Structure and properties of an overcrowded 1,2-dibromodigermene

Article abstract of DOI:10.1021/om050129n

A 1,2-dibromodigermene having Bbt groups (Bbt = 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl) was synthesized by the reaction of BbtLi with GeBr₂-dioxane. X-ray crystallographic analysis revealed that it retains the Ge=Ge double bond in the solid state, while the equilibrium between the 1,2-dibromodigermene and the corresponding bromogermylenes in solution was evidenced by the UV-vis spectroscopic studies and the chemical reactions. The reactions of the 1,2-dibromodigermene with elemental sulfur in toluene resulted in the formation of a cis-dithiadigermetane derivative, indicating the generation of a transient germathiocarbonyl bromide derivative via the sulfurization reaction of the Bbt-substituted bromogermylene generated in the equilibrium state.

Full text of DOI:10.1021/om050129n

Organometallics 2005, 24, 3309-3314
3309
Structure and Properties of an Overcrowded
1,2-Dibromodigermene
Takahiro Sasamori, Yusuke Sugiyama, Nobuhiro Takeda, and Norihiro Tokitoh*
Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
Received February 23, 2005
A 1,2-dibromodigermene having Bbt groups (Bbt ) 2,6-bis[bis(trimethylsilyl)methyl]-4-
[tris(trimethylsilyl)methyl]phenyl) was synthesized by the reaction of BbtLi with GeBr2‚
dioxane. X-ray crystallographic analysis revealed that it retains the GedGe double bond in
the solid state, while the equilibrium between the 1,2-dibromodigermene and the corre-
sponding bromogermylenes in solution was evidenced by the UV-vis spectroscopic studies
and the chemical reactions. The reactions of the 1,2-dibromodigermene with elemental sulfur
in toluene resulted in the formation of a cis-dithiadigermetane derivative, indicating the
generation of a transient germathiocarbonyl bromide derivative via the sulfurization reaction
of the Bbt-substituted bromogermylene generated in the equilibrium state.
Introduction
Tip2C6H3 (Tip ) 2,4,6-triisopropylphenyl), 2,6-Mes2C6H3
(Mes ) mesityl), and 2,6-Dip2C6H3 (Dip ) 2,6-diisopro-
pylphenyl) from the viewpoints of their unique struc-
tures and properties.7,8 The chlorogermylenes ArGeCl
(Ar ) 2,6-Tip2C6H3, 2,6-Mes2C6H3, and 2,6-Dip2C6H3)
behave as a divalent germanium species in solution but
are known to exist as a dimer of germylenes (1,2-
dichlorodigermene) in the solid state.9 In addition, the
arylchlorogermylenes are fascinating species as good
precursors for a variety of unique low-coordinated
organogermanium compounds such as Ar(Me)GedGe-
(Me)Ar,8 Ar(H)GedGe(H)Ar,10 and ArGetGeAr.7c,11 Dur-
ing the course of our studies on kinetic stabilization of
low-coordinated organogermanium compounds, we have
succeeded in the synthesis and isolation of a novel 1,2-
dibromodigermene, Bbt(Br)GedGe(Br)Bbt (1, Bbt ) 2,6-
Low-coordinated species of heavier group 14 elements
are one of the most fascinating subjects of organome-
tallic chemistry.1 The concept of kinetic stabilization is
evidenced to be of great use for the construction of such
reactive species. Since the isolation of the first stable
distannene, Dis2SndSnDis2,2 in 1973 and disilene, Mes2-
SidSiMes2,3 in 1981, a number of low-coordinated
species of heavier group 14 elements have been synthe-
sized by taking advantage of kinetic stabilization.1 On
the other hand, halometallylenes RMX (M ) heavier
group 14 element, X ) halogen) have attracted a great
deal of attention.4 However, the previously reported
examples, such as Mes*GeCl (Mes* ) 2,4,6-tri-tert-
butylphenyl),5 which was described to be a monomer
either in solution or in the solid state, and TsiGeCl‚LiCl‚
3THF [Tsi ) C(SiMe3)3]6 have not been structurally
characterized. Recently, much attention has been fo-
cused on arylchlorogermylenes (ArGeCl) kinetically
stabilized by a bulky m-terphenyl group such as 2,6-
(4) Other examples of kinetically and thermodynamically stabilized
chlorogermylenes have been reported. For example, see: (a) Saur, I.;
Alonso, S. G.; Barrau, J. Appl. Organomet. Chem. 2005, 19, 414-428.
(b) Bibal, C.; Mazieres, S.; Gornitzka, H.; Couret, C. Polyhedron 2002,
21, 2827-2834. (c) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R.
Chem. Rev. 2002, 102, 3031-3065. (d) Bibal, C.; Mazieres, S.; Gorni-
tzka, H.; Couret, C. Organometallics 2002, 21, 2940-2943. (e) Ding,
Y. Q.; Hao, H. J.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H. G.
Organometallics 2001, 20, 4806-4811. (f) Ding, Y. Q.; Roesky, H. W.;
Noltemeyer, M.; Schmidt, H. G.; Power, P. P. Organometallics 2001,
20, 1190-1194. (g) Bibal, C.; Mazieres, S.; Gornitzka, H.; Couret, C.
Angew. Chem., Int. Ed. 2001, 40, 952-954. (h) Yamashita, M.;
Murakami, H.; Unrin-in, T.; Kawachi, A.; Akiba, K.; Yamamoto, Y.
Chem. Lett. 2005, 34, 690-691.
* To whom correspondence should be addressed. Phone: +81-774-
38-3200.
Fax:
+81-774-38-3209.
E-mail:
tokitoh@
boc.kuicr.kyoto-u.ac.jp.
(1) For reviews, see: (a) Tsumuraya, T.; Batcheller, S. A.; Masam-
une, S. Angew. Chem., Int. Ed. Engl. 1991, 30, 902-930. (b) Escudie´,
J.; Couret, C.; Ranaivonjatovo, H.; Satge´, J. Coord. Chem. Rev. 1994,
130, 427-480. (c) Baines, K. M.; Stibbs, W. G. Adv. Organomet. Chem.
1996, 39, 275-324. (d) Brook, A. G.; Brook, M. A. Adv. Organomet.
Chem. 1996, 39, 71-158. (e) Driess, M.; Gru¨tzmacher, H. Angew.
Chem., Int. Ed. Engl. 1996, 35, 829-856. (f) Okazaki, R.; West, R. Adv.
Organomet. Chem. 1996, 39, 231-273. (g) Power, P. P. J. Chem. Soc.,
Dalton Trans. 1998, 2939-2951. (h) Power, P. P. Chem. Rev. 1999,
99, 3463-3503. (i) Tokitoh, N.; Okazaki, R. Coord. Chem. Rev. 2000,
210, 251-277. (j) Tokitoh, N.; Okazaki, R. Adv. Organomet. Chem.
2001, 47, 121-166. (k) Weidenbruch, M. Organometallics 2003, 22,
4348-4360. (l) Mackay, K. H. The chemistry of organic germanium,
tin and lead compounds; Patai, S., Ed.; Wiley: New York, 1995;
Chapter 2, pp 97-194.
(5) Jutzi, P.; Leue, C. Organometallics 1994, 13, 2898-2899.
(6) Ohtaki, T.; Ando, W. Organometallics 1996, 15, 3103-3105.
(7) (a) Simons, R. S.; Pu, L. H.; Olmstead, M. M.; Power, P. P.
Organometallics 1997, 16, 1920-1925. (b) Pu, L. H.; Olmstead, M. M.;
Power, P. P.; Schiemenz, B. Organometallics 1998, 17, 5602-5606. (c)
Pu, L. H.; Phillips, A. D.; Richards, A. F.; Stender, M.; Simons, R. S.;
Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 2003, 125, 11626-
11636.
(8) Stender, M.; Pu, L. H.; Power, P. P. Organometallics 2001, 20,
1820-1824.
(9) As for the case of ArGeCl (Ar ) 2,6-Tip2C6H3), two types of single
crystals were obtained. X-ray crystallographic analysis revealed that
one of them has a dimeric structure (digermene skeleton), while the
other has a monomeric (germylene) structure. See ref 8.
(10) Richards, A. F.; Phillips, A. D.; Olmstead, M. M.; Power, P. P.
J. Am. Chem. Soc. 2003, 125, 3204-3205.
(2) (a) Davidson, P. J.; Lappert, M. F. J. Chem. Soc., Chem.
Commun. 1973, 317-317. (b) Goldberg, D. E.; Harris, D. H.; Lappert,
M. F.; Thomas, K. M. J. Chem. Soc., Chem. Commun. 1976, 261-262.
(c) Lappert, M. F. Adv. Chem. Ser. 1976, 256-265. (d) Goldberg, D.
E.; Hitchcock, P. B.; Lappert, M. F.; Thomas, K. M.; Thorne, A. J.;
Fjeldberg, T.; Haaland, A.; Schilling, B. E. R. J. Chem. Soc., Dalton
Trans. 1986, 2387-2394.
(11) (a) Power, P. P. Chem. Commun. 2003, 2091-2101. (b) Stender,
M.; Phillips, A. D.; Wright, R. J.; Power, P. P. Angew. Chem., Int. Ed.
2002, 41, 1785-1787.
(3) West, R.; Fink, M. J.; Michl, J. Science 1981, 214, 1343-1344.
10.1021/om050129n CCC: $30.25 © 2005 American Chemical Society
Publication on Web 05/24/2005

3310 Organometallics, Vol. 24, No. 13, 2005
Sasamori et al.
Chart 1. Donor-Acceptor Bonding Model for 1
Table 1. Theoretically Optimized Structural
Parameters for Dibromodigermenes 3 and 4
[B3LYP/6-31+G(2d) for Ge,Br, 6-31G(d) for C,H]
Figure 1. ORTEP drawing of 1 (50% probability). Hydro-
gen atoms and the solvated toluene molecules are omitted
for clarity.
R ) H (3)
R ) Mes (4)
a
dGedGe
Br-Ge -R b
θc
2.378
101.7
53.2
2.414
104.7
48.1
a GedGe bond lengths in Å. b Br-Ge-R (R ) H or ipso-carbon
of Ph or Mes) bond angles in deg. c Out-of-plane angle θ (see Figure
2) in deg.
Figure 2. (a) Selected structural parameters (Å, deg) of
1. (b) Side view from the GedGe bond axis of 1.
Scheme 1
Figure 2) of 1 is the widest (ca. 44.6°) among those for
the previously reported digermenes (0-40°). The two
Br-Ge-C(Bbt) bond angles are essentially equal, at
100.04(10)°, which is obviously smaller than the Cl-
Ge-C(Ar) bond angles (ca. 109°) of Ar(Cl)GedGe(Cl)-
Ar (Ar
) 2,6-Tip2C6H3, 2,6-Mes2C6H3, and 2,6-
Dip2C6H3).7,8 These structural features of 1 are most
likely interpreted in terms of the weak donor-acceptor
bonds between two bromogermylene units of 2 (Chart
1).1e That is, the small Br-Ge-C(Bbt) bond angles
mean high p-character of the Br-Ge and Ge-C bonds
and high s-character of the n-orbital of the germanium
atom in the corresponding singlet germylene, BbtGeBr
(2), indicating that the degree of the intermolecular
donation of the n-orbital of 2 to the vacant p-orbital of
the other germylene 2 decreases due to the high
s-character of the n-orbital in germylene 2. It was
conceivable that the weaker donor-acceptor bond in 1
gave rise to the longer GedGe double bond and the
larger out-of-plane angle. Theoretically optimized struc-
tural parameters for the model compounds of trans-
dibromodigermenes R(Br)GedGe(Br)R [R ) H (3) and
Mes (4)] are summarized in Table 1. The optimized Br-
Ge-C bond angle and the out-of-plane angle (θ) in 4
were found to be similar to those observed in 1,
indicating that the p-character of the Ge-Br and Ge-
C(Bbt) bonds in 1 is little affected by the extremely
bulky Bbt group. On the other hand, the GedGe bond
length of 1 [2.5087(7) Å] was elongated as compared
with those optimized for the less hindered models, 3 and
4 (2.378-2.414 Å). Taking into consideration the slight
electronic perturbation of the Bbt group toward the
germylene unit 2, the marked elongation of the GedGe
bond observed for 1 is probably due to the steric
hindrance of the extremely bulky Bbt groups.
bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)me-
thyl]phenyl). We present here the synthesis of 1 and
its equilibrium with the corresponding bromoger-
mylenes (BbtGeBr, 2) in solution, which was evidenced
by UV-vis spectroscopy and supported by theoretical
calculations. The sulfurization reaction of the equilib-
rium mixture of 1 and 2 in solution is also discussed.
Results and Discussion
Treatment of BbtLi, which is prepared by the reaction
of BbtBr with t-BuLi, with GeBr2‚dioxane in THF at
-78 °C afforded an orange solution. After the removal
of inorganic salts followed by the concentration of the
filtrate and recrystallization, dibromodigermene 1 was
isolated as stable orange crystals in 88% yield. Di-
germene 1 is stable at room temperature under inert
atmosphere, and it decomposes at ca. 180 °C in the solid
state. The molecular structure of 1 was established by
the X-ray crystallographic analysis of the toluene-
solvated single crystal, [1‚2toluene]. In Figures 1 and 2
are shown the ORTEP drawing and the selected struc-
tural parameters of 1, respectively. Similarly to the case
of Ar(Cl)GedGe(Cl)Ar (Ar ) 2,6-Tip2C6H3, 2,6-Mes2C6H3,
or 2,6-Dip2C6H3),7,8 1 shows a trans-digermene struc-
ture, a dimer of the corresponding arylbromogermylenes
(BbtGeBr, 2), having a center of symmetry in the middle
of its GedGe bond. The GedGe bond length of 1 [2.5087-
(7) Å] is the longest among those of the previously
reported digermenes (2.21-2.44 Å) and is even longer
than the Ge-Ge single-bond lengths in (Ph2Ge)4 (2.465
Å) and (Ph2Ge)6 (2.457 Å). The out-of-plane angle (θ,
In benzene-d6 solution, 1H and 13C NMR spectra of 1
showed reasonable signals corresponding to the Bbt
1
groups. In variable-temperature (VT) H NMR spectra
of 1, the observed signals assignable to the Bbt groups
were found to shift in the range -80 to 50 °C,12 although
it was difficult to explain the situations by only these
spectra. The UV/vis spectrum of 1 in hexane showed a

Overcrowded 1,2-Dibromodigermene
Organometallics, Vol. 24, No. 13, 2005 3311
Scheme 2
Scheme 3
Figure 3. VT-UV/vis spectra of 1 in toluene (1.5 × 10-3
M, 1.0 cm cell).
characteristic absorption maximum at 449 nm, which
we believed to be assignable to the π f π* transitions
of the GedGe double bond of 1. However, VT-UV/vis
spectra of 1 in toluene showed unique dynamic charac-
ter in the range -20 to 70 °C. That is, the intensity of
the absorption at 449 nm increased as the temperature
was lowered and decreased on warming with almost no
shift for the absorption maxima (Figure 3). Such a
thermal change of the absorbance intensity can be
explained on the basis of the equilibrium between
dibromodigermene 1 and the corresponding bromoger-
mylenes 2 in toluene. It is generally accepted that
digermenes undergo ready dissociation into the corre-
sponding germylenes in solution. Indeed, the previously
reported 1,2-dichlorodigermenes Ar(Cl)GedGe(Cl)Ar (Ar
) 2,6-Tip2C6H3, 2,6-Mes2C6H3, and 2,6-Dip2C6H3) are
known to exist as the corresponding germylenes in
solution.7,8 In addition, the equilibrium between tet-
raaryldigermene E-Tbt(Mes)GedGe(Mes)Tbt (Tbt )
2,4,6-[CH(SiMe3)2]3C6H2) (λmax ) 439 nm) and dia-
rylgermylenes Tbt(Mes)Ge:, which showed characteris-
tic absorption maxima at longer wavelength (λmax ) 575
nm) assignable to the n f p electron transitions, was
successfully observed by VT-UV/vis spectra in hexane.13
In this case, the absorption maxima at 575 nm increased
with raising the temperature, indicating the shift of
equilibrium to the side of the germylene, Tbt(Mes)Ge:.
On the other hand, theoretical calculations on the
excited state of model compounds, trans-Mes(Br)Ged
Ge(Br)Mes 5 and Mes(Br)Ge: 6, gave us helpful infor-
mation to understand the dynamic behavior of 1 ob-
served in VT-UV/vis spectra. The TD-DFT calculations
indicated that the n f p electron transitions of 6 (466
nm, f ) 0.0094) should appear at a region very close to
those of the π f π* electron transitions of 5 (438 nm, f
) 0.2368). It can be concluded that the observed
absorption maxima at 449 nm of a toluene solution of 1
should be reasonably attributable to that for the over-
lapped absorptions of both of the π f π* electron
transitions of 1 and the n f p electron transitions of 2
as an equilibrium mixture.14 Therefore, the observed
decrease of the absorbance at higher temperature, which
should shift the equilibrium to 2 in analogy with the
case of trans-Tbt(Mes)GedGe(Mes)Tbt, can be under-
stood as the balance due to the smaller ꢀ of the n f p
absorption of 2 than the much more intense ꢀ of the π
f π* absorption of 1. The equilibrium between 1 and 2
in solution was further examined from the viewpoints
of chemical reactions. When a THF solution of dibro-
modigermene 1 was treated with an excess amount of
2,3-dimethyl-1,3-butadiene at room temperature, bro-
mogermolene 7, which should be formed via [1+4]-
cycloaddition reaction of 2 with 2,3-dimethyl-1,3-
butadiene, was obtained in 56% yield. The byproducts
in this reaction contained no corresponding [2+4]-
cycloadducts of 1, 1,2-digermacyclohex-4-ene 8, indicat-
ing that the digermene 1 could not undergo a [2+4]-
cycloaddition reaction under these conditions probably
due to steric reasons. On the other hand, the treatment
of a THF solution of 1 with an excess amount of 2,3-
dimethyl-1,3-butadiene at 50 °C afforded 7 in 71% yield,
supporting that the equilibrium between 1 and 2 in
solution should shift to 2 at higher temperature, as
indicated by the VT-UV/vis spectral change of 1 in
toluene. In the previous report of Ando et al., the
difference in the reactivity of digermene Mes2Ged
GeMes2 (9) and germylene Mes2Ge: (10) toward el-
emental sulfur (S8) was discussed as follows.15 The
photochemical reaction of trigermirane 11 in the pres-
ence of elemental sulfur (S8) gave thiadigermirane 12
and 1,3,2,4-dithiadigermetane 13. It was suggested that
12 was obtained by the sulfurization reaction of 9, while
the generation of 13 was reasonably explained by the
head-to-tail dimerization of the intermediary germaneth-
ione Mes2GedS (14) generated by the reaction of 10
with S8. Such results on the sulfurization reactions of
digermenes and/or germylenes prompted us to perform
a sulfurization reaction of 1 in solution in order to
investigate the reactivity of digermene 1 and germylene
2. Digermene 1 was treated with elemental sulfur (S8)
in toluene at -78 °C for 1 h and then heated to room
temperature. After the workup procedures, cis-1,3,2,4-
(12) In the range of 25-50 °C, the observed signals assignable to
the Bbt groups were found to shift to a small extent (ca. (0.3 ppm).
The signal corresponding to the ortho-benzyl protons of the CH(SiMe3)2
groups shifted to lower field as the temperature decreases. While the
TMS protons of the ortho-CH(SiMe3)2 groups were observed equiva-
lently as a singlet in the range of -60 to 50 °C, they were observed as
two broad and nonequivalent signals probably due to the diastereotopi-
cal nonequivalency of the trans-bent (E)-digermene 1. Such situations
indicated that the existence of the germylene 2 is dominant at room
temperature. See Supporting Information.
(14) (a) Such situations are reasonably supported by the report of
the experimental observation of transient germylenes and digermenes,
see: Leigh, W. J.; Harrington, C. R.; Vargas-Baca, I. J. Am. Chem.
Soc. 2004, 126, 16105-16116. (b) When THF was added to the toluene
solution of 1, the absorption maximum at 449 nm was weakened and
a new absorption maximum appeared as a shoulder around 300 nm.
The observed absorption around 300 nm probably corresponds to the
THF complex of bromogermylenes 2. Such phenomena also supported
the equilibrium between 1 and 2. See Supporting Information.
(15) Tsumuraya, T.; Sato, S.; Ando, W. Organometallics 1988, 7,
2015-2019.
(13) Kishikawa, K.; Tokitoh, N.; Okazaki, R. Chem. Lett. 1998, 27,
239-240.

3312 Organometallics, Vol. 24, No. 13, 2005
Sasamori et al.
Figure 4. Relative energies (kcal/mol) of 1,3,2,4-dithia-
digermetanes 21, 22, and two molecules of germathiocar-
bonyl bromide 23 [B3LYP/6-31G(d)].
Scheme 4
Figure 5. ORTEP drawing of 15 (50% probability).
Hydrogen atoms and the solvated hexane molecules are
omitted for clarity. Selected bond lengths (Å) and angles
(deg): Ge1-Br1 2.3188(6), Ge2-Br2 2.3172(6), Ge1-S1
2.2450(11), Ge1-S2 2.2379(11), Ge2-S1 2.2377(11), Ge2-
S2 2.2464(11), S1-Ge1-S2 92.38(4), S1-Ge2-S2 92.35-
(4), Ge1-S1-Ge2 84.62(4), Ge1-S2-Ge2 84.58(4).
Scheme 5
dithiadigermetane 15 was isolated exclusively in 94%
yield as a stable compound. The formation of 15
indicated the ready dimerization of intermediary ger-
mathiocarbonyl bromide 16 generated by the reaction
of germylene 2 with S8 as in the case of 13. No
thiadigermirane 17 was obtained in the sulfurization
reaction of 1, indicating that digermene 1 might have
low reactivity toward S8 under these conditions. In
addition, the stereoselectivity in this reaction could be
explained in analogy with the dimerization reaction of
the transient germanethione 18, Tbt(Mes)GedS (Tbt )
2,4,6-tris[bis(trimethylsilyl)methyl]phenyl).15 That is,
germanethione 18 generated by the desulfurization
reaction of tetrathiagermolane 19 was reported to
undergo immediate head-to-tail dimerization, giving cis-
1,3,2,4-dithiadigermetane 20 exclusively. As the sup-
porting information, calculations for the Mes-
substituted model compounds 21-23 in Figure 4 indi-
cated that cis-1,3,2,4-dithiadigermetane 21 is thermo-
dynamically more stable than trans-isomer 22 and
germathiocarbonyl bromide 23, although it is unclear
at present which isomer is the kinetically favorable
product. On the other hand, dithiadigermetane 15 was
obtained in 65% yield together with germolene 7 (24%)
without any other identifiable products in the sulfur-
ization reaction of 1 in toluene in the presence of an
excess amount of 2,3-dimethyl-1,3-butadiene. Since no
[2+4] adduct of 16 with 2,3-dimethyl-1,3-butadiene was
obtained, there is no concrete evidence for the genera-
tion of 16 at present. However, the explanation for the
intermediacy of 16 in the sulfurization of 1 might be
reasonable on the assumption that the dimerization of
16 and the cycloaddition reaction of 2 with a diene are
much faster than the trapping reaction of 16 with a
diene.16 X-ray crystallographic analysis revealed the cis-
configuration of 1,3,2,4-dithiagermetane 15 with a
folded rhombic dithiadigermetane ring. The significant
Scheme 6
deviation from planarity of the dithiadigermetane ring
of 15 is probably due to the extreme bulkiness of the
Bbt groups, since the theoretically optimized structure
of a parent 1,3,2,4-dithiadigermetane (H2GeS)2 showed
completely planar geometry of the central dithiadiger-
metane ring. The fold angle of two Ge-S-S planes of
the dithiadigermetane ring is 27.2°, which is smaller
than that observed for the more hindered 1,3,2,4-
dithiadigermetane 2017 (38°) and in good agreement
with that of the theoretically optimized structure of 21
(24.9°).
Conclusion
In this paper, dibromodigermene 1 was successfully
synthesized as a stable crystalline compound. The
extremely trans-bent structure of 1 was revealed by the
X-ray crystallographic analysis, showing the longest
GedGe bond length as compared with those for the
(16) Heating of 15 in benzene-d6 in the presence of an excess amount
of 2,3-dimethyl-1,3-butadiene resulted in the quantitative recovery of
15 without any adduct with 2,3-dimethyl-1,3-butadiene, indicating that
16 was not generated via the retro-[2+2]-cycloaddition of 15 under
these conditions or that the expected [2+4]-cycloaddition of 16 with
the diene was later than the re-dimerization of 16.
(17) (a) Tokitoh, N.; Matsumoto, T.; Ichida, H.; Okazaki, R. Tetra-
hedron Lett. 1991, 32, 6877-6878. (b) Tokitoh, N.; Matsumoto, T.;
Manmaru, K.; Okazaki, R. J. Am. Chem. Soc. 1993, 115, 8855-8856.
(c) Matsumoto, T.; Tokitoh, N.; Okazaki, R. J. Am. Chem. Soc. 1999,
121, 8811-8824.

Overcrowded 1,2-Dibromodigermene
Organometallics, Vol. 24, No. 13, 2005 3313
34.35 (d), 128.50 (d), 147.19 (s), 148.53 (s), 152.08 (s). Anal.
Calcd for C60H134Br2Ge2Si14: C, 46.37; H, 8.69. Found: C,
46.51; H, 8.76. The protonated molecular ion of germylene 2
was observed by the low-resolution mass spectrum (FAB): m/z
calcd for C30H68BrGeSi7 777 ([BbtGeBr+H]+), found 777
([BbtGeBr+H]+).
previously reported digermenes. The equilibrium be-
tween digermene 1 and germylene 2 in solution was
evidenced by the VT-UV/vis spectroscopic study and
chemical reactions. It was found that the sulfurization
reaction of 1 using S8 afforded cis-1,3,2,4-dithiadiger-
metane 15 stereoselectively, indicating that the inter-
mediary germathiocarbonyl bromide 16 was generated
via the sulfurization of 2 derived from 1 in the equilib-
rium. Dibromodigermene 1 and bromogermylene 2 are
fascinating compounds from the viewpoints of their
physical and chemical properties, and they are poten-
tially good precursors for novel compounds having
unique skeletons containing a germanium atom. The
results shown here might be of great interest for not
only organometallic chemistry but also heteroatom
chemistry. Further investigation of the chemical proper-
ties of 1 is currently in progress.
Reaction of 1 with 2,3-Dimethyl-1,3-butadiene at 50
°C. To an orange solution of 1 (50.1 mg, 0.032 mmol) in THF
(5 mL) was added 2,3-dimethyl-1,3-butadiene (1.0 mL, 16.8
mmol) at room temperature. After heating of the solution at
50 °C for 5 h, the orange color of the solution disappeared.
After removal of the solvent, the reaction mixture was
subjected to GPLC to give 1-bromo-1-{2,6-bis[bis(trimethyls-
lilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl}-3,4-dimeth-
ylgermolene (3, 38.9 mg, 0.045 mmol, 71%). 3: colorless
crystals, mp 211.0-212.0 °C; 1H NMR (300 MHz, 298 K,
CDCl3) δ 0.12 (s, 36H), 0.26 (s, 27 H), 1.80 (s, 6H), 2.04 (s,
2H), 2.26 (d, 2H, 2J ) 16 Hz), 2.53 (d, 2H, 2J ) 16 Hz), 6.77 (s,
2H); 13C NMR (75 MHz, 298 K, C6D6) δ 1.43 (q), 5.26 (q), 18.71
(q), 22.37 (s), 30.36 (d), 38.71 (t), 126.58 (d), 128.99 (s), 133.54
(s), 147.69 (s), 150.74 (s). Anal. Calcd for C36H77BrGeSi7: C,
50.33; H, 9.03. Found: C, 50.06; H, 9.11.
Experimental Section
General Procedure. All experiments were performed
under an argon atmosphere unless otherwise noted. All
solvents were purified by standard methods and/or The
Ultimate Solvent System (GlassContour Company)18 prior to
use. 1H NMR (300 MHz) and 13C NMR (75 MHz) spectra were
measured in CDCl3 or C6D6 with a JEOL JNM AL-300
spectrometer. A signal due to CHCl3 (7.25 ppm) or C6D5H (7.15
ppm) was used as an internal standard in 1H NMR, and that
due to CDCl3 (77.0 ppm) or C6D6 (128 ppm) was used in 13C
NMR. Multiplicity of signals in the 13C NMR spectra was
determined by DEPT technique. High-resolution mass spectral
data were obtained on a JEOL JMS-700 spectrometer. GPLC
(gel permeation liquid chromatography) was performed on an
LC-908 or LC-918 (Japan Analytical Industry Co., Ltd.)
equipped with JAIGEL 1H and 2H columns (eluent: toluene).
Preparative thin-layer chromatography (PTLC) was performed
with Merck Kieselgel 60 PF254 (Art. No. 7747). All 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. BbtBr19 and GeBr2‚
dioxane20 were prepared according to the reported procedures.
Synthesis of (E)-1,2-Dibromo-1,2-bis{2,6-bis[bis(trim-
ethylslilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl}-
digermene (1). To a THF solution (15 mL) of BbtBr (1.25 g,
1.75 mmol) was added t-BuLi (2.3 N in pentane, 1.57 mL, 3.61
mmol) at -78 °C. After stirring for 30 min, dibromogermylene
dioxane complex (67.2 mg, 2.11 mmol) was added at -78 °C.
After additional stirring for 30 min at -78 °C, the solution
was allowed to warm to room temperature. The solvent was
removed under reduced pressure, and hexane was added to
the residue. Insoluble inorganic salts were removed by filtra-
tion through Celite. Concentration of the filtrate at -40 °C
and recrystallization of the residue from hexane afforded
dibromodigermene 1 (1.194 g, 0.77 mmol, 88%). 1:12 orange
crystals, mp 181.5-182.5 °C (dec); 1H NMR (300 MHz, 298 K,
C6D6) δ 0.31 (s, 72H), 0.35 (s, 54H), 1.53 (s, 4H), 6.90 (s, 4H);
13C NMR (75 MHz, 298 K, C6D6) δ 1.81 (q), 5.56 (q), 22.86 (s),
Reaction of 1 with 2,3-Dimethyl-1,3-butadiene at Room
Temperature. To an orange solution of 1 (96.3 mg, 0.062
mmol) in THF (10 mL) was added 2,3-dimethyl-1,3-butadiene
(1.0 mL, 16.8 mmol) at room temperature. After stirring of
the solution at the same temperature for 12 h, the solvent was
removed under reduced pressure. Purification of the reaction
mixture using GPLC afforded 3 (59.9 mg, 0.070 mmol, 56%).
Reaction of 1 with Elemental Sulfur (S8). To a toluene
solution (20 mL) of 1 (186.3 mg, 0.120 mmol) was added
elemental sulfur (S8, 98.2 mg, 3.06 mmol as S) at -78 °C. After
stirring at the same temperature for 1 h, the reaction mixture
was allowed to warm to room temperature during 12 h. After
filtration of the reaction mixture to remove insoluble S8, the
filtrate was purified using GPLC to give cis-2,4-dibromo-2,4-
bis{2,6-bis[bis(trimethylslilyl)methyl]-4-[tris(trimethylsilyl)m-
ethyl]phenyl}-1,3,2,4-dithiadigermetane (15, 181.9 mg, 0.112
mmol, 94%). 15: colorless crystals, mp >300 °C; 1H NMR (300
MHz, 298 K,C6D6) δ 0.32 (s, 54H), 0.38 (s, 36H), 0.43 (s, 36H),
2.30 (s, 4H), 6.91 (s, 4H); 13C NMR (300 MHz, 298 K,C6D6) δ
1.75 (q), 2.15 (q), 5.62 (q), 22.90 (s), 31.53 (d), 128.71 (d), 135.58
(s), 149.29 (s), 149.56 (s); high-resolution MS (FAB) m/z calcd
for C60H13479Br274Ge2S2Si14 1616.3488 ([M]+), found 1616.3527
([M]+). Anal. Calcd for C60H134Br2Ge2S2Si14: C, 44.54; H, 8.35;
S, 3.96. Found: C, 44.92; H, 8.55; S, 4.14.
Reaction of 1 with Elemental Sulfur (S8) in the Pres-
ence of 2,3-Dimethyl-1,3-butadiene. To a toluene solution
(20 mL) of 1 (163.9 mg, 0.105 mmol) and 2,3-dimethyl-1,3-
butadiene (1.0 mL, 16.8 mmol) was added elemental sulfur
(S8, 63.1 mg, 1.97 mmol as S) at -78 °C. After stirring at the
same temperature for 1 h, the reaction mixture was allowed
to warm to room temperature during 12 h. After filtration of
the reaction mixture to remove insoluble S8, the filtrate was
purified using GPLC to give 15 (111.2 mg, 0.069 mmol, 65%)
and 3 (43.6 mg, 0.051 mmol, 24%).
Theoretical Calculations. All calculations were conducted
using the Gaussian 98 series of electronic structure pro-
grams.21 The geometries were optimized with density func-
(21) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.,
Jr.; Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.;
Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo,
C.; Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B. G.; Chen,
W.; Wong, M. W.; Andres, J. L.; Head-Gordon, M.; Replogle, E. S.;
Pople, J. A. Gaussian 98; Gaussian, Inc.: Pittsburgh, PA, 1998.
(18) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518-1520.
(19) Kano, N.; Tokitoh, N.; Okazaki, R. Organometallics 1998, 17,
1241-1244. Sasamori, T.; Arai, Y.; Takeda, N.; Okazaki, R.; Furukawa,
Y.; Kimura, M.; Nagase, S.; Tokitoh, N. Bull. Chem. Soc. Jpn. 2002,
75, 661-675. Sasamori, T.; Takeda, N.; Tokitoh, N. J. Phys. Org. Chem.
2003, 16, 450-462, and references therein.
(20) (a) Matsunaga, P. T.; Kouvetakis, J.; Groy, T. L. Inorg. Chem.
1995, 34, 5103-5104. (b) GeBr2‚dioxane can be obtained by using
GeBr4 instead of GeCl4 in a manner similar to the case of GeCl2‚
dioxane, see: Fjeldberg, T.; Haaland, A.; Schilling, B. E. R.; Lappert,
M. F.; Thorne, A. J. J. Chem. Soc., Dalton Trans. 1986, 1551-1556.

3314 Organometallics, Vol. 24, No. 13, 2005
Sasamori et al.
refined parameters, GOF ) 1.060, R1 ) 0.0423 and wR2
tional theory at the B3LYP level.22 It was confirmed by
frequency calculations that the optimized structures have
minimum energies. As for the structural optimization of 3 and
4, 6-31+G(2d) (for Ge and Br) and 6-31G(d) (for C and H) were
used as the basis sets. In the other cases, 6-31G(d) and
6-311+G(2d,p) basis sets were used in calculations of the
structural optimization and the excited state (TD-B3LYP),
respectively. Computation time was provided by the Super-
computer Laboratory, Institute for Chemical Research, Kyoto
University.
)
0.0859 [I > 2σ(I)], R1 ) 0.0713 and wR2 ) 0.0946 [for all data],
largest diff peak and hole 0.799 and -0.477 e Å-3. Single
crystals of [15‚2hexane] suitable for X-ray analysis were
obtained by slow recrystallization from hexane at room tem-
perature. A colorless, prismatic crystal of [15‚2hexane] was
mounted on a glass fiber. One of the C(SiMe3)3 groups at the
para-position of the Bbt group was disordered and the oc-
cupancies were refined (0.74:0.26). Some of the disordered
carbon atoms are restrained using DFIX, SIMU, and ISOR
instructions. Crystal data for [15‚2hexane]: C72H162Br2Ge2S2-
Si14, M ) 1790.40, T ) 103(2) K, monoclinic, P21/c (no. 14), a
) 18.5171(2) Å, b ) 9.39050(10) Å, c ) 57.6428(10) Å, â )
96.3281(7)°, V ) 9962.1(2) Å3, Z ) 4, Dcalc ) 1.194 gcm-3, µ )
1.650 mm-1, 2θmax ) 50.0, 90 746 measured reflections, 17 425
independent reflections (Rint ) 0.124), 911 refined parameters,
GOF ) 1.041, R1 ) 0.0462 and wR2 ) 0.1130 [I > 2σ(I)], R1 )
0.0779 and wR2 ) 0.1229 [for all data], largest diff peak and
X-ray Crystallographic Analyses of [1‚2toluene] and
[15‚2hexane]. The intensity data were collected on a Rigaku/
MSC Mercury CCD diffractometer with graphite-monochro-
mated Mo KR radiation (λ ) 0.71070 Å). The structures were
solved by a direct method (SHELXS-9723,24) and refined by full-
matrix least-squares procedures on F2 for all reflections
(SHELXL-9724). All hydrogen atoms were placed using AFIX
instructions, while all other atoms were refined anisotropically.
Single crystals of [1‚2toluene] suitable for X-ray analysis were
obtained by slow recrystallization from toluene at room
temperature. An orange, prismatic crystal of [1‚2toluene] was
mounted on a glass fiber. The C(SiMe3)3 groups at the para-
position of the Bbt groups were disordered and their occupan-
cies were refined (0.94:0.06). Crystal data for [1‚2toluene]:
C74H150Br2Ge2Si14, M ) 1738.20, T ) 103(2) K, monoclinic,
P21/n (no. 14), a ) 16.0618(3) Å, b ) 13.2169(3) Å, c ) 23.3214-
hole 0.917 and -0.787 e Å-3
.
Acknowledgment. This work was partially sup-
ported by Grants-in-Aid for Scientific Research on
Priority Areas (No. 14078213, “Reaction Control of
Dynamic Complexes”), Scientific Researches (Nos.
14204064 and 16750033), Exploratory Research (No.
15655011), COE Research on “Elements Science” (No.
12CE2005), and the 21st Century COE on Kyoto Uni-
versity Alliance for Chemistry from the Ministry of
Education, Culture, Sports, Science and Technology,
Japan.
(6) Å, â ) 107.7839(13)°, V ) 4714.26(18) Å3, Z ) 2, Dcalc
)
1.225 g cm-3, µ ) 1.699 mm-1, 2θmax ) 51.0, 40 395 measured
reflections, 8733 independent reflections (Rint ) 0.061), 455
(22) (a) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. 1988, B37, 785.
(b) Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652. (c) Becke, A. D.
Phys. Rev. 1988, A38, 3098-3100.
(23) Sheldrick, G. M. Acta Crystallogr. Sect. A 1990, 46, 467-473.
(24) Sheldrick, G. SHELX-97, Program for Crystal Structure Solu-
tion and the Refinement of Crystal Structures; Institu¨t fu¨r Anorga-
nische Chemie der Universita¨t Go¨ttingen: Tammanstrasse 4, D-3400
Go¨ttingen, Germany, 1997.
Supporting Information Available: X-ray crystallo-
graphic data of 1 and 15 in CIF format. These materials are
available free of charge via the Internet at http://pubs.acs.org.
OM050129N