Synthesis and structural characterization of a series of lanthanide(II) amides: Steric effect of amido ligand

Article abstract of DOI:10.1021/ic070162x

The synthesis and structures of a series of lanthanide(II) and lanthanide(III) complexes supported by the amido ligand N(SiMe₃)Ar were described. Several lanthanide(III) amide chlorides were synthesized by a metathesis reaction of LnCl₃ with lithium amide, including {[(C ₆H₅)(Me₃Si)N]₂YbCl(THF)} ₂·PhCH₃ (1), [(C₆H₃- ⁱPr₂-2,6)(SiMe₃)N]₂YbCl(μ-Cl) Li(THF)₃·PhCH₃ (4), [(C₆H ₃-ⁱPr₂-2,6)(SiMe₃)N]YbCl ₂(THF)₃ (6), and [(C₆H₃- ⁱPr₂-2,6)(SiMe₃)N]₂SmCl ₃Li₂(THF)₄ (7). The reduction reaction of 1 with Na-K alloy afforded bisamide ytterbium(II) complex [(C₆H ₅)(Me₃Si)N]₂Yb(DME)₂ (2). The same reaction for Sm gave an insoluble black powder. An analogous samarium(II) complex [(C₆H₅)(Me₃Si)N]₂Sm(DME) ₂ (3) was prepared by the metathesis reaction of SmI₂ with NaN(C₆H₅)(SiMe₃). The reduction reaction of ytterbium chloride 4 with Na-K alloy afforded monoamide chloride {[(C ₆H₃-ⁱPr₂-2,6)(SiMe ₃)N]Yb(μ-Cl)(THF)₂}₂ (5), which is the first example of ytterbium(II) amide chloride, formed via the cleavage of the Yb-N bond. The same reduction reaction of 7 gave a normal bisamide complex [(C ₆H₃-ⁱPr₂-2,6)(SiMe ₃)N]₂Sm(THF)₂ (8) via Sm-Cl bond cleavage. This is the first example for the steric effect on the outcome of the reduction reaction in lanthanide(II) chemistry. 5 can also be synthesized by the Na/K alloy reduction reaction of 6. All of the complexes were fully characterized including X-ray diffraction for 1-7.

Full text of DOI:10.1021/ic070162x

Inorg. Chem. 2007, 46, 5763−5772
Synthesis and Structural Characterization of a Series of Lanthanide(II)
Amides: Steric Effect of Amido Ligand
Liying Zhou,† Junfeng Wang,† Yong Zhang,† Yingming Yao,† and Qi Shen*,†
Key Laboratory of Organic Synthesis, Jiangsu ProVince, Department of Chemistry and Chemical
Engineering, Suzhou UniVersity, Suzhou 215123, PR China
Received January 30, 2007
The synthesis and structures of a series of lanthanide(II) and lanthanide(III) complexes supported by the amido
ligand N(SiMe3)Ar were described. Several lanthanide(III) amide chlorides were synthesized by a metathesis reaction
of LnCl3 with lithium amide, including
-Cl)Li(THF)3
PhCH3 (4), [(C6H3-iPr2-2,6)(SiMe3)N]YbCl2(THF)3 (6), and [(C6H3-iPr2-2,6)(SiMe3)N]2SmCl3Li2(THF)4
(7). The reduction reaction of 1 with Na K alloy afforded bisamide ytterbium(II) complex [(C6H5)(Me3Si)N]2Yb-
{
[(C6H5)(Me3Si)N]2YbCl(THF)}2‚PhCH3 (1), [(C6H3-iPr2-2,6)(SiMe3)N]2YbCl-
(
µ
‚
−
(DME)2 (2). The same reaction for Sm gave an insoluble black powder. An analogous samarium(II) complex
[(C6H5)(Me3Si)N]2Sm(DME)2 (3) was prepared by the metathesis reaction of SmI2 with NaN(C6H5)(SiMe3). The
reduction reaction of ytterbium chloride 4 with Na
Yb( -Cl)(THF)2 (5), which is the first example of ytterbium(II) amide chloride, formed via the cleavage of the
Yb
(THF)2 (8) via Sm
reaction in lanthanide(II) chemistry. 5 can also be synthesized by the Na/K alloy reduction reaction of 6. All of the
complexes were fully characterized including X-ray diffraction for 1 7.
−K alloy afforded monoamide chloride {
[(C6H3-iPr2-2,6)(SiMe3)N]-
µ
−
}
2
N bond. The same reduction reaction of 7 gave a normal bisamide complex [(C6H3-iPr2-2,6)(SiMe3)N]2Sm-
Cl bond cleavage. This is the first example for the steric effect on the outcome of the reduction
−
−
Introduction
reactivity in chemical transformations.2-7 Amido ligands, as
the alternatives, have recently attracted increasing attention
because their electronic and steric properties can be changed
conveniently by the variation of the substituents on the
nitrogen atom.8 Thus, quite a few lanthanide(II) complexes
based on amido ligands have been developed. The pyrrolide-
based lanthanide(II) complexes have been demonstrated to
The nature of the ancillary ligand plays a crucial role in
determining the reactivity/stability of lanthanide(II) com-
plexes. For example, the lanthanide(II) complexes supported
by cyclopentadienyl-based ligands have been proven to show
rich chemical transformations because the unique versatility
of the C5R5 ligand puts forth the electronic and steric
requirements necessary for stabilizing a wide variety of
complexes.1 Therefore, great effort has been made to develop
suitable ligands, other than cyclopentadienyl systems, for
stabilizing the divalent complexes, which show unique
(2) (a) Hende, J. R.; Hitchcock, P. B.; Holmes, S. A.; Lappert, M. F. J.
Chem. Soc., Dalton Trans. 1995, 1435. (b) Deacon, G. B.; Feng, T.;
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E.; Gitlits, A.; Rothwell, I. P.; Skelton, B. W.; White, A. H. Eur. J.
Inorg. Chem. 2001, 1505. (e) Deng, M. Y.; Yao, Y. M.; Shen, Q.;
Zhang, Y.; Sun, J. Dalton Trans. 2004, 944. (f) Deng, M. Y.; Yao, Y.
M.; Zhang, Y.; Shen, Q. Chem. Commun. 2004, 2742.
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Edelmann, F. T. Angew. Chem., Int. Ed. Engl. 1990, 29, 894.
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Chem. Commun. 2002, 1410. (b) Eisenstein, O.; Hitchcock, P. B.;
Khvostov, A. V.; Lappert, M. F.; Maron, L.; Perrin, L.; Protchenko,
A. V. J. Am. Chem. Soc. 2003, 125, 10790.
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Izod, K.; Lu, Z.-R.; Smith, J. D. Organometallics 1996, 15, 4783. (c)
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* Towhomcorrespondenceshouldbeaddressed.E-mail: qshen@suda.edu.cn.
† Suzhou University.
(1) (a) Evans, W. J. Coord. Chem. ReV. 2000, 206-207, 263. (b) Evans,
W. J. J. Organomet. Chem. 2002, 647, 2. (c) Evans, W. J.; Davis, B.
L. Chem. ReV. 2002, 102, 2119. (d) Arndt, S.; Spaniol, T. P.; Okuda,
J. Organometallics 2003, 22, 775. (e) Evans, W. J.; Zucchi, G.; Ziller,
J. W. J. Am. Chem. Soc. 2003, 125, 10. (f) Qian, C. T.; Zou, G.; Jiang,
W. H.; Chen, Y. F.; Sun, J.; Li, N. Organometallics 2004, 23, 4980.
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10.1021/ic070162x CCC: $37.00
Published on Web 06/07/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 14, 2007 5763

Zhou et al.
possess unique reactivity.6 The complexes Ln[N(SiMe3)2]2-
(Sol) are not only excellent precursors to a variety of
lanthanide(II) complexes, but also are precatalysts for
polymerization of polar monomers.7b-g Moreover, The bulky
silylamido ligand, [N(SiMe3)2], has been found to provide
the steric, electrostatic, and solubility characteristics required
for the divalent samarium halide, [(Me3Si)2NSm(µ-I)(DME)-
(THF)]2.7a However, the study on the steric effect of the
amido ligand on the reactivity of lanthanide(II) amide
complexes has been limited. However, whereas a variety of
examples revealed the influence of metal size on reactivity/
stability in lanthanide(III) complexes,9 less attention has been
paid to address the relationship between the stability/
reactivity and the size of the metal in the chemistry of
organolanthanide(II) complexes. This might be mainly
because the oxidation potential of metals plays a crucial role
in determining the structures and reactivity of lanthanide-
(II) complexes. For example, the reaction of metallocenes
(C5Me5)2Ln(II) with PhCtCH afforded a trivalent complex
[(C5Me5)2Sm]2(PhCdCdC)CPh) for Sm,10a a mixed-
valence complex [(C5Me5)2YbIII]2(µ-CtCPh)4YbII for Yb,
and a divalent complex [(C5Me5)Eu(µ-CtCPh)(THF)2]2 for
Eu,10b depending on the reduction potentials of the metals.
Moreover, the Sm(II) complexes show remarkable reactivity,
which may not found for Yb(II) and Eu(II).9a,10c,d
standard Schlenk techniques. Solvents were distilled from Na/
benzophenone ketyl prior to use. Deuterated benzene (C6D6) was
purchased from Acros, and was dried over sodium and vacuum-
transferred. ꢀ-CL was purchased from Acros, dried by stirring with
CaH2 for 48 h, and then distilled under reduced pressure. Anhydrous
LnCl3,11 HN(C6H5)(SiMe3),12 and HN(C6H3-iPr2-2,6)(SiMe3)12 were
prepared according to the literature procedures. Melting points were
determined in sealed Ar-filled capillary tubes and are uncorrected.
Metal analyses were carried out by complexometric titration.
Carbon, hydrogen, and nitrogen analyses were performed by direct
combustion on a Carlo-Erba EA ) 1110 instrument. The IR spectra
were recorded on a Magna-IR 550 spectrometer. 1H NMR spectra
were measured on a Unity Inova-400 spectrometer.
Synthesis of {[(C6H5)(Me3Si)N]2YbCl(THF)}2‚C7H8 (1). A
Schlenk flask was charged with HN(C6H5)(SiMe3) (2.66 mL, 17.60
mmol), hexane (10 mL), and a stir bar. The solution was cooled to
0 °C, and n-BuLi (15.04 mL, 17.60 mmol, 1.17 M in hexane) was
added. The solution was slowly warmed to room temperature and
stirred for 1 h. Then, this solution was added slowly to a pale-gray
slurry of YbCl3 (2.46 g, 8.80 mmol) in 20 mL of THF. The resulting
solution was stirred for 48 h at room temperature. The solvent was
removed under a vacuum, and the residue was extracted with
toluene to remove LiCl by centrifugation. After the extracts were
concentrated, red crystals (4.90 g, 85%, based on YbCl3) were
obtained at the room temperature for a few days. Mp 150-152 °C
1
(dec). The H NMR spectrum of this compound displayed very
broad resonances and proved uninformative because of the para-
magnetism of Yb metal. Anal. Calcd for C51H80Cl2N4O2Si4Yb2
(1310.53): C 46.74, H 6.15, N 4.28, Yb 26.41. Found: C 46.53,
H 6.02, N 4.30, Yb 26.16. IR (KBr pellet, cm-1): 3040 (w), 2959
(m), 2901 (w), 1605 (s), 1501 (s), 1439 (w), 1385 (m), 1296 (m),
1254 (s), 1157 (m), 995 (w), 899 (s), 841 (s), 752 (m), 694 (m),
625 (w), 505 (m).
During our study on the synthesis of a series of lanthanide-
(II) amides with different bulks of amido ligand, we found
that the outcome of the reduction reaction of bisamide
lanthanide chloride with Na/K depends both on the metal
size and on the bulk of amido ligand. Here, we would like
to report the results.
Synthesis of [(C6H5)(Me3Si)N]2Yb(DME)2 (2). A Schlenk flask
was charged with 1 (5.02 g, 3.83 mmol), THF (20 mL), and a stir
bar. Then the Na-K alloy (0.18 g, 0.04 g, 5 mL of toluene) was
added. The resulting solution was stirred for 72 h at 40 °C. The
solvent was centrifugated and NaCl was removed. The solvent was
removed under a vacuum and 15 mL of DME was added. After a
few days, orange-red crystals (3.55 g, 68%) were obtained at room
temperature. Mp 110 °C (dec). 1H NMR (400 MHz, C6D6, 25 °C,
δ): ) 6.64-7.20 (m, 10H, H-Ph); 3.24 (m, 8H, H-DME); 3.11 (s,
12H, H-DME); 0.14 (s, 18H, -Si(CH3)3). Anal. Calcd for C26H48N2O4-
Si2Yb (681.88): C 45.80, H 7.09, N 4.11, Yb 25.38. Found: C
45.66, H 6.92, N 4.30, Yb 25.85. IR (KBr pellet, cm-1): 3044
(w), 2955 (m), 2893 (m), 2824 (w), 1605 (s), 1501 (s), 1447 (w),
1385 (m), 1296 (s), 1250 (s), 1157 (s), 1107 (m), 1030(w), 995
(w), 903 (s), 841 (s), 752 (m), 694 (m), 637 (w), 556 (w), 505 (m).
Synthesis of [(C6H5)(Me3Si)N]2Sm(DME)2 (3).
Path A: A solution of LiN(C6H5)(SiMe3) (2.79 mL, 15.82 mmol,
20 mL hexane) was added slowly to a slurry of SmCl3 (2.03 g,
7.91 mmol) in THF (20 mL). The resulting solution was stirred
for 48 h at room temperature. To the resulting yellow solution, the
Na-K alloy (0.18 g, 0.04 g, 5 mL of toluene) was added. The
mixture was stirred for 72 h at 40 °C. The color of the solution
changed from yellow to dark brown, and an insoluble black solid
separated out from the resulting solution.
Experimental Section
General Procedures. All of the manipulations were performed
under pure Ar with rigorous exclusion of air and moisture using
(6) (a) Dube, T.; Gambarotta, S.; Yap, G. P. A. Angew. Chem., Int. Ed.
1999, 38, 1432. (b) Dube, T.; Gambarotta, S.; Yap, G. P. A.
Organometallics 2000, 19, 115. (c) Dube, T.; Gambarotta, S.; Yap,
G. P. A. Organometallics 2000, 19, 121. (d) Dube, T.; Conci, S.;
Gambarotta, S.; Yap, G. P. A. Organometallics 2000, 19, 1182. (e)
Dube, T.; Ganesan, M.; Conci, S.; Gambarotta, S.; Yap, G. P. A.
Organometallics 2000, 19, 3716. (f) Ganesan, M.; Gambarotta, S.;
Yap, G. P. A. Angew. Chem., Int. Ed. 2001, 40, 766. (g) Berube, C.
D.; Yazdanbakhsh, M.; Gambarotta, S.; Yap, G. P. A. Organometallics
2003, 22, 3742. (h) Wang, J.; Amos, R. I. J.; Frey, A. S. P.; Gardiner,
M. G. Organometallics 2005, 24, 2259.
(7) (a) Evans, W. J.; Drummond, D. K.; Zhang, H. M. and Atwood, J. L.
Inorg. Chem. 1988, 27, 575. (b) Evans, W. J.; Katsumata, H.
Macromolecules 1994, 27, 2330. (c) Edelmann, F. T. Top. Curr. Chem.
1996, 179, 113l. (d) Evans, W. J.; Clark, R. D.; Ansari, M. A.; Ziller,
J. W. J. Am. Chem. Soc. 1998, 120, 9555. (e) Evans, W. J.; Johnston,
M. A.; Clark, R. D.; Anwander, R.; Ziller, J. W. Polyhedron 2001,
20, 2483. (f) Hou, Z.; Koizumi, T.; Nishiura, M.; Wakatsuki, Y.
Organometallics 2001, 20, 3323. (g) Kirillov, E. N.; Fedoorova, E.
A.; Trifonov, A. A.; Bochkarev, M. N. Appl. Organomet. Chem. 2001,
12, 151. (h) Hou, Z.; Wakatsuki, Y. J. Organomet. Chem. 2002, 647,
61.
(8) (a) Bailey, P. J.; Pace, S. Coord. Chem. ReV. 2001, 214, 91. (b)
Bourget, M. L.; Lappert, M. F.; Severn, J. R. Chem. ReV. 2002, 102,
3031. (c) Gibson, V. C.; Spitzmesser, K. Chem. ReV. 2003, 103, 283.
(9) (a) Evans, W. J. Polyhedron 1987, 6, 803. (b) Piers, W. E.; Emslie,
D. J. H. Coord. Chem. ReV. 2002, 233-234, 131.
(10) (a) Evans, W. J.; Keyer, R. A.; Ziller, J. W. Organometallics 1993,
12, 2618. (b) Boncella, J. M.; Tilley, T. D.; Andersen, R. A. Chem.
Commun. 1984, 710. (c) Fedushkin, I. L.; Dechert, S.; Schumann, H.
Angew. Chem., Int. Ed. 2001, 40, 561. (d) Hou, Z. M.; Zhang, Y.;
Nishiura, M.; Wakatsuki, Y. Organometallics 2003, 22, 129.
Path B: A Schlenk flask was charged with SmI2 (30.0 mL, 3.00
mmol, 0.10 M in THF) and a stir bar, then NaN(C6H5)(SiMe3)
(12.25 mL, 6.00 mmol, 0.49 M in THF) was added by a syringe.
(11) Taylor, M. D.; Carter, C. P. J. Inorg. Nucl. Chem. 1962, 24, 387.
(12) Porskamp, P. A. T. W.; Zwanenburg, B.; Synthesis 1981, 369.
5764 Inorganic Chemistry, Vol. 46, No. 14, 2007

Characterization of a Series of Lanthanide(II) Amides
Scheme 1
The resulting solution was then stirred for another 24 h and removed
under a vacuum. The residue was extracted with toluene to remove
NaI by centrifugation. The solvent was removed under a vacuum
and 15 mL of DME was added. Black crystals (1.54 g, 78%) were
from orange to yellow. After workup, yellow crystals (2.70 g, 75%)
were obtained from the toluene solution.
Synthesis of [(C6H3-iPr2-2,6)(SiMe3)N]YbCl2(THF)3(6). A
Schlenk flask was charged with LiN(C6H3-iPr2-2,6)(SiMe3) (10.67
mmol, 20 mL hexane) prepared freshly. Then, this solution was
added slowly to a pale-gray slurry of YbCl3 (2.98 g 10.67 mmol)
in 20 mL THF. The resulting solution was stirred for 48 h at room
temperature. The solvent was removed under a vacuum, and the
residue was extracted with toluene to remove LiCl by centrifugation.
After the extracts were concentrated, orange-yellow crystals
(6.65 g, 88%) were obtained at room temperature for a few days.
Mp 122 °C (dec). The 1H NMR spectrum of this compound
displayed very broad resonances and proved uninformative. Anal.
Calcd for C27H50Cl2NO3SiYb (708.71): C 45.76, H 7.11, N 1.98,
Yb 24.42. Found: C 45.42, H 6.94, N 2.13, Yb 24.75. IR (KBr
pellet, cm-1): 2964(s), 2871(s), 2555(w), 1621(s), 1528(s), 1466-
(m), 1381(m), 1320(m), 1258(m), 1181(w), 1111(w), 1042(m), 880-
(m), 841(m), 795(m), 741(m), 664(m), 486(w).
1
obtained at 0 °C for a few days. Mp 115-116 °C. H NMR (400
MHz, C6D6, 25 °C, δ): ) 10.76 (br, 8H, H-DME); 7.42 (m, 4H,
H-Ph); 6.79 (m, 2H, H-Ph); 6.58 (m, 4H, H-Ph); -0.28 (s, 18H,
-Si(CH3)3); -1.26 (br, 12H, H-DME). Anal. Calcd for C26H48N2O4-
Si2Sm (659.19): C 47.37, H 7.34, N 4.25, Sm 22.81. Found: C
47.03, H 7.15, N 4.15, Sm 22.69. IR (KBr pellet, cm-1): 2956 (s),
2902 (s), 2871 (s), 1574 (s), 1474 (s), 1335 (s), 1328 (s), 1204
(m), 1173 (m), 1120 (w), 1026 (m), 880(m), 841(m), 741 (m), 702
(w), 602 (w), 533 (m), 448 (m).
Synthesis of [(C6H3-iPr2-2,6)(SiMe3)N]2YbCl(µ-Cl)Li(THF)3‚
PhCH3 (4). A solution of LiN(C6H3-iPr2-2,6)(SiMe3) (18.26 mmol,
20 mL hexane) was added slowly to a slurry of YbCl3 (2.55 g,
9.13 mmol) in THF (20 mL). The resulting solution was stirred
for 48 h at room temperature. The solvent was removed under a
vacuum, and proper toluene was added to remove LiCl by
centrifugation. Orange crystals (8.68 g, 90%) were obtained at room
Synthesis of [(C6H3-iPr2-2,6)(SiMe3)N]2SmCl3Li2(THF)4 (7).
Following the procedure similar to the synthesis of 4, using LiN-
(C6H3-iPr2-2,6)(SiMe3) (16.08 mmol, 20 mL hexane), SmCl3 (2.06
g, 8.04 mmol) and THF (20 mL), followed by crystallization from
toluene, yielded light-yellow crystals of 7 (7.21 g, 85%). Mp 73-
1
temperature from the toluene solution. Mp 103-104 °C. The H
NMR spectrum of this compound displayed very broad resonances
and proved uninformative because of the paramagnetism of Yb
metal. Anal. Calcd for C49H84Cl2LiN2O3Si2Yb (1056.24): C 55.72,
H 8.02, N 2.65, Yb 16.38. Found: C 55.34, H 7.91, N 2.55, Yb
16.15. IR (KBr pellet, cm-1): 2964(s), 2871(m), 1628(s), 1505-
(w), 1459(m), 1389(w), 1366(w), 1266(w), 1119(w), 1050(w), 749-
(m), 641(s).
1
74 °C. The H NMR spectrum of this compound displayed very
broad resonances and proved uninformative. Anal. Calcd for C46H84-
Cl3Li2N2O4Si2Sm (1055.91): C 52.33, H 8.02, N 2.65, Sm 14.24.
Found: C 52.21, H 7.87, N 2.83, Sm 14.53. IR (KBr pellet, cm-1):
3063(w), 2962(s), 2870(w), 1622(s), 1461(m), 1438(m), 1384-
(w), 1265(m), 1045(w), 788(m), 745(s), 592(m).
Synthesis of {[(C6H3-iPr2-2,6)(SiMe3)N]Yb(µ-Cl)(THF)2}2 (5).
Path A: To a THF (20 mL) solution of 4 (7.98 mmol) was added
the Na-K alloy (0.18 g, 0.04 g, 5 mL of toluene). The mixture
was stirred for 72 h at 40 °C. The color of the solution changed
from red to orange-yellow. The precipitate was separated by
centrifugation. After removal of THF/toluene, extraction with
toluene, and centrifugation to separate NaCl/KCl, a toluene solution
was obtained, which gave yellow crystals (3.26 g, 68%) at room
Synthesis of [(C6H3-iPr2-2,6)(SiMe3)N]2Sm(THF)2 (8). To a
THF (20 mL) solution of 7 (6.80 g, 6.44 mmol) was added the
Na-K alloy (0.15 g, 0.03 g, 5 mL toluene). The mixture was stirred
for 48 h at 40 °C. The color of the solution changed from yellow
to dark brown. Following the procedure similar to the synthesis of
5, crystallization from toluene obtained the black crystals (3.67 g,
1
72%) at 0 °C for a few days. Mp 129-130 °C. H NMR (400
1
temperature. Mp 162-163 °C. H NMR (400 MHz, C6D6, 25 °C,
MHz, C6D6, 25 °C, δ): 12.10 (br, 8H, H-THF); 10.78 (br, 12H,
CH(CH3)2); 8.05 (br, 2H, H-Ph); 6.76 (br, 4H, H-Ph); 5.58 (br,
8H, H-THF, H-Ph); -1.51 (br, 18H, Si(CH3)3); -2.04 (br, 12H,
CH(CH3)2); -13.59 (br, 4H, CH(CH3)2). Anal. Calcd for C38H68N2O2-
Si2Sm (791.47): C 57.67, H 8.66, N 3.54, Sm 19.00. Found: C
57.48, H 8.49, N 3.65, Sm 19.23. IR (KBr pellet, cm-1): 3071(w),
2963(s), 2870(w), 1624(s), 1462(m), 1439(m), 1385(m), 1250(s),
1215(m), 1157(s), 1046(w), 884(w), 841(w), 745(m), 637(w), 556-
(w), 505(m).
δ): 6.90-7.10 (m, 6H, H-Ph); 3.44-4.02 (m, 20H, H-THF and
-CH(CH3)2); 1.19-1.50 (m, 40H, H-THF and -CH(CH3)2), 0.46
(s, 18H, -Si(CH3)3). Anal. Calcd for C46H84Cl2N2O4Si2Yb2
(1202.31): C 45.95, H 7.04, N 2.33, Yb 28.78. Found: C 45.72,
H 6.91, N 2.54, Yb 28.87. IR (KBr pellet, cm-1): 2962(s), 2871-
(w), 1622(s), 1462(w), 1438(m), 1385(w), 1251(m), 1156(m), 746-
(m), 505(m).
Path B: To a THF (20 mL) solution of 6 (6.00 mmol) was added
the Na-K alloy (0.14 g, 0.03 g, 5 mL of toluene). The mixture
was stirred for 72 h at 40 °C. The color of the solution changed
X-ray Structural Determination of 1-7: Suitable single
crystals of 1-7 were each sealed in a thin-walled glass capillary,
Inorganic Chemistry, Vol. 46, No. 14, 2007 5765

Zhou et al.
Table 1. Details of the Crystallographic Data of 1-3 and 5-7
1
2
3
5
6
7
empirical
formula
fw
cryst color
T (K)
C51H80Cl2N4O2Si4Yb2 C26H48N2O4Si2Yb
C26H48N2O4Si2Sm C46H84Cl2N2O4Si2Yb2 C27H50Cl2NO3SiYb C46H84Cl3Li2N2O4Si2Sm
1310.53
red
193(2)
0.71070
681.88
orange-red
193(2)
659.19
black
153(2)
0.71070
1202.31
yellow
193(2)
708.71
orange-yellow
193(2)
1055.91
light-yellow
193(2)
wavelength
(Å)
0.71070
0.71070
0.71070
0.71070
size (mm3)
cryst syst
0.78 × 0.50 × 0.35
0.40 × 0.30 × 0.16 0.30 × 0.20 × 0.15 0.30 × 0.25 × 0.15
0.20 × 0.16 × 0.15 0.40 × 0.25 × 0.20
monoclinic
monoclinic
P21/n
monoclinic
P21/n
monoclinic
P21/n
monoclinic
P21/n
triclinic
P-1
space group c2/c
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
20.538(2)
8.6077(6)
21.5836(19)
17.2281(15)
90
8.5881(11)
21.815(3)
17.306(2)
90
91.856(3)
90
9.832(3)
15.097(4)
18.925(5)
90
99.434(10)
90
11.6025(14)
24.236(3)
11.4942(11)
90
91.401(3)
90
12.2771(7)
13.2851(7)
19.0245(16)
85.934(6)
86.278(6)
64.072(4)
2781.6(3)
2
9.9638(7)
29.368(3)
90
102.125(4)
90
91.921(3)
90
5875.6(9)
4
3198.9(5)
4
3240.5(7)
4
2771.0(13)
2
3231.2(6)
4
Dcalcd
1.481
1.416
1.351
1.441
1.457
1.261
(mg m-3
)
absorption
coefficient
3.375
3.028
1.916
3.531
3.123
1.280
(mm-1
)
F (000)
θ (deg)
reflns
2640
3.12-27.48
28 025
1392
3.03-27.48
35 672
1360
3.01-25.35
31 578
1216
3.08-25.35
26 456
1444
3.03-25.35
31 898
1106
3.01-25.35
27 867
collected
independent 6567
rflns
7323
5926
5039
5902
10 113
params
295
327
327
270
333
534
R [I > 2σ(I)] 0.0451
0.0288
0.0563
1.153
0.0363
0.0591
1.196
0.0749
0.1400
1.238
0.0556
0.0987
1.142
0.0448
0.1010
1.103
wR
0.1010
1.316
GOF on F2
and intensity data were collected on a Rigaku Mercury CCD
equipped with graphite-monochromatized Mo KR (λ ) 0.71073
Å) radiation. Details of the intensity data collection and crystal data
are given in Table 1. The crystal structures of these complexes
were solved by direct methods and expanded by Fourier techniques.
Atomic coordinates and thermal parameters were refined by full-
matrix least-squares analysis on F2. All the non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were all generated
geometrically with assigned appropriate isotropic thermal param-
eters. The structures were solved and refined using the SHELXS-
97 and SHELXL-97 programs.
structural determination revealed the crystals to be the dimer
{[(C6H5)(Me3Si)N]2YbCl(THF)}2 (1).
The reduction reaction of 1 with a slight excess of Na-K
alloy went smoothly in THF/toluene. The color change from
red to orange during the reaction indicates the formation of
Yb(II) species. After workup, the bisamide ytterbium(II)
complex [(C6H5)(Me3Si)N]2Yb(DME)2 (2) was obtained as
orange-red crystals from a DME solution in high yield
(Scheme 1). The X-ray structural analysis revealed 2 to be
a monomer. In comparison with the similar complex {Yb-
[N(C6H5)(SiMe3)][µ-N(C6H5)(SiMe3)](THF)}2, which has a
dimeric structure previously reported by Lappert et al.,13 the
difference in structural motifs between the two ytterbium-
(II) complexes should be attributed to the presence of
solvated DME molecules in 2, which led to the prevention
of the formation of amido bridges.
An attempt to synthesize the bisamide samarium(II)
complex with the same amido ligand by the similar reduction
reaction failed. The same reduction reaction of bisamide
samarium chloride, which was synthesized in situ by the
reaction of SmCl3 with 2 equiv of LiN(C6H5)(SiMe3), by
use of a slight excess of Na-K alloy afforded an insoluble
black powder. The black powder could be an Sm(O) species
or an insoluble Sm(II) oligomer because the demand of the
higher coordination number is larger for the Sm(II) ion
compared to that of Yb(II) ion. Whether it is the former or
the latter is not clear because the insolubility of the black
powder prevented further characterization. A similar situation
Results and Discussion
Synthesis and characterization of Arylamide Lan-
thanide Complexes. To address the steric effect of the amido
ligand on the synthesis, structures, and reactivity of lan-
thanide(II) amide complexes, the amido ligands N(SiMe3)-
Ar (Ar ) (C6H5) and (C6H3-iPr2-2,6)) were chosen as they
are available from the reaction of ClSiMe3 with the corre-
sponding arylamine or the reaction of ClSiMe3 with lithium
amide.12 Reduction reactions of trivalent bisamide ytterbium
chloride and bisamide samarium chloride with alkali metal
were studied here in an attempt to understand the effect of
metal size.
Thus, the trivalent bisamide ytterbium chloride was first
synthesized. The reaction of YbCl3 with the less bulky amide
salt LiN(C6H5)(SiMe3), which was synthesized in situ by the
reaction of HN(C6H5)(SiMe3) with n-BuLi in a mixture of
hexane and THF, in a 1:2 molar ratio, followed by crystal-
lization from toluene, yielded the red crystals in high yield.
The full characterization by elemental analysis and X-ray
(13) Hitchcock, P. B.; Khvostov, A. V.; Lappert, M. F.; Protchenko, A. V.
J. Organomet. Chem. 2002, 647, 198.
5766 Inorganic Chemistry, Vol. 46, No. 14, 2007

Characterization of a Series of Lanthanide(II) Amides
Scheme 2
Scheme 3
was also found in the reduction reaction of [(Cy2N)2Sm(µ-
YbCH3(µ-CH3)2Li(THF)3‚PhCH3 in the structural motif.15
The formation of an ate complex is not surprising because
lithium readily affords ate salt adducts in synthetic lanthanide
chemistry.16
Cl)(THF)]2 with alkali metal reported by Gambarotta et al.14
Further study found that the bisamide samarium(II)
complex could be successfully synthesized by the conven-
tional salt metathesis approach. The reaction of SmI2 with 2
equiv of NaN(C6H5)(SiMe3) proceeded smoothly in THF.
After workup, black crystals of samarium(II) complex
[(C6H5)(Me3Si)N]2Sm(DME)2 (3) were isolated from DME
solution (Scheme 2).
The reduction reaction of the ytterbium chloride with
Na-K alloy was then conducted in THF/toluene. The color
changed from red to orange-yellow gradually during the
reaction. After workup, yellow crystals were isolated in high
yield. To our surprise, the full characterization by elemental
analysis and X-ray structural determination revealed the
crystals isolated to be monoamide ytterbium(II) chloride
{[(C6H3-iPr2-2,6)(SiMe3)N]Yb(µ-Cl)(THF)2}2 (5), not the
expected bisamide complex [(C6H3-iPr2-2,6)(SiMe3)N]2Yb-
(THF)2 (Scheme 3). 5 can be reproduced. 5 is very sensitive
to air and moisture, but more stable compared to [(Me3-
Si)2NSm(µ-I)(DME)(THF)]2, which tends toward ligand
redistribution to SmI2 and Sm[N(SiMe3)2]2.7a
To see the influence of a bulk of amido ligand on the
reduction reaction, the bisamide ytterbium chloride with a
more bulky amido ligand, N(C6H3-iPr2-2,6)(SiMe3), was
synthesized by the metathesis reaction of YbCl3 with LiN-
(C6H3-iPr2-2,6)(SiMe3) in a 1:2 molar ratio. The chloride was
characterized by an X-ray structural determination. Although
the quality of the refinement is low, the overall structure of
the molecule was clearly established to be an “ate” complex
[(C6H3-iPr2-2,6)(SiMe3)N]2YbCl(µ-Cl)Li(THF)3‚PhCH3 (4)
(Supporting Information), which is similar to the anionic
lanthanide methyl complex [(C6H3-iPr2-2,6)(SiMe3)N]2-
5 can also be obtained by Na/K alloy reduction of the
monoamide ytterbium dichlorides [(C6H3-iPr2-2,6)(SiMe3)N]-
(15) Luo, Y. J.; Yao, Y. M.; Li, W. J.; Chen, J. L.; Zhang, Z. Q.; Zhang,
Y.; Shen, Q. J. Organomet. Chem. 2003, 679, 125.
(16) (a) Edelmann, F. T.; Freckmann, D. M. M. and Schumann, H. Chem.
ReV. 2002, 102, 1851. (b) Hou, Z. M.; Wakatsuki, Y. Coord. Chem.
ReV. 2002, 231, 1.
(14) Minhas, R. K.; Ma, Y.; Song, J. I. and Gambarotta, S. Inorg. Chem.
1996, 35, 1866.
Inorganic Chemistry, Vol. 46, No. 14, 2007 5767

Zhou et al.
Scheme 4
Scheme 5
YbCl2(THF)3 (6), which was prepared by the reaction of
YbCl3 with LiN(C6H3-iPr2-2,6)(SiMe3) in a 1:1 molar ratio
and characterized by X-ray crystal structural analysis (Scheme
4).
However, the metathesis reaction of YbI2 with 1 equiv of
NaN(C6H3-iPr2-2,6)(SiMe3) in THF did not occur, from
which only the starting materials were recovered.
Scheme 6
Generally, the reduction of lanthanide(III) chloride by
alkali metal often gives the corresponding Ln(II) complex
and a precipitate of alkali metal chloride.17 The result
obtained from Scheme 3 indicates that the reduction reaction
takes place via the cleavage of the Ln-N bond, not the Ln-
Cl bond. The cleavage of the Ln-N bond prior to the Ln-
Cl bond in the reduction reaction has never been found
before. To see whether this is a special case for Yb, the same
reduction reaction with samarium chloride was further tried.
Even the divalent Sm complex [(C6H3-iPr2-2,6)(SiMe3)N]2-
Sm(THF)2 has already been synthesized by the redox
transmetallation reaction of metal Sm with mercury(II)
complex Hg[N(C6H3-iPr2-2,6)(SiMe3)]2.18 Thus, the precur-
sor, samarium(III) chloride, was synthesized by the reaction
of SmCl3 with 2 equiv of LiN(C6H3-iPr2-2,6)(SiMe3) because
no such complex was reported previously. The reaction
occurred in a mixture of hexane and THF and after workup,
yielded the ate complex [(C6H3-iPr2-2,6)(SiMe3)N]2SmCl3-
Li2(THF)4 (7) in high yield as yellow crystals, which was
characterized by elemental analysis and X-ray crystal
structural analysis.
The reduction reaction of 7 with Na-K alloy yielded
indeed a normal reduction product [(C6H3-iPr2-2,6)(SiMe3)N]2-
Sm(THF)2 (8) via the cleavage of the Ln-Cl bond as black
crystals in high yield, not the chloride as in the case of
ytterbium(II) (Scheme 5).
The preparation of 5 and 8 by the similar reaction indicated
that the reduction reaction of a bisamide lanthanide(III)
chloride by alkali metal may take place according to two
modes: mode A via the cleavage of Ln-Cl bond and mode
B via the cleavage of Ln-N bond (Scheme 6). Normally,
mode A is preferable to mode B. In contrast, when the steric
repulsion is as large as the steric demand of the ligand, mode
B will be taken. So, for metal Yb, the reduction reaction of
bisamide chloride with the less bulky amido N(C6H5)(SiMe3)
gave the bisamide complex by mode A, whereas an amide
chloride proceeded by mode B with the more bulky amido
N(C6H3-iPr2-2,6)(SiMe3). For a given bulky amido ligand,
the reduction reaction afforded a bisamide complex for Sm-
(II), whereas a monoamide chloride for the smaller metal
Yb(II) compared to Sm(II), as the coordination sphere around
Yb, is more crowded than that around Sm for the complex
with the same coordination numbers. To the best of our
knowledge, this is the first example of metal size and steric
demand of amido dependence determining the reduction
reaction pathway in the chemistry of lanthanide(II) com-
plexes.
The examples presented here show that substantial dif-
ferences in outcome and reactivity can be achieved by using
the bulky ancillary ligand attached and using metals of
different size. The result may provide a platform for further
study of the relationship between the steric effect and
reactivity/stability of divalent complexes.
Crystal Structural Analyses. The molecular structures
of 1-7 were determined by X-ray diffraction. Crystals of 2
and 3 suitable for X-ray diffraction were grown in a DME
solution, whereas others were grown in a toluene solution.
The molecular structures of 1-7 are shown in Figures 1-6,
respectively. The details of the crystallographic data are given
in Table 1 and selected bond lengths and angles are given
in Tables 2-6, respectively.
X-ray structural analysis revealed that 1 is a dimer (Figure
1) in which each [(C6H5)(SiMe3)N]2YbCl(THF) moiety is
bonded together by two unsymmetrical chloro bridges with
Yb-Cl bond lengths of 2.6600(13) and 2.6864(4) Å,
respectively. The two chlorine atoms and two ytterbium
atoms are coplanar (sum of angles, 360°). Each ytterbium
ion is bound to two nitrogen atoms of two amido groups,
one oxygen atom from the THF molecule, and two chlorine
atoms, to form a formal coordination number of five in a
distorted trigonal bipyramidal geometry. The Yb-N bond
lengths (2.149(4) and 2.184(4) Å) are comparable to those
(17) (a) Arndt, S.; Okuda, J. Chem. ReV. 2002, 102, 1953. (b) Yao, Y. M.;
Zhang, Y.; Zhang, Z. Q.; Shen, Q. and Yu, K. B. Organometallics
2003, 22, 2876.
(18) Deacon, G. B.; Fallon, G. D.; Forsyth, C. M.; Schumann, H.; Weimann,
R. Chem. Ber. 1997, 130, 409.
5768 Inorganic Chemistry, Vol. 46, No. 14, 2007

Characterization of a Series of Lanthanide(II) Amides
Figure 1. Molecular structure of 1.
Figure 4. Molecular structure of 7.
Figure 2. Molecular structure of 2 and 3.
Figure 5. Molecular structure of 6.
Figure 3. Molecular structure of 4.
Figure 6. Molecular structure of 5.
two nitrogen atoms of two amido ligands and four oxygen
atoms from two DME molecules as shown in Figure 2. The
coordination geometry around the lanthanide ion for each
complex is best described as a distorted octahedral geometry.
The average Ln-N bond lengths for 2 and 3 are 2.427(2)
and 2.525(3) Å, respectively. The average Ln-O bond
lengths for 2 and 3 are 2.540(2) and 2.661(3) Å, respectively.
These values are comparable when the ionic radii difference
between Yb(II) and Sm(II) is considered. The N-Ln-N
in [(C6H3-iPr2-2,6)(SiMe3)N]2NdCl(THF) (2.276(2) and 2.264-
(2) Å),19 when the difference in the ionic radii between Yb
and Nd is considered.20 The N-Yb-N angle is 112.69(16)°.
2 and 3 have analogous solid structures and they both are
monomers with a six-coordinate lanthanide center ligated by
(19) Schumann, H.; Winterfeld, J.; Rosenthal, E. C. E.; Hemling, H.; Esser,
L. Z. Anorg. Allg. Chem. 1995, 621, 122.
(20) Shannon, R. D. Acta Crystallogr. Sect. A 1976, 32, 751.
Inorganic Chemistry, Vol. 46, No. 14, 2007 5769

Zhou et al.
Table 2. Selected Bond Distances (Angstroms) and Angles (Degrees) for 1
bond
Yb(1)-N(1)
(angstroms)
bond
Si(1)-C(7)
(angstroms)
2.149(4)
2.184(4)
2.318(4)
2.6600(13)
2.6864(12)
4.1777(5)
2.6864(12)
1.729(4)
1.872(7)
1.734(4)
1.872(6)
1.877(7)
1.880(6)
1.454(7)
1.470(7)
1.425(6)
1.412(6)
Yb(1)-N(2)
Yb(1)-O(1)
Yb(1)-Cl(1)
Yb(1)-Cl(1)#1
Yb(1)-Yb(1)#1
Cl(1)-Yb(1)#1
Si(1)-N(1)
Si(2)-N(2)
Si(2)-C(17)
Si(2)-C(16)
Si(2)-C(18)
O(1)-C(22)
O(1)-C(19)
N(1)-C(1)
N(2)-C(10)
Si(1)-C(9)
Si(1)-C(8)
1.855(7)
1.863(7)
Angle
(Degrees)
112.69(16)
98.42(15)
90.57(15)
101.94(12)
95.41(12)
154.58(10)
105.91(12)
141.38(11)
82.70(10)
77.22(4)
Angle
(Degrees)
107.94(12)
124.23(11)
119.57(9)
38.84(3)
38.39(3)
102.78(4)
108.5(3)
N(1)-Yb(1)-N(2)
N(1)-Yb(1)-O(1)
N(2)-Yb(1)-O(1)
N(1)-Yb(1)-Cl(1)
N(2)-Yb(1)-Cl(1)
O(1)-Yb(1)-Cl(1)
N(1)-Yb(1)-Cl(1)#1
N(2)-Yb(1)-Cl(1)#1
O(1)-Yb(1)-Cl(1)#1
Cl(1)-Yb(1)-Cl(1)#1
N(1)-Yb(1)-Yb(1)#1
N(2)-Yb(1)-Yb(1)#1
O(1)-Yb(1)-Yb(1)#1
Cl(1)-Yb(1)-Yb(1)#1
Cl(1)#1-Yb(1)-Yb(1)#1
Yb(1)-Cl(1)-Yb(1)#1
N(1)-Si(1)-C(9)
N(1)-Si(1)-C(8)
C(9)-Si(1)-C(8)
112.6(3)
109.1(3)
Table 3. Selected Bond Distances (Angstroms) and Angles (Degrees) for 2 and 3
bond
bond
(angstroms)
2
3
(angstroms)
2
3
Ln(1)-N(1)
2.431(2)
2.422(2)
1.711(2)
1.709(2)
2.528(3)
2.521(3)
1.704(3)
1.701(3)
Ln(1)-O(1)
2.538(2)
2.524(2)
2.521(2)
2.578(2)
2.631(3)
Ln(1)-N(2)
Si(1)-N(1)
Si(2)-N(2)
Ln(1)-O(2)
Ln(1)-O(3)
Ln(1)-O(4)
2.671(3)
2.627(3)
2.714(3)
Angle
2
3
Angle
2
3
(Degrees)
(Degrees)
N(2)-Ln(1)-N(1)
N(1)-Ln(1)-O(3)
N(1)-Ln(1)-O(2)
N(1)-Ln(1)-O(1)
N(2)-Ln(1)-O(3)
N(2)-Ln(1)-O(1)
110.09(7)
87.36(7)
163.46(7)
119.95(7)
161.43(7)
84.78(7)
109.74(9)
87.70(8)
121.14(9)
164.01(8)
162.09(8)
85.62(9)
N(1)-Ln(1)-O(4)
Si(1)-N(1)-Ln(1)
O(2)-Ln(1)-O(1)
O(3)-Ln(1)-O(4)
N(2)-Ln(1)-O(4)
N(2)-Ln(1)-O(2)
85.41(7)
126.37(11)
66.03(8)
66.31(8)
119.76(7)
85.27(7)
86.37(9)
125.06(14)
62.75(9)
63.02(8)
120.39(8)
85.69(8)
Table 4. Selected Bond Distances (Angstroms) and Angles (Degrees) for 7
bond
(angstroms)
bond
(angstroms)
Sm(1)-N(1)
Sm(1)-N(2)
Sm(1)-Cl(1)
Sm(1)-Cl(2)
Sm(1)-Cl(3)
Cl(1)-Li(1)
Cl(2)-Li(2)
Cl(2)-Li(1)
2.285(3)
2.308(4)
2.7368(11)
2.8470(11)
2.7360(11)
2.326(8)
Cl(3)-Li(2)
2.322(9)
1.733(3)
1.744(4)
1.916(9)
1.907(9)
1.894(13)
1.948(13)
1.908(10)
Si(1)-N(1)
Si(2)-N(2)
O(1)-Li(1)
O(2)-Li(1)
O(3A)-Li(2)
O(3B)-Li(2)
O(4)-Li(2)
2.342(9)
2.357(8)
Angle
(Degrees)
123.53(12)
93.16(8)
99.49(10)
89.04(9)
108.42(10)
144.80(4)
133.05(9)
103.41(10)
76.90(4)
Angle
(Degrees)
114.47(16)
108.85(17)
115.57(15)
109.33(16)
96.4(2)
151.9(3)
91.3(2)
92.8(2)
N(1)-Sm(1)-N(2)
N(1)-Sm(1)-Cl(3)
N(2)-Sm(1)-Cl(3)
N(1)-Sm(1)-Cl(1)
N(2)-Sm(1)-Cl(1)
Cl(3)-Sm(1)-Cl(1)
N(1)-Sm(1)-Cl(2)
N(2)-Sm(1)-Cl(2)
Cl(3)-Sm(1)-Cl(2)
Cl(1)-Sm(1)-Cl(2)
N(1)-Sm(1)-Li(2)
N(2)-Sm(1)-Li(2)
N(1)-Sm(1)-Li(1)
N(2)-Sm(1)-Li(1)
Li(1)-Cl(1)-Sm(1)
Li(2)-Cl(2)-Li(1)
Li(2)-Cl(2)-Sm(1)
Li(1)-Cl(2)-Sm(1)
Li(2)-Cl(3)-Sm(1)
94.6(2)
76.10(4)
angles in 2 (110.09(7)°) and 3 (109.74(9)°) are almost
identical and smaller than that of 8 (121.5(2)°),18 indicating
that the nonsubstituent arylamido ligand provides a more-
open coordination environment. The Ln-N bond lengths for
2 are similar with an average value of {Yb[N(C6H5)(SiMe3)]-
[µ-N(C6H5)(SiMe3)](THF)}2 (2.340 Å),13 when the difference
in the ionic radii between six- and four-coordinated Yb is
considered. The N-Ln-N angle (110.09(7)°) in 2 is larger
than that of {Yb[N(C6H5)(SiMe3)][µ-N(C6H5)(SiMe3)](THF)}2,
showing that the coordination environment around the Yb
in 2 is less crowded than that in {Yb[N(C6H5)(SiMe3)][µ-
N(C6H5)(SiMe3)](THF)}2.
The molecular structures of 4 and 7 are shown in Figures
3 and 4, respectively. Although the quality of the refinement
for 4 is low, the overall structure of the molecule was clearly
established. Both 4 and 7 are ate complexes; however, the
5770 Inorganic Chemistry, Vol. 46, No. 14, 2007

Characterization of a Series of Lanthanide(II) Amides
Table 5. Selected Bond Distances (Angstroms) and Angles (Degrees) for 6
bond
(angstroms)
bond
(angstroms)
Yb(1)-N(1)
Yb(1)-O(1)
Yb(1)-O(2)
Yb(1)-O(3)
2.218(5)
2.300(5)
2.439(5)
2.325(5)
Yb(1)-Cl(1)
Yb(1)-Cl(2)
Si(1)-N(1)
Si(1)-C(13)
2.5498(18)
2.5436(19)
1.721(6)
1.871(8)
Angle
(Degrees)
100.30(19)
103.50(18)
178.4(2)
156.20(18)
78.1(2)
78.11(19)
98.64(14)
97.83(14)
Angle
(Degrees)
163.40(6)
89.18(13)
87.05(13)
81.33(14)
89.85(13)
87.17(12)
82.26(14)
124.1(3)
N(1)-Yb(1)-O(1)
N(1)-Yb(1)-O(3)
N(1)-Yb(1)-O(2)
O(1)-Yb(1)-O(3)
O(1)-Yb(1)-O(2)
O(3)-Yb(1)-O(2)
N(1)-Yb(1)-Cl(2)
N(1)-Yb(1)-Cl(1)
Cl(1)-Yb(1)-Cl(2)
O(1)-Yb(1)-Cl(2)
O(3)-Yb(1)-Cl(2)
O(2)-Yb(1)-Cl(2)
O(1)-Yb(1)-Cl(1)
O(3)-Yb(1)-Cl(1)
O(2)-Yb(1)-Cl(1)
Si(1)-N(1)-Yb(1)
Table 6. Selected Bond Distances (Angstroms) and Angles (Degrees) for 5
bond
(angstroms)
bond
(angstroms)
Yb(1)-N(1)
Yb(1)-Cl(1)
Yb(1)-Cl(1)#1
Yb(1)-Yb(1)#1
Angle
N(1)-Yb(1)-O(2)
N(1)-Yb(1)-O(1)
N(1)-Yb(1)-Cl(1)
O(2)-Yb(1)-Cl(1)
O(1)-Yb(1)-Cl(1)
2.302(8)
2.718(2)
2.724(2)
4.0630(12)
(Degrees)
109.7(2)
107.3(2)
113.3(2)
87.67(16)
139.31(17)
Yb(1)-O(1)
Yb(1)-O(2)
2.402(7)
2.397(7)
1.401(11)
1.687(8)
(Degrees)
107.21(19)
82.15(18)
83.40(7)
113.33(18)
132.52(18)
N(1)-C(1)
Si(1)-N(1)
Angle
N(1)-Yb(1)-Cl(1)#1
O(1)-Yb(1)-Cl(1)#1
Cl(1)-Yb(1)-Cl(1)#1
Cl(1)-Yb(1)-C(1)
Cl(1)#1-Yb(1)-C(1)
21
difference in the molecular structure between them is
observed. In 4, two moieties, that is, [(C6H3-iPr2-2,6)-
(SiMe3)N]2YbCl and LiCl(THF)3, are bonded together
through a µ2-Cl bridge. The coordination geometry around
the Yb atom is best described as a distorted pseudo-
tetrahedron with two nitrogen atoms of amide ligands and
two Cl atoms. In 7, three moieties, [(C6H3-iPr2-2,6)(SiMe3)N]2-
SmCl and two LiCl(THF)2, are connected together by two
µ2-Cl and one µ3-Cl bridges. The central metal Sm atom is
coordinated by two double-bridging Cl atoms, one triple-
bridging Cl atom, and two nitrogen atoms of amido ligands,
resulting in a distorted trigonal bipyramidal geometry, which
is similar to the structure of [(iPr2N)2SmCl3(Li(TMEDA))2].14
Two N atoms and one Cl2 define the equatorial plane,
whereas the other two Cl atoms are placed at the axial
positions. The differences observed between the structural
motifs of 4 and 7 may result from the difference in metal
sizes. The Sm-N bond lengths of 2.285(3) and 2.308(4) Å
in 7 are longer than 2.218(5) and 2.202(5) Å in [(iPr2N)2-
SmCl3(Li(TMEDA))2], which may be attributed to the more
Me5)(µ-I)(THF)2]2 and [Yb(η5-C5Me4SiMe2NHtBu)(µ-I)-
(THF)2]2,22 when Cp* is regarded to occupy one position.
Each ytterbium atom coordinates to an amido group, two
bridged chlorines, and two THF molecules to form a distorted
trigonal bipyramid. The Yb-Cl bond lengths of 2.718(2)
and 2.724(2) Å are comparable to 3.134 (1) and 3.175 (1) Å
of Yb-I distances in [Yb(η5-C5Me5)(µ-I)(THF)2]2, when the
differences in ion radius between Cl and I, and five- and
seven-coordinated Yb are considered. The bond length of
Yb-N, 2.302(8) Å, is very close to 2.326(4) and 2.353(4)
Å observed for the complex {Yb[N(C6H5)(SiMe3)][µ-N(C6H5)-
(SiMe3)](THF)}}2.13
Conclusion
In summary, we have successfully synthesized a series of
di- and trivalent lanthanide complexes supported by sily-
larylamido ligands. It was found that the reduction reaction
of bisamide lanthanide chloride with Na/K depends on both
the metal size and the steric bulk of the amido ligand. The
same reduction reaction of bisamide ytterbium chloride with
Na-K alloy afforded bisamide complex {[(C6H5)(Me3-
Si)N]2Yb(DME)2} (2) via the normal cleavage of the Ln-
Cl bond with the less bulky amido, whereas monoamide
chloride {[(C6H3-iPr2-2,6)(SiMe3)N]Yb(µ-Cl)(THF)2}2 (5)
was formed via the cleavage of the Ln-N bond prior to the
Ln-Cl bond with a bulky amido group. The similar reduction
reaction with the same bulky amido group for the larger metal
Sm(II) compared to Yb(II) gave bisamide complex [(C6H3-
iPr2-2,6)(SiMe3)N]2Sm(THF)2 (8) via the normal cleavage
i
bulky silylaryl amido group compared to Pr2N.
6 is crystallized in the monoclinic spaces. The coordination
geometry around the Yb ion is best described as a distorted
octahedral geometry with one nitrogen atom of an amido
ligand, two Cl atoms, and three oxygen atoms from three
THF molecules as shown in Figure 5. The Yb(1)-N(1) bond
length is 2.218(5) Å. The bond angles of N(1)-Yb(1)-Cl-
(1) and N(1)-Yb(1)-Cl(2) are 98.64(14) and 97.83(14)°,
respectively. The bond angle of Cl(1)-Yb(1)-Cl(2) is
163.40(6)°.
The crystal structural determination reveals 5 to be a
centrosymmetric chloro-bridged dimer with trans-disposed
amido groups as shown in Figure 6. The structure is similar
to those found in metallocene ytterbium iodides [Yb(η5-C5-
(21) Constantine, S. P.; Delima, G. M.; Hitchcock, P. B.; Keates, J. M.;
Lawless, G. A. Chem. Commun. 1996, 2421.
(22) Trifonov, A. T.; Spaniol, T. P.; Okuda, J. Eur. J. Inorg. Chem. 2003,
5, 926.
Inorganic Chemistry, Vol. 46, No. 14, 2007 5771

Zhou et al.
Supporting Information Available: Supporting Information
Available: X-ray crystallographic data for 1-7 in CIF format.
Detailed crystallographic data, selected bond lengths, and angles
for 4. This material is available free of charge via the Internet at
http://pubs.acs.org.
of the Ln-Cl bond. Further work on the steric effect on the
stability/reactivity of lanthanide(II) complexes is proceeding
in our laboratory.
Acknowledgment. We are indebted to the Chinese
National Natural Science Foundation for financial support.
IC070162X
5772 Inorganic Chemistry, Vol. 46, No. 14, 2007