Tethered olefin studies of alkene versus tetraphenylborate coordination and lanthanide olefin interactions in metallocenes

Article abstract of DOI:10.1021/ja020957x

The tethered olefin cyclopentadienyl ligand, [(C₅Me₄)SiMe₂(CH₂CH= CH₂)]-, forms unsolvated metallocenes, [(C₅Me₄)SiMe₂(CH₂CH= CH₂)]₂Ln (Ln = Sm, 1; Eu, 2; Yb, 3), from [(C₅Me₄)SiMe₂(CH₂CH= CH₂)]K and Lnl₂(THF)₂ in good yield. Each complex in the solid state has both tethered olefins oriented toward the Ln metal center with the Ln-C(terminal alkene carbon) distances 0.2-0.3 A shorter than the Ln-C(internal alkene carbon) distances. The olefinic C-C bond distances in 2 and 3, 1.328(4) and 1.328(5) A, respectively, are normal. Like its permethyl analogue, (C₅Me₅)₂Sm(THF)₂, complex 1 reductively couples CO₂ to form the oxalate-bridged dimer {[(C₅Me₄)SiMe₂(CH₂CH= CH₂)]₂Sm}₂(μ-η²: η²-O₂CCO₂), 4, in which the tethered olefins are noninteracting substituents. Complex 1 reacts with AgBPh₄ to form an unsolvated cation that has the option of coordinating [BPh₄]^- or a pendant olefin, a competition common in olefin polymerization catalysis. The structure of {[(C₅Me₄)SiMe₂(CH₂ CH=CH₂)]₂Sm}[BPh₄], 5, shows that both pendant olefins are located near samarium rather than the [BPh₄]^- counterion.

Full text of DOI:10.1021/ja020957x

Published on Web 04/02/2003
Tethered Olefin Studies of Alkene versus Tetraphenylborate
Coordination and Lanthanide Olefin Interactions in
Metallocenes
William J. Evans,* Jeremy M. Perotti, Jason C. Brady, and Joseph W. Ziller
Contribution from the Department of Chemistry, UniVersity of California,
IrVine, California 92697-2025
Received July 12, 2002; E-mail: wevans@uci.edu
Abstract: The tethered olefin cyclopentadienyl ligand, [(C5Me4)SiMe2(CH2CHdCH2)]-, forms unsolvated
metallocenes, [(C5Me4)SiMe2(CH2CHdCH2)]2Ln (Ln ) Sm, 1; Eu, 2; Yb, 3), from [(C5Me4)SiMe2(CH2CHd
CH2)]K and LnI2(THF)2 in good yield. Each complex in the solid state has both tethered olefins oriented
toward the Ln metal center with the Ln-C(terminal alkene carbon) distances 0.2-0.3 Å shorter than the
Ln-C(internal alkene carbon) distances. The olefinic C-C bond distances in 2 and 3, 1.328(4) and 1.328(5)
Å, respectively, are normal. Like its permethyl analogue, (C5Me5)2Sm(THF)2, complex 1 reductively couples
CO2 to form the oxalate-bridged dimer {[(C5Me4)SiMe2(CH2CHdCH2)]2Sm}2(µ-η2:η2-O2CCO2), 4, in which
the tethered olefins are noninteracting substituents. Complex 1 reacts with AgBPh4 to form an unsolvated
cation that has the option of coordinating [BPh4]- or a pendant olefin, a competition common in olefin
polymerization catalysis. The structure of {[(C5Me4)SiMe2(CH2CHdCH2)]2Sm}[BPh4], 5, shows that both
pendant olefins are located near samarium rather than the [BPh4]- counterion.
Introduction
This tethered olefin ligand was chosen since it recently has
been useful in providing information related to olefin polym-
erization.17 In the prior study, this ligand provided information
on a previously undetected type of olefin metalation. This ligand
also had the potential to be useful in the study of olefin com-
plexation to cationic centers, since synthetic routes to unsolvated
lanthanide-based metallocene cations, [(C5Me5)2Ln]+ and
[(C5Me4R)2Ln)]+, have been well established.18,19 In complexes
containing simple C5R5 ligands, the [BPh4]- counteranions are
oriented toward the metal center via the phenyl groups. For-
mation of analogues with [(C5Me4)SiMe2(CH2CHdCH2)]-
would set up a competition between [BPh4]- and olefin
coordination so that the question of substrate versus counteranion
could be examined in a metallocene environment. Lanthanide
complexes are appropriate for this study, since they are active
in a variety of catalytic processes involving unsaturated
hydrocarbons including alkene20-27 and diene28 polymerization
Alkene coordination to cationic metallocenes is com-
monly accepted as a key component in both the initiation
and propagation of many homogeneous olefin polymeriza-
tion reactions involving single site catalysts.1-16 One of the
ongoing issues involving the reactivity of cationic polymer-
ization sites involves the interaction of the metal center with
the counteranion vis-a`-vis the incoming monomer. We report
here on the use of the alkene-substituted cyclopentadienyl ligand,
[(C5Me4)SiMe2(CH2CHdCH2)]-, to probe metal-olefin versus
metal-counteranion interactions in a cationic metallocene
environment.
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J. AM. CHEM. SOC. 2003, 125, 5204-5212
10.1021/ja020957x CCC: $25.00 © 2003 American Chemical Society

Tethered Olefin Studies of Interactions in Metallocenes
A R T I C L E S
and alkene hydrogenation,29-35 hydroamination,36-39 and
hydrosilylation.40-43
Preparation of the necessary lanthanide metallocene precur-
sors to the [(C5Me4R)2Ln]+ cations, namely [(C5Me4)SiMe2(CH2-
CHdCH2)]2Ln (Ln ) Sm, Eu, Yb), has proven to be indepen-
dently interesting. These neutral metallocenes have allowed the
investigation of lanthanide olefin interactions, a subject on which
few data are available.6-13,44-52,81
Experimental Section
The complexes described in the following are extremely air and
moisture sensitive. Syntheses and manipulations of these compounds
were conducted under nitrogen or argon with rigorous exclusion of air
and water by Schlenk, vacuum line, and glovebox techniques. THF
and diethyl ether were dried over activated alumina and sieves. Toluene
and hexanes were dried over Q-5 and molecular sieves. Benzene-d6
was distilled over an NaK alloy and benzophenone.
(C5Me4H)SiMe2(CH2CHdCH2),17 LnI2(THF)2 (Ln ) Sm, Eu, Yb),53
54
and AgBPh4 were prepared as previously described. KH was pur-
chased from Aldrich and washed with hexanes before use. NMR spectra
were measured using a Bruker 400 MHz spectrometer. IR samples were
prepared as thin films, and spectra were obtained using an ASI ReactIR
1000. Elemental analysis was provided by Desert Analytics, and
complexometric analyses were performed as previously described.55
Figure 1. Ball and stick figure of [(C5Me4)SiMe2(CH2CHdCH2)]2Sm, 1.
[(C5Me4)SiMe2(CH2CHdCH2)]2Sm, 1. A dark blue solution of
SmI2(THF)2 (127 mg, 0.232 mmol) in 3 mL of THF was added to a
slurry of [(C5Me4)SiMe2(CH2CHdCH2)]K (122 mg, 0.473 mmol) in
10 mL of THF. The color immediately changed to dark green, and a
white precipitate formed. The reaction was stirred for 4 h and
centrifuged to remove the insoluble material. Removal of THF under
vacuum gave oily dark solids which were extracted with hexanes to
produce a dark green solution and dark insoluble material. The reaction
was centrifuged, and the dark green solution was separated. The dark
solids were extracted with hexanes 2 times, and the combined hexane
solutions were evaporated to yield 1 (0.90 mg, 66%) as a dark green
waxy solid. Crystals suitable for X-ray diffraction were grown from
[(C5Me4)SiMe2(CH2CHdCH2)]K. (C5Me4H)SiMe2(CH2CHdCH2)
(2.0 g, 9.07 mmol) was added to a slurry of KH (360 mg, 8.98 mmol)
in 50 mL of diethyl ether. The mixture was stirred for 24 h during
which time a white solid precipitate formed. White [(C5Me4)SiMe2(CH2-
CHdCH2)]K (1.89 g, 80%) was collected by filtration, dried under
vacuum, and used without further purification.
(29) Evans, W. J.; Engerer, S. C.; Piliero, P. A.; Wayda, A. L. In Fundamental
Research in Homogeneous Catalysis; Tsutsui, M., Ed.; Plenum Publishing
Corp.: New York, 1979; Vol. 3, pp 941-952.
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1
toluene at -32 °C (Figure 1). H NMR (C6D6, 25 °C): δ -0.99 (s,
(31) Evans, W. J.; Bloom, I.; Hunter, W. E.; Atwood, J. L. J. Am. Chem. Soc.
1983, 105, 1401.
12H), 0.51 (s, 12H), 6.21 (s, 12H), 10.22 (s, 4H), 28.4 (s, 2H), 38.4 (s,
2H), 42.4 (s, 2H). µeff ) 3.76 at 298 K. IR (thin film): 3076w, 2964s,
2914s, 2860s, 1629s, 1444m, 1390w, 1328w, 1251s, 1220m, 1154m,
1096w, 1023m, 988w, 953w, 930w, 892m, 822m, br, 699w. Anal. Calcd
for C28H46Si2Sm: C, 57.08; H, 7.89; Sm, 25.51. Found: C, 56.99; H,
7.86; Sm, 25.55.
(32) Jeske, G.; Lauke, H.; Mauermann, H.; Schumann, H.; Marks, T. J. J. Am.
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6921.
(35) Roesky, P. W.; Denninger, U.; Stern, C. L.; Marks, T. J. Organometallics
1997, 16, 4486.
[(C5Me4)SiMe2(CH2CHdCH2)]2Eu, 2. A fluorescent-light green
solution of EuI2(THF)2 (87.0 mg, 0.158 mmol) in 3 mL of THF was
reacted with [(C5Me4)SiMe2(CH2CHdCH2)]K (82.0 mg, 0.317 mmol)
in 5 mL of THF to form 2 as a red waxy solid (65.3 mg, 70%). X-ray
quality crystals were obtained by cooling a concentrated hexanes
solution of 2 to -32 °C (Figure 2). 1H NMR (C6D6, 25 °C, broad
singlets ∆ν1/2 ) 24 Hz): δ -0.03, 0.28, 0.88, 1.10, 1.79, 1.89, 3.25.
IR (thin film): 3076w, 2964s, 2914s, 2860s, 1629s, 1559w, 1444m,
1320m, 1251s, 1220m, 1154m, 1108w, 1038m, 984m, 953w, 930w,
891m, 834m, br, 721w, 699w. Anal. Calcd For C28H46Si2Eu: C, 56.92;
H, 7.86; Eu, 25.72. Found: C, 56.66; H, 7.82; Eu, 25.74.
(36) Tian, S.; Arredondo, V. M.; Stern, C. L.; Marks, T. J. Organometallics
1999, 18, 2568.
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18, 1949.
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2001, 20, 2794.
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7157.
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Commun. 1991, 40.
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(45) Schultz, M.; Burns, C. J.; Schwartz, D. J.; Andersen, R. A. Organometallics
2000, 19, 781.
(46) Evans, W. J.; Coleson, K. M.; Engerer, S. C. Inorg. Chem. 1981, 20, 4320.
(47) Evans, W. J. High-Energy Processes in Organometallic Chemistry; Suslick,
K. S., Ed.; ACS Symposium Series 333; American Chemical Society:
Washington, DC, 1987; p 278.
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1995, 14, 992.
(50) Heinemann, C.; Schro¨der, D.; Schwarz, H. Chem. Ber. 1994, 127, 1807.
(51) Berg, D. J.; Louie, A.; Fei, X. Canadian Society of Chemistry 2002 National
Meeting: Vancouver, B.C., June 2002, #764.
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Society of Chemistry 2002 National Meeting: Vancouver, B.C., June 2002,
#510.
(53) Namy, J. L.; Girard, P.; Kagan, H. B. NouV. J. Chim. 1981, 5, 479.
(54) Jordan, R. F.; Echols, S. F. Inorg. Chem. 1987, 26, 383.
(55) Evans, W. J.; Grate, J. W.; Levan, K. R.; Bloom, I.; Peterson, T. T.;
Doedens, R. J.; Zhang, H.; Atwood, J. L. Inorg. Chem. 1986, 25, 3614.
[(C5Me4)SiMe2(CH2CHdCH2)]2Yb, 3. A yellow-green solution of
YbI2(THF)2 (68.0 mg, 0.119 mmol) in 3 mL of THF was reacted with
[(C5Me4)SiMe2(CH2CHdCH2)]K (65.0 mg, 0.251 mmol) in 5 mL of
THF to form 3 as a green waxy solid (65.5 mg, 90%). Crystals suitable
for X-ray diffraction were grown from toluene at -32 °C (Figure 3).
1H NMR (C6D6, 25 °C): δ 0.282 (s, 12H) SiMe2, 1.78 (d, J ) 8.4 Hz,
4H) CH2CHdCH2, 2.04 (s, 12 H) ring Me, 2.14 (s, 12H) ring Me,
4.51 (d, J ) 16.8 Hz, 2H) CH2CHdCH2, 4.85 (d, J ) 12.4 Hz, 2H)
CH2CHdCH2, 6.02 (m, 2H) CH2CHdCH2. 13C NMR (C6D6, 25 °C):
δ 1.20 SiMe2, 11.6 ring Me, 14.1 ring Me, 28.2 CH2CHdCH2, 107.1
ring CsSi, 107.9 CH2CHdCH2, 118.9 ring CsMe, 122.9 ring Cs
Me, 147.6 CH2CHdCH2. IR (thin film): 3076w, 2964s, 2914s, 2860s,
1629s, 1559w, 1444m, 1390w, 1328m, 1251s, 1220m, 1154m, 1108w,
9
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A R T I C L E S
Evans et al.
1258s, 1220w, 1154w, 1096s, 1023s, 988m, 953w, 930w, 891m, 834s,
803s, 699w. Anal. Calcd for C58H92O4Si4Sm2: C, 55.01; H, 7.34; Sm,
23.75. Found: C, 53.94; H, 7.26; Sm, 23.55.
{[(C5Me4)SiMe2(CH2CHdCH2)]2Sm}[BPh4], 5. A dark green
solution of 1 (68 mg, 0.115 mmol) in 8 mL of toluene was added to a
slurry of AgBPh4 (49 mg, 0.115 mmol) in 5 mL of toluene wrapped in
aluminum foil. The reaction was stirred for 12 h, during which time
the color changed to dark red/orange and a black solid precipitate
formed. The reaction was centrifuged to remove the insoluble material
leaving a red/orange solution. The toluene was removed leaving 5 as
a dark red oily solid (70 mg, 67%). Slow evaporation of a warm toluene
solution of 5 produced crystals suitable for X-ray diffraction studies.
1H NMR (C6D6, 25 °C): δ -1.33 (broad singlet) ring Me, 7.78 (broad
singlet) BPh4. IR (thin film): 2964s, 2918s, 2860s, 1629w, 1594w, br,
1482 w, 1432m, 1258s, 1154w, 1096s, 1023s, 953w, 892w, 834s, 803s,
745m, 703s. Anal. Calcd for C52H66BSi2Sm: C, 68.75; H, 7.34; Sm,
16.55. Found: C, 68.12; H, 7.33; Sm, 16.47.
Reaction of 1 With Ethylene. A dark green solution of 1 (25 mg,
0.042 mmol) in 15 mL of hexane was added to a round-bottom flask
equipped with a greaseless high vacuum stopcock. The solution was
evacuated to the boiling point of the solvent, and 1 atm of ethylene
was introduced. The dark green color remained, and noticeable amounts
of colorless precipitate formed within 3 min. The reaction was continued
until ethylene uptake ceased (1 h) and copious amounts of colorless
solids were observed. The reaction was quenched with D2O, and the
slurry was filtered yielding a colorless solid. The organic solution was
separated and analyzed by GC/MS. The solid was washed with 5%
HCl (3 × 5 mL), followed by washing with 2-propanol (3 × 15 mL).
The resulting white solid was dried under vacuum leaving 390 mg of
a fluffy white solid. mp ) 138 °C. The only major product in the
organic filtrate was the diene (C5Me4D)SiMe2(CH2CHdCH2).
X-ray Data Collection, Structure Solution, and Refinement for
1. A green crystal of approximate dimensions 0.14 × 0.16 × 0.26 mm3
was mounted on a glass fiber and transferred to a Bruker CCD platform
diffractometer. The SMART56 program package was used to determine
the unit-cell parameters and for data collection (25 s/frame scan time
for a sphere of diffraction data). The raw frame data was processed
using SAINT57 and SADABS58 to yield the reflection data file.
Subsequent calculations were carried out using the SHELXTL59
program. The diffraction symmetry was 2/m, and the systematic
absences were consistent with the monoclinic space groups C2, Cm,
or C2/m. It was later determined that the noncentrosymmetric space
group C2 was correct.
Figure 2. Thermal ellipsoid plot of [(C5Me4)SiMe2(CH2CHdCH2)]2Eu,
2, with ellipsoids drawn at the 50% probability level.
The structure was solved by direct methods and refined on F2 by
full-matrix least-squares techniques. The analytical scattering factors60
for neutral atoms were used throughout the analysis. Hydrogen atoms
were included using a riding model. The molecule was located on a
2-fold rotation axis. There was one molecule of toluene solvent present
per formula unit. The toluene was also located on a 2-fold axis. The
absolute structure was assigned by refinement of the Flack parameter.61
Similar experimental methods were used for all X-ray experiments.
Structural details are in the Supporting Information.
Figure 3. Thermal ellipsoid plot of [(C5Me4)SiMe2(CH2CHdCH2)]2Yb,
3, with ellipsoids drawn at the 50% probability level.
1023m, 988m, 953w, 930w, 892m, 834m, br, 687w. Anal. Calcd For
C28H46Si2Yb: C, 54.96; H, 7.59; Yb, 28.28. Found: C, 54.87; H, 7.39;
Yb, 28.11.
{[(C5Me4)SiMe2(CH2CHdCH2)]2Sm}2(µ-η2:η2-O2CCO2), 4. A
round-bottom flask fitted with a high vacuum greaseless stopcock
containing 1 (225 mg, 0.382 mmol) in 20 mL of hexanes was attached
to a high vacuum line and evacuated to the vapor pressure of the solvent.
The flask was charged with 1 atm of CO2, and the dark green color
changed to yellow/orange in 2 min. The reaction was stirred for 1 h,
after which the solvent was removed leaving 4 (230 mg, 95%) as an
orange solid. X-ray quality crystals were obtained by cooling a saturated
hexane solution of 4 to -32 °C. 1H NMR (C6D6, 25 °C): δ -3.67 (s,
12H) SiMe2, -1.19 (d, J ) 8.4 Hz, 4H) CH2CHdCH2, - 0.589 (s,
12H) ring Me, 4.00 (d, J ) 15.6 Hz, 2H) CH2CHdCH2, 4.22 (d, J )
12.0 Hz, 2H) CH2CHdCH2, 4.73 (m, 2H) CH2CHdCH2, 6.69 (s, 12H)
ring Me. 13C NMR (C6D6, 25 °C): δ -4.89 SiMe2, 15.1 ring Me, 22.0
ring Me, 28.1 CH2CHdCH2, 111.4 ring CsSi, 112.1 CH2CHdCH2,
122.5 ring CsMe, 133.5 CH2CHdCH2, 134.6 ring CsMe. IR (thin
film): 3076w, 2964s, 2914s, 2860s, 1653s, 1652s, 1444w, 1309m,
Results
The Cyclopentadienyl Potassium Precursor. (C5Me4H)-
SiMe2(CH2CHdCH2) is readily deprotonated with KH in diethyl
ether to make [(C5Me4)SiMe2(CH2CHdCH2)]K. The unsolvated
(56) SMART Software Users Guide, Version 5.1; Bruker Analytical X-ray
Systems, Inc.: Madison, WI, 1999.
(57) SAINT Software Users Guide, Version 6.0; Bruker Analytical X-ray
Systems, Inc.: Madison, WI, 1999.
(58) Sheldrick, G. M. SADABS, version 2.03; Bruker Analytical X-ray Systems,
Inc.: Madison, WI, 2000.
(59) Sheldrick, G. M. SHELXTL, version 5.10; Bruker Analytical X-ray Systems,
Inc.: Madison, WI, 1999.
(60) International Tables for X-ray Crystallography 1992, Vol. C.; Kluwer
Academic Publishers: Dordrecht, The Netherlands.
(61) Flack, H. D. Acta Crystallogr. 1983, A39, 876.
9
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Tethered Olefin Studies of Interactions in Metallocenes
A R T I C L E S
Table 1. Comparison of Alkene Resonances for [(C5Me4)SiMe2(CH2CHdCH2)]2Yb (3), 3 + THF, 3 + DME, 3 + Pyridine, 3 +
2,2-Bipyridine, C5Me4(SiMe2CH2CHdCH2)H, [(C5Me4)SiMe2(CH2CHdCH2)]Y(CH2SiMe3)2(THF)2 (6),
{[(C5Me4)SiMe2(CH2CHdCH2)]Y(O2CCH2SiMe3)2}2 (7), [(C5Me4)SiMe2(CH2CHdCH2)]2Sm (1), 1 + THF,
{[(C5Me4)SiMe2(CH2CHdCH2)]2Sm}2(µ-η2 : η2 -O2CCO2) (4), (C5Me5)2Y[η1-CH2CH2C(CH3)2CHdCH2] (11),
(C5Me5)2Y[η1-CH2CH2C(CH3)2CHdCH2](THF) (11‚THF), and 3,3-Dimethyl-1,4-pentadiene
1H NMR
13C NMR
compound
δ (dCH )
δ (sCHd)
δ (dCH )
δ (sCHd)
2
2
3
4.51 (d), 4.85 (d)
4.82 (d), 4.92 (dd)
4.70 (d), 4.90 (dd)
4.95 (m)
4.50 (d), 4.58 (d)
4.90 (m)
6.02 (m)
5.94 (m)
5.98 (m)
5.95 (m)
4.80 (m)
5.73 (m)
5.83 (m)
5.99 (m)
42.4 (s)
36.6 (s)
4.73 (s)
6.78 (dd)
5.78 (dd)
5.74 (dd)
107.9
111.0
111.1
112.0
112.0
113.7
113.5
112.7
a
147.6
140.5
140.1
138.1
136.0
135.5
136.1
136.5
a
3 + THF
3 + DME
3 + pyridine
3 + 2,2-bipyridine
C5Me4(SiMe2CH2CHdCH2)H
6
7
1
4.94 (m)
5.01 (m)
28.4 (s), 38.4 (s)
26.6 (s), 32.9 (s)
4.22 (d)
3.76 (d), 5.14 (d)
4.75 (m)
1 + THF
4
11
11‚THF
a
a
112.1
110.5
108.4
111.1
133.5
161.1
150.7
146.1
3,3-dimethyl-1,4-pentadiene
4.87 (d), 4.92 (d)
a Due to the paramagnetism of 1, the 13C NMR was uninformative.
potassium salt is insoluble in alkanes, arenes, and diethyl ether,
but it is partially soluble in THF. When the KH deprotonation
is conducted in THF, {[(C5Me4)SiMe2(CH2CHdCH2)]K-
(THF)}n is obtained,62 as shown in eq 1. The cyclopentadienyl
) Sm, 1; Eu, 2; Yb, 3), eq 3, in a reaction analogous to eq 2.
2[(C5Me4)Me2Si(CH2CHdCH2)]K +
LnI2(THF)2 f [(C5Me4)Me2Si(CH2CHdCH2)]2Ln + 2KI
(3)
Ln ) Sm, 1; Eu, 2; Yb, 3
Complexes 1-3 are very soluble in alkanes and like their
C5Me5 analogues they can be separated from the byproduct KI
by hydrocarbon extraction. A major difference between com-
plexes 1-3 and the analogous C5Me5 systems is that 1-3 are
isolated in an unsolvated state. In contrast, the permethyl
complexes, (C5Me5)2Ln, solvate readily and removal of coor-
dinated THF is not easy.45,66
Complexes 1-3 are intensely colored as is typical of divalent
lanthanide metallocenes.65 The dark green color of 1 is similar
to that of unsolvated (C5Me5)2Sm. Addition of THF to 1 changes
the color to a dark brown, whereas (C5Me5)2Sm(THF)2 is purple.
The dark red color of 2 is similar to that of (C5Me5)2Eu and
(C5Me5)2Eu(THF). The dark green color of 3 is like that of (C5-
Me4H)2Yb and (1,3-tBu2C5H3)2Yb, but (C5Me5)2Yb is dark
black/brown and (C5Me5)2Yb(THF) is red. The infrared spectra
of complexes 1, 2, and 3 are essentially identical. Each spectrum
contains peaks that can be assigned to the major functional
groups: 2964, 2914, and 2860 cm-1 were assigned to ring
methyl C-H stretches, 1629 cm-1 is assigned to the CdC
stretch of the tethered alkene, and 1251 cm-1 is assigned to the
Si-CH3 stretch.
rings in the polymeric structure of this complex are all bridging
such that they generate bent metallocene subunits to which THF
is attached. The tethered olefin appears to be oriented toward
the potassium, but the K‚‚‚C(internal alkene carbon) distance
of 3.58(3) Å and the K‚‚‚C(terminal alkene carbon) length of
4.20(3) Å are long.
Samarium, Europium, and Ytterbium Metallocenes. The
formation of lanthanide metallocenes of [(C5Me4)SiMe2-
(CH2CHdCH2)]- was attempted following the synthesis used
successfully for the C5Me5 analogues, eq 2.63-65
2(C5Me5)M + LnI2(THF)2 f (C5Me5)2Ln(THF)x + 2 MI
(2)
Ln ) Sm, x ) 2, M ) K
Ln ) Eu, x ) 1, M ) Na
Ln ) Yb, x ) 1, M ) Na
Initially, NMR spectroscopy was used to probe for coordina-
tion of the pendant olefins to the metal centers in the [(C5-
Me4)SiMe2(CH2CHdCH2)]2Ln complexes. Data are summa-
1
rized in Table 1. The H NMR spectrum of diamagnetic 3 in
[(C5Me4)SiMe2(CH2CHdCH2)]K reacts instantly with LnI2-
(THF)2 in THF to make [(C5Me4)SiMe2(CH2CHdCH2)]2Ln (Ln
C6D6 is free of THF, but gives no compelling evidence for
metal-alkene interactions. A pair of doublets centered at δ 4.51
and 4.85 is observed for the protons of the terminal alkene
carbon, and a multiplet at δ 6.02 is found for the proton on the
internal alkene carbon. These peaks are only slightly shifted
from those found in [(C5Me4)SiMe2(CH2CHdCH2)]Y(CH2-
(62) Evans, W. J.; Brady, J. C.; Giarikos, D. G.; Fujimoto, C. H.; Ziller, J. W.
J. Organomet. Chem. 2002, 649, 252.
(63) Evans, W. J.; Bloom, I.; Hunter, W. E.; Atwood, J. L. Organometallics
1985, 4, 112.
(64) Tilley, T. D.; Andersen, R. A.; Spencer, B.; Ruben, H.; Zalkin, A.;
Templeton, D. H. Inorg. Chem. 1980, 19, 2999.
(65) Evans, W. J.; Hughes, L. A.; Hanusa, T. P. J. Am. Chem. Soc. 1984, 106,
4270.
(66) Evans, W. J.; Hughes, L. A.; Hanusa, T. P. Organometallics 1986, 5, 1285.
9
J. AM. CHEM. SOC. VOL. 125, NO. 17, 2003 5207

A R T I C L E S
Evans et al.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
[(C5Me4)SiMe2(CH2CHdCH2)]2Sm, 1,
[(C5Me4)SiMe2(CH2CHdCH2)]2Eu, 2,
[(C5Me4)SiMe2(CH2CHdCH2)]2Yb, 3, and
{[(C5Me4)SiMe2(CH2CHdCH2)]2Sm}[BPh4], 5
SiMe3)2(THF)2, 6,17 and {[(C5Me4)SiMe2(CH2CHdCH2)]Y-
(O2CCH2SiMe3)2}2, 7,17 in which there is no evidence for
metal-olefin interaction in the solid state or in solution.
Addition of THF to 3 causes only small shifts of the ring and
silyl methyl resonances in the 1H NMR spectrum. The terminal
alkene protons remain as a pair of doublets, but they are shifted
to δ 4.82 and 4.92 and the multiplet from the internal alkene
proton shifts to δ 5.94. Two new peaks of equal intensity
corresponding to THF are observed at δ 1.45 and 3.59. Likewise,
addition of dimethoxyethane, pyridine, and 2,2-bipyridine to 3
also causes shifting of the terminal and internal alkene proton
resonances, Table 1.
compound
1
2
3
5
Ln(1)-Cnt1a
2.551
2.558
2.558
3.086
3.096
2.828(3)
2.822(3)
3.293(4)
3.008(3)
3.243(3)
3.089(3)
1.328(4)
1.328(4)
140.9
23.32(9)
24.05(8)
105.1
103.6
126.6(4)
127.7(3)
2.437
2.410
2.409
2.952
2.993
2.697(3)
2.697(3)
3.166(3)
2.878(3)
3.262(3)
2.854(3)
1.324(5)
1.316(5)
137.1
24.72(9)
23.66(9)
109.7
105.4
126.9(3)
126.9(3)
Ln(1)-Cnt2b
Ln(1)-Cnt3c
3.048
2.973
Ln(1)-Cnt4d
Ln(1)-C(ring 1)e
Ln(1)-C(ring 2)f
Ln(1)-C(13)
2.823(3)
2.720(2)
3.249(4)
3.004(3)
3.182(3)
2.905(3)
Ln(1)-C(14)
Ln(1)-C(27)
In contrast to the H NMR data, the 13C NMR spectrum of
1
Ln(1)-C(28)
3 had some unusual shifts. The 13C NMR spectrum contains
nine peaks as expected. However, the alkene carbon peaks, at
δ 147.6, assignable to the internal carbon, and at δ 107.9,
assignable to the terminal carbon, are shifted substantially from
the alkene carbon peaks in 6, δ 136.1 and 113.5, and 7, δ 136.5
and 112.7. No metal-alkene interaction is observed via 89Y-C
coupling in 6 and 7. Addition of THF to 3 in C6D6 causes the
internal alkene carbon to shift upfield to δ 140.5 ppm and the
terminal alkene carbon shifts downfield to 111.0. This is in the
direction of the resonances for 6 and 7 and the free ligand, Table
1. Addition of DME, pyridine, and 2,2-bipyridine causes similar
shifts in the 13C NMR spectra. Hence, it appears that the unusual
13C NMR shifts of unsolvated 3 arise from metal-olefin
interactions which can be disrupted by the addition of donor
solvents. This is further supported by the structural data on the
DME adduct of 3 described later.68 Variable temperature 13C
NMR studies on 3 and 3 + THF showed no significant variation
of the spectra, even at temperatures as low as -85 °C in C7D8.
No signal for either alkene carbon resonance is observable past
-60 °C in both 3 and 3 + THF.
C(13)-C(14)
1.415(7)
1.328(5)
C(27)-C(28)
Cnt1-Ln(1)-Cnt2
C(14)-Ln(1)-C(13)
C(28)-Ln(1)-C(27)
Cnt1-Ln(1)-C(14)
Cnt1-Ln(1)-C(28)
C(14)-C(13)-C(12)
C(28)-C(27)-C(26)
141.2
25.78(13)
141.9
24.66(10)
109.1
107.7
129.9(4)
126.4(3)
a Cnt1 is the centroid of the C(1)-C(5) ring. b Cnt2 is the centroid of
the C(15)-C(19) ring. c Cnt3 is the center of C(13)-C(14). d Cnt4 is the
center of C(27)-C(28). e Average of C(1)-C(5). f Average of C(15)-C(19).
also similar when the difference in ionic radii is considered
(eight coordinate Yb(II) is 0.11 Å smaller than eight coordinate
Eu(II)).69
In each complex, the metal is coordinated to the two
cyclopentadienyl rings in a typical metallocene fashion and no
coordinated THF is present. The average Ln-C(cyclopentadi-
enyl ring) distances and the (ring centroid)-Ln-(ring centroid)
angles of 1 and 2 are similar to those of (C5Me5)2Sm66and
(C5Me5)2Eu,66 as shown in Table 3. The parameters for 3 differ
slightly from the two unique molecules found in the asymmetric
unit for (C5Me5)2Yb:45 3 has a Yb-ring(average) distance 0.05-
0.06 Å longer and a (ring centroid)-Yb-(ring centroid) angle
3-4° smaller than those in decamethylytterbocene.
Both of the tethered olefins in each complex, 1-3, are oriented
toward the metal center. This provides the first comparative
crystallographic data on interactions of the three divalent
lanthanides, Eu, Yb, and Sm with olefins. The tethered alkenes
approach the metal in an unsymmetrical orientation, with the
terminal alkene carbon atoms 0.2-0.3 Å closer than the internal
carbons, as shown in Table 4. All of these Ln-C(alkene)
distances are longer than the Ln-C(cyclopentadienyl ring)
average lengths, as is typical for long distance lanthanide
hydrocarbon interactions.31,70-72 Long-range intermolecular
Ln‚‚‚C interactions were also observed in the solid state for
the analogous permethyl complexes, (C5Me5)2Ln.45,66
The NMR spectra of 1 are complicated by the paramagnetic
nature of Sm(II), but the following tentative H NMR assign-
1
ments can be made: ring methyl peaks at δ 6.21 and -0.99, a
methyl peak for the Me2Si bridge at δ 0.51, the CH2 attached
to Si at δ 10.2, and three peaks at δ 42.4, 38.4, and 24.8 in a
1:1:1 ratio assigned to the alkene protons. Upon addition of
THF, two new peaks of equal intensity corresponding to
coordinated THF are observed at δ 7.30 and -3.08. All of the
other peaks shift: the ring methyls to δ 4.10 and 1.03, the silyl
methyls to δ 2.33, the CH2 to δ 11.5, and the alkene protons to
δ 36.6, 32.9, and 26.6. The large shifts in the alkene resonances
of 1 upon addition of THF are consistent with the shifts for 3
upon addition of donor solvents and could result from displace-
ment of the tethered olefin from the vicinity of the metal. The
paramagnetism of [(C5Me4)SiMe2(CH2CHdCH2)]2Eu, 2, pre-
cluded detailed NMR analysis.
To obtain more information on the metal-olefin interactions
in 1-3, crystallographic data were sought. Although 1-3 were
isolated as waxy solids, single crystals of all three metallocenes
were obtainable (Figures 1-3). Complexes 1 and 3 are
isomorphous and crystallize with one molecule of toluene in
the unit cell. Complex 2 crystallized from hexane without any
solvent in the lattice. As shown in Table 2, the metallocene
structural parameters of 1 and 2 are similar. The data on 3 are
The only other structurally characterized divalent lanthanide
alkene complex in the literature involves a platinum coordinated
ethylene, (C5Me5)2Yb(µ-η2:η2-C2H4)Pt(PPh3)2, 8.44 The Yb-
C(alkene) distances for coordination of the single olefin in 8,
2.770(3) and 2.793(3) Å, are significantly shorter than those
for the two olefins in 3, 2.905(3) and 3.182 Å. In 8, the structural
parameters of the (C5Me5)2Yb and (C2H4)Pt(PPh3)2 components
were not very different from those of the free entities. Hence,
little metal-olefin interaction was revealed by the structure.
(67) Evans, W. J.; Keyer, R. A.; Ziller, J. W. J. Organomet. Chem. 1990, 394,
87.
(68) Crystallographic cell constants for 3‚DME: Hexagonal, space group P61,
a ) 19.1515(11) Å, c ) 18.2474(11) Å, V ) 5796.1(10) Å3.
(69) Shannon, R. D. Acta Crystallogr., Sect A. 1976, A32, 751.
9
5208 J. AM. CHEM. SOC. VOL. 125, NO. 17, 2003

Tethered Olefin Studies of Interactions in Metallocenes
A R T I C L E S
Table 3. Comparison of Selected Bond Distances (Å) and Angles (deg) for [(C5Me4)SiMe2(CH2CHdCH2)]2Sm (1), (C5Me5)2Sm,
[(C5Me4)SiMe2(CH2CHdCH2)]2Eu (2), (C5Me5)2Eu, [(C5Me4)SiMe2(CH2CHdCH2)]2Yb (3), and (C5Me5)2Yb
compound
1
(C Me5)2Sm
5
2
(C Me5)2Eu
5
3
(C Me5)2Yb
5
Ln-C(ring) average
2.823(3)
2.79(1)
2.53
2.828(3)
2.822(3)
2.558
2.552
140.9
2.79(1)
2.53
2.720(2)
2.66
2.67
2.38
Ln-ring centroid
2.551
141.2
2.437
141.9
ring centroid-Ln-
ring centroid
140.1
140.3
146
145
Table 4. MsC(alkene) Distances for
[(C5Me4)SiMe2(CH2CHdCH2)]2Sm (1),
[(C5Me4)SiMe2(CH2CHdCH2)]2Eu (2),
[(C5Me4)SiMe2(CH2CHdCH2)]2Yb (3),
{[(C5Me4)SiMe2(CH2CHdCH2)]2}Sm[BPh4] 5,
(C5Me5)2Yb(µ-η2:η2-C2H4)Pt(PPh3)2 (8a), and
[(C5Me5)2Sm][(µ-Ph)2BPh2] (9b)
compound
1
2
3
5
8a
9b
M-C(terminal) 3.004(3) 3.008(3) 2.905(3) 2.854(3) 2.770(3) 3.059(3)
3.089(3) 2.878(3) 3.175(3)
M-C(internal) 3.249(4) 3.243(3) 3.182(3) 3.166(3) 2.793(3) 2.825(3)
3.293(4) 3.262(3) 2.917(3)
a The terminal/internal distinction of carbon atoms does not apply in
this complex. b These are Sm-C(arene) distances.
Since 1-3 have comparatively longer Ln-C distances, these
complexes also show only a weak interaction between the two
olefins and the metal. Consistent with this, the C(alkene)-
C(alkene) distances in 2 and 3, 1.328(4) and 1.328(5) Å, for
C(13)-C(14) and C(27)-C(28), are similar to the 1.283(6) and
1.310(6) Å lengths in 4 (discussed later), in which the alkene
is noninteracting. The alkene carbon atoms in 1 have large
thermal ellipsoids that may arise from disorder. As a result, a
reliable C(alkene)-C(alkene) distance was not obtainable
for 1.
Figure 4. Thermal ellipsoid plot of {[(C5Me4)SiMe2(CH2CHdCH2)]2Sm}2-
(µ-η2:η2-O2CCO2), 4, with ellipsoids drawn at the 50% probability level.
Attempts to crystallize 1-3 in the presence of donor solvents,
to have structures of the divalent complexes with the olefin not
interacting, were largely unsuccessful. This differs considerably
from the (C5Me5)2Ln systems which readily form crystalline
(C5Me5)2LnLx complexes.44-45,64-67 However, in the case of
[(C5Me4)SiMe2(CH2CHdCH2)]2Yb in the presence of dimethox-
yethane, crystals of [(C5Me4)SiMe2(CH2CHdCH2)]2Yb(DME)
were obtained which showed coordination of both DME oxygen
donor atoms to the metal.68 Unfortunately, the structure was
not of high enough quality to provide more than connectivity.
This structure did show that donor solvents will coordinate to
the [(C5Me4)SiMe2(CH2CHdCH2)]2Ln complexes and that this
coordination could cause the changes observed in13C NMR shifts
upon addition of donor solvent.
{[(C5Me4)SiMe2(CH2CHdCH2)]2Sm}2(µ-η2:η2-O2CCO2), eq 4.
Complex 4 is isolated in 95% yield.
The color and 1H and 13C NMR spectra of 4 were consistent
with formation of a trivalent samarium complex. Resonances
attributable to the terminal protons of the tethered CH2CHd
CH2 group were found as doublets at δ 4.00 and 4.22 ppm.
The proton on the internal carbon was located as a multiplet at
δ 4.73. The 13C spectrum contains nine peaks as expected for
the cyclopentadienyl ligand, and an additional resonance is
observed at δ 199 ppm which could be assigned to the
quaternary carbons of the oxalate bridge. The terminal and
internal alkene carbon resonances were found at δ 112.1 and
133.5, respectively.
Reductive Reactivity of [(C5Me4)SiMe2(CH2CHdCH2)]2Sm.
To compare the reactivity of [(C5Me4)SiMe2(CH2CHdCH2)]2-
Sm with (C5Me5)2Sm(THF)2, the reaction of 1 with CO2 was
examined. (C5Me5)2Sm(THF)2 reductively couples CO2 to the
oxalate dianion, [(C5Me5)2Sm]2(µ-η2:η2-O2CCO2).73 [(C5-
Me4)SiMe2(CH2CHdCH2)]2Sm reacts similarly with CO2 in
minutes in hexanes to form a yellow-orange product, 4, which
was identified by X-ray crystallography as the direct analogue
(70) Evans, W. J.; Giarikos, D. G.; Robledo, C. B.; Leong, V. S.; Ziller, J. W.
The structure of 4, Figure 4, which is similar to that of
[(C5Me5)2Sm]2(µ-η2:η2-O2CCO2),73 provides the first detailed
Organometallics 2001, 20, 5648.
(71) Evans, W. J.; Ulibarri, T. A.; Ziller, J. W. J. Am. Chem. Soc. 1990, 112,
219.
(72) Evans, W. J.; Gonzales, S. L.; Ziller, J. W. J. Am. Chem. Soc. 1994, 116,
2600.
(73) Evans, W. J.; Seibel, C. A.; Ziller, J. W. Inorg. Chem. 1998, 37, 770.
9
J. AM. CHEM. SOC. VOL. 125, NO. 17, 2003 5209

A R T I C L E S
Evans et al.
structural information on this metallocene oxalate, since the data
on the C5Me5 analogue were not of high quality. The alkene
functionalities on the rings are oriented away from the metal
with C(alkene)-C(alkene) distances of 1.283(6) and 1.310(6)
Å. The tetradentate oxalate dianion, [O2CCO2]2-, bridges the
two Sm atoms by formation of two five-membered SmOCCO
rings, a typical coordination mode for the oxalate anion.73-76
The oxalate ligand is planar, as indicated by the angles about
C(29), and the 1.560(6) Å C(29)-C(29′) bond is normal for a
single bond.77 The 2.400(2) Å Sm(1)-O(1) and 2.398(2) Å
Sm(1)-O(2)′ distances in 4 are longer than the 2.303(4)-
2.317(4) Å Sm-O range found in the bridging carboxylate
dimers, [(C5Me5)2Sm(µ-O2CCH2CHdCH2)]2 and [(C5Me5)2Sm-
(µ-O2CC6H5)]2, which contain eight-membered SmOCO
SmOCO rings.78 The Sm-O distances in 4 are also longer than
the Sm-O distance of 2.30(1) Å found in (C5Me5)2Sm[µ-η4-
(PhN)OCCO(NPh)]Sm(C5Me5)2, which also contains five-
membered rings and eight-coordinate samarium centers
-
counting each six-electron C5Me5 ligand as occupying three
Figure 5. Thermal ellipsoid plot of {[(C5Me4)SiMe2(CH2CHdCH2)]2Sm}-
[BPh4], 5, with ellipsoids drawn at the 50% probability level.
coordination sites.79 However, the Sm-O distances in 4 are
shorter than those found with neutral oxygen donor ligands in
eight-coordinate trivalent samarium systems, which range from
2.44(2)-2.511(4) Å.80
is not present. To gain more definitive evidence on the alkene
versus [BPh4]- coordination question, an X-ray crystallographic
study was conducted.
Formation of a Cationic Species. To obtain a cationic
species to test the tethered alkene versus [BPh4]- anion
coordination issue, a reaction analogous to the (C5Me5)2Sm/
AgBPh4 system, eq 5, was examined. Like (C5Me5)2Sm,18
X-ray crystallography confirmed the composition of {[(C5-
Me4)SiMe2(CH2CHdCH2)]2Sm}[BPh4] for 5, which is analo-
gous to the permethyl product 9 obtained in eq 5. However,
X-ray crystallography also revealed that, unlike (C5Me5)2Sm-
(µ-Ph)2BPh2, in which the [BPh4]- anion is oriented toward
samarium through two of the arene rings, eq 5, the [BPh4]- ion
in 5 is not interacting with the metal. Instead, both pendant
olefins are oriented toward the Sm(III) center, Figure 5, eq 6.
[Me2Si(C5Me4)(CH2CHdCH2)]2Sm reacts with AgBPh4 in
toluene. The dark green color transforms over 12 h to a dark
red product, 5, with the formation of a black precipitate. The
1H NMR and 13C NMR spectra of 5 are not informative due to
1
the poor solubility of the complex. The H NMR spectrum
contains a broad singlet at δ -1.33 ppm that could be assigned
to one set of the ring methyls, but a resonance for the other set
was not identifiable. In comparison, the ring methyl protons in
[(C5Me5)2Sm][(µ-Ph)2BPh2], 9, were observed at δ -0.34 ppm.
A second broad singlet in the spectrum of 5 at δ 7.78 ppm was
observed and can be assigned to the phenyl protons of the
tetraphenylborate anion. A peak at δ 8.4 ppm was observed in
the spectrum of 9.
The IR spectrum of 5 is similar to those of 1-3, except that
absorbances attributable to the tetraphenylborate anion (similar
to absorptions observed for 9) are observed and the strong
absorbance at 1629 cm-1 for the CdC stretch observed for 1-3
Table 5 summarizes a comparison of selected bond lengths
and angles for 5, (C5Me5)2Sm(µ-Ph)2BPh2, and [(C5Me5)2Sm-
(THF)2][BPh4].25 The metrical parameters for the metallocene
part of 5 are not significantly different from those of the other
compounds. Similar to 1-3, the alkenes in 5 are oriented toward
samarium in an unsymmetrical fashion with the 2.854(3) and
2.878(3) Å Sm-C(terminal alkene) distances shorter than the
3.166(3) and 3.262(3) Å Sm-C(internal alkene) distances. These
Sm-C distances are shorter than those in 1 as expected for a
Sm(III) versus Sm(II) system. These Sm-olefin distances can
also be compared with the four closest Sm-C(arene) distances
in trivalent 9: 2.825(3), 2.917(3), 3.059(3), and 3.175(3) Å. The
1.324(5) and 1.316(5) Å C(alkene)-C(alkene) distances in 5
are indistinguishable from the C(alkene)-C(alkene) distances
in 2-4.
(74) Guillou, O.; Bergerat, P.; Kahn, O.; Bakalbassis, E.; Boubekeur, P.; Batail,
P.; Guillot, M. Inorg. Chem. 1992, 31, 110.
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21, 127.
(76) Kahwa, I. A.; Fronczerk, F. R.; Selbin, J. Inorg. Chim. Acta 1994, 82,
161.
(77) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A. G.;
Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1.
(78) Evans, W. J.; Seibel, C. A.; Ziller, J. W.; Doedens, R. J. Organometallics
1998, 17, 2103.
Discussion
The [(C5Me4)SiMe2(CH2CHdCH2)]- ligand, the neutral
metallocenes 1-3, and the cationic metallocene 5 are well suited
(79) Evans, W. J.; Drummond, D. K. J. Am. Chem. Soc. 1986, 108, 7440.
(80) Evans, W. J.; Foster, S. E. J. Organomet. Chem. 1992, 433, 79.
9
5210 J. AM. CHEM. SOC. VOL. 125, NO. 17, 2003

Tethered Olefin Studies of Interactions in Metallocenes
A R T I C L E S
Table 5. Comparison of Selected Bond Distances (Å) and Angles (deg) for {[(C5Me4)SiMe2(CH2CHdCH2)]2Sm}[BPh4] (5),
[(C5Me5)2Sm][(µ-Ph)2BPh2] (9), and [(C5Me5)2Sm(THF)2][BPh4], 10
compound
5
9
10
ring centroid-Sm-ring centroid
Sm-ring centroid
137.1
2.410
2.409
134.4(2)
2.420
2.422
134.2
2.423
Sm-C(ring) range
Sm-C(ring) average
Sm-C(L)a
2.630(3)-2.746(3)
2.670(3)-2.740(3)
2.66(3)-2.71(2)
2.69(2)
2.697(3)
2.70(2)
2.878(3)
3.166(3)
2.825(3)
3.059(3)
2.854(3)
2.917(3)
3.262(3)
3.175(3)
a L is alkene for 5 and arene for [(C5Me5)2Sm][(µ-Ph)2BPh2].
for studying metal-alkene chemistry in a metallocene environ-
ment. The tethered olefin can function simply as an ancillary
cyclopentadienyl substituent as seen in 4, {[(C5Me4)SiMe2-
(CH2CHdCH2)]Y(O2CCH2SiMe3)2}2,17 6, and [(C5Me4)SiMe2-
(CH2CHdCH2)]Y(CH2SiMe3)2(THF)2,17 7, in which is it not
interacting with the metal. Alternatively, as demonstrated by
1-3 and 5, it can function as a chelating ligand with which
metal-olefin coordination can be studied. It also can be a
reactant in metalation chemistry, as demonstrated by the
formation of {[(C5Me4)SiMe2(C3H3)]Y(L)}2 (L ) THF, DME)
from 7.17
ethylene has been reported.81 However, solid state evidence for
such a complex has been lacking. The only other structurally
characterized divalent lanthanide olefin complex in the literature
involves an olefin already coordinated to another metal, namely
the (C5Me5)2Yb(µ-η2:η2-C2H4)Pt(PPh3)2 complex, 8, made from
(C5Me5)2Yb and (C2H4)Pt(PPh3)2.44 In 8, both components
remain similar in structure to the uncomplexed precursors.
(C5Me5)2Sm is also known to form crystallographically char-
acterizable π complexes with olefins, but these typically involve
reductive complexation of these substrates due to the strong
reduction potential of Sm(II).70-72,82
The synthesis of lanthanide metallocenes of [Me2Si(C5Me4)-
(CH2CHdCH2)]- is similar to the preparation of the (C5Me5)-
analogues except that complexes 1-3 can be isolated from
preparations in THF in a form free of coordinating solvents.
This is a great advantage, since desolvation of (C5Me5)2Ln-
(THF)x is not particularly facile.45,66
The structures of the three complexes, 1-3, are similar, as
shown in Table 2. In addition, their structural parameters are
similar to those of the permethyl analogues, (C5Me5)2Ln, Table
3. This is reasonable, since both sets of bent metallocene
complexes have additional metal-ligand interactions in the solid
state to compensate for their coordinative unsaturation. The
solid-state structures of the base-free bent metallocenes
(C5Me5)2Sm,31 (C5Me5)2Yb,45 (C5Me4H)2Yb,45 and [(1,3-(Me3-
Si)2C5H3)]2Yb45 show that intermolecular interactions occur
which reduce the coordinative unsaturation. In [1,3-(tBu)2C5H3]2-
Yb, an intramolecular Yb-ring Me interaction is found.45
Complexes 1-3 use the tethered olefins to fill the coordination
sphere of the metal in the solid state.
Presumably, the origin of the desolvated nature of 1-3 is
the presence of the tethered olefin, since the olefin is oriented
toward the metal in the solid state. Shifts in the NMR spectra
of 1 and 3 in solution can also be interpreted as evidence for
tethered olefin coordination. In 1, the alkene proton resonances
are shifted downfield to δ 43.9, 39.8, and 25.5 ppm, indicating
that the olefin may be nearby the paramagnetic Sm(II) ion. In
3, a large shift in the 13C NMR spectrum is observed for the
internal (∆ ) 12.1 ppm) and terminal (∆ ) 5.8 ppm) alkene
carbons compared to those of the free diene (C5Me4H)SiMe2-
(CH2CHdCH2) and diamagnetic complexes 6 and 7. These
differences are similar to those reported for the 13C alkene
differences of the chelating (C5Me5)2Y[η1-CH2CH2C(CH3)2-
CHdCH2] complex, 11, and its free ligand 3,3-dimethyl-1,4-
pentadiene,10 Table 1. However, THF would be expected to be
a better donor and could displace the olefin. Consistent with
this, addition of THF to 1 and 3 causes shifts in the proton and
carbon resonances of the olefin in both complexes. Similar
shifting in the 1H and 13C NMR is seen when the THF solvate
is formed from complex 11. However, it would be expected
that the THF would remain solvated and THF adducts would
be isolated. This suggests that the tethered olefin is displaceable,
but it can protect the metal center from solvation upon
crystallization.
Comparison of the metrical data for 1-3 and 8 suggest that
the metal-olefin interactions in 1-3 are not strong. The Ln-
C(alkene) distances to the two olefins in 3 are significantly
longer than those to the single olefin in 8. Since the olefin in 8
was not perturbed significantly by the ytterbium, both ytterbium
complexes 3 and 8 represent systems of weak interaction. A
similar conclusion can be drawn for 1 and 2, since the metal-
olefin distances in 1, 2, and 3 are just as expected based on the
differences in radii of divalent ions.69
Since (C5Me5)2Sm can reduce dinitrogen,83 styrene,70 stil-
bene,70 and propene82 and it initiates polymerization of ethylene
presumably by a reductive route,21 reduction of the tethered
olefin was possible. However, the dark green color and NMR
spectra of 1 are consistent with an Sm(II) rather than an Sm(III)
product; that is, they give no evidence of reduction of the
tethered olefins. This is also supported by infrared spectros-
copy: complexes 1-3 display almost identical spectra, including
the terminal CdC stretch observed at 1629 cm-1 for each
complex.
The syntheses of 1 and 2 provided the first crystallographi-
cally characterized olefin complexes of samarium and europium.
Olefin complexes of lanthanide ions are rare, since these hard
ionic metals typically do not favor coordination of soft bases.
Metal vapor46,47 and FTICR48-50 studies have provided evidence
of interactions between olefins and lanthanide metals in the gas
phase, and in solution, an NMR study of (C5Me5)2Eu66 and
(81) Nolan, S. P.; Stern, D.; Marks, T. J. J. Am. Chem. Soc. 1989, 111, 7844.
(82) Evans, W. J.; Ulibarri, T. A.; Ziller, J. W. J. Am. Chem. Soc. 1990, 112,
2314.
(83) Evans, W. J.; Ulibarri, T. A.; Ziller, J. W. J. Am. Chem. Soc. 1988, 110,
6877.
9
J. AM. CHEM. SOC. VOL. 125, NO. 17, 2003 5211

A R T I C L E S
Evans et al.
The reactivity of 1 with CO2, ethylene, and AgBPh4 indicates
that it has chemical behavior similar to its C5Me5 analogue.
This is not unexpected, since 1 is structurally similar and the
olefins are not strongly interacting. Since the reactivities of 1
and (C5Me5)2Sm were similar, the AgBPh4 reaction was likely
to set up a situation in which there could be a competition for
the cationic metal site between the arene rings of the tetraphe-
nylborate and the tethered olefins.
One other point that bears discussion is the orientation of
the olefin. In 1-3 and 5, the terminal carbon is closer to the
metal than the internal carbon. This is not the case in the simple
potassium salt, [(C5Me4)Me2Si(CH2CHCH2)K(THF)]n,62 but
this is found in the cationic Zr(IV) complexes, [(C5H5)2Zr-
(OCMe2CH2CH2CHdCH2)]+ and [(S,S,R)-(EBI)Zr(OCMe2CH2-
CH2CHdCH2)]+ (EBI ) ethylene-1,2-bis(1-indenyl)), which
contain alkene ligands tethered via alkoxides.14 Jordan has
proposed two explanations for this similar orientation. One
explanation is that this orientation allows the positive charge
on the metal to be dispersed onto the internal alkene carbon,
thus giving rise to two resonance structures. The electrostatic
repulsion between the metal and buildup of partial charge on
the internal carbon results in an elongated interaction. This was
in agreement with the observed 13C data. A substantial shift (∆
) 12.1 ppm) of the internal alkene carbon peak is also observed
for 3. Another explanation involves overlap of the π-bonding
orbital on the terminal carbon with a Zr σ-acceptor orbital. A
similar explanation could pertain here except that the distances
are much longer and the orbital interactions are expected to be
much less for lanthanide systems.
The structure of the unsolvated cationic complex, {[(C5-
Me4)SiMe2(CH2CHdCH2)]2Sm}[BPh4], 5, indicates that, in the
solid state, coordination of the tethered olefins is favored over
the tetraphenylborate anion. This preference is somewhat surpris-
ing considering that the anionic [BPh4]- is known to coordinate
to cationic metal centers18,84and olefin coordination is expected
to be weak. In fact, in (C5Me5)2Sm(µ-Ph)2BPh2,18one of the
Sm-C(arene ring of BPh4) bonds, 2.825(3) Å, is shorter than
the shortest analogous bond in 5, which is 2.854(3) Å.
It is possible that the presence of the tethered olefin near the
metal rather than the [BPh4]- group is due to crystal packing
factors. Nevertheless, the structure of 5 demonstrates that there
is an environment in which an olefin is preferentially oriented
toward the metal compared to [BPh4]-. This may well be the
case at the active site of the best catalysts.
Conclusion
The [(C5Me4)Me2Si(CH2CHdCH2)]- ligand has proven again
to be useful in investigating metal-olefin interactions in a
metallocene environment. In this case, the use of the [(C5Me4)-
SiMe2(CH2CHdCH2)]- ligand with neutral and cationic lan-
thanide metallocenes has shown that tethered olefins can interact
preferentially with the metal center compared to [BPh4]- under
certain circumstances. If such a preference exists in some
catalytic olefin polymerization systems, this would provide the
optimum catalyst. These compounds also demonstrate that
lanthanide metallocene chemistry can be significantly affected
by the attachment of an alkene functional group to the
commonly used polyalkylcyclopentadienyl ligand. The tethered
olefin can make it easier to access metallocenes which are not
coordinated to solvents or counteranions and can allow olefin
complexes of lanthanides to be studied in solution and in the
solid state.
The structures of 1-3 and 5 allow the first comparison of
the interaction of an olefin with a neutral divalent lanthanide
complex versus a cationic trivalent lanthanide system. It could
be expected that the cationic trivalent system, which is more
electrophilic, would lead to tighter binding. On the other hand,
the neutral divalent system is a softer metal which may favor
coordination of the soft olefin ligand. The comparison will be
made between 5 and 2, since they have indistinguishable CdC
distances in the tethered olefin. Since eight-coordinate Sm(III)
is 0.171 Å smaller than eight-coordinate Eu(II) according to
Shannon radii,69 the distances equivalent to the 3.004(3) and
3.089(3) Å Eu(II)-C terminal carbon distances and 3.243(3) and
3.293(4) Å internal carbon distances in 2 would be expected to
be 2.837-2.918 Å (terminal) and 3.072-3.122 Å (internal) in
5 if the binding were similar. The analogous terminal carbon
distances in 5, 2.854(3) and 2.878(3) Å, are in this range.
However, the 3.166(3) and 3.262(3) Å internal carbon distances
are both longer than these extrapolated values. Hence, in terms
of the closest interaction of the olefin with metals, that is, the
terminal carbon, the divalent and trivalent systems appear to
be similar. This might be expected for ionic systems in which
there was no significant back-bonding: the distances are
equivalent when the size of the metal ion is considered. The
importance of the longer internal carbon metal distances in the
trivalent 5 is not clear.
Acknowledgment. For support of this research, we thank the
Division of Chemical Sciences, Geosciences and Biosciences,
Office of Basic Energy Sciences, Office of Sciences, U.S.
Department of Energy.
Supporting Information Available: X-ray diffraction data,
atomic coordinates, thermal parameters, and complete bond
distances and angles; listing of observed and calculated structure
factor amplitudes for compounds 1, 2, 3, 4, and 5 (PDF). This
material is available free of charge via the Internet at
http://pubs.acs.org.
(84) Evans, W. J.; Nyce, G. W.; Forrestal, K. J.; Ziller, J. W. Organometallics
2002, 21, 1050.
JA020957X
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5212 J. AM. CHEM. SOC. VOL. 125, NO. 17, 2003