Novel Cyclopentadienyl-Free Organolanthanides: The First Examples of Five-Membered Amidolanthanide Heterocycles

Article abstract of DOI:10.1021/ic961033b

Reactions of LnCl₃ (Ln = Nd, Gd, Yb) and [{Me₂SiN(R)Li}₂] (R = f-Bu, Ph) give the chloride-bridged dimers [{{(t-Bu)NSiMe₂SiMe₂N(t-Bu)}Ln(μ-Cl)(THF)₂}] (1, Ln = Nd'; 2, Ln = Gd; 3, Ln = Yb) and [{{(Ph)NSiMe₂-SiMe₂N(Ph)}Ln(μ-Cl)(THF) ₂}₂] (4, Ln = Nd; 5, Ln = Gd; 6, Ln = Yb) in good yields. Compounds 2 and 5 were structurally characterized by X-ray crystallography: 2, triclinic, P1?, a = 10.321(2) A?, b -11.116(2) A?, c = 13.434(3) A?, α = 107.57(3)°, β= 111.31(3)°, γ = 90.67(3)°, V = 1356.1(5) A?³, Z = l, A?= 0.0233; 5, monoclinic, P2₁In, a = 13.913(13) A?, b = 12.914(9) A?, c = 16.434(14) A?, β= 105.64(3)°, V = 2843(4) A?Z = 2, R = 0.0281. The chloro functions in 1-6 remain reactive, demonstrated by the isolation of the trifluoroacetate derivatives of 1 and 2. Treatment of 1 or 2 with 2 equiv of NaOCOCF₃ gives [{{(t-Bu)NSiMe₂SiMe₂N(t-Bu)}- Ln(μ-OCOCF₃)(THF)}₂] (7, Ln = Nd; 8, Ln = Gd). The structure of 8 was determined by a single-crystal X-ray diffraction analysis. Crystal data for 8: triclinic, P1?, a = 11.045(2) A?, b = 16.120(3) A?, c = 16.949(3) A?, α = 66.17(3)°, β= 85.51(3)°, y = 78.27(3)°, V = 2702.9(9) A?³Z=2,R = 0.0311. The structure of 8 shows the trifluoroacetate group adopting a bridging bidentate mode of coordination.

Full text of DOI:10.1021/ic961033b

1102
Inorg. Chem. 1997, 36, 1102-1106
Novel Cyclopentadienyl-Free Organolanthanides: The First Examples of Five-Membered
Amidolanthanide Heterocycles†
Syed A. A. Shah, Hendrik Dorn, Herbert W. Roesky,* Paolo Lubini, and
Hans-Georg Schmidt
Institut fu¨r Anorganische Chemie, Universita¨t Go¨ttingen, Tammannstrasse 4,
D-37077 Go¨ttingen, Germany
ReceiVed August 22, 1996X
Reactions of LnCl3 (Ln ) Nd, Gd, Yb) and [{Me2SiN(R)Li}2] (R ) t-Bu, Ph) give the chloride-bridged dimers
[{{(t-Bu)NSiMe2SiMe2N(t-Bu)}Ln(µ-Cl)(THF)}2] (1, Ln ) Nd; 2, Ln ) Gd; 3, Ln ) Yb) and [{{(Ph)NSiMe2-
SiMe2N(Ph)}Ln(µ-Cl)(THF)2}2] (4, Ln ) Nd; 5, Ln ) Gd; 6, Ln ) Yb) in good yields. Compounds 2 and 5
were structurally characterized by X-ray crystallography: 2, triclinic, P1h, a ) 10.321(2) Å, b ) 11.116(2) Å, c
) 13.434(3) Å, R ) 107.57(3)°, â ) 111.31(3)°, γ ) 90.67(3)°, V ) 1356.1(5) Å3, Z ) 1, R ) 0.0233; 5,
monoclinic, P21/n, a ) 13.913(13) Å, b ) 12.914(9) Å, c ) 16.434(14) Å, â ) 105.64(3)°, V ) 2843(4) Å3, Z
) 2, R ) 0.0281. The chloro functions in 1-6 remain reactive, demonstrated by the isolation of the trifluoroacetate
derivatives of 1 and 2. Treatment of 1 or 2 with 2 equiv of NaOCOCF3 gives [{{(t-Bu)NSiMe2SiMe2N(t-Bu)}-
Ln(µ-OCOCF3)(THF)}2] (7, Ln ) Nd; 8, Ln ) Gd). The structure of 8 was determined by a single-crystal X-ray
diffraction analysis. Crystal data for 8: triclinic, P1h, a ) 11.045(2) Å, b ) 16.120(3) Å, c ) 16.949(3) Å, R )
66.17(3)°, â ) 85.51(3)°, γ ) 78.27(3)°, V ) 2702.9(9) Å3, Z ) 2, R ) 0.0311. The structure of 8 shows the
trifluoroacetate group adopting a bridging bidentate mode of coordination.
Introduction
Much attention has been focused on the bulky heteroallylic
ligands, such as the N-silylated benzamidinate anions, to
stabilize relatively low coordination numbers around the large
4f ions by forming sterically saturated coordination com-
pounds.9,10 These homoleptic lanthanide(III) benzamidinates
have been called “steric cyclopentadienyl equivalents”.11 How-
ever, unlike preparations using the C5Me5 ligand, where the
formation of the (C5Me5)3Ln species is relatively difficult,12 care
must be taken to use an exact 1:2 stoichiometry for isolating
the lanthanide bis(benzamidinates); otherwise contamination of
the products with the tris(benzamidinates) will occur.13 This
is undesirable since the Ln-X unit, where X is the remaining
Since 1954, when the first well characterized organolan-
thanide complexes, (C5H5)3Ln, were reported,1 the organome-
tallic chemistry of the lanthanide metals has been dominated
by cyclopentadienyl ligands.2 In recent years, the use of the
pentamethylcyclopentadienyl ligand (C5Me5) has superseded the
unsubstituted C5H5 group and resulted in the discovery of many
interesting complexes and properties: for instance, unusual bent
metallocenes (C5Me5)2Ln (Ln ) Sm, Eu, Yb),3 lanthanide
complexes of dinitrogen,4 alkenes,5 and alkynes6 and the use
of lanthanide systems in CO insertion reactions and catalytic
olefin hydrogenations.7
(7) (a) Jeske, G.; Lauke, H.; Mauermann, H.; Schumann, H.; Marks, T.
J. J. Am. Chem. Soc. 1985, 107, 8111. (b) Evans, W. J.; Grate, J. W.;
Hughes, L. A.; Zhang, H.; Atwood, J. L. J. Am. Chem. Soc. 1985,
107, 3728. (c) Evans, W. J.; Drummond, D. K.; Chamberlain, L. R.;
Doedens, R. J.; Bott, S. G.; Zhang, H.; Atwood, J. L. J. Am. Chem.
Soc. 1988, 110, 4983. (d) Evans, W. J.; Drummond, D. K. J. Am.
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(8) (a) Edelmann, F. T. Angew. Chem. 1995, 107, 2647; Angew. Chem.,
Int. Ed. Engl. 1995, 34, 2466. (b) Evans, W. J. New J. Chem. 1995,
19, 525. (c) Edelmann, F. T. New. J. Chem. 1995, 19, 531. (d) Lee,
L.; Berg, D. J.; Bushnell, G. W. Inorg. Chem. 1994, 33, 5302.
(9) (a) Wedler, M.; Noltemeyer, M.; Pieper, U.; Schmidt, H.-G.; Stalke,
D.; Edelmann, F. T. Angew. Chem. 1990, 102, 941; Angew. Chem.,
Int. Ed. Engl. 1990, 29, 894. (b) Recknagel, A.; Kno¨sel, F.; Gornitzka,
H.; Noltemeyer, M.; Edelmann, F. T. J. Organomet. Chem. 1991, 417,
363. (c) Hagen, C.; Reddmann, H.; Amberger, H.-D.; Edelmann, F.
T.; Pegelow, U.; Shalimoff, G. V.; Edelstein, N. M. J. Organomet.
Chem. 1993, 462, 69. (d) Edelmann, F. T.; Richter, J. Eur. J. Solid
State Inorg. Chem. 1996, 33, 157.
(10) (a) Duchateau, R.; van Wee, C. T.; Meetsma, A.; Teuben, J. H. J.
Am. Chem. Soc. 1993, 115, 4931. (b) Duchateau, R.; van Wee, C. T.;
Meetsma, A.; van Duijnen, P. T.; Teuben, J. H. Organometallics 1996,
15, 2279. (c) Duchateau, R.; van Wee, C. T.; Teuben, J. H.
Organometallics 1996, 15, 2291.
(11) Edelmann, F. T. Coord. Chem. ReV. 1994, 137, 403.
(12) Evans, W. J.; Gonzales, S. L.; Ziller, J. W. J. Am. Chem. Soc. 1991,
113, 7423.
Despite the advantages of the C5Me5 ligand which make it
both sterically and electronically ideal for metals the size of
the lanthanides, it is important to develop other ancillary ligands
which can stabilize highly reactive organolanthanide species.8
† Dedicated to Professor John G. Verkade on the occasion of his 60th
birthday.
X Abstract published in AdVance ACS Abstracts, February 15, 1997.
(1) (a) Wilkinson, G.; Birmingham, J. M. J. Am. Chem. Soc. 1954, 76,
6210. (b) Birmingham, J. M.; Wilkinson, G. J. Am. Chem. Soc. 1956,
78, 42.
(2) (a) Edelmann, F. T. In ComprehensiVe Organometallic Chemistry II;
Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press:
Oxford, England, 1995. (b) Schaverian, C. J. AdV. Organomet. Chem.
1994, 36, 283. (c) Schumann, H.; Meese-Marktscheffel, J. A.; Esser,
L. Chem. ReV. 1995, 95, 865.
(3) (a) Evans, W. J.; Hughes, L. A.; Hanusa, T. P. J. Am. Chem. Soc.
1984, 106, 4270. (b) Evans, W. J.; Hughes, L. A.; Hanusa, T. P.
Organometallics 1986, 5, 1285. (c) Andersen, R. A.; Boncella, J. M.;
Burns, C. J.; Green, J. C.; Hohl, D.; Rosch, N. J. Chem. Soc., Chem.
Commun. 1986, 405.
(4) Evans, W. J.; Ulibarri, T. A.; Ziller, J. W. J. Am. Chem. Soc. 1988,
110, 6877.
(5) Evans, W. J.; Ulibarri, T. A.; Ziller, J. W. J. Am. Chem. Soc. 1990,
112, 219.
(6) Evans, W. J.; Keyer, R. A.; Zhang, H.; Atwood, J. L. J. Chem. Soc.,
Chem. Commun. 1987, 837.
(13) Wedler, M.; Kno¨sel, F.; Pieper, U.; Stalke, D.; Edelmann, F. T.;
Amberger, H.-D. Chem. Ber. 1992, 125, 2171.
S0020-1669(96)01033-6 CCC: $14.00 © 1997 American Chemical Society

Amidolanthanide Heterocycles
Inorganic Chemistry, Vol. 36, No. 6, 1997 1103
1182 (m), 1032 (s), 993 (s), 913 (s), 888 (m), 846 (m), 822 (m), 792
(s), 774 (s), 763 (s), 700 (s), 599 (s), 511 (m), 468 (m), 337 (m), 297
unsubstituted moiety, e.g. halide, is lacking and it is generally
this group which provides reactivity. To counter this problem,
we have utilized a diorganyldisilane to form a cyclic, cyclo-
pentadienyl-free ligand system which provides stability through
its bulk and the rigidity of the five-membered ring formed, as
well as allowing the retention of the reactive Ln-X species.
Herein we describe our findings.
(m) cm-1
.
[{{(Ph)NSiMe2SiMe2N(Ph)}Gd(µ-Cl)(THF)2}2] (5). The reaction
was performed by the procedure described for the preparation of 4.
GdCl3 (1.03 g, 3.91 mmol) in THF (40 mL) was treated with a solution
of Li(Ph)NSiMe2SiMe2N(Ph)Li (3.89 mmol) in THF (20 mL) at 0 °C.
After refluxing and extraction with toluene (30 mL), the colorless
solution was stored at -25 °C overnight. A yield of 1.66 g (67%)
of colorless crystals was obtained (mp 149 °C). Anal. Calcd for
C48H76Cl2Gd2N4O4Si4: C, 45.36; H, 6.03; N, 4.41. Found: C, 45.4;
H, 6.0; N, 4.4. IR (Nujol): 1584 (s), 1491 (m), 1467 (s), 1245 (s),
1232 (s), 1183 (m), 1024 (m), 992 (m), 913 (m), 888 (s), 844 (m), 818
(m), 777 (s), 762 (s), 734 (m), 699 (s), 601 (s), 519 (s), 365 (m), 337
Experimental Section
All reactions were carried out under a dry nitrogen atmosphere using
standard Schlenk techniques. Solvents were dried and purified by
known procedures and distilled from benzophenone ketyl under nitrogen
prior to use. Anhydrous LnCl3 (Ln ) Nd, Gd, Yb) and sodium
trifluoroacetate were purchased (Strem Chemicals, Inc.) and used
without further purification. The preparation of the 1,2-bis(organy-
lamino)-1,1,2,2-tetramethyldisilanes and their subsequent dilithiations
were performed according to literature methods.14 IR spectra were
recorded on a Perkin-Elmer Bio-Rad Digilab FTS-7 spectrometer (Nujol
mulls between CsI plates or Kel-F mulls between NaCl plates). Melting
points (uncorrected) were obtained by using a Bu¨chi 510 and an HWS
SG 3000 apparatus. Elemental analyses were carried out in the
analytical laboratory of our institute.
(m), 299 (m) cm-1
.
[{{(Ph)NSiMe2SiMe2N(Ph)}Yb(µ-Cl)(THF)2}2] (6). The reaction
was performed by the procedure described for the preparation of 4.
YbCl3 (0.88 g, 3.15 mmol) in THF (40 mL) was treated with a solution
of Li(Ph)NSiMe2SiMe2N(Ph)Li (3.16 mmol) in THF (20 mL) at 0 °C.
After refluxing and extraction with toluene (30 mL), the red solution
was stored at -25 °C overnight. A yield of 1.26 g (61%) of red crystals
was obtained (mp 138 °C). Anal. Calcd for C48H76Cl2N4O4Si4Yb2:
C, 44.26; H, 5.88; N, 4.30. Found: C, 44.1; H, 5.8; N, 4.3. IR
(Nujol): 1584 (s), 1492 (m), 1475 (s), 1243 (s), 1228 (s), 1169 (m),
1024 (s), 993 (m), 913 (s), 885 (m), 846 (m), 819 (m), 781 (m), 753
(m), 701 (s), 668 (m), 603 (s), 523 (s), 368 (m), 339 (m), 300 (m)
[{{(t-Bu)NSiMe2SiMe2N(t-Bu)}Nd(µ-Cl)(THF)}2] (1). To a slurry
of NdCl3 (0.60 g, 2.39 mmol) in THF (50 mL) was added a solution of
Li(t-Bu)NSiMe2SiMe2N(t-Bu)Li (2.39 mmol) in THF (20 mL) at 0 °C.
The mixture was refluxed for 12 h, and the THF was removed under
reduced pressure. Toluene (30 mL) was added to the residue, and the
mixture was filtered. A yield of 0.95 g (78%) of blue crystals was
obtained (mp 228 °C) after overnight standing at -25 °C. Anal. Calcd
for C32H76Cl2N4Nd2O2Si4: C, 37.66; H, 7.50; N, 5.49. Found: C, 37.6;
H, 7.5; N, 5.4. IR (Nujol): 1352 (m), 1248 (m), 1201 (s), 1181 (m),
1045 (s), 981 (s), 887 (m), 838 (s), 818 (s), 782 (s), 752 (s), 695 (s),
cm-1
.
[{{(t-Bu)NSiMe2SiMe2N(t-Bu)}Nd(µ-OCOCF3)(THF)}2] (7). To
a solution of 1 (1.00 g, 0.98 mmol) in THF (30 mL) was added a
solution of NaOCOCF3 (0.27 g, 1.98 mmol) in THF (20 mL) at 0 °C.
The mixture was refluxed for 12 h, and the THF was removed under
reduced pressure. Toluene (30 mL) was added, and the mixture was
filtered. A yield of 0.84 g (73%) of blue crystals was obtained (mp
204 °C) after overnight standing at -25 °C. Anal. Calcd for
C36H76F6N4Nd2O6Si4: C, 36.77; H, 6.51; F, 9.69; N, 4.76. Found: C,
36.6; H, 6.5; F, 9.6; N, 4.7. IR (Kel-F): 1689 (s), 1463 (m) cm-1. IR
(Nujol): 1355 (m), 1200 (s), 1155 (m), 1040 (m), 1027 (s), 874 (m),
842 (s), 792 (s), 752 (m), 720 (s), 662 (m), 607 (m), 524 (m), 491 (m),
658 (m), 520 (s), 486 (m), 422 (m), 283 (m) cm-1
.
[{{(t-Bu)NSiMe2SiMe2N(t-Bu)}Gd(µ-Cl)(THF)}2] (2). The reac-
tion was performed by the procedure described for the preparation of
1. GdCl3 (0.50 g, 1.90 mmol) in THF (40 mL) was treated with a
solution of Li(t-Bu)NSiMe2SiMe2N(t-Bu)Li (1.91 mmol) in THF (20
mL) at 0 °C. After refluxing and extraction with toluene (30 mL), the
colorless solution was stored at -25 °C overnight. A yield of 0.72 g
(72%) of colorless crystals was obtained (mp >300 °C). Anal. Calcd
for C32H76Cl2Gd2N4O2Si4: C, 36.72; H, 7.32; N, 5.35. Found: C, 36.7;
H, 7.3; N, 5.3. IR (Nujol): 1354 (m), 1238 (m), 1192 (s), 1032 (s),
1013 (s), 922 (m), 889 (m), 844 (s), 823 (s), 792 (s), 753 (s), 728 (s),
455 (m), 357 (m) cm-1
.
[{{(t-Bu)NSiMe2SiMe2N(t-Bu)}Gd(µ-OCOCF3)(THF)}2] (8). The
reaction was performed by the procedure described for the preparation
of 7. A solution of 2 (1.00 g, 0.96 mmol) in THF (30 mL) was treated
with a solution of NaOCOCF3 (0.28 g, 2.06 mmol) in THF (20 mL) at
0 °C. After refluxing and extraction with toluene (30 mL), the colorless
solution was stored at -25 °C overnight. A yield of 0.87 g (75%)
of colorless crystals was obtained (mp 210 °C). Anal. Calcd for
C36H76F6Gd2N4O6Si4: C, 35.98; H, 6.37; F, 9.48; N, 4.66. Found: C,
35.9; H, 6.3; F, 9.4; N, 4.6. IR (Kel-F): 1697 (s), 1469 (m) cm-1. IR
(Nujol): 1355 (m), 1202 (s), 1157 (m), 1039 (s), 1019 (s), 873 (m),
842 (s), 822 (m), 791 (s), 750 (m), 720 (m), 661 (m), 524 (m), 492
694 (m), 665 (m), 523 (s), 493 (s), 427 (m), 357 (m) 284 (m) cm-1
.
[{{(t-Bu)NSiMe2SiMe2N(t-Bu)}Yb(µ-Cl)(THF)}2] (3). The reac-
tion was performed by the procedure described for the preparation of
1. YbCl3 (0.50 g, 1.79 mmol) in THF (40 mL) was treated with a
solution of Li(t-Bu)NSiMe2SiMe2N(t-Bu)Li (1.80 mmol) in THF (20
mL) at 0 °C. After refluxing and extraction with toluene (30 mL), the
red-brown solution was stored at -25 °C overnight. A yield of 0.78
g (81%) of orange crystals was obtained (mp 244 °C). Anal. Calcd
for C32H76Cl2N4O2Si4Yb2: C, 35.64; H, 7.10; N, 5.20. Found: C, 35.6;
H, 7.1; N, 5.2. IR (Nujol): 1353 (m), 1238 (m), 1192 (s), 1032 (s),
1012 (s), 923 (m), 867 (m), 845 (s), 826 (m), 793 (s), 754 (m), 736
(m), 460 (m) cm-1
.
Crystal Structure Solution and Refinement. Diffraction data for
compound 2 were collected on a Siemens-Stoe AED four-circle
diffractometer at 120 K with Mo KR radiation (λ ) 0.710 73 Å).
Diffraction data for compounds 5 and 8 were collected at 193 K on a
Siemens-Stoe Huber four-circle diffractometer equipped with a SMART
CCD area detector and using Mo KR radiation (λ ) 0.710 73 Å). The
sample to detector distance was set to be 6 cm. Reflections were
collected by means of æ-scan (for 5) and æ- and ω-scan (for 8) rotations
(step width 0.3°), with an exposure time of 15 s/frame. Absorption
corrections were applied using a semiempirical method.
All three structures were solved by direct methods using SHELXS-
9015 and refined versus F2 by full-matrix least-squares procedures using
SHELXL-93.16 For all three compounds, all non-hydrogen atoms could
be refined anisotropically. The hydrogen atoms were inserted in
calculated positions and refined “riding” on their respective carbon
(s), 664 (m), 525 (s), 493 (m), 357 (m) 284 (m) cm-1
.
[{{(Ph)NSiMe2SiMe2N(Ph)}Nd(µ-Cl)(THF)2}2] (4). To a slurry
of NdCl3 (0.89 g, 3.55 mmol) in THF (50 mL) was added a solution of
Li(Ph)NSiMe2SiMe2N(Ph)Li (3.56 mmol) in THF (30 mL) at 0 °C.
The mixture was refluxed for 12 h, and the THF was removed under
reduced pressure. Toluene (30 mL) was added to the residue, and the
mixture was filtered. A yield of 1.38 g (71%) of blue crystals was
obtained (mp 148 °C) after overnight standing at -25 °C. Anal. Calcd
for C40H76Cl2N4Nd2O4Si4: C, 46.31; H, 6.15; N, 4.50. Found: C, 46.2;
H, 6.1; N, 4.4. IR (Nujol): 1582 (s), 1469 (s), 1256 (m), 1230 (s),
(14) (a) Wannagat, U.; Autzen, H.; Schlingmann, M. Z. Anorg. Allg. Chem.
1976, 419, 41. (b) Wannagat, U.; Eisele, G.; Schlingmann, M. Z.
Anorg. Allg. Chem. 1977, 429, 83.
(15) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(16) Sheldrick, G. M. SHELXL-93. University of Go¨ttingen, Germany,
1993.

1104 Inorganic Chemistry, Vol. 36, No. 6, 1997
Table 1. Crystallographic Data for 2, 5, and 8
Shah et al.
2‚C7H8
5
8
empirical formula
mol wt
crystal size (mm)
crystal system
space group
a (Å)
C32H76Cl2Gd2N4O2Si4‚C7H8
1138.86
C48H76Cl2Gd2N4O4Si4
1270.88
0.60 × 0.50 × 0.40
monoclinic
P21/n
13.913(13)
12.914(9)
16.434(14)
90
C36H78F6Gd2N4O6Si4
1203.88
0.80 × 0.40 × 0.40
triclinic
0.22 × 0.18 × 0.10
triclinic
P1h
P1h
10.321(2)
11.116(2)
13.434(3)
107.57(3)
111.31(3)
90.67(3)
1356(5)
11.045(2)
16.120(3)
16.949(3)
66.17(3)
85.51(3)
78.27(3)
2703(9)
b (Å)
c (Å)
R (deg)
â (deg)
105.64(3)
90
γ (deg)
V (Å3)
2843(4)
2
Z
1
2
D
calcd (g cm-3
)
1.395
1.484
1.479
µ (mm-1
)
2.643
2.532
2.581
2θ range (deg)
3.5-25
2-25
2.5-25
no. of reflns collected
no. of indep reflns
6013
26361
29288
4767
4836
9394
no. of restraints/parameters
169/310
0/294
412/609
0.0311
a
RF
0.0233
0.0634
0.0281
b
RwF
0.0720
0.0853
0.986 and -1.230
largest diff peak and hole (electrons Å-3
)
1.016 and -1.741
0.821 and -1.362
a RF ) ∑|Fo - Fc|/∑Fo (F > 4σ(F)). RwF ) [∑w(Fo - Fc2)2/∑w(Fo )2]1/2 (all data).
b
2
2
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 2
Table 4. Selected Bond Lengths (Å) and Angles (deg) for 8
Gd(1)-N(1)
Gd(1)-N(2)
Gd(1)-O(1)
Gd(1)-Cl(1)
Gd(1)-Cl(1a)
2.203(3)
2.211(2)
2.400(2)
2.7849(17)
2.7550(10)
N(1)-Si(1)
N(2)-Si(2)
Si(1)-Si(2)
N(1)-C(1)
N(2)-C(9)
1.723(3)
1.719(3)
2.3881(13)
1.479(4)
1.473(4)
Gd(1)-N(1)
Gd(1)-N(2)
Gd(1)-O(1)
Gd(1)-O(2)
Gd(1)-O(3)
N(1)-C(1)
N(2)-C(9)
2.190(3)
2.194(4)
2.322(3)
2.367(3)
2.424(3)
1.469(6)
1.448(7)
N(1)-Si(1)
N(2)-Si(2)
Si(1)-Si(2)
C(17)-O(2)
C(17)-O(1a)
C(17a)-O(2a)
C(17a)-O(1)
1.710(4)
1.701(4)
2.381(2)
1.221(5)
1.220(5)
1.199(5)
1.220(5)
N(1)-Gd(1)-N(2) 102.97(10) N(1)-Gd(1)-O(1)
N(1)-Gd(1)-Cl(1) 130.72(7) N(2)-Gd(1)-O(1)
N(2)-Gd(1)-Cl(1) 126.13(7) N(1)-Si(1)-Si(2)
N(1)-Gd(1)-Cl(1a) 99.26(7) N(2)-Si(2)-Si(1)
N(2)-Gd(1)-Cl(1a) 100.10(7) C(1)-N(1)-Gd(1)
92.70(9)
95.19(9)
107.05(10)
107.96(9)
124.14(19)
126.6(2)
N(1)-Gd(1)-N(2) 104.24(13) N(2)-Gd(1)-O(1)
N(1)-Si(1)-Si(2) 108.09(14) O(1)-Gd(1)-O(2)
N(2)-Si(2)-Si(1) 108.80(14) Gd(1)-O(2)-C(17)
97.89(14)
83.51(11)
145.5(3)
O(1)-Gd(1)-Cl(1)
80.14(6) C(1)-N(1)-Si(1)
Si(1)-N(1)-Gd(1) 109.48(18) Gd(1a)-O(1a)-C(17) 174.5(3)
Si(2)-N(2)-Gd(1) 109.19(19) Gd(1)-O(1)-C(17a) 162.3(4)
O(1)-Gd(1)-Cl(1a) 157.90(5) C(9)-N(2)-Gd(1)
Gd(1)-N(1)-Si(1) 108.71(13) C(9)-N(2)-Si(2)
123.15(19)
127.1(2)
N(1)-Gd(1)-O(1) 100.35(15) Gd(1a)-O(2a)-C(17a) 143.0(3)
Gd(1)-N(2)-Si(2) 109.52(13) Cl(1)-Gd(1)-Cl(1a) 77.96(3)
N(2)-Gd(1)-O(2) 127.32(14) O(2)-C(17)-O(1a)
N(1)-Gd(1)-O(2) 127.47(13) O(1)-C(17a)-O(2a)
128.9(4)
128.3(4)
Gd(1a)-Cl(1)-Gd(1) 102.04(3)
Table 3. Selected Bond Lengths (Å) and Angles (deg) for 5
1,2-bis(tert-butylamino)-1,1,2,2-tetramethyldisilane with the
Gd(1)-N(1)
Gd(1)-N(2)
Gd(1)-O(1)
Gd(1)-O(2)
Gd(1)-Cl(1)
Gd(1)-Cl(1a)
2.240(3)
2.314(3)
2.407(3)
2.476(3)
2.731(3)
2.8113(17)
N(1)-Si(1)
N(2)-Si(2)
Si(1)-Si(2)
N(1)-C(1)
N(2)-C(11)
1.725(3)
1.735(3)
2.379(2)
1.418(5)
1.396(5)
formation of dimeric [{{(t-Bu)NSiMe2SiMe2N(t-Bu)}Ln(µ-Cl)-
(THF)}2] (1, Ln ) Nd; 2, Ln ) Gd; 3, Ln ) Yb; Scheme 1).
Compounds 1-3 were isolated in good yields upon crystalliza-
tion from toluene. The IR spectra of all the compounds are
identical, inferring identical structural configurations.
Similarly, reaction of LnCl3 (Ln ) Nd, Gd, Yb) with 1 equiv
of the dilithium salt of 1,2-bis(phenylamino)-1,1,2,2-tetrameth-
N(1)-Gd(1)-N(2) 100.33(11) N(1)-Gd(1)-O(1)
98.90(10)
82.82(10)
85.91(10)
160.71(10)
109.28(11)
108.35(12)
130.1(2)
O(1)-Gd(1)-O(2)
N(1)-Gd(1)-Cl(1)
N(2)-Gd(1)-Cl(1)
74.80(9) N(1)-Gd(1)-O(2)
93.20(8) N(2)-Gd(1)-O(1)
96.29(8) N(2)-Gd(1)-O(2)
yldisilane gave dimeric [{{(Ph)NSiMe2SiMe2N(Ph)}Ln(µ-Cl)-
(THF)2}2] (4, Ln ) Nd; 5, Ln ) Gd; 6, Ln ) Yb; Scheme 1).
The IR spectra of 4-6 are also identical. The neodymium
complexes (1 and 4) are blue and the gadolinium complexes (2
and 5) are colorless, while the ytterbium complexes (3 and 6)
are orange and red, respectively.
From microanalytical analyses, it was observed that com-
plexes 1-3 have one molecule of THF coordinated to each metal
atom, while 4-6 have two coordinated THF molecules per metal
atom. This was confirmed by the elucidation of the structures
of 2 and 5 by single-crystal X-ray analysis. Complexes 2 and
5 are dimeric with bridging chlorine atoms (Figures 1 and
2). Selected bond lengths and angles are listed in Tables 2
and 3.
N(1)-Gd(1)-Cl(1a) 155.63(7) N(1)-Si(1)-Si(2)
N(2)-Gd(1)-Cl(1a) 103.46(10) N(2)-Si(2)-Si(1)
O(1)-Gd(1)-Cl(1) 167.13(6) C(1)-N(1)-Gd(1)
O(1)-Gd(1)-Cl(1a) 88.07(7) C(1)-N(1)-Si(1)
117.3(2)
O(2)-Gd(1)-Cl(1) 102.56(7) C(11)-N(2)-Gd(1) 128.6(2)
O(2)-Gd(1)-Cl(1a) 76.49(8) C(11)-N(2)-Si(2)
122.2(2)
Gd(1)-N(1)-Si(1) 110.67(14) Cl(1)-Gd(1)-Cl(1a) 79.08(4)
Gd(1)-N(2)-Si(2) 109.04(15) Gd(1a)-Cl(1)-Gd(1) 100.92(4)
atom. Crystals of 2 and 5 possess one half-molecule in the asymmetric
unit whereas crystals of 8 show two half-molecules per asymmetric
unit (root-mean-square of the fit of the two half-molecules in the
asymmetric unit is 0.22(5) Å, without taking into account the THF
molecules). In addition, one toluene molecule was found per molecular
unit of 2.
Crystallographic data are listed in Table 1, and selected bond lengths
and angles are given in Tables 2-4.
In 2, each gadolinium atom has a distorted square pyramidal
geometry, while the extra coordinated THF molecule causes
the gadolinium atoms in 5 to have a distorted octahedral
geometry. The THF molecules in 5 are in mutual cis positions
around the gadolinium atom with the O(1)-Gd(1)-O(2) angle
Results and Discussion
Anhydrous lanthanide trichlorides, LnCl3 (Ln ) Nd, Gd, Yb),
react in tetrahydrofuran with 1 equiv of the dilithium salt of

Amidolanthanide Heterocycles
Inorganic Chemistry, Vol. 36, No. 6, 1997 1105
The Gd-N bond distances in 2 are shorter than those in 5
(2.203(3) and 2.211(3) Å in 2 compared with 2.240(3) and
2.314(3) Å in 5). In the latter case, these compare well with
values for the known compound [{{(Me3Si)2N}2GdCl(THF)}2]17
(Gd-N(1) 2.239(5) Å and Gd-N(2) 2.264(5) Å). [{{(Me3-
Si)2N}2GdCl(THF)}2] also has two gadolinium bis(amido)
moieties bridged by two chlorine atoms, and the average Gd-
Cl bond distance (2.752(4) Å)17 closely approximates those for
2 (2.770(2) Å) and 5 (2.771(3) Å). The angles within the four-
membered gadolinium-chlorine ring are also similar for the
three compounds (Cl-Gd-Cl ) 77.96(3), 79.08(4), and 74.3-
(2)°, while Gd-Cl-Gd ) 102.04(3), 100.92(4), and 105.7(2)°
for 2, 5, and [{{(Me3Si)2N}2GdCl(THF)}2], respectively).
Figure 1. Stereoview of compound 2. Hydrogen atoms are omitted
for clarity. All bonds involving carbon are drawn with thin lines.
The dimeric natures of 2 and 5 are in agreement with the
structures of other disubstituted organolanthanide chlorides such
as [{(C5H5)2LnCl}2]2,18 and cyclopentadienyl-free complexes.8
The use of bulky amido groups has allowed the isolation of
similar halide-bridged dimers.17,19 Introduction of a trimeth-
ylsilyl moiety, bonded to the nitrogen atom of the amido group,
provides the steric bulk necessary to stabilize relatively low
coordination numbers around the lanthanide metal center. In
fact, all the lanthanide benzamidinates reported by Edelmann
and co-workers have a trimethylsilyl group attached to the
nitrogen atoms bonded to the lanthanide center and not a
C-substituted bulky group.9,13 It may be possible that the
stabilities of these amidinato systems are enhanced by the
inclusion of the silicon atom. Up to now, only the steric effect
of the trimethylsilyl group, and not any electronic contribution
to the stabilization by the N-Si system, has been considered.
Therefore, we assume that an “electronic silicon effect” has a
predominant influence on benzamidinates rather than just the
steric effect. Complexes 1-6 may be considered to be
inversions of these traditional bulky amido complexes. Instead
of a trimethylsilyl group allowed to rotate freely around the
nitrogen atom, two dimethylsilyl units form the backbone of a
five-membered ring. The bis(dimethylsilyl) backbone does not
provide steric bulk around the metal atom, and this function is
left to the organyl groups bonded to the nitrogen atoms.
Figure 2. Stereoview of compound 5. Hydrogen atoms are omitted
for clarity. All bonds involving carbon are drawn with thin lines.
Scheme 1
By use of these bis(organylamino)disilane ligands stable
lanthanide complexes, whose structures mimic those of the well-
known bis(cyclopentadienyl) halide-bridged dimers, are formed.
Due to the steric similarity between these two systems, it was
decided to also compare their reactivities by forming derivatives
of 1-6 through simple metathetical reactions.
Treatment of 1 or 2 with 2 molar equiv of sodium trifluo-
roacetate in tetrahydrofuran leads to [{{(t-Bu)NSiMe2SiMe2N-
(t-Bu)}Ln(OCOCF3)(THF)}2] (7, Ln ) Nd; 8, Ln ) Gd). In
the IR spectra of 7 and 8, the asymmetric carboxylate vibrations
can be found at 1689 and 1697 cm-1, respectively. The
being relatively small (74.80(9)°). Both 2 and 5 basically consist
of two five-membered gadolinium heterocycles linked by two
bridging chlorine atoms, thus forming a third four-membered
ring, which is exactly planar, as the molecules lie on an inversion
center (Figures 1 and 2). The gadolinium heterocycles in 2
and 5 are themselves almost planar with root-mean-square
deviations from the plane (Gd(1)-N(1)-Si(1)-Si(2)-N(2))
being 0.112 Å for 2 and 0.092 Å for 5. To the best of our
knowledge, compounds 2 and 5 represent the first structurally
characterized five-membered organolanthanide amido hetero-
cyclic systems.
symmetric vibrations for 7 and 8 are at 1463 and 1469 cm-1
,
respectively. The separations between the symmetric and
asymmetric stretching frequencies (∆ν) are approximately 225
cm-1 for both complexes, and this is similar to the ∆ν values
found for bridging bidentate group 4 fluoro carboxylates.20
Furthermore, many cyclopentadienyllanthanide carboxylates
have been shown to be dimeric with bridging bidentate
(17) Aspinall, H. C.; Bradley, D. C.; Hursthouse, M. B.; Sales, K. D.;
Walker, N. P. C.; Hussain; B. J. Chem. Soc., Dalton Trans. 1989,
623.
In the five-membered rings of 2 and 5, the silicon atoms are
in an almost perfect tetrahedral environment. However, the
geometry around the nitrogen atoms deviates from the expected
trigonal planar configuration of a sp3-hybridized amide nitrogen
atom.
(18) Schumann, H. Angew. Chem. 1984, 96, 475; Angew. Chem., Int. Ed.
Engl. 1984, 23, 474.
(19) Minhas, R. K.; Ma, Y.; Song, J.-I.; Gambarotta, S. Inorg. Chem. 1996,
35, 1866.
(20) Dorn, H.; Shah, S. A. A.; Parisini, E.; Noltemeyer, M.; Schmidt, H.-
G.; Roesky, H. W. Inorg. Chem. 1996, 35, 7181.

1106 Inorganic Chemistry, Vol. 36, No. 6, 1997
Shah et al.
manner with one set of Yb-O-C bond angles being 145(1)
and 171(1)° and the other being 164(1) and 150(1)°.
The coordinated THF molecules in 8 cause the gadolinium
atoms to adopt a distorted square pyramidal geometry, as in
the case of 2. Once again, the five-membered gadolinium
heterocycles (Gd(1)-N(1)-Si(1)-Si(2)-N(2)) are almost pla-
nar (root-mean-square deviation from the plane being 0.08(5)
Å for one molecule in the asymmetric unit and 0.05(2) Å for
the other). The angles and bond lengths of the five-membered
rings of 8 are similar to those found in 2 (Table 4).
Conclusion
Figure 3. Stereoview of compound 8. Hydrogen atoms are omitted
For the first time, five-membered organolanthanide amido
heterocyclic systems have been prepared. These cyclopenta-
dienyl-free complexes are structurally similar to well-known
cyclopentadienyllanthanide halides in that they are dimeric with
halide bridges. The stability of complexes 1-6 can be
considered to be due to the formation of the five-membered
heterocycle. One factor that may also influence their stabilities
is the possible electronic effect of the N-Si system on the metal
atom. Investigations into whether silicon attached to an amido
nitrogen atom plays a part in any such stabilization (a so-called
“electronic silicon effect”) are necessary before any firm
conclusions may be drawn.
The remaining chloro function in 1-6 allows further reaction,
shown by the isolation of the bis(µ-trifluoroacetato) complexes
(7 and 8). Thus, it may be possible to generate a range of
derivatives containing unusual ligand environments, and inves-
tigations in this respect are currently under way.
for clarity. All bonds involving carbon are drawn with thin lines.
carboxylate groups, either by spectral analysis21 or by X-ray
structural determinations.22 To confirm the bridging bidentate
coordination mode of the trifluoroacetate ligand in 7 and 8, a
single-crystal X-ray structure analysis of 8 was carried out.
The molecular structure of 8 is shown in Figure 3, and
selected bond lengths and angles are listed in Table 4. The
dimeric nature of 8 is maintained by the two trifluoroacetate
groups which link two gadolinium atoms in a bridging bidentate
manner. Therefore, 8 consists of two five-membered gado-
linium heterocycles, as was found for 2 and 5, and a central
eight-membered gadolinium trifluoroacetate ring. The CF3
groups of the trifluoroacetate ligands show some degree of
rotational disorder.
Within the internal ring formed by the trifluoroacetate ligands,
the Gd-O bond distances show no significant differences (Gd-
(1)-O(1) 2.322(3) Å and Gd(1)-O(2) 2.367(3) Å). However,
from the Gd-O-C bond angles it is clear that the bonding in
the bridging carboxylate groups is not symmetric (Gd(1)-O(2)-
C(17) 145.5(3)°, Gd(1a)-O(1a)-C(17) 174.5(3)°, Gd(1)-
O(1)-C(17a) 162.3(4)°, and Gd(1a)-O(2a)-C(17a) 143.0(3)°).
This phenomenon, where the angle at one carboxylate oxygen
is bent while the other is almost straight, was also observed in
the ytterbium complex [{(C5H5)2Yb(OCOC6F5)}2].22a The
pentafluorobenzoate ligands coordinate in a bridging bidentate
Acknowledgment. We thank the Deutsche Forschungsge-
meinschaft and the BMBF for support of this work. S.A.A.S.
is grateful to the Alexander von Humboldt Foundation for a
postdoctoral fellowship, and P.L. thanks the European Com-
munity for a postdoctoral grant (BBW 94.0162 CHBG CT
940731). We thank Wacker AG for a generous gift of
hexamethyldisilane.
Supporting Information Available: Listings of crystal data, atomic
coordinates, hydrogen positional and thermal parameters, anisotropic
displacement parameters, and bond distances and angles and figures
showing alternative ORTEP views for complexes 2, 5, and 8 (25 pages).
Ordering information is given on any current masthead page.
(21) Coutts, R. S. P.; Wailes, P. C. J. Organomet. Chem. 1970, 25, 117.
(22) (a) Deacon, G. B.; Fallon, G. D.; MacKinnon, P. I.; Newnham, R. H.;
Pain, G. N.; Tuong, T. D.; Wilkinson, D. L. J. Organomet. Chem.
1984, 277, C21. (b) Schumann, H.; Zietzke, K.; Weimann, R. Eur. J.
Solid State Inorg. Chem. 1996, 33, 121.
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