Alkylyttrium complexes supported by N,N′-dicyclohexyl-N″- bis(trimethylsilyl)guanidinate ligands

Article abstract of DOI:10.1021/om060280c

The reaction of anhydrous YCl₃ with an equimolar amount of lithium N,N′-dicyclohexyl-N″-bis-(trimethylsilyl)guanidinate, Li[(Me₃Si)₂NC(NCy)₂], in THF afforded the monoguanidinate dichloro complex [{(Me₃Si)₂NC(NCy) ₂}Y{(μ-Cl)₂Li(THF)₂}(μ-Cl)]₂ (1). X-ray diffraction study showed that complex 1 has a bimetallic tetranuclear dimeric core with six μ²-bridging chloro ligands. Treatment of complex 1 with 4 molar equiv of LiCH₂SiMe₃ in hexane at 0°C yielded the monomeric salt-free dialkyl complex {(Me₃Si) ₂NC(NCy)₂}Y(CH₂SiMe₃) ₂(THF)₂ (2). The monoguanidinate tetramethyl ate-complex {(Me₃-Si)₂NC(NCy)₂}Y[(μ-Me) ₂Li(TMEDA)]₂ (3) was prepared by the reaction of complex 1 with 8 equiv of MeLi in the presence of excess TMEDA in toluene at 20°C. The complexes 2 and 3 were structurally characterized. Alkylation of complex 1 with t-BuLi (1:4 molar ratio) in hexane resulted in the formation of the bis(guanidinate) alkyl yttrium complex {(Me₃Si)₂NC(NCy) ₂}₂Y(t-Bu) (4) in 42% yield. The guanidinate ligand redistribution was also observed in the reaction of the mono(guanidinate) dichloro yttrium complex {(Me₃Si)₂NC(NCy) ₂}YCl₂(Et₂O) (5) with 2 molar equiv of LiCH₂SiMe₃ in hexane at 0°C. This reaction afforded ate-complex {(Me₃Si)₂NC(NCy)₂} ₂Y(μ-CH₂SiMe₃)₂Li (6) in 34% yield. The X-ray diffraction study has revealed a low formal coordination number of the lithium atom in 6 and its agostic interaction with two methyl carbon atoms of SiMe₃ groups.

Full text of DOI:10.1021/om060280c

Organometallics 2006, 25, 3935-3942
3935
Alkylyttrium Complexes Supported by
N,N′-Dicyclohexyl-N′′-bis(trimethylsilyl)guanidinate Ligands
Alexander A. Trifonov,* Dmitrii M. Lyubov, Georgy K. Fukin, Evgenii V. Baranov, and
Yu. A. Kurskii
G. A. RazuVaeV Institute of Organometallic Chemistry of Russian Academy of Sciences, Tropinia 49,
603600 Nizhny NoVgorod GSP-445, Russia
ReceiVed March 30, 2006
The reaction of anhydrous YCl3 with an equimolar amount of lithium N,N′-dicyclohexyl-N′′-bis-
(trimethylsilyl)guanidinate, Li[(Me3Si)2NC(NCy)2], in THF afforded the monoguanidinate dichloro complex
[{(Me3Si)2NC(NCy)2}Y{(µ-Cl)2Li(THF)2}(µ-Cl)]2 (1). X-ray diffraction study showed that complex 1
has a bimetallic tetranuclear dimeric core with six µ2-bridging chloro ligands. Treatment of complex 1
with 4 molar equiv of LiCH2SiMe3 in hexane at 0 °C yielded the monomeric salt-free dialkyl complex
{(Me3Si)2NC(NCy)2}Y(CH2SiMe3)2(THF)2 (2). The monoguanidinate tetramethyl ate-complex {(Me3-
Si)2NC(NCy)2}Y[(µ-Me)2Li(TMEDA)]2 (3) was prepared by the reaction of complex 1 with 8 equiv of
MeLi in the presence of excess TMEDA in toluene at 20 °C. The complexes 2 and 3 were structurally
characterized. Alkylation of complex 1 with t-BuLi (1:4 molar ratio) in hexane resulted in the formation
of the bis(guanidinate) alkyl yttrium complex {(Me3Si)2NC(NCy)2}2Y(t-Bu) (4) in 42% yield. The
guanidinate ligand redistribution was also observed in the reaction of the mono(guanidinate) dichloro
yttrium complex {(Me3Si)2NC(NCy)2}YCl2(Et2O) (5) with 2 molar equiv of LiCH2SiMe3 in hexane at 0
°C. This reaction afforded ate-complex {(Me3Si)2NC(NCy)2}2Y(µ-CH2SiMe3)2Li (6) in 34% yield. The
X-ray diffraction study has revealed a low formal coordination number of the lithium atom in 6 and its
agostic interaction with two methyl carbon atoms of SiMe3 groups.
attention as potential precursors to cationic monoalkyl species6
that were found to be efficient catalysts of homo- and copo-
lymerization of olefins.7 The fact that reactivity of lanthanide
compounds is mainly determined by electrophilicity and coor-
dination unsaturation of the metal center emphasizes the
importance of design of new ancillary ligand sets as a means
of modification and control of the reactivity of complexes.
During the past five years increasing employment of new anionic
ancillaries allowed the synthesis and characterization of a
noticeable number of rare earth dialkyl derivatives supported
by noncyclopentadienyl ligands.8 Amidinate,9 triamino-amide,10
â-diketiminate,11 anilido-imine,12 amido diphosphine,13 and
deprotonated aza-18-crown-614 ligands were found to form a
Introduction
Hydrocarbyl derivatives of the rare earth metals are highly
active species that exhibit unique reactivity1 including hydro-
carbon activation2 and alkane functionalization.3 Extensive
research on the sandwich-type alkyl derivatives of the rare earth
metals has demonstrated their high potential in catalysis of a
wide range of conversions of unsaturated substrates.4 On the
contrary, the stoichiometric and catalytic performance of half-
sandwich bis(hydrocarbyl) complexes still remains poorly
explored5 because accessibility of these compounds was limited
by their instability and difficulties of synthesis and isolation.
Nevertheless these complexes have recently attracted significant
* To whom correspondence should be addressed. E-mail:
trif@imoc.sinn.ru. Fax: 00 7 (8312) 62 74 97.
(6) (a) Schaverien, C. J. Organometallics 1992, 11, 3476. (b) Arndt, S.;
Spaniol, T. P.; Okuda, J. Organometallics 2003, 22, 775.
(1) (a) Bochkarev, M. N.; Zakharov, L. N.; Kalinina, G. S. Organo-
deriVatiVes of Rare Earth Elements; Kluwer Academic Publishers: Dor-
drecht, 1995. (b) Cotton, S. A. Coord. Chem. ReV. 1997, 160, 93.
(2) (a) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J.;
Nolan, M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J. E. J. Am.
Chem. Soc. 1987, 109, 203. (b) Booij, M.; Deelman, B.-J.; Duchateau, R.;
Postma, D. S.; Mettsma, A.; Teuben, J. H. Organometallics 1993, 12, 3531.
(c) den Haan, K. H.; Wielstra, Y.; Teuben, J. H. Organometallics 1987, 6,
2053. (d) Fontaine, F.-G.; Don Tilley, T. Organometallics 2005, 24, 4340.
(3) (a) Sadow, A. D.; Don Tilley, T. Angew. Chem., Int. Ed. 2003, 42,
803.
(4) (a) Hou, Z.; Wakatsuki, Y. Coord. Chem. ReV. 2002, 231, 1. (b)
Nakayama, Y.; Yasuda, H. J. Organomet. Chem. 2004, 689, 4489. (c)
Yasuda, H. J. Organomet. Chem. 2002, 647, 128. (d) Molander, G. A.;
Romero, J. A. C. Chem. ReV. 2002, 102, 2161. (e) Molander, G. A.; Dowdy,
E. C. Top. Organomet. Chem. 1999, 2, 119. (f) Mueller, T. E.; Beller, M.
Chem. ReV. 1998, 98, 675. (g) Hong, S.; Marks, T. J. AdV. Chem. Res.
2004, 37, 673. (h) Douglass, M. R.; Stern, C. L.; Marks, T. J. J. Am. Chem.
Soc. 2001, 123, 10221. (i) Kawaoka, A. M.; Douglass, M. R.; Marks, T. J.
Organometallics 2003, 22, 4630. (j) Harrison, K. N.; Marks, T. J. J. Am.
Chem. Soc. 1992, 114, 9220. (k) Bijpost, E. A.; Duchateau, R.; Teuben, J.
H. J. Mol. Catal. A 1995, 95, 121.
(7) (a) Yasuda, H.; Ihara, E. Bull. Chem. Soc. Jpn. 1997, 70, 1745. (b)
Yasuda, H. J. Polym. Sci., Part A: Polym. Chem. 2001, 39, 1955. (c) Luo,
Y.; Baldamus, J.; Hou, Z. J. Am. Chem. Soc. 2004, 126, 13910. (d) Li, X.;
Baldamus, J.; Hou, Z. Angew. Chem., Int. Ed. 2005, 44, 962.
(8) (a) Edelmann, F. T.; Freckmann, D. M. M.; Schumann, H. Chem.
ReV. 2002, 102, 1851. (b) Piers, W. E.; Emslie, D. J. H. Coord. Chem.
ReV. 2002, 233-234, 131. (c) Mountford, P.; Ward, B. D. Chem. Commun.
2003, 1797.
(9) (a) Bambirra, S.; Brandsma, M. J. R.; Brussee, E. A. C.; Meetsma,
A.; Hessen, B.; Teuben, J. H. Organometallics 2000, 19, 3197. (b) Bambirra,
S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben, J. H. Chem. Commun.
2003, 522. (c) Bambirra, S.; Bouwkamp, M. W.; Meetsma, A.; Hessen, B.
J. Am. Chem. Soc. 2004, 126, 9182.
(10) (a) Bambirra, S.; van Leusen D.; Meetsma, A.; Hessen, B.; Teuben,
J. H. Chem. Commun. 2001, 637. (b) Bambirra, S.; Boot, S. J.; van Leusen,
D.; Meetsma, A.; Hessen, B. Organometallics 2004, 23, 1891. (c) Tazelaar,
C. G. J.; Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben,
J. H. Organometallics 2004, 23, 936.
(11) (a) Lee, L. W. M.; Piers, W. E.; Elsegood, M. R. J.; Clegg, W.;
Parvez, M. Organometallics 1999, 18, 2947. (b) Hayes, P. G.; Piers, W.
E.; Parvez, M. Organometallics 2005, 24, 1173. (c) Hayes, P. G.; Piers,
W. E.; Lee, L. W. M.; Knight, L. K.; Parvez, M.; Elsegood, M. R. J.; Clegg,
W. Organometallics 2001, 20, 2533.
(5) Arndt, S.; Okuda, J. Chem. ReV. 2002, 102, 1953.
10.1021/om060280c CCC: $33.50 © 2006 American Chemical Society
Publication on Web 07/01/2006

3936 Organometallics, Vol. 25, No. 16, 2006
TrifonoV et al.
Scheme 1
suitable coordination environment for the synthesis of isolable
bis(hydrocarbyl) species. Our recent studies were focused on
the tetrasubstituted guanidinate ligand framework,15 because it
is easily available and its electronic and steric properties can
be rationally modified by variation of the substituents at the
nitrogen atoms. Several examples of alkyl complexes of rare
earth metals supported by guanidinate ligands were described
recently.16 We employed the advantages of the {(Me3Si)2NC-
(NR)2}- (R ) i-Pr, Cy) coordination environment for the
stabilization of lanthanide monoalkyl17 and hydrido18 complexes.
We report here on the synthesis and structure of novel yttrium
neutral and -ate alkyl complexes supported by the bulky N,N′-
dicyclohexyl-N′′-bis(trimethylsilyl)guanidinate ligand.
Figure 1. ORTEP diagram (30% probability thermal ellipsoids)
of [{(Me3Si)2NC(NCy)2}Y{(µ-Cl)2Li(THF)2}(µ-Cl)]2 (1) showing
the non-hydrogen and non-carbon (except C(13)) atom numbering
scheme. Hydrogen atoms are omitted for clarity. Selected bond
distances [Å] and angles [deg]: Y(1)-N(2) 2.298(4), Y(1)-N(1)
2.304(5), Y(1)-Cl(2) 2.6227(16), Y(1)-Cl(1) 2.6385(16), Y(1)-
Cl(3) 2.7023(15), Y(1)-Cl(3A) 2.7065(15), Y(1)-C(13) 2.738(6),
Y(1)-Li(1) 3.540(10), Cl(1)-Li(1) 2.415(11), Cl(2)-Li(1) 2.344(10),
Cl(3)-Y(1A) 2.7065(15), Li(1)-O(2) 1.891(11), N(1)-C(13)
1.333(7), N(3)-C(13) 1.438(7), N(2)-C(13) 1.320(7), N(2)-Y(1)-
N(1) 57.76(16), Cl(2)-Y(1)-Cl(1) 84.23(5), Cl(3)-Y(1)-Cl(3A)
78.02(5).
Results and Discussion
The σ-bond metathesis reaction of tris(alkyl) complexes of
rare earth metals with the appropriate protio ligand precursor
is widely used as a synthetic approach to related mono- and
dialkyl species.6b,9,10,14,19 For the preparation of bis(guanidinate)
alkylylyttrium species we have successfully employed succes-
sive reactions of YCl3 with sodium (or lithium) guanidinates
and alkyllithium reagents.17 The same synthetic strategy was
used for the synthesis of mono(guanidinate) alkylyttrium
compounds. The mono(guanidinate) dichloro complex [{(Me3-
Si)2NC(NCy)2}Y{(µ-Cl)2Li(THF)2}(µ-Cl)]2 (1) was synthesized
by reaction of equimolar amounts of YCl3 and lithium N,N′-
dicyclohexyl-N′′-bis(trimethylsilyl)guanidinate, Li[(Me3Si)2NC-
(NCy)2], obtained in situ from Li(Et2O)[N(SiMe3)2] and the 1,3-
dicyclohexyl-substituted carbodiimide CyNdCdNCy in THF
at 20 °C. Evaporation of THF and recrystallization of the solid
residue from toluene allowed isolation of complex 1 in 95%
yield (Scheme 1).
Crystals suitable for a single-crystal X-ray diffraction study
of 1 were obtained from toluene solution by slow evaporation
of the solvent at room temperature. The molecular structure of
1 is depicted in Figure 1; the crystal and structural refinement
data are listed in Table 1. Complex 1 crystallizes in the triclinic
space group P1h with one molecule in the unit cell. The X-ray
diffraction study has revealed that 1 is a dimeric ate-complex
containing a bimetallic tetranuclear core, [Li(µ-Cl)2Y(µ-Cl)]2
(Figure 1), and its structure is different from those described
for related mono(cyclopentadienyl) dichlorides of rare earth
metals.20
All six chlorine atoms in complex 1 are µ2-bridging. Two of
them form bridges between two yttrium atoms, while four others
connect yttrium and lithium atoms. It is noteworthy that Y-Cl
bond distances in the Y2Cl2 (2.7023(15), 2.7065(15) Å) core
are somewhat longer than those in the YCl2Li fragments
(2.6277(16), 2.6385(16) Å). The Y-Cl bond lengths in the
planar Y2Cl2 fragment are slightly longer than the appropriate
distances in the bis(cyclopentadienyl) complexes [Cp2Y(µ-Cl)]2
(2.677(3), 2.693(3) Å),21 [(RC5H4)2Y(µ-Cl)]2 (R ) neo-menthyl,
2.693(4), 2.696(4), 2.671(4), 2.676(4) Å),22 and [(C5H4SiMe3)2Y-
(µ-Cl)]2 (2.684(4), 2.704(1) Å),23 but slightly shorter than those
in the bis(guanidinate) chloride [{(Me3Si)2NC(NiPr)2}2Y(µ-Cl)]2
Complex 1 was obtained as a colorless crystalline moisture-
and air-sensitive solid. It is soluble in THF and toluene and
sparingly soluble in hexane. The 1H and 13C{1H} NMR spectra
of complex 1 in C6D6 at 20 °C show the expected sets of
resonances due to the guanidinate part and the coordinated THF
molecules. The 1H NMR signals of the THF methylene protons
in 1 appear as broad singlets, reflecting labile coordination.
(12) Hayes, P. G.; Welch, G. C.; Emslie, D. J.; Noack, C. L.; Piers, W.
E.; Parvez, M. Organometallics 2003, 22, 1577.
(13) Fryzuk, M. D.; Giesbrecht, G.; Rettig, S. J. Organometallics 1996,
15, 3329.
(14) Lee, L.; Berg, D. J.; Einstein, F. W.; Batchelor, R. J. Organometallics
1997, 16, 1819.
(15) Bailey, P. J.; Pace, S. Coord. Chem. ReV. 2001, 214, 91.
(16) (a) Zhou, Y.; Yapp, G. P. A.; Richeson, D. S. Organometallics 1998,
17, 4387. (b) Lu, Z.; Yapp, G. P. A.; Richeson, D. S. Organometallics
2001, 20, 706. (c) Luo, Y.; Yao, Y.; Shen, Q.; Yu, K.; Weng, L. Eur. J.
Inorg. Chem. 2003, 318.
(17) Trifonov, A. A.; Lyubov, D. M.; Fedorova, E. A.; Fukin, G. K.;
Schumann, H.; Mu¨hle, S.; Hummert, M.; Bochkarev, M. N. Eur. J. Inorg.
Chem. 2006, 747-756.
(18) (a) Trifonov, A. A.; Fedorova, E. A.; Fukin, G. K.; Bochkarev, M.
N. Eur. J. Inorg. Chem. 2004, 4396. (b) Trifonov, A. A.; Skvortsov, G. G.;
Lyubov, D. M.; Skorodumova, N. A.; Fukin, G. K.; Baranov, E. V.;
Glushakova, V. N. Chem. Eur. J., accepted for publication.
(19) Skinner, M. E. G.; Tyrell, B. R.; Ward, B. D.; Mountford, P. J.
Organomet. Chem. 2002, 647, 145.
(20) For comparison see: (a) Zhongsheng, J.; Ninghai, H.; Yi, L.;
Xiaolong, X.; Guozhi, L. Inorg. Chim. Acta 1988, 142, 333. (b) Marsh, R.
E. Inorg. Chim. Acta 1989, 157, 1. (c) Guan, J.; Jin, S.; Lin, Y.; Shen, Q.
Organometallics 1992, 11, 2483. (d) Lamberts, W.; Hessner, B.; Lueken,
H. Inorg. Chim. Acta 1987, 139, 215. (e) Shen, Q.; Qi, M.; Lin, Y. J.
Organomet. Chem. 1990, 399, 247.
(21) Lobkovskii, E. B.; Soloveichik, G. L.; Bulichev, B. M.; Erofeev,
A. B. Zh. Strukt. Khim. (Russ.) 1984, 25, 170.
(22) Leung, W.-P.; Song, F.-Q.; Xue, F.; Zhang, Z.-Y.; Mac, T. C. W.
J. Organomet. Chem. 1999, 582, 292.

Alkylyttrium Complexes
Organometallics, Vol. 25, No. 16, 2006 3937
Table 1. Crystallographic Data and Structure Refinement Details for 1, 2, 3, and 6
1
2
3
6
empirical formula
fw
C54H112C16Li2N6O4Si4Y2
1426.26
C35H78N3O2Si4Y
774.27
C35H84Li2N7Si2Y
762.06
C48.50H108LiN6Si6Y
1039.80
temperature, K
wavelength, Å
cryst syst
space group
unit cell dimens
100(2)
0.71073
triclinic
P1h
a ) 10.7948(17) Å
R ) 77.585(4)°
b ) 12.651(2) Å
â ) 71.865(4)°
c ) 14.651(2) Å
γ ) 78.358(4)°
1837.2(5)
monoclinic
P2(1)/n
a ) 9.6134(5) Å
R ) 90°
b ) 21.0333(11) Å
â ) 99.5680(10)°
c ) 22.1719(11) Å
γ ) 90°
4420.8(4)
4
monoclinic
C2/c
a ) 13.5835(8) Å
R ) 90°
b ) 21.1121(13) Å
â ) 109.1320(10)°
c ) 17.6689(11) Å
γ ) 90°
4787.1(5)
4
monoclinic
C2/c
a ) 44.657(2) Å
R ) 90°
b ) 13.8992(7) Å
â ) 114.8090(10)°
c ) 22.3696(11) Å
γ ) 90°
12603.3(11)
8
1.096
volume, Å3
Z
1
density (calcd), mg/m3
absorp coeff, mm-1
F(000)
1.289
1.897
752
1.163
1.458
1680
1.057
1.297
1664
1.073
4536
cryst size, mm
θ range
0.14× 0.12 × 0.06
1.48 to 20.50°
-10 e h e 10
-12 e k e 12
-14 e l e 14
6470
0.20× 0.15 × 0.10
1.86 to 26.00°
-11 e h e 11
-25 e k e 25
-27 e l e 27
37 286
0.30× 0.17 × 0.09
1.86 to 25.50°
-16 e h e 16
-25 e k e 25
-21 e l e 21
19 308
0.16× 0.12 × 0.08
1.55 to 24.00°
-51 e h e 51,
-15 e k e 15
-25 e l e 25
44 507
index ranges
no. of reflns collected
no. of indep reflns
completeness to θ
absorp corr
3645 [Rint ) 0.0350]
99.1%
8665 [Rint ) 0.0319]
99.9%
4459 [Rint ) 0.0502]
100.0%
9877 [Rint ) 0.0649]
99.8%
SADABS
max. and min. transmn
refinement method
no. of data/restraints/
params
0.8947/ 0.7771
3645/12/352
0.8679/0.7592
8665/0/406
0.8922/0.6971
0.9191/0.8471
9877/22/982
full-matrix least-squares on F2
4459/0/382
goodness-of-fit on F2
final R indices [I > 2σ(I)]
1.010
1.032
0.980
0.952
R1 ) 0.0433,
wR2 ) 0.0988
R1 ) 0.0636,
wR2 ) 0.1052
0.772/-0.509
R1 ) 0.0303,
wR2 ) 0.0731
R1 ) 0.0400,
wR2 ) 0.0760
0.494/-0.324
R1 ) 0.0346,
wR2 ) 0.0746
R1 ) 0.0505,
wR2 ) 0.0789
0.488/-0.192
R1 ) 0.0416,
wR2 ) 0.0960
R1 ) 0.0672,
wR2 ) 0.1040
0.803/-0.682
R indices (all data)
largest diff peak and
hole, e Å-3
Scheme 2
(2.7173(150, 2.7253(15) Å).16b The Y-Cl bond lengths in the
YCl2Li fragment are comparable to the related distances in the
bis(cyclopentadienyl) ate-complex [C5Me4(CHCH2)]2Y(µ-Cl)2-
Li(Et2O)2 (2.6289(2), 2.621(2) Å)24 but expectedly shorter than
those in the bis(guanidinate) derivative [(Me3Si)2NC(NCy)2]2Y-
(µ-Cl)2Li(DME) (2.6693(3) Å).17
Complex 1 in the presence of a 20-fold molar excess of MAO
in toluene at 20 °C does not catalyze the polymerization of
ethylene and propylene.
yield (Scheme 2). Complex 2 contains two coordinated THF
molecules.
The colorless crystalline compound 2 is moisture- and air-
sensitive. The complex is fairly soluble in commonly used
organic solvents (THF, toluene, hexane). In an inert atmosphere,
it can be stored in the crystalline state at 0 °C without
decomposition, while in C6D6 solution at 20 °C it slowly
decomposes with elimination of Me4Si. In the 1H NMR
spectrum of complex 2 at 20 °C the hydrogen atoms of
methylene groups attached to the yttrium atom appear as a
doublet at -0.34 (2JYH ) 3.0 Hz); in the 13C{1H} NMR
spectrum the appropriate carbons give rise to a doublet at 35.3
ppm (2JYC ) 38.2 Hz). Chemical shifts and coupling constants
of the signals of methylene groups YCH2 in 2 are in a good
agreement with the values published for related dialkyl yttrium
species supported by monoanionic nitrogen-containing ligands
(Table 2). The guanidinate and THF ligands give expected sets
Alkylation of 1 with 4 equiv of LiCH2SiMe3 was performed
in hexane at 0 °C. Filtration of the reaction mixture and
recrystallization of the solid residue from hexane afforded the
mono(guanidinate) dialkyl derivative {(Me3Si)2NC(NCy)2}-
Y(CH2SiMe3)2(THF)2 (2) as a colorless crystalline solid in 96%
(23) Evans, W. J.; Sollberger, M. S.; Shreeve, J. L.; Olofson, J. M.; Hain,
J. H.; Ziller, J. W. Inorg. Chem. 1992, 31, 2492.
(24) Schumann, H.; Heim, A.; Demtschuk, J.; Muehle, S. Organome-
tallics 2003, 22, 118.
1
of signals in H and 13C NMR spectra.

3938 Organometallics, Vol. 25, No. 16, 2006
TrifonoV et al.
1
Table 2. Chemical Shifts of Signals of Methylene Groups Attached to Yttrium Atom, YCH2, in H and 13C Spectra of
Complexes (L)Y(CH2SiMe3)2 and Y-C Bond Distances in Complexes (L)Y(CH2SiMe3)2
1H NMR (YCH2)
13C NMR (YCH2)
Y-C bond
length, Å
complex
δ, ppm
2JY-H, Hz
δ, ppm
1JY-C, Hz
ref
trans-Y(MAC)(CH2SiMe3)2
-1.59
-0.26
-0.53
-0.83
-1.00
-0.62
-0.86
-0.94
-1.06
-0.92
- 0.91
-0.58
-0.20
-0.46
-0.11
2.5
3.3
2.1
3.0
2.1
not resolved
19.8
33.7
31.0
32.4
36.9
38.7
2.461(4)
2.476(5)
2.421(7)
14
9b
[N,N′-iPr2-trac-N′′-(CH2CH2)Nt-Bu]Y(CH2SiMe3)2
[N,N′-Me2-trac-N′′-(CH2CH2)Nt-Bu] Y(CH2SiMe3)2
29.8
28.5
35.4
38.9
9b
[Y{η5:η1-C5Me4SiMe2(C4H3O-2)}(CH2SiMe3)2 (THF)]
2.9
3.0
br s
9.7
32.1
41.2
6b
6b
12
[Y{η5:η1-C5Me4SiMe2(C4H2MeO-5)-2}(CH2SiMe3)2(THF)]
[(C6H3i-Pr2-2,6)NCH]C6H4(NC6H3i-Pr2-2,6)]Y(CH2SiMe3)2(THF)
[(C6H3i-Pr2-2,6)NCH]C6H4(NC6H3i-Pr2-2,6)]Y(CH2SiMe2Ph)2(THF)
37.5
35.1
40.3
40.0
2.318(4)
2.419(4)
2.374(4)
2.384(4)
2.427(2)
2.433(2)
2.463(2)
2.452(2)
[PhC(NC6H3 i-Pr2-2,6)2]Y(CH2SiMe3)2(THF)
[PhC(NC6H3i-Pr2-2,6)2]Y(CH2SiMe3)2(THF)2
{[Me2N(CH2)2]2N(t-Bu)}Y(CH2SiMe3)2
3.0
39.5
40.3
9b
9b
-0.54
-0.81
not resolved
30.9
36.6
10b
Crystals of 2 suitable for X-ray diffraction studies were
obtained by cooling its concentrated hexane solutions to -30
°C. The molecular structure of 2 is shown in Figure 2, and the
structure refinement data are listed in Table 1. Complex 2
crystallizes in the monoclinic space group P2(1)/n with four
molecules in the unit cell. X-ray diffraction study has revealed
that complex 2 is monomeric. The coordination sphere of the
yttrium atom consists of two nitrogen atoms of the bidentate
guanidinate ligand, two carbon atoms of the alkyl groups, and
two oxygen atoms of two THF molecules, resulting in the formal
coordination number 6. The coordination geometry of the
yttrium atom can be described as a distorted octahedron with
two carbon and two nitrogen atoms in equatorial positions and
two oxygen atoms in apical positions. It is noteworthy that the
coordination environment of the yttrium atom in complex 2 is
very different from that in the related six-coordinated amidinate
yttrium derivative [PhC(NC6H3i-Pr2-2,6)2]Y(CH2SiMe3)2(THF)2.
Thus in 2 the planes N(1)Y(1)N(2) and C(24)Y(1)C(20) are
nearly coplanar (the value of the dihedral angle between the
two planes is 7.7°), while in [PhC(NC6H3i-Pr2-2,6)2]Y(CH2-
SiMe3)2(THF)2 they are close to adopting an orthogonal
orientation (88.6°).9b
The Y-C bond lengths in complex 2 are 2.462(2) and
2.473(2) Å, which are comparable to the related distances in
dialkyl yttrium complexes (Table 2 and references therein). The
distances Y-N(1, 2) (2.3833(17), 2.4165(17) Å) differ only
slightly from each other. The C-N(1,2) bond lengths within
the guanidinate fragment are also very similar (1.337(3),
1.328(3) Å), thus proving electron delocalization within the
anionic NCN units. The considerably longer distance C(1)-
N(3) (1.443(3) Å) indicates that the N(SiMe3)2 moiety does not
take part in the conjugation. The opposite orientation of the
N(SiMe3)2 and the cyclohexyl groups relative to the NCN planes
corresponds to the minimization of their mutual steric repulsion.
The Y-O bond lengths in 2 (2.3777(14), 2.4029(14) Å) are
shorter than those in the related six-coordinated amidinate
yttrium complex [PhC(NC6H3i-Pr2-2,6)2]Y(CH2SiMe3)2(THF)2
(2.427(1), 2.451(1) Å).9b Obviously this reflects stronger steric
repulsion between THF ligands and bulkier diisopropylphenyl
radicals in the amidinate derivative than that in complex 2.
To generate cationic alkylyttrium species, reactions of
complex 2 with both Lewis ((C6H5)3B, (C6F5)3B) and Bro¨nsted
([NHMe2Ph][B(C6F5)4]) acids have been investigated. The
reactions have been carried out in THF or toluene at -78 °C in
1:1 molar ratio and afforded oily, viscous products. All attempts
to isolate individual organoyttrium compounds from the reaction
mixtures failed. Complex 2 has been found to be inactive in
ethylene and styrene polymerizations. Complex 2 activated by
an equimolar amount of (C6H5)3B or (C6F5)3B in toluene at 20
°C sluggishly oligomerizes ethylene. The catalytic tests with
ethylene were carried out under rigorously anaerobic conditions
in a sealed glass manometric system (toluene 5 mL, catalyst
concentration (1.2-2.6) × 10-3 mol/L, 20 °C, ethylene pressure
0.5 atm), which allows monitoring of the polymerization process
by absorption of the monomer. For both systems 2-(C6H5)3B
and 2-(C6F5)3B the monomer absorption did not exceed 4 mol
per mol of catalyst (the ethylene solubility in toluene is taken
into consideration) and the polymerization process was stopped
in 15 min.
Figure 2. ORTEP diagram (30% probability thermal ellipsoids)
of {(Me3Si)2NC(NCy)2}Y(CH2SiMe3)2(THF)2 (2) showing the non-
hydrogen and non-carbon (except C(1), C(20), and C(24)) atom
numbering scheme. Hydrogen atoms and carbon atoms of THF are
omitted for clarity. Selected bond distances [Å] and angles [deg]:
Y(1)-C(20) 2.462(2), Y(1)-C(24) 2.473(2), Y(1)-N(1) 2.4165-
(17), Y(1)-N(2) 2.3833(17), Y(1)-O(1) 2.3777(14), Y(1)-O(2)
2.4029(14), Y(1)-C(1) 2.838(2), N(1)-C(1) 1.337(3), C(1)-N(2)
1.328(3), C(20)-Y(1)-C(24) 112.40(7), N(2)-Y(1)-N(1) 55.80-
(6), O(1)-Y(1)-O(2) 174.50(5).

Alkylyttrium Complexes
Organometallics, Vol. 25, No. 16, 2006 3939
Scheme 3
The reaction of 1 with 8 molar equiv of MeLi in the presence
of TMEDA was carried out in toluene at 20 °C. Separation of
LiCl and recrystallization of the solid residue from diethyl ether
resulted in formation of colorless air- and moisture-sensitive
crystals of {(Me3Si)2NC(NCy)2}Y[(µ-Me)2Li(TMEDA)]2 (3) in
44% yield (Scheme 3). Complex 3 is soluble in Et2O and toluene
and insoluble in hexane.
the guanidinate NCN fragment are similar and indicate negative
charge delocalization.
Complex 3 has been found to be inactive in ethylene
polymerization.
We have attempted the synthesis of the mono(guanidinate)
dialkyl derivative {(Me3Si)2NC(NCy)2}Y(t-Bu)2 by the reaction
of complex 1 with 4 equiv of t-BuLi in hexane at 0 °C (Scheme
4). Unexpectedly after separation of LiCl and recrystallization
of the resulting off-white solid by cooling of the hexane solution
we isolated the bis(guanidinate) monoalkyl complex {(Me3-
Si)2NC(NCy)2}2Y(t-Bu) (4) in 42% yield. Recently we described
the synthesis and structure of complex 4, which was prepared
by the metathesis reaction of [(Me3Si)2NC(NCy)2]2YCl(THF)
with t-BuLi.
1
The H NMR spectrum of 3 at room temperature shows a
broadened singlet at -0.60 ppm due to the protons of the methyl
groups bridging the yttrium and lithium atoms. In the 13C{1H}
NMR spectrum a broad unresolved resonance at 7.2 ppm is
observed for the corresponding carbon atoms. These chemical
shifts are consistent with the values previously reported for
related complexes.16b,25,26 The protons of the (Me3Si)2N groups
give rise in the 1H NMR spectrum to two singlets (at 0.46 and
0.51 ppm, intensity ratio 1:2), and the appropriate carbon atoms
appear in the 13C{1H} spectrum also as a set of two signals
(2.7 and 2.8 ppm). This obviously points to nonequivalence of
the methyl groups due to a restricted rotation of the (Me3Si)2N
units caused by the environment of the bulky cyclohexyl
moieties. The TMEDA and cyclohexyl groups give expected
sets of signals in the 1H and 13C{1H} NMR spectra of complex
Apparently in the reaction of 1 with t-BuLi redistribution of
the guanidinate ligands occurs, which results in the formation
of 4. All attempts to isolate other organoyttrium compounds
from the reaction mixture failed.
7
3. The presence of lithium in 3 is proved by the Li NMR
spectrum, which contains a sole singlet at 4.16 ppm.
The molecular structure of 3 in the solid state was determined
by a crystal structure analysis on colorless crystals obtained by
slow cooling of its diethyl ether solution to -30 °C. Complex
3 crystallizes in the monoclinic, C2/c group with four molecules
in the unit cell. Crystallographic data are compiled in Table 1.
Figure 3 shows that the yttrium atom is coordinated by two
nitrogen atoms of the chelating guanidinate ligand, as well as
by four methyl carbon atoms, thus resulting in a formal
coordination number of 6.
The methyl groups bridge yttrium and lithium atoms. The
Y-C bond distances in complex 3 (2.5307(19), 2.5410(16) Å)
are slightly longer than those in the related ate-complexes Cp*-
[C6H5C(NSiMe3)2]Y(µ-Me)2Li(TMEDA) (2.480(3), 2.420(6)
Å)27 and {(Me3Si)2NC(Ni-Pr)2}2Y(µ-Me)2Li(TMEDA) (2.505(4),
2.508(4) Å)16b and are comparable to the lengths of the
µ-bridging bond in the dimeric complex [Cp2Y(µ-Me)]2
(2.553(10), 2.537(9) Å).28 The bond angles C(Me)-Y-C(Me)
in 3 are in the region of 87.43-107.50°, which is noticeably
larger than in the complexes Cp*[C6H5C(NSiMe3)2]Y(µ-Me)2-
Li(TMEDA) (89.67(11)°)27 and {(Me3Si)2NC(Ni-Pr)2}2Y(µ-
Me)2Li(TMEDA) (91.22(12)°).16b The N-C bond lengths within
Figure 3. ORTEP diagram (30% probability thermal ellipsoids)
of {(Me3Si)2NC(NCy)2}Y[(µ-Me)2Li(TMEDA)]2 (3) showing the
non-hydrogen and non-carbon (except C(1), C(11), C(12), C(11A),
and C(12A)) atom numbering scheme. Hydrogen atoms are omitted
for clarity. Selected bond distances [Å] and angles [deg]: Y(1)-
N(1A) 2.3934(13), Y(1)-N(1) 2.3934(13), Y(1)-C(11) 2.5307(19),
Y(1)-C(11A) 2.5307(19), Y(1)-C(12) 2.5410(16), Y(1)-C(12A)
2.5410(16), Li(1)-C(12) 2.150(3), Li(1)-C(11) 2.211(3), Li(1)-
N(4) 2.142(3), Li(1)-N(3) 2.153(3), N(1)-C(1) 1.3284(18), C(1)-
N(1A) 1.3284(18), N(1A)-Y(1)-N(1) 55.51(6), C(11)-Y(1)-
C(11A) 107.50(9), C(11)-Y(1)-C(12) 90.28(6), C(11A)-Y(1)-
C(12) 87.43(6), C(11)-Y(1)-C(12A) 87.43(6), C(11A)-Y(1)-
C(12A) 90.28(6), C(12)-Y(1)-C(12A) 176.13(8), C(1)-Y(1)-
C(11) 126.3(6), C(1)-Y(1)-C(12) 91.9(6).
(25) Duchateau, R.; van Wee, C. T.; Meetsma, A.; van Duijnen, P. T.;
Teuben, J. H. Organometallics 1996, 15, 2279.
(26) Shumann, H. J. Less-Common Met. 1985, 112, 327.
(27) Duchateau, R.; Meetsma, A.; Teuben, J. H. Organometallics 1996,
15, 1656.
(28) Holton, J.; Lappert, M. F.; Ballard, D. G. H.; Pearce, R.; Atwood,
J. L.; Hunter, W. E. J. Chem. Soc., Dalton Trans. 1979, 54.

3940 Organometallics, Vol. 25, No. 16, 2006
TrifonoV et al.
Scheme 4
Scheme 5
Scheme 6
To prepare mono(guanidinate) dialkyl complexes free of
Lewis base, we decided to use as a precursor a mono-
(guanidinate) dichloro yttrium complex containing diethyl ether,
which possesses weaker coordination ability. Replacement of
THF by diethyl ether in the reaction mixture prevented formation
of an ate-complex and allowed isolation of the neutral complex
{(Me3Si)2NC(NCy)2}YCl2(Et2O) (5). Reaction of YCl3 with
Li[(Me3Si)2NC(NCy)2] (1:1 molar ratio) obtained in situ from
Li(Et2O)[N(SiMe3)2] and the 1,3-dicyclohexyl-substituted car-
bodiimide has been carried out in diethyl ether at 20 °C.
Separation of LiCl by filtration, evaporation of the solvent, and
extraction of the residue with hot hexane resulted in isolation
of complex 5 as a microcrystalline colorless solid in 71% yield
(Scheme 5).
of complex {(Me3Si)2NC(NCy)2}2Y(µ-CH2SiMe3)2Li‚(C5H12)0.5.
The molecular structure of 6 is shown in Figure 4, and the crystal
and structure refinement data are listed in Table 1. Complex 6
crystallizes in the monoclinic space group C2/c with eight
molecules in the unit cell.
The X-ray diffraction study has revealed that complex 6 is a
monomeric ate-complex, where the yttrium atom is coordinated
by two nitrogen atoms of two bidentate guanidinate ligands and
Complex 5 was characterized by spectroscopic methods and
microanalysis; unfortunately all our attempts to obtain single
crystals of 5 suitable for X-ray investigation failed. Complex 5
is air- and moisture-sensitive; it is soluble in Et2O and THF
1
and sparingly soluble in hexane and toluene. The H and 13C-
{1H} NMR spectra of complex 5 in C6D6 at 20 °C show the
expected sets of resonances due to the guanidinate fragment
and the coordinated Et2O molecules and do not exhibit any
special features.
Complex 5 was used as a starting material for the preparation
of dialkyl species. Reaction of compound 5 with 2 molar equiv
of LiCH2SiMe3 in hexane at 0 °C afforded ate-complex {(Me3-
Si)2NC(NCy)2}2Y(µ-CH2SiMe3)2Li (6) instead of the expected
neutral dialkyl derivative. Complex 6 was isolated after recrys-
tallization from pentane in 34% yield (Scheme 6) as a colorless,
air- and moisture-sensitive crystalline compound, highly soluble
in hydrocarbon solvents.
Figure 4. ORTEP diagram (30% probability thermal ellipsoids)
of {(Me3Si)2NC(NCy)2}2Y(µ-CH2SiMe3)2Li (6) showing the non-
hydrogen and non-carbon (except C(13), C(32), C(39), and C(43))
atom numbering scheme. Hydrogen atoms are omitted for clarity.
Selected bond distances [Å] and angles [deg]: Y(1)-N(2) 2.3497(14),
Y(1)-N(4) 2.3626(15), Y(1)-N(5) 2.3914(13), Y(1)-N(1) 2.3998-
(14), Y(1)-C(39) 2.543(2), Y(1)-C(43) 2.5460(17), Y(1)-C(13)
2.8118(18), Y(1)-C(32) 2.8167(17), Y(1)-Li(1) 2.882(4), Li(1)-
C(43) 2.083(5), Li(1)-C(39) 2.103(5), Li(1)-C(41) 2.514(5),
Li(1)-C(45) 2.947(5), Li(1)-C(42) 3.551(5), Li(1)-C(44) 3.482(5),
N(1)-C(13) 1.336(2), N(2)-C(13) 1.3274(19), N(4)-C(32) 1.332-
(2), N(5)-C(32) 1.334(3), N(4)-Y(1)-N(5) 56.25(5), N(2)-Y(1)-
N(1) 56.33(4), C(39)-Y(1)-C(43) 88.95(6), C(39)-Li(1)-C(43)
116.78(4), C(39)-Si(5)-C(42) 110.99(9), C(39)-Si(5)-C(41)
108.91(10), C(39)-Si(5)-C(40) 114.59(9), C(43)-Si(6)-C(44)
110.67(9), C(43)-Si(6)-C(45) 109.39(10), C(43)-Si(6)-C(46)
114.82(10).
The methylene protons of the alkyl groups bridging the
1
yttrium and lithium atoms appear in the H NMR spectrum of
6 (20 °C) as a broadened singlet at -0.52 ppm, which is high-
field shifted compared to the signal of the methylene protons
of the terminal alkyl ligands in 2 (-0.25 ppm). The Me3Si
protons of the alkyl radicals give rise to a singlet at 0.29 ppm,
while a singlet at 0.36 ppm corresponds to the protons of the
(Me3Si)2N groups. The presence of a lithium atom in 6 is proved
by the 7Li NMR spectrum, which exhibits a singlet at 5.77 ppm.
Crystallization of 6 by prolonged cooling of the concentrated
pentane solutions to -20 °C resulted in single crystals of the
solvate containing a half molecule of pentane per one molecule

Alkylyttrium Complexes
Organometallics, Vol. 25, No. 16, 2006 3941
temperature for 40 min. Complex 1 was obtained as a colorless
crystalline solid (2.90 g, 95%). IR (Nujol, KBr, cm-1): 1620 s,
1320 m, 1240 s, 1270 m, 1200 m, 1150 m, 1100 m, 1050 m, 950
s, 930 s, 860 m, 830 s. 1H NMR (200 MHz, C6D6, 20 °C): δ 0.31,
0.37, 0.45 (s, together 36 H, NSi(CH3)3), 1.43-2.12 (br m, together
56 H, CH2 Cy, â-CH2, THF), 3.47 (br m, 4 H, CH Cy), 3.85 (br s,
8 H, R-CH2, THF). 13C{1H} NMR (50 MHz, C6D6, 20 °C): δ 1.8,
2.3, 2.7 [N(Si(CH3)3)2], 26.4 (â-CH2, THF), 25.3, 26.1, 35.7, 37.3
(CH2, Cy), 54.9 (CH, Cy), 70.1 (R-CH2, THF), 170.9 (CN3) ppm.
Anal. Calcd for C54H112Cl6N6O4Si4Y2 (1426.26): C, 45.43; H, 7.85;
Y, 12.48. Found: C, 45.80; H, 8.02; Y, 12.11.
two carbon atoms of alkyl groups, thus having coordination
number 6. Expectedly the bond distances between the yttrium
atom and µ-bridging methylene carbons in 6 (2.543(2), 2.5460(17)
Å) are noticeably longer than the Y-C bond lengths in
compounds with terminal alkyl ligands (2: 2.462(2), 2.473(2)
Å; for other examples see Table 2) and are comparable to those
found in ate-complex 3 (2.5307(19), 2.5410(16) Å). The most
interesting feature of this compound is an extremely low formal
coordination number of the lithium atom, which is coordinated
just by two methylene carbon atoms. Obviously the coordination
sphere of the lithium atom is saturated due to agostic interactions
with two methyl groups of the trimethylsilyl substituents. Two
short contacts between lithium and the methyl carbon atoms
are observed: Li(1)-C(41) 2.514(5) and Li(1)-C(45) 2.947(5)
Å. However the existence of the agostic interaction in 6 does
not effect the bond angles about the silicon atoms in the alkyl
fragments; they are rather similar and fall into the range 108.9-
114.8°, which is close to the value expected for an sp3-
hybridized silicon atom. The N-C bond lengths within both
guanidinate NCN fragments have very close values, reflecting
the negative charge delocalization.
Synthesis of [{(Me3Si)2NC(NCy)2}Y(CH2SiMe3)2(THF)2] (2).
To a solution of 1 (0.95 g, 0.67 mmol) in hexane (20 mL) was
added slowly a solution of Me3SiCH2Li (0.25 g, 2.67 mmol) in
hexane (10 mL) at 0 °C, and the reaction mixture was stirred for
1 h. The pale yellow solution was filtered and concentrated in vacuo
to approximately a quarter of its initial volume. The solution was
cooled to -30 °C and kept at that temperature for 3 days. The
mother liquor was decanted; the solid was washed with cold hexane
and dried in vacuo at room temperature for 30 min. 3 was isolated
as off-white crystals (0.99 g, 96%). IR (Nujol, KBr, cm-1): 1634
s, 1600 m, 1296 m, 1250 s, 1219 m, 1008 m, 958 s, 942 s, 842 s.
1H NMR (200 MHz, C6D6, 20 °C): δ -0.34 (d, 2JY-H ) 3.0 Hz, 4
H, YCH2), 0.28 (s, 18 H, NSi(CH3)3), 0.40 (s, 18 H, Si(CH3)3),
1.27-2.11 (br m, together 28 H, CH2 Cy, â-CH2 THF), 3.31 (br
m, 2 H, CH Cy), 3.69 (br s, 8 H, R-THF) ppm. 13C{1H} NMR (50
Conclusions
The N,N′-dicyclohexyl-N′′-bis(trimethylsilyl) guanidinate ligand
was found to form a suitable coordination environment for the
synthesis of monomeric neutral dialkyl yttrium complexes.
Employment of bulky guanidinate ligands also allowed prepara-
tion of mono- and bis(guanidinate) alkyl yttrium ate-complexes.
Unusually low formal coordination numbers and agostic interac-
tions with the methyl groups of the alkyl ligands have been
found for the lithium atom in the complex {(Me3Si)2NC-
(NCy)2}2Y(µ-CH2SiMe3)2Li (6) in the solid state.
MHz, C6D6, 20 °C): δ 2.4 (NSi(CH3)3)2), 4.6, 4.7 (CH2Si(CH3)3),
1
25.9 (â-CH2, THF), 25.4, 26.2, 37.7 (CH2, Cy), 35.3 (d, JY-C
)
38 Hz, YCH2), 54.8 (CH, Cy), 68.1 (R-CH2, THF), 169.0 (CN3)
ppm. Anal. Calcd for C35H76N3O2Si4Y (772.3): C, 54.38; H, 9.84;
Y, 11.52. Found: C, 54.73; H, 10.01; Y, 11.38.
Synthesis of [{(Me3Si)2NC(NCy)2}Y{(µ2-Me)2Li(TMEDA)}2]
(3). To a solution of 1 (1.12 g, 0.79 mmol) in toluene (20 mL)
were slowly added TMEDA (0.37 g, 3.16 mmol) and a solution of
MeLi in diethyl ether (4.0 mL, 1.6 M solution, 6.32 mmol) at 0
°C, and the reaction mixture was stirred for 45 min, allowed to
warm to room temperature, and stirred for 1.5 h. The brown solution
was filtered and the solvent evaporated in vacuo. Complex 3 was
isolated by recrystallization from diethyl ether as colorless crystals
(0.52 g, 44%). IR (Nujol, KBr, cm-1): 1627 w, 1355 s, 1288 s,
1253 s, 1190 m, 1155 m, 1069 m, 996 m, 954 s, 834 s, 788 m, 638
Experimental Details
All experiments were performed in evacuated tubes, using
standard Schlenk-tube techniques, with rigorous exclusion of traces
of moisture and air. After drying over KOH, THF was purified by
distillation from sodium/benzophenone ketyl, and hexane and
toluene were purified by distillation from sodium/triglyme ben-
zophenone ketyl prior to use. C6D6 was dried with sodium/
benzophenone ketyl and condensed in vacuo prior to use. N,N′-
Dicyclohexylcarbodiimide was purchased from Acros. Anhydrous
1
w cm-1. H NMR (200 MHz, C6D6, 20 °C): δ -0.60 (br s, 12 H,
Me), 0.46, 0.51 (s, together 18 H, Si(CH3)3), 1.23-2.20 (br m, 52
H, CH2 Cy, CH2, CH3, TMEDA), 3.58 (br m, 2 H, CH Cy). 13C-
{1H} NMR (50 MHz, C6D6, 20 °C): δ 2.7, 2.8 (Si(CH3)3), 7.2 (µ-
CH3), 26.3, 26.5, 26.6, 26.7 (CH2, Cy), 46.00 (N(CH3)), 54.9 (CH,
29
YCl3 and [(Me3Si)2NLi(Et2O)]30 were prepared according to
7
Cy), 57.0 (NCH2), 164.6 (CN3). Li NMR (77.73 MHz, C6D6, 20
literature procedures. All other commercially available chemicals
were used after the appropriate purification. NMR spectra were
recorded on a Bruker DPX 200 spectrometer (1H, 200 MHz; 13C,
50 MHz; 7Li, 77.7 MHz) in C6D6 at 20 °C, unless otherwise stated.
°C): δ 4.16 ppm. Anal. Calcd for C35H84Li2N7Si2Y (762.1): C,
55.11; H, 11.02; Y, 11.68. Found: C, 54.84; H, 11.40; Y, 11.39.
Reaction of 1 with t-BuLi (1:2). Synthesis of [(Me3Si)2NC-
(NCy)2]2Yt-Bu (4). To a solution of 1 (1.05 g, 0.74 mmol) in hexane
(30 mL) was added a solution of t-BuLi (1.97 mL, 1.5 N, 2.96
mmol) at 0 °C. The reaction mixture was stirred for 40 min. The
pale yellow solution was filtered and concentrated in vacuo to
approximately a quarter of its initial volume. Complex 4 was
isolated as colorless crystals (0.55 g, 42%) from hexane under
cooling. IR (Nujol, KBr, cm-1): 1620 s, 1330 m, 1220 s, 1260 m,
1
Chemical shifts for H and 13C spectra were referenced internally
using the residual solvent resonances and are reported relative to
TMS. IR spectra were recorded as Nujol mulls on FSM 1201 and
Specord M80 instruments. Lanthanide metal analyses were carried
out by complexometric titration. The C, H elemental analysis was
made in the microanalytical laboratory of IOMC.
Synthesis of [{(Me3Si)2NC(NCy)2}Y(µ2-Cl)(µ2-Cl)2Li(THF)2]2
(1). To a solution of [(Me3Si)2NLi(Et2O)] (1.02 g, 4.23 mmol) in
THF (30 mL) was added slowly 1,3-dicyclohexylcarbodiimide (0.87
g, 4.23 mmol) at 20 °C, and the reaction mixture was stirred for
45 min. YCl3 (0.83 g, 4.23 mmol) was added, and the reaction
mixture was stirred overnight. The solution was filtered, the solvent
evaporated in vacuo, and the solid residue extracted with toluene
(2 × 30 mL). The toluene extracts were filtered, and the solution
was slowly concentrated at room temperature to a quarter of its
volume, cooled to -30 °C, and left overnight. The crystalline
precipitate was washed with cold hexane and dried in vacuo at room
1
1205 m, 1150 m, 950 s, 930 s, 830 s. H NMR (200 MHz, C6D6,
20 °C): δ 0.28, 0.32, 0.36 (3 s, together 36 H, Si(CH3)3), 1.48 (s,
9 H, C(CH3)3), 1.27-2.04 (br m, 40 H, CH2 Cy), 3.45, 3.63 (2 br
m, together 4 H, CH Cy). 13C{1H} NMR (50 MHz, C6D6, 20 °C):
δ 2.3, 2.4, 2.8 (NSiCH3)2), 24.9, 25.9, 26.1, 26.2, 26.4 (CH2, Cy),
30.6, 30.7 (C(CH3)3), 37.5 (d, 1JY-C ) 56 Hz, C(CH3)3), 55.2 (CH,
Cy), 168.7 (CN3) ppm. Anal. Calcd for C42H89N6Si4Y (879.4): C,
57.36; H, 10.12; Y, 10.10. Found: C, 56.91; H, 9.77; Y, 9.80.
Synthesis of [(Me3Si)2NC(NCy)2]YCl2(Et2O) (5). To a solution
of [(Me3Si)2NLi(Et2O)] (0.94 g, 3.90 mmol) in Et2O (30 mL) was

3942 Organometallics, Vol. 25, No. 16, 2006
TrifonoV et al.
added slowly 1,3-dicyclohexylcarbodiimide (0.80 g, 3.90 mmol)
at 20 °C, and the reaction mixture was stirred for 45 min. YCl3
(0.76 g, 3.90 mmol) was added, and the reaction mixture was stirred
overnight. The solution was filtered, the solvent evaporated in
vacuo, and the solid residue extracted with hexane (2 × 30 mL).
The hexane extracts were filtered, and the solution was slowly
concentrated at room temperature to a quarter of its initial volume,
cooled to -30 °C, and left overnight. The crystalline precipitate
was washed with cold hexane and dried in vacuo at room
temperature for 60 min. 2 was isolated as a white microcrystalline
solid (1.66 g, 71%). IR (Nujol, KBr, cm-1): 1615 s, 1542 m, 1358
s, 1304 m, 1257 s, 1202 m, 1124 m, 1092 m, 1065 m, 1030 m,
1006 m, 951 s, 842 s, 760 m, 681 m, 638 m. 1H NMR (200 MHz,
C6D6, 20 °C): δ 0.43 (s, 18 H, Si(CH3)3), 1.07 (t, 3JH-H ) 6.8 Hz,
6 H, CH3, Et2O), 1.41-2.01 (br m, 20 H, CH2 Cy,), 3.23 (q, 3JH-H
) 7.0 Hz, 4 H, CH2, Et2O), 3.44 (br m, 2 H, CH Cy). 13C{1H}
NMR (50 MHz, C6D6, 20 °C): δ 2.7 (N(Si(CH3)3)2), 15.0 (CH3,
Et2O), 26.1, 26.5, 37.3 (CH2, Cy), 54.8 (CH, Cy), 65.7 (CH2, Et2O),
168.8 (CN3) ppm. Anal. Calcd for C23H50Cl2N3OSi2Y (600.65): C,
45.99; H, 8.38; Y, 14.80. Found: C, 46.40; H, 8.72; Y, 14.48.
Synthesis of {(Me3Si)2NC(NCy)2}2Y(µ-CH2SiMe3)2Li (6). To
a solution of 2 (0.83 g, 1.38 mmol) in hexane (20 mL) was added
a solution of Me3SiCH2Li (0.26 g, 2.76 mmol) in hexane (15 mL)
at 0 °C, and the reaction mixture was stirred for 30 min. The pale
yellow solution was filtered, and hexane was evaporated in vacuo.
Complex 4 was isolated upon cooling of a concentrated pentane
solution as colorless crystals (0.47 g, 34%). IR (Nujol, KBr, cm-1):
1351 m, 1252 s, 1190 m, 1135 m, 1073 w, 1002 m, 944 s, 858 s,
X-ray Crystallography. Low-temperature diffraction data of 1,
2, 3, and 6 were collected on a Bruker-AXS Smart Apex
diffractometer with graphite-monochromated Mo KR radiation (λ
) 0.71073 Å), performing æ- and ω-scans. All structures were
solved by Patterson (1) and direct (2, 3, 6) methods and refined
against F2 on all data by full-matrix least squares with SHELXTL.31
Absorption correction was applied using SADABS.32 All non-
hydrogen atoms were refined anisotropically. All hydrogen atoms
in 1 and 2 were included in idealized positions, and their Uiso values
were set to ride on the Ueq values of the parent carbon atoms (Uiso-
(H) ) 1.5Ueq for methyl carbons and 1.2Ueq for other carbons). In
3 and 6 H’s (except H atoms in the solvate of pentane) were located
from Fourier synthesis and refined isotropically. H atoms in the
solvate of pentane (6) were placed in idealized positions and refined
with Uiso(H) ) 1.5Ueq for methyl carbons and 1.2Ueq for methylene
carbons Crystallographic data and structure refinement details are
given in Table 1.
Acknowledgment. This work has been supported by the
Russian Foundation for Basic Research (Grant Nos. 05-03-
32390, 06-03-32728) and the Grant of President of Russian
Federation supporting scientific schools (Nos. 58.2003.3,
1652.2003.3, 8017.2006.3). A.T. thanks the Russian Foundation
for Science Support.
Supporting Information Available: This material is available
free of charge via the Internet at http://pubs.acs.org.
1
838 s, 721 m. H NMR (200 MHz, C6D6, 20 °C): δ -0.52 (br s,
OM060280C
4 H, µ-CH2), 0.30 (s, 18 H, Y(CH2Si(CH3)3)2), 0.36 (s, 36 H, NSi-
(CH3)3), 1.23-1.96 (br m, 40 H, CH2 Cy), 3.41 (br m, 4 H, CH
Cy). 13C{1H} NMR (50 MHz, C6D6, 20 °C): δ 2.3, 3.6 (CH2Si-
(CH3)3), 2.9 (NSi(CH3)3), 14.6 (d, 1JY-C ) 63 Hz, Y(CH2SiMe3)2-
Li), 26.0, 26.2, 26.3, 37.6, 37.8 (CH2, Cy), 54.8 (CH, Cy), 168.6
(CN3). Anal. Calcd for C46H102LiN6Si6Y (1003.72): C, 55.04; H,
10.24; Y, 8.87. Found: C, 54.72; H, 10.53; Y, 8.46.
(29) Taylor, M. D.; Carter, C. P. J. Inorg. Nucl. Chem. 1962, 24, 387.
(30) Manzer, L. E. Inorg. Chem. 1978, 17, 1552.
(31) Sheldrick, G. M. SADABS v.2.01, Bruker/Siemens Area Detector
Absorption Correction Program; Bruker AXS: Madison, WI, 1998.
(32) Sheldrick, G. M. SHELXTL v. 6.12, Structure Determination
Software Suite; Bruker AXS: Madison, WI, 2000.