Neutral and monocationic half-sandwich methyl rare-earth metal complexes: Synthesis, structure, and 1,3-butadiene polymerization catalysis

Article abstract of DOI:10.1002/ejic.200800040

Half-sandwich rare-earth metal tetramethylaluminate complexes [Ln(η⁵-C₅Me₄SiMe₃){(μ-Me) ₂(AlMe₂)}₂] (Ln = Y, La, Nd, Sm, Gd, Lu) were obtained by reaction of the neutral homoleptic tetramethylaluminate complex [Ln{(μ-Me)₂-(AlMe₂)}₃] with tetramethyl(trimethylsilyl)cyclopentadiene, (C₅Me₄H) SiMe₃. Protonolysis reaction of the neutral mono-(cyclopentadienyl) complexes with the Bronsted acid [NEt₃H]⁺[BPh ₄]^- in thf led to the formation of the monocationic methyl complexes [Ln(η⁵-C₅Me₄SiMe ₃)Me-(thf)₃]⁺[BPh₄]^- (Ln = Y, La, Nd, Sm, Lu). Single-crystal X-ray diffraction study on the Y, Sm, and Lu derivatives showed a four-legged piano-stool configuration. Upon activation with [Ph₃C]⁺[B(C₆F₅) ₄]^-, the neutral half-sandwich tetramethylaluminate complex [La(η⁵-C₅Me₄SiMe ₃){(μ-Me)₂(AlMe₂)}₂] catalyzed the polymerization of butadiene in the presence of [AliBu₃] to give trans-1,4-polybutadiene with narrow polydispersities (M_n/M _w = 1.05-1.09). Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800040

FULL PAPER
DOI: 10.1002/ejic.200800040
Neutral and Monocationic Half-Sandwich Methyl Rare-Earth Metal
Complexes: Synthesis, Structure, and 1,3-Butadiene Polymerization Catalysis
Dominique Robert,[a] Thomas P. Spaniol,[a] and Jun Okuda*[a]
Dedicated to Professor Wolfgang A. Herrmann on the occasion of his 60th birthday
Keywords: Rare-earth metals / Half-sandwich complexes / Alkyl complexes / Cationic complexes / Butadiene polymeri-
zation
Half-sandwich rare-earth metal tetramethylaluminate com-
plexes [Ln(η5-C5Me4SiMe3){(µ-Me)2(AlMe2)}2] (Ln = Y, La,
Nd, Sm, Gd, Lu) were obtained by reaction of the neutral
homoleptic tetramethylaluminate complex [Ln{(µ-Me)2-
(AlMe2)}3] with tetramethyl(trimethylsilyl)cyclopentadiene,
(C5Me4H)SiMe3. Protonolysis reaction of the neutral mono-
(cyclopentadienyl) complexes with the Brønsted acid
[NEt3H]+[BPh4]– in thf led to the formation of the mono-
diffraction study on the Y, Sm, and Lu derivatives showed a
four-legged piano-stool configuration. Upon activation with
[Ph3C]+[B(C6F5)4]–, the neutral half-sandwich tetramethyl-
aluminate complex [La(η5-C5Me4SiMe3){(µ-Me)2(AlMe2)}2]
catalyzed the polymerization of butadiene in the presence of
[AliBu3] to give trans-1,4-polybutadiene with narrow polydis-
persities (Mn/Mw = 1.05–1.09).
cationic
methyl
complexes
[Ln(η5-C5Me4SiMe3)Me-
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
(thf)3]+[BPh4]– (Ln = Y, La, Nd, Sm, Lu). Single-crystal X-ray
complexes as synthetic equivalents for bis(alkyl) half-sand-
wich complexes,[8b,8d] we report here the synthesis of mono-
cationic methyl complexes from mono(cyclopentadienyl)
bis(aluminate) complexes and their catalytic behavior in
homogeneous 1,3-butadiene polymerization.
Introduction
Half-sandwich complexes of the rare-earth elements have
been far less studied than their bis(cyclopentadienyl) homo-
logues.[1] Despite the higher tendency towards ligand redis-
tribution, they may exhibit enhanced reactivity through in-
creased electronic and steric unsaturation.[2] Cationic alkyl
mono(cyclopentadienyl) complexes [Ln(η5-C5RЈ5)R]+ have
been reported to be key intermediates in catalytic polymeri-
zations of unsaturated hydrocarbons.[3,4a] Although the re-
port of the first cationic alkyl half-sandwich rare-earth
complex by Schaverien dates back to 1992,[4b] only a limited
number of this type of potentially reactive complexes has
so far been reported in the literature.[5] The neutral tris[(tri-
methylsilyl)methyl] precursors [Ln(CH2SiMe3)(thf)n] and
the corresponding half-sandwich complexes [Ln(η5-C5Me4-
SiMe3)(CH2SiMe3)2(thf)] turned out to be exceedingly sen-
sitive and not reported for metal centers larger than Sm[6]
and Gd.[4a,5e,7] Moreover, the cationic derivatives [Ln(η5-
C5RЈ5)(CH2SiMe3)(thf)m]+[A]– were so far only generated
in situ and could not be structurally characterized.[5] Methyl
cations were expected to be easier to handle and to facilitate
the access to catalytically active cationic methyl species.
Prompted by the reports on half-sandwich bis(aluminate)
Results and Discussion
Mono(cyclopentadienyl) Bis(aluminate) Complexes
Neutral mono(cyclopentadienyl) bis(aluminate) com-
plexes [Ln(η5-C5Me4SiMe3){(µ-Me)2(AlMe2)}2] [Ln = Y (1-
Y), La (1-La), Nd (1-Nd), Sm (1-Sm), Gd (1-Gd), Lu (1-
Lu)] were obtained by alkane elimination reaction between
the homoleptic tris(aluminate) precursors [Ln{(µ-Me)2-
(AlMe2)}3] and (C5Me4H)SiMe3 (Scheme 1). All the com-
plexes (except for 1-Gd) display a pattern of four resonances
1
in their H NMR spectra: one singlet for the SiMe3 group
and two singlets for the two pairs of methyl groups at the
cyclopentadienyl ring, along with another signal for the
eight methyl groups of the aluminate moieties, indicating a
rapid exchange of the bridging and terminal methyl groups
on the NMR timescale. Broad signals were observed in the
13C NMR spectra for the methyl carbon atoms in the alu-
minate fragments. This high fluxionality of the aluminate
group was already reported in the literature.[8]
[a] Institute of Inorganic Chemistry, RWTH Aachen University,
Landoltweg 1, 52074 Aachen, Germany
Fax: +49-241-80-92644
E-mail: jun.okuda@ac.rwth-aachen.de
Eur. J. Inorg. Chem. 2008, 2801–2809
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2801

D. Robert, T. P. Spaniol, J. Okuda
FULL PAPER
Scheme 1.
Figure 1. ORTEP view of [Gd(η5-C5Me4SiMe3){(µ-Me)2-
(AlMe2)}2] (1-Gd). Displacement ellipsoids are drawn at the 50%
probability level. Only selected hydrogen atoms (all refined in their
positions) are shown. Selected bond lengths [Å] and angles [°]: Gd–
C13 2.704(2), Gd–C14 2.720(2), Gd–C17 2.563(2), Gd–C18
2.565(2), Gd···Al1 2.9367(9), Gd···Al2 3.1333(7), Al1–C13 2.056(2),
Al1–C14 2.051(2), Al1–C15 1.9557(19), Al1–C16 1.993(2), Al2–
C17 2.092(2), Al2–C18 2.077(2), Al2–C19 1.977(2), Al2–C20
1.979(2), Gd–Cpcent 2.393(2), Gd···C16 3.213(2); Gd–C13–Al1
74.81(6), Gd–C14–Al1 74.49(6), C13–Al1–C14 107.66(9), C15–
Al1–C16 114.42(9), Gd–C17–Al2 83.97(7), Gd–C18–Al2 84.21(7),
C17–Al2–C18 108.76(8), C19–Al2–C20 115.33(9).
In contrast to the (trimethylsilyl)methyl complex [Y(η5-
C5Me4SiMe3)(CH2SiMe3)2(thf)], which was reported to
slowly decompose at room temperature,[7a,9] complexes 1-
Ln could all be isolated as thermally robust microcrystals
in excellent yields and high purity. In addition, the yttrium
complex 1-Y could also be characterized by 89Y{1H} NMR
spectroscopy in [D6]benzene and [D8]thf, showing singlets
at δ = 171.5 and 312.6 ppm, respectively. The strong differ-
ence in chemical shifts obtained in deuterated benzene and
thf stems from the nature of the species present in solution:
whilst the structure of complex 1-Y is maintained in ben-
zene, the aluminate moieties are split by thf with formation
of the dimethyl complex [Y(η5-C5Me4SiMe3)Me2(thf)n]
along with the trimethylaluminum adduct [AlMe3-
(thf)].[8d,10–12]
Complex 1-Gd could not be characterized by NMR spec-
troscopy due to paramagnetism of the metal ion. Diffrac-
tion-quality crystals were grown from a saturated pentane
solution (Figure 1). As was observed in [La(η5-C5Me5){(µ-
Me)2(AlMe2)}2][8d] or, to a lesser extent, in [Lu(η5-
C5Me5){(µ-Me)2(AlMe2)}2],[8b] the two AlMe4 groups in 1-
Gd display a rather different coordination mode (Figure 1).
Whilst one AlMe4 moiety (Al2, C17, C18, C19 and C20)
coordinates the metal center in a classical η2 fashion with
an almost planar Ln(µ-Me)2Al skeleton [torsion angle Ln–
C–Al–C: Ln = La: 3.0°;[8d] Gd: 3.91(6)°; Lu: 6°[8b]], the sec-
ond aluminate moiety (Al1, C13, C14, C15 and C16) is
strongly distorted towards an η3 coordination mode with
rather small Ln–C–Al angles [torsion angle Ln–C–Al–C:
Ln = La: 47.3°;[8d] Gd: 45.55(8)°; Lu: 28°[8b]] and a short
Ln···C contact between the metal center and the carbon
atom of a terminal methyl group [Ln = La: 3.140(3) Å;[8d]
Gd: 3.213(2) Å; Lu: 3.447 Å[8b]]. It appears that the bending
of the aluminate group and the length of the additional
pentane-soluble half-sandwich dichlorido complex [Sc(η5-
C5Me4SiMe3)Cl2(thf)2], easily synthesized from ScCl3 and
[Li(C5Me4SiMe3)] in thf.[14] Reaction of the dichlorido pre-
cursor with 2 equiv. of [Li(AlMe4)] and 2 equiv. of [AlMe3]
in toluene yielded a red oil whose NMR spectroscopic data
fit with the formula [Sc(η5-C5Me4SiMe3){(µ-Me)2-
(AlMe2)}2] (2) (Scheme 2).
Scheme 2.
A broad signal typical for the AlMe4 moiety is observed
Ln···C contact vary proportionally to the ionic radius of in the 1H NMR spectrum at δ = –0.39 ppm in [D6]benzene.
the metal center: the larger the metal atom, the smaller the The compound could, however, not be isolated in pure
Ln–C–Al angles and the shorter the Ln···C agostic contact. form. The presence of [AlMe3] is required to trap the two
In order to access the scandium analogue [Sc(η5- thf molecules coordinated in [Sc(η5-C5Me4SiMe3)Cl2(thf)2].
C5Me4SiMe3){(µ-Me)2(AlMe2)}2], attempts to synthesize This quantity of thf would be sufficient to induce the split-
the neutral precursor [Sc{(µ-Me)2(AlMe2)}3] were under- ting of both AlMe3 moieties in 2. If the same reaction is
taken.[13] Reaction of ScCl3 with 3 equiv. of [Li(AlMe4)] in carried in the absence of [AlMe3], a product of formula
non-coordinating solvents such as CH2Cl2, toluene, or [Sc(η5-C5Me4SiMe3)Me2]n (3) is isolated as crystalline ma-
1
hexamethyldisiloxane all failed to provide the desired prod- terial from pentane. The H NMR spectrum of 3 in [D6]-
uct. An alternative method was found by employing the benzene displays the three-signal pattern for the C5Me4-
2802
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 2801–2809

Neutral and Monocationic Half-Sandwich Methyl Rare-Earth Metal Complexes
SiMe3 ring and a sharp singlet at δ = 0.13 ppm for the two
The Sc–C bond of the bridging methyl group is
methyl groups at the scandium center. In addition, no coor- longer than that of the terminal one by more than
dination of thf is observed, suggesting a polynuclear struc- 0.11 Å [Sc–C1 2.3129(15) Å and Sc–C2 2.1982(15) Å],
ture, as was observed for [Y(η5-C5Me5)Me2]3.[10] Mass spec- whereas an even longer contact is established with the
trometry showed 3 to be a dimer, an intense signal being methyl group belonging to the other half of the molecule
observed for m/z = 537.4, corresponding to the [M – H]+ [Sc–C1Ј 2.3415(16) Å]. The bond length to the terminal
fragment generated from [Sc(η5-C5Me4SiMe3)Me2]2. Sin- methyl group is in the range of commonly observed values,
gle-crystal X-ray structure determination of 3 revealed a di- such as in [Sc(η5-C5Me5)Me2(tBu3P=O)] [2.251(2) Å and
meric complex of Ci symmetry in the solid state (Figure 2). 2.252(2) Å][16] or in neutral “nacnac” complexes where con-
A typical dimer configuration of the type trans-M[2a] with tacts of 2.225 Å on average are observed.[17]
1
two three-legged piano-stool fragments can be recog-
As H NMR spectroscopic data in [D6]benzene revealed
only one signal for two equivalent methyl groups, the di-
meric nature of 3 must be lost in solution where the com-
pounds only exists as a monomeric species with Cs sym-
metry. Alternatively, a fast exchange of the bridging and
terminal methyl groups on the NMR timescale might ex-
plain the presence of a single signal for the two different
methyl moieties.
nized.[15]
Cationic Mono(cyclopentadienyl) Methyl Complexes
The ease with which the [Ln(µ-Me)2(AlMe2)] moiety can
be dissociated into [AlMe3] and an [Ln–Me] fragment in
the presence of donor solvent such as diethyl ether, thf, or
pyridine makes it useful as synthon for the trimethyl com-
plex.[10,11] We have established that the homoleptic rare-
earth aluminates [Ln{(µ-Me)2(AlMe2)}3] cleanly react in thf
with either 1 equiv. of [NEt3H]+[BPh4]– to yield the mono-
cationic dimethyl complex [LnMe2(thf)n]+[BPh4]– or with
2 equiv. of [NEt3H]+[BPh4]– to generate the dicationic
monomethyl complex [LnMe(thf)n]2+[BPh4]– .[3a,3b,18] Ap-
plying this protonolytic methodology to compounds 1-Y, 1-
La, 1-Nd, 1-Sm, and 1-Lu enabled easy access to cationic
half-sandwich compounds 4-Ln.
Upon treatment of the neutral complexes 1-Ln with a
substochiometric amount of the Brønsted acid [NEt3H]+-
[BPh4]– in thf, the monocationic derivatives [Ln(η5-C5Me4-
SiMe3)Me(thf)3]+[BPh4]– [Ln = Y (4-Y), La (4-La), Nd (4-
2
Figure 2. ORTEP view of [Sc(η5-C5Me4SiMe3)Me(µ-Me)2] (3).
Thermal ellipsoids are drawn at the 50% probability level. Hydro-
gen atoms are omitted for clarity. Primed atoms are related to the
unprimed ones by a center of inversion located in the center of the
Sc–C1–ScЈ–C1Ј ring. Selected bond lengths [Å] and angles [°]: Sc–
C1 2.3129(15), Sc–C2 2.1982(15), Sc–C1Ј 2.3415(16); Sc–Cpcent
2.152, Sc···ScЈ 3.1392(5); Cpcent–Sc–C1 122.97(15), Cpcent–Sc–C2
117.45(15), Cpcent–Sc–C1Ј 114.61(15), C1–Sc–C2 103.38(6), C2–
Sc–C1Ј 98.61(6), C1–Sc–C1Ј 95.18(5).
Table 1. Structurally characterized cationic methyl complexes of the rare-earth metals.
Compound
Ln–Me [Å]
Ref.
[Y(η5-C5Me4SiMe3)Me(thf)3]+[BPh4]– (4-Y)
[Sm(η5-C5Me4SiMe3)Me(thf)3]+[BPh4]– (4-Sm)
[Lu(η5-C5Me4SiMe3)Me(thf)3]+[BPh4]– (4-Lu)
trans-[YMe2(thf)5]+[BPh4]–
2.374(3)
2.406(5)
2.331(4)
2.526(2)/2.508(2)
2.438(2)/2.443(2)
2.343(3)/2.347(3)
2.201(2)/2.529(11)[a]
2.221(5)/2.703(6)[a]
2.699(4)
this work
this work
this work
[18]
[18]
[YMe2(12-crown-4)(thf)]+[BPh4]–
cis-[LuMe2(thf)5]+[BPh4]–
[18]
[Sc(η5-C5Me5)Me(tBu3P=O)(µ-Me)B(C6F5)3]
[Sc(nacnac)Me(µ-Me)B(C6F5)3][b]
[16]
[20a]
[20c]
[20c]
[20d]
[20b,20e]
[20e]
[20e]
[20f]
[Sc(nacnacЈ)(C6F5)(µ-Me)B(C6F5)3][c]
[Sc(nacnac)(R)(µ-Me)B(C6F5)3][b,d]
2.499(2)
[Sc(nacnac)(NHtBu)(µ-Me)B(C6F5)3][b]
[Sc(nacnacЈ)Me(η6-C6X5Br)]+[B(C6F5)4]–[c,f]
[Sc(nacnacЈ)Me(η6-C6H5CH3)]+[B(C6F5)4]–[c]
[Sc(nacnacЈ)Me(η6-C6H3Me3-1,3,5)]+[B(C6F5)4]–[c]
[Sc(nacnac)Me(µ-H)BMe(C6F5)2][b]
2.521(3)/2.537(3)[e]
2.162(5)
2.186(4)
2.212(4)
2.193(3)
[a] First value for the terminal methyl group, second value for the bridging one. [b] nacnac = η3-ArNC(tBu)CHC(tBu)NAr; Ar =
C6H3iPr2-2,6. [c] nacnacЈ = η3-ArNC(Me)CHC(Me)NAr; Ar = C6H3iPr2-2,6. [d] R = CH2SiMe2CH2SiMe3. [e] Value for each of the two
crystallographically independent molecules in the unit cell. [f] X = H, D.
Eur. J. Inorg. Chem. 2008, 2801–2809
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2803

D. Robert, T. P. Spaniol, J. Okuda
FULL PAPER
Nd), Sm (4-Sm), Lu (4-Lu)] were isolated in good yields and
high purity as thermally robust thf-supported monocations
(Scheme 3).
Scheme 3.
Apart from the series of thf-supported monocationic di-
methyl and dicationic monomethyl complexes [LnMe2-
(thf)x]+[BPh4]– and [LnMe(thf)y]2+[BPh4]– ,[18] only few
2
rare-earth cationic methyl complexes bearing non-cyclo-
pentadienyl ligands are known, bulky substituents such as
neutral macrocycles[19] or β-diketiminato ligands[20] being
required for their stabilization (Table 1). So far, the only
reported cationic half-sandwich methyl complex is the crys-
tallographically characterized scandium complex [Sc(η5-
C5Me5)Me(tBu3P=O)(µ-Me)B(C6F5)3] reported by Piers et
al. as a contact ion pair.[16,21] Complexes 4-Ln are the first
examples of charge-separated cationic half-sandwich methyl
complexes.
Crystals suitable for X-ray diffraction analysis could be
obtained for the three complexes 4-Y, 4-Sm and 4-Lu from
saturated thf solutions. Representative bond lengths and
angles are given in Table 2. Despite the large ionic radius
difference of 10 pm (CN = 6) between lutetium and samar-
ium,[22] the three compounds show all a coordination
Figure 3. ORTEP view of the cationic part of [Sm(η5-C5Me4SiMe3)-
Me(thf)3]+[BPh4]– (4-Sm) (top) and top view of the cationic part of
[Y(η5-C5Me4SiMe3)Me(thf)3]+[BPh4]– (4-Y) (bottom). Displace-
ment ellipsoids are drawn at the 50% probability level. Hydrogen
atoms are omitted for clarity.
number of five and adopt a distorted square-pyramidal ge- Y–O2 127.92(8)°, cf. 114° mean in 4-Y; Cpcent–Sm–O2
ometry (Figures 3 and 4). 131.56(15)°, cf. 114° mean in 4-Sm). In 4-Lu, it is found
The arrangement of the three thf molecules and the above the portion of the plane defined by C1 and O3. As a
methyl group in the base plane of the structure is very sim- result of the reduced steric hindrance around the methyl
ilar in all three products. However, the SiMe3 group at the group, no particular influence of the SiMe3 group on the
cyclopentadienyl ligand is found in two different positions. geometry of the structure can be seen in 4-Lu, where similar
It is found above the portion of the plane defined by O1, Cpcent–Lu–X angles (X = Me, thf) are observed. The Ln–
Ln and O2 in 4-Y and 4-Sm (which crystallize isotypically), Me bonds are rather short compared to those reported in
inducing enlarged Cpcent–Ln–O angles with the thf mole- the literature (Table 1), indicating a tighter bonding of the
cule nearest to the SiMe3 group in 4-Y and 4-Sm [Cpcent
–
methyl group to the cationic metal center.
Table 2. Selected bond lengths [Å] and angles [°] for complexes 4-Y, 4-Sm and 4-Lu.
[Y(η5-C5Me4SiMe3)Me(thf)3]+[BPh4]– [Sm(η5-C5Me4SiMe3)Me(thf)3]+[BPh4]– [Lu(η5-C5Me4SiMe3)Me(thf)3]+[BPh4]–
(4-Y)
(4-Sm)
(4-Lu)
Ln–C1
Ln–O1
Ln–O2
Ln–O3
Ln–Cpcent
C1–Ln–O1
O1–Ln–O2
O2–Ln–O3
O3–Ln–C1
Cpcent–Ln–C1 107.82(9)
Cpcent–Ln–O1 112.23(8)
Cpcent–Ln–O2 127.92(8)
Cpcent–Ln–O3 108.94(8)
2.374(3)
2.3757(18)
2.3479(18)
2.3808(18)
2.359(3)
85.46(8)
78.22(6)
75.41(6)
83.78(8)
2.406(5)
2.454(3)
2.435(3)
2.458(3)
2.331(4)
2.324(3)
2.300(2)
2.356(3)
2.314(4)
85.72(12)
77.23(9)
2.419(5)
85.42(16)
78.35(11)
75.08(11)
83.86(16)
104.94(18)
112.72(15)
131.56(15)
108.13(15)
75.25(9)
83.67(12)
114.55(15)
108.56(12)
116.62(12)
116.60(12)
2804
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 2801–2809

Neutral and Monocationic Half-Sandwich Methyl Rare-Earth Metal Complexes
complex results in upfield shifts of the resonance of δ =
–223 and –251 ppm, respectively (Table 3).[3a,23] In the lute-
tium complex 4-Lu, a singlet at δ = –0.72 ppm is observed
for the methyl group, whereas a broad signal at δ =
7.01 ppm is detected in the samarium derivative 4-Sm.
Complex 4-Y could also be synthesized in lower yield
by salt elimination reaction between the dicationic methyl
precursor [YMe(thf)6]2+[BPh4]– and
a stoichiometric
2
amount of [K(C5Me4SiMe3)].
Figure 4. ORTEP view of the cationic part of [Lu(η5-C5Me4-
SiMe3)Me(thf)3]+[BPh4]– (4-Lu). Displacement ellipsoids are drawn
at the 50% probability level. Hydrogen atoms are omitted for clar-
ity.
Polymerization of Butadiene
Upon activation with 1 equiv. of [Ph3C]+[B(C6F5)4]– in
toluene, the neutral precursors 1-La, 1-Nd and 1-Gd, were
found to efficiently initiate stereoselective 1,4-polymeriza-
tion of butadiene in the presence of 5 equiv. of [AliBu3]
(Table 4). A dependence of the stereoselectivity on the ionic
radius of the metal center in the catalyst was observed.
Thus, mainly 1,4-cis-polybutadiene was obtained with 1-Gd
(Run 9). The neodymium analogue 1-Nd gave an increased
1,4-trans microstructure (Run 7), and the lanthanum com-
plex 1-La gave high 1,4-trans contents (Run 3).[24] The cata-
lytic system 1-La/[Ph3C]+[B(C6F5)4]– was found to be inac-
tive at –40 °C even with a reaction time of up to 4 h. Upon
addition of a second equivalent of [Ph3C]+[B(C6F5)4]– to 1-
La or 1-Nd, deactivation of the catalytic system was ob-
served (Runs 6 and 8), consistent with the abstraction of
both methyl groups at the metal center and formation of
an inactive dicationic half-sandwich complex.[24–26] Re-
markably narrow molecular-weight distributions were ob-
tained using 1-La (Mn/Mw = 1.05–1.09). Less control was
achieved by its neutral parent complex [La{(µ-Me)2-
(AlMe2)}3] (Mn/Mw = 2.45) which also afforded low-molec-
ular-weight polymers (Mn = 7000 gmol–1). In the case of
the gadolinium system, going from the neutral homoleptic
[Gd{(µ-Me)2(AlMe2)}3] to the half-sandwich complex 1-Gd
induces a significant increase in stereoselectivity (from 42.2
to 91.1% 1,4-cis). This, however, was accompanied by a loss
in control of molecular-weight distributions (Mn/Mw from
3.09 to 4.24).
The 1H NMR spectrum of the yttrium derivative 4-Y
shows a doublet (2JYH = 2.1 Hz) at δ = –0.74 ppm for the
protons of the methyl group coupled with the yttrium cen-
ter, and a well-resolved quartet (2JYH = 2.1 Hz) is observed
1
in the H-coupled 89Y NMR spectrum at δ = 265.3 ppm.
As a result of the contribution of the positive charge at the
yttrium center, this value appears to be slightly shifted to
high field (∆δ = –47.3 ppm) compared to the value observed
for the neutral complex 1-Y (δ = 312.6 ppm in [D8]thf). This
observation confirms the trend initially observed in 89Y
NMR chemical shifts for the series of alkyl complexes
[Y(CH2SiMe3)n(thf)x](3–n)+[BPh4]–
in which successive
(3–n)
abstraction of the alkyl groups from the neutral tris(alkyl)
Table 3. 89Y{1H} NMR chemical shifts (ppm) for neutral, mono-
and dicationic derivatives of the same series.
Compound
Shift Solvent
Ref.
[Y(η5-C5Me4SiMe3){(µ-Me)2(AlMe2)}2] (1-Y) 171.5 [D6]benzene this work
[Y(η5-C5Me4SiMe3){(µ-Me)2(AlMe2)}2] (1-Y) 312.6 [D8]thf
this work
[Y(η5-C5Me4SiMe3)Me(thf)3]+[BPh4]– (4-Y)
265.3 [D8]thf
45.0 [D5]pyridine
882.7 [D8]thf
this work
[Y(η5-C5Me4SiMe3)(thf)4]2+[BPh4]–
[3c]
2
[18]
[18]
[18]
[Y(CH2SiMe3)3(thf)2]
[Y(CH2SiMe3)2(thf)4]+[BPh4]–
660.0 [D8]thf
[Y(CH2SiMe3)(thf)5]2+[BPh4]–
409.2 [D5]pyridine
2
Table 4. 1,3-Butadiene polymerization catalyzed by complexes 1-La, 1-Nd and 1-Gd, activated by [Ph3C]+[B(C6F5)4]–.[a]
t[b]
T[c]
Yield[d]
cis/trans/1,2[e] Mn
Mn/Mw
[f]
Run
Complex
Activator
[BD]/[Ln]
1
2
1-La
1-La
1-La
1-La
1-La
1-La
1-Nd
1-Nd
1-Gd
1
1
1
1
1
2
1
2
1
1
1
200
200
200
1000
200
200
200
200
200
200
200
5
19
19
19
19
–40
19
19
19
19
19
19
0
–
–
19
24
–
10
15
15
240
15
15
15
15
15
15
67
77
95
0
11
82
0
68
16
40
8.5/90.9/0.6
7.5/91.9/0.6
15.1/84.8/0.1 66
1.08
1.05
1.09
–
1.20
1.20
–
4.24
2.45
3.09
3
4[g]
5
–
–
5
6
7
8
9
10
11
9.4/90.1/0.5
69.1/30.2/0.7 28
–
91.1/8.2/0.7
16.5/83.3/0.2
42.2/57.3/0.5 23
–
49
7
[h]
LaAl3
[i]
GdAl3
[a] Conditions: 50 µmol of catalyst; solvent: toluene; Vtotal = 21 mL. [b] In min. [c] In °C. [d] In % (isolated polymer). [e] Determined by
1H and 13C NMR spectroscopy. [f] In gmol–1. [g] Vtotal = 36 mL. [h] LaAl3 represents [La{(µ-Me)2(AlMe2)}3]. [i] GdAl3 represents
[Gd{(µ-Me)2(AlMe2)}3].
Eur. J. Inorg. Chem. 2008, 2801–2809
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2805

D. Robert, T. P. Spaniol, J. Okuda
FULL PAPER
General Procedure for the Preparation of [Ln(η5-C5Me4SiMe3){(µ-
Me)2(AlMe2)}2] (1-Ln): To a pentane solution (6 mL) of [Ln{(µ-
Me)2(AlMe2)}3] was slowly added at room temperature a pentane
solution (4 mL) of 1 equiv. of (C5Me4H)SiMe3 under vigorous stir-
ring. Gas evolution was instantaneously observed, and after stir-
ring for 20 min, the solution was filtered. The volatiles were then
removed under vacuum to leave oily products that crystallized
within 1 h to yield the pure and microcrystalline compounds.
Conclusions
Half-sandwich bis(aluminate) complexes [Ln(η5-
C5Me4SiMe3){(µ-Me)2(AlMe2)}2] have been shown to be
efficient precursors for the synthesis of thermally robust
monocationic methyl complexes [Ln(η5-C5Me4SiMe3)Me-
(thf)3]+[BPh4]– by protonolysis. The scandium bis(alumin-
ate) [Sc(η5-C5Me4SiMe3){(µ-Me)2(AlMe2)}2] was obtained
by salt metathesis between the dichlorido half-sandwich
precursor and [Li(AlMe4)]. In the case of lanthanum and
neodymium, activation of the neutral bis(aluminate)
complexes [Ln(η5-C5Me4SiMe3){(µ-Me)2(AlMe2)}2] with
[Ph3C]+[B(C6F5)4]– generated active catalysts for the con-
trolled 1,4-trans polymerization of 1,3-butadiene in toluene
in the presence of [AliBu3]. Thus, monocationic methyl
complexes [Ln(η5-C5Me4SiMe3)Me(thf)3]+[BPh4]– serve as
functional models for rare-earth metal based 1,3-butadiene
polymerization catalysts.
[Y(η5-C5Me4SiMe3){(µ-Me)2(AlMe2)}2] (1-Y): According to the ge-
neral procedure, [Y{(µ-Me)2(AlMe2)}3] (700 mg, 2.0 mmol) was
treated with (C5Me4H)SiMe3 (389 mg, 2.0 mmol) to yield 1-Y
1
(809 mg, 89%) as a light yellow powder. H NMR ([D6]benzene):
2
δ = –0.29 (d, JYH = 2.0 Hz, 24 H, AlMe4), 0.23 (s, 9 H, SiMe3),
1.74 (s, 6 H, C5Me4), 1.99 (s, 6 H, C5Me4) ppm. 13C{1H} NMR
([D6]benzene): δ = 0.31 (br., AlMe4), 2.16 (SiMe3), 12.06 (C5Me4),
14.97 (C5Me4), 119.00 (C5Me4SiMe3, C bonded to SiMe3), 127.82
(C5Me4SiMe3, C bonded to Me4), 131.46 (C5Me4SiMe3, C bonded
to Me4) ppm. 89Y{1H} NMR ([D6]benzene): δ = 171.5 ppm.
89Y{1H} NMR ([D8]thf): δ = 312.6 ppm. C20H45Al2SiY (456.52):
calcd. C 52.62, H 9.94; found C 52.18, H 9.71.
[La(η5-C5Me4SiMe3){(µ-Me)2(AlMe2)}2] (1-La): According to the
general procedure, [La{(µ-Me)2(AlMe2)}3] (600 mg, 1.5 mmol) was
treated with (C5Me4H)SiMe3 (292 mg, 1.5 mmol) to yield 1-La
Experimental Section
1
(722 mg, 95%) as a light yellow powder. H NMR ([D6]benzene):
General Remarks: All operations were performed under argon
using standard Schlenk-line or glovebox techniques. The solvents
thf and pentane were distilled from sodium benzophenone ketyl
and sodium benzophenone ketyl triglyme, respectively; [D8]thf and
[D6]benzene were dried with sodium and distilled prior to use;
CDCl3 was dried with CaH2 and distilled prior to use. [Ln{(µ-Me)2-
δ = –0.25 (s, 24 H, AlMe4), 0.24 (s, 9 H, SiMe3), 1.81 (s, 6 H,
C5Me4), 2.09 (s, 6 H, C5Me4) ppm. 13C{1H} NMR ([D6]benzene):
δ = 2.18 (SiMe3), 2.36 (br., AlMe4), 11.83 (C5Me4), 14.97 (C5Me4),
122.83 (C5Me4SiMe3, C bonded to SiMe3), 130.21 (C5Me4SiMe3,
C bonded to Me4), 134.01 (C5Me4SiMe3, C bonded to Me4) ppm.
C20H45Al2LaSi (506.53): calcd. C 47.42, H 8.95; found C 47.44, H
9.04.
(AlMe2)}3],[8a,27] [YMe(thf)6]2+[BPh4]– ,[18] [Sc(η5-C5Me4SiMe3)-
2
Cl2(thf)2],[14] (C5Me4H)SiMe3
and [K(C5Me4SiMe3)][29] were
[28]
prepared according to literature procedures. [Li(AlMe4)] was pre-
pared according to a modification of a literature procedure.[30] All
other chemicals were commercially available and used after appro-
priate purification. NMR spectra were recorded at room tempera-
ture with a Bruker DRX 400 spectrometer (1H 400.1 MHz, 13C
100.6 MHz, 11B 128.4 MHz, 89Y 19.6 MHz) or a Varian Unity 500
spectrometer (1H 499.6 MHz, 13C 125.6 MHz, 11B 160.3 MHz); all
chemical shifts are given in ppm; chemical shifts for 1H and
13C{1H} NMR spectra were referenced internally using the residual
solvent resonances and reported relative to SiMe4; 11B NMR spec-
tra were referenced externally to a saturated solution of NaBH4 in
D2O; 89Y NMR spectra were referenced externally to a 1 molL–1
solution of YCl3 in H2O.
[Nd(η5-C5Me4SiMe3){(µ-Me)2(AlMe2)}2] (1-Nd): According to the
general procedure, [Nd{(µ-Me)2(AlMe2)}3] (608 mg, 1.5 mmol) was
treated with HC5Me4SiMe3 (292 mg, 1.5 mmol) to yield 1-Nd
1
(660 mg, 86%) as a light blue powder. H NMR ([D6]benzene): δ
= –3.03 (br. s, 9 H, SiMe3), 5.24 (br. s, 24 H, AlMe4), 8.83 (br. s, 6
H, C5Me4), 14.61 (br. s, 6 H, C5Me4) ppm. 13C{1H} NMR ([D6]-
benzene): δ = –20.05 (C5Me4), –10.71 (C5Me4), 8.95 (SiMe3),
232.57 (br., AlMe4), 237.72 (C5Me4SiMe3, C bonded to Me4),
254.15 (C5Me4SiMe3, C bonded to Me4) ppm. The signal for the
carbon atom bonded to the SiMe3 group was not detected.
C20H45Al2NdSi (511.86): calcd. C 46.93, H 8.86; found C 45.36, H
8.92.
[Sm(η5-C5Me4SiMe3){(µ-Me)2(AlMe2)}2] (1-Sm): According to the
general procedure, [Sm{(µ-Me)2(AlMe2)}3] (412 mg, 1.0 mmol) was
treated with (C5Me4H)SiMe3 (195 mg, 1.0 mmol) to yield 1-Sm
General Polymerization Procedure: In a typical polymerization ex-
periment, 50 µmol of the neutral mono(cyclopentadienyl) bis-
(aluminate) complex were dissolved in 10 mL of toluene. A fivefold
excess of cocatalyst [AliBu3] (250 µmol) was added, followed by 1
or 2 equiv. of activator [Ph3C]+[B(C6F5)4]– (50 or 100 µmol). The
resulting solution was stirred for 5 min, after which 200 equiv. of
butadiene (12.8 wt.-% solution in toluene) was added. After
15 min, the reaction was quenched by pouring the polymerization
mixture into 200 mL of methanol acidified with 4 mL of concen-
trated hydrochloric acid and containing 1 g of 2,6-di-tert-butylphe-
nol as stabilisator. The precipitated polymer was isolated by decan-
tation, washed with methanol and dried to constant weight. The
microstructure of the polybutadienes was determined by 1H
1
(503 mg, 97%) as a deep red powder. H NMR ([D6]benzene): δ =
–3.14 (br. s, 24 H, AlMe4), –0.64 (s, 9 H, SiMe3), –0.13 (s, 6 H,
C5Me4), 2.69 (s, 6 H, C5Me4) ppm. 13C{1H} NMR ([D6]benzene): δ
= –19.53 (br., AlMe4), 0.47 (SiMe3), 14.92 (C5Me4), 21.65 (C5Me4),
110.71 (C5Me4SiMe3, C bonded to SiMe3), 122.27 (C5Me4SiMe3,
C bonded to Me4), 129.57 (C5Me4SiMe3, C bonded to Me4) ppm.
C20H45Al2SiSm (518.01): calcd. C 46.37, H 8.76; found C 45.83, H
8.92.
[Gd(η5-C5Me4SiMe3){(µ-Me)2(AlMe2)}2] (1-Gd): According to the
general procedure, [Gd{(µ-Me)2(AlMe2)}3] (418 mg, 1.0 mmol) was
(400.1 MHz) and 13C (100.6 MHz) NMR spectroscopy in CDCl3 treated with (C5Me4H)SiMe3 (195 mg, 1.0 mmol) to yield 1-Gd
with a Bruker DRX 400 spectrometer. The weight- and number-
average molecular weights Mw and Mn were determined by GPC
with an Agilent 1100 Series instrument at 35 °C in thf against poly-
styrene standards.
(427 mg, 82%) as a white powder. Crystals suitable for X-ray dif-
fraction were grown from a saturated pentane solution at –35 °C.
Due to the paramagnetism of the gadolinium center, no NMR
spectroscopic data could be obtained for this compound.
2806
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 2801–2809

Neutral and Monocationic Half-Sandwich Methyl Rare-Earth Metal Complexes
C20H45Al2GdSi (524.87): calcd. C 45.77, H 8.64; found C 45.21, H 2JYH = 2.10 Hz) ppm. C49H68BO3SiY (832.87): calcd. C 70.66, H
9.16.
8.23, Y 10.67; found C 70.00, H 8.36, Y 10.45. By Salt Metathesis:
To a thf suspension (3 mL) of [YMe(thf)6]2+[BPh4]– (235 mg,
[Lu(η5-C5Me4SiMe3){(µ-Me)2(AlMe2)}2] (1-Lu): According to the
general procedure, [Lu{(µ-Me)2(AlMe2)}3] (655 mg, 1.5 mmol) was
treated with (C5Me4H)SiMe3 (292 mg, 1.5 mmol) to yield 1-Lu
(622 mg, 76%) as a pale yellow powder. 1H NMR ([D6]benzene): δ
= –0.13 (s, 24 H, AlMe4), 0.23 (s, 9 H, SiMe3), 1.77 (s, 6 H, C5Me4),
2.01 (s, 6 H, C5Me4) ppm. 13C{1H} NMR ([D6]benzene): δ = 1.69
(br. s, AlMe4), 2.16 (SiMe3), 12.02 (C5Me4), 14.85 (C5Me4), 117.45
(C5Me4SiMe3, C bonded to SiMe3), 126.53 (C5Me4SiMe3, C
bonded to Me4), 130.10 (C5Me4SiMe3, C bonded to Me4) ppm.
C20H45Al2LuSi (542.59): calcd. C 44.27, H 8.36; found C 43.54, H
8.23.
[Sc(η5-C5Me4SiMe3){(µ-Me)2(AlMe2)}2] (2): To a toluene suspen-
sion (3 mL) of [Li(AlMe4)] (188 mg, 2.00 mmol) and [AlMe3]
(144 mg, 2.00 mmol) was slowly added at room temperature a tolu-
ene solution (5 mL) of [Sc(η5-C5Me4SiMe3)Cl2(thf)2] (453 mg,
1 mmol). After stirring overnight, the mixture was filtered and
dried under vacuum to afford an orange oil. 1H NMR ([D6]ben-
zene): δ = –0.39 (br. s, 24 H, AlMe4), 0.28 (s, 9 H, SiMe3), 1.78 (s,
6 H, C5Me4), 2.11 (s, 6 H, C5Me4) ppm.
2
0.2 mmol) at –35 °C was added a thf suspension (3 mL) of
[K(C5Me4SiMe3)] (56 mg, 0.24 mmol). After completion of the ad-
dition, the suspension was warmed up to room temperature, stirred
for 2 h, and filtered. The volatiles were removed under vacuum, the
resulting solid washed with pentane (2ϫ10 mL) and dried under
vacuum to give 4-Y (92 mg, 69%) as an off-white solid. 1H, 13C
and 11B NMR spectroscopic data matched those obtained for the
product isolated by protonolysis.
[La(η5-C5Me4SiMe3)Me(thf)3]+[BPh4]– (4-La): According to the
general procedure, 1-La (101 mg, 0.2 mmol) in thf (3 mL) was
treated with a thf solution (3 mL) of [NEt3H]+[BPh4]– (76 mg,
1
0.18 mmol) to afford 4-La as a yellow powder (120 mg, 76%). H
NMR ([D8]thf): δ = –0.61 (s, 3 H, LaMe), 0.27 (s, 9 H, SiMe3),
1.77 (m, 12 H, β-CH2, thf), 1.97 (s, 6 H, C5Me4), 2.13 (s, 6 H,
3
C5Me4), 3.62 (m, 12 H, α-CH2, thf), 6.72 (t, JHH = 7.3 Hz, 4 H,
3
Ph-4), 6.86 (t, JHH = 7.3 Hz, 8 H, Ph-3), 7.27 (br. m, 8 H, Ph-2)
ppm. 13C{1H} NMR ([D8]thf): δ = 2.86 (SiMe3), 11.64 (C5Me4),
14.69 (C5Me4), 26.37 (β-CH2, thf), 68.22 (α-CH2, thf), 117.95
(C5Me4SiMe3, C bonded to SiMe3), 121.63 (Ph-4), 125.69 (Ph-3),
126.20 (C5Me4SiMe3, C bonded to Me4), 130.05 (C5Me4SiMe3, C
[Sc(η5-C5Me4SiMe3)Me(µ-Me)]2 (3): To
a toluene suspension
(3 mL) of [Li(AlMe4)] (193 mg, 2.05 mmol) was slowly added at
room temperature a toluene solution (5 mL) of [Sc(η5-C5Me4-
SiMe3)Cl2(thf)2] (453 mg, 1.0 mmol). After stirring overnight, the
mixture was filtered, dried under vacuum, and the resulting pale
yellow solid extracted with pentane (2ϫ 4 mL). After filtration, the
clear solution was stored at –40 °C. The product (180 mg, 44%)
could be isolated as single crystals within a few hours. 1H NMR
([D6]benzene): δ = 0.13 (s, 6 H, ScMe), 0.36 (s, 9 H, SiMe3), 1.89
(s, 6 H, C5Me4), 2.25 (s, 6 H, C5Me4) ppm. 13C{1H} NMR ([D6]-
benzene): δ = 2.13 (SiMe3), 11.62 (C5Me4), 15.13 (C5Me4), 120.18
(C5Me4SiMe3, C bonded to SiMe3), 126.31 (C5Me4SiMe3, C
bonded to Me4), 130.58 (C5Me4SiMe3, C bonded to Me4) ppm.
C28H54Sc2Si2 (536.82): calcd. C 62.65, H 10.14; found C 60.49, H
9.60.
General Procedure for the Preparation of [Ln(η5-C5Me4SiMe3)-
Me(thf)3]+[BPh4]– (4-Ln) by Protonolysis: To a thf solution of
[Ln(η5-C5Me4SiMe3){(µ-Me)2(AlMe2)}2] (1-Ln) was slowly added
at –35 °C a thf solution of [NEt3H]+[BPh4]– under vigorous stir-
ring. After the addition, the clear solution was warmed up to room
temperature and stirred for 30 min. The volatiles were then re-
moved under vacuum. Washing the oily residue with pentane
(3ϫ10 mL) and drying afforded the desired compound as micro-
crystalline solid.
1
bonded to Me4), 137.10 (Ph-2), 165.12 (q, JBC = 49.4 Hz, Ph-1)
ppm. The signal of the carbon atom of the methyl group bonded
to the lanthanum center could not be located. 11B{1H} NMR ([D8]-
thf): δ = –6.56 ppm. C49H68BLaO3Si (882.88): calcd. C 66.66, H
7.76; found C 65.55, H 6.98.
[Nd(η5-C5Me4SiMe3)Me(thf)3]+[BPh4]– (4-Nd): According to the
general procedure, 1-Nd (103 mg, 0.20 mmol) in thf (3 mL) was
treated with a thf solution (3 mL) of [NEt3H]+[BPh4]– (76 mg,
0.18 mmol) to afford 4-Nd as a pale green powder (125 mg, 78%).
1H NMR ([D8]thf): δ = 0.26 (br. s, 9 H, SiMe3), 1.74 (br. s, 12 H,
β-CH2, thf), 3.43 (br. s, 6 H, C5Me4), 3.53 (br. s, 12 H, α-CH2, thf),
6.57 (br. s, 12 H, Ph-3 + Ph-4), 6.73 (br. s, 8 H, Ph-2), 12.48 (br. s,
6 H, C5Me4) ppm. The signal of the methyl group bonded to the
neodymium center was not detected. 13C{1H} NMR ([D8]thf): δ =
–19.93 (C5Me4), –11.03 (C5Me4), 10.69 (SiMe3), 26.61 (β-CH2, thf),
68.26 (α-CH2, thf), 121.77 (Ph-4), 125.51 (Ph-3), 136.82 (Ph-2),
1
164.82 (q, JBC = 49.6 Hz, Ph-1), 203.98 (br., C5Me4SiMe3, C
bonded to Me4), 214.53 (br., C5Me4SiMe3, C bonded to Me4),
251.34 (C5Me4SiMe3, C bonded to SiMe3) ppm. The signal of the
carbon atom of the methyl group bonded to the neodymium center
was not detected. 11B{1H} NMR ([D8]thf): δ = –7.00 ppm.
C49H68BNdO3Si (888.21): calcd. C 66.26, H 7.72; found C 65.97,
H 7.33.
[Y(η5-C5Me4SiMe3)Me(thf)3]+[BPh4]– (4-Y). By Protonolysis: Ac-
cording to the general procedure, 1-Y (809 mg, 1.77 mmol) in thf
(15 mL) was treated with a thf solution (15 mL) of [NEt3H]+-
[BPh4]– (709 mg, 1.68 mmol) to afford 4-Y as an off-white powder
(1335 mg, 95%). Crystals suitable for X-ray diffraction were ob-
tained by cooling a saturated thf solution of 4-Y to –35 °C. 1H
[Sm(η5-C5Me4SiMe3)Me(thf)3]+[BPh4]– (4-Sm): According to the
general procedure, 1-Sm (104 mg, 0.20 mmol) in thf (3 mL) was
treated with a thf solution (3 mL) of [NEt3H]+[BPh4]– (76 mg,
0.18 mmol) to afford 4-Sm as a pink powder (94 mg, 58%). Crys-
tals suitable for X-ray diffraction were obtained by cooling a satu-
2
1
NMR ([D8]thf): δ = –0.74 (d, JYH = 2.13 Hz, 3 H, YMe), 0.30 (s,
rated thf solution of 4-Sm to 6 °C. H NMR ([D8]thf): δ = 0.11 (s,
9 H, SiMe3), 1.77 (m, 12 H, β-CH2, thf), 1.99 (s, 6 H, C5Me4), 2.13
9 H, SiMe3), 1.19 (s, 6 H, C5Me4), 1.81 (s, 6 H, C5Me4), 1.78 (m,
3
(s, 6 H, C5Me4), 3.62 (m, 12 H, α-CH2, thf), 6.73 (t, 3JHH = 7.3 Hz,
12 H, β-CH2, thf), 3.62 (m, 12 H, α-CH2, thf), 6.73 (t, JHH
7.3 Hz, 4 H, Ph-4), 6.86 (t, JHH = 7.3 Hz, 8 H, Ph-3), 7.01 (br. s,
=
3
3
4 H, Ph-4), 6.87 (t, JHH = 7.3 Hz, 8 H, Ph-3), 7.27 (br. m, 8 H,
Ph-2) ppm. 13C{1H} NMR ([D8]thf): δ = 2.35 (SiMe3), 11.35 3 H, SmMe), 7.25 (br. m, 8 H, Ph-2) ppm. 13C{1H} NMR ([D8]-
1
(C5Me4), 14.19 (C5Me4), 26.16 (β-CH2, thf), 26.6 (d, JYC
=
thf): δ = 1.80 (SiMe3), 15.56 (C5Me4), 17.52 (C5Me4), 26.33 (β-
CH2, thf), 68.22 (α-CH2, thf), 106.67 (C5Me4SiMe3, C bonded to
SiMe3), 121.84 (Ph-4), 123.29 (C5Me4SiMe3, C bonded to Me4),
55.8 Hz, YMe), 68.21 (α-CH2, thf), 110.97 (C5Me4SiMe3, C
bonded to SiMe3), 121.85 (Ph-4), 125.08 (C5Me4SiMe3, C bonded
to Me4), 129.57 (C5Me4SiMe3, C bonded to Me4), 125.69 (Ph-3), 125.35 (C5Me4SiMe3, C bonded to Me4), 125.65 (Ph-3), 137.08
1
1
137.11 (Ph-2), 165.20 (q, JBC = 49.4 Hz, Ph-1) ppm. 11B{1H}
(Ph-2), 165.10 (q, JBC = 49.3 Hz, Ph-1) ppm. The signal of the
NMR ([D8]thf): δ = –6.57 ppm. 89Y NMR ([D8]thf): δ = 265.3 (q,
carbon atom of the mehyl group bonded to the samarium center
Eur. J. Inorg. Chem. 2008, 2801–2809
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2807

D. Robert, T. P. Spaniol, J. Okuda
FULL PAPER
Table 5. Crystallographic and data-collection parameters for compounds 1-Gd, 3, 4-Y, 4-Sm, and 4-Lu.
1-Gd
3
4-Y
4-Sm
4-Lu
Empirical formula
Mr
C
524.86
20H45Al2GdSi
C14H27ScSi
268.41
C49H68BO3SiY·(C4H8O) C49H68BO3SiSm·(C4H8O) C49H68BLuO3Si·0.5(C4H8O)
904.95
966.39
956.20
Crystal size [mm]
Crystal color and habit
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
0.54ϫ0.32ϫ0.24 0.30ϫ0.30ϫ0.10 0.40ϫ0.32ϫ0.30
0.14ϫ0.13ϫ0.11
orange block
monoclinic
P21/n
10.8822(6)
37.917(2)
11.9654(7)
90
0.30ϫ0.13ϫ0.06
colorless fragment
monoclinic
C2/c
27.687(2)
24.6089(19)
16.4669(13)
90
colorless block
monoclinic
P21/n
colorless block
monoclinic
P21/n
colorless block
monoclinic
P21/n
10.189(3)
13.439(3)
19.217(5)
90
11.4405(11)
8.4494(8)
16.3691(16)
90
10.9037(7)
37.922(2)
11.9130(8)
90
β [°]
105.021(4)
90
2541.5(11)
4
1.372
130(2)
93.9675(14)
90
1578.5(3)
4
1.129
130(2)
93.1600(10)
90
4918.4(6)
4
1.222
130(2)
93.6190(10)
90
4927.3(5)
4
1.303
110(2)
123.4570(11)
90
9360.6(12)
8/2
1.357
130(2)
γ [°]
V [Å3]
Z
Dcalcd. [gcm–3
T [K]
]
µ(Mo-Kα) [mm–1
F(000)
]
2.727
1076
0.519
584
1.253
1936
1.259
2028
2.176
3975
θ range [°]
Number of reflections
collected
1.87–28.30
22467
2.25–30.75
23073
2.15–24.66
73877
2.35–21.29
36560
2.22–23.80
52036
Number of reflections
observed [IϾ2σ(I)]
Number of independent
5899
3752
9911
4693
9945
6301 (0.0316)
4701 (0.0454)
14467 (0.0688)
5455 (0.0858)
13650 (0.0724)
reflections (Rint
)
Data/restraints/parameters 6301/0/277
4701/0/176
0.950
0.0335, 0.0813
0.0438, 0.0842
14467/0/514
1.045
0.0551, 0.1291
0.0966, 0.1462
5455/2/544
1.042
0.0376, 0.0820
0.0468, 0.0859
0.891 and –0.597
13650/0/525
1.033
0.0476, 0.0907
0.0777, 0.1015
0.1893 and –0.794
Goodness-of-fit on F2
R1, wR2 [IϾ2σ(I)]
1.037
0.0192, 0.0481
0.0213, 0.0490
R1, wR2 (all data)
Largest difference in peak
0.739 and –1.279 0.485 and –0.273 1.033 and –0.674
and hole [eÅ–3
]
was not detected. 11B{1H} NMR ([D8]thf): δ = –6.59 ppm.
C49H68BO3SiSm (894.33): calcd. C 65.81, H 7.66; found C 64.99,
H 7.68.
groups in 1-Gd were refined in their positions. The structure of
4-Y was solved by isotypical replacement using the coordinates of
4-Sm. The crystal structures of 4-Y, 4-Sm and 4-Lu contain a co-
crystallized molecule of thf. CCDC-671767 (1-Gd), -671768 (3),
-671769 (4-Y), -671770 (4-Sm) and -671771 (4-Lu) contain the sup-
plementary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[Lu(η5-C5Me4SiMe3)Me(thf)3]+[BPh4]– (4-Lu): According to the
general procedure, 1-Lu (163 mg, 0.30 mmol) in thf (3 mL) was
treated with a thf solution (3 mL) of [NEt3H]+[BPh4]– (114 mg,
0.27 mmol) to afford 4-Lu as a pale yellow powder (232 mg, 94%).
Crystals suitable for X-ray diffraction were obtained by cooling a
saturated thf solution of 4-Lu to –35 °C. 1H NMR ([D8]thf): δ =
–0.70 (s, 3 H, LuMe), 0.29 (s, 9 H, SiMe3), 1.77 (m, 12 H, β-CH2,
thf), 2.01 (s, 6 H, C5Me4), 2.14 (s, 6 H, C5Me4), 3.62 (m, 12 H, α-
Acknowledgments
3
3
CH2, thf), 6.72 (t, JHH = 7.5 Hz, 4 H, Ph-4), 6.86 (t, JHH
=
We thank the European Commission in the FP6 Project (NMP3-
CT-2005-516972), the Deutsche Forschungsgemeinschaft (DFG),
and the Fonds der Chemischen Industrie for financial support. We
also thank Mr. Yutian Wang for collecting the X-ray data.
7.5 Hz, 8 H, Ph-3), 7.27 (br. m, 8 H, Ph-2) ppm. 13C{1H} NMR
([D8]thf): δ = 2.55 (SiMe3), 11.69 (C5Me4), 14.40 (C5Me4), 26.37
(β-CH2, thf), 30.94 (LuMe), 68.22 (α-CH2, thf), 116.71 (C5Me4S-
iMe3, C bonded to SiMe3), 121.86 (Ph-4), 124.45 (C5Me4SiMe3, C
bonded to Me4), 128.97 (C5Me4SiMe3, C bonded to Me4), 125.70
1
[1] a) C. J. Schaverien, Adv. Organomet. Chem. 1994, 36, 283–362;
b) H. Schumann, J. A. Meese-Marktscheffel, L. Esser, Chem.
Rev. 1995, 95, 865–986.
[2] a) S. Arndt, J. Okuda, Chem. Rev. 2002, 102, 1953–1976; b) J.
Okuda, Dalton Trans. 2003, 2367–2378.
[3] a) S. Arndt, J. Okuda, Adv. Synth. Catal. 2005, 347, 339–354;
b) P. M. Zeimentz, S. Arndt, B. R. Elvidge, J. Okuda, Chem.
Rev. 2006, 106, 2404–2433; c) P. Voth, Doctoral Thesis, RWTH
Aachen University, Aachen, Germany, 2004.
[4] a) Y. Luo, J. Baldamus, Z. Hou, J. Am. Chem. Soc. 2004, 126,
13910–13911; b) C. J. Schaverien, Organometallics 1992, 11,
3476–3478.
(Ph-3), 137.12 (Ph-2), 165.13 (q, JBC = 49.3 Hz, Ph-1) ppm.
11B{1H} NMR ([D8]thf): δ = –6.57 ppm. C49H68BLuO3Si (918.94):
calcd. C 64.05, H 7.46; found C 63.17, H 7.49.
X-ray Crystal-Structure Determination of 1-Gd, 3, 4-Y, 4-Sm, and
4-Lu: A summary of the crystallographic data is given in Table 5.
The data were collected using Mo-Kα radiation of a Bruker AXS
diffractometer with a CCD area detector using ω scans. The
SMART program package was used to determine the unit-cell pa-
rameters and for data collection; the raw frame data were processed
using SAINT and SADABS to yield the reflection data file.[31] Sub-
sequent calculations were carried out using the SHELXS and
SHELXL programs.[32] All hydrogen atoms were included into cal-
culated positions; the hydrogen atoms of the bridging methyl
[5] For cationic alkyl half-sandwich rare-earth metal complexes,
see: a) J. N. Christopher, K. R. Squire, J. A. M. Canich and
T. D. Schaffer (Exxon Chemical Patent Inc., USA), PCT Int.
2808
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 2801–2809

Neutral and Monocationic Half-Sandwich Methyl Rare-Earth Metal Complexes
Appl. WO2000018808, 2000; b) S. Arndt, T. P. Spaniol, J.
Okuda, Organometallics 2003, 22, 775–781; c) for an account
on polymerization by half-sandwich rare-earth metal catalysts,
see: Z. Hou, Y. Luo, X. Li, J. Organomet. Chem. 2006, 691,
3114–3121; d) L. Zhang, Y. Luo, Z. Hou, J. Am. Chem. Soc.
2005, 127, 14562–14563; e) X. F. Li, J. Baldamus, Z. Hou, An-
gew. Chem. Int. Ed. 2005, 44, 962–965; f) X. F. Li, Z. Hou,
Macromolecules 2005, 38, 6767–6769; g) X. Li, M. Nishiura,
K. Mori, T. Mashiko, Z. Hou, Chem. Commun. 2007, 4137–
4139; h) J. Hitzbleck, J. Okuda, Z. Anorg. Allg. Chem. 2006,
632, 1947–1949; i) J. Hitzbleck, J. Okuda, Organometallics
2007, 26, 3227–3235; j) isolation and crystallographic charac-
terization of [Sc(η5-C5Me4SiMe3)(CH2SiMe3)(thf)2]+[BPh4]–
have recently been completed: J. Hitzbleck, J. Okuda, unpub-
lished results.
[18]
a) S. Arndt, T. P. Spaniol, J. Okuda, Angew. Chem. Int. Ed.
2003, 42, 5075–5079; b) S. Arndt, K. Beckerle, P. M. Zeimentz,
T. P. Spaniol, J. Okuda, Angew. Chem. Int. Ed. 2005, 44, 7473–
7477; c) B. R. Elvidge, S. Arndt, P. M. Zeimentz, T. P. Spaniol,
J. Okuda, Inorg. Chem. 2005, 44, 6777–6788; d) M. U. Kramer,
D. Robert, S. Arndt, P. M. Zeimentz, T. P. Spaniol, A. Yahia,
L. Maron, O. Eisenstein, J. Okuda, manuscript in preparation.
[19]
[20]
S. Hajela, W. P. Schaefer, J. E. Bercaw, J. Organomet. Chem.
1997, 532, 45–53.
a) P. G. Hayes, W. E. Piers, R. McDonald, J. Am. Chem. Soc.
2002, 124, 2132–2133; b) P. G. Hayes, W. E. Piers, M. Parvez,
J. Am. Chem. Soc. 2003, 125, 5622–5623; c) P. G. Hayes, W. E.
Piers, M. Parvez, Organometallics 2005, 24, 1173–1183; d)
L. K. Knight, W. E. Piers, R. McDonald, Organometallics
2006, 25, 3289–3292; e) P. G. Hayes, W. E. Piers, M. Parvez,
Chem. Eur. J. 2007, 13, 2632–2640; f) K. D. Conroy, P. G.
Hayes, W. E. Piers, M. Parvez, Organometallics 2007, 26, 4464–
4470.
After submission of this work, the reaction of the lanthanum
complex [La(η5-C5Me5){(µ-Me)2(AlMe2)}2] with [B(C6F5)3] in
C6H5Cl was reported to generate a monocationic half-sand-
wich aluminate complex, see: M. Zimmerman, K. W. Törnroos,
R. Anwander, Angew. Chem. 2008, 120, 787–790.
R. D. Shannon, Acta Crystallogr., Sect. A 1976, 32, 751–767.
R. E. White, T. P. Hanusa, Organometallics 2006, 25, 5621–
5630.
A similar stereoselectivity/metal relationship was already ob-
served, see for example: S. Kaita, M. Yamanaka, A. C. Horiu-
chi, Y. Wakatsuki, Macromolecules 2006, 39, 1359–1363.
[6] a) For metal centers up to Sm, see: H. Schumann, D. M. M.
Freckmann, S. Dechert, Z. Anorg. Allg. Chem. 2002, 628, 2422–
2426 and references cited therein; b) the in situ synthesis of
tris(alkyl) complexes of the larger metal centers has been re-
ported, see for example: S. Bambirra, M. W. Bouwkamp, A.
Meetsma, B. Hessen, J. Am. Chem. Soc. 2004, 126, 9182–9183.
[7] a) K. C. Hultzsch, T. P. Spaniol, J. Okuda, Angew. Chem. Int.
Ed. 1999, 38, 227–230; b) O. Tardif, M. Nishiura, Z. Hou, Or-
ganometallics 2003, 22, 1171–1173; c) D. Cui, M. Nishiura, Z.
Hou, Macromolecules 2005, 38, 4089–4095; d) Z. Hou, Y. Luo,
X. Li, J. Baldamus, PCT Int. Appl. WO 2006004068, 2006.
[8] a) W. J. Evans, R. Anwander, J. W. Ziller, Organometallics 1995,
14, 1107–1109; b) R. Anwander, M. G. Klimpel, H. M. Di-
etrich, D. J. Shorokhov, W. Scherer, Chem. Commun. 2003,
1008–1009; c) A. Fischbach, E. Herdtwerck, R. Anwander, G.
Eickerling, W. Scherer, Organometallics 2003, 22, 499–509; d)
H. M. Dietrich, C. Zapilko, E. Herdtweck, R. Anwander, Orga-
nometallics 2005, 24, 5767–5771.
[21]
[22]
[23]
[24]
[25]
Reaction of the neutral species 1-Ln (Ln = Y, La, Nd, Sm, Lu)
with 2 equiv. of [NEt3H]+[BPh4]– in thf generates the corre-
sponding dicationic complexes [Ln(η5-C5Me4SiMe3)(thf)n]2+
-
[9] K. C. Hultzsch, Doctoral Thesis, Johannes-Gutenberg Univer-
sity, Mainz, Germany, 1999.
[10] H. M. Dietrich, H. Grove, K. W. Törnroos, R. Anwander, J.
Am. Chem. Soc. 2006, 128, 1458–1459.
[BPh4]– in quantitative yield.
2
[26]
Monocationic bis(cyclopentadienyl) species have been shown
to efficiently catalyze the butadiene polymerization upon acti-
vation with an alkylaluminium cocatalyst, see: a) S. Kaita, Z.
Hou, Y. Wakatsuki, Macromolecules 2001, 34, 1539–1541; b)
S. Kaita, Z. Hou, M. Nishiura, Y. Doi, J. Kurazumi, A. C.
Horiuchi, Y. Wakatsuki, Macromol. Rapid Commun. 2003, 24,
179–184; c) S. Kaita, Y. Doi, K. Kaneko, A. C. Horiuchi, Y.
Wakatsuki, Macromolecules 2004, 37, 5860–5862.
M. Zimmermann, N. Å. Frøystein, A. Fischbach, P. Sirsch, H.-
M. Dietrich, K. W. Törnroos, E. Herdtweck, R. Anwander,
Chem. Eur. J. 2007, 13, 8784–8800.
P. Coutrot, R. Pichon, J. Y. Salaun, L. Toupet, Can. J. Chem.
1991, 69, 661–672.
[11] a) J. Nolton, M. F. Lappert, D. G. H. Ballard, R. Pearce, J. L.
Atwood, W. E. Hunter, J. Chem. Soc. Dalt. Trans. 1979, 54–61;
b) H. M. Dietrich, G. Raudaschl-Sieber, R. Anwander, Angew.
Chem. Int. Ed. 2005, 44, 5303–5306.
[12] The AlEt4 moiety in [LnII(AlEt4)2] (LnII = Sm, Yb) was re-
ported to behave differently towards Lewis bases, see: a) M. G.
Klimpel, R. Anwander, M. Tafipolsky, W. Scherer, Organome-
tallics 2001, 20, 3983–3992; b) M. G. Schrems, H. M. Dietrich,
K. W. Törnroos, R. Anwander, Chem. Commun. 2005, 5922–
5924.
[27]
[28]
[29]
[13] [Sc{(µ-Me)2(AlMe2)}3] is not accessible by the AlMe3-mediated
transformation of an NMe2 group into AlMe4, see ref.[11b]
[14] J. Hitzbleck, K. Beckerle, J. Okuda, J. Organomet. Chem. 2007,
692, 4702–4707.
[15] [ScCp*Me2]n was mentioned previously, see: a) W. E. Piers,
E. E. Bunel, J. E. Bercaw, J. Organomet. Chem. 1991, 407, 51–
60; b) G. C. Bazan, W. P. Schaefer, J. E. Bercaw, Organometal-
lics 1993, 12, 2126–2130.
[16] L. D. Henderson, G. D. MacInnis, W. E. Piers, M. Parvez, Can.
J. Chem. 2004, 82, 162–165.
[17] See for example: a) P. G. Hayes, W. E. Piers, L. W. Lee, L. K.
Knight, M. Parvez, M. R. J. Elsegood, W. Clegg, Organometal-
lics 2001, 20, 2533–2544; b) L. K. Knight, W. E. Piers, P. Fleu-
rat-Lessard, M. Parvez, R. McDonald, Organometallics 2004,
23, 2087–2094.
W. J. Evans, B. L. Davis, J. W. Ziller, Inorg. Chem. 2001, 40,
6341–6348.
D. T. Hurd, J. Org. Chem. 1948, 13, 711–713.
[30]
[31]
ASTRO, SAINT and SADABS – Data Collection and Pro-
cessing Software for the SMART System, Siemens Analytical
X-ray Instruments Inc., Madison, Wisconsin, USA, 1996.
a) G. M. Sheldrick, SHELXS-86, Program for Crystal Struc-
ture Solution, University of Göttingen, Göttingen, Germany,
1986; b) G. M. Sheldrick, SHELXL-97, Program for Crystal
Structure Refinement, University of Göttingen, Göttingen,
Germany, 1997.
[32]
Received: January 15, 2008
Published Online: February 28, 2008
Eur. J. Inorg. Chem. 2008, 2801–2809
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2809