotactic PLA and syndiotactic PLA from rac- and meso-lactide.
The steric bulk of the ortho substituent has a profound
effect on both the polymerization rates and the stereocon-
trol. Hetero- and syndioselective stereocontrol during the
ROP of rac- and meso-LA is essentially governed by steric
factors: larger ortho substituents result in higher tacticity of
the polymers due to controlled monomer coordination to
Scheme 4. Synthesis of proACTHNUTRGENNGlU iACHUTNGTRENNUGgand 3.
the metal center. Additionally, chirality in the complex
backbone appears to have a strong influence on the control
of both efficiency and stereocontrol.[8] We report herein the
synthesis and lactide polymerization behavior of a new
series of Group 3 metal silylamide complexes containing a
bis(phenolate) ligand with various chiral and achiral back-
bones and ortho substituents.
Doye et al.[11] Cycloalkene was treated with bis
sulfide 2,2’-dithiobis[4,6-di(2-phenyl-2-propyl)phenol] in the
ACHTUNGTRENUN(NG phenol) di-
AHCTUNGTRENNUNG
presence of BF3·OEt2 in a mixture of nitromethane and di-
chloromethane (Scheme 5).
Results and Discussion
Synthesis of the Proligands
Following a variation of the procedure reported for the syn-
thesis of proACHTUNGTRENNUNGliACHTUNGTRENNUNG
gand 1,[9] 2-mercapto-4,6-bis(2-phenylpropan-
2-yl)phenol was treated with NaOMe and CH2Br2 in a mix-
ture of methanol and ethanol at reflux for 24 hours
(Scheme 3). After workup, proACHTNUTRGENNUGliACHUTGTNRENNgGU and 2 (chelate ring size 5-
4-5) was obtained as a colorless solid in 15% yield.
Scheme 5. Synthesis of proligands 4–6.
After workup and recrystallization, yellow (4) and orange
(6) solids were obtained in 74 and 15% yields, respectively.
Proligands 7, with a 5-4-5 chelate array, and 8, with a 5-5-5
chelate array, were prepared by following literature report-
s[12a,b] and isolated as brown powders in low yields
(Scheme 6). Proligands 1–8 are air-stable crystals and were
Scheme 3. Synthesis of proligands 1 and 2.
We have previously reported that flexible 1,5-dithiapenta-
nediyl-bridged scandium complexes form highly heterotac-
tic,[4g] poly(rac-lactides), and syndiotactic[7] poly(meso-lacti-
des). Another possibility to increase the flexibility of the
bridge was to synthesize a ligand with a methylene linker
between the sulfur atom and the aromatic group. Following
1
characterized by H and 13C NMR spectroscopy and elemen-
tal analysis.
Synthesis of the Complexes
a modification of the literature procedure,[10] pro
(giving a 6-5-6 chelate array) has been synthesized in one
pot, whereby ZnI2 was added to (2-hydroxy-3,5-di-tert-bu-
li
gand 3
Group 3 metal initiators containing a 1,w-dithiaalkanediyl-
bridged bis(phenolate) ligand are readily synthesized in 40–
70% yields by treatment of one equivalent of rare-earth
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Jun Okuda et al.
180 Hz is assigned to the
SiHMe2 protons and a doublet
at around d=0.5 ppm is as-
signed to SiHMe2 of the amide
ligand. The coupling constant
À
1J
ACTHNUTRGNE(UNG Si,H) indicates a weak b-Si
H interaction with the metal.[13]
The 13C NMR spectra show the
SCH2S resonances at about d=
50.0 ppm.
The stoichiometric reaction
of [Sc{N
ACHTUNGTRENNUG(SiMe2H)2}3ACHTUNGTRNEN(UGN thf)] with
proligand 3 (chelate ring size 6-
5-6) in n-pentane afforded col-
orless Sc–3 in 63% yield after
A
A
Scheme 6. Synthesis of proligands 7 and 8.
metal tris(dimethylsilylamide) precursors with one equiva-
lent of proligands 1–8 (Schemes 7 and 8).
The stoichiometric reaction of [Ln{NACTHUNTRGENNUG(SiHMe2)2}3ACHTUTGNREN(NUGN thf)x]
(Ln=Sc, x=1 or Ln=Y, x=2; thf=tetrahydrofuran) with 1
recrystallization from n-pentane. The methylene protons of
the SCH2CH2S bridge give rise to a broad singlet at d=
3.61 ppm. The methylene linker between the sulfur atom
and the aromatic group SCH2Ph appears as a broad singlet
at d=1.89 ppm. Other diagnostic features are similar to
those of complexes Ln–1 and Ln–2. The 13C NMR spectrum
of complex Sc–3 shows resonances for SCH2CH2S at d=
35.6 ppm, SCH2Ph at d=68.2 ppm, and the ipso-carbon
signal at d=160.3 ppm.
We previously reported the preparation of Ln–5.[7] Com-
plexes Ln–4 to Ln–6 (5-5-5 chelate arrays) were synthesized
by following similar methods. One equivalent of proligands
4 and 6 was added slowly to a solution of the rare-earth
metal precursors in benzene and reacted at 708C for
24 hours. After workup, colorless (Ln–4) and orange (Ln–6)
solids were obtained in good yields (Sc–4, 67%; Y–4, 61%;
1
Sc–6, 71%, and Y–6, 75%). The H NMR spectra shows the
SCH protons of the bridges as multiplet signals from d=2.6
to 2.7 ppm. For the amide group, Ln–4 exhibits septet reso-
3
nances at d=5.1–5.2 ppm with coupling constants, J
N
À
of around 3.0 Hz for the Si H protons and a doublet around
d=0.3–0.5 ppm for the SiHMe2 groups with identical cou-
pling constants. For Ln–6, the resonances are broad multip-
lets, indicating an increase in fluxionality within the back-
bone. The aromatic protons Ph-H3 und Ph-H5 are observed
as two doublets around d=7.5–7.7 ppm with a coupling con-
Scheme 7. Synthesis of complexes Ln–1 to Ln–3.
ACTHNUTRGNEUNG
stant of 3J(H,H)=3–5 Hz. The 13C NMR spectra of com-
À
or 2 in benzene for 24 hours at 708C led to the formation of
Sc–1, Y–1, Sc–2, and Y–2 (chelation ring size 5-4-5), which
were isolated in moderate to good yields as colorless pow-
ders after recrystallization from n-pentane at À308C
plexes Ln–4 and Ln–6 show resonances for S CH around
d=50 ppm for Ln–4 and d=55 ppm for Ln–6. The C1-O sig-
nals are around d=165–168 ppm.
The stoichiometric reaction of [Ln{NACTHUNTRGENNUG(SiHMe2)2}3ACHTUNGTRENNUNG(thf)x]
1
(Scheme 7). The H and 13C NMR spectra of complexes Ln–
(Ln=Sc, x=1 or Ln=Y, x=2) with proligands 7 and 8 in n-
pentane for 48 hours at 258C afforded Sc–7, Y–7, Sc–8, and
Y–8 (Scheme 8). After recrystallization from n-pentane, col-
orless solids were isolated in good yields. Complexes Sc–7
and Sc–8 seem to be more fluxional in solution than Y–7
and Y–8. In the scandium complexes, one broad signal at
about d=1.30 ppm for the b-protons and two signals of
equal intensity are detected between d=4.00–4.10 and 4.20–
4.30 ppm for the a-protons of THF. For the para-methyl
groups, two signals at about d=2.2–2.3 ppm are recorded.
The methyl protons of the 1-methylcyclohexyl group appear
1 and Ln–2 display similar signals. The 1H NMR spectra
shows the SCH2S protons of the bridge as a singlet at similar
shifts for Sc–1 (d=3.71 ppm), Y–1 (d=3.86 ppm), and Y–2
(d=3.64 ppm). As a consequence of the rigid geometry
around the scandium center in Sc–2, the SCH2S protons
appear to be diastereotopic, as indicated by two broad sig-
nals at d=3.50 and 3.64 ppm. Two broad resonances at
about d=1.0–1.5 and 3.0–4.1 ppm indicate the presence of
one THF molecule attached to the metal center. A septet at
3
1
d=5.1 ppm with JACHTUNGTRENNUNG(H,H)=3.0–3.2 Hz and JACHTUNGTNER(NUGN Si,H)=170.0–
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Stereoselective Polymerization of Lactide Monomers
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À
Figure 1. Molecular structure of Y–5. Hydrogen atoms, except for Si H,
and solvent were omitted for clarity. Selected bond lengths [ꢁ] and
À
À
À
À
angles [8]: Y1 O1 2.147(2), Y1 O2 2.147(2), Y1 O3 2.317(2), Y1 S1
À
À
2.9641(8) Y1 S2 2.8502(8), Y1 N1 2.242(3); O1-Y1-O2 143.64(8), S1-
Y1-S2 74.03(2), N1-Y1-S1 173.74(7), N1-Y1-O3 103.16(9), O3-Y1-S2
153.58(6).
Scheme 8. Synthesis of complexes Ln–4 to Ln–8.
as two singlet signals between about d=1.75 and 1.90 ppm.
For the aromatic protons, four signals are observed for Ph-
H3, Ph-H3’, Ph-H5, and Ph-H5’ between d=7.00 and
7.40 ppm. Similar signal patterns and splitting of the signals
for the a-THF protons were observed previously.[4g] The
1H NMR spectra of complexes Y–7 and Y–8 showed diag-
nostic resonances. Broad NMR signals for the protons of the
1-methylcyclohexyl groups in Ln–7 and Ln–8 (Figures S29,
S31, S33, and S35 in the Supporting Information) indicate
slow rotation of the bonds at room temperature.
Polymerization of rac-Lactide
The bis(phenolate) complexes Ln–1 to Ln–8 were tested in
the polymerization of rac-lactide (Scheme 9). The results are
summarized in Table 1.
Scheme 9. Formation of heterotactic PLA from rac-lactide.
Crystal Structure of Y–5
Single crystals of Y–5 suitable for X-ray diffraction analysis
were obtained by cooling a saturated solution of Y–5 in n-
pentane. The molecular structure is depicted in Figure 1.
The yttrium center in Y–5 is six coordinate with a distort-
ed octahedral geometry; bonded to the tetradentate bis(phe-
nolate) [OSSO]-type ligand, the bis(dimethylsilyl)amido
group, and one THF ligand. Both enantiomers of the C1-
symmetric molecule are found in the centrosymmetric crys-
tal. The two oxygen donors of the bis(phenolate) ligand are
arranged trans to each other, as indicated by the corre-
sponding angles N1-Y1-O3 103.16(9), N1-Y1-S1 173.74(7),
Most of the polymerizations in THF proceeded rapidly
with high monomer conversions in less than 3 hours. The
scandium complexes Sc–1, Sc–2, and Sc–7 (with a 5-4-5 che-
late array based on a rigid [OSSO]-type ligand) polymerized
rac-lactide with low conversions of 21–35% and gave atactic
poly(rac-lactides) (Table 1, entries 1, 3, and 12). This finding
indicates that a highly rigid system lowers the polymeri-
zation rate. We suggest that the coordination sphere around
the metal center is too crowded to coordinate the rac-lactide
monomers. In addition, bis(dimethylsilylamido) groups are
less nucleophilic than alkoxides, thus leading to a slow ini-
tiation of ROP. With the homologous yttrium complexes Y–
1, Y–2, and Y–7, conversions of 81, 93, and 97%, respective-
ly, were achieved, giving slightly heterotactic enriched poly(-
rac-lactides). In most cases, due to the larger metal center
and the larger coordination sphere for the lactide monomer,
the yttrium complexes were more active than the scandium
complexes. This trend has been reported in earlier reports
on rare-earth metal bis(phenolate) complexes in lactide pol-
À
and O1-Y1-O2 143.64(8)8. The Y O(phenolate) bond length
À
(2.147(2) ꢁ in Y–5) is within the range of Y O bond lengths
reported in the literature (2.104–2.177 ꢁ).[14–16] The Y N
bond length of 2.242(3) ꢁ is close to the values found for
À
the yttrium amide precursor (2.229(4)–2.276(4) ꢁ).[13a]
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Jun Okuda et al.
Table 1. ROP of rac-lactide initiated by complexes Ln–1 to Ln–8.[a]
We have previously shown
that an increase in the size of
the ortho substituent on the ar-
[c]
[c]
Entry
Init.
Conversion[b] [%]
Mn,exptl [gmolÀ1
]
Mw/Mn
Pr[d]
1
2
3
4
5
6
7
8
Sc–1
Y–1
Sc–2
Y–2
Sc–3
Sc–4
Y–4
Sc–5
Y–5
Sc–6
Y–6
Sc–7
Y–7
Sc–8
Y–8
26
81
35
93
91
80
55
98
98
86
98
21
97
94
98
6000
8250
1.13
1.05
1.19
1.65
1.53
1.11
1.10
1.09
1.15
1.65
1.42
1.24
1.45
1.61
1.66
0.49
0.59 omatic rings led to an increase
12000
18250
18500
24500
12500
11250
20750
18250
17000
22000
20000
23750
12250
0.50
0.61
0.72
0.85
0.68
0.74
0.68
0.64
0.63
0.50
in heterotacticity of the poly(-
rac-lactides).[4g] However, when
complexes Ln–8 (with
a 1-
methylcyclohexyl group in the
ortho-position of the 5-5-5 che-
lating ligand) were used to
polymerize rac-lactide, the het-
erotacticity of the polymers was
9
10
11
12
13
14
15
0.57 lower (71% for Sc–8 and 54%
0.71
0.54
for Y–8) than that obtained
with rare-earth metal com-
[a] Polymerization conditions: [LA]0/ACTHNUTRGNEUNG[Init]0 =100, 3 h, THF, 1 mL, 258C. [b] Conversion of monomer
plexes with tert-butyl groups in
the ortho positions (78% for
scandium and 68% for yt-
trium).[4g] A similar trend was
also observed when the hetero-
(([LA]0À[LA]t)/[LA]0). [c] Measured by gel-permeation chromatography (GPC), calibrated with polystyrene
(PS) standards in THF.[17] [d] Pr is the probability of obtain isi or sis tetrads.[18]
ymerization.[4h,7] However, Y–4 (with a 5-5-5 chelate array)
was less active than the scandium homologue.
tacticity of the polymers formed by complexes Ln–1
(Table 1, entries 1 and 2) and Ln–7 with a 5-4-5 chelate
array (Table 1, entries 12 and 13) was compared. In compar-
ison with the polymerization results for complexes with a
cumyl group in the ortho position, Ln–7 and Ln–8 were not
as active and selective.[4g]
By contrast, when the C1-bridged complexes Ln–1 and
Ln–2 based on 5-4-5 [OSSO]-type ligands were used for the
polymerization of rac-lactide, the yttrium complexes showed
higher heterotacticity than the homologous scandium com-
plexes, indicating that less compact yttrium complexes with
5-4-5 [OSSO]-type ligand were more prone to stereocenter
inversion. This is a rare example for Group 3 metal [OSSO]-
type bis(phenolate) complexes, in which the larger yttrium
complex is both more active and selective than the homolo-
gous scandium complexes in the ROP of lactide monomers.
Despite variation in the initial initiator/monomer ratio
and polymerization time, the poly(rac-lactides) obtained
when using complex Y–1 as the initiator showed the same
level of heterotacticity (59–62%) and polydispersity
(Table S1 in the Supporting Information).
Polymerization of meso-Lactide
The bis(phenolate) complexes Ln–1 to Ln–8 were tested in
the polymerization of meso-lactide (Scheme 10). The results
are shown in Table 2.
In contrast to the polymerization of rac-lactide, 1,3-di-
thiapropanediyl-bridged bis(phenolate)complexes Y–1, Y–2,
and Y–7 polymerized meso-lactide efficiently, reaching full
conversion within 0.5 hours. meso-Lactide is polymerized
faster because of its higher ring strain.[6h]
The polymer synthesized from rac-lactide displayed simi-
lar properties (Mn,exptl =18500 gmolÀ1, Mw/Mn =1.53, hetero-
tacticity of 72%), when complex Sc–3 based on 6-5-6
[OSSO]-type ligand was used (Table 1, entry 5). The poly(-
rac-lactide) obtained when using a scandium complex based
on the 5-5-5 [OSSO]-type ligand without a methylene linker
was comparable (Mn,exptl =18000 gmolÀ1, Mw/Mn =1.66, het-
erotacticity of 78%). These results indicate that adding flex-
ibility in the ligand has no direct effect. In contrast, the flex-
ibility of the backbone has a direct effect, as indicated by
the high heterotacticity (95%) found with a scandium com-
plex based on a 5-6-5 [OSSO]-type ligand.[4g]
When complexes Ln–4 to Ln–6 (based on 5-5-5 chelating
[OSSO]-type ligands, but differing in the cycloalkane ring
size) were compared, a decrease in the heterotacticity was
noted with increasing ring size for the scandium complexes
(heterotacticities of 85, 74, and 61%, respectively). More
rigid 1,2-cycloalkanediyl backbones led to higher heterotac-
ticity. Complexes Ln–4 and Ln–5 produced polymers with
low polydispersity (Mw/Mn <1.15; Table 1, entries 6–9).
The polymerization of meso-lactide by the scandium com-
plexes Sc–2 to Sc–8 led to high syndiotactic PLAs (Ps >
0.84). These syndiotacticity values are close to the highest
ones reported in the literature.[6a] The syndiotacticity of the
poly(meso-lactides) decreases with increasing the radius of
the metal center because all yttrium complexes led to lower
syndiotacticities (0.70ꢀPs ꢀ0.83). However, Sc–1 (based on
a rigid 5-4-5 [OSSO]-type ligand) showed a relatively low
syndiotacticity (Ps =0.66) even lower than the homologous
yttrium complex Y–1 (Ps =0.82). Data for the polymeri-
zation of meso-lactide by complex Y–1 with various initial
monomer/initiator ratios are collated in Table S2 in the Sup-
porting Information. After 3 hours, an increase from 1:100
to 1:300 resulted in increasing molecular weights (Mn,exptl
=
19500–44750 gmolÀ1) at 258C and high syndiotacticity
values (Ps >0.82). Carpentier et al. reported similar syndio-
tacticity values using an yttrium alkoxyamino bis(phenolate)
amide complex.[6e]
When meso-lactide was polymerized by the cumyl-substi-
tuted complex Sc–2, the poly(meso-lactides) obtained were
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Mechanistic Discussion
To understand the origin of the high syndioselectivity, one
equivalent of bis(phenolate) yttrium complex Y–5 was treat-
ed with one equivalent of (R)-(+)-methyl lactate or (S)-(À)-
methyl lactate to give complexes (R)-Y–5 and (S)-Y–5, re-
Scheme 10. Formation of syndiotactic PLA from meso-lactide.
1
spectively. The H NMR spectra
([D6]benzene) of complexes
(R)-Y–5 and (S)-Y–5 show
identical resonances diagnostic
of a dimeric structure.
Furthermore, we reported
that rare-earth metal bis(pheno-
late) complexes were able to
produce highly syndiotactic
PLAs with values of Ps >0.90,
when the ortho substituent was
cumyl.[7] Despite numerous var-
iations in the backbone, the
ortho position, and the leaving
Table 2. ROP of meso-lactide initiated by complexes Ln–1 to Ln–8.[a]
[c]
[c]
Entry
Init.
Conversion[b] [%]
Mn,exptl [gmolÀ1
]
Mw/Mn
Ps[d]
1
2
3
4
5
6
7
8
Sc–1
Y–1
Sc–2
Y–2
Sc–3
Sc–4
Y–4
Sc–5
Y–5
Sc–6
Y–6
Sc–7
Y–7
Sc–8
Y–8
96
>99
76
>99
>99
93
26
>99
79
>99
>99
82
>99
95
29500
19250
21000
14250
33250
43250
18250
32250
4750
38250
1300
33750
12250
23200
460
1.23
1.88
1.94
1.99
2.08
2.19
1.52
1.80
1.94
1.67
7.51
1.80
1.19
2.18
14.7
0.66
0.82
0.87
0.83
0.87
0.91
0.80
0.92
0.71
0.87
0.76
0.84
0.74
0.89
0.70
9
10
11
12
13
14
15
group,
syndiotactity
values
above 0.94 have never been
achieved. This led us to postu-
late intramolecular exchange of
diastereomers as an explanation
for this lack of syndiospecificity
(Scheme 11). Transesterification
>99
[a] Polymerization conditions: [LA]0/ACTHNUTRGNE[NUG Init]0 =100, 0.5 h, toluene, 1 mL, 258C. [b] Conversion of monomer
(([LA]0À[LA]t)/[LA]0). [c] Measured by GPC with PS standards in THF.[17] [d] Ps is the probability of a new s
tetrad.[18]
of higher syndiotacticity (Ps =0.87) than those obtained with
the tert-butyl-substituted complex Sc–1 (Ps =0.66). This indi-
cates that there is an increase in the syndiotacticity of the
poly(meso-lactides) with increasing the size of the ortho sub-
stituent.[7]
Using complex Sc–3 (based on 6-5-6 [OSSO]-type ligand)
to polymerize meso-lactide led to a loss over control of the
polymerization relative to the analogous scandium complex
based on a 5-5-5 [OSSO]-type ligand without the methylene
linker (Mw/Mn =2.08 and 1.29 respectively). Hence, the
change in the backbone resulted in increased fluxionality,
which caused loss of polymerization control. The syndiotac-
ticity of the polymer remained at a similar level.
due to fast polymerization rates could also explain this phe-
nomenon.
According to chain-end control, in which the chirality of
the last inserted unit influences the chirality of the next in-
serted monomer, metal chirality due to ligand fluxionality
(L,R and D,R) may not affect syndiotacticity. Furthermore,
when the rate constant for the exchange between diastereo-
mers, kinv, is lower than the rate constant for propagation,
kprop, the polymer should be syndiotactic. The errors in tac-
ticity are due to exchange between diastereomers (kinv
@
kprop). Suppression of the inversion between diastereomers
should lead to high syndiotactic PLAs. There is an interest-
ing analogy: Schrock and co-workers reported recently the
use of chiral-at-metal molybdenum catalysts for the ring-
opening metathesis polymerization of racemic norbornene
monomers that selectively gave cis, syndiotactic polymers.[19]
When complexes Ln–4 to Ln–6 (based on 5-5-5 [OSSO]-
type ligands with different cycloalkane ring sizes) are com-
pared, all scandium complexes showed high conversion and
high syndiotactic preference (Ps >0.87).
In contrast to the ROP of rac-lactide initiated by 1-meth-
ylcyclohexyl-substituted complexes Ln–7 and Ln–8, stereo-
control over meso-lactide polymerization was comparable to
the stereocontrol given by tert-butyl-substituted complex-
es.[4h] Based on a 5-4-5-chelate, syndiotacticities of Ps =0.66
(Sc–1) and 0.82 (Y–1) were obtained for tert-butyl-substitut-
ed complexes, while Sc–7 and Y–8 gave tacticity values of
Ps =0.84 (Sc–7) and Ps =0.74 (Y–7). This might result from
the different structure of the meso-lactide. The Mw/Mn
values are high for all poly(meso-lactides). Only Sc–1 and
Y–7 (based on a rigid 5-4-5 chelate) gave narrowly distribut-
ed polymers (Mw/Mn=1.23 (Sc–1), 1.19 (Y–7)).
Conclusion
Structurally defined initiators based on Group 3 metal com-
plexes with [OSSO]-type bis(phenolate) ligands and 5-4-5
and 5-5-5 chelate arrays polymerized lactide monomers effi-
ciently. The complexes led to heterotactic-biased poly(rac-
lactides) and highly syndiotactic poly(meso-lactides). The
scandium complexes gave polymers with higher heterotactic-
ity and syndiotacticity than those obtained when using the
homologous yttrium compounds. The complexes based on a
rigid C1-bridged, 5-4-5 [OSSO]-ligand (1, 2, and 7) behaved
differently. For the scandium complexes Sc–4 to Sc–6 (based
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ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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ÝÝ These are not the final page numbers!

Jun Okuda et al.
CH2Br2 (3.21 mL, 46 mmol, 1 equiv)
was added dropwise. The mixture was
heated at reflux for 16 h and the sol-
vents were evaporated under vacuum.
Water (200 mL) was added and the
mixture was extracted with Et2O (3ꢂ
100 mL). The organic phase was sepa-
rated, dried over anhydrous MgSO4,
filtered, and evaporated to give a col-
orless foam. Recrystallization from n-
pentane afforded colorless crystals of
2 (5.35 g, 7.26 mmol, 15%). 1H NMR
(400 MHz, CDCl3, 258C): d=7.33–
7.32 (m, 2H; Ph-H), 7.30–7.29 (m, 2H;
Ph-H), 7.29–7.28 (m, 6H; Ph-H), 7.27–
7.26 (m, 2H; Ph-H), 7.25–7.22 (m, 4H;
Ph-H), 7.18–7.14 (m, 4H; Ph-H), 6.15
(s, 2H; PhOH), 3.72 (s, 2H; SCH2S),
1.70 (s, 12H; C
ACHTUGNTRENUN(NG CH3)2), 1.65 ppm (s,
12H; C
AHCTUNGTRENNUNG
Scheme 11. Exchange of diastereomeric rare-earth metal bis(phenolato) initiators during meso-lactide poly-
CDCl3, 258C): d=152.9 (Ph-C), 150.6
(Ph-C), 150.2 (Ph-C), 142.2 (Ph-C),
135.1 (Ph-C), 132.0 (Ph-C), 128.2 (Ph-
C), 128.1 (Ph-C), 126.8 (Ph-C), 125.7
merization.
on a 5-5-5 chelate array), heterotacticity decreased with in-
(Ph-C), 125.6 (Ph-C3), 118.3 (Ph-C2), 42.7 (p-C
N
ACHTUNGTRENNUNG(CH3)2),
creasing 1,2-cycloalkanediyl ring size. The more rigid 1,2-cy-
cloalkanediyl backbone led to higher heterotacticity. In sum-
mary, the structure activity/stereoselectivity relationship re-
mains challenging to elucidate.
42.5 (SCH2S), 31.1 (o-C(CH3)2), 29.5 ppm (p-CCAHTUNGTRENNNUG
sis calcd (%) for C49H52O2S2 (737.06): C 88.53, H 7.67; found: C 88.15, H
7.65.
G
Synthesis of Compound 4
Cyclopentene (1.24 mL, 14 mmol, 1 equiv) and a solution of BF3·OEt2
(0.25 mL) were added to a solution of 2,2’-dithiobisACTHNUTRGNE[NUG 4,6-di-(2-phenyl-2-
Experimental Section
propyl)phenol] (10.0 g, 14 mmol, 1 equiv) in a mixture of nitromethane
(8 mL) and CH2Cl2 (8 mL) at À108C. The resulting mixture was stirred
at À108C for 3 h and at room temperature for an additional 72 h. The re-
sulting mixture was washed a saturated aqueous solution of NaHCO3 (3ꢂ
100 mL). After separation of the phases, the organic layer was dried over
MgSO4, filtered, and concentrated under vacuum. Recrystallization from
General
All operations were performed under an inert atmosphere of argon by
using standard Schlenk-line or glovebox techniques. Toluene (Fisher Sci-
entific), n-pentane (Fisher Scientific), and THF (Fisher Scientific) were
distilled under argon from sodium/benzophenone ketyl prior to use.
[D6]Benzene (Sigma-Aldrich) and CDCl3 (Sigma–Aldrich) were carefully
a mixture of acetonitrile/acetone (4:1, 200 mL) gave pure bis
rac-4 as a yellow solid (8.24 g, 10.4 mmol, 74%). 1H NMR (400 MHz,
CDCl3, 258C): d=7.35 (d, 3J
(H,H)=2.2 Hz, 2H; Ph-H), 7.30–7.27 (m,
4H; Ph-H), 7.27–7.25 (m, 4H; Ph-H), 7.25–7.20 (m, 6H; Ph-H), 7.19 (d,
3J
(H,H)=2.2 Hz, 2H; Ph-H), 7.18–7.16 (m, 4H; Ph-H), 7.16–7.11 (m,
4H; Ph-H), 6.64 (s, 2H; PhOH), 2.79 (brs 2H; SCH), 1.77–1.75 (m, 2H;
Cy-H), 1.70 (s, 12H; C(CH3)2Ph), 1.66 (s, 6H; C(CH3)2Ph), 1.65 (s, 6H;
ACHTUNGTRENNUNG(phenol)
AHCTUNGTRENNUNG
dried and stored in a glovebox. [Ln{N
ACHTUTNGRNEUNG(SiHMe2)2}3CAHTUNGTREN(NUNG thf)x] (Ln=Sc, x=1;
Y, x=2)[13c] and 2,2’-dithiobis[4,6-di-(2-phenyl-2-propyl)phenol][11] were
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
synthesized according to literature methods.[13c] meso-Lactide (Uhde In-
venta-Fischer) was recrystallized from isopropanol at À308C, washed
with diethyl ether, and dried under vacuum. All other chemicals were
commercially available and used after appropriate purification. Glass-
ware and vials used for polymerization were dried in an oven at 1208C
overnight and exposed to vacuum–argon cycles three times. NMR spectra
were recorded on a Bruker DRX 400 MHz spectrometer at 258C (1H:
400 MHz; 13C: 100.1 MHz). Chemical shifts for 1H and 13C NMR spectra
were referenced internally by using the residual solvent resonances and
are reported relative to tetramethylsilane. Molecular weights and polydis-
persities were determined by size exclusion chromatography (SEC) in
THF at 358C at a flow rate of 1 mLminÀ1 by utilizing an Agilent 1100
Series HPLC, G1310A isocratic pump, an Agilent 1100 Series refractive
index detector, and 8ꢂ600 mm, 8ꢂ300 mm, 8ꢂ50 mm PSS SDV linear M
columns. Calibration standards were commercially available narrowly dis-
tributed linear polystyrene samples that covered a broad range of molar
A
ACHTUNGTRENNUNG
CACTHNURGTNEG(UN CH3)2Ph), 1.45–1.43 (m, 2H; Cy-H), 1.35–1.33ppm, (m, 2H; Cy-H);
13C NMR (100.1 MHz, CDCl3, 258C): d=154.1 (Ph-C1), 151.1 (Ph-C),
150.8 (Ph-C), 142.0 (Ph-C4), 135.4 (Ph-C), 133.7 (Ph-C6), 128.9 (Ph-C),
128.3 (Ph-C), 128.0 (Ph-C), 127.0 (Ph-C5), 126.2 (Ph-C), 126.0 (Ph-C),
125.6 (Ph-C3), 119.1 (Ph-C2), 54.9 (SCH2), 42.9 (C
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
(Cy-C), 26.2 (Cy-C), 25.8 (Cy-C), 24.9 ppm (Cy-C); elemental analysis
calcd (%) for C53H58O2S2 (791.17): C 80.46, H 7.39; found: C 80.32, H
7.22.
Synthesis of Compound 6
Cyclooctene (7.40 mL, 56 mmol, 2 equiv) and a solution of BF3·OEt2
(0.25 mL) were added to a solution of 2,2’-dithiobisACTHNUTRGNE[NUG 4,6-di-(2-phenyl-2-
masses (103 <Mn <2ꢂ106 gmolÀ1
)
propyl)phenol] (20 g, 28 mmol) in a mixture of nitromethane (15 mL)
and CH2Cl2 (15 mL) at À108C. The resulting mixture was stirred at
À108C for 3 h and at room temperature for 72 h. The mixture was
washed with a saturated aqueous solution of NaHCO3 (3ꢂ100 mL). The
organic layer was dried over MgSO4, filtered, and concentrated under
vacuum. Recrystallization from a mixture of acetonitrile/acetone (4:1,
Synthesis of Compounds 1, 3, 5, Sc–5, and Y–5
These compounds were synthesized as previously reported.[7,9,10,20]
Synthesis of Compound 2
200 mL) gave pure bisACHTUNGTRENNUNG
NaOMe (5.35 g, 99 mmol, 2 equiv) was added to a mixture of 2-mercap-
to-4,6-bis(2-phenylpropan-2-yl)phenol (36.00 g, 99 mmol, 2 equiv) in
MeOH (100 mL) and EtOH (100 mL) and then heated at reflux until all
NaOMe was dissolved. The mixture was cooled to room temperature and
15%). 1H NMR (400 MHz, C6D6, 258C): d=7.60 (d, 3J
ACHTUNGTRENNUNG
Ph-H), 7.49 (d, 4J
N
4
4
(d, J
(H,H)=2.8 Hz, 2H; Ph-H5), 7.28 (d, J
A
7.26–7.22 (m, 2H; Ph-H), 7.19–7.13 (m, 2H; Ph-H), 7.10 (s, 2H; Ph-H),
Chem. Asian J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
7
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Stereoselective Polymerization of Lactide Monomers
FULL PAPERS
2.90 (brs 2H; SCH), 1.84 (s, 6H; C
G
G
C1), 139.2 (Ph-C6), 137.4 (Ph-C4), 129.0 (Ph-C3), 127.0 (Ph-C5), 123.8
1.73 (s, 12H; C(CH3)2Ph), 1.56–1.54(m, 2H; Cy-H), 1.44–1.42(m, 2H;
G
(Ph-C2), 71.9 (a-THF), 50.8 (SCH2S), 34.2 (C
ACHTUNTGRNENGU(CH3)3), 31.7 (6-CACHTUNGTRENNUNG(CH3)3),
Cy-H), 1.230–1.28 (m, 2H; Cy-H), 1.21–1.19 (m, 2H; Cy-H), 1.10–
1.08ppm (m, 2H; Cy-H); 13C NMR (100.1 MHz, C6D6, 258C): d=154.1
(Ph-C), 151.1 (Ph-C), 150.8 (Ph-C), 142.0 (Ph-C), 135.4 (Ph-C), 133.7
(Ph-C), 128.9 (Ph-C), 128.3 (Ph-C), 128.0 (Ph-C), 127.0 (Ph-C), 126.2
30.0 (4-C(CH3)3), 24.9 (b-THF), 3.3 ppm (Si(CH3)3); elemental analysis
calcd (%) for C37H64NO3S2ScSi2 (736.2): C 60.37, H 8.76, N 1.90; found:
C 57.13, H 8.39, N 1.78.
G
ACHTUNGTRENNUNG
Synthesis of Y–1
(Ph-C), 126.0 (Ph-C), 119.1 (Ph-C), 54.8 (SCH2), 42.9 (C
ACHTUNGTRENNUNG
A
U
[Y{NCATHNUGTERNU(NGN SiMe2H)2}3ACHUTGTNREN(UNG thf)2] (0.20 g, 0.4 mmol, 1 equiv) and proACHTUNGTRENNUNGliACHTUNGTRENNUNGgand 1
(Cy-C), 25.8 ppm (Cy-C); elemental analysis calcd (%) for C56H64O2S2
(832.25): C 80.72, H 7.74; found: C 79.58, H 7.71.
(0.20 g, 0.4 mmol, 1 equiv) were dissolved in benzene (2.5 mL) and the
solution was stirred for 24 h at 708C. After removing the solvent under
vacuum, the colorless precipitate formed was recrystallized from n-pen-
tane at À308C to give Y–1 as a colorless powder (0.18 g, 0.22 mmol,
Synthesis of Compound 7
54%). 1H NMR (400 MHz, C6D6, 258C): d=7.61 (d, 4J
ACHTUNGTRENNUNG
NaOMe (0.66 g, 12.2 mmol, 2 equiv) was added to a solution of 2-mer-
capto-4-methyl-6-(1-methylcyclohexyl)phenol (2.5 g, 12.2 mmol, 2 equiv)
in MeOH (25 mL) and the mixture was heated to reflux until all NaOMe
dissolved. After cooling to 08C, 1,1-dibromomethane (0.43 mL, 6.1 mmol,
1 equiv) was added slowly with a syringe and the mixture was heated to
reflux for 1 h. After removal of the solvent under vacuum, water
(100 mL) was added to dissolve NaBr. After addition of diethyl ether
(100 mL), the organic phase was separated, the aqueous phase was ex-
tracted with diethyl ether (2ꢂ50 mL), and the combined organic phases
were dried over Na2SO4. The crude product was recrystallized from n-
pentane to afford compound 7 as a yellow powder (1.13 g, 2.33 mmol,
2H; Ph-H), 7.39 (d, 4J(H,H)=2.7 Hz, 2H; Ph-H), 5.18 (sept, 3J
ACTHNUGTRENNUGN ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
C6D6, 258C): d=165.6 (Ph-C1), 138.7 (Ph-C6), 138.1 (Ph-C4), 129.8 (Ph-
C3), 127.2 (Ph-C5), 123.2 (Ph-C2), 69.9 (a-THF), 49.7 (SCH2S), 36.0 (6-
C
N
N
ACHTUNTGRENGU(N CH3)3), 30.0 (4-CACHTUNGTRNEN(UGN CH3)3), 24.1 (b-
AHCTUNGTRENNUNG
C37H64NO3S2YSi2 (780.1): C 56.97, H 8.27, N 1.80; found: C 55.54, H 8.19,
N 1.22.
38%). 1H NMR (400 MHz, CDCl3, 258C): d=7.12 (d, 4J
2H; Ph-H3), 7.09 (d, 4J
(H,H)=2.2 Hz, 2H; Ph-H5), 6.76 (s, 2H; Ph-
ACHTUNGTREN(NUNG H,H)=2.2 Hz,
Synthesis of Sc–2
AHCTUNGTRENNUNG
A solution of pro
was added slowly to
ACHUTGTNRENNUGliACHTUNGTRENNUNG
OH), 3.90 (s, 2H; SCH2), 2.27–2.26 (m, 2H; Ph-Cy-H), 2.25 (s, 6H; Ph-
CH3), 2.15–2.08 (m, 4H; Cy-H), 1.71–1.66 (m, 4H; Cy-H), 1.56–1.54 (m,
4H; Cy-H), 1.50–1.46 (m, 8H; Cy-H), 1.45–1.41 (m, 6H; Cy-H),
1.30 ppm (s, 6H; Cy-CH3); 13C NMR (100.1 MHz, CDCl3, 258C): d=
153.4 (Ph-C1), 135.6 (Ph-C6), 133.4 (Ph-C5), 131.4 (Ph-C4), 129.1 (Ph-
C3), 118.5 (Ph-C2), 45.0 (SCH2), 38.5 (Cy-C), 36.8 (Cy-C), 26.8 (Cy-C),
25.4 (Cy-C), 22.9 (Cy-CH3), 20.8 ppm (Ph-CH3); elemental analysis calcd
(%) for C29H40O2S2 (484.76): C 71.85, H 8.32; found: C 71.43, H 8.84.
a
G
CHTUNGTRENNUNG
0.14 mmol, 1 equiv) in benzene (1 mL) at 258C. The resulting orange so-
lution was stirred at 708C for 24 h. Removal of the solvent under vacuum
afforded a colorless powder that was dissolved in n-pentane (2 mL), fil-
tered, and stored at À308C for 2 weeks. After recrystallization, complex
Sc–2 was isolated as a colorless powder (0.085 g, 0.09 mmol, 64%).
1H NMR (400 MHz, C6D6, 258C): d=7.46 (brs 2H; Ph-H5), 7.32 (d, 3J-
A
ACHTUNGTNER(NUNG H,H)=7.7 Hz, 4H; Ph-H), 7.21–
Synthesis of Compound 8
AHCTUNGTRENNUNG
NaOH (0.85 g, 21.2 mmol, 2 equiv) was added to a solution of 2-mercap-
to-4-methyl-6-(1-methylcyclohexyl)phenol (5.0 g, 21.2 mmol, 2 equiv) in
MeOH (50 mL) and the mixture was heated to reflux until all NaOH dis-
solved. After cooling to 08C, 1,2-dibromoethane (0.92 mL. 10.6 mmol,
1 equiv) was added slowly with a syringe and the mixture was heated at
reflux for 1 h. After removal of the solvent under vacuum, water
(100 mL) was added to dissolve NaBr. After addition of diethyl ether
(200 mL), the organic phase was separated, the aqueous phase was ex-
tracted with diethyl ether (2ꢂ100 mL), and the combined organic phases
were dried over Na2SO4. After filtration and removal of the solvent
under vacuum, the crude product was recrystallized from n-pentane to
afford compound 8 as a brownish powder (0.81 g, 1.63 mmol, 15%).
1H NMR (400 MHz, CDCl3, 258C): d=7.13–7.11 (brs, 2H; Ph-H3), 7.11–
7.09 (brs 2H; Ph-H5), 7.08 (s, 2H; Ph-OH), 2.77 (s, 4H; SCH2), 2.24 (s,
6H; Ph-CH3), 2.16–2.08 (m, 4H; Cy-H), 1.74–1.66 (m, 4H; Cy-H), 1.60–
1.54 (m, 4H; Cy-H), 1.49–1.42 (m, 8H; Cy-H), 1.31 ppm; (s, 6H; Cy-
CH3); 13C NMR (100.1 MHz, CDCl3, 258C): d=153.6 (Ph-C1), 135.4 (Ph-
C6), 133.6 (Ph-C5), 131.0 (Ph-C4), 129.0 (Ph-C3), 118.2 (Ph-C2), 38.5
(Ph-CCH3), 36.8 (Cy-C), 36.3 (SCH2), 26.8 (Cy-C), 25.4 (Cy-C), 22.9 (Cy-
C), 20.9 ppm (Ph-CH3); elemental analysis calcd (%) for C30H42O2S2
(498.8): C 72.24, H 8.49; found: C 72.25, H 8.76.
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
(C6D6, 258C, 100.1 MHz): d=151.8 (Ph-C1), 138.8 (Ph-C6), 131.0 (Ph-
C4), 130.2 (Ph-C), 128.4 (Ph-C), 128.2 (Ph-C3), 127.9 (Ph-C), 127.1 (Ph-
C), 125.9 (Ph-C5), 125.7 (Ph-C2), 71.2 (a-THF), 52.4 (SCH2S), 43.3 (C-
G
R
ACHTUNTGRENNG(U CH3)2), 31.2 (CAHCTUNGTREN(NNGU CH3)2), 25.0 (b-THF),
G
ACHTUNGTRENNUNG
C57H72NO3S2ScSi2 (984.4): C 69.54, H 7.37, N 1.42; found: C 66.22, H
7.20, N 1.65.
Synthesis of Y–2
A solution of pro
was added slowly to
ACHUTGTNRENNUGliACHTUNGTRENNUNG
a
G
CHTUNGTRENNUNG
0.14 mmol, 1 equiv) in benzene (1 mL) at 258C. The orange solution was
stirred at 708C for 24 h. The solvent was removed under vacuum to
afford a colorless powder that was dissolved in n-pentane (2 mL), fil-
tered, and stored at À308C for 2 weeks. After recrystallization, complex
Y–2 was afforded as
a colorless powder (0.08 g, 0.08 mmol, 57%).
1H NMR (400 MHz, C6D6, 258C): d=7.50 (d, 4J
H5), 7.35 (d, 4J
(H,H)=2.6 Hz, 2H; Ph-H3), 7.34–7.326 (m, 8H; Ph-H),
ACHTUNGTREN(NUNG H,H)=2.6 Hz, 2H; Ph-
AHCTUNGTRENNUNG
7.20–7.16 (m, 4H; Ph-H), 7.09–7.05 (m, 6H; Ph-H), 6.89–6.85 (m, 6H;
Ph-H), 4.99–4.97 (m, 2H; SiH), 3.64 (s, 2H; SCH2S), 3.16–3.12 (brs 4H;
a-THF), 1.80 (s, 12H; CACTHUNTRGENN(UG CH3)2), 1.64 (s, 12H; CAHCTUNGTREN(NUGN CH3)2), 1.09–1.05 (brs
Synthesis of Sc–1
[Sc{NACHTUNGTRENNUNG(SiMe2H)2}3ACHTUNGTRENNUNG(thf)] (0.20 g, 0.4 mmol, 1 equiv) and proACHTUNEGRTGlNNUN iACHTUNGRTENNUGgand 1
(0.19 g, 0.4 mmol, 1 equiv) were dissolved in benzene (2.5 mL) and the
solution stirred for 24 h at 708C. After removing the solvent in vacuo,
the colorless solid formed was recrystallized from n-pentane at À308C to
give Sc–1 as a colorless powder (0.12 g, 0.16 mmol, 42%). 1H NMR
4H; b-THF), 0.40–0.38 (brs, 6H; SiCH3), 0.37–0.35 ppm (brs, 6H;
SiCH3); 13C NMR (100.1 MHz, C6D6, 258C): d=165.1 (Ph-C1), 152.1
(Ph-C), 151.5 (Ph-C), 138.1 (Ph-C6), 137.3 (Ph-C4), 131.5 (Ph-C3), 129.8
(Ph-C), 128.4 (Ph-C), 127.9 (Ph-C), 127.1 (Ph-C5), 126.6 (Ph-C), 125.9
(Ph-C), 124.8 (Ph-C), 121.1 (Ph-C2), 70.1 (a-THF), 51.7 (SCH2S), 43.2
(400 MHz, C6D6, 258C): d=7.71 (d, 4J
(H,H)=2.6 Hz, 2H; Ph-H), 7.51
4
(d, J
(H,H)=2.6 Hz, 2H; Ph-H), 5.40 (sept, J
U
(C
A
E
ACHTUNTGRENNG(U CH3)2), 30.2 (CAHCTUNGTREN(NNGU CH3)2), 25.2 (b-THF),
4.10 (s, 4H; a-THF), 3.71 (s, 2H; SCH2S), 1.83 (s, 18H; C
(s, 18H; C
ACHTUNGTRENNUNG
3.7 (Si
N
ACHTUNGTRENNUNG
N
ACHTUNGTRENNUNG
&
&
&8
&
www.chemasianj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 0000, 00, 0 – 0
ÝÝ These are not the final page numbers!

Jun Okuda et al.
C57H72NO3S2YSi2 (1028.39): C 66.57, H 7.06, N 1.36; found: C 65.93, H
6.77, N 1.34.
C3), 127.1 (Ph-C), 126.4 (Ph-C), 125.8 (Ph-C), 124.9 (Ph-C), 116.4 (Ph-
C2), 68.8 (a-THF), 51.9 (SCH), 43.1 (C(CH3)2), 42.6 (C(CH3)2), 31.2 (Cy-
C), 31.1 (C(CH3)2), 31.0 (Cy-C), 28.4 (C(CH3)2), 25.6 (b-THF), 23.2 (Cy-
C), 3.9 (Si(CH3)2), 3.8 ppm (Si(CH3)2); elemental analysis: calcd (%) for
G
ACHTUNGTRENNUNG
E
ACHTUNGTRENNUNG
Synthesis of Sc–3
N
ACHTUNGTRENNUNG
C61H78NO3S2YSi2 (1082.48): C 67.68, H 7.26, N 1.29; found: C 67.08, H
6.78, N 1.10.
Pro
ACHTUNGTRENNUNGliACHTUNGTRENNUNG
to a solution of [Sc{N
N
CHTUNGTRENNUNG
pentane (2 mL). The reaction was stirred at room temperature for 18 h.
The solvent was removed in vacuo to give a white powder that was dis-
solved in n-pentane (1 mL), filtered, and stored at À308C for 24 h. After
recrystallization, complex Sc–3 was isolated as a colorless powder (0.11 g,
0.14 mmol, 63%). 1H NMR (400 MHz, C6D6, 258C): d=7.51 (d, 4J-
Synthesis of Sc–6
A solution of pro
was added dropwise to
ACHUTGTNRENNUGliACHTUNGTRENNUNG
a
G
CHTUNGTRENNUNG
0.19 mmol, 1 equiv) in benzene (1 mL) at 258C. The orange solution was
stirred at 708C for 24 h. The solvent was removed under vacuum to
afford an orange oil, which was dissolved in a mixture of n-pentane/THF
(1:1, 3 mL), filtered, and stored at À308C for 3 d. After recrystallization,
complex Sc–6 was isolated as an orange powder (0.15 g, 0.14 mmol,
71%). 1H NMR (400 MHz, C6D6, 258C): d=7.61–7.59 (m, 2H; Ph-H5),
7.45–7.43 (m, 2H; Ph-H3), 7.31–7.25 (m, 8H; Ph-H), 7.20–7.16 (m, 6H;
Ph-H), 7.14–7.12 (m, 2H; Ph-H), 7.10–6.90 (m, 6H; Ph-H), 5.11–5.19 (m,
2H; SiH), 3.12–3.18 (m, 4H; a-THF), 2.83 (s, 1H; SCH), 2.73 (s, 1H;
SCH), 2.36 (s, 1H; Cy-H), 2.21 (s, 1H; Cy-H), 2.09–2.03 (m, 6H; Cy-H),
A
ACHTUNGTNER(NUNG H,H)=2.6 Hz, 2H; Ph-H3), 5.17
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(CH3)3), 1.32–1.30 (m, 4H; b-THF), 0.47 ppm (d, 3J
Si-CH3); 13C NMR (100.1 MHz, C6D6, 258C): d=160.3 (Ph-C1), 139.0
(Ph-C6), 137.3 (Ph-C4), 125.1 (Ph-C5), 124.8 (Ph-C3), 120.8 (Ph-C2), 68.2
(SCH2S), 68.1 (a-THF), 35.6 (S-CH2Ph), 32.2 (6-C
(CH3)3), 31.9 (6-C(CH3)3), 30.5 (4-C(CH3)3), 25.8 (THF), 2.8 ppm (Si-
(CH3)3); elemental analysis data could not be obtained.
ACHTUGNTRENN(UNG CH3)3), 32.0 (4-C-
A
R
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
1.82 (s, 3H; C
N
ACHTUNTGRENGU(N CH3)2), 1.67 (s, 6H; CACHUTNTGERN(NUGN CH3)2), 1.63
Synthesis of Sc–4
(s, 6H; C(CH3)2), 1.59 (s, 6H; C
N
ACHTUNGTRENNUNG
0.98 (m, 4H; b-THF), 0.35–0.31 ppm (m, 12H; SiCH3); 13C NMR
(100.1 MHz, C6D6, 258C): d=167.4 (Ph-C1’), 166.5 (Ph-C1), 151.9 (Ph-
C), 137.3 (Ph-C4’), 137.3 (Ph-C6’), 137.1 (Ph-C6), 135.9 (Ph-C4), 133.3
(Ph-C3’), 132.6 (Ph-C3), 128.8 (Ph-C), 127.9 (Ph-C), 127.1 (Ph-C), 126.8
(Ph-C), 126.1 (Ph-C), 125.8 (Ph-C), 125.0 (Ph-C), 117.2 (Ph-C2’), 116.3
A solution of proACHTUNGTRENNUNGliACHTUNGTRENNUNG
was added dropwise to
a
N
CHTUNGTRENNUNG
0.19 mmol, 1 equiv) in benzene (1 mL) at 258C. The orange solution was
stirred at 708C for 24 h. The solvent was removed under vacuum to
afford an orange oil, which was dissolved in a mixture of n-pentane/THF
(1:1, 3 mL, filtered, and stored at À308C for 3 d. After recrystallization,
complex Sc–4 was afforded as a colorless powder (0.13 g, 0.13 mmol,
(Ph-C2), 71.4 (a-THF), 56.3 (SCH), 53.9 (SCH), 43.2 (C
(CH3)2), 35.3 (C(CH3)2), 34.5 (C(CH3)2), 34.3 (C(CH3)2), 34.1 (C
31.3 (C(CH3)2), 31.1 (C(CH3)2), 28.5 (Cy-C), 27.7 (Cy-C), 27.4 (Cy-C),
27.2 (Cy-C), 26.9 (Cy-C), 26.1 (Cy-C), 25.7 (Cy-C), 25.0 (b-THF),
3.9 ppm (Si(CH3)2; elemental analysis calcd (%) for C64H84NO3S2ScSi2
ACHTUNGTRENNUNG
A
E
U
G
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
67%). 1H NMR (400 MHz, C6D6, 258C): d=7.68 (d, 4J
2H; Ph-H5), 7.55 (d, J
(H,H)=5.4 Hz,
3
(H,H)=7.5 Hz, 2H; Ph-H3), 7.34–7.28 (brs, 10H;
AHCTUNGTRENNUNG
Ph-H), 7.24–7.22 (m, 6H; Ph-H), 7.12–7.10 (m, 4H; Ph-H), 5.20–5.16 (m,
2H; SiH), 3.27–3.21 (m, 4H; a-THF), 2.70–2.68 (m, 2H; SCH), 2.19 (s,
(1080.61): C 71.13, H 7.84, N 1.30; found: C 69.35, H 7.91, N 1.21.
3H; CH3), 2.10 (s, 3H; C
2H; Cy-H), 1.73 (s, 3H; C
2H; Cy-H), 1.48–1.46 (brs, 2H; Cy-H), 1.13–1.109 (m, 4H; b-THF), 0.45
(d, 3J(H,H)=3.1 Hz, 6H; SiCH3), 0.42 ppm (d, 3J
(H,H)=3.1 Hz, 6H;
G
ACHTUNGTRENNUNG
Synthesis of Y–6
E
ACHTUNGTRENNUNG
A solution of pro
was added dropwise to a solution of [Y{N
ACHUTGTNRENNUGliACHTUNGTRENNUNG
G
G
N
CHTUNGTRENNUNG
SiCH3); 13C NMR (100.1 MHz, C6D6, 258C): d=166.5 (Ph-C1’), 165.9
(Ph-C1), 151.5 (Ph-C), 151.3 (Ph-C), 151.1 (PH-C), 151.0 (Ph-C), 137.3
(Ph-C6’), 137.0 (Ph-C6), 135.2 (Ph-C), 133.3 (Ph-C4’), 133.1 (Ph-C4),
128.2 (Ph-C3’), 128.0 (Ph-C3), 127.3 (Ph-C), 126.4 (Ph-C), 126.3 (Ph-C),
125.6 (Ph-C), 125.2 (Ph-C), 125.1 (Ph-C), 124.5 (Ph-C), 124.4 (Ph-C),
0.32 mmol, 1 equiv) in benzene (1 mL) at 258C. The solution was stirred
for 3 d at room temperature. The solvent was removed under vacuum to
afford an orange powder that was dissolved in a mixture of n-pentane/
THF (1:1, 5 mL), filtered, and stored at À308C for 5 d. After recrystalli-
zation, complex Y–6 was isolated as an orange powder (0.27 g, 0.24,
115.7 (Ph-C2), 70.8 (a-THF), 53.0 (SCH), 50.4 (SCH), 43.2 (C
42.6 (C(CH3)2), 42.4 (C(CH3)2), 41.9 (C(CH3)2), 33.1 (Cy-C), 30.7 (C-
(CH3)2), 30.4 (C(CH3)2), 30.3 (C(CH3)2), 29.2 (Cy-C), 28.8 (Cy-C), 28.2
(C(CH3)2), 27.0 (C(CH3)2), 24.3 (b-THF), 22.0 (Cy-C), 3.7 ppm (Si-
(CH3)2); elemental analysis: calcd (%) for C61H78NO3S2ScSi2 (1038.53): C
A
75%). 1H NMR (400 MHz, C6D6, 258C): d=7.57 (d, 4J
ACHTNGUTERN(UNG H,H)=2.5 Hz,
A
E
U
2H; Ph-H5), 7.34–7.30 (m, 6H; Ph-H), 7.29–7.27 (m, 2H; Ph-H3), 7.21–
7.17 (m, 4H; Ph-H), 7.12–7.09 (m, 4H; Ph-H), 7.08–7.04 (m, 4H; Ph-H),
A
R
ACHTUNGTRENNUNG
A
U
6.95 (t, 3J
ACHTUNGTRENNUNG
N
ACHTUNGTRENNUNG
70.55, H 7.48, N 1.36; found: C 68.90, H 7.49, N 0.98.
N
ACHTUNGTRENNUNG
0.35 (d, 3J(H,H)=3.0 Hz, 6H; SiCH3), 0.33 ppm (d, 3J
ACTHNUTRGENNUG ACHUTTGNREN(NUGN H,H)=3.0 Hz,
Synthesis of Y–4
6H; SiCH3), 13C NMR (100.1 MHz, C6D6, 258C): d=165.0 (Ph-C1), 152.0
(Ph-C), 151.8 (PH-C), 136.9 (Ph-C), 136.8 (Ph-C), 132.8 (Ph-C), 128.2
(Ph-C), 127.9 (Ph-C), 127.2 (Ph-C), 126.6 (Ph-C), 125.3 (Ph-C), 124.9
A solution of pro
was added dropwise to a solution of [Y{N
ACHTUNGTRENNUNGliACHTUNGTRENNUNG
U
CHTUNGTRENNUNG
0.16 mmol) in benzene (1 mL) at 258C. The orange solution was stirred
at 708C for 24 h. The solvent was removed under vacuum to afford an
orange oil, which was dissolved in a mixture of n-pentane/THF (1:1,
3 mL), filtered, and stored at À308C for 3 d. Complex Y–4 was isolated
as a colorless powder (0.13 g, 0.12 mmol, 61%). 1H NMR (400 MHz,
(Ph-C), 69.6 (a-THF), 58.8 (SCH), 43.2 (C
(C(CH3)2), 31.2 (C(CH3)2), 30.6 (Cy-C), 30.1 (Cy-C), 27.5 (Cy-C), 25.9
(Cy-C), 25.3 (b-THF), 3.7 ppm (Si(CH3)2); elemental analysis calcd (%)
ACHTUNTGRENNGU(CH3)2), 42.6 (CACHTUNGTERN(NUGN CH3)2), 31.3
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
for C64H84NO3S2YSi2 (1124.56): C 68.35, H 7.53, N 1.25; found: C 68.34,
H 7.43, N 0.99.
C6D6, 258C): d=7.59 (d, 3J
(H,H)=7.2 Hz, 4H; Ph-H3), 7.25 (dt, J
2H; Ph-H), 7.21 (d, 4J(H,H)=2.5 Hz, 2H; Ph-H), 7.17 (d, 3J
5.2 Hz, 2H; Ph-H), 7.15–7.11 (m, 6H; Ph-H), 7.06–7.02 (m, 4H; Ph-H),
4.97 (sept, 3J
(H,H)=3.0 Hz, 2H; SiH), 3.42–3.38 (m, 4H; a-THF), 2.63–
2.61 (m, 2H; SCH), 1.92 (s, 6H; C(CH3)2), 1.78 (s, 6H; C(CH3)2), 1.68–
1.64 (m, 4H; Cy-H), 1.63 (s, 6H; C(CH3)2), 1.62–1.60 (m, 2H; Cy-H),
1.60 (s, 6H; C (H,H)=
(CH3)2), 1.31–1.27 (m, 4H; b-THF), 0.36 (d, 3J
(H,H)=3.0 Hz, 6H; SiCH3);
(H,H)=2.5 Hz, 2H; Ph-H5), 7.34 (d, 3J-
ACHTUNGTRENNUNG
3
4
T
ACHUTGTNREN(NUG H,H)=3.1 Hz, JACHTNUGTRENNUNG
Synthesis of Sc–7
E
ACHTUNGTRENNUNG
Pro
ACHUTGTNRENNUGliACHTUNGTRENNUNG
N
slowly to a solution of [Sc{N
N
CHTUNGTRENNUNG
G
N
zene (3 mL). The yellow solution was stirred at 808C for 5 d. The solvent
was removed under vacuum to give a yellow powder that was dissolved
in n-pentane (3 mL), filtered, and stored at À308C for 3 d. After drying,
complex Sc–7 was isolated as a yellow powder (90 mg, 0.12 mmol, 57%).
1H NMR (400 MHz, 258C, C6D6): d=7.30–7.20 (m, 2H; Ph-H5), 7.06–
AHCTUNGTRENNUNG
G
ACHTUNGTRENNUNG
3.0 Hz, 6H; SiCH3), 0.33 ppm (d, 3J
ACHTUNGTRENNUNG
13C NMR (100.1 MHz, C6D6, 258C): d=167.1 (Ph-C1), 137.3 (Ph-C6’),
137.2 (Ph-C6), 134.2 (PH-C), 128.4 (Ph-C4), 128.2 (Ph-C3’), 127.9 (Ph-
6.90 (m, 2H; Ph-H3), 5.10 (sept, 3J
ACTHNUTRGNEU(GN H,H)=3.0 Hz, 2H; SiH), 4.14–3.90
Chem. Asian J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
9
&
&
&
These are not the final page numbers! ÞÞ

Stereoselective Polymerization of Lactide Monomers
FULL PAPERS
(m, 4H; a-THF), 3.94 (m, 2H; SCH2), 2.53–2.30 (m, 4H; Cy-H), 2.16 (s,
3H; Ph-CH3), 1.50 (s, 6H; Cy-CH3), 1.71–1.43 (m, 16H; Cy-H), 1.31–1.23
Synthesis of (S)-Y–5
l-Methyl lactate (0.003 g, 0.029 mmol, 1 equiv) was added to a solution
of complex Y–5 (0.030 g, 0.029 mmol, 1 equiv) in C6D6 (0.5 mL). The so-
lution was reacted at room temperature for 18 h.
ACTHNUTRGNEUNG
(m, 4H; b-THF), 0.39 ppm (d, 3J(H,H)=3.0 Hz, 12H; SiCH3); 13C NMR
(100.1 MHz, 258C, C6D6): d=164.4 (Ph-C1), 132.6 (Ph-C6), 132.1 (Ph-
C2), 128.6 (Ph-C5), 127.4 (Ph-C4), 125.8 (Ph-C3), 72.1 (a-THF), 51.5
(Cy-CACHTUNGTRENNUNG(CH3)), 38.9 (Cy-C), 37.4 (SCH), 27.4 (Cy-CH3), 25.2 (b-THF),
23.5 (Cy-C), 20.8 (Ph-CH3), 3.02 ppm (SiACHTUNRTGNEUNG(CH3)); elemental analysis could
Synthesis of (R)-Y–5
not be obtained.
d-Methyl lactate (0.003 g, 0.029 mmol, 1 equiv) was added to a solution
of complex Y–5 (0.030 g, 0.029 mmol, 1 equiv) in C6D6 (0.5 mL). The so-
lution was reacted at room temperature for 18 h.
Synthesis of Y–7
Pro
of [Y{N
ACHTUNGTRENNUNGliACHTUNGTRENNUNG
Crystal Structure Determination of Complexes Y–5
N
CHTUNGTRENNUNG
The yellow solution was stirred at 808C for 5 d. The solvent was removed
in vacuo to give a yellow powder that was dissolved in n-pentane (3 mL),
filtered, and stored at À308C for 3 d. After drying, complex Y–7 was iso-
lated as a yellow powder (98 mg, 0.13 mmol, 62%). 1H NMR (400 MHz,
Low-temperature single-crystal X-ray diffraction experiments were per-
formed with a MoKa radiation (l=0.71073 ꢁ) INCOATEC microsource
by using w scans and a multilayer optics monochromator. Single crystals
were mounted on a glass fiber in viscous hydrocarbon oil. Crystals were
quench-cooled to 100(2) K. Analysis of diffraction data collected with a
Bruker Apex II CCD diffractometer was performed by using SAINT+
within the SMART software package.[21a] Empirical absorption correc-
tions were applied to all data by using MULABS.[21b] The structures were
solved by direct methods using IR-92[21c] and refined against F2 using all
reflections with the SHELXL-97[21d] software within the graphical inter-
face WIN-GX.[21e] Graphics were generated by the program Diamond.[21f]
All non-hydrogen atoms in the structures were refined anisotropically;
all hydrogen atoms were generated in ideal positions and treated as
riding by using the riding model; only the atoms H1 and H2 (that are at-
tached to the silicon atoms) were refined in their position. Data are
given in Table 3.
258C, C6D6): d=7.26 (d, 4J
(H,H)=2.4 Hz, 2H; Ph-H3), 4.97 (sept, 3J
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
T
3.85–3.81 (m, 4H; a-THF), 3.77 (s, 2H; SCH2), 2.17 (s, 6H; Ph-CH3),
2.10–1.90 (m, 4H; Cy-H), 1.68 (s, 6H; Cy-CH3), 1.60–1.43 (m, 16H; Cy-
H), 1.30–1.26 (m, 4H; b-THF), 0.39 ppm (d, 3J
ACTHNUTRGNE(NUG H,H)=3.0 Hz, 12H;
SiCH3); 13C NMR (100.1 MHz, 258C, C6D6): d=165.8 (Ph-C1), 133.1
(Ph-C6), 132.1 (Ph-C2), 128.2 (Ph-C5), 127.9 (Ph-C4), 125.0 (Ph-C3), 71.1
(a-THF), 51.7 (Cy-CACHTUNGTRENNUNG(CH3)), 39.0 (Cy-C), 37.2 (SCH), 27.4 (Cy-CH3),
25.3 (b-THF), 23.5 (Cy-C), 20.8 (Ph-CH3), 3.20 ppm (SiACHTUNTRGNE(NUG CH3)); elemental
analysis could not be obtained.
Synthesis of Sc–8
Pro
ACHTUNGTRENNUNGliACHTUNGTRENNUNG
CCDC-841975 contains the supplementary 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
[Sc{N
N
CHTUNGTRENNUNG
yellow solution was stirred at 258C for 48 h. The solvent was removed in
vacuo to give a yellow powder that was dissolved in n-pentane (3 mL),
filtered, and stored at À308C for 3 d. After drying, complex Sc–8 was iso-
Polymerization of Lactide Monomers
1
lated as a yellow powder (209 mg, 0.28 mmol, 72%). H NMR (400 MHz,
A solution of catalyst Y–1 (10 mg) in toluene or THF (0.5 mL) was
added to a solution of the desired amount of meso- or rac-lactide (details
258C, C6D6): d=7.24 (s, 1H; Ph-H5’), 7.22 (s, 1H; Ph-H5), 7.04 (s, 1H;
Ph-H3’), 6.88 (s, 1H; Ph-H3), 5.24 (sept, 1H; 3J
ACTHNUTRGNEUNG(H,H)=3.1 Hz, SiH),
4.20–4.10 (m, 2H; a-THF), 4.04–3.93 (m, 2H; a-THF), 2.50–2.35 (m, 4H;
SCH), 2.17 (s, 3H; Ph-CH3), 2.16 (s, 3H; Ph-CH3), 2.08–1.93 (m, 4H; Cy-
H), 1.77 (s, 3H; Cy-CH3), 1.73–1.67 (m, 6H; Cy-H), 1.65 (s, 3H; Cy-
CH3), 1.63–1.48 (m, 10H; Cy-H), 1.25–1.21 (m, 4H; b-THF), 0.46 (d, 3J-
Table 3. Crystallographic data for complex Y–5.
Y–5
ACHTUNGTRENNUNG ACHTUNTGERN(NUGN H,H)=3.1 Hz, 6H; SiCH3);
(H,H)=3.1 Hz, 6H; SiCH3), 0.39 ppm (d, 3J
formula
Mr
cell setting
space group
a [ꢁ]
b [ꢁ]
c [ꢁ]
a [8]
b [8]
C129H172N2O6S4Si4Y2
13C NMR (100.1 MHz, 258C, C6D6): d=167.3 (Ph-C1’), 166.8 (Ph-C1),
137.3 (Ph-C6’), 136.3 (Ph-C6), 132.0 (Ph-C2’), 131.8 (Ph-C2), 131.6 (Ph-
C5’), 131.5 (Ph-C5), 126.2 (Ph-C4’), 125.4 (Ph-C4), 119.2 (Ph-C3’), 118.6
2265.11
monoclinic
P21/n
(Ph-C3), 72.3 (a-THF), 39.0 (Cy-C
(Cy-C), 37.3 (SCH), 37.0 (Cy-C), 27.5 (Cy-C), 26.5 (Cy-CH3), 25.2 (b-
THF), 23.6 (Cy-C), 20.9 (Ph-CH3), 3.8 (Si(CH3)), 3.6 ppm (Si(CH3)); ele-
ACHTUNGTERN(NUNG CH3)), 38.8 (Cy-C), 37.8 (Cy-C), 37.5
14.9108(11)
20.1511(16)
20.9690(16)
90.00(0)
98.940(2)
90.00(0)
6224.0(8)
2
A
ACHTUNGTRENNUNG
mental analysis calcd (%) for C38H62NO3S2ScSi2 (746.16): C 61.17, H 8.38,
N 1.88; found: C 56.02, H 7.53, N 1.19.
Synthesis of Y–8
g [8]
V [ꢁ3]
Z
Pro
li
U
[Y{N
N
CHTUNGTRENNUNG
1calcd [mgmÀ3
]
1.209
yellow solution was stirred at room temperature for 48 h. The solvent
was removed in vacuo to give a yellow powder that was dissolved in n-
pentane (3 mL), filtered, and stored at À308C for 3 d. After drying, com-
plex Y–8 was isolated as a yellow powder (0.19 g, 0.24 mmol, 76%).
radiation type
MoKa
1.086
m [mmÀ1
]
crystal form
color
data collection method
absorption correction
Tmin
plate
colorless
w scan
multiscan
0.6706
1H NMR (400 MHz, 258C, C6D6): d=7.23 (d, 4J
H5), 6.98 (d, 4J
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
3.97–3.83 (m, 4H; b-THF), 2.56–2.47 (m, 4H; SCH2), 2.18 (s, 6H; Ph-
CH3), 1.97–1.88 (m, 4H; Cy-H), 1.74–1.70 (m, 4H; Cy-H), 1.69 (s, 6H;
Cy-CH3), 1.68–1.53 (m, 12H; Cy-H), 1.24–1.20 (m, 4H; a-THF),
Tmax
0.9477
no. reflns measured
independent reflns
obsd reflns
Rint
73781
12766
8458
0.1163
ACHTUNGTRENNUNG
0.43 ppm (d, 3J(H,H)=3.0 Hz, 12H; SiCH3), 13C NMR (100.1 MHz,
258C, C6D6): d=167.3 (Ph-C1), 137.3 (Ph-C4), 132.2 (Ph-C2), 131.5 (Ph-
C5), 125.3 (Ph-C4), 118.8 (Ph-C3), 71.0 (a-THF), 39.0 (Cy-C), 37.0 (Cy-
C), 27.5 (Cy-C), 26.2 (Cy-C
ACHTNUGTERN(NUGN CH3)), 25.1 (Cy-CH3), 23.6 (Cy-CH3), 20.9
no. parameters
R1 (I>s(I))
wR2
688
0.0521
0.1125
(b-THF), 3.7 ppm (Si(CH3)); elemental analysis could not be obtained.
ACHTUNGTRENNUNG
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Jun Okuda et al.
are given in Tables 1 and 2), which was dissolved in toluene or THF
(1.5 mL). After the desired time, the polymerization mixture was
quenched with drops of moist hexane and was added slowly to cooled,
rapidly stirred hexane. The polymer was filtered over a Bꢃchner funnel,
washed with diethyl ether, and dried in vacuo. The polymer was dissolved
in a minimum quantity of CH2Cl2 and run through a flash silica gel
column (in a Pasteur pipette) to afford a colorless solution, which was
added slowly to cooled, rapidly stirred hexane. Finally, the colorless poly-
mer was filtered and dried in vacuo.
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Acknowledgements
We thank the Deutsche Forschungsgmeinschaft and the Fonds der Chem-
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generous gift of meso-lactide.
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Received: October 2, 2011
Published online: && &&, 0000
Chem. Asian J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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FULL PAPERS
Ring-Opening Polymerization
Andreas Kapelski, Jean-Charles Buffet,
Thomas P. Spaniol,
Jun Okuda*
&&&& — &&&&
Group 3 Metal Initiators with an
[OSSO]-Type Bis(phenolate) Ligand
for the Stereoselective Polymerization
of Lactide Monomers
Backbone requirements: A series of
rare-earth metal bis(dimethylsilyla-
mido) complexes with [OSSO]-type
bis(phenolate) ligands [Ln{N-
x=2; thf=tetrahydrofuran; see pic-
ture) were synthesized and used in the
ring-opening polymerization of rac-
and meso-lactides.
ACHUNTERGN(NUG SiHMe2)2}3ACHTUNGTREN(NUGN thf)x] (Ln=Sc, x=1; Y,
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Chem. Asian J. 0000, 00, 0 – 0
ÝÝ These are not the final page numbers!