Neutral and cationic rare-earth metal alkyl complexes that contain bis(2-methoxyethyl)(trimethylsilyl)amine, a neutral [ONO]-type ligand

Article abstract of DOI:10.1016/j.ica.2006.04.018

Neutral tris(trimethylsilylmethyl) complexes [Ln(CH₂SiMe₃)₃(L)] (Ln = Sc (1), Lu (2)) and cationic bis(trimethylsilylmethyl) complexes [Ln(CH₂SiMe₃)₂(L)(THF)]⁺[BPh₄]^-, (Ln = Sc (3), Lu (4)) that contain bis(2-methoxyethyl)(trimethylsilyl)amine (L = Me₃SiN(CH₂CH₂OMe)₂) as a neutral, tridentate ligand were synthesized and characterized by NMR spectroscopy. X-ray structural analysis was performed for the scandium complex 1 and exhibited a distorted octahedral coordination geometry with a facially arranged ligand at the neutral scandium center. NMR spectroscopy corroborated the coordination of the tertiary amine function of the ligand to the metal. Complexes 3 and 4 expand the still limited range of cationic rare-earth metal alkyl complexes with known neutral, multidentate ligands.

Full text of DOI:10.1016/j.ica.2006.04.018

Inorganica Chimica Acta 359 (2006) 4769–4773
www.elsevier.com/locate/ica
Neutral and cationic rare-earth metal alkyl complexes that contain
bis(2-methoxyethyl)(trimethylsilyl)amine, a neutral [ONO]-type ligand
*
Peter M. Zeimentz, Thomas P. Spaniol, Jun Okuda
Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, D-52074 Aachen, Germany
Received 13 March 2006; accepted 10 April 2006
Available online 22 April 2006
Dedicated to Professor Dr. Dr. h.c. mult. Wolfgang A. Herrmann.
Abstract
Neutral tris(trimethylsilylmethyl) complexes [Ln(CH2SiMe3)3(L)] (Ln = Sc (1), Lu (2)) and cationic bis(trimethylsilylmethyl) complexes
[Ln(CH2SiMe3)2(L)(THF)]+[BPh4]À, (Ln = Sc (3), Lu (4)) that contain bis(2-methoxyethyl)(trimethylsilyl)amine (L = Me3SiN(CH2-
CH2OMe)2) as a neutral, tridentate ligand were synthesized and characterized by NMR spectroscopy. X-ray structural analysis was
performed for the scandium complex 1 and exhibited a distorted octahedral coordination geometry with a facially arranged ligand at
the neutral scandium center. NMR spectroscopy corroborated the coordination of the tertiary amine function of the ligand to the metal.
Complexes 3 and 4 expand the still limited range of cationic rare-earth metal alkyl complexes with known neutral, multidentate ligands.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Scandium; Lutetium; Rare-earth metals; Cations; Coordination chemistry
1. Introduction
[7]. Here we report the use of bis(2-methoxyethyl)(trimeth-
ylsilyl)amine (L = Me3SiN(CH2CH2OMe)2) as a neutral,
chelating ligand to coordinate neutral and cationic scan-
dium and lutetium alkyl complexes and their characteriza-
tion by NMR spectroscopy and X-ray crystallography.
In contrast to the numerous neutral and anionic com-
plexes, only recently have cationic rare-earth organometal-
lic complexes been described [1]. The increased attention to
these cationic complexes is caused by the growing interest
in the development of more active catalysts for olefin poly-
merization [2]. In particular, a number of post-metallocene
alkyl complexes of the rare-earth metals have been
described [3]. The majority of these complexes incorporate
mono- and dianionic ligands. Examples of neutral, multi-
dentate ligands for the coordination of cationic rare-earth
metal alkyl complexes include 1,4,7-trimethyl-1,4,7-triaza-
cyclononane [4], tris(3,5-dimethylpyrazolyl)methane [4b],
1,1,1-tri{2-[(S)-4-isopropyl]oxazolyl}ethane [5] and 1,4,
7-trithiacyclononane [6]. We have recently succeeded in
utilizing crown ethers to isolate and structurally fully char-
acterize an extensive series of rare earth metal alkyl cations
2. Experimental
2.1. General considerations
All operations were performed under an inert atmosphere
of argon using standard Schlenk-line or glovebox techni-
ques. Anhydrous lanthanoid trichlorides (Aldrich or Strem)
were used as received. [Ln(CH2SiMe3)2(THF)3]+[BPh4]À
complexes [7c] and bis(2-methoxyethyl)(trimethylsilyl)-
amine [8] were synthesized according to the literature proce-
dures. Solvents and all other chemicals were commercially
available and used after appropriate purification. NMR
spectra were recorded on a Varian Unity 500 spectrometer
(1H, 499.6 MHz; 13C, 125.6 MHz; 11B, 160.3 MHz) at
*
Corresponding author. Tel.: +49 241 8094645; fax: +49 241 8092644.
1
25 ꢁC. Chemical shifts for H and 13C NMR spectra were
E-mail address: jun.okuda@ac.rwth-aachen.de (J. Okuda).
0020-1693/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.04.018

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P.M. Zeimentz et al. / Inorganica Chimica Acta 359 (2006) 4769–4773
referenced internally using the residual solvent resonances
and reported relative to tetramethylsilane, 11B NMR spectra
were referenced externally to a 1 M solution of NaBH4 in
D2O. Elemental analyses were performed by the Microana-
lytical Laboratory of the Johannes Gutenberg-Universita¨t
Mainz, Germany. In many cases the results were not satis-
factory and the best values from repeated runs were given.
Moreover the results were inconsistent from run to run
and therefore not reproducible. We ascribe this difficulty
observed also by other workers to the extreme sensitivity
of the material [9]. Metal analysis was performed by
complexometric titration using xylenol orange as indicator
[10].
methoxyethyl)(trimethylsilyl)amine (616 mg, 3.00 mmol) in
pentane (5 mL) at 0 ꢁC. After stirring for 2 h at this tem-
perature and filtering, the solvent was evaporated in vacuo.
Washing the oily residue with hexamethyldisiloxane (5 mL)
and drying in vacuo afforded a colorless powder of 2
1
(971 mg, 50%). H NMR (C6D5CD3): d = À0.79 (6H, s,
LuCH2SiCH3), 0.08 (9H, s, NSiCH3), 0.36 (27H, s, LuCH2-
3
SiCH3), 2.18 (4H, br, NCH2CH2O), 3.00 (4H, t, JHH
=
5.5 Hz, NCH2CH2O), 3.25 (6H, s, OCH3). 13C{1H} NMR
(C6D5CD3): d = À1.2 (NSiCH3), 5.1 (LuCH2SiCH3), 42.2
(LuCH2SiCH3), 46.0 (NCH2CH2O), 61.4 (OCH3), 72.1
(NCH2CH2O). Anal. Calc. for C21H56LuNO2Si4: C, 39.29;
H, 8.79; N, 2.18; Lu, 27.25. Found: C, 35.27; H, 8.68; N,
2.63; Lu, 27.19%.
2.2. Syntheses
2.2.3. Synthesis of [Sc(CH2SiMe3)2{(MeOCH2CH2)2N-
SiMe3} (THF)]+[BPh4]À (3)
2.2.1. Synthesis of [Sc(CH2SiMe3)3{(MeOCH2CH2)2N-
SiMe3}] (1)
A solution of bis(2-methoxyethyl)(trimethylsilyl)amine
(103 mg, 0.500 mmol) in THF (5 mL) was added dropwise
to a solution of [Sc(CH2SiMe3)2(THF)3]+[BPh4]À (377 mg,
0.500 mmol) in THF (15 mL) at 0 ꢁC. After stirring at this
temperature for 30 min, all volatiles were evaporated.
Washing with pentane (10 mL) and drying in vacuo at
Anhydrous scandium trichloride (454 mg, 3.00 mmol)
was stirred in THF (3 mL) at ambient temperature over-
night. After addition of pentane (23 mL) and diethyl ether
(23 mL), the suspension was treated dropwise at ambient
temperature with a solution of LiCH2SiMe3 (806 mg,
8.56 mmol) in pentane (9 mL). The resulting colorless sus-
pension was stirred at this temperature for 2 h. After filtra-
tion, the solvent was removed from the clear colorless
filtrate at 0 ꢁC in vacuo. The resulting oily yellow residue
was extracted with pentane (2 · 40 mL) at 0 ꢁC and the
1
0 ꢁC afforded a colorless powder of 3 (331 mg, 81%). H
NMR (THF-d8): d = À0.22 (4H, s, ScCH2SiCH3), À0.05
(18H, s, ScCH2SiCH3), 0.03 (9H, s, NSiCH3), 2.90 (4H, t,
3JHH = 6.1 Hz, NCH2CH2O), 3.24 (6H, s, OCH3), 3.26
3
(4H, t, JHH = 6.1 Hz, NCH2CH2O), 6.73 (4H, t,
3
extracts treated with
a
solution of bis(2-methoxy-
3JHH = 7.2 Hz, Ph-4), 6.87 (8H, t, JHH = 7.2 Hz, Ph-3),
ethyl)(trimethylsilyl)amine (585 mg, 2.85 mmol) in pentane
(5 mL) at 0 ꢁC. After stirring for 2 h at this temperature
and filtering, the solvent was evaporated in vacuo. Washing
the oily residue with hexamethyldisiloxane (5 mL) and dry-
ing in vacuo afforded a colourless powder of 1 (597 mg,
36%). Single crystals suitable for X-ray analysis were
7.27 (8H, br, Ph-2). 13C{1H} NMR (THF-d8): d = 0.3
(ScCH2SiCH3), 3.5 (NSiCH3), 45.0 (br, ScCH2SiCH3),
47.9 (NCH2CH2O), 58.5 (OCH3), 73.6 (NCH2CH2O),
121.6 (Ph-4), 125.5 (Ph-3), 136.8 (Ph-2), 164.8 (q,
1JBC = 49.4 Hz, Ph-1). 11B{1H} NMR (THF-d8):
d = À6.6. Anal. Calc. for C45H73BNO3ScSi3: C, 66.23; H,
9.02; N, 1.72; Sc, 5.51. Found: C, 66.37; H, 9.22; N, 1.69;
Sc, 5.56%.
1
obtained from a saturated toluene solution at À30 ꢁC. H
NMR (C6D5CD3): d = À0.04 (6H, s, ScCH2SiCH3), 0.08
(9H, s, NSiCH3), 0.35 (27H, s, ScCH2SiCH3), 2.42 (4H, t,
3
3JHH = 5.8 Hz, NCH2CH2O), 3.08 (4H, t, JHH = 5.8 Hz,
2.2.4. Synthesis of [Lu(CH2SiMe3)2{(MeOCH2CH2)2N-
SiMe3} (THF)]+[BPh4]À (4)
NCH2CH2O), 3.22 (6H, s, OCH3). 13C{1H} NMR
(C6D5CD3): d = À0.7 (NSiCH3), 4.5 (ScCH2SiCH3), 42.4
(br, ScCH2SiCH3), 46.5 (NCH2CH2O), 60.6 (OCH3), 72.6
(NCH2CH2O). Anal. Calc. for C21H56NO2ScSi4: C, 49.27;
H, 11.02; N, 2.74; Sc, 8.78. Found: C, 45.68; H, 12.47; N,
3.86; Sc, 8.78%.
A solution of bis(2-methoxyethyl)(trimethylsilyl)amine
(103 mg, 0.500 mmol) in THF (5 mL) was added dropwise
to a solution of [Lu(CH2SiMe3)2(THF)3]+[BPh4]À (443 mg,
0.500 mmol) in THF (15 mL) at 0 ꢁC. After stirring at this
temperature for 30 min all, volatiles were evaporated.
Washing with pentane (10 mL) and drying in vacuo at
1
2.2.2. Synthesis of [Lu(CH2SiMe3)3{(MeOCH2CH2)2N-
SiMe3}] (2)
0 ꢁC afforded a colorless powder of 4 (354 mg, 75%). H
NMR (THF-d8): d = À1.01 (4H, s, LuCH2SiCH3), À0.05
Anhydrous lutetium trichloride (840 mg, 3.00 mmol)
was stirred in THF (10 mL) at 40 ꢁC overnight. After evap-
oration of the solvent, the residue was suspended in pen-
tane (20 mL) and treated with a solution of LiCH2SiMe3
(856 mg, 9.09 mmol) in pentane (20 mL) at À78 ꢁC. The
resulting colorless suspension was allowed to warm to
0 ꢁC and stirred at this temperature for 1 h and for an addi-
tional 2 h at room temperature. After filtration at 0 ꢁC, the
clear colorless filtrate was treated with a solution of bis(2-
(18H, s, LuCH2SiCH3), 0.03 (9H, s, NSiCH3), 2.91 (4H,
3
t, JHH = 6.1 Hz, NCH2CH2O), 3.24 (6H, s, OCH3), 3.28
3
(4H, t, JHH = 6.1 Hz, NCH2CH2O), 6.73 (4H, t,
3
3JHH = 7.2 Hz, Ph-4), 6.87 (8H, t, JHH = 7.2 Hz, Ph-3),
7.28 (8H, br, Ph-2). 13C{1H} NMR (THF-d8): d = À0.1
(LuCH2SiCH3), 4.1 (NSiCH3), 39.8 (LuCH2SiCH3), 47.9
(NCH2CH2O), 58.5 (OCH3), 73.7 (NCH2CH2O), 121.7
(Ph-4), 125.5 (Ph-3), 136.8 (Ph-2), 164.8 (q, 1JBC = 49.4 Hz,
Ph-1). 11B{1H} NMR (THF-d8): d = À6.6. Anal. Calc. for

P.M. Zeimentz et al. / Inorganica Chimica Acta 359 (2006) 4769–4773
4771
SiMe3
SiMe3
N
+
N
O
O
O
O
Ln
[Ln(CH2SiMe3)3(THF)2]
SiMe3
toluene
Me3Si
Me3Si
Ln = Sc (1), Lu (2)
SiMe3
SiMe3
N
+
N
O
Ln
O
O
O
[BPh4]
[Ln(CH2SiMe3)2(THF)3]+[BPh4]-
O
THF
Me3Si
Me3Si
Ln = Sc (3), Lu (4)
Scheme 1. Synthesis of the neutral and cationic complexes.
C45H73BLuNO3Si3: C, 57.13; H, 7.78; Lu, 18.49; N, 1.48.
Found: C, 55.80; H, 7.68; Lu, 18.38; N, 1.49%.
The cationic complexes [Ln(CH2SiMe3)2(L)(THF)]+[BPh4]À
(Ln = Sc (3), Lu (4)) were obtained in good yield starting
from the cationic bis(alkyl) complexes [Ln(CH2SiMe3)2-
(THF)3]+[BPh4]À [7c] via exchange of THF by bis(2-meth-
oxyethyl)(trimethylsilyl)amine (Scheme 1). Although the
THF ligands in the cationic complexes are deemed to be less
labile than in the neutral complexes [7], exchange of THF
against L is smooth owing to the chelate effect.
2.3. X-ray investigation
2.3.1. Crystal data for 1
C21H56NO2ScSi4, M = 511.99, crystal dimensions
0.73 · 0.36 · 0.12 mm, space group P21/n, a = 9.7075
˚
˚
˚
(9) A, b = 15.661(2) A, c = 21.467(2) A, b = 102.991(4)ꢁ,
Single crystals of 1 suitable for crystallography were
obtained from a saturated toluene solution at À30 ꢁC.
Fig. 1 depicts the ORTEP diagram of the molecular struc-
ture of 1 in the solid state. The structure shows a distorted
octahedral coordination geometry around the metal center
with the ligand L coordinating to the scandium center in a
facial manner. The Sc–O bond distances of 2.308(2) and
3
3
˚
U = 3180.1(6) A , Z = 4, Dc = 1.069 g/cm , l (Mo Ka) =
0.398 mmÀ1, T = 120(2) K, h range 1.62–26.09ꢁ, number
of reflections 29134, number of unique reflections 6276,
number of parameters 276, R1 = 0.0529, wR2 = 0.1310
(I > 2r(I)), R1 = 0.0845, wR2 = 0.1498 (all data). Experi-
mental data were collected on a Bruker AXS diffractometer
with graphite monochromated Mo Ka radiation using /
and x scans. The data collection as well as the data reduction
and correction for absorption were carried out using the
program system SMART [11]. The structure was solved by
direct methods using SHELXS-86 [12] and refined with aniso-
tropic displacement parameters for all non-hydrogen atoms
by full-matrix least-squares based on F2 using SHELXL-97
[13]. Hydrogen atoms were included into calculated posi-
tions with isotropic displacement parameters and were
allowed to ride on the carbon atoms. For the graphical
representation, ORTEP-III for Windows was used as imple-
mented in the program system WINGX [14].
˚
2.341(2) A correspond to values found in other organome-
tallic scandium complexes with ether ligands,1 whereas the
˚
Sc–N bond length of 2.584(2) A is slightly longer than those
in other organometallic scandium complexes with a tertiary
amine ligand.2 This may be due to the reduced basicity of
the silylamine donor. In the only other crystallographically
characterized scandium complex with a silylamine donor
([Sc{N(SiMe3)(CH2CH2NSiMe3)2}Cl(THF)]), the donor
group is incorporated in a dianionic ligand, thus leading
˚
to a shorter Sc–N bond distance of 2.456(2) A for the silyl-
amine [16i]. The Sc–C bond lengths between 2.237(3) and
˚
2.270(3) A are in the range of those reported for other
scandium complexes with a trimethylsilylmethyl ligand.3
3. Results and discussion
1
˚
Sc–O(ether) separations between 2.098(15) and 2.423(3) A have been
The reaction of the neutral, in situ generated tris(alkyl)
complexes [Ln(CH2SiMe3)3(THF)2] [15] with bis(2-meth-
oxyethyl)(trimethylsilyl)amine L (L = Me3SiN(CH2CH2O-
Me)2) in toluene afforded the neutral complexes [Ln-
(CH2SiMe3)3(L)] (Ln = Sc (1), Lu (2)) in moderate yield.
reported, see Ref. [7c,16a–16o].
2
˚
Sc–N(tertiary amine) separations between 2.223(3) and 2.564(4) A
have been reported, see Ref. [16i,17a–17f].
3
˚
Sc–C(CH2SiMe3) separations between 2.166(2) and 2.295(3) A have
been reported, see Ref. [5,7c,16c,16g,16i–16o,17d,17e,18].

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4. Conclusions
We have shown that bis(2-methoxyethyl)(trimethylsi-
lyl)amine can be used as a neutral, tridentate [ONO]-type
ligand suitable for the coordination of neutral tris(tri-
methylsilylmethyl) and cationic bis(trimethylsilylmethyl)
complexes of the smallest rare earth metals, scandium
and lutetium.
Acknowledgements
Financial support by the Deutsche Forschungsgemein-
schaft and the Fonds der Chemischen Industrie is gratefully
acknowledged. We thank Prof. Dr. U. Englert for recording
the crystallographic data.
Appendix A. Supplementary material
CCDC-601302 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Cen-
tre via www.ccdc.cam.ac.uk/data_request/cif. Supplemen-
tary data associated with this article can be found, in the
online version, at doi:10.1016/j.ica.2006.04.018.
Fig. 1. Molecular Structure of compound 1 with the atomic numbering
scheme. Hydrogen atoms are omitted for clarity. Thermal ellipsoids are
˚
drawn at 30% probability. Selected bond distances (A) and angles (ꢁ): Sc–
C1 2.237(3), Sc–C5 2.270(3), Sc–C9 2.250(3), Sc–O1 2.308(2), Sc–O2
2.341(2), Sc–N 2.584(2); and C1–Sc–N 158.53(10), C5–Sc–O1 161.49(9),
C9–Sc–O2 164.28(10), C1–Sc–C5 98.72(11), C1–Sc–O1 92.96(9), O1–Sc–
O2 79.83(8).
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