Synthetic and structural studies of the cyclopentadienyl-free yttrium alkyl alkoxide and aryloxide complexes [(Me3Si)2CH]2y(μ-OCMe3) 2Li(THF) and[Me3SiCH2]2Y(OC6H 3tBu2-2,6)(THF)2

Article abstract of DOI:10.1021/om9508400

YCl₃ reacts with 2 equiv of LiCH(SiMe₃)₂ and 2 equiv of LiOCMe₃ in THF to form the dialkyl dialkoxide complex [(Me₃Si)₂CH]₂Y(μ-OCMe₃) ₂Li(THF), 1. The yttrium in 1 is surrounded by a distorted tetrahedral arrangement of two terminal alkyl groups and two bridging alkoxide groups, and the coordination around lithium is trigonal planar. The reaction of YCl₃ with 2 equiv of LiCH₂SiMe₃ and 1 equiv of LiOC₆H₃^tBu₂-2,6 in THF forms the neutral dialkyl aryloxide complex (Me₃SiCH₂)₂Y(OC₆H₃ ^tBu₂-2,6)(THF)₂ 2. The coordination geometry around yttrium in 2 is a distorted trigonal bipyramid with the THF groups in the apical positions.

Full text of DOI:10.1021/om9508400

Organometallics 1996, 15, 1351-1355
1351
Syn th etic a n d Str u ctu r a l Stu d ies of th e
Cyclop en ta d ien yl-F r ee Yttr iu m Alk yl Alk oxid e a n d
Ar yloxid e Com p lexes [(Me3Si)2CH]2Y(µ-OCMe3)2Li(THF )
t
a n d [Me3SiCH2]2Y(OC6H3 Bu 2-2,6)(THF )2
William J . Evans,* Randy N. R. Broomhall-Dillard, and J oseph W. Ziller
Department of Chemistry, University of California, Irvine, California 92717
Received October 23, 1995X
YCl3 reacts with 2 equiv of LiCH(SiMe3)2 and 2 equiv of LiOCMe3 in THF to form the
dialkyl dialkoxide complex [(Me3Si)2CH]2Y(µ-OCMe3)2Li(THF), 1. The yttrium in 1 is
surrounded by a distorted tetrahedral arrangement of two terminal alkyl groups and two
bridging alkoxide groups, and the coordination around lithium is trigonal planar. The
t
reaction of YCl3 with 2 equiv of LiCH2SiMe3 and 1 equiv of LiOC6H3 Bu2-2,6 in THF forms
t
the neutral dialkyl aryloxide complex (Me3SiCH2)2Y(OC6H3 Bu2-2,6)(THF)2, 2. The coordina-
tion geometry around yttrium in 2 is a distorted trigonal bipyramid with the THF groups in
the apical positions.
In tr od u ction
alkyl alkoxide complexes have appeared.22-26 Some of
these complexes appear to have high reactivity, but
further development in this area depends on convenient
syntheses of a greater variety of mixed-ligand alkyl
alkoxide species.
Although historically the organometallic chemistry of
yttrium and the lanthanide metals has been dominated
by cyclopentadienyl ligands, in recent years there has
been considerable interest in developing alternative
auxiliary ligands to solubilize and stabilize reactive
complexes of these metals.1-13 Alkoxide and aryloxide
ligands are attractive for this purpose since they form
strong bonds to these oxophilic metals and may allow a
wider range of reactions to be realized. Since these
ligands can be conveniently obtained in great variety
from alcohols, considerable variation in steric and
electronic features is possible.
To date the most straightforward syntheses of yttrium
alkyl alkoxides have involved cyclopentadienyl-contain-
ing systems, eq 1.5,27 Formation of cyclopentadienyl-
(C5Me5)Ln(OAr)2 + LiCH(SiMe3)2 hexanes8
(C5Me5)(OAr)Ln(CH(SiMe3)2) + LiOAr (1)
t
Ln ) Y, Ce; OAr ) OC6H3 Bu2-2,6
Previous studies in this area necessarily focused on
the basic chemistry of homoleptic alkoxide sys-
tems,11,12,14-22 but recently some reports of mixed-ligand
free yttrium alkyl alkoxides has been more complicated
as indicated in eqs 224 and 3.28 In a samarium system,
a dilithium species has been reported as shown in eq
4.25
X Abstract published in Advance ACS Abstracts, February 1, 1996.
(1) Evans, W. J . New J . Chem. 1995, 19, 525-533.
(2) Evans, W. J .; Sollberger, M. S.; Hanusa, T. P. J . Am. Chem. Soc.
1988, 110, 1841-1850.
(3) Evans, W. J .; Engerer, S. C.; Piliero, P. A.; Wayda, A. L. In
Fundamental Research in Homogeneous Catalysis; Tsutsui, M., Ed.;
Plenum Press: New York, 1979; Vol. 3, pp 941-952.
(4) Schaverien, C. J . Adv. Organomet. Chem. 1994, 36, 283-362.
(5) Schaverien, C. J .; Frijns, J . H.; Heeres, J . J .; van der Hende, J .
R.; Teuben, J . H.; Spek, A. L. J . Chem. Soc., Chem. Commun. 1991,
642-644.
(6) Schaverien, C. J . Organometallics 1994, 13, 69-82.
(7) Schaverien, C. J .; Orpen, A. G. Inorg. Chem. 1991, 30, 4968-
4978.
Reported here are two straightforward syntheses of
cyclopentadienyl-free alkyl yttrium alkoxide and aryl-
oxide complexes which show that by using the right
combinations of metal, alkyl, and alkoxide or aryloxide,
such complexes can be made directly from halide
(18) Evans, W. J .; Olofson, J . M.; Ziller, J . W. J . Am. Chem. Soc.
1990, 112, 2308-2314.
(19) Evans, W. J .; Golden, R. E.; Ziller, J . W. Inorg. Chem. 1991,
30, 4963-4968.
(8) Lee, L.; Berg, D. J .; Bushnell, G. W. Organometallics 1995, 14,
8-10.
(9) Edelmann, F. T. New J . Chem. 1995, 19, 535-550.
(10) Wedler, M.; Noltemeyer, M.; Pieper, U.; Schmidt, H.-G.; Stalke,
D.; Edelmann, F. T. Angew. Chem., Int. Ed. Engl. 1990, 29, 894-896.
(11) Barnhart, D. M.; Clark, D. L.; Gordon, J . C.; Huffman, J . C.;
Watkin, J . G. Zwick, B. D. J . Am. Chem. Soc. 1993, 115, 8461-8462.
(12) Barnhart, D. M.; Clark, D. L.; Huffman, J . C.; Vincent, R. L.;
Watkin, J . G. Inorg. Chem. 1993, 32, 4077-4083.
(13) Barhnart, D. M.; Clark, D. L.; Gordon, J . C.; Huffman, J . C.;
Vincent, R. L.; Watkin, J . G.; Zwick, B. D. Inorg. Chem. 1994, 33,
3487-3497.
(20) Bradley, D. C.; Chudzynska, H.; Frigo, D. M.; Hursthouse, M.
D.; Mazid, M. A. J . Chem. Soc., Chem. Commun. 1988, 1258-1259.
(21) Hitchcock, P. B.; Lappert, M. F.; Smith, R. G. Inorg. Chim. Acta
1987, 139, 183-184.
(22) Edelmann, A.; Gilje, J . W.; Edelmann, F. T. Polyhedron 1992,
11, 2421-2422.
(23) Evans, W. J .; Boyle, T. J .; Ziller, J . W. J . Am. Chem. Soc. 1993,
115, 5084-5092.
(24) Evans, W. J .; Boyle, T. J .; Ziller, J . W. J . Organomet. Chem.
1993, 46, 141-148.
(25) Clark, D. L.; Gordon, J . C.; Huffman, J . C.; Watkin, J . G.; Zwick,
B. D. Organometallics 1994, 13, 4266-4270.
(26) Schaverien, C. J .; Meijboom, N.; Orpen, A. G. J . Chem. Soc.,
Chem. Commun. 1992, 124-126.
(27) Heeres, H. J .; Meetsma, A.; Teuben, J . H.; Rogers, R. D.
Organometallics 1989, 8, 2637-2646.
(28) Evans, W. J .; Shreeve, J . L.; Broomhall-Dillard, R. N. R.; Ziller,
J . W. J . Organomet. Chem. 1995, 501, 7-11.
(14) Mehrotra, R. C.; Singh, A.; Tripathi, U. M. Chem. Rev. 1991,
91, 1287-1303.
(15) Evans, W. J .; Sollberger, M. S. Inorg. Chem. 1988, 27, 4417-
4423.
(16) Evans, W. J .; Olofson, J . M.; Ziller, J . W. Inorg. Chem. 1989,
28, 4308-4309.
(17) Gradeff, P. S.; Yunlu, K.; Deming, T. J .; Olofson, J . M.; Doedens,
R. J .; Evans, W. J . Inorg. Chem. 1990, 29, 420-424.
0276-7333/96/2315-1351$12.00/0 © 1996 American Chemical Society

1352 Organometallics, Vol. 15, No. 5, 1996
[(C9H7)Y(µ-OCMe3)(OCMe3)]2 +
Evans et al.
a colorless hexane soluble layer was separated from an oily
brown hexane insoluble layer and a white powder (presumably
LiCl). The hexane-soluble fraction was dried by rotary evapo-
ration to give 1 as a colorless solid (209 mg, 54%). Crystals
suitable for X-ray diffraction were grown from a concentrated
toluene solution at -35 °C. 1H NMR (C6D6): δ 3.32 (s, 4H,
THF), 1.32 (s, 9H, OC(CH3)3), 1.22 (s, 4H, THF), 0.48 (s, 18H,
(Si(CH3)3)2), -0.90 (d, 1H, CH(SiMe3)2, J Y-H ) 2.6 Hz). 13C
NMR (C6D6): δ 71.4 (OCMe3), 68.4 (THF), 34.3 (OC(CH3)3),
25.1 (THF), 5.9 (Si(CH3)3), 1.4 (CHSiMe3). IR (KBr): 2965 s,
2888 m, 1460 w, 1361 m, 1245 s, 1204 m, 1016 s, 957 s, 846 s,
763 m, 664 m cm-1. Anal. Calcd for C26H64LiO3Si4Y: C, 49.34;
H, 10.19; Li, 1.10; Y, 14.05. Found: C, 48.73; H, 10.21; Li,
1.39; Y, 14.35. Molecular weight (isopiestic, toluene): calcd,
633; found, 670. Thermal decomposition of 1 begins to be
evident at about 60 °C.
4LiCH2SiMe3 1. hexanes8
2. THF
2(Me3SiCH2)Y[(µ-CH2)2SiMe2][(µ-OCMe3)Li(THF)2]2
+ 2LiC9H7 (2)
YCl3 + 2LiCH2SiMe3 + 2LiOCMe3 THF8
{(Me3SiCH2)x(Me3CO)1-xY(µ-OCMe3)4[Li(THF)]4-
(µ4-Cl)}+[Y(CH2SiMe3)4]- (3)
Sm(OAr)3(THF)2 + 3LiCH2R THF8
[Li(THF)]2[Sm(OAr)3(CH2R)2] + LiCH2R (4)
[Me3SiCH2]2Y(OC6H3tBu 2-2,6)(THF )2 , 2. As described for
1, YCl3 (0.920 g, 4.71 mmol) was treated with LiCH2SiMe3
(0.887 g, 9.42 mmol) and LiOC6H3 Bu2-2,6 (1.00 g, 4.71 mmol)
i
OAr ) OC6H3 Pr2-2,6; R ) SiMe3
t
in THF and the clear yellow-brown solution was stirred for
18 h. THF was removed by rotary evaporation, and the
resulting off white solid was extracted with toluene. Removal
of toluene by rotary evaporation gave 2 as an off white solid
(2.69 g, 93%). After drying, 2 has only limited solublity in
toluene but is highly soluble in THF. Crystals suitable for
X-ray diffraction were grown from a concentrated toluene/THF
solution at -35 °C. 1H NMR (THF-d8): δ 6.97 (d, 2H,
phenoxide meta-H, J H-H ) 7.7 Hz), 6.34 (t, 1H, phenoxide para-
H, J H-H ) 7.7 Hz), 1.51 (s, 18H, OC6H3(Me3)2), -0.03 (s, 18H,
CH2SiMe3), -0.52 (d, 4H, CH2SiMe3, J Y-H ) 3.6 Hz). 13C NMR
(THF-d8): δ 138.2, 124.5, 114.7 (phenoxide), 68.2 (THF), 35.7
(OC6H3(CMe3)2), 32.1 (CH2SiMe3), 26.4 (THF), 4.9 (CH2SiMe3).
IR (KBr): 2954 s, 2892 s, 1580 m, 1456 m, 1410 s, 1380 m,
precursors. In the alkoxide case, the tert-butoxide
ligand is used since this group has been shown to have
an extensive chemistry with yttrium.2,15,18,23,24,28-30 For
the aryloxide case, the common 2,6-di-tert-butylphenox-
ide ligand is used.5,6,21,31,32
Exp er im en ta l Section
All of the chemistry described below was performed under
nitrogen with rigorous exclusion of air and water using
standard Schlenk, vacuum line and glovebox techniques.
Solvents were dried and distilled,33 and yttrium trichloride
(Rhoˆne-Poulenc) was dried as described previously.34 LiOCMe3
was prepared from LiCMe3 (freshly sublimed) and HOCMe3
(distilled from K) in hexanes and was purified by sublimation
before use.28 Bis(trimethylsilyl)chloromethane (Aldrich) was
dried over P2O5 and reacted with lithium powder (Aldrich,
-325 mesh) to produce (bis(trimethylsilyl)methyl)lithium,35
which was purified by sublimation. ((Trimethylsilyl)methyl)-
lithium (Aldrich, 1.0 M in pentanes) and tert-butyllithium
(Aldrich, 1.0 M in hexanes) were dried in vacuo to remove
solvent and purified by sublimation. Freshly sublimed 2,6-
di-tert-butylphenol (Aldrich) was reacted with the LiCMe3 in
1262 s, 1195 m, 1097 m, 1041 s, 862 s, 744 s, 651 m cm-1
.
Anal. Calcd for C30H59O3Si2Y: Y, 14.51. Found: Y, 13.5.
Molecular weight (isopiestic, THF): calcd for C30H59O3Si2Y,
613; found, 1100. Thermal decomposition of 2 begins to be
evident at about 60 °C.
X-r a y Da ta Collection , Str u ctu r e Deter m in a tion , a n d
Refin em en t for [(Me3Si)2CH]2Y(µ-OCMe3)2Li(THF ), 1. A
colorless crystal of approximate dimensions 0.17 × 0.33 × 0.42
mm was immersed in Paratone-D oil under nitrogen and then
manipulated in air onto a glass fiber and transferred to the
nitrogen stream of a Syntex P4 diffractometer.36 Determina-
tion of Laue symmetry, crystal class, unit cell parameters, and
the crystal’s orientation matrix were carried out according to
standard procedures.37 Low-temperature (163 K) intensity
data were collected via a 2θ-ω scan technique with Mo KR
radiation.
All 2612 data were corrected for Lorentz and polarization
effects and placed on an approximately absolute scale. The
Laue symmetry is 2/m, and the lattice type is C-centered (hkl;
h + k ) 2n). The systematic extinction observed is h0l for l )
2n + 1. The two possible monoclinic space groups are Cc and
C2/c.
All crystallographic calculations were carried out using the
UCI-modified version of the UCLA Crystallographic Comput-
ing Package38 and the SHELXTL39 program. The analytical
scattering factors40 for neutral atoms were used throughout
the analysis. The structure was solved and refined (SHELX-
TL) in both of the above space groups but neither initially
proved satisfactory. The molecular C2 symmetry does not
t
hexanes to form LiOC6H3 Bu2-2,6, which was filtered off, dried,
and purified by sublimation. 1H and 13C NMR spectra were
recorded on General Electric GN500 and Omega 500 spec-
trometers. 1H NMR chemical shifts were assigned relative to
residual protons in C6D6 at δ 7.15 and in THF-d8 at δ 1.79.
13C NMR chemical shifts were assigned relative to carbons in
C6D6 at δ 128.0 and in THF-d8 at δ 67.4. Infrared spectra were
obtained on a Perkin-Elmer 1600 FTIR. Elemental analyses
were done by Analytische Laboratorien, D-51547 Gummers-
bach, Germany.
[(Me3Si)2CH]2Y(µ-OCMe3)2Li(THF ), 1. In a glovebox,
YCl3 (120 mg, 0.62 mmol) was slurried in THF (ca. 10 mL)
and stirred. After 5 min, LiCH(SiMe3)2 (205 mg 1.23 mmol)
was added to form a clear pale yellow solution. Five minutes
later, LiOCMe3 (98.7 mg, 1.23 mmol) was added and the
mixture was stirred for 18 h. THF was removed from the clear
pale yellow solution by rotary evaporation, and the resulting
oily solid was extracted with hexanes. Upon centrifugation,
(29) Evans, W. J .; Boyle, T. J .; Ziller, W. J . Organometallics 1993,
12, 3998-4009.
(36) Further details appear in: Hope, H. Experimental Organome-
tallic Chemistry: A practicum in Synthesis and Characterization; ACS
Symposium Series No. 357; Wayda, A. L., Darensbourg, M. Y., Eds.;
American Chemical Society: Washington, DC, 1987.
(37) XSCANS Software Users Guide, Version 2.10, Siemens Indus-
trial Automation, Inc.: Madison, WI 1990-1995.
(38) UCLA Crystallographic Computing Package, University of
California: Los Angeles, 1981. Strouse, C. Personal communication.
(39) Siemens Analytical X-Ray Instruments, Inc., Madison, WI
1990-1995. Sheldrick, G. M. SHELXTL program.
(40) International Tables for X-Ray Crystallography; Kynoch
Press: Birmingham, U.K., 1992; Vol. C; (distributed by Kluwer Acad.
Pub., Dordrecht, The Netherlands).
(30) Bradley, D. C.; Chudzynska, H.; Hursthouse, M. B.; Motevalli,
M. Polyhedron 1991, 10, 1049-1059.
(31) Heeres, H. J .; Meetsma, A.; Teuben, J . H. J . Chem. Soc., Chem.
Commun. 1988, 962-963.
(32) Heeres, H. J .; Teuben, J . H. Recl. Trav. Chim. Pays-Bas 1990,
109, 226-229.
(33) Evans, W. J .; Chamberlain, L. R.; Ulibarri, T. A.; Ziller, J . W.
J . Am. Chem. Soc. 1988, 110, 6423-6432.
(34) Taylor, M. D.; Carter, C. P. J . Inorg. Nucl. Chem. 1962, 24,
387-391.
(35) Cotton, J . D.; Davidson, P .J .; Lappert, M. F. J . Chem. Soc.,
Dalton Trans. 1976, 2275-2286.

Yttrium Alkyl Alkoxide and Aryloxide Complexes
Organometallics, Vol. 15, No. 5, 1996 1353
Ta ble 1. Exp er im en ta l Da ta for th e X-r a y
Diffr a ction Stu d ies of
appear to be crystallographic. This may in part account for
the unsatisfactory refinement in the centrosymmetric space
group. It was necessary to refine four different models to
determine the most reasonable structure. Details of these
refinements follow.
[(Me3Si)2CH]2Y(µ-OCMe3)2Li(THF ), 1 a n d
(Me3SiCH2)2Y(OC6H3tBu 2-2,6)(THF )2, 2a
1
2
Mod el A (Sp a ce Gr ou p C2/c). In this model, yttrium,
O(2), and Li(1) are located on a 2-fold rotation axis and were
assigned site occupancy factors of 0.5. Thermal parameters
are higher than expected, and several light atoms cannot be
refined anisotropically. The metric parameters (distances and
angles) are not consistent with a well-resolved structure. The
tetrahydrofuran ring was disordered. Residual electron den-
sity was observed near all of the carbon atoms. The value of
wR2 was 0.3350 for this refinement (Y and Si atoms aniso-
tropic, hydrogens included except on the THF ligand), and R1
was 0.1382.
Mod el B (Sp a ce Gr ou p C2/c). This model was refined
with two separate components for each of the carbon atoms
labeled C(1) to C(11). Site occupancy factors were allowed to
refine and resulted in each carbon atom having a SOF of 0.50.
U(iso) values for the carbon atoms ranged from 0.05 to 0.09
Å2, and it was again necessary to refine the light atoms
isotropically. The U(eq) values for the silicon atoms were
slightly higher than expected at 0.06 and 0.07 Å2. The five
atoms of the THF ligand were include with SOF ) 0.5 for each.
Bond distances and angles were improved over the model A
refinement but were still deemed not acceptable. The value
of wR2 was 0.2558 (R1 ) 0.1041).
Mod el C (Sp a ce Gr ou p Cc). The refinement of this model
was carried out with site occupancy factors ) 1.0 for all atoms.
There are no atoms related by symmetry. This model refined
better than either A or B. Distances, angles, and thermal
parameters were more consistent, and all non-hydrogen atoms
were refined anisotropically. The value of wR2 was 0.1248
(R1 ) 0.0481). The refinement program (SHELXTL) flagged
this refinement indicating that a racemic twin was possible.
Mod el D (Sp a ce Gr ou p Cc). This refinement was identi-
cal to that for model C but included the TWIN and BASF
parameters in the SHELXTL program. Distances, angles, and
thermal parameters were again consistent and within accept-
able ranges. The value of wR2 decreased to 0.1136 for the
anisotropic refinement (R1 ) 0.0445). The BASF value
converged to 0.55 indicating a nearly equal racemic twin.
It was decided on the basis of the metrical data that the
refinements based on either of the two noncentrosymmetric
models were preferable to those based on the centrosymmetric
models. The structure reported here is that refined according
to model D which is based on refinement of a racemic twin.
Hydrogen atoms were included using a riding model.
X-r a y Da ta Collection , Str u ctu r e Deter m in a tion , a n d
Refin em en t for (Me3SiCH2)2Y(OC6H3tBu 2-2,6)(THF )2, 2. A
colorless crystal of approximate dimensions 0.20 × 0.23 × 0.30
mm was handled as described for 1. Although the intensity
data were weak, it was decided to proceed with data collection
(2θmax ) 40.0°). Low-temperature (163 K) intensity data were
collected via a θ-2θ scan technique with Mo KR radiation
under the conditions given in Table 1.
formula
fw
temp (K)
cryst system
space group
a (Å)
C26H54LiO3Si4Y C30H59O3Si2Y
632.98
163(2)
monoclinic
Cc
612.9
163(2)
triclinic
P1h
18.321(2)
14.406(3)
15.055(2)
90
104.603(9)
90
13.053(3)
15.910(3)
19.579(3)
67.184(13)
71.377(14)
89.68(2)
3519.1(11)
4
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
3845.2(10)
4
Z
Dcalcd (Mg/m3)
diffractometer
data collcd
scan type
scan range (deg)
scan speed (deg min-1
(in ω)
1.093
1.157
Siemens P4
+h,+k,(l
θ-θ
Siemens P4
+h,(k,(l
θ-2θ
1.2
1.12
)
3.0
3.0
2θ range (deg)
4.0-45.0
1.662
4.0-40.0
1.75
µ(Mo KR) mm-1
reflcns collcd
)
2612
6718
reflections with
2290
3305
(|Fo| > 4.0σ(|Fo|)
no. of variables
refinementb
317
319
R1, 5.69%;
wR2,11.36%
1.110
RF, 6.3%; RwF, 6.7%
goodness of fit
abs corr
1.67
none
semi-empirical
(æ-scan method)
a
Radiation: Mo KR (λh ) 0.710 730 Å). Monochromator: highly
oriented graphite. b R1 ) RF ) [∑||Fo| - |Fc||/∑|Fo|]; RwF ) [∑w(||Fo|
- |Fc||)/∑w|Fo|]; wR2 ) [∑[w(Fo - Fc2)2/∑[w(Fo2)2]]1/2
.
2
dispersion were included. The quantity minimized during
least-squares analysis was ∑w(Fo - Fc)2, where w-1 was
defined as σ2(|Fo|) + 0.0004(|Fo|)2.
The structure was solved by direct methods (SHELXTL) and
refined by full-matrix least-squares techniques. Hydrogen
atoms were included using a riding model. There are two
independent molecules of the formula unit present.
Resu lts
Th e (Me3Si)2CH/OCMe3 Ligan d Com bin ation . The
reaction of YCl3 with 2 equiv of LiCH(SiMe3)2 followed
by 2 equiv of LiOCMe3 in THF forms [(Me3Si)2CH]2Y-
(µ-OCMe3)2Li(THF), 1 (Figure 1), in moderate yield, ca.
50%, eq 5. The reaction is analogous to the reaction of
YCl3 + 2LiCH(SiMe3)2 + 2LiOCMe3 THF8
[(Me3Si)2CH]2Y(µ-OCMe3)2Li(THF) (5)
All 6718 data were corrected for absorption38 and for Lorentz
and polarization effects and were placed on an approximately
absolute scale. Any reflection with I(net) < 0 was assigned
the value |Fo| ) 0. There were no systematic extinctions nor
any diffraction symmetry other than the Friedel condition. The
two possible triclinic space groups are the noncentrosymmetric
P1 [C11; No. 1] or the centrosymmetric P1h [C11; No. 2]. Refine-
ment of the model using the centrosymmetric space group
proved it to be the correct choice.
Crystallographic calculations were carried out with the same
programs used for 1. The analytical scattering factors41 for
neutral atoms were used throughout the analysis; both the
real (∆f ′) and imaginary (i∆f ′′) components of anomalous
YCl3 with 2 equiv of LiCH2SiMe3 and 2 equiv of
LiOCMe3 (eq 3),28 but in this case the stoichiometrically
expected product is obtained instead of {(Me3SiCH2)x(Me3-
CO)1 -xY(µ-OCMe3 )4 [Li(TH F )]4 (µ4 -Cl)}+[Y(CH 2 -
SiMe3)4]-, 3. The simplicity of this reaction is therefore
likely to be due to the large steric bulk of the (Me3Si)2CH
ligand. In many cases, this ligand has proven to be the
best choice for obtaining stable alkyl complexes.25-28,42-50
Indeed, one might consider the alkyl, CH(SiMe3)2, to be
(42) van der Heijden, H.; Pasman, P.; de Boer, E. J . M.; Schaverien,
C. J . Organometallics 1989, 9, 1459-1467.
(43) den Haan, K. H.; de Boer, J . L.; Teuben, J . H.; Spek, A. L.;
Kojic-Prodic, B.; Hays, B. R.; Huis, R. Organometallics 1986, 5, 1726-
1733.
(41) SHELXTL Empirical Absorption Correction program (see ref
39).

1354 Organometallics, Vol. 15, No. 5, 1996
Evans et al.
trigonal planar, respectively. The tetrahedron of ligands
around yttrium is distorted as expected for a hetero-
leptic system with some bridging and some very bulky
terminal ligands. Hence, the 123.5(3)° C(1)-Y(1)-C(8)
angle between the R* groups is larger and the 83.1(2)°
O(1)-Y(1)-O(2) angle between the bridging alkoxides
is smaller than the normal tetrahedral angle. The four-
membered YO2Li metallacycle is only slightly distorted
from a square arrangement with angles of 83.1(2), 91.4-
(6), 94.1(6), and 91.4(7)°.
The Y(1)-O(1) and Y(1)-O(2) distances of 2.117(7)
and 2.125(8) Å for the bridging alkoxides in 1 are
slightly shorter than the 2.192(4) and 2.174(4) Å Y-O
distances in five-coordinate (Me3SiCH2)Y[(µ-CH2)2SiMe2]-
24
[(µ-OCMe3)Li(THF)2]2 and much shorter than the
average distance of 2.270(5) Å in 3 which also contains
a five coordinate yttrium.28 The 1.92(2) Å Li(1)-O(1)
and Li(1)-O(2) distances in 1 are equivalent within the
error limits to the 1.912(13) and 1.953(12) Å Li-(µ-O)
lengths in (Me3SiCH2)Y[(µ-CH2)2SiMe2][(µ-OCMe3)Li-
F igu r e 1. Thermal ellipsoid plot of [(Me3Si)2CH]2Y(µ-
OCMe3)2Li(THF), 1, drawn at the 50% probability level.
24
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for {[(Me3Si)2CH]2Y(µ-OCMe3)2Li(THF )}, 1
(THF)2]2 and the 1.996(13) Å average distance Li-(µ-
O) distance in 3,28 both of which have four-coordinate
Y(1)-O(1)
Y(1)-C(8)
Y(1)-Li(1)
Si(2)-C(1)
Si(4)-C(8)
Li(1)-O(2)
O(1)-C(15)
2.117(7)
2.440(9)
2.896(14)
1.827(8)
1.824(10)
1.92(2)
Y(1)-O(2)
Y(1)-C(1)
Si(1)-C(1)
Si(3)-C(8)
Li(1)-O(1)
Li(1)-O(3)
O(2)-C(19)
2.125(8)
2.462(9)
1.843(9)
1.858(9)
1.92(2)
lithium.
The 2.462(9) Å Y(1)-C(1) and 2.440(9) Å Y(1)-C(8)
distances are comparable to the 2.468(7) Å Y-C[CH-
(SiMe3)2] distance in Cp*2YCH(SiMe3)2,43 which is for-
mally seven coordinate excluding agostic interactions
which are common for this ligand.25,27,43-45,47,48 Cp*2-
YCH(SiMe3)2 has distorted Y-C-Si angles ranging
from 97.1(3) to 138.6(4)° due to the agostic interactions,
but in 1 the analogous angles span a narrower range:
105.6(4)-123.1(4)°. Within the limit of the crystal-
lographic data, no comments can be made about agostic
interactions in 1.
1.900(14)
1.435(12)
1.409(12)
O(1)-Y(1)-O(2)
O(2)-Y(1)-C(8)
O(2)-Y(1)-C(1)
Li(1)-O(2)-Y(1)
O(2)-Li(1)-O(1)
O(3)-Li(1)-O(2)
Si(1)-C(1)-Y(1)
Si(3)-C(8)-Y(1)
C(15)-O(1)-Y(1)
C(19)-O(2)-Y(1)
83.1(2)
114.7(3)
116.6(3)
91.4(7)
94.1(6)
137(2)
112.6(4)
121.9(4)
140.8(6)
151.6(7)
O(1)-Y(1)-C(8)
O(1)-Y(1)-C(1)
C(8)-Y(1)-C(1)
Li(1)-O(1)-Y(1)
110.3(3)
97.7(3)
123.5(3)
91.4(6)
O(3)-Li(1)-O(1)
Si(2)-C(1)-Y(1)
Si(4)-C(8)-Y(1)
C(15)-O(1)-Li(1)
C(19)-O(2)-Li(1)
127.5(12)
123.1(4)
105.6(4)
126.9(8)
116.9(9)
Attempts to prepare neutral alkyl alkoxide species
with these ligands did not lead to a single, readily
isolable complex. Hence, neither the reaction of YCl3
with 2 equiv of LiCH(SiMe3)2 and 1 equiv of LiOCMe3
nor the reaction with 1 equiv of the alkyl and 2 equiv
of the alkoxide produced a neutral complex in good yield.
Instead, in both cases, mixtures of complexes were
observed by NMR which included some 1 formed by
ligand redistribution.
The isolation of anionic [LnZ4]- “ate” salts (Z )
monoanionic ligand) such as 1 is not uncommon in
lanthanide chemistry. Numerous examples have been
reported and constitute a convenient way to increase
coordination number for these large metals.25,48,49,55-60
The fact that this mode of increasing the coordination
number involves bridging ligands which tend to be less
reactive than terminal ligands in these complexes5,6,52
probably adds to the stabilization obtained. The fact
that the alkyls in 1 are terminal and the alkoxides are
bridging is consistent with the relative sizes of the
ligands.
an “R*” ligand analogous to Cp*, C5Me5, in cyclopenta-
dienyl chemistry.
Complex 1 was initially characterized by 1H NMR
spectroscopy which indicated the presence of alkoxide
ligands and alkyl ligands in a 1:1 ratio. The alkyl
resonance was a doublet which displayed characteristic
yttrium coupling with J Y-H ) 2.6 Hz.24,43,51-54 Defini-
tive characterization of 1 was obtained by an X-ray
diffraction study.
The complex has the expected geometric arrangement
of ligands for the formally four-coordinate yttrium and
the three-coordinate lithium, namely tetrahedral and
(44) J eske, G.; Lauke, H.; Mauermann, H.; Swepston, P. N.; Schu-
mann, H.; Marks, T. J . J . Am. Chem. Soc. 1985, 107, 8091-8103.
(45) Hitchcock, P. B.; Lappert, M. F.; Smith, R. G.; Bartlett, R. A.;
Power, P. P. J . Chem. Soc., Chem. Commun. 1988, 1007-1009.
(46) Lappet, M. F.; Pearce, R. J . J . Chem. Soc., Chem. Commun.
1973, 107.
(47) Heeres, H. J .; Renkema, J .; Booij, M.; Meetsma, A.; Teuben, J .
H. Organometallics 1988, 7, 2495-2502.
(48) Atwood, J . L.; Lapert, M. F.; Smith, R. G.; Zhang, H. J . Chem.
Soc., Chem. Commun. 1988, 1308-1309.
(55) Evans, W. J .; Boyle, T. J .; Ziller, J . W. Inorg. Chem. 1992, 31,
1120-1122 and references therein.
(49) Hitchcock, P. B.; Lappert, M. F.; Smith, R. G. J . Chem. Soc.,
Chem. Commun. 1989, 369-371.
(56) Wayda, A. L.; Evans, W. J . J . Am. Chem. Soc. 1978, 100, 7119-
(50) Schaverien, C. J .; van Mechelen, J . B. Organometallics 1991,
10, 1704-1709.
7121.
(57) Atwood, J . L.; Hunter, W. E.; Rogers, R. D.; Holton, J .;
McMeeking, J .; Pearce, R.; Lappert, M. F. J . Chem. Soc., Chem.
Commun. 1978, 140-142.
(58) Edelmann, F. T.; Steiner, A.; Stalke, D.; Gilje, J . W.; J agner,
S.; Hakansson, M. Polyhedron 1994, 13, 539-546.
(59) Schumann, H.; Mueller, J .; Bruncks, N.; Lauke, H.; Pickardt,
J .; Schwarz, H.; Eckart, K. Organometallics 1984, 3, 69-74.
(60) Clark, D. L.; Watkin, J . G.; Huffman, J . C. Inorg. Chem. 1992,
31, 1554-1556.
(51) Evans, W. J .; Dominguez, R.; Levan, K. R.; Doedens, R. J .
Organometallics 1985, 4, 1836-1841.
(52) Evans, W. J .; Dominguez, R.; Hanusa, T. P. Organometallics
1986, 5, 263-270.
(53) Evans, W. J .; Drummond, D. K.; Hanusa, T. P.; Doedens, R. J .
Organometallics 1987, 6, 2279-2285.
(54) Holton, J .; Lappert, M. F.; Ballard, D. G. H.; Pearce, R.; Atwood,
J . L.; Hunter, W. E. J . Chem. Soc., Dalton Trans. 1979, 54-61.

Yttrium Alkyl Alkoxide and Aryloxide Complexes
Organometallics, Vol. 15, No. 5, 1996 1355
t
Attempts to make the [(Me3SiCH2)2Y(OC6H3 Bu2-
2,6)2]- “ate” salt analogous to 1 with this ligand com-
bination were unsuccessful. Reaction of YCl3 with 2
t
equiv of LiCH2SiMe3 followed by 2 equiv of LiOC6H3 -
Bu2-2,6 yielded a solution which by NMR spectroscopy
contained 2 as the main product. Crystallizations of
t
these solutions yielded [(THF)LiOC6H3 Bu2-2,6]2,61 rather
than the yttrium “ate” salt. Attempts to make the
t
neutral monoalkyl dialkoxide, (Me3SiCH2)Y(OC6H3 Bu2-
2,6)2(THF)x, were also unsuccessful. The reaction of
YCl3 with 1 equiv of LiCH2SiMe3 and 2 equiv of
t
LiOC6H3 Bu2-2,6 produced complicated NMR spectra
which included resonances for 2 formed by ligand
redistribution.
Discu ssion
Three direct YCl3/LiR/(LiOR or LiOAr) reactions have
now been reported in the literature to give fully char-
acterized products as shown in eqs 3, 5, and 6. The
basis for the preference to form these three different
types of products is not clear. The fact that complexes
1 and 2 could be isolated when many other ligand
combinations do not give crystallographically charac-
terizable alkyl alkoxide or aryloxide species is not easily
rationalized. Since 1 has large alkyl ligands and small
alkoxides and 2 has small alkyls and a large alkoxide,
there appears to be some balance in steric bulk in each
complex. However, the steric saturation needed to
isolate a stable complex can obviously be obtained by
other meanssformation of an “ate” salt or THF adduct
formation. The segregation of ligands in {Y(CH2-
SiMe3)x(OCMe3)5-x[Li(THF)]4Cl}+[Y(CH2SiMe3)4]-,28 eq
3, suggests that formation of mixed-ligand complexes
involving ligands of similar size may be disfavored
compared to the formation of homoleptic species. If
these initial results are general, then mixed alkyl
alkoxide or aryloxide complexes will be most readily
obtained using ligands of disparate sizes.
t
F igu r e 2. Thermal ellipsoid plot of (Me3SiCH2)2Y(OC6H3 -
Bu2-2,6)(THF)2, 2. drawn at the 50% probability level.
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for [(CH3)3SiCH2]2Y(OC6H3tBu 2-2,6)(THF )2, 2
Y(1)-O(1)
Y(1)-O(3)
Y(1)-C(5)
Si(2)-C(5)
2.084(11)
2.343(9)
2.411(13)
1.837(15)
Y(1)-O(2)
Y(1)-C(1)
Si(1)-C(1)
O(1)-C(9)
2.343(9)
2.427(16)
1.822(17)
1.334(21)
O(1)-Y(1)-O(2)
O(2)-Y(1)-O(3)
O(2)-Y(1)-C(1)
O(1)-Y(1)-C(5)
O(3)-Y(1)-C(5)
Y(1)-O(1)-C(9)
Y(1)-C(5)-Si(2)
85.7(4)
172.6(4)
92.4(4)
119.7(5)
92.5(4)
O(1)-Y(1)-O(3)
O(1)-Y(1)-C(1)
O(3)-Y(1)-C(1)
O(2)-Y(1)-C(5)
C(1)-Y(1)-C(5)
Y(1)-C(1)-Si(1)
86.9(4)
116.6(4)
91.0(4)
91.1(4)
123.7(5)
136.6(6)
178.8(10)
135.5(9)
Th e Me3SiCH2/OC6H3tBu 2-2,6 Liga n d Com bin a -
tion . This combination of ligands, in contrast to that
described above, readily forms a neutral complex.
Reaction of YCl3 with 2 equiv of LiCH2SiMe3 followed
by 1 equiv of LiOC6H3 Bu2-2,6 in THF forms (Me3-
SiCH2)2Y(OC6H3 Bu2-2,6)(THF)2, 2 (Figure 2), in >90%
yield, eq 6. The H NMR spectrum of 2 indicated the
t
t
1
YCl3 + 2LiCH2SiMe3 + LiOC6H3 Bu2-2,6 THF8
t
Con clu sion
t
Formation of mixed-ligand alkyl alkoxide and arylox-
ide complexes of yttrium can occur in a straightforward
manner if the appropriate combination of ligands is
used. Too little data on this subject are available to
attribute to steric or electronic factors the propensity
of the (Me3Si)2CH/OCMe3 combination to form the “ate”
(Me3SiCH2)2Y(OC6H3 Bu2-2,6)(THF)2 (6)
presence of alkyl ligands and aryloxide ligands in a 2:1
ratio, and the alkyl resonance appeared as a character-
istic doublet due to J Y-H ) 3.5 Hz.24,43,51,53,54 Again, for
definitive characterization of 2 an X-ray diffraction
study was necessary.
t
salt, 1, and the Me3SiCH2/OC6H3 Bu2-2,6 combination
to form the neutral complex, 2, but clearly the particular
mixture of ligands is critical. This is encouraging with
respect to the reactivity of these yttrium alkyl alkoxide
and aryloxide complexes, since these preferences, once
understood, may be useful in controlling reaction path-
ways.
The two independent molecules in the crystal struc-
ture of 2 are essentially the same. The following
discussion is based on data on the molecule of 2 labeled
1. Complex 2 crystallizes as a slightly distorted trigonal
bipyramid with a 172.6° O(THF)-Y-O(THF) angle
between the axial ligands. The largest ligands are in
the equatorial positions as expected. The 85.7(4), 91.1-
(4), and 92.4(4)° axial ligand-Y-equatorial ligand
angles are close to the expected 90°.
Ack n ow led gm en t. For support of this research, we
thank the Division of Chemical Sciences of the Office
of Basic Energy Sciences of the Department of Energy.
The 2.411(13) and 2.427(16) Å Y-C(CH2SiMe3) bond
distances in 2 are similar to the analogous distances in
the four-coordinate [Y(CH2SiMe3)4]- (2.382(8)-2.420-
(9) Å),28 eight-coordinate [(C5H5)2Y(CH2SiMe3)2]- (2.42(2)
Å average),51 and seven-coordinate (4,13-diaza-18-crown-
6)Y(CH2SiMe3) (2.45(2) Å).8 The 2.084(11) Å Y-
Su p p or tin g In for m a tion Ava ila ble: Text describing
X-ray procedures, figures showing the complexes, and tables
of crystal data, atomic coordinates, bond distances and angles,
and anisotropic displacement parameters (36 pages). Ordering
information is given on any current masthead page.
t
O(OC6H3 Bu2-2,6) distance in 2 is within error limits of
OM9508400
t
the analogous Y-O lengths in Y(OC6H3 Bu2-2,6)3 (2.00(2)
t
Å)21 and [(C5Me5)Y(OC6H3 Bu2-2,6)2 (2.096(4) and 2.059-
(61) Huffman, J . C.; Geerts, R. L.; Caulton, K. C. J . Cryst. Spec.
Res. 1984, 14, 541-547.
(3) Å).5