Synthesis, experimental/theoretical characterization, and thermolysis chemistry of CpBe(SiMe3), a molecule containing an unprecedented beryllium-silicon bond

Article abstract of DOI:10.1021/om0201720

The synthesis, characterization, and thermal decomposition of CpBe(SiMe₃) are presented as part of an exploratory investigation designed to obtain more effective chemical vapor deposition precursors of metallic beryllium. The title compound provides the first example of a direct bond between beryllium and a non-carbenoid group 14 element. The base-free reaction of LiSiMe₃ with CpBeCl in pentane affords the air-sensitive, volatile solid CpBe(SiMe₃) (ca. 70% yield based on CpBeCl), which was characterized by single-crystal CCD X-ray diffraction, multinuclear NMR, and mass spectrometric studies, and theoretically by DFT/NBO analysis. The solid-state molecular geometry of CpBe(SiMe₃) ideally conforms to C_3v symmetry (under assumed cylindrical symmetry for the C₅H₅ ring); the Be-Si bond length of 2.185(2) A is markedly longer than the sum of covalent radii (2.01 A). The DFT-optimized molecular geometry closely conforms to that determined crystallographically. Total fragment charges (based upon atomic charge NBO calculations) of -0.79 e for C₅H₅, +1.26 e for Be, +0.81 e for Si, and -1.28 e for the three Me groups constitute a polarity pattern consistent with the Be-Cp bonding interaction being mainly ionic and with the Be-Si bonding pair being polarized toward the more electronegative SiMe₃ fragment. Beryllium-9 and ²⁹Si NMR spectra exhibit a large J(Be-Si) coupling constant of 51 Hz; the ⁹Be chemical shift of δ -27.70 ppm, the highest field value recorded to date, is in accordance with the calculated bond-polarity pattern, as well as a bond to Si. Mass spectra (EI) exhibited peaks for the molecular ion and its isotopomers. Thermal decomposition of CpBe(SiMe₃) gives rise to trimethylsilane, CpBeMe, and CpBe(SiMe₂SiMe₃) as the major products, as determined by multinuclear NMR. The latter species is likewise formed by the reaction of CpBeCl with LiSiMe₂SiMe₃.

Full text of DOI:10.1021/om0201720

Organometallics 2003, 22, 407-413
407
Syn th esis, Exp er im en ta l/Th eor etica l Ch a r a cter iza tion ,
a n d Th er m olysis Ch em istr y of Cp Be(SiMe ), a Molecu le
3
Con ta in in g a n Un p r eced en ted Ber ylliu m -Silicon Bon d
Dovas A. Saulys* and Douglas R. Powell†
Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706
Received February 28, 2002
3
The synthesis, characterization, and thermal decomposition of CpBe(SiMe ) are presented
as part of an exploratory investigation designed to obtain more effective chemical vapor
deposition precursors of metallic beryllium. The title compound provides the first example
of a direct bond between beryllium and a non-carbenoid group 14 element. The base-free
reaction of LiSiMe
SiMe ) (ca. 70% yield based on CpBeCl), which was characterized by single-crystal CCD
X-ray diffraction, multinuclear NMR, and mass spectrometric studies, and theoretically by
DFT/NBO analysis. The solid-state molecular geometry of CpBe(SiMe ) ideally conforms to
3v symmetry (under assumed cylindrical symmetry for the C ring); the Be-Si bond length
3
with CpBeCl in pentane affords the air-sensitive, volatile solid CpBe-
(
3
3
C
5 5
H
of 2.185(2) Å is markedly longer than the sum of covalent radii (2.01 Å). The DFT-optimized
molecular geometry closely conforms to that determined crystallographically. Total fragment
charges (based upon atomic charge NBO calculations) of -0.79 e for C
0.81 e for Si, and -1.28 e for the three Me groups constitute a polarity pattern consistent
with the Be-Cp bonding interaction being mainly ionic and with the Be-Si bonding pair
5 5
H , +1.26 e for Be,
+
2
9
being polarized toward the more electronegative SiMe
spectra exhibit a large J (Be-Si) coupling constant of 51 Hz; the Be chemical shift of δ
27.70 ppm, the highest field value recorded to date, is in accordance with the calculated
bond-polarity pattern, as well as a bond to Si. Mass spectra (EI) exhibited peaks for the
molecular ion and its isotopomers. Thermal decomposition of CpBe(SiMe ) gives rise to
trimethylsilane, CpBeMe, and CpBe(SiMe SiMe ) as the major products, as determined by
multinuclear NMR. The latter species is likewise formed by the reaction of CpBeCl with
LiSiMe SiMe
3
fragment. Beryllium-9 and Si NMR
9
-
3
2
3
2
3
.
In tr od u ction
cium-silicon bonds have been inferred from the deriva-
tization of the products of metal-atom reactions of Ca
Prior to the chemistry reported here, beryllium-
silicon chemistry was virtually nonexistent. In fact, fully
characterized examples of bonds between the group 2
elements and silicon are known only for magnesium, for
which three (Me3Si)2Mg‚Base adducts (viz., Base )
3
with chlorosilanes. In the case of beryllium, previous
experimental work has been limited to the beryllium
doping of silicon by means of the high-temperature
evaporation and subsequent vapor deposition of Be
metal onto Si wafers; the resultant structures were
dimethoxyethane,1
a,b
tetramethylenediamine, and
1c
probed by means of absorption spectroscopy and electri-
1
d
tetramethyldiaminopropane ) have been described.
Characterization of other group 2 element-silicon link-
ages has been indirect. Bis(triphenylsilyl)barium was
reportedly isolated from a liquid ammonia solution of
Ba and Si2Ph6 and characterized by solvolysis reactions;
4-6
cal measurements.
The energies and structures of
7
beryllium doped into bulk silicon were also calculated.
8,9
10
In addition, ab initio and Hartree-Fock calculations
performed on hypothetical molecules containing cova-
lent Be-Si linkages (e.g., HBe(SiH3) and HBeSi(dO)H)
2
however, experimental details were not provided. Cal-
(
3) Mochida, K.; Manishi, M. Chem. Lett. 1984, 1077.
(4) Robertson, J . B.; Franks, R. K. Solid State Commun. 1968, 6,
825.
(5) Kleverman, M.; Grimmeiss, H. G. Semicond. Sci. Technol. 1986,
1, 45.
*
Corresponding author. Current address: Materials Research
Science and Engineering Center, University of Wisconsin, 1415
Engineering Dr., Madison, WI 53706. E-mail: dovas@amps.che.wisc.edu.
Tel: (608) 263-0346. Fax: (608) 265-3782.
†
Department of Chemistry, University of Kansas, Lawrence, KS
(6) Crouch, R. K.; Robertson, J . B.; Gilmer, T. E., J r. Phy. Rev. B
6
6045-7582.
1) B ) dimethoxyethane: (a) Rosch, L. Angew. Chem., Int. Ed. Engl.
977, 16, 247. (b) Claggett, A. R.; Ilsley, W. H.; Anderson, T. J .; Glick,
1972, 5, 3111.
(
(7) Tarnow, E.; Zhang, S. B.; Chang, K. J .; Chadi, D. J . Mater. Res.
Soc. Symp. Proc. 1991, 209, 119.
1
M. D.; Oliver, J . P. J . Am. Soc. 1977, 99, 1797. B ) tetramethyleth-
ylenediamine: (c) Goebel, D. W., J r.; Hencher, J . L.; Oliver, J . P.
Organometallics 1983, 2, 746. B ) tetramethyldiaminopropane: (d)
Rosch, L.; Pickardt, J .; Imme, G.; Borner, U. Z. Naturforsch., Teil B
(8) Luke, B. T.; Pople, J . A.; Krogh-J espersen, M. B.; Apeloig, Y.;
Chandrasekhar, J .; Schleyer, P. v. R. J . Am. Chem. Soc. 1986, 108 (8),
260.
(9) Coolidge, M. B.; Borden, W. T. J . Am. Chem. Soc. 1988, 110,
1
986, 41, 1523.
2) Wiberg, E.; Stecher, O.; Andrashek, H. J .; Kreuzbichler, L.;
Staude, E. Angew. Chem., Int. Ed. 1963, 2, 507.
2299.
(
(10) J ennings, J . L.; Wright, D. W. Main Group Met. Chem. 1994,
17, 387.
1
0.1021/om0201720 CCC: $25.00 © 2003 American Chemical Society
Publication on Web 12/31/2002

4
08 Organometallics, Vol. 22, No. 3, 2003
Saulys and Powell
Ta ble 1. Selected Bon d Dista n ces a n d An gles for
Cp Be(SiMe
3
) fr om X-r a y Cr ysta llogr a p h ic Stu d y
A. Bond Distances (Å)
Si-C(1)
1.891(2)
2.185(2)
1.894(13)
1.909(14)
1.393(7)
1.398(10)
1.395(5)
Si-C(2)
1.892(1)
1.880(5)
1.909(4)
1.927(7)
1.412(11)
1.391(7)
1.487
Si-Be
Be-C(5)
Be-C(6)
Be-C(7)
C(3)-C(7)
C(5)-C(6) a
Be-CENT
Be-C(4)
Be-C(3)
C(3)-C(4)
C(4)-C(5)
C(6)-C(7)
B. Bond Angles (deg)
C(1)-Si-C(2)
C(1)-Si-Be
C(5)-Be-Si
C(6)-Be-Si
C(7)-Be-Si
C(3)-C(4)-C(5)
C(5)-C(6)-C(7)
105.52(6)
114.52(8)
144.0(2)
139.5(2)
137.6(2)
106.6(10)
108.1(4)
C(2)-Si-C(2)#1
105.51(9)
112.51(5)
144.1(3)
141.1(4)
109.1(11)
109.3(6)
106.9(7)
C(2)-Si-Be
C(4)-Be-Si
C(3)-Be-Si
C(4)-C(3)-C(7)
C(6)-C(5)-C(4)
C(6)-C(7)-C(3)
F igu r e 1. ORTEP drawing of CpBe(SiMe
3
), with ellipsoids
shown at the 50% level.
a
CENT ) centroid of the five-membered ring.
8
have resulted in predictions of molecular bond lengths,
8
8,9
bond angles, bond dissociation energies, and NMR
average value of 1.398(8) Å for the five C-C distances
Table 1) comprising the cyclopentadienyl ring is virtu-
ally identical to that of 1.401 Å found for the η -bonded
chemical shift derivatives.10
(
The research reported herein is a result of our interest
in designing volatile, base-free group 2 compounds as
dopants for chemical vapor deposition. In this context,
the thermal stability and decomposition pathways of
compounds containing beryllium-silicon bonds are of
prime importance. This research was also motivated by
the fact that there had been no previous report of any
well-defined, discrete compounds containing a bond
between beryllium and a non-carbenoid group 14 ele-
ment.
5
Cp ring in the well-determined crystal structure of
11
BeCp2. The (essentially) perpendicular distance from
Be to the Cp ring centroid of 1.487 Å is also analogous
11
12
to those for BeCp2 (1.508 Å), CpBe(B5H8) (1.45 Å),
13
and CpBeCl (1.451 Å). The two independent Si-
C(methyl) distances of 1.891(2) and 1.892(1) Å are
14
representative of the Si-C(Me) bond. As is typical for
14
bonds between silicon and other main-group metals,
the Si-Be distance (2.185(2) Å) is significantly longer
than the sum of covalent radii (2.01 Å).
The ligand coordination about the Si atom is trigonal
pyramidal. The three Be-Si-C(methyl) bond angles (av
13.2°) exceed the ideal tetrahedral angle of 109.5°,
while the three C(methyl)-Si-C(methyl) bond angles
av 105.5°) are correspondingly lower. As the molecular
geometry offers no evidence for steric compression of the
methyl groups, the deviations of the angles around Si
from ideal tetrahedral values are consistent with a
moderate polarization of the Be-Si bonding pair toward
Si. Additional evidence regarding the polarity of the
beryllium-silicon bond is provided by the 29Si NMR
chemical shift data and calculational results (vide infra).
Resu lts a n d Discu ssion
Cp Be(SiMe3). (a ) Syn th esis a n d P h ysica l P r op -
er ties. The reaction of high-purity LiSiMe3 with CpBeCl
yields the volatile, base-free species CpBe(SiMe3) (eq 1),
the first fully characterized example of a beryllium-
silicon bond. It is soluble in hydrocarbons and reacts
spontaneously with aerial oxygen.
1
(
(
c) Th eor etica l An a lysis a n d Resu ltin g Im p lica -
(
b) Molecu la r Str u ctu r e fr om X-r a y Diffr a ction
15
tion s. Density functional theory (DFT) calculations,
performed at the B3LYP/6-31+G* level with the Gauss-
ian-98 package, were utilized to obtain the optimal
geometry of the CpBe(SiMe3) molecule. The calculated
bond distances and bond angles essentially reproduce
An alysis. Cyclopentadienyl(trimethylsilyl)beryllium crys-
tallizes under vacuum at ambient temperature as clear,
colorless prisms that appear to be stable indefinitely
under these conditions.
16
The molecular structure of CpBe(SiMe3) is shown in
Figure 1, and selected distances and bond angles are
shown in Table 1. Two molecules constitute the unit cell
of symmetry P21/m, such that one-half molecule is
crystallographically independent. Each molecule is bi-
sected by a mirror plane through Be, Si, and C(1), with
the entire cyclopentadienyl ligand disordered over two
equivalent sites. The equivalent Be-C(Cp) distances
(13) Goddard, R.; Akhtar, J .; Starowieyski, K. B. J . Organomet.
Chem. 1985, 282, 149.
(14) Sheldrick, W. S. In The Chemistry of Organic Silicon Com-
pounds; Patai, S., Rappoport, Z., Eds.; Wiley: Chichester, 1989; Part
1, Chapter 3, p 246.
(
15) Saulys, D. A.; Weinhold, F. Unpublished results.
(16) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J . R.; Zakrzewski, V. G.; Montgomery, J . A.,
J r.; Stratmann, R. E.; Burant, J . C.; Dapprich, S.; Millam, J . M.;
Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J .;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo,
C.; Clifford, S.; Ochterski, J .; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J . B.; Cioslowski, J .; Ortiz, J . V.; Baboul, A. G.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.;
Martin, R. L.; Fox, D. J .; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; J ohnson, B.; Chen,
W.; Wong, M. W.; Andres, J . L.; Gonzalez, C.; Head-Gordon, M.;
Replogle, E. S.; Pople, J . A. Gausian 98, Revision A.9; Gaussian, Inc.:
Pittsburgh, PA, 1998.
(
range 1.880(5)-1.927(7) Å, mean 1.904 Å), which are
similar to the crystallographically determined Be-C(Cp)
values for other CpBeX derivatives,1
1-13
establish that
Be is equally coordinated to the five ring carbons. The
(
11) Nugent, K. W.; Beattie, J . K.; Hambley, T. W.; Snow, M. R.
Aust. J . Chem. 1984, 37, 1601.
12) Gaines, D. F.; Walsh, J . L.; Morris, J . H.; Hillenbrand, D. F.
Inorg. Chem. 1978, 17, 1516.
(

CpBe(SiMe
3
), an Unprecedented Be-Si Bond
Organometallics, Vol. 22, No. 3, 2003 409
Ta ble 2. Com p a r ison betw een DF T-Op tim ized a n d
X-r a y-Deter m in ed Mea n Bon d Dista n ces a n d
3
An gles for Cp Be(SiMe ) u n d er P seu d o-C3v
a
Sym m etr y
distances (Å)/
angles (deg)
F igu r e 2. (a) Electron-pushing diagram denoting the NBO
Nb DFT-opt
X-ray detmn
difference
σ
Be-Si f σ*Si-C(Me) geminal donor-acceptor interaction. (b)
One of the three resonance structures of CpBe(SiMe
the ionic bonding limit.
3
) at
Si-C(Me)
Si-Be
3
1
5
1
5
3
3
15
1.917
2.197
1.928
1.501
1.422
105.9
112.8
111.3
1.892
2.185
1.904
1.487
1.398
105.5
113.2
0.025
0.012
0.024
0.014
0.024
0.4
Be-C(Cp)
Be-CENT
c
2
px (0.072 e), 2py (0.036 e), and 2pz (0.036 e) orbitals
C(Cp)-C(Cp)
C(Me)-Si-C(Me)
C(Me)-Si-Be
Si-C(Me)-H
(the Be-Si bond lies on the x axis).
0.4
The calculated natural atomic charge distribution in
CpBe(SiMe3) is unusual in that it includes sizable like
charges on adjacent Be (Q ) +1.258 e) and Si (Q )
+0.809 e) atoms, while the periphery of the molecule,
consisting of the Me (Q ) -0.43 e) and Cp groups, is
negatively charged. This polarity pattern is interesting
in several respects. The juxtaposition of positive charges
on Be and Si would be expected to facilitate homolysis
of the Be-Si bond, a reaction that is indeed observed,
although to a minor degree. This polarity pattern is also
a
Cp ligand is assumed to be cylindrically symmetric. b
N
denotes the number of symmetry-equivalent distances and angles
under C3v symmetry. CENT ) centroid of the five-membered
ring.
c
Ta ble 3. Na tu r a l Ch a r ges (e) in Cp Be(SiMe
Obta in ed fr om NBO An a lysis
3
)
Be
+1.258
-1.161
-0.432
-0.794
Si
H (Me)
H (Cp)
+0.809
+0.245
+0.273
C (Me)
C (Cp)
C5H5
2
1
conducive to geminal hyperconjugation (Figure 2a).
While vicinal donor-acceptor interactions predominate
in molecules comprised of first-row elements, the pres-
ence of second-row elements often enables geminal
those determined crystallographically; the values of
selected bond angles and distances are provided in Table
2
1
hyperconjugation.
The calculated pattern of natural atomic charges and
the geminal hyperconjugation centered on Si provides
a rationale for the proposed role of dimethysilylene in
the thermal decomposition mechanism of CpBe(SiMe3).
The formal transfer of the entire two-electron bonding
pair from σBe-Si to σ*Si-C(Me) of one Me group is depicted
in the resonance structure shown in Figure 2b.21 This
formulation is consistent with the presence of di-
methysilylene intermediates in the thermal decomposi-
tion of CpBe(SiMe3), as discussed below.
2
. Differences between corresponding calculated and
crystallographic values are in all cases less than 2% of
the latter values.
The natural bond orbital (NBO) technique, developed
by Weinhold and co-workers,17,18 was used to describe
the atomic charge distribution, geometry, and bonding
in CpBe(SiMe3). A key insight of NBO theory has been
the recognition of the potential significance of donor-
acceptor interactions (hyperconjugation) between local-
ized valence bonds (σ, π) and unoccupied antibonds
1
9
(d ) Ma ss Sp ectr om etr ic An a lysis. The mass spec-
trum of CpBe(SiMe3) is dominated by peaks due to the
Cp and SiMe3 ligands and fragments thereof. The major
Be-containing peaks are those due to the molecular ion
(σ*,π*). The energy lowering provided by these delo-
calizations can contribute to the driving force for chemi-
cal reactions, as is described in the calculational analy-
sis below.
+
and its isotopomers. In particular, the [CpBe] fragment
Natural atomic charges are displayed in Table 3.
Several important features of the NBO description merit
comment. The NBO method does not describe a covalent
bond between the Cp ring and the Be(SiMe3) moiety.
Instead, the analysis provides strong evidence that the
Cp ring is nearly anionic (Q ) -0.794 e) and interacts
peak is of minor intensity (8%), while that due to
+
+
[
SiMe3] is 77% as intense as the base peak, [HSiMe2] .
This is in sharp contrast to the fragmentation behavior
exhibited by the organic derivatives CpBeR. In an in-
depth electron ionization (EI) mass spectral study of
2
2
CpBeR compounds (R ) H, Me, Et, n-Bu, t-Bu), Bartke
with the Be atom via a number of delocalization
+
interactions20 that channel small amounts of electron
found that the [CpBe] fragment constitutes the base
peak in all spectra run at 70 eV, while peaks due to the
intact organic ligand, R , are minor or absent. While
density from the Cp ring π bonds to the Be-Si antibond
and the Be 2p atomic orbitals. The Be valence electrons
are localized primarily in the Be 2s orbital (0.59 e), with
much smaller amounts of electron density found in the
+
this difference in relative peak intensities is consistent
with the lower ionization potential of the SiMe3 radical
2
3
(
6.32 eV) relative to that of the organic fragments (Me,
2
4
(
17) Weinhold, F. In Encyclopedia of Computational Chemistry;
Wiley: New York, 1998; Vol. 3, p 1792.
18) Glendening, E. D.; Badenhoop, J . K.; Reed, A. E.; Carpenter,
J . E.; Weinhold, F. NBO Version 4.0 in Gaussian 98; Theoretical
Chemistry Institute, University of Wisconsin: Madison, WI, 1996.
9.84; Et, 8.12; t-Bu, 6.70), the differences in ionization
potentials are probably not large enough to completely
account for the relative differences in peak intensities.
The decreased stability of the CpBe unit in CpBe(SiMe3)
is likely a contributing factor. The larger ionic character
(
1
6
(19) The second-order energy lowering that arises from the delo-
calization of electron density from a doubly occupied σ bond, σAB, into
an empty antibond σ*CD can be approximated by means of a stan-
(
2)
dard Rayleigh-Schrodinger perturbation treatment: ∆Ε σfσ* )
(21) Glendening, E. D. Ph.D. Thesis, University of Wisconsin-
Madison, Madison, WI, Chapter 6.
(22) Bartke, T. C. Ph.D. Dissertation, University of Wyoming,
Laramie, Wyoming, 1975.
(23) Shin, S. K.; Corderman, R. R.; Beauchamp, J . L. Int. J . Mass
Spec. Ion Processes 1990, 101, 257.
(24) Shin, S. K.; Beauchamp, J . L. J . Am. Chem. Soc. 1989, 111,
900.
2
-
2〈σAB|F|σ*CD〉 /(ꢀ
element that describes the orbital interaction, and ꢀ
σ* ) 〈σ*CD|F|σ*CD〉 are the orbital energies. (See ref 17, p 1799.)
σ
- ꢀσ*), where 〈σAB|F|σ*CD〉 is the NBO Fock matrix
σ
) 〈σAB|F|σAB〉 and
ꢀ
(2)
(
20) Typical calculated strengths, ∆Ε , of relevant delocalizing
1
5
interactions range from -4 to -9 kcal/mol. The strength of the
geminal delocalizations centered on Si (discussed below), σBe-Si
σ*Si-C(Me), is -4.45 kcal/mol.
f

4
10 Organometallics, Vol. 22, No. 3, 2003
Ta ble 4. Ch em ica l Sh ift Da ta (δ) for Cp Be-Si Sp eciesa
Saulys and Powell
9
δ 29Si
δ 13
C
1Hc
δ Be
compound
δ
∆ω1/2b
SiMe3
SiMe2
Cp
SiMe2
SiMe3
Cp
SiMe2
SiMe3
CpBe(SiMe3)
CpBe(SiMe2SiMe3)
-27.70
-27.20
8.0
-27.31 q
-14.67
103.10
103.33
3.51
-1.14
5.54
5.62
0.21
0.17
-61.90 q
-3.62
0.205
a
q ) 1:1:1:1 quartet. b Peak width at half-height, in hertz. c Relative integration intensities are consistent with the molecular
formulations.
Ta ble 5. Cou p lin g Con sta n tsa (J ) for Cp Be-Si Sp eciesb
1J (Be-Si)
1J (Si-C)
2J (Si-H)
1J (C-H)
compound
Be-SiMen
Be-SiMen
Cp
Me
CpBe(SiMe3)
CpBe(SiMe2SiMe3)
51.4 q
48.3 q
50.2 d
36.0
41.5
5.4
4.28
177.7
c
117.8
c
a
In hertz. b q ) 1:1:1:1 quartet, d ) doublet. c Resonance not observed.
of the Be-Cp bond may, in turn, be attributed to the
decreased electronegativity of the Be-attached trimeth-
ylsilyl group relative to that of the Be-attached alkyl
groups. Proton NMR data (vide infra) support this
interpretation.
(
e) NMR Sp ectr a l An a lysis. The NMR chemical
9
shift range of Be for previously known CpBeX species
is from -18.5 to -22.1 ppm;25 the title compound (X )
SiMe3) doubles this range and extends it in the high-
field direction. To our knowledge, this 9Be chemical
shift, -27.70 ppm, is the highest field value recorded
to date. While high-field chemical shifts of Be nuclei in
cyclopentadienide derivatives are ascribed to ring-
current effects, this extension can be qualitatively
attributed to the electropositivity of silicon, by virtue
of a simple inductive effect and/or the subsequent
3
decrease in the [1/r ] factor of the paramagnetic shield-
ing term for the Be nucleus. The upfield shift, in part,
is also consistent with a higher electron density at the
Cp ring, resulting in a stronger ring-current effect. The
chemical shifts of the Cp ring protons are also of interest
in this regard. Proton chemical shifts of cyclic aromatic
2
6
compounds in general, and of metal cyclopentadienyls
2
7
F igu r e 3. 29Si NMR spectrum of CpBe(SiMe ) illustrating
the 1:1:1:1 quartet with J Be-Si ) 51.4 Hz.
in particular, have been shown to correlate roughly
with the π electron density in the ring: a higher Cp
electron density (i.e., a more ionic metal-Cp linkage)
usually results in shifts to lower frequency. In CpBeX
species, the Cp proton chemical shifts roughly track the
electronegativity of the nonaromatic ligand (X, chemical
3
The large J Be-Si coupling constant between beryllium
3
2
and silicon, 50.15 Hz (Table 5 and Figure 3), charac-
terizes several features of this linkage. A significant
degree of covalency, in accordance with a small elec-
tronegativity difference, ∆ø(Si-Be) ) 0.33, as well as a
high degree of s-orbital participation in the Be-Si bond
are indicated. Consistent with the latter indication, the
2
8
shift in ppm): SiMe3, 5.54; Me, 5.70; Cl, 5.75. The
resulting implication is that the relatively electroposi-
tive trimethylsilyl ligand gives rise to a somewhat more
ionic Be-Cp linkage than that found in organic or
halide derivatives, CpBeX. This hypothesis is consistent
with the mass spectral results discussed above.
1
value of J Si-C observed (Table 5) is in the low end of
(
25) Gaines, D. F.; Coleson, K. M.; Hillenbrand, D. F. J . Magn.
Silicon chemical shifts are thought to be dominated
Reson. 1981, 44, 84-88.
(26) Gunther, H. NMR Spectroscopy; J ohn Wiley and Sons: New
York, 1980; p 68.
(27) (a) Maddox, M. L.; Stafford, S. L.; Kaesz, H. D. Adv. Organomet.
Chem. 1965, 3, 38. (b) Fraenkel, G.; Carter, R. E.; McLachlan, A.;
Richards, J . H. J . Am. Chem. Soc. 1960, 82, 5846.
2
9
by the paramagnetic shielding term. Empirically,
however, it is commonly found that among similar
compounds, for example within the series XSiMe3 (e.g.,
X ) Li, SiMe3, O, Cl), shielding of the Si nucleus
(28) Samples run in cyclohexane as opposed to benzene exhibit a
3
0
decreases with increasing electronegativity of X. That
is, shifts to lower field are associated with a decrease
much greater chemical shift dispersion and thus demonstrate this
effect more clearly: ref 22.
(
29) (a) Williams, E. A.; Cargioli, J . D. Annu. Rep. NMR Spectrosc.
979, 5, 221. (b)Williams, E. A. Annu. Rep. NMR Spectrosc. 1983, 15,
235.
(30) Harris, R. K.; Kimber, B. J . J Magn. Reson. 1975, 17, 174.
31) Al-Hassan, M. I.; Al-Najjar, I. M.; Al-Oraify, I. M. Magn. Reson.
Chem. 1989, 27, 1112.
32) For purposes of comparison, note the reduced coupling constants
3
1
in electron density at the Si atom, and vice versa. By
this criterion, the electron density at Si in CpBe(SiMe3)
1
2
9
(
Si ) -27.3 ppm) is intermediate to that found in
(
LiSiMe3 (-38.0 ppm) versus those observed in trimeth-
ylsilyl groups bound to a moiety of equivalent (Si2Me6,
(
2
0
-2
-3
K (10 NA
m
) and J (Hz) for the following species: CpBeSiMe ,
3
-
19.7 ppm) or higher electronegativity (e.g., [Me3SiO]4-
Si, 7.6 ppm; or Me3SiCl, 29.4 ppm ).
29
9
13 9
K( Si- Be) ) 15.3, J ) 51.4; CpBeMe, K( C- Be) ) -7.4, J ) 31.3;
3
0
30
6
29
44a
3
LiSiMe , K( Li- Si) ) -6.0, J ) 21.1.

CpBe(SiMe
3
), an Unprecedented Be-Si Bond
Organometallics, Vol. 22, No. 3, 2003 411
Sch em e 1
the range for silicon-carbon couplings,29 as would be
predicted by Bent’s rule,33 which states that electro-
negative substituents (viz., Me groups) prefer hybrid
orbitals with less valence s AO character.
silylene acceptors are needed to precisely identify the
nature of the intermediate(s).
The Me SiH observed is most likely the result of
3
homolytic cleavage of the Be-Si bond to generate the
•
Cp Be(SiMe2SiMe3). An NMR tube-reaction mixture
of CpBeCl and LiSiMe3 that was briefly heated yielded
CpBe(SiMe3), CpBeMe, and a species identified as
Me Si radical, followed by hydrogen abstraction. In this
3
context, the fact that little Si Me H is observed could
2
5
be taken as an indication that the Be-SiMe SiMe3
2
9
CpBe(SiMe2SiMe3): the high-field Be chemical shift
linkage is more thermally robust (for reasons noted
(
Table 4) indicates a species bound to both a Cp ring
below) than Be-SiMe . The fate of the Be-containing
3
2
9
and silicon; in the Si NMR spectrum, the 1:1:1:1
splitting substantiates the bonding to Be (I ) 3/2), while
the high-field chemical shift is characteristic of a
homolysis product is undetermined: it is apparently not
possible to definitively characterize CpBeH by NMR.22
Th er m a l Decom p osition of LiSiMe . Upon stand-
3
3
4
secondary silicon in permethylated silicon derivatives.
ing at room temperature for long periods, a sealed-tube
1
13
The reactive species methyllithium and pentamethyl-
disilyllithium are indicated as thermal decomposition
products of LiSiMe3 (Scheme 1).
3 6 6
solution of pure LiSiMe in C D develops H, C, and
2
9
Si NMR peaks due to LiSiMe SiMe . Heating at 65
2
3
°C accelerates this transformation. Formation of LiSiMe2-
SiMe from LiSiMe with increasing temperature im-
As was the case for CpBe(SiMe3) in relation to
3
3
X(SiMe3) species, the 29Si chemical shifts for CpBe-
plies its higher thermal stability; apparently a tri-
methylsilyl group more effectively stabilizes the partial
negative charge on the Li-bearing Si than does a methyl
group. Derivatization experiments (vide supra) indicate
MeLi as a decomposition product and also confirm the
formation of LiSiMe SiMe . The formation of LiSiMe -
(SiMe2SiMe3) conform to patterns exhibited by other
2
9a
XSiMe2SiMe3 compounds.
The shielding of the Si
bound to X increases with decreasing electronegativity
of X (X, δ ppm): Cl, +22.8;2 SiMe3SiMe2, -44.7;
9a
29b
CpBe, -61.9; Li -79.3. The trimethylsilyl resonances
of X(SiMe2SiMe3) compounds have been observed to
exhibit the opposite relation with respect to the elec-
tronegativity of X, along with a significantly decreased
chemical-shift dispersion. The resonance for CpBe-
2
3
2
SiMe from Si Me in basic solution has been ascribed
3
2
6
3
6
to the cleavage of a silicon-carbon bond with LiSiMe
3
3
7
or MeLi. As none of the required byproducts (e.g.,
SiMe , C H ) of nucleophilic attack on Si Me is ob-
4
2
6
2
6
(SiMe2SiMe3) likewise fits this pattern (X, δ ppm): Cl,
served here, silylene intermediates, analogous to those
18.2;2 SiMe3SiMe2, -15.2; CpBe, -14.7; Li, -12.5.
9a
29b
-
invoked above in the decomposition of CpBe(SiMe ),
3
2
,38
Heating CpBe(SiMe3) for long periods at 217-235 °C
may be operative in this case (eq 2):
likewise generates CpBeMe and CpBe(SiMe2SiMe3),
along with Me3SiH. These thermolysis products are
compatible with at least two concurrent decomposition
pathways. The generation of CpBeMe and CpBe(SiMe2-
SiMe3) is consistent with the presence of dimethylsi-
lylene intermediates, while the formation of Me3SiH
implies a homolytic process. Whether “free” silylenes or
metal-complexed “silylenoids” are involved in the former
pathway is unclear. In this respect, the presence or
absence of particular side-products is instructive. Di-
methylsilylene, :SiMe2, readily inserts into the Si-
hydrogen bond of Me3SiH.35 Despite the continual
Although the mechanistic aspects of this reaction are
still under investigation, the bridge-bonded transition
state depicted in reaction 2 can account for the observed
products.
presence of Me3SiH in the thermolysis reaction mixture,
however, only minute amounts of the anticipated inser-
tion product, Me3SiMe2SiH, are observed. Whether this
indicates the absence of free silylene or is a testament
to the relative silylene acceptor capabilities of Be-Si
bonds is as yet unclear. (To our knowledge, the silylene
insertion behavior of main-group metal-silicon bonds
has not been systematically studied.) Kinetic studies as
well as trapping experiments utilizing well-defined
Exp er im en ta l Section
CAUTIONARY NOTE: Beryllium and its compounds are
extremely toxic. Finely divided metal, the vapor of its com-
pounds, and BeO (from aerial oxidation of Be compounds or
(
36) Hudrlik, P. F.; Waugh, M. A.; Hudrlik, A. M. J . Organomet.
(33) Bent, H. A. Chem. Rev. 1961, 61, 275.
Chem. 1984, 271, 69.
(
34) Williams, E. A. NMR Spectroscopy of Organosilicon Compounds.
(37) Krohn, K.; Khanbabaee, K. Angew. Chem., Int. Ed. Engl. 1994,
33 (1), 99.
In The Chemistry of Organic Silicon Compounds; Patai, S., Rappoport,
Z., Eds.; Wiley: New York, 1989; Chapter 8.
2
(38) L. Rosch has implicated Me Si: species, polysilanes, and Me-
Al bonds in the decomposition of Al(SiMe ) : Rosch, L. Angew. Chem.,
3 3
(35) Nefedov, O. M.; Skell, P. S. Dokl. Akad. Nauk. SSSR 1981, 259,
3
77
Int. Ed. Engl. 1977, 16, 7, 480.

4
12 Organometallics, Vol. 22, No. 3, 2003
Saulys and Powell
ignition of the metal) are all extremely toxic to the lungs.39
Physical exposure of any type, e.g., skin contact or inhalation,
is to be rigorously avoided. Bis(trimethylsilyl)mercury is also
hazardous, due both to its volatility and the facile formation
of elemental Hg upon exposure to air. Strict laboratory hygiene
is essential in dealing with these materials.40
Gen er a l Con sid er a tion s. All manipulations were carried
out in the absence of air and moisture by use of a standard
glass high-vacuum line or a nitrogen-filled glovebox. Five
millimeter NMR tubes (Wilmad) were either flamed with a
hand torch while under high vacuum or treated with liquid
tube was maintained at room temperature and monitored by
multinuclear NMR. After approximately 5 months, the initially
clear light green solution contained light and dark colored
solids; 59% of the integrated 1H NMR intensity was due to
4
4b
LiSiMe and 32% to LiSiMe SiMe : δ ppm (literature values)
3
2
3
1
13
H 0.28, (0.33), 6H, 0.19, (0.22), 9H; C -0.77 (-0.56), -2.64
(-2.51); 29Si -12.5 (-12.4), -79.3 (-79.6). Heating the tube
in an oil bath at 55 °C for 20 h produced no major change in
1
the H spectrum; after further heating for an additional 115
h at 65 °C, approximately equimolar amounts of LiSiMe
LiSiMe SiMe
peak intensity) were detected. Only minor resonances due to
hexamethyldisilane and no resonances indicative of methane,
ethane, or tetramethylsilane were observed.
3
and
2
3
(compromising ∼80% of the total integrated
3
Me SiCl to remove residual water; glass reaction vessels were
dried similarly. Solvents were purchased from Aldrich (anhy-
drous grade) and stored over sodium-potassium alloy. Fourier
9
1
transform NMR spectra at 70.28 ( Be), 500.13 ( H), 99.36
(
(
b) LiSiMe
of Cp Be(SiMe
vacuum stopcock was charged with 0.23 g (2.87 mmol) of
freshly recrystallized LiSiMe in a nitrogen-filled drybox,
3
+ Cp BeCl. Syn th esis a n d Ch a r a cter iza tion
2
9
13
Si), and 125.76 ( C) megahertz (MHz) were obtained on
Bruker AM-500 or Varian Unity 500 instruments. Proton NMR
spectra are referenced to the residual protons of C (7.15
triplet (128.0
ppm); positive chemical shifts are deshielded from the external
3
). A glass reactor fitted with a Teflon high-
6
D
6
1
3
3
6 6
ppm), and C spectra to the center of the C D
transferred to a high-vacuum line and evacuated; then CpBeCl
(0.21 g, 1.92 mmol) and pentane (12 mL) were condensed in.
After the mixture was magnetically stirred for 19 h, the
reaction products were separated by means of fractional
2
+ 9
standards: namely, aqueous Be(NO
and (CH )
3 4
3
)
2
, as [Be(H
Si ( C, H, and Si). All NMR spectra were recorded
at room temperature in sealed tubes with degassed C D
6
2
O)
4
]
( Be),
1
3
1
29
6
condensation. Material subsequently identified as CpBe(SiMe
0.19 g, 1.31 mmol, 68.2% yield based on CpBeCl) passed
through a trap held at 0 °C and was retained in a trap held at
3
)
solvent. Low-resolution mass spectra were acquired by use of
a Kratos MS-80 instrument operated at 70 eV, with the source
at ∼150 °C.
(
-
30 °C. NMR data are in Tables 4 and 5. MS (EI): m/z (Irel
)
Sta r tin g Ma ter ia ls. Be powder (10-20 µm, Alfa J ohnson-
Matthey) was heated in a quartz reactor at 400-470 °C for 2
h under high vacuum prior to use. Beryllium chloride was
prepared by the passing of chlorine gas (AGA, 99.99%) over
beryllium metal (99.9%, Aldrich) at 500-550 °C. Bis(trimeth-
+
+
+
3
7 (6%, C
3
H ), 38 (12%, C
] ), 59 (100%, HSiMe
3
H
2
), 39 (41%, C
), 65 (51%, C
3
H
3
), 58 (28.2%,
+
+
+
[SiC
2
H
6
2
5
H
5
), 66 (93%,
+
•
+), 74 (8%, C
), 149 (1%, CpBe SiMe
+
+•
C
5
H
6
), 73 (77%, SiMe
3
+•
5
H
5
Be ), 147 (18%, M ),
2
9
30
+•
148 (3%, CpBe SiMe
3
3
).
4
1
ylsilyl)mercury was prepared by reaction of mechanically
stirred lithium amalgam and trimethylchlorosilane in a slurry
of sodium chloride, sodium iodide, and diethyl ether for 3 days
in the dark; the resulting mercurial was then extracted in
pentane and sublimed under high vacuum. Base-free tri-
methylsilyllithium4 was synthesized by addition of an excess
of lithium powder (high sodium, 99%, Aldrich) to a stirred
X-r a y Cr ysta llogr a p h y of Cp Be(SiMe ). Capillaries of a
3
thickness suitable for X-ray diffraction were pulled from flame-
softened 5 mm Pyrex tubing, flame-sealed to standard tapered
glass joints, and evacuated on a high-vacuum line. Small
3
amounts of CpBe(SiMe ) were condensed in, and the capillaries
2
sealed off. After some months at room temperature, single
crystals appeared to form in all of the capillaries. Crystal
structure analysis: Intensity data were collected at 133(2) K
on a colorless prism-shaped crystal of dimensions 0.42 × 0.34
solution of Hg(SiMe
in the dark, the product was isolated by recrystallization from
5
the filtered reaction solution. A solution of NaCp (Cp ) C H )
3 2
) in hexane. After being stirred for 3 days
5
×
0.24 mm with a Bruker Smart CCD area detector mounted
in ether was prepared by removal of the solvent from a
commercial solution of NaCp in THF (2.0 M, Aldrich), after
which the residual solid was redissolved in diethyl ether.
on a Bruker P4 goniometer with Mo KR radiation (0.71073
Å). C 14BeSi: M ) 147.29, monoclinic, a ) 6.1881(5) Å, b )
0.2775(9) Å, c ) 8.2346(6) Å, â ) 110.206(3)°, V ) 491.48(7)
8
H
1
Addition of the latter solution to a solution of BeCl
2
in diethyl
3
3
Å ; P2
1
/m, Z ) 2, D ) 0.995 Mg/m ; F(000) ) 160 electrons. A
c
ether afforded bis-cyclopentadienylberyllium, which was twice
total of 2178 reflections were collected by 0.4° φ oscillation
sublimed at temperatures up to 150 °C in high vacuum.43
frames (10 s/frame) over 2.64° e θ e 28.24°. An empirical
Mixing of a slight excess of BeCl
which was purified by vacuum transfer.
Rea ction s w ith LiSiMe . (a ) Th er m a l Decom p osition
of LiSiMe . In a nitrogen-filled glovebox, a 5 mm NMR tube
was charged with 40 mg (0.50 mmol) of recently twice-
recrystallized LiSiMe . After deuterated benzene was added
2 2
with BeCp yielded CpBeCl,
-1
absorption correction (SADABS) was applied (µ ) 0.169 mm
for Mo KR radiation). The crystal structure was solved by
3
direct methods and refined by full-matrix anisotropic least
3
2
45
squares (based on F ). Refinement (1134 data/73 parameters/
2
no restraints) converged at wR
(
1
2
1
(F ) ) 0.0871 for all data; R -
3
2
F) ) 0.0328 for 982 observed data (I > 2σ(I)); GOF(on F ) )
via condensation on a high-vacuum line, the tube was sealed.
The resulting clear, light green solution was free of solids. The
initial spectra exhibited resonances (ppm) consistent with the
-3
.025; max./min. residual electron density, +2.26 /-0.28 e Å
Th er m a l Decom p osition of Cp Be(SiMe ). A sealed 5 mm
NMR tube containing a clear, colorless solution of 0.65 M
.
3
(literature values,4
ppm): H 0.26 (0.21); C 4.95 (5.1); Si -37.97 (-38.0). The
4a
exclusive presence of pure LiSiMe
3
29
1
13
3 6 6
CpBe(SiMe ) in C D was prepared on a high-vacuum line.
Initial 1H, C, 29Si, and 9Be NMR spectra exhibited only
resonances due to the metal silyl. The tube was heated in a
silicon oil bath and monitored by multinuclear NMR. Proton
13
(
39) For a concise discussion of Be toxicity see: Skilleter, D. N.
Chem. Br. 1990, 26, 26.
40) Laboratory handling, storage, and disposal procedures are
(
9
and Be NMR spectra indicated no change in the composition
described in (a) Toxic and Hazardous Industrial Chemicals Safety
Manual; The International Technical Information Institute, 1975. and
of the solution after prolonged (∼11 days) heating at temper-
(
b) The Sigma-Aldrich Library of Chemical Safety Data, ed. II, Vol. I;
Lenga, R. E., Ed.; Sigma-Aldrich Corp.: Milwaukee, WI, 1988.
41) Rosch, L.; Altnau, G.; Hahn, E.; Havemann H. Z. Naturforsch.
981, 36b, 1234.
atures up to 150 °C. After 26 h at 190 °C, a small doublet due
3
to the methyl hydrogens of Me SiH became visible in the
(
proton NMR. After an additional 177 h at 230-235 °C, the
clear, colorless solution contained a small amount of finely
divided black solid. Multinuclear NMR spectra revealed the
1
(42) Schaaf, T. F.; Oliver, J . P. J . Am. Chem. Soc. 1969, 91, 4327.
(43) Fischer, E. O.; Hofmann, H. P. Chem. Ber. 1959, 92, 482.
(44) (a) Nanjo, M.; Sekiguchi, A.; Sakurai, H. Bull. Chem. Soc. J pn.
1
998, 71, 741. (b) Nanjo, M.; Sekiguchi, A.; Sakurai, H. Bull. Chem.
Soc. J pn. 1999, 72, 1387. (c) Sekiguchi, A.; Nanjo, M.; Kabuto, C.;
Sakurai, H. Organometallics 1995, 14, 2630.
(45) Sheldrick, G. M. SHELXTL Version 5 Reference Manual;
Siemens Analytical X-ray Instruments: Madison, WI, 1994.

CpBe(SiMe
3
), an Unprecedented Be-Si Bond
Organometallics, Vol. 22, No. 3, 2003 413
presence of small amounts of CpBeMe46 ( Be δ -20.54; 13C δ
9
removed to a nitrogen-filled drybox for addition of 0.060 g (0.75
1
1
03.62, -25.46, 1:1:1:1 qt, J Be-C ) 31.3 Hz; H δ 5.70, 5H;
mmol) of BeCl
forming a viscous slush. After standing overnight, ∼20 mg
(0.25 mmol) of twice-recrystallized LiSiMe was added, and
2
. The two solids began to liquefy upon contact,
-
1.26, 3H) and CpBe(SiMe
2
SiMe
3
) (NMR data presented in
SiH
H δ 4.14 (4.20), decet,
H-Si-CH ) 3.5 (3.8) Hz, J Si-H ) 182.5 (183.8) Hz, 1H; δ 0.004
Tables 4 and 5), along with increased amounts of Me
3
3
3
0,47 1
(
literature values in parentheses):
the contents of the tube were heated momentarily with a heat
gun. The tube was then fitted with a high-vaccum stopcock
and removed to a glass high-vacuum line, where ∼0.5 mL of
3
J
(
0.20), d, J H-Si-CH ) 4.0 Hz, 9H; 13C δ -2.71 (-2.65); Si δ
16.12 (-16.34). Resonances due to the three CpBeX species
and Me SiH accounted for 97% of the total proton NMR
intensity. The relative molar ratios based on the integrated
intensities of the SiMe resonances (or the Me resonance in
the case of CpBeMe) were 37.5 (X ) SiMe ):3.1 (X ) Me):2.4
X ) SiMe SiMe ):1.0 (Me SiH). After an additional 25 days
3
29
-
6 6
dry C D was condensed in and the tube flame-sealed under
3
vacuum. Species identified by means of multinuclear NMR
4
6
9
13
1
included CpBeCl ( Be δ -18.79; C δ 105.11; H δ 5.75);
CpBeMe;46 CpBe(SiMe
); and CpBe(SiMe SiMe ) (NMR data
3
3
2
3
3
are presented in Tables 4 and 5). Cyclopentadienylberyllium
chloride remained in excess, while approximately equivalent
(
2
3
3
at 217-224 °C, ca. 85% of the total proton NMR intensity was
due to the four aformentioned species. The molar ratios were
amounts of the other CpBeX (X ) SiMe
3
, Me, SiMe
species were formed ( Be NMR integration).
2 3
SiMe )
9
4
.3:3.5:1.2:1.0. The remaining 15% of the 1H NMR intensity
was distributed among numerous small resonances in the Cp,
Ack n ow led gm en t. This work was financially sup-
ported by the Materials Research Science and Engi-
neering Center at the University of Wisconsin, Madison.
NMR instrumentation was supported by the National
Science Foundation (CHE-8306121, CHE-8813550, CHE-
Si-Me, Si-H, and CpBe-Me δ regions. Also observed were
resonances consistent with the presence of SiMe
3
SiMe
2
H: 1
H
)
3
3
δ 3.90, septet, J H-Si-CH ) 4.5 Hz, 1H, δ 0.10, d, J H-Si-CH
.0 Hz, 6H, δ 0.078, s, 9H; 2 Si δ -18.9, -39.1. The H NMR
9
1
4
3
intensity of the Si-H multiplet was 14% of that of Me SiH.
9
629688) and the National Institutes of Health (ISI-
Beryllium-9 NMR spectra exhibited resonances due to the
three beryllium species in question, along with a peak at
ORRO2388-01). We are indebted to Professor Frank
Weinhold for the theoretical results and insights therein,
and Professors Don Gaines and Larry Dahl for advice
and helpful discussions.
-
21.81 comprising ca. 4% of the total intensity.
Cyclop en ta d ien yl(p en ta m eth yld isilyl)ber ylliu m . Bis-
(cyclopentadienyl)beryllium, 0.080 g (0.58 mmol), was con-
densed into a 5 mm NMR tube on a high-vacuum line, then
Su p p or tin g In for m a tion Ava ila ble: Tables listing crys-
tallographic data for CpBe(SiMe ). This material is available
3
free of charge via the Internet at http://pubs.acs.org.
9
(
46) Proton, 13C, and Be NMR chemical shift data for CpBeMe and
CpBeCl were essentially identical to those of authentic samples. Proton
and Be data are also available in the literature: Drew, D. A.; Morgan,
G. L. Inorg. Chem. 1977, 16, 1704.
9
(47) Hunter, B. K.; Reeves. L. W. Can. J . Chem. 1968, 46, 1399.
OM0201720