Cs-symmetric ansa-lanthanocenes designed for stereospecific polymerization of methyl methacrylate. Synthesis and structural characterization of silylene-bridged fluorenyl cyclopentadienyl lanthanide halides, amides, and hydrocarbyls

Article abstract of DOI:10.1021/om000276f

A series of new C_s-symmetric organolanthanocene chlorides, [R₂Si(Flu)(R′Cp)Ln(μ-Cl)]₂ (Flu = C₁₃H₈, fluorenyl; Cp = C₅H₃) (R = Me, R′ = H, Ln = Y (1), Lu (2), Dy (3), Er (4); R = Ph, R′ = ^tBu, Ln = Y (5), Dy (6), has been synthesized by the reaction of anhydrous lanthanide chloride with the dilithium salt of the ligand Me₂Si(FluH)(CpH). Treatment of the resulting chlorides with ME(TMS)₂ (M = Li or K, E = N, CH) gave the amide and hydrocarbyl derivatives Me₂Si(Flu)(Cp)LnE(TMS)₂ (E = N, Ln = Dy (7), Er (9); E = CH, Ln = Dy (8), Er (10)). X-ray structures of chloride compounds reveal unusual Cp-SiMe₂-Cp bridging dimeric coordination. All of the amide and hydrocarbyl complexes show normal chelating structure and exhibit apparently intramolecular γ-agostic Ln-Me-Si interaction. These complexes are active for the polymerization of methyl methacrylate.

Full text of DOI:10.1021/om000276f

4134
Organometallics 2000, 19, 4134-4140
Cs-Sym m etr ic a n sa -La n th a n ocen es Design ed for
Ster eosp ecific P olym er iza tion of Meth yl Meth a cr yla te.
Syn th esis a n d Str u ctu r a l Ch a r a cter iza tion of
Silylen e-Br id ged F lu or en yl Cyclop en ta d ien yl La n th a n id e
Ha lid es, Am id es, a n d Hyd r oca r byls
Changtao Qian,* Wanli Nie, and J ie Sun
Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy Of Sciences, 354 Fenglin Lu, Shanghai 200032, China
Received March 30, 2000
A series of new Cs-symmetric organolanthanocene chlorides, [R2Si(Flu)(R′Cp)Ln(µ-Cl)]2
(Flu ) C13H8, fluorenyl; Cp ) C5H3) (R ) Me, R′ ) H, Ln ) Y (1), Lu (2), Dy (3), Er (4);
t
R ) Ph, R′ ) Bu, Ln ) Y (5), Dy (6)), has been synthesized by the reaction of anhydrous
lanthanide chloride with the dilithium salt of the ligand Me2Si(FluH)(CpH). Treatment of
the resulting chlorides with ME(TMS)2 (M ) Li or K, E ) N, CH) gave the amide and
hydrocarbyl derivatives Me2Si(Flu)(Cp)LnE(TMS)2 (E ) N, Ln ) Dy (7), Er (9); E ) CH,
Ln ) Dy (8), Er (10)). X-ray structures of chloride compounds reveal unusual Cp-SiMe2-
Cp bridging dimeric coordination. All of the amide and hydrocarbyl complexes show normal
chelating structure and exhibit apparently intramolecular γ-agostic Ln-Me-Si interaction.
These complexes are active for the polymerization of methyl methacrylate.
In tr od u ction
nolanthanocene complexes for the polymerization of
methyl methacrylate (MMA).5,6 In our previous work we
have reported the synthesis and characterization of the
CPh2-bridged Cs-symmetric complexes of lanthanocene
chloride and borohydride.7 Yasuda et al. reported the
catalysis of Me2Si-bridged Cs-symmetric rare-earth Ln-
(III)8 and Ln(II)9 complexes for polymerization of ethyl-
ene and R-olefin. As an extension of the ligand modifi-
cation for lanthanide complexes, we attempted to report
new type of Cs-symmetric silyene-bridged fluorenyl
cyclopentadienyl organolanthanide halide, amide, and
hydrocarbyl complexes to investigate the relation be-
tween the structures of rare-earth metal complexes and
their activity toward MMA.
In the past few decades, stereorigid early transition
and lanthanide element metallocenes have been estab-
lished as excellent catalysts or precatalysts for the
stereospecific polymerization of propylene and other
R-olefins. Especially exciting are the prospects for
tailoring the polymer microstructure by systematic,
rational variation of the substituents of the two cyclo-
pentadienyl ligands, particularly when they are con-
nected by an interannuler bridge.1 Thus, these “ansa”-
metallocene derivatives have been the subject of this
study, following the pioneering work by Brintzinger and
co-workers.2 Organometallic complexes containing two
cyclopentadienyl or tetramethylcyclopentadienyl ligands
bridged by Me2Si or Et2Si uints have been widely
empolyed in the synthesis of a variety of ansa-metal-
locenes including zirconium3 and lanthanide metals.4
More recently rare-earth metal complexes were found
to initiate living polymerization of polar and nonpolar
monomers and allow the synthesis of high molecular
weight polymers with extremely narrow molecular
weight distributions. Yasuda’s and Marks’s groups have
studied the activity of the C2v- and C1-symmetric orga-
Resu lts a n d Discu ssion
Syn th esis. These chloride, hydrocarbyl, and amide
complexes were synthesized as described in Scheme 1.
(4) (a) Haar, C. M.; Stern C. L.; Marks, T. J . Organometallics 1996,
15, 1765. (b) Coughlin, E. B.; Henling, L. M.; Bercaw, J . E. Inorg. Chim.
Acta 1996, 242, 205. (c) Giardello, M. A.; Sabat, M.; Rheingold, A. L.;
Stern, C. L. J . Am. Chem. Soc. 1994, 116, 10212. (d) Qaio, K.; Fisher
R. D.; Paolucci, G. J . Organomet. Chem. 1993, 456, 185. (e) Akhnoukh,
T.; Muller, J .; Qiao, K.; Li, X.-F.; Fischer, R. D. J . Organomet. Chem.
1991, 408, 47. (f) Stern, D.; Sabat, M.; Marks, T. J . J . Am. Chem. Soc.
1990, 112, 9558. (g) Heeres, H. J .; Renkema, J .; Meetrsma, A.; Teuben,
J . H. Organometallics 1988, 7, 2495.
* Corresponding author. E-mail: qianct@pub.sioc.ac.cn. Fax: 0086-
21-64166128.
(5) (a) Yasuda, H.; Ihara, E. Bull. Chem. Soc. J pn. 1997, 70, 1745.
(b) Yasuda, H.; Yamamoto, H.; Yamashita, M.; Yokota, K.; Nakamura,
A.; Miyake, S.; Kai, Y.; Kanehisa, N. Macromolecules 1993, 26, 7134.
(c) Yasuda, H.; Tamai, H. Prog. Polym. Sci. 1993, 18, 1097.
(6) Giardello, M. A.; Yamamota, Y.; Bard, L.; Marks, T. J . J . Am.
Chem. Soc. 1995, 117, 327.
(7) Qian, C.; Nie W.; Sun, J . J . Chem. Soc., Dalton Trans. 1999,
3283.
(8) (a) Yasuda, H.; Ihara, E. Adv. Polym. Sci. 1997, 133, 53. (b)
Yasuda, H.; Ihara, E.; Nitto, Y.; Kakehi, T.; Morimoto, M.; Nodono,
M. ACS Symp. Ser. 1998, 704, 149.
(1) (a) Kaminsky, W.; Kulper, K.; Brintzinger H. H.; Wild, F. R. W.
P. Angew. Chem., Int. Ed. Engl. 1985, 24, 507. (b) Ewen, J . A.; J ones
R. L.; Razavi, A. J . Am. Chem. Soc. 1988, 110, 6255. (c) Piccolrovazzi,
N.; Pino, P.; Consiglio, G.; Sironi A.; Moret, M. Organometallics 1990,
9, 3098. (d) Ewen, J . A.; Haspeslagh, L.; Atwood J . L.; Zhang, H. J .
Am. Chem. Soc. 1987, 109, 6544. (e) Rieger, B. J . Organomet. Chem.
1982, 428, C23. (f) Okuda, J . Angew. Chem., Int. Ed. Engl. 1992, 31,
47. (g) Razavi A.; Atwood, J . L. J . Organomet. Chem. 1993, 459, 117.
(2) Smikth, J . A.; Von Seyerl, J .; Hattner, G.; Brintzinger, H. H. J .
Organomet. Chem. 1979, 173, 175.
(9) Ihara, E.; Nodono, M.; Katsura, K.; Adachi, Y.; Yasuda, H.;
Yamagashira, M.; Hashimoto, H.; Kanehisa, N.; Kai, Y. Organome-
tallics 1998, 17, 3945.
(3) (a) Batgur, C. S.; Tikkanen W. R.; Peterson, J . L. Inorg. Chem.
1985, 24, 2539. (b) J utzi, P.; Dickbreder, R. Chem. Ber. 1986, 119, 1750.
10.1021/om000276f CCC: $19.00 © 2000 American Chemical Society
Publication on Web 09/07/2000

Cs-Symmetric ansa-Lanthanocenes
Organometallics, Vol. 19, No. 20, 2000 4135
Sch em e 1
By reaction of the dilithio salt of the ligands [Me2Si-
(C5H5)(C13H9)]10 with anhydrous lanthanide chloride we
got the solvent-free dimeric chlorides [Me2Si(C5H4)-
(C13H8)LnCl]2 (Ln ) Y (1), Lu (2), Er (3), Dy (4)). The
X-ray crystal structures indicated that all of the com-
plexes assume the Cp-SiMe2-Cp bridging structure
instead of the normal chelating structure. Organome-
tallic complexes containing two cyclopentadienyl or two
tetramethylcyclopentadienyl ligands bridged by silylene
units are genarally known to asssume the metal-
chelating structure,11 although only a rare example of
bridging structure is already reported.12 It still remains
unclear whether dialkylsilyene-linked biscyclopentadi-
enyl derivatives generally would be more stable as the
chelating or bridging isomer. To understand the effect
of different substituents on the coordination modes, we
synthesized solvent-free dimeric chlorides [Ph2Si(tBu-
C5H3)(C13H8) LnCl]2 (Ln ) Y (5), Dy (6)). X-ray analysis
revealed the existence of the C1-symmetric complex as
a bridging structure. This fact indicated that the bulkier
substituents on the Cp ring and on the silylene-bridged
atom did not hamper the formation of the bridging
structure.
The monomeric salt-free and solvent-free amido and
hydrocarbyl complexes [Me2Si(C5H4)(C13H8)]LnE(TMS)2
(E ) N, Ln ) Dy (7), Er (9); E ) CH, Ln ) Dy (8), Er
(10)) were synthesized by reaction of anhydrous LnCl3
with the dilithio salt of the silylene-bridged ligand in
ether, followed by the treatment with ME(TMS)2 (M )
K or Li; E ) N, CH) in toluene in a one-pot procedure.
The X-ray crystal structures displayed γ-agostic interac-
tions between the M and methyl group in all of the
amido and hydrocarbyl complexes.
The lanthanocene chlorides are readily dissolved in
THF and ether and just sparing soluble in toluene at
room temperature, but the amide and hydrocarbyl
complexes are very soluble in toluene and benzene and
sparingly soluble in hexane. All complexes remain air
and moisture sensitive, whether in both solid and
solution phases. Structures were confirmed by EA, MS,
FT-Raman, or X-ray crystal analysis.
Ma ss Sp ectr om etr ic Stu d y of th ese Bin u clea r
Or ga n ola n th a n id e Ch lor id es. It was known that the
ligands [MeSi2(C5R4)2]2- (DMCS) (R ) H, Me) should
bond to early d-transition, lanthanide, and actinide
metals to afford two different isomeric forms, I (chelat-
ing) and II (bridging) (Scheme 2), of the general type
[MeSi2(C5R4)2M(µ-Cl)]2. In 1990, R. Dieter Fischer13
demonstrated that mass spectrometry is a very powerful
and versatile tool to identify the specific type of isomer
in organolanthanide chemistry. He pointed out that the
complex exists as the isomeric form II corresponding
with almost exclusive binuclear fragments in the origi-
nal mass spectra, while the predominance of mono-
nuclear fragments might suggest the presence of a
chloride bridge, which only existed in isomer I. However
it can be seen from the Table 1 that complexes 1-6 show
relatively low signals of binuclear fragments (M, M-Cl,
Since the less sterically demanding ansa-ligands
promote the binding of additional ligands to the central
equatorial site, the eletrophilicity of the metal increased.
Consistent with this notion, the chlorides of [R2Si-
(C5H3R′)(C13H8)LnCl]2 (1-6) exist as dimeric structures
in the solid state.
(10) (a) Patsidis, K.; Alt, H. G.; Milius, W.; Palackal, S. J . J .
Organomet. Chem. 1996, 509, 63. (b) Chen, Y.; Rausch, M. D.; Chien,
J . C. W. J . Organomet. Chem. 1995, 497, 1.
(11) (a) Abriel, W.; Heck, J . J . Organomet. Chem. 1986, 302, 363.
(b) J eske, G.; Schock, L. E.; Swepston, P. N.; Schumann, H.; Marks,
T. J . J . Am. Chem. Soc. 1985, 107, 8103. (c) Fendrick, C. M.; Mintz, E.
A.; Schertz, L. D.; Marks, T. J .; Day, V. W. Organometallics 1984, 3,
819.
(12) Hock, N.; Oroschin, W.; Paolucci, G.; Fisher, R. D. Angew.
Chem., Int. Ed. Engl. 1986, 25, 5, 738.
(13) Qiao, K.; Fischer, R. D. Organometallics 1990, 9, 1361.

4136 Organometallics, Vol. 19, No. 20, 2000
Ta ble 1. Ma ss Sp ectr om etr ic Resu lts of th e Ch lor id e Com p lexes
Qian et al.
fragment (%)
[M]+
[M - LnCl2]+
[M - LnCl2-Flu]+
[M/2]+
[M/2 - Cl]+
1
2
3
4
5
6
820(5.54)
992(16.71)
974(14.17)
970(1.00)
663(3.64)
749(2.21)
743(8.31)
738
497(12.35)
583(4.65)
575(18.56)
572
410(100)
496(100)
487(81.06)
485(2.35)
374(40.25)
461(32.66)
453(100)
450(2.21)
554(0.32)
630(17.59)
1099(4.23)
665(60.89)
Ta ble 2. X-r a y Diffr a ction Da ta Collection P a r a m eter s for Com p lexes 1, 5, 7, 8, a n d 9
1
5
7
8
9
formula
fw
cryst syst
space group
a, Å
b, Å
c, Å
a, deg
â, deg
γ, deg
V, Å3
C
54H52Si2Cl2Y2
C74H66Si2Cl2Y2
1260.22
monoclinic
C2/c
25.996(4)
10.008(2)
24.261(3)
C26H36Si3NDy
609.33
monoclinic
P21/n
9.123(1)
11.843(9)
25.522(4)
C27H37Si3Dy
608.35
monoclinic
P21/n
13.759(2)
9.077(9)
45.18(1)
C26H36Si3NEr
614.09
monoclinic
P21/n
9.097(4)
11.759(4)
25.664(5)
1005.89
triclinic
P1h
11.669(2)
11.947(3)
9.286(2)
100.91(2)
100.00(1)
72.22(2)
1201.2(5)
1
96.27(1)
93.47(1)
91.06(2)
93.41(3)
6274(1)
4
1.334
2752.4(6)
4
1.470
5642(1)
8
1.432
2740(1)
4
1.488
Z
D
calcd, Mg/m3
1.390
F(000)
516.00
26.03
4249
2600.00
20.08
5958
1228.00
28.63
4407
2456.00
27.919
9901
1236.00
32.01
5420
µ, cm-1
no. reflns
no. observations
no. variables
3028
225
0.051; 0.064
1.22; -0.64
3652
349
0.051; 0.065
1.01; -0.69
3357
281
0.034; 0.053
0.99; -0.90
7315
559
0.052; 0.066
1.49; -1.35
4046
281
0.030; 0.039
1832; -1.60
a
final R, Rw
peak, hole/e Å3
a
R ) ∑||Fo| - |Fc||/∑|Fo|, Rw ) [∑w(|Fo| - |Fc|)2/∑|Fo|2]0.5
.
Ta ble 3. Selected An gles a n d Bon d s for Com p lexes
1 a n d 5
Sch em e 2
1
5
Bond Lengths (Å)
3.797(8)
2.649(2)
2.638(2)
2.601(6)
2.580(8)
2.599(8)
2.623(7)
2.635(5)
2.601(5)
2.681(6)
2.699(6)
2.651(6)
2.599(6)
Y-Y′
3.659(1)
2.633(2)
2.348(4)
2.604(6)
2.645(6)
2.702(6)
2.645(6)
2.648(5)
2.645(5)
2.632(6)
2.732(6)
2.825(6)
2.745(5)
Y-Cl
Y-Cl′
Y-C(1)
Y-C(2)
Y-C(3)
Y-C(4)
Y-C(5)
Y-C(6)
Y-C(7)
Y-C(8)
Y-C(9)
Y-C(10)
M-LnCl, M-LnCl-Flu) and strong signals for mono-
nuclear fragments (M/2, M/2-Cl, M/2-Cl-Me). This
result is not consistent with the conclusion made by D.
Fischer. This is perhaps due to different structures
between the two chloride systems.
Molecu la r Str u ctu r es. Crystals of 1, 5, 7, 8, and 9
were grown from toluene/n-hexane solution. Details of
the crystal data and refinements are shown in Table 2,
and selected bond lengths and internal angles in Tables
3-5, respectively. X-ray crystal structures of 1, 5, 7, and
8 are shown in Figures 1-4, respectively.
Bond Angles (deg)
91.82(6)
Y-Cl-Y′
Cl-Y-Cl′
C(5)-Si-C(6)
C(20)-Si-C(19)
88.0(1)
102.4(3)
116.1(2)
106.9(3)
88.18(6)
118.1(2)
107.9(4)
Dihedral Angle (deg)
137.62
planes (1) and (2)
139.65
Cs-symmetric compounds. It has a rhombic arrange-
ment. The angles Cl-Y-Cl′ and Y-Cl-Y′ are 88.0° and
102.4°, respectively. The Y-Y′ distance of 3.659 Å is
shorter than that of 3.797 Å in the analogues Cs-
symmetric complex 1. In these binuclear complexes the
Y-Cl (2.645 Å) for 1 and 2.641 Å for 5 are somewhat
longer than that in the mononuclear complexes (e.g., for
2.610 Å in Me2Si(Flu)(Cp*)YCl2Li(Et2O)2 (Cp* ) C5-
Me4)15 and for 2.627 Å in Me2Si[(SiMe3Cp)(CMe3Cp)]-
YCl2LiEt2O16).
In the crystal structure of complex 1, the Y2Cl2
skeleton is almost a square. The angles of Cl-Y-Cl′ and
Y-Cl-Y′ are 88.18° and 91.82°, respectively. The Y-Y′
distance of 3.797 Å is shorter than that of 3.987 Å in
the cheleting isomer I of [(C5H5)2Yb(µ-Cl)]2,14 while it
compare well with that of 3.750 Å for the bridging
isomer [Me2Si(C5H4)2Yb(µ-Cl)]2 (ionic radius of Y3+ is
12
only 0.03 Å larger than that of Yb3+). In the C1 complex
the Y2Cl2 skeleton is somewhat different from that of
(15) Lee, M. H.; Hwang, J .-E.; Kim, Y.; Kim, J .; Do, Y. Organome-
tallics 1999, 18, 5124.
(14) Lueken, H.; Schmitz, J .; Lambert, W.; Hannibal, P.; Handrick,
K. Inorg. Chim. Acta 1989, 156, 119.
(16) Marsh, R. E.; Schaefer, W. P.; Coughlin, E. B.; Bercaw, J . E.
Acta Crystallogr. 1992, C48, 1773.

Cs-Symmetric ansa-Lanthanocenes
Organometallics, Vol. 19, No. 20, 2000 4137
F igu r e 3. ORTEP diagram of [Me2Si(C13H8)(C5H4)]DyN-
(TMS)2 (7).
F igu r e 1. ORTEP diagram of [Me2Si(C13H8)(C5H4)Y(µ-
Cl)]2‚1/2toluene (1) with adopted atom numbering (most
H atoms and toluene omitted for clarity).
F igu r e 4. ORTEP diagram of [Me2Si(C13H8)(C5H4)]DyCH-
(TMS)2 (8).
ring) distances (2.604(6)-2.825(6) Å) no longer display
t
the typical η5-dispersion pattern. The Bu-Cp ring in
the complex 5 is coordinated to metal in both longer
Y-C(2) and Y-C(3) bonds and shorter Y-C(ring) bonds
at the unsubstituted side of the Cp ring. This phenom-
enon is also observed in various Me2SiCp”(R*Cp)-based
compounds.4a,c The longer Y-C(8, 9, 10) (2.732(6)-
2.825(6) Å) distances originated from the repulsive
F igu r e 2. ORTEP diagram of [Ph2Si(C13H8)(tBuC5H4)Y-
(µ-Cl)]2‚1/2toluene (5) with adopted atom numbering (most
H atoms and toluene omitted for clarity).
t
interaction between the Bu group and the fluorenyl
group which is on the other coordinated ligand.
The X-ray crystal structures display that in all of the
amide and hydrocarbyl complexes one of the trimeth-
ylsilyl substituents approaches the Ln3+ center with an
acute Ln-CR-Siâ(1) angle, as observed commonly for
Cp′2LnE(SiMe3)2 (E ) CH, N) derivatives. This geom-
etry has been attributed to an interaction between the
electron-deficient Ln3+ center and the electron-donating
property of the Si-C bond.17 In complex 7, one of the
Dy-N-Si angles is 106.8° and the other is 124.8°. This
type of multicenter Ln-Me-Si interaction has been
observed in numerous other organolanthanide amide
complexes, for example, (C5Me5)2LnSm(TMS)2,18 (S)-
[Me2Si(C5Me4)((+)-neomenthylCp)]LnN(TMS)2,4c (S)-
A characteristic feature of the bridging structure lies
in the unusually widened C(5)-Si-C(6) angles (118.1-
(2)°, 116.1°) and the dihedral angle between the Cp ring
plane (1) and Flu ring plane (2) (137.62°, 139.62°) in
complexes 1 and 5, respectively. The C(5)-Si-C(6)
angle of 5 is 2° larger than that in the dimethylsilyene-
bridged complex 1. The larger dihedral angle in 5
between the Cp and Flu ring planes reflects the effect
t
of the large Bu-substituent on the Cp ring.
A remarkable difference exists between the Cs-sym-
metric complex 1 and the C1-symmetric 5 in the bonding
mode of the Ln atom to the two π-ring planes. In 1 the
distances of Y-C(Cp, Flu ring) bonds ranging from
2.599 to 2.699 Å show the typical pattern of normal η5-
bonding fashion. However in complex 5 the Y-C(Cp, Flu
(17) Koga, N.; Morokuma, K. J . Am. Chem. Soc. 1988, 110, 108. (b)
Tatsumi, K.; Nakamura, A. J . Am. Chem. Soc. 1987, 109, 3195.

4138 Organometallics, Vol. 19, No. 20, 2000
Qian et al.
[Me2Si(C5Me4)((-)-menthylCp)]LnN(TMS)2,4a and [Me2-
Si(C5Me4)(C13H8)]YN(TMS)2,15 with the two Ln-N-Siâ
angles ranging from 103.6(6)° to 109.4(3)° (for Ln-
N-Siâ(1)) and from 121.5(5)° to 132.0(7)° (for Ln-N-
Siâ(2)). The short Dy-CH3 contact (2.901(8) Å) is an
apparent intermolecular γ-agostic Me-Ln interaction.
The mode of this interaction is reflected at the different
angles between N-Dy-C(2) (93.0(2)°) and N-Dy-C(3)
(98.7(2)°). In the hydrocarbyl complex 8, the two Dy-
C(27)-Si angles (96.8(3)° and 129.8(5)°) resemble those
observed in hydrocarbyl complexes (C5Me5)Y(OAr)CH-
(TMS)2,19 [Me2Si(C5H5)(C5Me4)]LuCH(TMS)2,20 (R/S)-
[Me2Si(C5Me4)((+)-(neomenthylCp))YCH(TMS)2,4c and
[Me2Si(C5Me4)(tBuN)SmCH(TMS)2,21 with the two Ln-
CR-Siâ angles ranging from 92.2(6)° to 101.6(4)° for
Ln-CR-Siâ(1) and from 126.3(8)° to 134.5(9)° for
Ln-CR-Siâ(2). The equal distances of the central
metal atom Ln to the two hydrogen H atoms on the
γ-methyl group (2.72, 2.50, and 2.61 Å in complexes 7,
8, 9, respectively) further demonstrate that there is a
âSi-Me-metal not a (γC)H-metal interaction. The
longer Dy-H(37) (2.71 Å) distance and wider Dy-
C(27)-H(37) (100.2(9)°) angle show that no (RC)H-
metal interaction exists in the hydrocarbyl complex 8.
There also exist some significant differences between
the corresponding CH(TMS)2 complexes and the amide
complexes. The Dy-N (2.207(5) Å) bond distance is
shorter than the corresponding distances for the other
crystallographically characterized amides (e.g., for
Cp′SmN(TMS)2 (Sm-N ) 2.301(3) Å), for Cp2′YN(TMS)2
(Y-N ) 2.274(5) Å)). This shorter Ln-N distance should
originate from the strong donation of the lone pair
electron on nitrogen to the electron-deficient lanthanide
metal center. The longer Dy-C(27) (2.364(9) Å) distance
compared with the Dy-N distance appears to increase
the agostic interactions between the Dy3+ and the Si-C
bond, reflecting the longer bond length of Dy-C(21)
(2.756 Å) in 8 and shorter Dy-C(26) (2.901 Å) in the
N(TMS)2 complex 7.
The remarkable difference of these amide and hydro-
carbyl complexes with their chloride precursor 1 is the
increased strain around the central metal atom. This
effect is caused by the bridged Si atom: it “pinches” the
Cp and Flu rings and this effect is reflected in the acute
dihedral angle between the Cp and Flu planes and
smaller angle between the two Cbridgehead-Si- Cbridgehead
when compared with those observed in the bridging
dimeric chloride 1. For example in complex 7, the two
angles are 99.7(3)° and 65.87°, respectively. The bonding
mode of the Dy atom with the fluorenyl ring fragments
(Dy-C(ring), 2.618(9)-2.843(6) Å) might be described
as being partially slipped toward η3- from η5-mode. The
Dy-C(Cp ring) distances ranging from 2.615(6) to 2.657-
(6) Å are very uniform, indicating that the Cp ring is
bonded to the Dy atom in the typical η5-mode.
Ta ble 4. Selected An gles a n d Bon d s for Com p lex 8
Bond Lengths (Å)
Dy-C(27)
Dy-C(21)
Dy-C(2)
2.364(9)
2.756(10)
2.66(1)
2.619(10)
2.592(8)
2.816(8)
2.666(8)
1.818(9)
1.88(2)
2.71
Dy-Si(2)
3.148(3)
2.589(10)
2.69(1)
2.604(9)
2.662(8)
2.830(9)
1.898(10)
1.840(8)
2.50
Dy-C(1)
Dy-C(3)
Dy-C(4)
Dy-C(5)
Dy-C(6)
Dy-C(8)
Dy-C(10)
Si(2)-C(27)
Si(2)-C(26)
Dy-H(37)
Dy-H(19)
Dy-C(7)
Dy-C(9)
Si(2)-C(21)
Si(3)-C(27)
Dy-H(21)
Dy-H(20)
3.68
2.50
Bond Angles (deg)
Dy-C(27)-H(37)
Dy-C(27)-Si(3)
C(19)-Si(1)-C(20)
C(3)-Dy-C(27)
100.2(9)
129.8(5)
108.2(5)
93.7(3)
Dy-C(27)-Si(2)
C(5)-Si(1)-C(9)
C(2)-Dy-C(27)
Si(2)-C(27)-Si(3)
96.8(5)
99.8(4)
102.8(4)
123.5(5)
Dihedral Angle (deg)
planes (1) and (2)
66.83
Ta ble 5. Selected An gles a n d Bon d s for Com p lexes
7 a n d 9
7
9
Bond Lengths (Å)
2.207(5)
3.569(8)
2.901(8)
3.407(2)
3.469(2)
3.152(2)
1.899(7)
1.701(6)
1.861(9)
1.699(5)
2.630(7)
2.657(8)
2.657(7)
2.615(7)
2.633(7)
2.618(6)
2.712(6)
2.843(6)
2.829(7)
2.675(6)
2.72
Ln-N
2.194(4)
3.667(7)
2.834(5)
3.382(2)
3.504(2)
3.106(2)
1.896(5)
1.697(4)
1.868(7)
1.705(4)
2.596(6)
2.652(6)
2.647(5)
2.599(5)
2.603(4)
2.604(5)
2.670(5)
2.815(5)
2.816(5)
2.685(5)
2.60
Ln-C(21)
Ln-C(26)
Ln-Si(1)
Ln-Si(2)
Ln-Si(3)
Si(3)-C(26)
Si(3)-N
Si(2)-C(21)
Si(2)-N
Ln-C(1)
Ln-C(2)
Ln-C(3)
Ln-C(4)
Ln-C(5)
Ln-C(6)
Ln-C(7)
Ln-C(8)
Ln-C(9)
Ln-C(10)
Ln-H(35)
Ln-H(36)
Ln-H(37)
2.71
3.88
2.61
3.78
Bond Angles (deg)
128.3(3)
Si(2)-N-Si(3)
Ln-N-Si(3)
127.1(2)
106.8(2)
124.8(3)
99.7(3)
107.8(4)
93.0(2)
98.7(2)
105.2(2)
127.6(2)
99.5(2)
107.7(3)
90.9(2)
98.2(2)
Ln-N-Si(2)
C(5)-Si(1)-C(6)
C(19)-Si(1)-C(20)
N-Ln-C(2)
N-Ln-C(3)
Dihedral Angle (deg)
65.87
planes (1) and (2)
65.26
solution, and after a fixed time the product was quenched
with acidified methanol. Triad microstructure analysis
1
of the polymer was carried out using H NMR spectra.
Results are summarized in Table 6.21,22 All of these Cs-
symmetric complexes show comparably high initiating
activity (60-100%) and high syndiotacticity (60-83%).
These results are very different from those reported by
P olym er iza tion of MMA. To examine the catalytic
ability of compounds 7, 8, 9, and 10 toward polar
monomers, polymerization of MMA has been examined.
Polymerization of MMA was performed in toluene
(21) Tian, S.; Arredondo, V. M.; Stern, C. L.; Marks, T. J . Organo-
metallics 1999, 18, 2568.
(18) Evans, W. J .; Keyer, R. A.; Ziller, J . W. Organometallics 1993,
12, 2618.
(19) Klooster, W. T.; Brammer, L.; Schaverien, C. J .; Budzelaar, P.
H. M. J . Am. Chem. Soc. 1999, 121, 1381.
(20) Stern, D.; Sabat, M.; Marks, T. J . J . Am. Chem. Soc. 1990, 112,
9558.
(22) Molecular weights and molecular weight distibutions for entry
4: Mw(×104), 255.8 and 6.66; Mw/Mn, 2.802 and 1.490. For entry 6: Mw-
(×104), 268.1 and 9.5; Mw/Mn, 1.472 and 1.577. For entry 9: Mw(×104),
260.2 and 13.4; Mw/Mn, 1.290 and 2.441. For entry 10: only one peak,
Mw(×104), 6.8; Mw/Mn, 1.215.

Cs-Symmetric ansa-Lanthanocenes
Organometallics, Vol. 19, No. 20, 2000 4139
Ta ble 6. Da ta for th e P olym er iza tion of Meth yl
Meth a cr yla tea
volume of two π-ring fragments via achiral Cs-symmetric
organo-rare-earth complexes
stereochem (%)
conversn
entry catalyst tp (h) Tp (°C)
(%)
rr
rm
mm
Exp er im en ta l Section
1
2
3
4
5
6
7
8
9
10
11
12
13
14b
15c
7
7
7
7
7
8
8
8
9
9
9
10
10
9
1
1
0.5
0.5
1
1
0.5
1
2
0.5
1
20
0
-20
-78
-95
20
80.5
81.7
98.2
90.1
100
100
88.6
61.4
67.5
100
82.7
100
61
64
59
73
80
60
59
52
67
82
83
56
68
55
60
31
27
26
21
20
33
34
36
26
18
17
29
26
8
9
4
6
0
7
7
12
7
0
All operations involving organometallics were carried out
under an inert atmosphere of argon using standard Schlenk
techniques. THF, toluene, and n-hexane were distilled from
Na-benzophenone ketyl under argon prior to use. Anhydrous
lanthanide chlorides23,24 and n-butyllithium were prepared
according to the procedures in the literature, and the reactant
0
10
-78
fluorene was purchased from Aldrich. (C13H8)Me2Si(C5H4)Li2
0
was synthesized using the method described in the literature
for related compounds. Methyl methacrylate was purified by
distillation from CaH2 followed by storage over activated
molecular sieves (3 Å) and then vacuum transferred using a
high-vacuum line prior to use. Mass spectra were recorded on
a HP 5989A spectrometer (T ) 50-400 °C, 1.3 kV). The solvent
C6D6 was degassed and dried over a Na/K alloy. 1H NMR was
performed on a Bruker Am-300 (300 MHz) spectrometer.
Elemental analyses were performed by the Analytical Labora-
tory of the Shanghai Institute of Organic Chemistry.
-78
-95
0
-78
12
0
15
4
0.5
0.5
3
48.3
56.3
28.5
9
3
12
a
Reaction conditions: Initiator connection, 0.5 mol % monomer;
b
solvent, toluene; Solv/[M0] ) 1 Vol/Vol. Solvent, THF; Solv/
[M0] ) 2 Vol/Vol. c Solvent, DME; Solv/[M0] ) 2 Vol/Vol.
Syn th esis of [Me2Si(C5H4)(C13H8)YCl]2 (1). A solution of
[Me2Si(C5H4)(C13H8)]Li2 (0.06 M, 106 mL in Et2O) was added
dropwise to a stirred suspension of YCl3 (1.024 g, 6.36 mmol)
in 20 mL of THF at -78 °C under argon. The reaction mixture
was then slowly warmed to room temperature and stirred for
2 days. The precipitate was filtered off. The solvent was
removed in vacuo and extracted with 50 mL of toluene. The
supernatant was decanted, concentrated slightly, and cooled
for crystallization at -20 °C. The yellow crystals generated
(558 mg, 21.4%) were dried and submitted for X-ray analysis.
Anal. Calcd for C54H22Si2Cl2Y2 (1): C, 61.84; H, 4.83. Found:
C, 62.12; H, 4.92. 1H NMR (300 MHz, C6D6): δ 8.06 (d, 2H,
FLu), 7.89 (d, 2H, Flu), 7.30 (m, 4H, Flu), 6.18 (t, 2H, Cp),
5.80 (t, 2H, Cp), 0.52 (s, 6H, SiMe2). EI mass spectrum (70
eV, 50-400 °C): m/z 820 (5.54, [M]+), 663 (3.64, [M - YCl2]+),
497 (12.35, [M - YCl2-Flu]+), 410 (100, [M/2]+), 374 (40.25,
[M/2 - Cl]+). FT-Raman (cm-1): 3067(m), 1527(s), 1437(s),
1336(vs), 1209(s), 1004(m), 740(m), 660(m), 521(w).
Youngkyn and co-workers in 1999.15 They used one of
the Si-bridged Cs-symmetric amide complexes, [Me2Si-
(C5Me4)(Flu)]YN(TMS)2, as catalyst, and they obtained
the iso-rich (56-58%) poly(MMA) in very low yield (4.2-
10.4%). Yasuda has also reported one of the C-bridged
alkyl complexes, [Me2C(2,7-tBu2-Flu)(Cp)]YCH(TMS)2,23
inducing syn-rich polymerization of MMA (75-78%). T.
J . Marks et al. reported the polymerziation of MMA
using chiral C1-symmetric rare-earth metal complexes.6
It is likely that the stereoregularity varies with subtle
difference in steric bulkiness between the complexes.
From the results we can see that the slightly different
R groups, when R ) N(TMS)2 and R ) CH(TMS)2, have
obviously different activity. When lowering the temper-
ature, the conversion and stereoregulation for the
polymerization by amide complexes increased, while
those by hydrocarbyls decreased. It can also be seen that
erbium complexes have higher stereoselectivity than the
dysprosium in this case.
Solvent effect has also been tested. We found that the
stereoselectivity of poly(MMA) still remained syn-rich
(about 50-60%) in THF or DME if 9 was used as an
initiator (entries 14 and 15 in Table 6).
Molecular weights and molecular weight distributions
of the polymers were determined by GPC in THF using
standard polystyrene. We found that some polymer
cannot be dissolved in THF or cannot pass through the
columns of GPC. In almost all cases, GPC shows a
bimodal pattern. One has very large molecular weights
(>106) with lower ratio, and the other peak is the main
products with high molecular weights (>105) and nar-
row molecular weight distributions.
Syn th esis of [Me2Si(C5H4)(C13H8)Lu Cl]2 (2). A procedure
similar to that for complex 1 was adopted for LuCl3 (1.277 g,
4.54 mmol), affording 2 as a yellow crystalline product (354
mg, 15.6%). Anal. Calcd for C54H22Si2Cl2Lu2 (2): C, 46.37; H,
1
3.48. Found: C, 46.19; H, 3.74. H NMR (300 MHz, C6D6): δ
8.04 (d, 2H, FLu), 7.89 (d, 2H, Flu), 7.27 (t, 2H, Flu), 7.16 (t,
2H, Flu), 6.06 (t, 2H, Cp), 5.67 (t, 2H, Cp), 0.54 (s, 6H, SiMe2).
EI mass spectrum (70 eV, 50-400 °C): m/z 992 (16.71, [M]+),
749 (2.21, [M - YCl2]+), 583(4.65, [M - YCl2-Flu]+), 496 (100,
[M/2]+), 461 (32.66, [M/2 - Cl]+). FT-Raman (cm-1): 3069(m),
1520(s), 1438(s), 1337(vs), 1209(s), 1170(m), 740(m), 660(m),
521(w), 419(m), 292(m).
Syn th esis of [Me2Si(C5H4)(C13H8)Er Cl]2 (3). A procedure
similar to that for complex 1 was adopted for ErCl3 (1.468 g,
5.35 mmol), affording 3 as a yellow crystalline product (500
mg, 19.2%). Anal. Calcd for C54H22Si2Cl2Er2 (3): C, 52.26; H,
4.11. Found: C, 52.35; H, 4.22. EI mass spectrum (70 eV, 50-
400 °C): m/z 974 (14.17, [M]+), 947 (3.88, [M - Cl]+), 743 (8.31,
[M - YCl2]+), 575 (18.56, [M - YCl2-Flu]+), 487 (81.06,
[M/2]+), 453 (100, [M/2 - Cl]+). FT-Raman (cm-1): 3067(m),
1527(s), 1438(s), 1338(vs), 1322(s), 1209(s), 1167(m), 1006(m),
740(m), 660(m), 521(w), 420(m), 290(m).
Con clu sion
In summary, we have successfully synthesized a
series of new silylene-bridged fluorenyl cyclopentadienyl
ansa-lanthanocene complexes with Cs symmetry and
characterized their structural features by X-ray diffrac-
tion studies. These Cs-symmetric organolanthanides can
be efficient catalysts for the syndio-rich polymerization
of methyl methacrylate. We assume that the ability of
a catalyst to control the syndiospecific entrance of the
monomer is strongly dependent on the different steric
Syn th esis of [Me2Si(C5H4)(C13H8)DyCl]2 (4). A procedure
similar to that for complex 1 was adopted for DyCl3 (1.110 g,
4.13 mmol), affording 4 as a yellow crystalline product (297
mg, 14.8%). Anal. Calcd for C54H22Si2Cl2Dy2 (4): C, 53.08; H,
(23) Yasuda, Y.; Ihara, E. Macromol. Chem. Phys., 1995, 196, 2417.
Until now no detailed description of the synthesis and structural
features of this complex have been reported.
(24) Chapman, J . H.; Owen, L. N. J . Chem. Soc. 1950, 579.

4140 Organometallics, Vol. 19, No. 20, 2000
Qian et al.
4.816. Found: C, 54.50; H, 4.27. EI mass spectrum (70 eV,
50-400 °C): m/z 970 (1.00, [M]+), 4.85 (2.35, [M/2]+), 450 (2.21,
[M/2 - Cl]+).
(1.304 g, 4.76 mmol) and KN(TMS)2 (1.08 g, 5.4 mmol),
affording 9 as a yellow crystalline product (330 mg, 11.5%).
Anal. Calcd for C26H36Si3NEr (9): C, 50.81; H, 5.86; N, 2.28.
Found: C, 50.68; H, 6.03; N, 2.51. EI mass spectrum (70 eV,
50-400 °C): m/z 615 (18.30, [M]+), 599 (9.31, [M - Me]+), 453
(6.98, [M - N(TMS)2]+), 146 (100, [N(TMS)2]+). FT-Raman
(cm-1): 3040(m), 2899(m), 1527(s), 1324(vs), 1211(s), 743(m),
656(m), 614(m), 520(w), 410(m), 378(m), 240(s).
Syn th esis of [Me2Si(C5H4)(C13H8)]Er CH(TMS)2 (10). A
procedure similar to that for complex 7 was adopted for ErCl3
(1.468 g, 5.35 mmol) and LiCH(TMS)2 (1.03 g, 6.2 mmol),
affording 10 as a yellow crystalline product (240 mg, 7.3%).
Anal. Calcd for C27H37Si3Er (10): C, 52.85; H, 6.04. Found:
C, 52.97; H, 6.01. EI mass spectrum (70 eV, 50-400 °C): m/z
613 (2.13, [M]+), 598 (2.08, [M - Me]+), 454 (100, [M -
N(TMS)2]+), 145 (46.84, [CH(TMS)2]+). FT-Raman (cm-1):
3048(m), 2896(m), 1530(s), 1324(vs), 1211(s), 742(m), 657(m),
578(m), 520(w), 431(m), 378(m), 239(s).
P olym er iza tion of MMA. A solution of preweighted cata-
lyst (0.5 mmol) in toluene was adjusted to a constant temper-
ature using an external bath. Into the well-stirred solution
was syringed 100 mmol of methyl methacrylate, and the
reaction was continuously stirred for an appropriate period
at that temperature. Polymerization was stopped by addition
of the acidic methanol. The resulting precipitated PMMA was
collected, washed with methanol several times, and dried in
vacuo at 50 °C for 12 h.
X-r a y Str u ctu r e Deter m in a tion . Single crystals were
sealed in thin-walled glass capillaries under an atmosphere
of argon. X-ray diffraction data were collected at a room
temperature using the ω-2θ scan technique to a maximum
2θ value of 50.0°. The intensities of three representative
reflection were measured after every 200 reflections. Over the
course of data collection, the standards decreased by 0.9%. A
linear correction factor was applied to the data to account for
this phenomenon. The data were corrected for Lorentz and
polarization effects. The structures were solved by heavy-atom
Patterson methods and expanded using Fourier techniques.
The non-hydrogen atoms were refined anisotropically. All
calculations were performed using the teXsan crystallographic
software package of Molecular Structure Corporation.
Syn th esis of [P h 2Si(t-Bu C5H3)(C13H8)YCl]2 (5). A pro-
cedure similar to that for complex 1 was adopted for YCl3 (1.10
g, 5.64 mmol), affording 5 as a yellow crystalline product (1.23
g, 37.1%). Anal. Calcd for C74H66Si2Cl2Y2 (5): C, 70.70; H, 5.34.
1
Found: C, 70.34; H, 5.57. H NMR (300 MHz, C6D6): δ 7.2-
8.2 (m, CH(Ar)), 5.6-6.3 (m, CHCp), 1.37 (s, CH(tBu)). EI mass
spectrum (70 eV, 50-400 °C): m/z 554 (0.32, [M/2 - Cl]+), 302
(100, [FluCPh2]+). FT-Raman (cm-1): 3046(m), 1587(s), 1529-
(s), 1335(vs), 1210(s), 998(vs), 672(m), 523(w), 425(m), 252-
(m).
Syn th esis of [P h 2Si(t-Bu C5H3)(C13H8)DyCl]2 (6). A pro-
cedure similar to that for complex 1 was adopted for DyCl3
(1.00 g, 3.72 mmol), affording 6 as a yellow crystalline product
(1.76 g, 71.5%). Anal. Calcd for C34H30SiCl2Dy (6): C, 59.56;
H, 4.38. Found: C, 59.66; H, 4.51. EI mass spectrum (70 eV,
50-400 °C): m/z 1099 (4.23, [M - DyCl2]+), 665 (60.89, [M/2]+),
630 (17.59, [M/2 - Cl]+), 614 (74.16, [M/2 - Cl-Me]+), 302
(100, [FluCPh2]).
Syn th esis of [Me2Si(C5H4)(C13H8)]DyN(TMS)2 (7). A
solution of [Me2Si(C5H4)(C13H8)]Li2 (0.038M, 5.69 mmol, 150
mL in Et2O) was added dropwise to a stirred suspension of
DyCl3 (1.53 g, 5.69 mmol) in 20 mL of THF at -78 °C under
argon. The reaction mixture was then slowly warmed to room
temperature and stirred for 2 days. The solvent was removed
in vacuo and replaced with toluene (100 mL). Next the mixture
was cooled to -78 °C, and KN(TMS)2 (1.05 g, 5.5 mmol) was
added slowly. The reaction mixture was allowed to warm to
room temperature for 1 day and then warmed to 60 °C and
stirred for 1 day. The precipitate was filtered off. The solvent
was decanted, concentrated slightly, and cooled overnight at
-20 °C for crystallization. Orange crystals were formed,
suitable for X-ray analysis (1.317 g, 39.3%). Anal. Calcd for
C26H36Si3NDy (7): C, 51.20; H, 5.91; N, 2.30. Found: C, 50.71;
H, 6.05; N, 2.67. EI mass spectrum (70 eV, 50-400 °C): m/z
610 (100, [M]+), 594 (47.90, [M - Me]+), 450 (75.55, [M -
N(TMS)2]+), 146 (47.41, [N(TMS)2]+). FT-Raman (cm-1): 3047-
(s), 2898(vs), 1526(m), 1322(m), 1009(m), 742(w), 655(w), 610-
(w), 518(w), 430(m), 377(m), 237(s).
Syn th esis of [Me2Si(C5H4)(C13H8)]DyCH(TMS)2 (8). A
procedure similar to that for complex 7 was adopted for DyCl3
(1.42 g, 5.30 mmol) and LiN(TMS)2 (1.03 g, 6.2 mmol),
affording 8 as a yellow crystalline product (523 mg, 12.6%).
Anal. Calcd for C27H37Si3Dy (8): C, 51.25; H, 5.91. Found: C,
47.90; H, 6.55. EI mass spectrum (70 eV, 50-400 °C): m/z 609
(1.29, [M]+), 594 (7.51, [M - Me]+), 450 (100, [M - N(TMS)2]+),
145 (30.38, [CH(TMS)2]+). FT-Raman (cm-1): 3047(s), 2899-
(vs), 1531(m), 1322(s), 1210(m), 742(m), 657(m), 577(m), 520-
(w), 431(m), 378(m), 236(s).
Ack n ow led gm en t. The authors are grateful to the
National Nature Science Foundation of China and
Shanghai-Hong Kong J oint Laboratory in Chemical
Synthesis for their financial support.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordination, thermal parameters, and interatomic distances
and angles for complexes 1, 5, 7, 8, and 9. This material is
available free of charge via the Internet at http://pubs.acs.org.
Syn th esis of [Me2Si(C5H4)(C13H8)]Er N(TMS)2 (9). A
procedure similar to that for complex 7 was adopted for ErCl3
OM000276F