Constrained geometry group 3 metal complexes of the fluorenyl-based ligands [(3,6-tBu2Flu)SiR2NtBu]: Synthesis, structural characterization, and polymerization activity

Article abstract of DOI:10.1021/om0304210

Alkane elimination between Y(CH₂SiMe₃)₃(THF)₂ and the diprotio ligands [(3,6-^tBu₂C₁₃H₇)SiR₂ NH^tBu] (R = Me, 1a; R = Ph, 1b) gave [η³:η¹- ((3,6-^tBu₂C₁₃H₆)SiR₂N ^tBu)Y-(CH₂SiMe₃)(THF)₂] (R = Me, 2a; R = Ph, 2b). 2a is thermally stable in toluene solution and shows a dynamic behavior connected to THF dissociation, while 2b is thermally unstable. Reaction of 2a with H₂ or PhSiH₃ led to the putative hydrido complex [(3,6-^tBu₂Flu) SiMe₂-N^tBu)YH(THF)]_n (3). Deprotonation of 1a with 1 and 2 equiv of ⁿBuLi gave [(3,6-^tBu₂C₁₃H₆) SiMe₂NH^tBu]Li (5) and [(3,6-^tBu₂C₁₃H₆) SiMe₂N^tBu]Li₂ (4), respectively, both of which were characterized crystallographically. Salt elimination reactions between LnCl₃-(THF)_n precursors (Ln = Y, La, Nd) and 1 equiv of 4 gave mixtures of complexes, from which ionic complexes that contain two chelated ligands per lanthanide center, [{η³:η¹- (3,6-^tBu₂C₁₃H₆) SiMe₂N^tBu}₂Ln]^- [Li(solvent)_n]⁺ (Ln = Y, solvent = THF, n = 4, 6; Ln = La, solvent = THF, n = 4, 7; Ln = La, solvent = Et₂O, n = 2, 8; Ln = Nd, solvent = THF, n = 4, 9), were isolated. The neutral dimeric chloro complex [η⁵:η¹- ((3,6-^tBu₂C₁₃H₆) SiMe₂N^tBu)Nd(μ-Cl)-(THF)]₂ (10) was also crystallized from the crude metathesis product. The solid-state structures of 2a, 8, 9, and 10 show versatile coordination modes of the fluorenyl ligands, either η³ or η⁵ symmetric, involving carbon atoms of the central Cp ring (8 and 10), or unusual η³ dissymmetric, involving carbon atoms of the central Cp and one adjacent phenyl rings (2a and 9). Some of the complexes obtained were explored as catalysts for ethylene and MMA polymerization.

Full text of DOI:10.1021/om0304210

Organometallics 2003, 22, 4467-4479
4467
“Con str a in ed Geom etr y” Gr ou p 3 Meta l Com p lexes of th e
F lu or en yl-Ba sed Liga n d s [(3,6-tBu 2F lu )SiR2NtBu ]:
Syn th esis, Str u ctu r a l Ch a r a cter iza tion , a n d
P olym er iza tion Activity
Evgueni Kirillov,† Loic Toupet,‡ Christian W. Lehmann,§ Abbas Razavi,| and
J ean-Franc¸ois Carpentier*,†
Organome´talliques et Catalyse, UMR 6509 CNRS, and Groupe Matie`re Condense´e et
Mate´riaux, Cristallochimie, UMR 6626 CNRS, Universite´ de Rennes 1,
35042 Rennes Cedex, France, Max-Planck-Institut fu¨r Kohlenforschung,
Chemical Crystallography, Postfach 101353, 45466 Mu¨lheim/ Ruhr, Germany, and
Atofina Research, Zone Industrielle C, 7181 Feluy, Belgium
Received J une 3, 2003
Alkane elimination between Y(CH2SiMe3)3(THF)2 and the diprotio ligands [(3,6-
tBu2C13H7)SiR2NHtBu] (R ) Me, 1a ; R ) Ph, 1b) gave [η3:η1-((3,6-tBu2C13H6)SiR2NtBu)Y-
(CH2SiMe3)(THF)2] (R ) Me, 2a ; R ) Ph, 2b). 2a is thermally stable in toluene solution and
shows a dynamic behavior connected to THF dissociation, while 2b is thermally unstable.
Reaction of 2a with H2 or PhSiH3 led to the putative hydrido complex “[(3,6-tBu2Flu)SiMe2-
NtBu)YH(THF)]n” (3). Deprotonation of 1a with 1 and 2 equiv of nBuLi gave [(3,6-
tBu2C13H6)SiMe2NHtBu]Li (5) and [(3,6-tBu2C13H6)SiMe2NtBu]Li2 (4), respectively, both of
which were characterized crystallographically. Salt elimination reactions between LnCl3-
(THF)n precursors (Ln ) Y, La, Nd) and 1 equiv of 4 gave mixtures of complexes, from which
ionic complexes that contain two chelated ligands per lanthanide center, [{η3:η1-(3,6-
tBu2C13H6)SiMe2NtBu}2Ln]-[Li(solvent)n]+ (Ln ) Y, solvent ) THF, n ) 4, 6; Ln ) La, solvent
) THF, n ) 4, 7; Ln ) La, solvent ) Et2O, n ) 2, 8; Ln ) Nd, solvent ) THF, n ) 4, 9), were
isolated. The neutral dimeric chloro complex [η5:η1-((3,6-tBu2C13H6)SiMe2NtBu)Nd(µ-Cl)-
(THF)]2 (10) was also crystallized from the crude metathesis product. The solid-state
structures of 2a , 8, 9, and 10 show versatile coordination modes of the fluorenyl ligands,
either η3 or η5 symmetric, involving carbon atoms of the central Cp ring (8 and 10), or unusual
η3 dissymmetric, involving carbon atoms of the central Cp and one adjacent phenyl rings
(2a and 9). Some of the complexes obtained were explored as catalysts for ethylene and
MMA polymerization.
In tr od u ction
newal with group 3 metals.1h Thus, the groups of Piers,4
Okuda,5 Marks,6 and Hou7 have reported a variety of
rare-earth complexes of bifunctional ligands having the
formula [Ln(η5:η1-C5Me4SiMe2NR)X(L)n]m (Ln ) Sc, Y,
Sm, Nd, Lu, Yb; R ) tBu, aryl; X ) H, carbyl, NR2; L )
Half-sandwich complexes of group 3 metals1 that
contain linked cyclopentadienyl-amido ligands have
attracted considerable attention. First designed by
Bercaw for organoscandium olefin polymerization “con-
strained geometry catalysts” (CGC),2 these ligands have
been extensively applied in and developed for group 4
metal chemistry.3 Recent years have witnessed a re-
(2) (a) Shapiro, P. J .; Bunel, E.; Schaefer, W. P.; Bercaw, J . E.
Organometallics 1990, 9, 867. (b) Piers, W. E.; Shapiro, P. J .; Bunel,
E. E.; Bercaw, J . E. Synlett 1990, 74. (c) Shapiro, P. J .; Cotter, W. D.;
Schaefer, W. P.; Labinger, J . A.; Bercaw, J . E. J . Am. Chem. Soc. 1994,
116, 4623.
(3) For reviews, see: (a) McKnight, A. L.; Waymouth, R. M. Chem.
Rev. 1998, 98, 2587. (b) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev.
2003, 103, 283.
* To whom correspondence should be addressed. Fax: (+33)(0)223-
236-939. E-mail: jean-francois.carpentier@univ-rennes1.fr.
† Organome´talliques et Catalyse, Universite´ de Rennes 1.
‡ Groupe Matie`re Condense´e et Mate´riaux, Universite´ de Rennes
1.
(4) Mu, Y.; Piers, W. E.; MacDonald, M.-A.; Zaworotko, M. J . Can.
J . Chem. 1995, 73, 2233.
§ Max-Planck-Institut fu¨r Kohlenforschung.
| Atofina Research.
(5) (a) Hultzsch, K. C.; Spaniol, T. P.; Okuda, J . Angew. Chem., Int.
Ed. 1999, 38, 227. (b) Hultzsch, K. C.; Voth, P.; Beckerle, K.; Spaniol,
T. P.; Okuda, J . Organometallics 2000, 19, 228. (c) Arndt, S.; Voth, P.;
Spaniol, T. P.; Okuda, J . Organometallics 2000, 19, 4690. (d) Okuda,
J .; Arndt, S.; Beckerle, K.; Hultzsch, K. C.; Voth, P.; Spaniol, T. P.
Pure Appl. Chem. 2001, 73, 351. (e) Okuda, J .; Arndt, S.; Beckerle, K.;
Hultzsch, K. C.; Voth, P.; Spaniol, T. P. In Organometallic Catalysts
and Olefin Polymerization; Blom, R., Follestad, A., Rytter, E., Tilset,
M., Ystenes, M., Eds.; Springer: Berlin, 2001; p 156. (f) Arndt, S.;
Trifonov, A.; Spaniol, T. P.; Okuda, J .; Kitamura, M.; Takahashi, T.
J . Organomet. Chem. 2002, 647, 158. (g) Voth, P.; Arndt, S.; Spaniol,
T. P.; Okuda, J .; Ackerman, L. J .; Green, M. L. H. Organometallics
2003, 22, 65.
(1) Recent organolanthanide reviews: (a) Schumann, H.; Meese-
Marktscheffel, J . A.; Esser, L. Chem. Rev. 1995, 95, 865. (b) Anwander,
R.; Herrmann, W. A. Top. Curr. Chem. 1996, 179, 1. (c) Edelmann, F.
T. Top. Curr. Chem. 1996, 179, 247. (d) Anwander, R. In Applied
Homogeneous Catalysis with Organometallic Compounds; Cornils, B.,
Herrmann, W. A., Eds.; Wiley: Weinheim, Germany, 1996; Vol. 2, p
866. (e) Molander, G. A. Chemtracts: Org. Chem. 1998, 11, 237. (f)
Anwander, R. Top. Organomet. Chem. 1999, 2, 1. (g) Molander, G. A.;
Dowdy, E. C. Top. Organomet. Chem. 1999, 2, 119. (h) For
a
comprehensive review on mono(cyclopentadienyl) complexes, see:
Arndt, S.; Okuda, J . Chem. Rev. 2002, 102, 1953. (i) Hou, Z.;
Wakatsuki, Y. Coord. Chem. Rev. 2002, 231, 1.
10.1021/om0304210 CCC: $25.00 © 2003 American Chemical Society
Publication on Web 09/30/2003

4468 Organometallics, Vol. 22, No. 22, 2003
Kirillov et al.
THF, PMe3; n ) 0-3; m ) 1, 2) and explored their
reactivity in some catalytic processes. Studies were also
concerned with “less constrained geometry” complexes
of the type [Y(η5:η1-C5Me4CH2SiMe2NtBu)(CH2SiMe3)-
(THF)],8 complexes of the tridentate ligands (C5Me4H)-
SiMe2NHCH2CH2R (R ) OMe, NMe2),9,10 and recently
divalent lanthanide complexes such as Ln(η5:η1-C5Me4-
SiMe2NPh)X(THF)n (Ln ) Sm, Yb; n ) 0-3)11 and Li-
[Yb{η5:η1-(3-tBuC5H3)SiMe2NCH2CH2X}2] (X ) NMe2,
OMe).12
NHtBu] (R ) Me, Ph). These ligands have been selected
for this study because (i) the two tert-butyl groups on
fluorene at the 3,6-positions should simplify H NMR
patterns, (ii) we expect an increase in solubility of
complexes as compared to nonsubstituted fluorene-
amido ligands, and (iii) they have played a unique role
in group 4 metal chemistry.15 The coordination of these
ligands onto lanthanides (Y, La, Nd) was investigated
using amine and alkane elimination routes as well as
salt elimination reactions.
1
As it appears from the aforementioned examples,
almost all of the constrained-geometry group 3 metal
complexes prepared so far are based on silylene-bridged
cyclopentadienyl-amido ligands.13 To our knowledge,
[Y(η5:η1-C9H6SiMe2NtBu)(CH2SiMe3)(THF)] constitutes
the sole congener of these half-sandwich lanthanide
complexes that bears a linked indenyl-amido ligand,5b
and there is so far no example of a constrained-geometry
organolanthanide complex based on a fluorenyl ligand.14
This situation, which contrasts markedly with the
variety of indenyl- and fluorenyl-amido ligands that
have been successfully associated to group 4 metals,3
largely stems from the synthetic difficulties encountered
in the preparation of constrained-geometry organo-
lanthanides. The latter remain essentially limited to
alkane5a,6,9 and amine4,11a eliminations, which have a
quite limited scope due to the thermal sensitivity of
lanthanide carbyl precursors6a and the moderate basic-
ity of lanthanide amido precursors, respectively. On the
other hand, the traditional salt elimination approach
is often plagued by the formation of undesired products,
such as ate complexes.1 We report here a new series of
silylene-bridged fluorenyl-amido organolanthanide com-
plexes derived from the ligands [(3,6-tBu2-C13H7)SiR2-
Resu lts a n d Discu ssion
Am in e a n d Alk a n e E lim in a t ion R ea ct ion s.
Amine4,11a and alkane5a,6,9 elimination reactions were
investigated as privileged routes, since both of these
previously proved efficient for the preparation of cyclo-
pentadienyl-amido as well as indenyl-amido neutral
organolanthanide complexes. First, we observed that the
lanthanide amides Ln[N(SiMe3)2]3 (Ln ) Y, La) and
Y[N(SiHMe2)2]3(THF)2 do not react with the diprotio
ligands (3,6-tBu2C13H7)SiR2NHtBu (R ) Me, 1a ; R ) Ph,
1b), either in THF-d8 or in toluene-d8, even on heating
above the boiling points of the solvents. In both cases,
the reagents were found intact after 1 week under these
conditions (eq 1).16 Earlier studies from our group have
(6) (a) Tian, S.; Arredondo, V. M.; Stern, C. L.; Marks, T. J .
Organometallics 1999, 18, 2568. (b) Arredondo, V. M.; Tian, S.;
McDonald, F. E.; Marks, T. J . J . Am. Chem. Soc. 1999, 121, 3633. (c)
Douglass, M. R.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 2001,
123, 10221. (d) Ryu, J .-S.; Marks, T. J .; McDonald, F. E. Org. Lett.
2001, 3, 3091. (e) Hong, S.; Marks, T. J . J . Am. Chem. Soc. 2002, 124,
7886.
shown that amine elimination between Ln[N(SiMe3)2]3
(Ln ) Y, La, Nd) and CpHCMe2FluH in THF proceeds
via the rapidly formed intermediates (η5-CpCMe2FluH)-
Ln[N(SiMe3)2]2, which undergo readily ligand redistri-
bution reactions (5-20 °C, minutes) to give the mono-
(amido)lanthanide
complexes
(η5-CpCMe2FluH)2-
(7) Nishiura, M.; Hou, Z.; Wakatsuki, Y.; Yamaki, T.; Miyamoto, T.
J . Am. Chem. Soc. 2003, 125, 1184.
Ln[N(SiMe3)2]; then, subsequent intramolecular amine
elimination between the remaining amido group and a
pending fluorenyl moiety takes place under THF reflux
to yield the ansa complexes (η5:η5-CpCMe2Flu)Ln(η5-
CpCMe2FluH).14g These results suggest that the inert-
ness of 1a ,b toward lanthanide amides does not stem
(8) Trifonov, A. A.; Spaniol, T. P.; Okuda, J . Organometallics 2001,
20, 4869.
(9) Mu, Y.; Piers, W. E.; MacQuarrie, D. C.; Zaworotko, M. J .; Young,
V. G. Organometallics 1996, 15, 2720.
(10) (a) Hultzsch, K. C.; Spaniol, T. P.; Okuda, J . Organometallics
1997, 16, 4845. (b) Yoder, J . C.; Day, M. W.; Bercaw, J . E. Organo-
metallics 1998, 17, 4946.
(11) (a) Hou, Z.; Koizumi, T.; Nishiura, M.; Wakatsuki, Y. Organo-
metallics 2001, 20, 3323. (b) Hou, Z.; Wakatsuki, Y. J . Organomet.
Chem. 2002, 647, 61.
(15) (a) Razavi, A. Thewalt, U. J . Organomet. Chem. 2001, 621, 267.
(b) Razavi, A.; Baekelmans, D.; Bellia, V.; De Brauwer, Y.; Hortmann,
K.; Lambrecht, M.; Miserque, O.; Peters, L.; Slawinski, M.; Van Belle,
S. In Organometallic Catalysts for Olefin Polymerization, Blom, R.,
Ed.; Springer-Verlag: Berlin, 2001; pp 267-279. For other group 4
metal constrained-geometry complexes having nonsubstituted fluore-
nyl-amido ligands, see: (c) Hasan, T.; Nishii, K.; Shiono, T.; Ikeda,
T. Macromolecules 2002, 35, 8933 and references therein. (d) Xu, G.;
Cheng, D. Macromolecules 2001, 34, 2040 and references therein.
(16) A possible explanation for this nonreactivity is the lower acidity
of the fluorenyl proton in 1a ,b, as compared to that of the cyclopen-
tadienyl and indenyl equivalents. Standard pKa values: CpH, 16; IndH,
20; FluH, 23. See the following: (a) March, J . Advanced Organic
Chemistry, 4th ed.; Wiley: New York, 1992; Chapter 8. (b) Bordwell,
F. G.; Bausch, M. J . J . Am. Chem. Soc. 1983, 105, 6188. (c) pKa values
in C6D6/THF-d8 (20:1) determined according to the modified method
of Fraser: FluH, 24.0-24.2; IndH, 21.7; 9-(SiHMe2)-FluH, 23.1;
3-(SiHMe2)-IndH, 20.2; 2-Me-IndH, 23.1. Eppinger, J .; Spiegler, M.;
Hieringer, W.; Herrmann, W. A.; Anwander, R. J . Am. Chem. Soc.
2000, 122, 3080. An alternative, more complicated mechanism for the
initial metalation involving π-donation of the cyclopentadienyl group
to the lanthanide has been proposed to account for the fairly good
reactivity of relatively low acidic derivatives, e.g. Me2Si(C5Me4H).16c
(12) Trifonov, A. T.; Spaniol, T. P.; Okuda, J . Eur. J . Inorg. Chem.
2003, 926.
(13) For constrained-geometry organolanthanide complexes based
on silylene-linked cyclopentadienyl-non-amido ligands: (a) Tardif, O.;
Hou, Z.; Nishiura, M.; Koizumi, T.; Wakatsuki, Y. Organometallics
2001, 20, 4565. (b) Arndt, S.; Spaniol, T. P.; Okuda, J . Organometallics
2003, 22, 775.
(14) For ansa-organolanthanidocene complexes that contain a bridged
fluorenyl ligand, see the following. (a) (η5:η5-FluSiMe2Cp′)Y[N(SiMe3)2]:
Lee, M. H.; Hwang, J .-W.; Kim, Y.; Kim, J .; Han, Y.; Do, Y.
Organometallics 1999, 18, 5124. (b) [(η5:η5-FluSiR2Cp′)Ln(µ-Cl)]2 (R
) Me, Ph; Ln ) Y, Lu, Dy, Er) and (η5:η5-FluSiMe2Cp)Ln[E(SiMe3)2]
(Ln ) Dy, Er, E ) N, CH): Qian, C.; Nie, W.; Sun, J . Organometallics
2000, 19, 4134. (c) [(η5:η5-FluCPh2Cp)LnCl2][Li(THF)4] (Ln ) Lu, Y):
Qian, C.; Nie, W.; Sun, J . J . Chem. Soc., Dalton Trans. 1999, 3283. (d)
[(η5:η5-FluCPh2Cp)Nd(BH4)2][K(18-crown-6)]: Qian, C.; Nie, W.; Sun,
J . J . Organomet. Chem. 2001, 626, 171. (e) (η5:η5-FluCPh2Cp)Lu-
(N(SiMe3)2): Qian, C.; Nie, W.; Sun, J . J . Organomet. Chem. 2002,
645, 82; See also: (f) Nie, W.; Qian, C.; Chen, Y.; Sun, J . J . Organomet.
Chem. 2002, 647, 114. (g) (η5:η5-CpCMe2Flu)Ln(η5-CpCMe2FluH)-
(THF)n (Ln ) Y, La, Nd; n ) 0, 1): Dash, A., K.; Razavi, A.; Mortreux,
A.; Lehmann, C.; Carpentier, J .-F. Organometallics 2002, 21, 3238.

“Constrained Geometry” Group 3 Metal Complexes
Organometallics, Vol. 22, No. 22, 2003 4469
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta
2a
4‚0.5(toluene)
5
8
9‚(toluene)‚THF
10
formula
cryst size, mm
mol wt
cryst syst
space group
a, Å
C
39H66NO2Si2Y
C42.50H67NO3SiLi2
C
31H50NO2SiLi
C62H98N2O2Si2LiLa C85H134LiN2NdO6Si2
C
62H94Cl2N2Nd2O2Si2
0.10 × 0.09 × 0.05 0.19 × 0.15 × 0.11 0.48× 0.33 × 0.33 0.46 × 0.36 × 0.34 0.42 × 0.38 × 0.32
0.36 × 0.32 × 0.32
1314.95
monoclinic
A2/a
11.0801(1)
26.0401(3)
23.2813(3)
90
97.869(1)
90
6654.0(1)
4
716.95
monoclinic
P21/n
12.3702(5)
23.0023(11)
14.9881(7)
90
106.021(2)
90
681.94
monoclinic
P21/c
24.1847(3)
16.5846(2)
22.2003(3)
90
113.0210(10)
90
503.75
monoclinic
P21/n
11.7950(4)
19.2352(2)
14.9331(6)
90
108.653(1)
90
3210.0(2)
4
1105.46
monoclinic
Cc
1487.30
monoclinic
P21/c
24.4430(2)
14.2723(2)
19.9580(2)
90
13.6015(2)
20.0120(2)
30.4072(4)
90
b, Å
c, Å
R, deg
â, deg
118.955(1)
90
97.426(1)
90
γ, deg
V, Å3
4099.1(3)
4
1.162
8195.26(18)
8
1.105
6092.2(1)
4
8207.2(2)
4
Z
D
calcd, g cm-3
1.042
1.205
1.202
1.313
T, K
100(2)
5.30-23.38
1.511
100(2)
4.55-26.40
0.094
89 182
16 703
10 741
110(1)
1.79-27.53
0.098
31 822
7386
110(2)
1.72-27.49
0.781
61 586
6916
120(2)
2.53-27.48
0.711
87 138
18 574
12 224
120(2)
2.09-27.49
1.698
15 613
7629
5331
θ range, deg
µ, mm-1
no. of measd rflns 22 815
no. of indep rflns 5842
no. of rflns with
I > 2σ(I)
3431
4056
6634
no. of params
goodness of fit
R1 (I > 2σ(I))
wR2
417
915
1.058
0.0787
0.1556
0.520/-0.291
329
1.030
0.0682
0.1632
0.405/-0.451
649
1.059
0.0304
0.0753
2.47/-0.715
849
1.048
0.064
0.144
326
1.017
0.037
0.084
1.048
0.0766
0.1558
largest diff, e Å-3 0.632/-0.482
2.650/-0.996
1.241/-0.618
only from the poor acidity of the fluorenyl functional-
ity.16 Indeed, because of the ability of SiR3 groups to
stabilize negative charges at the R-position, the fluore-
nyl proton in 1a ,b is much more acidic than that in
CpHCMe2FluH.16c Rather, they suggest that prelimi-
nary coordination of the other functionality of the ansa
ligand, i.e., Cp-H for the carbon-bridged ligand and
tBuN-H for 1a ,b, which in turn enforces the pending
fluorenyl moiety in the coordination sphere or immedi-
ate proximity of the metal center, may be a prerequisite
for the proton transfer from the fluorenyl fragment to
the amido moiety to occur. This initial process easily
takes place with CpHCMe2FluH (vide supra) but does
Quantitative conversion of 1a to 2a was achieved by
adding 0.3 extra equiv (vs 1a ) of Y(CH2SiMe3)3(THF)2
to the reaction mixture. Increase of the temperature to
50 °C slightly accelerated the reaction of 1a and Y(CH2-
SiMe3)3(THF)2, but it proved again necessary to re-add
some carbyl precursor after a while to achieve total
conversion of the ligand. Adjustment of the reaction
balance is likely due to slow decomposition of Y(CH2-
SiMe3)3(THF)2, which is quite thermally sensitive.18
Complex 2a is stable in benzene solution at 50 °C for
several hours without noticeable decomposition, in
contrast to the parent yttrium complex (C5Me4SiMe2-
NtBu)Y(CH2SiMe3)(THF) (half-life 600 ( 10 min at 50
°C in C6D6).5b The synthesis of 2a was conveniently
carried out on a gram scale batch by generation of in
situ Y(CH2SiMe3)3(THF)2 from YCl3(THF)3.5 and LiCH2-
SiMe3, subsequent protonolysis with 1a , and crystal-
lization from pentane at -35 °C to give yellow crystals
in 68% yield. The new carbyl complex 2a was character-
ized by elemental analysis, NMR, and an X-ray diffrac-
tion study (Table 1).
In the solid state, the molecule of 2a features a
different structure than the pseudo-tetrahedral geom-
etry usually observed for related cyclopentadienyl- and
indenyl-amido constrained-geometry yttrium and scan-
dium complexes.2,5b The formal 14-electron yttrium
center is coordinated in a distorted-octahedral fashion
by the trimethylsilylmethyl ligand, two THF molecules,
and the chelating amido and fluorenyl moieties, which
are bonded in a dissymmetric η3 fashion (Figure 1). The
presence of an additional THF molecule in 2a , as
compared to monosolvated complexes (η5:η1-C5Me4-
SiMe2NtBu)Y(CH2SiMe3)(THF) and (η5:η1-C9H6SiMe2-
NtBu)Y(CH2SiMe3)(THF),5b is apparently directly con-
nected to the reduced hapticity of the fluorenyl ligand.
t
not for 1a ,b, likely because the BuN-H functionality
is even less acidic than the fluorenyl group (vide
infra).16,17
In contrast to amine elimination, alkane elimination
is a more efficient synthetic route, likely because Ln-C
bonds are protonically more reactive.1 In situ monitoring
by 1H NMR spectroscopy showed that Y(CH2SiMe3)3-
(THF)2 reacts with 1 equiv of diprotio ligand 1a at room
temperature in benzene to give [(3,6-tBu2C13H6)SiMe2-
NtBu]Y(CH2SiMe3)(THF)2 (2a ), with concomitant re-
lease of 2 equiv of SiMe4 (eq 2). No intermediate could
(17) In contrast to amine elimination reactions involving bulky
silylene-bridged bis(indenyl) ligands,16c it seems unlikely that the
exchange reactions of lanthanide amides with our ligands could be
hampered by the steric bulkiness of the reagents.
(18) Considering the even higher thermal instability of La(CH-
(SiMe3)2)3,6a σ-bond metathesis between this reagent and 1a was not
attempted. Coordination of 1a to larger lanthanides (La, Nd) was
investigated using salt metathesis routes.
be detected, suggesting that coordination of the second
functionality (tBuN-H or Flu-H) proceeds faster than
t
the first one (Flu-H or BuN-H). The conversion of 1a
was 37% after 1 h at 20 °C, with >98% selectivity for
2a , and reached a plateau at 90% after a few days,
where no more starting carbyl complex was detected.

4470 Organometallics, Vol. 22, No. 22, 2003
Kirillov et al.
been presented by Bochmann et al. in [(η5:η3-CpCMe2-
Flu)Zr(µ-H)(Cl)]2, with Zr-C(Flu) bond distances in the
range 2.608(3)-2.686(3) Å.22,23 Recently, we have re-
ported a similar exocyclic η3 bonding mode, together
with a new exocyclic η1(η2) bonding mode (E ), in the
unique, three polymorphic anion complex [(η3:η5-FluCMe2-
Cp)(η1:η5-FluCMe2Cp)Y]-[Li(Et2O)(THF)3]+, with Y-C(1)
in the range 2.690(7)-2.789(12) Å, Y-C(9A) in the
range 2.749(7)-2.806(8) Å, and Y-C(9) in the range
2.894(8)-3.065(8) Å.24 Complex 2a features the same
η3-allyl bonding mode (D), slipped more toward the
central five-membered ring than the six-membered ring,
with Y(1)-C(9) ) 2.584(7), Y(1)-C(9A) ) 2.732(7) Å,
and Y(1)-C(1) ) 2.885(8) Å. The distance between the
metal center and the bridgehead carbon atom C(9) of
the central ring falls in the range for the Y-Cp(Flu)
bond lengths of 2.56(2)-2.74(2) Å observed in (η5:η5-
CpSiMe2Flu)Y(N(SiMe3)2) and (η5:η3-CpSiMe2Flu)YCl2-
Li(OEt2)2.14a Because of the dissymmetric coordination
of the fluorenyl ligand, the bite angles in 2a cannot be
discussed as they usually can with Cp centroids. None-
theless, the relevant bond angles Si(1)-N(1)-Y(1) (102.5-
(3)°) and N(1)-Si(1)-C(9) (101.5(3)°) resemble the
corresponding angles in (η5:η1-C5Me4SiMe2NCMe2Et)Y-
(CH2SiMe3)(THF) (102.2(2) and 97.0(3)°)5b and [(η5:η1-
C5Me4SiMe2NCMe2R)Y(THF)(µ-Cl)]2 (104.2(2) and
97.4°),5c which suggests comparable chelate constraints.
Also, other bond distances associated to the carbyl,
amido, and THF ligands in 2a are similar to those found
in (C5Me4SiMe2NCMe2Et)Y(CH2SiMe3)(THF).5b
F igu r e 1. Molecular structure of complex 2a . Thermal
ellipsoids are drawn at the 50% probability level; hydrogen
atoms are omitted for clarity. Selected bond distances (Å)
and angles (deg): Y(1)-C(9), 2.584(7); Y(1)-C(9A), 2.732-
(7); Y(1)-C(1), 2.885(8); Y(1)-N(1), 2.200(6); Y(1)-C(19),
2.391(8); Y(1)-O(4), 2.322(5); Y(1)-O(5), 2.378(5); N(1)-
Y(1)-C(9), 70.5(2); N(1)-Y(1)-C(9A), 88.5(2); N(1)-Y(1)-
C(19), 107.8(2); N(1)-Y(1)-O(4), 94.9(2); N(1)-Y(1)-O(5),
158.5(2); C(19)-Y(1)-C(9), 148.2(3).
Ch a r t 1. Bon d in g Mod es of th e F lu or en yl Moieties
Obser ved in Gr ou p 3 a n d Gr ou p 4 Meta llocen es
Complex 2a is readily soluble in aliphatic and aro-
matic hydrocarbons such as pentane, benzene, and
1
toluene. The low-temperature (-70 °C) H NMR spec-
trum (toluene-d8) of 2a contains two singlets and four
doublets characteristic for the six fluorenyl protons, two
broad doublets for the diastereotopic CHHSiMe3 protons
(2J HH ) ca. 8 Hz), two singlets for the SiMe2 moiety,
two well-separated signals for the R-CH2 THF protons,
and one broadened signal for the â-CH2 THF protons
t
t
and each of the Bu (fluorene), Bu (amido), and SiMe3
groups (Figure 2). This pattern indicates an asymmetric
coordination sphere around yttrium and is consistent
with a fixed distorted-octahedral geometry similar to
that observed in the solid state for the bis(THF) complex
(Figure 1). It suggests that reduced haptacity (η3) of the
fluorenyl moiety in 2a is retained in solution; however,
the NMR data provide no conclusive evidence about the
exact bonding mode, i.e., symmetric (B) or dissymmetric
(D).25 As the temperature is raised from -70 °C to room
temperature, the pairs of fluorenyl, CHHSiMe3, SiMe2,
The bonding of the fluorenyl moiety in 2a is unusual.
Chart 1 shows various bonding modes of fluorenyl
ligands found in ansa and simple metallocenes of
lanthanides and zirconium previously established by
X-ray diffraction studies.19 In most complexes the metal
is essentially symmetrically η5 bonded to the five-
membered ring of the fluorenyl ligand (A), e.g. in
(η5:η5-CpSiMe2Flu)Y[N(SiMe3)2],14a η3 bonded (B), e.g.
in (η5:η3-Flu)2Sm(THF)220 and (η5:η3-CpSiMe2Flu)YCl2-
Li(OEt2)2,14a or, more seldomly, symmetrically η1 bonded
(C) as in (η5-C5H4Me)2Zr(η1-Flu)(Cl).21 An unusual non-
symmetric η3-allyl bonding mode (D) involving the
bridgehead carbon atom of the central ring and the two
adjacent carbon atoms of one six-membered ring has
1
and R-CH2 THF H NMR resonances of 2a each broaden
and collapse to a single resonance (Tcoal for CHHSiMe3
1
is -35 °C at 300 MHz; ∆Gq
) 11.3 kcal/mol). The H
coal
NMR spectrum of 2a in benzene or toluene at 20 °C
(22) Bochmann, M.; Lancaster, S. J .; Hursthouse, M. B.; Mazid, M.
Organometallics 1993, 12, 4718.
(23) A similar exocyclic η3 coordination of fluorenyl ligands has been
observed in the solid-state structures of alkaline-earth-metal complexes
(η3:η3-FluSiMe2Flu)2M(THF)n (M ) Ca, n ) 3; M ) Ba, n ) 4): Harder,
S.; Lutz, M.; Straub, W. G. Organometallics 1997, 16, 107.
(24) Kirillov, E.; Toupet, L.; Razavi, A.; Kahlal, S.; Saillard, J .-Y.;
Carpentier, J .-F. Organometallics 2003, 22, 4038.
(19) Arene type η6 coordination of fluorenyl ligands by the six-
membered rings has been also observed in the solid state. (a) Bimetallic
lanthanide-aluminum complexes [(η6-Me3Si-fluorene)AlMe3]2Sm and
[(η6-Me3Si-fluorene)AlMe3]Sm[η5-Me3Si-fluorenyl]: Nakamura, H.; Na-
kayama, Y.; Yasuda, H.; Maruo, T.; Kanehisha, N.; Kai, Y. Organo-
metallics 2000, 19, 5392. (b) Fluorenyllithium (η6-FluLi)2: U¨ ffing, C.;
Ko¨ppe, R.; Schno¨ckel, H. Organometallics 1998, 17, 3512.
(20) Evans, W. J .; Gummersheimer, T. S.; Boyle, T. J .; Ziller, J . W.
Organometallics 1994, 13, 1281.
(25) In contrast to Bochmann’s complex [(η5:η3-CpCMe2Flu)Zr(µ-H)-
(Cl)]2,22 in which the dissymmetry of the molecule observed by NMR
in solution is clearly indicative of a dissymmetric bonding of the
fluorenyl moiety, the dissymmetry of the molecule of 2a is determined
by the overall octahedral geometry, irrespective of the bonding mode
of the fluorenyl group to the metal center.
(21) Schmid, M. A.; Alt, H. G.; Milius, W. J . Organomet. Chem. 1997,
541, 3.

“Constrained Geometry” Group 3 Metal Complexes
Organometallics, Vol. 22, No. 22, 2003 4471
1
F igu r e 2. Temperature dependence of the H NMR spectrum of 2a in toluene-d8 (S denotes solvent resonances).
features one series of sharp signals, consistent with a
symmetric structure on the NMR time scale (Figure 2).
These line-shape changes are all reversible upon lower-
ing the temperature. Also, the 13C{1H} NMR spectrum
(C6D6) at 20 °C shows seven resonances for the fluorenyl
carbon atoms, two signals for the THF carbons, one
signal for the SiMe2 bridge, and one doublet for the
methylene carbon of the carbyl ligand (2J YH ) 3.3 Hz).
The coordinated THF ligands in 2a are labile on the
NMR time scale, as indicated by the temperature
dependence of the chemical shifts of the R- and â-
methylene THF protons, which undergo substantial low-
field shifts when the temperature is raised from -30 to
60 °C (Figure 3). Addition of excess THF-d8 resulted in
the immediate exchange of all coordinated THF. These
observations are in agreement with the existence of an
equilibrium involving THF dissociation (eq 3), fast on
-THF
[(3,6-tBu2C13H6)SiMe2NtBu]Y(CH2SiMe3)(THF)2
y
z
+THF
F igu r e 3. Temperature dependence of the chemical shift
of the R- and â-CH2 protons of the coordinated THF
molecules in 2a in toluene-d8.
2a
[(3,6-tBu2C13H6)SiMe2NtBu]Y(CH2SiMe3)(THF)
(3)
2a ′
at 38% (vs 1b) after 96 h at 50 °C; however, the reaction
mixture was soiled by excess THF and insoluble decom-
position products arising from the yttrium carbyl re-
agent, and this procedure proved to be inoperative on a
larger scale to isolate pure carbyl complex 2b. Also,
significant decomposition of 2b was observed at this
temperature over several hours.
Hyd r ogen olysis of Ca r byl Com p lex 2a . Numerous
lanthanide hydrido complexes are described in the
literature,26 including a number of half-sandwich hy-
drido complexes derived from cyclopentadienyl-amido
systems.5a-c,9 However, to our knowledge, no fluorenyl
hydrido complex of group 3 metals has been reported
both the chemical and NMR time scales.5b It is note-
worthy that neither pumping of solid 2a under high
vacuum for prolonged periods nor repeated stripping of
toluene solutions of 2a yielded the monosolvated com-
plex (2a ′), suggesting that THF coordination is rather
strong.
The diphenylsilylene-bridged ligand 1b was found to
be quite less reactive toward Y(CH2SiMe3)3(THF)2 than
1
its dimethylsilylene analogue 1a . H NMR monitoring
of a 1:1 mixture in toluene-d8 showed that no reaction
occurs at 20 °C for several days. Heating at 50 °C for 2
days resulted in the formation of [(3,6-tBu2C13H6)SiPh2-
NtBu]Y(CH2SiMe3)(THF)x (2b) in 25% NMR yield (vs
1b) and full decomposition of the starting yttrium carbyl
(eq 2). On using an excess of Y(CH2SiMe3)3(THF)2 vs
1b (4:1 ratio), the NMR yield of 2b reached a maximum
(26) (a) Ephritikhine, M. Chem. Rev. 1997, 97, 2193. (b) Desurmont,
G.; Li, Y.; Yasuda, H.; Maruo, T.; Kanehisa, N.; Kai, Y. Organometallics
2000, 19, 1811.

4472 Organometallics, Vol. 22, No. 22, 2003
Kirillov et al.
Sch em e 1. P u ta tive Dim er ic Hyd r id o Str u ctu r es
for th e Hyd r ogen olysis P r od u ct of 2a
terization are very arduous. X-ray-quality crystals of 4
were successfully grown from a THF/toluene solution
(Figure 4, Table 1). On the other hand, attempts to
characterize 4 by NMR in THF-d8 solution systemati-
cally resulted in complicated spectra. The presence of a
partially protonated species, i.e., the monolithiated
derivative 5, was suspected, likely due to adventitious
hydrolysis with trace amounts of protic compounds in
solvents or on glassware. Compound 5 was indepen-
dently prepared by the reaction of 1a with 1 equiv of
nBuLi in DME and recrystallized from a DME/pentane
solution (eq 5). Again, no conclusive information was
obtained in solution (NMR), but the solid-state charac-
terization proved successful (Figure 5, Table 1).
The solid-state structure of 4 features a “neutral” tris-
THF solvate, unlike several dilithium salts of ansa-bis-
(fluorenyl) ligands which are presented by solvent-
separated ion pairs, e.g. [Me2Si(Flu)2Li(THF)2]-[Li-
(THF)4]+ (I),23 [(CH2)n(Flu)2Li]-[Li(THF)4]+ (n ) 2, 6),28
and [{Flu(Me2N)B-B(NMe2)Flu}Li(THF)]-[Li(THF)4]+.29
The unit cell of 4 contains two independent molecules
with similar geometries of the coordinated fluorenyl-
amido moieties. The “amido” lithium atom Li(1) is in a
three-coordinate planar environment (sum of the bond
angles around Li(1) 357.4 and 355.9° in the two inde-
pendent molecules), and the coordination environment
of the “fluorenyl” lithium atom Li(2) is pseudo-tetrahe-
dral. Interestingly, both lithium atoms are bonded to
the nitrogen atom (Li(1)-N ) 1.974(6) and 1.969(6) Å,
Li(2)-N ) 2.002(5) and 2.019(6) Å in the two indepen-
dent molecules) and bridged by a THF molecule to give
a nonplanar Li(1)-O(21)-Li(2)-N(1) core. Likewise, in
[Me2Si(Flu)2Li(THF)2]-[Li(THF)4]+,23 the lithium atom
Li(2) in 4 is bonded to the fluorenyl group in an η1
fashion with a fluorenyl Cipso-Li bond distance (2.396-
(6) and 2.446(6) Å) comparable to those found in the
former ansa-bis(fluorenyl) compound (2.353(8) and 2.399-
(8) Å).
so far. Hydrogenolysis of 2a in benzene (20 °C, 1 atm)
proceeds smoothly with precipitation of a microcrystal-
line pale yellow powder (3) and concomitant production
of SiMe4 (1H NMR). The same compound was obtained
in nearly quantitative yield upon reacting 2a and
PhSiH3 (5 equiv) in benzene solution at 20 °C for 1 h.
This convergent reactivity of carbyl complex 2a with
both of the reagents traditionally used to prepare early-
transition-metal hydrides5a-c,9 and elemental analyses
are in agreement with the formation of a hydrido
complex of the proposed dimeric composition “[(3,6-tBu2-
Flu)SiMe2NtBu)YH(THF)]2” (3) (Scheme 1). This prod-
uct is, however, totally insoluble in THF, DME, meth-
ylene chloride, and hydrocarbons (pentane, benzene,
toluene), hampering recrystallization and NMR char-
acterization.27
Sa lt Elim in a tion Rea ction s. Salt elimination reac-
tions between lanthanide halogenides LnX3 (X ) Cl, Br,
I) and 1 equiv of deprotonated ligand salts [L]2-
(L ) e.g. bis(cyclopentadienyl), cyclopentadienyl-amido
ligands) is usually carried out to access neutral or ate
halogeno complexes of larger lanthanides of the type
{[L]LnX}n (n ) 1, 2) and {[L]LnX2}-.1 The latter can be
then further transformed into potentially valuable car-
byl or amido complexes. Such salt elimination reactions
are most often performed in ethereal media (Et2O,
DME) to ensure solubility of the initial reagents and
promote precipitation of the formed alkali-metal halide
salts. Deprotonation of ligand 1a is readily achieved
with 2 equiv of nBuLi (eq 4). The corresponding dil-
The coordination in monolithiated species 5 is differ-
ent. The fluorenyl group is η5 bonded to lithium via the
five-membered ring with Li-C bond distances in the
range 2.291(5)-2.375(5) Å. A DME molecule completes
the coordination sphere of the three-coordinate lithium
atom, and the nitrogen atom of the pendant amino
group is still protonated. This evidences the higher
acidity of the fluorene functionality vs the amino moiety
(vide supra).
(27) Recently we prepared the new hydrido complex [(CpCMe2Flu)Y-
(THF)(µ-H)]2, which was shown by X-ray diffraction to be dimeric in
the solid state and which features also extremely low solubility in most
usual solvents: Kirillov, E.; Toupet, L.; Razavi, A.; Lehmann, C. W.;
Carpentier, J .-F. Manuscript in preparation.
(28) Becker, B.; Enkelmann, V.; Mullen, K. Angew. Chem., Int. Ed.
Engl. 1989, 28, 458.
(29) Littger, R.; Metzler, N.; Noth, H.; Wagner, M. Chem. Ber. 1994,
27, 1901.
ithium salt 4 is, however, extremely reactive toward
protic sources, and its isolation, handling, and charac-

“Constrained Geometry” Group 3 Metal Complexes
Organometallics, Vol. 22, No. 22, 2003 4473
F igu r e 4. Molecular structure of [(3,6-tBu2C13H6)SiMe2NtBu]Li2(THF)3‚0.5C7H8 (4). Two views and parameters of one of
the two independent molecules are given; thermal ellipsoids are drawn at the 50% probability level, and hydrogen atoms
are omitted for clarity. Selected bond distances (Å) and angles (deg): Li(1)-N(1), 1.974(6); Li(1)-O(21), 1.971(6); Li(1)-
O(51), 1.901(6); Li(2)-C(9), 2.396(6); Li(2)-C(9a), 2.896(6); Li(2)-N(1), 2.002(5); Li(2)-O(21), 2.190(5); Li(2)-O(41), 1.915-
(5); N(1)-Si(1)-C(9), 103.50(12); N(1)-Si(1)-Li(2), 47.37(13); C(9)-Si(1)-Li(2), 59.69(14); Li(1)-N(1)-Li(2), 77.8(2); Si(1)-
N(1)-Li(1), 109.0(2).
presence of two major products (accounting for >95%
of the sample) in comparable proportion (Y, 1.4:1; La,
1.2:1), which each feature one set of sharp resonances
for a [(3,6-tBu2C13H6)SiMe2NtBu] moiety symmetrically
coordinated to the metal center on the NMR time scale.
No change in the intensity ratio or broadening of the
1H NMR signals was observed upon heating to 60 °C,
indicating that no isomerization nor exchange takes
place between these species under such conditions.
Elemental analysis of both Y and La crude products did
not match with calculated values for various formulas,
confirming a mixture composition. Okuda et al. have
reported that the reaction of YCl3(THF)3.5 with 1 equiv
of [C5Me4SiMe2NCH2CH2OMe]Li2 in toluene or THF
resulted in complex mixtures of inseparable products;10a
only the reaction of anhydrous LnCl3 (Ln ) Y, Lu) with
2 equiv of [C5Me4SiMe2NCH2CH2X]Li2 (X ) OMe,
NMe2) in THF afforded the isolable ionic bis(ligand)
complexes Li[Ln(η5:η1-C5R4SiMe2NCH2CH2X)2].10a Re-
crystallization of our crude 1:1 products proved more
successful, leading reproducibly to a set of anionic
complexes (eq 6).
F igu r e 5. Molecular structure of [(3,6-tBu2C13H6)SiMe2-
NHtBu]Li(DME) (5). Thermal ellipsoids are drawn at the
50% probability level; hydrogen atoms, except that on the
N atom, are omitted for clarity. Selected bond distances
(Å) and angles (deg): Li(1)-O(1), 1.939(5); Li(1)-O(2),
1.927(5); Li(1)-C(1), 2.342(5); Li(1)-C(6), 2.304(5); Li(1)-
C(7), 2.291(5); Li(1)-C(8), 2.336(5); Li(1)-C(13), 2.375(5);
Cent-Li, 1.982; N(1)-Si(1)-C(7), 107.15(12); Si(1)-C(7)-
Li(1), 118.67(17); Cent-Li(1)-O(1), 139.73; Cent-Li(1)-
O(2), 137.31 Cent is the centroid of C(1)-C(6)-C(7)-C(8)-
C(13).
Considering the high sensitivity of dilithiated ligand
4, the latter was generated in situ just prior to salt
metathesis reactions with LnCl3(THF)n precursors. The
first experiments were conducted with yttrium and
lanthanum chlorides, since valuable NMR information
is readily accessible for complexes of these diamagnetic
metals and allows a thorough investigation of the
reaction process. When carried out at room temperature
in diethyl ether as the solvent, salt elimination from
YCl3(THF)3.5 and LaCl3(THF)1.5 with 1 equiv of 4 gave
crude products as yellow microcrystalline powders. The
latter are only sparingly soluble in benzene and toluene
and highly soluble in Et2O, THF, and DME, suggesting
an ionic structure. The 1H and 13C NMR spectra in THF-
d8 of both the Y and La crude products showed the
Recrystallization of the Y and La crude products from

4474 Organometallics, Vol. 22, No. 22, 2003
Kirillov et al.
THF/pentane at -30 °C gave yellow crystals of the ionic
complexes [{(3,6-tBu2C13H6)SiMe2NtBu}2Ln]-[Li(THF)4]+
(Ln ) Y, 6; Ln ) La, 7) in 25% and 81% yields (vs 1a ),
respectively. Elemental analyses were in agreement
with the proposed formulas for complexes 6 and 7,
indicating in particular that there is essentially no Cl.
The isolated complexes show the same solubility trend
as the initial crude products: that is, quite poor solubil-
ity in hydrocarbons and high solubility in ether solvents.
In fact, 1H and 13C NMR spectroscopy established
unambiguously that complex 7 corresponds to the
initially minor species present in the crude La product.
1
On the other hand, the H NMR spectrum of 6 in THF-
d8 at 20 °C displays one set of sharp signals character-
istic of a symmetrically coordinated [(3,6-tBu2C13H6)-
SiMe2NtBu], yet the chemical shifts are significantly
different from those of both species present in the crude
Y product. The identity of the latter thus still remains
obscure. Although no crystal of 6 or 7 suitable for X-ray
diffraction studies could be obtained, the molecular
structure of a close neodymium parent complex (9) was
further established (vide infra).
F igu r e 6. Molecular structure of 8. Thermal ellipsoids are
drawn at the 50% probability level; hydrogen atoms are
omitted for clarity. Selected bond distances (Å) and angles
(deg): La(1)-C(6), 3.025(4); La(1)-C(7), 2.806(4); La(1)-
C(8), 2.883(4); La(1)-C(27), 2.843(4); La(1)-C(28), 2.766-
(4); La(1)-C(29), 3.068(4); Li(1)-C(7), 2.279(9); La(1)-N(1),
2.396(3); La(1)-N(2), 2.378(3); Li(1)-C(8), 2.439(9); Li(1)-
O(1), 1.919(9); Li(1)-O(2), 1.910(9); N(1)-La(1)-N(2),
101.76(12); Cent(1)-La(1)-N(1), 75.86; Cent(2)-La(1)-
N(2), 76.38; C(7)-Si(1)-N(1), 101.01(17); C(28)-Si(2)-
N(2), 100.84(17). Cent(1) is the centroid of C(6)-C(7)-C(8);
Cent(2) is the centroid of C(27)-C(28)-C(29).
Recrystallization of the crude La product (obtained
from LaCl3(THF)1.5 and in situ generated 4 in Et2O)
under different conditions, i.e., from an Et2O/hexane
mixture, afforded the ionic compound [{(3,6-tBu2C13H6)-
SiMe2NtBu}2La]-[Li(Et2O)2]+ (8) as orange-yellow crys-
tals in 33% yield (vs 1a ). Complex 8 is sparingly soluble
in toluene and highly soluble in THF and diethyl ether,
1
consistent with its ionic structure. The H NMR spec-
trum of 8 at 20 °C in THF-d8 (as well as that in toluene-
d8) displays broad signals indicative of a fluxional
behavior and does not correspond to either of the two
sets of resonances observed for the initial crude La
product. Fast exchange on the NMR time scale occurs
when the temperature is raised to 60 °C, with the
characteristic pattern of sharp resonances for a sym-
metrically coordinated [(3,6-tBu2C13H6)SiMe2NtBu] moi-
ety.
is also coordinated to the Li atom (2.806(4)-3.025(4) and
2.766(4)-3.068(4) Å) and are similar to those observed
in [(η5:η5-CpCPh2Flu)La(BH4)2]-[Li(THF)4]+ (2.788(3)-
3.010(3) Å)14c and in the chelated ring of (η5:η5-CpCMe2-
Flu)La(η5-CpCMe2FluH)(THF) (2.811(5)-2.997(6) Å).14g
The La-N(tBu) bond distances in 8 (2.378(3)-2.396(3)
Å) fall in the same range as those observed in other
related La-amido species; e.g., La[CyNC(NSiMe3)2NCy]-
[N(SiMe3)2]2 (2.377(3)-2.382(3) Å)30 and Cp*2La(NHMe)-
(H2NMe) (2.323(10) Å).31 These values are consistent
with a π-dative interaction between the Lewis acidic La
center with the free electron pair on nitrogen,32 also
indicated by the sp2 hybridization of the N atoms (sum
of the bond angles: around N(1), 359.9(1)°; around N(2),
360.0(1)°). This La-N(tBu) distance is longer than that
observed in (η5:η1-C5Me4SiMe2NtBu)Sm[N(SiMe3)2]
(2.257(4) Å),6a (η5:η1-C5Me4SiMe2NCMe2Et)Y(CH2-
SiMe3)(THF) (2.208(6) Å),5b and [η5:η1-(3,6-tBu2C13H6)-
SiMe2NtBu]ZrCl2 (2.040(8) Å),15a as expected from the
major influence of effective ionic radii of the metal
centers.33 Complex 8 features very narrow bite angles.
The angle FluCent-La-N (FluCent and N of the same
ligand; Cent(1)-La(1)-N(1) ) 75.9° and Cent(2)-La-
(1)-N(2) ) 76.4° considering centroids of C(6)-C(7)-
C(8) and C(27)-C(28)-C(29), respectively; Cent′(1)-
La(1)-N(1) ) 85.2° considering a fluorenyl C5 ring
centroid) is much narrower than that observed in Li-
An X-ray diffraction study confirmed the nature of 8
(Figure 6, Table 1). The solid-state molecular structure
features a closely associated ion pair with two chelating
ligands per lanthanum center, and this fragment is
therefore anionic. The counterion is characterized by a
lithium atom coordinated in a pseudo-tetrahedral fash-
ion by two diethyl ether molecules and two carbon atoms
of the central five-membered ring (C(7) and C(8)) of one
fluorenyl moiety. The formal 16-electron lanthanum
atom is coordinated in a distorted-tetrahedral geometry
by a pair of amido and fluorenyl moieties. Each of the
latter is coordinated in an η3 fashion involving the
bridgehead carbon atom of the central five-membered
ring (C(7) and C(28)) and the two adjacent carbon atoms
fusing the five- and six-membered rings (C(6), C(8) and
C(27), C(29)). The η3 coordination mode of the two
fluorenyl ligands is, however, not as symmetric as in
the ideal case (B, Chart 1). The La atom is slipped on
one side of the fluorenyl system, resulting in a ca. 0.2
Å difference between the bond distances of La with the
two terminus carbon atoms (C(6), C(8) and C(27), C(29)),
a deviation likely attributable to the chelating con-
straints imposed by the silylene bridge or crystal
packing. The La-C(Flu) bond distances are somewhat
different in both fluorenyl rings, since one of the latter
(30) Giesbrecht, G. R.; Whitener, G. D.; Arnold, J . J . Chem. Soc.,
Dalton Trans. 2001, 923.
(31) Gagne´, M. R.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1992,
114, 275.
(32) Lauher, J . W.; Hoffmann, R. J . Am. Chem. Soc. 1976, 98, 1729.
(33) Effective ionic radii for eight-coordinate metal centers: La3+
,
1.160 Å; Nd3+, 1.109 Å; Sm3+, 1.079 Å; Y3+, 1.019 Å; Zr4+, 0.84 Å.
Shannon, R. D. Acta Crystallogr., Sect. A 1976, A32, 751.

“Constrained Geometry” Group 3 Metal Complexes
Organometallics, Vol. 22, No. 22, 2003 4475
Sch em e 2
[Y(η5:η1-C5Me4SiMe2NCH2CH2OMe)2] (95.7°)10 and
[η5:η1-(3,6-tBu2C13H6)SiMe2NtBu]ZrCl2 (104.7°).15a
shortest and the longest bond distances indicates that
this fluorenyl ring may be in a stage of approaching
toward reduced hapticity (η2 or η1 bonding mode). This
is consistent with a 16-electron count on the metal
complex, equivalent to that of 8, considering two-σ-
electron donation from the coordinated THF.
On the other hand, neutral complex 10 shows in the
solid state a dimeric Ci-symmetric structure. Each
(equivalent) neodymium atom is coordinated by two
bridging chlorine atoms, a THF molecule, and the amido
and fluorenyl moieties of a chelating ligand. The struc-
ture can be regarded as the trans-heterochiral dimer,
according to the classification in Chart 2.34 The same
diastereoselectivity in the crystal has been observed
The same salt elimination synthetic approach was
applied to neodymium chemistry (Scheme 2). Efficient
purification procedures and corresponding X-ray struc-
tural information were crucial in this case, since com-
plicated and usually uninformative NMR data are
obtained for complexes of this paramagnetic metal.
Thus, crystallization of the crude product obtained from
the reaction of NdCl3(THF)2 with 1 equiv of dilithium
salt 4 (generated in situ) in Et2O was attempted under
different conditions. Crystallization from a THF/toluene/
pentane solution gave in poor yield (10% vs 1a ) golden
yellow crystals of [η3:η1-{(3,6-tBu2C13H6)SiMe2NtBu}2Nd-
(THF)]-[Li(THF)4]+ (9). The ionic complex 9 is the Nd
homologue of Y and La complexes 6 and 7, respectively.
On the other hand, using a Et2O/hexane solution
allowed us to isolate green crystals of the neutral chloro
complex [η5:η1-{(3,6-tBu2C13H6)SiMe2NtBu}Nd(µ-Cl)-
(THF)]2 (10) (38% vs Nd). The identity of 9 and 10 was
unambiguously established by single-crystal X-ray dif-
fraction studies (Figures 7 and 8, Table 1).
The molecular structure of 9 comprises a fully dis-
sociated ion pair in the solid state. The cation is
composed by a lithium atom coordinated by four THF
molecules, as observed in other ionic lanthanido-
cenes.14d-g The neodymium atom is coordinated in a
distorted-trigonal-bipyramidal geometry by one THF
molecule and a pair of amido and fluorenyl moieties. In
contrast with the anionic bis(ligand) lanthanum complex
8, but similarly to neutral yttrium carbyl 2a , both
fluorenyl moieties in 9 are coordinated to Nd in a
dissymmetric fashion. A clear dissymmetric η3 bonding
mode (D, Chart 1) is established for one fluorenyl ligand
(C(28), C(29), C(30)), with Nd-C(Flu) bond distances
in the range of 2.789(5)-3.017(5) Å. The corresponding
Nd-C(Flu) bond distances of the second fluorenyl
moiety are in the range of 2.710(5)-3.184(5) Å, with the
phenyl carbon atom (C(3)) being farther away from the
metal center. The difference of nearly 0.5 Å between the
F igu r e 7. Molecular structure of the anion of 9. Thermal
ellipsoids are drawn at the 50% probability level; hydrogen
atoms are omitted for clarity. Selected bond distances (Å)
and angles (deg): Nd(1)-C(1), 2.710(5); Nd(1)-C(2), 3.068-
(5); Nd(1)-C(3), 3.184(5); Nd(1)-C(28), 2.789(5); Nd(1)-
C(29), 2.901(5); Nd(1)-C(30), 3.017(5); Nd(1)-N(1), 2.353-
(4); Nd(1)-N(2), 2.298(4); Nd(1)-O(5), 2.522(3); N(1)-
Nd(1)-N(2), 102.20(14); N(1)-Nd(1)-C(1), 67.87(14); N(1)-
Nd(1)-C(2), 84.06(13); N(2)-Nd(1)-C(28), 66.53(14); N(2)-
Nd(1)-C(29), 90.53(14); C(1)-Si(1)-N(1), 104.7(2); C(28)-
Si(2)-N(2), 103.7(2).

4476 Organometallics, Vol. 22, No. 22, 2003
Kirillov et al.
2.861(4) Å; Nd-Cl-Nd ) 106.3(1)°; Cl-Nd-Cl ) 73.7-
(1)°)37 and the aforementioned parent CGC yttrium
complex.5c The fluorenyl moieties in 10 are η5 coordi-
nated to the central five-membered ring (mode A, Chart
1) with Nd-C(Flu) bond distances in the range of 2.646-
(3)-2.900(4) Å and average of 2.784(4) Å, a value
smaller than the average bond distance of 2.845(4) Å
in [(η5:η5-CpCPh2Flu)Nd(BH4)2]-[Li(THF)4]+ 14c and 2.883-
(4) Å in (η5:η5-CpCMe2Flu)Nd(η5-CpCMe2FluH)(THF).14g
The Nd-N(tBu) bond distances in 9 (2.298(4)-2.353-
(4) Å) are slightly shorter than those in the lanthanum
complex 8, reflecting the decrease by 4% in the ionic
radii.33 They compare well with the bond distances
observed in other amido-neodymium complexes, e.g.
[Nd{N(SiMe3)2}2(THF)(µ-Cl)]2 (2.300(8)-2.335(8) Å)36
and Nd[N(SiHMe2)2]3(THF)2 (2.326(5)-2.353(5) Å),30
while the distance in 10 (2.259(3) Å) is slightly shorter.
As for 8, these values are consistent with a π-dative
interaction between the Lewis acidic Nd center with the
free electron pair on nitrogen,32 also indicated by the
sp2 hybridization of the N atoms (sum of the bond
angles: around N(1) in 9, 359.9(2)°; around N(2) in 9,
359.9(2)°; around N(1) in 10, 360.0(3)°). The bite angle
FluCent-Nd(1)-N(1) (94.13°) in the constrained-geom-
etry complex 10 is much smaller than the FluCent-Nd-
Cpcent bite angle observed in [(η5:η5-CpCPh2Flu)Nd-
(BH4)2]-[Li(THF)4]+ (ca. 106°)14c and (η5:η5-CpCMe2Flu)-
Nd(η5-CpCMe2FluH)(THF) (105.08°)14g and even smaller
than that in silylene-bridged bis(cyclopentadienyl)-
Nd systems, e.g. {Me2Si(η5-C5Me4)2}Nd[CH(SiMe3)2]
(121.6°)38 and [rac-{Me2Si(η5-2-SiMe3-4-tBuC5H4)2}Nd-
(µ-Cl)2Li(THF)2] (118.9°).39
F igu r e 8. Molecular structure of 10. Thermal ellipsoids
are drawn at the 40% probability level; hydrogen atoms
are omitted for clarity. Selected bond distances (Å) and
angles (deg): Nd(1)-C(1), 2.646(3); Nd(1)-C(2), 2.801(3);
Nd(1)-C(7), 2.900(4); Nd(1)-C(8), 2.862(4); Nd(1)-C(13),
2.709(4); Nd(1)-Cent, 2.502; Nd(1)-N(1), 2.259(3); Nd(1)-
Cl(1), 2.7888(10); Nd(1)-Cl(1_7), 2.8622(10); Nd(1)-O(1),
2.493(3); Cent-Nd(1)-N(1), 94.13; Cent-Nd(1)-Cl(1),
127.87; Cent-Nd(1)-Cl(1_7), 110.15; Cl(1)-Nd(1)-N(1),
99.25(9); Cl(1)-Nd(1)-Cl(1_7), 74.05(3); O(1)-Nd(1)-N(1),
89.33(11). Cent is the centroid of C(1)-C(2)-C(7)-C(8)-
C(13).
All of the above results show that salt elimination
reactions of lanthanide chlorides with 1 equiv of the
dilithiated species of linked fluorenyl-amido ligand 1a
are quite versatile. Two classes of products are formed:
homoleptic ionic complexes that contain two chelating
ligand units per metal center (A)40 and heteroleptic
neutral chloro complexes with one chelating ligand unit
(B). Only the major product isolated from neodymium
chloride belongs to the latter (most preferred) class. The
same selectivity for neutral chloro complexes of type B
was described by Bercaw et al. in the chemistry of
scandium constrained-geometry complexes.2c This is
rather surprising, since the organometallic chemistry
of Nd and Sc are known to be quite different,1 in
particular because of the large difference in the ionic
radii of these elements.33 On the other hand, yttrium
and lanthanum, despite their large difference in ionic
radius, both induce ionic species of type A. A few
examples of formation of such ionic complexes that
contain two chelating units per metal center in the
course of equimolar salt metathesis reactions have been
Ch a r t 2
previously for the parent complex [Y(η5:η1-C5Me4SiMe2-
NCMe2Et)(µ-Cl)(THF)]25c and dimeric scandium hydride
and carbyl complexes of the tridentate ligand CpHNMe
-
(35) Other dimeric THF-free bis(cyclopentadienyl)neodymium chlo-
rides exhibit more symmetric rhomboidal Nd2Cl2 cores. (a) [Nd(η5-C5H4-
{CH(SiMe3)2})2(µ-Cl)]2 (Nd-Cl ) 2.805(1), 2.786(1) Å; Nd-Cl-Nd )
103.24(3)°; Cl-Nd-Cl ) 76.76(3)°): Hitchcock, P. B.; Lappert, M. F.;
Tian, S. Organometallics 2000, 19, 3420. (b) [Nd(1,3-tBu2C5H3)2(µ-Cl)]2
(Nd-Cl ) 2.837(1), 2.841(1) Å): Marks, T. J .; Grynkewich, G. W. Inorg.
Chem. 1976, 15, 1302.
(36) Berg, D. J .; Gendron, R. A. L. Can. J . Chem. 2000, 78, 454.
(37) J in, Z.; Liu, Y.; Chen, W. Sci. Sin., Ser. B 1987, 1, 1.
(38) J eske, G.; Schock, L. E.; Swepston, P. N.; Schumann, H.; Marks,
T. J . J . Am. Chem. Soc. 1985, 107, 8103.
SiMe2NHtBu.9 The metrical features of the rhomboidal
Nd2Cl2 core (Nd(1)-Cl(1) ) 2.789(1) Å; Nd(1)-Cl(1_7)
) 2.862(1) Å; Nd(1)-Cl(1)-Nd(1) ) 105.95(3); Cl(1)-
Nd(1)-Cl(1_7) ) 74.05(3)°) indicate asymmetry in the
chloride bridges35 comparable to that observed in [Nd-
{N(SiMe3)2}2(THF)(µ-Cl)]2 (Nd-Cl ) 2.791(3) and 2.854-
(3) Å; Nd-Cl-Nd ) 106.3(1)°; Cl-Nd-Cl ) 73.66-
(10)°),36 [(η5-Cp)2Nd(THF)(µ-Cl)]2 (Nd-Cl ) 2.787(4) and
(39) Bogaert, S.; Chenal, T.; Mortreux, A.; Nowogrocki, G.; Lehmann,
C. W.; Carpentier, J .-F. Organometallics 2001, 20, 199.
(40) For the neutral parent complex (η5:η1-C5Me4SiMe2NtBu)Sm(η5-
C5Me4SiMe2NHtBu), see ref 6a.
(34) Von Zelewsky, A. Stereochemistry of Coordination Compounds;
Wiley: Chichester, U.K., 1996; p 78.

“Constrained Geometry” Group 3 Metal Complexes
Organometallics, Vol. 22, No. 22, 2003 4477
Ta ble 2. P olym er iza tion of MMA P r om oted by 2a ,
3, a n d 10a
Con clu sion
In summary, we have shown that alkane elimination
is a viable route toward new fluorenyl-based constrained-
geometry carbyl complexes of yttrium. On the other
hand, salt elimination reactions of yttrium and lantha-
num chlorides with 1 equiv of the dilithiated species of
linked fluorenyl-amido ligand 1a lead to chlorine-free,
ionic complexes that contain two chelating ligand units
per metal center. The latter are likely formed by
disproportionation of intermediary neutral chloro fluo-
renyl-amido complexes, a class of which only the
neodymium complex could be isolated in valuable yield.
One of the most striking features of these novel con-
strained-geometry complexes, in addition to their very
narrow FluCent-Ln-N bite angles, is the versatility of
the coordination mode of the fluorenyl ligand observed
in the solid state. In the four structurally characterized
rare-earth complexes reported in this paper, at least
three distinct bonding modes have been observed: η3-
and η5-symmetric modes involving carbon atoms of the
central Cp ring (8, 10) and an unusual η3-dissymmetric
mode involving carbon atoms of the central Cp and one
adjacent phenyl rings (2a , 9). Reduced hapticity (η3) of
the fluorenyl moiety in the carbyl complex has been
found to be associated with the coordination of extra
donor solvent molecules (THF), as compared to analo-
gous cyclopentadienyl-amido complexes, a phenomenon
that might account for the poor catalytic performances
observed in polymerization.
tacticityc
103Mw Mw/Mn mm mr rr
temp, yield,
b
b
compd conditions
°C
%
2a
2a
3
toluened
20
50
20
20
50
2
2
13
26
65
nde
nde
19
250
216
nde
nde
2.8
2.8
3.6
42 29 29
40 29 32
41 26 33
34 40 26
39 40 21
7
bulk
7
a
b
Conditions: [MMA]/[cat.] ) 500; reaction time 12 h. Average
weight molecular mass and polydispersity as determined by GPC.
c Determined by 1H NMR in CDCl3. As 0.5-1.0 M solutions.
d
e PMMA not soluble in THF.
reported: e.g., [Lu{ArN(CH2)3NAr}2]-[LuCl2(THF)5]+,41
and [(FluCMe2Cp)2Y]-[Li(Et2O)(THF)3]+.24 The mecha-
nistic pathway for the formation of complexes A such
as 6-9 remains unclear. Disproportionation of inter-
mediary species of type B appears as the most likely
hypothesis. However, in such cases, we see no obvious
reason to account for the instability of the latter neutral
chloro yttrium and lanthanum complexes as compared
to the fairly stable neodymium product (10).
P olym er ization Activity of Flu or en yl-Based CGC.
Effective polymerization of ethylene and polar mono-
mers, such as tert-butyl acrylate, with cyclopentadi-
enyl-amido yttrium carbyl and hydride CGC has been
reported by Okuda et al.5a,c We were therefore interested
in evaluating the polymerization ability of some of the
fluorenyl-amido complexes we prepared. Yttrium car-
byl 2a and its “hydrido” derivative 3 were found to be
inactive toward ethylene in the temperature range 20-
80 °C (1 atm of C2H4). The inactivity of 2a likely arises
from the initial presence of two THF molecules in the
coordination sphere of yttrium, as compared to the
active cyclopentadienyl analogue (C5Me4SiMe2NtBu)Y-
(CH2SiMe3)(THF), which contains only one coordinated
THF molecule.5c Despite the fact that the first THF
molecule in 2a dissociates rather quickly above room
temperature (vide supra), the remaining THF ligand
might block the “active site”. Dimeric neodymium
chloride 10, when activated with 1 equiv of LiCH-
(SiMe3)2,42 polymerizes ethylene with low activity (1.3
kg of PE/((mol of Nd) h atm) at 20 °C and 4 atm of C2H4)
to yield polyethylene with Tm ) 134 °C, Mn ) 140 000,
and Mw/Mn ) 2.46. Only traces of polyethylene were
obtained on using the in situ combinations 10/Mg-
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were performed
under a purified argon atmosphere using standard high-
vacuum Schlenk techniques or in a glovebox. Solvents were
freshly distilled from Na/benzophenone (THF, Et2O, DME) and
Na/K alloy (toluene, pentane) under nitrogen and degassed
thoroughly by freeze-thaw-vacuum cycles prior to use. Deu-
terated solvents (benzene-d6, toluene-d8, THF-d8; pyridine-d5
>99.5% D, Eurisotop) were vacuum-transferred from Na/K
alloy into storage tubes. YCl3(THF)3.5 and LaCl3(THF)1.5 were
obtained after repeated extraction of YCl3 and LaCl3 (Strem)
from THF. NdCl3(THF)2 was generously provided by Rhodia.
Y[N(SiHMe2)2]3(THF)2,30 Ln[N(SiMe3)2]3 (Ln ) Y, La),14g and
45
Y(CH2SiMe3)3(THF)2 were prepared by following literature
procedures. The ligands (3,6-tBu2C13H7)SiR2NHtBu (R ) Me,
1a ; R ) Ph, 1b) were provided by TotalFinaElf and recrystal-
lized from pentane prior to use. NMR spectra were recorded
on Bruker AC-200 and AC-300 spectrometers in Teflon-valved
NMR tubes. 1H and 13C chemical shifts are reported in ppm
vs SiMe4 and were determined by reference to the residual
solvent peaks. Assignment of signals was made from 1H-1H
COSY, 1H-13C HMQC, and HMBC NMR experiments. Cou-
pling constants are given in hertz. Elemental analyses were
performed by the Microanalytical Laboratory at the Institute
of Chemistry of Rennes and are the average of two independent
determinations.
(
n,sBu)2 (1:40)39 and 10/DIBALH/nBuLi (1:20:20)43 as
catalyst systems under similar conditions. Also, modest
performance was observed in the polymerization of
MMA (Table 2). Quite surprisingly, anionic lanthanum
complex 7 reacts smoothly with bulk MMA at room
temperature and 50 °C to give high-molecular-weight
atactic PMMA. The mechanism for MMA polymeriza-
tion with this complex remains unclear and might
involve initiation via insertion into either an La-
fluorenyl or La-amido bond.1i,44
[η3:η1-(3,6-tBu 2C13H6)SiMe2NtBu ]Y(CH2SiMe3)(THF)2 (2a).
(a ) NMR-Sca le Rea ction . An NMR tube was charged with
Y(CH2SiMe3)3(THF)2 (32 mg, 0.065 mmol) and 3,6-tBu2C13H7-
SiMe2NHtBu (1a ; 27 mg, 0.065 mmol). Benzene-d6 (ca. 0.6 mL)
was vacuum-transferred in at -196 °C, and the tube was
warmed to room temperature. Progress of the reaction was
monitored periodically by 1H NMR spectroscopy, which showed
selective formation of 2a (>98% vs ligand), with concomitant
(41) Roesky, P. W. Organometallics 2002, 21, 4756.
(42) Reaction of 10 and 1 equiv (vs Nd) of LiCH(SiMe3)2 in toluene
at room temperature proceeded with precipitation of a white solid,
assumed to be LiCl. Attempts to isolate analytically pure samples and
to grow crystals suitable for X-ray diffraction of the putative hydro-
carbyl complex [(3,6-tBu2C13H6)SiMe2NtBu]Nd(CH(SiMe3)2)(THF)x (red
gummy solid) were unsuccessful.
(43) Boisson, C.; Barbotin, F.; Spitz, R. In Progress and Development
in Catalytic Olefin Polymerization; Sano, T., Uozomi, T., Nakatani, H.,
Terano, M., Eds.; Technology and Education Publishers: Tokyo, 2000;
p 75.
(44) Giardello, M. A.; Yamamoto, Y.; Brard, L.; Marks, T. J . J . Am.
Chem. Soc. 1995, 117, 3276.
(45) Lappert, M. F.; Pearce, R. J . Chem. Soc., Chem. Commun. 1973,
126.

4478 Organometallics, Vol. 22, No. 22, 2003
Kirillov et al.
release of 1 equiv of SiMe4, in 37% conversion after 1 h and
50% after 3 h, reaching a plateau at 90% after 3 days, where
no more starting carbyl complex was detected (δ -0.71 (d, 2J YH
) 2.3, 6H, YCH2), 0.27 (s, 27H, SiCH3)).
bar) at 20 °C for 12 h to yield after similar workup a pale
yellow insoluble product with similar characteristics (30 mg,
31%). Anal. Calcd for C62H96N2O2Si2Y2: C, 65.59; H, 8.52; N,
2.47. Found: C, 63.85; H, 8.45; N, 2.49.46
[(3,6-tBu 2C13H6)SiMe2NtBu ]Li2(THF )3 (4). To a solution
of 1a (120 mg, 0.294 mmol) in THF (20 mL) at -40 °C was
added with stirring 2 equiv of nBuLi (0.37 mL of a 1.6 M
solution in hexane, 0.588 mmol). The reaction mixture was
warmed to room temperature and stirred for 8 h. Volatiles
were removed under vacuum to yield [(3,6-tBu2C13H6)SiMe2-
NtBu]Li2 as a bright orange powder (172 mg, 92%). Crystals
of 4 suitable for X-ray diffraction were grown from a THF/
pentane solution at -35 °C.
(b) P r ep a r a tive-Sca le Rea ction . YCl3 (338 mg, 1.73
mmol) was slurried in THF (15 mL) and stirred at 80 °C for 1
h. The solvent was removed in vacuo, and the solid residue
was suspended in pentane (20 mL). The suspension was cooled
to -78 °C, LiCH2SiMe3 (5.2 mL of a 1.0 M solution in pentane,
5.2 mmol) was added by syringe, and the suspension was
stirred at 0 °C for 2 h. The suspension was filtered, and the
white solid was extracted with pentane (2 × 10 mL). LiCl was
filtered off, and a solution of 1a (578 mg, 1.42 mmol) in pentane
(30 mL) was added at 0 °C. The reaction mixture was warmed
to room temperature and stirred for 30 h. The solution was
filtered and concentrated in vacuo. The crude product was
recrystallized from pentane at -35 °C to give pale yellow
crystals of 2a (0.63 g, 68%), which proved suitable for X-ray
diffraction. 1H NMR (C6D6, 200 MHz, 20 °C): δ 8.35 (d, 2H,
[(3,6-tBu 2C13H6)SiMe2NHtBu ]Li(DME) (5). To a solution
of 1a (100 mg, 0.245 mmol) in DME (20 mL) at -40 °C was
added with stirring 1 equiv of nBuLi (0.15 mL of a 1.6 M
solution in hexane, 0.245 mmol). The reaction mixture was
warmed to room temperature and stirred for 8 h. Volatiles
were removed under vacuum to give in quantitative yield [(3,6-
tBu2C13H6)SiMe2NHtBu]Li as an orange powder. Crystals of 5
suitable for X-ray diffraction were grown from a DME/pentane
solution at -35 °C.
3
4J HH ) 2.0, 4,5-H), 8.01 (d, 2H, J HH ) 8.3, 1,8-H), 7.50 (dd,
2H, J HH ) 2.0 and 8.3, 2,7-H), 3.06 (m, 8H, R-CH2 THF), 1.54
(s, 9H, NCCH3), 1.48 (s, 18H, CCH3(Flu)), 1.14 (m, 8H, â-CH2
THF), 0.89 (s, 6H, SiCH3), 0.24 (s, 9H, CH2SiCH3), -1.11 (d,
Sa lt Elim in a tion Rea ction betw een [(3,6-tBu 2C13H6)-
SiMe2NtBu ]Li2 (4) a n d YCl3(THF )3.5 (1:1). P r ep a r a tion of
[{(3,6-tBu 2C13H6)SiMe2NtBu }2Y]-[Li(THF )4]+ (6). To a solu-
tion of 1a (108 mg, 0.265 mmol) in Et2O (20 mL) at -10 °C
was added with stirring 2 equiv of nBuLi (0.33 mL of a 1.6 M
solution in hexane, 0.530 mmol). The reaction mixture was
warmed to room temperature and stirred for 8 h. To the
resulting orange solution cooled to -20 °C was added a
suspension of YCl3(THF)3.5 (previously prepared from 52 mg
(0.265 mmol) of YCl3) in Et2O (30 mL). The mixture was stirred
and warmed to room temperature; it turned yellow after 30-
40 min. The yellow solution was decanted from the precipitate,
volatiles were removed in vacuo, and the resulting residue was
washed with pentane (2 × 20 mL) to give a yellow powder (101
1
J YH ) 3.3, 2H, YCH2). H NMR (toluene-d8, 200 MHz, 20 °C):
4
3
δ 8.29 (d, 2H, J HH ) 1.4, 4,5-H), 7.94 (d, 2H, J HH ) 8.6, 1,8-
H), 7.42 (dd, 2H, J HH ) 1.4 and 8.6, 2,7-H), 3.03 (m, 8H, R-CH2,
THF) 1.49 (s, 9H, NCCH3), 1.45 (s, 18H, CCH3(Flu)), 1.17 (m,
8H, â-CH2, THF), 0.84 (s, 6H, SiCH3), 0.16 (s, 9H, CH2SiCH3),
-1.27 (d, J YH ) 3.1, 2H, YCH2). 1H NMR (toluene-d8, 300 MHz,
-70 °C, slow exchange): δ 8.51 (s, 1H, 4-H), 8.35 (s, 1H, 5-H),
3
3
8.12 (d, 1H, J HH ) 7.7, 1-H), 7.96 (d, 1H, J HH ) 7.7, 2-H),
3
3
7.90 (d, 1H, J HH ) 7.7, 8-H), 7.49 (d, 1H, J HH ) 7.7, 7-H),
3.45 (br s, 2H, R-CH2 THF), 3.19 (br s, 2H, R-CH2 THF), 1.70
(s, 9H, NCCH3), 1.57 (s, 18H, CCH3(Flu)), 1.07 (br s, 4H, â-CH2
THF), 0.99 (s, 3H, SiCH3), 0.78 (s, 3H, SiCH3), 0.44 (s, 9H,
CH2SiCH3), -0.59 (d, J YH ) 7.0, 1H, YCHH), -1.07 (d, J YH
)
7.0, 1H, YCHH). 13C{1H} NMR (benzene-d6, 75 MHz, 20 °C):
δ 141.9, 140.1, 130.9, 124.6, 118.5, 117.4, 82.9 (C-9), 70.3 (R-
THF), 55.1 (NCCH3), 37.1 (NCCH3), 35.9 (Flu-CCH3), 33.0
1
mg). H NMR indicated the presence of two species in a 1.4:1
ratio; 1H NMR(THF-d8, 200 MHz, 20 °C): major product, δ
7.89 (d, 2H, 4J HH ) 2.1, 4,5-H), 7.69 (d, 2H, 3J HH ) 8.6, 1,8-H),
6.90 (dd, 2H, J HH ) 2.1, 8.6, 2,7-H), 1.36 (s, 18H, CCH3(Flu)),
1.20 (s, 9H, NCCH3), 0.38 (s, 6H, SiCH3); minor product, δ 7.83
1
(Flu-CCH3), 30.6 (d, J Y-C ) 45.2, YCH2), 25.8 (â-THF), 6.8
(SiCH3), 5.2 (CH2SiCH3). Anal. Calcd for C39H66NO2Si2Y: C,
64.52; H, 9.16; N, 1.92. Found: C, 63.86; H, 9.32; N, 2.21.
NMR-Sca le Rea ction of Y(CH2SiMe3)3(THF )2 a n d (3,6-
tBu 2C13H7)SiP h 2NHtBu (1b). Gen er ation of [(3,6-tBu 2C13H6)-
SiP h 2NtBu ]Y(CH2SiMe3)(THF )x (2b). An NMR tube was
charged with Y(CH2SiMe3)3(THF)2 (39 mg, 0.079 mmol) and
1b (42 mg, 0.079 mmol). Benzene-d6 (ca. 0.6 mL) was con-
densed in at -196 °C, and the tube was warmed to 50 °C. The
progress of the reaction was monitored periodically by 1H NMR
spectroscopy. After 48 h at 50 °C, formation of 2b in 25%
conversion vs 1b (>98% selectivity), but with total exhaustion
of the initial yttrium carbyl, was observed. Prolonged heating
resulted in progressive decomposition of 2b to form unidenti-
fied, insoluble products. 1H NMR (benzene-d6, 200 MHz, 20
°C), selected signals for 2b: δ 8.40 (d, 2H, 4J HH ) 1.1, 4,5 -H),
8.05-7.96 (m, 4H, 1,2,7,8-H), 7.6-7.1 (m, SiPh2, overlapped
with SiPh2 protons in 1b), 3.42 (m, 8H, R-CH2, THF) 1.78 (s,
9H, NCCH3), 1.49 (s, 18H, CCH3(Flu)), 1.38 (m, 8H, â-CH2,
THF), 0.32 (s, 9H, CH2SiCH3), -0.82 (d, J YH ) 3.3, 2H, YCH2).
R ea ct ion of [(3,6-t Bu 2C13H6)SiMe2Nt Bu ]Y(CH 2SiMe3)-
(THF )2 (2a ) w ith H2 or P h SiH3. P r ep a r a tion of “{[(3,6-
tBu 2C13H6)SiMe2NtBu ]Y(H)(THF )}2” (3). Meth od A. To a
solution of 2a (100 mg, 0.137 mmol) in benzene (5 mL) was
added PhSiH3 (85 mL, 0.688 mmol) at 20 °C. The mixture was
stirred at this temperature for 1 h, over which period a yellow
precipitate formed. The latter was filtered, washed with
benzene (ca. 2 mL), and dried in vacuo to give a pale yellow
microcrystalline product insoluble in THF and hydrocarbons
(3; 70 mg, 90%).
4
3
(m, 2H, J HH ) 2.1, 4,5-H), 7.54 (d, 2H, J HH ) 8.6, 1,8-H),
6.84 (dd, 2H, J HH ) 2.1, 8.6, 2,7-H), 1.35 (s, 18H, CCH3(Flu)),
1.11 (s, 9H, NCCH3), 0.40 (s, 6H, SiCH3). The crude product
was recrystallized from Et2O/THF/pentane (ca. 0.5:1:3) to give
yellow crystals of 6 (88 mg, 25%). 1H NMR (THF-d8, 300 MHz,
4
3
20 °C): δ 7.94 (d, 2H, J HH ) 1.8, 4,5-H), 7.72 (d, 2H, J HH
)
8.3, 1,8-H), 7.13 (dd, 2H, J HH ) 1.8, 8.3, 2,7-H), 1.43 (s, 9H,
NCCH3), 1.36 (s, 18H, CCH3(Flu)), 0.27 (s, 6H, SiCH3). 13C-
{1H} NMR (THF-d8, 75 MHz, 20 °C): δ 144.6, 137.8, 133.7,
121.1 (C-1,8), 120.0 (C-2,7), 115.5 (C-4,5), 79.0 (C-9), 54.7
(NCCH3), 36.9 (NCCH3), 35.4 (Flu-CCH3), 33.2 (Flu-CCH3), 6.2
(SiCH3). Anal. Calcd for C70H110N2O4LiSi2Y: C, 69.86; H, 9.21;
N, 2.33. Found: C, 69.05; H, 8.96; N, 2.38.
Sa lt Elim in a tion Rea ction betw een [(3,6-tBu 2C13H6)-
SiMe2NtBu ]Li2 (4) a n d La Cl3(THF )1.5 (1:1). P r ep a r a tion
of [{(3,6-tBu 2C13H6)SiMe2NtBu }2La ]-[Li(THF )4]+ (7). The
same procedure as that described above was carried out from
LaCl3(THF)1.5 (previously prepared from 186 mg, 0.758 mmol
of LaCl3) and 1a (310 mg, 0.760 mmol) to give a yellow
1
microcrystalline solid (440 mg). The H NMR spectrum of this
crude product showed that it contains two species in a 1.2:1
ratio. 1H NMR (THF-d8, 200 MHz, 20 °C): major product, δ
4
7.93 (d, 2H, J HH ) 2.0, 4,5-H), 7.73 (dd, 2H, J HH ) 0.5, 8.6,
(46) Low carbon values were repetitively obtained. We ascribe this
problem to the presence of silicon, which is known to form noncom-
bustible SiC. Similar difficulty in obtaining satisfactory elemental
analyses for hydrido constrained-geometry or silicon-containing com-
plexes of group 3 metals has been encountered by other workers; see
refs 5b,c and: Mitchell, P.; Hajela, S.; Brookhart, S. K.; Hardcastle,
K. I.; Henling, L. M.; Bercaw, J . E. J . Am. Chem. Soc. 1996, 118, 1045.
Meth od B. A solution of 2a (125 mg, 0.172 mmol) in
benzene (5 mL) was exposed to a dihydrogen atmosphere (1

“Constrained Geometry” Group 3 Metal Complexes
Organometallics, Vol. 22, No. 22, 2003 4479
1,8-H), 6.94 (dd, 2H, J HH ) 2.1, 8.6, 2,7-H), 1.41 (s, 18H, CCH3-
(Flu)), 1.24 (s, 9H, NCCH3), 0.44 (s, 6H, SiCH3); minor product,
δ 7.83 (m, 2H, J HH ) 2.1, 4,5-H), 7.54 (d, 2H, J HH ) 8.6, 1,8-
squares refinement based on F2 (programs Shelxs-97 and
Shelxl-97).47 Many hydrogen atoms could be found from the
difference Fourier map. Carbon-bound hydrogen atoms were
placed at calculated positions and forced to ride on the attached
carbon atom. The hydrogen atom contributions were calculated
but not refined. All non-hydrogen atoms were refined with
anisotropic displacement parameters. The locations of the
largest peaks in the final difference Fourier map calculation
and the magnitude of the residual electron densities were of
no chemical significance (note that in 5 two peaks were
observed near the La atom with an electronic density of ca.
2.5 e Å-3; however, the distance being lower than the van der
Waals radii, these were not considered). The cell of 4 was found
to contain one molecule of crystallization of toluene and that
of 9 one toluene molecule and one THF molecule. Crystal data
and details of the data collection and structure refinement are
given in Table 1. Atomic coordinates, thermal parameters, and
complete listings of bond lengths and angles are available as
Supporting Information.
Typ ica l P r oced u r e for Eth ylen e P olym er iza tion . Tolu-
ene (50 mL) was introduced in a 300 mL glass reactor (TOP-
Industrie) equipped with a mechanical stirrer rotating at
speeds up to 1500 rpm. Toluene was saturated with ethylene
(Air Liquide, N35; 4 atm, kept constant via a back-pressure
regulator). At the same time, a mixture of chloroneodymium
complex 10 (163 mg; 0.248 mmol) and LiCH(SiMe3)2 (41 mg,
0.248 mmol) in toluene (10 mL) was stirred for 1 h at 20 °C.
The resulting pale green solution was then transferred via
syringe into the reactor with stirring. The ethylene flow rate
was monitored using a mass flowmeter (Aalborg, GFM17)
connected to a totalizing controller (KEP) which acts as a flow
rate integrator. The reaction was quenched by addition of 3
mL of a 10% HCl methanol solution to the mixture. The
resulting precipitate was filtered, washed with methanol, and
dried under vacuum.
Typ ica l P r oced u r e for MMA P olym er iza tion . In a
Schlenk tube containing a magnetic stir bar and solid recrys-
tallized complex 7 (20 mg, 0.016 mmol) (in 10-15 mL of
toluene for reactions carried out in solution), methyl meth-
acrylate (ACROS, previously dried from CaH2; 1.0 mL, 9.3
mmol) was added by syringe and vigorous stirring at the
appropriate temperature was immediately started. After 12
h, the Schlenk tube was opened to air and acetone (30 mL)
was added to quench the reaction and dissolve the polymer
formed. The polymer was precipitated by adding methanol (ca.
200 mL), filtered, washed twice with methanol (30 mL), and
dried in vacuo. The number-average molecular weight Mn and
the weight-average molecular weight Mw were determined by
GPC in THF using universal calibration relative to polystyrene
standards. The polymer microstructure was determined by 1H
NMR in CDCl3.
4
H), 6.84 (dd, 2H, J HH ) 2.1, 8.6, 2,7-H), 1.35 (s, 18H, CCH3-
(Flu)), 1.16 (s, 9H, NCCH3), 0.42 (s, 6H, SiCH3). Recrystalli-
zation of the crude product from a 1:4 THF/pentane mixture
1
gave pale orange crystals of 7 (380 mg, 81%). H NMR (THF-
d8, 300 MHz, 20 °C): δ 7.82 (d, 2H, 4J HH ) 1.8, 4,5-H), 7.53 (d,
3
2H, J HH ) 8.2, 1,8-H), 6.84 (dd, 2H, J HH ) 1.8, 8.2, 2,7-H),
1.35 (s, 18H, CCH3(Flu)), 1.12 (s, 18H, NCCH3), 0.40 (s, 6H,
SiCH3). 13C{1H} NMR (THF-d8, 75 MHz, 20 °C): δ 144.4, 131.4,
127.7, 119.5 (C-1,8), 118.5 (C-2,7), 114.9 (C-4,5), 84.4 (C-9),
50.7 (NCCH3), 35.5 (Flu-CCH3), 35.4 (NCCH3), 34.1 (Flu-
CCH3), 6.9 (SiCH3). Anal. Calcd for C70H110N2O4LiSi2La: C,
67.49; H, 8.90; N, 2.25. Found: C, 67.31; H, 8.37; N, 2.40.
Sa lt Elim in a tion Rea ction betw een [(3,6-tBu 2C13H6)-
SiMe2NtBu ]Li2 (4) a n d La Cl3(THF )1.5 (1:1). Syn th esis of
[η3:η1-{(3,6-tBu 2-C13H6)SiMe2NtBu }2La ]-[Li(Et2O)2]+ (8). To
a solution of 1a (340 mg, 0.834 mmol) in Et2O (30 mL) at -10
n
°C was added with stirring 2 equiv of BuLi (1.0 mL of a 1.6
M solution in hexane, 1.66 mmol). The reaction mixture was
warmed to ambient temperature and stirred for 8 h. To the
resulting orange solution cooled to -35 °C in the glovebox was
added LaCl3(THF)1.5 (295 mg, 0.834 mmol). The mixture was
stirred and warmed to room temperature; it turned orange-
yellow after 20 min. After 12 h, the yellow solution was
decanted from the precipitate and concentrated in vacuo and
hexane (ca. 2 mL) was added. Orange-yellow crystals of 8,
which proved suitable for X-ray diffraction, were recovered
after 10 h (300 mg, 33%). 1H NMR (THF-d8, 200 MHz, 60 °C):
4
δ 7.79 (d, 4H, J HH ) 2.0, 4,5-H), 7.25 (d, 4H, J HH ) 8.4, 1,8-
H), 7.00 (dd, 4H, J HH ) 2.0, 8.4, 2,7-H), 3.36 (q, 8H, CH2OCH3),
1.51 (s, 18H, NCCH3), 1.36 (s, 36H, CCH3(Flu)), 1.08 (t, 12H,
CH2OCH3), 0.17 (s, 12H, SiCH3). 13C{1H} NMR (THF-d8, 75
MHz, 60 °C): δ 144.7, 134.7, 119.5, 114.7 (C-1,8), 130.5 (C-
10,13), 117.5 (C-11,12), 81.9 (C-9), 54.9 (NCCH3), 35.5 (Flu-
CCH3), 37.0 (NCCH3), 34.7 (Flu-CCH3), 7.7 (SiCH3). Anal.
Calcd for C62H98N2O2Si2LaLi: C, 67.36; H, 8.93; N, 2.53.
Found: C, 68.23; H, 8.54; N, 2.45.
Sa lt Elim in a tion Rea ction betw een [(3,6-tBu 2C13H6)-
SiMe2Nt Bu ]Li2 (4) a n d Nd Cl3(THF )2 (1:1). Syn th esis of
[η3 :η1 -{(3 ,6 -t B u 2 C 1 3 H 6 )S i M e 2 N t B u }2 N d (T H F )]-[L i -
(THF )4]+ (9) a n d [η5:η1-{(3,6-tBu 2C13H6)SiMe2NtBu }Nd (µ-
Cl)(THF )]2 (10). The same procedure as that described above
for the preparation of 6 was carried out from NdCl3(THF)2 (245
mg, 0.623 mmol) and 1a (253 mg, 0.623 mmol) to yield a yellow
1
microcrystalline solid (390 mg). The H NMR spectrum of this
product displayed very broad resonances and proved uninfor-
mative. Crystallization of the crude product from a 1:5:3 THF/
toluene/pentane solution gave golden yellow crystals of 9,
which proved suitable for X-ray diffraction (40 mg, 10%). Anal.
Calcd for C85H134LiN2O6Si2Nd (9‚THF‚(toluene)): C, 68.64; H,
9.08; N, 1.88. Calcd for C74H118LiN2O5Si2Nd (9): C, 67.17; H,
8.99; N, 2.12. Found: C, 67.60; H, 8.74; N, 2.41. In another
experiment, the crude product was recrystallized from a 5:1
Et2O/hexane solution to afford green crystals of neutral
complex 10, some of which were also found suitable for X-ray
Ack n ow led gm en t. We gratefully thank TotalFi-
naElf for supporting this research (postdoctoral fellow-
ship to E.K.). We are most grateful to Mr. V. Bellia
(AtoFina) for technical support and to Mr. S. Foley and
Prof. R. F. J ordan (University of Chicago) for GPC
analysis of the PE sample.
crystallographic studies (150 mg, 38%). Anal. Calcd for C62H94
-
Cl2N2O2Si2Nd2 (10): C, 56.63; H, 7.20; N, 2.13; Cl, 5.39.
Found: C, 57.01; H, 7.61; N, 1.82; Cl, 4.73.
Su p p or tin g In for m a tion Ava ila ble: Details of structure
determinations of complexes 2a , 4, 5, and 8-10, as well as
that of free ligand 1a , including final coordinates, thermal
parameters, bond distances, and bond angles. This material
is available free of charge via the Internet at http://pubs.acs.org.
Cr ysta l Str u ctu r e Deter m in a tion s of Com p lexes 2a ,
4, 5, a n d 8-10. Suitable single crystals of all investigated
compounds were mounted onto glass fibers using the “oil-drop”
method. All diffraction data were collected at 100-120 K using
a NONIUS Kappa CCD diffractometer with graphite-mono-
chromated Mo KR radiation (λ ) 0.710 73 Å). A combination
of ω and æ scans was carried out to obtain at least a unique
data set. Crystal structures were solved by means of the
Patterson method, and remaining atoms were located from
difference Fourier synthesis followed by full-matrix least-
OM0304210
(47) (a) Sheldrick, G. M. SHELXS-97, Program for the Determina-
tion of Crystal Structures; University of Go¨ttingen, Go¨ttingen, Ger-
many, 1997. (b) Sheldrick, G. M., SHELXL-97, Program for the
Refinement of Crystal Structures; University of Go¨ttingen, Go¨ttingen,
Germany, 1997.