Isospecific polymerizations of alkyl methacrylates with a bis(alkyl)Yb complex and formation of stereocomplexes with syndiotactic poly(alkyl methacrylate)s

Article abstract of DOI:10.1016/j.tet.2003.07.014

Yb[C(SiMe₃)₃]₂ initiates the living polymerization of methyl methacrylate (MMA) at -78°C to give the polymer with M_n of 51.0×10⁴ (M_w/M _n=1.1) and high isotacticity (97%) in a quantitative yield. Mixing of the acetone solution of resulting polymer (M_n=16.3×10 ⁴) with the acetone solution of syndiotactic poly(MMA) (M _n=15.7×10⁴) prepared by the (C₅Me ₅)₂SmMe(THF) initiator produces desired stereocomplex in high yield bearing very high T_m whose tensile modulus is higher than the respective isotactic and syndiotactic poly(MMA)s. Yb[C(SiMe ₃)₃]₂ also generated isotactic (98%) poly[2-(dimethylamino)ethyl methacrylate] (DMEMA), and (C₅Me ₅)₂SmMe(THF) affords the syndiotactic (97%) polymer in high yields. The combination of isotactic poly(MMA)-block-poly(DMEMA) (97/3) and syndiotactic poly(MMA)-block-poly(DMEMA) (97/3) provides the amphiphathic stereocomplex. In sharp contrast to the catalysis of Yb[C(SiMe₃) ₃]₂ in toluene, the addition of THF or HMPA resulted in the formation of syndio-rich poly(MMA).

Full text of DOI:10.1016/j.tet.2003.07.014

Tetrahedron 59 (2003) 10409–10418
Isospecific polymerizations of alkyl methacrylates with a
bis(alkyl)Yb complex and formation of stereocomplexes with
syndiotactic poly(alkyl methacrylate)s
Guizhong Qi, Yuu Nitto, Akira Saiki, Taketoshi Tomohiro, Yuushou Nakayama
*
and Hajime Yasuda
Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, 1-4-1 Higashi-Hiroshima,
Higashi-Hiroshima 739-8527, Japan
Received 24 April 2003; accepted 30 July 2003
Abstract—Yb[C(SiMe3)3]2 initiates the living polymerization of methyl methacrylate (MMA) at 2788C to give the polymer with Mn of
51.0£104 (Mw/Mn¼1.1) and high isotacticity (97%) in a quantitative yield. Mixing of the acetone solution of resulting polymer
(Mn¼16.3£104) with the acetone solution of syndiotactic poly(MMA) (Mn¼15.7£104) prepared by the (C5Me5)2SmMe(THF) initiator
produces desired stereocomplex in high yield bearing very high Tm whose tensile modulus is higher than the respective isotactic and
syndiotactic poly(MMA)s. Yb[C(SiMe3)3]2 also generated isotactic (98%) poly[2-(dimethylamino)ethyl methacrylate] (DMEMA), and
(C5Me5)2SmMe(THF) affords the syndiotactic (97%) polymer in high yields. The combination of isotactic poly(MMA)-block-
poly(DMEMA) (97/3) and syndiotactic poly(MMA)-block-poly(DMEMA) (97/3) provides the amphiphathic stereocomplex. In sharp
contrast to the catalysis of Yb[C(SiMe3)3]2 in toluene, the addition of THF or HMPA resulted in the formation of syndio-rich poly(MMA).
q 2003 Elsevier Ltd. All rights reserved.
1. Introduction
samariummethyl complexes were carried out to
reduce the cost of initiator from the industrial point of
view.6
Novel rare earth metal initiators such as SmMe(C5Me5)2-
(THF) 1 or [SmH(C5Me5)2]2 have been found to realize the
highly syndiotactic poly(MMA) (.95%) with high
molecular weight (Mn.100£104) and low polydispersity
(Mw/Mn,1.05) in a quantitative yield by the unique living
polymerization.1,2 Since this reaction proceeds in a living
fashion, we could isolate the 1:4 stoichiometric reaction
product between [SmH(C5Me5)2]2 and methyl methacrylate
(MMA), which could be analyzed by X-ray analysis to
include an eight-membered ring. By the further addition of
100 equiv. of MMA, this adduct shows the excellent
catalytic activity giving a polymer of ca. Mn¼10000 with
extremely low polydispersity (Mw/Mn¼1.02) in a quanti-
tative yield. This sort of initiator also displays high
catalytic efficiency for living polymerizations of alkyl
acrylates,3 lactones,4 and cyclic carbonates.5 More
recently, polymerizations of MMA using trimethylsilyl-
and bis-(trimethylsilyl)-substituted bis(cyclopentadienyl)-
On the other hand, the preparation method for high
molecular weight isotactic poly(MMA)s has not been
established until now. The molecular weights obtained so
far for isotactic polymer (.96%) are only 12000–20800 by
the use of BuMgBr or t-BuMgBr in toluene.7,8 Therefore,
we have explored a variety of metallocene complexes such
as cyclopentadienyl(indenyl)SmMe-(THF) and cyclo-
pentdienyl(fluorenyl)SmMe-(THF) for fixation of the
reaction site to one direction. However, all the attempts
failed, since these initiators always produce the syndiotactic
polymers. Therefore, we have next examined the
polymerization using a variety of non-metallocene type
rare earth metal complexes. As
a consequence,
Yb[C(SiMe3)3]2 was found for the first time to generate
high molecular weight isotactic poly(MMA)s in high yield.
Then we have explored the synthesis of stereocomplex by
mixing the acetone solution of the resulting syndiotactic and
isotactic poly(MMA)s. As an extension of this reaction, we
are succeeded in preparation of both syndiotactic and
isotactic poly[2-(dimethylamono)ethylene methacrylate]
Keywords: rare earth metal complexes; methyl methacrylate; 2-
(dimethylamino)ethyl methacrylate; stereocomplex; dialkylytterbium
complex; dialkylsamarium.
(DMEMA)
Yb[C(SiMe3)3]2, respectively (Scheme 1).
using
SmMe(C5Me5)2(THF)
or
*
Corresponding author. Tel.: þ81-824-24-7730; fax: þ81-824-24-5494;
e-mail: yasuda@hiroshima-u.ac.jp
0040–4020/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2003.07.014

10410
G. Qi et al. / Tetrahedron 59 (2003) 10409–10418
2. Results and discussion
2.1. Preparation of isotactic poly(MMA) with high
molecular weight
In order to realize the isotactic poly(MMA) (isotacticity
.90%) with high molecular weight (Mn.200000), we have
explored the polymerizations using Et2Si(C5H4)(C5Me4)YH
and (C5H5)(fluorenyl)SmMe(THF) for fixation of the
reaction site at the less bulky (C5H5) direction by the
assistance of bulky C5Me4 or fluorenyl group. However,
the polymerizations always produce only syndiotactic
poly(MMA)s (78 and 82%, respectively) with high
molecular weights (Mn¼6–8£104) and low polydispersities
(Mw/Mn¼1.15–1.27) at 08C.
Therefore, we have explored the catalysis of non-
metallocene type rare earth metal complexes using
(perfluorophenyl)2Yb(THF)4 2,9 Ln(CuCPh)2 3,10
Sm[CH(SiMe3)2]3 4,11 Sm[N(SiMe3)2]2(THF)2 5,12 and
Yb[C(SiMe3)3]2 6 (Fig. 1).13 As a consequence, all of
these complexes exhibit excellent catalysis by themselves at
2788C toward the polymerization of MMA without
presence of any cocatalyst such as methylaluminoxane
(MAO) or metal oxide (Table 1). (Perfluorophenyl)2-
Yb(THF)4 and Ln(CuCPh)2 produced syndiotactic
poly(MMA)s in high yields, and Sm[CH(SiMe3)2]3 and
Sm[N(SiMe3)2]2(THF)2 produced atactic poly(MMA)s in
Scheme 1. Non-metallocene type initiators used for the polymerizations.
Figure 1. Molecular structure of 9.

G. Qi et al. / Tetrahedron 59 (2003) 10409–10418
Table 1. Polymerizations of methyl methacrylate with non-metallocene complexesa
10411
mm
Initiator
Temperature (8C)
Time (h)
Yield (%)
Mn/104
Mw/Mn
rr
mr
(PhCuC)2Ybb 2
0
278
278
20
6
20
0
52
100
7.7
12.1
1.5
1.5
83
82
8
8
9
10
(C6F5)2Yb(THF)4 3
0
278
278
20
6
20
0
67
100
3.0
4.4
1.3
1.2
82
80
17
18
1
2
[(Me3Si)2N]2Sm(THF)2 4
[(Me3Si)2CH]3Sm 5
0
278
278
20
6
20
0
21
35
0.6
0.7
1.2
1.3
27
27
34
35
39
38
0
278
278
20
6
20
13
3
5
0.5
3.3
6.6
2.0
1.4
1.4
45
49
50
34
42
41
21
9
9
[(Me3Si)3C]2Yb 6
0
278
278
20
6
20
98
75
100
15.3
32.7
51.0
1.2
1.2
1.1
9
1
1
13
2
2
78
97
97
a
Polymerization conditions: [M]0/[I]0¼1000 mol/mol, solvent toluene, toluene/[M]0¼2.0 vol/vol.
moderate yields. In contrast to these initiators, we have
found that Yb[C(SiMe3)3]2 produced high isotactic poly-
(MMA) in excellent yield as evidenced from 1H NMR
spectrum (Me, 1.18 ppm in CDCl3 while that of syndiotactic
polymer at 0.88 ppm). Resulting Mn is 51.0£104 and Mw/Mn
is 1.1. To understand more precise reaction conditions, the
monomer/initiator ratio was varied using a very pure
complex (Table 2). When the reaction temperature was
fixed to 2788C and the reaction time to 3 h, we could obtain
isotactic (97%) poly(MMA) with Mn of 49.9£104 by using
[M]0/[I]0 ratio of 2900 mol/mol. The use of decreased [M]0/
[I]0 ratio of 200 mol/mol at 2788C resulted in the formation
of Mn of 3.2£104 with high isotacticity (97%). Thus, Mn
increased linearly with an increase of [M]0/[I]0 ratio
suggesting the occurrence of living polymerization. To
further confirm the livingness, two step polymerization was
carried out, i.e. polymerization of MMA (500 equimole)
first takes place for 3 h at 2788C using Yb[C(SiMe3)3]2 as
an initiator. Resulting Mn is 7.3£104 (Mw/Mn¼1.1) in 100%
yield, and then further addition of 500 equimole of MMA
followed by the polymerization at 2788C resulted in the
formation of poly(MMA) having Mn of 15.2£104 (Mw/
Mn¼1.3) in 100% yield (in total 200% yield). This behavior
clearly indicates the occurrence of living polymerization.
Isotactic polymerization should occur by the enantio-
morphic site control. The divalent species should be
converted to trivalent species by the addition of MMA as
shown in Scheme 2.
Scheme 2. Reaction mode for initiation of MMA polymerization.
In fact, head-to-head dimer of MMA could be isolated by
the hydrolysis of 1:1 reaction mixture in 67% yield. Isotactic
polymer should be formed without formation of an eight-
membered ring intermediate, holding the linear structure as
described in Scheme 3.
The syndiotactic polymerization of MMA proceeds via an
eight-membered ring containing Sm atom as revealed by the
X-ray analysis of (C5Me5)2Sm(MMA)2H species.1,2
Table 2. Yb[C(SiMe3)3]2 initiated polymerization of MMA
[M]0/[I]0 Yield (mol/mol) Mn (%) Mw/Mn 104
Tacticity
mm mr
rr
Scheme 3. Reaction mechanism for initiation of MMA polymerization.
200
500
.99
.99
.99
.99
.99
28
3.2
7.3
16.3
32.2
49.9
3.2
1.2
1.2
1.1
1.2
1.2
1.7
–
97
97
97
97
97
1
2
2
2
2
2
1
1
1
1
1
2.2. Formation of high molecular weight stereocomplex
of poly(MMA)
1000
2000
2900
500a
1000
Recently, preparation of stereocomplexes using low
molecular weight isotactic and syndiotactic poly(MMA)
has been reported.14 Since we could prepare both high
molecular isotactic and syndiotactic poly(MMA)s using
Yb[C(SiMe3)3]2 and (C5Me5)2SmMe(THF), respectively,
12 87
–
0.8
–
–
–
Polymerization conditions: 2788C for 3 h in toluene. [toluene]/[M]0¼3.0
vol/vol.
a
2788C for 3 h in THF.

10412
G. Qi et al. / Tetrahedron 59 (2003) 10409–10418
i.e. syn-1: syndiotacticity 95%, Mn¼13.2£104,
Mw/Mn¼1.04, syn-2: syndiotacticity 93%, Mn¼38.2£104,
Mw/Mn¼1.08, iso-1: isotacticity 98.5%, Mn¼16.5£104, Mw/
Mn¼1.20, iso-2: isotacticity 98%., Mn¼35.7£104, Mw/
Mn¼1.20. The gel formation occurred in high conversion
(89–95%) by mixing iso-1 with syn-1 or by mixing iso-2
with syn-2 in the 1/2 molar ratio, while gel formation
between iso-2 and syn-1 markedly decreased. However, the
gel formation between iso-2 with syn-1 in 1/4 ratio indicates
highyield.Inthiscase, isotacticpolymershouldbesurrounded
by two equimoles of the syndiotactic polymer chain.
Table 3. Preparation of stereocomplexes between syndiotactic and isotactic
poly(MMA)
Iso/syndio ratio (mol/mol)
Yield (%)
Tm (8C)
Tg (8C)
1/3
1/2
1/1
2/1
43
83
52
15
207
208
204
204
94.3
94.6
93.8
93.2
Stereocomplexes were obtained as a gel by mixing of syndiotactic
poly(MMA) with isotactic poly(MMA) dissolved in acetone.
Scheme 4. Formation of high molecular weight stereocomplexes.
we explored the synthesis of high molecular weight
stereocomplexes by the addition of the acetone solution of
isotactic poly(MMA) to the acetone solution of syndiotactic
poly(MMA). Gel formation occurred immediately after
mixing these two solutions as white precipitates. The
addition of isotactic poly(MMA) (Mn¼16.3£104, Mw/
Mn¼1.11) to 2 equimolar amount of syndiotactic
poly(MMA) (Mn¼15.7£104, Mw/Mn¼1.01) provides
highest yield of the stereocomplex (Table 3), whose
molecular structure was proposed by Challa et al. to be
9/1 double-stranded helix (isotactic polymer is surrounded
by syndiotactic poly(MMA) (Scheme 4).15,16 This product
exhibits high Tm of 2088C. The 1/3 and 2/1 addition of
isotactic polymer to syndiotactic polymer yielded the
stereocomplex in only 43 and 15%, respectively, whose
Tm are 207 and 2048C. The composition of gel is
iso/syndio¼ca. 1/2 regardless the 1/3 or 2/1 addition of
iso/syndio polymers, as analyzed by GPC in CHCl3
(stereocomplex is dissociated into respective iso- and
syndiotactic polymers in CHCl3). These polymers show
intermediate Tg between isotactic poly(MMA) (Tg¼558C)
and syndiotactic poly(MMA) (Tg¼1308C). An annealing of
the resulting 1/2 stereocomplex in the DSC cell at 180 and
2008C for 5 days resulted in the increase of Tm to 208 and
2288C, respectively, due to the thermodynamic phase
transition (Table 4). We used four kinds of different
molecular weight poly(MMA)s with either high isotactic
or syndiotactic regulation to construct the stereocomplexes,
Mechanical properties of the stereocomplex are examined
using the isolated gel. In order to prepare rigid films, we
dissolved the gel to CHCl3 followed by the addition of
acetone (2/1 vol/vol ratio) and then the solution was
gradually evaporated to precipitate the film samples.
Table 5 shows the result of mechanical properties for
iso-1/syn-1, iso-2/syn-2 stereocomplexes together with
homopoly(syn-1) and homopoly(iso-1). Syn-1 exhibits
high tensile strength and high tensile modulus, while iso-1
has high elongation. The stereocomplex composed of iso-1/
syn-1 shows a little smaller tensile modulus, whereas iso-2/
syn-2 stereocomplex revealed higher tensile modulus
(131.2 kgf/mm2) than syn-2 homopolymer (116.1 kgf/
mm2). Tensile strengths of stetreocomplexes indicate the
intermediate value between iso-1 and syn-1 polymers, while
the elongation was lower than the homopolymers. Thus,
stereocomplexes exhibit rigid structure with high tensile
modulus and high tensile elongation.
Table 5. Mechanical properties of stereocomplexes and homopoly(MMA)
Polymers
Tensile modulus
(kgf/mm2)
Tensile strength
(kgf/mm2)
Elongation
(%)
Iso-1
Syn-1
Iso-1/syn-1
Iso-2/syn-2
30.2
116.1
96.3
8.0
42.9
35.6
30.7
435.2
42.9
12.4
9.8
131.2
Film samples were prepared by evaporation of acetone/CHCl3 (1/2 vol/vol)
mixture.
Table 4. Effect of annealing temperature on Tm
2.3. Preparation of high molecular weight syndiotactic
and isotactic poly[2-(dimethylamino)ethyl methacrylate]
Iso/syndio ratio (mol/mol)
Annealing temperature (8C)
Tm (8C)
1/2
1/2
180
200
210
228
As an extension of the present studies, we have explored
the polymerization of 2-(dimethylamino)ethyl metha-
cryrate (DMEMA) using SmMe(C5Me5)2(THF) and
Heated for 5 days.

G. Qi et al. / Tetrahedron 59 (2003) 10409–10418
10413
and low polydispersity (Table 6). The polymerization
completes in 4 h at 2788C giving polymers quantitatively
with Mn of 9.2£104 in the case of [M]0/[I]0¼1200 mol/mol.
Syndiotactcity reached 97%. The use of higher polymeriz-
ation temperatures resulted marked decrease of
syndiotacticity.
Table 6. Polymerizations of 2-(dimethylamono)ethyl methacrylate with
Cpp2SmMe(THF)
[M]0/[I]0
(mol/mol)
Temperature Time Yield Mn Mn 104
Tacticity
(8C)
(h)
(%)
mm mr rr
100
200
300
600
1200
25
0
278
278
278
0.5
1
5
5
5
100 1.1
100 1.9
1.18
1.08
1.14
1.20
1.22
1
1
0
0
0
21 78
13 86
Isotactic poly(DMEMA) was also available using
Yb[C(SiMe3)3]2 as an initiator. The Mn was measured in
water (see Section 4). The polymer yield reached 99% when
we used [M]0/[I]0 ratio of 200 mol/mol at 2788C (Table 7).
However, increasing polymerization temperature to 258C
lacks the catalytic activity, presumably due to the thermal
instability of the intermediate because of the formation of
unstable alkyl complex. Thus, isotacticity of 97% was
realized at 2788C.
99
99
98
3.0
5.3
9.4
3
3
3
97
97
97
Polymerization conditions, solvent toluene, toluene/[M]0¼3.0 vol/vol.
Yb[C(SiMe3)3]2 as initiators. Resulting polymers exhibit
high molecular weights and are soluble in water freely. Due
to growing concerns on environmental protections, water-
soluble polymers have undergone a fast development.
Cationic polyelectrolites are now a center of growing
interest in view of their various applications in areas such as
flocculation, adhesives, emulsion and dispersion
stabilizer.17,18 In this regard, the anionic polymerization of
DMEMA, the quaternization of which is straightforward,
has been considered to be promising. To our best
knowledge, the only preceding report on its anionic
polymerization has been published by Nazarov and Jerome,
who used butyllithium19 and diphenylmethyllithium/LiCl,20
respectively, as initiators. The polymerizations of DMEMA
were also reported using living radical initiators.21,22 We
wish to report here its polymerizations and copolymeriza-
tions with rare earth metal compounds.
The attempt to construct the stereocomplex by mixing the
water solution of isotactic and syndiotactic poly(DMEMA)s
failed, because of the formation of water-insoluble fraction
(yellow powder) only in very low yield (2 wt%).
Therefore, block copolymerizations of DMEMA with
MMA were carried out with (C5Me5)2SmMe(THF) or
Yb[C(SiMe3)3]2 (Table 8). The use of excess MMA
(MMA/DMEMA¼96/4) resulted in high yield of block
copolymers composed of 97/3 ratio (Scheme 4). The mixing
of the acetone solutions of the resulting isotactic and
syndiotactic block copolymers immediately generates the
stereocomplex as a gel (Table 9). Resulting polymer serves
as a novel amphipathic molecule toward both organic
solvent and water. The formation of stereocomplex was
confirmed by observing the high temperature of Tm [homo
iso- and syn-poly(MMA) do not show Tm values]. Resulting
The polymerization of DMEMA proceeded expectedly by
using (C5Me5)2SmMe(THF) to provide for the first time
highly syndiotactic polymers with high molecular weight
Table 7. Polymerizations of 2-(dimethylamino)ethyl methacrylate with Yb[C(SiMe3)3]2
[M]0/[I]0 mol/mol
Temperature (8C)
Time (h)
Yield (%)
Mn
Mn 104
Tacticity
mr
mm
rr
200
200
200
500
1000
25
0
278
278
278
1
1
5
5
5
11
34
99
89
45
1.5
1.6
3.0
8.7
4.53
3.85
1.35
1.74
2.11
16
21
98
98
98
21
30
1
2
2
63
49
1
0
0
12.5
Polymerization conditions, solvent toluene, toluene/[M]0¼5.0 vol/vol.
Table 8. Block copolymerization of DMEMA with MMA
Initiator
[M]0/[I]0
(mol/mol)
Feeded ratio
DMEMA/MMA
Yield
(%)
Composition
DMEMA/MMA
Mn
Mn 104
Tacticity
mr
mm
rr
Cpp2SmMe
Yb[C(SiMe3)2]2
200
200
4/96
4/96
99
99
3/97
3/97
9.5
9.4
1.16
1.28
0.1
92.4
6.2
5.1
93.7
2.5
Polymerization conditions, DMEMA was polymerized for 0.5 h followed by the polymerization of MMA for 3 h at 2788C. Polymerization conditions; solvent
toluene.
Table 9. Stereocomplex between isotactic poly(MMA-co-DMEMA) and syndiotactic poly(MMA-co-DMEMA)
Polymer
Iso/syn ratio, feeded ratio
Iso/syn, found
Yield (%)
T
m (8C)
Tg (8C)
iso-Poly(MMA-co-DMEMA)/syn-poly(MMA-co-DMEMA)
iso-Poly(MMA-co-DMEMA)/syn-poly(MMA)
1.0/2.0
1.0/2.0
1.0/2.0
1.0/2.1
85
78
198
196
110
113
Acetone solution of isotactic poly(MMA-co-DMEMA) was mixed with syndiotactic poly(MMA-co-DMEMA).

10414
G. Qi et al. / Tetrahedron 59 (2003) 10409–10418
Scheme 5. Block copolymerizations of MMA with DMEMA.
stereocomplexes exhibit no solubility in acetone and THF,
but are soluble freely in CHCl3 (Scheme 5).
2788C by stirring for 10 h, whose Mn is 38.5£104
(Mw/Mn¼2.5), and tacticity is mm/mr/rr¼2/27/71.
2.4. Polymerizations of MMA with Ln(CH2SiMe3)3
2.5. Polymerization of other monomers with
Yb[C(SiMe3)3]2 or Sm[C(SiMe3)3]2
To compare with the catalysis of divalent Ln[C(SiMe3)3]2,
those of trivalent Ln(CH2SiMe3)3 was studied using Y and
Sm complexes. Y(CH2SiMe3)3(THF)2 7 and Sm(CH2-
SiMe3)3(THF)2 8 were prepared according to the known
method.23 The polymerization was carried out in both
toluene and THF (Table 10). The complex 7 produced iso-
rich polymer at ambient temperature, while the atactic
polymerization preferred by lowering the reaction tempera-
ture in toluene. The reason is not clear at present. Similar
trend was observed using complex 8 as an initiator. In
contrast to the behavior in toluene, the polymerizations in
THF generate syndio-rich polymers especially at low
temperatures using complex 7. Similar behavior was also
observed using the complex 8. This is presumably due to the
occurrence of chain control by the coordination of strong
donor. Nearly the same result was obtained by the addition
of HMPA (hexamethylphosphorous triamide) to
Yb[C(SiMe3)3]2, i.e. Yb[C(SiMe3)3]2/HMPA (1:5 molar
ratio) affords the syndio-rich poly(MMA) in 99% yield at
(C5Me5)2SmMe(THF) has high catalytic activity for
polymerizations of 1-caprolactone (CL) as reported
previously.4 Yb[C(SiMe3)3]2 also showed high catalytic
activity for polymerizations of 1-caprolactone at ambient
temperature. This system yielded the polymer
(Mn¼6.6£104, Mw/Mn¼1.58) after 2 h in quantitative
yield, when we used [M]0/[I]0 ratio of 500 mol/mol.
However, we failed random or block copolymerization
of DMEMA with CL, due to the preferred polymerization
of 1-caprolactone in 35–37% yield at 08C, although
the block copolymerization proceeds in high yield
(91%) between MMA and CL (MMA was first
polymerized at 2788C for 3 h followed by the copolymer-
ization with CL at 258C for 3 h in toluene). Mn is 2.6£104
(Mw/Mn¼1.25) when we employed [M]0/[I]0 ratio of
150 mol/mol and MMA/CL ratio of 50/50 mol/mol.
Resulting MMA/CL ratio in the block copolymer is
52/48 mol/mol.
Table 10. Polymerizations of MMA with Ln(CH2SiMe3)3 in toluene and THF
Initiator
Solvent
Temperature (8C)
Yield (%)
Mn
Mn 104
Tacticity
mr
mm
rr
Y(CH2SiMe3)3
Toluene
THF
278
0
25
99
69
55
18.2
7.5
4.1
1.65
2.52
3.15
29
64
70
43
24
20
28
12
10
278
0
25
99
88
45
14.1
5.6
3.4
1.60
1.55
1.47
2
7
10
26
34
36
72
59
54
Sm(CH2SiMe3)3
Toluene
THF
278
0
25
99
99
55
13.3
5.6
3.7
1.72
1.98
2.35
40
73
75
37
18
19
23
9
6
278
0
25
99
72
33
10.5
7.9
4.5
1.85
1.76
1.72
1
5
6
15
29
33
84
66
61
[M]0/[I]0 ratio¼200 mol/mol, solvent/[M]¼2.0 vol/vol.

G. Qi et al. / Tetrahedron 59 (2003) 10409–10418
10415
Relating complex, Sm[C(SiMe3)3]2, exhibits less activity
for polymerizations of MMA as compared with
Yb[C(SiMe3)3]2. The exact molecular structure of
Sm[C(SiMe3)3]2, which was prepared from SmI2 and
(SiMe3)CK (see Section 4) was determined by X-ray
analysis (Fig. 1). Resulting complex is Sm(II) species,
containing no donor molecules. The Sm–C bonds are
summarizes the polymerizations of alkyl isocyanates. When
the polymerizations were carried out at temperatures higher
than 08C, an alkyl isocyanate converted into cyclic trimer
quantitatively by holding the solution for 2 h. The polymer
yield increases to 57 to 62% by the addition of THF to
toluene at 2788C. Mn was 10.4£104 (Mw/Mn¼1.4–1.5) and
sometimes Mn reached 116£104.
˚
2.58 A and the C–Sm–C angle is 143.48. The polymeriz-
ation of MMA using [M]0/[I]0 ratio of 200 mol/mol at 0–
258C for 2 h gave only 8–17% yield. At these temperatures,
74–65% of isotacticities and Mn of 43£104 (Mw/Mn¼1.14)
were observed.
3. Conclusion
The isotactic living polymerization of MMA was realized
using Yb[C(SiMe3)3]2 as a novel initiator at 2788C, giving
the polymer with Mn of 51.0£104 (Mw/Mn¼1.1) and high
isotacticity (97%). Mixing of the acetone solution of the
isotactic poly(MMA) (Mn¼16.3£104) with the acetone
solution of syndiotactic poly(MMA) (Mn¼15.7£104)
generates a stereocomplex bearing very high Tm in high
yield, whose tensile modulus is higher than respective
However, the catalysis of Sm[C(SiMe3)3]2 toward the
polymerizations of acrylonitrile is much higher than
Yb[C(SiMe3)3]2 (Table 11, Scheme 6). The polymer yield
reaches 55% when the polymerization was carried out in the
bulk state. The resulting Mn is 2.5–2.8£104 and molecular
weight distributions were relatively narrow. In sharp
contrast to alkyllanthanide complexes, metallocene type
rare earth metal complexes such as (C5Me5)2SmMe(THF)
or [(C5Me5)2SmH]2 are completely inert toward the
polymerizations of acrylonitrile.
isotactic
and
syndiotactic
homopoly(MMA)s.
Yb[C(SiMe3)3]2 also produced highly isotactic (98%)
poly[2-(dimethylamino)ethyl methacrylate] (DMEMA),
and (C5Me5)2SmMe(THF) affords highly syndiotactic
(97%) polymer in quantitative yields. The mixing of
isotactic poly(MMA)-block-poly(DMEMA) (97/3) and
syndiotactic poly(MMA)-block-poly(DMEMA) (97/3)
provides the desired stereocomplex. MCH2SiMe3(THF)2
(M¼Y, Sm) conducts the syndiotactic polymerizations of
MMA at ambient temperature while the atactic polymeriz-
ation preferred by lowering the reaction temperature. The
catalysis of Sm[C(SiMe3)3]2 toward the polymerization of
Table 11. Polymerization of acrylonitrile with Sm[C(SiMe3)3]2
[M]0/[I]0
(mol/mol)
Temperature
(8C)
Time
(h)
Yield
(%)
Mn 104
Mw/Mn
200
200
200
25
0
278
4
4
4
21
35
55
2.6
2.5
2.9
1.68
1.49
1.38
acrylonitrile
is
higher
than
Yb[C(SiMe3)3]2
Polymerization was conducted in the bulk state.
Sm[CH(SiMe3)2]3 revealed a moderate activity for
polymerization of hexyl isocyanate.
4. Experimental
Scheme 6. Polymerizations of alkyl isocyanates.
4.1. General methods
Although metallocene type rare earth metal complexes also
show no catalytic activity for polymerizations of alkyl
isocyanate, Sm[CH(SiMe3)2]3 revealed moderate activi-
ties toward the polymerizations of hexyl isocyanate and
butyl isocyanate at 240 to 2788C, due to the presence of
strong inductive effect of alkyl group (Scheme 7). Table 12
All the operations were performed under argon by using
standard Schlenk techniques. Tetrahydrofuran (THF) and
toluene were dried first over CaH2 for 1 week, then over Na
metal, and distilled before use. Commercially available
MMA (Aldrich) was dried over CaH2 for 10 days, then
distilled, and further dried over molecular sieves 4A for
more than 5 days. SmCl3(THF)2 was gifted from Rhodia,
11
1
France. H NMR spectra were recorded on a JEOL JMN-
LA400 spectrometer. Chemical shifts were calibrated with
CHCl3 in CDCl3 at 7.26 ppm. Elemental analysis was
performed on a Perkin–Elmer-2400 Series II CHNS/O
analyzer. Number-average molecular weight (Mn) and
molecular weight distributions (Mw/Mn) of polymers were
determined by gel permeation chromatography (GPC) on a
Tosoh SC-8010 high-speed liquid chromatograph equipped
with a differential refractometer with CHCl3 as an eluent at
408C (flow rate, 1.0 mL). The columns used were TSK gel
G5000H, G4000H, G3000H, and G2000H. Molecular
weights were determined with a universal curve plotted
with polystyrene standards, the Mw value of which were
determined by a light scattering method. GPC analysis of
poly(DMEMA) was carried out in MeOH/0.1N NaCl
aqueous solution (50/50) including 0.5% of triethylamine
Scheme 7. Polymerizations of acrylonitrile.
Table 12. Polymerizations of alkyl isocyanates with Sm[CH(SiMe3)2]3
Monomer
Temperature Time Toluene/ Yield Mn 104 Mw/Mn
(8C)
(h)
THF
(mL)
(%)
HexylNCO
BuNCO
240
278
278
15
15
12
15.0/0.0
15.0/0.0
7.0/0.8
39
11
57
5.2
116.2
10.4
3.65
1.78
1.57
240
278
15
12
15.0/0.0
7.0/0.8
43
62
3.5
9.8
9.71
1.45
Polymerization conditions; initiator concentration 1.0 mol% of monomer.

10416
G. Qi et al. / Tetrahedron 59 (2003) 10409–10418
using Shodex OH-pak SB-805, SB-804, and SB-803
columns at 408C. The Mn and Mw/Mn were calibrated
using poly(ethylene oxide) (Mn¼660000 and 25000) and
poly(ethylene glycol) (Mn¼1470) dissolved in MeOH/0.1N
NaCl solution (50/50). GPC analysis of poly(acrylonitrile)
was operated on a Tosoh CO-800 instrument using 0.01 M
LiCl/DMF solution and HXL-1 and GMHXL2 columns at
358C. Mn and Mw/Mn were calibrated with polystyrene
standards. The glass-transition temperature (Tg) and melting
point (Tm) were measured on a Seiko SSC-5100 DSC-22C
apparatus. The polymer samples were scanned from 2100
to 1208C at a heating rate of 108C min21 under a nitrogen
stream. The Tm and heat of fusion at melting point (2DHm)
were determined in the first heating, whereas Tg was
determined on the second heating.
in diethyl ether (50 mL), and the reaction mixture was
refluxed for 20 h. The solution was evaporated to dryness,
and the resulting residue was washed with hexane and
extracted with benzene (80 mL) at 608C. The extract was
concentrated and cooled to 08C to afford colorless crystals in
11% yield (3.1 g, 11.5 mmol). 1H NMR (C6D6, 400 MHz) d
2.99 (q, 4H, OCH2CH3), 0.89 (t, 6H, CH2CH3), 0.45 (s,
27H, SiCH3) ppm.
4.1.5. Preparation of ytterbiumdiiodide. To a solution of
NH4I (2.54 g, 17.5 mmol) in NH3 (50 mL) at 2788C was
added slowly powdered Yb metal (1.6 g, 9.2 mmol). After
stirring at 2788C for 1 h, the cooling bath was removed to
allow NH3 boil away. The resulting green–yellow residue
was dried under vacuum at 1808C to afford YbI2 as yellow
powder in 89% yield (3.5 g, 8.2 mmol).
4.1.1. Preparation of tris(trimethylsilyl)methane. To
CHBr3 (58.1 g, 20 mL, 230 mmol) in THF (450 mL) was
added 90 mL of Me3SiCl (77.1 g, 710 mmol) and the
mixture was cooled to 2788C. BuLi dissolved in hexane
(800 mmol) was slowly added to the mixture taking over
2 h, and then warmed to 258C. The reaction mixture was
quenched with dilute HCl aqueous solution, and the organic
layer was dried over Na2SO4. The yellow solution was
filtered and distilled under vacuum (808C/2 mm Hg) to give
38.5 g (166 mmol) of tris(trimethylsilyl)methane as a
colorless liquid in 72% yield. 1H NMR (CDCl3,
400 MHz) d 0.08 (s, SiMe3), 0.35 (s, CH) ppm.
4.1.6. Preparation of bis[tris(trimethylsilyl)methyl]-
methylytterbium. To a suspension of YbI2 (1.15 g,
2.7 mmol) in benzene (40 mL) was added at room
temperature a solution of (Me3Si)3CK (1.46 g, 5.4 mmol)
in benzene (50 mL). After stirring the mixture for 48 h at
258C, all volatiles were removed by evaporation and the
resulting residue was extracted with hexane (40 mL). The
solution was concentrated and cooled to 2208C to afford
red crystals (plate) of title compound in 54% yield
1
(0.93 g, 1.5 mmol). H NMR (C6D6, 400 MHz) d 0.032 (s,
SiCH3) ppm.
4.1.2. Preparation of tris(trimethylsilyl)methyl iodide.
MeLi in diethyl ether (200 mmol) was dropwise added to
56 mL of (Me3Si)CH (46.3 g, 199 mmol) in THF (300 mL)
at 08C and the mixture was refluxed for 12 h. To the reaction
mixture was added dropwise at 2788C 1,2-diiodoethene
(58 g, 200 mmol) dissolved in THF (60 mL). The mixture
was stirred at 258C for 1 h, washed with Na2S2O3 aqueous
solution, and the organic layer was dried over Na2SO4. After
the evaporation of the solution to dryness, the residue was
extracted with hexane (300 mL). The solution was evapor-
ated to give white–yellow powder of title compound
(59.9 g, 165 mmol) in 83% yield. 1H NMR (CDCl3,
400 MHz) d 0.24 (s, SiMe3) ppm.
4.1.7. Preparation of bis[tris(trimethylsilyl)methyl]-
samarium. To a suspension of SmI2 (1.09 g, 2.7 mmol) in
benzene (40 mL) was added at room temperature a solution
of (Me3Si)3CK (1.46 g, 5.4 mmol) in benzene (50 mL).
After stirring for 48 h at 258C, all volatiles were removed by
evaporation and the resulting residue was extracted with
hexane (40 mL). The solution was concentrated and cooled
to 2208C to afford black needle crystals of title compound
in 36% yield (0.48 g, 1.0 mmol). 1H NMR (C6D6, 400 MHz)
d 20.42 (s, SiCH3) ppm.
4.1.8. Preparation of tris(trimethylsilyl)methyl-
yttrium(THF)2. Anhydrous yttrium trichloride (1.47 g,
7.6 mmol) was suspended in THF (90 mL) and stirred at
558C for 30 min. The solution was evaporated to dryness
and the resulting YCl3(THF)2 was suspended in hexane
(60 mL) and cooled to 2788C. The hexane solution (60 mL)
of Me3SiCH2Li (23.0 mmol) was added at once to the
hexane solution. The mixture was stirred at 08C for 3 h, and
the filtration gave a white precipitate, which was then
extracted with hexane (10 mL£2). LiCl was filtered off, and
the solution was concentrated and cooled to 2258C to
4.1.3. Preparation of tris(trimethylsilyl)methyl-
lithium(Et2O)2. (SiMe3)3CI (65.0 g, 181 mmol) in diethyl
ether (210 mL) was dropwise added to a suspension of Li
powder (3.14 g, 453 mmol) in diethyl ether (30 mL) at
2788C with vigorous magnetic stirring. The reaction
mixture was slowly warmed to room temperature, stirred
for 4 h, and centrifuged using glass tube bearing two
gateways. The supernatant liquid was filtered through a
glass wool to afford a pale yellow ether solution of the title
compound in 99% yield. A portion of this solution was
treated with 0.1N HCl aq. solution and 0.1N NaOH solution
using phenolphthalein as indicator. 1H NMR (C6D6,
400 MHz) d 3.00 (q, 8H, OCH2CH3), 0.89 (t, 12H,
CH2CH3), 0.40 (s, 27H, SiCH3); 13C NMR (C6D6,
100 MHz) d 66.1 (OCH2CH3), 15.0 (OCH2CH3), 7.7
(SiCH3), 3.4 (LiCSi) ppm.
1
provide the title complex in 34% yield. H NMR (C6D6) d
0.26 (d, 6H, YCH2), 0.34 (S, 27H, SiCH3), 1.46 (m, 8H,
THF), 3.64 (m, 8H, THF) ppm. Anal. for C20H41O2Si3Y,
calcd C 49.35; H 8.49. Found C 49.20; H 8.61.
4.1.9. Preparation of tris(trimethylsilyl)methyl-
samarium(THF)2. SmCl3(THF)2 (1.35 g, 7.6 mmol) was
suspended in hexane (60 mL) and cooled to 2788C. The
hexane solution (60 mL) of Me3SiCH2Li (23.0 mmol) was
added to the hexane suspension. The mixture was stirred at
08C for 3 h. LiCl was removed by centrifugation, and the
solution was concentrated and cooled to 2258C to provide
4.1.4. Preparation of tris(trimethyl)methylpotas-
sium(Et2O). t-BuOK (12.6 g, 112 mmol) in diethyl ether
(150 mL) was added to LiC(SiMe3)3 (107 mmol) dissolved

G. Qi et al. / Tetrahedron 59 (2003) 10409–10418
10417
Table 13. Crystal data and data collection for 9
Chem form
Formula weight
Color
C20H54Si6Sm
613.56
F000
mMo Ka
Temperature
Scan-type
2umax
No of reflections
Struct. Solution
Refinement
No of observation
No of variables
GOF
1280.00
19.87 cm21
23.08C
v–2u
50.0
5127
Direct method (SHELEX86)
Full-matrix least squares
4647
244
1.64
Black
0.23£0.20£0.15
Cryst dimension (mm3)
Crystal system
Lattice parameters
Monoclinic
˚
a (A)
9.010(4)
23.666(7)
15.691(5)
95.20(4)8
3332.3(2)
P21/n (#14)
4
˚
b (A)
˚
c (A)
b
3
˚
V (A )
Space group
Z
Dcalcd
R
Rw
0.118
0.187
1.223 g/cm3
1
the title complex in 25% yield. H NMR (C6D6) d 0.24 (d,
6H, YCH2), 0.33 (s, 27H, SiCH3), 1.44 (m, 8H, THF), 3.64
(m, 8H, THF) ppm. Anal. for C20H41O2Si3Sm, calcd: C
43.82; H 7.54. Found C 43.67; H 7.78.
Yb[C(SiMe3)3]2 (8.6 mg, 0.05 mmol) or (C5Me5)2-
SmMe(THF) (29.0 mg, 0.05 mmol) as initiators. Toluene
(5 mL) was used as solvent and the polymerization was
conducted at 2788C for 3 h. Resulting polymer was poured
into excess methanol to precipitate the polymer, which was
then dried in vacuo.
4.1.10. X-Ray structure determination. A black needle
crystal of 9 was sealed in a glass capillary under argon. The
X-ray data were collected at 238C on a Rigaku AFC7R
diffractometer with graphite monochromated Mo Ka radi-
ation. No empirical absorption correction was applied. The
basic crystallographic parameters are listed in Table 13. Cell
constants and the orientation matrix for data collection,
obtained from a least-square refinement using the setting
angles of 258, carefully centered reflections in the range
23.41,2u,28.778 correspond to a primitive monoclinic
cell with dimensions. The standard reflections were
monitored at every 150 reflections and did not show any
significant change. The structure was solved by the direct
method and expanded using Fourier techniques. Some non-
hydrogen atoms were anisotropically refined, while the rest
were isotropically refined. Hydrogen atoms were included
but not refined. All the calculations were performed by the
use of Crystal Structure crystallographic software package.
4.1.14. Formation of stereocomplex. The acetone solution
(10 mL) of isotactic poly(MMA) or poly(MMA-co-
DMEMA) (0.5 g) was mixed with the acetone solution
(10 mL) of syndiotactic poly(MMA) or poly(MMA-co-
DMEMA) (1.0 g) at ambient temperature. Immediately
after mixing, the gel formation occurred. Resulting gel was
dried in vacuo. Annealing of the stereocomplexes was
carried out at 180 and 2008C for 3–7 days at the DSC cell in
an Ar stream. Then the DSC measurement took place after
cooling the sample to ambient temperature.
4.1.15. Polymerization of 1-caprolactone with
Sm[C(SiMe3)3]2. To a stirred mixture of 1-caprolactone
(1.11 mL, 10 mmol) and toluene (10 mL) cooled to 2788C
was added Sm[C(SiMe3)3]2 (43.2 mg, 0.1 mmol) dissolved
in toluene (2 mL). A mixture was stirred at 258C for 2 h to
conduct the polymerization. Resulting polymer was poured
into excess methanol to precipitate the polymer.
4.1.11. Stoichiometric reaction of Yb[C(SiMe3)3]2 with
MMA. The 1:1 reaction of Yb[C(SiMe3)3]2 (1.73 g,
10 mmol) with MMA (1 mL, 10 mmol) takes place at
2788C for 3 h, and the resulting mixture was hydrolyzed
with water at 08C. The organic layer was extracted with
hexane (80 mL) and distilled in vacuo to give
MeO(CO)CH(Me)CH2CH2CH(Me)(CO)OMe in 67%
4.1.16. Polymerization of acrylonitrile with
Sm[C(SiMe3)3]2. To acrylonitrile (1.4 mL, 20 mmol) dis-
solved in toluene (5 mL) cooled to 2788C was added
Sm[C(SiMe3)3]2 (43.2 mg, 0.1 mmol) in toluene (2 mL). A
mixture was stirred at a fixed temperature for 4 h to conduct
the polymerization. Resulting polymer was poured into
excess methanol to precipitate the polymer, which was then
dried in vacuo.
1
yield. H NMR (C6D6) d 1.18 (d, 6H, Me), 1.88 (m, 4H,
CH2), 2.22 (m, 2H, CH), 3.62 (s, 6H, OMe) ppm. EIMS
(relative ratio) m/z 170 (Mþ, 6), 139 (Mþ2OMe, 25), 11
(Mþ2COOMe, 15), 108 (M22OMe, 100).
5. Supporting information available. Crystallographic
data for the structural analysis of 9 have been deposited
with the Cambridge Crystallographic Data Center, CCDC No.
215993. Copies of these informations may be obtained free of
charge fromThe Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (fax: þ44-1223-336033 or e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
4.1.12. Polymerization of MMA with Yb[C(SiMe3)3]2. To
a stirred mixture of MMA (3.0 mL, 30 mmol) and toluene
(9 mL) cooled to 2788C was added Yb[C(SiMe3)3]2
(5.1 mg, 0.03 mmol) dissolved in toluene (1 mL). A mixture
was stirred for 3–12 h at a fixed temperature to conduct the
polymerization. Resulting polymer was poured into excess
methanol to induce the precipitation of the polymer, which
was then dried in vacuo.
Acknowledgements
4.1.13. Block copolymerization of MMA with DMEMA.
Block copolymerization of MMA (0.96 mL, 9.6 mmol) with
DMEMA (0.07 mL, 0.4 mmol) was carried out using
We are indebted to a Grant-in-Aid for Scientific research
(Grant No. 14350488) from the Ministry of Education,
Culture, Sports, Science and Technology.

10418
G. Qi et al. / Tetrahedron 59 (2003) 10409–10418
146, C43. (b) Deacon, G. B.; Koplick, A. J.; Raverty, W. D.;
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