New divalent samarocenes for butadiene polymerisation: Influence of the steric effect and the electron density on the catalytic activity

Article abstract of DOI:10.1016/j.jorganchem.2003.10.011

Two new divalent samarocenes, Cp*′₂Sm(THF) (1) and (Cp^Ph3)₂Sm(THF) (2) (Cp*′=C₅Me₄ⁿPr, Cp^Ph3=H₂C₅Ph₃-1,2,4), were synthesized and characterized by ¹H NMR and elemental analysis. The activity of 1 and 2 as butadiene polymerisation catalysts was studied, in the presence of MAO and MMAO, and compared to this of Cp*₂Sm(THF)₂ (3) and (Cp⁴ⁱ)₂Sm (4) (Cp=C₅ Me₅, Cp⁴ⁱ=C₅Hⁱ Pr₄), in the same conditions. The 1/MAO system presents the highest activity. The less active 2/MAO system leads to a high cis-1,4 regular structure up to 97%. The MMAO cocatalyst is found very sensitive to the steric hindrance of the samarocenes: the activity decreases from 1/MAO to 1/MMAO, and no activity is observed in the case of complexes 2 and 4, associated to MMAO. Complexes 1 and 2 can be both oxidized with AlMe₃ to give the corresponding Sm/Al bimetallics 1′ and 2′, respectively.

Full text of DOI:10.1016/j.jorganchem.2003.10.011

Journal of Organometallic Chemistry 689 (2004) 264–269
www.elsevier.com/locate/jorganchem
New divalent samarocenes for butadiene polymerisation: influence
of the steric effect and the electron density on the catalytic activity
*
*
F. Bonnet, M. Visseaux , D. Barbier-Baudry
Laboratoire de Syntheꢀse et d’Electrosyntheꢀse Organomeꢁtalliques (LSEO, UMR 5188 CNRS), Dept. Chimie, Universiteꢁde Bourgogne,
BP 47870, 21078 Dijon Cedex, France
Received 22 August 2003; accepted 8 October 2003
Abstract
Two new divalent samarocenes, Cp2ꢀ0Sm(THF) (1) and (CpPh3)2Sm(THF) (2) (Cpꢀ0 ¼ C5Men4Pr, CpPh3 ¼ H2C5Ph3-1,2,4), were
synthesized and characterized by 1H NMR and elemental analysis. The activity of 1 and 2 as butadiene polymerisation catalysts was
studied, in the presence of MAO and MMAO, and compared to this of Cpꢀ2Sm(THF)2 (3) and (Cp4i)2Sm (4) (Cpꢀ ¼ C5Me5,
Cp4i ¼ C5HiPr4), in the same conditions. The 1/MAO system presents the highest activity. The less active 2/MAO system leads to a
high cis-1,4 regular structure up to 97%. The MMAO cocatalyst is found very sensitive to the steric hindrance of the samarocenes:
the activity decreases from 1/MAO to 1/MMAO, and no activity is observed in the case of complexes 2 and 4, associated to MMAO.
Complexes 1 and 2 can be both oxidized with AlMe3 to give the corresponding Sm/Al bimetallics 10 and 20, respectively.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Lanthanides; Diene polymerisation; Samarocenes
1. Introduction
efficient single component catalysts for the polymerisa-
tion of ethylene or acrylates [6]. However, these com-
plexes have shown their limits, being inactive towards
conjugated dienes. The divalent lanthanocenes are not
active either [7], because of the formation of a stable
Ln(III)(g3-allyl) complex [8]. Very recently, Wakatsuki
and his co-workers [9] reported that polymerisation of
butadiene was possible with Cpꢀ2Sm(THF)2 (3) activated
by aluminium derivatives: MMAO (modified methyl-
aluminoxane containing both isobutyl and methyl
groups [10]) or AlR3/[Ph3C][B(C6F5)4] (R ¼ Me, Et,
iBu). The authors obtained regular cis-1,4 polybutadiene
and discussed the reactivity of the catalytic system in
regard to the nature of the aluminium reagent. They
showed that the microstructure of the synthesized
polybutadiene was more influenced than the activity of
the dual component catalyst. It is noteworthy that the
active species was a Sm(III) one.
Synthesis of polydienes is a field of major interest,
because of their various applications in the rubber (ty-
res, adhesive, etc.) industry. Several Ziegler–Natta het-
erogeneous catalytic systems are able to polymerise
conjugated dienes with a high cis-1,4 stereospecificity [1].
Traditional homogeneous d-block-metal catalysts asso-
ciated to methylaluminoxane (MAO) are less stereo-
specific, but they allow a better control of molecular
weight [2]. Rare earths systems become more and more
appreciated in this specific field of catalysis [3,4]. They
are known to give the highest rates of cis-1,4-polydiene
(up to 99%) while providing a good control of molecular
weight [5].
Organolanthanide chemistry has provided well-de-
fined single site catalysts and particularly the traditional
Cpꢀ2LnR. These trivalent lanthanocenes are known as
In the course of our studies concerning the use of
early organolanthanides for dienes polymerisation [11],
we undertook to compare a set of lanthanocenes. We
wanted to focus on the influence of the nature of the
cyclopentadienyl ligands on the behaviour of Sm/Al
* Corresponding authors. Tel.: +33-3-80-39-60-61; fax: +33-3-80-39-
60-84.
E-mail addresses: mvisseau@u-bourgogne.fr (M. Visseaux),
baudryd@u-bourgogne.fr (D. Barbier-Baudry).
0022-328X/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2003.10.011

F. Bonnet et al. / Journal of Organometallic Chemistry 689 (2004) 264–269
265
catalysts. With this aim, we synthesized two new diva-
lent samarocenes, Cpꢀ20Sm(THF) (1) and (CpPh3
)
2
Sm(THF) (2), bearing the n-propyl-tetramethylcyclo-
pentadienyl (Cpꢀ0 ¼ C5Me4nPr) and the 1,2,4-triphenyl-
cyclopentadienyl (CpPh3 ¼ H2C5Ph3-1,2,4), respectively.
The synthesis, and some reactivity of 1 and 2 are pre-
sented and discussed. Complexes 1, 2 and 3, but also the
unsolvated (Cp4i)2Sm, 4 (Cp4i ¼ C5HiPr4) described in a
previous paper [12], have been tested for the polymeri-
sation of 1,3-butadiene in the presence of MAO or
MMAO. The influence of the nature of the cyclopen-
tadienyl ligand on the activity of the complex and on the
microstructure of the polymer is discussed.
Fig. 1. 1H NMR spectrum of 1 in C6D6 at 333 K.
2. Results and discussion
2.1. Samarocenes syntheses
THF
SmI2 þ 2KCpPh3 ! ðCpPh3ÞSmðTHFÞ þ 2KI
ð2Þ
2
We present here the synthesis of two new divalent
samarocenes, Cp2ꢀ0Sm(THF) (1) and (CpPh3)2Sm(THF)
(2). The syntheses were all conducted in THF, using the
procedure described in 1985 by Evans and co-workers
[7] for the preparation of Cpꢀ2Sm(THF)2 (3). Recently,
some of us prepared in the same way the desolvated
analogue (Cp4i)2Sm (4). Scheme 1 summarizes the mo-
lecular structure of these divalent samarocenes, used
thereafter for polymerisation experiments.
Contrarily to complex 3 which was isolated as a bis-
tetrahydrofuran adduct, both new samarocenes contain
only one THF molecule per Sm according to the ele-
1
mental and H NMR analyses.
The 1H NMR spectrum of complex 1 is shown in
Fig. 1. Despite the paramagnetism, one can easily at-
tribute the resonances to the corresponding protons, as
indicated. The presence of one unique THF, for both 1
and 2, may be related to the higher steric hindrance
induced by the propyl chain in 1, and by the three
phenyl groups in 2.
Complexes 1 and 2 were obtained from the reaction
of 2 equivalents of the corresponding potassium ligand
with SmI2, according to
One can note that the electron donating ability of
CpPh3, bearing three withdrawing phenyl substituents,
seems weaker than this of Cpꢀ, leading a priori to a
better affinity towards THF. But the much larger size
of the bulky ligand might preclude the coordination
of more than one THF per Sm. As for complex 4,
the absence of THF was postulated as being the
consequence of both steric and electronic saturation
[12].
THF
SmI2 þ 2KCpꢀ0 ! Cpꢀ20SmðTHFÞ þ 2KI
ð1Þ
1
Ph
Ph
Ph
Ph
Sm
THF
Sm
THF
Ph
Ph
2.2. Oxidation of samarocenes 1 and 2
Wakatsuki showed that the bimetallic complex
[Cpꢀ2Sm(l-Me)2AlMe2]2 ð30Þ was efficient in butadiene
polymerisation in the presence of AlR3/[Ph3C]
[B(C6F5)4] (R ¼ Me, Et, Bu) [9]. This bimetallic com-
2
1
i
plex had been prepared by Evans et al. [13] upon an
oxidizing/alkylating process of 3 with AlMe3. In pre-
liminary experiments, we checked that 1 and 2 could be
readily oxidized by a similar procedure. We observed b0y
1H NMR the formation of the analogues of 3 :
[(Cpꢀ0)2Sm(l-Me)2AlMe2]2 ð10Þ and [(CpPh3)2Sm(l-Me)2
AlMe2]2 ð20Þ [Eqs. (3) and (4), respectively]. Unfortu-
nately, the new materials, obtained as an orange oil, did
not crystallize, even at low temperature (ꢁ20 °C):
THF
THF
Sm
Sm
4
3
Scheme 1. Molecular structure of samarocenes 1–4.

266
F. Bonnet et al. / Journal of Organometallic Chemistry 689 (2004) 264–269
Et)2AlEt2] exhibits a value of 80° [14], whereas the (l-
3Cpꢀ20SmðTHFÞ
Me)Sm(l-Me) angle in the dimeric 3a0 is found at 85°.
The value of this angle is also clearly depending on the
bulkiness of the two cyclopentadienyl surrounding
the opposite side of the metal: the more bulky the Cp,
the smaller the (l-R)Sm(l-R) angle. Thus, one may
conclude that the preferential form for a complex
bearing bulky Cp ligands would be the monomeric one,
since it is the form with the lowest value of (l-R)Sm(l-
R) angle. This is in accordance with our NMR obser-
vations concerning the CpPh3 series.
1
THF
þ 4AlMe3 ! 3Cpꢀ0Smðl-MeÞ AlMe2 þ Al
ð3Þ
ð4Þ
2
2
10
3CpP2h3SmðTHFÞ
2
THF
þ 4AlMe3 ! 3CpP2h3Smðl-MeÞ AlMe2 þ Al
2
20
Nevertheless, despite the paramagnetism of the sa-
marium, it was possible to make a unambiguous inter-
pretation of the NMR spectra. It has previously been
shown by 1H NMR that 30 adopted in solution a dimeric
structure, 30a, in equilibrium with a monomeric one, 30b
[13]. The non-bridged Al–Me signals of the dimeric 30a
and monomeric 30b were recorded at d ¼ ꢁ2:26 and
1.63 ppm, respectively. We recorded analogous signals
at d ¼ ꢁ2:11 and 1.70 ppm for 10, which might be
connected to the presence of both dimeric 10a and mo-
nomeric 10b, in equilibrium (Scheme 2). On the other
hand, only one signal appeared in the spectrum of 20
(d ¼ 2:3 ppm), indicating that the monomeric 20a is
largely predominant.
The presence of a propyl chain instead of a methyl
group does not induce a dramatic change of the struc-
ture in solution. With the larger, bulky CpPh3 ligand, the
percentage of dimeric form is strongly decreased.
Also, as reported by Evans et al. [14], the (l-Et)Sm(l-
Et) angle of the monomeric form of [Cpꢀ2Sm(l-
2.3. Butadiene polymerisations with divalent samarocenes/
MAO
It was shown that complex 3 was able to polymerise
1,3-butadiene in the presence of aluminium cocatalysts,
with a very high level of cis-1,4 microstructure [9].
Similarly, we studied the catalytic properties of the new
complexes and Table 1 summarizes the results of the
reactions performed in toluene at 50 °C with the divalent
samarocenes (1)–(4), in the presence of MAO.
All the samarocenes showed some activity. The
highest one was obtained with complex Cpꢀ20Sm(THF)
(1) (72% yield in 1 h 30 min, run 1). In similar condi-
tions, with decamethylsamarocene 3, a yield of 40% is
obtained in 20 h (run 3). This result could be explained
by the presence of one additional THF molecule in 3 vs.
1, leading to a decrease of catalytic activity.
Al
Me
Me
Me
Me
Me
Al
Sm
Sm
2
Sm
Me
Me
Me
Al
Scheme 2. Equilibrium between the dimer and the monomer of the bimetallic compound 10.
Table 1
Polymerisation of 1,3-butadiene with samarocene/MAO in toluenea
Microstructureb
Run
Samarocene
[BD]0/[Sm]
Time (h)
Yield (%)
cis-1,4 (%)
trans-1,4 (%)
1,2 (%)
1
2
3
4
1
2
3
4
1420
960
1 h 30 min
72
13
40
10
39.1
97.1
50.9
76.2
55.9
2.9
5
20
20
16
ꢂ0
1300
1480
44.3
19.5
4.8
4.3
a Polymerisation conditions: [Sm] ¼ 4 ꢃ 10ꢁ3 M; V(toluene) ¼ 4.5 mL for runs 1–3 and 5; 6.5 mL for run 4; T ¼ 50 °C; [MAO]0/[Sm]0 ¼ 200; [BD]0:
initial butadiene concentration.
b Measured by 1H and 13C NMR in CDCl3.

F. Bonnet et al. / Journal of Organometallic Chemistry 689 (2004) 264–269
267
When comparing the runs 1–4 it appears that the
activity is higher for the more electron rich catalysts.
Indeed, the better electron donation of the cyclopenta-
dienyl ligand could be related to the facility of insertion
of the monomer into the Sm active bond (Scheme 3).
In runs 1, 3 and 4, mixtures of cis-1,4- and trans-1,4-
polybutadiene were obtained. This feature is in accor-
dance with an g4-coordination of the monomer to the
metal, followed by the anti/syn isomerization [15].
For the 4/MAO catalyst, the high bulkiness of the
Cp4i ligand could induce an g2-coordination but the low
percentage of 1,2-polymer is characteristic of the g4-
coordination, furthered by the absence of coordinated
THF in 4, and followed by the anti/syn isomerization.
2.4. Butadiene polymerisations with samarocene/MMAO
The divalent samarocenes were also tested for the
polymerisation of 1,3-butadiene in the presence of
MMAO. This modified methylaluminoxane, less bridg-
ing but more bulky cocatalyst, contains both isobutyl
and methyl substituents [16]. Table 2 summarizes the
results of the reactions carried out with complexes 1–4 in
the presence of MMAO, in toluene at 50 °C.
In the case of complex 3, no real difference of ste-
reospecificity can be observed between MMAO (run 7)
and MAO (run 3) as cocatalyst. With complex 1, rather
than the nature of the cocatalyst, the stereospecificity
appears to follow the concentration of monomer (runs
5/1/6, from 26% to 85% cis-1,4). Thus, the isomerisation
from anti to syn, consecutive to the g4-coordination, is
not favoured in the presence of a high proportion of
monomer.
Concerning the activity, the use of MMAO rather
than MAO really improves the activity of complex 3, as
reported by Wakatsuki and co-workers [9]: in similar
reaction conditions, the yield increases from 40% (run 3)
to 92% (run 7). The behaviour is different for complexes
1, 2 and 4. In the case of 1/MMAO, the yield actually
reaches 100%, although this requires significantly longer
reaction times (run 5 vs. run 1). Even with an increase of
the butadiene concentration (run 6), the rate of poly-
merisation remains quite slow. Complexes 2 and 4 are
totally inactive in the same conditions (runs 8 and 9).
This decrease of activity between complex 3, and com-
plexes 1, 2 and 4, can be related to the steric hindrance.
The presence of the propyl chain of the Cpꢀ0 in 1, the
voluminous Cp ligands in 2 and 4, clearly appears to be
a drawback when used associated to the bulky cocata-
lyst MMAO.
The result is different for run 2: with the (CpPh3
)
2
Sm(THF)/MAO catalyst, a high cis-stereospecificity
(97.1%) is observed. In this system, the samarium atom
bears Cp ligands containing electron-withdrawing sub-
stituents, which will favour an g4-coordination step,
bringing 4 electrons to the demanding samarium metal
(Scheme 3). The g4-coordination is also favoured in case
of low steric hindrance, and the bimetallic active species
resulting from the reaction of 2 with MAO was found
monomeric, instead of partly dimeric with 1 and 3 (see
Section 2.2). Moreover, the activity is low (13% yield in
20 h). Thus, the crucial point in the propagation seems
to be the insertion of the monomer into the active bond,
rather than the coordination. In this case (run 2), the
more electron-withdrawing the ligands, the easier
the coordination of the monomer, but the more difficult
the migration of the alkyl group (which results in the
insertion into the active bond).
[Sm]
R
[Sm]
R
η2 coordination
η4 coordination
[Sm]
R
[Sm]
R
Finally, it must be noted that the two bimetallic
complexes 10 and 20 were tested for 1,3-butadiene poly-
Scheme 3.
Table 2
Polymerisation of 1,3-butadiene with samarocene/MMAO in toluenea
Microstructureb
Run
Samarocene
[BD]0/[Sm]
Time (h)
Yield (%)
cis-1,4 (%)
trans-1,4 (%)
1,2 (%)
5
6
7
8
9
1
1
3
2
4
680
20
19
15
16
15
100
28
92
–
26.2
85.4
56.4
–
68.9
10.8
40.0
–
4.9
3.8
3.6
–
2030
1330
900
1480
–
–
–
–
a Polymerisation conditions: [Sm] ¼ 4 ꢃ 10ꢁ3 M; V(toluene) ¼ 4.5 mL; T ¼ 50 °C; [MMAO]0/[Sm]0 ¼ 200; [BD]0: initial butadiene concentration.
b Measured by 1H and 13C NMR in CDCl3.

268
F. Bonnet et al. / Journal of Organometallic Chemistry 689 (2004) 264–269
merisation, alone or in presence of Al(iBu)3/
HNEt3BPh4, and that no polymerisation occurred.
Chemical shifts are expressed in parts per millions
downfield from external TMS. Elemental analyses were
performed with a Fisons EA 1108 CHON apparatus.
Butadiene was dried in a solution of Cp2TiCl2/AlEt3 in
toluene. SmI2 was purchased from Aldrich and used
without purification. AlMe3 (toluene solution, 2 M) and
MAO (toluene solution, 10 wt%) were purchased from
Aldrich, MMAO (heptane solution, 7% Al wt.) from
Akzo Nobel. Cp2ꢀSm(THF)2 (3) [7], (Cp4i)2Sm (4) [12],
KCpꢀ0 [17], were synthesized as described in the litera-
ture. KCpPh3 was prepared by treatment of the corre-
sponding diene [18] with KH in THF.
3. Conclusion
By using quite different cyclopentadienyl ligands,
Cpꢀ0 and CpPh3, we obtained the corresponding new
divalent
samarocenes
Cpꢀ20Sm(THF)
(1)
and
(CpPh3)2Sm(THF) (2), both monosolvated according to
NMR data and elemental analysis.
The ability of these complexes to polymerise 1,3-bu-
tadiene was evaluated in the presence of MAO or
MMAO. In order to discuss the influence of the nature
of the cyclopentadienyl ligands on the activity and the
microstructure, Cpꢀ2Sm(THF)2 (3) and (Cp4i)2Sm (4),
were tested in the same conditions.
Complex 1 shows the highest activity, in the presence
of MAO, giving a mixture of cis-1,4 and trans-1,4-
polybutadiene. At the opposite, 2/MAO leads to up to
97% of cis-1,4 regular structure but with a low activity.
MMAO cocatalyst is very sensitive to the steric hin-
drance of the samarocene it is used with: the activity
decreases from 1/MAO to 1/MMAO system, and no
activity is observed in the case of complexes 2 and 4.
Actually, MMAO appears to be suitable only in asso-
ciation with decamethylsamarocene 3.
4.1. Preparation of (Cpꢀ0)2Sm(THF) (1)
SmI2 (500 mg, 1.23 mmol) and KCpꢀ0 (475 mg, 2.34
mmol) were dissolved in 50 ml of THF. The dark brown
solution was stirred at room temperature for 12 h. After
filtration, the solvent was removed and 40 mL of toluene
were added on the brown oil. Some salts were eliminated
by a second filtration, the toluene was evaporated and
537 mg of a brown solid of 1 were obtained (79%). Anal.
Calc. for C28H46SmO: C, 61.27; H, 8.38. Found: C,
1
62.63; H, 8.44%. NMR (C6D6, 333 K): H: d 15.66 (br,
4H, THF), 8.66 (t, 3H, CH3 (nPr)), 6.93 (br, 4H, THF),
6.31 (s, 6H, C5Men4Pr), 1.66 (br, 2H, CH2 (nPr)), 0.03 (s,
6H, C5Men4Pr), )1.61 (br, 2H, CH2 (nPr)).
As a summary, steric hindrance of the less electron
donating CpPh3 ligands, in complex 2, does not impede
the g4-coordination of the monomer. To explain the
slowness of the polymerisation in this case, one must
exclude the anti–syn isomerisation, because it would lead
to the formation of trans-polyisoprene. The determining
step of the whole process is more likely the insertion,
which might be disfavoured with the less electron rich
metallocene 2.
On the other hand, the reactivity of complex 4 seems
to be strictly governed by steric factors, the Cp4i ligands
hindering the coordination of the monomer.
Complexes 1 and 3 behave as efficient catalysts, their
peralkyl substituted Cp ligands are good compromises
for both coordination and insertion steps.
4.2. Preparation of (CpPh3)2Sm(THF) (2)
SmI2 (250 mg, 0.62 mmol) and KCpPh3 (394 mg, 1.18
mmol) were dissolved in 40 ml of THF. The dark
brown-red solution was stirred at room temperature for
12 h. After filtration, the solvent was removed and the
brown oily residue was extracted with 30 mL of toluene.
The toluene was slowly evaporated to dryness, leaving
315 mg of a black-brown solid of 2 (63%). Anal. Calc.
for C50H42SmO: C, 74.21; H, 5.23. Found: C, 73.97; H,
5.14%. NMR (C6D6, 298 K): 1H: d 12.11 (br, 4H, THF),
11.41 (br, 2H, C5H2Ph3), 10.90 (br, 2H, m0-), 10.68 (br,
4H, o-), 10.05 (br, 2H, o0-), 8.95 (br, 4H, m-), 8.58 (t, 1H,
p0-), 7.66 (t, 2H, p-), 1.98 (br, 4H, THF) (o-, m-, p- are
relative to the 2 equivalent phenyl groups and o0-, p0-, m0-
to the third non-equivalent to the others).
The bimetallic complexes 10 and 20, obtained by
treatment of 1 and 2 with AlMe3, were found inactive
alone or in presence of Al(iBu)3/HNEt3BPh4.
4.3. Oxidation reaction of 1 and 2
4. Experimental
An excess of AlMe3 (toluene solution 5.47 mL, 10.9
mmol) was slowly added at ambient temperature to a
brown solution of (Cpꢀ0)2Sm(THF) (1) (182 mg, 0.30
mmol) in 30 mL of toluene. The reaction was stirred at
room temperature for 24 h. A red-orange solution was
obtained and a blackish, metal-like precipitate depos-
ited. The mixture was filtered and the precipitate was
washed once with toluene. The solvent was evaporated
to dryness and a deep orange oil (112 mg, 66%) was
All manipulations were carried out under argon using
standard vacuum line techniques and a glove box. The
solvents were dried on sodium-benzophenone ketyl and
deoxygenated by distillation immediately before use.
NMR spectra were recorded on Bruker Avance 300 or
DRX 500 spectrometers in C6D6 (organometallics) or
CDCl3 (polymers) at 300 or 500 MHz, respectively.

F. Bonnet et al. / Journal of Organometallic Chemistry 689 (2004) 264–269
269
obtained. NMR analysis was consistent with the for-
mation of [(Cpꢀ0)2Sm(lMe)2AlMe2]2 ð10Þ: (C6D6, 298
K): 1H: d 3.09 (q, 2H, CH2(nPr)), 2.18 (q, 2H,
CH2(nPr)), 1.94 (t, 2H, CH2(nPr)), 1.8 (t, 3H, CH3(nPr)),
1.70 (br, 3H, (lMe)2AlMe2 1b0), 1.57 (t, 2H, CH2(nPr)),
1.34 (t, 3H, CH3(nPr)), 0.90, 0.74, 0.68, 0.72 (s, 6H,
C5Men4Pr each), ꢁ2.11 (s, 3H, (lMe)2AlMe2 1a0),
ꢁ14.22 (br, 3H, (lMe)2AlMe2 1a0), ꢁ17.41 (br, 3H,
(lMe)2AlMe2 1b0).
d 4.8–5.2 (@CH2 of 1,2-butadiene unit), 5.2–5.8 (–CH@
of 1,4-butadiene unit and –CH@ of 1,2-butadiene unit).
13C{1H}: 27.4 (1,4-cis-polybutadiene), 32.7 (1,4-trans-
polybutadiene), 127.7–131.8 (1,4-polybutadiene unit)
and 113.8–114.8 and 143.3–144.7 (1,2-polybutadiene
unit).
Following the same procedure, from (CpPh3)2Sm
(THF)2 (2) (200 mg, 0.247 mmol) and an excess of
AlMe3 (7.4 mL, 14.8 mmol) in 15 mL of toluene, an
orange oil (125 mg, 61%) was obtained, which did not
become solid even after a prolonged evaporation. NMR
analysis was consistent with the formation of
(CpPh3)2Sm(lMe)2AlMe2 ð2Þ0: (C6D6, 298 K): 1H: d
15.57 (s, 2H, C5H2Ph3), 6.65 (t, 2H, p-), 6.35 (t, 4H, m-),
6.07 (t, 1H, p0-), 5.97 (d, 4H, o-), 5.91–5.81 (overlapped
signals, 2H, 2H, o0-, m0-), 2.3 (br, 3H, (lMe)2AlMe2),
ꢁ15.5 (br, 3H, (lMe)2 AlMe2).
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The microstructure of the polybutadienes was deter-
mined by 1H and 13C NMR spectroscopy in CDCl3. 1H: