Lanthanide(II) complexes bearing linked cyclopentadienyl-anilido ligands: Synthesis, structures, and one-electron-transfer and ethylene polymerization reactions

Article abstract of DOI:10.1021/om010261x

Reactions of Ln[N(SiMe₃)₂]₂(thf)₂ Ln = Sm, Yb) with 1 equiv of (C₅Me₄H)SiMe₂NHPh afforded the first linked cyclopentadienyl-anilido (or amido) lanthanide(II) complexes Me₂-Si(C₅Me₄)(NPh)Ln(thf)_x (1, Ln = Yb, x = 3; 2, Ln = Sm, x = 0-1) in 75-84% isolated yields. Recrystallization of 1 from toluene/hexane yielded the less solvated complex [Me₂Si(C₅Me₄)-(NPh)Yb(thf)]₂ (1′). Complex 1 adopts a monomeric structure containing one chelating Cp-anilido ligand and three thf ligands, while 1′ forms a dimeric structure through an intermolecular Yb-Ph π-interaction. Reaction of 1 or 1′ with azobenzene gave the binuclear Yb(III) complex Me₂Si(C₅Me₄)(NPh)Yb(thf)(μ,η² : η³-N₂Ph₂)Yb (NPh)(C₅Me₂ (3), which contains a cis-oriented azobenze dianion unit bonding in a η³ fashion to one Yb atom and in a η² fashion to the other Yb atom. Reaction of 1 with 1 equiv of fluorenone gave the corresponding Yb(III) ketyl complex Me₂Si(C₅Me₄)(NPh)Yb(thf)₂ (OC₁₃H₈) (4) in 75% isolated yield. Treatment of 4 with hexane/ether led to formation of the pinacolate complex [Me₂Si-(C₅Me₄)(NPh)Yb(thf)₂ (μ-O₂C₂₆H₁₆ (5), in which the pinacolate unit is arranged in a gauche conformation. Dissolving of 5 in THF cleaved the central C-C bond of the pinacolate unit in 5 and regenerated 4 quantitatively. The Sm(II) complex 2 showed moderate activity (44.8 kg of polymer (mol of Sm)^-1 h^-1) for the polymerization of ethylene under 1 atm at room temperature, yielding linear polyethylene with M_n = 7.26 × 10⁵ and M_w/M_n = 1.58.

Full text of DOI:10.1021/om010261x

Organometallics 2001, 20, 3323-3328
3323
La n th a n id e(II) Com p lexes Bea r in g Lin k ed
Cyclop en ta d ien yl-An ilid o Liga n d s: Syn th esis,
Str u ctu r es, a n d On e-Electr on -Tr a n sfer a n d Eth ylen e
P olym er iza tion Rea ction s
Zhaomin Hou,* Take-aki Koizumi,† Masayoshi Nishiura,† and Yasuo Wakatsuki*
Organometallic Chemistry Laboratory, RIKEN (The Institute of Physical and
Chemical Research), Hirosawa 2-1, Wako, Saitama 351-0198, J apan
Received March 29, 2001
Reactions of Ln[N(SiMe3)2]2(thf)2 (Ln ) Sm, Yb) with 1 equiv of (C5Me4H)SiMe2NHPh
afforded the first linked cyclopentadienyl-anilido (or amido) lanthanide(II) complexes Me2-
Si(C5Me4)(NPh)Ln(thf)x (1, Ln ) Yb, x ) 3; 2, Ln ) Sm, x ) 0-1) in 75-84% isolated yields.
Recrystallization of 1 from toluene/hexane yielded the less solvated complex [Me2Si(C5Me4)-
(NPh)Yb(thf)]2 (1′). Complex 1 adopts a monomeric structure containing one chelating Cp-
anilido ligand and three thf ligands, while 1′ forms a dimeric structure through an
“intermolecular” Yb-Ph π-interaction. Reaction of 1 or 1′ with azobenzene gave the binuclear
Yb(III) complex Me2Si(C5Me4)(NPh)Yb(thf)(µ,η2: η3-N2Ph2)Yb(NPh)(C5Me4)SiMe2 (3), which
contains a cis-oriented azobenzene dianion unit bonding in a η3 fashion to one Yb atom and
in a η2 fashion to the other Yb atom. Reaction of 1 with 1 equiv of fluorenone gave the
corresponding Yb(III) ketyl complex Me2Si(C5Me4)(NPh)Yb(thf)2(OC13H8) (4) in 75% isolated
yield. Treatment of 4 with hexane/ether led to formation of the pinacolate complex [Me2Si-
(C5Me4)(NPh)Yb(thf)]2(µ-O2C26H16) (5), in which the pinacolate unit is arranged in a gauche
conformation. Dissolving of 5 in THF cleaved the central C-C bond of the pinacolate unit
in 5 and regenerated 4 quantitatively. The Sm(II) complex 2 showed moderate activity (44.8
kg of polymer (mol of Sm)-1 h-1) for the polymerization of ethylene under 1 atm at room
temperature, yielding linear polyethylene with Mn ) 7.26 × 105 and Mw/Mn ) 1.58.
In tr od u ction
are of great interest in view of the unique chemistry
that has been developed with divalent lanthanide
complexes bearing other ligand systems,3 such a lan-
thanide(II) complex has not been reported to date.4
During our recent studies on lanthanide(II) complexes
bearing mixed (unlinked) C5Me5/ER ligands (ER ) a
monodentate anionic ligand such as an aryloxide, thio-
late, amido, or phosphido group),5 we found that the
mixed-ligand-supported lanthanide(II) complexes, par-
ticularly those of samarium(II), could serve as a unique
catalytic system for polymerization reactions.5c These
Lanthanide complexes bearing silylene-linked cyclo-
pentadienyl-amido ligands (e.g., [Me2Si(C5Me4)NtBu]2-
)
have received much current interest, because of their
electronically more unsaturated and sterically more
accessible properties as compared to those of the met-
allocene analogues.1,2 These types of lanthanide com-
plexes reported so far in the literature have, however,
been limited solely to those in the +3 oxidation state.
Although analogous complexes in the +2 oxidation state
† Special Postdoctoral Researcher under the Basic Science Program
of RIKEN.
(3) Reviews on the chemistry and application of low-valent lan-
thanides: (a) Evans, W. J . Coord. Chem. Rev. 2000, 207-207, 263. (b)
Hou, Z.; Wakatsuki, Y. Top. Organomet. Chem. 1999, 2, 233. (c) Boffa,
L. S.; Novak, B. M. Tetrahedron 1997, 53, 15367. (d) Molander, G. A.;
Harris, C. R. Chem. Rev. 1996, 96, 307. (e) Edelmann, F. T. In
Comprehensive Organometallic Chemistry II; Abel, E. W., Stone, F.
G. A., Wilkinson, G., Lappert, M. F., Eds.; Pergamon: Oxford, U.K.,
1995; Vol. 4, Chapter 2. (f) Schaverien, C. J . Adv. Organomet. Chem.
1994, 36, 283. (g) Evans, W. J . Polyhedron 1987, 6, 803.
(4) An ytterbium(II) complex bearing linked cyclopentadienyl-siloxo
ligand was recently reported. See: Trifonov, A. A.; Kirillov, E. N.;
Fisher, A.; Edelmann, F. T.; Bochkarev, M. N. Chem. Commun. 1999,
2203.
(5) (a) Hou, Z. J . Synth. Org. Chem. J pn. 2001, 59, 82. (b) Hou, Z.;
Kaita, S.; Wakatsuki, Y. Pure Appl. Chem. 2001, 73, 291. (c) Hou, Z.;
Zhang, Y.; Tezuka, H.; Xie, P.; Tardif, O.; Koizumi, T.; Yamazaki, H.;
Wakatsuki, Y. J . Am. Chem. Soc. 2000, 122, 10533. (d) Hou, Z.;
Wakatsuki, Y. J . Alloys Compd. 2000, 203-204, 75. (e) Zhang, Y.; Hou,
Z.; Wakatsuki, Y. Macromolecules 1999, 32, 939. (f) Hou, Z.; Tezuka,
H.; Zhang, Y.; Yamazaki, H.; Wakatsuki, Y. Macromolecules 1998, 31,
8650. (g) Zhang, Y.; Hou, Z.; Wakatsuki, Y. Bull. Chem. Soc. J pn. 1998,
71, 1381. (h) Hou, Z.; Zhang, Y.; Yoshimura, T.; Wakatsuki, Y.
Organometallics 1997, 16, 2963.
(1) For recent reviews on lanthanide (including Sc and Y) and group
4 metal complexes bearing linked cyclopentadienyl-amido ligands,
see: (a) Okuda, J .; Eberle, T. In Metallocenes; Togni, A., Halterman,
R. L., Eds.; Wiley-VCH: Weinheim, Germany, 1998; Vol. 1, p 415. (b)
McKnight, A. L.; Waymouth, R. M. Chem. Rev. 1998, 98, 2587.
(2) (a) Arndt, S.; Voth, P.; Spaniol, T. P.; Okuda, J . Organometallics
2000, 19, 4690. (b) Hultzsh, K. C.; Voth, P.; Beckerle, K.; Spaniol, T.
P.; Okuda, J . Organometallics 2000, 19, 228. (c) Hultzsch, K. C.;
Spaniol, T. S.; Okuda, J . Angew. Chem., Int. Ed. 1999, 38, 227. (d)
Arrendondo, V. M.; Tian, S.; McDonald, F. E.; Marks, T. J . J . Am.
Chem. Soc. 1999, 121, 3633. (e) Tian, S.; Arrendondo, V. M.; Stern, C.
L.; Marks, T. J . Organometallics 1999, 18, 2568. (f) Hultzsch, K. C.;
Spaniol, T. P.; Okuda, J . Organometallics 1998, 17, 485. (g) Hultzsch,
K. C.; Spaniol, T. P.; Okuda, J . Organometallics 1997, 16, 4845. (h)
Mu, Y.; Piers, W. E.; MacQuarrie, D. C.; Zaworotko, M. J .; Young, V.
G., J r. Organometallics 1996, 15, 2720. (i) Mu, Y.; Piers, W. E.;
MacDonald, M.-A.; Zaworotko, M. J . Can. J . Chem. 1995, 73, 2233. (j)
Shapiro, P. J .; Cotter, W. D.; Schaefer, W. P.; Labinger, J . A.; Bercaw,
J . E. J . Am. Chem. Soc. 1994, 116, 4623. (k) Shapiro, P. J .; Bunel, E.
E.; Schaefer, W. P.; Bercaw, J . E. Organometallics 1990, 9, 867. (l)
Piers, W. E.; Shapiro, P. J .; Bunel, E. E.; W. D.; Bercaw, J . E. Synlett
1990, 74.
10.1021/om010261x CCC: $20.00 © 2001 American Chemical Society
Publication on Web 06/28/2001

3324 Organometallics, Vol. 20, No. 15, 2001
Hou et al.
findings have now promoted us to examine the analo-
gous lanthanide(II) complexes bearing linked cyclopen-
tadienyl-monodentate anionic ligand systems, since
such complexes could be anticipated to offer a ligand
environment similar to that of the C5Me5/ER-ligated
analogues but would not suffer from the ligand redis-
tribution problems that usually occur with the unlinked,
mixed-ligand systems.5h In this paper, we report the
synthesis and structures of the first linked cyclopenta-
dienyl-anilido lanthanide(II) complexes, Me2Si(C5Me4)-
(NPh)Ln(thf)x (1, Ln ) Yb, x ) 3; 1′, Ln ) Yb, x ) 1; 2,
Ln ) Sm, x ) 0-1), as well as some preliminary results
that demonstrate the utility of these new complexes as
one-electron-reducing agents and ethylene polymeriza-
tion precatalysts.
F igu r e 1. ORTEP drawing of 1 with 30% thermal el-
lipsoids. Selected bond lengths (Å) and angles (deg): Yb-
(1)-O(1), 2.464(8); Yb(1)-O(2), 2.393(8); Yb(1)-O(3), 2.418-
(8); Yb(1)-N(1), 2.359(8); Yb(1)-C(1), 2.52(1); Yb(1)-C(2),
2.66(1); Yb(1)-C(3), 2.74(1); Yb(1)-C(4), 2.74(1); Yb(1)-
C(5), 2.57(1); Yb(1)-Cp(centroid), 2.366(13); N(1)-Yb(1)-
Cp(centroid), 94.7(11); N(1)-Si(1)-C(1), 102.1(5).
Resu lts a n d Discu ssion
Syn th esis a n d Str u ctu r es of Sa m a r iu m (II) a n d
Ytter biu m (II) Com p lexes. The conventional meta-
thetical approaches that have been successfully used for
the synthesis of lanthanide(III) complexes bearing
linked cyclopentadienyl-amido ligands2f-l could not be
straightforwardly extended to the synthesis of the
lanthanide(II) analogues.6 However, the acid-base re-
actions between lanthanide(II) bis(silylamide) com-
pounds and the aniline ligand (C5Me4H)SiMe2NHPh
proved to be a useful route to the corresponding cyclo-
pentadienyl-anilido lanthanide(II) complexes.7,8 Thus,
the reaction of Yb[N(SiMe3)2]2(thf)2 with 1 equiv of (C5-
Me4H)SiMe2NHPh in THF at room temperature oc-
curred smoothly to give the Yb(II) complex Me2Si(C5-
Me4)(NPh)Yb(thf)3 (1) in 75% isolated yield, with
quantitative release of HN(SiMe3)2 (eq 1). An analogous
An X-ray analysis showed that 1 adopts a monomeric
structure, in which the Yb(II) center is bonded to one
chelating Cp-anilido ligand and three thf terminal
ligands (Figure 1). The Yb-C(Cp) bond distances in 1
range from 2.52 to 2.74 Å, with an average value (2.65
Å) being almost the same as that found in the Yb(II)
metallocene complex (C5Me5)2Yb(thf) (2.66 Å).10 The
Yb-Cp(centroid) (2.37(1) Å) and Yb-N (2.359(8) Å) bond
distances in 1 are respectively longer than those found
in the Cp-amido ytterbium(III) complexes Me2Si(C5-
Me4)(NtBu)Yb(CH(SiMe3)2) (Yb-Cp(centroid) ) 2.254 Å;
Yb-N ) 2.164(4) Å)2e and [Me2Si(C5Me4)(NtBu)Yb(µ-
H)]2 (Yb-Cp(centroid) ) 2.33(1), 2.32(1) Å; Yb-N )
2.231(7), 2.197(8) Å),2a which is in accordance with the
difference in ion size between Yb(II) and Yb(III).11 The
N-Yb-Cp(centroid) angle in 1 (95(1)°) is somewhat
smaller than that found in the C5Me5/N(SiMe3)2-ligated
Yb(II) complex (C5Me5)Yb(N(SiMe3)2)(C5Me5)Na(thf)3
(115°)5c and those in the linked Cp-amido Yb(III)
complexes Me2Si(C5Me4)(NtBu)Yb(CH(SiMe3)2) (100.2-
(1)°)2e and [Me2Si(C5Me4)(NtBu)Yb(µ-H)]2 (99(1)°).2a
Complex 1′ adopts a dimeric structure via an “inter-
molecular” interaction between the Yb atom and the Ph
group, and the whole molecule possesses a crystal-
lographic 2-fold axis symmetry (eq 2 and Figure 2). The
Yb-Ph distances range from 2.80(1) to 3.05(1) Å, which
reaction of Sm[N(SiMe3)2]2(thf)2 with (C5Me4H)SiMe2-
NHPh afforded the corresponding Sm(II) complex Me2-
Si(C5Me4)(NPh)Sm(thf)x in 84% yield (2, x ) 0-1 on the
basis of elemental analysis) (eq 1).9 Two of the three
thf ligands in 1 could be removed by recrystallization
of 1 from toluene/hexane, which gave [Me2Si(C5Me4)-
(NPh)Yb(thf)]2 (1′) in almost quantitative yield (eq 2).
(6) The reactions between LnI2(thf)2 (Ln ) Sm, Yb) and Li2[Me2Si-
(C5Me4)NtBu] did not give the expected salt-free, cyclopentadienyl-
amido lanthanide(II) complexes. In the case of Sm, an unidentified
yellow product, possibly a Sm(III) compound, was obtained, while in
the case of Yb, incorporation of LiI seemed to take place.
(7) An acid-base approach for the synthesis of indenyl-derived
ytterbocene(II) complexes has been recently reported. See: Klimpel,
M. G.; Herrmann, W. A.; Anwander, R. Organometallics 2000, 19, 4666.
(8) Similar reactions of Ln[N(SiMe3)2]2(thf)2 with the less protonic
alkylamine ligand (C5Me4H)SiMe2NHtBu did not give the correspond-
ing cyclopentadienyl-amido complexes but instead yielded the met-
allocene-type complexes Ln(C5Me4SiMe2NHtBu)2 (Ln ) Sm, Yb).
(9) Complex 2 might adopt a dimeric structure similar to that of 1′,
although
a single-crystal suitable for X-ray analysis was not yet
obtained. The lower THF content of the Sm(II) complex 2 as compared
to that of the Yb(II) complex 1 might be due to the larger ion radius of
Sm(II), which would thus more easily lead to formation of a further
assembled structure through “intermolecular” metal-ligand interac-
tions.
(10) Tilley, T. D.; Andersen, R. A.; Spencer, B.; Ruben, H.; Zalkin,
A.; Templeton, D. H. Inorg. Chem. 1980, 19, 2999.
(11) Yb(II) is ca. 0.155 Å larger in radius than Yb(III) when both
have the same coordination number. See: Shannon, R. D. Acta
Crystallogr., Sect. A 1976, 32, 751.

Lanthanide(II) Complexes with Cp-Anilido Ligands
Organometallics, Vol. 20, No. 15, 2001 3325
F igu r e 2. ORTEP drawing of 1′ with 30% thermal
ellipsoids. Selected bond lengths (Å) and angles (deg): Yb-
(1)-N(1), 2.393(9); Yb(1)-O(1), 2.405(8); Yb(1)-C(1), 2.577-
(11); Yb(1)-C(2), 2.682(10); Yb(1)-C(3), 2.803(11); Yb(1)-
C(4), 2.768(11); Yb(1)-C(5), 2.610(12); Yb(1)-C(12)*,
3.099(9); Yb(1)-C(13)*, 2.941(12); Yb(1)-C(14)*, 2.798(14);
Yb(1)-C(15)*, 2.796(13); Yb(1)-C(16)*, 2.916(11); Yb(1)-
F igu r e 3. ORTEP drawing of 3 with 30% thermal el-
lipsoids. The lattice azobenzene is omitted for clarity.
Selected bond lengths (Å) and angles (deg): Yb(1)‚‚‚Yb(2),
3.6919(4); Yb(1)-O(1), 2.355(5); Yb(1)-N(1), 2.339(5); Yb-
(1)-N(2), 2.271(5); Yb(1)-N(3), 2.283(5); Yb(2)-N(1), 2.281-
(5); Yb(2)-N(2), 2.367(5); Yb(2)-N(4), 2.189(6); Yb(1)-
C(13), 2.500(7); Yb(1)-C(14), 2.546(7); Yb(1)-C(15), 2.635(8);
Yb(1)-C(16), 2.658(7); Yb(1)-C(17), 2.600(6); Yb(2)-C(30),
2.529(6); Yb(2)-C(31), 2.588(6); Yb(2)-C(32), 2.678(7); Yb-
(2)-C(33), 2.718(6); Yb(2)-C(34), 2.641(6); Yb(1)-C(1),
2.747(6); Yb(2)-C(25), 2.748(6); N(1)-N(2), 1.468(7); Yb-
(1)-Cp13-17(centroid), 2.287(6); Yb(2)-Cp30-34(centroid),
2.335(9); Yb(1)-N(1)-Yb(2), 106.1(2); Yb(1)-N(2)-Yb(2),
105.5(2); N(3)-Yb(1)-Cp13-17(centroid), 99.2(2); N(4)-Yb-
(2)-Cp30-34(centroid), 96.8(2); N(3)-Si(1)-C(13), 98.4(3);
N(4)-Si(2)-C(30), 95.6(3).
C(17)*, 3.046(10); Yb(1)-Cp1-5(centroid), 2.406; Cp1-5
-
(centroid)-Yb(1)-N(1), 95.16; Cp1-5(centroid)-Yb(1)-O(1),
109.67; N(1)-Si(1)-C(1), 100.6(5).
are in agreement with the interactions between a
lanthanide ion and a neutral π donor ligand found in
other complexes.12 Other structural data for 1′ can be
compared with those of 1 (Figures 1 and 2).
On e-Electr on -Tr a n sfer Rea ction s. The reaction of
1 or 2 mol of 1 or 1′ with 1 mol of azobenzene in toluene
afforded the same 2:1 product 3 (eq 3), which is in
contrast with the previously reported analogous reac-
tions of lanthanide(II) complexes bearing other ligand
systems such as (C5Me5)2Sm(thf)2,13a (C5H5)2Yb(thf),13a
and Sm[HB(3,5-Me2pz)3]2 (pz ) pyrazolyl).13b Single
Ph interaction, Yb1 is bonded to a thf ligand. All these
structural features are in sharp contrast with those
found in the samarocene(III)-azobenzene complex [(C5-
Me5)2Sm]2(µ,η1:η1-N2Ph2) and the half-metallocene Sm-
(III) and Yb(III) complexes [(C5Me5)(thf)Sm]2[µ,η2:η2-
N2Ph2]2 and [(C5H5)(thf)Yb]2[µ,η2:η2-N2Ph2]2.13a
The reaction of 1 with 1 equiv of fluorenone gave the
corresponding Yb(III) ketyl complex 4 in 75% isolated
yield (Scheme 1 and Figure 4). Treatment of 4 with
hexane/ether removed one of the two thf ligands in 4
and led to the dimerization of the radical unit to give
the pinacolate complex 5 (Scheme 1 and Figure 5).
Dissolution of 5 in THF cleaved the central C-C bond
of the pinacolate unit in 5 and regenerated the ketyl
species 4 quantitatively. These reactions are closely
analogous to those reported for the bis(aryloxide)- or bis-
(silylamido)-supported lanthanide(III) ketyl/pinacolate
complexes14 but are different from those for the lan-
thanidocene(III) ketyl complexes (C5Me5)2Ln(OC13H8)-
(thf) (Ln ) Sm, Yb). The latter remained unchanged
under similar conditions.14a It is also noteworthy that
the pinacolate unit in 5 is arranged in a gauche
conformation (O1-C35-C48-O2 torsion angle -59(1)°)
(Figure 3), in sharp contrast with the trans form found
in the bis(aryloxide)- or bis(silylamido)-supported pina-
colate complexes.14 Complex 5 represents a rare ex-
ample of a non-trans-oriented 1,2-diolate complex.
crystals suitable for diffraction studies were obtained
in the form of 3‚0.5N2Ph2 from the reaction of 1 with 1
equiv of azobenzene. An X-ray analysis established that
3 is a dimeric Cp-anilido-chelated Yb(III) complex with
a bridging azobenzene dianion ligand ([PhNNPh]2-
)
(Figure 3). The azobenzene unit adopts a cis form, which
is bonded in a η3 fashion to one Yb atom (Yb1) and in a
η2 fashion to the other (Yb2). The Yb-N distances to
the bridging azobenzene unit are highly asymmetric.
The Yb1-N2 bond (2.271(5) Å) is much shorter than
the Yb1-N1 bond (2.339(5) Å), while the Yb2-N2 bond
(2.367(5) Å) is much longer than the Yb2-N1 bond
(2.281(5) Å). An interaction between Yb2 and the Ph
group (C25) of the Yb1-bonded anilido ligand was also
observed (Yb2-C25 ) 2.748(6) Å). Instead of such a Yb-
(12) For a review on lanthanide complexes with neutral π donor
ligands, see: Deacon, G. B.; Shen, Q. J . Organomet. Chem. 1996, 506,
1.
(13) (a) Evans, W. J .; Drummond, D. K.; Chamberlain, L. R.;
Doemons, R. J .; Bott, S. G.; Zhang, H.; Atwood, J . L. J . Am. Chem.
Soc. 1988, 110, 4983. (b) Takats, J .; Zhang, X. W.; Day, V. W.;
Eberspacher, T. A. Organometallics 1993, 12, 4286.
(14) (a) Hou, Z.; Fujita, A.; Zhang, Y.; Miyano, T.; Yamazaki, H.;
Wakatsuki, Y. J . Am. Chem. Soc. 1998, 120, 754. (b) Hou, Z.; Miyano,
T.; Yamazaki, H.; Wakatsuki, Y. J . Am. Chem. Soc. 1995, 117, 4421.

3326 Organometallics, Vol. 20, No. 15, 2001
Hou et al.
Sch em e 1
F igu r e 4. ORTEP drawing of 4 with 30% thermal el-
lipsoids. Selected bond lengths (Å) and angles (deg): Yb-
(1)-N(1), 2.28(2); Yb(1)-C(1), 2.59(3); Yb(1)-C(2), 2.64(2);
Yb(1)-C(3), 2.70(3); Yb(1)-C(4), 2.68(3); Yb(1)-C(5), 2.61-
(3); Yb(1)-O(1), 2.15(2); Yb(1)-O(2), 2.37(2); Yb(1)-O(3),
2.38(2); O(1)-C(18), 1.31(3); Yb(1)-Cp(centroid), 2.34(5);
N(1)-Yb(1)-Cp(centroid), 96(1); Yb(1)-O(1)-C(18), 170-
(2); N(1)-Si(1)-C(1), 99(1).
F igu r e 5. ORTEP drawing of 5 with 30% thermal el-
lipsoids. The lattice solvent is omitted for clarity. Selected
bond lengths (Å) and angles (deg): Yb(1)-O(1), 2.035(8);
Yb(1)-O(3), 2.29(1); Yb(2)-O(2), 2.043(8); Yb(2)-O(4),
2.27(1); Yb(1)-N(1), 2.21(1); Yb(2)-N(2), 2.24(1); Yb(1)-
C(1), 2.51(1); Yb(1)-C(2), 2.57(1); Yb(1)-C(3), 2.67(1); Yb-
(1)-C(4), 2.67(1); Yb(1)-C(5), 2.56(1); Yb(2)-C(18), 2.50(1);
Yb(2)-C(19), 2.57(1); Yb(2)-C(20), 2.66(1); Yb(2)-C(21),
2.71(2); Yb(2)-C(22), 2.62(2); O(1)-C(35), 1.40(1); O(2)-
C(48), 1.41(1); C(35)-C(48), 1.59(2); Yb(1)-Cp1-5(centroid),
The Sm(II) complex 2 also underwent electron-
transfer reactions with azobenzene and fluorenone, but
single crystals of the resulting products suitable for
X-ray analysis were not yet obtained.
2.30(2); Yb(2)-Cp18-22(centroid), 2.32(2); N(1)-Yb(1)-Cp1-5
-
(centroid), 98.6(6); N(2)-Yb(2)-Cp18-22(centroid), 97.6(6);
Yb(1)-O(1)-C(35), 156.3(8); Yb(2)-O(2)-C(48), 148.9(7);
N(1)-Si(1)-C(1), 96.6(5); N(2)-Si(2)-C(18), 96.2(6); O(1)-
C(35)-C(48)-O(2), -59(1).
Eth ylen e P olym er iza tion . The Yb(II) complex 1 or
1′ showed no activity for ethylene polymerization in
toluene at room temperature under 1 atm, which is in
agreement with the results previously reported for other
Yb(II) complexes.4,5c In contrast, the more reducing Sm-
(II) complex 2 showed a moderate activity (44.8 kg of
polymer (mol of Sm)-1 h-1) for the polymerization of
ethylene under the same conditions, which yielded
linear polyethylene with high molecular weight (Mn )
7.26 × 105) and narrow polydispersity (Mw/Mn ) 1.58).
These polymerization data can be compared with those
reported for the C5Me5/NHAr-ligated Sm(II) complex
In summary, we have shown that the silylene-linked
cyclopentadienyl-anilido unit [C5Me4SiMe2NPh]2- can
serve as a useful ancillary ligand system for the divalent
lanthanides. The results presented in this paper dem-
onstrate that these types of lanthanide(II) complexes
can constitute a new family of one-electron-reducing
agents and polymerization precatalysts.
Exp er im en ta l Section
t
[(C5Me5)Sm(NHAr)(C5Me5)K(thf)2]n (Ar ) C6H2 Bu3-
2,4,6; 57.6 kg of polymer (mol of Sm)-1 h-1, Mn ) 5.0 ×
105, Mw/Mn ) 2.9)5c but are in contrast with those for
the samarocene(II) complex (C5Me5)2Sm(THF) (5.06 kg
of polymer (mol of Sm)-1 h-1, Mn < 2.5 × 104, Mw/Mn )
2.28)5c,15 and for the bis(silylamido) Sm(II) complex Sm-
[N(SiMe3)2]2(thf)2, which was inert toward ethylene
under the same conditions.5c
Gen er a l Meth od s. All reactions were carried out under a
dry and oxygen-free argon atmosphere by using Schlenk
techniques or under a nitrogen atmosphere in an MBraun
glovebox. The argon was purified by being passed through a
Dryclean column (4A molecular sieves, Nikka Seiko Co.) and
a Gasclean GC-XR column (Nikka Seiko Co.). The nitrogen in
the glovebox was constantly circulated through a copper/
molecular sieves (4A) catalyst unit. The oxygen and moisture
concentrations in the glovebox atmosphere were monitored by
an O2/H2O Combi-Analyzer (MBraun) to ensure both were
always below 1 ppm. Samples for NMR spectroscopic measure-
ments were prepared in the glovebox by use of J . Young valve
(15) (a) Ihara, E.; Nodono, M.; Katsura, K.; Adachi, Y.; Yasuda, H.;
Yamagashira, M.; Hashimoto, H.; Kanehisa, N.; Kai, Y. Organome-
tallics 1998, 17, 3975. (b) Evans, W. J .; Keyer, R. A.; Ziller, J . W. J .
Organomet. Chem. 1990, 394, 87.

Lanthanide(II) Complexes with Cp-Anilido Ligands
Organometallics, Vol. 20, No. 15, 2001 3327
Ta ble 1. Su m m a r y of Cr ysta l Da ta
1
1′
3‚0.5N2Ph2
4
5‚Et2O
formula
fw
cryst syst
space group
a (Å)
C
29H47NO3Yb
C42H62N2O2Si2Yb2
1029.20
monoclinic
C2/c (No. 15)
17.855(5)
C56H69N5OSi2Yb2
1230.44
triclinic
P1h (No. 2)
12.1982(9)
12.8501(9)
19.509(1)
103.685(1)
93.698(1)
114.185(1)
2665.1(3)
2
35.75
1232.00
1.533
13 801
8657 (x ) 2)
595
C38H47NO3SiYb
766.92
orthorhombic
Pbca (No. 61)
18.599(6)
C72H88N2O5Si2Yb
1463.75
triclinic
P1h (No. 2)
13.457(1)
14.421(1)
19.964(1)
111.647(1)
98.953(2)
96.177(2)
3499.3(4)
2
27.38
1484.00
1.389
18 588
10359 (x ) 2)
703
658.82
monoclinic
P21/c (No. 14)
12.401(3)
13.045(3)
19.345(4)
b (Å)
c (Å)
9.204(3)
26.354(8)
41.820(8)
9.081(2)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
108.31(3)
99.629(6)
2971(1)
4
32.16
1344.00
1.473
8752
4270(2)
4
44.44
2048.00
1.601
16 133
6081 (x ) 2)
232
7063(2)
8
27.17
3120.00
1.422
6862
µ (cm-1
F(000)
)
Dcalcd (g cm-3
)
no. of unique rflns
no. of rflns with (I > xσ(I))
no. of variables
2652 (x ) 2)
316
4039 (x ) 3)
397
R
Rw
0.043
0.042
0.069
0.129
0.040
0.045
0.069
0.131
0.074
0.094
NMR tubes (Wilmad 528-J Y). 1H NMR spectra were recorded
on a J NM-EX 270 (FT, 270 MHz) spectrometer. Elemental
analyses were carried out by the Chemical Analysis Laboratory
of RIKEN. Solvents were distilled from sodium/benzophenone
ketyl, degassed by the freeze-thaw method (three times), and
dried over fresh Na chips in the glovebox. (C5Me4H)SiMe2Cl,
BuLi, and PhNH2 were obtained from Aldrich. LnI2(thf)2 16 and
Ln[N(SiMe3)2]2(thf)2 17 (Ln ) Sm, Yb) were prepared according
to literature methods.
was concentrated under reduced pressure. Layering of hexane
yielded brown crystals of 1′ (71 mg, 91%). H NMR (22.5 °C,
C6D6): δ 6.81 (br s, 4 H, C6H5-o,m), 5.82 (s, 1 H, C6H5-p), 3.56
1
(br s, 12 H, THF), 2.56 (s, 6 H, C5Me4), 2.34 (s, 6 H, C5Me4),
1
1.40 (br s, 12 H, THF), 1.08 (s, 6 H, SiMe2). In THF-d8, the H
NMR spectrum of 1′ was identical with that of 1. Anal. Calcd
for C42H62N2O2Si2Yb2: C, 49.01; H, 6.07; N, 2.72. Found: 48.89;
H, 6.02; N, 2.74.
Me2Si(C5Me4)(NP h )Sm (th f)x (2; x ) 0-1). To a THF
solution (20 mL) of Sm[N(SiMe3)2]2(THF)2 (500 mg, 0.815
mmol) was added a THF solution (2 mL) of C5Me4HSiMe2-
NHPh (221 mg, 0.815 mmol) at room temperature. The
mixture turned immediately from purple to dark brown. After
this mixture was stirred for 3 days, the solvent was removed
under reduced pressure. The resulting brown powder was
washed with hexane and dried in vacuo to give 2 (312 mg,
(C5Me4H)SiMe2NHP h .18 To a THF solution (20 mL) of (C5-
Me4H)SiMe2Cl (500 mg, 2.33 mmol) was added a THF solution
(10 mL) of PhNHLi (250 mg, 2.52 mmol), which was prepared
by reaction of BuLi with 1 equiv of PhNH2 in THF. The
reaction mixture was stirred at room temperature for 24 h.
After removal of the solvent under reduced pressure, the
residue was extracted with hexane. Evaporation of hexane
gave (C5Me4H)SiMe2NHPh as a pale yellow oil (600 mg, 95%).
1H NMR (22.5 °C, C6D6): δ 7.14 (t, 2 H, J ) 7.2 Hz, C6H5-m),
6.82 (t, 1 H, J ) 7.2 Hz, C6H5-p), 6.58 (d, 2 H, J ) 7.2 Hz,
C6H5-o), 3.07 (s, 1 H, NH), 3.04 (s, 1 H, C5Me4H), 1.89 (s, 6 H,
C5Me4H), 1.79 (s, 6 H, C5Me4H), 0.06 (s, 6 H, SiMe2).
1
84% based on x ) 0.5). H NMR (22.5 °C, THF-d8): δ 6.01 (br
s, 3 H, C6H5-m,p), 4.36 (d, J ) 7.15 Hz, 2 H, C6H5-o), 2.96 (s,
3 H, C5Me4), 2.70 (s, 3 H, C5Me4), 1.42 (s, 3 H, C5Me4), -0.11
(s, 3 H, C5Me4), -0.67 (s, 3 H, SiMe2), -1.47 (s, 3 H, SiMe2).
Anal. Calcd for C17H23NSiSm (x ) 0): C, 48.64; H, 5.52; N,
3.34. Calcd for C19H27NO0.5SiSm (x ) 0.5): C, 50.06; H, 5.97;
N, 3.07. Calcd for C21H31NOSiSm (x ) 1): C, 51.27; H, 6.35;
N, 2.85.; Found: 49.49; H, 6.40; N, 3.02.
Me2Si(C5Me4)(NP h )Yb(th f)3 (1). To a THF solution (20
mL) of Yb[N(SiMe3)2]2(thf)2 (1.00 g, 1.57 mmol) was added a
THF solution (2 mL) of C5Me4HSiMe2NHPh (341 mg, 1.57
mmol) at room temperature. The mixture turned immediately
from orange to reddish brown. After this mixture was stirred
for 1 day, the solvent was removed under reduced pressure.
The resulting orange powder was washed with hexane and
then dissolved in THF. After reduction of the solution volume
under reduced pressure, hexane was layered to give orange
crystals of 1 (776 mg, 75%). A reaction in toluene was not as
Me2Si(C5Me4)(NP h )Yb(th f)(µ,η2:η3-P h NNP h )Yb(NP h )-
(C5Me4)SiMe2 (3). To a toluene solution (2 mL) of 1 (150 mg,
0.228 mmol) was added azobenzene (42 mg, 0.228 mmol) at
room temperature. The solution color turned from dark blue
to dark brown in 30 min. After this mixture was stirred for 2
h, the solvent was removed under reduced pressure. The
resulting dark brown solid was washed with hexane and then
dissolved in toluene. Concentration of the solution under
reduced pressure deposited reddish green crystals of 3‚0.5N2-
Ph2 (88 mg, 63% based on 1).19 Anal. Calcd for C56H69N5OSi2-
Yb2 (3‚0.5N2Ph2): C, 54.66; H, 5.65; N, 5.69. Found: 54.74;
H, 5.79; N, 5.46. A similar reaction of azobenzene with 2 equiv
of 1 afforded azobenzene-free 3 in 75% yield.
Me2Si(C5Me4)(NP h )Yb(OC13H8)(th f)2 (4). To a toluene
solution (5 mL) of 1 (360 mg, 0.568 mmol) was added a toluene
solution (1 mL) of 9-fluorenone (170 mg, 0.568 mmol) at room
temperature. The reaction mixture changed immediately from
dark blue to deep purple. After this mixture was stirred for 2
h, the solvent was removed under reduced pressure. The
resulting dark brown solid was washed with hexane and then
dissolved in THF. After reduction of the solution volume under
reduced pressure, hexane was layered to give dark purple
1
clean as that in THF. H NMR (22.5 °C, C6D6): δ 6.76 (br s, 4
H, C6H5-o,m), 5.77 (s, 1 H, C6H5-p), 3.64 (br s, 12 H, THF),
2.47 (s, 6 H, C5Me4), 2.27 (s, 6 H, C5Me4), 1.44 (br s, 12 H,
THF), 1.01 (s, 6 H, SiMe2). 1H NMR (22.5 °C, THF-d8): δ 6.68
(t, J ) 7.15 Hz, 2 H, C6H5-m), 6.17 (d, J ) 7.15 Hz, 2 H, C6H5-
o), 5.95 (t, J ) 7.15 Hz, 1 H, C6H5-p), 2.01 (s, 6 H, C5Me4),
1.99 (s, 6 H, C5Me4), 0.46 (s, 6 H, SiMe2). Anal. Calcd for C29H47
-
NO3SiYb: C, 52.86; H, 7.19; N, 2.12. Found: 52.37; H, 7.18;
N, 2.08.
[Me2Si(C5Me4)(NP h )Yb(th f)]2 (1′). Dissolution of 1 (100
mg) in toluene gave a dark blue solution (the color change
could be caused by the change in THF coordination), which
(16) Watson, P. L.; Tulip, T. H.; Williams, I. Organometallics 1990,
9, 1999.
(17) Evans, W. J .; Drummond, D. K.; Zhang, H.; Atwood, L. Inorg.
Chem. 1988, 27, 575.
(18) Stevens, J . C.; Timmers, F. J .; Wilson, D. R.; Schmidt, G. F.;
Nickias, P. N.; Rosen, R. K.; Knight, G. W.; Lai, S. (Dow). Eur. Pat.
Appl. 0 416 815 A2, 1991.
(19) The 1H NMR spectra of 3-5 did not offer any structural
information, owing to the strong paramagnetic influence of the Yb-
(III) ion and/or the ketyl radical species.

3328 Organometallics, Vol. 20, No. 15, 2001
Hou et al.
crystals of 4, which after being dried under vacuum for 30 min
afforded “4-THF” (301 mg, 75%).19 Anal. Calcd for C34H39NO2-
SiYb (4-THF): C, 58.77; H, 5.66; N, 2.02. Found: C, 58.70; H,
5.95; N, 1.84.
[Me2Si(C5Me4)(NP h )Yb(th f)]2(µ-O2C26H16) (5). Into a di-
ethyl ether solution (1 mL) of “4-THF” (100 mg, 0.144 mmol)
was slowly layered 5 mL of hexane. After 24 h, orange crystals
of 5‚OEt2 (95 mg, 95%) were deposited. Similar treatment of
4 with Et2O/hexane also gave 5‚OEt2.19 Anal. Calcd for
performed at 20 °C on a Bruker SMART APEX diffractometer
with a CCD area detector, using graphite-monochromated Mo
KR radiation (λ ) 0.710 69 Å). The determination of crystal
class and unit cell parameters was carried out by the SMART
program package.20 The raw frame data were processed using
SAINT21 and SADABS22 to yield the reflection data file. Data
collection for 4 was performed at 20 °C on a Rigaku RAXIS
CS imaging plate diffractometer with graphite-monochromated
Mo KR radiation (λ ) 0.710 70 Å). All structures were solved
by using the teXsan software package. Refinements were
performed anisotropically for all non-hydrogen atoms by the
full-matrix least-squares method. Hydrogen atoms were placed
at the calculated positions and were included in the structure
calculation without further refinement of the parameters. The
residual electron densities were of no chemical significance.
Crystal data and processing parameters are summarized in
Table 1.
C
72H88N2O5Si2Yb2 (5‚OEt2): C, 59.07; H, 6.06; N, 1.91.
Found: 59.15; H, 6.22; N, 1.83.
P olym er iza tion of Eth ylen e. In the glovebox, 2 (23 mg,
0.05 mmol), a magnetic stir bar, and toluene (15 mL) were
placed in a 100 mL three-neck flask. The flask was taken
outside, set in a water bath (25 °C), and then connected to a
Schlenk line, a well-purged ethylene line, and a mercury-
sealed stopper. Introduction of ethylene resulted in immediate
formation (precipitation) of polyethylene. The mixture was
stirred for 10 min, during which a slightly positive ethylene
pressure was maintained by the stopper. MeOH (20 mL) was
added. The resultant mixture was poured into 300 mL of
MeOH in a 1 L beaker and then stirred to further precipitate
the polymer product. After filtration, the polymer product was
dried under vacuum in an oven (80 °C) overnight, yielding 370
mg of polyethylene. The molecular weight (against polystyrene
standard) and polydispersity of the polymer were measured
by gel permeation chromatography (GPC) at 135 °C using
o-dichlorobenzene as an eluent.
Ack n ow led gm en t. This work was partly supported
by a grant-in-aid from the Ministry of Education,
Culture, Sports, Science and Technology of J apan.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, thermal parameters, and bond distances and
angles for 1, 1′, and 3-5. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM010261X
X-r a y Cr ysta llogr a ph ic Stu d ies. Crystals for X-ray analy-
ses were obtained as described in the preparations. The
crystals were manipulated in the glovebox under a microscope
mounted on the glovebox window and were sealed in thin-
walled glass capillaries. Data collections for 1, 1′, 3, and 5 were
(20) SMART Software Users Guide, version 4.21; Bruker AXS, Inc.,
Madison, WI, 1997.
(21) SAINT+, Version 6.02; Bruker AXS, Inc., Madison, WI, 1999.
(22) Sheldrick, G. M. SADABS; Bruker AXS, Inc., Madison, WI,
1997.