Synthesis and olefin polymerization catalysis of new divalent samarium complexes with bridging bis(cyclopentadienyl) ligands

Article abstract of DOI:10.1021/om971099u

This paper deals with the preparation and olefin polymerization catalysis of six new divalent samarium complexes. These bridged bis(cyclopentadienyl) (Cp) complexes exhibit various structures with regard to the bridging group and the position of substitue

Full text of DOI:10.1021/om971099u

Organometallics 1998, 17, 3945-3956
3945
Syn th esis a n d Olefin P olym er iza tion Ca ta lysis of New
Diva len t Sa m a r iu m Com p lexes w ith Br id gin g
Bis(cyclop en ta d ien yl) Liga n d s
Eiji Ihara,† Mitsufumi Nodono,† Kenji Katsura,† Yoshifumi Adachi,†
Hajime Yasuda,*,† Mizue Yamagashira,‡ Hiroshi Hashimoto,‡
Nobuko Kanehisa,‡ and Yasushi Kai*,‡
Department of Applied Chemistry, Faculty of Engineering, Hiroshima University,
Higashi-Hiroshima 739-8527, J apan, and Department of Applied Chemistry,
Faculty of Engineering, Osaka University, Suita 565-0871, J apan
Received December 15, 1997
This paper deals with the preparation and olefin polymerization catalysis of six new
divalent samarium complexes. These bridged bis(cyclopentadienyl) (Cp) complexes exhibit
various structures with regard to the bridging group and the position of substituents on the
Cp rings: rac-tBu, Me2Si(2-Me3Si-4-tBuC5H2)2Sm(THF)2 (7); rac-tBuMe2Si, Me2Si(2-Me3Si-
4-tBuMe2SiC5H2)2Sm(THF)3 (8); C1 symmetric, Me2Si[2,4-(Me3Si)2C5H2][3,4-(Me3Si)2C5H2]-
Sm(THF)2 (9); meso, [1,2-(Me2Si)(Me2SiOSiMe2)](3-tBuC5H2)2Sm(THF)2 (10); C2v symmetric
(Ph2Si), Ph2Si[3,4-(Me3Si)2C5H2]2Sm(THF)2 (11); C2v symmetric [(SiOSi)2], [1,2-(Me2-
SiOSiMe2)2](3-tBuC5H2)2Sm(THF)2 (12). The structures of 7, 8, 10, and 12 were confirmed
by X-ray crystallographic analysis. Among these divalent complexes, meso type complex 10
showed the highest activity for polymerizations of ethylene (5 × 105 g of PE/(mol h)) and
C1-symmetric 9 afforded the highest molecular weight of polyethylene (Mn ) 145 × 104).
Only racemic complexes 7 and 8 could polymerize 1-olefins such as 1-pentene and 1-hexene,
giving highly isotactic polymers. Moreover, rac-7 induces catalytic cyclopolymerization of
1,5-hexadiene to give poly(methylene-1,3-cyclopentane).
In tr od u ction
catalytic activity toward olefins even in the absence of
“methylaluminoxane”. Bis(pentamethylcyclopentadie-
nyl) (Cp*) rare-earth-metal hydrides, LnH(C5Me5)2 (Ln
) La, Nd, Sm), have been reported to be quite active
for ethylene polymerization, although these are com-
pletely inactive for the 1-olefin polymerization.5c Re-
cently, modified Cp-based complexes such as [(C5Me4)-
SiMe2(η-NCMe3)Sc(η-H)]2,6 [rac-Me2Si(2-SiMe3-4-CMe3-
C5H2)2YH]2,7 and the mixed Cp*-alkoxide complex
[Y(C5Me5)(OC6H3-2,6-tBu2)(η-H)]28 have been reported
to be active for the polymerizations of 1-olefins. The
reactivity of the latter complexes suggests that the
synthesis of high-molecular-weight polyethylene can be
achieved by the appropriate substitution of Cp ligand
in rare-earth-metal complexes.
Rare-earth-metal complexes have attracted much
attention because of their unique reactivity as polym-
erization initiators.1 Living polymerization of methyl
methacrylate (MMA) was first achieved by the unique
catalytic function of trivalent rare-earth-metal com-
plexes with two pentamethylcyclopentadienyl ligands,
Cp*2SmR, affording highly syndiotactic poly(MMA)
quantitatively in a short period.2 Furthermore, the bis-
Cp*-based rare-earth-metal complexes promote the liv-
ing polymerization of alkyl acrylate (methyl acrylate,
ethyl acrylate, and butyl acrylate),3 which is very
difficult to attain by conventional catalysts because of
the presence of acidic protons in the main chain. Four-,
six-, and seven-membered lactones can also be polym-
erized in a living manner by these complexes.4
Divalent samarium complexes also catalyze ethylene
polymerization as trivalent complexes do as noted
above.9 Although bis-Cp* complexes such as Cp*2Sm
and Cp*2Sm(THF)2 show high polymerization activity
toward ethylene, molecular weights of the resulting
Furthermore, rare-earth-metal complexes are very
effective for polymerization of nonpolar monomers such
as ethylene and 1-olefins.5 The greatest advantage of
rare-earth-metal catalysts lies in high polymerization
(5) (a) Watson, P. L.; Parshall, G. W. Acc. Chem. Res. 1985, 18, 51.
(b) Burger, B. J .; Thompson, M. E.; Cotter, W. D.; Bercaw, J . E. J .
Am. Chem. Soc. 1990, 112, 1566. (c) Yang, X.; Stern, C. L.; Marks, T.
J . Organometallics 1991, 10, 840.
(6) Coughlin, E. B.; Bercaw, J . E. J . Am. Chem. Soc. 1992, 114, 7606.
(7) (a) Coughlin, E. B.; Shapiro, P. J .; Bercaw, J . E. Polym. Prepr.,
Am. Chem. Soc. Div. Polym. Chem. 1992, 33, 1266. (b) Shapiro, P. J .;
Cotter, W. D.; Schaefer, W. P.; Labinger, J . A.; Bercaw, J . E. J . Am.
Chem. Soc. 1994, 116, 4623.
† Hiroshima University.
‡ Osaka University.
(1) (a) Yasuda, H.; Tamai, H. Prog. Polym. Sci. 1993, 18, 1097. (b)
Yasuda, H.; Ihara, E. Adv. Polym. Sci. 1997, 133, 53.
(2) (a) Yasuda, H.; Yamamoto, H.; Yamashita, M.; Yokota, K.;
Nakamura, A.; Miyake, S.; Kai, Y.; Kanehisa, N. Macromolecules 1993,
26, 7134. (b) Yasuda, H.; Yamamoto, H.; Yokota, K.; Miyake, S.;
Nakamura, A. J . Am. Chem. Soc. 1992, 114, 4908.
(3) Ihara, E.; Morimoto, M.; Yasuda, H. Macromolecules 1995, 28,
7886.
(8) Schaverien, C. J . Organometallics 1994, 13, 69.
(9) (a) Watson. P. L.; Herskovitz, T. ACS Symp. Ser. 1983, No. 212,
459. (b) Evans, W. J .; Ulibarri, T. A.; Ziller, J . W. J . Am. Chem. Soc.
1990, 112, 2314.
(4) Yamashita, M.; Takemoto, Y.; Ihara, E.; Yasuda, H. Macromol-
ecules 1996, 29, 1798.
S0276-7333(97)01099-6 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 08/06/1998

3946 Organometallics, Vol. 17, No. 18, 1998
Ihara et al.
Ch a r t 1
Sch em e 1
polymers are rather low (Mn < 25 000). Furthermore,
Cp*2Sm reacts with various 1-olefins to give stable
π-allyl complexes and lacks the activity for polymeri-
zation of 1-olefins.9b J udging from the result of the
divalent complexes, there may be a great possibility of
improving the catalytic action toward olefin polymeri-
zation by modification of the ligand environment with
bulky substituents. Herein, we describe the preparation
of six new divalent samarium complexes bearing various
substituted bis-Cp ligands and the result of ethylene
and 1-olefin polymerizations.
Resu lts a n d Discu ssion
Liga n d Syn th esis. To investigate the relationship
between the structure of the initiator and its polymer-
ization activity, we first synthesized a series of ligands
which afforded various type of rare-earth-metal com-
plexes. Six ligands used in this study are summarized
in Chart 1 (preparation methods are given in the
Supporting Information). All the reactions proceed
smoothly to afford the desired complexes in good yield.
During the preparation of these complexes, the fol-
lowing points became apparent. (1) t-Bu and t-BuMe2-
Si substituents can be fixed at the 3- and 4-positions in
bridging Cp ligands 1 and 2. (2) The positions of C-C
double bonds and Me3Si groups in the Cp ring cannot
be fixed in the case of 1-4. Therefore, we could not
determine the precise structures of 1-4 by the NMR
method because of the existence of various isomers.
However, a single samarium complex was formed when
these were complexed with Sm (vide infra).
SmI2. Since the Me3Si or Me2Si group in the Cp ligand
is very sensitive to KH, potassium salts of the ligands
were prepared by lithiation with n-BuLi followed by
cation exchange reaction with t-BuOK.
(a ) Ra cem ic Com p lexes 7 a n d 8. The reaction of
dipotassium salt of 1 with SmI2 afforded Me2Si(2-Me3-
Si-4-tBuC5H2)2Sm(THF)2 (7)(rac-tBu), as purple crystals
(Scheme 1). The 1H NMR spectrum of 7 shows each
t-Bu, Me3Si, and bridging Me2Si signal as one singlet,
suggesting that 7 has a C2-symmetric structure. The
integral ratio of the NMR spectrum shows the presence
of two THF molecules coordinated to the Sm center.
Single-crystal X-ray analysis clearly reveals the racemic
structure (Figure 1). Crystal data for complexes 7, 8,
10, and 12 are given in Table 1 and selected bond
lengths and angles in Table 2. Each t-Bu and Me3Si
group is located on the 2- and 4-positions, respectively,
on both Cp rings, and the C2-symmetric structure was
formed. The arrangement of the substituents is just the
same as that of the trivalent Y complex rac-Me2Si(2-
Me3Si-4-tBuC5H2)2YCl2Li(THF)2, reported by Bercaw et
al.7 The Cp′(centroid)-Sm-Cp′(centroid) bite angle is
115.8(4)°, ca. 20° smaller than that of (C5Me5)2Sm(THF)2
bearing no Me2Si bridge.11 The decrease of the bite
angle corresponds to the increase of the space around
the metal center, from which we can expect high
catalytic reactivity for olefin monomers.12
On the other hand, we can easily characterize the
1
structure of 5 by the analysis of its H NMR spectrum.
Since three correlated signals of protons on Cp rings
are observed in an ABX pattern, it is apparent that
these protons are connected to an sp2 carbon on the five-
membered ring. Accordingly, two Me3Si groups are on
the same sp3 carbon at 3-positions as shown in the
formula. However, when this ligand was reacted with
the appropriate rare-earth-metal, a (3,4-bis(trimethyl-
silyl)cyclopentadienyl)metal compound was obtained as
a result of sigmatropic rearrangement.10
Syn th esis of Sm (II) Com p lexes. All the divalent
samarium complexes were synthesized by the reaction
of the dipotassium salt of the corresponding ligand with
In a similar manner, rac-Me2Si(2-Me3Si-4-tBuMe2-
SiC5H2)2Sm(THF)3 (8)(rac-tBuMe2Si) was synthesized
(10) (a) J utzi, P. Chem. Rev. 1986, 86, 983. (b) Ustynyuk, Yu. A.;
Kisin, A. V.; Pribytkova, J . M.; Zarkin, A. A.; Antonova, N. D. J .
Organomet. Chem. 1972, 42, 47. (c) Grishin, Yu. K.; Luzikov, Yu. N.;
Ustynyuk, Yu. A. Dokl. Acad. Nauk SSSR 1974, 216, 321.
(11) Evans, W. J .; Grate, J . W.; Choi, H. W.; Bloom, I.; Hunter, W.
E.; Atwood, J . L. J . Am. Chem. Soc. 1985, 107, 941.
(12) J eske, G.; Schock, L. E.; Swepston, P. N.; Schumann, H.; Marks,
T. J . J . Am. Chem. Soc. 1985, 107, 8103.

New Divalent Samarium Complexes
Organometallics, Vol. 17, No. 18, 1998 3947
Ta ble 1. Cr ysta l Da ta for 7, 8, 10, a n d 12
7
8
10
12
formula
fw
cryst syst
space group
a/Å
C
34H62O2SmSi3
C42H82O3SmSi5
925.94
monoclinic
P21/c
12.147(3)
20.780(3)
21.718(2)
103.55(1)
5329(1)
4
1.154
1964
12.47
10172
3540
0.082 (0.074)
C32H56O3SmSi3
1171.55
orthorhombic
Pbca
19.386(6)
25.251(4)
17.386(4)
C34H62O4SmSi4
797.60
orthorhombic
P212121
17.316(5)
20.093(4)
11.761(4)
737.52
monoclinic
Cc
12.309(2)
17.153(2)
19.496(3)
103.45(1)
4003(1)
4
1.224
1544
15.84
4986
b/Å
c/Å
â/deg
V/Å3
8510(3)
8
4092(1)
4
1.295
1664
15.87
5236
4117
Z
D
calcd/(g cm-3
)
1.129
3008
14.91
10648
3556
0.079
F(000)
µ(Mo KR)/cm-1
no. of measd rflns
no. of obsd rflns (Fo = 3.0σ(Fo))
Ra (Rw)b
3110
0.076 (0.048)
0.057 (0.066)
a
b
2
R ) ∑||Fo| - |Fc||/∑|Fo|. Rw ) (∑w(|Fo| - |Fo|)2/∑w|Fo| )1/2; w ) 1/σ2(Fo).
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg)
7
8
10
12
Bond Lengths
C(11)-C(12)
C(12)-C(13)
C(13)-C(14)
C(14)-C(15)
C(15)-C(11)
1.58(4) 1.55(4) 1.42(4) 1.42(2)
1.55(2) 1.45(4) 1.46(4) 1.42(2)
1.40(3) 1.43(4) 1.39(4) 1.42(2)
1.28(3) 1.48(5) 1.43(4) 1.39(2)
1.59(4) 1.45(4) 1.42(4) 1.42(2)
C(21)-C(22)
C(22)-C(23)
C(23)-C(24)
C(24)-C(25)
C(25)-C(21)
1.28(4) 1.42(4) 1.40(4) 1.42(2)
1.25(3) 1.43(4) 1.42(4) 1.43(2)
1.45(3) 1.38(5) 1.40(4) 1.41(2)
1.59(4) 1.42(4) 1.41(4) 1.40(2)
1.27(4) 1.41(4) 1.43(4) 1.41(2)
Si(1)-C(1)
Si(1)-C(2)
Sm-O(3)
Sm-O(4)
1.73(5) 1.87(4) 1.86(3)
1.98(4) 1.90(3) 1.85(4)
2.61(2) 2.58(3) 2.54(2) 2.669(9)
2.67(2) 2.63(3) 2.56(2) 2.591(9)
C(12)-Si(12)
C(22)-Si(22)
C(14)-Si(14)
C(24)-Si(24)
C(12)-Si(2)
C(22)-Si(3)
C(11)-Si(2)
C(12)-Si(4)
C(21)-Si(3)
C(22)-Si(5)
1.80(2)
1.93(4)
1.88(3)
1.91(3)
1.85(2)
1.89(3)
1.88(1)
1.87(1)
1.85(1)
1.84(1)
Bond Angles
O(3)-Sm-O(4)
Si(2)-O(1)-Si(3)
Si(2)-O(2)-Si(5)
Cp(centroid)-Sm-Cp(centroid) 115.8
Cp′-Cp′ 78.2
80.2(7) 77.8(10) 94.4(8) 99.6(3)
142(1) 147.2(7)
F igu r e 1. Structure of racemic-tBu 7.
142.8(7)
by the path shown in Scheme 1. The 1H NMR spectrum
of 8 reveals C2-symmetric features, in which tBu, Me3-
Si, and Me2Si groups appear as singlets. Two diaste-
reotopic Me signals for tBuMe2Si indicate the presence
116.5
77.3
116.5
76.0
133.4
55.4
among these molecules. Furthermore, two of the THF
molecules can be removed by repeated washing with
toluene or heating. This procedure is especially impor-
tant to obtain a higher activity of 8 toward olefin
polymerization.
1
of a chiral center. Supporting the result of H NMR,
X-ray analysis reveals the racemic structure of 8 (Figure
2). The formation of a racemic complex from 2 is in good
accord with the data for a trivalent Y complex with this
ligand, Me2Si(2-Me3Si-4-tBuMe2SiC5H2)2YCl2Li(THF)2.13
The Cp′(centroid)-Sm-Cp′(centroid) bite angle is 116.5°,
again 20° smaller than that of the nonbridged bis-Cp
complex Cp*2Sm(THF)2.
The remarkable difference observed between 7 and 8
is the number of THF molecules coordinated to the
complexes (2 in 7, 3 in 8). Though one of the THF
molecules in 8 does not coordinate in the X-ray struc-
ture, all three THF molecules appear equivalently in
1H NMR, indicating the existence of rapid exchange
The dihedral angle between the planes containing
Cp′(centroid)-Sm-Cp′(centroid) and O(THF)-Sm-
O(THF) is 72.7° for 7 and 76.4° for 8, respectively.
Comparing these data with those of other divalent
complexes, 86.2° for Cp*2Sm(THF)2, 89.4° for 10, and
88.2° for 12, the deviation of the dihedral angle from
90° is concluded to be a characteristic structural feature
of the racemic complexes. In these racemic complexes,
oxygen atoms of THF molecules cannot exist in the
equatorial plane defined by two Cp rings because of the
presence of bulky substituents at the 4-position on the
Cp ring. As will be described later in this paper, only
these racemic complexes showed high activities toward
(13) Yasuda, H.; Ihara, E. Tetrahedron 1995, 51, 4563.

3948 Organometallics, Vol. 17, No. 18, 1998
Ihara et al.
Sch em e 3
of the C1-symmetric samarium(III) species, in which two
Me3Si groups are at 2,4-positions in one Cp and at 3,4-
positions in the other Cp.
It should be noted that the divalent C1-symmetric
complex was formed exclusively, presumably due to the
large steric bulk of two coordinated THF molecules,
whereas a mixture of racemic and C1-symmetric com-
plexes was obtained in the case of trivalent complexes
because of the reduced steric bulk.14
(c) m eso Typ e Com p lexes 10. The ligand 4, which
has two bridging groups of different length (-Me2Si-,
-Me2SiOMe2Si-), was designed to afford a meso type
F igu r e 2. Structure of racemic-tBuMe2Si 8.
1
structure after complexation (Scheme 3). The H NMR
Sch em e 2
spectrum of the complex obtained by the reaction of the
potassium salt of 4 with SmI2 shows each bridging group
(Me2SiOSiMe2, Me2Si) as two singlets and tBu groups
as one singlet, indicating that this complex has Cs
symmetry. On the basis of X-ray structure analysis, we
finally confirmed the meso type structure for 10 (Figure
4). Despite the presence of an additional bridging group
(Me2SiOSiMe2), the Cp(centroid)-Sm-Cp(centroid) bite
angle is 116.5°, which is very close to that of 7 and 8
bearing one Me2Si bridge. Thus, the presence of the
additional SiOSi bridge did not affect the bite angle.
The O(3)-Sm-O(4) angle is 94.4°, which is about 15°
larger than those of 7 and 8. Whereas the C(R)-O-
C(R) plane of one THF molecule is nearly parallel to the
equatorial plane defined by Sm, O(3), and O(4) (dihedral
angle 2.5°), the plane of the other THF is nearly
perpendicular to this plane (dihedral angle 89.2°). This
orientation of the latter THF molecule allows the oxygen
to form a π-bond with Sm. Though the coordination
mode of these two THF molecules is energetically the
most stable, other divalent Sm complexes including
the polymerization of 1-olefins. Thus, the reactivity to
1-olefins may be closely related to the structural per-
turbation caused by the bulky substituents.
(b) C1-Sym m etr ic Com p lexes 9. The C1-symmetric
Sm(II) complex Me2Si[2,4-(Me3Si)2C5H2][3,4-(Me3Si)2-
C5H2]Sm(THF)2 (9), in which two Me3Si groups are
located at 3,4-positions in one Cp ring and at 2,4-
positions in another ring, was prepared by the reaction
of dipotassium salt 3 with SmI2 in THF (Scheme 2). The
1H NMR spectrum of 9 is shown in Figure 3. Each
signal of four Me3Si and four Cp H groups and two
bridging Me2Si groups appears separately. In the
synthesis of trivalent Sm complexes with this ligand,
we obtained a mixture of racemic and C1-symmetric
(14) A mixture of the racemic and C1-symmetric trivalent Sm
complexes was obtained by the reaction of the dilithium salt of 3 with
SmCl3, and they were separated by using their different solubilities
in hexane. Full details about these trivalent complexes will be reported
elsewhere. Racemic Me2Si[2,4-(SiMe3)2C5H2]2SmCl2Li(THF)2: 1H NMR
(400 MHz, C6D6) δ -1.73 (s, 18H, SiMe3), 0.01 (s, 18H, SiMe3), 2.01 (s,
8H, THF-â), 2.27 (s, 6H, Me2Si), 4.76 (s, 8H, THF-R), 5.84 (s, 2H, Cp
H), 16.37 (s, 2H, Cp-H); cell data triclinic, P1h (No. 2), a ) 12.611(4) Å,
b ) 17.109(3) Å, c ) 12.134(4) Å, R ) 99.74(3)°, â ) 115.16(2)°, γ )
90.91(3)°, Dcalcd(Z ) 2) ) 1.211 g/cm3. Least-squares refinement based
on 4239 reflections converged to R ) 0.115 and Rw ) 0.128. C1-
symmetric Me2Si[2,4-(SiMe3)2C5H2][3,4-(SiMe3)2C5H2]SmCl2Li(THF)2:
1H NMR (400 MHz, C6D6) δ -2.33 (s, 9H, SiMe3), -0.82 (s, 9H, SiMe3),
-0.54 (s, 9H, SiMe3), 1.14 (s, 3H, Me2Si), 1.18 (s, 9H, SiMe3), 1.85 (s,
8H, THF-â), 2.97 (s, 3H, Me2Si), 4.01 (s, 1H, Cp H), 4.43 (s, 8H, THF-
R), 9.73 (s, 1H, Cp H), 10.35 (s, 1H, Cp H), 17.10 (s, 1H, Cp H); cell
data monoclinic, P21/c (No. 14), a ) 17.483(3) Å, b ) 13.427(3) Å, c )
19.475(2) Å, â ) 104.23(1)°, Dcalcd(Z ) 4) ) 1.270 g/cm3. Least-squares
refinement based on 3851 reflections converged to R ) 0.068 and Rw
) 0.049.
1
complexes and confirmed their structures by H NMR
1
and X-ray analysis.14 Whereas the H NMR spectrum
of this tris racemic complex showed highly symmetrical
features (two Me3Si, two Cp H, and one bridging Me2Si
signal) much the same as those of 7, four Me3Si, four
Cp H, and two bridging Me2Si signals appeared in the
spectrum in the case of the trivalent C1-symmetric
complex. Thus, the NMR spectrum of 9 resembles that

New Divalent Samarium Complexes
Organometallics, Vol. 17, No. 18, 1998 3949
F igu r e 3. 1H NMR spectrum of C1-symmetric 9.
Sch em e 4
a Me2Si bridge.15 The steric repulsion of the Ph group
with the Me3Si group at the 2-position of the Cp ring
will prevent the formation of racemic complex in the
case of the trivalent complexes.
The complexation of dipotassium salt of 5 with SmI2
gave the divalent complex 11 as purple crystals (Scheme
4). The 1H NMR spectrum of complex 11 (Figure 5)
shows only one signal for Me3Si groups and Cp H
protons, respectively. Therefore, we can readily con-
clude that 11 has a highly symmetrical structure, a C2v-
symmetric structure where all four Me3Si groups are
at 3,4-positions of both Cp rings. The structure in which
two Me3Si groups are located at 2,5- or 2,4-positions can
be neglected for steric reasons.
Comparing the result of the complexation of divalent
samarium complexes (C1 from 3, C2v from 5) and
trivalent complexes (C1 and racemic from 3, C1 from 5),
we can conclude that the arrangement of two Me3Si
groups at 3- and 4-positions on the Cp ring will be more
F igu r e 4. Structure of meso 10.
Cp*2Sm(THF)2 cannot produce such a stable structure
because of the severe steric repulsion between THF and
Me substituents on Cp rings. As will be discussed later
in this paper, such a difference of the initiator structure
is reflected on the reactivity for olefins.
(d ) C2v-Sym m etr ic (P h 2Si) Com p lex 11. In the
ligand 5, a Ph2Si bridge was used in place of Me2Si, to
investigate the effect of a bulky bridging group on the
structure of the resulting complex. In the complexation
with a trivalent Sm metal, 5 afforded the C1-symmetric
complex exclusively, whereas a mixture of racemic and
C1-symmetric complexes was obtained from 3, bearing
(15) Cell data for C1-symmetric Ph2Si[2,4-(SiMe3)2C5H2][3,4-(SiMe3)2-
C5H2]SmCl2Li(THF)2: triclinic, P1h (No. 2), a ) 14.557(2) Å, b ) 15.145-
(2) Å, c ) 13.184(2) Å, R ) 104.47(1)°, â ) 92.99(1)°, γ ) 83.17(1)°,
Dcalcd(Z ) 2) ) 1.155 g/cm3. Least-squares refinement based on 8814
reflections converged to R ) 0.058 and Rw ) 0.072.

3950 Organometallics, Vol. 17, No. 18, 1998
Ihara et al.
F igu r e 5. 1H NMR spectrum of C2v-symmetric (Ph2Si) 11.
Sch em e 5
favorable in the case of divalent complexes. This may
arise from the different mode of coodination to the metal
(steric bulk of Sm center: L2M[THF]2 > L2MCl2Li-
[THF]2) and/or the different electronic natures of di- and
trivalent Sm metals.
(e) C2v-Sym m etr ic[(SiOSi)2] Com p lex 12. The
ligand 6 with two Me2SiOSiMe2 bridging groups also
afforded a C2v-symmetric structure after complexation
with divalent samarium complexes (Scheme 5). Its
F igu r e 6. Structure of C2v-symmetric [(SiOSi)2] 12.
1
divalent samarium complexes reported in this text are
given schematically. The following points are obvious
from the illustration.
(1) Each complex has an unique shape of the vacant
space around the samarium center, when we consider
neglecting the coordinated THF.
(2) In a series of Me2Si-bridged complexes (7-12), the
size of the vacant space around the metal center
increases gradually in the order C2v(Ph2Si) 11 < C2v-
[(SiOSi)2] 12 < C1 9 < racemic 7 < meso 10 (the racemic
8 cannot be included in this order since the effect of the
larger substituent, tBuMe2Si, on the size of the space
cannot be easily estimated). Thus, the movement of the
substituent on the Cp ring resulted in an increase of
structure was characterized by H NMR and finally by
X-ray structure analysis (Figure 6). One t-Bu, one Cp-
H, and two Me2SiOSiMe2 signals appear as singlets in
1H NMR, indicating a C2v-symmetric structure for 12.
Cp′(centroid)-Sm distances are 2.64 and 2.63 Å, which
are similar to those of the other complexes studied here.
The Cp′(centroid)-Sm-Cp′(centroid) bite angle (133.4°)
is very close to that of Cp*2Sm(THF)2 (137°). Thus, the
use of long bridging groups did not result in the
elongation of the Cp′(centroid)-Sm distance but re-
sulted in an increase in the Cp′(centroid)-Sm-Cp′-
(centroid) bite angle.
(f) Str u ctu r a l P er sp ective of th e Diva len t Sm
Com p lexes. In Chart 2, the structures of all the

New Divalent Samarium Complexes
Organometallics, Vol. 17, No. 18, 1998 3951
Ch a r t 2
Ch a r t 3
the vacant space around the metal center, as shown in
Chart 3.
field desorption mass spectrometry (FD-MS).17 They
proposed the polymerization mechanism as shown in
Scheme 6. The initiation is the formation of a 2:1
complex of Cp*2Sm with ethylene followed by electron
transfer, giving a trivalent alkyl complex with two
Sm-C bonds. In fact, the 2:1 complexes of Cp*2Sm with
unsaturated compounds have been isolated and crys-
tallographically characterized in the case of dinitrogen,17
azobenzene,19 styrene,20 trans-stilbene,20 and diphenylb-
utadiyne.21 Then, the propagation is supposed to follow
the successive insertion of ethylene into the Sm-C bond,
where the catalyst behaves as a bifunctional initiator.
Thus, experimental results were consistent with the
proposed mechanism. The polymerization under a D2
atmosphere also resulted in the quantitative incorpora-
tion of deuterium atoms into both chain ends of ethylene
The effective volumes Veff, the space around the metal
atom for olefin coordination, were calculated using the
SV program16 for complexes 7, 8, 10, and 12, respec-
tively (calculation was carried out for the THF-free
molecule) (Figure 7). The Veff values in the complexes
are in the order 8 = 7 = 10 > 12, indicating that the
reactivity for olefin polymerization increases in this
order. In fact, low catalytic activity for complex 12 is
well-interpreted in terms of resulting effective volume.
However, the accuracy of this calculation is not so high
as to differentiate the effective volumes among 8, 7, and
10.
Eth ylen e P olym er iza tion . Ethylene polymeriza-
tion was explored by using the resulting six divalent
Sm complexes. Although the divalent samarium com-
plex does not possess a carbon-metal bond into which
ethylene can insert, it can polymerize the monomer
effectively. Recently, Evans et al. have investigated the
mechanism of ethylene polymerization by Cp*2Sm using
(17) Evans, W. J .; DeCoster, D. M.; Greaves, J . Macromolecules
1995, 28, 7929.
(18) Evans, W. J .; Ulibarri, T. A.; Ziller, J . W. J . Am. Chem. Soc.
1988, 110, 6877.
(19) Evans, W. J .; Drummond, D. K.; Bott, S. G.; Atwood, J . L.
Organometallics 1986, 5, 2389.
(20) Evans, W. J .; Ulibarri, T. A.; Ziller, J . W. J . Am. Chem. Soc.
1990, 112, 219.
(21) Evans, W. J .; Keyer, R. A.; Ziller, J . W. Organometallics, 1993,
12, 2618.
(16) Nemoto, T.; Ohashi, Y. SV Program for Viewing Crystal and
Molecular Structures; Tokyo Institute of Technology, Tokyo, J apan,
1993.

3952 Organometallics, Vol. 17, No. 18, 1998
Ihara et al.
coordinated THF by heating or washing with toluene
is required. From the results noted above, we can
conclude the following.
(1) The activity of the ethylene polymerization by
divalent Sm complexes varies depending upon how easy
the incoming ethylene coordinates to the Sm atom.
Thus, optimum space around the metal center is neces-
sary for high activity (the optimum space not only is
defined by vacant space around the metal but also is
effected by the number of coordinated THF atoms and
the steric environment derived from the substituents).
(2) The coordination of two or three THF molecules
prevents the approach of ethylene to the Sm atom, and
as a result only low activity was observed. When
complete elimination of coordinated THF is realized, we
will be able to determine the more detailed reaction
mechanism.
(3) The initiation mechanism for 10, 7, and 9 is
illustrated in Chart 4. The largest vacant site was
observed in the case of 10 and the smallest one in the
case of 9. Thus, we can estimate the real vacant site
by considering the complexation between one ethylene
molecule and two lanthanide complexes.
Molecu la r Weigh t of P olyet h ylen es. As can be
seen from Table 3, the meso type complex 10 with the
highest activity gave the lowest molecular weight of the
polymers (Mn < 50 000). On the other hand, racemic
and C1- and C2v-symmetric complexes gave very high
molecular weight polyethylenes (Mn >> 100 000). The
molecular weight of polyethylene should vary depending
upon how often the termination or chain transfer
reaction will occur (the most feasible side reaction in
this polymerization is the â-elimination). The transition
state for â-H elimination is given in Chart 5, in which
a â-agostic interaction is present that forces the polym-
erization chain either up or down directly into the
ligand. The R-agostic interaction, which is present in
the transition state for propagation, will force the
polymer chain into direct interaction with ligand, slow-
ing the propagation. However, this effect is relatively
smaller than expected (compare the reaction period for
9 and 10 listed in Table 3). Thus, racemic and C1- and
C2v-symmetric complexes will favorably assume the
structure to perform the propagation reaction rather
than â-H elimination by the steric effect of the substit-
uents lying at 3,4-positions on the Cp ring. Thus, the
polymerization by the C1-symmetric complex afforded
F igu r e 7. Effective volumes (Veff) for monomer coordina-
tion to metal.
oligomers. Thus, we can readily estimate the initiation
mechanism for complexes 7-12 as insertion of ethylene
between two divalent complexes.17
Activity of th e Com p lexes. The result of the
ethylene polymerization is summarized in Table 3. In
a series of the complexes with two (or one) coordinated
THF molecules, the activity of the ethylene polymeri-
zation decreases in the order meso 10 > racemic 7> C2v-
symmetric(Ph2Si) 11 > racemic 8 > C1-symmetric 9 >>
C2v-symmetric[(SiOSi)2] 12. The order of activity changes
primarily depending upon the size of the vacant space
around the Sm center. Thus, the meso complex 10
exhibited the highest activity due to the large space
around the Sm center and the C2v-symmetric[(SiOSi)2]
12 complex showed the lowest activity. The racemic
complex with the t-BuMe2Si group 8 and the C2v
complex (Ph2Si) 11 did not show polymerization activity
at all when the complex is coordinated by two or three
THF molecules. Inhibition of polymerization is mainly
due to their large steric bulk, and removal of the
Sch em e 6

New Divalent Samarium Complexes
Organometallics, Vol. 17, No. 18, 1998 3953
Ta ble 3. Eth ylen e P olym er iza tion by Diva len t Sm Com p lexesa
reacn
period, min
activity, 10-4
of PE/(mol h)
g
initiator
10-4Mn
Mw/Mn
rac-tBu 7
1
3
6.18
13.9
11.6
35.6
1.43
1.60
rac-tBuMe2Si(THF)3) 8
rac-tBuMe2Si(THF)1) 8
no polymerization
5
10
3.02
2.60
13.1
14.2
3.54
4.33
C1-symmetric 9
meso 10
15
30
1.57
1.42
100
145
1.60
1.89
5
10
14.6
47.0
1.94
4.73
3.29
3.49
C
C
2v-symmetric(Ph2Si)(THF)2) 11
2v-symmetric(Ph2Si)(THF)1) 11
no polymerization
5
10
10.4
5.22
16.0
49.6
1.84
2.42
C
2v-symmetic[(SiOSi)2] 12
14 h
130 g of PE/(mol h)
42.9
3.04
a
Reaction conditions: temperature, 23 °C; initiator concentration, 1.0 mM; solvent, toluene; ethylene pressure, 1 atm.
Ch a r t 4
1-Olefin P olym er iza tion . In contrast to the high
activity of the divalent Sm complexes toward ethylene
polymerization, only racemic complexes 7 and 8 are
active for 1-olefin polymerization. Bercaw et al. reported
that the trivalent racemic yttrium complex was active
for stereoselective 1-olefin polymerization.6 Thus, the
racemic structure seems to be essential to gain the
activity. As mentioned in the former section, the
characteristic feature of these racemic complexes lies
in the deviation of the O(THF)-Sm-O(THF) plane from
the equatorial plane defined by two Cp rings. The
perturbation arising from the deviation may be related
to the reactivity of 1-olefins toward these racemic
complexes.
The result of the 1-olefin polymerization is sum-
marized in Table 4. The polymerization proceeded in a
highly stereoselective manner (isotactic) reflecting the
C2-symmetric structure. On the basis of 13C NMR
analysis for the resulting poly(1-olefin)s, the isomer
selectivities were higher than 95% (Figure 8).22 Thus,
the polymerization mechanism for the present rare-
earth-metal complexes is the same as that of group 4
metal Kaminsky type catalysts; i.e., rac-Et(Ind)2MCl2/
methylalumoxane (M ) Ti, Zr, Hf)23-26 and rac-Me2Si-
(2-Me-4-naphthylindenyl)2ZrCl2/methylalumoxane27 pro-
duce isotactic polypropylene. In these cases, propylene
always inserts from the same site (the structure of the
racemic complex given in Chart 4 is consistent with this
expectation). More recently, C1 type threo-Me2C(3-tBu-
C5H3)(3-tBu-C9H5)ZrCl2 coupled with methylalumoxane
was found to promote the isotactic polymerization of
propylene.28 The meso type complex 10 should afford
the allylic complex as a result of â-H elimination (the
color of the complex turned from purple to orange in
the reaction with 1-hexene). In fact, both divalent (C5-
Ch a r t 5
(22) Asakura, T.; Demura, M.; Nishiyama, Y. Macromolecules 1994,
24, 2334.
(23) Ewen, J . A. J . Am. Chem. Soc. 1984, 106, 6355.
(24) Kaminsky, W.; Kulper, K.; Britzinger, H. H.; Wild, F. R. Angew.
Chem., Int. Ed. Engl. 1985, 24, 507.
(25) Kaminsky, W.; Kulper, K.; Niedoba, S. Makromol. Chem.
Macromol. Symp. 1986, 3, 377.
(26) Ewen, J . A.; Haspeslagh, L.; Atwood, J . L.; Zhang, H. J . Am.
Chem. Soc. 1987, 109, 6544.
(27) Spaleck, W.; Kuber, F.; Winter, A.; Rohrmann, J .; Bachmann,
B.; Antberg, M.; Dolle-Paulus, E. F. Organometallics 1994, 13, 945.
(28) Miyake, S.; Okumura, Y.; Inazawa, S. Macromolecules 1995,
28, 3074.
the highest molecular weight polyethylene. On the
other hand, in the polymerization by a meso type
complex with a large space around the metal center,
â-elimination should occur more easily to result in the
formation of rather low molecular weight polymers.

3954 Organometallics, Vol. 17, No. 18, 1998
Ta ble 4. 1-Olefin P olym er iza tion by Diva len t Sm Com p lexesa
Ihara et al.
reacn
period, h
activity, g of
polymer/(mol h)
initiator
rac-tBu 7
monomer
1-pentene
10-4Mn
Mw/Mn
12
24
12
24
36
48
48
161
90
138
112
230
98
1.06
1.21
0.83
1.14
2.85
0.59
0.83
1.48
1.50
1.55
1.72
1.88
1.70
1.58
1-hexene
1,5-hexadieneb
1-pentene
1-hexene
rac-tBuMe2Si(THF)1) 8
118
a
b
Reaction conditions: temperature, 23 °C; initiator, 0.01 mmol; solvent, 3.0 mL of toluene; monomer, 2.0 mL. Initiator, 0.02 mmol.
mouth in the case of (C5H5)2ZrCl2, (C5Me5)2ZrCl2, and
(S,S)-(EBETHI)ZrBINOL.32,33
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All operations were performed
under argon by using standard Schlenk techniques. Tetrahy-
drofuran and hexane were dried over Na/K alloy and distilled
before use. Toluene used for polymerization was dried over
Na/K alloy and thoroughly degassed by trap-to-trap distilla-
tion. Ethylene (Nakamura Oxygen Co.) was used without
further purification. 1-Pentene, 1-hexene, and 1,5-hexadiene
were dried over Na/K alloy and distilled. Me3SiCl, Me2SiCl2,
Ph2SiCl2, tBuMe2SiCl, and ClMe2SiOSiMe2Cl were dried over
CaH2 for 1 week and used after distillation. The preparation
of ligand 2 was already reported by Evans.11 tBuCp-H was
prepared by the reaction of tBuBr with CpNa, and Me3SiCp-H
was prepared by the reaction of Me3SiCl with CpNa. (Me3-
Si)2Cp-H was prepared by the reaction of Me3SiCl with Me3-
SiCpNa. SmI2 was prepared from Sm metal and diiodoethane
in THF. 1H NMR spectra were recorded on a Bruker AMX
400wb spectrometer (400.13 MHz), and chemical shifts were
calibrated using benzene (δ 7.20 ppm). 13C NMR spectra were
recorded on a J EOL J NM-LA 400 spectrometer (99.45 MHz),
and chemical shifts were calibrated using the center peak of
benzene (δ 128 ppm). Complexometric metal analyses were
conducted by the method reported by Atwood and Evans.34 Mn
and Mw/Mn values of poly(1-pentene) and poly(1-hexene) were
determined by gel permeation chromatography (GPC) on a
Tosoh SC-8010 using TSKgel G2000, G3000, G4000, and
G5000 columns in chloroform at 40 °C. Mn and Mw/Mn values
of polyethylene were determined by GPC on a Waters 150C
using a Shodex AT806MS column in 1,2,4-trichlorobenzene at
140 °C. Mn and Mw/Mn were calibrated from standard poly-
styrene.
F igu r e 8. 13C NMR spectrum of poly(1-pentene) obtained
by use of complex 7.
Sch em e 7
Me5)2Sm(THF)x (x ) 0, 2)29 and trivalent [(C5Me5)2Sm-
(µ-H)]230 complexes react with olefins to make only allyl
products. During this procedure, the bite angle Cp-
(centroid)-Sm-Cp(centroid) should change freely from
116 to ca. 130°, because of the absence of a bridging
group. In contrast to this observation, C1 complex 9 and
C2v complexes 11 and 12 are completely inert toward
1-olfins due to steric reasons and the initial 9, 11, and
12 were recovered quantitatively.
Str u ctu r e Solu tion a n d Refin em en t for Com p lexes 7,
8, 10, a n d 12. All the diffraction measurement were per-
formed on a Rigaku AFC-5R diffractometer with graphite-
monochromatized Mo KR radation. As the complexes are very
air-sensitive, crystals were sealed in a thin-walled glass
capillary tube under an argon atmosphere. The X-ray data
were collected at room temperature using the ω-2θ scan
technique to a maximum 2θ value of 55.0°. The data were
corrected for conventional absorption, Lorentz, and polariza-
tion effects.
In addition to the high activities of racemic complex
7 toward 1-pentene and 1-hexene, this complex is also
active for the cyclopolymerization of 1,5-hexadiene,
affording poly(methylene-1,3-cyclopentane) exclusively.
The analysis of 13C NMR spectra of the resulting
polymer shows that the selectivity of the ring-closing
process is very low and the polymerization gave the
methylene-1,3-cyclopentane structure within nearly a
1:1 cis:trans ratio (Scheme 7).31 High trans selectivity
of poly(1,5-hexadiene) was already reported by Way-
The crystal structures were solved by the heavy-atom
method and were expanded by successive Fourier syntheses.
The non-hydrogen atoms except for complex 7 (applied only
for Sm, Si, O, and two C atoms in this case) were refined
anisotropically by full-matrix least-squares methods, while the
(29) Evans, W. J .; Grate, W. J .; Choi, H. W.; Bloom, I.; Hunter, W.
E.; Atwood, J . L. J . Am. Chem. Soc. 1985, 107, 941.
(30) Evans, W. J .; Bloom, I.; Hunter, W. E.; Atwood, J . L. J . Am.
Chem. Soc. 1983, 105, 1401.
(31) Coates, G. W.; Waymouth, R. M. J . Am. Chem. Soc. 1993, 115,
91.
(32) Cavallo, L.; Guerra, G.; Corradini, P.; Resconi, L.; Waymouth,
R. M. Macromolecules 1993, 26, 1260.
(33) Coates, G. W.; Waymouth, R. M. J . Am. Chem. Soc. 1993, 115,
91.
(34) Atwood, J . L.; Hunter, W. E.; Wayda, A. L.; Evans, W. J . Inorg.
Chem. 1981, 20, 4115.

New Divalent Samarium Complexes
Organometallics, Vol. 17, No. 18, 1998 3955
hydrogen atoms were fixed at their standard geometries and
were not refined. All the calculations were performed by the
use of the teXsan crystallographic software package (teXsan:
Crystal Structure Analysis Package, Molecular Structure Corp.
(1985 and 1992)).
Me2Si), 6.92 (s, 9H, SiMe3), 7.72 (s, 9H, SiMe3), 17.85 (s, 9H,
SiMe3), 20.69 (s, 1H, Cp H), 23.83 (s, 1H, Cp H), 49.86 (s, 1H,
Cp H). Anal. Calcd for SmC32H62Si5O2: Sm, 19.54. Found:
Sm, 19.22.
P r ep a r a tion of 10. To a stirred solution of 4 (3.39 g, 7.87
mmol) in THF (60 mL) was added n-BuLi (9.5 mL of 1.70 M
solution in hexane, 15.7 mmol) at 0 °C. After the solution was
stirred for 6 h at room temperature, t-BuOK (20 mL of 0.80
M solution in THF, 16.0 mmol) was added. The reaction
mixture was refluxed for 12 h, and the solution was evaporated
to dryness. The product was washed with hexane (50 mL ×
2) to afford the dipotassium salt of 4 in 96% yield as a white
powder. A THF suspension (120 mL) of the dipotassium salt
of 4 (3.82 g, 7.53 mmol) was added to SmI2 (80 mL of THF
solution, 7.40 mmol). The reaction mixture was refluxed for
12 h, and the solution was evaporated. Then, toluene (50 mL)
was added to the residue and insoluble solid was removed by
centrifugation. After the solvent was removed in vacuo, the
residue was extracted with THF (15 mL × 2). Recrystalliza-
tion from THF/hexane afforded 10 as purple crystals in 66%
yield. 1H NMR (400 MHz, C6D6): δ -4.99 (s, 18H, tBu), -2.54
(s, 3H, Me2Si), -1.09 (s, 6H, Me2SiOSiMe2), 3.19 (s, 8H, THF-
â), 6.30 (s, 2H, Cp H), 10.51 (s, 8H, THF-R), 10.75 (s, 3H, Me2-
Si), 11.26 (s, 6H, Me2SiOSiMe2), 41.26 (s, 2H, Cp H). 13C NMR
(99 MHz, C6D6): δ 4.63, 24.30, 28.90, 29.82, 30.95, 35.10, 42.80,
44.91. Anal. Calcd for SmC32H56Si3O3: Sm, 20.78. Found:
Sm, 20.40.
P r ep a r a tion of 7. To a stirred solution of 1 (3.01 g, 6.77
mmol) in THF (60 mL) was added n-BuLi (8.2 mL of 1.66 M
solution in hexane, 13.5 mmol) at 0 °C. After the reaction
mixture was stirred for 6 h at room temperature, t-BuOK (20
mL of 0.68 M solution in THF, 13.6 mmol) was added at that
temperature. The resulting reaction mixture was refluxed for
12 h, and the solution was evaporated to dryness. The product
was washed with hexane (30 mL × 2), affording the dipotas-
sium salt of 1 in 70% yield as a white powder. To 40 mL of
THF were added at once at room temperature a THF suspen-
sion (80 mL) of the dipotassium salt of 1 (5.64 g, 10.8 mmol)
and SmI2 (80 mL of THF solution, 10.0 mmol). Then the
reaction mixture was refluxed for 12 h and the solution was
evaporated. Toluene (50 mL) was added to the residue, and
insoluble solid was removed by centrifugation. After the
solvent was removed in vacuo, the residue was extracted with
THF (15 mL × 2). Recrystallization from THF/hexane afforded
7 as purple crystals in 35% yield. 1H NMR (400 MHz, C6D6):
δ -12.82 (s, 2H, Cp H), -2.64 (s, 6H, Me2Si), -1.05 (s, 8H,
THF-â), 3.56 (s, 18H, SiMe3), 4.05 (s, 8H, THF-R), 10.67 (s,
18H, tBu), 46.54 (s, 2H, Cp H). 13C NMR (99 MHz, C6D6): δ
-5.01, 25.22, 29.83, 31.88, 46.05, 67.03. Anal. Calcd for
SmC34H62Si3O2: Sm, 20.39. Found: Sm, 20.14.
P r ep a r a tion of 11. To a stirred solution of 5 (4.75 g, 7.90
mmol) in THF (60 mL) was added n-BuLi (9.6 mL of 1.64 M
solution in hexane, 15.8 mmol) dropwise at 0 °C. After the
solution was stirred for 6 h at room temperature, t-BuOK (30
mL of 0.63 M solution in THF, 19.0 mmol) was added. The
reaction mixture was refluxed for 36 h, and the solution was
evaporated to dryness. The product was washed with hexane
to afford dipotassium salt of 5 as white powder. A THF
suspension (40 mL) of the dipotassium salt of 5 (7.90 mmol)
was added to a THF solution of SmI2 (60 mL, 3.46 mmol) at
-78 °C, and the temperature of the reaction mixture was
raised gradually to room temperature. After the reaction
mixture was refluxed for 12 h, the solution was evaporated.
Toluene (70 mL) was then added to the residue and insoluble
solid was removed by centrifugation. Recrystallization of the
toluene solution afforded 11 as purple crystals in 54% yield.
1H NMR (400 MHz, C6D6): δ 29.41 (br s, 4H, Cp H), 14.10 (br
s, 8H, THF-R), 8.83 (d, J ) 6.5 Hz, 4H, Ph H [ortho]), 8.56 (t,
J ) 6.5 Hz, 4H, Ph H [meta]), 8.31 (t, J ) 6.5 Hz, 2H, Ph H
[para]), 2.15 (br s, 8H, THF-â), 0.22 (s, 36H, Me3Si). Anal.
Calcd for SmC42H66Si5O2: Sm, 16.82. Found: Sm, 16.13.
P r ep a r a tion of 8. To a stirred solution of 2 (4.70 g, 8.37
mmol) in THF (60 mL) was added n-BuLi (10.5 mL of 1.63 M
solution in hexane, 17.0 mmol) dropwise at 0 °C. After the
solution was stirred for 6 h at room temperature, t-BuOK (30
mL of 0.57 M solution in THF, 17.0 mmol) was added and the
reaction mixture was refluxed for 12 h. A THF-hexane
suspension of the dipotassium salt of 2 (8.37 mmol) was added
to a THF solution (40 mL) of SmI2 (90 mL, 8.0 mmol), and the
reaction mixture was refluxed for 12 h. After removal of
insoluble solid by centrifugation, the solvent was distilled out.
A 50 mL portion of toluene was added to the residue, and
insoluble solid was removed again by centrifugation. After the
solution was evaporated, 30 mL of dimethoxyethane was added
to the residue and the mixture was stirred for 12 h at room
temperature. Removal of dimethoxyethane in vacuo followed
by recrystallization of the residue from THF-hexane afforded
8 in 17% yield as purple crystals. 1H NMR (400 MHz, C6D6):
δ -8.50 (s, 2H, Cp H), -4.89 (s, 6H, tBuMe2Si or Me2Si), -2.27
(s, 6H, tBuMe2Si or Me2Si), -1.04 (s, 18H, SiMe3), 0.77 (s, 8H,
THF-â), 5.14 (s, 8H, THF-R), 8.90 (s, 18H, tBu), 13.45 (s, 6H,
tBuMe2Si or Me2Si), 41.80 (s, 2H, Cp-H). 13C NMR (99 MHz,
C6D6) δ 11.60, 19.76, 20.93, 24.89, 27.46, 28.26, 29.83, 38.80.
Anal. Calcd. for SmC42H82Si5O3: Sm, 16.24. Found: Sm,
16.54.
P r ep a r a tion of 9. To a stirred solution of 3 (9.10 g, 19.1
mmol) in THF (80 mL) was added n-BuLi (23.4 mL of 1.63 M
solution in hexane, 38.2 mmol) at 0 °C. The solution was
stirred for 6 h at room temperature, and t-BuOK (30 mL of
1.33 M solution in THF, 40.0 mmol) was added. After the
reaction mixture was refluxed for 12 h, the solution was
evaporated to dryness. The product was washed with hexane
(50 mL × 2), affording the dipotassium salt of 3 in 94% yield
as a white powder. To a THF suspension (120 mL) of the
dipotassium salt of 3 (9.9 g, 17.9 mmol) was added SmI2 (180
mL of THF solution, 17.0 mmol). The reaction mixture was
refluxed for 12 h, and then the solvent was removed under
vacuum. Toluene (50 mL) was added to the residue, and
insoluble solid was removed by centrifugation. After the
solution was evaporated, the residue was extracted with THF
(15 mL × 2). Recrystallization from THF/hexane afforded 9
as purple crystals in 28% yield. 1H NMR (400 MHz, C6D6) δ
-17.92 (s, 1H, Cp H), -6.16 (s, 3H, Me2Si), -2.54 (s, 9H,
SiMe3), -1.58 (s, 8H, THF-â), 2.37 (s, 8H, THF-R), 4.12 (s, 3H,
P r ep a r a tion of 12. To a stirred solution of 6 (3.39 g, 6.71
mmol) in THF (45 mL) was added n-BuLi (9.8 mL of 1.64 M
solution in hexane, 16.1 mmol) at 0 °C. After the solution was
stirred for 5 h at ambient temperature, t-BuOK (20 mL of 1.18
M solution in THF, 35.4 mmol) was added. The reaction
mixture was stirred for 12 h, and the solution was evaporated
to dryness. The product was washed with hexane (80 mL),
affording the dipotassium salt of 6 as a white powder. To a
THF solution of SmI2 (50 mL, 5.7 mmol) was added a THF
suspension (50 mL) of the dipotassium salt of 6 (6.71 mmol)
at room temperature. Then the reaction mixture was stirred
for 12 h at room temperature and the solution was evaporated
to dryness. At this point toluene (50 mL) was added to the
residue and insoluble solid was removed by centrifugation.
After the solvent was again removed under reduced pressure,
recrystallization from THF/hexane afforded 12 as purple
crystals in 23% yield. 1H NMR (400 MHz, C6D6): δ -1.37 (s,
18H, tBu), 2.60 (s, 8H, THF-â), 3.10 (s, 12H, Me2SiOSiMe2),
6.18 (s, 12H, Me2SiOSiMe2), 6.70 (s, 4H, Cp H), 11.63 (s, 8H,
THF-R). 13C NMR (99 MHz, C6D6): δ 13.08, 19.21, 23.30,
29.49, 43.55, 50.90. Anal. Calcd for SmC34H62Si4O4: Sm,
18.85. Found: Sm, 19.03.

3956 Organometallics, Vol. 17, No. 18, 1998
Ihara et al.
Typ ica l P r oced u r e for Eth ylen e P olym er iza tion .
A
Ack n ow led gm en t. This work was supported by a
Grant-in-Aid for Scientific Research on Priority Areas
(No. 283, “Innovative Synthetic Reactions”) from Mon-
busho.
solution of an initiator (0.02 mmol) in 20 mL of toluene was
exposed to 1 atm of ethylene. The reaction mixture was stirred
for an appropriate period at room temperature. The polym-
erization was stopped by the addition of methanol. The
resulting polyethylene was washed with methanol twice and
dried in vacuo.
Typ ica l P r oced u r e for 1-Olefin P olym er iza tion . To a
toluene solution (3 mL) of an initiator (0.02 mmol) was added
2 mL of a monomer at room temperature. The reaction
mixture was stirred for an appropriate period at room tem-
perature. The polymerization was stopped by addition of
methanol. The resulting polymer was washed with methanol
twice and dried in vacuo.
Su p p or tin g In for m a tion Ava ila ble: Text and figures
detailing the preparation methods for ligands 1-6 and tables
of atomic coordinates and equivalent isotropic displacement
parameters, bond distances, bond angles, and hydrogen atom
coordinates for complexes 7, 8, 10, and 12 (62 pages). Ordering
information is given on any current masthead page.
OM971099U