Neutral and cationic trimethylsilylmethyl complexes of the rare earth metals supported by a crown ether: Synthesis and structural characterization

Article abstract of DOI:10.1039/b305964b

The synthesis of a series of thermally robust, isolable trimethylsilylmethyl complexes of the rare earth metals stabilized by 12-crown-4 [Ln(CH₂SiMe₃)₃(12-crown-4)] (Ln = Sc, Y, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) is reported. The crystallographically characterized yttrium and lutetium complexes [Ln(CH ₂SiMe₃)₃(12-crown-4)] exhibit facial coordination of the crown ether at the neutral lanthanide trialkyl unit. The coordination geometry can be derived from a capped octahedron. VT NMR spectroscopic studies revealed a labile coordination of the crown ether in thf solution. Reaction of the diamagnetic derivatives with triethylammonium tetraphenylborate in thf results in the clean formation of the cationic dialkyl complexes [Ln(CH₂SiMe₃)₂(12-crown-4)(thf) _y][BPh₄] (Ln = Sc, Y, y = 0; Ln = Lu, y = 1), which also exhibit an exocyclic coordination of the crown ether to the cationic dialkyl lanthanide fragment.

Full text of DOI:10.1039/b305964b

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Neutral and cationic trimethylsilylmethyl complexes of the rare
earth metals supported by a crown ether: synthesis and structural
characterization
Stefan Arndt,a Peter M. Zeimentz,a Thomas P. Spaniol,a Jun Okuda,*†a Masaru Hondab and
Kazuyuki Tatsumib
a Institut für Anorganische Chemie und Analytische Chemie,
Johannes Gutenberg-Universität Mainz, Duesbergweg 10–14, D-55099 Mainz, Germany
b Department of Chemistry, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
Received 27th May 2003, Accepted 21st July 2003
First published as an Advance Article on the web 8th August 2003
The synthesis of a series of thermally robust, isolable trimethylsilylmethyl complexes of the rare earth metals
stabilized by 12-crown-4 [Ln(CH2SiMe3)3(12-crown-4)] (Ln = Sc, Y, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) is reported.
The crystallographically characterized yttrium and lutetium complexes [Ln(CH2SiMe3)3(12-crown-4)] exhibit facial
coordination of the crown ether at the neutral lanthanide trialkyl unit. The coordination geometry can be derived
from a capped octahedron. VT NMR spectroscopic studies revealed a labile coordination of the crown ether in thf
solution. Reaction of the diamagnetic derivatives with triethylammonium tetraphenylborate in thf results in the clean
formation of the cationic dialkyl complexes [Ln(CH2SiMe3)2(12-crown-4)(thf )y][BPh4] (Ln = Sc, Y, y = 0; Ln = Lu,
y = 1), which also exhibit an exocyclic coordination of the crown ether to the cationic dialkyl lanthanide fragment.
Introduction
Cationic alkyl complexes of the rare earth metals are becoming
increasingly important as active homogeneous ethylene poly-
merization catalysts.1 A number of monoanionic ancillary
ligands L such as deprotonated aza-18-crown-6, N,NЈ-R2-tacn-
i
NЉ-(CH2)2NtBu (tacn = 1,4,7-triazacyclononane, R = Pr, Me),
Scheme 1 x = 2 (Ln = Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu); x = 3
benzamidinate ArN᎐CPh–NAr (Ar = 2,6-iPr C H ), C Me Si-
(Ln = Sm); y = 0 (Ln = Sc, Y), y = 1 (Ln = Lu). Conditions: i. 12-crown-4
᎐
2
6
3
5
4
in pentane, 15 min, Ϫ20 to 25 ЊC; ii. (a) BPh3 in thf, 20 min, 25 ЊC, (b)
12-crown-4, 5 min, 25 ЊC, X = R; iii. [NEt3H][BPh4] in thf, 24 h, 25 ЊC,
X = Ph.
Me2(C5H3O-2) have been used to stabilize the cationic alkyl rare
earth metal fragments [Ln(L)R]ϩ.1,2 Because of the synthetic
difficulty of preparing and handling even simple trialkyl com-
plexes such as [Ln(CH2SiMe3)3(thf )x],3 the development of
structurally well-characterized alkyl cations has been rather
slow.4 Recently we have succeeded in stabilizing in situ gener-
ated dialkyl cations [Ln(CH2SiMe3)2]ϩ for Ln = Y and Lu using
crown ethers as ancillary ligands.5 We report here that the use
of 12-crown-4 also results in the stabilization of the thermally
sensitive [Ln(CH2SiMe3)3] unit, giving a series of isolable
complexes [Ln(CH2SiMe3)3(12-crown-4)].
As shown in Fig. 1, the 1H NMR spectrum of [Y(CH2-
SiMe3)3(12-crown-4)] in thf-d8 at 25 ЊC shows broad signals for
all three equivalent trimethylsilylmethyl groups and a broad
resonance for the methylene protons of the crown ether. At Ϫ10
ЊC, separate signals are observed for coordinated and non-
coordinated crown ether. The diastereotopic methylene protons
of the coordinated crown ether give rise to two broad reson-
ances at 3.88 and 4.04 ppm, whereas the methylene protons of
the noncoordinated crown ether appear as a singlet at 3.61
1
ppm. In addition, at lower temperatures the H and 13C NMR
Results and discussion
spectra exhibit separate signals for the alkyl groups of [Y(CH2-
SiMe3)3(thf )x] and [Y(CH2SiMe3)3(12-crown-4)], indicating
Synthesis and structure in solution
When [Y(CH2SiMe3)3(thf )2] is treated in pentane with one
equivalent of 12-crown-4, careful workup at lower temperatures
allowed the isolation of the new compound [Y(CH2SiMe3)3(12-
crown-4)] in good yield as analytically pure, colorless crystals
(Scheme 1). Due to the tedious isolation of the thf complex
[Y(CH2SiMe3)3(thf )2], a practically simple one-pot method
was developed starting with anhydrous yttrium trichloride.
The thermal stability is evidently enhanced over that of the
thf complex, crystals of [Y(CH2SiMe3)3(12-crown-4)] being
unchanged after standing for 2 weeks at room temperature.
This complex is sparingly soluble in hydrocarbons and soluble
in thf, dichloromethane and 1,2-dichloroethane. However,
when a solution in dichloromethane is left standing in daylight
for 1 h, the formation of a mixture of chlorinated products
[Y(CH2SiMe3)3ϪnCln(12-crown-4)] (n = 1, 2) was observed.
Fig. 1 1H NMR spectra of [Y(CH2SiMe3)3(12-crown-4)] in thf-d8 at
various temperatures. Signals denoted with (*) are due to the residual
protons of thf-d8. Signals denoted with (†) are assigned to non-
coordinated crown ether and [Y(CH2SiMe3)3(thf )x], respectively.
† Present address: Institute of Inorganic Chemistry, Aachen University
of Technology (RWTH), Prof.-Pirlet-Strasse 1, D-52056 Aachen,
Germany.
D a l t o n T r a n s . , 2 0 0 3 , 3 6 2 2 – 3 6 2 7
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
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reversible dissociation of the crown ether. The dissociation con-
stant in thf-d8 at Ϫ80 ЊC was estimated to be 0.05 0.5 mol LϪ1
.
In the less Lewis basic solvent CD2Cl2 no dissociation of the
1
crown ether was observed even at Ϫ80 ЊC. In the H NMR
spectrum at 25 ЊC, the methylene protons at yttrium appear as
a doublet at Ϫ0.81 ppm with J(YH) = 3.1 Hz, whilst the
trimethylsilyl groups are observed as a sharp singlet at
Ϫ0.09 ppm. The methylene protons of 12-crown-4 at 3.74 and
4.12 ppm are recorded as higher-order multiplets. These feature
indicate that 12-crown-4 is coordinated to the trivalent yttrium
center in an exocyclic fashion analogous to that reported for the
numerous 12-crown-4 complexes of lanthanide chlorides and
nitrates.6
Following the analogous one-pot procedure scandium and
an extensive series of lanthanide complexes [Ln(CH2SiMe3)3-
(12-crown-4)] (Ln = Sc, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu)
could be prepared and isolated. The only exceptions are the
larger elements La, Ce, Pr and Nd, for which the formation of
the starting complex [Ln(CH2SiMe3)3(thf )x] appeared to be not
possible. Also the europium derivative could not be prepared,
probably due to the facile reduction to the divalent state;7
Fig. 3 ORTEP diagram of [Y(CH2SiMe3)3(12-crown-4)] illustrating
the geometry of a distorted capped octahedron (open bonds) around
the yttrium center. Noncoordinating atoms omitted for clarity.
cf.: E 0(Eu3ϩaq ϩ eϪ
Eu2ϩaq) = Ϫ0.35 V versus SHE at
pH = 0 in aqueous solution.7a The diamagnetic scandium and
lutetium complexes as well as the paramagnetic samarium
complex show similar NMR spectroscopic features as those
described for the yttrium complex.
lutetium complexes with a trimethylsilylmethyl ligand.10 The
lutetium–oxygen bond distances range from 2.52(1) to 2.60(1)
Å and are slightly elongated compared to those in the related
cationic complex11 in accordance with a tighter coordination.
The puckered conformation of the coordinated crown ether
corresponds to that found in other related complexes. No
significant change in bond parameters upon coordination was
observed.6
Crystal structure
Single crystals of [Y(CH2SiMe3)3(12-crown-4)] suitable for an
X-ray diffraction study were obtained from a saturated CD2Cl2
solution at ambient temperature. Fig. 2 depicts the ORTEP
diagram of the molecular structure in the crystal. The overall
structure resembles that of a three-legged piano-stool with
12-crown-4 coordinating to yttrium in a facial manner. The
coordination geometry around the central atom can be best
described as a capped octahedron, with one of the oxygen
donors (O(3)) acting as the cap (Fig. 3). Notably, the cationic
complex [Lu(CH2SiMe3)2(12-crown-4)(thf )][BPh3(CH2SiMe3)]
shows a configuration derived from a capped trigonal prism.5
Cation formation
Previously we reported that the lutetium dialkyl cation
[Lu(CH2SiMe3)2(thf )x]ϩ in situ generated from the reaction of
the trialkyl [Lu(CH2SiMe3)3(thf )2] and triphenyl borane in thf
can be trapped by the addition of a crown ether and easily
isolated as ion pairs [Lu(CH2SiMe3)2(12-crown-4)(thf )][B(CH2-
SiMe3)Ph3].5 We found that the use of the neutral crown ether
trialkyl complexes [Ln(CH2SiMe3)3(12-crown-4)] as starting
material for the cation formation instead of the corresponding
bis(thf ) complexes is advantageous because of its enhanced
thermal stability. The trialkyl complexes [Ln(CH2SiMe3)3-
(12-crown-4)] of scandium, yttrium and lutetium smoothly
react with triethylammonium tetraphenylborate to give the
dialkyl tetraphenylborate [Ln(CH2SiMe3)2(12-crown-4)(thf )y]-
[BPh4] (y = 0 for Ln = Sc, Y; y = 1 for Ln = Lu) in high yields.
These complexes are thermally stable and insoluble in aliphatic
or aromatic hydrocarbons and highly soluble in pyridine. In
contrast to [Lu(CH2SiMe3)2(12-crown-4)(thf )][B(CH2SiMe3)-
Ph3],5 the dialkyl tetraphenylborates are only sparingly soluble
in thf.
The lutetium and yttrium complexes [Ln(CH2SiMe3)2-
(12-crown-4)(thf )y][BPh4] exhibit NMR spectroscopic features
for the cations that are essentially identical to those found for
[Ln(CH2SiMe3)2(12-crown-4)(thf )][B(CH2SiMe3)Ph3], consist-
ent with the presence of isolated ion pairs in solution. The
resonance of the methylene protons of the scandium complex
[Sc(CH2SiMe3)2(12-crown-4)][BPh4] appears at Ϫ0.21 ppm and
is slightly shifted to higher field in comparison with the analo-
gous lutetium and yttrium compounds. Similar to the values
observed for the cationic complexes of lutetium and yttrium,
the diastereotopic protons of the crown ether ligand at scan-
dium give rise to two multiplets at 3.33 and 3.65 ppm in the 1H
NMR spectrum at 25 ЊC in thf-d8. In contrast to the neutral
complex [Y(CH2SiMe3)3(12-crown-4)], the NMR spectra in
thf-d8 of the cationic alkyl [Y(CH2SiMe3)2(12-crown-4)][BPh4]
show no significant temperature dependence (Ϫ80 to 60 ЊC),
Fig. 2 ORTEP diagram of [Y(CH2SiMe3)3(12-crown-4)]. Hydrogen
atoms omitted for clarity, thermal ellipsoids drawn at 30% probability
level. Y–C(9) 2.422(7), Y–C(13) 2.399(6), Y–C(17) 2.430(6), Y–O(1)
2.600(6), Y–O(2) 2.571(7), Y–O(3) 2.626(7), Y–O(4) 2.627(6) Å; C(13)–
Y–O(1) 174.4(2), C(17)–O(4)–O(2) 90.3(2), O(4)–O(2)–C(9) 90.4(2),
O(2)–C(9)–C(17) 88.5(2), C(9)–C(17)–O(4) 90.8(2)Њ.
The yttrium–carbon bond distances range from 2.399(6) to
2.430(6) Å, comparable to those reported for other yttrium
complexes with a trimethylsilylmethyl ligand.8 The yttrium–
oxygen bond distances range from 2.571(7) to 2.627(6) Å and
correspond to values found in other related complexes.9
The analogous lutetium complex is isostructural with the
yttrium complex. Lutetium–carbon bond distances range from
2.36(1) to 2.40(1) Å, comparable to those reported for other
D a l t o n T r a n s . , 2 0 0 3 , 3 6 2 2 – 3 6 2 7
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indicating that crown ether dissociation is slow. In accordance
with these findings, in the presence of excess crown ether the
NMR spectrum in thf-d8 shows well separated signals for co-
ordinated and noncoordinated crown ether. There was also no
indication for the formation of a bis(crown ether) complex
[Y(CH2SiMe3)2(12-crown-4)2][BPh4].
In contrast to the lutetium complex, the isolated scandium
and yttrium complexes do not contain a thf ligand. For the
scandium complex, this may be due to steric factors. The iso-
lation of the yttrium complex [Y(CH2SiMe3)2(12-crown-4)]-
[BPh4] as a thf-free complex after drying in vacuo may be due to
the more labile nature of the thf, since yttrium is less Lewis
acidic/electrophilic as compared with lutetium.12 The ion pairs
presented here are not active in olefin polymerization.
36%) (Found C, 46.0; H, 10.1; Sc, 9.2. C20H49O4ScSi3 requires
C, 49.8; H, 10.2; Sc, 9.3%.). δH(thf-d8) Ϫ0.59 (3 × 2 H, br s,
ScCH2SiCH3), Ϫ0.11 (3 × 9 H, s, ScCH2SiCH3) and 3.59 (16 H,
br s, 12-crown-4); δH(CD2Cl2) Ϫ0.40 (3 × 2 H, br s, ScCH2-
SiCH3), Ϫ0.06 (3 × 9 H, s, ScCH2SiCH3) and 4.03 (16 H, br s,
12-crown-4); δC(CD2Cl2) 3.8 (ScCH2SiCH3), 40.0 (br, ScCH2-
SiCH3) and 70.0 (12-crown-4).
[Y(CH2SiMe3)3(12-crown-4)]. Anhydrous yttrium trichloride
(0.586 g, 3.00 mmol) was stirred in thf (10 mL) at 45 ЊC over-
night. After removal of thf the residue was taken up in pentane
(20 mL) and treated dropwise at Ϫ78 ЊC with a solution of
LiCH2SiMe3 (0.856 g, 9.09 mmol) in pentane (20 mL). The
resulting colourless suspension was allowed to warm to
0 ЊC and stirred at this temperature for 2 h. After filtration at
0 ЊC the clear colourless filtrate was treated with a solution of
12-crown-4 (0.529 g, 3.00 mmol) in pentane (5 mL) to form a
precipitate immediately. Decanting off the supernatant, wash-
ing the residue with pentane (10 mL) and drying in vacuo
afforded a colourless powder of [Y(CH2SiMe3)3(12-crown-4)]
(1.261 g, 80%) (Found C, 44.5; H, 9.2; Y, 17.4. C20H49O4Si3Y
requires C, 45.6; H, 9.4; Y, 16.9%.). δH(thf-d8) Ϫ0.86 (3 × 2 H,
br, YCH2SiCH3), Ϫ0.09 (3 × 9 H, s, SiMe3) and 3.67 (16 H,
br s, 12-crown-4); δH(thf-d8, Ϫ10 ЊC) Ϫ0.83 (3 × 2 H, br,
YCH2SiCH3), Ϫ0.11 (3 × 9 H, s, SiMe3), 3.61 (6 H, br s, free
12-crown-4) and 3.88, 4.04 (10 H, 2 × br s, coordinated 12-
crown-4); δH(thf-d8, Ϫ30 ЊC) Ϫ0.92 (0.5 × 3 × 2 H, br, YCH2-
SiCH3(thf )), Ϫ0.83 (3 × 2 H, br, YCH2SiCH3(12-crown-4)),
Ϫ0.11 (3 × 9 H, s, SiMe3(12-crown-4)), Ϫ0.09 (0.5 × 3 × 9 H, s,
SiMe3(thf )), 3.62 (0.5 × 16 H, br s, free 12-crown-4) and
3.93, 4.03 (16 H, 2 × br s, coordinated 12-crown-4); δH(thf-d8,
Ϫ60 ЊC) Ϫ0.94 (0.5 × 3 × 2 H, br, YCH2SiCH3(thf )), Ϫ0.87
(3 × 2 H, br, YCH2SiCH3(12-crown-4)), Ϫ0.13 (3 × 9 H, s,
SiMe3(12-crown-4)), Ϫ0.10 (0.5 × 3 × 9 H, s, SiMe3(thf )), 3.60
(0.5 × 16 H, br s, free 12-crown-4) and 3.96, 4.00 (16 H, 2 × br s,
coordinated 12-crown-4); δH(thf-d8, Ϫ80 ЊC) Ϫ0.95 (0.5 × 3 ×
2 H, br, YCH2SiCH3(thf )), Ϫ0.90 (3 × 2 H, br, YCH2SiCH3-
(12-crown-4)), Ϫ0.14 (3 × 9 H, s, SiMe3(12-crown-4)), Ϫ0.11
(0.5 × 3 × 9 H, s, SiMe3(thf )), 3.60 (0.5 × 16 H, br s, free
12-crown-4) and 3.98 (16 H, br s, coordinated 12-crown-4);
δH(CD2Cl2) Ϫ0.81 (3 × 2 H, d, J(YH) = 3.1 Hz, YCH2SiCH3),
Ϫ0.09 (3 × 9 H, s, YCH2SiCH3), and 3.74, 4.12 (2 × 8 H, 2 m,
12-crown-4); δC(thf-d8, Ϫ80 ЊC) 4.8 (YCH2SiCH3(thf )), 5.0
(YCH2SiCH3(12-crown-4)), 29.8 (d, J(YC) = 33.6 Hz, YCH2-
SiCH3(12-crown-4)), 30.9 (d, J(YC) = 34.7Hz, YCH2SiCH3-
(thf )), 69 (br, 12-crown-4); δC(CD2Cl2) 4.4 (YCH2SiCH3), 32.5
(d, J(YC) = 35.7 Hz, YCH2SiCH3) and 67.2 (12-crown-4).
Single crystals suitable for X-ray analysis were obtained from a
saturated CD2Cl2 solution at ambient temperature.
Conclusion
We have shown that tris(trimethylsilylmethyl) complexes of a
rather extensive series of rare earth elements can be isolated in a
one-pot method as their thermally robust 12-crown-4 com-
plexes [Ln(CH2SiMe3)3(12-crown-4)] starting from the rare
earth metal trichloride. This type of compounds may become
useful for further derivatizations, as could be demonstrated for
the smooth alkyl abstraction to form the dialkyl cations
[Ln(CH2SiMe3)2(12-crown-4)(thf )y]ϩ.
Experimental
General considerations
All operations were performed under an inert atmosphere
of argon using standard Schlenk-line or glovebox techniques.
Diethyl ether and thf were distilled from sodium benzophenone
ketyl. Pentane was purified by distillation from sodium/triglyme
benzophenone ketyl. Anhydrous lanthanide trichlorides
(Aldrich or Strem) were used as received. 12-crown-4 was dried
over sodium and distilled before use. All other chemicals were
commercially available and used after appropriate purification.
NMR spectra were recorded on a Bruker DRX 400 spectro-
meter at 25 ЊC (1H, 400.1 MHz; 13C, 100.6 MHz; 11B, 128.4
1
MHz) unless otherwise stated. Chemical shifts for H and 13C
NMR spectra were referenced internally using the residual sol-
vent resonances and reported relative to tetramethylsilane. 11B
NMR spectra were referenced externally to a 1 M solution of
BF3ؒEt2O in CDCl3. Elemental analyses were performed by the
Microanalytical Laboratory of this department. In many cases
the results were not satisfactory and the best values from
repeated runs were given. Moreover, the results were incon-
sistent from run to run and therefore not reproducible. We
ascribe this difficulty observed to the extreme sensitivity of the
material. Metal analysis was performed by complexometric
titration using xylenol orange as indicator.2e
[Sm(CH2SiMe3)3(12-crown-4)]. Anhydrous samarium tri-
chloride (0.770 g, 3.00 mmol) was stirred in thf (3 mL) at room
temperature for 20 min. After removal of thf, Et2O (23 mL) and
pentane (23 mL) were added. To this suspension was added
dropwise at room temperature a solution of LiCH2SiMe3 (0.806
g, 8.56 mmol) in pentane (9 mL) and the resulting yellow sus-
pension stirred for 1 h. After filtration the clear yellow filtrate
was cooled to Ϫ40 ЊC and the solvent was removed in vacuo.
The resulting oily yellow residue was extracted with pentane
(3 × 30 mL) at Ϫ30 ЊC and the extracts treated with a solu-
tion of 12-crown-4 (0.502 g, 2.85 mmol) in pentane (5 mL) at
Ϫ20 ЊC to form a precipitate immediately. Decanting off the
supernatant, washing with pentane (10 mL) and drying in vacuo
at 0 ЊC afforded a yellow powder of [Sm(CH2SiMe3)3(12-crown-
4)] (0.636 g, 38%) (Found C, 39.8; H, 8.0; Sm, 27.7. C20H49O4-
Si3Sm requires C, 40.8; H, 8.4; Sm, 25.6%.). δH(thf-d8) Ϫ0.28
(3 × 2 H, s, SmCH2SiCH3), Ϫ0.09 (3 × 9 H, s, SmCH2SiCH3)
and 3.60 (16 H, br, 12-crown-4); δC(thf-d8) 3.0 (SmCH2SiCH3)
and 70.0 (br, 12-crown-4). The signal of the methylene group
attached to samarium could not be detected.
Syntheses
[Sc(CH2SiMe3)3(12-crown-4)]. Anhydrous scandium trichlor-
ide (0.454 g, 3.00 mmol) was stirred in thf (10 mL) at 40 ЊC
overnight. After removal of thf the residue was taken up in a
mixture of thf (3 mL), pentane (23 mL) and Et2O (23 mL) and
treated dropwise at ambient temperature with a solution of
LiCH2SiMe3 (0.806 g, 8.56 mmol) in pentane (9 mL). The
resulting colourless suspension was stirred at this temperature
for 2 h. After filtration the solvent was removed from the clear
colourless filtrate at 0 ЊC in vacuo. The resulting oily yellow
residue was extracted twice with pentane (45 and 30 mL) at 0 ЊC
and the extracts treated with a solution of 12-crown-4 (0.502 g,
2.85 mmol) in pentane (5 mL) at 0 ЊC to form a precipitate
immediately. The supernatant was decanted, the product
washed with pentane (10 mL) and dried in vacuo to afford a
colourless powder of [Sc(CH2SiMe3)3(12-crown-4)] (0.499 g,
D a l t o n T r a n s . , 2 0 0 3 , 3 6 2 2 – 3 6 2 7
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[Gd(CH2SiMe3)3(12-crown-4)]. Anhydrous gadolinium tri-
chloride (0.791 g, 3.00 mmol) was stirred in thf (3 mL) at room
temperature for 15 min. Et2O (23 mL) and pentane (23 mL)
were added. To this suspension was added dropwise at 0 ЊC
a solution of LiCH2SiMe3 (0.808 g, 8.58 mmol) in pentane
(9 mL) and the reaction mixture stirred at 0 ЊC for 2.5 h. After
filtration at 0 ЊC the solvent was removed from the clear yellow
filtrate. The resulting oily yellow residue was extracted with
pentane (45 and 30 mL) at 0 ЊC and the extracts treated with a
solution of 12-crown-4 (0.500 g, 2.84 mmol) in pentane (5 mL)
at 0 ЊC to form a precipitate immediately. Decanting off the
supernatant, washing with pentane (10 mL) and drying in vacuo
at 0 ЊC afforded a colourless powder of [Gd(CH2SiMe3)3-
(12-crown-4)] (1.214 g, 72%) (Found C, 38.8; H, 6.9; Gd, 26.1.
C20H49GdO4Si3 requires C, 40.4; H, 8.3; Gd, 26.4%.).
precipitate immediately. Decanting off the supernatant, wash-
ing with pentane (10 mL) and drying in vacuo afforded a slightly
pink powder of [Er(CH2SiMe3)3(12-crown-4)] (1.050 g, 58%)
(Found C, 38.9; H, 8.0; Er, 27.4. C20H49ErO4Si3 requires C, 39.7;
H, 8.2; Er, 27.6%.).
[Tm(CH2SiMe3)3(12-crown-4)]. [Tm(CH2SiMe3)3(12-crown-
4)] was synthesized in a manner analogous to that to pre-
pare [Er(CH2SiMe3)3(12-crown-4)] from thulium trichloride
(0.826 g, 3.00 mmol), LiCH2SiMe3 (0.856 g, 9.09 mmol) and
12-crown-4 (0.529 g, 3.00 mmol) to yield 1.161 g (64%) of a
colorless powder (Found C, 39.0; H, 7.3; Tm, 28.5. C20H49-
O4Si3Tm requires C, 39.6; H, 8.1; Tm, 27.8%.).
[Yb(CH2SiMe3)3(12-crown-4)]. Anhydrous ytterbium tri-
chloride (0.838 g, 3.00 mmol) was stirred in thf (10 mL) at 45 ЊC
overnight. After evaporation of the solvent, the residue was
suspended in pentane (20 mL) and treated with a solution
of LiCH2SiMe3 (0.856 g, 9,09 mmol) in pentane (20 mL) at
Ϫ78 ЊC. The resulting brownish suspension was allowed to
warm to 0 ЊC and stirred at this temperature for 1 h and for an
additional 2 h at room temperature. After filtration at 0 ЊC the
clear red filtrate was treated with 12-crown-4 (0.529 g, 3.00
mmol) in pentane (5 mL) at 0 ЊC to form a precipitate immedi-
ately. Decanting off the supernatant, washing with pentane
(10 mL) and drying in vacuo afforded an orange powder of
[Yb(CH2SiMe3)3(12-crown-4)] (0.608 g, 33%) (Found C, 39.5;
H, 7.6; Yb, 28.0. C20H49O4Si3Yb requires C, 39.3; H, 8.1;
28.3%.). δH(thf-d8) Ϫ18.2 (16 H, br, 12-crown-4), 5.5 (33 H, br
overlap, YbCH2SiCH3).
[Tb(CH2SiMe3)3(12-crown-4)]. Anhydrous terbium trichlor-
ide (0.796 g, 3.00 mmol) was stirred in thf (2 mL) at room
temperature for 15 min. Et2O (23 mL) and pentane (23 mL)
were added. To this suspension was added dropwise at 0 ЊC
a solution of LiCH2SiMe3 (0.805 g, 8.55 mmol) in pentane
(9 mL) and the reaction mixture stirred at 0 ЊC for 1 h and at
room temperature for 45 min. After filtration at 0 ЊC the solvent
was removed from the clear yellow filtrate in vacuo. The result-
ing oily yellow residue was extracted with pentane (60 and
20 mL) at 0 ЊC and the extracts treated with a solution of
12-crown-4 (0.529 g, 3.00 mmol) in pentane (5 mL) at 0 ЊC to
form a precipitate immediately. Decanting off the supernatant,
washing with pentane (10 mL) and drying in vacuo at 0 ЊC
afforded a colourless powder of [Tb(CH2SiMe3)3(12-crown-4)]
(0.910 g, 54%) (Found C, 39.5; H, 7.6; Tb, 26.5. C20H49O4Si3Tb
requires C, 40.3; H, 8.3; 26.6%.).
[Lu(CH2SiMe3)3(12-crown-4)]. Anhydrous lutetium trichlor-
ide (0.840 g, 3.00 mmol) was stirred in thf (10 mL) at 40 ЊC for
2 h. After evaporation of the solvent, the residue was suspended
in pentane (20 mL) and treated with a solution of LiCH2SiMe3
(0.856 g, 9.09 mmol) in pentane (20 ml) at Ϫ78 ЊC. The resulting
colourless suspension was allowed to warm to 0 ЊC and stirred
at this temperature for 1 h and for additional 2 h at room tem-
perature. After filtration at 0 ЊC the clear colourless filtrate was
treated with 12-crown-4 (0.529 g, 3.00 mmol) in pentane (5 mL)
to form a precipitate immediately. Decanting off the super-
natant, washing with pentane (10 mL) and drying in vacuo
afforded a colourless powder of [Lu(CH2SiMe3)3(12-crown-4)]
(1.237 g, 68%) (Found C, 39.1; H, 7.0; Lu, 28.3. C20H49LuO4Si3
requires C, 39.2; H, 8.1; Lu, 28.6%.). δH(thf-d8) Ϫ1.12 (3 × 2 H,
s, LuCH2SiCH3), Ϫ0.09 (3 × 9 H, s, LuCH2SiCH3) and 3.61 (16
H, br, 12-crown-4); δH(CD2Cl2) Ϫ1.02 (3 × 2 H, s, LuCH2-
SiCH3), Ϫ0.08 (3 × 9 H, s, LuCH2SiCH3) and 3.74, 4.14 (2 ×
8 H, 2 m, 12-crown-4); δC(CD2Cl2) 4.4 (LuCH2SiCH3), 39.6
(LuCH2SiCH3) and 68.1 (12-crown-4). Single crystals suitable
for X-ray analysis were obtained from a saturated CH2Cl2
solution at Ϫ40 ЊC.
[Dy(CH2SiMe3)3(12-crown-4)]. Anhydrous dysprosium tri-
chloride (0.811 g, 3.02 mmol) was stirred in thf (10 mL) at 40 ЊC
overnight. After evaporation of the solvent, the residue was
suspended in a mixture of thf (3 mL), pentane (23 mL) and
Et2O (23 mL), treated with a solution of LiCH2SiMe3 (0.811 g,
8.61 mmol) in pentane (9 mL) at 0 ЊC and the colourless reac-
tion mixture stirred at this temperature for 2 h. After filtration
at 0 ЊC the solvent was removed from the clear colourless filtrate
at 0 ЊC. The resulting oily residue was extracted with pentane
(45 and 30 mL) at 0 ЊC and the extracts treated with a solution
of 12-crown-4 (0.508 g, 2.88 mmol) in pentane (5 mL) at 0 ЊC to
form a precipitate immediately. Decanting off the supernatant,
washing with pentane (2 × 10 mL) and drying in vacuo at 0 ЊC
afforded a colourless solid of [Dy(CH2SiMe3)3(12-crown-4)]
(0.169 g, 10%) (Found C, 37.1; H, 8.3; Dy, 26.9. C20H49DyO4Si3
requires C, 40.0; H, 8.2; Dy, 27.1%.).
[Ho(CH2SiMe3)3(12-crown-4)]. [Ho(CH2SiMe3)3(12-crown-
4)] was synthesized in a manner analogous to that to pre-
pare [Y(CH2SiMe3)3(12-crown-4)] from holmium trichloride
(0.814 g, 3.00 mmol), LiCH2SiMe3 (0.856 g, 9.09 mmol) and
12-crown-4 (0.529 g, 3.00 mmol) to yield 0.263 g (15%) of a
pink powder (Found C, 39.9; H, 8.1; Ho, 27.4. C20H49HoO4Si3
requires C, 39.9; H, 8.1; Ho, 27.4%.). The low yield is probably
due to the difficulty in preparing the holmium starting materials
in a reproducible way.
[Sc(CH2SiMe3)2(12-crown-4)][BPh4]. A mixture of [Sc(CH2-
SiMe3)3(12-crown-4)] (0.100 g, 0.207 mmol) and [NEt3H][BPh4]
(0.870 g, 0.207 mmol) was stirred in thf (15 mL) at Ϫ100 ЊC and
allowed to slowly warm to room temperature. After stirring for
24 h, the solvent was removed in vacuo, the crude product was
washed with Et2O (20 mL) and dried in vacuo to give colourless
microcrystals (0.125 g, 85%) (Found: C, 66.5; H, 7.9; Sc, 6.4.
C40H58BO4ScSi2 requires C, 67.2; H, 8.2; Sc, 6.3%.). δH(thf-d8)
Ϫ0.21 (2 × 2 H, s, ScCH2SiCH3), Ϫ0.09 (2 × 9 H, s, ScCH2-
SiCH3), 3.33, 3.65 (2 × 8 H, 2 m, 12-crown-4), 6.80 (4 H, t,
J(HH) = 7.3 Hz, 4-Ph), 6.94 (4 × 2 H, t, J(HH) = 7.3 Hz, 3-Ph),
7.33 (4 × 2 H, br, 2-Ph); δC(thf-d8) 3.8 (ScCH2SiCH3), 68.9
(12-crown-4), 122.4 (4-Ph), 126.1 (3-Ph), 137.1 (2-Ph) and 165.0
(q, J(BC) = 49.1 Hz, 1-Ph). The signal of the methylene group
at Sc could not be detected; δB(thf-d8) Ϫ6.7.
[Er(CH2SiMe3)3(12-crown-4)]. Anhydrous erbium trichloride
(0.822 g, 3.00 mmol) was stirred in thf (10 mL) at 45 ЊC over-
night. After evaporation of the solvent the residue was sus-
pended in pentane (20 mL) and treated with a solution of
LiCH2SiMe3 (0.856 g, 9,09 mmol) in pentane (20 mL) at
Ϫ78 ЊC. The resulting colourless suspension was allowed to
warm to 0 ЊC and stirred at this temperature for 1 h and for
additional 3 h at room temperature. After filtration at 0 ЊC the
clear pink solution was treated with a solution of 12-crown-4
(0.529 g, 3.00 mmol) in pentane (5 mL) at 0 ЊC to form a
[Y(CH2SiMe3)2(12-crown-4)][BPh4]. A mixture of [Y(CH2-
SiMe3)3(thf )2] (0.300 g, 0.606 mmol), [NEt3H][BPh4] (0.256 g,
D a l t o n T r a n s . , 2 0 0 3 , 3 6 2 2 – 3 6 2 7
3625

View Article Online
(c) J. N. Christopher, L. R. Squire, J. A. M. Canich and T. D. Shaffer,
WO 2000018808; J. N. Christopher, L. R. Squire, J. A. M. Canich
and T. D. Shaffer, Chem. Abstr., 2000, 132, 265592; (d ) S. Bambirra,
D. van Leusen, A. Meetsma, B. Hessen and J. H. Teuben, Chem.
Commun., 2001, 637; (e) P. G. Hayes, W. E. Piers and R. McDonald,
J. Am. Chem. Soc., 2002, 124, 2132; ( f ) S. Bambirra, D. van Leusen,
A. Meetsma, B. Hessen and J. H. Teuben, Chem. Commun., 2003,
522.
2 (a) L. Lee, D. J. Berg, F. W. Einstein and R. J. Batchelor,
Organometallics, 1997, 16, 1819; (b) L. W. M. Lee, W. E. Piers,
M. R. J. Elsegood, W. Clegg and M. Parvez, Organometallics, 1999,
18, 2947; (c) W. E. Piers and D. J. H. Emslie, Coord. Chem. Rev.,
2002, 233, 131; (d ) P. G. Hayes, G. C. Welch, D. J. H. Emslie, C. L.
Noack, W. E. Piers and M. Parvez, Organometallics, 2003, 22, 1577;
(e) S. Arndt, T. P. Spaniol and J. Okuda, Organometallics, 2003, 22,
775.
3 (a) M. F. Lappert and R. Pearce, J. Chem. Soc., Chem. Commun.,
1973, 126; (b) for the crystal structure of the tris(thf ) adduct, see:
W. J. Evans, J. C. Brady and J. W. Ziller, J. Am. Chem. Soc.,
2001, 123, 7711; (c) J. L. Atwood, W. E. Hunter, R. D. Rogers,
J. Holton, J. McMeeking, R. Pearce and M. F. Lappert, J. Chem.
Soc., Chem. Commun., 1978, 140; (d ) H. Schumann and J. Müller,
J. Organomet. Chem., 1978, 146, C5; (e) H. Schumann and
J. Müller, J. Organomet. Chem., 1979, 169, C1; ( f ) M. Niemeyer,
Acta Crystallogr. Sect. E, 2001, E57, 553; (g) H. Schumann, D. M.
M. Freckmann and S. Dechert, Z. Anorg. Allg. Chem., 2002, 628,
2422.
0.606 mmol) and 12-crown-4 (0.096 mL, 0.606 mmol) was
stirred in thf (50 mL) at Ϫ78 ЊC and allowed to slowly warm to
room temperature. After stirring for 24 h, a colourless byprod-
uct was removed by filtration. All volatiles were removed from
the filtrate in vacuo, the crude product was washed with Et2O
(20 mL) and dried in vacuo to give colourless microcrystals
(0.402 g, 87%) (Found: C, 63.4; H, 7.9; Y, 11.6. C40H58BO4Si2Y
requires C, 63.3; H, 7.7; Y, 11.8%.). δH(thf-d8) Ϫ0.89 (2 × 2 H, d,
J(YH) = 2.9 Hz, YCH2SiCH3), Ϫ0.10 (2 × 9 H, s, YCH2SiCH3),
3.37, 3.61 (2 × 8 H, 2 m, 12-crown-4), 6.82 (4 H, t, J(HH) = 7.2
Hz, 4-Ph), 6.96 (4 × 2 H, t, J(HH) = 7.2 Hz, 3-Ph) and 7.35 (4 ×
2 H, br, 2-Ph); δC(thf-d8) 4.5 (YCH2SiCH3), 34.4 (d, J(YC) =
40.5 Hz, YCH2SiCH3), 68.5 (12-crown-4), 122.4 (4-Ph), 126.2
(3-Ph), 137.1 (2-Ph) and 165.0 (q, J(BC) = 49.3 Hz, 1-Ph);
δB(thf-d8) Ϫ6.7.
[Lu(CH2SiMe3)2(12-crown-4)(thf)][BPh4].
A
mixture of
[Lu(CH2SiMe3)3(12-crown-4)] (0.100 g, 0.163 mmol) and
[NEt3H][BPh4] (0.069 g, 0.163 mmol) was stirred in thf (10 mL)
at Ϫ100 ЊC and allowed to slowly warm to room temperature.
After stirring for 48 h, a colourless byproduct was removed by
filtration. All volatiles were removed from the filtrate in vacuo to
give colourless microcrystals (0.102 g, 70%) (Found: C, 57.1; H,
7.3; Lu, 19.2. C44H66BLuO5Si2 requires C, 57.6; H, 7.3; Lu,
19.1%.). δH(CD2Cl2) Ϫ1.11 (2 × 2 H, s, LuCH2SiCH3), Ϫ0.12
(2 × 9 H, s, LuCH2SiCH3), 2.02 (4 H, m, β-CH2, thf ), 3.29, 3.67
(2 × 8 H, m, 12-crown-4), 4.04 (4 H, m, α-CH2, thf ), 6.92 (4 H,
t, J(HH) = 7.3 Hz, 4-Ph), 7.06 (4 × 2 H, t, J(HH) = 7.3 Hz, 3-Ph)
and 7.37 (4 × 2 H, br, 2-Ph); δH(thf-d8) Ϫ1.12 (2 × 2 H, s,
LuCH2SiCH3), Ϫ0.10 (2 × 9 H, s, LuCH2SiCH3), 1.76 (4 H, m,
β-CH2, thf ), 3.36 (8 H, 2 m, 12-crown-4), 3.62 (4 ϩ 8 H, m,
α-CH2, thf and 12-crown-4), 6.82 (4 H, t, J(HH) = 7.0 Hz,
4-Ph), 6.95 (4 × 2 H, t, J(HH) = 7.3 Hz, 3-Ph) and 7.34 (4 × 2 H,
br, 2-Ph); δC(thf-d8) 4.4 (LuCH2SiCH3), 38.5 (LuCH2SiCH3),
71.4 (12-crown-4), 122.4 (4-Ph), 126.2 (3-Ph), 137.1 (2-Ph) and
165.0 (q, J(BC) = 49.1 Hz, 1-Ph). δB(thf-d8) Ϫ6.7.
4 F. T. Edelmann, D. M. M. Freckmann and H. Schumann, Chem.
Rev., 2002, 102, 1851.
5 S. Arndt, T. P. Spaniol and J. Okuda, Chem. Commun., 2002,
896.
6 R. D. Rogers and C. B. Bauer, in Comprehensive Supra-
molecular Chemistry, ed. G. W. Gokel, Pergamon, Oxford, 1996,
vol. 1.
7 For redox potentials of Eu3ϩ/Eu2ϩ in both aqueous and organic
solutions, see: (a) L. J. Nugent, R. D. Baybarz, J. L. Burnett and
J. L. Ryan, J. Phys. Chem., 1973, 77, 1528; (b) I. Marolleau,
J.-P. Gisselbrecht, M. Gross, F. Arnaud-Neu and M.-J. Schwing-
Weill, J. Chem. Soc., Dalton Trans., 1989, 367; (c) I. Marolleau,
J.-P. Gisselbrecht, M. Gross, F. Arnaud-Neu and M.-J. Schwing-
Weill, J. Chem. Soc., Dalton Trans., 1990, 1285; (d ) K. Mikami,
M. Terada and H. Matsuzawa, Angew. Chem., 2002, 114, 3704;
K. Mikami, M. Terada and H. Matsuzawa, Angew. Chem., Int. Ed.,
2002, 41, 3554.
Crystal structure analysis
8 (a) [{YCp2(CH2SiMe3)2}2Li2(dme)2(C4H8O2)]: Y–C
= 2.402(6),
2.445(6) Å, see: W. J. Evans, R. Dominguez, K. R. Levan and
R. J. Doedens, Organometallics, 1985, 4, 1836; (b) (Me3SiCH2)-
Y[(µ-CH2)2SiMe2][(µ-OCMe3)Li(thf )2]2: Y–C = 2.450(8) Å, see:
W. J. Evans, T. J. Boyle and J. W. Ziller, J. Organomet. Chem., 1993,
462, 141; (c) {(Me3SiCH2)x(Me3CO)1ϪxY(µ-OCMe3)4[Li(thf )]4-
(µ4-Cl)}ϩ [Y(CH2SiMe3)4]Ϫ: Y–C = 2.382(8)–2.420(9) Å, see: W. J.
Evans, J. L. Shreeve, R. N. R. Broomhall-Dillard and J. W. Ziller,
J. Organomet. Chem., 1995, 501, 7; (d ) [Y(DAC)(CH2SiMe3)]:
Y–C = 2.45(2) Å, see: L. Lee, D. J. Berg and G. W. Bushnell,
Crystallographic data for [Y(CH2SiMe3)3(12-crown-4)]: C20H49-
O4Si3Y, 526.77 g molϪ1, monoclinic, a = 9.771(1) Å, b =
16.2169(8) Å, c = 19.137(1) Å, β = 98.057(7)Њ, U = 3002.4(4) Å3,
P21/n (non-standard setting of P21/c, no. 14), Z = 4, T = 293(2)
K, µ(MoKα) = 2.081 mmϪ1; 12264 data, 7122 unique; structure
solution by direct methods and difference Fourier syntheses;
refinement converged with R = 0.081, Rw = 0.137 [I > 2σ(I )].
CCDC reference number 211480.
t
Organometallics, 1995, 14, 8; (e) [(Me3SiCH2)2Y(OC6H3 Bu2-
Crystallographic data for [Lu(CH2SiMe3)3(12-crown-4)]:
C20H49LuO4Si3, 612.83 g molϪ1, monoclinic, a = 9.753(4) Å, b =
16.163(2) Å, c = 19.119(3) Å, β = 99.24(2)Њ, U = 2975(1) Å3, P21/
n (non-standard setting of P21/c, no. 14), Z = 4, T = 293(2) K,
µ(MoKα) = 3.458 mmϪ1; 8027 data, 7596 unique; structure
solution by isotypic replacement using the coordinates of the
yttrium complex; the refinement converged with R = 0.082, Rw =
0.174 [I > 2σ(I )].
2,6)(thf )2]: Y–C = 2.411(13), 2.427(16) Å, see: W. J. Evans, R. N. R.
Broomhall-Dillard and J. W. Ziller, Organometallics, 1996, 15, 1351;
( f ) [trans-Y(MAC)(CH2SiMe3)2]: Y–C = 2.461(4) Å, see: L. Lee,
D. J. Berg, F. W. Einstein and R. J. Batchelor, Organometallics, 1997,
t
16, 1819; (g) {(Me3SiCH2)2Y(OC6H3 Bu2-2,6)2}{[(thf )3Li]2Cl}: Y–C
= 2.404(8), 2.420(8) Å, see: W. J. Evans and R. N. R. Broomhall-
t
Dillard, J. Organomet. Chem., 1998, 569, 89; (h) [Y{(C5H3 Bu)2Si
Me2}(CH2SiMe3)(thf )]: Y–C = 2.399(2) Å, see: G. A. Molander,
E. D. Dowdy and B. C. Noll, Organometallics, 1998, 17,
3754; (i) [O(CH2CH2C9H6)2]Y(CH2SiMe3): Y–C = 2.376(8) Å, see:
C. Qian, G. Zou and J. Sun, J. Chem. Soc., Dalton Trans., 1999, 519;
CCDC reference number 211481.
See http://www.rsc.org/suppdata/dt/b3/b305964b/ for crystal-
lographic data in CIF or other electronic format.
(j) [Y(η5:η1-C5Me4SiMe2NCMe2Et)(CH2SiMe3)(thf )]: Y–C
=
2.388(7) Å, see: K. C. Hultzsch, P. Voth, K. Beckerle, T. P. Spaniol
and J. Okuda, Organometallics, 2000, 19, 228; (k) [Y(CH2-
SiMe3)3(thf )3]: Y–C = 2.427(19) Å, see ref. 3(b); (l ) [Y{N,NЈ-iPr2-
tacn-NЉ-(CH2)2NtBu)}(CH2SiMe3)2]: Y–C = 2.421(7), 2.476(5) Å,
see ref. 1(d).
Acknowledgements
We thank the Deutsche Forschungsgemeinschaft and the Fonds
der Chemischen Industrie for generous financial support. M. H.
was a fellow of the International Max Planck Research School
for Polymer Science.
9 [Y(OH2)5(12-crown-4)]Cl3ؒ2 H2O: Y–O(12-crown-4)
= 2.42(1)–
2.59(1) Å, see: R. D. Rogers, A. N. Rollins and M. M. Benning,
Inorg. Chem., 1988, 27, 3826.
10 [LuCp2(CH2SiMe3)(thf )]: Lu–C
= 2.376(16) Å, see: (a) H.
Schumann, W. Genthe and N. Bruncks, Angew. Chem., 1981, 93,
126; H. Schumann, W. Genthe and N. Bruncks, Angew. Chem., Int.
Ed., 1981, 20, 129; H. Schumann, W. Genthe, N. Bruncks and
J. Pickardt, Organometallics, 1982, 1, 1194; (b) [Li(thf )3]Lu(η5-
C5Me5)(CH2SiMe3){CH(SiMe3)2}Cl: Lu–C = 2.314(18), 2.344(18) Å
(two crystallographically independent molecules), see: H. van der
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D a l t o n T r a n s . , 2 0 0 3 , 3 6 2 2 – 3 6 2 7
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2,6)Lu(µ-Cl)(CH2SiMe3)]2: Lu–C = 2.39(3) Å, see: M. P. Hogerheide,
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Å, see ref. 3(g); ( f ) [Lu(CH2SiMe3)2(12-crown-4)(thf )][B(CH2-
SiMe3)Ph3]: Lu–C = 2.340(2), 2.354(2) Å, see ref. 5.
11 [Lu(CH2SiMe3)2(12-crown-4)(thf )][B(CH2SiMe3)Ph3]:
crown-4) = 2.438(1)–2.503(1) Å, see ref. 5.
Lu–O(12-
12 Relative Lewis acidities of lanthanide compounds were determined
by tandem mass spectrometry, see: H. Tsuruta, K. Yamaguchi and
T. Imamoto, Chem. Commun., 1999, 1703.
t
SiCH2)2Lu(OC6H3 Bu2-2,6)2][Li(thf )4](thf )2: Lu–C = 2.29(2), 2.42(3)
Å, see ref. 8(g); (e) [Lu(CH2SiMe3)3(thf )2]: Lu–C = 2.346(3)–2.380(3)
D a l t o n T r a n s . , 2 0 0 3 , 3 6 2 2 – 3 6 2 7
3627