Reactivity of monocationic Bis(alkyl) and dicationic mono(alkyl) yttrium complexes toward ketones and carbon dioxide

Article abstract of DOI:10.1021/om0610290

Cationic alky 1 yttrium complexes [Y(CH₂SiMe₃) ₂(THF)₄][A] (1a, A = BPh₄; 1b, A = Al(CH ₂SiMe₃)₄) react with benzophenone and fluorenone at ambient temperature to produce bis(alkoxy) complexes cis[Y{OC(CH₂SiMe₃)R′₂} ₂(THF)₄][BPh₄] (3a, R′ = Ph; 4a, R′₂ = C₁₂H₈), while two isomers, cis- and trans[Y{OC(CH₂SiMe₃)R′₂} ₂(THF)₄][Al(CH₂SiMe₃)₄] (3b, R′ = Ph; 4b, R' = C₁₂H₈), were obtained from the reaction of the aluminate lb with benzophenone or fluorenone. The reaction of the crown ethersupported monocationic bis(alkyl) complex [Y(CH ₂SiMe₃)₂(12-crown-4)(THF)][A] (1′a, A = BPh₄; 1′b, A = Al(CH2SiMe3)4) with benzophenone or fluorenone results in the formation of cw-[Y{OC(CH2-SiMe₃)R′₂} ₂(12-crown-4)(THF)][A] (3′a, R′ = Ph, A = BPh ₄; 4′a, R′₂ = C₁₂H₈, A = BPh₄; 3′b, R = Ph, A = Al(CH₂SiMe₃) ₄). Complex la reacts with carbon dioxide to produce a dinuclear carboxylato complex, [Y(μ-η¹:η¹-O ₂CR)(μ-η¹:η²-O₂CR)(THF) ₃]₂[BPh₄]₂ (6a) (R = CH ₂SiMe₃). The reaction of the crown ether complex [Y(CH₂SiMe₃)₂(12-crown-4)(THF)][B(C ₆H₄F-4)₄] (1'c) with carbon dioxide also produced a product of insertion, [Y(μ-η¹:η¹- O₂CR)₂(12-crown-4)]₂[B(C₆H ₄F-4)₄]₂ (7'c). The structures of 4a, 6a, and 7'c were determined by single-crystal X-ray structural analysis. Reaction of the dicationic mono(alkyl) complex [Y(CH₂SiMe₃)(THF) ₅][BPh₄]₂ (2a) with benzophenone, fluorenone, and carbon dioxide resulted in the formation of the corresponding dicationic alkoxy complex [Y{OC(CH₂SiMe₃)R′₂}(THF) ₅]-[BPh₄]₂ (8a, R′ = Ph; 9a, R′₂ = C₁₂H₈) and the carboxylato complex [Y(O₂CR)(THF)₅][BPh₄]₂ (10a).

Full text of DOI:10.1021/om0610290

1270
Organometallics 2007, 26, 1270-1278
Reactivity of Monocationic Bis(alkyl) and Dicationic Mono(alkyl)
Yttrium Complexes toward Ketones and Carbon Dioxide
Yumiko Nakajima and Jun Okuda*
Institute of Inorganic Chemistry, RWTH Aachen UniVersity, Landoltweg 1, D-52074 Aachen, Germany
ReceiVed NoVember 8, 2006
Cationic alkyl yttrium complexes [Y(CH2SiMe3)2(THF)4][A] (1a, A ) BPh4; 1b, A ) Al(CH2SiMe3)4)
react with benzophenone and fluorenone at ambient temperature to produce bis(alkoxy) complexes cis-
[Y{OC(CH2SiMe3)R′2}2(THF)4][BPh4] (3a, R′ ) Ph; 4a, R′2 ) C12H8), while two isomers, cis- and trans-
[Y{OC(CH2SiMe3)R′2}2(THF)4][Al(CH2SiMe3)4] (3b, R′ ) Ph; 4b, R′ ) C12H8), were obtained from
the reaction of the aluminate 1b with benzophenone or fluorenone. The reaction of the crown ether-
supported monocationic bis(alkyl) complex [Y(CH2SiMe3)2(12-crown-4)(THF)][A] (1′a, A ) BPh4; 1′b,
A ) Al(CH2SiMe3)4) with benzophenone or fluorenone results in the formation of cis-[Y{OC(CH2-
SiMe3)R′2}2(12-crown-4)(THF)][A] (3′a, R′ ) Ph, A ) BPh4; 4′a, R′2 ) C12H8, A ) BPh4; 3′b, R ) Ph,
A ) Al(CH2SiMe3)4). Complex 1a reacts with carbon dioxide to produce a dinuclear carboxylato complex,
[Y(µ-η1:η1-O2CR)(µ-η1:η2-O2CR)(THF)3]2[BPh4]2 (6a) (R ) CH2SiMe3). The reaction of the crown ether
complex [Y(CH2SiMe3)2(12-crown-4)(THF)][B(C6H4F-4)4] (1′c) with carbon dioxide also produced a
product of insertion, [Y(µ-η1:η1-O2CR)2(12-crown-4)]2[B(C6H4F-4)4]2 (7′c). The structures of 4a, 6a,
and 7′c were determined by single-crystal X-ray structural analysis. Reaction of the dicationic mono-
(alkyl) complex [Y(CH2SiMe3)(THF)5][BPh4]2 (2a) with benzophenone, fluorenone, and carbon dioxide
resulted in the formation of the corresponding dicationic alkoxy complex [Y{OC(CH2SiMe3)R′2}(THF)5]-
[BPh4]2 (8a, R′ ) Ph; 9a, R′2 ) C12H8) and the carboxylato complex [Y(O2CR)(THF)5][BPh4]2 (10a).
several complexes without any ancillary ligands [YR2(THF)4]-
[BPh4] (R ) CH2SiMe3, 1a) and the dication [YR(THF)5]-
[BPh4]2 (2a) have been described.5,6 These complexes contain
labile THF ligands and a higher reactivity can be expected. In
addition to the olefin insertion into the metal alkyl bond at a
cationic metal center, initial studies have revealed a high
reactivity of these complexes, including the C-H bond activa-
tion of pyridine.6c,7 For further applications of these cationic
rare earth metal alkyls, understanding their fundamental reactiv-
ity appears to be essential. Since a highly polarized rare earth
metal-carbon bond is combined with a Lewis acidic cationic
metal center, both nucleophilic and electrophilic properties can
be anticipated for these complexes.8 We have examined whether
the trimethylsilylmethyl group of the cationic yttrium complexes
still acts as a nucleophile.9 Herein we report on the reactivity
of the monocationic bis(alkyl) complex [YR2(THF)4][A] (1a,
A ) BPh4; 1b, A ) AlR4) as well as the dicationic mono-
Introduction
In the context of developing homogeneous ethylene,1
R-olefin,1e,f,2 and 1,3-diene3 polymerization catalysts based on
rare earth metals,4 we and others have established that cationic
alkyl complexes of the rare earth metals play a pivotal role as
the active species.1-3,5 Since the first isolation and structural
characterization of a cationic alkyl lutetium complex in 2002,6a
* Corresponding author. Fax: +49 241 8092644. E-mail:
jun.okuda@ac.rwth-aachen.de.
(1) (a) Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben,
J. H. Chem. Commun. 2003, 522. (b) Bambirra, S.; Bouwkamp, M. W.;
Meetsma, A.; Hessen, B. J. Am. Chem. Soc. 2004, 126, 9182. (c) Bambirra,
S.; Boot, S. J.; van Leusen, D.; Meetsma, A.; Hessen, B. Organometallics
2004, 23, 1891. (d) Hayes, P. G.; Piers, W. E.; McDonald, R. J. Am. Chem.
Soc. 2002, 124, 2132. (e) Lawrence, S. C.; Ward, B. D.; Dubberley, S. R.;
Kozak, C. M.; Mountford, P. Chem. Commun. 2003, 2880. (f) Tredget, C.
S.; Bonnet, F.; Cowley, A. R.; Mountford, P. Chem. Commun. 2005, 3301.
(g) Arndt, S.; Spaniol, T. P.; Okuda, J. Angew. Chem., Int. Ed. 2003, 42,
5075. (h) Li, X.; Baldamus, J.; Hou, Z. Angew. Chem., Int. Ed. 2005, 44,
962. (i) Li, X.; Hou, Z. Macromolecules 2005, 38, 6767.
(5) (a) Zeimentz, P. M.; Arndt, S.; Elvidge, B. R.; Okuda, J. Chem. ReV.
2006, 106, 2404. (b) Arndt, S.; Okuda, J. AdV. Synth. Catal. 2005, 347,
339. (c) Elvidge, B. R.; Stefan, A.; Spaniol, T. P.; Okuda, J. Dalton Trans.
2006, 7, 890.
(2) (a) Hajela, S.; Schaefer, W. P.; Bercaw, J. E. J. Organomet. Chem.
1997, 532, 45. (b) Ward, B. D.; Bellemin-Laponnaz, S.; Gade, L. H. Angew.
Chem., Int. Ed. 2005, 44, 1668.
(3) (a) Taube, R. In Metalorganic Catalysts for Synthesis and Polymeri-
sation; Kaminsky, W., Ed.; Springer: Berlin, New York, 1999; p 531. (b)
Kaita, S.; Hou, Z.; Nishiura, M.; Doi, Y.; Kurazumi, J.; Horiuchi, A. C.;
Wakatsuki, Y. Macromol. Rapid Commun. 2003, 24, 179. (c) Arndt, S.;
Beckerle, K.; Zeimentz, P. M.; Spaniol, T. P.; Okuda, J. Angew. Chem.,
Int. Ed. 2005, 44, 7473. (d) Zhang, L.; Luo, Y.; Hou, Z. J. Am. Chem. Soc.
2005, 127, 14562. (e) Kaita, S.; Yamanaka, M.; Horiuchi, A. C.; Wakatsuki,
Y. Macromolecules 2006, 39, 1359. (f) Kaita, S.; Hou, Z.; Wakatsuki, Y.
Macromolecules 1999, 32, 9078. For a review, see: (g) Friebe, L.;
Nuyken, O.; Obrecht, W. AdV. Polym. Sci. 2006, 204, 1.
(4) For reviews on polymerization catalysts based on rare earth metal
complexes, see: (a) Hou, Z.; Wakatsuki, Y. Coord. Chem. ReV. 2002, 231,
1. (b) Molander, G. A.; Romero, J. A. C. Chem. ReV. 2002, 102, 2161. (c)
Arndt, S.; Okuda, J. Chem. ReV. 2002, 102, 1953. (d) Okuda, J. Dalton
Trans. 2003, 2367. (e) Gromada, J.; Carpentier, J.-F.; Mortreux, A. Coord.
Chem. ReV. 2004, 248, 397.
(6) (a) Arndt, S.; Spaniol, T.; Okuda, J. Chem. Commun. 2002, 896.
(b) Arndt, S.; Zeimentz, P. M.; Spaniol, T. P.; Okuda, J.; Honda, M.;
Tatsumi, K. Dalton Trans. 2003, 3622. (c) Elvidge, B. R.; Arndt, S.;
Zeimentz, P. M.; Spaniol, T. P.; Okuda, J. Inorg. Chem. 2005, 44, 6777.
For earlier observations, see: (d) Schaverien, C. J. Organometallics 1992,
11, 3476.
(7) Arndt, S.; Elvidge, B. R.; Zeimentz, P. M.; Spaniol, T. P.; Okuda, J.
Organometallics 2006, 25, 793.
(8) For an example of reactions of neutral rare earth metal alkyl
complexes, see: (a) Dietrich, H. M.; Meermann, C.; To¨rnroos, K. W.;
Anwander, R. Organometallics 2006, 25, 4316. (b) Duchateau, R.; Brussee,
E. A. C.; Meetsma, A.; Teuben, J. H. Organometallics 1997, 16, 5506. (c)
Duchateau, R.; van Wee, C. T.; Teuben, J. H. Organometallics 1996, 15,
2291. For an example of reaction of anionic alkyl ate-complexes, see:
Schumann, H.; Mu¨ller, J.; Bruncks, N.; Lauke, H.; Pickardt, J. Organo-
metallics 1984, 3, 69.
10.1021/om0610290 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 01/26/2007

Cationic Yttrium Alkyl Complexes
Scheme 1
Organometallics, Vol. 26, No. 5, 2007 1271
Figure 1. Molecular structure of cis-4a (ellipsoids drawn at the
50% probability level, tetraphenyl borate anion, disordered carbon
atoms of a tetrahydrofuran, and hydrogen atoms omitted for clarity).
Selected bond lengths (Å) and angles (deg): Y-O1 2.0533(18),
Y-O2 2.0680(18), C1-O1 1.402(3), C5-O2 1.406(3), Y-O1-
C1 167.31(17), Y-O2-C5 156.01(17), C3-C1-O1 112.1(2), C4-
C1-O1 111.3(2), C2-C1-O1 109.7(2), C7-C5-O2 109.1(2),
C8-C5-O2 112.3(2), C6-C5-O2 110.1(2).
(alkyl) complex [YR(THF)5][BPh4]2 (2a) toward the C-O
double bond of some ketones and carbon dioxide.
Results and Discussion
Reaction with Benzophenone and Fluorenone. The cationic
bis(trimethylsilylmethyl) yttrium complex [YR2(THF)4][BPh4]
(1a) was found to be highly reactive toward aliphatic ketones
(acetone, pentanone-3, acetophenone) in THF solution at
ambient temperature, resulting in intractable mixtures of several
compounds. Presumably both insertion of the C-O double bond
into the Y-C bond and â-H deprotonation (enolization)
occurred. When 1a reacted with a 3-fold excess of benzophe-
none in THF at room temperature, the bis(alkoxy) complex,
cis-[Y(OCRPh2)2(THF)4][BPh4] (3a), was formed as the only
product and isolated in analytically pure form (Scheme 1).
Likewise, the cationic complex 1a reacted with excess fluo-
renone in THF at room temperature to give a similar complex,
cis-[Y(OCRC12H8)2(THF)4][BPh4] (4a), in high yield.
trum of this complex, the â-carbon atom bonded to the amido
nitrogen was reported as a doublet with a coupling constant of
2JYC ) 5 Hz. The NMR spectroscopic data of cis-4a are similar
to those of cis-3a. Complex cis-4a exhibits one set of signals
for the trimethylsilylmethyl group at δ 1.76 (CH2Si) and δ
1
-0.69 (SiMe3) in the H NMR spectrum. In the 13C NMR
spectrum, a doublet was observed at δ 85.4 (2JYC ) 3.7 Hz)
for the quaternary carbon of the alkoxy group.
The structure of cis-4a was determined by a single-crystal
X-ray diffraction study. Suitable single crystals were obtained
from a CH2Cl2/Et2O solution at -30 °C. The ORTEP diagram
as well as selected bond distances and angles is depicted in
Figure 1. The structure of cis-4a in the crystal is consistent with
the above-mentioned spectroscopic data in solution. The coor-
dination geometry around the yttrium center, coordinated by
two cis-arranged alkoxy ligands and four THF molecules, is
distorted octahedral. The structure of the starting complex 1b
with a tetrakis(trimethylsilylmethyl) aluminate counteranion also
possesses two cis-arranged trimethylsilylmethyl ligands.1g The
Y-O bond lengths of the alkoxy groups, Y-O1 ) 2.0533(18)
Å and Y-O2 ) 2.0680(18) Å, are consistent with Y-O single
bonds of terminal alkoxy groups coordinated to an yttrium center
(1.99-2.12 Å).10 The C-O bond lengths observed in both
alkoxy groups are ca. 1.40 Å, corresponding to a normal C-O
single bond. The bond angles of O1-C1-C2-4 and O2-C5-
C6-8, 109-113°, indicate sp3-character of the carbon atoms,
and the angles at the alkoxy oxygen atoms, Y-O1-C1 167.31-
(17)° and Y-O2-C5 156.01(19)°, suggest pronounced π-dona-
tion. Preliminary experiments revealed that the monocationic
bis(alkyl) complex of scandium, [ScR2(THF)3][BPh4], also
reacted with benzophenone to give the bis(alkoxy) complex [Sc-
(OCRPh2)2(THF)n][BPh4] (n ) 3, 4).11
The bis(alkoxy) complexes cis-3a and cis-4a were identified
1
by H and 13C NMR spectroscopy as well as by elemental
analysis. In the 1H NMR spectrum of cis-3a, the two equivalent
alkoxy groups give rise to one doublet and two triplets in the
aromatic region, assigned to phenyl groups. The two equivalent
trimethylsilylmethyl groups are observed as a singlet at δ 1.95
(CH2Si) and δ -0.35 (SiMe3). The 13C NMR spectroscopic data
of cis-3a are consistent with a structure containing two
equivalent alkoxy ligands. The trimethylsilylmethyl groups
exhibit only one set of methyl and methylene signals. The phenyl
group gives rise to four signals in the aromatic region. Notably,
the carbon atom attached to the alkoxy oxygen atom is recorded
as a doublet at δ 83.5 with a coupling to yttrium (2JYC ) 5.4
Hz). This coupling to yttrium indicates a strong interaction of
yttrium with the alkoxy ligand, as previously reported by Teuben
et al. for the dinuclear benzamidinato yttrium complex [{PhC-
(NSiMe3)2}2Y(µ-NHCMedCHCN)]2.8c In the 13C NMR spec-
(9) Not unexpectedly, the neutral yttrium tris(alkyl) complex [Y(CH2-
SiMe3)3(THF)2] was found to react with 3 equiv of benzophenone to give
a neutral tris(alkoxy) complex, [Y{OCPh2(CH2SiMe3)}3(THF)3]. 1H NMR
(400 MHz, C6D6, 25 °C): δ -0.05 (s, 27H, SiMe3), 1.34 (m, â-THF), 1.92
3
(s, 6H, CH2Si), 3.57 (m, R-THF), 7.09 (t, JHH ) 7.3 Hz, 6H, p-Ph), 7.20
3
3
(t, JHH ) 7.8 Hz, 12H, m-Ph), 7.59 (d, JHH ) 7.8 Hz, 12H, o-Ph). 13C
(10) (a) Evans, W. J.; Boyle, T. J.; Ziller, J. W. Organometallics 1993,
12, 3998. (b) Schaverien, C. J.; Frijns, J. H. G.; Heere, H. J.; van den Hende,
J. R.; Teuben, J. H.; Spek, A. L. J. Chem. Soc., Chem. Commun. 1991,
642. (c) Evans, W. J.; Dominguez, R.; Hanusa, T. P. Organometallics 1986,
5, 1291.
NMR (100 MHz, C6D6, 25 °C): δ -0.81 (SiMe3), 25.6 (â-THF), 37.7 (CH2-
2
Si), 68.5 (R-THF), 81.2 (d, JYC ) 5.2 Hz, OC), 125.8 (p-Ph), 127.6 (o-
Ph), 127.6 (m-Ph), 154.0 (ipso-Ph). Preliminary crystallography of
[Y{OCPh2(CH2SiMe3)}3(THF)3] showed a facial configuration.

1272 Organometallics, Vol. 26, No. 5, 2007
Nakajima and Okuda
Scheme 2
spectra (+50 °C) of a mixture containing both cis-3b and trans-
3b did not show any change in the molar ratio or in the chemical
shifts, suggesting that the exchange between cis-3b and trans-
3b does not occur at 50 °C.
Although the X-ray diffraction study using a single-crystal
obtained from cold THF/pentane solution showed that complex
1b has two alkyl groups cis to each other,1g trans-1b presumably
exists in solution. The related monocationic dimethyl complex,
[YMe2(THF)5][BPh4], adopts a trans configuration.3c As shown
previously, there is an equilibrium between the aluminate
complex 1b and the neutral tris(alkyl) complex [YR3(THF)2]
(5) and [AlR3(THF)] as a result of a transfer of an alkyl group
between the aluminum center and the yttrium center depending
on the solvent polarity.12 On the basis of this observation, it is
probable that an isomerization process occurs between cis-1b
and trans-1b via the neutral tris(alkyl) complex 5 at room
temperature (Scheme 4). Since the thermodynamically more
stable cis-1b predominantly exists at low temperature, the cis
complex 3b was obtained as the sole product when the reaction
was conducted at low temperature, whereas at higher temper-
atures both cis and trans isomers reacted with the ketone. On
the other hand, no exchange reaction was observed on the NMR
time scale between the bis(alkyl) cation 1a with tetraphenylbo-
rate anion and tris(alkyl) 5. This observation is consistent with
the result that the reaction of 1a with benzophenone or
fluorenone produced only the cis isomer cis-3a or cis-4a.
In the case of the crown ether complex [YR2(12-crown-4)-
(THF)][AlR4] (1′b), the tetradentate crown ether ligand only
allows complex 1′b to adopt a cis configuration. Consequently,
the reaction of 1′b with benzophenone gave only one bis(alkoxy)
complex, [Y(OCRPh2)2(12-crown-4)(THF)][AlR4] (3′b) with cis
alkoxy ligands.
The previously reported crown ether complex [YR2(12-crown-
4)(THF)][BPh4] (1′a)6c also reacted with benzophenone and
fluorenone in THF at room temperature to produce the corre-
sponding bis(alkoxy) complexes 3′a and 4′a (Scheme 2).
Complexes 3′a and 4′a exhibit two multiplets for the diaste-
reotopic methylene protons of the coordinated crown ether. The
trimethylsilylmethyl group of 3′a is observed at δ 1.84 (CH2-
1
Si) and δ -0.36 (SiMe3) in the H NMR spectrum. Complex
4′a exhibits one methylene signal and one methyl signal for
the trimethylsilylmethyl group at δ 1.66 and δ -0.68. The
quaternary carbon in 3′a and 4′a appears as a singlet at δ 83.2
and δ 84.5 in the 13C NMR spectrum.
Changing the counteranion affected the reactivity of the
cationic bis(alkyl) complex. The reaction of the tetrakis-
(trimethylsilylmethyl)aluminate complex, [YR2(THF)4][AlR4]
(1b), with benzophenone produced two isomeric bis(alkoxy)
complexes, cis-3b and trans-3b in a 9:1 ratio (Scheme 3).
Analogously, two isomers, cis-4b and trans-4b, were formed
in the reaction of 1b with fluorenone.
Reaction with Carbon Dioxide. Carbon dioxide insertion
into a lanthanide alkyl bond is a well-known reaction to give
lanthanide carboxylato complexes, which serve as catalyst
precursors for isoprene polymerization.13 The bis(alkyl) mono-
cation 1a underwent insertion of carbon dioxide (1 bar) in THF
at room temperature to produce the dinuclear cationic tetrakis-
(trimethylsilylacetato) complex [Y(µ-η1:η1-O2CR)(µ-η1:η2-O2-
CR)(THF)3]2[BPh4]2 (6a) in quantitative yield.
In the 1H NMR spectrum of cis-3b and trans-3b, each
complex shows one set of signals for alkyl groups, δ 1.97 (CH2-
Si) and δ -0.38 (SiMe3) for cis-3b and δ 1.87 (CH2Si) and δ
-0.35 (SiMe3) for trans-3b. In the 13C NMR spectrum, cis-3b
and trans-3b each exhibit one doublet at δ 83.6 (2JYC ) 5.3
Hz) and δ 82.2 (2JYC ) 5.2 Hz), which are assigned to the
quaternary carbon atom, as a result of coupling to the yttrium
center. Complexes cis-4b and trans-4b also exhibit doublets
for the quaternary carbon atoms at δ 85.8 (2JYC ) 6.1 Hz) and
δ 85.2 (2JYC ) 5.0 Hz), respectively. The spectra of cis-3b and
cis-4b show almost identical signals to cis-3a and cis-4a. Only
cis-3b was obtained when the reaction of 1b with benzophenone
was performed at -30 °C. Even after the solution of cis-3b
was kept at room temperature overnight, formation of trans-3b
was not observed. Furthermore, the high-temperature NMR
Complex 6a precipitated from THF solution and was identi-
fied on the basis of the 1H and 13C NMR spectra in pyridine-d5
1
as well as by elemental analysis. In the H NMR spectrum,
signals for the trimethylsilylmethyl groups are observed at δ
(11) The reaction of [Sc(CH2SiMe3)2(THF)3][BPh4] with benzophenone
produced the homologous scandium [Sc(OC(CH2SiMe3)Ph2)2(THF)4][BPh4]
(12) Kramer, M. U.; Robert, D.; Nakajima, Y.; Englert, U.; Spaniol, T.
P.; Okuda, J. Eur. J. Inorg. Chem., in press.
quantitatively. The resulting alkoxy complex was identified by 1H and 13
C
NMR spectroscopy. 1H NMR (400 MHz, THF-d8, 25 °C): δ -0.22 (s,
18H, SiMe3), 1.74 (m, â-THF), 1.79 (s, 4H, CH2Si), 3.58 (m, R-THF), 6.69
(13) (a) Evans, W. J.; Miller, K. A.; Ziller, J. W. Inorg. Chem. 2006,
45, 424. (b) Fischbach, A.; Perdih, F.; Herdtweck, E.; Anwander, R.
Organometallics 2006, 25, 1626. (c) Evans, W. J.; Champagne, T. M.;
Giarikos, D. G.; Ziller, J. W. Organometallics 2005, 24, 570. (d) Evans,
W. J.; Perotti, J. M.; Ziller, J. W. J. Am. Chem. Soc. 2005, 127, 3894. (e)
Evans, W. J.; Miller, K. A.; Lee, D. S.; Ziller, J. W. Inorg. Chem. 2005,
44, 4326. (f) Evans, W. J.; Champagne, T. M.; Ziller, J. W. Organometallics
2005, 24, 4882. (g) Kwang, G. Macromolecules 2002, 35, 4875. (h)
Fischbach, A.; Perdih, F.; Sirsch, P.; Scherer, W.; Anwander, R. Organo-
metallics 2002, 21, 4569. (i) Campion, B. K.; Heyn, R. H.; Tilley, T. D.
Inorg. Chem. 1990, 29, 4355. (j) Schumann, H.; Meese-Marktscheffel, J.
A.; Dietrich, A.; Go¨rlitz, F. H. J. Organomet. Chem. 1992, 430, 299.
3
3
(t, JHH ) 7.2 Hz, 4H, 4-CH BPh4), 6.83 (t, JHH ) 7.3 Hz, 8H, 3-CH
BPh4), 7.06 (t, 3JHH ) 7.3 Hz, 4H, p-Ph), 7.17 (t, 3JHH ) 7.7 Hz, 8H, m-Ph),
7.24 (br, 8H, 2-CH BPh4), 7.47 (d, JHH ) 7.1 Hz, 8H, o-Ph). 13C NMR
3
(100 MHz, THF-d8, 25 °C): δ 0.35 (SiMe3), 25.3 (â-THF), 33.1 (CH2Si),
67.4 (R-THF) 86.1 (OC), 121.9 (4-CH BPh4), 125.7 (3-CH BPh4), 126.6
(p-Ph), 126.8 (o-Ph), 128.3 (m-Ph), 137.2 (2-CH BPh4), 151.5 (ipso-Ph),
165.2 (q, 1JBC ) 49.5 Hz, 1-CH BPh4). HMQC (THF-d8, 25 °C): -0.22-
0.35, 1.79-33.1, 6.69-121.9, 6.83-125.7, 7.06-126.6, 7.17-128.3, 7.24-
137.2, 7.47-126.8. Anal. Calcd for C74H94BO6ScSi: Sc, 3.77. Found: Sc,
3.63.

Cationic Yttrium Alkyl Complexes
Organometallics, Vol. 26, No. 5, 2007 1273
Scheme 3
Scheme 4
2.18 (CH2Si) and δ 0.13 (SiMe3) at room temperature. These
resonances did not change their shape even at -50 °C, although
6a has two sets of inequivalent carboxylato ligands according
to its solid-state structure. The 13C NMR spectrum is consistent
known,15 complex 6a is the first example of a cationic
carboxylato rare earth metal complex that is prepared by
insertion reaction of carbon dioxide.
In the course of the reaction, intermediates were detected by
monitoring the reaction of 1a with CO2 by means of 1H NMR
spectroscopy. Immediately after CO2 (ca. 10 equiv) was
transferred into the NMR tube, all of the starting complex 1a
was consumed and the formation of three intermediates, A, B,
and C, was observed. After 30 min, intermediate A disappeared
1
with the H NMR spectrum, and only one signal assigned to
all four carboxylato carbon atoms was observed at δ 191.3.
Ligand exchange between THF and pyridine-d5 is fast when
the cationic rare earth metal complex is dissolved in pyridine.7
The structure of 6a in the solid state was determined by a
single-crystal X-ray diffraction study. The ORTEP diagram
together with selected bond lengths and angles is depicted in
Figure 2. The crystal system is monoclinic, and the structure
of 6a possesses an inversion center on the center of the Y-Y′
axis. Complex 6a contains two yttrium centers bridged by two
symmetrical µ-η1:η1 and two unsymmetrical µ-η1:η2 carboxylato
ligands. The Y‚‚‚Y′ distance is 3.8632(6) Å. Each yttrium center
is eight-coordinate and attached to two symmetrically bridging
carboxylato oxygen atoms, one η1 and two η2 oxygen atoms of
the unsymmetrically bridging µ-η1:η2 carboxylato, and three
THF oxygen atoms. The coordination geometry can be described
as triangular dodecahedron. Y-O (carboxylato) distances are
in the range 2.2-2.6 Å, which are comparable with the Y-O
single-bond distance of dimeric yttrium complexes bridged by
a µ2-oxo ligand.10a,c The Y-O2 bond length of the µ-η1:η2
carboxylato ligand of 2.3334(19) Å is slightly longer than the
other Y′-O2 bond, 2.532(2) Å. This inequivalence in Y-O
bond lengths of a bridging carboxylato ligand is observed in
other structurally related dimeric yttrium carboxylato com-
plexes.14 Although several examples of structurally characterized
cationic carboxylato rare earth metals or lanthanides are
1
and only B and C were detected in a ratio of 4:1. In the H
NMR spectrum, the intermediate A exhibits one set of reso-
nances for the trimethylsilylmethyl bonded to yttrium, viz., one
doublet at δ -0.93 (CH2Si) and one singlet at δ -0.13 (SiMe3).
Intermediate A could not be fully characterized because of its
short life time. The two other intermediates, B and C, exhibit
one set of alkyl signals at δ 1.88 (CH2Si) and 0.12 (SiMe3) for
B and δ 1.92 (CH2Si) and 0.13 (SiMe3) for C, respectively.
The intermediates B and C also show a carboxylato carbon at
δ 192.0 and 187.7 in the 13C NMR spectrum. It was confirmed
that both B and C are easily converted into the dimeric complex
6a without any additional CO2 molecule, as the mixture of B
and C produced 6a quantitatively in vacuum. These results
indicate that B and C have already incorporated two CO2
molecules on each yttrium center. On the basis of this observa-
tion, monomeric dicarboxylato complexes with cis/trans ge-
ometry are proposed for B and C.13b
The cationic crown ether-supported complex 1′ also reacted
with carbon dioxide to produce a dinuclear yttrium tetracar-
boxylato complex. Although complex 1′a, with a tetraphenylbo-
(15) (a) Sawase, H.; Koizumi, Y.; Suzuki, Y.; Shimoi, M.; Ouchi, A.
Bull. Chem. Soc. Jpn. 1984, 57, 2730. (b) Schleid, T.; Meyer, G. Z. Anorg.
Allg. Chem. 1990, 583, 46. (c) Ma, B.-Q.; Zhang, D.-S.; Gao, S.; Jin, T.-
Z.; Yan, C.-H.; Xu, G.-X. Angew. Chem., Int. Ed. 2000, 39, 3644.
(14) (a) Wang, X.; Guo, Y.; Wang, E.; Duan, L.; Xu, X.; Hu, C. J. Mol.
Struct. 2004, 691, 171. (b) Evans, W. J.; Brady, J. C.; Ziller, J. W. J. Am.
Chem. Soc. 2001, 123, 7711.

1274 Organometallics, Vol. 26, No. 5, 2007
Nakajima and Okuda
Figure 3. Molecular structure of 7′c (ellipsoids drawn at the 50%
probability level, tetra(p-fluorophenyl)borate, dichloromethane in
the lattice, and hydrogen atoms were omitted for clarity). Selected
bond lengths (Å) and angles (deg): Y‚‚‚Y′ 4.0695(5), O2-Y 2.222-
(2), O3-Y 2.2534(19), O1-Y′ 2.2709(19), O4-Y′ 2.2392(19),
O1-C1-O2 122.6(3), O3-C3-O4 123.5(3), Si1-C2-C1 112.4-
(2), Si2-C4-C3 113.5(2).
Figure 2. Molecular structure of 6a (ellipsoids drawn at the 50%
probability level, tetraphenylborate anion, tetrahydrofuran molecules
in the lattice, and hydrogen atoms omitted for clarity). Selected
bond lengths (Å) and angles (deg): Y‚‚‚Y′ 3.8632(6), O1-Y 2.333-
(2), O2-Y 2.3334(19), O2-Y′ 2.532(2), O3-Y 2.2693(19), O4-
Y′ 2.2729(19), O1-C1-O2 118.9(3), O3-C3-O4 124.2(3), Si1-
C2-C1 111.1(2), Si2-C4-C3 114.4(2).
expected to be less nucleophilic than that in the monocationic
complex 1. However, the reaction of 2a with benzophenone
and fluorenone smoothly proceeded in THF to produce the
corresponding alkoxy complexes [Y(OCRPh2)(THF)5][BPh4]2
(8a) and [Y(OCRC12H8)(THF)5][BPh4]2 (9a), respectively
(Scheme 5). Both complexes 8a and 9a exhibited one set of
rate counteranion, reacted with carbon dioxide instantaneously,
the resulting compound was found to be sparingly soluble in
organic solvents and could not be identified. Therefore, the
reaction of 1′ with carbon dioxide was performed using the more
soluble derivative [YR2(12-crown-4)(THF)][B(C6H4F-4)4] (1′c),
with a tetra(p-fluorophenyl)borate anion, to produce the di-
(yttrium) tetracarboxylato complex [Y(µ-η1-η1-O2CR)2(12-
crown-4)]2[B(C6H4F-4)4]2 (7′c) quantitatively. The reaction with
carbon dioxide is faster than that of 1a, and no intermediates
were observed during the reaction, the final product 7′c being
obtained quantitatively after 2 h.
1
trimethylsilylmethyl and phenyl groups in the H NMR spec-
trum. In the 13C NMR spectrum, one doublet assignable to the
carbon atom attached to an oxygen atom appeared at δ 85.6
(2JYC ) 5.2 Hz) for 8a and δ 88.1 (2JYC ) 6.1 Hz) for 9a as a
result of coupling to yttrium.
The dicationic complex 2a also reacted with carbon dioxide (1
bar) in THF under insertion into the yttrium-carbon bond to pro-
duce the carboxylato complex [Y(O2CR)(THF)5][BPh4]2 (10a). In
contrast to the reaction of the monocation 1a with carbon diox-
ide, no intermediates were observed by 1H NMR spectroscopic
monitoring. The resulting complex 10a was characterized by 1H
NMR, 13C NMR, and IR spectroscopy as well as elemental anal-
ysis. In the 1H NMR spectrum, signals of the trimethylsilylmeth-
yl group were observed at δ 2.19 (CH2Si) and δ 0.13 (SiMe3).
In the 13C NMR spectrum the carboxylato carbon signal
appeared at δ 191.4. Since the spectra of 10a were measured
in pyridine-d5, the coordination number of the solvent at the
yttrium center is obscured. As a consequence of the double
positive charge and by the number of THF molecules, we
1
Complex 7′c was identified by H NMR, 13C NMR, and IR
spectra as well as by elemental analysis. Single crystals of 7′c
were obtained from cold CH2Cl2/Et2O solution, and the structure
of 7′c was determined by X-ray structural analysis. The
molecular structure is shown in Figure 3 together with selected
bond lengths and bond angles. The crystal system is monoclinic,
and a crystallographic inversion center relates both yttrium
atoms. In 7′c, the geometry around the yttrium center, sur-
rounded by eight oxygen atoms, is square antiprismatic with
the 12-crown-4 ether coordinating to the yttrium center via four
oxygen atoms. In contrast to the structure of 6a, all four
carboxylato ligands bridge the two yttrium centers in a sym-
metrical µ-η1-η1 fashion and the Y-Y′ bond length (4.0695(5)
Å) is slightly longer than that in 6a. This can be accounted for
by the increased valence electron number of the 11-electron
fragment [Y(12-crown-4)] in 7′c versus the 9-electron fragment
[Y(THF)3] in 6a.
assume that this complex, [Y(O2CCH2SiMe3)(THF)5]2+[BPh4]- ,
2
has a pentagonal bipyramidal configuration with a possibly
chelating carboxylate ligand.16 Carboxylato ligands at highly
positively charged metal centers tend to be chelating, although
the structure found in the dicationic tris(tert-butylsiloxy)-
silanolate yttrium complex [Y{OSi(OtBu)3}(THF)6]2+[BPh4]-
2
with six THF ligands contains a nonchelating silanolate ligand.5c
Conclusion
Addition of metal alkyls such as Grignard or alkyl lithium
reagents to carbonyl compounds is one of the most fundamental
Reaction of the Dicationic Mono(alkyl) Complex. Due to
the high ionic charge, the trimethylsilylmethyl group at the
dicationic yttrium center in [YR(THF)5][BPh4]2 (2a)6c was
(16) Preliminary single-crystal X-ray analysis indicated that the solid-
state structure of 10a is mononuclear.

Cationic Yttrium Alkyl Complexes
Organometallics, Vol. 26, No. 5, 2007 1275
Scheme 5
reactions in organic synthesis.17 In these reactions, competitive
pathways such as enolization and reduction decrease the
selectivity of the formation of the normally desired alcohol. It
has recently been demonstrated that the addition of a lanthanide
salt promotes the addition of organometallic reagents as a result
of the Lewis acid-induced activation of the carbonyl group by
the lanthanide salts.18 Although CeCl3 is the most commonly
used reagent in these systems, any lanthanide or yttrium
trichloride has been recognized to be applicable,19 although there
are not many examples for facile addition of well-defined alkyl
lanthanide complexes to a carbonyl group.8a,9 Despite the cat-
ionic charge,20 the nucleophilicity of the trimethylsilylmethyl
group in the cationic alkyl yttrium complexes 1 and 2 appears
to be retained. Cationic alkoxy complexes were formed selec-
tively as a result of insertion of the C-O double bond of a
ketone into the yttrium-carbon bond. Notably, even the tri-
methylsilylmethyl group in dicationic 2 remains highly polarized
and acts as a nucleophile. At the same time, the polarity of the
trimethylsilymethyl group appears to be also pronounced, as
facile C-H bond activation of pyridine by [Y(CH3)(THF)6]-
[BPh4]2 has shown.7 Application of cationic rare earth metal
alkyl complexes for other C-C bond forming processes beyond
olefin polymerization will depend on the ability to harness this
strongly polarized bond.
crown-4)(THF)][AlR4] (1b′), and [Y(CH2SiMe3)(THF)5][BPh4]2
(2a), were prepared according to published procedures.6c [Y(CH2-
SiMe3)2(12-crown-4)(THF)][B(C6H4F-4)4] (1′c) was prepared from
the reaction of [YR3(THF)2] with [PhNMe2H][B(C6H4F-4)4] and
12-crown-4 following the published procedures.6c All solvents were
dried over sodium benzophenone ketyl and distilled. THF-d8 was
dried over sodium benzophenone ketyl, and CD2Cl2 and pyridine-
d5 were dried over calcium hydride. Benzophenone (Fluka) and
fluorenone (Acros Organics) were purified by sublimation. CO2
was obtained by Westfalen (DIN 32526-C1) and used without any
purification. The 1H and 13C NMR were recorded on a Bruker DRX
400 spectrometer, Varian Unity 500 spectrometer, or Varian Unity
1
200 spectrometer. Chemical shifts for H and 13C NMR spectra
were referenced to the residual solvent resonances. The 19F NMR
was recorded on a Bruker DRX 400 spectrometer, and the chemical
shifts were referenced externally to CCl3F. Elemental analyses were
performed by the Microanalytical Laboratory of the department.
The results occasionally show incorrect values for carbon content,
despite acceptable hydrogen and yttrium measurements. We ascribe
this difficulty to the sensitivity of the material and to the possibility
of solvent loss during sample manipulation.5c Metal analyses were
performed by complexometric titrations.21
Bis{1,1-diphenyl(2-trimethylsilyl)ethoxy}tetra(tetrahydrofuran)-
yttrium Tetraphenylborate (3a). To a solution containing 1a (30
mg, 0.035 mmol) in THF (0.6 mL) was added solid benzophenone
(20 mg, 0.11 mmol) at room temperature, and the reaction mixture
was stirred for 20 min. After an excess amount of pentane was
added, the reaction mixture was cooled to -30 °C to give pure 3a
as a white precipitate, which was washed with pentane (2 × 0.8
Experimental Section
General Procedures. All operations were performed under an
inert atmosphere of argon using Schlenk line and glovebox
techniques. The starting materials, [Y(CH2SiMe3)2(THF)4][BPh4]
(1a), [Y(CH2SiMe3)2(12-crown-4)(THF)][BPh4] (1a′), [Y(CH2-
SiMe3)2(THF)4][AlR4] (1b) (R ) CH2SiMe3), [Y(CH2SiMe3)2(12-
1
mL) and dried in Vacuo; yield: 38 mg (0.031 mmol, 89%). H
NMR (400 MHz, THF-d8, 25 °C): δ -0.35 (s, 18H, SiMe3), 1.71
(br s, â-THF), 1.95 (s, 4H, CH2Si), 3.56 (br s, R-THF), 6.70 (t,
3JHH ) 7.2 Hz, 4H, 4-CH BPh4), 6.84 (t, 3JHH ) 7.4 Hz, 8H, 3-CH
BPh4), 7.18-7.30 (m, 20H, 2-CH BPh4, m+p-Ph, 20H), 7.47 (d,
3JHH ) 7.1 Hz, 8H, o-Ph). 13C NMR (100 MHz, THF-d8, 25 °C):
δ 0.14 (SiMe3), 26.3 (â-THF), 40.2 (CH2Si), 68.2 (R-THF) 83.5
(17) (a) Negishi, E. Organometallics in Organic Synthesis; Wiley: New
York, 1980. (b) Davies, S. G. Organo-Transition Metal Chemistry:
Application to Organic Synthesis; Pergamon: Oxford, 1982. (c) Organo-
metallics in Synthesis, 2nd ed.; Schlosser, M., Ed.; Wiley: New York, 2002.
(d) Hegedus, L. S. Transition Metals in the Synthesis of Complex Organic
Molecules; University Science Books: Mill Valley, CA, 1994. (e) Tsuji, J.
Transition Metal Reagents and Catalysts; Wiley: New York, 2001.
(18) (a) Imamoto, T. Pure. Appl. Chem. 1990, 62, 747. (b) Imamoto,
T.; Takiyama, N.; Nakamura, K.; Hatajima, T.; Kamiya, Y. J. Am. Chem.
Soc. 1989, 111, 4392. (c) Evans, W. J.; Feldman, J. D.; Ziller, J. W. J. Am.
Chem. Soc. 1996, 118, 4581.
(19) (a) Evans, W. J.; Ansari, M. A.; Feldman, J. D.; Doedens, R. J.;
Ziller, J. W. J. Organomet. Chem. 1997, 545-546, 157. (b) Krasovskiy, A.;
Kopp, F.; Knochel, P. Angew. Chem., Int. Chem. 2006, 45, 497.
(20) The disproportionation of a main group alkyl to give an ion pair
has been studied in some detail: Fabicon, R. M.; Richey, H. G., Jr.
Organometallics 2001, 20, 4018, and references therein.
2
(d, JYC ) 5.4 Hz, OC), 121.8 (4-CH BPh4), 125.7 (3-CH BPh4),
127.1 (p-Ph), 128.2 (o-Ph), 128.8 (m-Ph), 137.1 (2-CH BPh4), 151.7
(ipso-Ph), 165.1 (q, 1JBC ) 49.4 Hz, 1-CH BPh4). Anal. Calcd for
C78H102BO7Si2Y: C, 71.65; H, 7.86; Y, 6.80. Found: C, 71.59; H,
7.17; Y, 6.85.
Bis(trimethylsilylmethylfluorenoxy)tetra(tetrahydrofuran)-
yttrium tetraphenylborate (4a). Complex 1a (30 mg, 0.035 mmol)
was dissolved in THF (0.6 mL) and treated with solid fluorenone
(20 mg, 0.11 mmol) at room temperature. After the reaction mixture
(21) Arndt, S.; Spaniol, T. P.; Okuda, J. Organometallics 2003, 22, 775,
and references therein.

1276 Organometallics, Vol. 26, No. 5, 2007
Nakajima and Okuda
was stirred for 20 min, excess pentane was added and the solution
cooled to -30 °C, to afford a white precipitate. Washing the
precipitate with excess pentane (× 2) and drying in Vacuo afforded
product 4a; yield: 36 mg (0.029 mmol, 85%). Single crystals were
obtained by cooling a solution of CH2Cl2/Et2O (1:1 v/v) containing
4a.
NMR (100 MHz, CD2Cl2, 25 °C): δ -1.46 (SiMe3), 25.5 (â-THF),
33.2 (CH2Si), 67.2 (12-crown-4), 69.7 (R-THF), 84.5 (br s, OC),
119.7 (C5), 122.0 (4-CH BPh4), 123.5 (C4), 125.8 (3-CH BPh4),
127.5 (C3), 127.8 (C2), 136.0 (2-CH BPh4), 138.8 (C1), 152.2 (C6),
1
164.0 (q, JBC ) 49.4 Hz, 1-CH BPh4). HSQC (CD2Cl2, 25 °C):
6.88-122.0, 7.01-125.8, 7.20-127.5, 7.29-123.5, 127.8, 136.0,
7.61-119.7. Anal. Calcd for C70H82BO7SiY: C, 70.58; H, 6.94;
Y, 7.46. Found: C, 69.31; H, 6.79; Y, 7.75.
cis/trans-Bis{1,1-diphenyl(2-trimethylsilyl)ethoxy}tetra-
(tetrahydrofuran)yttrium Tetrakis(trimethylsilyimethyl)aluminate
(cis/trans-3b). To the THF solution of 1b (55 mg, 0.059 mmol)
was added benzophenone (30 mg, 0.16 mmol) at room temperature.
After the solution was stirred for 10 min at room temperature, excess
pentane was added to the solution. The solution was cooled to
-30 °C, and a colorless slurry was obtained. After removal of the
supernatant and washing with excess pentane twice, a mixture of
cis-3b (90%) and trans-3b (10%) was obtained as an oil. 1H NMR
(400 MHz, THF-d8, 25 °C): δ -1.24 (br, 8H, AlCH2), -0.38 (s,
18H, SiMe3), -0.13 (s, 36H, AlCH2SiMe3), 1.70 (br s, â-THF),
1H NMR (400 MHz, THF-d8, 25 °C): δ -0.69 (s, 18H, SiMe3),
1.71 (br s, â-THF), 1.76* (CH2Si), 3.57 (br s, R-THF), 6.76 (t,
3JHH ) 7.2 Hz, 4H, 4-CH BPh4), 6.83 (t, 3JHH ) 7.3 Hz, 8H, 3-CH
BPh4), 7.19 (t, 3JHH ) 7.3 Hz, 4H, C3-H), 7.24 (br, 8H, 2-CH BPh4),
7.25* (C4-H), 7.34 (d, 3JHH ) 7.3 Hz, 4H, C2-H), 7.64 (d, 3JHH
)
7.6 Hz, 4H, C5-H). *The signals observed at δ 1.76 and 7.25 were
assigned on the basis of an HSQC spectrum. 13C NMR (100 MHz,
25 °C, THF-d8): δ -1.07 (SiMe3), 25.1 (â-THF), 34.6 (CH2Si),
68.0 (R-THF), 85.4 (d, 2JYC ) 3.7 Hz, OC), 120.3 (C5), 121.6 (4-
CH BPh4), 124.0 (C2), 125.4 (3-CH BPh4), 128.0 (C3), 128.3 (C4),
136.8 (2-CH BPh4), 139.4 (C1), 154.5 (C6), 164.9 (q, 1JBC ) 39.4
Hz, 1-CH BPh4). COSY (THF-d8, 25 °C): 7.64-7.25, 7.34-7.19,
7.25-7.19, 6.83-6.76, 6.83-7.24. HSQC (THF-d8, 25 °C): -0.69
to -1.07, 1.76-34.6, 6.76-121.6, 6.83-125.4, 7.19-128.0, 7.24-
136.8, 7.25-128.3, 7.34-124.0, 7.64-120.3. Anal. Calcd for
C78H98BO7Si2Y: C, 71.87; H, 7.58; Y, 6.82. Found: C, 70.15; H,
7.00; Y, 6.96. The elemental analysis indicated that five molecules
of THF per yttrium are present, whereas the crystal structure
determination by an X-ray diffraction study showed four THF
molecules.
3
1.97 (s, 4H, CH2Si), 3.55 (br s, R-THF), 7.19 (t, JHH ) 7.2 Hz,
4H, p-Ph), 7.26 (t, 3JHH ) 7.3 Hz, 8H, m-Ph), 7.48 (d, 3JHH ) 7.0
Hz, 8H, o-Ph). 13C NMR (100 MHz, THF-d8, 25 °C): δ 1.99
(sextet, 3JHH ) 61.2 Hz, AlCH2), 0.15 (SiMe3), 4.22 (AlCH2SiMe3),
2
26.3 (â-THF), 40.2 (CH2Si), 68.2 (R-THF), 83.6 (d, JYC ) 5.3
Hz, OC), 127.1 (p-Ph), 128.2 (o-Ph), 128.7 (m-Ph), 151.6 (ipso-
Ph). trans-3b: 1H NMR (400 MHz, THF-d8, 25 °C) δ -1.24 (s,
8H, AlCH2), -0.35 (s, 18H, SiMe3), -0.13 (s, 36H, AlCH2SiMe3),
1.70 (br s, â-THF), 1.87 (s, 4H, CH2Si), 3.55 (br s, R-THF), 7.02
3
3
(t, JHH ) 7.2 Hz, 4H, p-Ph), 7.09 (t, JHH ) 7.3 Hz, 8H, m-Ph),
7.45 (d, JHH ) 7.5 Hz, 8H, o-Ph). 13C NMR (100 MHz, THF-d8,
3
3
25 °C): δ 1.99 (sextet, JHH ) 61.9 Hz, AlCH2), 0.05 (SiMe3),
4.22 (AlCH2SiMe3), 26.3 (â-THF), 38.9 (CH2Si), 68.2 (R-THF),
2
82.2 (d, JYC ) 5.2 Hz, OC), 125.8 (p-Ph), 127.7 (o-Ph), 128.5
(m-Ph), 154.3 (ipso-Ph). Since 3b was obtained as an oil, elemental
Bis{1,1-diphenyl(2-trimethylsilyl)ethoxy}(12-crown-4)(tet-
rahydrofuran)yttrium Tetraphenylborate (3a′). To a THF solu-
tion of 1′a (50 mg, 0.048 mmol) was added solid benzophenone
(40 mg, 0.22 mmol) at room temperature. After the reaction mixture
was stirred for 2 h at room temperature, the solvent was removed
in Vacuo. The solid residue was washed with pentane (3 × 0.8
mL) and dried under reduced pressure to afford 3′a as a white solid;
analysis was not performed.
Reaction of 1b with Benzophenone at -30 °C. A THF solution
containing 1b (30 mg, 0.032 mmol) and a THF solution containing
benzophenone (15 mg, 0.082 mmol) were mixed together at
-30 °C. The reaction mixture was gradually warmed to room
temperature and stirred for 30 min. The reaction mixture was again
cooled at -30 °C after excess pentane was added, and a colorless
slurry was obtained at the bottom of the reaction vessel. After
removal of the supernatant, washing with excess pentane (×2), and
drying in Vacuo, complex cis-3b was obtained as the sole product.
1
yield: 41 mg (0.035 mmol, 73%). H NMR (400 MHz, THF-d8,
25 °C): δ -0.36 (s, 18H, SiMe3), 1.70 (br s, â-THF) 1.84 (s, 4H,
CH2Si), 3.15 (m, 8H, 12-crown-4), 3.24 (m, 8H, 12-crown-4), 3.56
3
(br s, R-THF), 6.73 (t, JHH ) 7.2 Hz, 4H, 4-CH BPh4), 6.86 (t,
3JHH ) 7.3 Hz, 8H, 3-CH BPh4), 7.14 (t, 3JHH ) 7.2 Hz, 4H, p-Ph),
7.21 (t, 3JHH ) 7.4 Hz, 8H, m-Ph), 7.25 (br, 8H, 2-CH BPh4), 7.40
Bis(trimethylsilylmethylfluorenoxy)tetra(tetrahydrofuran)-
yttrium Tetrakis(trimethylsilylmethyl)aluminate (4b). The reac-
tion of 1b (35 mg, 0.038 mmol) with fluorenone (20 mg, 0.11
mmol) was carried out at room temperature in the same manner as
the reaction of 1b with benzophenone. A mixture of cis-4b (86%)
and trans-4b (14%) was obtained as an oily slurry. cis-4b: 1H NMR
(400 MHz, THF-d8, 25 °C) δ -1.24 (br, 8H, AlCH2), -0.70 (s,
18H, SiMe3), -0.12 (s, 36 H, AlCH2SiMe3), 1.70 (br s, â-THF),
3
(d, JHH ) 8.0 Hz, 8H, o-Ph). 13C NMR (100 MHz, THF-d8, 25
°C): δ 0.37 (SiMe3), 24.9 (â-THF), 39.2 (CH2Si), 68.2 (12-crown-
4), 68.3 (R-THF), 83.2 (d, 2JYC ) 5.2 Hz, OC), 122.2 (4-CH BPh4),
125.9 (3-CH BPh4), 126.7 (p-Ph), 128.0 (o-Ph), 128.7 (m-Ph), 137.1
1
(2-CH BPh4), 152.8 (ipso-Ph), 165.0 (q, JBC ) 49.4 Hz, 1-CH
BPh4). HSQC (THF-d8, 25 °C): -0.36-0.37, 1.70-24.9, 1.84-
39.2, 3.15, 3.24-68.2, 3.56-68.3, 6.73-122.2, 6.86-125.9, 7.14-
126.7, 7.21-128.7, 7.40-128.0, 7.25-137.1 Anal. Calcd for
C70H86BO7SiY: C, 70.34; H, 7.25; Y, 7.44. Found: C, 68.04; H,
7.60; Y, 7.17.
3
1.79 (s, 4H, CH2Si), 3.56 (br s, R-THF), 7.19 (t, JHH ) 7.34 Hz,
3
3
4H, C3-H), 7.26 (t, JHH ) 7.54 Hz, 4H, C4-H), 7.34 (d, JHH
)
7.53 Hz, 4H, C2-H), 7.63 (d, 3JHH ) 7.28 Hz, 4H, C5-H). 13C NMR
1
(100 MHz, THF-d8, 25 °C): δ -0.85 (SiMe3), 1.99 (sextet, JAlC
) 60.6 Hz, AlCH2SiMe3), 4.2 (AlCH2SiMe3), 26.4 (â-THF), 34.8
Bis(trimethylsilylmethylfluorenoxy)(12-crown-4)(tetrahydro-
furan)yttrium Tetraphenylborate (4a′). The reaction was per-
formed in the same manner as the reaction of 1′a with benzophe-
none. From the reaction of 1′a (50 mg, 0.048 mmol) with fluorenone
(40 mg, 0.22 mmol), complex 4′a was obtained; yield: 56 mg
(0.047 mmol, 99%). 1H NMR (400 MHz, CD2Cl2, 25 °C): δ -0.68
(s, 18H, SiMe3), 1.66 (s, 4H, CH2Si), 1.81 (m, â-THF), 2.99 (m,
8H, 12-crown-4), 3.16 (m, 8H, 12-crown-4), 3.75 (m, R-THF), 6.88
2
(CH2Si), 67.4 (R-THF), 85.8 (d, JYC ) 6.1 Hz, OC), 120.6 (C5),
124.3 (C2), 128.3 (C3), 128.6 (C4), 139.7 (C1), 154.7 (C6). COSY
(THF-d8, 25 °C): 7.19-7.34, 7.26, 7.26-7.63. HSQC (THF-d8,
25 °C): 7.19-128.3, 7.26-128.6, 7.34-124.3, 7.63-120.6. trans-
4b: 1H NMR (400 MHz, THF-d8, 25 °C) δ -1.24 (br, 8H, AlCH2),
-0.69 (s, 18H, SiMe3), -0.12 (s, 36 H, AlCH2SiMe3), 1.70 (br s,
3
â-THF), 1.78 (s, 4H, CH2Si), 3.56 (br s, R-THF), 7.07 (t, JHH
)
3
3
3
(t, JHH ) 7.2 Hz, 4H, 4-CH BPh4), 7.01 (t, JHH ) 7.4 Hz, 8H,
7.28 Hz, 4H, C3-H), 7.12 (t, JHH ) 7.0 Hz, 4H, C4-H), 7.51 (d,
3JHH ) 7.3 Hz, 4H, C2-H), 7.53 (d, 3JHH ) 7.3 Hz, 4H, C5-H). 13
NMR (100 MHz, THF-d8, 25 °C): δ -0.81 (SiMe3), 1.99 (sextet,
3
3-CH BPh4), 7.20 (t, JHH ) 7.0 Hz, 4H, C3-H), 7.29 (m, 16H,
C
2-CH BPh4 + C2,C4-H), 7.61 (d, JHH ) 7.5 Hz, 4H, C5-H). 13C
3

Cationic Yttrium Alkyl Complexes
Organometallics, Vol. 26, No. 5, 2007 1277
3
1JAlC ) 60.6 Hz, AlCH2SiMe3), 4.22 (AlCH2SiMe3), 26.4 (â-THF),
(br s, R-THF), 6.69 (t, JHH ) 7.4 Hz, 4H, 4-CH BPh4), 6.83 (t,
2
36.8 (CH2Si), 68.2 (R-THF), 85.2 (d, JYC ) 5.0 Hz, OC), 119.7
3JHH ) 7.2 Hz, 8H, 3-CH BPh4), 7.25 (br, 8H, 2-CH BPh4). 13C
NMR (100 MHz, THF-d8, 25 °C): δ -0.72 (SiMe3), 26.4 (â-THF),
30.5 (CH2Si), 68.2 (R-THF), 121.8 (4-CH BPh4), 125.7 (3-CH
BPh4), 137.2 (2-CH BPh4), 165.2 (q, 1JBC ) 49.4 Hz, 1-CH BPh4),
187.7 (CO).
(C5), 125.2 (C2), 127.2 (C3), 127.6 (C4), 139.6 (C1), 157.1 (C6).
COSY (THF-d8, 25 °C): 7.07-7.51, 7.12-7.53. HSQC (THF-d8,
25 °C): 7.07-127.2, 7.12-127.6, 7.51-125.2, 7.53-119.7.
Bis{1,1-diphenyl(2-trimethylsilyl)ethoxy}(12-crown-4)(tet-
rahydrofuran)yttrium Tetrakis(trimethylsilylmethyl)aluminate
(3b′). Complex 1′b (30 mg, 0.034 mmol) was dissolved in THF,
and benzophenone (20 mg, 0.11 mmol) was added at room
temperature. The reaction mixture was stirred for 2 h at room
temperature. To the reaction mixture was added excess pentane to
terminate the reaction. After cooling the reaction mixture at -30 °C,
a colorless slurry was obtained. The resulting slurry was washed
with pentane twice and dried in Vacuo. Complex 3′b was obtained
Reaction of 1a with Carbon Dioxide under Reduced Pressure.
A THF solution containing compound 1a (60 mg, 0.069 mmol)
was charged into the reaction vessel equipped with a Teflon valve.
After the evacuation of the reaction mixture at -195 °C, carbon
dioxide (1 bar) was transferred into the reaction vessel at room
temperature. After the reaction mixture was stirred for 10 min at
room temperature, the solvent was removed under reduced pressure.
On starting the evacuation, a large amount of white crystalline 6a
formed at the bottom of the vessel. Complete removal of the solvent
and washing the resulting crystals with THF (×2) afforded clean
6a; yield: 43 mg (0.024 mmol, 70%).
1
as an oily compound. H NMR (400 MHz, THF-d8, 25 °C): δ
-1.24 (br, 8H, AlCH2), -0.35 (s, 18H, SiMe3), -0.11 (s, 36H,
AlCH2SiMe3), 1.70 (br s, â-THF), 1.91 (s, 4H, CH2Si), 3.56 (br s,
R-THF), 3.66 (m, 16H, 12-crown-4), 7.16 (t, 3JHH ) 7.28 Hz, 4H,
(12-Crown-4)tetrakis{(trimethylsilylacetato}yttrium Tetra-
(p-fluorophenyl)borate (7′c). A THF solution (1 mL) of [Y(CH2-
SiMe3)2(12-crown-4)(THF)][B(C6H4F-4)4] (1′c) (80 mg, 0.089
mmol) was charged in an ampule. After the solution was degassed
at -195 °C, carbon dioxide (1 bar) was transferred into the reaction
vessel at room temperature. The reaction mixture was stirred at
room temperature for 2 h. Removal of the solvent in Vacuo afforded
a slurry. Washing the residue with pentane (0.8 mL × 1) gave 7′c
as a white solid: yield 81 mg (0.044 mmol, 99%). From a CH2-
Cl2/Et2O solution at -30 °C, a single crystal of 7′c was obtained.
1H NMR (400 MHz, THF-d8, 25 °C): δ -0.09 (s, 36H, SiMe3),
obscured in residual THF (CH2Si), 3.81 (br, 16H, 12-crown-4), 4.13
(br, 16H, 12-crown-4), 6.61 (t, JHH ) JHF ) 8.2 Hz, 16H, 3-CH
B(C6H4F-4)4), 7.14 (br m, 16H, 2-CH B(C6H4F-4)4). 13C NMR
(100 MHz, THF-d8, 25 °C): δ -1.48 (SiMe3), 30.9 (CH2Si), 71.5
(12-crown-4), 112.3 (dq, JCF ) 18.2 Hz, JBC ) 3.1 Hz, 3-CH
B(C6H4F-4)4), 137.6 (2-CH B(C6H4F-4)4), 159.4 (q, JBC ) 49.7
3
3
p-Ph), 7.23 (t, JHH ) 7.41 Hz, 8H, m-Ph), 7.46 (d, JHH ) 7.78
Hz, 8H, o-Ph). 13C NMR (100 MHz, THF-d8, 25 °C): δ 0.37
(SiMe3), 2.1 (sextet, 1JAlC ) 60.3 Hz, AlCH2), 4.3 (AlCH2SiMe3),
26.4 (â-THF), 39.3 (CH2Si), 68.2 (R-THF), 68.5 (12-crown-4), 83.3
(d, 2JYC ) 5.2 Hz, OC), 126.8 (p-Ph), 128.0 (m-Ph), 128.7 (o-Ph),
152.7 (ipso-Ph).
Tetrakis{(trimethylsilylacetato}hexa(tetrahydrofuran)yttri-
um Tetraphenylborate (6a). A glass ampule equipped with a
Teflon valve was charged with 1a (30 mg, 0.035 mmol) and THF
(1 mL). After degassing of the ampule at -195 °C, carbon dioxide
(1 bar) was transferred at room temperature. The reaction mixture
was stirred at room temperature, and a white solid of complex 6a
was gradually formed over hours. After 9 h, volatiles were removed
in Vacuo and complex 6a was obtained in good yield: 24 mg (0.014
mmol, 78%). 1H NMR (400 MHz, pyridine-d5, 25 °C): δ 0.13 (s,
36H, SiMe3), 2.18 (s, 8H, CH2Si), 1.60 (m, â-THF), 3.63 (m,
3
3
2
3
1
Hz 1-CH B(C6H4F-4)4,), 160.9 (d, 1JCF ) 237.6 Hz, B(C6H4F-4)4),
180.9 (CO). 19F NMR (376.4 MHz, THF-d8, 25 °C): δ -125.01
(B(C6H4F-4)4). THF coordinated at yttrium was obscured by THF-
d8 signals in the 13C NMR spectrum. IR (KBr): ν ) 3081,3017,
2957, 2888, 1615, 1581 (νsym CO, RCO2), 1489, 1443 (νasym CO,
RCO2), 1381, 1298, 1285, 1251, 1211, 1157, 1131, 1114, 1072,
1018, 934, 867, 853, 814, 780, 707, 633, 552. cm-1. Anal. Calcd
for C84H108B2F8O10Si4Y2: C, 54.91; H, 5.92; Y, 9.68. Found: C,
54.45; H, 5.66; Y, 8.82.
3
R-THF), 7.13 (t, JHH ) 7.2 Hz, 8H, 4-CH BPh4), 7.31 (t, 16H,
3JHH ) 7.4 Hz, 3-CH BPh4), 8.10 (br s, 16H, 2-CH BPh4). 13C
NMR (100 MHz, pyridine-d5, 25 °C): δ -0.95 (SiMe3), 30.3 (CH2-
Si), 25.8 (â-THF), 67.8 (R-THF), 122.3 (4-CH BPh4), 126.2 (3-
1
CH BPh4), 137.2 (2-CH BPh4), 165.1 (q, JBC ) 49.0 Hz, 1-CH
BPh4), 191.3 (s, CO). IR (KBr): ν ) 3055, 3036, 2982, 2897, 1591,
1579, 1553 (νsym CO, RCO2), 1480, 1431 (νasym CO, RCO2), 1375,
1240, 1114, 1032, 1015, 855, 734, 705, 680, 638, 612 cm-1. Anal.
Calcd for C92H132B2O14Si4Y2: C, 62.29; H, 7.50; Y, 10.02.
Found: C, 62.95; H, 7.75; Y, 10.09.
{1,1-Diphenyl(2-trimethylsilyl)ethoxy}penta(tetrahydrofuran)-
yttrium Bis(tetraphenylborate) (8a). Complex 2a (70 mg, 0.060
mmol) was reacted with benzophenone (30 mg, 0.16 mmol) in THF
(0.7 mL) at room temperature for 20 min. All volatiles were
removed under reduced pressure, and the resulting solid was washed
with pentane (2 × 0.8 mL) and dried in Vacuo to afford 8a as a
Monitoring the Reaction of 1a with Carbon Dioxide. The
NMR sample tube was charged with 1a (10 mg, 0.012 mmol) and
THF-d8. After the solution was evacuated at -195 °C, carbon
dioxide (1 bar, 0.09 mmol) was transferred into the sample tube
using a balloon. The sample tube was kept at room temperature
and the reaction was followed by taking a 1H NMR spectrum. The
molar ratio of complexes was calculated on the relative integral
intensity to TMS. After 10 min, complex 1a was completely
consumed and intermediates A, B, and C were observed. The
relative integral intensities of methyl signals are 5%, 76%, and 19%,
respectively. After 30 min, only B and C were observed with yields
of 80% and 20%. At the end of the reaction, single crystals of 6a,
which were suitable for X-ray diffraction study, were obtained in
the NMR sample tube. A: 1H NMR (200 MHz, THF-d8, 25 °C) δ
1
yellow powder; yield: 75 mg (0.056 mmol, 92%). H NMR (400
MHz, THF-d8, 25 °C): δ -0.38 (s, 9H, SiMe3), obscured in residual
THF (CH2Si), 1.70 (br s, â-THF), 3.55 (br s, R-THF), 6.72 (t, 3JHH
3
) 7.2 Hz, 16H, 4-CH BPh4), 6.86 (t, JHH ) 7.4 Hz, 16H, 3-CH
BPh4), 7.26 (br, 16H, 2-CH BPh4), 7.45 (br, 4H, p-Ph), 7.55 (br,
2H, m-Ph), 7.74 (br, 4H, o-Ph). 13C NMR (100 MHz, THF-d8, 25
°C): δ -0.07 (SiMe3), 26.4 (â-THF), 40.0 (CH2Si), 68.2 (R-THF),
2
85.6 (d, JYC ) 5.2 Hz, OC), 122.0 (4-CH BPh4), 125.8 (3-CH
BPh4), 128.2 (p-Ph), 129.0 (o-Ph), 129.5 (m-Ph) 137.1 (2-CH BPh4),
149.1 (ipso-Ph), 165.1 (q, 1JBC ) 54.8 Hz, 1-CH BPh4). Anal. Calcd
for C85H101B2O6SiY: C, 72.21; H, 7.50; Y, 6.55. Found: C, 74.28;
H, 7.17; Y, 6.63.
2
-0.93 (d, JYH ) 3.2 Hz, CH2Si), -0.13 (s, SiMe3). B: 1H NMR
(400 MHz, THF-d8, 25 °C) δ 0.12 (s, SiMe3), 1.72 (br s, â-THF),
1.88 (s, CH2Si), 3.56 (br s, R-THF), 6.69 (t, 3JHH ) 7.4 Hz, 4-CH
BPh4), 6.83 (t, 3JHH ) 7.2 Hz, 3-CH BPh4), 7.25 (br, 2-CH BPh4).
13C NMR (100 MHz, THF-d8, 25 °C): δ -1.01 (SiMe3), 26.4 (â-
{(Trimethylsilylmethyl)fluorenoxy}penta(tetrahydrofuran)-
yttrium Bis(tetraphenylborate) (9a). Complex 2a (25 mg, 0.021
mmol) was dissolved in THF (0.6 mL) and treated with fluorenone
(20 mg, 0.11 mmol) at room temperature. After the solution was
stirred for 20 min, all volatiles were removed in Vacuo. The residue
was washed with pentane (2 × 0.8 mL) and dried in Vacuo to give
THF), 30.2 (d, 3JYC ) 2.6 Hz, CH2Si), 68.2 (R-THF), 121.8 (4-CH
1
BPh4), 125.7 (3-CH BPh4), 137.2 (2-CH BPh4), 165.2 (q, JBC
)
49.4 Hz, BPh4), 192.0 (CO). C: 1H NMR (400 MHz, THF-d8,
25 °C) δ 0.13 (s, SiMe3), 1.72 (br s, â-THF), 1.92 (s, CH2Si), 3.56

1278 Organometallics, Vol. 26, No. 5, 2007
Nakajima and Okuda
Table 1. Experimental Data for Crystal Structure Determinations of Complexes 4a, 6a, and 7′c
4a
6a
7'c
empirical formula
Mr
C74H90BO6Si2Y
1231.36
C92H132B2O14Si4Y2‚2(C4H8O)
1917.98
C84H108B2F8O16Si4Y2‚CH2Cl2
1922.43
cryst syst
space group
a (Å)
b (Å)
c (Å)
monoclinic
P21/a
21.6997(11)
12.2426(6)
24.9387(13)
monoclinic
P21/n
12.4231(10)
13.6526(11)
29.791(2)
monoclinic
C2/c
29.708(2)
13.3582(11)
23.4492(19)
R (deg)
â (deg)
γ (deg)
V (Å3)
94.546(2)
93.001(2)
92.171(2)
6604.4(6)
4
1.238
130
0.971
5045.9(7)
2
1.262
130
1.253
9299.0(12)
4
1.373
130
1.428
Z
D
T (K)
calc (g‚cm-3
)
µ(Mo KR) (mm-1
F(000)
)
2616
2040
3992
cryst size
θ range (deg)
no. of reflns collected
0.19 × 0.20 × 0.46
2.33-26.58
79 201
0.23 × 0.26 × 0.44
2.22-28.57
33 647
0.16 × 0.28 × 0.47
2.17-29.58
66 746
no. of reflns obsd [I > 2σ(I)]
9484
7947
8431
no. of indep reflns (Rint
)
13 772 (0.1020)
13 772/0/753
empirical
1.021
0.0504, 0.1040
0.0891, 0.1179
0.545 and -0.352
12 334 (0.0605)
12 334/0/554
empirical
1.005
0.0548, 0.1242
0.1008, 0.1416
0.604 and -0.404
12 971(0.0819)
12 971/0/529
empirical
1.014
0.0506, 0.1151
0.0973, 0.1341
1.432 and -1.363
no. of data/restraints/params
absorp corr
goodness-of-fit on F2
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
largest diff peak and hole (e Å-3
)
9a as a yellow powder; yield: 19 mg (0.014 mmol, 67%). 1H NMR
(400 MHz, pyridine-d5, 25 °C): δ -0.50 (s, 9H, SiMe3), 1.60 (m,
â-THF), 2.40 (s, 2H, CH2Si), 3.64 (m, R-THF), 7.09 (t, 3JHH ) 7.2
CCD area detector diffractometer.22 The SADABS program was
used for absorption correction.22 The structure of 4a was solved
using the Patterson method, and the structures of 6a and 7′c were
solved by direct methods using the SHELXS-97 program,23
followed by successive cycles of full-matrix least-squares refinement
on F2. In the structure of 4a, two carbons of a yttrium-coordinated
tetrahydrofuran are disordered with 61.0% and 38.1% occupancy
for each site. In the lattice of 6a, two disordered tetrahydrofuran
molecules are included with 56.4% and 43.6% occupancy, respec-
tively. In the lattice of 7′c, one disordered methylene chloride
molecules was included with occupancy of 50:50. All non-hydrogen
atoms except the disordered carbon and chloride atoms were refined
anisotropically. Hydrogen atoms of methylene, methyl, and phenyl
groups were included in the structure factor calculations in idealized
positions. Least-squares refinement was carried out using SHELXL-
97.24 Relevant crystallographic data for 4a, 6a, and 7′c are
summarized in Table 1.
3
Hz, 8H, 4-CH BPh4), 7.26 (t, JHH ) 7.4 Hz, 16H, 3-CH BPh4),
3
3
7.30 (t, JHH ) 7.5 Hz, 2H, C12H8), 7.47 (t, JHH ) 7.5 Hz, 2H,
3
3
C12H8), 7.69 (d, JHH ) 7.5 Hz, 2H, C12H8), 7.88 (d, JHH ) 7.5
Hz, 2H, C12H8), 8.05 (br, 16H, 2-CH BPh4). 13C NMR (100 MHz,
pyridine-d5, 25 °C): -0.71 (SiMe3), 25.8 (â-THF), 31.2 (CH2Si),
2
67.9 (R-THF), 88.1 (d, JYC ) 6.1 Hz, OC), 121.1 (C12H8), 122.4
(4-CH BPh4), 124.5 (C12H8), 126.2 (3-CH BPh4), 128.4 (C12H8),
129.6 (C12H8), 137.2 (2-CH BPh4), 139.6 (C12H8), 151.2 (C12H8),
165.1 (q, 1JBC ) 49.4 Hz, 1-CH BPh4). Anal. Calcd for C85H99B2O6-
SiY: C, 75.33; H, 7.36; Y, 6.56. Found: C, 75.49; H, 7.43; Y,
6.30.
(Trimethylsilylacetato)penta(tetrahydrofuran)yttrium Bis(tet-
raphenylborate) (10a). In an ampule, complex 2a (75 mg, 0.064
mmol) was dissolved in THF (1.2 mL) and exposed to 1 bar of
CO2 for 22 h at room temperature. After all volatiles were removed
under reduced pressure, the resulting solid was washed with pentane
(2 × 0.8 mL). After drying in Vacuo, the carboxylato complex was
Acknowledgment. Financial support by the Deutsche For-
schungsgemeinschaft, the Fonds der Chemischen Industrie, and
the Alexander von Humboldt-Foundation (postdoctoral fellow-
ship to Y.N.) is gratefully acknowledged. We thank Prof. U.
Englert and Dr. T. P. Spaniol for help with the crystallography.
1
obtained as a white solid; yield: 60 mg (0.049 mmol, 77%). H
NMR (400 MHz, pyridine-d5, 25 °C): δ 0.13 (s, 9H, SiMe3), 2.19
(s, 2H, CH2Si), 1.60 (m, 20H, â-THF), 3.64 (m, 20H, R-THF),
3
3
7.10 (t, JHH ) 7.2 Hz, 8H, 4-CH BPh4), 7.27 (t, JHH ) 7.5 Hz,
16H, 3-CH BPh4), 8.06 (br, 16H, 2-CH BPh4). 13C NMR (100 MHz,
pyridine-d5, 25 °C): δ -0.91 (SiMe3), 25.8 (â-THF), 30.4 (CH2-
Si), 67.9 (R-THF), 122.4 (4-CH BPh4), 126.3 (3-CH BPh4), 137.2
(2-CH BPh4), 165.8 (q, 1JBC ) 49.4 Hz, 1-CH BPh4), 191.4 (CO).
IR (KBr): ν ) 3055, 3036, 2983, 2898, 1612, 1557 (νasym CO,
RCO2), 1480, 1441 (νasym CO, RCO2), 1375, 1251, 1112, 1032,
1014, 856, 733, 704, 634, 612 cm-1. Anal. Calcd for C73H91B2O7-
SiY: C, 71.92; H, 7.52; Y, 7.29. Found: C, 71.50; H, 7.40; Y,
7.35.
Supporting Information Available: CIF files of all crystal data
and refinement parameters, atomic parameters including hydrogen
atoms, and bond lengths and angles for 4a, 6a, and 7′c. This material
is available free of charge via the Internet at http://pubs.acs.org.
OM0610290
(22) Siemens. ASTRO, SAINT, and SADABS, Data Collection and
Processing Software for the SMART System. Siemens Analytical X-ray
Instruments Inc.: Madison, WI, 1996.
(23) Sheldrick G. M. SHELXS-97, Program for crystal structure deter-
mination; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(24) Sheldrick G. M. SHELXL-97, Program for crystal structure deter-
mination; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
Crystal Structure Analysis of 4a, 6a, and 7′c. The diffraction
data of 4a, 6a, and 7′c were collected on a Bruker SMART Apex