Synthesis and properties of a new kinetically stabilized digermyne: New insights for a germanium analogue of an alkyne

Article abstract of DOI:10.1021/ja057205y

The reduction of an overcrowded (E)-1,2-dibromodigermene, Bbt(Br)Ge=Ge(Br)Bbt (2) [Bbt = 2,6-bis[bis(trimethylsilyl)methyl]-4- [tris(trimethylsilyl)methyl]phenyl], with KC₈ afforded a stable digermyne, BbtGe≡GeBbt (1). The Ge≡Ge triple-bond characters of 1 were revealed by the X-ray crystallographic analysis and spectroscopic studies (UV/vis and Raman spectra) together with theoretical calculations. The Ge≡Ge bond lengths of the two nonidentical molecules of 1 observed in the unit cell were shorter than that of the previously reported digermyne, Ar′e≡GeAr′ (Ar′ = 2,6-Dip₂C₆H ₃, Dip = 2,6-diisopropylphenyl).

Full text of DOI:10.1021/ja057205y

Published on Web 12/31/2005
Synthesis and Properties of a New Kinetically Stabilized
Digermyne: New Insights for a Germanium Analogue of an
Alkyne
Yusuke Sugiyama,† Takahiro Sasamori,† Yoshinobu Hosoi,‡ Yukio Furukawa,‡
Nozomi Takagi,§ Shigeru Nagase,§ and Norihiro Tokitoh*,†
Contribution from the Institute for Chemical Research, Kyoto UniVersity, Gokasho, Uji, Kyoto
611-0011, Japan, Department of Chemistry, School of Science and Engineering, Waseda
UniVersity, 3-4-1 Okubo, Shinjyuku-ku, Tokyo 169-8555, Japan, and Department of Theoretical
Molecular Science, Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan
Received October 22, 2005; E-mail: tokitoh@boc.kuicr.kyoto-u.ac.jp.
Abstract: The reduction of an overcrowded (E)-1,2-dibromodigermene, Bbt(Br)GedGe(Br)Bbt (2) [Bbt )
2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl], with KC8 afforded a stable digermyne,
BbtGetGeBbt (1). The GetGe triple-bond characters of 1 were revealed by the X-ray crystallographic
analysis and spectroscopic studies (UV/vis and Raman spectra) together with theoretical calculations. The
GetGe bond lengths of the two nonidentical molecules of 1 observed in the unit cell were shorter than
that of the previously reported digermyne, Ar′GetGeAr′ (Ar′ ) 2,6-Dip2C6H3, Dip ) 2,6-diisopropylphenyl).
Introduction
chemistry of unsaturated chemical bonding systems of heavier
group 14 elements has been extended to that of the heavier
Multiply bonded compounds between heavier group 14
elements cannot exist as monomers under normal conditions
due to their inherent high reactivity. Since the synthesis and
isolation of the first examples of a stable distannene, Dis2Snd
SnDis2,1 by M. F. Lappert et al. in 1973 and a stable disilene,
Mes2SidSiMes2 (Mes ) Mesityl),2 by R. West et al. in 1981,
the idea of kinetic stabilization using bulky substituents has led
to the successful isolation of several types of double-bond
compounds of heavier group 14 elements (dimetallenes).3 The
donor-acceptor bonding model is well-known as a reasonable
explanation for the features of double-bond compounds between
heavier group 14 elements, such as the trans-bent structures
and the ready dissociation into metallylenes.3 Recently, the
analogues of alkynes (dimetallynes), i.e., disilynes, digermynes,
distannynes, and diplumbynes. The most important question is
the definition of a triple bond between heavier group 14
elements. It is common knowledge that the dominant criteria
for a carbon-carbon triple bond are (i) a linear structure, (ii) a
shorter CtC bond length than those for CsC and CdC bonds,
and (iii) a larger bond energy than those of CsC and CdC
bonds. It should be of great interest whether the criteria for
carbon systems can be applied to the case of a triple bond
between heavier group 14 elements. Although a number of
theoretical calculations have predicted their unique structures
different from CtC triple bonds, e.g., not linear but trans-bent
structures,4 all attempts to isolate such triple-bond compounds
have been unsuccessful and no stable examples have been
reported for triple-bond compounds between heavier group 14
elements so far.5 Recently, the idea of kinetic stabilization was
proven to be very effective for the heavier dimetallynes by
Power and co-workers; that is, they have achieved the synthesis
and isolation of the first stable digermyne,6 distannyne,7 and
diplumbyne8 derivatives by taking advantage of their original
bulky m-terphenyl ligands.9 The crystallographic structural
† Kyoto University.
‡ Waseda University.
§ Institute for Molecular Science.
(1) (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.
(2) West, R.; Fink, M. J.; Michl, J. Science 1981, 214, 1343-1344.
(3) For reviews, see: (a) Tsumuraya, T.; Batcheller, S. A.; Masamune, 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. 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. (m) Kira, M.; Iwamoto, T. J.
Organomet. Chem. 2000, 611, 236-247. (n) Weidenbruch, M. J. Orga-
nomet. Chem. 2002, 646, 39-52.
(4) (a) Danovich, D.; Ogliaro, F.; Karni, M.; Apeloig, Y.; Cooper, D. L.; Shaik,
S. Angew. Chem., Int. Ed. 2001, 40, 4023-4029. (b) Chesnut, D. B.
Heteroat. Chem. 2002, 13, 53-62. (c) Karni, M.; Apeloig, Y. Silicon Chem.
2002, 1, 61-66. (d) Kobayashi, K.; Nagase, S. Organometallics 1997, 16,
2489-2491. (e) Nagase, S.; Kobayashi, K.; Takagi, N. J. Organomet. Chem.
2000, 611, 264-271. (f) Takagi, N.; Nagase, S. Organometallics 2001,
20, 5498-5500. (g) Power, P. P. Chem. Commun. 2003, 2091-2101. (h)
Weidenbruch, M. Angew. Chem., Int. Ed. 2005, 44, 514-516. (i) Lein,
M.; Krapp, A.; Frenking, G. J. Am. Chem. Soc. 2005, 127, 6290-6299.
(5) (a) Sekiguchi, A.; Zigler, S. S.; West, R.; Michl, J. J. Am. Chem. Soc.
1986, 108, 4241-4242. (b) Pietschnig, R.; West, R.; Powell, D. R.
Organometallics 2000, 19, 2724-2729. (c) Wiberg, N.; Niedermayer, W.;
Fischer, G.; No¨th, H.; Suter, M. Eur. J. Inorg. Chem. 2002, 1066-1070.
9
10.1021/ja057205y CCC: $33.50 © 2006 American Chemical Society
J. AM. CHEM. SOC. 2006, 128, 1023-1031
1023

A R T I C L E S
Sugiyama et al.
Scheme 1
analyses revealed that the digermyne, Ar′GetGeAr′ (Ar′ ) 2,6-
Dip2C6H3, Dip ) 2,6-diisopropylphenyl), and the distannyne,
Ar′SntSnAr′, showed a trans-bent geometry with the shorter
MtM bond (M ) Ge, Sn) than the corresponding single and
double bonds, though the very long PbsPb bond of the
diplumbyne, Ar*PbtPbAr* (Ar* ) 2,6-Tip2C6H3, Tip ) 2,4,6-
triisopropylphenyl), indicated its bisplumbylene characters
(Ar*PbsPbAr*) rather than the triply bonded character. Wiberg
and co-workers have designed a new steric protection group,
SiMe[Si(t-Bu)3]2 (R*), which they call a “megasilyl group”, for
the stabilization of a triple bond between silicon atoms. Although
they succeeded in the synthesis of the corresponding disilyne,
R*SitSiR*, the detailed structural parameters have not been
reported.5c,10 Very recently, the stable disilyne, RSiSitSiRSi [RSi
) Si(Dis)2(i-Pr), Dis ) CH(SiMe3)2],11 was synthesized and
structurally characterized by Sekiguchi et al., and its unique
structure and properties have attracted much attention. It was
found that the disilyne has a trans-bent geometry and a shorter
SitSi bond length than those of the typical SidSi double bonds.
In these cases, the triple-bond character of the kinetically
stabilized examples has been discussed mainly based on their
X-ray crystallographic structural analysis (in particular, MsM
bond lengths) together with the electronic properties observed
by their UV/vis spectra (in particular, π-π* electron transitions).
The key to the success for the synthesis of the heavier triple-
bond compounds is undoubtedly the choice of the steric
protection groups and the proper synthetic method. We have
also developed very effective protection groups, 2,4,6-tris[bis-
(trimethylsilyl)methyl]phenyl (denoted as Tbt) and 2,6-bis[bis-
(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl (Bbt)
groups, during the course of our investigation on the kinetic
stabilization of low-coordinated highly reactive species. These
efficient steric protection groups enabled us to synthesize a
variety of unique low-coordinated species of heavier main group
elements, such as heavy ketones,12 metallylenes (dimetallenes),3f,i,j
metallaaromatics,13 and heavy azo-compounds,14 as stable
compounds. In 2001, Nagase et al. predicted by theoretical
calculations that TbtGetGeTbt and Ar*GetGeAr* could be
isolated without any dimerization or migration of substituents
and discussed the differences of the substituent effects between
Tbt and Ar* in the digermyne system.4f These situations
Scheme 2
prompted us to synthesize a GetGe compound using Tbt or
Bbt groups with a view to investigate the properties of
diaryldigermynes more in detail. We present here the synthesis
and characterization of a new digermyne, BbtGetGeBbt (1,
Scheme 1),15 focusing on the following points: (i) shortening
of the GetGe bond as judged by X-ray crystallographic analysis
(in the solid state) compared with the optimized structural
parameters using DFT calculations (in the gas phase); (ii)
properties of the valence bond orbital in ArGe units based on
theoretical calculations, i.e., the energy gap between the doublet
ground state (2Π) and the quartet state (4Σ) of the ArGe unit;
(iii) strength of the GetGe triple bond as judged by the
corresponding stretching vibration in the solid state; (iv) π-π*
electron transitions for the GetGe chromophore in solution as
judged by the UV-vis spectra; and (v) reactivities of the Get
Ge triple bond.
Results and Discussions
Synthesis and Structures of BbtGetGeBbt (1). The
reduction of trans-dibromodigermene 2,16 which was prepared
by the reaction of BbtLi with GeBr2‚dioxane, using two
equimolar amounts of potassium graphite (KC8) in benzene at
room temperature afforded the corresponding digermyne, BbtGet
GeBbt (1), almost quantitatively as red crystals stable under an
inert atmosphere (Scheme 2).17
The molecular structure of 1 was definitively determined by
the X-ray crystallographic analysis, where two nonidentical
molecules (1A and 1B) were found in the unit cell. The ORTEP
drawings and the selected bond lengths and angles are shown
in Figures 1 and 2, respectively. Both of 1A and 1B have a
trans-configuration with a slightly distorted CsGesGesC
torsion angle [1A: 160.2(3)°, 1B: 168.9(3)°]. The observed
GesGe bond lengths [2.2060(7) Å for 1A and 2.2260(7) Å for
(6) (a) Stender, M.; Phillips, A. D.; Wright, R. J.; Power, P. P. Angew. Chem.,
Int. Ed. 2002, 41, 1785-1787. (b) Power, P. P. Chem. Commun. 2003,
2091-2101. (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.
(7) Phillips, A. D.; Wright, R. J.; Olmstead, M. M.; Power, P. P. J. Am. Chem.
Soc. 2002, 124, 5930-5931.
(8) Pu, L. H.; Twamley, B.; Power, P. P. J. Am. Chem. Soc. 2000, 122, 3524-
3525.
(9) Twamley, B.; Haubrich, S. T.; Power, P. P. AdV. Organomet. Chem. 1999,
44, 1-65.
(14) (a) Tokitoh, N.; Arai, Y.; Okazaki, R.; Nagase, S. Science 1997, 277, 78-
80. (b) Tokitoh, N.; Arai, Y.; Sasamori, T.; Okazaki, R.; Nagase, S.; Uekusa,
H.; Ohashi, Y. J. Am. Chem. Soc. 1998, 120, 433-434. (c) Sasamori, T.;
Takeda, N.; Tokitoh, N. Chem. Commun. 2000, 1353-1354. (d) Sasamori,
T.; Takeda, N.; Fujio, M.; Kimura, M.; Nagase, S.; Tokitoh, N. Angew.
Chem., Int. Ed. 2002, 41, 139-141. (e) Sasamori, T.; Arai, Y.; Takeda,
N.; Okazaki, R.; Furukawa, Y.; Kimura, M.; Nagase, S.; Tokitoh, N. Bull.
Chem. Soc. Jpn. 2002, 75, 661-675. (f) Sasamori, T.; Takeda, N.; Tokitoh,
N. J. Phys. Org. Chem. 2003, 16, 450-462. (g) Nagahora, N.; Sasamori,
T.; Takeda, N.; Tokitoh, N. Chem.sEur. J. 2004, 10, 6146-6151.
(15) We chose a Bbt group as a steric protection group in consideration of the
empirical result that BbtBidBiBbt has higher solubility in common organic
solvents in contrast to the extremely low solubility of TbtBidBiTbt; see
ref 14e.
(10) Wiberg, N.; Vasisht, S. K.; Fischer, G.; Mayer, P. Z. Anorg. Allg. Chem.
2004, 630, 1823-1828.
(11) Sekiguchi, A.; Kinjyo, R.; Ichinohe, M. Science 2004, 305, 1755-1757.
(12) (a) Okazaki, R.; Tokitoh, N. Acc. Chem. Res. 2000, 33, 625-630. (b)
Tokitoh, N.; Okazaki, R. AdV. Organomet. Chem. 2001, 47, 121-166.
(13) (a) Tokitoh, N.; Wakita, K.; Okazaki, R.; Nagase, S.; Schleyer, P. v. R.;
Jiao, H. J. Am. Chem. Soc. 1997, 119, 6951-6952. (b) Wakita, K.; Tokitoh,
N.; Okazaki, R.; Nagase, S.; Schleyer, P. v. R.; Jiao, H. J. Am. Chem. Soc.
1999, 121, 11336-11344. (c) Wakita, K.; Tokitoh, N.; Okazaki, R.; Nagase,
S. Angew. Chem., Int. Ed. 2000, 39, 634-636. (d) Nakata, N.; Takeda, N.;
Tokitoh, N. Organometallics 2001, 20, 5507-5509. (e) Nakata, N.; Takeda,
N.; Tokitoh, N. J. Am. Chem. Soc. 2002, 124, 6914-6920. (f) Takeda, N.;
Shinohara, A.; Tokitoh, N. Organometallics 2002, 21, 256-258. (g) Takeda,
N.; Shinohara, A.; Tokitoh, N. Organometallics 2002, 21, 4024-4026. (h)
Nakata, N.; Takeda, N.; Tokitoh, N. Organometallics 2003, 22, 481-489.
(i) Tokitoh, N. Acc. Chem. Res. 2004, 37, 86-94. (j) Tokitoh, N. Bull.
Chem. Soc. Jpn. 2004, 77, 429-441.
(16) Sasamori, T.; Sugiyama, Y.; Takeda, N.; Tokitoh, N. Organometallics 2005,
24, 3309-3314.
(17) Attempted synthesis of the BbtGeCl has been examined; see the Supporting
Information.
9
1024 J. AM. CHEM. SOC. VOL. 128, NO. 3, 2006

Kinetically Stabilized Digermyne
A R T I C L E S
Figure 1. ORTEP drawings of two nonidentical molecules of 1 (1A and 1B, 50% probability). Hydrogen atoms are omitted for clarity.
Figure 2. Selected structural parameters (Å, deg) of 1 (geometries 1A and 1B).
1B] are shorter than those of the previously reported di-
germenes18 and digermyne Ar′GetGeAr′ [3: Ar′ ) 2,6-
Dip2C6H3, Dip ) 2,6-diisopropylphenyl; 2.2850(6) Å],6 indi-
cating that BbtGetGeBbt (1) features the GetGe triple-bond
character satisfactorily. Although 3 has a center of symmetry
in the middle of the GetGe bond with the central aryl rings of
the Ar′ ligands almost parallel to the GesGesC plane,
digermyne 1 showed C1 symmetry in both geometries of 1A
and 1B. One can see the arrangement of the aryl rings of the
Bbt groups of 1A and 1B in Figure 3, which shows the ball-
and-stick models of 1A and 1B viewed along the GetGe bond.
Theoretical calculations have already been carried out on
Ar*GetGeAr* and TbtGetGeTbt as imaginary models having
C2 symmetric structures.4f In this work, three minima for the
optimized structure of BbtGetGeBbt were found by the
theoretical calculations at the B3PW91/6-311+G(2df) (for Ge),
6-31G(d) (for Si, C, H) level. One of them was restrained to
have C2 symmetry, and the others showed the geometries very
close to those of experimentally observed molecules 1A and
1B. The three geometries found by the calculations will be called
C2′, 1A′ and 1B′, respectively. The observed and theoretically
optimized structural parameters are summarized in Table 1
together with those for the Ar′GetGeAr′ (3). The relative
energies of the geometries of C2′ (0.0 kcal/mol), 1A′ (-0.50
kcal/mol), and 1B′ (-1.07 kcal/mol) are nearly the same, while
Figure 3. Ball and stick views of 1A and 1B from Ge1-Ge2 and Ge3-
Ge4 axes, respectively.
1B′ has the most stable geometry among the optimized
structures. In addition, their GetGe bond lengths are almost
the same (2.235-2.237 Å). Therefore, the GesGesC angles
and the dihedral angles between the GesGesC plane and the
aryl ring of the Bbt group in 1 should not be considered as
effective factors responsible for the central GetGe bond lengths
and the thermodynamic energies. It should be noted that the
GetGe bond lengths of C2′, 1A′, and 1B′ in the gas phase
obtained by calculations are slightly longer than those experi-
mentally observed in the crystalline state [2.2060(7) Å for 1A
and 2.2260(7) Å for 1B]. The geometries and the GetGe bond
lengths of 1 (1A and 1B) may be affected by the packing force
in the crystalline state. On the other hand, the structural
optimization of Ar′GetGeAr′ having C2 symmetry in the gas
phase was performed at the same level as in the case of BbtGet
GeBbt (1) with the intention of comparison with the observed
structural parameters reported by Power and co-workers. The
calculated GetGe bond lengths of Ar′GetGeAr′ (2.258 Å) in
the gas phase were found to be slightly longer but nearly the
(18) The GedGe bond lengths have been reported in a range of ca. 2.21-2.44
Å; see ref 3h. Those observed for Dep2GedGeDep2 (Dep ) 2,6-
diethylphenyl) and Tip2GedGeTip2 (Tip ) 2,4,6-triisopropylphenyl) are
exceptionally shorter [2.213(2) and 2.213(1) Å, respectively] than those
for the others; see: Snow, J. T.; Murakami, S.; Masamune, S.; Williams,
D. J. Tetrahedron Lett. 1984, 25, 4191-4194. Scha¨fer, H.; Saak, W.;
Weidenbruch, M. Organometallics 1999, 18, 3159-3163. Since we have
computed that the optimized GedGe bond lengths (in gas phase) of Dep2-
GedGeDep2 and Tip2GedGeTip2 are 2.2314 Å in both cases [B3PW91/
6-311+G(2df) (for Ge), 6-31G(d) (for C and H)], it is most likely considered
that the relatively short GedGe bonds observed for the digermenes
substituted by Dep or Tip groups should be affected by the packing force
in the crystalline states.
9
J. AM. CHEM. SOC. VOL. 128, NO. 3, 2006 1025

A R T I C L E S
Sugiyama et al.
Table 1. Observed and Calculated Structural Parameters of
BbtGetGeBbt (1)
a
b
dGeGe
AGeGeC
Dc
Obsdd
1A
1B
3e
2.2060(7)
2.2260(7)
2.2850(6)
136.18(14)
126.19(13)
138.66(14)
123.60(13)
128.67(8)
160.2(3)
168.9(3)
180.0
Calcdf
C2′
1A′
2.237
2.238
134.3
135.2
131.9
138.9
127.8
130.0
161.1
167.8
1B′
2.235
2.258
179.7
172.8
3g
a Ge-Ge bond lengths in Å. b Ge-Ge-C bond angles in deg. c C-Ge-
Ge-C torsion angles in deg. d Observed by X-ray crystallographic analysis.
e Reference 6a. f Calculated at the B3PW91/6-311+G(2df) (for Ge), 6-31G(d)
(for Si, C, H) level. g C2 symmetry.
same as those observed by the X-ray crystallographic analysis
[2.2850(6) Å], indicating the observed geometries of Ar′Get
GeAr′ might be very little affected by the packing force. From
the viewpoints of the shortening of the GetGe bond length in
1 as judged by the theoretical calculations (in the gas phase)
and X-ray crystallographic analysis (in the solid state), it can
be concluded that the digermyne 1 shows almost the same or
slightly higher triple-bond character as compared with that of
Ar′GetGeAr′ (3).
Figure 4. Interaction modes of two ArGe units.
Doublet-Triplet Energy Gap of ArGe Units. To under-
stand the features of GetGe triple bonds in 1 and Ar′Get
GeAr′, it should be helpful to consider the doublet-quartet
energy differences of the ArGe unit (Ar ) Ar′ or Bbt).19 It is
instructive to view ArGetGeAr as being composed of two
ArGe units. Two interaction modes between ArGe units (a) and
(b) are conceivable for ArGetGeAr as shown in Figure 4.4d,19
It is known that the ArGe unit has a doublet ground state (2Π)
more stable than the corresponding quartet state (4Σ). For
example, the doublet states of HGe and PhGe are more stable
than the quartet states by 44.2 and 44.1 kcal/mol [B3PW91/6-
311+G(2df) (for Ge), 6-31G(d) (for C, H)], respectively, while
the HC unit has a doublet state which is only 16.7 (spectroscopic
data) and 17.9 (3-21G*) kcal/mol more stable than the quartet
state.4d,20 The higher stability of the doublet state of ArGe unit
than the quartet state originates from the strong tendency of
heavier atoms to keep the intrinsic valence electronic config-
uration, such as (4s)2(4p)1(4p)1 in the case of the germanium
atom. Therefore, it can be considered in forming ArGetGeAr
from two ArGe units that the trans-bent structure with the
interaction mode (a) is more stable than the linear structure with
the interaction mode (b). Such discussions regarding the valence
orbitals of ArGe lead to the interpretation that the molecular
orbitals of ArGetGeAr were considerably contributed by the
mixing of σ* and π orbitals of the GesGe bond resulting in
the “slipped π bond” (Figure 5). One can see that the overlap
of the p orbitals should be decreased in HOMO-1 (bu) as the
GesGe bond is inclined, while the σ bond orbital (ag) and π
bond orbital vertical to the ArsGesGesAr plane (au) should
Figure 5. Schematic diagrams of the orbital interactions in ArGetGeAr.
Table 2. Doublet-Quartet Energy Differences of RGe Systems
RGe
energya (kcal/mol)
HGe
44.2
44.1
52.4
52.2
45.9
47.1
PhGe
Ar*Ge
Ar′Ge
TbtGe
BbtGe
a Calculated at the B3PW91/6-311+G(2df) (for Ge), 6-31G(d) (for Si,
C, H) level.
maintain their bonding characters. Consequently, the doublet-
quartet energy difference of the ArGe units should be a helpful
indicator for the discussion of the triple-bond characters, in
particular, the bonding character of the slipped π bond in
HOMO-1 (bu), since the doublet-quartet energy closeness
should make the interaction mode (b) more favorable and form
the concrete GetGe triple bond. In Table 2 are shown the results
of theoretical calculations for the doublet-quartet energy
differences in several RGe systems (R ) H, Ph, Ar*, Ar′, Tbt,
and Bbt) at the B3PW91/6-311+G(2df) (for Ge), 6-31G(d) (for
Si, C, H) level. The doublet-quartet energy difference of BbtGe
(19) The detailed studies on the bonding character of triply bonded systems
between heavier group 14 elements have been reviewed, see ref. (4) and
references therein.
(20) Huber, K. P.; Herzberg, G. Molecular Spectra and Molecular Structure;
Van Nostrand-Rheinhold: New York, 1979; Vol. IV.
9
1026 J. AM. CHEM. SOC. VOL. 128, NO. 3, 2006

Kinetically Stabilized Digermyne
A R T I C L E S
Table 3. Observeda and Calculatedb,c Vibrational Frequencies
(cm-1) for the Ge-Ge Triple-, Double-, and Single-Bond
Compounds
obsda
calcd
RGetGeR
397
R ) Bbt (1)
1A′
1B′
R ) Mes
R ) Ph
R ) H
395b
396b
371c
373c
332c
R(Br)GedGe(Br)R
R ) Bbt (2)
R ) Bbt (4)
355
R ) Mes
343c
283c
Figure 6. UV-vis spectrum of 1 in hexane (2.7 × 10-5 M).
RH2GesGeH2R
267
R ) Mes
calculated vibrational frequencies for the model compounds.
Digermyne 1 showed a characteristic Raman shift at 397 cm-1
corresponding to the frequency of the GetGe stretching
vibration. The assignment of the Raman shift was supported
by DFT calculations for BbtGetGeBbt (geometries 1A′ and
1B′) and the model compounds HGetGeH, PhGetGePh, and
MesGetGeMes (Mes ) mesityl). The observed GetGe
a Observed Raman shifts in the solid state (excitation: He-Ne laser 633
nm). b Calculated frequencies at the B3PW91/6-311+G(2df) (for Ge),
6-31G(d) (for Si, C, H) level. c Calculated frequencies at the B3LYP/6-
31G(d) level.
was calculated to be smaller than that of Ar′Ge by ca. 4 kcal/
mol, indicating the slightly stronger GetGe bond of 1 vs that
of Ar′GetGeAr′.21 Consequently, it was found that the Get
Ge triple bond character should depend on the electronic
properties of the substituents to some degree. Since the TbtGe
has the smallest double-quartet energy difference among the
ArGe systems substituted by the bulky aryl substituents (Ar*,
Ar′, Tbt, and Bbt), TbtGetGeTbt may have the shorter Get
Ge triple-bond length than that of 1, though it has not been
synthesized and isolated yet so far.
stretching frequency of 1 was higher than those of 2 (355 cm-1
)
and 4 (267 cm-1), which should correspond to those for the
GedGe and GesGe vibrations, respectively, and consistent with
those calculated for the corresponding model compounds.
Consequently, the order of the frequencies of GesGe stretching
vibrations was 1 > 2 > 4, reflecting their GesGe bond
strengths.
UV-vis Spectra of BbtGetGeBbt (1). Generally, multiply
bonded systems between heavier group 14 elements are colored
in solution due to the central MsM multiple-bond chro-
mophores, which appear as absorption maxima corresponding
to the π-π* electron transitions at wavelengths longer than 300
nm. The UV-vis spectrum of 1 in hexane (Figure 6) showed
the absorption maxima at 373 (ꢀ 32 000) and 495 (ꢀ 1500) nm,
which are comparable to those observed for the previously
reported digermynes, Ar′GetGeAr′ (371 and 501 nm) and
Ar*GetGeAr* (390 and 490 nm). We performed TD-DFT
calculations [TD-B3LYP/6-311+G(2d,p)//B3LYP/6-31G(d)] for
the model compound, MesGetGeMes,26 to find mixed transi-
tions for the two π-π* transitions (HOMO-1 to LUMO and
HOMO to LUMO+1, see Figure 7) as two strong absorption
maxima at 370 and 494 nm, which are comparable to the
observed λmax values for 1. In addition, the π-π* transitions
observed for 1 were longer than those reported for RSiSitSiRSi
(λmax ) 259 and 328 nm), for which the additional, weak, and
broad peaks at 483 and 690 nm were assigned as the sym-
metrically forbidden HOMO-LUMO transition. Although the
HOMO-LUMO electron transition for the model compound,
MesGetGeMes, was estimated to appear around 1524 nm by
the TD-DFT calculations, no absorptions were observed for 1
in such a longer wavelength region.
GetGe Vibrational Spectra BbtGetGeTbt (1). Vibrational
spectroscopy should provide useful information for the nature
of doubly bonded systems,22 but only a few reports using IR or
resonance Raman spectroscopy are available for the vibrational
spectra of the doubly bonded systems of heavier group 14
elements.23 There has been two reports on the vibrational data
for digermenes, a kinetically stabilized digermene (Dis2Ged
GeDis2) and a transient digermene (Me2GedGeMe2). The Ged
24a
Ge stretching vibrations of Dis2GedGeDis2 and Me2Ged
GeMe2 are observed at 300 and 404 cm-1 in the Raman
24b
spectra, which is much higher than that of the corresponding
GesGe single bond (275 cm-1 for Me3GesGeMe3) and lower
than those of the SidSi double bonds (e.g., 539 cm-1 for Mes2-
SidSiMes2).23 To evaluate the triple-bond characters of 1 on
the basis of vibrational spectra, we have performed the measure-
ment of Raman spectra (in the solid state) for digermyne 1
together with (E)-Bbt(Br)GedGe(Br)Bbt (2) and BbtH2Ges
GeH2Bbt (4)25 as related compounds. The observed Raman
spectral data were summarized in Table 3 together with the
(21) Although it was difficult to calculate the bond orders for 1 and 3 due to
their numerous numbers of atoms for the calculations, the binding energies
[B3PW91/6-311+G(2df) (for Ge), 6-31G(d) (for C, H, and Si)] of Get
Ge triple bonds for C2′, 1A′, 1B′, and 3 were computed as 36.6, 37.1,
37.7, and 29.4 kcal/mol, respectively, indicating the stronger GetGe triple
bond of BbtGetGeBbt than that of Ar′GetGeAr′.
(22) In particular, the bonding characters of the doubly bonded systems between
heavier group 15 elements have been well characterized by the Raman
spectra; see ref 14.
(23) The SidSi vibrations observed by the Raman spectra have been reported
for Mes2SidSiMes2 (539 cm-1) and Mes(t-Bu)SidSi(t-Bu)Mes (525 cm-1);
see: West, R. Angew. Chem., Int. Ed. Engl. 1987, 26, 1201-1211.
(24) (a) Davidson, P. J.; Harris, D. H.; Lappert, M. F. J. Chem. Soc., Dalton
Trans. 1976, 2268-2274. (b) Bleckmann, P.; Minkwits, R.; Neumann, W.
P.; Schriewer, M.; Thibud, M.; Watta, B. Tetrahedron Lett. 1984, 25, 2467-
2470.
(25) Tetrahydrodigermane BbtH2Ge-GeH2Bbt (4) was prepared by the reaction
of BbtGeH2Li with CBr4 and satisfactorily characterized. The detailed
synthetic procedures and the spectral data were shown in the Supporting
Information.
Reactions of BbtGetGeBbt (1). Power et al. argued the
biradical character of Ar*GetGeAr* on the basis of its
reactivity toward 2,3-dimethyl-1,3-butadiene (Scheme 3).27 To
(26) Since the highly symmetric structure of 1 in solution was suggested by the
1
simple H NMR spectra of 1 in C6D6, the MesGetGeMes, the optimized
structure of which had a center of symmetry in the middle of GetGe bond,
should be considered as a proper model compound in solution rather than
C2′, 1A′, or 1B′. The TD-DFT calculations [B3PW91/6-311+G(2df) (for
Ge), 6-31G(d) (for C, H)] of C2′ and 1B′ indicated their two characteristic
absorption maxima at 349 and 405 nm and at 339 and 400 nm, which
were miscalculated to a small extent compared with observed values of 1
in hexane.
9
J. AM. CHEM. SOC. VOL. 128, NO. 3, 2006 1027

A R T I C L E S
Sugiyama et al.
Figure 8. Interaction of the frontier orbitals between digermyne and
butadiene.
Next, the reaction of 1 with 2,3-dimethyl-1,3-butadiene was
performed to draw a comparison with the case of Ar′Get
GeAr′.27 Digermyne 1 was found to react with 1 equiv of 2,3-
dimethyl-1,3-butadiene to afford germylene 9, which was air-
and moisture-sensitive and underwent slow decomposition at
room temperature even under an inert atmosphere. The structure
of the germylene 9 was supported by the results of the thermal
intramolecular cyclization giving compound 1029 and the
trapping experiments using 2,3-dimethyl-1,3-butadiene and
MeOH leading to the formation of digermanes 1129 and 12,
respectively, together with the spectroscopic analyses (Scheme
5).30 It should be noted that compound 13, which was the Bbt-
analogue of the product obtained in the reaction of Ar′Get
GeAr′ with 2,3-dimethyl-1,3-butadiene,27 was not obtained in
this reaction at all. Although compound 9 can be simply
considered as the [1 + 4] cycloadduct of digermyne 1 with 2,3-
dimethyl-1,3-butadiene, the direct [1 + 4] cycloaddition of 1
with the diene should be unfavorable taking into account their
interaction mode of the frontier orbitals (Figure 8). Hence, the
two possible pathways can be postulated for the generation of
9. The first one is the [1 + 2] cycloaddition between digermyne
1 and the diene with a bisgermylene-type contribution for 1 to
afford 14, followed by the ready isomerization giving 9 as in
the case of silylenes.31 Since no contribution of bisgermylene
species in the digermyne 1 can be evidenced by the reaction of
1 with H2O, MeOH, and Et3SiH as described above, the
formation of compound 9 is most likely interpreted in terms of
the second pathway, that is, the intermediacy of 1,2-digerma-
1,4-hexadiene derivative 15, the [2 + 4] cycloadduct of 1 with
2,3-dimethyl-1,3-butadiene. Intermediary cyclic digermene 15
should reasonably undergo ready isomerization via the 1,2-
migration leading to the formation of 932 on the basis of the
previous reports on the isomerization of the less-congested
Figure 7. Kohn-Sham molecular orbitals of MesGetGeMes [B3LYP/
6-31G(d)].
Scheme 3
Scheme 4
assess the triple-bond character of 1, we first investigated the
reactions of 1 with Et3SiH and H2O, the reactions of which with
Ar*GetGeAr* and Ar′GetGeAr′ have not been reported.
Heating of 1 in C6D6 in the presence of an excess amount of
Et3SiH at 50 °C resulted in the complete recovery of 1, while
the SisH bond of Et3SiH should be reactive even toward radical
species. On the other hand, 1,1-dimethoxydigermane 5 was
obtained by the addition of MeOH to the THF solution of 1 in
91% yield, where the addition reaction of MeOH toward the
GesGe π bond of 1 might occur twice in this reaction.
Treatment of 1 with an excess amount of H2O in THF
exclusively afforded 1,1-dihydroxydigermane 6, which was
found to decompose slowly during the purification process, in
45% yield. The formation of 6 is most likely interpreted in terms
of the intermediacy of hydroxydigermene 7 or its keto-tautomer
8, though it is unclear which tautomer should be the dominant
species (Scheme 4).28 It can be considered that the stereose-
lectivity in the reaction of 1 with H2O should reflect the Get
Ge triple-bond character.
(29) The X-ray crystallographic data of 10 and 11 are available as cif files. In
the case of 10, the quality of the crystal data is not satisfactory due to the
disordered moiety. See the Supporting Information.
(30) Unfortunately, single crystals of 9 suitable for the X-ray crystallographic
analysis have not been obtained at present.
(31) The reaction of silylenes with 1,3-dienes has been known to proceed via
the initial [1+2] cycloaddition giving the corresponding 2-vinylsiliranes,
followed by their isomerization into the corresponding 3-silolenes. See:
(a) Zhang, S.; Conlin, R. T. J. Am. Chem. Soc. 1991, 113, 4272-4278. (b)
Weidenbruch, M.; Kroke, E.; Marsmann, H.; Pohl, S.; Saak, W. J. Chem.
Soc., Chem. Commun. 1994, 1233-1234. (c) Kroke, E.; Willms, S.;
Weidenbruch, M.; Saak, W.; Pohl, S.; Marsmann, H. Tetrahedron Lett.
1996, 37, 3675-3678. (d) Hermanns, J.; Schmidt, B. J. Chem. Soc., Perkin
Trans. 1 1998, 2209-2230. (e) Takeda, N.; Tokitoh, N.; Okazaki, R. Chem.
Lett. 2000, 622-623.
(27) (a) Stender, M.; Phillips, A. D.; Power, P. P. Chem Commun. 2002, 1312-
1313. (b) Power, P. P. Appl. Organomet. Chem. 2005, 19, 488-493.
(28) In the theoretical calculations for the Dmp-substituted model compounds
(Dmp ) 2,6-dimethylphenyl) [B3LYP/6-31G(d)], it was found that the keto
tautomer DmpGe(O)sGeH2Dmp was more stable by 9.9 kcal/mol than
the enol tautomer Dmp(HO)GedGeHDmp.
(32) Although the trapping reaction of 15 at low temperature was attempted, it
could not be trapped by MeOH at -80 °C probably due to its ready
isomerization leading to the formation of 9 even at this temperature.
Addition of 2,3-dimethyl-1,3-butadiene to the solution of 1 at -80 °C
followed by the quenching with MeOH at the same temperature did not
give the expected trapping product of 15 but afforded 5 (35%) and 12 (35%).
9
1028 J. AM. CHEM. SOC. VOL. 128, NO. 3, 2006

Kinetically Stabilized Digermyne
A R T I C L E S
Scheme 5
dimetallenes giving the corresponding metallylenes via the 1,2-
migration of the substituent.33,34 Such reactivity of digermyne
1 toward 2,3-dimethyl-1,3-butadiene is of great importance as
that reflecting the neutral character of the GetGe triple bond
of 1.
also elemento chemistry. We hope further application of the
kinetic stabilization to the highly reactive species of heavier
main group elements will lead to future progress in the chemistry
of a unique class of low-coordinated main group element
compounds.
Conclusion
Experimental Section
In this paper, we reported the synthesis, structure, and
properties of a new example of a stable diaryldigermyne,
BbtGetGeBbt (1). The triple-bond character of 1 was fully
examined based on the results of the spectroscopic and X-ray
crystallographic analyses, theoretical calculations, and studies
on the reactivities. Digermyne 1 showed shorter GetGe bond
lengths than those of the previously reported digermene, Ar′Get
GeAr′ (3). In addition, it was found that the vibrational
spectroscopy should be a good method to discuss the bonding
property of an unprecedented multiple bond of heavier main
group elements. Digermyne 1 showed no biradical character in
the reactions with H2O, Et3SiH, and 2,3-dimethyl-1,3-butadiene.
Although 1 is not the first example of a stable diaryldigermyne,
the extended knowledge described here should be important
from the standpoint of not only organometallic chemistry but
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
1
Company)35 prior to use. H NMR (400 or 300 MHz) and 13C NMR
(100 or 75 MHz) spectra were measured in CDCl3 or C6D6 with a JEOL
JNM AL-400 or 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 13C NMR spectra
was determined by a 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 chroma-
tography (PTLC) and Wet column chromatography (WCC) were
performed with Merck Kieselgel 60 PF254 and Wakogel C-200,
respectively. All melting points were determined on a Yanaco mi-
cromelting point apparatus and are uncorrected. Elemental analyses were
carried out at the Microanalytical Laboratory of the Institute for
Chemical Research, Kyoto University. (E)-Bbt(Br)GedGe(Br)Bbt was
prepared according to the reported procedures.16
(33) It has been experimentally and theoretically demonstrated that the dimet-
allenes R2MdM′R2 (M, M′ ) Si, Ge, Sn, or Pb) can undergo isomerization
to afford the corresponding metallylenes R3MsMR via the 1,2-migration
of the substituent (R) in some cases. See: (a) Grev, R. S.; Schaefer, H. F.;
Baines, K. M. J. Am. Chem. Soc. 1990, 112, 9458-9467. (b) Baines, K.
M.; Cooke, J. A. Organometallics 1992, 11, 3487-3488. (c) Grev, R. S.;
Schaefer, H. F. Organometallics 1992, 11, 3489-3492. (d) Schmedake,
T. A.; Haaf, M.; Apeloig, Y.; Muller, T.; Bukalov, S.; West, R. J. Am.
Chem. Soc. 1999, 121, 9479-9480. (e) Michl, J.; West, R. Acc. Chem.
Res. 2000, 33, 821-823. (f) Fukaya, N.; Ichinohe, M.; Kabe, Y.; Sekiguchi,
A. Organometallics 2001, 20, 3364-3366.
1,2-Bis{2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)-
methyl]phenyl}digermyne (1). To a C6H6 solution (5 mL) of dibro-
modigermene 2 (110.6 mg, 0.065 mmol) was added potassium graphite
(KC8, 21.1 mg, 0.156 mmol) at room temperature. After the solution
was stirred for 12 h, solvent was removed under reduced pressure, and
hexane was added to the residue. The suspension was filtered to remove
graphite and inorganic salts. The filtrate was condensed and recrystal-
lized from hexane to afford 1,2-bis{2,6-bis[bis(trimethylsilyl)methyl]-
4-[tris(trimethylsilyl)methyl]phenyl} digermyne 1 (89.5 mg, 99%). 1:
(34) Theoretical calculations on the model compounds for 9 and 15, i.e., 9′ and
15′, in which the Bbt groups were replaced with the Dmp groups, showed
that 9′ was thermodynamically more stable by ca. 5 kcal/mol than 15′ at
the B3LYP/6-31G(d) level.
1
red crystals, mp 210-211 °C (dec); H NMR (300 MHz, C6D6, 298
(35) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.; Timmers,
F. J. Organometallics 1996, 15, 1518-1520.
9
J. AM. CHEM. SOC. VOL. 128, NO. 3, 2006 1029

A R T I C L E S
Sugiyama et al.
K) δ 0.35 (s, 54 H), 0.36 (s, 72 H), 2.98 (s, 4H), 6.99 (s, 4H); 13C
NMR (75 MHz, C6D6, 298 K) δ 1.65 (q), 5.47 (q), 22.82 (s), 39.50
(d), 128.27 (d), 145.40 (s), 147.67 (s), 152.87 (s). UV-vis (hexane)
(s), 28.92 (d), 31.91 (s), 32.15 (d), 53.83 (q), 127.61 (d), 128.16 (d),
128.51 (s), 129.17 (s), 132.58 (s), 133.63 (s), 146.30 (s), 147.56 (s),
151.10 (s), 151.80 (s). IR (KBr, νGe-H, cm-1) 2079. High-resolution
MS (FAB) m/z Calcd for C62H14274Ge2O2Si14 1458.6227 ([M + H]+).
Found 1458.6195 ([M + H]+). Anal. Calcd for C62H142O2Si14Ge2: C,
51.07; H, 9.82%. Found: C, 50.81; H, 9.74%.
λ
max (nm, ꢀ) ) 373 (32 000, sh), 495 (1500). High-resolution MS (FAB)
m/z Calcd for C60H13474Ge2Si14 1394.5679 ([M]+). Found 1394.5708
([M]+). Since it was difficult to obtain the satisfactory data of the
elemental analysis due to the extremely high air and moisture sensitivity,
Reaction of Digermyne 1 with H2O. To a THF solution (5.0 mL)
of 1 (94.0 mg, 0.067 mmol) was added an excess amount of H2O (1.0
mL). After the solution stirred for 3 h, the solvent was removed under
reduced pressure, and the residue was extracted with hexane, washed
with water, and then dried over anhydrous magnesium sulfate. After
filtration, the solvent of the filtrate was removed under reduced pressure,
and the residue was purified by GPLC to give 1,2-bis{2,6-bis[bis-
(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl}-1,1-dihy-
droxydigermane 6 (43.3 mg, 45%) as colorless crystals. 6: colorless
1
the purity was confirmed by the H NMR spectrum as shown in the
Supporting Information.
X-ray Crystallographic Analyses of 1 and 11. The intensity data
were collected on a Rigaku/MSC Mercury CCD diffractometer with
graphite monochromated Mo KR radiation (λ ) 0.710 70 Å). Single
crystals suitable for X-ray analysis were obtained by slow recrystalli-
zation from hexane (for 1 and 11) and toluene (for 10) at room
temperature. A red crystal of 1 and colorless crystals of 10 and 11
were mounted on a glass fiber, respectively. The structures were solved
by a direct method (SHELXS-9736,37) and refined by full-matrix least-
squares procedures on F2 for all reflections (SHELXL-9737). All
hydrogen atoms were placed using AFIX instructions, while all other
atoms were refined anisotropically. In the case of 1, there are two
nonidentical molecules in the unit cell (1A and 1B). In both cases of
1A and 1B, the C(SiMe3)3 groups at para-positions of the Bbt groups
were disordered and their occupancies were refined (0.78:0.22 for 1A,
0.67:0.33 for 1B). Crystal data for 1: C60H134Ge2Si14, M ) 1394.11, T
) 103(2) K, triclinic, P1h (no.2), a ) 12.7522(5) Å, b ) 19.8609(7) Å,
c ) 35.8127(16) Å, R ) 93.306(2)°, â ) 91.725(3)°, γ ) 103.854-
1
crystals, mp 222-223 °C (dec); H NMR (300 MHz, C6D6, 298 K) δ
0.33 (s, 27 H), 0.35 (s, 36 H), 0.36 (s, 27H), 0.37, (s, 36H), 2.42 (s,
2H), 2.81 (s, 2H), 5.26 (s, 2H), 7.00 (s, 2H), 7.05 (s, 2H); 13C NMR
(75 MHz, C6D6, 298 K) δ 1.84 (q), 1.93 (q), 5.61 (q), 5.65 (q), 23.0
(s), 30.06 (d), 30.20 (s), 32.41 (d), 127.00 (d), 126.61 (d), 129.94 (s),
136.16(s), 147.14 (s), 147.99 (s), 150.15 (s), 152.15 (s). IR (KBr, νGe-H
,
cm-1) 2081. High-resolution MS (FAB) m/z Calcd for C60H139O2Ge2-
74
Si14 1430.5890 ([M + H]+). Found 1430.5913 ([M + H]+). Anal.
Calcd for C60H138O2Ge2Si14: C, 50.25; H, 9.98%. Found: C, 50.14;
H, 9.89%.
Reaction of Digermyne 1 with 1 equiv of 2,3-Dimethyl-1,3-
butadiene. To a hexane solution (7 mL) of 1 (199.3 mg, 0.143 mmol)
was added a hexane solution (0.5 mL) of 2,3-dimethyl-1,3-butadiene
(0.27 N) at room temperature. After the solution stirred for 24 h, the
solvent was removed under reduced pressure. Recrystallization of the
residue from hexane at -40 °C afforded the diene adduct 9 (149.5
mg, 71%) as yellow crystals. 9: yellow crystals, mp 165 °C (dec); 1H
NMR (400 MHz, C6D6, 298 K) δ -0.17 (s, 2 H), 0.29 (s, 36 H), 0.34
(3)°, V ) 8440.5(6) Å3, Z ) 4, Dcalcd ) 1.097 gcm-3, µ ) 0.942 mm-1
,
2θmax ) 51.0, 61 366 measured reflections, 30 320 independent
reflections (Rint ) 0.0728), 1497 refined parameters, GOF ) 1.093, R1
) 0.0591 and wR2 ) 0.0867 [I > 2σ(I)], R1 ) 0.1517 and wR2 )
0.0982 [for all data], largest diff. peak and hole 1.118 and -0.913 e
Å-3 (around Ge atoms). Crystal data for 11: C78H168Ge2Si14, M )
1644.56, T ) 103(2) K, triclinic, P1h (no.2), a ) 12.4319(7) Å, b )
13.0130(8) Å, c ) 14.7938(11) Å, R ) 85.759(5)°, â ) 84.425(3)°, γ
) 91.478(3)°, V ) 2374.1(3) Å3, Z ) 1, Dcalc ) 1.150 gcm-3, µ )
0.847 mm-1, 2θmax ) 50.0, 19 402 measured reflections, 8267
independent reflections (Rint ) 0.0294), 457 refined parameters, GOF
) 1.044, R1 ) 0.0662 and wR2 ) 0.1858 [I > 2σ(I)], R1 ) 0.0770 and
wR2 ) 0.1953 [for all data], largest diff. peak and hole 0.983 and
-0.839 e Å-3. Crystal data for 10 are shown in the Supporting
Information.
2
(s, 36 H), 0.40 (s, 27H), 0.43 (s, 27H), 1.74 (s, 6H), 2.32 (d, J ) 20
Hz, 2H), 2.73 (d, 2J ) 20 Hz, 2H), 3.57 (s, 2H), 6.88 (s, 2H), 7.04 (s,
2H); 13C NMR (75 MHz, C6D6, 298 K) δ 2.50 (q), 2.66 (q), 5.70 (q),
5.98 (q), 20.15 (q), 21.67 (s), 22.18 (s), 30.71 (d), 32.58 (d), 37.75 (t),
127.74 (d), 127,80 (d), 132.61 (s), 143.82 (s), 144.15 (s), 144.38 (s),
151.10 (s), 162.15 (s). UV-vis (hexane) λmax (nm, ꢀ) ) 321 (1300,
sh), 440 (1200). High-resolution MS (FAB) m/z Calcd for
C66H14474Ge2Si14 1476.6487 ([M]+). Found 1476.6486 ([M]+). Since it
was difficult to obtain the satisfactory data of the elemental analysis
due to the extremely high air and moisture sensitivity, the purity was
confirmed by the 1H NMR spectrum as shown in the Supporting
Information.
Reaction of Digermyne 1 with Triethylsilane. To a C6D6 solution
(3.5 mL) of triethylsilane (0.31 N) was added digermyne 1 (13.0 mg,
9.3 µmol). The solution was degassed and sealed in an NMR tube.
After standing at room temperature for a week, no change was observed
1
by the H NMR spectrum. After the NMR sample tube was heated at
Reaction of Digermyne 1 with an Excess Amount of 2,3-
Dimethyl-1,3-butadiene. To a hexane solution (5 mL) of 1 (81.8 mg,
0.057 mmol) was added an excess amount of 2,3-dimethyl-1,3-butadiene
(1.0 mL) at room temperature. After the solution stirred for 24 h, the
solvent was removed under reduced pressure, and the residue was
purified by GPLC and WCC to give 10 (37 mg, 0.025 mmol, 44%)
and 11 (33 mg, 0.021 mmol, 38%). 10: colorless crystals, mp 216 °C
(dec); 1H NMR (300 MHz, C6D6, 298 K) δ 0.26 (s, 9H), 0.31 (s, 9H),
0.32 (s, 9H), 0.36 (s, 9H), 0.37 (s, 36H), 0.39 (s, 27H), 0.40, (s, 27H),
1.35 (s, 1H), 1.74 (s, 6H), 2.30 (s, 2H), 2.67-2.83 (m, 4H), 6.35 (s,
1H), 6.89 (m, 3H), 6.99 (d, 4J ) 2 Hz, 1H); 13C NMR (75 MHz, C6D6,
298 K) δ 1.22 (q), 2.25 (q), 2.60 (q), 3.43 (q), 3.86 (q), 19.68 (q),
21.81 (s), 22.71 (s), 30.17 (t), 30.42 (d), 32.02 (q), 35.81 (d), 36.96
(s), 124.44 (d), 126.51 (d), 127.52 (d), 131.71 (s), 138.40 (s), 146.26
1
50 °C for 24 h, the H NMR spectrum showed no signals other than
those for the starting materials.
Reaction of Digermyne 1 with MeOH. To a THF solution (5.0
mL) of 1 (72.0 mg, 0.051 mmol) was added an excess amount of MeOH
(1.0 mL). After the solution stirred for 20 h, the solvent was removed
under reduced pressure, and the residue was extracted with hexane,
washed with water, and then dried over anhydrous magnesium sulfate.
After filtration, the solvent of the filtrate was removed under reduced
pressure, and the residue was purified by GPLC to give 1,2-bis{2,6-
bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl}-1,1-
dimethoxydigermane 5 (67.9 mg, 91%) as colorless crystals. 5:
1
colorless crystals, mp 214 °C (dec); H NMR (300 MHz, C6D6, 298
K) δ 0.35 (s, 54 H), 0.40 (s, 36 H), 0.42 (s, 36 H), 2.44 (s, 2H), 3.04
(s, 2H), 3.53 (s, 6H), 5.17 (s, 2H), 6.93 (s, 2H), 7.00 (s, 2H); 13C NMR
(75 MHz, C6D6, 298 K) δ 2.35 (q), 2.38 (q), 5.68 (q), 5.70 (q), 22.21
(s), 146.52 (s), 147.24 (s), 151.34 (s), 152.03 (s), 157.55 (s). IR (KBr,
74
ν
Ge-H, cm-1) 2144. High-resolution MS (FAB) m/z Calcd for C66H145
-
Ge2Si14 1477.6565 ([M + H]+). Found 1477.6536 ([M + H]+). Anal.
Calcd for C66H145Ge2Si14: C, 53.70; H, 9.83%. Found: C, 53.58; H,
9.93%. 11: colorless crystals, mp 233 °C (dec); H NMR (300 MHz,
(36) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467-473.
(37) Sheldrick, G. SHELX-97 Program for Crystal Structure Solution and the
Refinement of Crystal Structures; Institu¨t fu¨r Anorganische Chemie der
Universita¨t Go¨ttingen: Tammanstrasse 4, D-3400 Go¨ttingen, Germany,
1997.
1
C6D6, 298 K) δ 0.16 (s, 36H), 0.23 (s, 36H), 0.36 (s, 54H), 1.33 (brs,
2
2
4H), 1.74 (s, 12H), 2.08 (d, J ) 16 Hz, 4H), 2.19 (d, J ) 16 Hz,
9
1030 J. AM. CHEM. SOC. VOL. 128, NO. 3, 2006

Kinetically Stabilized Digermyne
A R T I C L E S
4
4
4H), 6.91 (d, J ) 2 Hz, 2H), 6.99 (d, J ) 2 Hz, 2H); 13C NMR (75
MHz, C6D6, 298 K) δ 1.05 (q), 1.69 (q), 5.28 (q), 19.25 (q), 28.36 (t),
30.17 (s), 31.15 (d), 124.47 (d), 125.46 (d), 128.68 (s), 129.03 (s),
130.71 (s), 141.99 (s), 146.02 (s). Anal. Calcd for C72H154Si14Ge2: C,
55.49; H, 9.96%. Found: C, 55.07; H, 10.07%.
Theoretical Calculations. All calculations were conducted using
the Gaussian 98 series of electronic structure programs.38 The geom-
etries were optimized with the density functional theory at the B3PW91
or B3LYP level. The basis sets used for the structural optimization
and the excited state were noted on each occasion.
Thermal Reaction of the Diene Adduct 9. A C6D6 solution (3.5
mL) of 9 (11.0 mg, 0.007 mmol) was degassed and sealed in an NMR
tube. After the solution was heated at 45 °C for 28 h, the signals for 1
disappear and those for compound 10 were observed. The purification
procedure of the solution using PTLC (hexane) afforded compound
10 (7.9 mg, 0.005 mmol, 76%) in a pure form.
Acknowledgment. This work was partially supported by
Grants-in-Aid for COE Research on “Elements Science” (No.
12CE2005), Creative Scientific Research (17GS0207), Scientific
Research on Priority Area (No. 14078213, “Reaction Control
of Dynamic Complexes”), Young Scientist (B) (No. 16750033),
Nanotechnology Support Program, and the 21st Century COE
on Kyoto University Alliance for Chemistry from Ministry of
Education, Culture, Sports, Science and Technology, Japan. We
are grateful to Dr. Nobuhiro Takeda, Assistant Professor,
Institute for Chemical Research, Kyoto University, for the
fruitful discussions.
Reaction of the Diene Adduct 9 with MeOH. To a THF solution
(3.0 mL) of 9 (40.2 mg, 0.027 mmol) was added an excess amount of
MeOH (1.0 mL). After the solution stirred for 24 h, the solvent was
removed under reduced pressure, and the residue was purified by GPLC
to give compound 12 (39.6 mg, 97%) as colorless crystals. 12: colorless
1
crystals, mp 191 °C (dec); H NMR (300 MHz, C6D6, 298 K) δ 0.32
(s, 18 H), 0.36 (s, 18 H), 0.37 (s, 27 H), 0.38 (s, 18H), 0.39 (s, 27H),
0.42 (s, 18H), 1.71 (s, 6H), 2.16 (s, 2H), 2.22 (s, 2H), 2.37-2.80 (m,
4H), 3.40 (s, 3H), 6.77 (s, 1H), 6.90 (s, 2H), 6.95 (s, 2H); 13C NMR
(75 MHz, C6D6, 298 K) δ 2.48 (q), 2.61 (q), 2.91 (q), 3.07 (q), 5.90
(q), 6.13 (q), 18.98 (q), 19.01 (q), 21.76 (s), 22.10 (s), 32.04 (d), 32.85
(d), 33.06 (t), 33.48 (t), 59.03 (q), 127.13 (d), 127.36 (d), 128.73 (s),
128.81 (s), 129.01 (s), 131.44 (s), 131.90 (s), 136.78 (s), 138.50 (s),
Supporting Information Available: X-ray crystallographic
data of 1, 10, and 11 in a CIF format. Experimental procedure
for BbtH2Ge-GeH2Bbt (4) in PDF format. Complete refs 17,
29, and 38. This material is available free of charge via the
Internet at http://pubs.acs.org.
146.49 (s), 146.74 (s), 151.50 (s), 151.80 (s). IR (KBr, νGe-H, cm-1
)
2005. High-resolution MS (FAB) m/z Calcd for C67H14874Ge2OSi14
JA057205Y
1508.6750 ([M]+). Found 1508.6766 ([M]+). Anal. Calcd for C67H148
Ge2OSi14: C, 55.35; H, 9.89%. Found: C, 55.47; H, 9.79%.
-
(38) Frisch, M. J. et al. Gaussian 98; Gaussian, Inc.: Pittsburgh, PA, 1998.
9
J. AM. CHEM. SOC. VOL. 128, NO. 3, 2006 1031