Cationic methyl complexes of the rare-earth metals: An experimental and computational study on synthesis, structure, and reactivity

Article abstract of DOI:10.1021/ic801259n

Synthesis, structure, and reactivity of two families of rare-earth metal complexes containing discrete methyl cations [LnMe_(2-x)(thf) _n]^(1+x)+ (x = 0, 1; thf = tetrahydrofuran) have been studied. As a synthetic equivalent for the elusive trimethyl complex [LnMe ₃], lithium methylates of the approximate composition [Li ₃LnMe₆(thf)_n] were prepared by treating rare-earth metal trichlorides [LnCl₃(thf)_n] with 6 equiv of methyllithium in diethyl ether. Heteronuclear complexes of the formula [Li₃Ln₂Me₉L_n] (Ln = Sc, Y, Tb; L = Et₂O, thf) were isolated by crystallization from diethyl ether. Single crystal X-ray diffraction studies revealed a heterometallic aggregate of composition [Li₃Ln₂Me₉(thf)_n(Et ₂O)_m] with a [LiLn₂Me₉]^2- core (Ln = Sc, Y, Tb). When tris(tetramethylaluminate) [Ln(AlMe ₄)₃] (Ln = Y, Lu) was reacted with less than 1 equiv of [NR₃H][BPh₄], the dimethyl cations [LnMe ₂(thf)_n][BPh₄] were obtained. The coordination number as well as cis/trans isomer preference was studied by crystallographic and computational methods. Dicationic methyl complexes of the rare-earth metals of the formula [LnMe(thf)_n][BAr₄]₂ (Ln = Sc, Y, La-Nd, Sm, Gd-Lu; Ar = Ph, C₆H₄F-4) were synthesized, by protonolysis of either the ate complex [Li₃LnMe₆(thf) _n] (Ln = Sc, Y, Gd-Lu) or the tris(tetramethylaluminate) [Ln(AlMe₄)₃] (Ln = La-Nd, Sm, Dy, Gd) with ammonium borates [NR₃H][BAr₄] in thf. The number of coordinated thf ligands varied from n = 5 (Ln = Sc, Tm) to n = 6 (Ln = La, Y, Sm, Dy, Ho). The configuration of representative examples was determined by X-ray diffraction studies and confirmed by density-functional theory calculations. The highly polarized bonding between the methyl group and the rare-earth metal center results in the reactivity pattern dominated by the carbanionic character and the pronounced Lewis acidity: The dicationic methyl complex [YMe(thf) ₆]²⁺ inserted benzophenone as an electrophile to give the alkoxy complex [Y(OCMePh₂)(thf)₅]²⁺. Nucleophilic addition of the soft anion X^- (X^- = I ^-, BH₄^-) led to the monocationic methyl complexes [YMe(X)(thf)₅]⁺.

Full text of DOI:10.1021/ic801259n

Inorg. Chem. 2008, 47, 9265-9278
Cationic Methyl Complexes of the Rare-Earth Metals: An Experimental
and Computational Study on Synthesis, Structure, and Reactivity
Mathias U. Kramer,† Dominique Robert,† Stefan Arndt,† Peter M. Zeimentz,† Thomas P. Spaniol,†
Ahmed Yahia,‡ Laurent Maron,*,‡ Odile Eisenstein,§ and Jun Okuda*,†
Institute of Inorganic Chemistry, RWTH Aachen UniVersity, Landoltweg 1,
D-52074 Aachen, Germany, UniVersite´ de Toulouse; INSA, UPS, LPCNO, 135 aVenue de
Rangueil, F-31077 Toulouse, France, CNRS, LPCNO, F-31077 Toulouse, France, and
Institut Charles Gerhardt, CNRS, Case courrier 1501, UniVersite´ Montpellier 2,
F-34095 Montpellier Cedex 05, France
Received July 5, 2008
Synthesis, structure, and reactivity of two families of rare-earth metal complexes containing discrete methyl cations
[LnMe(2-x)(thf)n](1+x)+ (x ) 0, 1; thf ) tetrahydrofuran) have been studied. As a synthetic equivalent for the elusive
trimethyl complex [LnMe3], lithium methylates of the approximate composition [Li3LnMe6(thf)n] were prepared by
treating rare-earth metal trichlorides [LnCl3(thf)n] with 6 equiv of methyllithium in diethyl ether. Heteronuclear complexes
of the formula [Li3Ln2Me9Ln] (Ln ) Sc, Y, Tb; L ) Et2O, thf) were isolated by crystallization from diethyl ether.
Single crystal X-ray diffraction studies revealed a heterometallic aggregate of composition [Li3Ln2Me9(thf)n(Et2O)m]
with a [LiLn2Me9]2- core (Ln ) Sc, Y, Tb). When tris(tetramethylaluminate) [Ln(AlMe4)3] (Ln ) Y, Lu) was reacted
with less than 1 equiv of [NR3H][BPh4], the dimethyl cations [LnMe2(thf)n][BPh4] were obtained. The coordination
number as well as cis/trans isomer preference was studied by crystallographic and computational methods. Dicationic
methyl complexes of the rare-earth metals of the formula [LnMe(thf)n][BAr4]2 (Ln ) Sc, Y, La-Nd, Sm, Gd-Lu;
Ar ) Ph, C6H4F-4) were synthesized, by protonolysis of either the ate complex [Li3LnMe6(thf)n] (Ln ) Sc, Y,
Gd-Lu) or the tris(tetramethylaluminate) [Ln(AlMe4)3] (Ln ) La-Nd, Sm, Dy, Gd) with ammonium borates
[NR3H][BAr4] in thf. The number of coordinated thf ligands varied from n ) 5 (Ln ) Sc, Tm) to n ) 6 (Ln ) La,
Y, Sm, Dy, Ho). The configuration of representative examples was determined by X-ray diffraction studies and
confirmed by density-functional theory calculations. The highly polarized bonding between the methyl group and
the rare-earth metal center results in the reactivity pattern dominated by the carbanionic character and the pronounced
Lewis acidity: The dicationic methyl complex [YMe(thf)6]2+ inserted benzophenone as an electrophile to give the
-
alkoxy complex [Y(OCMePh2)(thf)5]2+. Nucleophilic addition of the soft anion X- (X- ) I-, BH4 ) led to the
monocationic methyl complexes [YMe(X)(thf)5]+.
Introduction
on the electronegativity and oxidation state of the metal
center, as well as on the ancillary ligand sphere and the
charge. In some cases, the polarity reflects carbanionic,
radical, as well as carbocationic, behavior. An example is
methylcobaltamine with a formally cationic cobalt(III) center
that can show all three reactivity patterns within the identical
macrocyclic corrin-type ligand scaffold, depending on the
substrate.3 An overall positive charge may result in enhanced
Brønsted acidity of the C-H bond, enabling an entry into
doubly bonded methylene ligands, as exemplified by Schrock’s
synthesis of [Ta(η5-C5H5)2Me(dCH2)]+ by deprotonation of
the dimethyl cation [Ta(η5-C5H5)2Me2]+.4
Since the report of dimethylzinc ZnMe2 as one of the first
organometallic complexes by Frankland,1 methyl complexes
have been considered as the exemplary organometallic
compound for any electropositive element.2 The transition
metal-methyl bond exhibits polarity that critically depends
* To whom correspondence should be addressed. E-mail: jun.okuda@
ac.rwth-aachen.de.
†
RWTH Aachen University.
Universite´ de Toulouse.
Universite´ Montpellier 2.
‡
§
(1) Frankland, E. Liebigs Ann. Chem. 1849, 71, 171–213. For a historical
account, see Seyferth, D. Organometallics 2001, 20, 2940–2955.
10.1021/ic801259n CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 20, 2008 9265
Published on Web 09/25/2008

Kramer et al.
Group 3 metal-carbon bonds are generally considered to
be “ionic”, as rare-earth metals (group 3 metals Sc, Y, La to
Lu) are located between the electropositive alkaline-earth
metals and the more electronegative early transition metals
of group 4.5 Because of the large ionic radii of these metals
[LnMe(2-x)(thf)n](1+x)+ (x ) 0,1). The dicationic methyl
complexes [LnMe(thf)n]2+ have been prepared for all rare-
earth metals except promethium and europium. To establish
a reactivity pattern for this unique type of organometallic
cations that combines both carbanionic and Lewis acidic
behavior, the reactivity of the representative complex
[YMe(thf)6]2+ has been examined.
and the small steric size of the methyl group, the synthesis
6a-c
of polymeric trimethyl complex [LnMe3]n
has only
recently been claimed for Ln ) Y and Lu by a cleavage
reaction of [Ln(AlMe4)3].6d,e Apart from the apparent
synthetic challenge, fundamental knowledge on the carban-
ionic methyl group at a strongly electropositive, Lewis-acidic
cationic metal center is limited. Historically the organome-
tallic chemistry of the rare-earth metals has been dominated
by neutral and anionic compounds.7 Although trianionic
hexamethylate complexes [{Li(L2)}3LnMe6] (L2 ) N,N,N′,N′-
tetramethylethylenediamine, tmeda; 1,2-dimethoxyethane,
dme) have been known since the early 1980s through the
work by Schumann et al. for nearly the complete range of
rare-earth metals,8 they have not been considered as a
synthetic equivalent for the elusive trimethyl [LnMe3]. We
and others have found evidence that methyl and other
hydrocarbyl cations are involved as active species in the
homogeneous polymerization of R-olefins and 1,3-dienes by
rare-earth metal catalyst precursors.9 Such cationic hydro-
carbyl complexes of the rare-earth metals can now be
prepared by the reaction of neutral hydrocarbyls with a Lewis
or Brønsted acid.9,10 We report here on the preparation and
structural characterization of a series of discrete mono- and
dicationic rare-earth metal methyl complexes of the type
Results and Discussion
Methylate Complexes. Initial studies on the reactivity of
Schumann’s hexamethylate complexes [{Li(L2)}3LnMe6] (L2
) tmeda, dme)8 toward various Brønsted acids in different
stoichiometric ratios suggested no straightforward formation
of any neutral or cationic methyl species. However, proto-
nolysis of the hexamethylate complexes [Li3LnMe6(thf)n] (1),
generated in situ in thf solution, with 5 equiv of [NEt3H]-
[BPh4] gave the dicationic methyl complexes [LnMe(thf)n]-
[BPh4]2 (4).11
To explore the nature of the hexamethylate complexes
[Li3LnMe6(thf)n] (1), we isolated compounds 1 by reacting
the trichlorides [LnCl3(thf)n] with 6 equiv of methyllithium
in diethyl ether (Scheme 1). The products are thermally
extremely sensitive and could so far only be isolated for the
smaller metals Sc, Y, and Gd-Lu. This kind of size
dependence on the thermal stability was also observed during
the preparation of compounds of the type [Ln(CH2Si-
Me3)3(thf)x] which could only be isolated for metals up to
Sm.12 Broad peaks in the NMR spectra of the diamagnetic
complexes 1-Sc, 1-Y, and 1-Lu down to -80 °C suggest an
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9266 Inorganic Chemistry, Vol. 47, No. 20, 2008

Methyl Cations of the Rare-Earth Metals
Scheme 1
Figure 1. ORTEP drawing of 1′-Sc with thermal ellipsoids at the 50%
level. Hydrogen atoms and all carbon atoms of the thf and Et2O ligands
are omitted for clarity.
Sc-µ3-Me bond lengths are longer (Sc-C3: 2.487(4) Å and
Sc-C3′: 2.500(4) Å).8c,14 Similar bond lengths were ob-
served in the sterically encumbered compounds [(ScCp*2)2(µ2-
Me)][B(C6F5)4] (2.519 and 2.454 Å),13k as well as in silylene-
bridged metallocene aluminate complexes [{(Me2Si)2(η5-
Scheme 2
C5H2 Bu)(η5-C5HiPr2)}Sc(µ2-Me)2(AlMe2)] and [{Me2Si(η5-
t
C5H3 Bu)2}Sc(µ2-Me)2(AlMe2)] (2.414 and 2.442 Å,13l 2.490
t
and 2.425 Å13m).
NMR spectra of the diamagnetic complexes 1′-Sc and 1′-Y
in thf-d8 do not differ significantly from those of the parent
substances 1-Sc and 1-Y, indicating that the aggregate
structure is highly fluxional in solution. The reactivity of 1
and 1′ is similar and both can be regarded as synthetic
equivalent for [LnMe3]. Treatment of 1 with 5 equiv of
[NEt3H][BPh4] gave the dicationic species 4 (vide infra).
When using 1′, only 3.5 equiv of acid per rare-earth metal
Ln are needed, in agreement with the formulation [Ln2-
Me9]3-. In the absence of chelating ligands such as dme or
tmeda, apparently exhaustive methylation of the rare-earth
metal center to give [LnMe6]3- does not occur or upon
crystallization from diethyl ether, the equilibrium is shifted
toward [LnMe3].
equilibrium between several fluxional species. This contrasts
to the crystallographically characterized tmeda and dme
adducts [{Li(L2)}3LnMe6], which display narrower 1H NMR
signals for the methyl groups.8 Crystallizing 1-Sc, 1-Y, and
1-Tb from saturated diethyl ether solutions gave the hetero-
nuclear complexes [Li3Ln2Me9(thf)n(Et2O)m] (1′-Sc′ n ) 2,
m ) 3; 1′-Y, 1′-Tb n ) 3, m ) 2) as shown by X-ray
diffraction studies (Figure 1).
Synthesis and Structure of Dimethyl Monocations.
Dimethyl monocations of the type [LnMe2(thf)n][BPh4] (3)
have been isolated and fully characterized for Ln ) Y (3-
Y)11b,c and Lu (3-Lu). They can be prepared from the ate
complex [Li3LnMe6(thf)n] (1) by protonolysis with [NEt3H]-
[BPh4], by nucleophilic attack of the methyl dication
[LnMe(thf)n][BPh4]2 (4) (vide infra) with methyllithium, or
by protonolysis of [Ln(AlMe4)3] (2) with [NEt3H][BPh4].
Only the latter method allowed isolation of the monocations
3, as these compounds cannot be separated from LiBPh4 that
is formed by the former two methods. We have obtained
analytically pure 3-Y and 3-Lu from the reactions of 2-Y
and 2-Lu in thf using less than 1 equiv of [NEt3H][BPh4]
(Scheme 2). The methyl groups in 3-Lu give rise to one
sharp singlet at δ -0.94 ppm in the 1H NMR spectrum and
The three C2-symmetrical structures with a LiLn2 core are
similar (1′-Y and 1′-Tb are isotypical). Each lanthanide
center is surrounded by six methyl groups describing a
distorted octahedral geometry. The Sc-µ2-Me bond distances
ranging from 2.294(4) to 2.397(4) Å are longer than
Sc-Me(terminal) bonds reported,13a-j as found in ꢀ-diketim-
inato scandium methyl complexes, ranging from 2.162 to
2.245 Å,13a-f in [ScCp*2Me] (2.243 Å),13g in [ScCp*Me2-
(tBu3PO)] (2.251 and 2.252 Å),13h in [ScCp*Me(tBu3PO)(µ-
Me)B(C6F5)3] (2.201 Å),13h in [Sc(OEP)Me] (2.246 Å, OEP
) octaethylporphyrin),13i and [Sc(η5-C5Me4H)(η5-C5H4CH2N-
Me2-κN)Me] (2.346 Å).13j The relatively long Sc-C dis-
tances can be explained by the formally anionic nature of
the [Sc2Me9]3- unit, as well as by the steric crowding around
the octahedrally coordinated Sc centers. As expected, the
Inorganic Chemistry, Vol. 47, No. 20, 2008 9267

Kramer et al.
δ 27.3 ppm in the 13C NMR spectrum in thf-d8.15 The sharp
signals indicate that there is no fast exchange of methyl
groups between Lu centers on the NMR-time scale. The
previously communicated yttrium dimethyl cation 3-Y
2
exhibits two doublets at 1.07 and 0.95 with JYH ) 1.7 Hz,
indicative of the presence of two isomers, one 13C NMR
resonance at 17.5 ppm (1JYC ) 46.8 Hz), and a peak in the
89Y{1H} NMR spectrum in thf-d8 at 650.9 ppm. This value
is similar to the 89Y NMR chemical shift of [Y(CH2Si-
Me3)2(thf)4][BPh4] (660.0 ppm)15 and in remarkable agree-
ment with Hanusa’s empirical study on the contribution of
charges and ligands on the 89Y NMR chemical shifts: The
expected shift in thf-d8 is 651 ppm (a Me group “contributes”
288 ppm, a positive charge 75 ppm).16
Recrystallization from saturated thf solutions afforded
single crystals of 3-Lu. The structure of 3-Lu differs signifi-
cantly from that of previously reported trans-[YMe2(thf)5]-
[BPh4] (3-Y).11b,c Instead of five coordinating thf molecules,
3-Lu contains only four solvent molecules. The C-Lu-C
angle of 96.39(12)° leaves the alkyl groups in a cis-geometry
in a distorted octahedron (Figure 2). The average Lu-O(thf)
distances of 2.316 Å are comparable to the distances
Figure 2. ORTEP drawing of the cation portion of 3-Lu at the 50%
probability level. Hydrogen atoms are omitted for clarity.
apply to rare-earth metal coordination chemistry.20 An
elongation of the Lu-O bonds trans to the Me groups was
also observed in the results of density-functional theory
(DFT) calculations (vide infra).
17
found in [Lu(η5-C5Me4 Pr)2Me(thf)] (2.325 Å)
and
i
[LuCp*(CH2SiMe3)2(thf)] (2.255 Å).18 Both Lu-O bonds
trans to the Lu-C bonds are significantly longer (average
2.366 Å) than the two Lu-O bonds trans to each other
(average 2.266 Å). Similar structural features were ob-
served in the six-coordinated monocationic complexes
[Y(CH2SiMe3)2(thf)4][E(CH2SiMe3)4] (E ) Al,11a Ga10e) and
[ScPh2(thf)4][BPh4].19 A strong structural trans-influence is
ascribed to methyl groups, but these observations are usually
explained by molecular-orbital considerations, which do not
Both Lu-Me distances are virtually identical (2.343(3)
and 2.347(3) Å) and shorter than those of reported neutral
and anionic compounds, such as [Lu(η5-C5Me4 Pr)2Me(thf)]
i
(2.369 Å)17 or [Li(tmeda)2][LuCp*Me3] (2.59, 2.56, and 2.39
Å).21 This mirrors previous observations of shortening
metal-carbon bond distances with increasing cationic
charge.11 The structure of 3-Y, displaying a pentagonal
bipyramidal trans-geometry around the yttrium centers,
appears to be unusual. Monocationic dialkyl complexes
[Y(CH2SiMe3)2(thf)4][E(CH2SiMe3)4] (E ) Al,11a Ga10e
)
display a cis-geometry of the alkyl groups around the yttrium
centers, similar to 3-Lu.
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W. E.; McDonald, R. J. Am. Chem. Soc. 2002, 124, 2132–2133. (g)
Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J.; Nolan,
M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J. E. J. Am. Chem.
Soc. 1987, 109, 203–219. (h) Henderson, L. D.; MacInnis, G. D.; Piers,
W. E.; Parvez, M. Can. J. Chem. 2004, 82, 162–165. (i) Arnold, J.;
Hoffman, C. G.; Dawson, D. Y.; Hollander, F. J. Organometallics
1993, 12, 3645–3654. (j) Schumann, H.; Erbstein, F.; Herrmann, K.;
Demtschuk, J.; Weimann, R. J. Organomet. Chem. 1998, 562, 255–
262. (k) Bouwkamp, M. W.; Budzelaar, P. H. M.; Gercama, J.; Del
Hierro Morales, I.; de Wolf, J.; Meetsma, A.; Troyanov, S. I.; Teuben,
J. H.; Hessen, B. J. Am. Chem. Soc. 2005, 127, 14310–14319. (l) Day,
M. W.; Bercaw, J. E.; Zubris, D. L., private communication to the
CCDC, 2003; ccdc 103059. (m) Day, M. W.; Schofer, S. J.; Bercaw,
J. E., private communication to the CCDC, 2005; ccdc 192902.
(14) A similar dimeric structure was obtained from LuCl3 with an excess
of methyllithium in Et2O in the presence of 2 equiv of tetraethyleth-
ylenediamine; ref 7 in ref 8c Schumann, H.; Lauke, H.; Hahn, E.
Abstract of Papers, XI. International Conference on Organometallic
Chemistry; Pine Mountain: GA, 1983.
To explain this structural difference, calculations for the
experimentally found six- and seven-coordinated 3-Lu and
3-Y as well as a hypothetical six-coordinated [YMe2(thf)4]+
were carried out at the DFT level. In all cases both the cis
and the trans complexes were found as minima on the
potential energy surface (PES). Selected bond lengths and
angles of the experimentally found and calculated structures
of 3-Lu and 3-Y and their respective cis and trans calculation
results are given in Table 1 (See details in the Supporting
Information).
The calculated geometry parameters for 3-Lu are in
good agreement with the experimental values. The Lu-Me
distances are reproduced within 0.01Å. The Lu-O(thf)
distances are less satisfactory (maximum deviation of 0.1
Å for the Lu-O distances trans to the methyl groups;
0.06 Å for those cis). The longer Lu-O distances for the
thf ligands trans to the methyl group are found both in
the experiment and in the calculation.
(15) Elvidge, B. R.; Arndt, S.; Zeimentz, P. M.; Spaniol, T. P.; Okuda, J.
Inorg. Chem. 2005, 44, 6777–6788.
(16) White, R. E.; Hanusa, T. P. Organometallics 2006, 25, 5621–5630.
(17) Schumann, H.; Keitsch, M. R.; Winterfeld, J.; Mu¨hle, S.; Molander,
G. A. J. Organomet. Chem. 1998, 559, 181–190.
The bond between lutetium and the methyl group is found
to be strongly polarized at the Natural Bond Orbital (NBO)
(18) Cameron, T. M.; Gordon, J. C.; Scott, B. L. Organometallics 2004,
23, 2995–3002.
(19) Zeimentz, P. M.; Okuda, J. Organometallics 2007, 26, 6388–6396.
(20) Coe, B. J.; Glenwright, S. J. Coord. Chem. ReV. 2000, 203, 5–80.
(21) Schumann, H.; Albrecht, I.; Pickardt, J.; Hahn, E. J. Organomet. Chem.
1984, 276, C5-C9.
9268 Inorganic Chemistry, Vol. 47, No. 20, 2008

Methyl Cations of the Rare-Earth Metals
Table 1. Selected Experimentally Observed and Calculated Bond
Lengths (Å) and Bond Angles (deg) for 3-Lu and 3-Y11b
Scheme 3
[LuMe2
(thf)4]+
[YMe2
d
b
3-Lu
3-Yc
(thf)5]+
calc
calc
Ln-C1
Ln-C2
Ln-O1
Ln-O2
Ln-O3
Ln-O4
Ln-O5
2.343(3)
2.347(3)
2.367(2)a
2.3655(19)a
2.260(2)
2.271(2)
2.332
2.334
2.459a
2.483a
2.329
2.329
2.526(2) [2.513(3)]
2.508(2) [2.516(3)]
2.397(2) [2.393(3)]
2.399(2) [2.422(2)]
2.406(2) [2.380(2)]
2.395(2) [2.392(3)]
2.418(2) [2.377(2)]
2.481
2.486
2.467
2.460
2.451
2.471
2.453
C-Ln-C 96.39(12)
105.3
174.03(8) [178.46(11)] 178.1
a thf trans to Me group. b cis isomer. c values in square brackets
more stable. However, the presence of the fifth thf molecule
is increasing the steric hindrance around the metal center.
The additional stability caused by the C5 arrangement of the
five thf molecules makes the trans isomer more stable than
the cis isomer.
correspond to second molecule in unit cell. d trans isomer.
level (contribution of 89% from the methyl sp3 and 11%
from the metal 5d for the cis isomer) and is found to be
quite similar for both isomers (contribution of 91% of the
methyl sp3 and 9% from the lutetium 5d for the trans isomer).
This is different from the situation in neutral species [LnMe3]
where the bonds are almost purely ionic,6c in line with more
contracted atomic orbitals for a monocationic complex than
for a neutral complex. The two Ln-Me bonds are found to
be equivalent, in agreement with the two similar Ln-C
distances (Table 1). This bonding situation leads to a highly
positive charge at the Lu center (cis isomer, +2.01, and trans
isomer, +2.10) and strong negative charges at the methyl
groups (-0.73 and -0.79, respectively). The Lu-Me bonds
in [LuMe2(thf)4][BPh4] are calculated to be much shorter for
the cis than for the hypothetical trans isomer (the important
electrostatic part of the bonding has been verified by a NBO
analysis, see charge given above). Thus, the electrostatic
attractions are found to be stronger in the cis than in the
trans isomer. The smaller C-Ln-C angle leads to an
important electrostatic repulsion between the two negatively
charged methyl groups. Moreover, the longer Ln-O dis-
tances in the cis than in the trans isomer reduce the energy
difference between the two isomers. The energy difference
between the two isomers results from a subtle mixing of
these effects (demonstrated by a smaller lutetium charge for
the cis than for the trans isomer despite a shorter Lu-C
distance for the former than the latter). As a result, both the
six-coordinated isomers are found to be almost isoenergetic
with only a slight preference for the cis isomer (around
0.2-0.3 kcal · mol-1).
The coordination of a fifth thf molecule in the seven-
coordinated 3-Y leads to an energy stabilization of 7.5
kcal· mol-1. The trans isomer has been calculated to be
slightly more stable than the cis isomer (1.3 kcal · mol-1).
As was the case for the six-coordinated species, shorter
Y-Me distances are found for the cis than for the trans
isomer, but Y-O(thf) distances are shorter for the trans than
for the cis isomer. Similarly, the Y-Me bonds are also
strongly polarized (contribution of 93% of the methyl sp3
and 7% from the yttrium 4d for the trans isomer and of 91%
of the methyl sp3 and 9% from the metal 4d for the cis
isomer). This leads to an yttrium charge of +2.13 and of
-0.76 for the methyl groups in the trans isomer (+2.03 and
-0.73 in the cis isomer). Thus, similar effects to those
presented for the six-coordinated species should apply here
and one would expect the cis configuration to be slightly
Synthesis and Structure of Methyl Dications. When 5
equiv of [NEt3H][BPh4] were added to thf solutions of 1,
compounds 4 precipitated (Scheme 3). Because of the
unavailability of the ate complex 1 for the larger metals La,
Ce, Pr, Nd, and Sm, these dicationic methyl complexes were
prepared by protonolysis of the homoleptic aluminates
[Ln(AlMe4)3] (2) using [NEt3H][BPh4] as Brønsted acid. An
excess of acid did not lead to abstraction of the last remaining
methyl group. A similar observation had been made for the
trimethylsilylmethyl cations,15 whereas exhaustive proto-
nolysis of neutral [La(CH2C6H4Me-4)3(thf)3] and anionic
[Li(thf)4][La(CH2C6H4Me-4)4] with an excess of [NPhMe2H]-
[B(C6F5)4] was reported to give La3+.10d
Compounds 4-La, 4-Ce, 4-Pr, 4-Nd, and 4-Sm are
significantly less stable at room temperature and in thf than
their smaller analogues. A colorless suspension of 4-La in
thf turned orange when left at room temperature for several
hours. Previously the thf ring opening reaction by 4-Nd to
the pentoxy complex [Nd{O(CH2)4Me}(thf)6][BPh4]2 was
reported.11b When a suspension of 4-Sm in thf was left at
room temperature and in daylight, solid 4-Sm gradually
dissolved to give the purple divalent complex [Sm(thf)7]-
[BPh4]2.22 This was ascribed to the homolysis of the Sm-Me
bond to give Sm(II) and a methyl radical, but attempts to
trap this radical with TEMPO remained unsuccessful.
Single crystals of 4-Sc, 4-Y,11a 4-Dy, 4-Ho,11b and 4-Tm
could be obtained when thf solutions of the corresponding
compounds 1 were reacted with less than 4 equiv of acid,
followed by layering the remaining acid as a thf solution on
top of the reaction mixture. The yttrium, dysprosium, and
holmium dicationic complexes crystallized isostructurally
with six thf molecules surrounding the metal centers.
Although the crystal quality of 4-Sc and 4-Tm was poor,
the composition and connectivity of both compounds was
unequivocally established. Both cationic parts crystallized
with five thf molecules coordinating to the Ln center in an
octahedral geometry.
In crystalline 4-Dy the metal center adopts a pentagonal
bipyramidal geometry (for details, see Supporting Informa-
tion). The methyl group is situated in the axial position with
five thf molecules in the equatorial plane. Even though
(22) Evans, W. J.; Johnston, M. A.; Greci, M. A.; Gummersheimer, T. S.;
Ziller, J. A. Polyhedron 2003, 22, 119–126.
Inorganic Chemistry, Vol. 47, No. 20, 2008 9269

Kramer et al.
good agreement with the experimentally found value of 2.418
Å. A comparison of bond distances and angles is given in
Table 2. As was the case for the monocationic complex, the
bond between Y and the methyl group is strongly polarized
toward methyl (contribution of 93% of the methyl sp3 and
7% from the metal 4d). This leads to a charge of +2.19 for
Y and -0.74 for the methyl group. When the bonding
situation in 3-Y and 4-Y is compared, the Y-Me bonds are
similar, and the charge at the metal center and the charge of
the methyl group are marginally different in the two
complexes. The metal charge is slightly more positive in 4-Y
leading to shorter Y-Me distance in 4-Y than in 3-Y.
For Ln ) La, the capped octahedral structure was found
to be more stable than the pentagonal bipyramid (1.37
kcal · mol-1). The calculated La-Me distance of 2.480 Å is
similar to the experimental value of 2.456(6) Å. As expected,
such an arrangement allows a closer metal-methyl contact
and the La-Me distance for a hypothetical pentagonal
bipyramidal structure would be 2.506 Å. The preference for
the capped octahedral structure is electrostatically driven,
since the shorter La-Me distance allows a stronger electro-
static interaction (as in the previous section, the highly
polarized nature of the bonding has been verified by a NBO
analysis). The longer La-O distances indicate a smaller
contribution from the steric hindrance around the metal
center, in contrast to the situation for Ln ) Y where the
Y-O distances are shorter by up to 0.2 Å. The bond is also
found to be highly polarized in this system and similar to
the bonding in 4-Y (contribution of 93% of the methyl sp3
and 7% from the metal 4d). The charge is, however, higher
in 4-La than in 4-Y (+2.6 for La and -0.74 for Me) despite
the longer La-Me distance with respect to Y-Me. The
charge of the methyl group indicates that the bond is similar
for 4-Y and 4-La. The difference of metal charge is in
agreement with the fact that La-O(THF) distances are much
longer than the Y-O(THF) bonds.
Figure 3. ORTEP drawing of the cationic portion of 4′-La at the 30%
level of probability. Hydrogen atoms are omitted for clarity.
dysprosium has a slightly larger ionic radius (91 pm, CN 6)
than yttrium and holmium (90 pm),23 the Dy-C bond
distance (2.401(10) Å) has the same length (within the
standard error) as was found in 4-Y (2.418(3) Å) and in 4-Ho
(2.378(4) Å).11 In all three cases, no elongation of the bond
length of the thf trans to the methyl groups relative to the
equatorial thf ligands is observed, since the equatorial thf
molecules are located further away from the metal center
because of greater steric repulsions in the equatorial plane.
Crystals of [LaMe(thf)6][B(C6H4F-4)4]2 (4′-La) and [SmMe-
(thf)6][B(C6H4F-4)4]2 (4′-Sm) were grown by reaction of
2-La and 2-Sm with substoichiometric amounts of [NEt3H][B-
(C6H4F-4)4] in thf and subsequent layering with thf solutions
of the acid (for the structure of 4′-La see Figure 3, for 4′-
Sm see Supporting Information). Unexpectedly, the two
compounds are not isostructural to the smaller rare-earth
metal derivatives with six thf ligands. Instead of the
pentagonal bipyramidal structure, a methyl-capped octahedral
geometry is adopted. This structure allows a closer metal-
alkyl contact, which is clearly visible when the structure of
4-Y is compared to that of 4′-Sm. The Y-C distance of
2.418(3) Å11a is longer than the Sm-C distance of 2.385(8)
Å even though the ionic radius of Y is 6 pm smaller than
that of Sm (90 pm versus 96 pm).23 The La-C distance of
2.456(6) Å reflects the increase in ionic radius from Sm to
La (103 pm).23 The average La-O(thf) bond distance of
2.593 Å is longer than in the dicationic benzyl complex [La-
(CH2C6H4Me-4)(thf)6][BPh4]2 (2.586 Å).10d
For Ln ) Sm, both calculated structures are isoenergetic.
The ionic radius of Sm (96 pm) is almost midway between
that of La and that of Y (103 and 90 pm, respectively).23
A
subtle balance between the reduced steric hindrance around
the metal center and increased electrostatic Sm-Me attrac-
tions is indicated. For the capped octahedral structure, the
Sm-Me distance was calculated to be 2.406 Å (to be
compared with 2.385(8) Å found experimentally) whereas a
value of 2.430 Å is expected for the pentagonal bipyramid.
Reactivity of the Yttrium Methyl Cations. Three rep-
resentative reaction types were found for the cationic metal
complexes: (a) because of its carbanionic nature, the methyl
group acts as a nucleophile toward electrophiles (Scheme
4); (b) the Lewis acidic cationic metal center reacts with a
nucleophile (Scheme 4); (c) the methyl group reacts as a
Brønsted base in deprotonation reactions.25 Owing to the
diamagnetic nature and medium sized ionic radius (Sc: 75
pm, Y: 90 pm, La: 103 pm),23 methyl cations of yttrium
3-Y and 4-Y were chosen to explore the reactivity of this
family of compounds.
For seven-coordinate complexes, the commonly adopted
geometries (capped octahedron, capped trigonal prism, and
pentagonal bipyramid) are similar in energy with the Repul-
sion Energy Coefficients X ranging from X ) 3.230 to
3.266.24 DFT calculations led to minima on the PES for both
the observed capped octahedral and pentagonal bipyramidal
structures of [LnMe(thf)6]2+ (Ln ) La, Sm, Y). According
to calculations for Ln ) Y, the pentagonal bipyramidal
structure is more stable by 2.0 kcal · mol-1 than the capped
octahedron. The calculated Y-Me distance of 2.361 Å is in
(23) Shannon, R. D. Acta Crystallogr. 1976, A32, 751–767.
(24) Kepert, D. L. Coordination Numbers and Geometries. In Comprehen-
siVe Coordination Chemistry; Wilkinson, G., Gilliard, R. D., Mc-
Cleverty, J. A., Eds.; Pergamon: Oxford, U.K., 1987, pp 31-108.
(25) Arndt, S.; Elvidge, B. R.; Zeimentz, P. M.; Spaniol, T. P.; Okuda, J.
Organometallics 2006, 25, 793–795.
9270 Inorganic Chemistry, Vol. 47, No. 20, 2008

Methyl Cations of the Rare-Earth Metals
Table 2. Selected Bond Lengths (Å) and Angles (deg) of 4-Y,11a 4′-La, and 4′-Sm and Their Calculated Structures
a
b
b
4-Y
[YMe(thf)6]2+
4′-La
[LaMe(thf)6]2+
4′-Sm
[SmMe(thf)6]2+
Ln-C
Ln-O
2.418(3)
2.352(3)c
2.426(3)c
2.355(3)c
2.427(3)c
2.377(3)c
2.427(3)d
2.361
2.436
2.456
2.437
2.474
2.456
2.598
175.4
2.456(6)
2.556(2)e
2.679(3)f
2.664(3)f
2.578(4)e
2.583(5)f
2.497(3)e
2.480
2.631
2.644
2.649
2.638
2.648
2.609
2.385(8)
2.411(4)e
2.472(3)e
2.495(6)e
2.573(4)f
2.603(4)f
2.512(8)f
2.406
2.520
2.534
2.559
2.566
2.576
2.593
C-Ln-Og
176.5(1)
a Calculated pentagonal bipyramidal isomer. b Calculated capped octahedral isomer. c Equatorial thf. d Axial thf. e thf in top plane. f thf in bottom plane.
g thf trans to Me.
Scheme 4
slightly shorter than that reported for terminal alkoxo ligands
in the monocationic cis-[Y(OCRC12H8)2(thf)4][BPh4] (R )
CH2SiMe3, 2.0533 and 2.0680 Å)26 and the neutral [Y(OC14-
H11)2(µ-OC14H11)]2(9-fluorenone) (2.028 and 2.049 Å),6b
because of the dicationic charge of the compound. The thf
molecule trans to the alkoxy ligand is situated further away
from the metal center, as was the case in 3-Lu (vide supra).
The results of a DFT investigation of the reaction between
benzophenone and both 3-Y and 4-Y resulted in the free
energy profile depicted in Figure 5. The reactions are
calculated to be kinetically and thermodynamically favorable
for 3-Y and 4-Y, in agreement with the experimental
observation. It should be noted that, for 3-Y, only insertion
into one Y-Me bond has been considered. The reaction is
both thermodynamically and kinetically slightly more favor-
able for the dicationic rather than for the monocationic
complex with respect to the separated reactants. As the MOs
are more contracted in the dicationic complex, the insertion
would be expected to be less facile than in the monocationic
complex. On the other hand, the higher metal charge leads
to stronger electrostatic interactions. Analyzing the energy
profile and in agreement with the metal charge (related to
mainly electrostatic interaction), the benzophenone adduct
is found to be more stable for 4-Y than 3-Y. With respect to
the adduct formation, the barrier is higher for 4-Y (35.7
kcal ·mol-1) than for 3-Y (21.3 kcal ·mol-1), in line with the
charge effect.
When the dication 4-Y was reacted with soft nucleophiles
of the type M+X- (M ) Li, Na, K) in thf, monocationic
yttrium compounds of the type [YMeX(thf)n][BPh4] were
formed. Isolation of the resulting cations was difficult, as
[YMeX(thf)n][BPh4] had to be separated from [M(thf)m]-
[BPh4]. Upon reaction of 4-Y with 1 equiv of NaI in thf, the
iodo methyl yttrium cation [YMeI(thf)5][BPh4] (7) could be
isolated. Further reaction with 1 equiv of NaI resulted in
the formation of neutral [YMeI2(thf)3] (8). Comparable to 7
is the η3-allyl chloro monocation [Nd(η3-C3H5)Cl(thf)5]-
[BPh4].27 A number of divalent and trivalent compounds of
the general formula LnRX and LnRX2/LnR2X (X ) halide)
were generated by direct reaction of Ln0 with RX.28 In
A typical reaction for the insertion of unsaturated mol-
ecules into Ln-C bonds is the reaction with benzophenone
or fluorenone.6b,26 Upon reaction of 3-Y with 2 equiv of
benzophenone the dialkoxy complex [Y(OCMePh2)2-
(thf)4][BPh4] (5) formed. When 1 equiv of benzophenone
was reacted with 4-Y in thf, the reaction mixture instanta-
neously turned clear and crystals of [Y(OCMePh2)(thf)5]-
[BPh4]2 (6) precipitated out of solution. The structure of the
cationic part of the compound 6 is depicted in Figure 4. In
the distorted octahedral cation the central yttrium atom is
coordinated by the alkoxy ligand and five thf molecules. The
Y-O bond distance to the alkoxy ligand (1.9990(16) Å) is
(26) Nakajima, Y; Okuda, J. Organometallics 2007, 26, 1270–1278.
(27) Taube, R.; Maiwald, S.; Sieler, J. J. Organomet. Chem. 2001, 621,
327–336.
(28) For examples of divalent complexes, see. (a) Evans, D. F.; Fazakerley,
G. V.; Phillips, R. F. J. Chem. Soc. A 1971, 1931–1934. (b) For
examples of trivalent complexes, see Dolgoplosk, B. A.; Tinyakova,
E. I.; Markevich, I. N.; Soboleva, T. V.; Chernenko, G. M.; Sharaev,
O. K.; Yakovlev, V. A. J. Organomet. Chem. 1983, 255, 71–79.
Figure 4. ORTEP drawing of the cationic portion of 6 at 50% probability
level. Hydrogen atoms are omitted for clarity.
Inorganic Chemistry, Vol. 47, No. 20, 2008 9271

Kramer et al.
Figure 5. Calculated energy profile for benzophenone insertion into the Y-Me bond for both 3-Y and 4-Y.
addition, a series of [LnPhCl2(thf)n] (Ln ) Pr, Sm, Gd)29
and some complexes of the type [LnRCl2(thf)n] with bulky
aryl groups (R ) 2,6-dimesitylphenyl or 2,6-di(1-nap-
htyl)phenyl)30,31 were prepared by reacting LiR with LnCl3
in 1:1 ratio. A further example is the η3-allyl dichloro
complex [Nd(C3H5)Cl2(thf)2] prepared by the compropor-
tionation of the homoleptic tri(allyl) complex [Nd(η3-
C3H5)3(diox)] with [NdCl3(thf)2].32 Recently, Anwander et
al. reported on mixed rare-earth methyl chloro compounds
either isolated as [LnaAlbMecCld]n (a + b ) 1, a > b, c +
d ) 3, d > c; Ln ) Sc, Y, La, Nd) or prepared in situ from
compounds 2-Ce, 2-Pr and 2-Nd and Et2AlCl in varying
amounts as a chlorinating agent.6e,33 Compound 8 is an
analogue to cerium reagents of the type LiR/CeX3 or MgRX/
CeX3, used as a source of nucleophilic alkyls, where pure
lithium alkyls or Grignard reagents undergo undesirable side
reactions such as enolization of the carbonyl substrates. The
exact nature of these compounds is, however, not well
understood.34
Unlike Grignard reagents, 7 and 8 are not involved in
Schlenk equilibria in pyridine-d5 because a fast exchange
(on the NMR-time scale) of the methyl groups can be
1
excluded on the basis of a coupling of both H and 13C to
89Y (I ) 1/2).35 A single, well defined peak in the 89Y NMR
spectrum at δ 543 ppm confirmed that only one species is
present in pyridine-d5 solution. This is analogous to the 47Ti
and 49Ti spectra of [TiMeCl3], where also only one species
was detected.36 Single crystals of a pyridine adduct of 8 could
be grown from a pyridine/pentane solution of 8. The resulting
crystals of [YMeI(py)5]I (8′) were pseudomerohedrically
twinned with strong disorder of iodo and methyl ligands.
The result of the structure determination confirmed the
composition and atomic connectivity, in particular, the trans
arrangement of the methyl group and the iodo ligand. Within
the crystal, the second iodide is separated from the yttrium
(33) Meermann, C.; To¨rnroos, K. W.; Nerdal, W.; Anwander, R. Angew.
Chem., Int. Ed. 2007, 46, 6508–6513.
(34) (a) Imamoto, T.; Kusumoto, T.; Yokoyama, M. J. Chem. Soc., Chem.
Commun. 1982, 1042–1044. (b) Imamoto, T. In ComprehensiVe
Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon: Oxford,
1991; Chapter 1.8 and references therein. (c) Liu, H.-J.; Shia, K.-S.;
Shang, X.; Zhu, B.-Y. Tetrahedron 1999, 55, 3803–3830. (d) Molan-
der, G. A. Chem. ReV. 1992, 92, 29–68.
(35) (a) Akitt, J. W.; Mann, B. E. NMR and Chemistry, 4th ed.; Nelson
Thornes: Cheltenham, U.K., 2002. (b) Hore, P. J. Nuclear Magnetic
Resonance; Oxford University Press: Oxford, U.K., 2001.
(36) Berger, S.; Bock, W.; Frenking, G.; Jonas, V.; Mu¨ller, F. J. Am. Chem.
Soc. 1995, 117, 3820–3829.
(29) Lin, G.; Jin, Z.; Zhang, Y.; Chen, W. J. Organomet. Chem. 1990,
396, 307–313.
(30) Rabe, G. W.; Be´rube´, C. D.; Yap, G. P. A.; Lam, K.-C.; Concolino,
T. E.; Rheingold, A. L. Inorg. Chem. 2002, 41, 1446–1453.
(31) Rabe, G. W.; Be´rube´, C. D.; Yap, G. P. A. Inorg. Chem. 2001, 40,
2682–2685.
(32) Maiwald, S.; Taube, R; Hemling, H.; Schumann, H. J. Organomet.
Chem. 1998, 552, 195–204.
9272 Inorganic Chemistry, Vol. 47, No. 20, 2008

Methyl Cations of the Rare-Earth Metals
ion pairs in the crystal lattice), comparable to one of the
distances in [Y(BH4)3(thf)3] (2.350 Å and 2.412 Å)40 but
longer than those observed in the six-coordinated cationic
part of [Y(BH4)2(thf)4][Y(BH4)4] (2.30, 2.33, 2.34 and
2.32 Å).42
Calculations at the DFT level have reproduced the structure
of 9 well. The tridentate nature of the borohydride ligand,
the trans-arrangement of the BH4 and Me groups, as well
as the Y-X (X ) C, B, O) bond lengths are all in good
agreement with the experimental results (for details, see
Supporting Information).
Conclusion
The present study demonstrates that thf-solvated rare-earth
metal methyl dications [LnMe(thf)n][BAr4]2 can be prepared
by protonolysis of synthetic equivalents of the elusive
trimethyl metal compounds [LnMe3] such as [Li3LnMe6(thf)n]
and [Ln(AlMe4)3]. The configuration is either octahedral,
pentagonal bipyramidal, or capped octahedral, depending on
the radius of the metal center. Computations confirm a highly
electrostatic bonding between the methyl group and the rare-
earth metal center. Therefore the carbanionic character of
the methyl group is pronounced despite the double positive
charge. This is manifested in the facile nucleophilic attack
on an electrophile such as benzophenone, whereas the Lewis
acidic character is evidenced by the addition of soft nucleo-
philes, such as iodide or tetrahydroborate to give monoca-
tionic methyl complexes of the type [YMe(X)(thf)5]+ (X-
Figure 6. ORTEP drawing of the cationic portion of 9 at the 50%
probability level. Only those hydrogen atoms of the BH4 group are shown
for clarity.
center, affording a charge separated ion pair [YMeI(py)5]I.
1
Accordingly, the identical H NMR shifts of the methyl
groups in 7 and 8/8′ suggest a charge separated ion pair in
solution. Complex 8 is relatively stable in pyridine-d5 and
neither pyridine orthometalation15,25 nor methyl group
transfer to a pyridine ring19 occurred within 24 h.
When 4-Y was reacted with 1 equiv of NaBH4 in thf, the
mixed alkyl borohydride compound [YMe(BH4)(thf)5][BPh4]
(9) was isolated as colorless crystals. The IR spectrum
exhibits a sharp band at ν ) 2425 cm-1 and a strong broad
band at 2230 cm-1, indicating a tridentate coordination of
the BH4 group.37 The 1H NMR spectrum of 9 in thf-d8 shows
a 1:1:1:1 quartet for the BH4 group, suggesting a fast
rearrangement of the coordination modes on the NMR time
scale. Cationic borohydride complexes of the f-elements are
rare and with the exception of a cationic uranium(IV)
borohydride,38 only recently have cationic rare-earth metal
tetrahydridoborate complexes [Ln(BH4)2(thf)5]+ become
accessible.39
Single crystals of 9 were obtained by slow cooling of a
saturated thf solution (Figure 6). The geometry around the
yttrium center is best described as a pentagonal bipyramid,
as for 3-Y. The BH4 and Me groups are almost perfectly
trans to each other with a C-Y-B angle of 179.1(3)°. The
Y-C bond distance of 2.450(8) Å is slightly shorter than in
3-Y (2.526 Å and 2.508 Å) and slightly longer than in 4-Y
(2.418 Å).11 Within the standard deviation, the Y-B distance
of 2.563(10) Å is equal to the corresponding distances in
[Y(BH4)3(thf)3] (2.58 Å).40 Theoretical studies on [Y(BH4)2-
(H2O)4]+ with different bonding modes of the borohydride
(η2 versus η3) have shown a theoretical Y-B distance of
2.56 or 2.58 Å for the tridentate ligation.41 The average Y-O
distance of 2.413 Å is slightly longer than the averages
observed in 3-Y (2.403 and 2.393 Å for two independent
) I-, BH4 ). In conclusion, the methyl dications of the rare-
-
earth metals contain a nucleophilic methyl group acting as
methyl anion source, but at a relatively soft Lewis acidic
metal center. This situation is related to that commonly
associated with the active sites of Ziegler catalysts,9,10 where
both a Lewis acidic/electrophilic metal center and a (soft)
nucleophilic alkyl (and hydride) chain are invoked for the
polyinsertion of R-olefins. As recently demonstrated by
Evans et al. in pioneering works on permethylcyclopenta-
dienyl cations,43 unsolvated alkyl cations of the rare-earth
metals therefore promise even higher reactivity.
Experimental Section
General Considerations. All operations were performed under
an inert atmosphere of argon using standard Schlenk-line or
glovebox techniques. Diethyl ether, thf, and toluene were distilled
from sodium benzophenone ketyl. Pentane was purified by distil-
lation from sodium/triglyme benzophenone ketyl. Alternatively, the
above solvents were dried using an MBraun SPS-800 solvent
purification system. For the previously reported compounds 1-Sc,
1-Y, 1-Ho, 1-Yb, 1-Lu, 4-Sc, 4-Y, 4-Nd, 4-Ho, 4-Yb, and 4-Lu
optimized procedures are given for reasons of completeness.11 The
rare-earth metal aluminates 2 were prepared according to published
procedures.6e [NR3H][BAr4] (Ar ) Ph, C6H4F-4) was obtained by
reaction of aqueous solutions of NaBAr4 and of [NR3H]Cl, followed
(37) Ephritikhine, M. Chem. ReV. 1997, 97, 2193–2242.
(38) Cendrowski-Guillaume, S. M.; Lance, M.; Nierlich, M.; Ephritikhine,
M. Organometallics 2000, 19, 3257–3259.
(39) (a) Robert, D.; Kondracka, M.; Okuda, J. Dalton Trans. 2008, 2667–
2669. (b) Visseaux, M.; Mainil, M.; Terrier, M.; Mortreux, A.; Roussel,
P.; Mathivet, T.; Destarac, M. Dalton Trans. 2008, 4558–4561.
(40) Segal, B. G.; Lippard, S. J. Inorg. Chem. 1978, 17, 844–850.
(41) Xu, Z.; Lin, Z. Inorg. Chem. 1996, 35, 3964–3966.
(42) Lobkovskii, E. B.; Kravchenko, S. E.; Kravchenko, O. V. Zh. Strukt.
Khim. 1982, 23, 111–114.
(43) (a) Evans, W. J.; Perotti, J. M.; Ziller, J. W. J. Am. Chem. Soc. 2005,
127, 3894–3909. (b) Evans, W. J.; Perotti, J. M.; Ziller, J. W. J. Am.
Chem. Soc. 2005, 127, 1068–1069. (c) Evans, W. J.; Champagne,
T. M.; Ziller, J. W. Organometallics 2007, 26, 1204–1211.
Inorganic Chemistry, Vol. 47, No. 20, 2008 9273

Kramer et al.
Table 3. Crystallographic Data for 1′-Sc, 3-Lu, 4′-La, and 9
compound
1′-Sc
3-Lu
4′-La
9
empirical formula
Mr
C29H73Li3O5Sc2
612.61
C46H66BLuO5
884.77
C73H83B2F8LaO6
1368.92
C45H67B2O5Y
798.52
wavelength (Å)
crystal system
space group
a (Å)
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
0.71073
tetragonal
I41cd
16.340(3)
16.340(3)
29.970(2)
90
90
90
8002(2)
8
0.71073
monoclinic
P21/c
12.6950(10)
28.004(2)
13.0130(10)
90
111.0390(10)
90
4317.9(6)
4
1.361
130(2)
2.329
0.71073
monoclinic
P21/n
14.4672(12)
12.7014(11)
18.2100(15)
90
103.8331(18)
90
3249.1(5)
2
1.399
110(2)
0.733
0.71073
monoclinic
P21/c
13.5304(16)
13.0945(16)
24.622(3)
90
90.700(2)
90
4362.0(9)
4
1.216
120(2)
1.379
Z
Dcalc (g·cm-3
T (K)
)
1.017
130(2)
0.367
2704
µ(Mo KR) (mm-1
F(000)
)
1832
1416
1704
Crystal size (mm3)
0.75 × 0.50 × 0.30
2.23-27.55
48000
4610 (0.0369)
0.8979 and 0.7705
4610/1/183
1.064
0.0585, 0.1557
0.0708, 0.1679
0.456 and -0.251
0.35 × 0.30 × 0.24
2.22-30.72
52690
12660 (0.0805)
0.572 and 0.437
12660/0/480
0.872
0.0354, 0.0626
0.0613, 0.0663
2.082 and -0.653
0.70 × 0.40 × 0.40
2.30-29.85
44720
9115 (0.0493)
0.7428 and 0.6152
9115/0/421
1.096
0.0632, 0.1668
0.0890, 0.1811
0.928 and -0.558
0.30 × 0.20 × 0.20
1.51-29.20
61684
11731 (0.0822)
0.7623 and 0.6757
11731/0/495
1.089
0.0838, 0.2281
0.1250, 0.2495
3.428 and -0.674
θ Range (°)
reflections collected
independent reflections (Rint
Max. and min. transmission
Data/restraints/parameters
goodness-of-fit on F2
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
)
largest diff. peak and hole (e Å-3
)
by washing with H2O and Et2O (Ar ) Ph) or pentane (Ar ) C6H4F-
4) and subsequent drying under vacuum. All other chemicals were
commercially available and were used after appropriate purification.
Solid methyllithium was obtained by removing all volatiles from
1.6 M solutions in diethyl ether (Acros). For the preparations of
compounds 4 from 1, idealized molecular weights according to
mono-thf adducts of 1 are used, because of varying thf content
from batch to batch.
NMR spectra were recorded at room temperature on a Bruker
DRX 400 spectrometer (1H, 400.1 MHz; 13C, 100.6 MHz; 11B, 128.4
MHz; 89Y, 19.6 MHz) or on a Varian Unity 500 spectrometer (1H,
500 MHz; 13C, 125.6 MHz; 11B, 160.3 MHz). thf-d8 (Aldrich) was
distilled from sodium, and pyridine-d5 was distilled from CaH2.
Chemical shifts for 1H and 13C NMR spectra are referenced
internally using the residual solvent resonances and reported relative
to tetramethylsilane. 11B NMR spectra are referenced externally to
a 1 M solution of NaBH4 in D2O. 19F NMR spectra are referenced
externally to neat CFCl3. 89Y NMR spectra are referenced externally
to a 1 M solution of YCl3 in D2O. Elemental analyses were
performed by the Microanalytical Laboratory of the Organic
Chemistry Department of RWTH Aachen University. Metal analysis
was performed by complexometric titration. The sample (20-30
mg) was dissolved in acetonitrile (2 mL) and titrated with a 0.005
M aqueous solution of EDTA using xylenol orange as indicator
and a 1 M ammonium acetate buffer solution (20 mL). IR spectra
were recorded using KBr plates using a Nicolet Avatar 360 FT-IR
spectrometer.
(br s, 18H, ScMe), 1.77 (m, 4H, ꢀ-CH2, thf), 3.62 (m, 4H, R-CH2,
thf). 13C{1H} NMR (100 MHz, thf-d8): δ 14.2 (v br, ScMe), 26.3
(ꢀ-CH2, thf), 68.2 (R-CH2, thf). Anal. Calcd for C10.8H27.6Li3O1.2Sc:
Sc, 18.54. Found: Sc, 18.74. Cooling a saturated Et2O solution of
1-Sc afforded 1′-Sc as colorless crystals.
[Li3YMe6(thf)1.3] (1-Y).11b Following the procedure described
for 1-Sc, anhydrous YCl3 (5.260 g, 26.7 mmol) was reacted with
methyllithium (3.516 g, 160 mmol) to afford 1-Y after workup;
yield: 6.350 g, (81%). 1H NMR (500 MHz, thf-d8): δ -1.10 (br s,
18H, YMe), 1.73 (m, 4H, ꢀ-CH2, thf), 3.57 (m, 4H, R-CH2, thf).
13C{1H} NMR (126 MHz, thf-d8): δ 25.1 (ꢀ-CH2, thf), 67.3 (R-
CH2, thf). Signals due to the YMe groups could not be detected.
7Li{1H} NMR (194 MHz, thf-d8): δ 1.1. Anal. Calcd for
C11.2H28.4Li3O1.3Y: Y, 30.27. Found: Y, 30.13. Cooling a saturated
Et2O solution of 1-Y afforded 1′-Y as colorless crystals.
[Li3GdMe6(thf)2.4] (1-Gd). Following the procedure described
for 1-Sc, anhydrous GdCl3 (1318 mg, 5 mmol) was reacted with
methyllithium (659 mg, 30 mmol) to afford 1-Gd after workup;
yield: 989 mg, (45%). Anal. Calcd for C15.6H37.2GdLi3O2.4: Gd,
35.63. Found: Gd, 35.79.
[Li3TbMe6(thf)1.5] (1-Tb). Following the procedure described
for 1-Sc, anhydrous TbCl3 (1.326 g, 5 mmol) was reacted with
methyllithium (659 mg, 30 mmol) to afford 1-Tb after workup;
yield: 1.200 g, (63%). Anal. Calcd for C12H30Li3O1.5Tb: Tb, 42.03.
Found: Tb, 42.12. Cooling a saturated Et2O solution of 1-Tb
afforded 1′-Tb as colorless crystals.
[Li3DyMe6(thf)1.65] (1-Dy). Following the procedure described
for 1-Sc, anhydrous DyCl3 (1.344 g, 5 mmol) was reacted with
methyllithium (659 mg, 30 mmol) to afford 1-Dy after workup;
yield: 1.500 g, (76%). Anal. Calcd for C12.6H31.2DyLi3O1.65: Dy,
41.40. Found: Dy, 41.34.
[Li3ScMe6(thf)1.2] (1-Sc).11b Anhydrous ScCl3 (757 mg, 5 mmol)
was suspended in thf (20 mL) and stirred at 50 °C overnight. All
volatiles were removed in vacuo and the solid residue was
suspended in Et2O (50 mL). The suspension was cooled to -78
°C and treated dropwise with a freshly prepared solution of
methyllithium (659 mg, 30 mmol) in Et2O (50 mL). The reaction
mixture was stirred for 1 h at 0 °C and for further 2 h at room
temperature. After filtering off a colorless precipitate and removing
all volatiles under reduced pressure, the resulting sticky solid was
triturated with pentane to give 1-Sc as an off-white solid after
drying; yield: 1.010 g (83%). 1H NMR (400 MHz, thf-d8): δ -0.90
[Li3HoMe6(thf)1.2] (1-Ho).11b Following the procedure described
for 1-Sc, anhydrous HoCl3 (1.356 g, 5 mmol) was reacted with
methyllithium (659 mg, 30 mmol) to afford 1-Ho after workup;
yield: 920 mg, (53%). Anal. Calcd for C10.8H27.6HoLi3O1.2: Ho,
45.50. Found: Ho, 45.22.
[Li3ErMe6(thf)2] (1-Er). Following the procedure described for
1-Sc, anhydrous ErCl3(1.368 g, 5 mmol) was reacted with meth-
9274 Inorganic Chemistry, Vol. 47, No. 20, 2008

Methyl Cations of the Rare-Earth Metals
1
yllithium (659 mg, 30 mmol) to afford 1-Er after workup; yield:
1.515 g, (72%). Anal. Calcd for C14H34ErLi3O2: Er, 39.58. Found:
Er, 39.40.
[Li3TmMe6(thf)1.7] (1-Tm). Following the procedure described
for 1-Sc, anhydrous TmCl3 (1.376 g, 5 mmol) was reacted with
methyllithium (659 mg, 30 mmol) to afford 1-Tm after workup;
yield: 1.495 g, (74%). Anal. Calcd for C12.8H31.6Li3O1.7: Tm, 41.97.
Found: Tm, 41.49.
125.6 (q, 3JBC ) 2.6 Hz, Ph-3), 137.1 (m, Ph-2), 165.1 (q, JBC
)
49.4 Hz, Ph-1). 11B{1H} NMR (160 MHz, thf-d8): δ -6.56. Anal.
Calcd for C42H58BLuO4: C, 62.07; H, 7.19. Found: C, 61.69; H,
7.31.
[ScMe(thf)5][BPh4]2 (4-Sc).11b A mixture of 1-Sc (100 mg, 0.438
mmol) and [NEt3H][BPh4] (923 mg, 2.19 mmol) was treated at 25
°C with thf (10 mL), resulting in the evolution of gas. After the
colorless suspension was stirred for 30 min at 25 °C, the supernatant
was decanted. The volatiles were removed under reduced pressure
[Li3YbMe6(thf)] (1-Yb).11b Following the procedure described
for 1-Sc, anhydrous YbCl3 (1.397 g, 5 mmol) was reacted with
methyllithium (659 mg, 30 mmol) to afford 1-Yb after workup;
yield: 720 mg, (40%). Anal. Calcd for C10H26Li3OYb: Yb, 48.58.
Found: Yb, 48.38.
1
to give colorless microcrystals of 4-Sc (193 mg, 42%). H NMR
(500 MHz, pyridine-d5): δ 0.87 (s, 3H, ScMe), 1.60 (m, 20H,
ꢀ-CH2, thf), 3.64 (m, 20H, R-CH2, thf), 7.08 (t, JHH ) 7.8 Hz,
3
8H, Ph-4), 7.26 (m, 16H, Ph-3), 8.04 (m, 16H, Ph-2). 13C{1H} NMR
(126 MHz, pyridine-d5): δ 25.5 (ꢀ-CH2, thf), 46.6 (ScMe), 67.5
(R-CH2, thf), 122.0 (Ph-4), 125.8 (Ph-3), 136.8 (Ph-2), 164.8 (q,
1JBC ) 49.3 Hz, Ph-1). 11B{1H} NMR (160 MHz, pyridine-d5): δ
5.8. Anal. Calcd for C69H83B2O5Sc: Sc, 4.25. Found: Sc, 4.20.
[YMe(thf)6][BPh4]2 (4-Y).11 Following an analogous procedure
to prepare 4-Sc, 1-Y (1.50 g, 5.51 mmol) and [NEt3H][BPh4] (11.6
[Li3LuMe6(thf)] (1-Lu).11b Following the procedure described
for 1-Sc, anhydrous LuCl3 (1.407 g, 5 mmol) was reacted with
methyllithium (659 mg, 30 mmol) to afford 1-Lu after workup;
yield: 1.640 g, (92%). 1H NMR (400 MHz, thf-d8): δ -1.03 (br s,
18H, LuMe), 1.77 (m, 4H, ꢀ-CH2, thf), 3.61 (m, 4H, R-CH2, thf).
13C{1H} NMR (100 MHz, thf-d8): δ 9.0, 17.1 (br, LuMe), 26.2
(ꢀ-CH2, thf), 68.2 (R-CH2, thf). Anal. Calcd for C10H26Li3LuO:
Lu, 48.86. Found: Lu, 48.98.
1
g, 27.6 mmol) gave 4-Y as colorless crystals (4.24 g, 65%). H
NMR (400 MHz, pyridine-d5): δ 0.69 (d, 2JYH ) 2.1 Hz, 3H, YMe),
1.63 (m, 24H, ꢀ-CH2, thf), 3.67 (m, 24H, R-CH2, thf) 7.10 (t, 3JHH
) 7.0 Hz, 8H, Ph-4), 7.26 (t, 3JHH ) 7.4 Hz, 16H, Ph-3), 8.04 (m,
16H, Ph-2). 13C NMR (100 MHz, pyridine-d5): δ 27.6 (ꢀ-CH2, thf),
[YMe2(thf)5][BPh4] (3-Y).11b To a solution of [Y(AlMe4)3] (2-
Y) (250 mg, 0.714 mmol) in thf (2.5 mL) was added dropwise a
solution of [NEt3H][BPh4] (300 mg, 0.712 mmol) in thf (4 mL)
under stirring. Upon complete addition, the clear solution was
treated with pentane (7 mL), resulting in precipitation of a colorless
solid. The supernatant solution was decanted, and the solid dried
thoroughly under reduced pressure. Recrystallization from thf/
pentane, subsequent washing with pentane (3 × 5 mL) and drying
under vacuum gave 3-Y as colorless microcrystals (395 mg, 69%).
1
1
32.8 (dq, JYC ) 53.6 Hz, JCH ) 105.5 Hz, YMe), 69.7 (R-CH2,
1
thf), 124.2 (Ph-4), 128.0 (Ph-3), 139.0 (Ph-2), 166.8 (q, JBC
)
49.2 Hz, Ph-1). 11B{1H} NMR (128 MHz, pyridine-d5): δ -4.7.
89Y{1H} NMR (19.6 MHz, pyridine-d5): δ 433.2. Anal. Calcd for
C73H91B2O6Y: C, 74.16; H, 8.00; Y, 7.57. Found: C, 73.27; H, 7.22;
Y, 7.33.
2
1H NMR (400 MHz, thf-d8): δ -1.07 and -0.95 (d, JYH ) 1.7
[LaMe(thf)6][BPh4]2 (4-La). To a solution of [La(AlMe4)3] (2-
La) (200 mg, 0.5 mmol) in cold thf (3 mL) was added dropwise
[NEt3H][BPh4] (422 mg, 1 mmol) in thf (5 mL) under stirring. An
immediate gas evolution and precipitation of an off-white solid was
observed. Upon complete addition, the reaction mixture was stirred
for a further 5 minutes. The suspension was decanted, and the solid
was washed with thf and pentane. Drying of the solid under reduced
pressure gave 4-La as an off-white solid (434 mg, 71%). H (400
MHz, pyridine-d5): δ 0.11 (1:1:1 t, 2JHD ) 2.0 Hz, CH3D), 0.77 (s,
LaMe), 1.63 (m, 24H, ꢀ-CH2, thf), 3.66 (m, 24H, R-CH2, thf), 7.08
Hz, 6H, YMe2), 1.77 (m, 20H, ꢀ-CH2, thf), 3.62 (m, 20H, R-CH2,
thf), 6.73 (t, 3JHH ) 7.1 Hz, 4H, Ph-4), 6.87 (t, 3JHH ) 7.1 Hz, 8H,
Ph-3), 7.28 (m, 8H, Ph-2). 13C{1H} (100 MHz, thf-d8): δ 17.5 (d,
1JYC ) 46.8 Hz, YMe2), 26.3 (ꢀ-CH2, thf), 68.2 (R-CH2, thf), 121.8
3
(Ph-4), 125.6 (q, JBC ) 2.6 Hz, Ph-3), 137.0 (Ph-2), 165.0 (q,
1JBC ) 49.4 Hz, Ph-1). 11B{1H} (128 MHz, thf-d8): δ 6.6. 89Y{1H}
NMR (19.6 MHz, thf-d8): δ 650.9. 1H NMR (400 MHz, pyridine-
d5): δ -0.02 (d, 2JYH ) 1.3 Hz, 6H, YMe2), 1.67 (m, 20H, ꢀ-CH2,
thf), 3.67 (m, 20H, R-CH2, thf), 7.08 (t, 3JHH ) 7.0 Hz, 4H, Ph-4),
1
3
3
3
6.87 (t, JHH ) 7.5 Hz, 8H, Ph-3), 7.28 (m, 8H, Ph-2). 13C{1H}
(t, JHH ) 7.3 Hz, 8H, Ph-4), 7.24 (t, JHH ) 7.5 Hz, 16H, Ph-3),
8.03 (m, 16H, Ph-2). The sample was prepared at -40 °C and
immediately frozen with liquid N2 prior to measurement. Methane
evolution due to decomposition was observed as soon as the solvent
melted. The intensity of the LaMe protons was therefore found to
be too low and the signal for CH3D was detected. Because of the
fast decomposition, no 13C NMR was recorded. 1H NMR (200 MHz,
suspension in thf-d8): δ -0.30 (s, 3H, LaMe), 1.77 (m, 28H, ꢀ-CH2,
1
1
NMR (100 MHz, pyridine-d5): δ 18.0 (d, JYC ) 39.0 Hz, JCH
)
102.5 Hz, YMe2), 26.1 (ꢀ-CH2, thf), 68.2 (R-CH2, thf), 122.5 (Ph-
4), 126.3 (q, 3JBC ) 2.6 Hz, Ph-3), 137.3 (Ph-2), 165.1 (q, 1J11(B)C
1
) 49.4 Hz, septet, J10(B)C ) 16.5 Hz, Ph-1). 11B{1H} NMR (128
MHz, pyridine-d5): δ -5.9. 89Y{1H} NMR (19.6 MHz, pyridine-
d5): 216.4 (Y(pyridyl)2), 349.5 (YMe(pyridyl)), 571.8 (YMe2). Anal.
Calcd for C46H66BO5Y: C, 69.17; H, 8.33. Found: C, 68.98; H,
8.22.
3
4
thf), 3.61 (m, 28H, R-CH2, thf), 6.73 (tt, JHH ) 7.3 Hz, JHH
)
3
[LuMe2(thf)4][BPh4] (3-Lu). To
a
stirred solution of
2.2 Hz, 8H, Ph-4), 6.87 (t, JHH ) 7.3 Hz, 16H, Ph-3), 7.27 (m,
16H, Ph-2). Anal. Calcd for C73H91B2LaO6: C, 71.57; H, 7.49.
Found: C, 72.05; H, 7.66.
[Lu(AlMe4)3] (2-Lu) (200 mg, 0.458 mmol) in thf (3 mL) was
added dropwise a solution of [NEt3H][BPh4] (183 mg, 0.435 mmol)
in thf (1.5 mL). After complete addition the reaction mixture was
stirred for a further 10 min. All volatiles were removed under
reduced pressure, and the resulting colorless solid was dissolved
in a minimum amount of thf. The saturated solution was cooled to
-20 °C overnight. The resulting diffraction quality crystals were
washed with pentane and dried in vacuo. (230 mg, 65% based on
[NEt3H][BPh4]). 1H NMR (400 MHz, thf-d8): δ -0.94 (s, 6H,
LuMe2), 1.77 (m, 16H, ꢀ-CH2, thf), 3.62 (m, 16H, R-CH2, thf),
[LaMe(thf)6][B(C6H4F-4)4]2 (4′-La). To a stirred solution of of
[La(AlMe4)3] (2-La) (60 mg, 0.150 mmol) in thf (2 mL) was added
dropwise a solution of [NEt3H][B(C6H4F-4)4] (67 mg, 0.135 mmol)
in thf (2 mL). Upon complete addition, the solution was cooled to
-30 °C and a second solution of [NEt3H][B(C6H4F-4)4] (81 mg,
0.165 mmol) in thf (2 mL) was carefully layered on top of the
cold solution. The solution was kept at -30 °C overnight, after
which diffraction quality crystals had formed. Washing with thf (2
× 5 mL) and pentane (2 × 5 mL) and drying in vacuo afforded a
colorless solid (155 mg, 72%). 1H NMR (400 MHz, thf-d8): δ -0.22
(s, LaMe), 1.77 (m, 24H, ꢀ-CH2, thf), 3.61 (m, 24H, R-CH2, thf),
3
3
6.72 (t, JHH ) 7.3 Hz, 4H, Ph-4), 6.87 (t, JHH ) 7.3 Hz, 8H,
Ph-3), 7.27 (m, 8H, Ph-2). 13C{1H} NMR (126 MHz, thf-d8): δ
26.3 (ꢀ-CH2, thf), 27.3 (LuMe2), 68.2 (R-CH2, thf), 121.9 (Ph-4),
Inorganic Chemistry, Vol. 47, No. 20, 2008 9275

Kramer et al.
3
6.60 (t, JHH ) 9.3 Hz, 16H, C6H4F-3), 7.16 (m, 16H, C6H4F-2).
overnight. Anal. Calcd for C73H91B2GdO6: C, 70.52; H, 7.38; Gd,
12.64. Found: C, 69.94; H, 7.39; Gd, 12.52.
13C NMR (100 MHz, thf-d8): δ 26.4 (ꢀ-CH2, thf), 68.2 (R-CH2,
thf), 112.2 (C6H4F-3), 137.7 (C6H4F-2), 159.44 (q, JBC ) 50.3
Hz, C6H4F-1), 162.1 (C6H4F-4). The signal of the methyl carbon
was not observed. 19F NMR (188 MHz, thf-d8): δ -121.6. Anal.
Calcd for C73H83B2F8LaO6: C, 64.05; H, 6.11. Found: C, 64.16; H,
6.10.
1
[TbMe(thf)6][BPh4]2 (4-Tb). This compound was prepared
analogous to 4-Gd via route A by reaction of 1-Tb (150 mg, 0.439
mmol) with [NEt3H][BPh4] (924 mg, 2.19 mmol) to yield 4-Tb as
an off-white solid; yield: 354 mg (65%). Anal. Calcd for
C73H91B2O6Tb: Tb, 12.76. Found: Tb, 12.65.
[CeMe(thf)6][BPh4]2 (4-Ce). To
a
stirred solution of
[DyMe(thf)6][BPh4]2 (4-Dy). This compound was prepared
analogous to 4-Gd via route A by reaction of 1-Dy (150 mg, 0.434
mmol) with [NEt3H][BPh4] (914 mg, 2.17 mmol) to yield 4-Dy as
a very pale yellow solid; yield: 295 mg (54%). Anal. Calcd for
C73H91B2DyO6: Dy, 13.01. Found: Dy, 12.69.
[Ce(AlMe4)3] (2-Ce) (40 mg, 0.100 mmol) in thf (1 mL) was added
dropwise a solution of [NEt3H][BPh4] (40 mg, 0.095 mmol) in thf
(1 mL). Gas evolution was observed and upon complete addition
the stirrer bar was removed and the solution cooled to -30 °C. A
solution of [NEt3H][BPh4] (44 mg, 0.105 mmol) in thf (1 mL) was
carefully layered on top, and the reaction was left to stand at -30
°C. Overnight colorless crystals of 4-Ce formed which were washed
with thf (2 × 3 mL) and pentane (2 × 3 mL) and subsequently
dried under reduced pressure (104 mg, 85%). Anal. Calcd for
C73H91B2CeO6: C, 71.50; H, 7.48. Found: C, 70.79; H, 7.45.
[PrMe(thf)6][BPh4]2 (4-Pr). To a stirred solution of [Pr(AlMe4)3]
(2-Pr) (50 mg, 0.124 mmol) in thf (1 mL) was added dropwise a
solution of [NnBu3H][BPh4] (57 mg, 0.113 mmol) in thf (1 mL).
Gas evolution was observed and upon complete addition the stirrer
bar was removed and the green solution cooled to -30 °C. A
solution of [NnBu3H][BPh4] (69 mg, 0.136 mmol) in thf (1 mL)
was carefully layered on top, and the reaction was left to stand at
-30 °C. Pale green crystals of 4-Pr formed overnight which were
washed with thf (2 × 3 mL) and pentane (2 × 3 mL) and dried
under reduced pressure; yield: 120 mg (79%). Anal. Calcd for
C73H91B2O6Pr: C, 71.46; H, 7.48. Found: C, 70.28; H, 7.34.
[NdMe(thf)6][BPh4]2 (4-Nd).11b 4-Nd was prepared analogous
to 4-La from [Nd(AlMe4)3] (2-Nd) (304 mg, 0.749 mmol) and
[NEt3H][BPh4] (632 mg, 1.50 mmol) to afford 4-Nd as a pale blue
solid; yield: 650 mg (70%). Anal. Calcd for C73H91B2NdO6: C,
71.26; H, 7.45. Found: C, 70.22; H, 7.46.
[SmMe(thf)6][BPh4]2 (4-Sm). To a solution of [Sm(AlMe4)3]
(2-Sm) (180 mg, 0.437 mmol) in thf (2 mL) [NEt3H][BPh4] (162
mg, 0.384 mmol) in thf (1 mL) were added dropwise under stirring.
An immediate gas evolution was observed. After complete addition,
the reaction mixture was cooled to -30 °C. A solution of
[NEt3H][BPh4] (207 mg, 0.491 mmol) in thf (1 mL) was then
carefully layered on top, and the reaction mixture was left to stand
overnight at -30 °C. The resulting dark-red crystals of 4-Sm were
washed thoroughly with thf and pentane and subsequently dried
under reduced pressure; yield 476 mg (88%). Anal. Calcd for
C73H91B2O6Sm: C, 70.91; H, 7.42. Found: C, 70.03; H, 7.59.
[SmMe(thf)6][B(C6H4F-4)4]2 (4′-Sm). Following the same pro-
cedure as for 4′-La diffraction quality single crystals were obtained
overnight.
[HoMe(thf)6][BPh4]2 (4-Ho).11b This compound was synthesized
from 1-Ho (100 mg, 0.287 mmol) and [NEt3H][BPh4] (605 mg,
1.437 mmol) analogous to the synthesis of 4-Sc to yield pink
microcrystals of 4-Ho (359 mg, 100%). Anal. Calcd for C73H91B2-
HoO6: Ho, 13.18. Found: Ho, 13.23.
[ErMe(thf)6][BPh4]2 (4-Er). This compound was prepared
analogous to 4-Gd via route A by reaction of 1-Er (150 mg, 0.428
mmol) with [NEt3H][BPh4] (902 mg, 2.14 mmol) to yield 4-Er as
a pink solid (287 mg, 54%). Anal. Calcd for C73H91B2ErO6: Er,
13.34. Found: Er, 13.07.
[TmMe(thf)5][BPh4]2 (4-Tm). This compound was prepared
analogous to 4-Gd via route A by reaction of 1-Tm (150 mg, 0.426
mmol) with [NEt3H][BPh4] (898 mg, 2.13 mmol) to yield 4-Tm
as a yellow-green solid (414 mg, 82%). Anal. Calcd for
C69H83B2O5Tm: Tm, 14.28. Found: Tm, 14.68.
[YbMe(thf)6][BPh4]2 (4-Yb).11b This compound was synthesized
from 1-Yb (100 mg, 0.281 mmol) and [NEt3H][BPh4] (592 mg,
1.404 mmol) analogous to the synthesis of 4-Sc to yield 4-Yb as
yellow microcrystals (339 mg, 96%). Anal. Calcd for C73H91B2-
YbO6: Yb, 13.74. Found: Yb, 13.69.
[LuMe(thf)6][BPh4]2 (4-Lu).11b This compound was synthesized
from 1-Lu (100 mg, 0.279 mmol) and [NEt3H][BPh4] (588 mg,
1.396 mmol) analogous to the synthesis of 4-Sc to yield 4-Lu as
off-white microcrystals (292 mg, 83%). 1H NMR (500 MHz,
pyridine-d5): δ 0.68 (s, 3H, LuMe), 1.59 (m, 24H, ꢀ-CH2, thf),
3.64 (m, 24H, R-CH2, thf), 7.10 (t, 3JHH ) 7.3 Hz, 8H, Ph-4), 7.24
(m, 16H, Ph-3), 8.07 (m, 16H, Ph-2). 13C{1H} NMR (126 MHz,
pyridine-d5): δ 25.5 (ꢀ-CH2, thf), 34.5 (LuMe), 67.5 (R-CH2, thf),
1
122.0 (Ph-4), 125.8 (Ph-3), 136.8 (Ph-2), 164.8 (q, JBC ) 49.4
Hz, Ph-1). 11B{1H} NMR (160 MHz, pyridine-d5): δ -5.8. Anal.
Calcd for C73H91B2LuO6: C, 69.53; H, 7.27; Lu, 13.87. Found: C,
70.86; H, 7.49; Lu, 13.83.
[Y(OCMePh2)2(thf)4][BPh4] (5). To a stirred solution of 3-Y
(100 mg, 0.125 mmol) in thf (2.3 mL), solid benzophenone (46
mg, 0.250 mmol) was added. The reaction mixture was stirred for
5 min. Subsequently pentane (3 mL) was added to give a suspension
of light pink microcrystals. Decanting the solvent and subsequently
washing the solid with pentane and drying in vacuo yielded 5; yield:
123 mg, (90%). 1H NMR (400 MHz, pyridine-d5): δ 1.61 (m, 16H,
ꢀ-CH2, thf), 1.97 (s, 6H, OCMePh2), 3.64 (m, 16H, R-CH2, thf),
[GdMe(thf)6][BPh4]2 (4-Gd). Method A. To a solution of 1-Gd
(150 mg, 0.441 mmol) in thf (4 mL) was slowly added solid
[NEt3H][BPh4] (929 mg, 2.20 mmol) under stirring. An immediate
gas evolution and precipitation of a solid toward the end of the
addition was observed. Upon complete addition, the reaction
mixture was stirred for a further 45 min. The suspension was
decanted, and the solid washed thoroughly with thf and subsequently
with pentane. Drying of the solid under reduced pressure yielded
4-Gd as an off-white solid (207 mg, 38%).
Method B. To a stirred solution of 2-Gd (80 mg, 0.191 mmol)
in thf (2 mL) was added dropwise a solution of [NEt3H][BPh4]
(73 mg, 0.172 mmol) in thf (1 mL). The solution was cooled to
-40 °C. Subsequently a solution of [NEt3H][BPh4] (89 mg, 0.210
mmol) was layered on top of the reaction mixture and left at -40
°C. Diffraction quality crystals of 4-Gd formed (152 mg, 64%)
3
7.10 (t, JHH ) 7.0 Hz, 4H, Ph-4), 7.17-7.24 and 7.47-7.53
3
(various m, 20H, OCMePh2), 7.28 (t, JHH ) 7.3 Hz, 8H, Ph-3),
8.07 (m, 8H, Ph-2). 13C{1H} NMR (100 MHz, pyridine-d5): δ 25.9
2
(ꢀ-CH2, thf), 33.3 (OCMePh2), 67.9 (R-CH2, thf), 80.5 (d, JYC
)
6.1 Hz, OCMePh2), 122.4 (Ph-4), 126.2 and 126.3 (OCMePh2),
126.3 (Ph-3), 127.0 and 128.1 (OCMePh2), 137.2 (Ph-2), 152.64
(OCMePh2), 165.1 (q, 1JYC ) 48.6 Hz, Ph-1). 11B{1H} NMR (128
MHz, pyridine-d5): δ -5.7. Anal. Calcd for C68H78BO6Y: Y, 8.15.
Found: Y, 7.61.
[Y(OCMePh2)(thf)5][BPh4]2 (6). A stirred suspension of 4-Y
(60 mg, 51 µmol) in thf (4 mL) was reacted with solid benzophe-
9276 Inorganic Chemistry, Vol. 47, No. 20, 2008

Methyl Cations of the Rare-Earth Metals
none (9.3 mg, 51 µmol). The resulting colorless solution was heated
to 50 °C overnight to give diffraction quality crystal of 6 (52 mg,
-6.52 (BPh4), -30.2 (quintet, 1JBH ) 80.5 Hz, BH4). 89Y{1H} NMR
(19.6 MHz, thf-d8): δ 343.8. IR (KBr): ν ) 2230 (strong br, BH4),
2425 cm-1 (sharp, BH4). Anal. Calcd for C45H67B2O5Y: Y, 11.13.
Found: Y, 11.31.
1
79%). H NMR (400 MHz, pyridine-d5): δ 1.66 (m, 20H, ꢀ-CH2,
thf), 2.00 and 2.26 (s, 3H, OCMePh2), 3.68 (m, 20H, R-CH2, thf),
3
3
Computational Method. On the basis of our previous work, it
has been shown that the lanthanide center could be treated with
f-in-core effective core potentials (ECPs).44 Thus, La, Sm, and Lu
were treated with a Stuttgart-Dresden pseudopotential in combina-
tion with its adapted basis set.45 In both cases, the basis set has
been augmented by a set of polarization functions. Carbon, oxygen,
and hydrogen atoms have been described with a 6-31G(d,p)
double-ꢁ basis set.46 Calculations were carried out at the DFT level
of theory using the hybrid functional B3PW91.47,48 Geometry
optimizations were carried out without any symmetry restrictions,
and the nature of the extrema (minima) was verified with analytical
frequency calculations. All these calculations were performed with
the Gaussian 0349 suite of programs. The electronic density has
been analyzed using the Natural Bond Orbital (NBO) technique.50
Crystal Structure Determinations. All X-ray diffraction experi-
ments were carried out at on a Bruker SMART diffractometer using
Mo KR X-radiation (λ ) 0.71073 Å) and ω-scans. Diffracted
intensities were integrated from several series of exposures.51
Absorption corrections were based on multiple and symmetry-
equivalent measurements. The structures were solved with the
program SHELXS-8652 using direct methods and were refined using
7.09 (t, JHH ) 7.3 Hz, 8H, Ph-4), 7.25 (t, JHH ) 7.5 Hz, 16H,
Ph-3), 7.33-7.61 (various m, 10H, OCMePh2), 8.03 (m, 16H, Ph-
2). 13C{1H} NMR (100 MHz, pyridine-d5): δ 25.9 (ꢀ-CH2, thf),
2
33.3 (OCMePh2), 68.0 (R-CH2, thf), 83.5 (d, JYC ) 5.2 Hz,
OCMePh2), 122.5 (Ph-4), 126.2 (q, JBC ) 3.4 Hz, Ph-3), 127.0,
3
127.4, 127.7, 128.1, 128.7 (all OCMePh2), 137.2 (Ph-2), 165.1 (q,
1JBC ) 49.4 Hz, Ph-1). 11B{1H} NMR (128 MHz, pyridine-d5): δ
-5.8. Anal. Calcd for C82H93B2O6Y: Y, 6.92. Found: Y, 7.02.
[YMeI(thf)5][BPh4] (7). To a stirred suspension of 4-Y (1.500
g, 1.28 mmol) in thf (5 mL) was added solid sodium iodide (191
mg, 1.28 mmol) at once. After ∼2 min the solid dissolved and a
colorless precipitate formed quickly. The reaction mixture was
stirred overnight. Filtration, thorough washing with thf (3 × 4 mL),
pentane, and drying in vacuo yielded 7 as a colorless powder (908
1
2
mg, 78%). H NMR (400 MHz, pyridine-d5): δ 0.44 (d, JYH
)
2.0 Hz, 3H, YMe), 1.60 (m, ꢀ-CH2, thf), 3.64 (m, R-CH2, thf),
3
3
7.12 (t, JHH ) 7.3 Hz, 4H, Ph-4), 7.29 (t, JHH ) 7.5 Hz, 8H,
Ph-3), 8.07 (m, 8H, Ph-2). 13C NMR (100 MHz, pyridine-d5): δ
1
25.8 (R-CH2, thf), 26.7 (d, JYC ) 52.0 Hz, YMe), 67.9 (ꢀ-CH2,
thf), 122.4 (Ph-4), 126.6 (m, Ph-3), 137.2 (m, Ph-2), 165.1 (q, 1JBC
) 49.4 Hz, Ph-1). 11B{1H} NMR (128 MHz, pyridine-d5): δ -5.72.
Anal. Calcd for C45H63BIO5Y: Y, 9.76. Found: Y, 8.75.
SHELXL53 against all Fo data with hydrogen atoms riding in
2
calculated positions. All other atoms were refined anisotropically.
Only the structure of 4-La′ was solved by isotypic replacement
using the coordinates of 4-Sm′. The hydrogen atoms of the BH4-
group in 9 could be localized in a Fourier difference map and refined
in their position. 4-Dy contains co-crystallized thf in the lattice, 8
contains the solvent molecule pyridine. For the graphical repre-
sentation, the Oak Ridge Thermal Ellipsoid Plot (ORTEP) program
was used as implied in the program system WinGX.54 Selected
crystal parameters and results of the structure refinements are given
in Table 3. Crystallographic information has been deposited to the
Cambridge Crystallographic Data Centre.
[YMeI2(thf)3] (8). To a stirred suspension of 4-Y (1.800 g, 1.53
mmol) in thf (6 mL) were added at once 2 equiv of dry sodium
iodide (459 mg, 3.06 mmol) at room temperature. After a few min
part of the solid dissolved but soon after a colorless precipitate
formed. The reaction mixture was stirred overnight and filtered.
Repeated washing of the precipitate with thf and pentane, followed
by drying in vacuo afforded 8 as a colorless powder (440 mg, 50%).
2
1H NMR (400 MHz, pyridine-d5): δ 0.44 (d, JYH ) 1.8 Hz, 3H,
YMe), 1.60 (m, 12H, ꢀ-CH2 thf), 3.63 (m, 12H, R-CH2 thf).13C
NMR (100 MHz, pyridine-d5): δ 25.86 (ꢀ-CH2, thf), 27.23 (d, 1JYC
) 52.0 Hz), 67.9 (R-CH2, thf). 89Y NMR (19.6 MHz, pyridine-d5):
δ 543.0. Anal. Calcd for C13H27I2O3Y: C, 27.20; H, 4.74. Found:
C, 27.00; H, 4.56.
[YMeI(py)5]I (8′). Solid 8 was dissolved in a minimum amount
of pyridine, and pentane was layered on top of the solution. Cooling
the mixture to -40 °C resulted in the formation of a biphasic
mixture, which became homogeneous again upon warming to room
temperature. From this mixture, single crystals of 8′ formed after
standing overnight. Anal. Calcd for C26H28I2N5Y: C, 41.43; H, 3.75;
N, 9.30. Found: C, 42.00; H, 3.84; N, 9.72.
Acknowledgment. Financial support of this work by the
Fonds der Chemischen Industrie (Kekule´ Scholarship to
M.U.K.) and the Deutsche Forschungsgemeinschaft is grate-
(44) (a) Maron, L.; Eisenstein, O. J. Phys. Chem. A 2000, 104, 7140–7143.
(b) Maron, L.; Eisenstein, O. J. Am. Chem. Soc. 2001, 123, 1036–
1039. (c) Perrin, L.; Maron, L.; Eisenstein, O. Inorg. Chem. 2002,
41, 4355–4362. (d) Maron, L.; Perrin, L.; Eisenstein, O. J. Chem. Soc.,
Dalton Trans. 2002, 534–539. (e) Maron, L.; Werkema, E. L.; Perrin,
L.; Eisenstein, O.; Andersen, R. A. J. Am. Chem. Soc. 2005, 127,
279–292. (f) Werkema, E. L.; Messines, E.; Perrin, L.; Maron, L.;
Eisenstein, O.; Andersen, R. A. J. Am. Chem. Soc. 2005, 127, 7781–
7795.
(45) (a) Dolg, M.; Stoll, H.; Savin, A.; Preuss, H. Theor. Chim. Acta 1989,
75, 173–194. (b) Dolg, M.; Stoll, H.; Preuss, H. Theor. Chim. Acta
1993, 85, 441–450.
(46) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972, 56,
2257–2261.
(47) See for example (a) Burke, K.; Perdew, J. P.; Yang, W. In Electronic
Density Functional Theory: Recent Progress and New Directions;
Dobson, J. F., Vignale, G., Das, M. P. Eds.; Plenum: New York, 1998.
(48) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652.
(49) Frisch, M. J. et al. Gaussian 03 (Revision D.02); Gaussian, Inc.:
Pittsburgh, PA, 2006.
[YMe(BH4)(thf)5][BPh4] (9). To a stirred suspension of 4-Y
(2.400 g, 2.04 mmol) in thf (15 mL) was added at once solid NaBH4
(77 mg, 2.04 mmol), and the resulting clear solution was stirred
for 30 min, after which it was filtered. All volatiles were removed
under reduced pressure, and the resulting solid was redissolved at
room temperature in a minimum amount of thf. Cooling this
saturated solution to -30 °C yielded a first crop of 9 (734 mg,
45%). This process of fractional crystallization could be repeated
several times to increase the total yield. Diffraction quality crystals
were grown from slow cooling of a saturated thf solution of 9. 1H
2
NMR (400 MHz, thf-d8): δ -0.89 (d, JYH ) 1.8 Hz, 3H, YMe),
-0.01 (q, 1JBH ) 80.5 Hz, 4H, YBH4), 1.76 (m, 20H, ꢀ-CH2, thf),
3.61 (m, 20H, R-CH2, thf), 6.71 (t, 3JHH ) 7.3 Hz, 4H, Ph-4), 6.85
(50) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. ReV. 1988, 88, 899–
926.
3
(t, JHH ) 7.3 Hz, 8H, Ph-3), 7.27 (m, 8H, Ph-2). 13C NMR (100
(51) ASTRO, SAINT and SADABS. Data Collection and Processing
Software for the SMART System; Siemens Analytical X-ray Instruments
Inc.: Madison, WI, 1996.
(52) Sheldrick, G. M. SHELXS-86: A Program for Crystal Structure
Solution; University of Go¨ttingen: Go¨ttingen, Germany, 1986.
MHz, thf-d8): δ 20.9 (d, 1JYC ) 51.2 Hz, YMe), 26.2 (ꢀ-CH2, thf),
68.2 (R-CH2, thf), 121.7 (Ph-4), 125.5 (m, Ph-3), 137.0 (m, Ph-2),
1
165.0 (q, JBC ) 49.4 Hz, Ph-1). 11B NMR (128 MHz, thf-d8): δ
Inorganic Chemistry, Vol. 47, No. 20, 2008 9277

Kramer et al.
Supporting Information Available: Complete ref 49; complete
CIF files giving full crystallographic data for 1′-Sc, 1′-Y, 1′-Tb,
3-Lu, 4′-La, 4′-Sm, 4-Dy, 6, 8′, and 9; lists of selected bond lengths
and angles of all the above structures; crystallographic data of all
structures; details of calculated structures. This material is available
free of charge via the Internet at http://pubs.acs.org.
fully acknowledged. L.M and A.Y. thank the CINES and
CALMIP for generous grant of computing time. L.M. is
member of the Institut Universitaire de France. We thank
Professor T. P. Hanusa for helpful discussions.
(53) Sheldrick, G. M. SHELXL-97: A Program for Crystal Structure
Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(54) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837–838.
IC801259N
9278 Inorganic Chemistry, Vol. 47, No. 20, 2008