Heavy metallocenes of the group 8 metals: Ferrocene and ruthenocene derivatives

Article abstract of DOI:10.1246/bcsj.20130235

Metallocene (ferrocene and ruthenocene) derivatives, featuring three heavy group 14 elements in one of the cyclopentadienyl ligands, were synthesized by the reaction of the lithium disilagermacyclopentadienide [(tBu2MeSi)3GeSi2-(CH) (CPh)]-·[Li+(thf)] wit

Full text of DOI:10.1246/bcsj.20130235

1466 Bull. Chem. Soc. Jpn. Vol. 86, No. 12, 1466-1471 (2013)
© 2013 The Chemical Society of Japan
Heavy Metallocenes of the Group 8 Metals:
Ferrocene and Ruthenocene Derivatives
Vladimir Ya. Lee,* Risa Kato, and Akira Sekiguchi*
Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba,
Tsukuba, Ibaraki 305-8571
Received August 23, 2013; E-mail: leevya@chem.tsukuba.ac.jp, sekiguch@chem.tsukuba.ac.jp
Metallocene (ferrocene and ruthenocene) derivatives, featuring three heavy group 14 elements in one of the cyclo-
pentadienyl ligands, were synthesized by the reaction of the lithium disilagermacyclopentadienide [(tBu2MeSi)3GeSi2-
¹
(CH)(CPh)] ¢[Li+(thf)] with either in situ-generated [Cp*Fe(acac)] or tetrameric [(Cp*RuCl)4] complexes. X-ray struc-
tural and NMR spectroscopic studies showed that both heavy ferrocene and heavy ruthenocene exhibited remarkable cyclic
π-delocalization within the heavy cyclopentadienyl ligand and its powerful π-donating ability toward the transition metal.
Metallocenes, compounds of the general formula [(η5-
C5H5)2M] (where M is a transition metal in the oxidation state
II), constitute a fundamentally important class of organometallic
complexes in which a transition metal is sandwiched between
the two pentahaptocoordinated cyclopentadienyl ligands.1 Since
the landmark discovery of the archetypal ferrocene, bis(η5-
cyclopentadienyl)iron(II) [(η5-C5H5)2Fe], by Kealy and Pauson
in 19512 (followed by its independent structural characteri-
zation by Wilkinson3a and Fischer3b) and following synthesis
of ruthenocene [(η5-C5H5)2Ru] by Wilkinson in 1952,4 a huge
number of metallocenes with a variety of transition metals have
been prepared.1 Nowadays, metallocenes, which revolutionized
the field of organometallic chemistry more than six decades ago,
are still among the most important coordination compounds,
being widely used in the field of material science (asymmetric
catalysis, large-scale olefin polymerization, supramolecular
chemistry, carbon nanotubes, molecular magnets, nonlinear
optics, luminescent and fluorescent materials, medicine, etc.).5
Although heterometallocenes, featuring heavy main group ele-
ments (mostly, of group 15) in the cyclopentadienyl rings, are
well known,6 there are only a few examples of such complexes
incorporating heavy group 14 elements (Si or Ge), all reported
by Tilley and co-workers (metallocene sandwiches of groups 4,
5, and 8 metals having sila- or germacyclopentadiene ligands).7
Our group has also contributed to the field of heavy metal-
locenes with the synthesis of a heavy ferrocene derivative as
the first coordination compound with several heavy group 14
elements in one of the cyclopentadienyl rings,8 representing
the closest approach to the highly challenging (albeit still
experimentally unknown) entirely inorganic ferrocenes [(η5-
H5E5)2Fe] (E = Si-Pb).9 In this contribution, we present a full
account on the chemistry of heavy metallocenes, including
preliminarily reported heavy ferrocene8 and newly synthesized
heavy ruthenocene.
pentadienide MC5H5.5 However, as this synthetically attractive
and straightforward method was proved to be ineffective in
the case of our precursor, lithium disilagermacyclopentadienide
¹
[(tBu2MeSi)3GeSi2(CH)(CPh)] ¢[Li+(thf)] 1,10 we developed
a novel strategy based on the use of [Cp*Fe(acac)] complex
(Cp*: η5-C5Me5, acac: 2,4-pentanedionate) as a selective source
of the Cp*Fe fragment.11 Accordingly, [Cp*Fe(acac)] (gener-
ated in situ from [Fe(acac)2] and Cp*Li) was reacted with an
equimolar amount of 1 at low temperature in THF,12 forming
the target heavy ferrocene 2 isolated using glove box silica gel
column chromatography in 31% yield as a room temperature
stable red crystalline material (Scheme 1).
The isostructural heavy ruthenocene 3 was prepared accord-
ing to a straightforward procedure previously used by Tilley
and co-workers in the synthesis of a ruthenocene derivative
with an η5-germacyclopentadienyl ligand by the reaction of
the transient lithium germacyclopentadienide {C4Me4Ge[Si-
¹
(SiMe3)3]} ¢Li+ and [(Cp*RuCl)4] complex.7a We employed
this synthetic strategy to prepare our ruthenocene derivative 3,
featuring an η5-disilagermacyclopentadienyl ligand. Thus, reac-
tion of the lithium disilagermacyclopentadienide 1 with 1/4
equivalent of [(Cp*RuCl)4] in THF resulted in the formation of
the desired heavy ruthenocene 3, isolated using glove box silica
gel column chromatography as room temperature stable red
crystals in 22% yield (Scheme 1).
The spectroscopic characteristics of both heavy ferrocene 2
and ruthenocene 3 are all indicative of perhaptocoordination
of the C2Si2Ge ligand to iron or ruthenium metal. For exam-
1
ple, the H NMR spectrum revealed a singlet resonance of the
cyclic PhC=CH proton at 4.49 ppm (in 2) and at 4.37 ppm (in
3), which is in the region diagnostic of the hydrogen atoms of
η5-Cp-ligands in transition-metal cyclopentadienyl complexes.5
Furthermore, all cyclic C and Si atoms of the heavy cyclo-
pentadienyl ligand in 2 (and in 3) were notably shielded upon
complexation compared with those of the starting salt 1 (NMR
chemical shifts in ppm for: 2 (3) vs. 1: 80.5 (78.6) vs. 143.2
(for PhCCH), 108.1 (109.4) vs. 181.4 (for PhCCH), ¹49.3
(¹45.8) and 1.1 (¹8.0) vs. 54.4 and 69.1 (for SiSiGe and
Results and Discussion
The parent ferrocene [(η5-C5H5)2Fe] is readily available by
the classical coupling of FeCl2 with the alkali metal cyclo-
Published on the web October 5, 2013; doi:10.1246/bcsj.20130235

V. Y. Lee et al.
Bull. Chem. Soc. Jpn. Vol. 86, No. 12 (2013) 1467
[Cp∗Fe(acac)] / THF
– Li(acac)
Fe
Ph
H
C
C
Si
R3Si
Ge
Li+(thf)
Si
[Cp∗: 5-(C5Me5),
η
acac: 2,4-pentanedionate]
Ph
SiR3
H
C
R3Si
C
R3Si Ge
2
Si
Si
SiR3
R3Si
1/4 [(Cp∗RuCl)4] / THF
– LiCl
1
Ru
[R3Si = SiMetBu2]
Ph
Ge
H
C
C
R3Si
Si
Si
SiR3
R3Si
3
Scheme 1. Synthesis of the heavy ferrocene 2 and heavy ruthenocene 3.
Figure 1. Molecular structures (ORTEP, 30% probability, hydrogen atoms are omitted): (A) heavy ferrocene 2, (B) heavy
ruthenocene 3. Selected bond lengths in ¡ (for 2/for 3): Ge1-Si1 = 2.3038(9)/2.2927(13), Si1-Si2 = 2.2465(11)/2.2498(15),
Ge1-C1 = 1.924(3)/1.925(4), Si2-C2 = 1.827(3)/1.830(4), C1-C2 = 1.419(4)/1.421(6). Selected bond angles (°) (for 2/for 3):
Ge1-Si1-Si2 = 96.26(5)/96.34(4), Si1-Si2-C2 = 100.06(14)/99.49(10), Si2-C2-C1 = 124.7(3)/125.7(2), C2-C1-Ge1 =
118.2(3)/117.8(2), C1-Ge1-Si1 = 98.84(15)/98.71(9).
SiSiGe)). Such characteristic shielding of the skeletal atoms
in the heavy ferrocene and heavy ruthenocene 2 and 3, which
occurs upon complexation of 1 with transition-metal fragments,
can be best described in terms of a greater extent of the cyclic
π-delocalization in the GeSi2C2-ring of 2 and 3 (compared with
that of the starting lithium salt 1 on the one hand, and δ-back-
donation from the transition metal to the ligand on the other
hand).13
The sandwich composition of both heavy ferrocene 2 and
heavy ruthenocene 3 can be clearly visualized in the diagnostic
pentahaptocoordination of the nearly coplanar Cp* and heavy
Cp ligands to the transition metal (Fe or Ru) center (Figure 1).14
The transition metal, sandwiched between the heavy Cp and
Cp* rings, is remote from their least-squares planes at 1.686 ¡
(for 2)/1.823 ¡ (for 3) and 1.705 ¡ (for 2)/1.865 ¡ (for 3),
respectively. The observation of longer distances for heavy
ruthenocene 3 came as no surprise given the larger atomic radius
of Ru compared with that of Fe: 1.34 ¡ vs. 1.24 ¡,15 and
consequently longer ruthenium-to-Cp-ligand bonds. As in the
case of some metallocenes featuring Cp* ligands,16 both 2 and
3 manifested a staggered conformation of their Cp-ligands
caused by the notable repulsive interaction between their sub-
stituents, although staggering in the heavy ruthenocene 3 is
less pronounced than that in the heavy ferrocene 2 because
of the greater interplanar distance between the five-membered
rings in the former. The staggered conformation of the heavy
ruthenocene 3 contrasts sharply with the eclipsed conformation
reported for the parent ruthenocene Cp2Ru17 and even for the
decamethylruthenocene Cp*2Ru.18
The substantial extent of the cyclic 6π-electron delocalization
within the heavy GeSi2C2-cyclopentadiene ring in both 2 and 3
can be clearly seen in their solid-state structures (Figure 1).
Thus, the lengths of all cyclic bonds are just in between those
of typical single and double bonds. Furthermore, these skeletal

1468 Bull. Chem. Soc. Jpn. Vol. 86, No. 12 (2013)
Heavy Metallocenes of the Group 8 Metals
H
C
SiR3
SiR3
C
Ph
Si
Si
Ge
R3Si
SiR3
4
[R3Si = SiMetBu2]
Figure 2. Structural comparison of the disilagermacyclopentadiene 4, lithium disilagermacyclopentadienide 1 and heavy
t
ruthenocene 3 (hydrogen atoms, Bu2MeSi substituents and Cp* ligand on Ru atom are omitted): (A) for 4 (its structure is
shown: R3Si = SiMetBu2), (B) for 1, (C) for 3.
bonds in both 2 and 3 (Figure 1) are quite similar to each
other and reasonably comparable with those of the aromatic
lithium disilagermacyclopentadienide 110 (bond lengths (in ¡)
of 2/3 are given vs. 1: 2.3038(9)/2.2927(13) vs. 2.3220(5)
[Ge-Si], 2.2465(11)/2.2498(15) vs. 2.2403(7) [Si-Si],
1.827(3)/1.830(4) vs. 1.8269(18) [Si-C], 1.419(4)/1.421(6)
vs. 1.402(2) [C-C], 1.924(3)/1.925(4) vs. 1.9303(17) [Ge-C]).
The other manifestations of the cyclic π-delocalization in
2 and 3 are the remarkable flattening of the heavy Cp-ring and
the planarization around the skeletal atoms that takes place
upon complexation (structural parameters of 2/3 are given vs.
those of 110): 538.1/538.0° vs. 536.3° (sum of the interior bond
angles within the five-membered ring); 360.0/359.9° vs. 342.9°
(for Ge), 355.6/354.9° vs. 350.8° (for Si bound to Ge), 359.0/
359.4° vs. 357.8° (for Si bound to C) (sum of the bond angles).
In addition, the extent of the deviation of the skeletal atoms
from the GeSi2C2 least-squares plane in both 2 and 3 is smaller
than that in their precursor 1.10 The flattening of the heavy Cp-
ligand in 2 and 3 can definitely be attributed to the steric effect
main group elements in the cyclopentadienyl fragments,21 the
dominant covalent interaction involves strong π-donation from
the occupied π-orbitals of the Cp ligand to the vacant d-orbitals
of appropriate symmetry at the iron metal of the CpFe+ unit,
whereas ligand-to-metal σ-donation and metal-to-ligand δ-back-
donation are substantially weaker and contribute much less to
the overall bonding. Our preliminary study showed that the
same holds true for the heavy ferrocene 2,8 and current inves-
tigations proved that this concept can also be applied to the
heavy ruthenocene 3. Thus, one of the most important in-phase
orbital interactions, namely, π-donation from the heavy cyclo-
pentadiene ligand π-orbital to the iron atom d-orbital, can be
clearly seen in the HOMO of 3¤ (3¤: model heavy ruthenocene
t
with the Me3Si-groups replacing real Bu2MeSi-substituents)
(Figure 3).22 Because of the low symmetry (C1) of the heavy
cyclopentadiene ligand in 3¤, its symmetric all-bonding π-orbital
was not found, thus preventing ligand-to-metal σ-donation in 3¤
and, accordingly, minimizing the contribution of σ-type bond-
ing to the overall structure of 3¤.
t
of the bulky Bu2MeSi-substituents, which is also responsible
Electrochemical measurements on the heavy ferrocene 2
revealed two irreversible oxidation waves at Ep = ¹0.53 and
¹0.24 V (vs. Ag/Ag+([nBu4N]ClO4/MeCN), CH2Cl2, room
temperature, 0.1 M [nBu4N]ClO4), whereas the parent deca-
methylferrocene Cp*2Fe displayed one fully reversible oxida-
tion wave at Ep = ¹0.32 V under the same measurement condi-
tions (Figure 4). This implies that, in contrast to the quite stable
decamethylferrocenium cation, cationic species formed upon
electrochemical oxidation of the heavy ferrocene 2 are unstable/
highly reactive under the measurement conditions. However,
what is even more important is the fact that 2 oxidizes at a
substantially more negative potential than the parent Cp*2Fe
and even bis(η5-germacyclopentadienyl)iron(II) derivative [{η5-
Me4C4Ge[Si(SiMe3)3]}2Fe] (irreversible, ¹0.45 V vs. SCE,
CH2Cl2, 0.1 M [nBu4N]ClO4.)7h This suggests that the heavy
for the staggering of the Cp-ligands. Moreover, one can notice
that on going from the nonaromatic 4 (disilagermacyclopenta-
diene derivative 4, precursor for 119) to the aromatic 1 and
to the heavy ruthenocene 3, the Ph-substituent on one of the
cyclic carbons successively changes its orientation relative to
the GeSi2C2 five-membered ring from nearly orthogonal (80.8°
in 4) to more coplanar (58.3° in 1 and 39.4° in 3), becoming
progressively more and more available for conjugation with the
heavy cyclopentadiene ring, thus allowing for more effective
delocalization of the π-electrons in the latter (Figure 2).
The nature of the bonds between the cyclopentadiene ligand
and the transition metal is among the central themes in metal-
locene chemistry. Previous theoretical studies showed that in
ferrocene itself,20 as well as in its analogues containing heavy

V. Y. Lee et al.
Bull. Chem. Soc. Jpn. Vol. 86, No. 12 (2013) 1469
Ru
Me3Si
SiMe3
Si
Si
Me3Si
Ge
C
C
H
Ph
3' (model heavy ruthenocene)
Figure 3. HOMO (¹0.172 eV) of 3¤ (MO plot is given at the isovalue 0.04, H atoms are omitted).
Figure 4. Cyclic voltammograms with the peak potentials: (A) heavy ferrocene 2, (B) heavy ruthenocene 3 (CH2Cl2, room
temperature, 0.1 M [nBu4N]ClO4).
Cp-ligand in 2 is a very powerful π-electron donor to the
transition-metal fragment, surpassing such strong π-donors
as the Cp* group and even germacyclopentadienyl ligand.23
Similar electrochemical trends have also been observed in the
case of heavy ruthenocene 3, for which the CV measurement
revealed an irreversible oxidation wave at Ep(ox) = ¹0.14 V
(cf.: the parent decamethylruthenocene Cp*2Ru under the same
measurement conditions yielded a fully reversible oxidation
wave at 0.35 V) (Figure 4).
mirror in vacuum prior to use. NMR spectra were recorded
on Bruker AC-300FT (1H NMR at 300.1 MHz; 13C NMR at
75.5 MHz; 29Si NMR at 59.6 MHz) and Bruker ARX-400FT
(1H NMR at 400.2 MHz; 13C NMR at 100.6 MHz; 29Si NMR at
79.5 MHz) NMR spectrometers. Electrochemical measurements
were performed on an ALS/CH Instruments Electrochemical
Analyzer Model 600A with Ag/Ag+ as the reference electrode
and a Pt bead as the working electrode. The oxidation poten-
tials, evaluated by cyclic voltammetry at room temperature
using 10¹3 M solutions, were measured using calibration on the
ferrocene/ferricenium couple. The starting lithium disilager-
macyclopentadienide 1 was prepared according to a previously
published procedure.10
Synthesis of (η5-1,2,3-tris[di-tert-butyl(methyl)silyl]-4-
phenyl-1,2-disila-3-germacyclopentadienyl)(η5-pentameth-
ylcyclopentadienyl)iron (2). A mixture of [Fe(acac)2] (55
mg, 0.22 mmol) and Cp*Li (32 mg, 0.22 mmol) was placed in
a glass tube with a magnetic stirring bar in a glove box, then
dry oxygen-free THF (2.0 mL) was transferred into this tube
through the vacuum line, and the tube was sealed under
vacuum. After stirring for 15 min at ¹78 °C, the cooling bath
was removed, and the mixture was gradually warmed to room
temperature. The color of the reaction mixture turned to dark
yellowish red, and the resulting Li(acac) was precipitated.
The THF solution of [Cp*Fe(acac)] and 1 (166 mg, 0.21 mmol)
Conclusion
In summary, the syntheses, structures, and bonding proper-
ties of the heavy ferrocene 2 and heavy ruthenocene 3, as the
first examples of metallocene derivatives featuring more than
one heavy group 14 element in one of the cyclopentadienyl
ligands, are reported in this paper. The important π-delocaliza-
tion within the heavy cyclopentadiene ring and its rather strong
π-donating ability were established on the basis of a set of
experimental (NMR, X-ray, CV) data.
Experimental
General.
All experiments involving air-sensitive com-
pounds were performed using high-vacuum line techniques
or in an argon atmosphere using an MBRAUN MB 150B-G
glove box. All solvents were dried and degassed over potassium

1470 Bull. Chem. Soc. Jpn. Vol. 86, No. 12 (2013)
Heavy Metallocenes of the Group 8 Metals
were mixed at ¹78 °C, and the resulting reaction mixture was
stirred for 15 min at this temperature and an additional 30 min at
room temperature. After evaporation of solvent, the residue was
dissolved in hexane (2.0 mL), and the side product Li(acac) was
removed by centrifugation. The target complex 2 was isolated
using glove box silica gel column chromatography (eluent:
hexane), followed by recrystallization from pentane, as red
graphite-monochromatized Mo Kα radiation (- = 0.71070 ¡).
The structure was solved by the direct method using the
SIR-9224 program and refined by the full-matrix least-
squares method by the SHELXL-9725 program. Crystal data
for 3 at 120 K: C45H84GeRuSi5, Mr = 939.23, orthorhombic,
Pca21, a = 22.5990(2), b = 9.2160(7), c = 23.9410(8) ¡, V =
4986.2(4) ¡3, Z = 4, Dcalcd = 1.251 g cm¹3. The final R factor
was 0.0382 for 5829 reflections with Io > 2σ(Io) (Rw = 0.1063
for all data, 6052 reflections), GOF = 1.052. The X-ray crystal-
lographic data for 3 have been deposited at the Cambridge
Crystallographic Data Centre (CCDC) under deposition num-
ber CCDC 954608. These data can be obtained free of charge
from the CCDC (www.ccdc.cam.ac.uk/data_request/cif).
1
crystals; mp 203-205 °C. Yield: 58 mg (31%). H NMR (400
MHz, C6D6): ¤ 0.54 (s, 3H, Me), 0.59 (s, 3H, Me), 0.74 (s, 3H,
Me), 1.03 (s, 9H, tBu), 1.20 (s, 9H, tBu), 1.26 (s, 9H, tBu), 1.27
t
t
t
(s, 9H, Bu), 1.31 (s, 9H, Bu), 1.35 (s, 9H, Bu), 1.91 (s, 15H,
C5Me5), 4.49 (s, 1H, C=CH), 7.10 (t, J = 7.4 Hz, 1H, Hpara),
7.22 (t, J = 7.4 Hz, 2H, Hmeta), 7.94 (d, J = 7.4 Hz, 2H, Hortho);
13C NMR (100.6 MHz, C6D6): ¤ ¹2.8 (Me), ¹1.19 (Me), ¹1.15
(Me), 14.0 (C5Me5), 21.2 (CMe3), 21.3 (CMe3), 21.5 (CMe3),
22.2 (CMe3), 22.3 (CMe3), 22.8 (CMe3), 29.4 (CMe3), 29.9
(CMe3), 30.6 (CMe3), 30.7 (CMe3), 30.9 (CMe3), 31.0 (CMe3),
80.5 (C=CH), 84.2 (C5Me5), 108.1 (PhC=C), 124.7 (Carom),
127.3 (Carom), 131.7 (Carom), 151.1 (Cipso); 29Si NMR (79.5
MHz, C6D6): ¤ ¹49.3, 1.1, 26.5, 29.4, 33.4; Anal. Found: C,
60.01; H, 9.64%. Calcd for C45H84FeGeSi5: C, 60.45; H, 9.47%.
The X-ray crystallographic data for 2 have been deposited at the
Cambridge Crystallographic Data Centre (CCDC) under dep-
osition number CCDC 954607. These data can be obtained free
of charge from the CCDC (www.ccdc.cam.ac.uk/data_request/
cif). For the crystallographic and computational data for the
heavy ferrocene 2, see Ref. 8.
We appreciate financial support from the Grant-in-Aid for
Scientific Research program from the Ministry of Educa-
tion, Science, Sports and Culture of Japan (Nos. 24109006,
24245007, and 24550038). We also thank Dr. Andreas Krapp
and Professor Gernot Frenking (Philipps-Universität Marburg,
Germany) for valuable discussions.
Supporting Information
Tables of crystallographic data, including atomic positional
and thermal parameters for the heavy ruthenocene 3; com-
putational details, including total energy, atomic coordinates
and geometry of the optimized structure, for the model heavy
ruthenocene 3¤.
Synthesis of (η5-1,2,3-tris[di-tert-butyl(methyl)silyl]-4-
phenyl-1,2-disila-3-germacyclopentadienyl)(η5-pentameth-
ylcyclopentadienyl)ruthenium (3). A mixture of 1 (68 mg,
0.087 mmol) and [(Cp*RuCl)4] complex (24 mg, 0.022 mmol)
was placed in a glass tube with a magnetic stirring bar in a glove
box, then dry oxygen-free THF (1.5 mL) was transferred into
this tube through the vacuum line, and the tube was sealed
under vacuum. After stirring for 15 min at ¹78 °C, the cooling
bath was removed, and the mixture was gradually warmed to
room temperature. After stirring for 1 h at room temperature,
the solvent was evaporated, the residue was dissolved in dry
hexane (2.0 mL), and the inorganic salt (LiCl) was removed by
centrifugation. The target heavy ruthenocene 3 was isolated
using glove box silica gel column chromatography (eluent:
hexane), followed by recrystallization from dry pentane, as red
crystals; mp >180 °C (dec.). Yield: 18 mg (22%). 1H NMR (300
MHz, C6D6): ¤ 0.43 (s, 3H, Me), 0.48 (s, 3H, Me), 0.56 (s,
3H, Me), 1.01 (s, 9H, tBu), 1.16 (s, 9H, tBu), 1.277 (s, 9H, tBu),
1.283 (s, 18H, 2 Bu), 1.30 (s, 9H, Bu), 1.96 (s, 15H, C5Me5),
4.37 (s, 1H, PhC=CH), 7.05 (t, J = 7.6 Hz, 1H, Harom), 7.19
(t, J = 7.6 Hz, 2H, Harom), 7.72 (d, J = 7.6 Hz, 2H, Harom);
13C NMR (75.5 MHz, C6D6): ¤ ¹3.6 (Me), ¹2.0 (Me), ¹1.9
(Me), 13.4 (C5Me5), 21.09 (CMe3), 21.12 (CMe3), 21.4 (CMe3),
22.0 (2 © CMe3), 22.5 (CMe3), 29.4 (CMe3), 29.8 (CMe3),
30.48 (CMe3), 30.52 (CMe3), 30.76 (CMe3), 30.78 (CMe3), 78.6
(PhC=CH), 90.4 (C5Me5), 109.4 (PhC=CH), 124.9 (Carom),
127.2 (Carom), 131.6 (Carom), 149.9 (Cipso); 29Si NMR (59.6
MHz, C6D6): ¤ ¹45.8, ¹8.0, 22.9, 25.9, 30.8.
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Rheingold, Organometallics 2002, 21, 1734. See also a mono-
graph: i) V. Ya. Lee, A. Sekiguchi, Organometallic Compounds
The single crystals of 3 for X-ray diffraction analysis were
grown from a saturated pentane solution. Diffraction data were
collected at 120 K on a Mac Science DIP2030 Image Plate
Diffractometer with a rotating anode (50 kV, 90 mA) employing

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8
V. Ya. Lee, R. Kato, A. Sekiguchi, A. Krapp, G. Frenking,
16 For example, the parent ferrocene [Cp*2Fe] itself manifests
a staggered conformation (see Ref. 5).
J. Am. Chem. Soc. 2007, 129, 10340.
9
For the computational studies on the hypothetical persila-
17 G. L. Hardgrove, D. H. Templeton, Acta Crystallogr. 1959,
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18 M. O. Albers, D. C. Liles, D. J. Robinson, A. Shaver, E.
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10 V. Ya. Lee, R. Kato, M. Ichinohe, A. Sekiguchi, J. Am.
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11 E. E. Bunel, L. Valle, J. M. Manriquez, Organometallics
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19 V. Ya. Lee, M. Ichinohe, A. Sekiguchi, J. Am. Chem. Soc.
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12 J. M. Manríquez, E. E. Bunel, B. Oelckers, C. Vásquez,
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20 V. M. Rayón, G. Frenking, Organometallics 2003, 22,
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21 a) J. Frunzke, M. Lein, G. Frenking, Organometallics 2002,
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42, 2504.
22 Geometry optimization of the model heavy ruthenocene
[Cp*Ru{η5-[(Me3Si)3GeSi2](CH)(CPh)}] (3¤) was performed with
the Gaussian 03 program package at the DFT B3LYP level of
theory with the 6-31G(d) basis set (for H, C, Si, and Ge atoms) and
3-21G(d) basis set (for Ru atom).
23 The analogous conclusion on the remarkable π-donating
power of the cyclopentadienyl ligands incorporating heavy group
14 elements was previously drawn for other heavy metallocene
derivatives: see Refs. 7h, 8, and 14.
13 The diagnostic shielding of the skeletal atoms of the heavy
cyclic polyene ligand upon its complexation to the transition-metal
fragment was well documented in our previous studies: a) see
Ref. 8. b) K. Takanashi, V. Ya. Lee, T. Matsuno, M. Ichinohe, A.
Sekiguchi, J. Am. Chem. Soc. 2005, 127, 5768. c) K. Takanashi,
V. Ya. Lee, M. Ichinohe, A. Sekiguchi, Angew. Chem., Int. Ed.
2006, 45, 3269. d) K. Takanashi, V. Ya. Lee, M. Ichinohe, A.
Sekiguchi, Eur. J. Inorg. Chem. 2007, 5471. e) K. Takanashi,
V. Ya. Lee, A. Sekiguchi, Organometallics 2009, 28, 1248.
f) V. Ya. Lee, K. Takanashi, A. Sekiguchi, Dalton Trans. 2010,
39, 9229.
24 A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi,
M. C. Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr. 1994,
27, 435.
25 G. M. Sheldrick, SHELXL-97: Program for Crystal
Structure Refinement, University of Göttingen, Germany, 1997.
14 Only one example of a heavy ruthenocene derivative con-
taining three silicon atoms in one of the cyclopentadienyl ligands
has previously been prepared, although its crystal structure was not
reported because of poor refinement: H. Yasuda, V. Ya. Lee, A.