Neodymium alkoxides: Synthesis, characterization and their combinations with dialkylmagnesiums as unique systems for polymerization and block copolymerization of ethylene and methyl methacrylate

Article abstract of DOI:10.1002/1521-3765(20020816)8:16<3773::AID-CHEM3773>3.0.CO;2-S

The synthesis and characterization (NMR and x-ray) of a variety of neodymium alkoxides derived from simple and functionalized tertiary monoalcohols, and their application as inorganic precursors in combination with dialkylmagnesium reagents for ethylene and methyl methacrylate (MMA) (co)-polymerization have been investigated. Salt metathesis reactions between NdCl₃ and sodium alkoxides in THF led to the formation of trinuclear complexes [Nd₃(μ₃-OR)₂(μ₂- OR)₃(OR)₄(thf)₂] with R = tBu (1), tAm (2), while aggregate structure [Nd₁₂(OtAm)₂₆(HOtAm)₂Cl₁₁Na] ·(OEt₂)₂ (3) was obtained when the synthesis was performed in Et₂O. [Nd₃(μ₃-OtBu)₂(μ₂- OtBu)₃(OtBu)₄(HOtBu)₂] (4), prepared by aminolysis of Nd[N(SiMe₃)₂]₃ in hexane, slowly decomposed in toluene into oxo complex [Nd₅(μ₅-O)(μ₃-OtBu)₄ (μ₂-OtBu)₄(OtBu)₅] (5). Finally, the dimer [Nd₂(μ₂,η²-OR)₂ (η²-OR)₂(η¹-OR)₂] (OR = OCMe₂CH₂CH₂OMe) (6) was synthesised by aminolysis reaction from the corresponding γ-donor-functionalized alcohol. Some of these neodymium alkoxides, in particular homoleptic complex 1, when associated in situ to one equivalent of a dialkylmagnesium, allow the formation of an active catalyst for ethylene polymerization. Under mild conditions (0°C, 1 bar), the latter catalyst system exhibited a moderate activity (5-10 kgmol^-1 h^-1 bar-¹). Effective transfer reactions were observed in the presence of H₂ or PhSiH₃ and renewal/improvement of activity occurred upon extra addition of dialkylmagnesium. The most outstanding feature of this catalytic system lies in the precipitation of the active Nd-polyethylenyl species during the ethylene polymerization course as solid S which could be isolated. This heterogeneity was turned to good account, enabling to achieve heterogeneous solid-gas ethylene polymerization and to prepare diblock PE-PMMA copolymers with high diblock efficiency and high molecular weights (M_n > 200 000). A catalytic cycle for this unique system is proposed based on the isolation of a transmetallation product (7) from a neodymium alkoxide/dialkylmagnesium combination and NMR studies of the latter.

Full text of DOI:10.1002/1521-3765(20020816)8:16<3773::AID-CHEM3773>3.0.CO;2-S

FULL PAPER
Neodymium Alkoxides: Synthesis, Characterization and Their Combinations
with Dialkylmagnesiums as Unique Systems for Polymerization and Block
Copolymerization ofEthylene and Methyl Methacrylate
[
a]
[a]
[a]
[b]
J e¬ r o√ me Gromada, Andr e¬ Mortreux, Thomas Chenal, Joseph W. Ziller,
[
c]
[d]
Fr e¬ d e¬ ric Leising, and Jean-FranÁois Carpentier*
Abstract: The synthesis and character-
ization (NMR and X-ray) of a variety of
neodymium alkoxides derived from sim-
ple and functionalized tertiary monoal-
cohols, and their application as inorgan-
ic precursors in combination with dia-
lkylmagnesium reagents for ethylene
and methyl methacrylate (MMA) (co)-
polymerization have been investigated.
Salt metathesis reactions between NdCl3
and sodium alkoxides in THF led to the
formation of trinuclear complexes
[Nd (m -O)(m -OtBu) (m -OtBu) (OtBu) ]
ment of activity occurred upon extra
addition of dialkylmagnesium. The most
outstanding feature of this catalytic
system lies in the precipitation of the
active ™Nd-polyethylenyl∫ species dur-
ing the ethylene polymerization course
as solid S which could be isolated. This
heterogeneity was turned to good ac-
count, enabling to achieve heterogene-
ous solid ± gas ethylene polymerization
and to prepare diblock PE-PMMA co-
polymers with high diblock efficiency
5
5
3
4
2
4
5
2
(5). Finally, the dimer [Nd (m ,h -OR) -
2
2
2
2
1
(h -OR) (h -OR) ] (OR ˆ OCMe CH -
2
2
2
2
CH OMe) (6) was synthesised by ami-
2
nolysis reaction from the corresponding
g-donor-functionalized alcohol. Some of
these neodymium alkoxides, in particu-
lar homoleptic complex 1, when associ-
ated in situ to one equivalent of a
dialkylmagnesium, allow the formation
of an active catalyst for ethylene poly-
merization. Under mild conditions (08C,
1 bar), the latter catalyst system exhib-
[
Nd (m -OR) (m -OR) (OR) (thf) ] with
and high molecular weights (Mn
>
3
3
2
2
3
4
2
R ˆ tBu (1), tAm (2), while aggregate
ited
10 kgmol
a
moderate
activity
(5 ± 200000). A catalytic cycle for this
À1 À1
À1
structure [Nd (OtAm) (HOtAm) Cl -
h
bar ). Effective transfer
unique system is proposed based on
the isolation of a transmetallation prod-
uct (7) from a neodymium alkoxide/
dialkylmagnesium combination and
NMR studies of the latter.
12
26
2
11
Na] ¥ (OEt ) (3) was obtained when the
reactions were observed in the presence
of H or PhSiH and renewal/improve-
2
2
synthesis was performed in Et O.
2
2
3
[
Nd (m -OtBu) (m -OtBu) (OtBu) (HOt-
3 3 2 2 3 4
Bu) ] (4), prepared by aminolysis of
2
Keywords:
magnesium ¥ polymerization
lanthanides
¥
Nd[N(SiMe ) ] in hexane, slowly de-
3
2 3
composed in toluene into oxo complex
Introduction
[
a] J. Gromada, Prof. A. Mortreux, Dr. T. Chenal
Laboratoire de Catalyse de Lille
UPRESA 8010 CNRS-Universit e¬ de Lille 1
Trivalent lanthanide hydride and alkyl complexes stabilized
5
9652 Villeneuve d×Ascq Cedex (France)
[1]
by two cyclopentadienyl-type ligands, Cp LnR, have at-
[
[
b] Dr. J. W. Ziller
2
Department of Chemistry, University of California
Irvine, 92697 CA (USA)
tracted much attention because of their high efficiency in
polymerizing ethylene and also polar monomers. Because of
[2]
[
c] Dr. F. Leising
Rhodia Recherches
the permanent search for new-generation polymerization
catalysts, there is currently considerable interest in developing
related organolanthanide complexes involving ancillary li-
gands other than the commonly used cyclopentadienyl-type
ligands.[ In this respect, hard, electronegative p-donor
ligands such as alkoxides/aryloxides are particularly attractive
because they offer strong metalÀoxygen bonds that are
9
3308 Aubervilliers Cedex (France)
d] Prof. J.-F. Carpentier
Laboratoire Organom e¬ talliques et Catalyse
UMR 6509 CNRS-Universit e¬ de Rennes 1
3]
3
5042 Rennes Cedex (France)
Fax : (‡33) 2-23-23-69-39
E-mail: jean-francois.carpentier@univ-rennes1.fr
expected to stabilize complexes of these electropositive
metals. Also, the great variety of these ligands conveniently
obtained from alcohols allows considerable variation in steric
and electronic features.[ The efficient use in polymerization
Supporting information for this article is available on the WWW under
1
http://www.chemeurj.org or from the author: H NMR spectra of 1:1
mixtures of [Nd
and [Y (OtBu) Cl
3
(m
3
-OtBu)
2
(m
2
-OtBu)
3 4 2 2
(OtBu) (thf) ] (1)/Mg(n-hex)
4]
3
7
2
(thf)
2
/Mg(n-hex)
2
] (three pages).
Chem. Eur. J. 2002, 8, No. 16
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0947-6539/02/0816-3773 $ 20.00+.50/0
3773

J.-F. Carpentier et al.
FULL PAPER
of organolanthanide complexes with alkoxide co-ligands was
first achieved with the mixed Cp-aryloxide system
[
{Y(C Me )(O-2,6-tBu C H )(h-H)} ] that is active for the
5 5 2 6 3 2
[5]
polymerization of ethylene and higher a-olefins. Recently,
other mixed Cp-aryloxide complexes of samarium(ii) have
been shown to be active for the polymerization and block-
copolymerization of ethylene and styrene.[ On the other
hand, among the dozen of structurally well-defined cyclo-
6]
pentadienyl-free lanthanide alkyl-alkoxide(aryloxide) com-
plexes that have been reported to this date,[
7±16]
only the
neutral dialkyl-aryloxide complex [Y{CH(SiMe ) } (O-2,6-
3
2 2
tBu C H )(thf) ] has been shown to exhibit very low ethylene
2
6
3
2
À3
À1 À1
À1
polymerization activity (9 Â 10 kgPEmol(Y)
h bar at
RT).[
9, 18, 19]
This poor ability for ethylene polymerization is
rather surprising since alkoxy ligands are expected to render
the metal center more electron-deficient and more Lewis
acidic.
Further to our work devoted to in situ alkylation of
chlorolanthanocene precursors with dialkylmagnesium re-
agents as alternative, efficient combinations for olefin poly-
merization,[ we have undertaken a study aimed at replacing
chlorolanthanocenes by homoleptic alkoxide lanthanides.
Although much data have been collected to date on alkoxide
complexes of rare earth elements,[4] most of them have
focused on yttrium, lanthanum and lutetium because these
Scheme 1. Routes to neodymin alkoxides.
20]
a) [Nd (m -OR) (m -OR) (OR) (thf) ] [R ˆtBu (1), tAm (2)]:
3
3
2
2
3
4
2
The reaction of NdCl with 3 equiv NaOtBu in THF at 208C
3
for three days gives a single primary product (1), that can be
routinely isolated in 80 ± 90% yield as a pale blue solid
[Scheme 1, Equation (1)]. Compound 1 was also obtained in
90% crude yield by treatment of Nd[N(SiMe ) ] with an
metals provide diamagnetic compounds characterizable by
NMR.[
21±26]
In this study we have chosen to work with
neodymium because complexes of this metal have given some
of the most active group III metallocene based catalysts for
3
2 3
excess (15 equiv) of tert-butyl alcohol in THF at 208C for
three days [Scheme 1, Equation (1)]. Elemental analysis of
the bulk materials was consistent with the composition
[Nd (OtBu) (thf) ]. Compound 1 dissolves easily in benzene,
[2]
olefin polymerization. Considering the complexity of the
alkoxo chemistry of lanthanides,[4] we felt it was essential to
obtain structural information on the alkoxide materials we
would use as precursors for polymerization. Hence, in this
report we describe first the preparation and the structural
3
9
2
1
toluene and hexane. Rather simple H NMR spectra were
expected for 1 because of the single resonance per type of tert-
butoxide ligand and the splitting of the resonances due to the
investigation of some neodymium complexes having simple
and functionalized tert-alkoxide ligands.[
23, 27±30]
In a second
presence of paramagnetic neodymium metal centers. Variable
1
part we show that some of these compounds act as efficient
inorganic pre-catalysts, once combined with dialkylmagnesi-
um compounds, for the controlled polymerization of ethylene
and ethylene-methyl methacrylate block copolymerization.
Insights into the mechanistic aspects of the formation of active
species and polymerization reactions are also given. Part of
this work has already been communicated.[
temperature H NMR spectra in [D ]toluene of crude samples
8
obtained by either Equation (1) or (2) were, however,
complex with broad resonances. The spectra of samples
produced by salt metathesis using NaOtBu [Eq. (1)] and
subsequently recrystallized from toluene proved much more
informative, featuring at 58C seven well-resolved peaks in the
31]
[34, 35]
region ranging from d 45 to À30 ppm (Figure 1).
Correlation between chemical shift and coordination mode
of the alkoxide groups has been previously noted in yttrium
and lanthanum complexes of this type; that is, increased
bridging is associated with lower field shifts.[
21, 22, 36]
This could
Results and Discussion
not be applied, however, to determine unambiguously the
geometry of 1 in solution, due to the effects of the para-
magnetic neodymium centers, and a crystallography study was
therefore undertaken.
X-ray quality crystals of 1 were grown at À58C from a
concentrated toluene solution of a sample prepared from
NaOtBu. Complex 1 is a trimetallic compound in which the
three neodymium atoms comprise a triangle with doubly
Synthesis and structural diversity ofneodymium alkoxides : To
explore structural, steric and electronic effects on polymer-
ization catalysis, a set of neodymium alkoxide complexes was
prepared. In addition to known mononuclear homoleptic
[32]
complexes, that is [Nd(O-2,6-tBu -4-Me-C H ) ]
and
several new complexes were synthe-
sized by varying two parameters which have proven essential
2
6
2 3
[
27a]
[
Nd(OCtBu ) (thf)],
3 3
bridging alkoxide groups along the edges of the Nd triangle
3
[4]
in the field: i) the nature of the alkoxide ligand and ii) the
synthetic route.[ A summary of the chemistry presented in
this section is given in Scheme 1.
and triply bridging groups above and below the Nd plane
3
33]
(Figure 2). One neodymium atom has two terminal tert-
butoxy ligands and one terminal tert-butoxy ligand and a THF
3774
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Chem. Eur. J. 2002, 8, No. 16

Neodymium Alkoxides
3773±3788
The terminal NdÀO distances of the alkoxide ligands
Nd1ÀO3 2.147(4), Nd2ÀO4 2.163(3) ä) (Table 1) compare
(
well with those found in related complexes, for eaxample
[
[24]
Nd (OCH tBu) ] (2.138(8) ä), [Nd (OCHiPr ) (L) ] (for
4 2 12 2 2 6 2
L ˆ THF: 2.146(4) ± 2.160(4) ä, for L ˆ Py: 2.133(4) ±
[
29]
2
2
2
.158(4) ä),
[Nd(OCtBu ) (CH CN) ]
(2.149(5) ±
3
3
3
2
.171(5) ä),[
.171(3) ä).[
28a]
27b]
and [Nd(OCtBu ) (m-Cl)Li(thf) ] (2.150(3) ±
3
3
3
Doubly bridging NdÀO distances are, as
expected, somewhat longer than those of the terminal
alkoxide ligands, one m -OtBu ligand forming a symmetric
2
bridge to the two equivalent Nd atoms (Nd1ÀO5 2.399(3) ä),
2
while the two other m -OtBu ligands form a disymmetric
bridge (Nd1ÀO2 2.333(3), Nd2ÀO2 2.458(3) ä) and average
2
2
.396 ä. The latter values are comparable to m -bridging
Figure 1. 1H NMR spectrum of [Nd
3
3 2 2 3 4 2
(m -OtBu) (m -OtBu) (OtBu) (thf) ]
NdÀO distances of 2.383(4) ± 2.394(4) ä found in [Nd (O-
(
1) ([D
8
]toluene, 58C; * labels indicate residual solvent resonances).
2
[
29]
CHiPr ) (L) ] (L ˆ thf, py, dme),
and of 2.320(12) ±
The same comments
2
6
2
[
24]
2
.381(12) ä in [Nd (OCH tBu) ].
4 2 12
apply to the triply bridging NdÀO bond length (Nd1ÀO1
2
.409(3), Nd2ÀO1 2.624(3) ä). Due to the steric demands in
the bridges, all of the three Nd atoms are highly distorted from
the ideal octahedral geometry. The Nd1-O3-C9 angle of
1
77.8(4)8 is nearly linear, showing that the thf ligand does not
bring significant steric hindrance. On the other hand, because
of the replacement of the thf by a terminal bulky OtBu ligand,
the Nd2-O4-C13 angle is bent to 167.3(4)8. The elongated
Nd1ÀO6(thf) distance of 2.661(4) ä, compared with the
[
38]
2
.50 ± 2.58 ä distances found in [NdCl (thf) ],
[Nd (O-
3
4
2
[24]
5
[39]
CHiPr ) (thf) ],
[(h -C H ) Nd(thf)],
and
[{(h-
2
6
2
5
5
[
3
40]
C H ) Nd(thf) }{Nd(h-C H ) }], gives another evidence for
8
8
3
2
8
8 2
steric crowding in this molecule.
Retrospectively, the pattern of seven resonances with an
integrated ratio of ca. 2:2:1:1:2:2:1 in the H NMR spectrum
3 3 2 2 3 4 2
Figure 2. ORTEP plot of [Nd (m -OtBu) (m -OtBu) (OtBu) (thf) ] (1) with
probability ellipsoids at 30% (hydrogen atoms omitted for clarity).
1
at 58C (Figure 1) correlates well with the structure of 1
(
Figure 2) which contains nine OtBu groups in five distinct
[41]
molecule ligate each of the two other neodymium atoms.
Thus, each neodymium atom in 1 is six-coordinated. The same
structure framework has been observed previously in hetero-
leptic complexes [Y (m -OtBu)(m -Cl)(m -OtBu) (OtBu) -
environments and two equivalent thf molecules.
This
suggests that the solid state structure of 1 is retained in
hydrocarbon solutions; in particular, this may indicate that
there is no transformation at this temperature between the
two possible isomers differing in the location of the THF
ligands.
3
3
3
2
3
4
thf)2][
21a]
and [Y (m -OtBu)(m -Cl)(m -OtBu) (OtBu) Cl-
3 3 3 2 3 3
and of homoleptic complex [La (OtBu) (tBuO-
3 9
(
[
21b]
(
thf) ],
2
[
23a, 37]
H)2]
The exact location of the tert-butyl alcohol mole-
The preparation of neodymium tert-amyloxide from NdCl
3
cules in the latter lanthanum complex could not be formally
and NaOtAm in THF at room temperature was similarly
established because of disorder problems.[
23a]
In both of the
performed, giving a pale-blue solid (2) in 66% yield. The
1
aforementioned yttrium complexes, the THF molecules were
variable temperature H NMR spectra of 2 in [D
]toluene and
8
found to be located on the same side of the Y plane, as the
In contrast, complex 1 has one THF
molecule on each side of the trimetallic plane.
in [D ]THF are complex. In fact, the expected multiplicity
8
3
chloride ligands.[
21a,b]
(singlets, triplets, quartets) for the different types of hydrogen
was hampered by the paramagnetic neodymium centers and
the spectra featured many singlet-like resonances that turned
out uninformative. Previous reports have shown that the tert-
butoxide and the tert-amyloxide groups enforce similar
structures in group III (Y, La, Pr) alkoxide chemistry.[
It is therefore reasonable to assume that 2 has the same
structure as 1. This hypothesis is comforted by the nearly
identical reactivity of 1 and 2 in ethylene polymerization
chemistry (see below).
Table 1. Selected bond lengths [ä] and angles [8] for complex 1.
Nd1ÀO3
2.147(4)
2.333(3)
2.399(3)
2.409(3)
2.661(4)
2.163(3)
2.458(3)
2.624(3)
3.6318(6)
3.7161(4)
3.7161(4)
Nd1-O1-C1
Nd2-O1-C1
Nd1-O2-C5
Nd2-O2-C5
Nd1-O5-C17
Nd1-O3-C9
Nd2-O4-C13
Nd1-O1-Nd1'
Nd1-O1-Nd2
Nd1'-O1-Nd2
Nd1-O2-Nd2
123.1(3)
120.0(3)
131.9(3)
126.4(3)
130.82(9)
177.8(4)
167.3(4)
94.92(11)
95.11(11)
92.51(11)
101.68(12)
23a, 42]
Nd1
ÀO2
Nd1ÀO5
Nd1ÀO1
Nd1ÀO6
Nd2ÀO4
Nd2ÀO2
Nd2ÀO1
Nd1ÀNd1'
Nd1ÀNd2
Nd2ÀNd1'
b) [Nd (OtAm) (HOtAm) Cl Na] ¥ (OEt ) (3): When the
1
2
26
2
11
2 2
above salt metathesis reactions between NdCl and 3 equiv of
3
NaOtBu or NaOtAm were carried out in diethyl ether instead
Chem. Eur. J. 2002, 8, No. 16
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3775

J.-F. Carpentier et al.
FULL PAPER
of THF as the solvent, the reactions took a different course
Table 2. Selected bond lengths [ä] and angles [8] for complex 3.
(
Scheme 1, Equation (3)). The crude products recovered after
À
Nd1 O5
Nd1ÀO2
Nd1ÀO1
Nd1ÀCl5
Nd1ÀCl1
Nd2ÀCl7
Nd2ÀCl1
Nd3ÀO3
2.100(7)
2.348(7)
2.521(6)
2.842(3)
2.992(2)
2.834(3)
3.009(2)
2.483(7)
2.848(3)
3.010(3)
2.109(7)
2.374(7)
2.380(7)
2.442(7)
2.545(7)
2.090(7)
2.370(8)
2.555(7)
2.792(3)
2.991(3)
2.808(3)
2.870(3)
2.945(3)
2.961(3)
2.799(3)
Nd1-O5-C21
Nd1-O2-C6
Nd1-O1-C1
163.7(8)
127.4(7)
118.9(5)
169.49(13)
177.4(2)
169.11(12)
100.1(2)
98.0(3)
usual workup were slightly soluble in hexane and toluene, and
their H NMR spectra were complex, featuring many
1
Nd1-Cl5-Nd4
Nd1-Cl1-Na1
Nd8-Cl7-Nd2
Nd2-Cl1-Na1
Nd3-O3-Nd2
O12-Nd4-Cl5
Cl5-Nd4-Cl2
Nd5-O14-C66
Nd5-O10-Nd6
Nd5-O9-Nd4
Nd5-O8-Nd6
Nd5-O13-C61
Nd7-O19-C91
Nd8-O17-Nd7
Nd8-O16-Nd7
Nd7-Cl6-Nd6
Nd7-Cl3-Na1
O20-Nd8-Cl7
Nd9-Cl1-Nd8
O20-Nd8-Cl3
Nd10-Cl4-Nd12
Nd12-Cl9-Nd3
resonances with variable line shape. Recrystallization of the
crude products from toluene gave crystalline products in low
yield in both cases; however, the latter were no longer soluble
in toluene nor in THF. X-ray quality crystals were obtained
for the tert-amylate derivative (3) that allowed to establish its
geometry in the solid state.
Compound 3 has an unprecedented complex aggregate
structure basically formed of four independent trinuclear Nd3
units that are linked by sharing m -chloro ligands (Figure 3). In
Nd4-Cl5
Nd4ÀCl2
Nd5ÀO14
91.9(2)
90.87(8)
176.7(9)
103.2(3)
103.3(3)
98.2(2)
147.0(6)
171.1(9)
105.9(3)
96.3(2)
173.00(14)
165.2(2)
95.3(2)
85.72(7)
173.6(2)
77.39(6)
170.39(12)
Nd5 O10
Nd5ÀO9
Nd5ÀO8
Nd5ÀO13
Nd7ÀO19
Nd7ÀO17
Nd7ÀO16
Nd7ÀCl6
Nd7ÀCl3
Nd8ÀCl7
Nd8ÀCl10
Nd8ÀCl3
Nd10ÀCl4
Nd12ÀCl9
À
2
in D, is clearly revealed by the longer NdÀO bond lengths
Nd5ÀO13 2.545(7) ä, Nd11ÀO28 2.435(12) ä) compared
with the adjacent and other terminal Nd-OtAm groups
Nd5ÀO14 2.109(7) ä, Nd11ÀO26 2.089(8) ä). This is also
reflected in the smaller La-O-C bond angles (Nd5-O13-C61
47.0(6)8, Nd11-O28-C136 158.2(18)8) for the coordinated
alcohols, which have only one lone pair for p-donation for
donation into vacant metal orbitals, versus the angles of the
adjacent covalently bound tert-amyloxy groups which have
two lone pairs and therefore approach a limiting angle of 1808
(Nd5-O14-C66 176.7(9)8, Nd11-O26-C126 174.0(10)8). Each
(
(
2 2 2
Figure 3. ORTEP plot of [Nd12(OtAm)26(HOtAm) Cl11Na] ¥ (OEt ) ] (3)
with probability ellipsoids at 30% (carbon and hydrogen atoms omitted for
clarity).
1
addition, a sodium atom is present which is coordinated by
four chlorine atoms related to three Nd3 units and that
enforces no symmetry in the molecular structure.[ Schemati-
cally, it is possible to divide the structure of 3 in four
trimetallic fragments A ± D and one NaCl molecule (Fig-
ure 3). The formulas for A ± D, that do not describe the
bridging between the fragments, that is [Nd (m -OtAm)(m -
43]
of the four Nd
lengths in the range of 2.945(3) ± 3.022(3) ä, values that
units has one m
-Cl ligand with NdÀCl bond
3
3
compare well with that observed in [Nd
(OiPr)17Cl]
6
(3.05(1) ä)[ where the chloride atom is equidistant from
the six Nd atoms in a trigonal prism. All fragments A ± D, as
defined with the above formula units, have coordinative
vacancies which are filled by linking A ± B, B ± C, C ± D, D ± A
and A ± C through symmetrically bridging chloride ligands
44]
3
3
3
Cl)(m -OtAm) (OtAm) Cl] (A: Nd1ÀNd3), [Nd (m -OtAm)-
2
3
3
3
3
(
m -Cl)(m -OtAm) (OtAm) Cl(HOtAm)] (B: Nd4ÀNd6),
3
2
3
3
[Nd (m -OtAm)(m -Cl)(m -OtAm) (m -Cl)(OtAm) Cl]
(C:
3
3
3
2
3
2
3
Nd7ÀNd9) and [Nd (m -OtAm)(m -Cl)(m -OtAm) (m -Cl)(O-
with normal Nd-(m -Cl) distances (2.792(3)-2.848(3) ä). The
3
3
3
2
3
2
3
tAm) Cl(HOtAm)] (D: Nd10ÀNd12), show structural rela-
Nd-Cl-Nd bond angles for the links between the fragments are
all similar (four in the range 169.11(12) ± 173.00(14)8), except
the one linking fragments C and D (151.97(13)8). This narrow
angle likely results from the constraint induced by the
coordination of the Na atom. Indeed, the latter is four-
3
tionships between these fragments and heteroleptic trinuclear
complexes reported in the literature. Thus, fragments A and B
have a formula unit related to [Y (m -OtBu)(m -Cl)(m -Ot-
3
3
3
2
[21b]
Bu) (OtBu) Cl(tHF) ]
and, structurally, these units are
3
3
2
nearly identical. Fragments C and D feature also a similar
structure and a formula unit related to A and B except that a
m -Cl ligand has replaced a m -OtBu ligand. As shown in
coordinated by one m
bridging two Nd
units, with NaÀCl distances in the range of
3.222(11) ± 3.339(11) ä. These NaÀCl distances are much
longer than those observed in [LnNa (OtBu)10Cl] complexes
3
-Cl, two internal m -Cl and one m -Cl
2
3
3
2
2
Table 2, the bond length observed for the terminal alkoxide
8
(
2.090(8)À2.113(7) ä in A and B; 2.070(7)À2.100(7) ä in C
(Ln ˆ Y, Eu; 2.642(5) ± 3.032(5) ä; average NaÀCl,
2.82(13) ä).[
43]
and D), the bridging Nd-O(m -OR) (2.347(7)À2.497(7) ä in A
2
and B; 2.314(7)À2.380(7) ä in C and D) and Nd-O(m -OR)
3
(
2.442(7) ± 2.521(6) ä in A and B; 2.452(7) ± 2.555(7) ä in C
c) [Nd (m -OtBu) (m -OtBu) (OtBu) (HOtBu) ] (4): The re-
3
3
2
2
3
4
2
and D) are similar to those found in 1. The presence of two
coordinated molecules of HOtAm, one in fragment B and one
action of Nd[N(SiMe ) ] with 8 equiv (per mol Nd) of tert-
butyl alcohol in n-hexane at 208C gives a single primary
3 2 3
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Chem. Eur. J. 2002, 8, No. 16

Neodymium Alkoxides
3773±3788
product in 90% yield. Crystallization from toluene yielded
violet-blue crystals that analyzed for [Nd (OtBu) (HOtBu) ]
3
9
2
1
(
4) (Scheme 1, Equation (4)). Variable temperature H NMR
studies were carried out to derive structural information on
this alkoxide in solution. The room temperature 200 MHz
1
H NMR spectrum of 4 in [D ]toluene showed very broad
8
resonances characteristic of a fluxional behavior and temper-
atures below 58C were required to slow down the exchange
process. Due to effects of the paramagnetic neodymium
centers, important variations in the chemical shifts were
observed in the temperature range of À75 to 58C, causing
incidental, potentially misleading, overlapping of some reso-
nances, for example at À15 and À658C (see Experimental
1
Section). The H NMR spectrum of 4 at À458C showed a
major series, accounting for 96 Æ 2% of total OtBu groups, of
six well-resolved, relatively sharp resonances with intensities
in the ratio 18:36:9:2:18:18, from lower to higher field. This
pattern is fully consistent with the trinuclear geometry
5 5 3 4 2 4 5
Figure 4. ORTEP plot of [Nd (m -O)(m -OtBu) (m -OtBu) (OtBu) ] (5)
with probability ellipsoids at 30% (carbon and hydrogen atoms omitted for
clarity).
established for the equivalent yttrium and lanthanum com-
pounds,[
23a]
isostructural to 1, that contains two capping m3-
Table 3. Selected bond lengths [ä] and angles [8] for complex 5.
OtBu groups magnetically equivalent (singlet of relative
Nd1ÀO1
Nd1ÀO2
Nd1ÀO5
2.146(9)
2.418(5)
2.473(9)
2.523(3)
2.351(3)
2.138(6)
2.4933(8)
1.402(18)
1.458(10)
1.415(13)
1.423(12)
Nd1-O1-C1
Nd1-O2-C4
Nd2-O2-C4
Nd1-O2-Nd2
Nd2-O3-C7
Nd2-O3-Nd2C
Nd2-O4-C10
Nd2-O5-Nd2A
Nd1-O5-Nd2
Nd2B-O5-Nd2
Nd1-O5-Nd2B
180.000(3)
126.5(5)
121.1(3)
95.38(15)
131.18(12)
96.73(18)
178.8(6)
170.4(4)
94.8(2)
intensity 2), three bridging m -OtBu groups in two different
2
environments (2‡1), and two terminal ligands for each metal
of which two out of six are the coordinated tBuOH (2‡4).
Beside this major set of resonances, a significant minor series
of six peaks was also observed in the variable temperature
NMR spectra; its relative intensity versus the major series
Nd2 O2
Nd2ÀO3
Nd2ÀO4
Nd2ÀO5
O1ÀC1
À
(
4 Æ 2%) did not vary within uncertainty in the temperature
O2ÀC4
range of À75 to 58C. This suggests, as in the case of 1, the
existence of two isomeric structures differing in the relative
location of the coordinated alcohols, that is either both on the
O3ÀC7
89.60(3)
94.8(2)
O4ÀC10
same side or on opposite sides of the Nd plane.
3
bonds in complexes 1, 3, 4, and the aforementioned neo-
dymium alkoxy complexes. Also, the terminal ligands are
associated to nearly linear Nd-O-C angles (178.8(6) ±
180.0(0)8), much larger than those for bridging ligands
(121.1(3) ± 131.18(12)8). Contrary to the lanthanum equiva-
d) [Nd (m -O)(m -OtBu) (m -OtBu) (OtBu) ] (5): Stirring a
toluene solution of complex 4 for two weeks at room
temperature resulted in the formation of complex 5
5
5
3
4
2
4
5
(
Scheme 1, Equation (5)). The variable temperature
1
[22b]
[43]
H NMR spectra in the range of À70 to 208C displayed
broad, unresolved resonances and did not provide an insight
into the solution structure of 5. The identity of 5 was
established by X-ray diffraction (Figure 4, Table 3). The
molecular structure corresponds to a pentagonal cluster made
of four basal and one apical neodymium centers having each
one terminal OtBu group, connected by four m - and four m -
lent of 5,
apical Nd-m
but as observed in [Nd (m -O)(OiPr)13], the
-oxo bond length (Nd1ÀO5 2.473(9) ä) is only
5 5
5
slightly shorter than those involving the basal neodymium
centers (Nd2ÀO5 2.4933(8) ä).
2
2
1
e) [Nd (m ,h -OR) (h -OR) (h -OR) ] (OR ˆ OCMe CH -
2
2
2
2
2
2
2
CH OMe) (6): The foregoing examples have shown that
3
2
2
bridging OtBu groups and comprising a central m -oxo ligand.
This corresponds to the basic square pyramidal framework
neodymium centers expand readily their coordination sphere
by additional adduct formation despite the presence of the
relatively bulky tert-butoxy and tert-amyloxy ligands. To
enforce a lower degree of agglomerization we investigated
the use of a g-donor-functionalized alcohol. The aminolysis
reaction of Nd[N(SiMe ) ] with three equivalents of the
5
observed for lanthanide oxoisopropoxides [Ln (m -
5
5
[45±47]
O)(OiPr) ]
and the lanthanum equivalent of 5, which
1
3
has been independently reported during the course of this
study.[
22b]
The Nd square pyramid in 5 is quite regular as
5
3 2 3
revealed by the equivalence of the basal Nd atoms and the
nearly 908 Nd-O-Nd bond angles (Nd2B-O5-Nd2 89.60(3)8,
Nd1-O5-Nd2 94.8(2)8), with the apical/basal Nd ¥¥¥ Nd dis-
tance longer than the basal/basal one (3.6550(6) versus
monoclinching alcohol 4-methoxy-2-methylbutan-2-ol in ben-
zene at 208C gives, after recrystallization from toluene, blue
[
48]
crystals of 6 [Eq. (6)].
Again, the variable temperature
1
H NMR spectra in [D ]toluene of this compound showed
8
3
.5139(5) ä). The NdÀO distances of the terminal alkoxide
broad, unresolved resonances and proved uninformative with
regard to its solution structure.
An X-ray diffraction study revealed that complex 6 adopts
in the solid-state a symmetric dinuclear structure in which the
ether-alkoxide ligand is found in three different ligation
ligands (Nd1ÀO1 2.146(9), Nd2ÀO4 2.138(6) ä), the doubly
bridging ligands (Nd2ÀO3 2.351(3) ä) and the triply bridging
ligands (Nd1ÀO2 2.418(5), Nd2ÀO2 2.523(3) ä) all fall within
the range of values observed for the terminal NdÀO(alkoxy)
Chem. Eur. J. 2002, 8, No. 16
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J.-F. Carpentier et al.
FULL PAPER
2
modes (Figure 5). As shown in Table 4, the neodymium
distance in the m ,h -ligand (Nd1ÀO3 2.5198(13) ä) is com-
2
2
centers are symmetrically bridged by two m ,h -ligands
parable to values found in much less crowded complexes, for
example [NdCl (thf) ] (average 2.50 ä).
3 3
The solid-state structure of 6 differs significantly from that
observed in the homoleptic dinuclear complex [Lu (OCMe -
CH OMe) ], synthesized according to the silylamide route
from the corresponding b-donor-functionalized alcohol.
[Lu (OCMe CH OMe) ] features an asymmetric structure
2
[38]
through the O(alkoxide) atoms (Nd1ÀO4 2.3977(12) and
2
.3992(12) ä; bite angle O4-Nd1-O3 78.26(4)8). Each neo-
2
dymium center possesses one terminal h -ether-alkoxide
ligand (bite angle O2-Nd1-O1 70.70(5)8) and one terminal
h -alkoxide ligand, and is thus six-coordinated. The axial O1-
2
2
2
6
1
[25]
Nd1-O6 angle of 163.73(5)8 is distorted from the idealized
2
2
2
6
2
1808, likely because of steric demands in the bridge and in the
with three m ,h -bridging ligands, resulting in a completely
2
six-membered chelate ring. This steric crowding is further
documented by the bending of the terminal OtBu ligand
different alkoxide environment for the two lutetium centers
that are, respectively, six-coordinated and seven-coordinated.
Enhanced steric flexibility of our b-functionalized alkoxy
ligand and a large difference in the effective ionic radii of the
six-coordinated metal centers (Lu 1.00 ä; Nd 1.12 ä)
presumably account for these structural changes.
(
Nd1-O6-C16 163.57(13)8), as discussed for 1. The NdÀO(alk-
oxide) bond lengths in 6 lie within the range of values
observed for the different structural types of OtBu ligands in
complexes 1, 3, 4, 5 and the other aforementioned neodymium
alkoxy complexes. The terminal NdÀO(alkoxide) bond length
3‡
3‡
[49]
2
in the h -ligand (Nd1ÀO2 2.1759(13) ä) is only slightly
f) Comments on synthetic and structural aspects related to
neodymium alkoxides: A set of polynuclear neodymium
alkoxides, featuring a remarkable structural diversity and
complexity, has been obtained from simple monometallic
precursors. Although the detailed intermediates and inter-
conversion processes involved in the construction of these
polymetallic alkoxides remain to be clarified, the results
described above give clear evidence how specific factors
substantially influence the outcome of the syntheses.
1
elongated compared to that in the h -ligand (Nd1ÀO6
2
.1526(13) ä); this indicates rather weak ring strain in the
2
terminal h -ligand. The NdÀO(ether) contact within this
chelate ring (Nd1ÀO1 2.6629(14) ä) compares well with the
long NdÀO(thf) distance of 2.661(4) ä observed in 1, ascribed
to steric crowding. On the other hand, the NdÀO(ether)
Particularly striking is the importance of the reaction
details, that is, the choice of alkali metal countercation and
ether solvent, during simple ionic metathesis reactions
between NdCl and alkali metal alkoxides. Given the numer-
3
ous examples in group III organometallic chemistry in which
the presence and specific nature of the cation strongly
influences the chemistry,[
1, 4]
it is not unreasonable to see
somewhat different results in the NaOR versus KOR (R ˆ
tBu, tAm) reactions.[ Wider variety of products and, in
particular, presence of several alkali metal atoms in yttrium
alkoxides has been often associated to LiOtBu (versus
NaOtBu) since lithium appears to be more readily carried
along in these systems.[ The incorporation of alkali metal
atoms and of chloride in the yttrium systems has been
35]
21]
2
2
1
Figure 5. ORTEP plot of [Nd
2
(m
2
,h -OR)
2
(h -OR)
2
(h -OR)
2
] (OR ˆ OC-
[21]
suggested to result from steric considerations; contrary to
Me CH CH OMe) (6) with probability ellipsoids at 30% (hydrogen atoms
2
2
2
3‡
3‡
[49]
omitted for clarity).
relatively large lanthanides (La 1.17 ä, Nd 1.12 ä), an
yttrium analogue of 1, that is, [Y (m -OtBu) (m -OtBu) (O-
3
3
2
2
3
tBu) (thf) ], would be too crowded because of the two m -OtBu
Table 4. Selected bond lengths [ä] and angles [8] for complex 6.[a]
4
2
3
3‡
groups, but the small Y (1.04 ä) would sterically accom-
Nd1ÀO6
Nd1ÀO2
Nd1ÀO4
Nd1ÀO4'
Nd1ÀO3
Nd1ÀO1
Nd1ÀNd1'
2.1526(13)
2.1759(13)
2.3977(12)
2.3992(12)
2.5198(13)
2.6629(14)
3.8615(2)
O4-Nd1-O3
O4'-Nd1-O3
O2-Nd1-O1
O4-Nd1-O1
O4'-Nd1-O1
O3-Nd1-O1
C1-O1-C2
Nd1-O1-C1
Nd1-O1-C2
Nd1-O2-C4
Nd1-O3-C8
Nd1-O3-C7
Nd1-O4-C10
Nd1'-O4-C10
Nd1-O4-Nd1'
Nd1-O6-C16
C13-O5-C14
78.26(4)
150.45(4)
70.70(5)
84.40(4)
92.17(5)
[
21]
modate more easily the less bulky chloride and lithium ions.
3
‡
The formation with the early lanthanide Nd of homoleptic
alkoxides 1, 2 and heteroleptic complex aggregate 3, upon
replacing THF by Et O, respectively, suggests that factors
2
79.13(5)
106.6(2)
other than steric considerations should be also taken into
account. The discrepancy noticed between ethers could be
due to the different solubility of metal alkali chlorides and/or
LnCl in these solvents. In addition, the ability of LnCl to
119.98(13)
126.82(16)
151.88(12)
129.22(12)
115.49(14)
132.30(11)
120.41(10)
107.22(4)
163.57(13)
112.0(2)
O6-Nd1-O1
O2-Nd1-O4
O2-Nd1-O4'
O6-Nd1-O2
O6-Nd1-O3
O6-Nd1-O4
O6-Nd1-O4'
O4-Nd1-O4'
O2-Nd1-O3
163.73(5)
154.46(5)
112.67(5)
98.62(5)
89.12(5)
104.34(5)
103.46(5)
72.78(4)
91.21(5)
3
3
form THF adducts (LnCl ¥ OEt adducts are not reported in
3
2
the literature) can also be a likely reason for such differences.
Olefin polymerization catalysis
As highlighted in the Introduction and will be further
illustrated later on in the present study, alkyl/alkoxide meta-
[
a] Only the major site-occupancy for C2 and C3 are listed.
3778
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Neodymium Alkoxides
3773±3788
thesis reactions have proved complicated and rather unpre-
dictable. Therefore, a systematic investigation of the reactivity
of each lanthanide alkoxide complex we prepared with a
variety of potential alkylating reagents would be extremely
time- and energy-consuming. In addition, previous work in
the field has shown that the isolation of peculiar, structurally
well-defined alkyl-alkoxy-lanthanide complexes does not
warrant the identification of active olefin polymerization
systems (see Introduction). Thus, to explore the ability of the
lanthanide alkoxides to serve as Cp-free precursors for olefin
polymerization and to detect promising new catalyst systems,
we decided to use a more rapid screening approach by
investigating directly the reactivity of in situ combinations.
oxo-complex 5 and dinuclear complex 6 with a g-donor-
functionalized alkoxy ligand proved completely ineffective.
It is noteworthy that, although trinuclear complexes 1 and 2
contain two coordinated THF molecules, the addition of
1 mol equiv THF per mol Nd (i.e., 0.3 equiv per mol 1) proved
sufficient to inhibit all polymerization activity.[ Inhibition
was also observed when 1 equiv NaCl (or KCl) per mol Nd
51]
was added to the 1/Mg(n-hex) (1:1) system. These results
2
show the extreme sensitivity of the active species generated
from this combination towards Lewis bases. This may account
for the inefficiency of the systems based on Grignard reagents
since these potential activators are only available as ether
solutions, and those based on complexes 3 and 6, since they
each contain ™poisoning∫ moieties within their structure.[
52]
a) Ethylene polymerization promoted by Nd (OR) L /MR
z
x
y
n
combinations prepared in situ: A variety of in situ combina-
b) Slurry-phase ethylene polymerization promoted by 1/
tions between lanthanide alkoxides and alkylating agents
MgR in situ combinations: In situ combinations of tert-
2
MR , which may be compared to classic multi-component
butoxy complex 1 and dialkylmagnesium in toluene were
selected for further investigations. Representative results are
summarized in Table 5 and Figures 6 and 7. In terms of
z
Ziegler± Natta catalysts, was evaluated in ethylene polymer-
ization by varying both alkyl/alkoxide metathesis (step 1) and
polymerization (step 2) conditions, that is, Nd/MRz ratio,
reaction time and temperature, and solvent. The most striking
result of this preliminary screening is that only dialkylmagne-
sium reagents lead to active systems under 1 atm ethylene in
toluene; no polymerization activity was detected upon using
nBuLi, tBuLi, AlMe , Al(n-oct) , AlH(iBu) , [nBuAlH-
3
3
2
(
iBu) ][Li], BEt3 or even Grignard reagents (PhMgBr,
2
EtMgBr), under various reaction conditions. It is noteworthy
that this does not necessarily imply the absence of alkyl/
alkoxide metathesis processes between some of these re-
agents and the neodymium alkoxides (see below).
Using one equivalent of di(n-hexyl)magnesium per mol Nd
as co-reagent and toluene or hexane as the solvent, several
neodymium alkoxides proved to be effective polymerization
catalyst precursors. tert-Butoxy- and tert-amyloxy neodymium
complexes 1 and 2, prepared by salt metathesis, equally as
bulk or recrystallized materials,[ showed a comparable
activity, observed since À508C and which proved moderate
in the temperature range of À20 to 408C. The average activity
Figure 6. Ethylene flowrates observed with 1/Mg(n-hex)
Nd ˆ 1.0, 1 ˆ 0.33 mmol, 08C, 1 atm).
2
systems (Mg/
33]
polymerization efficiency, the alkyl/alkoxy metathesis appears
to be best conducted at 08C for 1 h with different dialkyl-
magnesium reagents. The nature of the latter affects the
activity of the system as judged by the amount of polyethylene
recovered after 1 h and also by the ethylene flow rates
(Figure 6). Compared to n-butylethylmagnesium and di(tri-
methylsilylmethyl)magnesium, di(n-hexyl)magnesium gives
the most productive catalyst. The activity of this system hits
its maximum after a few minutes and then decreases,
concomitantly with the appearance of an insoluble polymer-
like material (see below), to reach a plateau, apparently
independent of the dialkylmagnesium used (Figure 6). Such a
behavior is observed, however, only for a definite Nd to Mg
ratio of 1.0, as deviation from this value resulted in a rapid
drop of the activity (Figure 7). This contrasts markedly with
chlorolanthanocene/dialkylmagnesium systems that proved to
over 1 h under 1 atm at 08C is A
complex (1,2) ˆ 5 ±
0
8C
À1 À1
À1
8
kgmol(Nd) h bar (range observed over 10 different
experiments and/or batches of 1 or 2). Activities in the same
range were obtained upon using samples of 1 prepared by
alcoholysis of the silylamide precursor [Nd(N(TMS) ) ] with a
2
3
slight excess of tBuOH in THF [Eq. (2)]; this establishes that
possible minor chlorine contamination in samples of 1
prepared by salt metathesis does not interfere to a significant
extent. On the other hand, the in situ system based on tert-
butoxy complex 4, prepared by a similar alcoholysis route but
using benzene as solvent [Eq. (4)] and which is analogous
to 1 except that the THF ligands have been replaced
by tBuOH, showed an activity about two orders of magni-
tude lower under similar conditions (A
(complex 4)
0
8C
À1 À1
À1 [50]
ꢀ
0.08 kgmol
h
bar ).
Homoleptic mononuclear com-
plexes of tritox, [Nd(OCtBu ) (thf)], and of a usual bulky
accommodate up to 40 equiv MgR per mol Ln with still high
3
3
2
ethylene polymerization activity.[ The activity of the 1/
20]
aryloxy ligand, [Nd(O-2,6-tBu -4-Me-C H ) ], led also to
2
6
2 3
poorly active systems, both requiring temperatures above
Mg(n-hex) combination at 08C, that is, A (complex 1) ˆ
2
08C
À1 À1
À1
À1 À1
À1 [53]
2
08C to initiate polymerization (A
ˆ 0.6 kgmol
h
bar
5 ± 8 kg mol(Nd)
h
bar ,
corresponds to a moderate
4
08C
[50]
[17]
for both systems).
Chloro-bridged complex aggregate 3,
value on absolute Gibson×s activity scale, which obviously
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J.-F. Carpentier et al.
FULL PAPER
combination toward transfer agents was briefly evaluated
using phenylsilane and hydrogen. The introduction of
1
0 equiv PhSiH (per mol Nd) after 5 min of polymerization
3
did not affect the ethylene flow rate shown in Figure 6 and the
related productivity at 08C. The analysis of the polymer
recovered after 1 h revealed, however, that a transfer reaction
had occurred, as the M decreased to 14300 with M /M ˆ 25.
n
w
n
1
13
H and C NMR analysis of the polymer clearly showed the
[54]
formation of end-capped PhSiH -polyethylene.
Dihydro-
2
gen proved an even better transfer agent: compared to the
reaction carried out with pure ethylene, using 2% (v/v) of H2
in ethylene led to a similar activity profile but with almost
À1 À1
À1
doubled productivity (9 ± 10 kgmol
h bar ) (Figure 6).
Figure 7. Influence of the Mg/Nd ratio on the polymerization activity of
Analysis of six aliquots sampled every 10 min over the
polymerization course under those conditions indicated a
the 1/Mg(n-hex)
2
system (1 ˆ 0.33 mmol, 08C, 1 atm C
2 4
H ).
constant M value of 17000 (Æ500) and a molecular weight
n
distribution M /M of 5.8, showing that an efficient transfer
does not compete with the best multi-component Ziegler±
w
n
Natta and metallocene catalysts described so far.[2, 3] It
has also occurred. Effective response of the catalyst system to
H was observed in the range 1 ± 10% (v/v). Nevertheless, this
remains, however, somewhat higher than that for an equiv-
alent lanthanocene system, for example, [Cp* SmCl Li(OEt ) ]/
2
could not be used to prevent catalyst decay at temperatures
above 08C; for example, the productivity of the 1/Mg(n-hex)2
2
2
2 2
À1 À1
À1
nBuEtMg (1:1) gave 0.34 kgmol
h bar under the same
reaction conditions.[
20c]
combination at 208C in the presence of 2% (v/v) of H
2
À1 À1
À1
decreased to 4.4 kgmol
h
bar (M ˆ 7800; M /M ˆ 37).
The polyethylenes recovered under these conditions, after
methanol quenching, workup and drying, are highly crystal-
line (85 ± 90% according to DSC and XRD) with consistent
n
w
n
d) Reactivation ofin situ systems –Isolation ofheterogene-
ous active polymerization species: The apparent polymer-
high Tm in the range 139 ± 1438C, M ˆ 200000 ± 400000 and
n
ization activity (ethylene flow rate) of the 1/Mg(n-hex)2
M /M ˆ 2.3 ± 2.5. Analysis of aliquots sampled during the
w
n
combination decreases after a few minutes to reach a plateau
polymerization course showed that the polyethylene charac-
teristics do not vary significantly; in particular, high molecular
weight polyethylene (M ˆ 200000, M /M ˆ 2.30) is already
after 60 min, at ꢀ1/10 of the maximal activity (Figure 6). We
observed that the latter could be rapidly, although partially
n
w
n
restored upon adding 1.0 equiv Mg(n-hex) per mol Nd to the
present after 5 min. The monomodality of the GPC profiles is
consistent with the formation of only one type of active
species. No low molecular weight chains with vinyl end groups
were detected (NMR) in the final polymer produced under
these conditions, indicating that at 08C, b-H elimination and
transfer reactions to the monomer are almost absent, if any.
Raising the temperature over 208C led, however, to a severe
decrease in the polymer yield as well as in the molecular
weight (e.g., at 808C: Table 5, entry 8: M ˆ 1700, M /M ˆ
2
reaction mixture; then, polymerization proceeded as in the
initial batch (Figure 8, straight line). Similar restoration of
n
w
n
1.55, 29% vinyl chain ends). This is tentatively ascribed to a
process involving b-H elimination and subsequent deactiva-
tion of the resulting neodymium-hydride species (see below).
c) Slurry-phase ethylene polymerizations conducted in the
presence oftrans fe r agents : The reactivity of the 1/Mg(n-hex)2
Table 5. Ethylene polymerization using 1/MgR
2
combinations. Influence
of reaction conditions on the polymer yield.[
a]
2
Figure 8. Effect of the addition of 1.0 equiv Mg(n-hex) (per mol Nd) to
the reaction mixtures with (––) and without (* * * *) supernatant solution
on the ethylene flowrates (1.0 mmol Mg and Nd used to prepare the in situ
system, 08C, 1 atm).
MgRR'
R, R' ˆ
T alkyl
[8C]
t alkyl
[min]
T polym
[8C]
PE
[g]
1
2
3
4
5
6
7
8
CH
2
SiMe
3
0
0
0
0
0
20
0
0
60
60
180
60
180
60
60
0
0
0
0
0
0
40
80
1.80
1.19
0.53
4.70
1.69
1.09
2.75
0.56
nBu, Et
nBu, Et
n-hex
n-hex
n-hex
activity was achieved three times consecutively from the same
initial in situ combination. This shows that the decrease in the
ethylene flow rate does not stem from an irreversible
deactivation process but suggests rather a gradual ™drowsi-
ness∫ of the active species, that may be associated to the
concomitant accumulation of insoluble, high molecular
weight materials over the reaction course.
n-hex
n-hex
60
[
a] Reactions were carried out in toluene under 1 atm of ethylene for 1 h
using 0.33 mmol of 1 and 1.0 mmol of dialkylmagnesium.
3780
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Neodymium Alkoxides
3773±3788
In order to determine the distribution of total and active Nd
in solution (homogeneous) and in the polymeric material
precipitated (heterogeneous) during the reaction course, the
latter was isolated from the reaction mixture by filtration and
subsequently washed with toluene under rigorous exclusion of
oxygen and water at 08C. The beige solid (S) recovered was
subjected to microanalyses which revealed, over three differ-
ent samples, that 15 Æ 2% of initial Nd (and 20 Æ 4% of Mg) is
present in the precipitate.[ The Nd/Mg ratio in S, 1.2 Æ 0.4
approaches therefore that introduced for the in situ system
precipitate S from the reaction mixture, that contains 80 ±
85% of Nd and Mg initially introduced but proved inactive
towards ethylene, does initiate the polymerization of MMA to
give atactic PMMA in moderate activity.[
57]
On the other hand, the crude polymer recovered from the
reaction of MMA with a slurry of solid S in fresh toluene at
1
08C contained only 3% of extractable products; H NMR
analysis showed that the latter are low molecular weight
MMA-rich block copolymers (MMA/ethylene ꢀ 3). The
MMA molar fraction in the THF-insoluble material obtained
under typical conditions (see Experimental Section) is 7 Æ 2%
55]
(
Nd/Mg ˆ 1.0). Most interestingly, when S was contacted with
1
ethylene in a fresh toluene slurry (1 atm, 08C), polymerization
took place with the same activity than in the corresponding in
situ experiment, just before its isolation. On the other hand,
the clear filtrate that contains 85 Æ 2% of initial Nd proved
completely inactive toward ethylene, even upon reactivation
according to the weight increase, H NMR and SEC analyses.
The DSC analysis revealed the T of the PMMA block at
g
1228C and the T of the PE block as a narrow peak at 1428C.
m
The SEC analyses of the polyethylene obtained from the
hydrolysis of an aliquot of S (before addition of MMA) and of
the final THF-insoluble material showed an enhancement of
the molecular weight from M ˆ 200000 to M ˆ 250000 with
with fresh Mg(n-hex) . These results establish that all of the
2
active species generated from the in situ combination of 1 with
n
n
Mg(n-hex) (1:1) are contained in solid S. As a matter of fact,
a M /M of 4.0 (monomodal) in both cases. All of these results
w n
2
it turned out that S polymerizes ethylene under solid-gas
confirm the true diblock nature of the polymer and, in turn,
À1 À1
À1
conditions with significant activity (6 kgmol
0 min at 08C).
Noteworthy, when a fresh toluene suspension of S was
h
bar over
that ethylene polymerization using the 1/Mg(n-hex) combi-
2
3
nation proceeds in a ™pseudo-living∫ fashion to give the Nd-
polyethylenyl intermediate S. In addition to the monomer
efficiency of the diblock polymerization process, especially
interesting is the possibility to attain block lengths as high as
200000 for the PE block and ꢀ50000 for the PMMA block.
As far as we are aware, these values are significantly higher
than those realized with lanthanocene initiators,[ and allow
to consider these materials as valuable compatibilizers.[
treated with 1.0 equiv Mg(n-hex) (per mol Nd used in the in
2
situ combination to prepare S), the ethylene polymerization
activity could be strongly enhanced as compared to the initial
À1 À1
À1
polymerization reaction (up to 100 kgmol
h bar ) (Fig-
2]
ure 8, dotted line). To clarify this phenomenon, which is in
direct line with the aforementioned restoration of the
58]
catalytic activity upon addition of Mg(n-hex) to the in situ
2
system, separate experiments were conducted. No redistrib-
ution of Nd metal between the solid and the supernatant
toluene solution (ICP elemental analysis) was observed upon
treatment of a toluene suspension of S with excess of Mg-
Mechanistic aspects ofNd (OR) L /MgR systems
x
y
n
2
The above polymerization results, in particular the effective
transfer reactions using PhSiH and H and the possibility to
3
2
(
n-hex) . These results rule out the hypothesis of a simple
achieve efficient ethylene-MMA block-copolymerization, are
in direct line with reactivity trends observed for alkyllantha-
nocene initiators.[ This suggests a polymerization mechanism
through coordination ± insertion of the monomer onto a alkyl-
neodymium species, that would be produced by alkyl/alkoxide
metathesis between the alkoxy-lanthanide precursor and the
dialkylmagnesium co-reagent. In this section we described our
efforts to document this issue.
2
transmetallation process between the dialkylmagnesium re-
agent and insoluble (slowly active) Nd-polyethylenyl species
contained in S to form soluble (highly active) Nd-alkyl
species. Two other hypotheses that remain to be supported
are: i) a scavenging action of MgR comparable to the well-
documented effect of trialkylaluminums in group IV-promot-
ed polymerization[ and/or ii) formation of new active sites.
2]
2
56]
e) Ethylene-methyl methacrylate diblock copolymerizations:
A major interest of alkyl-lanthanides in polymerization relies
on their unique propensity to induce both polymerization of
ethylene and polar monomers.[ We investigated therefore
the ability of the new in situ catalyst combination 1/Mg(n-
a) Isolation ofmetathesis products rfom Nd (OR) L /MR
z
x
y
n
systems: Repeated attempts to isolate and/or crystallize
product(s) formed during the reaction of 1 with dialkylmag-
nesiums were unsuccessful. Valuable structural information
was obtained only with the [Nd(O-2,6-tBu -4-Me-C H ) ]/
2]
2
6
2 3
hex) and of isolated compound S to initiate the diblock
Mg(n-hex) system; the reaction of these precursors in a 1:1
2
2
copolymerization of ethylene and methyl methacrylate
ratio at room temperature in toluene gives mixed alkyl/
aryloxide magnesium compound 7, which was isolated in 90%
yield as colourless crystals and fully characterized by NMR
and a X-ray diffraction study (Figure 9).[
(
MMA). The crude polymer, obtained by initial polymer-
ization of ethylene with the in situ system and subsequent
addition of MMA to the reaction mixture at 08C, was shown
to contain 15 ± 20% of atactic homo-PMMA (Soxhlet extrac-
tion with THF for 3 d). This suggests that the in situ
59, 60]
Unfortunately, the neodymium co-product of this meta-
thesis reaction could not be isolated nor identified in solution
due to the paramagnetic Nd centers. One may reasonably
propose, however, a stoichiometry of the process as outlined
combination 1/Mg(n-hex) generates more than one active
2
species for the polymerization of MMA, of which only one is
able to initiate the polymerization of ethylene. Indeed, we
checked that the solution recovered after filtration of
in Scheme 2.[ Monitoring the reaction at 208C b y H NMR
60]
1
showed the gradual formation of uncoordinated 1-hexene (up
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J.-F. Carpentier et al.
FULL PAPER
at 208C for 30 min led to the same mixture of products. When
nBuMgEt was reacted with 1 under similar conditions, the
formation of 1-butene was observed from À308C and reached
a maximum of 14% per mol Nd after 15 min at 208C. The
parallel release of ethylene (d ˆ 5.26) was detected at temper-
atures as low as À608C but the amount of this monomer in the
reaction medium started to decrease from À208C and no
ethylene was detected at 08C; simultaneously, the formation
of polyethylene in the NMR tube was observed. This
phenomenon is simply rationalized considering the polymer-
ization activity of the 1/MgR systems towards ethylene and
2
its inactivity towards a-olefins (1-hexene, 1-butene).[ Fast
release of 1-butene was also observed from the 1/nBuLi
combination since À608C (up to 20% per mol Nd after
2]
1
5 min). This suggests rapid alkyl/alkoxy metathesis and
subsequent b-H elimination from the resulting nBu-[Nd]
species. The high instability of the latter likely accounts for the
impossibility to achieve ethylene polymerization from neo-
dymium alkoxide/alkyllithium systems; this also indicates that
dialkylmagnesiums may serve not only as alkylating reagents
of the alkoxy precursor but also as stabilizers of the resulting
2 6 2 2
Figure 9. ORTEP plot of [(n-hex)Mg(O-2,6-tBu -4-Me-C H )] (7) with
probability ellipsoids at 50%.
alkyl-[Nd] species, as they do in chlorolanthanocene/MgR
2
systems through m-alkyl bridging.[ The 1:1 combination of 1
20]
tBu
with Mg(CH SiMe ) , an alkylating reagent with no H at the
2
3 2
RT
Nd O
Me
+ Mg(n-hex)2
b-position, proved more thermally stable (although not more
active for polymerization) but release of isobutene was
observed from 08C and amounted 40% per mol Nd after
tBu
3
1/2 [(ArO)Mg(n-hex)]2 + 1/n "{(ArO)2Nd(n-hex)}n"
2
4 h at 208C. Some other alkylating reagents lead also to
7
(90%)
isobutene when combined to 1 but in lower amounts (maximal
amount per mol Nd observed after 24 h at 208C: Mg(n-hex)2,
Scheme 2. Proposed pathway for the formation of metathesis product 7.
4
%; nBuMgEt, 2%, nBuLi, 12%). Formation of isobutene
(
alkene) has been reported in some cases to occur via simple
to 30% per mol Nd after 17 h). Considering the stability of
dialkylmagnesium derivatives in general, and of Mg(n-hex)2
in particular, towards b-H elimination, this observation
suggests that the expected primary product, ™[(n-hex)Nd(O-
thermolysis of tert-butoxy (alkoxy) lanthanide complexes,
without any assistance of alkylating reagent.[ Nonetheless,
the smooth conditions under which the release of isobutene
proceeds (08C) and the nearly 1:1 concomitant formation of
61]
1
13
2
,6-tBu -4-Me-C H ) ] ∫, is not stable under these conditions
isobutene and SiMe (identified by H and C NMR) upon
using Mg(CH SiMe ) suggest that the loss of isobutene
3 2
4
2
6
2 2 n
and rapidly undergoes b-H elimination to form concomitantly
-hexene and so far unidentified lanthanide products.
2
1
proceeds in this case through concerted dealkylation of a
OtBu group by an adjacent alkyl (hydride) group rather than
by another OtBu group. Regardless of the mechanism
involved, the expected inorganic co-product is an oxo species,
such as for example 5, but it could not be formally identified
so far.
b) NMR monitoring of1/MR combinations: The reactions of
z
1
with alkylating reagents were also monitored by variable
temperature NMR and led to the following observations,
showing similar release of the corresponding a-olefin. The
1
H NMR spectrum of a 1:1 mixture of 1 and Mg(n-hex) in
2
[
D ]toluene at À808C showed signals for the unreacted
c) NMR monitoring ofdiamagnetic Ln (OR) L /MgR sys-
8
x
y
n
2
reagents. On raising the temperature, the latter progressively
decreased to the profit of at least two sets of resonances
attributed to tBuO ligands of new neodymium species and the
formation of 1-hexene was observed from À208C. No further
evolution of the system was noticed after 15 h at 58C where
tems: Alkyl derivatives of diamagnetic lanthanide centres can
be easily detected by their intrinsic alkyl chemical shifts. Thus,
to get additional clues for the probable formation of alkyl-
lanthanide species in the systems studied, we have examined
metathesis reactions between dialkylmagnesium reagents and
[La (OtBu) (thf) ] and [Y (OtBu) Cl (thf) ]. Although com-
4
0% of Mg(n-hex) was transformed into 1-hexene and 1 was
2
3
9
2
3
7
2
2
completely converted to two new species present in a ꢀ10:1
binations of these alkoxides of lanthanum and yttrium with
1
ratio according to H NMR spectrum. Six resonances in the
Mg(n-hex) were found to be significantly less efficient than
2
those based on 1 for ethylene polymerization,[ one might
expect from their structural relation to 1 some common
reactivity features. In fact, when the reaction of a 1:1 mixture
of [La (OtBu) (thf) ] and Mg(n-hex) in [D ]toluene was
53]
range of d ˆ À70 to 26 ppm with an integrated ratio of
2
:1:2:2:1:1 were unambiguously attributed to the major
species and suggested a polynuclear structure with tBuO
ligands in variable (terminal, bridging) environment. React-
ing a 1:1 mixture of 1 and Mg(n-hex) in [D ]toluene directly
3
9
2
2
8
1
monitored by variable temperature H NMR, a new multiplet
2
8
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Chem. Eur. J. 2002, 8, No. 16

Neodymium Alkoxides
3773±3788
[
16]
signal at d ˆ À0.90 ppm, characteristic of a La-CH moiety,
2
appeared from À108C and was observed up to 208C.
However, its relative intensity remained small with respect
to other resonances (tBuO, CH2 from MgR ) and the
2
progressive formation of 1-hexene was observed. When the
same experiment was carried out using Mg(CH SiMe ) , the
2
3 2
methylene singlet resonance for this reagent (d À1.37)
disappeared to the benefit of three new singlet resonances
in a ꢀ1:4:2 ratio (d ˆ À1.13, À1.23, À1.99, respectively).
Another informative observation was made upon monitoring
the reaction of a 1:1 mixture of [Y (OtBu) Cl (thf) ] and
3
7
2
2
1
Mg(n-hex) in [D ]toluene at 208C. The H NMR spectra
2
8
showed the formation of a new multiplet signal at d ˆ
À0.13 ppm, with couplings of 4 Hz, consistent with
2
89
1
[7, 9±12]
J( Y, H) splitting
and products of general formula
[
Y(OtBu) Cl (n-hex) ] were indicated; release of 1-hexene
x y z
was observed at the same time. These experiments provide
therefore clues supporting alkyl/tert-butoxide metathetic ex-
[
60]
change between lanthanide and magnesium metal centres.
Not surprisingly in light of previous work in this field,[7±16]
NMR spectroscopy revealed complex selectivity and stoichi-
ometry of these reactions.
All together these results strongly suggest the formation of
one or several [Nd]-{n-hex} species from Mg(n-hex)2 and
neodymium tert-butoxide 1 that show(s) reactivity towards
ethylene and some polar monomers similar to that of well-
identified alkyl-lanthanocene complexes. A rational repre-
sentation for the in situ generation of such species, its use as
either initiator or catalyst for polymerization and possible
decomposition pathways, is proposed in Scheme 3.
Scheme 3. Proposed general mechanism for activation and deactivation
pathways of tert-butoxy-neodymium/dialkylmagnesium polymerization
systems.
argue that electron-withdrawing alkoxide ligands, compared
to good s-donor Cp-type ligands, increase the electrophilicity
of the metal center and, therefore, facilitate b-H elimination
from alkyl-alkoxy-lanthanide species. This simple view may
allow for the easy release of a-olefins observed from
combinations of lanthanide alkoxides with alkylating agents
in the absence of ethylene. On the other hand, the relative
thermodynamics of Ln-C versus Ln-H bond dissociation
energies suggests that chain termination (b-H elimination,
chain transfer) reactions should be further inhibited or slow,
in comparison with the rate of propagation by replacement of
Cp* ligands by hard, electronegative tert-butoxide ligands.[
Such arguments have been used to account for the stability of
the bridging alkyl groups in [{Y(C Me )(O-2,6-tBu C H )} (m-
Conclusion
Our results demonstrate that the association of an homoleptic
alkoxy neodymium complex with a dialkylmagnesium co-
reagent can generate significantly active species for ethylene
polymerization. As expected from parallel work in group IV
chemistry,[ these Cp-free systems show similar (and some-
times superior) polymerization performance to the corre-
sponding metallocene systems. It confirms thus the ability of
some alkoxy/aryloxy residues to act as valuable ancillary
ligands for lanthanide metals in the field of polymerization.
Several questions arise, however, concerning the difficulties to
produce and stabilize such active species. In line with the
unsuccessful attempts in this direction,[7±16] our results high-
light the narrow window in which effective polymerization
can be achieved with regards to the nature of the alkoxy-
lanthanide precursor and alkylating co-reagent.
3]
62]
5
5
2
6
3
2
[5c]
H)(m-CH CH R)] toward b-H elimination and fit well with
2
2
the formation of high molecular weight polymer observed
with the [Nd (OtBu) (thf) ]/MgR /ethylene systems.
3
9
2
2
The high sensitivity of the active species generated from 1/
MgR combinations towards Lewis bases suggests that usual
2
In fact, to find an adequate balance between the thermal
stability of the alkyl-alkoxy-lanthanide species and their
reactivity toward olefin monomers appears as the major issue
of this chemistry. NMR investigations indicate a relative
easiness of the alkyl/alkoxy metathesis reaction to proceed
and the tendency of the resulting alkyl-alkoxy-lanthanide
species to undergo rapid b-H elimination and ligand (tert-
butoxy) thermolysis. In this regard, the exact influence of
alkoxy ancillary ligands on the reactivity of alkyl-lanthanide
remains a quite controversial issue. On one hand, one may
strategies, based on the introduction of additional donor
atoms within the ligand framework (e.g. in 6),[ may be
inappropriate to stabilize alkyl-alkoxy-lanthanide species
aimed at ethylene polymerization. We suspect that the
adequate (although not ultimate) balance between stability
4d]
and activity found in 1/MgR combinations may originate
2
from the degree of aggregation (nuclearity) of the active
species and specificities of dialkylmagnesiums (e.g. the
electronegativity of Mg which is equivalent to that of the
lanthanides).
Chem. Eur. J. 2002, 8, No. 16
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3783

J.-F. Carpentier et al.
FULL PAPER
Formation of dimers and higher polymetallic species has
been often related to decreased polymerization activity in
group IV chemistry.[3] In this regard, it is remarkable that we
X-ray diffraction (XRD, Siemens D5000 spectrometer, CuKa1,2 , 58 < 2q <
5
58) analysis.
4-Methoxy-2-methylbutan-2-ol:
100 mL of a 3.0m solution, 0.3 mol) in a 250 mL round-bottom flask fitted
with an addition funnel under nitrogen was cooled to 08C. Methyl
-methoxypropionate (14.2 g, 0.12 mol) in diethyl ether (90 mL) was added
A
diethyl ether solution of MeMgI
(
have detected only sluggish polymerization systems derived
from mononuclear lanthanide precursors such as [Nd(O-2,6-
tBu -4-Me-C H ) ] and [Nd(tritox) ]. Considering the large
3
2
6
2
3
3
dropwise over 40 min at 08C and the reaction mixture was allowed to stir
for 18 h at room temperature. The reaction mixture was poured in ice (50 g)
bulkiness and robustness of these ligands, one may assume
and treated with a saturated aqueous solution of NH
separation of the two phases occurred. The aqueous layer was extracted
with Et O (15 mL). The organic layers were combined, washed first with a
cold saturated aqueous solution of NaHCO (30 mL) and then cold water
4
Cl until clear
that they induce the formation of monolanthanide alkyl-
alkoxy(aryloxy) species.[
7±16]
Much more active polymeriza-
2
tion systems derive from trinuclear precursor 1 based on the
tert-butoxy ligand, which often leads to polynuclear structures
due to its relative moderate bulkiness.[4] Therefore, it is not
unreasonable to think that aggregation to some extent of
3
(2 Â 30 mL), and dried over MgSO
4
. Removal of the solvent and distillation
of the residue (Eb ˆ 858C under 95 Torr) gave a colorless liquid (8.4 g,
1
5
9%). H NMR (300 MHz, CDCl
3
): d ˆ 1.21 (s, 6H; CH ), 1.73 (t, J ˆ
3
5
.9 Hz, 2H; CH
2
), 3.17 (s, 1H; OH), 3.33 (s, 3H; OCH
3
), 3.60 (t, J ˆ 5.9 Hz,
™
[(tBuO) LnR]∫ moieties may contribute to stabilize an
13
2
2H; OCH ); C NMR (75 MHz, CDCl ): d ˆ 29.3 (CMe ), 41.4 (CH ), 58.9
2
3
2
2
active polymerization site. A considerable difficulty usually
associated to the chemistry of lanthanide alkoxides relies in
their high tendency to form a variety of cluster aggregates,
which hampers their isolation in pure form and their
characterization. This may prove, however, to be also a key
issue for the successful development of new alkoxy-based
lanthanide catalysts. Current work is focused on structural
investigations of model systems related to these neodymium
alkoxide/dialkylmagnesium combinations.
(MeO), 70.2 (OCH ), 70.8 (COH).
2
[Nd (m -OtBu) (m -OtBu) (OtBu) (thf) ] (1)
3
3
2
2
3
4
2
Salt metathesis route: In the glovebox, tBuONa (2.88 g, 30.0 mmol) was
dissolved in THF (50 mL) and transferred to a flask containing a
suspension of NdCl (2.51 g, 10.0 mmol) in THF (50 mL). The mixture
3
was stirred with a magnetic stir bar for 3 d at 258C. The solution was
decanted overnight and filtered, leaving behind a pasty solid that was
discarded. Removal of solvents from the solution at 208C and drying the
À3
residue under 10 Torr for 6 h offered a pale blue solid (3.36 g, 82%).
1
H NMR (400 MHz, [D
8
]toluene): d (58C) ˆ 41.0 (s, 18H), 17.2 (s, 18H),
À1.5 (s, 9H), À14.7 (s, 9H), À21.7 (s, 18H), À25.8 (s, 18H), À29.5 (s, 9H);
d (278C) ˆ 34.2 (brs, 18H), 14.8 (brs, 18H), À0.5 (brs, 9H), À9.9 (s, 9H),
À20.2 (brs, 27H), À22.8 (s, 18H); elemental analysis calcd (%) for
C H Nd O (1) (1234.97): C 42.79, H 7.92; found: C 41.32, H 7.74; crude
Experimental Section
4
4
97
3
11
samples of 1 prepared by salt metathesis and worked-up as described above
General: All operations were performed under dry argon using standard
Schlenk techniques or in a dry glove box under nitrogen. Solvents and
deuterated solvents were freshly distilled from sodium/potassium amalgam
were shown to contain less than 0.5% of Cl.
Amide alcoholysis route: In a Schlenk tube, tBuOH (3.0 mL, 31 mmol) was
added dropwise to a stirred solution of Nd[N(SiMe ) ] (1.25 g, 2.0 mmol)
3 2 3
in THF (20 mL). The resulting clear light-blue solution was stirred for 3 d at
room temperature. Removal of volatiles under high vacuum for 10 h at
under argon and degassed prior to use. Anhydrous NdCl
3
(99.9%) was
purchased from Strem and used as received. tert-Butyl and tert-amyl
alcohol were dried over and distilled from CaH
and tBuOK (95%, Aldrich) were dried at 1308C under 10 Torr prior to
use. Sodium tert-amylate was prepared from sodium and tert-amyl alcohol
2
. tBuONa (97%, Aldrich)
room temperature gave a light-blue solid that was subsequently recrystal-
À3
1
lized from toluene (0.48 g, 57%). The H NMR spectra ([D
8
]toluene, 58C)
of the crystals featured reproducibly as the major (ca. 70%) peaks the
seven resonances observed for samples of 1 prepared from NaOtBu along
with additional (ca. 30%) rather broad resonances at d ˆ 46.8, 45.5, 40.0,
at 258C; excess alcohol was removed by evaporation and tAmONa was
3 2 3
dried at 1308C under high vacuum. Complexes [Nd{N(SiMe ) }
(thf)],[
63]
[
27a]
[32]
[
Nd(OCtBu
3
)
3
(thf)]
and [Nd(O-2,6-tBu
2
-4-Me-C
6
H
2
)
3
]
were prepared
2
2.3, 15.1, À27.3, À33.0, À34.1, À42.6.
according to the reported procedures and sublimed prior to use. Ethylene
X-ray crystal structure determination of1 ¥ THF : Crystals of 1 ¥ THF were
grown from a concentrated toluene solution of the crude product obtained
from tBuONa at À58C. A pale blue crystal of approximate dimensions
(
(
Air Liquide, N35) was purified by passage through a moisture filter
Chrompack, No. 7971). MMA (99%, Aldrich) was distilled twice over
CaH
oct)
Alkyl), Mg(n-hex)
1.0m solution in THF), EtMgBr (3.0m solution in THF), BEt
solution in hexanes), nBuLi (1.6m solution in hexanes) and tBuLi (1.7m
solution in pentane) (all Aldrich) were used as received. Mg(CH SiMe
][Li] was prepared
and nBuLi.
2
and stored at À208C under argon. Alkylating agents AlMe
, AlH(iBu) (Schering), nBuEtMg (20 wt% solution in heptane, Texas
(1.33m solution in heptane, Texas Alkyl), PhMgBr
(1.0m
3
, Al(n-
0
.19 Â 0.20 Â 0.21 mm was mounted on a glass fiber. X-ray measurements
3
2
were made using a Bruker SMART CCD area-detector diffractometer with
2
MoKa (l ˆ 0.71073 ä) at Tˆ 158(2) K.
(
3
Crystal data:[ orthorhombic Pbcn: a ˆ 17.0538(10), b ˆ 20.0343(12), c ˆ
65]
3
1
7.7400(11) ä; Vˆ 6061.1(6) ä ; formula unit: C44
97 3 4 8
H O11Nd ¥ C H O with
F(000) ˆ 2676; m(MoKa) ˆ
2
3 2
)
À3
was prepared according to literature.[ [nBuAlH(iBu)
64]
Z ˆ 4;
F
w
:
1307.04;
1
calcd ˆ 1.432 gcm
;
2
À1
2
.581mm . 38059 reflections were collected (1.578 > V> 28.278). The
prior to use from equimolar amounts of AlH(iBu)
2
[
66]
structure was solved by direct methods. The tert-butoxide ligand located
on the two-fold axis and the thf ligands were disordered. The carbon atoms
associated with these ligands were included using multiple components
with partial site-occupancy-factors. There was also one disordered THF
solvent molecule present per formula unit. Hydrogen atoms associated with
the disordered tert-butoxide ligand and with the solvent molecule were not
NMR spectra of lanthanide alkoxides were recorded on Bruker AC-200,
AC-300 or AM-400 spectrometers in Teflon-valved NMR tubes at 238C
1
13
unless otherwise indicated. H (200, 300 and 400 MHz) and C (50, 75 and
00 MHz) chemical shifts are reported versus SiMe and were determined
1
4
by reference to the residual solvent peaks. Elemental analyses were
performed by Pascher Laboratories, Erlangen (Germany) and at Rhodia
Research Center, Aubervilliers (France). Molecular weights of polymers
were determined by size-exclusion chromatography (SEC) using polystyr-
ene gel columns at 135 ± 1558C and ortho-dichlorobenzene as the solvent,
with either a PL220 (Polymer Laboratories) apparatus or a Waters
apparatus equipped with coupled refractometer and viscosity detectors.
2
included in the refinement. Full-matrix least-squares refinement on F
based on 7315 independent reflections converged with 213 variable
parameters and 30 restraints. R1 ˆ 0.0410 (for those 5589 data with I >
2
[67]
À3
2
s(I)); wR2 ˆ 0.1044; GoF (F ) ˆ 1.059. D1max ˆ 1.505 and À1.027 eä
.
[
Nd
pared by salt metathesis similar to 1, starting from NdCl
0.0 mmol) and tAmONa (3.31 g, 30.0 mmol) in THF (100 mL). Workup
3
(m
3
-OtAm)
2
(m
2
-OtAm)
3
(OtAm)
4
(thf)
2
] (2): Compound 2 was pre-
3
(2.51 g,
The number-average molecular weight (M
n
w
) and polydispersity ratio (M /
1
M
n
) were calculated by universal calibration in reference to polystyrene
1
13
left compound 2 as a pale blue solid (3.1 g, 66%). This crude material was
directly used for polymerization experiments.
standards. H and C NMR spectra of polymers were recorded on a Bruker
AM-400 spectrometer at 1308C in C Cl . Melting points (T ), glass
2
D
2
4
m
transition temperature (T
by DSC (Setaram DSC 141 apparatus, 108Cmin , under nitrogen) and
g
), and crystallinity of polymers were determined
[Nd12(OtAm)26Cl11Na] ¥ 2(Et
(1.67 g, 15.1 mmol) was dissolved in Et
2
O) (3 ¥ 2Et
2
O): In
a glovebox, tAmONa
À1
2
O (25 mL) and transferred to a
3784
¹ 2002 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
0947-6539/02/0816-3784 $ 20.00+.50/0
Chem. Eur. J. 2002, 8, No. 16

Neodymium Alkoxides
3773±3788
flask containing a suspension of NdCl
3
(1.25 g, 5.0 mmol) in Et
2
O (25 mL).
stirred for 36 h at room temperature. Evaporation of volatiles, followed by
drying under high vacuum for 6 h at 508C, gave a blue pasty solid in
quantitative yield. Crystallization from toluene at À58C offered pure blue
crystals suitable for X-ray diffraction (0.58 g, 58%). Elemental analysis
The mixture was stirred with a magnetic stir bar for 3 d at 258C. The
solution was decanted overnight and filtered, leaving behind a pasty solid
which was discarded. Removal of solvents from the solution at 208C and
À3
drying the residue under 10 Torr for 6 h left a blue solid (1.52 g). X-ray
2
calcd (%) for C36H78Nd O12 (991.46): C 43.61, H 7.93; found: C 43.2, H 7.81.
quality crystals of 3 were isolated in low yield from a concentrated solution
of this material in toluene at À58C. The crystals, once isolated, were
insoluble even in THF.
X-ray crystal structure determination of6 : A pale purple crystal of
approximate dimensions 0.28 Â 0.48 Â 0.48 mm was mounted on a glass
fiber. X-ray measurements were made using a Bruker SMART CCD area-
detector diffractometer with MoKa (l ˆ 0.71073 ä) at Tˆ 163(2) K.
2
X-ray crystal structure determination of3 ¥ 2Et O: A pale blue crystal of
approximate dimensions 0.40 Â 0.42 Â 0.51 mm was mounted on a glass
fiber. X-ray measurements were made using a Bruker SMART CCD area-
detector diffractometer with MoKa (l ˆ 0.71073 ä) at Tˆ 163(2) K.
Crystal data:[65] triclinic P1: a ˆ 9.4496(3), b ˆ 10.7702(4), c ˆ 12.8522(5) ä;
≈
3
a ˆ 96.7120(10), b ˆ 96.5560(10), g ˆ 115.7290(10)8; Vˆ 1150.21(7) ä ;
formula unit: C36
H
78Nd
2
O
12 with Z ˆ 1; formula weight: 991.46; 1calcd
ˆ
Crystal data:[65] monoclinic P2
/c: a ˆ 30.7931(14), b ˆ 19.9495(9), c ˆ
1
1
.431 gcm ; F(000) ˆ 510; m(MoKa) ˆ 2.282mm . 12462 reflections were
À3
À1
3
3
C
4.4764(15) ä, b ˆ 105.3890(10)8; Vˆ 20419.7(16) ä ; formula unit:
collected (1.628 > V> 28.308). The structure was solved by direct meth-
140
H
310Cl11NaNd12
O
28 ¥ 2(C
4
H
10O) with Z ˆ 4; formula weight: 4733.94;
ods.
[66]
Carbon atoms C2 and C3 were disordered and included using
À3
À1
1
calcd ˆ 1.540 gcm ; F(000) ˆ 9504; m(MoKa) ˆ 3.190mm . 153104 reflec-
multiple components with partial site-occupancy-factors (major 0.70;
tions were collected (0.698 > V> 23.268). The structure was solved by direct
2
minor 0.30). Full-matrix least-squares refinement on F based on 5448 in-
[
66]
methods. There were two molecules of diethyl ether solvent present per
formula unit. Two of the tert-butoxide ligands were disordered. It was
necessary to employ geometric and thermal parameter restraints (2815 to-
tal) to all carbon atoms and the solvent molecules via the SHELXTL using
the SAME, EADP and PART commands. Disordered atoms were included
using multiple components with partial site-occupancy-factors. Hydrogen
dependent reflections converged with 341 variable parameters and no
restraints. R1 ˆ 0.0178 (for those 5286 data with I > 2s(I)); wR2 ˆ 0.0449;
2
[67]
À3
GoF (F ) ˆ 1.033. D1max ˆ 0.801 and À0.610 eä
.
Ethylene polymerizations promoted by Nd
prepared in situ: In a typical experiment, a solution of complex 1 (0.37 g,
.30 mmol) in toluene (10 mL) was added to a solution of Mg(n-hex)
x y z
(OR) /MR combinations
0
2
atoms were not included in the refinement. Full-matrix least-squares
refinement on F2 based on 29327 independent reflections converged with
(0.98 g, 1.0 mmol) in toluene (10 mL) and the reaction mixture was stirred
for 1 h at 08C. The resulting brown solution was injected through a syringe
into a 500 mL Schlenk tube containing toluene (80 mL) kept at 08C under
1 atm ethylene (previously saturated solution). Magnetic stirring was
started (1100 rpm) and the ethylene consumption was monitored by a mass
flowmeter (Aalborg, GFM17) connected to a totalling controller (KEP),
which acts as a flow rate integrator. The reaction was quenched by addition
of a 5% HCl methanol solution (200 mL) to the reaction mixture and the
polymer was recovered by filtration and dried under vacuum.
9
59 variable parameters and 2815 restraints. R1 ˆ 0.0544 (for those 24067
2 [67]
data with I > 2s(I)); wR2 ˆ 0.1645; GoF (F ) ˆ 1.053. D1max ˆ 2.469 and
À3
À2.199 eä
Nd (m
tBuOH (7.0 mL, 73.0 mmol) was slowly added over ca. 5 min to a stirred
solution of Nd[N(SiMe (3.85 g, 6.15 mmol) in n-hexane (60 mL). The
.
[
3
3 2 2 3 4 2
-OtBu) (m -OtBu) (OtBu) (HOtBu) ] (4): In a Schlenk tube,
3 2 3
) ]
resulting clear light-blue solution was stirred for 3 d at room temperature.
Volatiles were then removed by evaporation in vacuum for 12 h at room
temperature to give a light blue solid (2.30 g, 90% based on Nd).
Crystallization from toluene offered analytically pure blue crystals
Experiments conducted at different temperatures, Nd/Mg ratios or in the
presence of a transfer agent (feed with a preformed C H /H mixture or
2 4 2
introduction of PhSiH3 through a syringe in the reaction mixture after
5 min), and preliminary experiments aimed at evaluating the ability of
other lanthanide alkoxide/alkylating reagent combinations, were conduct-
ed using a similar procedure.
1.55 g, 61%). 1H NMR (200 MHz, [D
1
(
8
]toluene, À158C): d ˆ 19.5 (s,
8H), 6.4 (s, 45H), À13.5 (s, 2H; OH), À25.2 (s, 18H), À32.0 (s, 18H);
-OtBu), À4.3 (s,
H; OH), À34.2 (s, 18H), À38.1 (s, 18H); (À658C): d ˆ 27.3 (s, 18H), 10.9
(
À458C): d ˆ 23.8 (s, 18H), 9.0 (s, 36H), 5.5 (s, 9H; 1-m
2
2
(
s, 36H), 2.7 (s, 9H; 1-m
2
-OtBu), À6.0 (s, 2H; OH), À42.4 (s, 36H);
Isolation ofsolid catalyst S : A typical ethylene polymerization experiment
was conducted as described above over 30 min. The resulting reaction
mixture was placed under argon and filtrated over a sintering glass funnel
while keeping temperature at 08C. The clear filtrate was collected under
argon at 08C for analytical purposes and polymerization catalysis assays.
The solid recovered was washed with cold toluene (2 Â 50 mL) at 08C, to
give S as a beige gummy solid, which was rapidly used for further
polymerization. ICP microanalyses of three different batches of S prepared
under the above conditions showed that it contains 15 Æ 2% of Nd and
elemental analysis calcd (%) for C44
3
H101Nd O11 (1239.00): C 42.65, H 8.22;
found: C 41.8, H 7.92.
[
Nd
5 5 3 4 2 4 5
(m -O)(m -OtBu) (m -OtBu) (OtBu) ] (5): In a glovebox, 4 (0.720 g,
1.74 mmol Nd) was dissolved in toluene (ca. 5 mL) and the clear blue
solution was allowed to stand at room temperature for two weeks. After
concentration to ca. 2 mL under vacuum, the solution was placed at À58C,
leaving X-ray quality crystals of 5 ¥ 2(toluene) (which looses toluene in
vacuo) (0.310 g, 53%). Elemental analysis calcd (%) for the toluene-free
complex C52
H
117Nd
5
O
14 (1687.7): C 37.00, H 6.99; found: C 36.2, H 7.56.
20 Æ 4% of Mg initially introduced (as 1 and Mg(n-hex)
2
, respectively), and
the balance for these metals was found in the filtrate. Chlorine content in S
X-ray crystal structure determination of5 ¥ 2(toluene) : A pale purple
crystal of approximate dimensions 0.33 Â 0.41 Â 0.52 mm was mounted on a
glass fiber. X-ray measurements were made using a Bruker SMART CCD
area-detector diffractometer with MoKa (l ˆ 0.71073 ä) at Tˆ 163(2) K.
Crystal data:[65] tetragonal P4/nmm: a ˆ 16.6902(6), b ˆ 16.6902(6), c ˆ
3
was below detection limit of elemental analysis.
Ethylene polymerizations promoted by isolated solid catalyst S: a) Gas
phase ethylene polymerization: The polymerization was carried out directly
in the sintering glass funnel by contacting isolated solid 7 with 1 atm of
ethylene at 08C. In a typical experiment, upon using a solution of 1 (0.37 g,
1
4.0266(7) ä; Vˆ 3907.3(3) ä ; formula unit: C52
H
117Nd
5
À3
O
;
14 ¥ 2(C
F(000) ˆ 1882;
7
H
8
) with
Z ˆ 2; formula weight: 1871.92;
1
calcd ˆ1.591 gcm
0.30 mmol) activated by Mg(n-hex) (0.98 g, 1.0 mmol) in toluene (100 mL)
2
À1
for 1 h at 08C allowed to collect, after 10 min of reaction with 1 atm
m(MoKa) ˆ 3.317mm
. 40230 reflections were collected (1.458 > V>
[
66]
ethylene at 08C, 3.4 g S as a beige precipitate. The latter was filtered off at
08C and washed twice with cold toluene (2 Â 50 mL). Ethylene (1 atm) was
then contacted onto the beige solid, resulting in the rapid growth of white
efflorescence of polyethylene and a consumption of 0.5 g ethylene over
90 min. Upon stirring with a magnetic stir bar in the bottom of the sintering
funnel, 1.4 g ethylene were additionally polymerized over 30 min. Quench-
ing and workup as described above afforded 5.4 g polyethylene.
2
8.298). The structure was solved by direct methods. There were two
molecules of toluene solvent present per formula unit. Two of the tert-
butoxide ligands were disordered. Carbon atoms C2, C3, C11, C12 and C13
were included using partial site-occupancy-factors. The toluene methyl
carbon C17 was also disordered and included as above. Hydrogen atoms
were not included in the refinement. Full-matrix least-squares refinement
2
on F based on 2710 independent reflections converged with 90 variable
parameters and no restraints. R1 ˆ 0.0452 (for those 2410 data with I >
b) Slurry phase ethylene polymerization: In a glovebox, freshly prepared
solid S (typically 4 ± 5 g) was introduced into a 500 mL Schlenk. Cold
toluene (100 mL) was introduced and the resulting mixture was placed at
08C. After purging with 1 atm ethylene, magnetic stirring was rapidly
started (1100 rpm). Ethylene consumption monitoring and final quenching
were performed as described above.
2
[67]
À3
2
s(I)); wR2 ˆ 0.1266; GoF (F ) ˆ 1.086. D1max ˆ 2.561 and À1.211 eä
.
[
Nd
butan-2-ol (0.718 g, 6.06 mmol) dissolved in benzene (10 mL) was added
dropwise via canula to a stirred solution of Nd[N(SiMe (1.266 g,
.02 mmol) in benzene (10 mL). The resulting clear light-blue solution was
2 2 2 2 6
(OCMe CH CH OMe) ] (6): In a Schlenk tube, 4-methoxy-2-methyl-
3 2 3
) ]
2
Chem. Eur. J. 2002, 8, No. 16
¹ 2002 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
0947-6539/02/0816-3785 $ 20.00+.50/0
3785

J.-F. Carpentier et al.
FULL PAPER
Diblock ethylene-MMA copolymerization: Diblock ethylene-MMA co-
polymerization was achieved by reacting a suspension of solid S in toluene
with MMA at 08C. A typical experiment is as follows: Upon using a
[1] For organolanthanide reviews, see: a) H. Schumann, J. A. Meese-
Marktscheffel, L. Esser, Chem. Rev. 1995, 95, 865 ± 986; b) R. An-
wander, W. A. Herrmann, Top. Curr. Chem. 1996, 179, 1 ±32; c) F. T.
Edelmann, Top. Curr. Chem. 1996, 179, 247 ± 276; d) R. Anwander in
Applied Homogeneous Catalysis with Organometallic Compounds,
Vol. 2 (Eds: B. Cornils, W. A. Herrmann), Wiley, Weinheim, 1996,
pp. 866 ± 892; e) G. A. Molander, Chemtracts: Org. Chem. 1998, 11,
237 ± 263; f) R. Anwander, Top. Organomet. Chem. 1999, 2, 1 ±61;
g) G. A. Molander, E. C. Dowdy, Top. Organomet. Chem. 1999, 2,
119 ± 154.
2
solution of 1 (0.37 g, 0.30 mmol) activated by Mg(n-hex) (0.98 g, 1.0 mmol)
in toluene (100 mL) for 1 h at 08C allowed to collect, after 10 min of
reaction with 1 atm ethylene at 08C, S (3.3 g) as a beige precipitate. The
latter was filtered-off at 08C, washed twice with cold toluene (2 Â 50 mL)
and introduced into a Schlenk-tube with toluene (100 mL) at 08C. Freshly
distilled MMA (9.0 mL, 90 mmol) was then introduced rapidly (ca. 5 s)
through a syringe and the reaction mixture was stirred magnetically
(
(
1100 rpm) for 1 h at 08C. After addition of a 5% HCl/methanol solution
200 mL), crude polymer was obtained by filtration (4.8 g). Soxhlet
[2] For leading references, see: a) D. G. H. Ballard, A. Courtis, J. Holton,
J. McMeeking, R. Pearce, Chem. Commun. 1978, 994 ± 995; b) P. L.
Watson, G. W. Parshall, Acc. Chem. Res. 1985, 18, 51 ± 56; c) P. L.
Watson, T. Herskovitz, ACS Symp. Ser. 1983, 212, 459 ± 479; d) G.
Jeske, H. Lauke, H. Mauermann, P. N. Swepston, H. Schumann, T. J.
Marks, J. Am. Chem. Soc. 1985, 107, 8091 ± 8103; e) G. Jeske, L. E.
Schock, P. N. Swepston, H. Schumann, T. J. Marks, J. Am. Chem. Soc.
extraction with boiling THF for 72 h led to the solubilization of only 3%
of the crude material. Most of analytical data for the final copolymer are
À1
provided in the text. IR (KBr): nÄ ˆ 1729, 1194, 1148 cm
Reaction of[Nd(O-2 ,6-tBu -4-Me-C
(n-hex)Mg(O-2,6-tBu -4-Me-C )]
Nd(O-2,6-tBu -4-Me-C ] (0.42 g, 0.52 mmol) in a minimum of toluene
was added to a solution of dry Mg(n-hex) (1.01 g, 0.52 mmol) in toluene.
.
2
6
H
2
)
3
] with Mg(n-hex)
2
; synthesis of
[
[
2
6
H
2
2
(7): In a glovebox, a solution of
1
985, 107, 8103 ± 8110; f) B. J. Burger, M. E. Thompson, D. W. Cotter,
2
6 2 3
H )
J. E. Bercaw, J. Am. Chem. Soc. 1990, 112, 1566 ± 1577; g) M. A.
Giardello, Y. Yamamoto, L. Brard, T. J. Marks, J. Am. Chem. Soc.
2
The mixture was allowed to stand at À408C for three days, resulting in the
1
995, 117, 3276 ± 3279; h) H. Yasuda, Prog. Polym. Sci. 2000, 25, 573 ±
formation of colourless crystals of 7 that were separated out from the
1
626, and references therein.
supernatant solution (0.227 g, 90%). H NMR (300 MHz, C
6
D
6
): d ˆ 0.04
hex), 1.24 (m, 6H,
), 2.25 (s, 3H; CH Ar),
): d ˆ 7.6, 14.6, 21.4, 23.3,
), 35.1, 38.2, 127.1, 129.0, 139.4, 154.3; elemental
Mg (657.62): C 76.71, H 11.04; found: C
[
3] a) G. J. P. Britovsek, V. C. Gibson, D. F. Wass, Angew. Chem. 1999,
(
dd, J ꢀ8 Hz, 2H, CH
2
Mg), 0.85 (t, J ˆ 7.0 Hz, 3H, CH
3
1
11, 448 ± 468; Angew. Chem. Int. Ed. 1999, 38, 428 ± 447, and
references therein; b) R. F. Jordan, Adv. Organomet. Chem. 1991,
2, 325 ± 387; c) H. H. Brintzinger, D. Fischer, R. Mulhaupt, B. Rieger,
CH CH CH ), 1.54 (s, 6H; tBu), 1.63 (m, 2H; CH
2
2
2
2
3
1
3
7.15 (s, 2H; H arom); C NMR (75 MHz, C
6
D
6
3
2
9.1, 32.5, 32.9 (CMe
3
R. M. Waymouth, Angew. Chem. 1995, 107, 1255 ± 1283; Angew.
Chem. Int. Ed. Engl. 1995, 34, 1143 ± 1170; d) M. Bochmann, J. Chem.
Soc. Dalton Trans. 1996, 255 ± 270.
analysis calcd (%) for C42
6.9, H 10.91.
X-ray crystal structure determination of7
H
72
O
2
2
7
:
A colorless crystal of
[
4] For reviews on alkoxo and aryloxo chemistry of lanthanides, see:
a) K. G. Caulton, L. G. Hubert-Pfalzgraf, Chem. Rev. 1990, 90, 969 ±
approximate dimensions 0.29 Â 0.32 Â 0.46 mm was mounted on a glass
fiber. X-ray measurements were made using a Bruker SMART CCD area-
detector diffractometer with MoKa (l ˆ 0.71073 ä) at Tˆ 163(2) K.
995; b) R. C. Mehrotra, A. Singh, U. M. Triptathi, Chem. Rev. 1991, 91,
1287 ± 1303; c) L. G. Hubert-Pfalzgraf, New J. Chem. 1995, 19, 727 ±
750; d) R. Anwander, Top. Curr. Chem. 1996, 179, 149 ± 245, and
Crystal data:[65] triclinic P1: a ˆ 9.3991(4), b ˆ 9.8064(4), c ˆ 11.5627(5) ä;
≈
3
a ˆ 92.2830(10), b ˆ 106.1100(10), g ˆ 97.9190(10)8; Vˆ 1010.72(7) ä ;
references therein.
formula unit: C42
H
72
O
2
Mg
2
with Z ˆ 1; formula weight: 657.62; 1calcd
ˆ
[
[
5] a) C. J. Schaverien, J. Chem. Soc. Chem. Commun. 1992, 11 ± 13;
b) C. J. Schaverien, J. Mol. Catal. 1994, 90, 177 ± 183; c) C. J. Schaver-
ien, Organometallics 1994, 13, 69 ± 82.
6] a) Z. Hou, Y. Zhang, H. Tezuka, P. Xie, O. Tardif, T.-a. Koizumi, H.
Yamazaki, Y. Wakatsuki, J. Am. Chem. Soc. 2000, 122, 10533 ± 10543;
b) Z. Hou, S. Kaita, Y. Wakatsuki, Pure Appl. Chem. 2001, 73, 291 ±
À3
À1
1
.080 gcm ; F(000) ˆ 364; m(MoKa) ˆ 0.091mm . 10924 reflections were
collected (1.848 > V> 28.298). The structure was solved by direct meth-
ods. The molecule was located about an inversion center. Hydrogen
atoms were located from a difference-Fourier map and refined (x, y, z and
U
[
66]
2
iso). Full-matrix least-squares refinement on F based on 4783 independ-
ent reflections converged with 352 variable parameters and no restraints.
2
94.
7] W. J. Evans, R. N. R. Broomhall-Dillard, J. W. Ziller, Organometallics
996, 15, 1351 ± 1355.
2
R1 ˆ 0.0381 (for those 3952 data with I > 2s(I)); wR2 ˆ 0.1006; GoF (F ) ˆ
[
[
67]
À3
1
.027. D1max ˆ 0.365 and À0.189 eä
.
1
NMR monitoring of1/MgR
2
combinations: In a typical experiment, in a
[8] W. J. Evans, J. L. Shreeve, R. N. R. Broomhall-Dillard, J. W. Ziller, J.
Organomet. Chem. 1995, 501, 7 ±11.
[9] W. J. Evans, R. N. R. Broomhall-Dillard, J. W. Ziller, J. Organomet.
Chem. 1998, 569, 89 ± 97.
glovebox, a Teflon valve NMR tube was charged with 1 (33.6 mg,
.027 mmol), Mg(n-hex) ¥ 0.5heptane (20.0 mg, 0.080 mmol) and 1,2,4,5-
tetramethylbenzene (10.6 mg, 0.079 mmol; NMR internal standard).
0
2
[
D
8
]Toluene was then transferred under vacuum at À808C, the solution
[10] W. J. Evans, T. J. Boyle, J. W. Ziller, J. Organomet. Chem. 1993, 462,
141 ± 148.
[11] W. J. Evans, T. J. Boyle, J. W. Ziller, J. Am. Chem. Soc. 1993, 115,
5084 ± 5092.
[12] P. Biagini, G. Lugli, L. Abis, R. Millini, J. Organomet. Chem. 1994, 474,
C16 ± C18.
[13] J. C. Gordon, G. R. Giesbrecht, J. T. Brady, D. L. Clark, D. W. Keogh,
B. L. Scott, J. G. Watkin, Organometallics 2002, 21, 127 ± 131.
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Power, J. Chem. Soc. Chem. Commun. 1988, 1007 ± 1009.
[15] D. L. Clark, J. C. Gordon, J. C. Huffman, J. G. Watkin, B. D. Zwick,
Organometallics 1994, 13, 4266 ± 4270.
was made homogeneous at this temperature and the tube was introduced in
the pre-cooled NMR probe. The progress of the reaction was monitored
upon raising the temperature by 108C intervals. The formation of 1-hexene
1
13
(
d ( H) ˆ 4.98 (m, 2H), 5.72 (m, 1H); d ( C) ˆ 108.2, 132.9; confirmed by
1
GC/MS) was observed from À308C and that of isobutene (d ( H) ˆ 4.70
1
3
(
1
s); d ( C) ˆ 111.0, 141.7) from 08C. After 14 h at 208C, the amounts of
-hexene and isobutene were 40 and 2%, respectively. Resonances for two
new Nd species were observed at d ˆ 23.7 (relative intensity, 20), 18.5 (10),
À5.0 (20), À8.2 (20), À11.1 (10), À69.8 (10) and d ˆ 25.7 (2), 19.9 (1), 15.6
(
2), 11.3 (1), À6.8 (2), À12.3 (2); other resonances attributable to these
species possibly overlapped with signals of diamagnetic species in the range
of 4 to À1 ppm.
[16] C. J. Schaverien, N. Meijboom, A. G. Orpen, J. Chem. Soc. Chem.
Commun. 1992, 124 ± 126.
3 9 2 3 7 2 2
Reactions performed with [La (OtBu) (thf) ] and [Y (OtBu) Cl (thf) ]
were conducted using a similar protocol.
[17] Rating of the effectiveness of catalysts for ethylene polymerization is
based on Gibson×s scale,[
3a]
ranging from very low (activity
À1 À1
À1
À1 À1
<
1 gmmol
h
bar ), moderate (activity ˆ 10 ± 100 gmmol
h
À1
À1 À1
À1
Acknowledgement
bar ), to very high (activity >1000 gmmol
h
bar ).
[
18] Ethylene polymerization studies with Cp-free group III and lantha-
nide systems bearing ancillary ligands other than alkoxides have also
been conducted, showing very low to high polymerization activity:
Tris(pyrazolyl)borate Y and Ln complexes gave moderate activity:
a) D. P. Long, P. A. Bianconi, J. Am. Chem. Soc. 1996, 118, 12453 ±
12454; some benzamidinate and bis(silylamido)biphenyl Y complexes
We gratefully acknowledge Rhodia Electronics & Catalysis for support of
this research and for a PhD grant to J.G. We thank Dr. T. Mathivet
(
Rhodia) for helpful discussions, Prof. R. F. Jordan (University of Chicago)
and Mrs. A.-M. Caze, N. Djelal and L. Burylo (University of Lille) for GPC,
DSC and XRD measurements.
3786
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Chem. Eur. J. 2002, 8, No. 16

Neodymium Alkoxides
3773±3788
1
have shown very low activity: b) R. Duchateau, C. T. van Wee, A.
Meetsma, J. H. Teuben, J. Am. Chem. Soc. 1993, 115, 4931 ± 4932;
c) R. Duchateau, C. T. van Wee, J. H. Teuben, Organometallics 1996,
[34] Due to the paramagnetic Nd centers, the H NMR spectra of 1 proved
highly temperature sensitive and optimal resolution (minimal reso-
nances overlapping, line shape) was observed at 58C.
1
1
5, 2291 ± 2302; d) T. I. Gountchev, T. D. Tilley, Organometallics 1999,
8, 2896 ± 2905; Sc complexes containing amide-diphosphane and
[35] Recrystallized samples prepared by salt metathesis using KOtBu (1)
or by alcoholysis of the Nd amide (2) showed invariably more complex
1
triaza ligands are capable of polymerizing ethylene, although no
activity data were reported: e) M. D. Fryzuk, G. Giesbrecht, S. J.
Rettig, Organometallics 1996, 15, 3329 ± 3336; f) S. Hajela, W. P.
Schaefer, J. E. Bercaw, J. Organomet. Chem. 1997, 532, 45 ± 53;
cationic alkyl-triaza(monoamido)yttrium complexes have shown high
ethylene polymerization activity: g) S. Bambirra, D. van Leusen, A.
Meetsma, B. Hessen, J. H. Teuben, Chem. Commun. 2001, 637 ± 638.
8
H NMR spectra. These spectra ([D ]toluene, 58C) featured reprodu-
cibly as the major (ca. 70%) peaks the seven resonances observed for
samples of 1 prepared from NaOtBu along with additional (ca. 30%)
rather broad resonances (see Experimental Section).
[36] M. L. Brown, K. S. Mazdiyasni, Inorg. Chem. 1970, 9, 2783 ± 2786.
[37] [La (OtBu) (thf) ], prepared by salt metathesis from LaCl and
3 9 2 3
NaOtBu in THF, has been suggested also to be isostructural to 1 on
the basis of NMR data.[
21a]
Not surprisingly, Nd-alkoxide chemistry
[
[
19] The in situ combination of Al(iBu)
complex (Al/Nd ˆ 15), prepared by reacting calix[8]arene with
sodium in a mixture of benzene and 2-propanol and then with NdCl
has been briefly reported to be slowly active in the polymerization of
3
with a calix[8]arene neodymium
proved much more related to La than Y chemistry.
[38] C. Wenqi, J. Zhongsheng, X. Yan, F. Yuguo, Y. Guangdi, Inorg. Chim.
Acta 1987, 130, 125 ± 129.
[39] F. Benetollo, G. Bombieri, C. Bisi Castellani, W. Jahn, R. D. Fischer,
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1978, 17, 625 ± 631.
[41] The THF resonances could not distinguished unambiguously from
those of some tBuO groups, considering the similar integral ratio, that
is 8H vs. 9H, and the experimental uncertainty due to variable line
shape.
3
,
À1 À1
À1
ethylene (2 kgmol
Chen, Y.-F. Zhang, R.-Q. Kou, L.-S. Chen, Eur. Polym. J. 2001, 37,
181 ± 1184.
20] a) X. Olonde, A. Mortreux, F. Petit, K. Bujadoux, J. Mol. Catal. 1993,
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h
bar at 808C over 0.5 h): Z.-Q. Shen, Y.-F.
1
8
France [Chem. Abst. 1993, 119, 271958s]; c) J.-F. Pelletier, A.
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1
994, 89, 249 ± 258; d) J.-F. Pelletier, A. Mortreux, X. Olonde, K.
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been reported: W. J. Evans, M. S. Sollenberger, J. W. Ziller, J. Am.
Chem. Soc. 1993, 115, 4120 ± 4127; b) synthesis of [Li Sm(OtBu) ]: H.
8
(OtBu)10Cl] complexes (Ln ˆ Y, Eu) has
1
813 ± 1822; f) S. Bogaert, T. Chenal, A. Mortreux, G. Nowogrocki,
C. W. Lehmann, J.-F. Carpentier, Organometallics 2001, 20, 199 ± 205.
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5
8
[
Schumann, G. Kociok-Koehn, A. Dietrich, F. H. Goerlitz, Z. Natur-
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M. A. Mazid, J. Chem. Soc. Chem. Commun. 1988, 1258 ± 1259;
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[
[
[47] M. Kritikos, M. Moustiakimov, M. Wijk, G. Westin, J. Chem. Soc.
Dalton Trans. 2001, 1931 ± 1938.
[48] When the aminolysis reaction was performed in THF, an oily residue
was recovered after removal of the volatiles under vacuum. Attempts
to extract or to recrystallize this residue were unsuccessful.
[49] a) R. D. Shannon, C. T. Prewitt, Acta Crystallogr. Sect. B 1969, 25,
925 ± 946; b) R. D. Shannon, Acta Crystallogr. Sect. B 1970, 26, 1046 ±
1048; c) R. D. Shannon, Acta Crystallogr. Sect. A 1976, 32, 751 ± 767.
[50] Deviation from a Nd/Mg ratio of 1.0, in particular use of an excess of
[
[
[
[
26] G. B. Deacon, B. M. Gatehouse, Q. Shen, G. N. Ward, E. R. T.
Tiekink, Polyhedron 1993, 12, 1289 ± 1294.
2
MgR to take into account the presence of two tBuOH ligands in 4,
27] a) M. Wedler, J. W. Gilje, U. Pieper, D. Stalke, M. Noltemeyer, F. T.
Edelmann, Chem. Ber. 1991, 124, 1163 ± 1165; b) F. T. Edelmann, A.
Steiner, D. Stalke, J. W. Gilje, S. Jagner, M. Hakansson, Polyhedron
and/or modification of the alkoxy/alkyl metathesis conditions (tem-
perature and time) did not bring any significant improvement of the
ethylene polymerization activity of these in situ systems.
Me
1
994, 13, 539 ± 546.
28] a) W. A. Herrmann, R. Anwander, M. Kleine, W. Scherer, Chem. Ber.
992, 125, 1971 ± 1979; b) W. A. Herrmann, R. Anwander, W. Scherer,
2
[51] Ethylene polymerization proceeds with (Tp )YR complexes having
[
two coordinated thf molecules but is inhibited in THF solution;
dissociation of coordinated thf from yttrium significantly affects the
steric saturation at the metal center and appears to be a controlling
factor in the initiation of these polymerizations. See ref. [18a].
1
Chem. Ber. 1993, 126, 1533 ± 1539.
[
[
[
29] D. M. Barnhart, D. L. Clark, J. C. Huffman, R. L. Vincent, J. G.
Watkin, Inorg. Chem. 1993, 32, 4077 ± 4083.
30] P. B. Hitchcock, M. F. Lappert, I. A. MacKinnon, J. Chem. Soc. Chem.
Commun. 1988, 1557 ± 1558.
31] J. Gromada, T. Chenal, A. Mortreux, J. W. Ziller, F. Leising, J.-F.
Carpentier, Chem. Commun. 2000, 2183 ± 2184.
[52] The inefficiency of 3/Mg(n-hex)
polymerization may be related to the presence of chloro bridges in
precursor 3 and to the inhibiting effect of NaCl onto the 1/Mg(n-hex)
2
combinations to promote ethylene
2
combination. However, the sole presence of chloro ligands in the
alkoxy-lanthanide precursor does not preclude the formation of active
systems; see ref. [53].
[
[
32] M. F. Lappert, A. Singh, R. G. Smith, Inorg. Synth. 1990, 27, 164 ± 168.
33] Aware of the importance of minor details on the outcome of the
reactions in this area, special attention has been paid in this study to
the reproducibility of the syntheses. Also, it is often questionable how
a particular crystal chosen for a single-crystal structure determination
is indeed representative of the bulk sample. To address this issue, and
given the final objectives of our research, we have checked that
isolated crystals and initial bulk materials feature comparable
catalytic behavior for olefin polymerization.
[53] Ethylene polymerizations (toluene, 08C, 1 atm, 1 h using in situ
combinations of Mg(n-hex)
Ln ˆ 1.0) showed lower activities and gave low molecular weight
polymers and/or oligomers: ™Sm (OtBu) (thf) ∫ (this compound was
prepared by salt metathesis between SmCl
2
and other lanthanide tert-butoxides (Mg/
3
9
2
3
and NaOtBu in THFand is
1
supposed to be isostructural to 1 on the basis of H NMR data; see also
À1 À1
À1
note [37] and ref. [21a]), A ˆ 1.65 kgmol(Sm)
h
bar , T
m
(final
/M of
PE) ˆ 1398C, PE recovered after 5 min had M
n
ˆ 2500 and M
w
n
Chem. Eur. J. 2002, 8, No. 16
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3787

J.-F. Carpentier et al.
FULL PAPER
À1 À1
À1
6
.1; [La
Bu) Cl (thf)
54] 1H (C
Cl
3
(OtBu)
9
21b]
(thf)
2
],[21a] A ˆ 0.43 kgmol(La)
h
bar
; [Y
3
(Ot-
Cl
N. Y. Turova, Inorg. Chim. Acta 1981, 53, L73 ± L76; c) H. Schumann,
W. Genthe, N. Brunks, Organometallics 1982, 1, 1194 ± 1200; d) A.
Gulino, N. Casarin, V. P. Conticello, J. G. Gaudiello, T. J. Marks,
Organometallics 1988, 7, 2360 ± 2364.
[
À1 À1
À1
7
2
2
],
A ˆ 0.25 kgmol(Y)
h bar .
[
[
[
2
D
2
4
, 1308C): d ˆ 4.33 (PhSiH
2
), 0.19 (CH
2
Si); 13C (C
2
D
2
4
,
1
1
308C): d ˆ 10.0 (CH
2
Si): P.-F. Fu, T. J. Marks, J. Am. Chem. Soc. 1995,
17, 10747 ± 10748.
[61] R. Duchateau, T. Tuinstra, E. A. C. Brussee, A. Meetsma, P. T.
van Duijnen, J. H. Teuben, Organometallics 1997, 16, 3511 ± 3522 and
references therein.
[62] a) J. W. Bruno, T. J. Marks, L. R. Morss, J. Am. Chem. Soc. 1983, 105,
6824 ± 6832; b) J. W. Bruno, H. A. Stecher, L. R. Morss, D. C. Son-
nenberger, T. J. Marks, J. Am. Chem. Soc. 1986, 108, 7275 ± 7280;
c) S. P. Nolan, D. Stern, T. J. Marks, J. Am. Chem. Soc. 1989, 111,
7844 ± 7853.
55] Similar distribution of the lanthanide metal between the toluene
solution and the solid precipitated was observed from the ™Sm (Ot-
Bu) (thf) ∫/Mg(n-hex) /ethylene system.
56] a) Ref. [3]; b) A. D. Horton, J. F. Van Baar, P. A. Schut, G. M. M.
Van Kessel, K. L. Von Hebel, PCT Int. Appl. WO 9921899 [Chem.
Abs. 1999, 130, 325493]; c) J. A. Ewen, M. J. Elder, Eur. Pat. Appl.
EP 426638 [Chem. Abs. 1991, 115, 136987].
3
9
2
2
[
57] Atactic PMMA with high molecular weight distribution arises from
initiation by alkylmagnesium species; the in situ combination 1/Mg(n-
[63] a) D. C. Bradley, J. S. Ghotra, F. A. Hart, J. Chem. Soc. Dalton Trans.
1973, 1021 ± 1023; b) R. A. Andersen, D. H. Templeton, A. Zalkin,
Inorg. Chem. 1978, 17, 2317 ± 2319.
hex)
2
initiates the controlled polymerization of MMA to give
syndiotactic-rich PMMA with very narrow molecular weight distri-
bution: J. Gromada, C. Fouga, T. Chenal, A. Mortreux, J.-F.
Carpentier, Macromol. Chem. Phys. 2002, 203, 550 ± 555.
[64] R. A. Andersen, G. Wilkinson, J. Chem. Soc. Dalton Trans. 1977, 809 ±
811.
[65] CCDC-144860 (1 ¥ THF), -177096 (3 ¥ 2Et O), -177094 (5 ¥ 2toluene), -
2
[
58] a) For a recent review on compatibilization of polymer blends, see: C.
Koning, M. Van Duin, C. Pagnoulle, R. Jerome, Prog. Polym. Sci.
177095 (6), -177097 (7) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB21EZ,
UK; fax: (‡44)1223-336-033; or deposit@ccdc.cam.uk).
1
998, 23, 707 ± 757; b) G. Desurmont, Guillaume, M. Tanaka, Y. Li, H.
Yasuda, T. Tokimitsu, S. Tone, A. Yanagase, J. Polym. Sci. Part A:
Polym. Chem. 2000, 38, 4095 ± 4109.
[
59] Successful isolation of a mixed alkyl/aryloxy magnesium complex
[66] a) SMART Software Users Guide, Version 5.0, Bruker Analytical
X-Ray Systems, Madison, WI, 1999; b) SAINT Software Users Guide,
Version 6.0, Bruker Analytical X-Ray Systems, Madison, WI, 1999;
c) G. M. Sheldrick, SADABS, Bruker Analytical X-Ray Systems,
Madison, WI, 1999; d) G. M. Sheldrick, SHELXTL Version 5.10,
Bruker Analytical X-ray Systems, Madison, WI, 1999.
2 6 2 3 2
from the [Nd(O-2,6-tBu -4-Me-C H ) ]/Mg(n-hex) system likely
results, at least in part, from the beneficial effect of the bulky aryloxy
ligand in crystallizing one of the metathesis products. As pointed out
by a referee, the basicity of OR may also considerably affect ligand
exchange; see ref. [60] for examples of effective metathesis reactions
between alkoxy lanthanide complexes and alkylating agents.
2
2
2
2
2
1/2
[67] R1 ˆ j jF
o
j À j F
c
j j/ j F j ; wR2 ˆ [[w(F
o
1/2
o
À F
o
† ]/[w(F
o
† ]] ; GoF ˆ
2
2
2
[
60] The reaction of Ce(OiPr)
4
¥ iPrOH with 2 equiv MgCp
2
led to
[[w(F
o
À F † ]/(n À p)] where n is the number of reflections and p is
c
[
Cp Ce(OiPr)] and Mg(OiPr)
3
2
: a) A. Greco, S. Cesca, G. Bertolini,
the total number of parameters refined.
J. Organomet. Chem. 1976, 113, 321 ± 330; for lanthanide-alkoxy/alkyl
metathesis reactions involving alkylating agents other than dialkyl-
magnesiums, see: b) V. A. Shreider, E. P. Turevskaya, N. L. Kozlova,
Received: January 14, 2002 [F3800]
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Chem. Eur. J. 2002, 8, No. 16