Reactions of a germacyclopropabenzene with elemental chalcogens: Syntheses and structures of a series of stable 2H-benzo[c][1,2]chalcogenagermetes

Article abstract of DOI:10.1021/om049216q

Thermal reactions of a stable germacyclopropabenzene, Tbt(Dip)GeC ₆H₄ (Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl)phenyl, Dip = 2,6-diisopropylphenyl), with elemental chalcogens in C₆D ₆ at 130°C resulted in the formation of novel Ge-containing four-membered heterocycles, 2H-benzo[c][1,2]chalcogenagermete derivatives. This is the first example of a ring expansion reaction of cyclopropabenzene derivatives using elemental chalcogen, while several types of ring-opening reactions have been explored for cyclopropabenzene so far. In addition, the 2H-benzo[c] [1,2]telluragermete is the first stable compound as a tellurete derivative. Structures of the chalcogenagermetes obtained here were elucidated by X-ray crystallographic analysis, and the experimentally obtained structural parameters were supported by theoretical calculations. The skeletons of chalcogenagermetes have very little strain in their four-membered rings annelated with a benzene ring.

Full text of DOI:10.1021/om049216q

612
Organometallics 2005, 24, 612-618
Reactions of a Germacyclopropabenzene with Elemental
Chalcogens: Syntheses and Structures of a Series of
Stable 2H-Benzo[c][1,2]chalcogenagermetes
Takahiro Sasamori, Takayo Sasaki, Nobuhiro Takeda, and Norihiro Tokitoh*
Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
Received October 9, 2004
Thermal reactions of a stable germacyclopropabenzene, Tbt(Dip)GeC6H4 (Tbt ) 2,4,6-tris-
[bis(trimethylsilyl)methyl]phenyl, Dip ) 2,6-diisopropylphenyl), with elemental chalcogens
in C6D6 at 130 °C resulted in the formation of novel Ge-containing four-membered
heterocycles, 2H-benzo[c][1,2]chalcogenagermete derivatives. This is the first example of a
ring expansion reaction of cyclopropabenzene derivatives using elemental chalcogen, while
several types of ring-opening reactions have been explored for cyclopropabenzene so far. In
addition, the 2H-benzo[c][1,2]telluragermete is the first stable compound as a tellurete
derivative. Structures of the chalcogenagermetes obtained here were elucidated by X-ray
crystallographic analysis, and the experimentally obtained structural parameters were
supported by theoretical calculations. The skeletons of chalcogenagermetes have very little
strain in their four-membered rings annelated with a benzene ring.
Introduction
analogues of a cyclopropabenzene derivative, and re-
ported their structures and physical properties. The key
point to our success is the development of a synthetic
method under mild conditions, i.e., the reaction of a
dilithiometallane6 having effective steric protection
groups, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (de-
noted as Tbt) and 2,6-diisopropylphenyl (denoted as
Dip), with 1,2-dibromobenzene at -78 °C. Furthermore,
a similar synthetic approach led us to the isolation of
the first stable bis(silacyclopropa)benzene derivatives.4,7
Experimental and theoretical studies on the structural
features of these metallacyclopropabenzenes of heavier
group 14 elements revealed that they have less strain
than cyclopropabenzenes most likely due to the longer
and softer metal-carbon bonds than carbon-carbon
bonds. That is, it can be concluded that a three-
membered ring containing a heavier group 14 element
can undergo annelation with a benzene ring with much
less perturbation than the case of hydrocarbon systems.
At the next stage, we became interested in the chemical
properties of metallacyclopropabenzenes. While a great
number of papers on the reactivity of cyclopropabenzene
have appeared so far,1 most of them are the addition
reactions leading to the ring opening and ring expansion
of its three-membered ring to release the strain energy.
In most cases, the reagents added were found to attack
the electron-rich π-bond or the strained σ-bond of the
three-membered ring. By contrast, 1 and 2 do not react
with MeOH, MesCNO, and mCPBA at all. Very re-
cently, we have found the novel reactivity of germacy-
clopropabenzene 2 toward group 6 metal hexacarbonyl
complexes [M(CO)6] (M ) Cr, Mo, W), leading to the
Structures and properties of cyclopropabenzene de-
rivatives have fascinated many organic chemists so far,
because the balance of the aromatic character of the
arene moiety and the angular strain in the three-
membered ring results in their unique properties.1 On
the other hand, many studies on attempted synthesis
of a heteracyclopropabenzene, which has a heteroatom
as the bridging atom of its cyclopropabenzene skeleton
instead of a carbon atom, have been reported.2 However,
no stable examples of heteracyclopropabenzenes have
been known until our research project, because they
might undergo polymerization or isomerization im-
mediately due to their extremely high reactivities and/
or inherent instability.2 Recently, we have succeeded in
the synthesis of the first stable silacyclopropabenzene
(1)3,4 and germacyclopropabenzene (2),5 heavier element
* 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) (a) Halton, B. Chem. Rev. 1989, 89, 1161-1185. (b) Halton, B.
Chem. Rev. 2003, 103, 1327-1369. (c) Soncini, A.; Havenith, R. W. A.;
Fowler, P. W.; Jenneskens, L. W.; Steiner, E. J. Org. Chem. 2002, 67,
4753-4758. (d) Bachrach, S. M. J. Organomet. Chem. 2002, 643, 39-
46. (e) Naka, A.; Yoshizawa, K.; Kang, S.; Yamabe, T.; Ishikawa, M.
Organometallics 1998, 17, 5830-5835. (f) Kyushin, S.; Kitahara, T.;
Matsumoto, H. Chem. Lett. 1998, 471-472. (g) EckertMaksic, M.;
Glasovac, Z.; Hodoscek, M.; Lesar, A.; Maksic, Z. B. J. Organomet.
Chem. 1996, 524, 107-114.
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(5) Tokitoh, N.; Hatano, K.; Sasaki, T.; Sasamori, T.; Takeda, N.;
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(6) (a) Tokitoh, N.; Hatano, K.; Sadahiro, T.; Okazaki, R. Chem. Lett.
1999, 28, 931-932. (b) Tokitoh, N.; Sadahiro, T.; Hatano, K.; Sasaki,
T.; Takeda, N.; Okazaki, R. Chem. Lett. 2002, 31, 34-35.
(7) Tajima, T.; Hatano, K.; Sasaki, T.; Sasamori, T.; Takeda, N.;
Tokitoh, N. Chem. Lett. 2003, 32, 220-221.
(3) Hatano, K.; Tokitoh, N.; Takagi, N.; Nagase, S. J. Am. Chem.
Soc. 2000, 122, 4829-4830.
(4) Tajima, T.; Hatano, K.; Sasaki, T.; Sasamori, T.; Takeda, N.;
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118-126.
10.1021/om049216q CCC: $30.25 © 2005 American Chemical Society
Publication on Web 01/14/2005

2H-Benzo[c][1,2]chalcogenagermetes
Organometallics, Vol. 24, No. 4, 2005 613
Scheme 1
the corresponding 2H-benzo[c][1,2]chalcogenagermete
derivatives 4 and 5 were obtained as a sole product,
respectively. It should be noted again that 4 and 5
showed no over-chalcogenation products under these
conditions. The selenization and tellurization products
were stable enough to be purified by HPLC and column
chromatography on silica gel. The structures of 3, 4, and
5 were fully supported by 1H and 13C NMR spectra,
mass spectra (FAB), elemental analyses, and X-ray
crystallographic analysis (vide infra). In the multi-
nuclear NMR spectroscopic analyses, 4 and 5 showed
one characteristic singlet signal at 352.0 ppm (77Se NMR
of 4 in C6D6) and 612.3 ppm (125Te NMR of 5 in C6D6),
respectively.
Previous reports on the reactivities of cyclopropaben-
zenes indicate that the cyclopropabenzenes have two
active sites in their three-membered rings, that is, the
annelated CdC double bond and the strained C-C
single bond.1 For typical examples, several types of
addition reactions and insertion reactions on the two
active sites of cyclopropabenzene have been reported for
the reactions with electron-deficient dienes9 and transi-
tion metal (Ni, Pd, and so on) complexes.10 On the other
hand, an interesting result was reported in the reaction
of cyclopropabenzene with dichloro- or dibromocar-
bene,11 where the corresponding ring-expanded cyclob-
utabenzene 7 was afforded in a quantitative yield
possibly via an initial [1+2] cycloaddition leading to 6
followed by its ready isomerization involving re-aroma-
tization of the fused ring (Scheme 3). Considering the
formation of cyclic germoxycarbene metal complexes.8
In this paper, we present the reactions of germacyclo-
propabenzene 2 with elemental chalcogens, such as
sulfur, selenium, and tellurium. In all cases, insertion
reactions of a chalcogen atom into the three-membered
ring of the germacyclopropabenzene occurred to give the
corresponding chalcogenagermete derivatives. The iso-
lated novel four-membered heterocycles, 2H-benzo[c]-
[1,2]chalcogenagermetes, have been structurally char-
acterized by X-ray crystallographic analysis.
Scheme 2
Results and Discussion
Scheme 3
Reactions of Germacyclopropabenzene with El-
emental Chalcogens. Heating of a C6D6 solution of
germacyclopropabenzene 2 with an excess amount of
elemental sulfur (S8, 16 equiv as S) at 135 °C for 4.5
days in a sealed tube afforded the corresponding 2H-
benzo[c][1,2]thiagermete 3 exclusively in 63% isolated
yield. In this reaction, no other identifiable products
were observed, as judged by 1H NMR spectra of the
crude reaction products. Therefore, it was conceivable
that 3 may not undergo an over-sulfurization reaction
leading to the formation of five- or six-membered cyclic
compounds under these conditions. On the other hand,
silacyclopropabenzene 1 was quite inert toward elemen-
tal sulfur under the same conditions. The lack of
reactivity of 1 toward S8 compared with 2 is most likely
interpreted in terms of the difference of steric congestion
around the metallacyclopropene skeleton due to the
shorter Si-C bond lengths than Ge-C bond lengths.
Indeed, 2 is gradually hydrolyzed, leading to Tbt(Dip)-
Ge(Ph)OH through column chromatographic separation
on silica gel, though 1 is very inert toward hydrolysis
under the same conditions.3-5
Successful isolation of 3 naturally prompted us to
examine the chalcogenation reactions of 2 with heavier
elemental chalcogens, i.e., selenium and tellurium, in
the hope of obtaining the heavier 2H-benzo[c][1,2]-
chalcogenagermetes as stable compounds. When 2 was
treated with an excess amount of elemental selenium
(5 equiv) or elemental tellurium (5 equiv) under the
same conditions as those for the sulfurization reaction
of 2 (in a C6D6 sealed tube, at 135 °C, for a few days),
reactivity of cyclopropabenzenes,1 it can be considered
that the germacyclopropabenzene 2 should have two
active sites, the strained Ge-C bond and the CdC bond
in the three-membered ring systems. That is, addition
of elemental chalcogens toward germacyclopropaben-
zene 2 might take place not only at the Ge-C bond but
also at the CdC bond in the fused three-membered ring,
leading to two types of products, type I and type II,
respectively (Chart 1). Since only type I products were
obtained in the chalcogenation reactions of 2, it can be
simply concluded that the Ge-C bond of 2 might be
more reactive toward elemental chalcogens than its Cd
C bond. However, it is also conceivable that the reaction
(9) (a) Neidlein, R.; Kohl, M.; Kramer, W. Helv. Chim. Acta 1989,
72, 1311-1318. (b) Brinker, U. H.; Wuster, H. Tetrahedron Lett. 1991,
32, 593-596. (c) Saracoglu, N.; Durucasu, I.; Balci, M. Tetrahedron
1995, 51, 10979-10986. (d) Halton, B.; Russell, S. G. G. Aust. J. Chem.
1990, 43, 2099-2105. (e) Saito, K.; Ishihara, H.; Kagabu, S. Bull.
Chem. Soc. Jpn. 1987, 60, 4141-4142.
(10) (a) Stang, P. J.; Song, L.; Halton, B. J. Organomet. Chem. 1990,
388, 215-220. (b) Kru¨ger, C.; Laakmann, K.; Schroth, G.; Schwager,
H.; Wilke, G. Chem. Ber. 1987, 120, 471-475. (c) Schwager, H.; Kru¨ger,
C.; Neidlein, R.; Wilke, G. Angew. Chem., Int. Ed. Engl. 1987, 26, 65-
67. (d) Schwager, H.; Benn, R.; Wilke, G. Angew. Chem., Int. Ed. Engl.
1987, 26, 67-68. (e) Benn, R.; Schwager, H.; Wilke, G. J. Organomet.
Chem. 1986, 316, 229-231. (f) Neidlein, R.; Rufinska, A.; Schwager,
H.; Wilke, G. Angew. Chem., Int. Ed. Engl. 1986, 25, 640-642.
(11) (a) Kagabu, S.; Saito, K. Tetrahedron Lett. 1988, 29, 675-676.
(b) Durucasu, I.; Sarac¸oglu, N.; Balci, M. Tetrahedron Lett. 1991, 32,
7097-7098.
(8) Tajima, T.; Sasaki, T.; Sasamori, T.; Takeda, N.; Tokitoh, N.
Chem. Commun. 2004, 402-403.

614 Organometallics, Vol. 24, No. 4, 2005
Sasamori et al.
Chart 1
Scheme 5
Table 1. Calculated Relative Energiesa of Model
Compounds (R ) R′ ) H) for Type I and Type II
kcal/mol
type I
type II
a Calculated free energies (298 K, 1.0 atm) at the B3LYP/
6-311G(2d,p) level.
Ch ) S
Ch ) Se
Ch ) Te
0.0 (0.0)
0.0 (0.0)
0.0 (0.0)
77.4 (78.0)
75.0 (75.7)
69.8
is much less endothermic than that from 1,1-diphe-
nylgermacyclopropabenzene (Scheme 5).
a At the B3LYP/TZ(2d) level for Ge, Lanl2DZdp for S, Se, Te,
6-311(2d,p) for C, H [values in parentheses are at the B3LYP/6-
311G(2d,p) level].
Crystal Structures of the 2H-Benzo[c][1,2]-
chalcogenagermetes. The molecular structures of
diaryl-substituted 2H-benzo[c][1,2]chalcogenagermetes
3, 4, and 5 were revealed by X-ray crystallographic
analysis (Table 2). In Figures 1, 2, and 3 are shown the
ORTEP drawings of 3, 4, and 5, respectively. Although
an inevitable disorder of its benzothiagermete moiety
was observed in the case of 3 in every data collection
and analyses with a number of different single crystals
at low temperature (-170 °C), the molecular structure
of 3 was solved adequately (Figure 4).
Scheme 4
products, chalcogenagermetes, may not be necessarily
kinetic products. The reason only the product of type I
was obtained here might be the large difference of the
thermodynamic stability between type I and type II.
This was supported by calculated thermodynamic ener-
gies of model compounds shown in Table 1. That is, a
formal [1+2] cycloaddition of a chalcogen atom to the
CdC double bond affords the type II compound, which
might undergo immediate isomerization to give the type
I product under these reaction conditions as well as the
reaction of cyclopropabenzene with dichlorocarbene.
Thus, the mechanisms of chalcogenation reactions of 2
are unclear at present. Investigation of the reaction
mechanisms of heavier cyclopropabenzenes with el-
emental chalcogens is attractive and currently in
progress.
It should also be noted that the reactivity of the
germacyclopropabenzene differs from that of germacy-
clopropenes (germirenes). Thermal reaction of an over-
crowded germirene 8, which was prepared as a stable
crystalline compound by the reaction of germylene Tbt-
(Tip)Ge: (Tip ) 2,4,6-triisopropylphenyl) with diphe-
nylacetylene, with elemental tellurium reportedly af-
fords the stable germanetellone 9, Tbt(Tip)GedTe
(Scheme 4).12 The key step in this reaction is the
generation of germylene 10, which was allowed to react
with elemental tellurium to give germanetellone 9, via
the thermal cycloreversion of germacyclopropene 8. That
is, no telluragermete derivative was obtained in the
tellurization reaction of 8 because the germirene more
easily undergoes thermal retro-cycloaddition reaction to
give the corresponding germylene than the germacy-
clopropabenzene. Indeed, theoretical calculations [B3LYP/
6-311G(2d,p)] showed that the generation of a ger-
mylene (Ph2Ge:) from 1,1-diphenylgermacyclopropene
Figure 1. ORTEP drawing of the major part of 3 with
thermal ellipsoid plots (50% probability). Hydrogen atoms
were omitted for clarity.
Selected bond lengths and angles of 3, 4, and 5 are
summarized in Table 3. One can see that their ben-
zochalcogenagermete rings in the solid state are com-
pletely planar within the limits of error. In addition,
the disordered moieties in benzothiagermete 3 lie on the
same plane. In all cases, the observed bond lengths and
bond angles in the benzene rings are 1.367-1.412 Å and
117.0-122.7°, respectively. It is obvious that the struc-
tural parameters of the benzene rings of 3, 4, and 5 are
close to those of an unperturbed benzene; that is, almost
no bond alternation was observed for 3, 4, and 5 as well
as the parent cyclobutabenzene.13 Since benzochalco-
(12) Tokitoh, N.; Matsumoto, T.; Okazaki, R. J. Am. Chem. Soc.
1997, 119, 2337-2338.
(13) Boese, R.; Bla¨ser, D. Angew. Chem., Int. Ed. Engl. 1988, 27,
304-305.

2H-Benzo[c][1,2]chalcogenagermetes
Organometallics, Vol. 24, No. 4, 2005 615
Table 2. Crystal Data for 3, 4, and 5
3
4
5
formula
fw
C
45H80GeSSi6
C
45H80GeSeSi6
C
45H80GeSi6Te
894.28
941.18
989.82
color
colorless
prismatic
0.30 × 0.20 × 0.02
-170
triclinic
P1h (#2)
10.125(3)
11.941(3)
22.971(7)
76.768(11)
83.650(12)
72.101(9)
2570.3(13)
2
pale-yellow
prismatic
0.15 × 0.10 × 0.03
-170
triclinic
P1h (#2)
11.874(4)
12.500(5)
19.770(6)
77.426(17)
88.937(16)
65.979(5)
2607.8(16)
2
orange
habit
prismatic
0.25 × 0.25 × 0.05
-170
dimensions/mm
temp/°C
cryst syst
space group
a/Å
monoclinic
P21/n (#14)
13.8849(14)
18.3366(13)
20.7964(15)
90
93.7513(10)
90
5283.5(8)
4
b/Å
c/Å
R/deg
â/deg
γ/deg
V/Å3
Z
no. of data/params
R1 [I>2σ(I)]
wR2 (all data)
GOF
8857/509
0.0522
9156/500
0.0670
9304/500
0.0479
0.1004
0.1502
0.1097
1.115
0.930
0.964
genagermetes 3, 4, and 5 have inherently longer Ge-
Ch bonds (Ch ) S, Se, Te) than C-C bond, the inner
bond angles around the juncture carbon atoms of their
chalcogenagermete rings (R3 and R4) are all wider than
those of highly strained, parent cyclobutabenzene
(93.5°),13 which is largely deviated from the ideal bond
angle of an sp2 carbon atom (120°). On the other hand,
Table 3) provided us with helpful evidence to justify our
treatment of the inevitable disorder of 3 in the X-ray
crystallographic analysis as judged by the good agree-
ment of calculated values with experimentally observed
ones.
Figure 3. ORTEP drawing of 5 with thermal ellipsoid
plots (50% probability). Hydrogen atoms were omitted for
clarity.
Figure 2. ORTEP drawing of 4 with thermal ellipsoid
plots (50% probability). Hydrogen atoms were omitted for
clarity.
remarkably narrow inner bond angles are found around
both germanium and chalcogen atoms. Interestingly, the
angles of Ge-Ch-C of 3-5 showed a marked decrease
on going from sulfur (3) to tellurium (5), while no
regular fluctuation was observed for the angles around
the germanium atom.
The theoretical calculations indicate that the extreme
bulkiness of the combination of Tbt and Dip groups
results in very little perturbation to the chalcogenager-
mete rings, since the computed values for model com-
pounds 11a-c, 12a-c, and 13a-c (Scheme 6), which
have much less hindered substituents such as H, Me,
and Ph on the germanium atom, are very close to the
observed parameters for 3, 4, and 5. The optimized
structural parameters for 11c, 12c, and 13c were shown
in Table 3 as representatives. In addition, the structural
optimization for the real molecule of 3 (Figure 5 and
Figure 4. Ball-and-stick models of the disordered mol-
ecules of benzothiagermetes 3.
Conclusion
In this paper, we reported novel reactivity of an
overcrowded germacyclopropabenzene 2 with elemental

616 Organometallics, Vol. 24, No. 4, 2005
Sasamori et al.
Table 3. Observed and Theoretically Optimized [B3LYP/TZ(2d) for Ge, Lanl2DZdp for S, Se, Te,
6-311G(2d,p) for C and H] Structural Parameters (Å, deg) of 3, 4, 5, 11c, 12c, and 13c
11c (Ch ) S)
12c (Ch ) Se)
13c (Ch )Te)
3 (obsd)
4 (obsd)
5 (obsd)
3 (calcd)
(calcd)
(calcd)
(calcd)
R, R′
d1
Tbt, Dip
1.970(4)
2.3284(18)
1.783(4)
1.386(5)
1.393(5)
1.384(6)
1.376(6)
1.395(6)
1.385(5)
74.21(12)
76.46(13)
110.2(3)
99.0(2)
Tbt, Dip
1.971(6)
2.4280(12)
1.904(7)
1.412(9)
1.393(9)
1.397(9)
1.386(9)
1.405(9)
1.385(9)
76.05(19)
73.3(2)
Tbt, Dip
1.999(4)
2.6293(6)
2.130(5)
1.405(7)
1.367(7)
1.400(7)
1.379(7)
1.404(6)
1.369(7)
76.41(14)
69.18(13)
108.8(3)
105.5(3)
118.5(4)
122.0(5)
118.3(5)
121.3(5)
118.7(5)
121.2(5)
359.9
Tbt, Dip
1.973
2.376
1.783
1.410
1.397
1.397
1.398
1.400
1.394
74.16
75.78
111.13
98.93
119.25
121.49
118.39
120.76
120.39
119.72
360.0
720.0
Ph, Ph
1.957
2.320
1.813
1.404
1.387
1.395
1.393
1.396
1.386
76.1
Ph, Ph
1.961
2.452
1.954
1.404
1.387
1.395
1.392
1.395
1.388
76.8
Ph, Ph
1.966
2.648
2.147
1.406
1.388
1.395
1.391
1.395
1.390
77.4
d2
d3
d4
d5
d6
d7
d8
d9
R1
R2
75.5
72.1
67.7
R3
110.2(4)
100.1(4)
119.6(6)
121.0(6)
118.2(6)
121.6(6)
119.7(6)
119.9(6)
359.7
110.4
97.9
110.0
101.1
119.8
121.3
118.2
121.1
120.2
119.4
360.0
720.0
109.6
105.3
119.6
120.9
118.7
120.9
120.1
119.7
360.0
719.9
R4
R5
119.2(3)
122.7(3)
117.0(4)
121.4(4)
121.0(4)
118.8(4)
359.9
120.0
121.3
118.0
121.3
120.2
119.2
359.9
720.0
R6
R7
R8
R9
R10
∑R1-4
a
b
∑R5-10
720.1
720.0
720.0
aThe sum of interior angles of the chalcogenagermete ring. b The sum of interior angles of the benzene ring.
[c][1,2]chalcogenagermetes. Small-ring compounds con-
taining a heavier element fused with a benzene moiety
should be attractive research targets because of their
unique properties. Further investigation of the physical
and chemical properties of 2H-benzo[c][1,2]chalco-
genagermetes obtained here is currently in progress.
Experimental Section
General Procedures. All experiments were performed
under an argon atmosphere unless otherwise noted. All
solvents were dried by standard methods and freshly distilled
prior to use. 1H NMR (400 or 300 MHz) and 13C NMR (100 or
75 MHz) spectra were measured in C6D6 with a JEOL JNM
AL-400 or JEOL JNM AL-300 spectrometer. A signal due to
C6D5H (7.15 ppm) was used as references in 1H NMR and that
due to C6D6 (128 ppm) was used in 13C NMR. Multiplicity of
signals in the 13C NMR spectra was determined by DEPT
technique. 77Se NMR (57 MHz) and 125Te NMR (94 MHz)
spectra were measured in C6D6 with a JEOL AL-300 spec-
trometer using diphenyldiselenide (460 ppm) and diphenyldi-
telluride (450 ppm) as an external standard, respectively.
High- and low-resolution mass spectral data were obtained on
a JEOL JMS-700 spectrometer. HPLC (high-performance
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) and flash column chroma-
tography (FCC) were performed with Merck Kieselgel 60
PF254 and Merck silica gel 60, respectively. 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. Germacyclopropabenzene 2 was
prepared according to the reported procedures.5
Figure 5. Theoretically optimized structure of 3 at the
B3LYP/6-31G(d) level.
Scheme 6
chalcogens (S, Se, Te) leading to the synthesis and
isolation of a series of 2H-benzo[c][1,2]chalcogenagermete
derivatives 3, 4, and 5. X-ray structural analysis and
theoretical calculations revealed the intrinsic structural
features of 2H-benzo[c][1,2]chalcogenagermetes, i.e.,
completely planar skeletons with an unstrained benzene
ring. It was evidenced here that the germacyclopropa-
benzene could be a good precursor for the synthesis of
unprecedented small-ring compounds such as 2H-benzo-
Reaction of 1-(2,6-Diisopropylphenyl)-1-{2,4,6-tris[bis-
(trimethylsilyl)methyl]phenyl}-1-germacyclopropaben-
zene 2 with Elemental Sulfur. A benzene-d6 solution (0.6
mL) of germacyclopropabenzene 2 (30 mg, 0.035 mmol) and
elemental sulfur (S8, 18 mg, 16 equiv as S) was degassed and
sealed in an NMR tube. After heating the solution at 135 °C
for 120 h, the signals of 2 disappeared and the signals that
correspond to 2H-benzo[c][1,2]thiagermete 3 were observed as

2H-Benzo[c][1,2]chalcogenagermetes
Organometallics, Vol. 24, No. 4, 2005 617
3
those for a main product in the 1H NMR spectrum. The
reaction mixture was separated by HPLC (toluene) and PTLC
(hexane) to give 2-(2,6-diisopropylphenyl)-2-{2,4,6-tris[bis-
(trimethylsilyl)methyl]phenyl}-2H-benzo[c][1,2]thiagermete (3,
20 mg, 0.022 mmol, 63%). 3: colorless crystals, mp 203.1-
203.8 °C; 1H NMR (400 MHz, 338 K, C6D6) δ 0.07 (s, 18H,
TMS), 0.17 (s, 18H, TMS), 0.24 (s, 18H, TMS), 1.10 (br, 6H,
) 1.5 Hz, arom ring), 7.02 (ddd, 1H, JHH ) 7.5 Hz, 7.5 Hz,
4JHH ) 1.5 Hz, arom ring), 7.07 (dd, 1H, JHH ) 7.5 Hz, JHH
3
4
) 1.5 Hz, arom ring), 7.10 (d, 2H, 3JHH ) 5.9 Hz, m-arom-CH
3
of Dip), 7.18 (t, 1H, JHH ) 5.9 Hz, p-arom-CH of Dip), 7.42
(dd, 1H, JHH ) 7.5 Hz, JHH ) 1.5 Hz, arom ring); 13C NMR
(75 MHz, 323 K, C6D6) δ 1.17 (q), 1.18 (q), 2.24 (q), 2.65 (q),
25.5 (q), 29.0 (q), 29.7 (q), 31.1 (d), 36.0 (d), 123.8 (d), 124.8
(d), 125.8 (d), 129.3 (d), 130.2 (d), 130.6 (s), 130.8 (d), 133.3
(d), 136.0 (d), 139.6 (s), 140.0 (s), 144.6 (s), 150.6 (s), 154.1 (s),
162.4 (s); 125Te NMR (94 MHz, 343 K, C6D6) δ 612.3; high-
resolution MS (FAB) m/z calcd for C45H8074GeSi6128Te 990.3150
([M]+), found 990.3140 ([M]+). Anal. Calcd for C45H80GeSi6Te:
C, 54.60; H, 8.15. Found: C, 54.78; H, 8.40.
3
4
3
CH3 of Dip), 1.30 (d, 6H, JHH ) 6.5 Hz, CH3 of Dip), 1.48 (s,
1H, p-CH of Tbt), 2.60 (brs, 1H, o-CH of Tbt), 3.10 (brs, 1H,
3
o-CH of Tbt), 3.50 (sept, 2H, JHH ) 6.5 Hz, CH of Dip), 6.5-
6.8 (br, 2H, m-arom-CH of Tbt), 6.9-7.0 (m, 3H, arom ring),
3
7.10 (d, 2H, JHH ) 7.5 Hz, m-arom-CH of Dip), 7.19 (t, 1H,
3JHH ) 7.5 Hz, p-arom-CH of Dip), 7.50 (d, 1H, 3JHH ) 7.5 Hz,
arom ring); 13C NMR (100 MHz, 338 K, C6D6) δ 1.50 (q), 1.56
(q), 2.36 (q), 2.46 (q), 2.78 (q), 26.1 (q), 29.1 (q), 31.5 (d), 36.1
(d), 124.3 (d), 124.8 (d×2), 125.3 (d), 130.4 (d), 131.3 (d), 132.0
(d), 132.5 (s), 140.4 (s), 140.7 (s), 145.3 (s), 148.9 (s), 150.5 (s),
signals due to ortho-benzyl, ortho- and meta-aromatic carbon
atoms of the Tbt group were not observed. Anal. Calcd for
C45H80GeSSi6: C, 60.44; H, 9.02. Found: C, 60.63; H, 9.21.
X-ray Crystallographic Analyses of 3, 4, and 5. Crystal
data of 3, 4, and 5 are summarized in Table 2. The intensity
data were collected on a Rigaku/MSC Mercury CCD diffrac-
tometer with graphite-monochromated Mo KR radiation (λ )
0.71070 Å) at -170 °C to 2θmax ) 50°. The structures were
solved by a direct method (SIR-9714 for 3 and 5, SHELXS-9715
for 4) and refined by full-matrix least-squares procedures on
F2 for all reflections (SHELXL-9715). All hydrogen atoms were
placed using AFIX instructions, while all the other atoms were
refined anisotropically unless otherwise noted.
Single crystals of 3 suitable for X-ray analysis were obtained
by slow recrystallization from hexane at room temperature.
A colorless, prismatic crystal of 3 was mounted on a glass fiber.
The benzothiagermete moiety was disordered, and their oc-
cupancies were refined (0.87:0.13). The hexagonal skeleton of
the benzene ring in the minor part of the disordered thiager-
mete moiety was restrained using AFIX instructions and
refined isotropically. Single crystals of 4 suitable for X-ray
analysis were obtained by slow recrystallization from acetone
at room temperature. A pale yellow, prismatic crystal of 4 was
mounted on a glass fiber. Single crystals of 5 suitable for X-ray
analysis were obtained by slow recrystallization from acetone
at room temperature. An orange, prismatic crystal of 5 was
mounted on a glass fiber.
Theoretical Calculations. All calculations were conducted
using the Gaussian 98 series of electronic structure pro-
grams.16 The geometries were optimized with density func-
tional theory at the B3LYP level.17 It was confirmed by
frequency calculations that the optimized structures have
minimum energies. The basis sets used in the calculations
were described each time in the text (Tables or Schemes). The
basis sets of TZ(2d) for Ge mean the triple-ú basis sets ([3s3p])
augmented by two sets of d polarization functions (d exponents
0.382 and 0.108) with effective core potential.18 The Lanl2DZdp
basis sets for S, Se, and Te were obtained from the Extensible
Computational Chemistry Environment Basis Set Database
(http://www.emsl.pnl.gov/forms/basisform.html), as developed
Reaction of 1-(2,6-Diisopropylphenyl)-1-{2,4,6-tris[bis-
(trimethylsilyl)methyl]phenyl}-1-germacyclopropaben-
zene 2 with Elemental Selenium. A benzene-d6 suspension
(0.6 mL) of germacyclopropabenzene 2 (50 mg, 0.058 mmol)
and elemental selenium (gray Se, 23 mg, 5 equiv as Se) was
degassed and sealed in an NMR tube. After heating the
solution at 135 °C for 216 h, the signals of 2 disappeared and
the signals that correspond to 2H-benzo[c][1,2]selenagermete
1
4 were observed as those for a main product in the H NMR
spectrum. The reaction mixture was separated by PTLC
(hexane) to give 2-(2,6-diisopropylphenyl)-2-{2,4,6-tris[bis-
(trimethylsilyl)methyl]phenyl}-2H-benzo[c][1,2]-
selenagermete (4, 31 mg, 0.033 mmol, 56%). 4: pale yellow
crystals, mp 203.5-204.0 °C; 1H NMR (400 MHz, 343 K, C6D6)
δ 0.08 (s, 18H, TMS), 0.17 (s, 18H, TMS), 0.23 (s, 18H, TMS),
3
3
1.14 (d, 6H, JHH ) 6.3 Hz, CH3 of Dip), 1.27 (d, 6H, JHH
)
6.3 Hz, CH3 of Dip), 1.48 (s, 1H, p-CH of Tbt), 2.65 (brs, 1H,
o-CH of Tbt), 3.11 (brs, 1H, o-CH of Tbt), 3.61 (sept, 2H, 3JHH
) 6.3 Hz, CH of Dip), 6.64 (brs, 2H, m-arom-CH of Tbt), 6.97
3
4
(m, 2H, arom ring), 7.04 (dd, 1H, JHH ) 6.0 Hz, JHH ) 2.7
Hz, arom ring), 7.10 (d, 2H, 3JHH ) 8.4 Hz, m-arom-CH of Dip),
7.19 (t, 1H, JHH ) 8.4 Hz, p-arom-CH of Dip), 7.42 (dd, 1H,
3
3JHH ) 5.3 Hz, 4JHH ) 3.2 Hz, arom ring); 13C NMR (100 MHz,
338 K, C6D6) δ 1.51 (q), 2.44 (q), 2.65 (q), 26.7 (q), 29.0 (q),
31.4 (d), 36.1 (d), 124.0 (d), 124.8 (d), 124.9 (d), 128.1 (d), 129.4
(d), 129.8 (s), 130.3 (d), 131.2 (d), 132.0 (s), 133.2 (d), 140.1
(s), 142.2 (s), 145.0 (s), 151.3 (s), 152.3 (s), 153.7 (s); 77Se NMR
(57 MHz, 343 K, C6D6) δ 352.0; high-resolution MS (FAB) m/z
calcd for C45H8074Ge78SeSi6 942.3268 ([M]+), found 942.3260
([M]+). Anal. Calcd for C45H80GeSeSi6: C, 57.43; H, 8.57.
Found: C, 57.58; H, 8.59.
Reaction of 1-(2,6-Diisopropylphenyl)-1-{2,4,6-tris[bis-
(trimethylsilyl)methyl]phenyl}-1-germacyclopropaben-
zene 2 with Elemental Tellurium. A benzene-d6 solution
(0.6 mL) of germacyclopropabenzene 2 (50 mg, 0.058 mmol)
and elemental tellurium (37 mg, 5 equiv as Te) was degassed
and sealed in an NMR tube. After heating the solution at 135
°C for 336 h, the signals of 2 disappeared and the signals that
correspond to 2H-benzo[c][1,2]telluragermete 5 were observed
as those for a main product in the 1H NMR spectrum. The
reaction mixture was separated by HPLC (toluene) and FCC
(hexane) to give 2-(2,6-diisopropylphenyl)-2-{2,4,6-tris[bis-
(trimethylsilyl)methyl]phenyl}-2H-benzo[c][1,2]-
telluragermete (5, 31 mg, 0.032 mmol, 54%). 5: orange
crystals, mp 168.0-169.0 °C; 1H NMR (300 MHz, 343 K, C6D6)
δ 0.06 (s, 18H, TMS), 0.16 (s, 9H, TMS), 0.17 (s, 9H, TMS),
(14) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115-119.
(15) 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: Tammanstrasse 4, D-3400 Go¨ttingen,
Germany, 1997.
(16) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; J. A. Montgomery,
J.; 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.; Baboul, A. G.; 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.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Andres, J. L.; Gonzalez, C.; Head-Gordon, M.; Replogle, E. S.; Pople,
J. A. Gaussian 98; Gaussian, Inc.: Pittsburgh, PA, 1998.
3
0.24 (s, 18H, TMS), 1.14 (d, 6H, JHH ) 6.8 Hz, CH3 of Dip),
3
1.23 (d, 6H, JHH ) 6.8 Hz, CH3 of Dip), 1.47 (s, 1H, p-CH of
(17) (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.
Tbt), 2.76 (brs, 1H, o-CH of Tbt), 3.22 (brs, 1H, o-CH of Tbt),
3
3.67 (sept, 2H, JHH ) 6.8 Hz, CH of Dip), 6.64 (brs, 2H,
m-arom-CH of Tbt), 6.94 (ddd, 1H, 3JHH ) 7.5 Hz, 7.5 Hz, 4JHH
(18) Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284-298.

618 Organometallics, Vol. 24, No. 4, 2005
Sasamori et al.
and distributed by the Molecular Science Computing Facility,
Environmental and Molecular Sciences Laboratory, which is
part of the Pacific Northwest Laboratory, P.O. Box 999,
Richland, WA 99352, and funded by the U.S. Department of
Energy. The Pacific Northwest Laboratory is a multiprogram
laboratory operated by Battelle Memorial Institute for the U.S.
Department of Energy under contract DE-AC06-76RLO 1830.
Contact David Feller or Karen Schuchardt for further infor-
mation. Computation time was provided by the Supercomputer
Laboratory, Institute for Chemical Research, Kyoto University.
the 21st Century COE on Kyoto University Alliance for
Chemistry from the Ministry of Education, Culture,
Sports, Science and Technology, Japan. The manuscript
was written at TU Braunschweig during the tenure of
a von Humboldt Senior Research Award of one of the
authors (Tokitoh), who is grateful to von Humboldt
Stiftung for their generosity and to Profs. R. Schmutzler
and W.-W. du Mont for their warm hospitality.
Supporting Information Available: Theoretically opti-
mized coordinates of 3, 11a-c, 12a-c, and 13a-c in PDF
format. X-ray crystallographic files of 3, 4, and 5 in CIF format.
This material is available free of charge via the Internet at
http://pubs.acs.org.
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 Research (A) (No.
14204064), Exploratory Research (No. 15655011), COE
Research on “Elements Science” (No. 12CE2005), and
OM049216Q