Synthesis and characterization of an extremely hindered tetraaryl-substituted digermene and its unique properties in the solid state and in solution

Article abstract of DOI:10.1016/S0277-5387(01)01035-X

An extremely hindered digermene (E)-Tbt(Mes)Ge=Ge(Mes)Tbt (1; Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl; Mes = mesityl) was synthesized. X-ray crystallographic analysis of the hexane solvated single crystal [1·0.5hexane] revealed that 1 has an extremely long germanium-germanium double bond [2.416(2) A?] as that of a carbon-substituted digermene. The temperature-dependent change of UV-Vis absorption of digermene 1 in solution indicated the quantitative interconversion between 1 and the corresponding germylene Tbt(Mes)Ge: (3). The thermodynamic parameters (ΔH = 14.7 ± 0.2 kcal mol^-1 and ΔS = 42.4 ± 0.8 cal mol^-1 deg^-1) for the dissociation of digermene 1 to germylene 3 were obtained from temperature dependence of the absorption of 1. Since the reactivity of germylene 3 is much higher than that of digermene 1, almost all the intermolecular reactions of 1 in solution proceeded via dissociated 3. For instance, the reaction of 1 with oxygen in solution resulted in a non-stereospecific formation of the cis- and trans-1,3,2,4-dioxadigermetanes 11 and 7 via the initial formation of germanone 12 derived from oxygenation of the dissociated germylene 3. In case of the oxidation in the solid state, however, digermene 1 reacted with O₂ without dissociation to give the corresponding trans-substituted 1,3,2,4-dioxadigermetane stereospecifically. The reaction of digermene 1 with W(CO)₅(THF) was also examined to give the corresponding terminal tungsten complex of the dissociated germylene 3, i.e. Tbt(Mes)Ge=W(CO)₅ (23), as a marginally stable orange yellow paste.

Full text of DOI:10.1016/S0277-5387(01)01035-X

Polyhedron 21 (2002) 563–577
www.elsevier.com/locate/poly
Synthesis and characterization of an extremely hindered
tetraaryl-substituted digermene and its unique properties in the
solid state and in solution
Norihiro Tokitoh a,b,*, Kuniyuki Kishikawa b, Renji Okazaki b,c, Takahiro Sasamori a,
Norio Nakata a, Nobuhiro Takeda a
a Institute for Chemical Research, Kyoto Uni6ersity, Gokasho, Uji, Kyoto 611-0011, Japan
b Department of Chemistry, Graduate School of Science, The Uni6ersity of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan
c Department of Chemical and Biological Sciences, Faculty of Science, Japan Women’s Uni6ersity, 2-8-1 Mejirodai, Bunkyo-ku,
Tokyo 112-8681, Japan
Received 4 September 2001; accepted 27 November 2001
Abstract
An extremely hindered digermene (E)-Tbt(Mes)GeꢀGe(Mes)Tbt (1; Tbt=2,4,6-tris[bis(trimethylsilyl)methyl]phenyl; Mes=
mesityl) was synthesized. X-ray crystallographic analysis of the hexane solvated single crystal [1·0.5hexane] revealed that 1 has an
,
extremely long germanium–germanium double bond [2.416(2) A] as that of a carbon-substituted digermene. The temperature-de-
pendent change of UV–Vis absorption of digermene 1 in solution indicated the quantitative interconversion between 1 and the
corresponding germylene Tbt(Mes)Ge: (3). The thermodynamic parameters (DH=14.790.2 kcal mol−1 and DS=42.490.8 cal
mol−1 deg−1) for the dissociation of digermene 1 to germylene 3 were obtained from temperature dependence of the absorption
of 1. Since the reactivity of germylene 3 is much higher than that of digermene 1, almost all the intermolecular reactions of 1 in
solution proceeded via dissociated 3. For instance, the reaction of 1 with oxygen in solution resulted in a non-stereospecific
formation of the cis- and trans-1,3,2,4-dioxadigermetanes 11 and 7 via the initial formation of germanone 12 derived from
oxygenation of the dissociated germylene 3. In case of the oxidation in the solid state, however, digermene 1 reacted with O2
without dissociation to give the corresponding trans-substituted 1,3,2,4-dioxadigermetane stereospecifically. The reaction of
digermene 1 with W(CO)5(THF) was also examined to give the corresponding terminal tungsten complex of the dissociated
germylene 3, i.e. Tbt(Mes)GeꢀW(CO)5 (23), as a marginally stable orange yellow paste. © 2002 Published by Elsevier Science Ltd.
Keywords: Digermene; Germylene; X-ray crystallographic analysis; Dissociation; Equilibrium; Bond dissociation energy; Dioxadigermetane;
Terminal tungsten complexes
thesized and the intrinsic nature of the metal–metal
double bonds in those dimetallenes has been elucidated
1. Introduction
to a considerable extent. For example, the thermal
dissociation of a disilene into silylenes [3] and that of a
distannene into stannylenes [4] in solution have been
experimentally demonstrated on the basis of their reac-
tivities and spectroscopic properties, and energetics for
their dissociation processes have been estimated. As for
digermenes, a unique 1,2-migration of the mesityl group
has been reported in the thermolysis of tetramesityldi-
germene (Mes2GeꢀGeMes2) leading to the formation of
mesityl(trimesitylgermyl)germylene [5], while the ther-
molysis of more hindered tetraaryldigermenes (E)- and
(Z)-Mes(Tip)GeꢀGe(Tip)Mes (Tip=2,4,6-triisopropyl-
During the last two decades remarkable progress has
been made in the chemistry of low-coordinate com-
pounds of heavier group 14 elements, especially in
those of dimetallenes and metallylenes because of their
unique structures and reactivities [1]. Since the first
isolation of a stable disilene by West et al. in 1981 [2],
a number of stable dimetallenes (disilene [1c–e], diger-
mene [1b,d,f], and distannene [1b,d,f]) have been syn-
* Corresponding author. Tel.: +81-774-38-3200; fax: +81-774-38-
3209.
E-mail address: tokitoh@boc.kuicr.kyoto-u.ac.jp (N. Tokitoh).
0277-5387/02/$ - see front matter © 2002 Published by Elsevier Science Ltd.
PII: S0277-5387(01)01035-X

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N. Tokitoh et al. / Polyhedron 21 (2002) 563–577
which showed a quite unique structure and reactivity.
Here, we present the synthesis and characterization of
this extremely hindered digermene 1, which led us to
the first spectroscopic observation of an equilibrium
between a digermene and germylenes. Digermene 1
provided us with a good opportunity to perform the
first measurement of a bond dissociation energy for the
germanium–germanium double bond.
Scheme 1.
lphenyl) resulted in the rotational isomerization be-
tween these two stereoisomers [6]. Furthermore, te-
trakis(2,6-diethylphenyl)digermene (Dep2GeꢀGeDep2;
Dep=2,6-diethylphenyl) was reportedly converted into
the corresponding cyclotrigermane on heating, proba-
bly via dissociation into the germylene (Dep)2Ge: fol-
lowed by its cyclotrimerization [1c]. Such thermal
dissociation into the corresponding germylenes has also
been postulated in the thermolysis of [(Me3Si)2CH]2Geꢀ
Ge[CH(SiMe3)2]2 [7] and (2-tBu-4,5,6-Me3C6H)2Geꢀ
Ge(2-tBu-4,5,6-Me3C6H)2 [8], but the evidence for the
dissociation was provided only by trapping reactions of
the germylenes [9]. To the best of our knowledge, no
experimental estimation for the bond dissociation en-
ergy of a GeꢀGe double bond has been reported so far.
In view of these situations, we became interested in
2. Results and discussion
2.1. Synthesis and structure
Reaction of dichlorogermane [Tbt(Mes)GeCl2, 2]
with lithium naphthalenide in THF at −78 °C gave a
dark-brown solution. The solvent exchange from THF
to hexane followed by filtration of inorganic salts and
sublimation of naphthalene in vacuo afforded the cor-
responding (E)-substituted digermene 1 exclusively as
orange crystals (Scheme 1). Although digermene 1 is
stable at room temperature under inert atmosphere, it
undergoes decomposition at 92 °C in the solid state.
The molecular structure of 1 was determined by
X-ray crystallographic analysis of the hexane solvated
single crystal [1·0.5hexane], the ORTEP drawing of
which is shown in Fig. 1 along with the selected bond
lengths and angles.
the properties of
a digermene, Tbt(Mes)GeꢀGe-
(Mes)Tbt (1; Tbt=2,4,6-tris[bis(trimethylsilyl)methyl]-
phenyl [10], Mes=mesityl), the silicon analogue of
Fig. 1. ORTEP drawing of (E)-Tbt(Mes)GeꢀGe(Mes)Tbt·0.5hexane (1·0.5hexane) with thermal ellipsoid plots (30% probability). The fragment of
,
solvated hexane is omitted for clarity. Selected bond lengths (A) and angles (°): Ge(1)ꢁGe(2) 2.416(2), Ge(1)ꢁC(1) 2.017(12), Ge(1)ꢁC(28)
1.960(14), Ge(2)ꢁC(37) 2.045(13), Ge(2)ꢁC(64) 1.996(14), C(1)ꢁGe(1)ꢁC(28) 108.0(5), C(1)ꢁGe(1)ꢁGe(2) 130.5(3), C(28)ꢁGe(1)ꢁGe(2) 118.1(4),
C(37)ꢁGe(2)ꢁC(64) 109.1(5), C(37)ꢁGe(2)ꢁGe(1) 132.7(4), C(64)ꢁGe(2)ꢁGe(1) 113.5(3).

N. Tokitoh et al. / Polyhedron 21 (2002) 563–577
565
absorption shown in Fig. 2 clearly indicates that 1
dissociates into the corresponding germylenes 3 at room
temperature, while it does not at low temperature
(Scheme 2), because tetraaryldigermenes and di-
arylgermylenes reportedly have their umax in the range
of 408–440 nm [1f,8] and 466–581nm [15], respectively.
The absorptions observed at 190 K (umax=439 nm, m
2.0×104) and 295 K (umax=575 nm, m 1.6×103) are
assignable to the p–p* transition of digermene 1 and
the n–p transition of germylene 3, respectively. The
isosbestic points observed at 335, 390 and 509 nm
indicate the quantitative interconversion between 1 and
3. The structure of digermene 1 in solution is reason-
ably assumed to be the (E)-isomer as in the solid state,
since the (Z)-isomer has obviously much severer steric
repulsion between two extremely bulky substituents
(Tbt groups) facing each other.
Fig. 2. Temperature-dependent UV–Vis spectra of 1 in hexane (3.7×
10−4 M).
The thermodynamic parameters (DH=14.790.2
kcal mol−1 and DS=42.490.8 cal mol−1 deg−1) for
the dissociation of digermene 1 to germylene 3 were
obtained from the temperature dependence of the ab-
sorptions shown in Fig. 2. This bond dissociation en-
ergy (14.7 kcal mol−1) of digermene 1 into germylene 3
is much smaller than the calculated value (30–45 kcal
mol−1) for the parent system (H2GeꢀGeH2) [7a,16],
indicating that the germanium–germanium double
bond in 1 is considerably weakened due to the severe
steric repulsion between the bulky substituents. In this
connection, it is intriguing that Tbt(Tip)Ge: (Tip=
2,4,6-triisopropylphenyl) [15c,15d] and Tip(Mes)Ge: [6],
which are more and less sterically demanding than 3,
have been shown to exist only as a monomer and a
dimer, respectively, in solution. These observations
point to the subtle effect of the size of substituents on
the equilibrium between a digermene and germylenes. It
is interesting that disilene Tbt(Mes)SiꢀSi(Mes)Tbt bear-
ing the same substituents as 1 exists essentially as a
dimer (i.e. disilene) [3,17]. The bis(trimethylsilyl)methyl-
substituted disilene–digermene pair, [(Me3Si)2CH]2Mꢀ
M[CH(SiMe3)2]2, (M=Si, Ge), is known to show a
similar phenomenon [7,18]. In these systems, the disi-
lene does not undergo any thermal dissociation in
solution, but the digermene is reportedly isolable only
in the solid state and readily dissociates in solution into
the corresponding germylenes at room temperature
[7,18]. It should be noted that the interconversion be-
tween 1 and 3 is the first example of an experimentally
Scheme 2.
,
The Ge(1)ꢁGe(2) bond length [2.416(2) A] of diger-
mene 1 is remarkably longer than the germanium–ger-
manium double bond lengths of previously reported
digermenes bearing carbon substituents [2.21–2.35 A]
,
[6–8,11] and close to the germanium–germanium single
,
,
bond length [2.465 A in (Ph2Ge)4 or 2.463 and 2.457 A
in (Ph2Ge)6] [12], reflecting the large steric repulsion
between Tbt and Mes groups. Weidenbruch et al. have
already reported that strongly twisted (E)-1,2-diamino-
1,2-disilyldigermenes having a unique skeleton have
extremely elongated GeꢀGe double bonds [2.453–2.460
,
A] [13]. The sums of the bond angles around Ge(1) and
Ge(2) of 1 are 356.6° and 355.3°, respectively. The twist
angles along the germanium–germanium bond axis are
16.5(8)° and 34.6(7)°. These structural features of 1
indicate that 1 still retains sp2 hybridized germanium
centers even though its GeꢀGe double bond is weak
and elongated.
observed equilibrium between
a
digermene and
germylenes [19].
2.2. Beha6ior in solution
2.3. Reactions in solution
Interestingly, a hexane solution of 1 showed a re-
versible thermochromism; the hexane solution of 1
(3.7×10−4 M) was blue (umax=575 nm) at room
temperature, but it turned orange yellow (umax=439
nm) at low temperature [14]. The change in UV–Vis
In order to investigate the reactivity of digermene 1
having an extremely elongated GeꢀGe double bond, a
solution of digermene 1 was treated at −100 °C with
methanol which is known to add readily across a

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N. Tokitoh et al. / Polyhedron 21 (2002) 563–577
dark, the color changed into pale yellow and two
conformational isomers of trans-1,3,2,4-dioxadiger-
metanes 7a (13%) and 7b (49%) were obtained after
usual chromatographic separation (Scheme 3).
In this reaction cis-1,3,2,4-dioxadigermetane was not
obtained. These facts show that the reaction of the
digermene with oxygen proceeds stereospecifically. Al-
though the oxidation of disilenes is known to take place
stereospecifically in solution or in the solid state [20],
there have been very few reports on the stereochemistry
of the oxidation of a digermene. As for the case of
(Z)-1,2-diamino-1,2-disilyldigermene, Weidenbruch et
al. have reported the stereospecific oxidation reaction
with molecular oxygen leading to the formation of the
corresponding cis-1,3,2,4-dioxadigermetane.
Scheme 3.
The mechanistic studies of the oxidation of (E)-
Mes(t-Bu)SiꢀSi(t-Bu)Mes (8) in solution have revealed
that the reaction of 8 with oxygen first gives the [2+
2]cycloadducts,
(E)-1,2,3,4-dioxadisiletane
(9),
Scheme 4.
stereospecifically, which then undergoes rearrangement
to afford trans-1,3,2,4-dioxadisiletane 10 [20d]. In the
solid state, (E)-1,2,3,4-dioxadisiletane (9) rearranged
stereospecifically to afford trans-1,3,2,4-dioxadisiletane
10 (Scheme 4) [20d]. These facts suggest that the oxida-
tion of (E)-digermene 1 might take place in two steps
via 1,2,3,4-dioxadigermetane intermediate with reten-
tion of the stereochemistry although the observation of
the intermediate was not successful in this case.
The structures of the two conformational isomers of
the trans-1,3,2,4-dioxadigermetanes 7a and 7b were de-
termined by the X-ray crystallographic analysis as
shown in Figs. 3 and 4. Single crystals of trans-1,3,2,4-
dioxadigermetane 7a were obtained as those solvated
with hexane and have been revealed to have two non-
identical trans-1,3,2,4-dioxadigermetane molecules in
the unit cell, while no solvation with hexane was ob-
served for the conformational isomer 7b. In Fig. 3 are
shown the ORTEP drawings of [7a·hexane] (fragments 1
and 2, respectively). Fig. 4 shows the ORTEP drawing of
another trans-1,3,2,4-dioxadigermetane 7b.
GeꢀGe double bond [1f,11a], but the orange–yellow
color of the solution due to 1 did not disappear after
the solution was kept for 6 h at the same temperature.
Upon warming up to room temperature the solution
became colorless to give a methoxygermane 4 (44%),
the insertion product of germylene 3 into the OꢁH
bond of methanol (Scheme 2). These facts show that
the GeꢀGe double bond in 1 is so effectively protected
by the surrounding four bulky aryl groups as revealed
by X-ray crystallographic analysis that 1 is incapable of
reacting with methanol at low temperatures. At ele-
vated temperatures, however, digermene 1 dissociates
into the corresponding germylene 3, which readily re-
acts with methanol to give the methoxygermane 4.
Germylene 3 generated by dissociation of digermene 1
also reacted with Et3SiH and 2,3-dimethyl-1,3-butadi-
ene at room temperature to afford the corresponding
adducts 5 (70%) and 6 (62%), respectively (Scheme 2).
2.4. Oxidation reactions
Figs. 5 and 6 show the selected bond lengths and
angles of the central dioxadigermetane rings of 7a and
7b. The dioxadigermetane rings of the fragment 1 and
fragment 2 of 7a and that of 7b are almost planar with
the sum of the interior bond angles being 360.0°,
359.9°, and 360.0°, respectively. The germanium–ger-
manium distances of fragments 1 and 2 of 7a and that
Since the reaction with oxygen can be performed
either in the solid state or in solution, we made a
careful investigation of the oxidation reactions of the
extremely hindered digermene 1 to elucidate the intrin-
sic reactivity.
,
of 7b [2.653(2), 2.660(2), and 2.691(4) A, respectively]
are much longer than a typical GeꢁGe single bond
2.4.1. Reaction of 1 with oxygen in the solid state
At first, the oxidation of digermene 1 was examined
in the solid state. When a finely powdered orange
sample of 1 was exposed to oxygen for 3 days in the
,
length (2.457–2.463 A) [12]. Dihedral angles of 7a and
7b formed by two OꢁGeꢁO planes are 2.5°, 3.9°, and
1.9°, respectively, as shown in Figs. 7 and 8. There is
Fig. 3. ORTEP drawings of trans-1,3,2,4-dioxadigermetane [7a·hexane] with thermal ellipsoid plots (30% probability). (a) Fragment 1; and (b)
fragment 2 for the independent molecules in the unit cell. The fragment of solvated hexane is omitted for clarity.

N. Tokitoh et al. / Polyhedron 21 (2002) 563–577
567
Fig. 3.

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N. Tokitoh et al. / Polyhedron 21 (2002) 563–577
Fig. 4. ORTEP drawing of trans-1,3,2,4-dioxadigermetane 7b with thermal ellipsoid plots (30% probability).
planes (8.4°) is slightly larger in 7a and 7b. In this
connection, there have been some interesting reports on
the structural properties of dioxadisiletanes. Although
the 1,3,2,4-dioxadisiletane rings are generally nearly
little difference in the geometries of the four-membered
rings of 7a between the two fragments as shown in Figs.
5 and 7.
The molecular structure of 7a is different from that
of 7b in dihedral angles between the central four-mem-
bered ring and Tbt, Mes aromatic ring planes (com-
pound 7b: 44.8° and 41.9° for the Tbt rings and 61.0°
and 61.2° for the Mes rings; fragment 1: 49.6° and 72.3°
for the Tbt rings and 67.1° and 56.6° for the Mes rings;
fragment 2: 48.2° and 74.6° for the Tbt rings and 68.5°
and 57.4° for the Mes rings).
Although we cannot understand at present why the
conformational isomers are isolated as stable com-
pounds, it is probably due to hindered rotation of the
aromatic rings with regard to the four-membered ring
1
in the case of 7b. Since H NMR spectrum of 7a shows
two signals in the aromatic region, each of two Tbt and
Mes groups are equivalent and hence they rotate with
regard to the four-membered ring. In contrast, 1H
NMR spectrum of 7b shows four signals in the aro-
matic region, suggesting that the Tbt and Mes groups
do not rotate. Furthermore, compound 7b exhibits a
,
Fig. 5. Selected bond lengths (A) and angles (°) for 7a (fragments 1
and 2).
1
very complicated H NMR spectrum in other regions,
suggesting greater steric congestion around Tbt and
Mes groups than its isomer 7a. Consequently, the ger-
manium–germanium distance of 7b is slightly longer
than that of 7a and the angles of GeꢁOꢁGe and
OꢁGeꢁO are larger and smaller than those of 7a,
respectively.
,
Fig. 6. Selected bond lengths (A) and angles (°) for 7b.
The structures of the four-membered rings of 7a and
7b are similar to that of the previously reported te-
trakis(2,6-diethylphenyl)-1,3,2,4-dioxadigermetane [21],
although its dihedral angle between two OꢁGeꢁO
Fig. 7. Dihedral angles of 7a (fragments 1 and 2).

N. Tokitoh et al. / Polyhedron 21 (2002) 563–577
569
Fig. 8. A dihedral angle of 7b.
Scheme 7.
Fig. 9. Schematic representation for the core ring structure of 1,3,2,4-
dioxadisiletanes.
Scheme 8.
long enough to release the repulsion between the oxy-
gen atoms.
2.4.2. Reaction of 1 with oxygen in solution
The reaction of digermene 1 with oxygen in solution
gave trans-1,3,2,4,-dioxadigermetane 7a (20%) and cis-
1,3,2,4,-dioxadigermetane 11 (38%) as shown in Scheme
5, although the reaction of 1 with oxygen in the solid
state gave only the trans-1,3,2,4-dioxadigermetanes 7a
and 7b stereospecifically (vide supra). The most plausi-
ble reaction mechanism is that digermene 1 dissociates
into the corresponding germylene 3 in solution and 3
readily reacts with molecular oxygen to give the germa-
nium–oxygen double-bond species (germanone) 12,
which might dimerize to afford trans- and cis-1,3,2,4,-
dioxadigermetanes as in the case of the previously
reported germylene (Scheme 6) [24].
It is noteworthy that Tbt- and Mes-substituted metal-
lanethiones (14a and 14b) and metallaneselone 14c
derived from the dechalcogenation of 1,2,3,4,5-tetra-
chalcogenamatallolanes 13 dimerized to give only the
cis-substituted 1,3,2,4-dichalcogenadimetalletanes 15
(Scheme 7) [25].
Scheme 5.
planar as in the case of the dioxadigermetane rings, the
silicon–silicon distances are as long as, or even shorter
than a typical SiꢁSi single bond lengths [22]. Two
extreme qualitative explanations have been postulated
for these structures (Fig. 9): (1) there is a s bond
between the two silicon atoms, and the SiꢁO bonds are
necessarily electron deficient (structure A) and (2) the
strong repulsion between the oxygen atoms causes the
silicon atom to be close together, but there is no
bonding between them (structure B). NMR studies
confirmed the view that there is no s bonding between
the silicons [23].
The structural difference between the 1,3,2,4-dioxa-
disiletane and their germanium analogues is explained
as follows; the SiꢁO bond lengths are too short to
release the repulsion between the oxygen atoms. As a
result, the silicon–silicon distances are close to a SiꢁSi
single bond length, whereas the GeꢁO bond lengths are
The lack of stereoselectivity in the dimerization of
germanone 12 is explicable in terms of its high reactiv-
ity. It has already been reported that the germanone
Tbt(Tip)GeꢀO (16) readily underwent intramolecular
CꢁSi insertion to give 17 and 18 in solution (Scheme 8),
Scheme 6.

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N. Tokitoh et al. / Polyhedron 21 (2002) 563–577
Fig. 10. ORTEP drawing of cis-1,3,2,4-dioxadigermetane 11 with thermal ellipsoid plots (30% probability).
although Tbt(Tip)GeꢀS (19) and Tbt(Tip)GeꢀSe (20)
In order to investigate the possible interconversion
were stable in solution [25,26]. The fact that germanone
between them, the thermolysis of 7a and 7b was moni-
1
16 shows quite
a different reactivity from ger-
tored by H NMR spectroscopy. Although no change
manethione 19 and germaneselone 20 is probably due
to the difference in the polarity of GeꢀX (X=O, S, and
Se) [25,26]. The high polarity of the GeꢀO has been
predicted by ab initio calculation for dimethylger-
manone [27].
was observed for compound 7a at 85 °C, compound 7b
decomposed to afford the trans-1,3,2,4-dioxadiger-
metane 7a (34%) under the same conditions (Scheme 9).
When a mixture of 7b and methanol or mesitonitrile
oxide, which are useful trapping reagents for a ger-
manone [26], was heated at 85 °C, the corresponding
trapping product of germanone 12, i.e. methoxyger-
manol 21 (56%) or dioxazagermole 22 (33%), was ob-
tained together with the isomerized trans-1,3,2,4-
dioxadigermetane 7a (Scheme 9) [26]. On the other
hand, 7a did not give any methanolysis products in the
presence of methanol under the same conditions. These
The molecular geometry of the cis-1,3,2,4-dioxadiger-
metane 11 was also determined by X-ray crystallo-
graphic analysis. In Fig. 10 is shown the ORTEP
drawing of 11, and some selected structural parameters
for 11 are schematically illustrated in Fig. 11. Fig. 11(a)
shows selected bond lengths and angles for the central
dioxadigermetane ring in 11. Fig. 11(b) shows that the
dihedral angle formed by two OꢁGeꢁO planes is 19.4°.
In the case of trans-1,3,2,4-dioxadigermetanes 7a (frag-
ment 1 and fragment 2) and 7b, the dihedral angles of
the central ring are 2.5°, 3.9°, and 1.9°, respectively.
These facts show that the steric repulsion between two
Tbt groups facing each other may be released by fold-
ing the four-membered ring in the cis-1,3,2,4-dioxadi-
germetane 11. The large folding angles have also been
observed in the Tbt- and Mes-substituted cis-1,3,2,4-
dichalcogenadimetalletane derivatives [25].
2.4.3. Stability of the oxidation products
In the oxidation of digermene 1 in the solid state, two
conformational isomers (7a and 7b) of a 1,3,2,4-
dioxadigermetane were obtained as oxidation products.
,
Fig. 11. (a) Selected bond lengths (A) and angles (°) for 11. (b) A
dihedral angle between planes O(1)ꢁGe(1)ꢁO(2) and
O(1)ꢁGe(2)ꢁO(2).

N. Tokitoh et al. / Polyhedron 21 (2002) 563–577
571
results show that germanone 12 is only generated by the
photolysis of the more hindered conformational isomer
7b of the two trans-1,3,2,4-dioxadigermetanes.
2.4.4. Reaction of germylene 3 deri6ed from digermene
1 with W(CO)5·THF
In order to verify the ability of steric protection
afforded by the combination of Tbt and Mes groups,
we have examined the reaction of the diarylgermylene,
Tbt(Mes)Ge: (3), generated by the dissociation of the
corresponding digermene 1 in solution, with tungsten
pentacarbonyl tetrahydrofuran complex.
When digermene 1 was treated with W(CO)5·THF in
THF at room temperature, the color of the solution
changed from blue to orange suggesting the formation
of the expected terminal tungsten complex of
germylene, Tbt(Mes)GeꢀW(CO)5 (23) (Scheme 11). Al-
though the tungsten complex 23 was separated from the
reaction mixture by silica gel column chromatography,
the further purification by GPLC resulted in the de-
composition probably due to the reaction with moisture
or oxygen even if toluene was used as an eluent. This
marginal stability of 23 is in sharp contrast to that of
the more crowded germylene–tungsten complex, Tbt-
(Tip)GeꢀW(CO)5 [15c], which is quite stable in solution
or in the solid state and can be purified by GPLC and
silica gel column chromatography without any decom-
position. These results suggest that at least the steric
protection afforded by the combination of Tbt and Tip
groups is indispensable to isolate the germylene-transi-
tion metal complexes as stable compounds.
Scheme 9.
Scheme 10.
3. Conclusion
An extremely hindered digermene (E)-Tbt(Mes)-
GeꢀGe(Mes)Tbt (1) was synthesized, and its X-ray
crystallographic analysis revealed a remarkable elonga-
tion of the GeꢀGe double bond of 1. The temperature-
dependent change in the electronic spectra of 1
indicated the quantitative interconversion between 1
and the corresponding germylene Tbt(Mes)Ge: (3) in
solution. Since the reactivity of germylene 3 is much
higher than that of digermene 1, almost all the inter-
molecular reactions of 1 in solution proceeded via
dissociated 3. For example, the reaction of 1 with
oxygen in solution resulted in a non-stereospecific for-
mation of the cis- and trans-1,3,2,4-dioxadigermetanes
11 and 7 via the initial formation of germanone 12
derived from oxygenation of the dissociated germylene
3. In case of the oxidation of 1 in the solid state,
however, digermene 1 reacted with O2 molecule as a
GeꢀGe double bond compound to give the correspond-
ing trans-1,3,2,4-dioxadigermetanes (7a and 7b; isolable
and separable conformational isomers) stereospecifi-
cally. In addition, it was revealed that an extremely
Scheme 11.
facts show that germanone 12 is generated in the ther-
molysis of 7b and then 12 reacts with methanol or
mesitonitrile oxide to give the methoxygermanol 21 or
[3+2]cycloadduct 22, respectively.
Since the 1,3,2,4-dioxadigermetane 7b was found to
dissociate thermally into the germanone 12, we next
examined the photolysis of 7a and 7b. Upon photolysis
7b gave another trans-1,3,2,4-dioxadigermetane 7a
(71%). Dioxadigermetane 7b was irradiated in the pres-
ence of methanol to afford 7a (76%) and methoxyger-
manol 21 (9%) (Scheme 10). On the other hand,
photolysis of 7a in the presence of methanol under the
same conditions did not give any photoreaction prod-
ucts but resulted in the complete recovery of 7a. These

572
N. Tokitoh et al. / Polyhedron 21 (2002) 563–577
hindered tetraaryl-substituted trans-1,3,2,4-dioxadiger-
metane 7b decomposes to generate the corresponding
germanone 12 by both thermolysis and photolysis.
Further investigation of physical and chemical prop-
erties of the newly obtained, overcrowded digermene 1
and dioxadigermetanes 7 and 11 is currently in
progress.
ml) of digermene 1 (3.2 mg). After two freeze–pump–
thaw cycles, the cell was evacuated and sealed. The
absorbance of the solution was observed at each tem-
perature (Fig. 2) on a variable temperature liquid nitro-
gen cryostat DN1704 (Oxford Instruments Limited)
and the temperature was monitored by a temperature
controller model ITC (Oxford Instruments Limited)
with the calibration error being 90.2 °C.
The thermodynamic parameters (DH, DS) for disso-
ciation of digermene 1 to germylene 3 were calculated
by the equation below.
4. Experimental
All experiments were performed under argon atmo-
sphere otherwise noted. THF was purified by distilla-
tion from sodium benzophenone ketyl before use. All
solvents used in the reactions were purified by the
ln(A2B/AA)= −DH/RT+(DS/R−ln(mA/m2B))
AB= −(2mB/mA)AA+C
(1)
(2)
1
reported method. The H (500 MHz), 13C (126 MHz)
AA and mA are the absorbance and the molar absorp-
tion coefficient of 1, respectively, and AB and mB are that
of 3. C is a constant. The absorbances of digermene 1
and germylene 3 were obtained at 439 nm for 1 and at
575 nm for 3. The mB was determined by a separate
experiment for a hexane solution which was prepared
by adding hexane (6 ml) to a hexane solution (3 ml) of
1 (2.0 mg, 0.0013 mmol). Their statistical errors were
calculated by a standard method.
NMR spectra were measured in CDCl3 and C6D6 with
a Bruker AM-500, JEOL a-500, or JEOL AL-300 spec-
trometer with CHCl3 and C6D5H as internal standard.
Preparative gel permeation liquid chromatography
(GPLC) was performed on LC-908 (JAI gel 1H and 2H
columns) with chloroform as an eluent. Preparative
thin-layer chromatography (PTLC) and dry column
chromatography (DCC) were performed with Merck
Kieselgel 60 PF 254 (Art. No. 7747) and ISN silica
DCC 60A. Electronic spectra were recorded on a
JASCO Ubest-50 UV–Vis spectrometer. All melting
points (m.p.) were determined on a Yanaco micro
melting point apparatus and are uncorrected. Elemental
analyses were carried out at the Microanalytical Labo-
ratory of Department of Chemistry, Faculty of Science,
The University of Tokyo.
DH=14.790.2 kcal mol−1 and
DS=42.490.8 cal mol−1 K−1
(umax=439 nm, mB 2.0×104)
(umax=575 nm, mA 1.6×103)
4.1. Preparation of (E)-1,2-dimesityl-1,2-bis{2,4,6-
tris[bis(trimethylsilyl)methyl]phenyl}digermene (1)
4.3. Reaction of digermene 1 with methanol
To an orange–yellow solution of 1 (65.5 mg, 0.044
mmol) in THF (5 ml) was added methanol (50 ml, 1.23
mmol) at −100 °C. The orange–yellow color due to 1
did not disappear after 6 h at same temperature, but the
solution became colorless on warming up to r.t. After
removal of the solvent, the reaction residue was chro-
matographed over GPLC and PTLC (SiO2 with hex-
ane) to afford methoxygermene 4 (30.2 mg, 0.039
mmol, 44%).
To a solution of dichlorogermane 2 [28] (1.36 g, 1.67
mmol) in THF (70 ml) was added lithium naph-
thalenide (0.54 M, 3.6 mmol) at −78 °C, and the
mixture was warmed up to room temperature (r.t.).
After removal of the solvent, hexane was added to the
residue to precipitate inorganic salts. The filtrate was
subjected to sublimation in vacuo for 3 h at 60 °C.
Then the residue was washed with hexane several times
to afford digermene 1 (288 mg, 0.19 mmol, 23%).
1
4: White crystals, m.p. 174–176 °C; H NMR (500
1
1: Orange crystals (hexane), m.p. (dec.) 92 °C; H
MHz, CDCl3, 300 K) l −0.15 (s, 9H), −0.08 (s, 9H),
0.048 (s, 18H), 0.051 (s, 18H), 1.11 (s, 1H), 2.18 (s, 1H),
2.26 (s, 3H), 2.47 (s, 6H), 2.57 (s, 1H), 3.39 (s, 3H), 6.24
(s, 1H), 6.40 (s, 1H), 6.45 (s, 1H), 6.82 (s, 2H); 13C
NMR (126 MHz, CDCl3, 300 K) l 0.33 (q), 0.63 (q),
0.74 (q), 0.81 (q), 0.95 (q), 1.31 (q), 21.08 (q), 23.75 (q),
26.68 (d), 26.78 (d), 30.34 (d), 53.70 (q), 122.77 (d),
127.40 (d), 128.21 (s), 128.79 (d), 133.10 (s), 139.38 (s),
143.38 (s), 144.37 (s), 150.20 (s), 150.82 (s). Anal. Calc.
for C37H74OGeSi6: C, 57.26; H, 9.61. Found: C, 56.88;
H, 9.45%.
NMR (500 MHz, C6D6, 300 K) l 0.19 (s, 18H), 0.21 (s,
18H), 0.23 (s, 18H), 1.52 (s, 1H), 2.15 (s, 2H), 2.17 (s,
3H), 2.59 (brs, 6H), 6.55 (s, 1H), 6.67 (s, 1H), 6.77 (s,
2H).
4.2. Obser6ation of an equilibrium between digermene 1
and germylene 3 and estimation of the thermodynamic
parameters (ZH, ZS) for the dissociation of 1 to 3
In a quartz UV cell was placed a hexane solution (5

N. Tokitoh et al. / Polyhedron 21 (2002) 563–577
573
4.4. Reaction of 1 with Et3SiH
dioxadigermetanes (7a) (6.3 mg, 0.0041 mmol, 13%)
and 7b (23.9 mg, 0.0199 mmol, 49%).
To a solution of 1 (63.7 mg, 0.043 mmol) in THF (3
ml) was added Et3SiH (100 ml, 0.63 mmol) at r.t. The
solution was stirred for overnight. After removal of the
solvent, the reaction residue was chromatographed over
GPLC and WCC (SiO2 with hexane) to afford silylger-
mane 5 (51.5 mg, 0.060 mmol, 70%).
7a: White crystals (CHCl3–EtOH), m.p. \300 °C;
1H NMR (500 MHz, C6D6, 350 K) l −0.04 (s, 72H),
0.00 (s, 36H), 1.51 (s, 2H), 2.13 (s, 6H), 2.85 (brs, 12H),
3.09 (s, 2H), 6.57 (s, 4H), 6.73 (s, 4H) (the peak
assignable to methine protons of o-bis(trimethylsi-
lyl)methyl groups of Tbt group was not observed);
HRMS (FAB) m/z 1519.6611 ([M+H]+), calc. for
C72H140O272Ge74GeSi12 1519.6595. Anal. Calc. for
C72H140O2Ge2Si12: C, 56.88; H, 9.28. Found: C, 56.10;
H, 8.76%.
7b: White crystals (CHCl3–EtOH), m.p. (dec.) 153–
155 °C; 1H NMR (500 MHz, C6D6, 350 K) l −0.07 (s,
36H), 0.19 (s, 18H), 0.23 (s, 18H), 0.32 (s, 18H), 0.48 (s,
18H), 1.53 (s, 2H), 1.87 (s, 2H), 2.16 (s, 6H), 2.26 (s,
6H), 2.94 (s, 6H), 3.40 (s, 2H), 6.63 (s, 2H), 6.69 (s,
2H), 6.74 (s, 2H), 6.78 (s, 2H); Anal. Calc. for
C72H140O2Ge2Si14: C, 56.88; H, 9.28. Found: C, 56.08;
H, 9.01%.
1
5: White crystals, m.p. (dec.) 168–170 °C; H NMR
(500 MHz, CDCl3, 300 K) l −0.20 (s, 9H), −0.14 (s,
9H), 0.02 (s, 9H), 0.03 (s, 9H), 0.09 (s, 9H), 0.10 (s,
9H), 0.77 (q, J=7.8 Hz, 6H), 0.89 (t, J=7.8 Hz, 9H),
1.26 (s, 1H), 1.96 (brs, 3H), 1.98 (s, 1H), 2.05 (s, 1H),
2.19 (s, 3H), 2.50 (brs, 3H), 5.09 (s, 1H), 6.29 (s, 1H),
6.41 (s, 1H), 6.63 (s, 1H), 6.78 (s, 1H); 13C NMR (126
MHz, CDCl3, 300 K) l 0.91 (q), 1.01 (q), 1.05 (q), 1.17
(q), 1.68 (q), 1.78 (q), 5.21 (t), 8.12 (q), 20.96 (q), 25.48
(q), 26.52 (q), 29.10 (d), 29.55 (d), 30.13 (q), 122.78 (d),
128.04 (d), 128.46 (dx2), 133.60 (s), 136.86 (s), 137.36
(s), 141.94 (s), 142.49 (s), 143.47 (s), 149.30 (s), 149.90
(s). Anal. Calc. for C42H86GeSi7·H2O: C, 57.43; H,
10.10. Found: C, 57.79; H, 9.63%.
4.7. Reaction of digermene 1 with oxygen in solution
4.5. Reaction of 1 with 2,3-dimethyl-1,3-butadiene
To a solution of 1 (67.0 mg, 0.045 mmol) in THF (5
ml) was bubbled oxygen dried by passing through
sulfuric acid and Sicapent® at r.t. The solution was
stirred overnight. After removal of the solvent, the
reaction residue was chromatographed over GPLC and
PTLC (SiO2 with hexane) to afford trans-1,3,2,4-
dioxadigermetane 7a (13.7 mg, 0.009 mmol, 20%) and
cis - 2,4 - dimesityl - 2,4 - bis{2,4,6 - tris[bis(trimethylsilyl)-
methyl]phenyl}-1,3,2,4-dioxadigermetane (11) (25.8 mg,
0.017 mmol, 38%).
To a solution of 1 (59.5 mg, 0.040 mmol) in THF (5
ml) was added 2,3-dimethyl-1,3-butadiene (90 ml, 0.80
mmol) at r.t. The solution was stirred for overnight.
After removal of the solvent, the reaction residue was
chromatographed over GPLC and PTLC (SiO2 with
hexane) to afford germacyclopentene 6 (40.7 mg, 0.049
mmol, 62%).
1
6: White crystals, m.p. (dec.) 190–192 °C; H NMR
(500 MHz, CDCl3, 300 K) l −0.08 (s, 36H), 0.02 (s,
18H), 1.24 (s, 1H), 1.69 (s, 6H), 1.90 (s, 1H), 2.01 (s,
1H), 2.03 (ABq, JAB=16 Hz, wAB=130 Hz, 4H), 2.20
(s, 3H), 2.35 (s, 6H), 6.24 (s, 1H), 6.36 (s, 1H), 6.75 (s,
2H); 13C NMR (126 MHz, CDCl3, 300 K) l 0.83 (q),
1.04 (q), 1.28 (q), 19.31 (q), 20.79 (q), 25.68 (q), 27.48
(d), 27.61 (d), 30.05 (d), 34.56 (t), 122.54 (d), 127.71 (d),
129.01 (d), 130.76 (s), 132.32 (s), 137.67 (s), 141.13 (s),
142.35 (s), 142.73 (s), 150.40 (s), 150.64 (s). Anal. Calc.
for C42H80GeSi6: C, 61.06; H, 9.76. Found: C, 60.77; H,
9.48%.
11: White crystals (CHCl3–EtOH), m.p. \300 °C;
1H NMR (500 MHz, C6D6, 350 K) l 0.19 (s, 18H), 0.25
(s, 36H), 0.38 (s, 18H), 0.40 (s, 18H), 0.51 (s, 18H), 1.57
(s, 2H), 2.07 (s, 2H), 2.12 (s, 6H), 2.45 (s, 6H), 2.75
(brs, 6H), 3.25 (s, 2H), 6.38 (s, 2H), 6.65 (s, 4H), 6.69
(s, 2H); HRMS (FAB) m/z 1519.6611 ([M+H]+), calc.
for C72H140O272Ge74GeSi12 1519.6595. Anal. Calc. for
C72H140O2Ge2Si12: C, 56.88; H, 9.28. Found: C, 56.80;
H, 8.99%.
4.8. Thermolysis of 1,3,2,4-dioxadigermetane 7b
4.6. Reaction of digermene 1 with oxygen in the solid
state
In a 5 mm NMR tube was placed a C6D6 solution
(0.6 ml) of 7b (12.8 mg, 0.0084 mmol). After three
freeze–pump–thaw cycles, the tube was evacuated and
sealed. When the solution was heated at 85 °C for 18.5
h, the 1H NMR spectrum of the reaction mixture
showed the absence of starting material 7b. After re-
moval of the solvent, the residue was separated by
PTLC (SiO2 with hexane) to afford 7a (4.3 mg, 0.0028
mmol, 34%).
Finely powdered orange crystals of digermene 1 (47.5
mg, 0.0319 mmol) were exposed to oxygen in the dark
for 3 days, during which time the color changed into
pale yellow. The crystals were chromatographed over
GPLC and PTLC (SiO2 with hexane) to give two
conformational isomers of trans-2,4-dimesityl-2,4-
bis{2,4,6 - tris[bis(trimethylsilyl)methyl]phenyl} - 1,3,2,4-

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N. Tokitoh et al. / Polyhedron 21 (2002) 563–577
4.9. Thermolysis of 1,3,2,4-dioxadigermetane 7a
4.12. Thermal reaction of 7a with methanol
In a 5 mm NMR tube was placed a C6D6 solution
(0.6 ml) of 7a (13.2 mg, 0.0087 mmol). After three
freeze–pump–thaw cycles, the tube was evacuated and
sealed. When the solution was heated at 85 °C for 21 h,
In a 5 mm NMR tube was placed a CDCl3 solution
(0.6 ml) of 7a (13.0 mg, 0.0086 mmol) and methanol (50
ml, 1.24 mmol). After three freeze–pump–thaw cycles,
the tube was evacuated and sealed. When the solution
was heated at 85 °C for 21 h, no change was observed
1
no change was observed in the H NMR spectrum.
1
in the H NMR spectrum.
4.10. Thermal reaction of 7b with methanol
4.13. Photolysis of 7b
In a 5 mm NMR tube was placed a CDCl3 solution
(0.6 ml) of 7b (13.0 mg, 0.0086 mmol) and methanol (50
ml, 1.24 mmol). After three freeze–pump–thaw cycles,
the tube was evacuated and sealed. When the solution
In a 5 mm NMR tube was placed a CDCl3 solution
(0.6 ml) of 7b (12.5 mg, 0.0082 mmol). After five
freeze–pump–thaw cycles, the tube was evacuated and
sealed. The solution was irradiated with a 400 W high
pressure Hg lamp approximately −45 °C for 14 min.
After removal of the solvent, the residue was separated
by PTLC (SiO2 with hexane) to afford 7a (8.8 mg,
0.0058 mmol, 71%).
1
was heated at 85 °C for 18.5 h, the H NMR spectrum
of the reaction mixture showed the absence of starting
material 7b. After removal of the solvent the residue
was separated by PTLC (SiO2 with hexane) to afford 7a
(4.9 mg, 0.0032 mmol, 37%) and (hydroxyl)mesityl-
(methoxy){2,4,6-tris[bis(trimethylsilyl)methyl]-phenyl}-
germane (21) (7.5 mg, 0.0097 mmol, 56%).
4.14. Photolysis of 7b in the presence of methanol
1
21: H NMR (500 MHz, CDCl3, 300 K) l −0.18 (s,
In a 5 mm NMR tube was placed a CDCl3 solution
(0.6 ml) of 7b (12.5 mg, 0.0082 mmol) and methanol (50
ml, 1.2 mmol). After three freeze–pump–thaw cycles,
the tube was evacuated and sealed. When the solution
was irradiated with a 400 W high-pressure Hg lamp at
approximately −45 °C for 16 min. After removal of
the solvent, the residue was separated by PTLC (SiO2
with hexane) to afford 7a (9.5 mg, 0.063 mmol, 76%)
and hydroxy(methoxy)germane 21 (1.2 mg, 0.0015
mmol, 9%).
9H), −0.11 (s, 9H), 0.028 (s, 18H), 0.032 (s, 18H), 1.30
(s, 1H), 1.41 (s, 1H), 2.25 (s, 3H), 2.50 (s, 6H+1H),
2.81 (s, 1H), 3.35 (s, 3H), 6.25 (s, 1H), 6.39 (s, 1H), 6.81
(s, 2H); 13C NMR (126 MHz, CDCl3, 300 K) l 0.37 (q),
0.70 (q), 0.82 (q), 1.13 (q), 1.43 (q), 21.00 (q), 23.96 (q),
26.91 (d×2), 30.50 (d), 50.34 (q), 122.90 (d), 127.63
(d), 129.29 (d), 129.59 (s), 131.96 (s), 139.83 (s), 143.67
(s), 145.28 (s), 150.58 (s), 150.90 (s).
4.11. Thermal reaction of 7b with mesitonitrile oxide
4.15. Photolysis of 7a in the presence of methanol
In a 5 mm NMR tube was placed a CDCl3 solution
(0.6 ml) of 7b (14.4 mg, 0.0093 mmol) and mesitonitrile
oxide (79.8 mg, 0.50 mmol). After three freeze–pump–
thaw cycles, the tube was evacuated and sealed. When
the solution was heated at 85 °C for 32 h, the 1H NMR
spectrum of the reaction mixture showed the absence of
starting material 7b. After removal of the solvent, the
residue was separated by GPLC and PTLC (SiO2 with
hexane) to afford 7a (4.0 mg, 0.0026 mmol, 28%), and
the second fraction was again separated by PTLC (SiO2
with CHCl3–hexane 1/1) to afford 2-mesityl-2-{2,4,6-
tris[bis(trimethylsilyl)methyl]phenyl}-4-mesityl-1,3,5,2-
dioxazagermole (22) (5.8 mg, 0.0063 mmol, 34%).
In a 5 mm NMR tube was placed a CDCl3 solution
(0.6 ml) of 7a (11.8 mg, 0.0078 mmol) and methanol (60
ml, 1.4 mmol). After three freeze–pump–thaw cycles,
the tube was evacuated and sealed. The solution was
irradiated with a 400 W high pressure Hg lamp at
approximately −45 °C for 20 min. The 1H NMR
spectrum of the reaction mixture showed no signal of
21.
4.16. [{2,4,6-Tris[bis(trimethylsilyl)methyl]phenyl}-
(2,4,6-trimethylphenyl)germylidene]penta-
carbonyltungsten(0) (23)
1
22: H NMR (500 MHz, CDCl3, 300 K) l −0.07 (s,
18H), 0.00 (s, 9H), 0.03 (s, 9H), 0.05 (s, 9H), 0.06 (s,
9H), 1.38 (s, 1H), 2.07 (s, 6H), 2.10 (s, 1H), 2.22 (s,
1H), 2.23 (s, 6H), 2.52 (s, 6H), 6.36 (s, 1H), 6.49 (s,
1H), 6.775 (s, 2H), 6.782 (s, 2H); HRMS (FAB) m/z
922.4185 ([M+H]+), calc. for C46H82O2N74GeSi6
922.4173.
To a THF solution (2 ml) of digermene 1 (0.279 g,
0.187 mmol) was added an excess of W(CO)5(THF),
which was prepared by the photolysis of W(CO)6 (0.173
g, 0.491 mmol) in 15 ml of THF using a 100 W high
pressure mercury lamp [29]. After stirring for 12 h at
r.t., the reaction mixture was evaporated to give an

N. Tokitoh et al. / Polyhedron 21 (2002) 563–577
575
1.107 g cm−3, m(Mo Ka)=8.11 cm−1, 2qmax=50°,
T=296(2) K, R1=0.0945 [I\2|(I)] and wR2=0.2651
(all data), GOF=0.928. The largest difference peak
orange–yellow paste. The orange–yellow paste was
purified by flush column chromatography (SiO2–hex-
ane) to give the pentacarbonyltungsten(0) complex 23
(0.124 g, ca. 31%) as an orange solid. Complete purifi-
cation of 23 was failed due to its instability in the open
and hole were 0.849 and −1.266 e A−3. The final cycle
,
of full-matrix least-squares refinement was based on
25212 reflections and 1631 variable parameters with 20
restraints.
1
air. 23: H NMR (CDCl3, 300 MHz) l −0.04 (s, 9H),
0.04 (s, 9H), 0.05 (s, 27H), 0.10 (s, 9H), 1.37 (s, 1H),
2.21 (s, 6H), 2.24 (s, 3H), 2.45 (s, 1H), 2.48 (s, 1H), 6.37
(br s, 1H), 6.44 (br s, 1H), 6.75 (s, 2H). IR(KBr)
1943,1949, 2068 cm−1. UV–Vis(CH2Cl2) 432 nm (m,
14 000).
Crystal data for 7b: C72H140Ge2O2Si12, FW=
1520.10, crystal dimensions 0.20×0.10×0.05 mm, tri-
(
clinic, space group P1 (c2), a=21.28(2),
,
b=16.103(13), c=16.105(14) A, h=84.36(7)°, i=
3
,
109.00(7)°, k=71.01(7)°, V=4804(8) A , Z=2,
D
calc=1.051 g cm−3, m(Mo Ka)=8.10 cm−1, 2qmax
=
4.17. X-ray data collection for [1·0.5hexane],
[7a·hexane], 7b, and 11
45°, T=296(2) K, R1=0.1013 [I\2|(I)] and wR2=
0.1735 (all data), GOF=0.807. The largest difference
peak and hole were 0.371 and −0.664 e A−3. The final
,
Single crystals of [1·0.5hexane], [7a·hexane], 7b, and
11 were grown by the slow evaporation of the saturated
solution of each compounds in hexane at r.t. All mea-
surements were made on a Rigaku AFC7R diffrac-
tometer (for [1·0.5hexane], [7a·hexane], and 7b) with
graphite monochromated Mo Ka radiation (u=
cycle of full-matrix least-squares refinement was based
on 12566 reflections and 784 variable parameters with
two restraints. The rigid-bond restraint to Uij-values of
two bonded atoms using DELU construction were ap-
plied to the ortho- and para- CꢁC bonds of one Tbt
group (C40ꢁC44 and C42ꢁC45).
,
0.71069 A) and a rotating anode generator and on a
Crystal data for 11: C72H140Ge2O2Si12, FW=
1520.10, crystal dimensions 0.60×0.55×0.10 mm, or-
thorhombic, space group Pna21 (c33), a=22.135(6),
Rigaku/MSC Mercury CCD for 11 with graphite
,
monochromated Mo Ka radiation (u=0.71070 A). An
orange prismatic crystal of [1·0.5hexane] was mounted
in a glass capillary, while the other crystals of
[7a·hexane], 7b, and 11 were subjected to data collec-
tion without sealing. The structure was solved by direct
methods (SHELXS-97) and refined by full-matrix least-
squares procedures on F2 for all reflections (SHELXL-97)
[30]. In all cases non-hydrogen atoms were refined
anisotropically, while all hydrogens except for those of
solvated hexane were placed using AFIX instructions.
As for the solvated hexane for [1·0.5hexane] and
[7a·hexane], all non-hydrogen atoms were refined
isotropically, and the intramolecular CꢁC bond lengths
and angles are restrained to be ideal lengths using
DFIX instruction.
,
b=30.788(8), c=13.214(4) A, h=i=k=90°, V=
3
9005(4) A , Z=4, Dcalc=1.121 g cm−3, m(Mo Ka)=
,
8.64 cm−1, 2qmax=50°, T=103(2) K, R1=0.1049
[I\2|(I)] and wR2=0.2495 (all data), GOF=1.079.
The largest difference peak and hole were 0.864 and
−0.989 e A−3. The final cycle of full-matrix least-
,
squares refinement was based on 14179 reflections and
793 variable parameters with eight restraints. One of
the carbon atoms of the trimethylsilyl group at para-
position of a Tbt group was restrained to be approxi-
mately isotropic (C56).
5. Supplementary material
Crystal data for [1·0.5hexane]: C72H140Ge2Si12·
0.5C6H14, FW=1531.19, crystal dimensions 0.30×
0.20×0.15 mm, monoclinic, space group P21/c (c14),
All the crystallographic data (excluding structure fac-
tors) of [1·0.5hexane], [7a·hexane], 7b, and 11 have
already been deposited at the Cambridge Crystallo-
graphic Data Centre as supplementary publication
numbers CCDC 169633, 169634, 169635, and 169636,
respectively. Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, Cam-
bridge CB21EZ, UK (fax: +44-1233-336-033, e-mail:
deposit@ccdc.cam.ac.uk).
,
a=18.779(7), b=18.375(7), c=28.495(16) A, i=
3
96.53(4)°, V=9769(7) A , Z=4, Dcalc=1.041 g cm−3
,
,
m(Mo Ka)=7.96 cm−1, 2qmax=50°, T=173(2) K,
R1=0.1177 [I\2|(I)], wR2=0.2991 (all data),
GOF=0.841. The largest difference peak and hole
were 0.816 and −0.605 e A−3. The final cycle of
,
full-matrix least-squares refinement was based on 17158
reflections and 799 variable parameters with nine re-
straints.
Crystal data for 7a·hexane: C72H140Ge2O2Si12·C6H14,
FW=1606.27, crystal dimensions 0.60×0.55×0.05
Acknowledgements
(
mm, triclinic, space group P1 (c2), a=23.735(7),
,
b=30.169(11), c=13.533(3) A, h=95.60(3)°, i=
This work was partially supported by Grants-in-Aid
for Scientific Research from the Ministry of Education,
3
,
90.47(2)°, k=88.16(3)°, V=9639(5) A , Z=4, Dcalc
=

576
N. Tokitoh et al. / Polyhedron 21 (2002) 563–577
(b) A. Sekiguchi, H. Yamazaki, C. Kabuto, H. Sakurai, J. Am.
Chem. Soc. 117 (1995) 8025;
(c) M. Kira, T. Iwamoto, T. Maruyama, C. Kabuto, H. Sakurai,
Organometallics 15 (1996) 3767.
Culture, Sports, Science and Technology, Japan. We
are also grateful to Shin-etsu Chemical Co., Ltd., and
Tosoh Akzo Co., Ltd., for the generous gift of chloro-
silanes and alkyllithiums, respectively. T. S. thanks
Research Fellowships of the Japan Society for the
Promotion of Science for Young Scientists.
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was observed for a solution of persilylated digermenes. The
authors suggested that the thermochromism originated from an
equilibrium between two different structures around the GeꢀGe
bond. See Ref. [11c].
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