Sterically hindered lanthanide allyl complexes and their use as single-component catalysts for the polymerization of methyl methacrylate and ε-caprolactone

Article abstract of DOI:10.1021/om0499097

The reaction of KL³ (L³ = 1,3-C₃H ₃(SiMe₃)₂) with NdI₃(THF) _3.5 affords two products, L³NdI₂(THF) _1.25 and (L³)₂NdI(THF)₂ (1). The latter has been crystailographically characterized; it has a distorted trigonal-bipyramidal structure with the THF ligands in trans position. The reaction of YCl₃ with 2 equiv of the ansa-bis(allyl) ligand K ₂[3-(C₃H₃SiMe₃-1) ₂SiPh₂] in tetrahydrofuran followed by recrystallization from diethyl ether gives [Y{3-(η³-C₃H ₃SiMe_3- 1)₂SiPh_2}2{μ-K}(THF) _0.5(Et₂O)_1.5]_∞ (2) as a bright orange solid. Reaction of Cp″₂LnCl₂Li(THF) ₂ (Cp″ = 1,3-C₅H₃(SiMe₃₎₂); Ln = Y or Sm) with [K₂{3-(n³-C₃H ₃SiMe₃-1)₂SiMe₂] in THF leads to ligand redistribution to give [Li(OEt₂)(THF)₃][Ln{3- (η³C₃H₃SiMe₃-1) ₂SiMe_2}2] (3, Ln = Y; 4, Ln = Sm). The identity of 3 was confirmed by single-crystal X-ray diffraction. Reaction of Cp″₂YCl₂Li(THF)₂ with [K ₂{3-(η³-C₃H₃SiMe ₃-1)₂SiPh₂] affords 2, while Cp″₂SmCl₂Li(THF)₂ and [K ₂{3-(η³-C₃H₃SiMe ₃-1)₂SiPh₂] give a red crystalline solid, identified by single-crystal X-ray analysis as the mono-Cp complex [Cp″Sm{3-(η³-C₃H₃SiMe ₃-1)₂SiPh₂}(μ-Cl)Li(THF)₃}] (5). Above 50 °C complexes 1 as well as (L³)₂LnCl(THF) (7) and (L³)₂YCl (8) initiate the rapid polymerization of ε-caprolactone. The anionic complexes 2, 3, 4, and [Y{3-(η³- C₃H_3- SiMe₃-1)SiMe_2}2{μ-K(THF)} ·(THF)_n]_∞ (6) are very active for both ε-caprolactone and methyl methacrylate polymerization at room temperature. The stereoselectivity is dependent on the solvent and the countercation, with lithium salts of 3 and 4 in THF producing syndiorich poly(methyl methacrylate).

Full text of DOI:10.1021/om0499097

2972
Organometallics 2004, 23, 2972-2979
Ster ica lly Hin d er ed La n th a n id e Allyl Com p lexes a n d
Th eir Use a s Sin gle-Com p on en t Ca ta lysts for th e
P olym er iza tion of Meth yl Meth a cr yla te a n d
E-Ca p r ola cton e
Timothy J . Woodman, Mark Schormann, David L. Hughes, and
Manfred Bochmann*
Wolfson Materials and Catalysis Center, School of Chemical Sciences,
University of East Anglia, Norwich, NR4 7TJ , U.K.
Received February 3, 2004
The reaction of KL3 (L3 ) 1,3-C3H3(SiMe3)2) with NdI3(THF)3.5 affords two products,
L3NdI2(THF)1.25 and (L3)2NdI(THF)2 (1). The latter has been crystallographically character-
ized; it has a distorted trigonal-bipyramidal structure with the THF ligands in trans position.
The reaction of YCl3 with 2 equiv of the ansa-bis(allyl) ligand K2[3-(C3H3SiMe3-1)2SiPh2] in
tetrahydrofuran followed by recrystallization from diethyl ether gives [Y{3-(η3-C3H3SiMe3-
1)2SiPh2}2{µ-K}(THF)0.5(Et2O)1.5]∞ (2) as a bright orange solid. Reaction of Cp′′2LnCl2Li(THF)2
(Cp′′ ) 1,3-C5H3(SiMe3)2); Ln ) Y or Sm) with [K2{3-(η3-C3H3SiMe3-1)2SiMe2] in THF leads
to ligand redistribution to give [Li(OEt2)(THF)3][Ln{3-(η3-C3H3SiMe3-1)2SiMe2}2] (3, Ln )
Y; 4, Ln ) Sm). The identity of 3 was confirmed by single-crystal X-ray diffraction. Reaction
of Cp′′2YCl2Li(THF)2 with [K2{3-(η3-C3H3SiMe3-1)2SiPh2] affords 2, while Cp′′2SmCl2Li(THF)2
and [K2{3-(η3-C3H3SiMe3-1)2SiPh2] give a red crystalline solid, identified by single-crystal
X-ray analysis as the mono-Cp complex [Cp′′Sm{3-(η3-C3H3SiMe3-1)2SiPh2}(µ-Cl)Li(THF)3}]
(5). Above 50 °C complexes 1 as well as (L3)2LnCl(THF) (7) and (L3)2YCl (8) initiate the
rapid polymerization of ꢀ-caprolactone. The anionic complexes 2, 3, 4, and [Y{3-(η3-C3H3-
SiMe3-1)SiMe2}2{µ-K(THF)}‚(THF)n]∞ (6) are very active for both ꢀ-caprolactone and methyl
methacrylate polymerization at room temperature. The stereoselectivity is dependent on
the solvent and the countercation, with lithium salts of 3 and 4 in THF producing syndio-
rich poly(methyl methacrylate).
In tr od u ction
acrylates (Cp ) C5Me5, Ln ) Y, Sm, R ) Me),5 alkyl
isocyanates (Cp ) C5Me5, Ln ) La, R ) CH(SiMe3)2),6
ꢀ-caprolactone (Cp ) C5Me5, Ln ) Sm, R ) Me)7 and
Organometallic complexes of the lanthanide metals
have been shown to be extremely versatile as catalysts
for a wide range of polymerizations, of both polar1 and
nonpolar monomers.2 The most commonly studied sys-
tems have traditionally been those derived from the
cyclopentadienyl ligand; for instance, Cp2LnR (R ) H,
alkyl) complexes are excellent single-component cata-
lysts for the polymerization of ethylene (Cp ) C5Me5,
Ln ) La, Nd, R ) H),3 1-alkenes (Cp2 ) rac-Me2Si(2-
SiMe3-4-CMe3C5H2)2, Ln ) Y, R ) H),2b alkyl meth-
acrylates (Cp ) C5Me5, Ln ) Sm, R ) H),4 alkyl
t
styrene (Cp ) BuCp, Ln ) Pr, Nd, Gd, R ) Me).6,8
Catalysts derived from allyl lanthanide complexes are
less well-known; notable exceptions are the use of
neodymium and lanthanum complexes as stereospecific
butadiene polymerization catalysts9 and the recent use
of samarium and ytterbium complexes for the polym-
erization of methyl methacrylate.10 Sterically demand-
ing silyl substituents allow the isolation of stable
homoleptic allyl complexes of first-row transition metals,
whereas the compounds M(C3H5)n are either thermally
* Corresponding author. E-mail: m.bochmann@uea.ac.uk.
(1) (a) Yasuda, H.; Yamamoto, H.; Yokota, K.; Miyake, S.; Naka-
mura, A. J . Am. Chem. Soc. 1992, 114, 4908. (b) Yamashita, M.;
Takernoto, Y.; Ihara, E.; Yasuda, H. Macromolecules 1996, 29, 1798.
(c) Giardello, M. A.; Yamamoto, Y.; Brard, L.; Marks, T. J . J . Am. Chem.
Soc. 1995, 117, 3276.
(2) (a) J eske, G.; Lauke, H.; Mauermann, H.; Swepston, P. N.;
Schumann, H.; Marks, T. J . J . Am. Chem. Soc. 1985, 107, 8091. (b)
Coughlin, E. B.; Bercaw, J . E. J . Am. Chem. Soc. 1992, 114, 7606. (c)
Burger, B. J .; Thompson, M. E.; Cotter, D. W.; Bercaw, J . E. J . Am.
Chem. Soc. 1990, 112, 1566. (d) Watson, P. L.; Parshall, G. W. Acc.
Chem. Res. 1985, 18, 51. (e) Hultzsch, K. C.; Voth, P.; Beckerle, K.;
Spaniol, T. P.; Okuda, J . Organometallics 2000, 19, 228. (f) Evans, W.
J .; DeCoster, D. M.; Greaves, J . Organometallics 1996, 15, 3210. (g)
Edelmann, F. Top. Curr. Chem. 1996, 179, 247.
(5) (a) Ihara, E.; Morimoto, M.; Yasuda, H. Macromolecules 1995,
28, 7886. (b) Suchoparek, M.; Spvacek, J . Macromolecules 1993, 26,
102.
(6) Tanaka, K.; Furo, M.; Ihara, E.; Yasuda, H. J . Polym. Sci. Polym.
Chem. 2001, 39, 1382.
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1798.
(8) Yang, M.; Chan, C.; Shen, Z. Polym. J . 1990, 22, 919.
(9) (a) Taube, R.; Windisch, H.; Maiwald, S.; Hemling, H.; Schu-
mann, H. J . Organomet. Chem. 1996, 513, 49. (b) Taube, R.; Maiwald,
S.; Sieler, J . J . Organomet. Chem. 2001, 621, 327. (c) Taube, R.;
Windisch, H.; Hemling, H.; Schumann, H. J . Organomet. Chem. 1998,
555, 201. (d) Taube, R.; Windisch, H.; Go¨rlitz, F. H.; Schumann, H. J .
Organomet. Chem. 1993, 445, 85. (e) Maiwald, S.; Taube, R.; Hemling,
H.; Schumann, H. J . Organomet. Chem. 1998, 552, 195.
(10) Ihara, E.; Koyama, K.; Yasuda, H.; Kanehisa, N.; Kai, Y. J .
Organomet. Chem. 1999, 574, 40.
(3) J eske, G.; Schock, L. E.; Swepston, P. N.; Schumann, H.; Marks,
T. J . J . Am. Chem. Soc. 1985, 107, 8103.
(4) Yasuda, H. J . Organomet. Chem. 2002, 647, 128.
10.1021/om0499097 CCC: $27.50 © 2004 American Chemical Society
Publication on Web 05/05/2004

Sterically Hindered Lanthanide Allyl Complexes
Organometallics, Vol. 23, No. 12, 2004 2973
Ch a r t 1
unstable (M ) Co, V, Ni)11 or not known (M ) Fe, Mn).
Thus the 1,3-bis(trimethylsilyl)allyl ligand (Chart 1,
ligand L3)12 has been used to prepare the complexes
M(L3)2 (M ) Co,13 Ni,13 Fe,14 and Cr14), with the iron
and chromium complexes being stable to sublimation
at relatively high temperatures (ca. 60-80 °C). Recently
some Zr(III) and Ti(III) ethene and propene polymeri-
zation catalysts containing the 1,3-bis(tert-butyldi-
methylsilyl)allyl ligand have been reported.15 Lappert
et al. have used the ansa-bis(allyl) ligand [Me2Si(CHCH-
CHSiMe3)2]2- (L4) to prepare the complexes M(L4)2 (M
) Zr, Hf); the zirconium complex polymerizes ethene
in the presence of methylalumoxane (MAO).16 The
samarium(II) complexes (1,3-C3H3R2)2Sm(THF)2 (R )
Ph, SiMe3) have been reported, although they were
not fully characterized.10 We have recently described
complexes such as Y(L1)3 and Y(L2)3, (L3)2LnCl(THF)n
(Ln ) Y, n ) 0; Ln ) La, n ) 1), the mono-allyl
compound (L3)NdI2(THF)1.25, and the structurally char-
acterized “ate” complex (L3)2ScCl2Li(THF)2.17 With the
ansa-bis(allyl) ligand L4 we unexpectedly obtained
the lanthanate complexes [Ln(L4)2{µ-K(THF)}‚(THF)n]∞
(Ln ) La, n ) 0.5; Ln ) Y, n ) 1; Ln ) Sc, n ) 1),
[Nd(L4)2{µ-K}]∞, and [Li(OEt2)4][Sm(L4)2].18 The lan-
thanum complex features potassium ions playing an
important structural role as bridging atoms by means
of π and agostic interactions. This bridging role of
K+ was also seen in the first structurally charac-
terized samarium(II) allyl complex [Sm(L3)3{µ-
K(THF)2}]2, where the potassium atoms allow the
formation of a K2Sm2 tetrametallic ring structure.19
These “ate” complexes initiate the polymerization of
methyl methacrylate with very high activities. We
report here further synthetic and structural studies on
this class of allyl complexes.
F igu r e 1. Molecular structure of one of the two indepen-
dent molecules of 1, showing the atomic numbering scheme.
Thermal ellipsoids are drawn at 50% probability. Hydrogen
atoms are omitted for clarity.
Resu lts a n d Discu ssion
The reaction of NdI3(THF)3.5 with KL3 leads to two
products, the less soluble mono-allyl complex (L3)NdI2-
17
(THF)1.25 and the bis-allyl (L3)2NdI(THF)n (1) (eq 1);
the latter was mentioned in a preliminary communica-
tion.19 During the course of this work we have now been
able to obtain crystals of 1 suitable for X-ray crystal-
lography, by recrystallization from light petroleum at
- 20 °C. There are two discrete essentially identical
molecules of 1 in the crystal structure, one of which is
depicted in Figure 1, with selected bond lengths and
interatomic distances collected in Table 1.
(11) Wilke, G.; Bogdanovic, B.; Hardt, P.; Heimbach, P.; Keim, W.;
Kroner, M.; Oberkirch, W.; Tanaka, K.; Walter, D. Angew. Chem., Int.
Ed. Engl. 1966, 5, 151.
(12) Fraenkl, G.; Chow, A.; Winchester, W. R. J . Am. Chem. Soc.
1990, 112, 1382.
(13) Garratt, S.; Unpublished results, University of East Anglia.
2001.
(14) Smith, J . D.; Hanusa, T. P.; Young, J r., V. G. J . Am. Chem.
Soc. 2001, 123, 6455.
(15) Ray, B.; Neyroud, T. G.; Kapon, M.; Eichen, Y.; Eisen, M. S.
Organometallics 2001, 20, 3044.
(16) Ferna´ndez-Gala´n, R.; Hitchcock, P. B.; Lappert, M. F.; Antinolo,
A.; Rodr´ıguez, A. M. J . Chem. Soc., Dalton Trans. 2000, 1743.
(17) Woodman, T. J .; Schorman, M.; Bochmann, M. Isr. J . Chem.
2002, 42, 283.
(18) Woodman, T. J .; Schorman, M.; Bochmann, M. Organometallics
2003, 22, 2938.
(19) Woodman, T. J .; Schorman, M.; Hughes, D. L.; Bochmann, M.
Organometallics 2003, 22, 3028.
The coordination environment of the neodymium
atom is comprised of the two η3-allyl ligands, the iodide,
and the two molecules of THF. The neodymium-carbon
bond distances lie in the range 2.671(6)-2.781(6) Å, with
an average of 2.73 Å (molecule 1) and 2.72 Å (molecule
2). These values compare closely with those in previ-
ously reported complexes; for instance in [{η3-C3H5}2-
NdCl(THF)2]2‚2THF the Nd-C distances are in the
range 2.674(5)-2.748(5) Å, with an average of 2.717 Å.9e
This implies that the bulky silyl substituents of the allyl
ligands in the current example have little effect on the
bond distances. The Nd-O(THF) distances are in the
range 2.512(4)-2.519(4) Å and, as such, are shorter than
in previously described complexes, e.g., [{η3-C3H5}2-

2974 Organometallics, Vol. 23, No. 12, 2004
Woodman et al.
(THF)n]∞ and [Li(OEt2)4][Sm(L4)2]. In both cases cooling
of the light petroleum washings from the preparation
of 3 and 4 to -20 °C yielded crystals of Cp′′2LnCl2Li-
(THF)2 and, in the case of 4, also Cp′′3Sm, as shown by
comparison of the NMR spectra with literature re-
ports.21,22 Clearly 3 and 4 have formed as the result of
ligand redistribution, a well-known phenomenon when
attempting to prepare mixed-ligand lanthanide com-
plexes.
The identity of 3 was confirmed by a single-crystal
X-ray diffraction (Figure 2). Selected bond lengths and
angles collected in Table 2. The structure of 3 resembles
that of the previously reported samarium complex
[Li(OEt2)4][Sm(L4)2],18 with the same anti, syn arrange-
ment of the ansa-bis(allyl) ligands around the metal.
The yttrium-carbon bond lengths are in the range
2.625(3)-2.727(3) Å, with an average of 2.682 Å. These
are longer than those in the complex Y(η3-C3H5){N(SiMe2-
CH2PMe2)2}(µ-Cl)2 (Y-C ) 2.587(5), 2.609(5), and 2.621-
(5) Å),23 indicating greater steric congestion in 3. The
C-C-C bond angles in 3 are 127.7(3)°, 128.9(3)°,
127.2(3)°, and 127.5(3)° compared with 126.1(6)° in
Y(η3-C3H5){N(SiMe2CH2PMe2)2}(µ-Cl)2.
Ta ble 1. Selected In ter a tom ic Dista n ces (Å) a n d
Bon d An gles (d eg) for 1
molecule 1
molecule 2
Nd(1)-I(1)
3.1547(7) Nd(2)-I(2)
3.1419(7)
2.757(5)
2.752(5)
2.678(5)
2.719(6)
2.748(6)
2.679(6)
2.513(4)
2.514(4)
1.404(7)
1.399(8)
1.390(8)
1.397(7)
Nd(1)-C(111)
Nd(1)-C(11)
Nd(1)-C(121)
Nd(1)-C(131)
Nd(1)-C(13)
Nd(1)-C(141)
Nd(1)- O(15)
Nd(1)-O(16)
C(11)-C(111)
C(11)-C(121)
C(13)-C(131)
C(11)-C(141)
2.781(6) Nd(2)-C(211)
2.758(5) Nd(2)-C(21)
2.671(6) Nd(2)-C(221)
2.760(6) Nd(2)-C(231)
2.754(6) Nd(2)-C(23)
2.683(6) Nd(2)-C(241)
2.519(4) Nd(2)- O(25)
2.512(4) Nd(2)-O(26)
1.385(7) C(21)-C(211)
1.413(8) C(21)-C(221)
1.391(8) C(23)-C(231)
1.390(8) C(23)-C(241)
C(111)-C(11)-C(121) 126.1(6) C(211)-C(21)-C(221) 128.2(5)
C(131)-C(13)-C(141) 126.2(6) C(231)-C(23)-C(241) 127.3(5)
NdCl(THF)2]2‚2THF, where the corresponding distance
is 2.555(3) Å, and the dioxane adduct {η3-C3H5}3Nd-
(C4H8O2) (Nd-O 2.612(3) and 2.605(3) Å).9a The Nd-I
bond distances, 3.1547(7) and 3.1419(7) Å, resemble
those in the hydrotris(pyrazolyl)borate complex (TpH)-
NdI2(THF)2 (Nd-I 3.062(3) and 3.136(3) Å).20
As stated above, lanthanide complexes of the ansa-
bis(allyl) ligand L4 are highly active in the polymeriza-
tion of methyl methacrylate but give limited stereose-
lectivity. It was hoped that a sterically more hindered
ligand, [Ph2Si(CHCHCHSiMe3)2]2- (L5), might produce
higher syndiotacticity. Ph2Si(CH2CHCHSiMe3)2 was
prepared from allyltrimethylsilane and diphenyldichlo-
In a similar manner, the reaction of Cp′′2YCl2Li-
(THF)2 with K2L5 in THF gave 2. In this case a
potassium atom was retained as the counterion, even
in the presence of lithium cations. The reaction of
Cp′′2SmCl2Li(THF)2 with K2L5 in THF produced a deep
red solution. Removal of the solvent and extraction of
the resulting solids with light petroleum afforded a crop
n
rosilane in high yield. Reaction with BuLi followed by
1
addition of KOtBu in diethyl ether allows the facile
isolation of the dipotassium salt K2L5. The reaction of
2 equiv of this salt with YCl3 in THF, removal of the
volatiles, and recrystallization from diethyl ether pro-
of maroon crystals of 5. The H NMR spectrum of this
compound was complicated; however, in contrast to the
formation of 2-4 it was clear that cyclopentadienyl as
well as allyl ligands were present. The solubility proper-
ties also suggested a different structure from the tetra-
(allyl) lanthanate complexes. This was confirmed by
single-crystal X-ray diffraction, which identified com-
pound 5 as a zwitterionic mixed-ligand complex, [Cp′′Sm-
(L5){µ-ClLi(THF)3}] (Scheme 3).
The formation of 5 is an unusual example of the
displacement of a cyclopentadienyl ligand while a
chloride ligand has been retained. It seems likely that
the steric congestion at the lanthanide center is the
principal reason for the preferential loss of the Cp′′
ligand. The reaction exemplifies the sensitivity of ligand
exchange equilibria in lanthanide mixed-ligand com-
plexes to steric factors.
The crystal structure of 5 is depicted in Figure 3, with
selected bond lengths and angles collected in Table 3.
The ligand environment of the samarium atom is
comprised of the η5-bonded cyclopentadienyl group, the
ansa-bis(allyl) ligand, and a chloride ion bridging to a
lithium cation. The bond distances to the cyclopentadi-
enyl group are similar to those reported previously; for
example, in Cp′′3Sm the average Sm-C bond distance
is 2.76(4) Å,22 whereas in 5 the distances lie in the range
2.705(4)-2.741(4) Å (average 2.73 Å). In contrast to the
situation found in Cp′′3Sm, the shortest Sm-C bond
distance is to the carbon between the two Me3Si-
vides [Y(L5)2{µ-K}(THF)0.5(Et2O)1.5 ∞
] (2) in moderate
yield as a bright orange microcrystalline solid (Scheme
1). As with the similar complexes derived from L4, 2 is
only sparingly soluble in hydrocarbons such as light
petroleum and toluene, and NMR spectra had to be
recorded in THF-d8. The spectra and solubility were
similar to the previously isolated tetra(allyl) ate com-
plexes, which suggests that 2 is likely to possess a
similar structure, although it was not possible to
confirm this crystallographically.
In view of the successful use of the bis-cyclopentadi-
enyl ligand environment in lanthanide polymerization
catalysts, attempts were made to extend the family of
allyl complexes to mixed-ligand compounds of the type
[Cp2Ln(allyl)2]-, with the aim of generating catalysts
that could combine high polymerization activity with
improved control of polymer microstructure. Thus a
range of reactions was undertaken with Cp′′2LnCl2Li-
(THF)2 (Cp′′ ) 1,3-C5H3(SiMe3)2; Ln ) Sm or Y) and
the potassium salts K2L4 and K2L5. Treatment of Cp′′2-
LnCl2Li(THF)2 with K2L4 in THF gave brightly colored
solutions (orange for yttrium, deep red for samarium).
Removal of volatiles, washing with light petroleum, and
recrystallization of the solids from diethyl ether at -20
°C afforded [Li(OEt2)(THF)2][Ln(L4)2] (3, Ln ) Y; 4, Ln
) Sm) as orange and deep red crystalline solids,
respectively (Scheme 2). The NMR spectra of 3 and 4
closely correspond to those of [Y(L4)2{µ-K(THF)}‚
(21) Lappert, M. F.; Singh, A. J . Chem. Soc., Chem. Commun. 1981,
1190.
(22) Evans, W. J .; Keyer, R. A.; Ziller, J . W. J . Organomet. Chem.
1990, 394, 87.
(20) Long, D. P.; Chandrasekaran, A.; Day, R. O.; Bianconi, P. A.;
Rheingold, A. L.; Inorg. Chem. 2000, 39, 4476.
(23) Fryzuk, M. D.; Haddad, T. S.; Rettig, S. J . Organometallics
1992, 11, 2967.

Sterically Hindered Lanthanide Allyl Complexes
Organometallics, Vol. 23, No. 12, 2004 2975
Sch em e 1
Sch em e 2
Ta ble 2. Selected In ter a tom ic Dista n ces (Å)a n d
Bon d An gles (d eg) for 3
Y-C(16)
2.625(3) Y-C(21)
2.671(3) Y-C(24)
2.680(3) Y-C(22)
2.682(3) Y-C(12)
2.701(3) Y-C(14)
2.720(3) Y-C(23)
2.631(3)
2.675(3)
2.679(3)
2.688(3)
2.705(3)
2.727(3)
Y-C(15)
Y-C(26)
Y-C(25)
Y-C(11)
Y-C(13)
C(11)-C(12)
C(14)-C(15)
C(21)-C(22)
C(24)-C(25)
1.407(4) C(12)-C(13)
1.401(4) C(15)-C(16)
1.401(4) C(22)-C(23)
1.396(4) C(25)-C(26)
1.390(4)
1.401(4)
1.450(4)
1.405(4)
Li-O(5)
Li-O(3)#1
1.927(6) Li-O(6)
1.958(6) Li-O(4)
1.958(6)
1.961(6)
C(13)-C(12)-C(11) 128.9(3) C(14)-C(15)-C(16) 127.7(3)
C(21)-C(22)-C(23) 127.2(3) C(24)-C(25)-C(26) 127.5(3)
cyclopentanide, solv ) THF or Et2O; Ln ) Sm, Eu, Gd,
Tb, Dy, Ho, Er, Tm, and Yb)25 and in the amides
[(Me3Si)2N]3Ln(µ-Cl)Li(THF)3 (Ln ) Nd, Sm, Eu).26 In
these complexes the Ln-Cl-Li bridge deviates from
linearity by 10° or less. By contrast, in complex 5 the
Sc-Cl-Li angle is more acute, 143.30(19)°. This may
well be due to increased steric hindrance at the metal
center.
P olym er iza tion Stu d ies. The activities of 2, 3, 4,
and, for comparison, [Y(L4)2{µ-K(THF)}‚(THF)n]∞‚(6)18
for the polymerization of methyl methacrylate were
investigated under a range of conditions. The results
are collected in Table 5. All the complexes were found
to be efficient catalysts, with the highest activity being
found for 3 with a TON of 45 100 mol MMA (mol Y)-1
h-1 in toluene at 0 °C. It was hoped that the use of a
more sterically hindered ligand would have some effect
F igu r e 2. Molecular structure of one of the complex anions
in 3. Thermal ellipsoids are drawn at 50% probability.
Hydrogen atoms are omitted for clarity.
substituted carbons (C(12)); in Cp′′3Sm this is regarded
as the most sterically crowded position. As in other
ansa-allyl complexes, the ligand adopts an anti, syn
configuration. The Sm-C(allyl) bond distances lie in the
range 2.681(4)-2.759(4) Å (average 2.712 Å), very
similar to those in [Li(OEt2)4][Sm(L4)2] (2.695(4)-2.744-
(5) Å, average 2.722 Å), whereas in (C5Me5)2Sm(CH2-
CHCH2) the allyl ligand is slightly more tightly bonded
(Sm-C 2.630(15), 2.668(18), and 2.643(18) Å).24 A single
halide ligand bridging to lithium has precedence in
lanthanide chemistry and is found, for example, in a
series of structurally characterized compounds L3Ln-
(µ-Cl)Li(solv)3 (L ) 2,2,5,5-tetramethyl-2,5-disila-1-aza-
(25) J ust, O.; Rees, J r., W. S. Inorg. Chem. 2001, 40, 1751.
(26) Zhou, S.-L.; Wang, S.-W.; Yang, G.-S.; Liu, X.-Y.; Sheng, E.-H.;
Zhang, K.-H.; Cheng, L.; Huang, Z.-X. Polyhedron 2003, 22, 1019.
(24) Evans, W. J .; Ulibarri, T. A.; Ziller, J . W. J . Am. Chem. Soc.
1990, 112, 2314.

2976 Organometallics, Vol. 23, No. 12, 2004
Woodman et al.
Sch em e 3
syndiotacticity.26 The lithium salts 3 and 4 show a
similar behavior, with an rr triad content in THF of up
to 65.7%. By contrast, the stereoselectivity of PMMA
samples obtained with potassium compounds 2 and 6
is little affected by either temperature or solvent.
The reasons for this tacticity difference may well lie
in some degree of monomer activation by coordination
to the alkali metal cation, with the smaller and thus
more Lewis acidic lithium cation showing a more
effective coordination than potassium. Changes in PMMA
tacticity upon addition of a Lewis acid, for example Al-
(C6F5)3, have been seen for both metallocene and non-
metallocene initiators. For example, tert-butyllithium
on its own produces isotactic PMMA (mm ) 75.0% at -
78 °C), whereas the addition of 2 equiv of Al(C6F5)3 gives
PMMA with up to 95.0% rr.27
In general these tetraallyl lanthanate systems pro-
duce high molecular weight poly(methyl methacrylate)
(Mw typically ≈ 80 000-300 000). There is a significant
difference between polymers produced in toluene and
in THF. THF reactions tend to give PMMA with lower
molecular weights (e.g., entry 8, Mw 83 300) and poly-
dispersities closer to 2, whereas polymers obtained in
toluene show higher Mw but broader polydispersity
(entry 9, Mw 183 000 and Mw/Mn 5.4).
The neutral allyl complexes 1, the previously reported
compounds (L3)2LaCl(THF) (7) and (L3)2YCl (8),17 and
the ionic compounds 2, 3, 4, and 6 are highly effective
catalysts for the polymerization of ꢀ-caprolactone (CL)
(Table 6). With the neutral catalysts at 20 °C only traces
of polymer were detected, whereas at 50 °C polymeri-
zation was extremely rapid, with 85-95% conversion
in 60 s. The anionic complexes are already highly active
at 20 °C. Surprisingly, 2 gave significantly higher
conversions than the closely related yttrium compounds
3 and 6. In these cases there was little discernible
influence of the nature of the alkali cation. The resulting
polymers have narrow polydispersities (typically 1.2-
1.5). In all cases high molecular weight polymers were
obtained, with the neodymium complex 1 giving the
highest values, Mw ) 165 000.
F igu r e 3. Molecular structure of 5, showing the atomic
numbering scheme. Thermal ellipsoids are drawn at 50%
probability. Hydrogen atoms are omitted for clarity.
Ta ble 3. Selected In ter a tom ic Dista n ces (Å) a n d
Bon d An gles (d eg) for 5a
Sm-C(1)
2.733(4)
2.705(4)
2.741(4)
2.729(4)
2.734(4)
2.724(4)
Sm-C(34)
Sm-C(41)
Sm-C(34)
Sm-C(45)
Sm-C(5)
Sm-Cl(9)
2.704(4)
2.681(4)
2.759(4)
2.706(4)
2.699(4)
2.6930(13)
Sm-C(12)
Sm-C(2)
Sm-C(211)
Sm-C(121)
Sm-C(3)
Sm-C(1x)
Sm-C(3x)
2.449
2.486
Sm-C(5x)
2.506
C(1x)-Sm-C(3x)
C(1x)-Sm-C(5x)
C(1x)-Sm-C(19)
106.4
139.1
107.5
C(3x)-Sm-C(5x) 99.9
C(3x)-Sm-Cl(9) 112.0
C(5x)-Sm-Cl(9) 90.4
Li(1)-O(6)
Li(1)-O(7)
1.910(8)
1.925(8)
Li(1)-O(8)
Li(1)-Cl(9)
1.923(8)
2.320(8)
Li(1)-Cl(9)-Sm(1) 143.30(19)
C(3)-C(34)
C(45)-C(5)
1.383(6)
1.396(6)
C(34)-C(41)
C(42)-C(45)
1.403(6)
1.378(5)
a
C(1x) is the centroid of the cyclopentadienyl ring; C(3x) and
C(5x) are the centroids of the allyl-C3 groups about C(34) and
C(45).
in the polymerization. The comparison of the activities
of 2 and 6 is instructive. The most obvious contrast is
the relatively poor activity of 2 in toluene (TON 564 mol
MMA (mol Y)-1 h-1) when compared with 6 (86 400 mol
MMA (mol Y)-1 h-1, both at 0 °C). The activities are
solvent-dependent; for example in the case of complex
4, the TON in toluene is >30 times higher than in THF.
The situation is even more striking for 6, where the
presence of THF reduces the TON to 970 mol MMA (mol
Y)-1 h-1 (entries 11 and 13).
Recent studies have emphasized the effect of solvent
polarity on both activity and the resulting PMMA
microstructure, with more polar solvents (THF and
dimethoxyethane) for the system [(Me3Si)2N]3Ln(µ-Cl)-
Li(THF)3 (Ln ) Nd, Sm, and Eu) giving increased
Con clu sion
Silyl-substituted allyl ligands give facile access to a
range of stable lanthanide complexes with good solubil-
ity and crystallization characteristics. While allyl ligands
such as [Me3SiCHCHCHSiMe3]- give neutral lan-
thanide complexes of the type (allyl)2LnX, ansa-bis(allyl)
ligands favor ate complexes, [Ln(allyl)4]-, even if bulky
cyclopentadienyl complexes are used as starting materi-
als. Clean routes to the isolation of three new members
of the ansa-bis(allyl) class of complexes were found,
including two fully characterized complexes with lithium
(27) Bolig, A. D.; Chen, E. Y.-X. J . Am. Chem. Soc. 2001, 123, 7943.

Sterically Hindered Lanthanide Allyl Complexes
Organometallics, Vol. 23, No. 12, 2004 2977
Ta ble 4. Cr ysta l Da ta a n d Su m m a r y of Da ta Collection a n d Refin em en t Deta ils for 1, 3, a n d 5
1
3
5
formula
cryst size (mm)
cryst color, shape
fw
C
26H58INdO2Si4
C
28H60Si6Y, C16H34O4Li
C47H79ClLiO3Si5Sm, 0.5(C6H14
0.13 × 0.13 × 0.12
red cubes
)
0.45 × 0.30 × 0.15
green blocks
786.2
0.60 × 0.50 × 0.40
orange blocks
951.6
1068.5
cryst class
space group
a, Å
triclinic
P1h (no. 2)
10.770(1)
orthorhombic
Pbca (no. 61)
17.065(3)
monoclinic
P21/n (no. 14)
13.669(3)
b, Å
19.056(3)
20.137(4)
30.451(6)
c, Å
19.453(1)
32.896(7)
14.158(3)
R, deg
72.94(2)
89.61(1)
80.44(1)
3760.0(7)
â, deg
96.24(3)
γ, deg
V, Å3
11304(4)
5858(2)
Z
D
4
8
4
calcd, Mg/m3
1.389
2.348
1596
1.118
1.193
4218
1.211
1.185
2246
µ, mm-1
F(000)
no. of indep reflns
12 001 (Rint ) 0.053)
9784 (Rint ) 0.038)
10 732 (Rint ) 0.091)
no. of obsd reflns (I > 2σi)
no. of params refined
goodness of fit
9476
7431
6555
609
1.032
537
1.046
544
0.900
final R indices (all data)
final R indices (obsd data)
largest diff peak and hole, e Å-3
location of largest diff peak(s)
R1 ) 0.064, wR2 ) 0.146
R1 ) 0.051, wR2 ) 0.137
1.00 and -1.91
close to Nd or I atoms
R1 ) 0.0612, wR2 ) 0.1047
R1 ) 0.0401, wR2 ) 0.0947
0.361 and -0.830
close to Si(3)
R1 ) 0.086, wR2 ) 0.096
R1 ) 0.043, wR2 ) 0.089
0.60 and -0.89
remote from all molecules
not resolved
Ta ble 5. P olym er iza tion of MMA w ith An ion ic La n th a n id e Allyl Com p lexesa
tacticityc
solvent
(5 mL)
time
(min)
temp
(°C)
yield
(g)
conversion
(%)
d
d
run
cat.
TONb
rr
mr
mm
Mw
Mn
Mw/Mn
1
2
3
4
5
6
7
8
2
2
2
2
3
3
4
4
toluene
toluene
THF
THF
THF
toluene
THF
THF
toluene
toluene
toluene
toluene
THF
60
60
20
85
15
3
30
30
3
20
0
20
0
20
0
20
0
20
0
0
20
0
0.686
1.056
0.728
0.662
0.298
0.422
0.367
0.112
0.149
0.257
1.348
1.060
0.454
36.5
56.2
38.8
35.3
15.9
22.5
19.5
6.0
366
564
1170
250
637
45 100
392
27.1
27.9
32.9
33.5
61.8
31.4
62.6
65.7
28.8
31.2
25.0
24.8
33.7
53.8
51.9
54.2
57.4
34.2
26.9
33.2
30.7
28.2
25.6
53.9
54.6
55.4
19.1
20.2
12.9
9.1
4.0
41.7
4.2
192 000
358 000
112 000
104 000
83 100
288 000
73 500
83 300
183 000
221 000
297 000
242 000
195 000
103 000
174 000
62 600
50 700
44 900
52 900
43 300
45 900
33 900
44 800
99 900
97 700
101 000
1.85
2.06
1.79
2.05
1.85
5.40
1.70
1.82
5.39
4.92
2.97
2.48
1.94
120
3.6
9
4
4
7.9
1590
4120
86 400
67 900
970
43.0
43.2
21.1
20.6
10.9
10
11
12
13
2
13.7
72.0
56.6
24.2
6e
6e
6
0.5
0.5
15
a
b
Conditions: Ln 1.87 × 10-5 mol, MMA/Ln ) 1000. TON ) mol MMA (mol Ln)-1 h-1
.
c Determined by triad analysis of the 1H NMR
spectra in CDCl3.29 Determined by GPC relative to polystyrene standards. e See ref 18.
d
Ta ble 6. P olym er iza tion of E-Ca p r ola cton e w ith Neu tr a l a n d An ion ic La n th a n id e Ca ta lystsa
c
c
run
catalyst
time (min)
temp (°C)
yield (g)
conversion (%)
TONb
Mw
Mn
Mw/Mn
1
2
3
4e
5
6
7
8
1
1
20
1
1
1
1
2
1
3
20
50
50
50
20
20
20
20
traces
1.768
1.828
1.934
1.729
0.397
1.246
0.641
85.8
88.7
93.9
83.9
19.3
60.3
31.1
25 700
26 600
28 200
25 200
2790
165 000
63 700
129 000
46 700
25 000
27 900
53 000
127 000
51 300
87 500
24 400
16 800
16 800
37 600
1.30
1.24
1.48
1.91
1.49
1.66
1.42
L32LaCl(THF) (7)
L32YCl (8)
2
3
4
6
17 500
3110
a
b
Conditions: Ln 3.61 × 10-5 mol, CL/Ln ) 500. TON ) mol CL (mol Ln)-1 h-1
.
c Determined by GPC relative to polystyrene
standards.
as the countercation. The synthesis of a mixed-ligand
Cp-allyl complex was, however, successful in the case
of samarium, which gave the zwitterionic product
[Cp′′Sm(L5){µ-ClLi(THF)3}].
The anionic lanthanate complexes are highly active
for the polymerization of methyl methacrylate. While
the allyl ligands have limited influence on polymer
stereochemistry, the simple expedient of conducting
polymerization reactions in the more polar THF as
solvent, rather than toluene, did result in polymer with
a much higher syndiotactic content. The most pro-
nounced effect was seen for catalysts with a lithium
cation rather than potassium.
Both the neutral (L3)2LnX complexes and the ansa-
bis(allyl) complexes are active for the ring-opening
polymerization of ꢀ-caprolactone. While the neutral
complexes are active at only elevated temperatures, the
anionic complexes rapidly activate polymerization at
ambient temperature. Since such ROP reactions are
initiated by nucleophilic attack on the monomer, the
observed reactivity differences may well reflect differ-
ences in the nucleophilicity of the allyl ligands in the

2978 Organometallics, Vol. 23, No. 12, 2004
Woodman et al.
filtrate to ca. 30 mL and cooling of the solution to -20 °C
afforded orange crystals of 2, yield 1.10 g (1.01 mmol, 40.4%).
Rea ction of Cp ′′2YCl2Li(THF )2 w ith K2L4. A solution of
Cp′′2YCl2Li(THF)2 (2.01 g, 2.75 mmol) in THF (100 mL) was
treated with solid portions of K2{3-(η3-C3H3SiMe3-1)2SiMe2}
(1.00 g, 2.75 mmol). The reaction rapidly became orange and
was stirred for 16 h at room temperature. The volatiles were
removed in vacuo, and the resulting solids were extracted with
light petroleum (150 mL). The remaining solids were extracted
with diethyl ether (100 mL), concentrated, and cooled to -20
°C to give orange crystals of [Li(THF)2(OEt2)][Y(L4)2] (3), yield
0.87 g (0.99 mmol, 35.9%). Anal. Calcd for C40H86LiO3Si6Y: C,
54.57; H, 9.85. Found: C, 54.12; H, 9.21. 1H NMR (THF-d8,
20 °C): δ -0.16 (s, 12 H, SiMe2), 0.04 (s, 36 H, SiMe3), 1.11 (t,
6 H, J HH ) 7 Hz, OCH2CH3), 1.78 (m, 8 H, m-THF), 3.37 (q, 4
H, J HH ) 7 Hz, OCH2CH3). 3.39 (d, 4 H, J HH ) 17.2 Hz, allyl),
3.60 (m, 8 H, o-THF), 3.79 (d, 4 H, J HH ) 11.8 Hz, allyl), 7.02
(dd, 4 H, J HH ) 11.8, 17.2 Hz, allyl). 13C NMR (THF-d8, 20
°C): δ -3.82 (SiMe2), 1.85 (SiMe3), 15.69 (OCH2CH3), 26.36
(m-THF), 66.30 (OCH2CH3), 68.22 (o-THF), 70.86 (allyl), 87.64
(allyl), 163.07 (allyl).
Rea ction of Cp ′′2Sm Cl2Li(THF )2 w ith K2L4. A solution
of Cp′′2SmCl2Li(THF)2 (2.48 g, 3.13 mmol) in THF (100 mL)
was treated with solid portions of K2{3-(η3-C3H3SiMe3-1)2-
SiMe2} (1.13 g, 3.13 mmol). The reaction rapidly became red-
orange and was stirred for 16 h at room temperature. The
volatiles were removed in vacuo, the resulting solids were
extracted with light petroleum (150 mL), and the filtrate was
concentrated to ca. 40 mL and cooled to -20 °C to give a
mixture of Cp′′3Sm and Cp′′2SmCl2Li(THF)2 as orange and
yellow crystals, total yield 0.77 g (0.99 mmol, 31.6% based on
Cp′′2SmCl2Li(THF)2). The remaining solids were extracted
with diethyl ether (100 mL); concentrating and cooling the
filtrate afforded red crystals of [Li(THF)2(OEt2)][Sm(L4)2] (4),
yield 0.64 g (0.68 mmol, 21.7%). Anal. Calcd for C40H86LiO3-
Si6Sm: C, 51.06; H, 9.21. Found: C, 50.06; H, 9.27 (some loss
of the donor solvent occurred under reduced pressure). 1H
NMR (THF-d8, 20 °C): δ -2.46 (dd, 4 H, J HH ) 11.3 Hz, 16.4
Hz, allyl), 0.24 (s, 36 H, SiMe3), 1.12 (t, 6 H, J HH ) 7.2 Hz,
OCH2CH3), 1.78 (s, 12 H, SiMe2), 1.78 (m, 8 H, m-THF), 3.39
(q, 4 H, J HH ) 7.2 Hz, OCH2CH3), 3.61 (m, 8 H, o-THF), 6.82
(d, 4 H, J HH ) 11.3 Hz, allyl), 12.85 (d, J HH ) 16.4 Hz, 4 H,
allyl).
neutral compounds and anionic complexes, respectively.
In all cases high molecular weight polymers with good
conversions and narrow polydispersities were obtained.
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were performed
under an atmosphere of dry nitrogen using standard Schlenk
line techniques. Solvents were distilled under nitrogen from
sodium (toluene), sodium benzophenone (diethyl ether, THF),
and sodium-potassium alloy (light petroleum, bp 40-60 °C).
Deuterated solvents were degassed by several freeze-thaw
cycles and stored over 4 Å molecular sieves. NMR spectra were
recorded on a Bruker DPX-300 spectrometer. 1H NMR spectra
(300.1 MHz) were referenced to residual solvent protons; 13C
NMR spectra were referenced internally to the D-coupled 13C
resonances of the NMR solvent. Polymer molecular weights
were determined by gel permeation chromatography in THF
using a Polymer Laboratories GPC-220 instrument equipped
with a refractive index and a PD2040 dual-angle light scat-
tering detector and PL gel 2 × mixed bed-B, 30 cm, 10 µm
columns. YCl3(thf)3.5 was prepared from the corresponding
oxide following a literature procedure;28 NdI3(thf)3.5 was pre-
pared from Nd and CH2I2 in THF.9b 1,3-Bistrimethylsilylpro-
pene12 and Me2Si(CH2CHCHSiMe3)216 were prepared via modi-
fications of literature procedures. Complexes 6,18 7, 8,17 and
Cp′′2LnCl2Li(THF)2 (Ln ) Sm and Y)21 were prepared accord-
ing to the published methods.
(L3)2Nd I(THF )2 (1). Solid NdI3(THF)3.5 (3.80 g, 4.89 mmol)
was added slowly in small portions to a solution of K{1,3-C3H3-
(SiMe3)2} (KL3, 2.20 g, 9.79 mmol) in 150 mL of THF over 30
min. Copious amounts of precipitate formed. After stirring the
light green mixture for 16 h at 20 °C the volatiles were
removed. The residue was extracted with light petroleum (2
× 100 mL), concentrated, and cooled to -20 °C to give dark
green crystals of 1 (2.71 g, 70.5%). Anal. Calcd for C26H58INdO2-
Si4: C, 39.72; H, 7.44. Found: C, 39.34; H, 7.01. 1H NMR
(benzene-d6, 20 °C): δ -8.67 (br s, 8 H, THF), -4.00 (br s, 8
H, THF), 3.41 (br s, 36 H, SiMe3), 4.76 (br s, 4 H, allyl), 11.89
(br s, 2 H, allyl).
[Y(L5)2{µ-K}(THF )0.5(Et2O)1.5 ∞ (2). A solution of K2{3-(η3-
]
C3H3SiMe3-1)2SiPh2} (4.55 g, 9.38 mmol) in THF (100 mL) was
treated with solid portions of YCl3 (0.92 g, 4.71 mmol). After
complete addition the reaction was heated at ca. 50 °C for 4
h, during which time an intense orange color developed. The
solvent was removed in vacuo, and the resulting orange solid
extracted with diethyl ether (150 mL). Concentration of this
solution to ca. 30 mL and cooling to -20 °C overnight afforded
a crop of orange crystals, yield 2.34 g (22.9%). Anal. Calcd for
Rea ction of Cp ′′2Sm Cl2Li(THF )2 w ith K2L5. A solution
of Cp′′2SmCl2Li(THF)2 (1.05 g, 1.32 mmol) in THF (40 mL) was
treated with solid portions of K2{3-(η3-C3H3SiMe3-1)2SiPh2}
(0.54 g, 1.32 mmol). After stirring for 16 h the solution was
deep red. Removal of volatiles in vacuo gave a red solid.
Extraction with light petroleum (100 mL), concentration to ca.
40 mL, and cooling to -20 °C afforded red crystals, yield 0.35
g. The 1H NMR spectrum of these crystals could not be fully
assigned; however there were resonances associated with both
cyclopentadienyl and ansa-allyl groups. A suitable crystal was
selected and subjected to X-ray diffraction analysis, and was
identified as [Cp′′Sm{3-(η3-C3H3SiMe3-1)2SiPh2}{µ-Cl}Li(THF)3]
(5).
C
56H87KO2Si6Y: C, 61.72; H, 8.05. Found: C, 61.35; H, 8.06.
1H NMR (THF-d8, 20 °C): δ -0.14 (s, 36 H, SiMe3), 1.13 (t, 9
H, J HH ) 7 Hz, OCH2CH3), 1.78 (m, 2 H, m-THF), 3.39 (q, 6
H, J HH ) 7 Hz, OCH2CH3) 3.48 (d, 4 H, J HH ) 17.5 Hz, allyl),
3.63 (m, 2 H, o-THF), 4.24 (d, 4 H, J HH ) 11.6 Hz, allyl), 7.03
(m, 12 H, phenyl), 7.38 (dd, 4 H, J HH ) 17.5 Hz, 11.6 Hz), 7.55
(m, 8 H, phenyl). 13C NMR (THF-d8, 20 °C): δ 1.45 (SiMe3),
15.68 (OCH2CH3), 26.36 (m-THF), 66.30 (OCH2CH3), 68.21
(o-THF), 76.04 (allyl), 81.60 (allyl), 127.12 (Ph), 127.60 (Ph),
136.37 (Ph), 140.27 (i-Ph), 164.24 (allyl).
P olym er iza tion s. A solution of the catalyst in either
toluene or THF (5 mL) was maintained at the chosen temper-
ature. Neat monomer was then added (2 mL), with a catalyst/
monomer ratio of 1000:1 for MMA and 500:1 for CL. The
polymerizations were terminated by methanol addition (10
mL). The resulting polymer was precipitated from methanol
(150 mL), filtered, and dried in vacuo. Polymer microstructure
Rea ction of Cp ′′2YCl2Li(THF )2 w ith K2L5. A solution of
Cp′′2YCl2Li(THF)2 (1.83 g, 2.50 mmol) in THF (100 mL) was
treated with solid portions of K2{3-(η3-C3H3SiMe3-1)2SiPh2}
(1.21 g, 2.50 mmol). The reaction rapidly became orange and
was stirred for 16 h at room temperature. The volatiles were
removed in vacuo and the resulting solids extracted with light
petroleum (100 mL). The remaining solid was extracted with
diethyl ether (100 mL). Concentration of the bright orange
1
was determined by H NMR in chloroform-d1.29
X-r a y Cr yst a llogr a p h ic An a lyses. Crystal data and
refinement results are collated in Table 4. Suitable single
crystals were selected under dried perfluoropolyether, mounted
(29) Bovey, F. A. In Comprehensive Polymer Science; Allen, G.,
Bevington, J . C., Eds.; Booth, C., Price, C., Vol. 1 Eds.; Pergamon:
Oxford, 1989; Chapter 17, pp 348-353.
(28) Burton, N. C.; Cloke, F. G. N.; Hitchcock, P. B.; de Lemos, H.
C.; Sameh, A. A. J . Chem. Soc., Chem. Commun. 1989, 1462.

Sterically Hindered Lanthanide Allyl Complexes
Organometallics, Vol. 23, No. 12, 2004 2979
on a glass fiber, and fixed in a cold nitrogen stream (140 K)
on a Rigaku R-Axis II image plate diffractometer equipped
with a rotating anode X-ray source (Mo KR radiation) and
graphite monochromator. For each 48 exposures were made
using 4° oscillations; max θ for each was 25.4°. Data were
processed using the DENZO/SCALEPACK programs.30 The
structures were determined by direct methods using the XS
program31 and were refined by full-matrix-least-squares meth-
ods, on F2, in SHELXL.32 For 1 there are two independent
molecules in the crystal, one of which has a disordered (and
not fully resolved) THF ligand. The non-hydrogen atoms
(except for the carbon atoms of the disordered ligand) were
refined with anisotropic thermal parameters. Hydrogen atoms
were included in idealized positions (except in the disordered
ligand), and their Uiso values were set to ride on the Ueq values
of the parent carbon atoms. For 3 the non-hydrogen atoms
were refined with anisotropic thermal parameters, and the
hydrogen atoms were treated as for 1, with the exception of
the hydrogen atoms on the C3 allyl core labeled with a “*”,
which were refined freely. In 5 the solvent molecule is
disordered about a center of symmetry and not fully resolved;
four distinct carbon atoms with site occupancies of 0.7-0.8
were refined isotropically. For each analysis, scattering factors
for neutral atoms were taken from ref 33. Computer programs
were run on a Silicon Graphics Indy at the University of East
Anglia or on a DEC Alpha Station in the Biological Chemistry
Department, J ohn Innes Centre.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic information for compounds 1, 3, and 5. This material
is available free of charge via the Internet at http://pubs.acs.org.
(30) Otwinowski, Z.; Minor, W. Methods Enzymol. 1996, 276, 307.
(31) Sheldrick, G. M. SHELXTL Package, including XS for structure
determination, XL for refinement, and XP for molecular graphics;
Siemens Analytical Inc., 1995.
OM0499097
(32) Sheldrick, G. M. SHELX97 Programs for Crystal Structure
Determination (SHELXS) and Refinement (SHELXL); University of
Gottingen: Germany, 1997.
(33) International Tables for X-ray Crystallography; Kluwer Aca-
demic Publishers: Dordrecht, 1992; Vol. C, pp 500, 219, and 193.