1,2-bis(ferrocenyl)digermene: A d-π electron system containing a Ge=Ge unit

Article abstract of DOI:10.1021/om300064q

The synthesis and structural analysis of the 1,2-bis(ferrocenyl)digermene (E)-Tip(Fc)Ge=Ge(Fc)Tip (Tip = 2,4,6-triisopropylphenyl, Fc = ferrocenyl), a stable crystalline compound, is reported. In this digermene, two ferrocenyl d electron systems are bridged by a Ge=Ge π spacer. As is evident from X-ray crystallographic, spectroscopic, and electrochemical analysis, this 1,2-bis(ferrocenyl)digermene shows effective d-π interaction and the Ge=Ge π bond is stable in the solid state. The Ge=Ge double bond is cleaved at elevated temperatures in the presence of butadiene, with concomitant loss of the π conjugation in the molecule.

Full text of DOI:10.1021/om300064q

Article
pubs.acs.org/Organometallics
1,2-Bis(ferrocenyl)digermene: A d−π Electron System Containing a
GeGe Unit
Takahiro Sasamori,*,† Hisashi Miyamoto,† Heisuke Sakai,‡ Yukio Furukawa,‡ and Norihiro Tokitoh*,†
†Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
‡Department of Chemistry & Biochemistry, School of Advanced Science and Engineering, Waseda University, 3-4-1 Okubo,
Shinjuku-ku, Tokyo 169-8555, Japan
S
* Supporting Information
ABSTRACT: The synthesis and structural analysis of the 1,2-
bis(ferrocenyl)digermene (E)-Tip(Fc)GeGe(Fc)Tip (Tip =
2,4,6-triisopropylphenyl, Fc = ferrocenyl), a stable crystalline
compound, is reported. In this digermene, two ferrocenyl d electron
systems are bridged by a GeGe π spacer. As is evident from X-ray
crystallographic, spectroscopic, and electrochemical analysis, this
1,2-bis(ferrocenyl)digermene shows effective d−π interaction and
the GeGe π bond is stable in the solid state. The GeGe double
bond is cleaved at elevated temperatures in the presence of
butadiene, with concomitant loss of the π conjugation in the molecule.
he systematic investigation of intramolecular electronic
communication between transition-metal centers (d
solution,9−11 as well as the ability of the GeGe moiety to
respond to external thermal, chemical, and photoinduced
stimuli, should moreover result in highly interesting reactivity
patterns. In the following, we present the synthesis, structure,
and spectroscopic properties of the 1,2-bis(ferrocenyl)-
digermene (E)-Tip(Fc)GeGe(Fc)Tip (2).
T
electron systems) via organic π-conjugated spacers is important
for the understanding of the fundamental electrochemical
processes in multistep redox systems.1 These d−π electron
systems also represent a good model for compounds with
mixed-valence oxidation states. Multinuclear ferrocenyl systems
with organic π-conjugated spacers such as FcCCFc,2
Ph(Fc)CC(Fc)Ph,3 and FcNNFc1b,4 (Fc = ferrocenyl)
have already attracted considerable interest, due to the
extraordinary stability and the characteristic electrochemical
properties of the ferrocene redox system. Previously, we have
reported the successful synthesis of the stable 1,2-bis-
(ferrocenyl)disilene (E)-Tip(Fc)SiSi(Fc)Tip (1; Tip =
2,4,6-triisopropylphenyl), which is a heavier element analogue
of olefins, bridging two ferrocenyl units with a SiSi π bond.5
As opposed to olefins, disilenes (R2SiSiR2) are usually highly
reactive and difficult to isolate.6 By the attachment of bulky
substituents such as Tip (kinetic stabilization) and/or by π-
electron conjugation (thermodynamic stabilization), the
reactive SiSi moiety in 1 can be stabilized sufficiently in
order to allow handling under ambient conditions. The
electrochemical analysis of 1 showed a stable four-step−five-
electron redox system with high HOMO and low LUMO
levels. The observed HOMO−LUMO gap for the SiSi π
bond was smaller compared to that observed for CC π
bonds,7 facilitating effective interaction between the two d-
electron units.1
RESULTS AND DISCUSSION
■
Ferrocenylgermane 3 was prepared from the reaction of
TipGeH2Cl with ferrocenyllithium. Bromination of 3 with
CBr4 in C6H6 resulted in the formation of dibromogermane 4,
which was subsequently reduced with KC8 in THF to give the
1,2-bis(ferrocenyl)digermene 2 as a stable, orange crystalline
solid (overall yield 21%, see Scheme 1). Digermene 2 is stable
in the solid state (mp 159.4 °C dec), but slow decomposition
was observed in solution (t1/2 = ca. 0.5 h at 60 °C in C6D6),
resulting in a complex mixture of products. Interestingly,
disilene 1 exhibited much higher thermal stability in toluene-d8
and no decomposition was apparent, even when 1 was heated
to 90 °C for 10 days.5 The high reactivity of the GeGe π
bond in digermene 2 is also reflected in its sensitivity toward
atmospheric oxygen, resulting in the facile formation of the
corresponding 1,3,2,4-dioxadigermetane 5.12
The molecular structure of 2 was obtained from single-crystal
X-ray diffraction analysis,13 showing a center of symmetry in
the middle of the GeGe bond (see Figure 1). The GeGe
bond length of 2.3320(5) Å is slightly longer than that of
Tip2GeGeTip2 (6; 2.2130(9) Å).14 Digermene 2 exhibits a
significantly larger trans-bent angle (θ = 43.7°) in comparison
to those of previously reported tetraaryldigermenes (e.g., θ =
Digermenes (R2GeGeR2), the heavier analogues of olefins
and disilenes, are known to exhibit even smaller HOMO−
LUMO gaps8 and should therefore be even better candidates
for use as π spacers in d−π electron systems. The ability of
digermenes to readily undergo controlled retrodimerizations in
Received: January 26, 2012
Published: May 8, 2012
© 2012 American Chemical Society
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tion processes (i.e. the equilibrium between digermene 2 and
germylenes 7) occur more quickly on the NMR time scale than
the rotation of the Tip−Ge bond.16 The UV−vis spectrum of 2
in hexane showed a strong and broadened absorption between
380 and 500 nm (λmax = 430 nm (ε = 17 000 M−1 cm−1), 500
nm (sh)). TD-DFT calculations for 2 suggested a combination
of several MLCT modes to be responsible for the observed
absorption.17 The calculation results furthermore suggested
effective interaction for the d electrons of the ferrocenyl units
with the π electrons of the GeGe moiety in the form of the
HOMO−LUMO transition (d−π* transition). The HOMO
orbital contains predominantly contributions from Fe d orbitals
and minor contributions from the Cp π orbital, whereas the
LUMO orbital contains predominantly contributions from the
Scheme 1. Synthesis of Ferrocenylgermanes 3 and 4 and 1,2-
Bis(ferrocenyl)digermene 2
1
GeGe π* orbital and the Cp π orbital. The H NMR and
UV−vis spectra of 2 at slightly elevated temperatures (T ≤ 70
°C) were almost identical with those measured at ambient
temperature. A concentration increase of germylene 7, as a
result of the thermally induced dissociation of the GeGe
double bond in 2, can accordingly be neglected.
Figure 1. Molecular structure of 1,2-bis(ferrocenyl)digermene 2 (left)
and a schematic representation of the GeGe core (right) with
experimental and calculated17 (in parentheses) structural parameters.
Thermal displacement ellipsoids are drawn at the 50% probability
level, all hydrogen atoms have been omitted for clarity, and selected
atoms have been labeled. Selected bond lengths (Å) and angles (deg):
Ge1−Ge1′, 2.3320(5); Ge1−C1(Fc), 1.935(3); Ge2−C2(Tip),
1.981(2); C1(Fc)−Ge1−Ge1′, 114.56(8); C2(Tip)−Ge1−Ge1′,
116.49(7); C1(Fc)−Ge1−C2(Tip), 106.78(11).
Figure 2. Cyclic voltammograms of 1,2-bis(ferrocenyl)digermene 2:
(a) oxidation region (2 mM, 0.1 M [(n-Bu)4N][PF6] in THF); (b)
reduction region (2 mM, 0.1 M [(n-Bu)4N][B(C6F5)4] in o-
dichlorobenzene).
12.3° in 6).14 These metric parameters indicate a relatively
weak GeGe double bond in 2 and suggest the possibility of
thermally controlled dissociation of 2 in solution, to give 2
equiv of the corresponding germylene Tip(Fc)Ge: (7). In the
solid-state Raman spectrum of 2, one strong absorption line at
340 cm−1 was observed for the νGeGe vibration. This value is in
good agreement with those for previously reported digermenes
(ca. 300−400 cm−1; e.g. 300 cm−1 for Dis2GeGeDis2),15
indicating a comparable degree of double-bond character for
the GeGe bond in 2. The combined results of the solid-state
Raman spectrum (comparable magnitude of the νGeGe
vibration) and the X-ray crystallographic analysis (GeGe
bond length and trans-bent angle) suggest a weak, but
nevertheless distinct, GeGe double bond in 2 in the solid
The cyclic voltammogram of 2 exhibited one reversible redox
couple in the reduction region at E1/2 = −2.27 V (1e). The
silicon analogue 1 showed, in contrast, two reversible redox
couples at E1/2 = −2.64 (2e) and −3.09 V (1e) V (E1/2 vs FcH/
FcH+ in THF with 0.1 M Bu4NPF6) (see Figure 2). The
significantly lower reduction potential of 2 relative to 1 suggests
a lower LUMO level of the GeGe π bond with respect to the
LUMO level of the corresponding SiSi π bond.18 In the
−0.41 (1e) and +0.03 V (1e) (E1/2 vs FcH/FcH+ in o-
dichlorobenzene and 0.1 M Bu4NB(C6F5)4) was observed for 2,
suggesting a desirable coupling of the two ferrocenyl moieties
through the GeGe π bond. Interestingly, the first oxidation
potential was much lower than that of ferrocene or disilene 1,
which also showed two redox couples in the oxidation region at
E1/2 = +0.05 (1e) and +0.24 V (1e).5 The separation of the
half-wave oxidation potentials ΔE1/2 is thereby indicative of the
magnitude of the electronic interaction between two redox
centers. ΔE1/2 is significantly larger in 2 (ΔE1/2 = 0.44 V)
compared to those in disilene 1 (ΔE1/2 = 0.19 V)5 and (E)-
Ph(Fc)CC(Fc)Ph (ΔE1/2 = 0.31 V),3c respectively, reflecting
again an increased degree of d−π electron conjugation in 2. In
conclusion, the electrochemical analysis indicated that 2 is a
very effective d−π electron system with stable, multistep redox
behavior. Moreover, a consolidated analysis of the photo-
physical and electrochemical properties suggested an effective
overlapping of d and π* orbitals in 2.
oxidation region, a two-step reversible redox couple at E1/2
=
1
state. The H NMR spectrum of 2 in C6D6 was indicative of a
symmetric structure. Only one singlet signal for the meta aryl
protons of the Tip groups, one septet signal for the ortho
benzyl protons of the Tip groups, one singlet for the free Cp
groups, and two sets of pseudotriplets for the α and β protons
of the Ge-substituted Cp groups were observed. The presence
of two independent doublet signals for the methyl protons of
the o-isopropyl groups would support a trans-bent structure for
2, but the assumed trans-bent structure would in turn be
inconsistent with equivalent resonances for the α and β protons
of the Ge-substituted Cp groups. This assignment is based on
the assumption that facile vertex inversion of the Ge moiety
and/or GeGe bond dissociation and subsequent recombina-
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We turned our attention then to the chemical reactivity of
the GeGe π bond in 2, which represents a heavier element
homologue of olefins. Since digermenes are known to react
easily with elemental chalcogens with formation of the
corresponding heterocycles,19,9g we were interested in the
reactions of 2 with O2, S8, and Se (see Scheme 2 and Figure 3).
metane 11 could be observed. This result is in sharp contrast to
previously reported sulfurization reactions of digermenes with
S8, which typically result in the formation of the corresponding
thiadigermirane and/or 1,3,2,4-dithiadigermetane.19 In these
cases, the 1,3,2,4-dithiadigermetane is most likely formed via a
head-to-tail dimerization of the intermediary germanethione
(R2GeS). We carried out theoretical calculations,17 which
suggested both thiadigermirane 9 and 1,2,3,4-dithiadigermetane
10 to be the kinetic rather than the thermodynamic products.
The sulfurization reaction of 2 to give 11 was found to be
highly exothermic (76.4 kcal/mol), relative to those resulting in
the formation of 9 and 10 (39.9 and 39.4 kcal/mol,
respectively). All attempts to induce thermal interconversion
between 9 and 10 (i.e., sulfurization of 9 and/or desulfurization
of 10), as well as the thermal isomerization of 10 to obtain 11,
were unsuccessful, supporting the direct reaction of digermene
2 (not germylene 7) with S8 to give 9 and 10. We wish to point
out that the activation energy barrier for the isomerization of 10
into the thermally stable isomer 11 is, as a result of the steric
demand of the ferrocenyl substituents, probably very high. The
formation of 8−10 strongly suggests the interpretation of 2 in
solution and at room temperature in terms of a digermene, not
a germylene.
Scheme 2. Chalcogenation Reactions of 2 with Formation of
8−10
Heating a benzene solution of 2 to reflux for 1 h in the
presence of an excess amount of 2,3-dimethyl-1,3-butadiene
resulted in the formation of germolene 129f,19−21 and
germylgermolene 1311,21 in 55% and 36% yields, respectively
(see Scheme 3 and Figure 4). The [2 + 4] cycloaddition
Scheme 3. [1 + 4] Cycloaddition Reactions of 2, 7, and 15
with 2,3-Dimethyl-1,3-butadiene Compounds
Figure 3. Molecular structures of 1,3,2,4-dioxadigermetane 5 (a),
selenadigermirane 8 (b), thiadigermirane 9 (c), and 1,2,3,4-
dithiadigermirane 10 (d). Thermal displacement ellipsoids are set at
the 50% probability level, all hydrogen atoms have been omitted for
clarity, and selected atoms have been labeled. Selected bond lengths
(Å) and angles (deg) are as follows. 5: Ge−O, 1.8169(11),
1.8153(11); Ge−O−Ge, 92.82(5); O−Ge−O, 87.18(5). 8: Ge−Se,
2.3961(4), 2.4017(4); Ge−Ge, 2.3701(4); Ge−Se−Ge, 59.207(12);
Se−Ge−Ge, 60.513(12), 60.280(12). 9: Ge−S, 2.2740(6), 2.2752(6);
Ge−Ge, 2.3588(3); Ge−S−Ge, 62.463(17); S−Ge−Ge, 58.743(16),
58.794(16). 10: Ge−S, 2.2856(5), 2.2871(5); Ge−Ge, 2.4730(3); S−
S, 2.0995(7); Ge−S−S, 90.75(2), 91.10(2); Ge−Ge−S, 82.292(15),
81.923(15).
Figure 4. Molecular structures of germolene 12 (a) and
germylgermolene 13 (b). Only one of the two independent molecules
of 13 per unit cell is shown here. Thermal displacement ellipsoids are
set at the 50% probability level, all hydrogen atoms have been omitted
for clarity, and selected atoms have been labeled. Selected bond
lengths (Å) for 12: Ge−C1, 1.968(2); C1−C2, 1.517(3); C2−C3,
1.335(3); C3−C4, 1.514(3); C4−Ge, 1.9716(19). Selected bond
lengths (Å) for 13: Ge1−Ge2, 2.4665(15), 2.4605(13); Ge1−C1,
1.958(8), 1.974(9); C1−C2, 1.503(12), 1.527(11); C2−C3,
1.319(12), 1.344(12); C3−C4, 1.540(12), 1.494(12); C4−Ge1,
1.967(9), 1.970(9).
Exposure of a benzene solution of 2 to atmospheric oxygen
resulted in the formation of 1,3,2,4-dioxadigermetane 5,
probably via the intermediary 1,2,3,4-dioxadigermetane and
subsequent isomerization.9c,f The corresponding reaction of 2
with elemental selenium was found to proceed readily and
afforded selenadigermirane 8 in high yield (94%). The
analogous sulfurization of 2 with S8 resulted in the formation
of both thiadigermirane 9 and 1,2,3,4-dithiadigermetane 10,
whereas no evidence for the formation of 1,3,2,4-dithiadiger-
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DZVP (for Fe).26 Frequency calculations confirmed minimum
energies for the optimized structures. Computation time was provided
from the Supercomputer Laboratory at the Institute for Chemical
Research, Kyoto University. 2,4,6-Triisopropylphenylchlorogermane
(TipGeH2Cl) was prepared according to literature procedures.27
Synthesis of Ferrocenyl-2,4,6-triisopropylphenylgermane
(3). A solution of ferrocene (3.07 g, 16.5 mmol) and potassium tert-
butoxide (0.17 g, 1.5 mmol) in THF (120 mL) was cooled to −78 °C,
before t-BuLi (1.57 M pentane solution, 21 mL, 33 mmol) was added
dropwise. The reaction mixture was stirred at −78 °C for 1 h, warmed
to room temperature, where stirring was continued for 1 h before the
solution was cooled to −78 °C again. This solution containing the
resulting lithioferrocene was transferred via cannula to a solution of
2,4,6-triisopropylphenylchlorogermane (4.70 g, 15.0 mmol)26 in Et2O
(60 mL) at −78 °C. After it was stirred at −78 °C for 1 h, the solution
was warmed to room temperature, stirred for 10 h, and then quenched
by the addition of saturated aqueous NH4Cl solution. The aqueous
phase was extracted with Et2O, and the combined organic phases were
dried over MgSO4, filtered, and evaporated in vacuo. The obtained
residue was purified by column chromatography (hexane/Et2O) to
give TipFcGeH2 (3; 4.88 g, 10.5 mmol, 70%). 3: orange solid; mp
56.8−58.7 °C. 1H NMR (300 MHz, room temperature, C6D6): δ 1.22
(d, 6H, p-i-Pr-Me, 3J(H−H) = 6.9 Hz), 1.29 (d, 12H, o-i-Pr-Me,
product digermacyclohexene 14 could not be observed.22 The
generation of 12 and 13 is tentatively explained here by an
initial nucleophilic attack of one CC double bond of
butadiene toward the low-lying LUMO orbital of the GeGe
moiety. The weakening of the GeGe double bond
subsequently leads to either expulsion of 1 equiv of 7 with
formation of 12 or a thermally induced 1,2-migration of one of
the Tip groups (leading to 1 equiv of 13).23 Heating C6D6
solutions of germolene 12 or germylgermolene 13 to 80 °C in
the presence of an excess amount of isoprene did not initiate
any further reactions. The regeneration of germylene 7 from 12
or 13 via a potential retro-[1 + 4] cycloaddition was not
observed. Exposing a C6D6 solution of 2 in the presence of an
excess amount of 2,3-dimethyl-1,3-butadiene to photoirradia-
tion did not induce any reaction, demonstrating the
extraordinary stability of 2 toward UV light. In conclusion,
2,3-dimethyl-1,3-butadiene can be used as an effective thermal
trigger to scissor the d−π electron system in 2. In contrast,
reactions of 1,2-bis(ferrocenyl)disilene 1 with excess 2,3-
dimethyl-1,3-butadiene afforded under similar reaction con-
ditions complex mixtures from which we were unable to
identify any distinct products. The cleavage of digermene 2,
induced by the addition of 2,3-dimethyl-1,3-butadiene, can
therefore be directly associated with the intrinsic nature of the
GeGe π bond.
3
3J(H−H) = 6.8 Hz), 2.79 (sept, 1H, p-i-Pr-CH, J(H−H) = 6.9 Hz),
3.54 (sept, 2H, o-i-Pr-CH 3J(H−H) = 6.8 Hz), 4.05 (s, 5H, Cp), 4.12
(pseudo-t, 2H, Cp), 4.17 (pseudo-t, 2H, Cp), 5.33 (s, 2H, GeH), 7.15
(s, 2H, Ar-H). 13C NMR (75 MHz, room temperature, C6D6): δ 24.20
(q), 24.70 (q), 34.81 (d), 34.90 (d), 68.25 (s), 69.13 (d), 70.77 (d),
74.28 (d), 121.26 (d), 130.28 (s), 150.49 (s), 154.64 (s), HRMS
(FAB): m/z calcd for C25H3456Fe74Ge 464.1228 ([M]+), found
464.1221 ([M]+). Anal. Calcd for C25H34FeGe: C, 64.85; H, 7.40.
Found: C, 65.08; H, 7.53.
We have shown here, in conclusion, the synthesis and
characterization of 1,2-bis(ferrocenyl)digermene 2, which
contains a highly unusual d−π electron system. Digermene 2
exhibits a stable, three-step redox couple in solution, and the
thermal reaction with 2,3-dimethyl-1,3-butadiene leads to the
corresponding [1 + 4] cycloaddition products with cleavage of
the GeGe π-bond.
Synthesis of Ferrocenyl-2,4,6-triisopropylphenyldibromo-
germane (4). A solution of ferrocenylgermane 3 (2.32 g, 5.00
mmol) and CBr4 (4.97 g, 15.0 mmol) in benzene (50 mL) was heated
to reflux for 1 h. After the mixture was cooled to ambient temperature,
all volatiles were removed under reduced pressure. The reaction
mixture was extracted with hexane and filtered through a pad of Celite,
and the filtrate was evaporated in vacuo. The obtained residue was
purified by GPLC (toluene) to give TipFcGeBr2 (4; 2.13 g, 3.43
EXPERIMENTAL SECTION
■
General Procedures and Instrumentation. Unless otherwise
stated, all experiments were performed under a dry argon atmosphere
free of oxygen. All solvents were purified by standard methods and/or
the use of “The Ultimate Solvent System” (Glass Contour Co.).24 1H
NMR (300 MHz), 13C NMR (75 MHz) and 77Se NMR (76 MHz)
spectra were measured in C6D6 with a JEOL JNM AL-300
spectrometer, referenced to residual protic impurities of the NMR
solvent (C6D5H 7.15 ppm for 1H NMR spectra) or the NMR solvent
itself (C6D6 128 ppm for 13C NMR spectra). The signal of Ph2Se2
(460 ppm) was used as an external standard for the measurements of
77Se NMR spectra. The multiplicity of signals in the 13C NMR spectra
was determined by DEPT techniques. High-resolution mass
spectrometry data were obtained on a JEOL JMS-700 spectrometer
(FAB) or on a Bruker microTOF (APPI-TOF). UV/vis spectra were
measured on a JASCO Ubest V-570 instrument. GPLC (gel
permeation liquid chromatography) purifications were performed on
an LC-908 or LC-918 instrument (Japan Analytical Industry Co., Ltd.)
equipped with JAIGEL 1H and 2H columns (eluent toluene).
Electrochemical experiments were carried out with an ALS 600A
potentiostat/galvanostat using a glassy-carbon-disk working electrode,
a Pt-wire counter electrode, and an Ag/0.01 M AgNO3 reference
electrode. Measurements were carried out with scan rates of 10 mV
s−1, at ambient temperature in an argon-filled glovebox using o-
dichlorobenzene or THF solutions, containing 0.1 M [(n-Bu)4N][B-
(C6F5)4] or [(n-Bu)4N][PF6] as the supporting electrolyte. Melting
points were determined on a Yanaco micro melting point apparatus
and are uncorrected. Elemental analyses were carried out at the
Microanalytical Laboratory of the Institute for Chemical Research,
Kyoto University. Theoretical calculations were conducted using
electronic structure programs of the Gaussian 03 series.25 Geometries
were optimized with density functional theory at the B3PW91 level
using the basis sets of 6-31+G(2d) (for Ge), 6-31G(d) (for C, H), and
1
mmol, 59%). 4: yellow crystals; mp 146.9−148.3 °C. H NMR (300
MHz, room temperature, C6D6): δ 1.12 (d, 6H, p-i-Pr-Me, 3J(H−H) =
6.9 Hz), 1.22 (d, 12H, o-i-Pr-Me, 3J(H−H) = 6.7 Hz), 2.66 (sept, 1H,
p-i-Pr-CH, 3J(H−H) = 6.9 Hz), 3.93 (sept, 2H, o-i-Pr-CH, 3J(H−H) =
6.7 Hz), 4.15 (pseudo-t, 2H, Cp), 4.31 (s, 5H, Cp), 4.44 (pseudo-t,
2H, Cp), 7.08 (s, 2H, Ar-H). 13C NMR (75 MHz, room temperature,
C6D6): δ 23.83 (q), 25.00 (q), 33.22 (d), 34.56 (d), 70.86 (d), 71.06
(d), 73.11 (d), 84.87 (s), 123.01 (d), 133.94 (s), 152.73 (s), 154.39
(s). HRMS (EI): m/z calcd for C25H32Br256Fe74Ge 619.9430 ([M]+),
found 619.9435 ([M]+). Anal. Calcd for C25H32Br2FeGe: C, 48.37; H,
5.20. Found: C, 48.60; H, 5.30.
Synthesis of (E)-1,2-Bis(ferrocenyl)-1,2-bis(2,4,6-
triisopropylphenyl)digermene (2). KC8 (222 mg, 1.64 mmol)
was added to a solution of 4 (500 mg, 0.805 mmol) in THF (20 mL)
at −78 °C. After the suspension was stirred at −78 °C for 1 h, the
reaction mixture was warmed to −50 °C and stirred for 30 min at this
temperature. After all volatiles were removed under reduced pressure
at room temperature, the residue was taken up in hexane and filtered
through a pad of Celite. All volatiles were removed from the filtrate in
vacuo, and the resulting residue was purified by recrystallization from
hexane to give Tip(Fc)GeGe(Fc)Tip (2; 189 mg, 0.205 mmol,
51%). 2: orange crystals; mp 159.4 °C dec. 1H NMR (300 MHz, room
3
temperature, C6D6): δ 1.28 (d, 12H, p-i-Pr-Me, J(H−H) = 6.9 Hz),
1.47 (d, 12H, o-i-Pr-Me, 3J(H−H) = 6.8 Hz), 1.51 (d, 12H, o-i-Pr-Me,
3
3J(H−H) = 6.8 Hz), 2.89 (sept, 2H, p-i-Pr-CH, J(H−H) = 6.9 Hz),
3.93 (pseudo-t, 4H, Cp), 3.95 (s, 10H, Cp), 3.99 (sept, 4H, o-i-Pr-
CH), 4.00 (pseudo-t, 4H, Cp), 7.36 (s, 4H, Ar-H); 13C NMR (75
MHz, room temperature, C6D6): 24.26 (q), 24.29 (q), 26.26 (q),
34.80 (d), 38.32 (d), 68.74 (d), 71.28 (d), 73.85 (d), 78.38 (s), 121.50
(d), 140.08 (s), 150.77 (s), 154.91 (s); HRMS (ESI TOF): m/z calcd
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for C50H6556Fe274Ge2 923.2235 ([M + H]+), found: 923.2208 ([M +
H]+).
found 956.1815 ([M]+). Anal. Calcd. for C50H64Fe2Ge2S: C, 62.94; H,
6.76. Found: C, 62.68; H, 6.96. 10: orange crystals, mp 96.2−97.1 °C.
3
Reaction of (E)-1,2-Bis(ferrocenyl)-1,2-bis(2,4,6-
triisopropylphenyl)digermene (2) with Atmospheric Oxygen.
At room temperature, a solution of 2 (20.4 mg, 22.1 μmol) in benzene
(5 mL) was exposed to air through a tube filled with CaCl2. An instant
color change of the solution to yellow was observed. After removal of
all volatiles, the crude mixture was recrystallized from hexane to give
1,3,2,4-dioxadigermetane 5 (8.4 mg, 8.8 μmol, 40%). 5: yellow crystals;
mp 150.1−151.3 °C. 1H NMR (300 MHz, room temperature, C6D6):
1H NMR (300 MHz, 70 °C, C6D6): δ 1.26 (d, 6H, p-i-Pr-Me, J(H−
H) = 7.0 Hz), 1.27 (d, 6H, p-i-Pr-Me, 3J(H−H) = 7.0 Hz), 1.12−1.59
(br, 24H, i-Pr-Me), 2.86 (pseudosept, p-i-Pr-CH, 2H), 3.97−4.02 (m,
Cp, 6H), 4.19 (s, Cp, 10H), 4.33−4.36 (m, Cp, 2H), 7.25 (s, Ar-H,
4H), Signals for o-i-Pr-CH (4H) were not observed probably due to
extensive broadening. 13C NMR (75 MHz, 70 °C, C6D6): δ 24.00 (q),
24.02 (q), 25.25 (q), 27.06 (q), 34.56 (d), 35.42 (d), 69.14 (d), 69.80
(d), 71.12 (d), 73.48 (d), 75.62 (d), 80.71 (s), 122.49 (d), 132.65 (s),
151.07 (s), 155.60 (s). HRMS (FAB+): m/z calcd for
C50H6456Fe274Ge232S2 988.1594 ([M]+), found 988.1625 ([M]+).
Anal. Calcd for C50H64Fe2Ge2S2: C, 60.90; H, 6.54. Found: C,
60.90; H, 6.76.
3
δ 1.20 (d, 12H, p-i-Pr-Me, J(H−H) = 7.0 Hz), 1.34 (d, 12H, o-i-Pr-
Me, 3J(H−H) = 6.8 Hz), 1.64 (d, 12H, o-i-Pr-Me, 3J(H−H) = 6.8 Hz),
2.79 (sept, 2H, p-i-Pr-CH, 3J(H−H) = 7.0 Hz), 4.03 (sept, 4H, o-i-Pr-
CH, 3J(H−H) = 6.8 Hz), 4.04 (pseudo-t, 4H), 4.19 (s, 10H, Cp), 4.23
(pseudo-t, 4H), 7.30 (s, 4H, Ar-H). 13C NMR (75 MHz, room
temperature, C6D6): 24.08 (q), 25.56 (q), 25.65 (q), 34.77 (d), 34.89
(d), 69.08 (d), 71.21 (d), 72.99 (d), 74.18 (s), 121.85 (d), 133.11 (s),
151.85 (s), 155.16 (s). HRMS (EI): m/z calcd for C50H6456Fe274Ge2O2
956.2054 ([M]+), found 956.2003 ([M]+).
Reaction of (E)-1,2-Bis(ferrocenyl)-1,2-bis(2,4,6-
triisopropylphenyl)digermene (2) with 2,3-Dimethyl-1,3-buta-
diene. 2,3-Dimethyl-1,3-butadiene (0.27 mL, 2.2 mmol) was added to
a solution of 2 (20.3 mg, 22.0 μmol) in benzene (5 mL). The reaction
mixture was heated to 80 °C for 1 h. After removal of all volatiles, the
crude mixture was extracted with hexane and filtered through a pad of
Celite and all volatiles were evaporated from the filtrate in vacuo. The
residue was purified by GPLC (toluene) to give 1-ferrocenyl-1-(2,4,6-
triisopropylphenyl)-3,4-dimethyl-3-germolene (12; 13.2 mg, 24.3
μmol, 55%) and 1-ferrocenyl-1-{bis(2,4,6-triisopropylphenyl)-
ferrocenyl}germyl-3,4-dimethyl-3-germolene (13; 7.9 mg, 7.9 μmol,
Reaction of (E)-1,2-Bis(ferrocenyl)-1,2-bis(2,4,6-
triisopropylphenyl)digermene (2) with Elemental Selenium.
At room temperature, elemental selenium (17.7 mg, 22.4 μmol) was
added to a solution of 2 (20.6 mg, 22.3 μmol) in benzene (5 mL) and
the reaction mixture was stirred for 1 h. After removal of all volatiles,
the crude mixture was purified by GPLC (toluene) to give the
corresponding selenadigermirane 8 (20.9 mg, 20.9 μmol, 94%). 8:
orange crystals; mp 112.5 °C dec. 1H NMR (300 MHz, room
temperature, C6D6): δ 1.18 (d, 6H, i-Pr-Me, 3J(H−H) = 7.0 Hz), 1.21
1
36%). 12: orange crystals; mp 107.0 °C dec. H NMR (300 MHz,
3
room temperature, C6D6): δ 1.25 (d, 6H, p-i-Pr-Me, J(H−H) = 7.0
Hz), 1.28 (d, 12H, o-i-Pr-Me, 3J(H−H) = 6.8 Hz), 1.84 (s, 6H,
2
3
3
CCH3), 2.21 (dd, 4H, CCH2, J(H−H) = 15.7 Hz, 33.0 Hz), 2.82
(d, 6H, i-Pr-Me, J(H−H) = 6.9 Hz), 1.22 (d, 6H, i-Pr-Me, J(H−H)
3
= 7.0 Hz), 1.23 (d, 6H, i-Pr-Me, 3J(H−H) = 7.0 Hz), 1.57 (d, 6H, i-Pr-
(sept, 1H, p-i-Pr-CH, J(H−H) = 7.0 Hz), 3.28 (sept, 2H, o-i-Pr-CH,
3J(H−H) = 6.8 Hz), 4.10 (s, 5H, Cp), 4.12 (pseudo-t, 2H), 4.16
(pseudo-t, 2H), 7.14 (s, 2H, Ar-H). 13C NMR (75 MHz, room
temperature, C6D6): δ 19.31 (q), 24.23 (q), 25.49 (q), 30.92 (t), 34.71
(d), 35.35 (d), 68.45 (d), 70.17 (d), 72.84 (d), 76.13 (s), 121.67 (d),
131.05 (s), 134.24 (s), 149.96 (s), 154.67. HRMS (FAB): m/z calcd
for C31H4256Fe74Ge 544.1856 ([M]+), found 544.1850 ([M]+). Anal.
Calcd for C31H42FeGe: C, 68.55; H, 7.79. Found: C, 68.81; H, 8.03.
3
3
Me, J(H−H) = 7.0 Hz), 1.81 (d, 6H, i-Pr-Me, J(H−H) = 6.9 Hz),
2.81 (sept, 2H, i-Pr-CH, 3J(H−H) = 7.0 Hz), 3.65 (sept, 2H, i-Pr-CH,
3J(H−H) = 7.0 Hz), 3.83−3.85 (m, 2H, Cp), 3.87−3.89 (m, 2H, Cp),
3.90−3.93 (m, 2H, Cp), 4.03−4.05 (m, 2H, Cp), 4.20 (s, 10H, Cp),
3
4.67 (sept, 2H, i-Pr-CH, J(H−H) = 7.0 Hz), 7.16 (d, 2H, Ar-H,
4J(H−H) = 1.5 Hz), 7.31 (d, 2H, Ar-H, J(H−H) = 1.5 Hz). 13C
4
NMR (75 MHz, room temperature, C6D6): δ 24.07 (q), 24.10 (q),
24.17 (q), 25.37 (q), 26.26 (q), 26.36 (q), 34.64 (d), 36.81 (d), 37.72
(d), 69.20 (d), 69.94 (d), 70.65 (d), 72.23 (d), 74.75 (d), 75.10 (s),
121.24 (d), 122.94 (d), 131.61 (s), 151.26 (s), 154.04 (s), 156.13 (s).
77Se NMR (76 MHz, room temperature, C6D6): δ −331.0. HRMS
1
13: orange crystals; mp 142.0 °C dec. H NMR (300 MHz, room
temperature, C6D6): δ 0.46 (d, 3H, i-Pr-Me, 3J(H−H) = 6.4 Hz), 0.54
3
3
(d, 3H, i-Pr-Me, J(H−H) = 6.4 Hz), 0.74 (d, 3H, i-Pr-Me, J(H−H)
= 6.8 Hz), 1.17 (d, 3H, i-Pr-Me, 3J(H−H) = 7.0 Hz), 1.18 (d, 3H, i-Pr-
3
3
Me, J(H−H) = 7.0 Hz), 1.22 (d, 3H, i-Pr-Me, J(H−H) = 7.0 Hz),
1.23 (d, 3H, i-Pr-Me, 3J(H−H) = 7.0 Hz), 1.25 (d, 3H, i-Pr-Me,
(EI): m/z calcd for C50H6456Fe274Ge280Se 1004.1326 ([M]+), found
1004.1354 ([M]+). Anal. Calcd for C53H71Fe2Ge2Se: C, 60.97; H, 6.85.
Found: C, 60.67; H, 6.89.
3J(H−H) = 7.0 Hz), 1.38 (d, 3H, i-Pr-Me, J(H−H) = 6.6 Hz), 1.44
3
3
3
(d, 3H, i-Pr-Me, J(H−H) = 6.7 Hz), 1.46 (d, 3H, i-Pr-Me, J(H−H)
Reaction of (E)-1,2-Bis(ferrocenyl)-1,2-bis(2,4,6-
triisopropylphenyl)digermene (2) with Elemental Sulfur (S8).
At room temperature, elemental sulfur (5.9 mg, 23 μmol) was added
to a solution of digermene 2 (20.3 mg, 22.0 μmol) in benzene (5 mL)
and the reaction mixture was stirred for 30 min. After removal of all
volatiles, the crude mixture was purified by GPLC (toluene) to give a
3
= 6.3 Hz), 1.47 (d, 3H, i-Pr-Me, J(H−H) = 6.9 Hz), 1.87 (s, 3H,
CCH3), 1.90 (s, 6H, CCH3), 2.26 (m, 2H, CCH2), 2.42 (dd, 2H,
CCH2, 2J(H−H) = 17.0 Hz, 61.3 Hz), 2.72 (sept, 1H, i-Pr-CH, 3J(H−
H) = 6.8 Hz), 2.80 (sept, 1H, i-Pr-CH, 3J(H−H) = 7.0 Hz), 3.20−3.41
(m, 3H, i-Pr-CH), 3.53 (sept, 1H, i-Pr-CH, 3J(H−H) = 6.6 Hz), 3.56
(m, 1H, Cp), 3.92 (m, 1H, Cp), 3.977 (s, 5H, Cp), 3.984 (s, 5H, Cp),
4.13 (m, 1H, Cp), 4.23 (m, 1H, Cp), 4.25 (m, 1H, Cp), 4.33 (m, 1H,
1
mixture of thiadigermirane 9 (54%, as evident from the H NMR
spectrum) and 1,2,3,4-dithiadigermetane 10 (40%, as evident from the
1H NMR spectrum). Product separation and purification was achieved
by GPLC and subsequent recrystallization from hexane to give small
amounts of compounds 9 and 10 in the form of single crystals. 9:
orange crystals; mp 118.8−120.1 °C. 1H NMR (300 MHz, room
4
Cp), 4.38 (m, 1H, Cp), 4.51 (m, 1H, Cp), 6.97 (d, 1H, Ar-H, J(H−
H) = 1.7 Hz), 7.00 (d, 1H, Ar-H, 4J(H−H) = 1.7 Hz), 7.10 (d, 1H, Ar-
4
4
H, J(H−H) = 1.7 Hz), 7.22 (d, 1H, Ar-H, J(H−H) = 1.7 Hz). 13C
NMR (75 MHz, room temperature, C6D6): δ 19.63 (q), 19.69 (q),
23.65 (q), 24.01 (q), 24.14 (q), 24.18 (q), 24.21 (q), 24.25 (q), 25.58
(q), 25.86 (q), 26.29 (q), 26.39 (q), 26.68 (q), 27.25 (q), 29.53 (t),
30.88 (t), 32.67 (d), 34.39 (d), 34.52 (d), 35.10 (d), 35.82 (d), 36.65
(d), 68.63 (d), 69.04 (d), 69.27 (d), 69.79 (d), 70.24 (d), 70.68 (d),
73.31 (d), 73.69 (d), 74.51 (d), 76.33 (d), 77.52 (s), 83.28 (s), 122.02
(d), 122.26 (d), 122.51 (d), 122.89 (d), 132.30 (s), 133.03 (s), 137.59
(s), 140.07 (s), 148.91 (s), 149.53 (s), 152.50 (s), 153.35 (s), 154.40
(s), 154.75 (s). HRMS (FAB): m/z calcd for C56H7456Fe274Ge2
1006.2942 ([M]+), found 1006.2940 ([M]+). Anal. Calcd for
C56H74Fe2Ge2: C, 66.98; H, 7.43. Found: C, 66.95; H, 7.65.
3
temperature, C6D6): δ 1.22 (d, 18H, i-Pr-Me, J(H−H) = 7.0 Hz),
1.23 (d, 6H, i-Pr-Me, 3J(H−H) = 7.0 Hz), 1.58 (d, 6H, i-Pr-Me,
3
3J(H−H) = 7.0 Hz), 1.83 (d, 6H, i-Pr-Me, J(H−H) = 6.8 Hz), 2.81
3
(sept, 2H, i-Pr-CH, J(H−H) = 7.0 Hz), 3.67 (sept, 2H, i-Pr-CH,
3J(H−H) = 7.0 Hz), 3.81−3.84 (m, 2H, Cp), 3.85−3.88 (m, 2H, Cp),
3.89−3.92 (m, 2H, Cp), 4.00−4.03 (m, 2H, Cp), 4.24 (s, 10H, Cp),
4.59 (sept, 2H, i-Pr-CH 3J(H−H) = 6.8 Hz), 7.17 (d, 2H, Ar-H,
4
4J(H−H) = 1.7 Hz), 7.32 (d, 2H, Ar-H, J(H−H) = 1.7 Hz). 13C
NMR (75 MHz, room temperature, C6D6): δ 24.10 (q), 24.11 (q),
24.34 (q), 25.21 (q), 25.75 (q), 26.52 (q), 34.66 (d), 36.51 (d), 37.43
(d), 69.06 (d), 69.99 (d), 70.86 (d), 72.15 (d), 74.55 (d), 75.99 (s),
121.35 (d), 122.76 (d), 132.49 (s), 151.32 (s), 154.23 (s), 155.94 (s).
HRMS (EI+): m/z calcd for C50H6456Fe274Ge232S 956.1851 ([M]+),
Reaction of Germolene 12 with Isoprene. Isoprene (44 μL,
0.44 mmol) was added to a solution of 8 (2.4 mg, 4.4 μmol) in C6D6.
The reaction mixture was heated to 80 °C for 36 h. No change was
1
observed in the H NMR spectrum.
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Organometallics
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Reaction of Germylgermolene 13 with Isoprene. Isoprene
(5.0 μL, 50 μmol) was added to a solution of 13 (3.1 mg, 3.1 μmol) in
C6D6. The reaction mixture was heated to 80 °C for 4 h. No change
Chem. Rev. 2002, 226, 125. (c) Distefano, A. J.; Wishart, J. F.; Isied, S.
S. Coord. Chem. Rev. 2005, 249, 507. (d) Szafert, S.; Gladysz, J. A.
Chem. Rev. 2006, 106, Pr1. (e) Kaim, W.; Lahiri, G. K. Angew. Chem.,
Int. Ed. 2007, 46, 1778.
1
was observed in the H NMR spectrum.
Photoirradiation of Digermene 2 in the Presence of 2,3-
Dimethyl-1,3-butadiene. 2,3-Dimethyl-1,3-butadiene (15 μL, 0.13
mmol) was added to a solution of 2 (5.5 mg, 6.0 μmol) in C6D6. The
reaction mixture was exposed to photoirradiation from a medium-
pressure Hg lamp at room temperature for 1 h. No change was
(2) (a) Powers, M. J.; Meyer, T. J. J. Am. Chem. Soc. 1978, 100, 4393.
(b) Mcmanis, G. E.; Gochev, A.; Nielson, R. M.; Weaver, M. J. J. Phys.
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(3) (a) Bildstein, B.; Hradsky, A.; Kopacka, H.; Malleier, R.; Ongania,
K. H. J. Organomet. Chem. 1997, 540, 127. (b) Hradsky, A.; Bildstein,
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(4) Nishihara, H. Coord. Chem. Rev. 2005, 249, 1468.
(5) (a) Sasamori, T.; Yuasa, A.; Hosoi, Y.; Furukawa, Y.; Tokitoh, N.
Organometallics 2008, 27, 3325. (b) Yuasa, A.; Sasamori, T.; Hosoi, Y.;
Furukawa, Y.; Tokitoh, N. Bull. Chem. Soc. Jpn. 2009, 82, 793.
(6) For recent reviews on disilenes, see: (a) Kira, M.; Iwamoto, T.
Adv. Organomet. Chem. 2006, 54, 73. (b) Scheschkewitz, D. Chem. Eur.
J. 2009, 15, 2476.
(7) Jacobsen, H.; Ziegler, T. J. Am. Chem. Soc. 1994, 116, 3667.
(8) Nagase, S.; Kudo, T. J. Mol. Struct. (THEOCHEM) 1983, 12, 35.
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Chem. Soc., Chem. Commun. 1984, 480. (b) Goldberg, D. E.;
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Trans. 1986, 2387. (c) Tsumuraya, T.; Batcheller, S. A.; Masamune, S.
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(f) Tokitoh, N.; Kishikawa, K.; Okazaki, R.; Sasamori, T.; Nakata, N.;
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Takeda, N.; Tokitoh, N. Organometallics 2005, 24, 3309.
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3479.
1
observed in the H NMR spectrum.
X-ray Diffraction Analysis of 2, 4, 5, 8·0.5C6H14, 9·0.5C6H14,
10·C6H14, 12, and 13·0.5C6H14. Intensity refraction data were
collected on a Rigaku/MSC Mercury CCD diffractometer with
graphite-monochromated Mo Kα radiation (λ = 0.710 70 Å) for 4,
10 and 12 and on a RIGAKU Saturn70 CCD(system) with VariMax
Mo Optic using Mo Kα radiation (λ = 0.710 70 Å) for 2, 5, 9, and 13.
The data set of 8 was collected on the BL38B1 beamline in Spring-8,
using a diffractometer and an ADSC Quantum315 CCD detector
(2011A1409). Single crystals suitable for X-ray analysis were obtained
either by slow recrystallization from hexane (for 4, 5, 12, and 13) or
benzene (5) at room temperature or by recrystallization from hexane
at −40 °C (for 2, 8, 9, and 10). Individual crystals were mounted on a
glass fiber. Structures were solved by direct methods (SIR-97,28 SIR-
2004,29 SHELXS-9730) and refined by full-matrix least-squares
procedures on F2 for all reflections (SHELXL-97).29 All hydrogen
atoms were placed using AFIX instructions, while all other atoms were
refined anisotropically. Crystallographic data for the structures
reported in this paper are contained in the Supporting Information
and have also been deposited with the Cambridge Crystallographic
Data Centre under the following reference codes: CCDC-856393 (2),
CCDC-856394 (4), CCDC-856395 (5), CCDC-856396
(8·0.5C6H14), CCDC-856397 (9·0.5C6H14), CCDC-856398
(10·C6 H1 4 ), CCDC-856399 (12), and CCDC-856400
(13·0.5C6H14). These can be obtained free of charge from the
Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.
uk/data_request/cif.
(11) 1,2-Migration of substituents in digermenes (R2GeGeR2) to
give the corresponding germylgermylenes R3Ge−GeR has been
reported: (a) Trinquier, G. J. Am. Chem. Soc. 1990, 112, 2130.
(b) Grev, R. S.; Schaefer, H. F. Organometallics 1992, 11, 3489.
(c) Richards, A. F.; Phillips, A. D.; Olmstead, M. M.; Power, P. P. J.
Am. Chem. Soc. 2003, 125, 3204.
ASSOCIATED CONTENT
* Supporting Information
Tables giving X-ray crystallographic data and Cartesian
coordinates of the optimized structure of 2 and CIF files
giving X-ray crystallographic data. This material is available free
of charge via the Internet at http://pubs.acs.org.
■
S
(12) The formation of 1,3,2,4-dioxadigermetane 5 can be explained
by the facile isomerization of the corresponding 1,2,3,4-dioxadigerme-
tane, which is generated initially from the addition of aerobic oxygen
onto the GeGe π-bond of 2.9c,f
AUTHOR INFORMATION
Corresponding Author
*Tel: +81-774-38-3202. Fax: +81-774-38-3209. E-mail:
sasamori@boc.kuicr.kyoto-u.ac.jp (T.S.); tokitoh@boc.kuicr.
kyoto-u.ac.jp (N.T.).
■
(13) Crystallographic data of the compounds described here are
shown in the Supporting Information.
(14) Schafer, H.; Saak, W.; Weidenbruch, M. Organometallics 1999,
̈
18, 3159.
(15) Davidson, P. J.; Harris, D. H.; Lappert, M. F. J. Chem. Soc.,
Dalton Trans. 1976, 2268.
Notes
The authors declare no competing financial interest.
(16) Another possible explanation for the observed NMR spectrum
of digermene 2 would be the retention of the trans-bent structure in
solution, with free rotation around the Tip−Ge bonds. In this case, the
equivalent α and β protons of the Ge-substituted Cp groups can be
interpreted in terms of a coincidental overlap of the independent
signals. Alternatively, fast inversion at both Ge atoms and facile
rotation around the Ge−Ge bond could also explain the observed
NMR features with time-averaged C2h or C2v symmetry. At this point,
an unequivocal assignment of the observed spectral features of
digermene 2 in solution is not possible.
ACKNOWLEDGMENTS
■
This work was partially supported by Grants-in-Aid for
Scientific Research (B) (No. 22350017), Young Scientist (A)
(No. 23685010), and the Global COE Program B09 from
Ministry of Education, Culture, Sports, Science and Technol-
ogy of Japan. The synchrotron radiation experiments were
performed at the BL38B1 of Spring-8 with the approval of the
Japan Synchrotron Radiation Research Institute (JASRI) (No.
2011A1409). We thank Dr. U. F. J. Mayer for assistance with
the paper.
(17) B3PW91/6-31G(d) for C, H, 6-31+G(2d) for Ge, DZVP for Fe.
(18) Schafer, A.; Weidenbruch, M.; Muller, T.; Pravinkumar, K.;
̈
Becker, J. Y. Chem. Eur. J. 2009, 15, 8424.
(19) Tsumuraya, T.; Sato, S.; Ando, W. Organometallics 1988, 7,
2015.
REFERENCES
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(21) Hurni, K. L.; Rupar, P. A.; Payne, N. C.; Baines, K. M.
Organometallics 2007, 26, 5569.
(22) (a) Fukaya, N.; Ichinohe, M.; Sekiguchi, A. Angew. Chem., Int.
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(23) The reaction between tetramesityldigermene and 2,3-dimethyl-
1,3-butadiene in THF results exclusively in the formation of the
corresponding mesityl(trimesitylgermyl)germacyclopentene, which
was explained by a 1,2-shift of a mesityl group in tetramesityldi-
germene, followed by subsequent trapping with the diene. No clear
evidence for the formation of the corresponding dimesitylgermacy-
clopentene could be observed. As a result, the possible dissociation of
tetramesityldigermene in THF solution at temperatures below 60 °C
to give 2 equiv of germylene was discarded (see: Hurni, K. L.; Rupar,
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our case, high-temperature 1H NMR spectra as well as high-
temperature UV−vis measurements of 2 did not show any evidence
for the presence of tractable amounts of germylene 7. It is therefore
feasible to assume the initial step to proceed from the reaction
between 2,3-dimethyl-1,3-butadiene and digermene 2.
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dx.doi.org/10.1021/om300064q | Organometallics 2012, 31, 3904−3910