Ring-opening of a furyl group appended to the cyclopentadienyl ligand in rare-earth metal half-sandwich complexes

Article abstract of DOI:10.1021/om0701726

A series of scandium, lutetium, and yttrium complexes containing a tetramethylcyclopentadienyl ligand with a pendant furyl group, [Ln{η⁵-C₅Me₄SiMe₂(C ₄H₂RO-2)}(CH₂SiMe₃) ₂(THF)] (Ln = Se, Lu, Y; R = H, Me), have been synthesized and structurally characterized. Single-crystal X-ray diffraction studies of the scandium complexes [Sc{η⁵-C₅Me₄SiMe ₂(C₄H₂RO-2)}CH₂SiMe ₃)₂(THF)] (R = H, Me) revealed a pseudo-four-coordinate metal center without additional coordination of the furyl group. The previously elusive lutetium complex [Lu{η⁵-C₅Me ₄SiMe₂(C₄H₂MeO-2)}(CH ₂SiMe₃)₂(THF)] could be isolated and exhibited structural features analogous to those of the scandium compound. Variable-temperature ¹H NMR spectroscopic studies of the entire series confirmed the labile nature of both the THF ligands and furyl donor in solution. Rates for the ring-opening reaction, triggered by intramolecular C-H bond activation, were shown to depend primarily on the metal size. The ring-opening reaction resulted in the formation of the corresponding dinuclearyne-enolate complexes [Ln{η⁵:η¹-C ₅Me₄SiMe₂(C≡CCH=CRO)}(CH₂- SiMe₃)]₂ (Ln = Se, Lu, Y; R -H, Me). Substitution at the 5-furyl position did not markedly influence the rate of the ring-opening reaction but shifted the position of the monomer-dimer equilibrium toward the monomer. Only a large excess of THF allowed the observation of monomeric yne-enolate complexes such as [Y{η⁵:η¹-C ₅Me₄SiMe₂(C≡CCH=CHO)}(CH ₂SiMe₃)(THF)₂], which was characterized by X-ray crystallography. Addition of THF increased the stability of the lutetium bis(alkyl) complexes and allowed the formation of the corresponding cationic compounds by treatment with [NEt₃H][BPh₄] to yield [Lu{η⁵:η¹-C₅Me₄SiMe ₂(C₄H₂RO-2)}(CH₂SiMe ₃)(THF)_n][BPh₄] (Ln = Lu; R = H, Me), which resisted ring- opening of the furyl group.

Full text of DOI:10.1021/om0701726

Organometallics 2007, 26, 3227-3235
3227
Ring-Opening of a Furyl Group Appended to the Cyclopentadienyl
Ligand in Rare-Earth Metal Half-Sandwich Complexes
Julia Hitzbleck and Jun Okuda*
Institute of Inorganic Chemistry, RWTH Aachen UniVersity, Landoltweg 1, D-52074 Aachen, Germany
ReceiVed February 23, 2007
A series of scandium, lutetium, and yttrium complexes containing a tetramethylcyclopentadienyl ligand
with a pendant furyl group, [Ln{η5-C5Me4SiMe2(C4H2RO-2)}(CH2SiMe3)2(THF)] (Ln ) Sc, Lu, Y; R )
H, Me), have been synthesized and structurally characterized. Single-crystal X-ray diffraction studies of
the scandium complexes [Sc{η5-C5Me4SiMe2(C4H2RO-2)}(CH2SiMe3)2(THF)] (R ) H, Me) revealed a
pseudo-four-coordinate metal center without additional coordination of the furyl group. The previously
elusive lutetium complex [Lu{η5-C5Me4SiMe2(C4H2MeO-2)}(CH2SiMe3)2(THF)] could be isolated and
1
exhibited structural features analogous to those of the scandium compound. Variable-temperature H
NMR spectroscopic studies of the entire series confirmed the labile nature of both the THF ligands and
furyl donor in solution. Rates for the ring-opening reaction, triggered by intramolecular C-H bond
activation, were shown to depend primarily on the metal size. The ring-opening reaction resulted in the
formationofthecorrespondingdinuclearyne-enolatecomplexes[Ln{η5:η1-C5Me4SiMe2(CtCCHdCRO)}(CH2-
SiMe3)]2 (Ln ) Sc, Lu, Y; R ) H, Me). Substitution at the 5-furyl position did not markedly influence
the rate of the ring-opening reaction but shifted the position of the monomer-dimer equilibrium toward
the monomer. Only a large excess of THF allowed the observation of monomeric yne-enolate complexes
such as [Y{η5:η1-C5Me4SiMe2(CtCCHdCHO)}(CH2SiMe3)(THF)2], which was characterized by X-ray
crystallography. Addition of THF increased the stability of the lutetium bis(alkyl) complexes and allowed
the formation of the corresponding cationic compounds by treatment with [NEt3H][BPh4] to yield [Lu-
{η5:η1-C5Me4SiMe2(C4H2RO-2)}(CH2SiMe3)(THF)n][BPh4] (Ln ) Lu; R ) H, Me), which resisted ring-
opening of the furyl group.
reactivity pattern is also pronounced. Along with the tendency
to undergo ligand redistribution reactions, C-H bond activation
is made responsible for the fast catalyst degradation.2a,4 We have
selected furyl-substituted cyclopentadienyl ligands as typical
hemi-labile ligand systems5 and investigated the stability and
reactivity of these complexes. Rare-earth metal complexes have
previously been reported to yield ortho-metalation products with
aromatic heterocycles such as furan, thiophene, and pyridine.6
Unexpectedly, with the furan group appended to the cyclopen-
tadienyl ligand the metalation does not proceed at the 2-position
but rather involves the ring proton in the 3-position, resulting
Introduction
The rare-earth metal centers in half-sandwich complexes are
electronically and sterically less saturated than those in metal-
locene complexes1,2 and show reactivity distinct from that
observed for the latter.3 Intra- and intermolecular C-H bond
activation via σ-bond metathesis, particularly well documented
for lanthanocene alkyl complexes, has also been reported for
half-sandwich complexes.2a,b For the monocationic complexes,1j,k
the active species proposed for homogeneous olefin polymer-
ization catalysis based on mono(cyclopentadienyl) systems, this
* To whom correspondence should be addressed. Tel. +49 241 80 94645.
Fax: +49 241 80 92644. E-mail: jun.okuda@ac.rwth-aachen.de.
(1) (a) Edelmann, F. T., In ComprehensiVe Organometallic Chemistry
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179, 247. (c) Kilimann, U.; Edelmann, F. T. Coord. Chem. ReV. 1995, 141,
1. (d) Richter, J.; Edelmann, F. T. Coord. Chem. ReV. 1996, 147, 373. (e)
Gun’ko, Y.; Edelmann, F. T. Coord. Chem. ReV. 1996, 156, 1. (f) Edelmann,
F. T.; Gun’ko, Y. K. Coord. Chem. ReV. 1997, 165, 163. (g) Edelmann, F.
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L. J. Am. Chem. Soc. 1983, 105, 6491. (c) Watson, P. L. Chem. Commun.
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51. (e) 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.
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13, 1147. (g) Evans, W. J.; Davies, B. L. Chem. ReV. 2002, 102, 2119. (h)
Evans, W. J.; Champagne, T. M.; Ziller, J. W. J. Am. Chem. Soc. 2006,
128, 14270. (i) Evans, W. J.; Davies, B. L.; Champagne, T. M.; Ziller, J.
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Elvidge, B. R.; Zeimentz, P. M.; Spaniol, T. P.; Okuda, J. Organometallics
2006, 25, 793.
10.1021/om0701726 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 05/22/2007

3228 Organometallics, Vol. 26, No. 13, 2007
Hitzbleck and Okuda
Chart 1. Rare-Earth-Metal Half-Sandwich Bis(alkyl) Complexes Discussed in This Work
Scheme 1
in a ring-opening reaction of the furyl group to give yne-enolate
complexes.7 We present here the results of a study aimed at
rationalizing this unusual reactivity as a function of metal size,
ionic charge, and substitution pattern in the furyl group.
Results and Discussion
Synthesis and Characterization. A series of rare-earth-metal
half-sandwich complexes of the type [Ln{η5-C5Me4SiMe2(C4H2-
RO-2)}(CH2SiMe3)2(THF)] (5a-7a, 5b-7b: Ln ) Sc (5) Lu
(6), Y (7); R ) H (a) Me (b)) (Chart 1) have been prepared in
good yield in pentane by reacting the respective rare-earth metal
tris((trimethylsilyl)methyl) complexes [Ln(CH2SiMe3)3(THF)x]8
(Ln ) Sc (1) Lu (2), x ) 2; Ln ) Y (3), x ) 3) with the
substituted cyclopentadienes C5Me4H{SiMe2(C4H2RO-2)} (R
) H (4a), Me (4b))7 at room temperature over a period of
2-6 h (Scheme 1, Chart 1). The previously elusive lutetium
compound 6b7 could now be isolated in crystalline form under
these reaction conditions, albeit in low yield. The yttrium
congener 7b in this series decomposed immediately in an
intramolecular C-H bond activation, triggering the formation
of the thermally more stable dimeric yne-enolate product 7b*
(vide infra).7
strength of furan is lower than that of THF,6f,7,9 suppressing
replacement of the THF donor. The argument of the unfavorable
steric strain in such a chelating system does not hold in the
case of the small scandium center, as the THF donor is replaced
in the analogous 2-pyridyl-substituted complex [Sc{η5:η1-C5-
Me4SiMe2(C5H4N-2)}(CH2SiMe3)2].10 This complex displays an
angle between the cyclopentadienyl ring and pyridyl donor
similar to that in the furyl system. Overall, the structure of 5a,b
is comparable to that of related structurally characterized
scandium half-sandwich complexes, e.g., [Sc(η5-C5Me4-
SiMe3)(CH2SiMe3)2(THF)]11 and [Sc{η5-C5Me4SiMe2(C6F5)}-
(CH2SiMe3)2(THF)],12 with the η5-coordinated cyclopentadienyl
ring in the apical position (Sc-Cp(cent) ) 2.172 Å (5a), 2.198
Å (5b)) and the remaining ligands and donors in the basal plane
(Sc-C ) 2.220(2)-2.2437(13) Å; Sc-O ) 2.171(2) Å).
Variable-temperature 1H NMR spectroscopic data of 5a,b did
not indicate any interaction of the furyl ring with the scandium
The solid-state structures of the scandium complexes 5a,b
(Figures 1 and 2) display the typical piano-stool geometry of
half-sandwich complexes. In contrast to the lutetium compound
6a reported earlier,7 the pendant furyl moiety does not coordinate
to the scandium center. This is the result of the significantly
smaller size of scandium compared with the sizes of lutetium
and yttrium and, thus, the preference for a pseudo-four-
coordinate metal center in 5a,b over the pseudo-five-coordinate
trigonal-bipyramidal structure of 6a.7 Furthermore, the donor
(9) (a) Berthelot, M.; Besseau, F.; Laurence, C. Eur. J. Org. Chem. 1998,
925. (b) Evans, W. J.; Fujimoto, C. H.; Johnston, M. A.; Ziller, J. W.
Organometallics 2002, 21, 1825.
(10) Hitzbleck, J.; Okuda, J. Unpublished results.
(11) Luo, Y.; Baldamus, J.; Hou, Z. J. Am. Chem. Soc. 2004, 126, 13910.
(12) Hitzbleck, J.; Okuda, J., Z. Anorg. Allg. Chem. 2006, 632, 1947.
(7) Arndt, S.; Spaniol, T. P.; Okuda, J. Organometallics 2003, 22, 775.
(8) (a) Lappert, M. F.; Pearce, R. Chem. Commun. 1973, 126. (b)
Hultzsch, K. C.; Spaniol, T. P.; Okuda, J. Angew. Chem., Int. Ed. 1999,
38, 227. (c) Schumann, H.; Freckmann, D. M. M.; Dechert, S. Z. Anorg.
Allg. Chem. 2002, 628, 2422.

Furyl-Functionalized Complexes of Sc, Y, and Lu
Organometallics, Vol. 26, No. 13, 2007 3229
Figure 3. Logarithmic plot of furyl ring-opening via C-H bond
activation in complexes 5a,b, 6a,b, and 7a under yne-enolate
formation.
Figure 1. Molecular structure of 5a. Hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and angles (deg):
Sc-O41, 2.171(2); Sc-C21, 2.220(2); Sc-C31, 2.211(2); Sc-
C(1-5), 2.478(3)-2.493(3); C21-Sc-C31, 103.92(11); C21-Sc-
O41, 92.24(10); C31-Sc-O41, 105.05(9).
low temperature, these complexes were still too fluxional on
the NMR time scale to indicate possible agostic C-H contacts
which promote the ring-opening reaction observed in solution
(vide infra).
Ring-Opening of the Furyl Group. The metalation of
(hetero)aromatic systems by organometallic complexes, usually
in the position ortho to the heteroatom, is a well-documented
reaction in the literature.3e,f,4,6d,f,g The subsequent ring-opening
reaction in the case of furan, on the other hand, has been reported
but only studied in detail in a few cases.6f,7 With the aforemen-
tioned series of complexes in hand, we have now correlated
the reactivity and structural trends influencing the intramolecular
C-H bond activation reaction. The furyl-substituted half-
sandwich complexes 5-7 showed decreasing thermal stability
with increasing metal size,13 facilitating the ring-opening
reaction of the furyl moiety in a noncoordinating solvent with
yne-enolate formation (Scheme 2).
The small size of the scandium center allowed formation of
the thermally stable bis(alkyl) complexes 5a,b which only slowly
converted into the corresponding yne-enolate complexes 5a′
(t1/2(40 °C) ) 41.1 h for 5a) and 5b′ (t1/2(40 °C) ) 61.7 h for
5b) at 40 °C (Figure 3). The slightly higher stability of 5b can
be rationalized by the higher rotation barrier of the 5-methyl-
substituted furyl donor. An increase in size of the metal center
by 0.116 Å12 from scandium to lutetium led to a more
pronounced tendency toward C-H bond activation in the furyl
group of the corresponding complexes 6a (t1/2(40 °C) ) 8.9 h)
and 6b (t1/2(40 °C) ) 8.6 h), but significant influence of the
5-methyl substitution at the furyl moiety could not be observed.
The yttrium complexes 7a (t1/2(40 °C) ) 0.9 h) and 7b (t1/2
(10 °C) ) 2.0 h)7 are even less stable, and the 5-methyl
substitution of the furyl donor drastically reduced the stability
in this case. Monitoring the reaction of 7a was hampered by
the decomposition of the yne-enolate complex 7a′ formed at
40 °C in solution.
Figure 2. Molecular structure of 5b. Hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and angles (deg):
Sc-O41, 2.1709(9); Sc-C21, 2.2437(13); Sc-C31, 2.2282(13);
Sc-C(1-5), 2.4799(12)-2.5411(13); C21-Sc-C31, 103.93(5);
C21-Sc-O41, 95.74(4); C31-Sc-O41, 103.76(4).
metal center in solution, consistent with their solid-state structure
discussed above. No characteristic shift changes of the aromatic
furyl CH signals could be observed in the temperature range of
-60 to +60 °C (Table 1), as would be expected for coordination
of the furyl moiety to the Lewis acidic metal center. The
methylene protons of the two CH2SiMe3 groups appeared as
broad signals even at -60 °C, indicating a highly fluxional
structure. The corresponding data for the larger congeners 6a,b
and 7a indicated a fluxional structure in solution at room
temperature with dissociatively labile THF.7 At -80 °C the
methylene proton signals of 6a and 7a became diastereotopic,
corresponding to a Cs-symmetric structure, and the furyl proton
signals were significantly shifted downfield (Table 1). In
contrast, the slightly larger steric demand of the 5-methylfuryl
substituent apparently prevents such an additional stabilization
in 6b, as indicated by temperature-independent shift values for
the furyl substituent. Similar to the structures of 5a,b, no
diastereotopic methylene protons were observed for 6b at low
temperature. Despite the more rigid structures of 6a and 7a at
Mechanism of the Ring-Opening. The mechanism of these
types of ring-opening reactions has been discussed previously
for 7b.7 For the formation of the related yttrocene complex
[Y(η5-C5Me5)2(η2-C4H3O)], no clear pathway for the formation
of the yne-enolate complexes was proposed by Teuben et al.,
due to inconclusive data from kinetic experiments.6f The chelate
(13) r(Sc3+) ) 0.745 Å, r(Lu3+) ) 0.861 Å, and r(Y3+) ) 0.900 Å for
coordination number 6: Shannon, R. D. Acta Crystallogr. 1976, A32, 751.
(14) Bambirra, S.; Meetsma, A.; Hessen, B. Organometallics 2006, 25,
3486.

3230 Organometallics, Vol. 26, No. 13, 2007
Hitzbleck and Okuda
1
Table 1. Furyl Proton Signals (δ (ppm)) in the H NMR Spectra of 5a,b, 6a,b, and 7a in [D8]Toluene at Different Temperatures
5a
6a
7a7
5b
6b
H-3
H-4
H-5
H-3
H-4
H-5
H-3
H-4
H-5
H-3
H-4
H-3
H-4
+60 °C
+25 °C
-60 °C
6.49
6.53
6.55
6.14
6.14
6.09
7.53
7.42
7.25
6.50
6.56
6.56
5.83
5.85
5.85
6.52
6.27
6.15
6.01
7.53
8.07
6.47
6.24
6.17
6.24
7.92
8.19
6.53
6.55
5.83
5.80
Scheme 2
furyl ring is probably more steric than electronic in nature. The
sterically constrained scandium complexes 5a,b hinder the
rotation of the pendant donor, with slightly higher steric
interactions of the methyl-substituted furyl complex leading to
increased stability of 5b. For the larger lutetium complexes 6a,b
this effect is reversed. Although both complexes display similar
ring-opening rates, 6a displays a strong Lu-O interaction in
the solid state as well as in solution, while the furyl donor in
6b is not in the vicinity of the metal center, as indicated by 1H
NMR spectroscopic data. Determination of the activation
parameters of 6a,b from an Eyring plot (Figure 4) gave: ∆Hq
) 62.2 ( 2.2 kJ mol-1 K-1 and ∆Sq ) -140.2 ( 6.6 J mol-1
K-1 for 6a and ∆Hq ) 88.6 ( 2.2 kJ mol-1 K-1 and ∆Sq )
-52.9 ( 6.6 J mol-1 K-1 for 6b. These data suggest an ordered
transition state for the rate-determining step of the C-H
activation reaction, indicated by the large negative values for
the entropy of activation. The methyl-substituted donor in 6b
raises the activation enthalpy but lowers the transition state
energy, leading to a slightly higher C-H bond metalation rate.
For the intramolecular C-H bond activation in the 1,4,7-
triazacyclononane-amide complex [La{iPr2TACN(SiMe2)Nt-
Bu}(CH2SiMe3)2], Hessen et al. reported the activation param-
eters ∆Hq ) 54.6 ( 0.5 kJ mol-1 K-1 and ∆Sq ) +27 ( 20 J
mol-1 K-1 as a simple first-order kinetic process.14 While the
activation energies for the TACN complexes 6a,b appear
comparable, the positive entropy of activation indicates faster
C-H bond activation for the larger lanthanum complex. The
reported half-life of 30 min (35 °C) is in the range of that for
the yttrium complex 7a. The strong coordination of the furyl
substituent allows isolation of 7a, whereas the steric hindrance
of the 5-methyl substituent in 7b leads to concomitant formation
of the C-H bond activation product 7b*, as observed in the
1H NMR spectrum.7 Hence, the formation of potentially close
contacts for C-H bond activation by positioning the 3-furyl
ring proton in the proximity of the metal (and CH2SiMe3 ligand)
seems to be critical. These contacts are expected to increase
with the size of the metal and the need for coordinative
saturation. Finally, the possibility of ring methyl metalation to
give a so-called tucked-in complex prior to C-H bond activation
of the 3-furyl ring proton cannot be excluded at this stage.1,3,4
effect of the heteroatom fragment has been proposed to be a
critical factor influencing the ring-opening mechanism.7 Moni-
toring the intramolecular C-H bond activation and subsequent
yne-enolate formation by 1H NMR spectroscopy showed first-
order kinetics as well as an increase in the rate of the reaction
with increasing metal size (Figure 3). While this is in agreement
with the higher tendency of the furyl substituent to chelate to
the coordinatively unsaturated metal center of the larger metals,
the 5-methyl substituent is expected to display a stronger
influence on the hindered rotation. Intramolecular C-H bond
activation has also been reported by Evans et al. for the related
half-sandwich complex [Y{η5-C5Me4SiMe2(CH2CHdCH2)}(CH2-
SiMe3)2(THF)], without any significant yttrium-olefin interac-
tion in solution.15 Nonetheless, this compound was observed to
convert into [Y{η5-C5Me4SiMe2(C3H3)}(L)]2) (L ) THF, DME)
at room temperature over several days under double C-H bond
activation of the allyl function by the (trimethylsilyl)methyl
group with SiMe4 elimination.15
Bercaw et al. discussed two possible transition states for the
σ-bond metathesis reaction of C-H bonds of hydrocarbon
fragments with aromatic C-H bonds.3e C-H bond activation
in a position R to an oxygen or nitrogen donor atom in the
aromatic heterocycles occurs via a four-center, six-electron
arrangement. Thus, a similar transition state can also be assumed
when the orientation of the C-H bond is enforced by steric
effects, as found for the chelating C5Me4SiMe2R ligands derived
from 4a,b (Scheme 3). Rotation of the pendant donor around
the SiMe2-(2-furyl) bond orients the hydrogen in the 3-position
to close proximity of the metal center.
Complex stabilization by weak agostic C-H contacts, which
subsequently result in σ-bond metathesis reactions, is reduced
in the presence of a coordinating solvent. Monitoring the stability
of complexes 5b and 6b in [D8]THF showed no signs of
decomposition for 5b at room temperature over a period of 2
weeks and very slow ring opening for 6b (t1/2(25 °C) ) ∼48
h). The retarding influence of Lewis base donors on the
decomposition of hydrocarbyl complexes has been mentioned
for the related complex [Y(η5-C5Me5)2(η2-C4H3O)] upon coor-
dination of THF.6f In return, the rigid structure observed in the
solid state as well as at low temperature blocks C-H contacts
at the metal center and explains the reasonable stability of these
compounds as crystalline solids.
Estimation of the Ln-H3(furyl) distance by simple rotation
of the furyl group around the C5Me4-SiMe2 bond as well as
the SiMe2-furyl bond (Scheme 3) generates close contacts
which decrease with increasing metal size (Sc-H ) 2.774 Å
in 5a; Sc-H ) 2.551 Å in 5b; Lu-H ) 2.004 Å in 6a). This
suggests that the size of the metal center and the resulting close
contacts of the Ln-C and C-H bonds mainly affect the C-H
bond activation rate. The effect of the 5-methyl group at the
Structure of an Yne-Enolate Complex. The monomeric
structure of 7a′ resembles that of so-called constrained-geometry
(15) Evans, W. J.; Brady, J. C.; Ziller, J. W. J. Am. Chem. Soc. 2001,
123, 7711.

Furyl-Functionalized Complexes of Sc, Y, and Lu
Organometallics, Vol. 26, No. 13, 2007 3231
Scheme 3
Figure 4. Eyring plot of furyl ring-opening in complexes 6a,b.
Figure 5. Molecular structure of the ring-opening product 7a′.
Hydrogen atoms have been omitted for clarity. Selected bond
distances (Å) and angles (deg): Y-O17, 2.167(2); Y-O31, 2.374-
(2); Y-O41, 2.413(2); Y-C21, 2.419(3); Y-C(1-5), 2.662(3)-
2.788(3); O31-Y-O41, 155.28(8); C21-Y-O17, 100.04(9);
C21-Y-O31, 87.07(9); C21-Y-O41, 90.59(9); O17-Y-O31,
79.11(8); O17-Y-O41, 77.08(8).
half-sandwich complexes at first sight (Figure 5).16 However,
the longer pendant yne-enolate function leads to a O-Y-Cpcent
angle (154.87°) much wider than the close to 90° coordination
of a short amido linkage, as seen, for example, in [Y{η5-C5-
Me4SiMe2(NC5H11)}(CH2SiMe3)(THF)].16a The yne-enolate in
7a′ formally replaces one alkyl ligand in 6a, and the additional
THF donor forces the remaining alkyl group trans and the two
THF donors cis to the yne-enolate. The resulting trigonal-
bipyramidal structure with the cyclopentadienyl ring, enolate,
and alkyl group in the equatorial plane and the two THF donors
on the apices only differs from 6a in the orientation of the
ligands around the metal center. The Y-C and Y-O distances
(Y-C ) 2.419(3) Å, Y-Cpcent ) 2.443 Å, Y-O(en) ) 2.167-
(2) Å, Y-O(THF) ) 2.374(2), 2.413(2) Å, CN ) 7) are in the
expected range,16a although they are slightly longer (0.04-0.05
Å) than in the related dimeric structure of 7b*, as expected from
the higher coordination number.7 In return, the Y-O distance
is much shorter in 7a′ (0.376 Å) as a result of the enolate
bridging in 7b*. The C-C distances in the yne-enolate side
chain of 7a′ compare well to those in 7b* (C-C ) 1.405(7),
1.423(7) Å, CdC ) 1.323(6), 1.333(6) Å, CtC ) 1.197(6),
1.226(7) Å) and the related bis(cyclopentadienyl) ynyl-enolate
complex [{Y(η5-C5Me5)2}2(µ-OCHdCHCtC)] (C-C ) 1.435-
(14) Å, CdC ) 1.323(16) Å, CtC ) 1.227(13) Å).6f
in benzene indicate dimerization of 7a′ to form 7a*, similar to
the behavior of the other ring-opened products 6a* and 6b*.
The dimeric structure of the unsubstituted yne-enolate in 6a*
is preferred even in the presence of excess THF (1:1 [D6]-
benzene-[D8]THF: 6a* (87%), 6a′ (13%)), but the slightly
larger steric demand induced by the methyl substituent in 6b′
resulted in the complete formation of the monomeric species
([D6]benzene with 1 equiv of THF per metal center: 6b′ (67%),
6b* (33%)).
Cationic Complexes. The poor styrene polymerization activ-
ity of the precatalysts 5-717 could be ascribed to the tendency
of the furyl group at the cyclopentadienyl ligand to undergo a
ring-opening reaction in the corresponding cationic species under
polymerization conditions in a weakly coordinating solvent such
as toluene or bromobenzene. Due to the intermediate thermal
stability of the lutetium species in this series, complexes 6a,b
were selected for the comparison of the stability of the
corresponding cations. Addition of 1 equiv of the Brønsted acid
[NEt3H][BPh4] to 6a,b in THF resulted in clean formation of
the cationic half-sandwich complexes [Lu{η5-C5Me4SiMe2(C4H2-
Interestingly, the monomeric structure of 7a′ observed in the
1
solid state is retained only in THF solution. H NMR spectra
(16) (a) Hultzsch, K. C.; Voth, P.; Beckerle, K.; Spaniol, T. P.; Okuda,
J. Organometallics 2000, 19, 228. (b) Arndt, S.; Spaniol, T. P.; Okuda, J.
Eur. J. Inorg. Chem. 2001, 73. (c) Arndt, S.; Trifonov, A.; Spaniol, T. P.;
Okuda, J.; Kitamura, M.; Takahashi, T. J. Organomet. Chem. 2002, 647,
158.
(17) Styrene polymerization experiments with 5b and 6b in toluene with
[Ph3C][B(C6F5)4] in the presence of 10 equiv of AliBu3 produced a
maximum activity of ∼5 kg of sPS (mol of Ln)-1 h-1, with decreasing
activity upon prolonged polymerization time.

3232 Organometallics, Vol. 26, No. 13, 2007
Hitzbleck and Okuda
Scheme 4
Table 2. Experimental Data for the Crystal Structure Determinations of the Complexes 5a,b and 7a′
5a
5b
7a′
Crystal Data
formula
fw
C27H47O2ScSi3
532.88
C28H53O2ScSi3
550.93
C27H45O3Si2Y
562.72
cryst color
cryst size, mm
space group
a, Å
b, Å
c, Å
colorless
colorless
0.90 × 0.80 × 0.70
P21/n (No. 14)
10.711(1)
15.971(2)
20.006(2)
104.203(2)
3317.6(6)
4
colorless
0.62 × 0.28 × 0.20
P21/c (No. 14)
16.875(4)
10.176(2)
17.594(4)
99.049(6)
2983.8(11)
4
0.60 × 0.27 × 0.25
P21/c (No. 14)
18.278(10)
9.313(5)
19.002(10)
103.093(10)
3151(3)
â, deg
V, Å3
Z
F
4
calcd, g cm-3
1.123
0.368
1152
1.103
0.351
1200
1.253
2.059
1192
µ(Mo KR), mm-1
F(000)
Data Collection
T, K
130(2)
143(2)
133(2)
λ, Å
0.71073
1.14-27.33
0.71073
1.65-27.50
0.71073
2.32-27.08
θ range
index ranges
h
k
l
-23 to +23
-9 to +11
-21 to +24
-13 to +13
-20 to +20
-25 to +25
-15 to +21
-12 to +13
-21 to +22
Solution and Refinement
no. of rflns measd
19 430
42 219
20 294
no. of indep rflns
no. of obsd rflns
GOF
6957 (R(int) ) 0.0463)
5101 (I > 2σ(I))
1.036
0.0532, 0.1412
0.0775, 0.1573
0.739, -0.350
7610 (R(int) ) 0.0259)
6894 (I > 2σ(I))
1.045
0.0318, 0.0875
0.0358, 0.0918
0.375, -0.328
6520 (R(int) ) 0.0532)
4832 (I > 2σ(I))
1.023
0.0408, 0.0934
0.0687, 0.1061
0.687, -0.419
final R indices R1,a wR2b (obsd data)
final R indices R1, wR2 (all data)
largest e(max), e(min), e Å-3
2
2
2
a R1(F) ) ∑||Fo| - |Fc||/∑|Fo|. b wR2(F) ) [∑w(Fo - Fc )2/∑w(Fo )2]1/2
.
RO-2)}(CH2SiMe3)(THF)3][BPh4] (R ) H (8a), Me (8b))
overnight (Scheme 4).
and coordination of the furyl donor in 8a, but only partial
coordination (25%) of the furyl donor was observed for 8b.
Thus, the 5-methyl group seems to have a strong steric influence,
restricting the rotation around the SiMe2-furyl bond for
potential coordination as well as close contacts for C-H bond
activation.
The cationic complexes 8a,b showed high stability in THF
solution (t1/2(25 °C) ) 100 days for 8a; t1/2(25 °C) . 100 days
for 8b), even higher than that observed for the neutral complexes
1
6a,b in THF. In 8a,b three THF donors (on the basis of H
NMR spectroscopic data) coordinate to the metal center, one
replacing the eliminated alkyl group along with one additional
THF, increasing the coordination number by 1. Therefore, the
metal centers in the cationic species seem to be more sterically
encumbered than in the neutral dialkyl complex in THF solution.
Furthermore, the lutetium complexes demonstrate the weaker
Lewis base donor strength of furan in comparison with that of
THF and pyridine. The 1H NMR spectra of 8a,b in [D5]pyridine
revealed no interaction between the furyl donor and the metal
center, in agreement with a chemical shift value for the
methylene protons of -0.11 ppm due to the higher donor
strength of pyridine. The complexes 8a,b in [D8]THF showed
a high-field shift of the methylene proton signal (-0.75 ppm)
Conclusion
The series of scandium, lutetium, and yttrium complexes
containing a furyl-substituted cyclopentadienyl ligand showed
that intramolecular C-H bond activation at the aromatic ring
primarily depends on the steric and electronic saturation of the
metal center. For compounds of similar overall geometry, the
rate of C-H bond activation increases with increasing metal
size (Y . Lu > Sc). This may be a result of the increasing
M-C bond polarity and thus decreasing M-C bond dissociation

Furyl-Functionalized Complexes of Sc, Y, and Lu
Organometallics, Vol. 26, No. 13, 2007 3233
5-furyl). 13C{1H} NMR ([D8]toluene, -60 °C): δ 0.6 (SiMe2), 4.6
(CH2SiMe3), 12.0, 14.9 (C5Me4), 24.9 (â-THF), 39.3 (ScCH2), 71.2
(R-THF), 110.2 (2-furyl), 112.3 (ipso-C5Me4), 121.1 (3-furyl),
124.3, 128.2 (C5Me4), 146.43 (4-furyl), 160.1 (5-furyl). Anal. Calcd
for C27H51O2ScSi3 (536.91): Sc, 8.37. Found: Sc, 8.33.
enthalpy,18 concomitant with a decrease in steric saturation of
the metal center. The sterically more bulky 5-methyl-substituted
furyl donor hinders the free rotation of the pendant donor due
to repulsion with the remaining ligands in the coordination
sphere. The addition of a coordinating solvent such as THF also
significantly reduces the decomposition rate, as the coordination
number of the metal center increases. The fine balance between
favorable steric demand and number of coordinated ligands as
well as an intramolecularly coordinated donor allows the
formation of stable cationic lutetium half-sandwich complexes
that do not undergo significant ring opening in THF solution,7
whereas the parent bis(alkyl) complexes gradually decompose.
In the absence of THF, as is the case during olefin polymeri-
zation, rapid decomposition of the cationic active species by
C-H bond activation is likely to occur.
[Sc{η5:η1-C5Me4SiMe2(CtCCHdCHO)}(CH2SiMe3)-
(THF)] (5a′). A sample of 5a was heated to 40 °C for 12 h. Slow
1
conversion into the enolate complex was monitored by H NMR
spectroscopy. Product distribution after 12 h: 5a (80%), 5a′ (20%).
1H NMR of 5a′ (200 MHz, [D8]toluene): δ -0.40 (s, 2H, CH2-
SiMe3), 0.19 (s, 9H, CH2SiMe3), 0.57 (s, 6H, SiMe2), 1.40 (t, 2H,
â-THF), 1.74, 1.80, 2.09, 2.21 (s, 4 × 3H, C5Me4), 3.50 (s, 2H,
3
3
R-THF), 4.45 (d, JHH ) 5.2 Hz, 1H, 3-enolate), 6.96 (d, JHH
)
5.2 Hz, 1H, 2-enolate).
[Sc{η5-C5Me4SiMe2(C4H2MeO-2)}(CH2SiMe3)2(THF)] (5b). A
solution of 4b (0.781 g, 3.00 mmol) in pentane (10 mL) was added
to 1 (1.352 g, 3.00 mmol), and the mixture was stirred at room
temperature for 3 h. The solution was filtered and the solvent
volume reduced to ∼3 mL. Cooling to -40 °C gave colorless
Experimental Section
General Remarks. All operations were carried out under argon
using standard Schlenk-line and glovebox techniques. Pentane was
distilled from sodium/triglyme benzophenone ketyl, THF, and
toluene from sodium benzophenone ketyl under argon. NMR spectra
were recorded on Varian Unity-500 (1H, 499.6 MHz; 13C, 125.6
MHz), Bruker Avance II 400 MHz (1H, 400.1 MHz; 13C, 100.6
MHz), and Varian Mercury-200 (19F, 188.1 MHz) spectrometers
in [D6]benzene, [D8]THF, [D8]toluene at 20 °C, unless stated
otherwise; the chemical shifts were referenced to the residual solvent
resonances. C, H analysis of crystalline samples repeatedly gave
poor results with inconsistent values from run to run. This difficulty
is attributed to the extreme sensitivity of the material and has been
described previously.19 Metal analysis was performed by com-
plexometric titration;20 the samples (20-30 mg) were dissolved in
acetone (10 mL) and titrated with EDTA (0.005 M) using xylenol
orange as an indicator and ammonium acetate (1 M) as buffer
solution (10 mL). The substituted cyclopentadienes 4a,b7 and the
complexes [Ln(CH2SiMe3)3(THF)x] (Ln ) Sc (1), Lu (2), x ) 2;
Ln ) Y (3), x ) 3)8 were prepared according to literature
procedures.
1
crystals of 5b (1.124 g, 2.04 mmol): yield 68.0%. H NMR (500
MHz, [D6]benzene): δ -0.24 (s, 4H, CH2SiMe3), 0.28 (s, 18H,
CH2SiMe3), 0.66 (s, 6H, SiMe2), 1.22 (s, 4H, â-THF), 1.95, 2.17
(s, 2 × 6H, C5Me4), 2.09 (s, 3H, 5-Me-furyl), 3.64 (s, 4H, R-THF),
5.85 (s, 1H, 4-furyl), 6.56 (s, 1H, 3-furyl). 13C{1H} NMR ([D6]-
benzene): δ 1.0 (SiMe2), 4.4 (CH2SiMe3), 12.1, 14.9 (C5Me4), 24.9
(â-THF), 40.6 (b, ScCH2), 71.3 (R-THF), 106.6 (4-furyl), 113.3
(ipso-C5Me4), 122.2 (3-furyl), 124.8, 128.4 (C5Me4), 127.3 (2-furyl),
156.3 (5-furyl). 1H NMR (500 MHz, [D8]toluene, 60 °C): δ -0.30
(s, 4H, CH2SiMe3), 0.19 (s, 18H, CH2SiMe3), 0.61 (s, 6H, SiMe2),
1.43 (s, 4H, â-THF), 1.98 (s, 6H, C5Me4), 2.15 (s, 3 + 6H, 5-Me-
furyl + C5Me4), 3.76 (s, 4H, R-THF), 5.83 (s, 1H, 4-furyl), 6.50
(s, 1H, 3-furyl). 13C{1H} NMR ([D8]toluene, 60 °C): δ 0.8 (SiMe2),
4.4 (CH2SiMe3), 12.1, 14.9 (C5Me4), 13.8 (Me-furyl), 25.1 (â-THF),
41.1 (ScCH2), 71.2 (R-THF), 106.7 (2-furyl), 113.5 (ipso-C5Me4),
122.3 (3-furyl), 125.1, 128.6 (C5Me4), 156.3 (4-furyl), 159.5 (5-
1
furyl). H NMR ([D8]toluene, -60 °C): δ -0.24 (s, 4H, CH2-
SiMe3), 0.28 (s, 18H, CH2SiMe3), 0.66 (s, 6H, SiMe2), 1.22 (s,
4H, â-THF), 1.95, 2.17 (s, 2 × 6H, C5Me4), 2.09 (s, 3H, 5-Me-
furyl), 3.64 (s, 4H, R-THF), 5.85 (s, 1H, 4-furyl), 6.56 (s, 1H,
3-furyl). 13C{1H} NMR ([D8]toluene, -60 °C): δ 0.8 (SiMe2), 4.6
(CH2SiMe3), 12.0, 15.2 (C5Me4), 13.8 (Me-furyl), 24.9 (â-THF),
39.3 (ScCH2), 71.2 (R-THF), 106.6 (2-furyl), 112.7 (ipso-C5Me4),
122.3 (3-furyl), 124.3, 128.0 (C5Me4), 156.2 (4-furyl), 158.3 (5-
furyl). 1H NMR (400 MHz, [D8]THF): δ -0.43 (s, 4H, CH2SiMe3),
0.00 (s, 18H, CH2SiMe3), 0.59 (s, 6H, SiMe2), 1.85 (s, 4H, â-THF),
2.08, 2.16 (s, 2 × 6H, C5Me4), 2.36 (s, 3H, 5-Me-furyl), 3.69 (s,
[Sc{η5-C5Me4SiMe2(C4H3O-2)}(CH2SiMe3)2(THF)] (5a). A
solution of 4a (0.739 g, 3.00 mmol) in pentane (10 mL) was added
to 1 (1.352 g, 3.00 mmol), and the mixture was stirred at room
temperature for 3 h. The solution was filtered and the solvent
volume reduced to ca. 3 mL. Cooling to -40 °C gave colorless
crystals of 5a (1.417 g, 2.64 mmol); yield: 88.0%. 1H NMR (500
MHz, [D8]toluene): δ -0.29 (s, 4H, CH2SiMe3), 0.22 (s, 18H, CH2-
SiMe3), 0.59 (s, 6H, SiMe2), 1.32 (s, 4H, â-THF), 1.94, 2.10 (s, 2
× 6H, C5Me4), 3.67 (s, 4H, R-THF), 6.14 (dd, 3JHH ) 3.4, 1.8 Hz,
4H, R-THF), 6.02 (d, 3JHH ) 3.0 Hz, 1H, 4-furyl), 6.53 (d, 3JHH
)
3.0 Hz, 1H, 3-furyl). 13C{1H} NMR ([D8]THF): δ 0.2 (SiMe2),
3.4 (CH2SiMe3), 11.2, 12.8 (C5Me4), 14.1 (Me-furyl), 24.4 (â-THF),
39.2 (b, ScCH2), 66.1 (R-THF), 105.8 (2-furyl), 112.9 (ipso-C5-
Me4), 121.6 (3-furyl), 124.1, 127.8 (C5Me4), 155.9 (4-furyl), 158.2
(5-furyl). Anal. Calcd for C28H53O2ScSi3 (550.93): Sc, 8.33.
Found: Sc, 8.16.
3
1H, 4-furyl), 6.53 (d, JHH ) 3.4 Hz, 1H, 3-furyl), 7.42 (s, 1H,
1
5-furyl). H NMR ([D8]toluene, 60 °C): δ -0.27 (s, 4H, CH2-
SiMe3), 0.18 (s, 18H, CH2SiMe3), 0.55 (s, 6H, SiMe2), 1.44 (s,
4H, â-THF), 2.00, 2.10 (s, 2 × 6H, C5Me4), 3.72 (s, 4H, R-THF),
6.14 (dd, 3JHH ) 3.4, 1.8 Hz, 1H, 4-furyl), 6.49 (d, 3JHH ) 3.4 Hz,
3
1H, 3-furyl), 7.53 (d, JHH ) 1.5 Hz, 1H, 5-furyl). 13C{1H} NMR
[Sc{η5:η1-C5Me4SiMe2(CtCCHdCMeO)}(CH2SiMe3)-
(THF)] (5b′). A sample of 5b was heated to 40 °C for 20 h. Slow
([D8]toluene, 60 °C): δ 0.9 (SiMe2), 4.2 (CH2SiMe3), 12.1, 14.8
(C5Me4), 25.3 (â-THF), 41.4 (ScCH2), 70.4 (R-THF), 110.5 (2-
furyl), 112.4 (ipso-C5Me4), 120.9 (3-furyl), 125.4, 129.0 (C5Me4),
1
conversion into the enolate complex was monitored by H NMR.
1
1
Product distribution after 12 h: 5b (84%), 5b′ (16%). H NMR
146.5 (4-furyl), 163.1 (5-furyl). H NMR (-60 °C): δ -0.29 (s,
for 5b′ (200 MHz, [D6]benzene): δ -0.40 (s, 2H, CH2SiMe3), 0.28
(s, 9H, CH2SiMe3), 0.53, 0.66 (s, 2 × 3H, SiMe2), 1.30 (s, 4H,
â-THF), 1.95, 2.10, 2.17, 2.30 (s, 4 × 3H, C5Me4), 3.64 (s, 4H,
R-THF), 4.54 (s, 1H, 3-enolate).
4H, CH2SiMe3), 0.33 (s, 18H, CH2SiMe3), 0.64 (s, 6H, SiMe2),
0.98 (s, 4H, â-THF), 1.85, 2.09 (s, 2 × 6H, C5Me4), 3.34 (s, 4H,
R-THF), 6.09 (s, 1H, 4-furyl), 6.55 (s, 1H, 3-furyl), 7.25 (s, 1H,
[Lu{η5:η1-C5Me4SiMe2(CtCCHdCHO)}(CH2SiMe3)]2 (6a*).
A sample of 6a was heated to 40 °C for 12 h. Slow conversion
into the enolate complex was monitored by 1H NMR. Product
(18) Schock, L. E.; Seyam, A. M.; Sabat, M.; Marks, T. J. Polyhedron
1988, 7, 1517.
(19) (a) Mitchell, J. P.; Hajela, S.; Brookhart, S. K.; Hardcastle, K. I.;
Henling, L. M.; Bercaw, J. E. J. Am. Chem. Soc. 1996, 118, 1045. (b)
Bambirra, S.; Brandsma, M. J. R.; Brussee, E. A. C.; Meetsma, A.; Hessen,
B.; Teuben, J. H. Organometallics 2000, 19, 3197.
1
distribution after 12 h: 6a (33%), 6a* (67%). H NMR for 6a*
(200 MHz, [D8]toluene): δ -0.96, -0.51 (d, 2JHH ) 11.2 Hz, 2 ×
2H, CH2SiMe3), 0.24 (s, 2 × 9H, CH2SiMe3), 0.46, 0.58 (s, 2 ×
(20) Das, B.; Shome, S. C. Anal. Chim. Acta 1971, 56, 483.

3234 Organometallics, Vol. 26, No. 13, 2007
Hitzbleck and Okuda
3
6H, SiMe2), 1.80, 1.86, 2.15, 2.26 (s, 4 × 6H, C5Me4), 4.51 (d,
8H, R-THF), 4.53 (d, JHH ) 5.1 Hz, 1H, OCHdCH), 6.96 (dd,
3
3JHH ) 5.2 Hz, 2H, 2-enolate), 7.01 (d, JHH ) 5.3 Hz, 2H,
3JHH ) 5.1 Hz, JYH ) 2.3 Hz, 1H, OCHdCH). 13C{1H} NMR
3
3-enolate). Addition of excess THF led to complete formation of
[Lu{η5:η1-C5Me4SiMe2(CtCCHdCHO)}(CH2SiMe3)(THF)2] (6a′);
stepwise addition of THF led to a mixture of 6a* and 6a′. 1H NMR
for 6a* (87%), 6a′ (13%), and 6a′ (200 MHz, [D6]benzene/[D8]-
THF (1:1)): δ -1.25 (s, 2H, CH2SiMe3), -0.30 (s, 9H, CH2SiMe3),
([D6]benzene): δ 0.0, 1.2 (SiMe2), 3.8 (CH2SiMe3), 10.3, 11.2, 13.2,
14.5 (C5Me4), 25.1 (â-THF), 34.0, 34.5 (d, YCH2, 1JYC ) 50.3 Hz),
67.1 (R-THF), 84.0 (CHCtC), 100.4 (SiCtC), 100.8 (SiCtC),
115.4 (ipso-C5Me4), 121.4, 124.0, 125.6, 127.9 (C5Me4), 163.0
(OCHdCH). Anal. Calcd for C27H45O3Si2Y (562.72): Y, 15.81.
Found: Y, 15.80.
3
0.40 (s, 6H, SiMe2), 1.96, 1.98 (s, 2 × 6H, C5Me4), 4.28 (d, JHH
3
) 4.6 Hz, 1H, 2-enolate), 7.38 (d, JHH ) 4.6 Hz, 1H, 3-enolate).
[Lu{η5:η1-C5Me4SiMe2(C4H3O)}(CH2SiMe3)(THF)3][BPh4] (8a).
[NEt3H][BPh4] (0.106 g, 0.25 mmol) and 6a (0.167 g, 0.25 mmol)
were dissolved in THF (5 mL) and stirred overnight. The product
was precipitated by addition of pentane (5 mL), filtered off, and
washed with pentane to give a colorless powder of 8a (0.219 g,
0.21 mmol); yield 83.9%. 1H NMR (400 MHz, [D8]THF): δ -0.75
(s, 2H, CH2SiMe3), -0.01 (s, 9H, CH2SiMe3), 0.64 (s, 6H, SiMe2),
[Lu{η5-C5Me4SiMe2(C4H2MeO-2)}(CH2SiMe3)2(THF)] (6b).
A solution of 6b (0.781 g, 3.00 mmol) in pentane (10 mL) was
added to 2 (1.742 g, 3.00 mmol) and stirred at room temperature
for 3 h. The solution was filtered and the solvent volume reduced
to ∼3 mL. Cooling to -40 °C gave colorless crystals of 6b
1
(0.480 g, 0.72 mmol); yield 24.0%. H NMR (400 MHz, [D8]-
toluene): δ -0.85 (s, 4H, CH2SiMe3), 0.24 (s, 18H, CH2SiMe3),
0.61 (s, 6H, SiMe2,), 1.27 (br s, 4H, â-THF), 1.98, 2.18 (s, 2 ×
6H, C5Me4), 2.11 (s, 3H, 5-Me-furyl), 3.60 (br s, 4H, R-THF), 5.83
(dd, 3JHH ) 3.1, 1.0 Hz, 1H, 4-furyl), 6.53 (d, 3JHH ) 3.1 Hz, 1H,
3-furyl). 1H NMR (-80 °C): δ -0.76 (s, 4H, CH2SiMe3), 0.37 (s,
18H, CH2SiMe3), 0.67 (s, 6H, SiMe2,), 0.88 (s, 4H, â-THF), 1.89,
2.19 (s, 2 × 6H, C5Me4), 2.02 (s, 3H, 5-Me-furyl), 3.23 (br s, 4H,
3
2.10, 2.17 (s, 2 × 6H, C5Me4), 6.56 (dd, 1H, JHH ) 3.3, 1.8 Hz,
3
4-furyl), 6.81 (t, 5H, JHH ) 7.3 Hz, p-Ph + 3-furyl), 6.95 (t, 8H,
3
3JHH ) 7.4 Hz, o-Ph), 7.37 (br s, 8H, m-Ph), 7.76 (d, 1H, JHH
)
1.8 Hz, 2-furyl). 13C{1H} NMR: δ 0.0 (CH2SiMe3), 3.8 (SiMe2),
11.0, 13.6 (C5Me4), 25.7 (â-THF), 35.7 (LuCH2), 67.4 (R-THF),
110.6 (ipso-C5Me4), 112.3 (2-furyl), 121.0 (p-Ph), 121.4 (3-furyl),
124.8 (m-Ph), 125.0, 129.2 (C5Me4), 146.4 (4-furyl), 136.3 (o-Ph),
161.3 (5-furyl), 163.6, 164.0, 164.5, 165.0 (ipso-Ph). 11B NMR: δ
-6.54. 1H NMR (400 MHz, [D5]pyridine): δ -0.11 (s, 2H, CH2-
SiMe3), -0.01 (s, 9H, CH2SiMe3), 0.58 (s, 6H, SiMe2), 1.66 (t,
12H, â-THF), 1.88, 1.93 (s, 2 × 6H, C5Me4), 3.70 (t, 12H, R-THF),
6.66 (dd, 1H, 3JHH ) 3.3 Hz, 1.5 Hz, 4-furyl), 6.93 (d, 3JHH ) 3.3
3
3
R-THF), 5.80 (dd, JHH ) 3.0, 1.0 Hz, 1H, 4-furyl), 6.56 (d, JHH
) 3.0 Hz, 1H, 3-furyl). 13C{1H} NMR ([D8]toluene, -80 °C): δ
0.9 (SiMe2), 4.9 (CH2SiMe3), 11.7, 14.7 (C5Me4), 13.9 (Me-furyl),
24.8 (â-THF), 38.8 (s, LuCH2), 70.6 (R-THF), 106.7 (2-furyl), 110.6
(ipso-C5Me4), 122.9, 126.1 (C5Me4), 122.2 (3-furyl), 156.3 (4-furyl),
1
158.6 (5-furyl). H NMR (400 MHz, [D8]THF): δ -1.12 (s, 4H,
Hz, 3-furyl), 7.19 (t, 4H, 3JHH ) 7.2 Hz, p-Ph), 7.37 (t, 8H, 3JHH
)
CH2SiMe3), -0.12 (s, 18H, CH2SiMe3), 0.45 (s, 6H, SiMe2), 2.00
3
(s, 12H, C5Me4), 2.23 (s, 3H, Me-furyl), 5.90 (dd, 3JHH ) 3.0, 1.0
7.4 Hz, o-Ph), 7.98 (d, JHH ) 1.5 Hz, 5-furyl), 8.16 (br s, 8H,
m-Ph); 13C{1H} NMR ([D5]pyridine): δ 0.0 (CH2SiMe3), 3.5
(SiMe2), 11.3, 13.7 (C5Me4), 25.2 (â-THF), 38.0 (LuCH2), 67.2
(R-THF), 110.4 (ipso-C5Me4), 112.1 (2-furyl), 121.5 (3-furyl), 122.4
(p-Ph), 125.7 (m-Ph), 125.4, 129.3 (C5Me4), 136.3 (o-Ph), 146.7
3
Hz, 1H, 4-furyl), 6.43 (d, JHH ) 3.0 Hz, 1H, 3-furyl). 13C{1H}
NMR ([D8]THF): δ 1.0 (SiMe2), 4.3 (CH2SiMe3), 12.1, 14.7
(C5Me4), 24.5 (â-THF), 39.3 (ScCH2), 68.2 (R-THF), 106.5 (2-
furyl), 112.6 (ipso-C5Me4), 117.4 (3-furyl), 123.5, 126.8 (C5Me4),
156.8 (4-furyl), 159.4 (5-furyl). Anal. Calcd for C28H53LuO2Si3
(680.95): Lu, 26.69. Found: Lu, 26.65.
(4-furyl), 159.7 (5-furyl), 163.8, 164.3, 164.7, 165.2 (ipso-Ph). 11
B
NMR ([D5]pyridine): δ -5.68. Anal. Calcd for C55H76BLuO4Si2
(1043.16): C, 63.33; H, 7.34; Lu, 16.77. Found: C, 63.86; H, 7.71;
Lu, 17.21. After 2 weeks at room temperature small signals (7%)
characteristic of the yne-enolate ring-opening product 8a′ appeared
[Lu{η5:η1-C5Me4SiMe2(CtCCHdCMeO)}(CH2SiMe3)-
(THF)2] (6b′) + [Lu{η5:η1-C5Me4SiMe2(CtCCHdCMeO)}-
(CH2SiMe3)]2 (6b*). A sample of 6b was heated to 40 °C for 23.5
h. Slow conversion into the enolate complex was monitored by 1H
NMR. Product distribution after 12 h: 6b, 39%; 6b′ + 0.5 6b*,
61%. 1H NMR (200 MHz, [D6]benzene): 6b′, δ -0.96 (s, 2H, CH2-
SiMe3), 0.22 (s, 2 × 9H, CH2SiMe3), 0.57 (s, 6H, SiMe2,), 1.41 (s,
8H, â-THF), 1.66 (s, 3H, Me-enolate), 1.83, 2.27 (s, 2 × 6H, C5-
Me4), 3.60 (s, 8H, R-THF), 4.48 (s, 1H, 3-enolate); 6b*, -0.76,
-0.84 (d, 2JHH ) 11.5 Hz, 2 × 2H, CH2SiMe3), 0.21, 0.20 (s, 2 ×
9H, CH2SiMe3), 0.46, 0.55 (s, 2 × 6H, SiMe2), 1.78 (s, 6H, Me-
enolate), 1.92, 1.95, 2.18, 2.23 (s, 4 × 6H, C5Me4), 4.48 (s, 2H,
3-enolate). Addition of excess THF led to complete formation of
6b′.
3
in [D5]pyridine at δ 4.58 (d, 1H, JHH ) 4.5 Hz, 3-enolate) and
3
7.46 (d, 1H, JHH ) 4.5 Hz, 2-enolate).
[Lu{η5-C5Me4SiMe2(C4H2MeO)}(CH2SiMe3)(THF)3][BPh4]
(8b). [NEt3H][BPh4] (0.106 g, 0.25 mmol) and 6b (0.170 g, 0.25
mmol) were dissolved in THF (5 mL) and stirred overnight. The
product was precipitated by addition of pentane (5 mL), filtered
off, and washed with pentane to yield a colorless powder of 8b
(0.218 g, 0.20 mmol); yield 82.5%. The NMR shows a mixture of
two complexes with free and coordinating furyl donor function
(chemical shift values in parentheses) in the ratio ∼1:0.25. 1H NMR
([D8]THF): δ -0.85 (-0.87) (s, 2H, CH2SiMe3), -0.10 (-0.12)
(s, 9H, CH2SiMe3), 0.47 (0.51) (s, 6H, SiMe2), 1.97, 2.06 (s, 2 ×
[Y{η5:η1-C5Me4SiMe2(CtCCHdCHO)}(CH2SiMe3)-
(THF)2] (7a′). Recrystallization of 7a (1.000 g, 1.722 mmol) from
THF after stirring at 25 °C for 48 h led to the isolation of 7a′ (0.879
3
6H, C5Me4), 2.25 (s, 3H, Me-furyl), 5.96 (6.44) (dd, JHH ) 3.0,
3
1.0 Hz, 1H, 4-furyl), 6.46 (7.63) (dd, JHH ) 3.0, 1.0 Hz, 1H,
1
g, 1.562 mmol); yield: 90.7%. H NMR of 7a′ (400 MHz, [D8]-
3-furyl), 6.80 (t, 4H, 3JHH ) 7.3 Hz, p-Ph), 6.93 (t, 3JHH ) 7.5 Hz,
8H, o-Ph), 7.35 (br s, 8H, m-Ph). 13C{1H} NMR ([D8]THF): δ 0.0
(CH2SiMe3), 3.9 (SiMe2), 11.1, 13.5 (C5Me4), 12.8 (22.3) (Me-furyl),
25.4 (â-THF), 34.2 (34.9) (LuCH2), 67.3 (R-THF), 106.2 (ipso-
C5Me4), 113.4 (110.6) (2-furyl), 120.9 (p-Ph), 121.4 (3-furyl), 124.8
(m-Ph), 122.5, 129.2 (C5Me4), 125.9 (4-furyl), 136.3 (o-Ph), 156.2
(157.7) (5-furyl), 163.5, 164.0, 164.5, 165.0 (ipso-Ph). 11B NMR
2
THF): δ -1.24 (d, 2H, JYH ) 3.5 Hz, CH2SiMe3), 0.17 (s, 9H,
CH2SiMe3), 0.37 (d, 6H, SiMe2), 1.96, 2.01 (s, 2 × 6H, C5Me4),
4.20 (d, 3JHH ) 4.3 Hz, 1H, OCHdCH), 7.26 (dd, 3JHH ) 4.3, 2.3
Hz, 1H, OCHdCH). 13C{1H} NMR ([D8]THF): δ 2.9 (SiMe2),
4.7 (CH2SiMe3), 12.2, 14.6 (C5Me4), 26.3 (â-THF), 34.1, 34.6 (d,
1JYC ) 46.0 Hz, YCH2), 68.2 (R-THF), 80.9 (CHCtC), 97.6 (SiCt
C), 105.7 (SiCtC), 115.2 (ipso-C5Me4), 122.9, 124.3 (C5Me4),
1
[Y{η5:η1-C5Me4-
([D8]THF): δ -6.54. H NMR ([D5]pyridine): δ -0.75 (s, 2H,
170.5
(OCHCH).
Dimerization
to
CH2SiMe3), -0.01 (s, 9H, CH2SiMe3), 0.64 (s, 6H, SiMe2), 2.07,
SiMe2(CtCCHdCHO)}(CH2SiMe3)]2 (7a*) is observed in a non-
3
1
2.16 (s, 2 × 6H, C5Me4), 2.35 (s, 3H, Me-furyl), 6.27 (d, JHH
)
coordinating solvent. H NMR for 7a* (400 MHz, [D6]benzene):
3.0 Hz, 1H, 4-furyl), 6.83 (d, 3JHH ) 3.0 Hz, 1H, 3-furyl), 6.78 (t,
3JHH ) 7.3 Hz, 4H, p-Ph), 6.93 (t, 3JHH ) 7.4 Hz, 8H, o-Ph), 7.35
(br s, 8H, m-Ph). 13C{1H} NMR ([D5]pyridine): δ 0.0 (CH2SiMe3),
2
2
δ -0.69, -0.23 (dd, JHH ) 11.1 Hz, JYH ) 3.7 Hz, 2H, CH2-
SiMe3), 0.31 (s, 9H, CH2SiMe3), 0.44, 0.58 (d, 6H, SiMe2), 1.41
(t, 8H, â-THF), 1.78, 1.89, 2.10, 2.33 (s, 4 × 3H, C5Me4), 3.58 (t,

Furyl-Functionalized Complexes of Sc, Y, and Lu
Organometallics, Vol. 26, No. 13, 2007 3235
3.5 (SiMe2), 11.3, 13.8 (C5Me4), 13.2 (Me-furyl), 25.2 (â-THF),
38.1 (LuCH2), 67.2 (R-THF), 106.6 (ipso-C5Me4), 112.9 (2-furyl),
121.8 (p-Ph), 122.8 (3-furyl), 125.6 (m-Ph), 125.3, 129.3 (C5Me4),
136.3 (4-furyl), 136.6 (o-Ph), 156.2 (5-furyl), 163.8, 164.3, 164.7,
165.3 (ipso-Ph). 11B NMR ([D5]pyridine): δ -5.67. Anal. Calcd
for C56H78BLuO4Si2 (1057.18): C, 63.62; H, 7.44; Lu, 16.55.
Found: C, 62.68; H, 7.22; Lu, 16.63. No signals characteristic of
the yne-enolate complex were observed after 1 week.
SHELXL-97 software. The non-hydrogen atoms were refined
anisotropically, and hydrogen atoms were placed in calculated
positions.22
Acknowledgment. Financial support of this work by the
Fonds der Chemischen Industrie and the Deutsche Forschungs-
gemeinschaft is gratefully acknowledged.
Supporting Information Available: CIF files giving full
crystallographic data for 5a,b and 7a′. This material is available
free of charge via the Internet at http://pubs.acs.org.
X-ray Crystal Structure Determination. Crystallographic data
for 5a,b and 7a′ are summarized in Table 2. X-ray diffraction data
were collected on a Bruker CCD area-detector diffractometer with
Mo KR radiation (graphite monochromator, λ ) 0.710 73 Å) using
æ and ω scans. The SMART program package was used for the
data collection and unit cell determination; processing of the raw
frame data was performed using SAINT; absorption corrections
were applied with SADABS.21 The structures were solved by direct
methods and refined against F2 using all reflections with the
OM0701726
(21) ASTRO, SAINT and SADABS: Data Collection and Processing
Software for the SMART System; Siemens Analytical X-ray Instruments
Inc., Madison, WI, 1996.
(22) Sheldrick G. M. SHELXL-97, Program for Crystal Structure
Determination; University of Go¨ttingen, Go¨ttingen, Germany, 1997.