Synthesis and photochemistry of l,2-digermacyclohexa-3,5-dienes and related compounds

Article abstract of DOI:10.1021/om970799w

Some new germanium analogues of 1,3-cyclohexadiene, 3,4,5,6-tetraphenyl-, 3,6-diphenyl-, and 3,4,5,6-tetramethyl-l,2-digermacyclohexa-3,5-diene and 3,4,5,6-tetraphenyl-1-germa-2-silacyclohexa-3,5-diene, were prepared and fully characterized by spectroscopic methods. On photolysis, the l,2-digermacyclohexa-3,5-diene underwent extrusion of dialkylgermylene (R₂Ge:) to give the corresponding germacyclopentadiene. On irradiation the 1-germa-2-sila-cyclohexa-3,5-diene yielded preferentially the silacyclopentadiene via extrusion of R₂Ge:. The mechanism of these photolyses is discussed.

Full text of DOI:10.1021/om970799w

1782
Organometallics 1998, 17, 1782-1789
Syn th esis a n d P h otoch em istr y of
1,2-Diger m a cycloh exa -3,5-d ien es a n d Rela ted
Com p ou n d s
Kunio Mochida* and Miyuki Akazawa
Department of Chemistry, Faculty of Science, Gakushuin University,
1-5-1 Mejiro, Tokyo 171, J apan
Midori Goto
National Institute of Materials and Chemical Research,
1-1 Higashi, Tsukuba, Ibaraki 305, J apan
Akiko Sekine and Yuji Ohashi
Department of Chemistry, Faculty of Science, Tokyo Institute of Technology,
Ookayama, Meguro-ku, Tokyo 155, J apan
Yasuhiro Nakadaira
Department of Chemistry, The University of Electro-Communications,
Chofu, Tokyo 182, J apan
Received September 11, 1997
Some new germanium analogues of 1,3-cyclohexadiene, 3,4,5,6-tetraphenyl-, 3,6-diphenyl-,
and 3,4,5,6-tetramethyl-1,2-digermacyclohexa-3,5-diene and 3,4,5,6-tetraphenyl-1-germa-2-
silacyclohexa-3,5-diene, were prepared and fully characterized by spectroscopic methods.
On photolysis, the 1,2-digermacyclohexa-3,5-diene underwent extrusion of dialkylgermylene
(R2Ge:) to give the corresponding germacyclopentadiene. On irradiation the 1-germa-2-sila-
cyclohexa-3,5-diene yielded preferentially the silacyclopentadiene via extrusion of R2Ge:.
The mechanism of these photolyses is discussed.
In tr od u ction
reported to afford 1-silabicyclo[3.1.0]hex-3-ene and 4-vi-
nyl-1-silacyclobuta-2-ene and 5,6-disilabicyclo[2.1.1]hex-
2-ene and 2,6-disilabicyclo[3.1.0]hex-3-ene, respectively.
Recently, we have reported the first photochemical
isomerization of one of the germanium analogues of a
1,3-cyclohexadiene, namely of a 1-germacyclohexa-2,4-
diene, which yields the corresponding 4-vinyl-1-germa-
cyclobut-2-ene.9 We describe here the preparation,
structural characterization, and photochemical trans-
formation of some other types of germanium analogues
of a 1,3-cyclohexadiene, namely 3,4,5,6-tetraphenyl-, 3,6-
diphenyl-, and 3,4,5,6-tetramethyl-1,2-digermacyclohexa-
3,5-diene (1-3) and 3,4,5,6-tetraphenyl-1-germa-2-
silacyclohexa-2,4-diene (4). The photochemical behavior
of these germanium analogues, 1-4, has been investi-
gated mainly by means of trapping experiments. The
mechanism of these photochemical isomerizations is
discussed and compared with that of silicon analogues.
Although photochemical isomerization of 1,3-cyclo-
hexadienes to 1,3,5-hexatrienes has been investigated
extensively in connection with the chemistry of vitamin
D, with conservation of orbital symmetry, and also with
preparation of a medium-sized ring,1-6 only a few
photochemical studies of the group 14 element (silicon
and germanium) analogues of 1,3-cyclohexadienes have
been reported. Recent studies of the photolysis of silicon
analogues of 1,3-cyclohexadiene reveal interesting el-
emental as well as substitution effects on products
formed. These were accounted for by assuming a triene-
like intermediate that contains a silicon-silicon double
bond.7,8 Thus, on irradiation some 1-silacyclohexa-2,4-
dienes and 1,2-disilacyclohexa-3,5-dienes have been
(1) Fonken, G. J .; In Organic Photochemistry; Chapman, O. L., Ed.;
Marcel Dekker: New York, 1967; Vol. 1, p 222.
(2) Sanders, G. B.; Pot, J . M.; Havinga, E. Fortschr. Chem. Org.
Naturst. 1969, 27, 129.
(3) Woodward, R. B.; Hoffmann, R. The Conservation of Orbital
Symmetry; Academic Press: New York, 1970.
(4) Padwa, A.; Brodsky, L.; Clough, S. J . Am. Chem. Soc. 1972, 94,
6767.
Resu lts a n d Discu ssion
P r ep a r a tion a n d Ch a r a cter iza tion of Ger m a -
n iu m An a logu es of a 1,3-Cycloh exa d ien e a n d Re-
(5) Spangler, S. W.; Hennis, R. P. J . Chem. Soc., Chem. Commun.
1972, 24.
(6) Dauben, W. D.; Kellog, M. S.; Seeman, J . I.; Vietmeyer, N. D.;
Wendschuh, J . Am. Chem. Soc. 1973, 95, 3932.
(7) Nakadaira, Y.; Kanouchi, S.; Sakurai, H. J . Am. Chem. Soc. 1974,
96, 5622.
(8) Nakadaira, Y.; Kanouchi, S.; Sakurai, H. J . Am. Chem. Soc. 1974,
96, 5623.
(9) Mochida, K.; Nohara, C.; Ohhori, T.; Kako, M.; Nakadaira, Y.
Chem. Lett. 1994, 1962.
S0276-7333(97)00799-1 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 03/31/1998

1,2-Digermacyclohexa-3,5-dienes
Organometallics, Vol. 17, No. 9, 1998 1783
la ted Com p ou n d s. Some 1,2-digermacyclohexa-3,5-
dienes and 1-germa-2-silacyclohexa-3,5-diene derivatives
were prepared by the reaction of an appropriate 1,4-
dilithiobutadiene with 1,1,2,2-tetraalkyl-1,2-dichlorodi-
germane and (dialkylchlorosilyl)dialkylchlorogermane
in the case of 4, respectively.8,10 Thus, 1,1,2,2-tetra-
alkyl-3,4,5,6-tetraphenyl-1,2-digermacyclohexa-3,5-
dienes (1a , E ) Ge, R1 ) R2 ) Ph, R3 ) Me; 1b, E )
Ge, R1 ) R2 ) Ph, R3 ) Et) were obtained by the
reaction of 1,4-dilithio-1,2,3,4-tetraphenyl-1,3-butadiene
with the corresponding 1,1,2,2-tetraalkyl-1,2-dichloro-
digermane. Similarly, 1,1,2,2-tetramethyl-3,6-diphenyl-
F igu r e 1. ORTEP drawing of the molecular structure of
1a with atoms represented as 50% probability ellipsoids.
1,2-digermacyclohexa-3,5-diene (2) was prepared by the
reaction of 1,4-dilithio-1,4-diphenyl-1,3-butadiene with
1,1,2,2-tetramethyl-1,2-dichlorodigermane. On the other
hand, 1,1,2,2,3,4,5,6-octamethyl-1,2-digermacyclohexa-
3,5-diene (3) was prepared via 1,1-bis(η5-cyclopentadi-
enyl)-1,2,3,4-tetramethyl-1-zirconacyclopenta-2,4-di-
ene.11,12 By treatment with iodine followed by reaction
of the diiodo-1,3-butadiene thus produced with n-butyl-
lithium, the zirconacycle was converted to (1Z,3Z)-1,4-
dilithio-1,2,3,4-tetramethly-1,3-butadiene. Reaction of
the latter with 1,1,2,2-tetramethyl-1,2-dichlorodiger-
mane afforded the 1,2-digermacyclohexa-3,5-diene 3.
1,1,2,2-Tetraethyl-3,4,5,6-tetraphenyl-1-germa-2-silacy-
clohexa-3,5-diene (4) was prepared by the treatment of
1,4-dilithio-1,2,3,4-tetraphenyl-1,3-butadiene with (di-
ethylchlorosilyl)diethylchlorogermane. Germacyclo-
hexadienes 1, 2, and 4 are yellow solids, and 3 is a
colorless liquid.
The UV maxima of 1, 2, and 4 are located around 330
nm (1a , 330 nm; 1b, 335 nm; 2, 328 nm; 4, 339 nm). On
the other hand, the permethyl species 3, which has no
phenyl groups on the butadienyl moiety, shows its
absorption maximum at much shorter wavelength, 289
nm, which is at much larger wavelength than the UV
maximum of the corresponding isoelectronic, wholly
organic 1,3-cyclohexadiene derivative. The character-
istic red shift of absorption bands of these germacycles
1-4 should be ascribable to appreciable orbital interac-
tion between the σ orbital of the Ge-Ge or Ge-Si bonds
and the π orbital developed over the butadienyl moiety
of 1,2-digerma- or 1-germa-2-sila-cyclohexa-3,5-diene.8,13
F igu r e 2. ORTEP drawing of the molecular structure of
2 with atoms represented as 50% probability ellipsoids.
In other words, the steric constraint caused by the
substituents on the cyclic diene results in puckering,
and this brings about the pronounced σ-π conjugation
described above. However, the UV absorption of 3 is
quite different from that of 1, 2, and 4.
To clarify the detailed structures of these 1,2-dimet-
allacyclohexadienes, X-ray analyses have been carried
out on single crystals of 1a and 2, obtained by recrys-
tallization from ether/acetone. ORTEP drawings of 1a
and 2 are shown in Figures 1 and 2, and the crystal-
lographic data and structure refinement and selected
bond lengths and bond angles for 1a and 2 are listed in
Tables 1 and 2, respectively. The 1,2-digermacyclohexa-
3,5-diene rings of 1a and 2 are puckered with dihedral
angles of 53 and 23°, respectively, between the two
planes Ge(1)-Ge(2)-C(1)-C(2) and Ge(1)-C(4)-C(3)-
C(2). In addition, from the points of the σ-π conjuga-
tion mentioned above, the dihedral angles of Ge(1)-
Ge(2)-C(1)-C(2) and Ge(2)-Ge(1)-C(4)-C(3) are not
0° but 50.0 and 27.1° for 1a and 23.3 and 12.0° for 2,
respectively. This indicates that considerable orbital
interaction must occur between the Ge-Ge σ bond and
the π orbitals of the terminal carbon atoms C(1) and
C(4). The Ge-Ge-C and Ge-C-C bond angles con-
(10) Sakurai, H.; Nakadaira, Y.; Tobita, H. Chem. Lett. 1982,
1855.
(11) Ashe, A. J ., III; Kampf, J . W.; Pilotek, S.; Rousseau, R.
Organometallics 1994, 13, 4067.
(12) Bankwitz, U.; Sohn, H.; Powell, D. S. West, R. J . Organomet.
Chem. 1995, 499, C7.
(13) Bock, H.; Solouki, B. In The Chemistry of Organic Silicon
Compounds; Patai, S., Rapport, Z., Eds.; Wiley: New York, 1989, Part
1, Chapter 9.

1784 Organometallics, Vol. 17, No. 9, 1998
Mochida et al.
Ta ble 1. Cr ysta llogr a p h ic Da ta for
1,2-Diger m a cyclo-3,5-d ien es 1a a n d 2
π orbital on the butadienyl groups. The X-ray struc-
tures of 1a and 2 do not show the best geometry for σ-π
interaction; i.e., the dihedral angles of Ge(1)-Ge(2)-
C(1)-C(2) and Ge(2)-Ge(1)-C(4)-C(3) are only 50.0
and 27.1° for 1a . The UV absorption of 3 is quite
different from those of 1a and 2. As expected, the
phenyl groups on the butadienyl moiety strongly influ-
ence the UV maxima of the cyclic dienes as well as the
σ-π interaction.
P h otoch em istr y of 1-4. We have investigated the
photochemical behavior of 1-4 and compared it with
that of silicon and carbon analogues. When a degassed
C6D6 solution of 1,1,2,2-tetramethyl-3,4,5,6-tetraphenyl-
1,2-digermacyclohexa-3,5-diene (1a ) in a Pyrex NMR
tube was irradiated with a 450-W high-pressure Hg arc
lamp for 30 min at room temperature, 1,1-dimethyl-
2,3,4,5-tetraphenyl-1-germacyclopenta-2,4-diene (5a )17
was obtained quantitatively as the sole isolable product
(eq 2). One equivalent of dimethylgermylene must have
chem formula
fw
C32H32Ge2 (1a )
561.79
C20H24Ge2 (2)
409.59
cryst syst
space group
a (Å)
monoclinic
P21/n
monoclinic
C2/c
9.839(1)
22.960(3)
12.821(2)
99.606(7)
2855.8(7)
4
40.120(18)
6.683(2)
14.826(5)
101.64(3)
3893(3)
4
b (Å)
c (Å)
â (deg)
V (Å3)
Z
D
T (°C)
calc (g cm-3
)
1.231
1.384
20
23
cryst dimens (mm)
X-radiation
0.6 × 0.3 × 0.7
0.3 × 0.25 × 0.25
Cu KR
Mo KR
λ (Å)
1.5418
6 < 2θ < 130
2θ/ω
0.70 + tan θ
4472
4214
0.710 73
5 < 2θ < 55
2θ/ω
1.21 + tan θ
4478
data range, 2θ (deg)
scan type
scan width (deg)
no. of rflns recorded
no. of nonequiv
rflns recorded
4478
T
max, Tmin
0.999, 0.774
0.058
0.998, 0.953
0.055
Rmerge (on I)
no. of params refined
R(F) (Fo > 4σFo)
RW (F2) (Fo > 4σFo)
642
0.0550
0.0700 for
4472 rflns
1.1224
211
0.067
0.164 for
3212 rflns
1.076
goodness of fit
max shift/esd in the
final least-squares
cycle
2.290
0.001
final max, min
0.66, -0.91
0.86, -1.55
∆F (e Å-3
)
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 1a a n d 2
been extruded from 1a in the photolysis. In confirma-
tion, when 1a was photolyzed in the presence of a
germylene trapping agent, 2,3-dimethylbuta-1,3-diene,18
under similar conditions, the expected germylene trapped
product, namely, 1,1,3,4-tetramethyl-1-germacyclopent-
3-ene,18 was obtained in 78% yield.
Similar irradiation of a C6D6 solution of 1,1,2,2-
tetraethyl-3,4,5,6-tetraphenyl-1,2-digermacyclohexa-3,5-
diene (1b) gave 1,1-diethyl-2,3,4,5-tetraphenyl-1-ger-
macyclopenta-2,5-diene (5b ) via extrusion of diethyl-
germylene in 98% yield. The extruded diethylgermylene
was trapped in part with 2,3-dimethylbuta-1,3-diene in
another experiment to give the corresponding 1-germa-
cyclopent-3-ene in 24% yield. The remainder of the
diethylgermylene was converted to miscellaneous, uni-
dentified oligo(diethylgermylene)s.19
Permethylated 1,2-digermacyclohexa-3,5-diene (3)
showed similar photochemical behavior, giving, via ex-
trusion of Me2Ge:, 1,1,2,3,4,5-hexamethyl-1-germacy-
clopenta-2,5-diene (10) quantitatively. On consideration
of the irradiation time required to consume the starting
cyclohexadienes, methyl derivative 3 may be presumed
to be less reactive than tetraphenyl derivative 1.
When diphenyl derivative 2 in degassed C6D6 solution
in a Pyrex NMR tube was irradiated for 2 h under
similar conditions, 2,5-diphenyl-1,1-dimethyl-1-germa-
cyclopenta-2,4-diene (6) was produced, as expected, in
11% yield, together with the three dimers 7 (36%), 8
(14%), and 9 (8%). The photodimers 7-9 were isolated
1a
2
Ge1-Ge2
Ge2-C1
C1-C2
2.389(1)
1.988(4)
1.335(5)
1.510(5)
1.344(5)
1.970(3)
1.960(5)
1.955(5)
1.944(5)
1.962(5)
1.494(5)
2.40(2)
1.95(2)
1.35(2)
1.48(2)
1.35(2)
1.96(2)
1.97(2)
1.94(2)
1.95(2)
1.97(2)
1.50(2)
C2-C3
C3-C4
Ge1-C4
Ge1-C5
Ge1-C6
Ge2-C7
Ge2-C8
C1-C9
Ge1-Ge2-C1
Ge2-C1-C2
C1-C2-C3
C2-C3-C4
C4-Ge1-C6
C4-Ge1-C5
Ge2-Ge1-C5
Ge2-C1-C9
C2-C1-C9
93.5(1)
101.3(8)
123.5(8)
131.0(8)
132.3(6)
109.6(4)
111.5(5)
109.1(6)
117.2(8)
118.8(8)
123.3(3)
124.0(3)
125.3(3)
110.5(2)
109.6(2)
111.2(2)
113.0(2)
123.0(3)
structing the six-membered ring are in the range 93.1-
93.4 and 121.6-123.4° (1a ) and 101.0-101.3 and 122.5-
123.5° (2), respectively. The dihedral angles and the
Ge-Ge-C bond angles in 1a are largely distorted due
to steric repulsion by the four phenyl groups. The Ge-
Ge bond lengths of 1a and 2 are 2.39-2.40 Å, shorter
than those of Ph6Ge2 (2.437 Å)14 and cyclic polyger-
manes (2.45-2.48 Å).15,16
The most favorable geometry of σ-π interaction is
that in which the σ (Ge-Ge) orbital is orthogonal to the
(16) Mochida, K.; Kawajiri, Y.; Goto, M. Bull. Chem. Soc. J pn. 1993,
66, 2773 and references therein.
(17) Dubac, J .; Laporterie, A.; Manuel, G. Chem. Rev. 1990, 90,
215.
(14) Drager, M.; Ross, L. Z. Anorg. Allg. Chem. 1980, 460, 207.
(15) J ensen, W.; J acobson, R.; Benson, J . Cryst. Struct. Commun.
1975, 4, 299.
(18) Shriewer, M.; Neumann, W. P. J . Am. Chem. Soc. 1983, 105,
897.
(19) Mochida, K.; Chiba, H. J . Organomet. Chem. 1994, 473, 45.

1,2-Digermacyclohexa-3,5-dienes
Organometallics, Vol. 17, No. 9, 1998 1785
Ta ble 3. Cr ysta llogr a p h ic Da ta for [2 + 2]
P h otod im er s 7-9
chem formula
C60H52Ge2 (7) C60H52Ge2 (8) C60H52Ge2 (9)
fw
918.256
monoclinic
C2/c
20.995(2)
9.9414(4)
14.851(1)
90
105.691(2)
90
2984.2(3)
4
918.256
monoclinic
P2/c
18.020(3)
10.060(2)
17.090(2)
90
90.02(1)
90
3059.9(7)
4
918.256
triclinic
P12
cryst syst
space group
a (Å)
b (Å)
c (Å)
12.253(2)
13.429(1)
9.663(2)
95.10(2)
104.383(9)
97.64(8)
1513.5(4)
2
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
D
calc (g cm-3
)
1.353
2.04
23
1.319
1.99
23
1.334
1.99
23
µ (Mo KR)(mm-1
T (°C)
)
cryst dimens
(mm)
0.4 × 0.4 ×
0.5 × 0.5 ×
0.3 × 0.25 ×
0.2
0.4
0.1
X-radiation
λ (Å)
data range,
2θ (deg)
scan type
scan width (deg)
Mo KR
0.710 73
5 < 2θ < 55
Mo KR
0.710 73
5 < 2θ < 55
Mo KR
0.710 73
5 < 2θ < 55
2θ/ω
2θ/ω
2θ/ω
1.5 + 0.35
tan θ
1.5 + 0.35
tan θ
1.5 + 0.35
tan θ
no. of rflns
9204
7033
6917
recorded
no. of nonequiv
rflns recorded
3145
7029
6916
T
max, Tmin
1.000, 0.540
0.058
182
1.000, 0.382
0.058
355
1.000, 0.609
0.055
343
and purified by rapid chromatography with a short silica
column followed by recrystallization from ethanol. The
germole 6 was identified by comparing its H NMR and
Rmerge (on I)
no. of params
refined
1
MS spectra with those of an authentic sample.17 Fur-
thermore, photodimers 7-9 were characterized by their
1H and 13C NMR, 1H-1H COSY, 1H-13C COSY, and MS
spectra. Finally, X-ray crystallographic analysis un-
ambiguously established the structures of 7-9. The
photodimers 7-9 were assigned anti-trans, anti-cis, and
syn-cis structures, respectively, by comparison of these
spectral data with those of the corresponding silyl
dimers.20,21 The structures of the dimers 7-9 were
confirmed by X-ray crystallographic analysis. Their
crystal data are described in Tables 3 and 4.
ORTEP drawings of the molecular structures of 7-9
are presented in Figures 3-5, and selected bond lengths
and bond angles are listed in Tables 3 and 4. The
structural results show that two 1-germacyclopentene
moieties adopt a trans configuration about the four-
membered ring of 7 but a cis conformation of 8 and 9.
The four-membered rings of 7 and 8 are nearly planar,
but that of 9 is slightly distorted, possibly by the steric
bulk of two neighboring phenyl groups on the ring.
Under similar conditions, photolysis of 2 in the
presence of 2,3-dimethylbuta-1,3-diene yielded the ex-
pected germylene trapping product 1,1,3,4-tetramethyl-
1-germacyclopent-3-ene in 26% yield. 2,2,4,4,6,6-Hex-
amethyl-1,3,5-trioxa-2,4,6-trigermacyclohexane also was
formed in 10% yield, together with trace amounts of
dodecamethylcyclohexagermane (1%) and decamethyl-
cyclopentagermane (<1%). Dimethylgermylene is readily
polymerized to yield permethylated cyclic and linear
oligogermanes.22 The 1,3,5-trioxa-2,4,6-trigermacyclo-
hexane conceivably is formed by trimerization of di-
methylgermanone or its equivalent arising from oxida-
tion of dimethylgermylene.23
R(F) (Fo > 4 σFo)
0.042
0.075
0.055
R
W(F2) (Fo > 4σFo) 0.102 for
0.194 for
4513 rflns
1.004
0.136 for
4574 rflns
1.001
2222 rflns
1.070
0.000
goodness of fit
max shift/esd
in the final
least-squares
cycle
0.000
0.000
final max, min
0.57, -0.58
1.31, -1.33
0.90, -0.83
∆F (e Å-3
)
To show clearly that the photodimers 7-9 were
derived from the photodimerization of 6 formed during
the photolysis of 2, 6 was independently irradiated with
a 450 W high-pressure Hg arc lamp in C6D6 for 2 h. The
three [2 + 2] photodimers 7-9 were produced in a 4:2:1
ratio (eq 4). Only the anti-trans photodimer 7 had been
>300 nm
6 {
} 7, 8, and 9
(4)
<300 nm
reported as the product of the photoirradiated 6 in
ether.20 While the organosilicon photoproducts of types
7-9 were fairly stable thermally under photoirradiation
with a medium-pressure Hg arc lamp,21 irradiation of
degassed C6D6 solutions of the germanium compounds
7-9 in a quartz NMR tube with a low-pressure Hg arc
lamp afforded 1-germacyclopenta-2,4-diene 6, giving the
reaction mixture composed of 6 and the three dimers.
Thus, the [2 + 2] photodimers 7-9 undergo photochemi-
cal cycloreversion to give germacyclopentadiene 6 on
irradiation with a low-pressure Hg arc lamp.
Thus, 2,5-diphenyl-1-germacyclopenta-2,4-diene 6 is
readily dimerized upon irradiation, but in contrast the
tetraphenyl derivative 5a is photochemically stable
under similar irradiation conditions. This probably is
attributable to the steric hindrance caused by phenyl
(20) Barton, T. J .; Nelson, A. J . Tetrahedron Lett. 1969, 5037.
(21) Nakadaira, Y.; Sakurai, H. Tetrahedron Lett. 1971, 1183.
(22) Carberry, E.; Dombek, D. B.; Cohen, S. C. J . Organomet. Chem.
1972, 36, 61.
(23) Mochida, K.; Tokura, S. Bull. Chem. Soc. J pn. 1992, 65, 1642.

1786 Organometallics, Vol. 17, No. 9, 1998
Ta ble 4. Selected Bon d Dista n ces (Å) a n d An gles (d eg) for Dim er s 7-9a
Dimer 7
Mochida et al.
Ge1-C18
Ge1-C4
Ge1-C1
1.945(4)
1.952(3)
1.992(3)
C1-C2#
1.586(4)
1.500(5)
1.586(4)
C1-C11
C1-C2
1.499(5)
1.562(4)
C3-C4
C4-C5
1.334(5)
1.469(5)
C2-C3
C2-C1#
C18-Ge1-C4
C4-Ge1-C17
C4-Ge1-C1
C11-C1-C2
C2-C1-C2#
116.0(2)
112.2(2)
91.42(14)
117.4(3)
90.0(2)
C18-Ge1-C17
C18-Ge1-C1
C17-Ge1-C1
C11-C1-C2#
C11-C1-Ge1
108.6(2)
C2-C1-Ge1
C3-C2-C1
C1-C2-C1#
C3-C4-C5
C5-C4-Ge1
103.7(2)
113.0(3)
90.0(2)
125.1(3)
126.2(3)
C2#-C1-Ge1
C3-C2-C1#
C4-C3-C2
113.2(2)
121.8(3)
121.5(3)
108.7(3)
114.2(2)
113.8(2)
119.9(3)
110.3(2)
C3-C4-Ge1
Dimer 8
1.954(8)
1.963(6)
2.005(6)
1.514(8)
Ge1-C18
Ge1-C4
Ge1-C17
Ge1-C1
1.916(8)
1.932(6)
1.959(8)
1.978(5)
Ge2-C18B
Ge2-C4B
Ge1-C1B
C1-C11
Ge2-C17B
C1-C2B
C2-C1B
C4-C5
1.945(7)
1.583(8)
1.555(8)
1.500(8)
C1-C2
C2-C3
C3-C4
1.567(8)
1.501(9)
1.333(8)
C18-Ge1-C4
C4-Ge1-C17
C4-Ge1-C1
C17B-Ge2-C18B
C18B-Ge2-C4B
C18B-Ge2-C1B
C11-C1-C2
115.4(4)
112.5(3)
91.1(2)
107.3(4)
115.8(4)
110.8(3)
117.3(5)
C18-Ge1-C17
C18-Ge1-C1
C17-Ge1-C1
C17B-Ge2-C4B
C17B-Ge2-C1B
C4B-Ge2-C1B
C11-C1-C2B
106.0(4)
C2-C1-C2B
C2-C1-Ge1
C3-C2-C1B
C1B-C2-C1
C3-C4-C5
88.9(4)
105.1(4)
118.7(5)
91.8(4)
123.7(6)
125.2(4)
C11-C1-Ge1
109.1(4)
119.7(3)
111.9(3)
110.5(3)
120.8(3)
91.5(2)
C2B-C1-Ge1
C3-C2-C1
C4-C3-C2
C3-C4-Ge1
121.4(4)
112.6(5)
120.2(6)
110.9(4)
C5-C4-Ge1
113.7(5)
Dimer 9
Ge1-C18
Ge1-C4
Ge1-C17
Ge1-C1
1.960(5)
1.932(6)
1.946(5)
1.980(4)
Ge2-C18B
Ge2-C4B
C2-C2B
C1-C11
1.951(5)
Ge2-C17B
1.951(4)
1.502(6)
1.342(6)
1.480(6)
C1-C2
Ge2-C1B
C1-C1B
1.571(6)
2.038(4)
1.619(6)
1.970(5)
1.574(6)
1.496(6)
C2-C3
C3-C4
C4-C5
C18-Ge1-C4
C4-Ge1-C17
C4-Ge1-C1
C17B-Ge2-C18B
C18B-Ge2-C4B
C18B-Ge2-C1B
C11-C1-C2
109.3(2)
119.5(2)
90.8(2)
104.8(2)
112.4(2)
110.1(2)
116.0(4)
C18-Ge1-C17
C18-Ge1-C1
C17-Ge1-C1
C17B-Ge2-C4B
C17B-Ge2-C1B
C4B-Ge2-C1B
C11-C1-C1B
108.0(3)
C2-C1-C1B
C2-C1-Ge1
C3-C2-C1
C4-C3-C2
C3-C4-C5
C5-C4-Ge1
91.8(2)
103.4(3)
111.0(4)
121.3(4)
123.9(4)
127.6(3)
C11-C1-Ge1
C1B-C1-Ge1
C3-C2-C2B
C2B-C2-C1
C3-C4-Ge1
113.2(3)
121.8(3)
115.7(4)
90.1(3)
110.2(2)
118.0(2)
112.9(2)
124.7(2)
91.8(2)
108.5(3)
112.4(3)
a
Symmetry transformations used to generate equivalent atoms: (#) -x + 1/2, -y + 1/2, -z.
groups on the C3 and C4 positions of the five-membered
ring. Furthermore, on prolonged irradiation of a C6D6
solution of 1,1,2,3,4,5-hexamethyl-1-germacyclopenta-
2,4-diene (10) with a high-pressure Hg arc lamp, none
of the [2 + 2] photodimers of 10 could be detected by
NMR and GC-MS spectroscopy. This also may be due
to the steric hindrance of the methyl groups on C3 and
C4 of the ring.
To examine the effect of the metalloidal element on
the photochemical behavior of 1,2-dimetallacyclohexa-
diene, 1,1,2,2-tetraethyl-3,4,5,6-tetraphenyl-1-germa-2-
silacyclohexa-3,5-diene (4) in benzene was irradiated
with a high-pressure Hg arc lamp. The main photolysis
product was 1,1-diethyl-2,3,4,5-tetraphenyl-1-silacyclo-
penta-2,4-diene (11) accompanied by a small amount of
F igu r e 3. ORTEP drawing of the molecular structure of
7 with atoms represented as 50% probability ellipsoids. All
hydrogens have been omitted for clarity.
1,1-diethyl-2,3,4,5-tetraphenyl-1-germacyclopenta-2,4-
diene (5b). In comformity with the results above,
tity to be detected. In the photolysis of 4, the prefer-
ential formation of silole 11 and diethylgermylene may
be rationalized in terms of the difference in the bond
dissociation energy of a Ge-C vs that of a Si-C bond24,25
and of the stability of germyl and silyl radicals.26
Mech a n istic Con sid er a tion s. In contrast to the
1,2-disilacyclohexadiene, 1,2-digerma- and 1-germa-2-
(24) J ackson, R. A. J . Organomet. Chem. 1979, 166, 17.
(25) Basch, H.; Hoz, T. In The Chemistry of Organic Germanium,
Tin and Lead Compounds; Patai, S., Ed.; Wiley: New York, 1995;
Chapter 1.
(26) Mackay, K. M. In The Chemistry of Organic Germanium, Tin
and Lead Compounds, Patai, S. Ed.; Wiley: New York, 1995;
Chapter 2.
diethylgermylene was readily trapped with 2,3-dimeth-
ylbuta-1,3-diene as the corresponding 1-germacyclopent-
3-ene in 37% yield. However, the trapping product
originating from diethylsilylene could not be detected;
probably the silylene is generated in too smaller quan-

1,2-Digermacyclohexa-3,5-dienes
Organometallics, Vol. 17, No. 9, 1998 1787
F igu r e 4. ORTEP drawing of the molecular structure of
8 with atoms represented as 50% probability ellipsoids. All
hydrogens have been omitted for clarity.
F igu r e 5. ORTEP drawing of the molecular structure of
9 with atoms represented as 50% probability ellipsoids. All
hydrogens have been omitted for clarity.
silacyclohexadienes 1-4 undergo a photoinduced ring
contraction reaction with extrusion of the corresponding
germylene. This reminds us of the photochemistry of
vinyldisilane and -digermane. The vinyldisilane 12 is
transformed to either the corresponding silacyclopro-
pane 14 or silene 15 via 1,2- or 1,3-Si migration,
respectively (eq 6),27-34 but in contrast, the vinyldiger-
tochemical isomerization to afford 2,6-disilabicyclo[3.1.0]-
hex-3-ene and 5,6-disilabicyclo[2.1.1]hex-2-ene, possibly
by way of a conjugated disilatriene intermediate.10
Since disilacycles are rather photochemically stable and
only undergo efficient photochemical interconversion via
photoinduced 1,3-Si migration, on photolysis of the 1,2-
disilacyclohexadiene the silacyclopentadiene is formed
in just a trace amount after prolonged irradiation. From
consideration of the photochemistry of vinyldisilane 12
and -digermane 13, the novel photochemical behavior
of 1-4 could be accouned for in terms of the character-
istic properties of the germanium atom, as depicted in
Scheme 1.
Germanium-containing dimetallacyclohexadienes 1-4
are expected to be readily converted to bicyclic com-
pounds 19, 19′, and 20 (E ) Ge, Si) via facile cyclization
of dimetallotriene intermediate 18 (E ) Ge, Si). In
comparison with a silacyclopropane, a germacyclopro-
pane is much more strained and labile due to its longer
and weaker C-Ge bonds.25,36 Thus, bicycles 19 and/or
19′ with a germacyclopropane ring would expel the
corresponding germylene much more readily to yield a
metallacyclopentadiene, as was observed. Since a ger-
myl radical will be thermodynamically more stable than
silyl and carbon radicals,26 another possibility would be
extrusion of a germylene from a germacyclopropane
equivalent such as the biradical 19′′ (E ) Ge, Si), which
contains a more stable (5)-membered silacycle that could
be formed directly from dimetallotriene intermediate 18
(E ) Ge, Si).
Hence, on the photolysis of 4, one would expect that
the silacyclopentadiene should be formed preferentially,
possibly by way of 19′′ (E ) Si), which contains a more
stable germyl radical and five-membered silacycle.
However, the dimetallatriene 18 and bicyclic intermedi-
ates 19 and 20 could not be detected by either NMR
spectroscopy or trapping experiments using methanol
and chloroform under these conditions.
mane 13 is converted to vinylgermane 16 with extrusion
of the corresponding germylene via 1,2-Ge migration or
possibly a germacyclopropane or its equivalent 17 (eq
7).35 On the other hand, one of the silicon analogues of
1,3-cyclohexadiene, namely a 1,2-disilacyclohexa-3,5-
diene, has been reported to undergo quantitative pho-
(27) Lambert, R. L., J r.; Seyferth, D. J . Am. Chem. Soc. 1972, 94,
9246.
(28) Boudjouk, P.; Sommer, L. H. J . Chem. Soc., Chem. Commun.
1973, 54.
(29) Seyferth, D.; Haas, C. K.; Annarelli, D. C. J . Organomet. Chem.
1973, 56, C7.
(30) Bush, R. D.; Golino, C. M.; Homer, G. D.; Sommer, L. H. J .
Organomet. Chem. 1974, 80, 37.
(31) Sakurai, H.; Kamiyama, Y.; Nakadaira, Y. J . Am. Chem. Soc.
1976, 98, 9285.
(32) Ishikawa, M.; Fuchigami, T.; Kumada, M. J . Organomet. Chem.
1976, 117, C58; 1978, 149, 37.
(33) Seyferth, D.; Duncan, D. P.; Vick, S. C. J . Organomet. Chem.
1977, 125, C5.
(34) Seyferth, D.; Vick, S. C.; Shannon, M. L.; Lim, T. F.; Duncan,
D. P. J . Organomet. Chem. 1977, 135, C35.
(35) Mochida, K.; Kikkawa, H.; Nakadaira, Y. Bull. Chem. Soc. J pn.
1991, 64, 2772.
(36) Neumann, W. P. Chem. Rev. 1991, 91, 311.

1788 Organometallics, Vol. 17, No. 9, 1998
Mochida et al.
Sch em e 1
dimethyl-2,3,4,5-tetraphenyl-1-germapenta-2,4-diene,44 1,1-di-
ethyl-2,3,4,5-tetraphenyl-1-germacyclopenta-2,4-diene,45 1,1-
diet h yl-2,3,4,5-t et r a ph en yl-1-sila cyclopen t a -2,4-dien e,46
1,1,2,3,4,5-hexamethyl-1-germacyclopenta-2,4-diene,47 1,1,3,4-
tetramethyl-1-germacyclopent-3-ene,48 1,1-diethyl-3,4-dimethyl-
1-germacyclopent-3-ene,49 and 1,1,2,2-tetramethyl-3,4-diphenyl-
1,2-digermacyclohexa-3,5-diene10 were prepared as reported
in the literature.
Exp er im en ta l Section
Gen er a l Meth od s. All photochemical reactions were car-
ried out in a degassed NMR tube. THF and C6D6 were dried
by refluxing over sodium benzophenone ketyl and distilled
immediately before use. Chloroform, methanol, and 2,3-di-
methylbuta-1,3-diene were distilled before use. NMR spectra
were obtained on a Varian Unity Inova 400 MHz NMR
spectrometer. GC-MS spectra were measured on a J EOL
J MS-DX 303 mass spectrometer. The infrared spectra were
recorded with a Shimadzu FT IR 4200 spectrometer. The UV
and UV-vis spectra were recorded on a Shimadzu UV 2200
P r ep a r a tion of (Dieth ylch lor oger m yl)d ieth ylch lor o-
sila n e. Into a mixture of (phenyldiethylsilyl)phenyldieth-
ylgermane (16.7 g, 45 mmol) and a catalytic amount of AlCl3
(0.1 g) in anhydrous benzene (200 mL) was bubbled HCl gas,
generated from concentrated HCl and NH4Cl, at 40 °C for 3
h. The chlorodephenylation reaction was monitored by means
of GC. After the solvent was evaporated, the residue was
distilled under reduced pressure to give (diethylchlorosilyl)-
diethylchlorogermane (12.1 g, 42 mmol, 93%): bp 150 °C/2
spectrometer. Gas chromatography was performed on
a
Shimadzu GC 8A with a 1 m 20% SE30 column. Liquid chrom-
atography was performed on a Twincle with an Asahipak GS
310 column. X-ray crystallographic data and diffraction
intensities were measured on a four-cycle Enraf-Nonius CAD-4
diffractometer using Cu KR (λ ) 1.6518 Å) radiation or a
Rigaku AFC6/S diffractometer utilizing Mo KR (λ ) 0.71073
Å) radiation with a graphite monochromator. The structures
were solved by direct methods using the program system
MULTAN 78. Calculations were carried out on a FACOM
M-780 with UNICS III.
Ma ter ia ls. Diphenylacetylene, n-butyllithium, and lithium
metal were commercially available. Dimethyldichloroger-
mane,37 diethyldichlorogermane,38 diethyldichlorosilane,39
1,1,2,2-tetramethyl-1,2-dichlorodigermane,40 1,1,2,2-tetraethyl-
1,2-dichlorodigermane,41 1,4-dibromo-1,4-diphenylbuta-1,3-di-
ene,42 (1Z,3Z)-1,4-diiodo-1,2,3,4-tetramethylbuta-1,3-diene,11,12
1,1-dimethyl-2,5-diphenyl-1-germacyclopenta-2,4-diene,43 1,1-
1
mmHg; H NMR (C6D6) δ 0.82-1.08 (m, 10H), 1.08-1.24 (m,
10H); 13C NMR (C6D6) δ 7.6, 9.4, 9.6, 10.2, 10.4, 13.0, 13.3.
Anal. Calcd for C8H20Cl2SiGe: C, 33.38; H, 7.00. Found: C,
33.52: H, 7.20.
P r ep a r a tion of 1,1,2,2-Tetr a m eth yl-3,4,5,6-tetr a p h en -
yl-1,2-d iger m a cycloh exa -3,5-d ien e (1a ). A mixture of
lithium metal (0.5 g, 0.072 mol) and diphenylacetylene (13 g,
0.072 mol) in anhydrous diethyl ether was stirred for 16 h at
room temperature. To this solution was added anhydrous
ether (150 mL) and then dimethyldichlorogermane (10.0 g,
0.036 mol) in ether (20 mL). After it was refluxed for 3 h, the
mixture was hydrolyzed with water. The organic layer was
extracted with diethyl ether and dried over Na2SO4. After the
(37) Finholt, A. E. Nucl. Sci. Abstr. 1957, 6, 617.
(38) Horvitz, L.; Flood, E. A. J . Am. Chem. Soc. 1933, 55, 5055.
(39) Sommer, L. H.; Bailey, D. L.; Whitmore, F. C. J . Am. Chem.
Soc. 1948, 70, 7869.
(40) Kumada, M.; Sakamoto, S.; Ishikawa, M. J . Organomet. Chem.
1969, 17, 235.
(41) Bulten, E. J .; Noltes, J . G. Tetrahedron Lett. 1966, 3471.
(42) Theis, R. J .; Dessy, R. E. J . Org. Chem. 1966, 31, 4248.
(43) Barton, T. J .; Nelson, A. J .; Clardy, J . J . Org. Chem. 1972, 37,
895.
(44) Hota, N. K.; Willis, C. J . J . Organomet. Chem. 1968, 15, 84.
(45) J utzi, P.; Kari, A. J . Organomet. Chem. 1981, 215, 19.
(46) Resibois, B.; Hode, C.; Picart, B.; Brunet, J . C. Ann. Chim. 1969,
4, 203.
(47) Laporterie, A.; Manuel, G.; Dubac, J .; Mazerolles, P. Nouv. J .
Chim. 1982, 6, 67.
(48) Mazerolles, P.; Manuel, G. Bull. Soc. Chim. Fr. 1973, 1.
(49) Marchand, A.; Gerval, P.; Duboudin, F.; J oanny, F.; Mazerolles,
P. J . Organomet. Chem. 1984, 267, 93.

1,2-Digermacyclohexa-3,5-dienes
Organometallics, Vol. 17, No. 9, 1998 1789
solvent had been evaporated, the residue was diluted with
acetone to cause crystallization of pure 1,1,2,2-tetramethyl-
3,4,5,6-tetraphenyl-1,2-digermacyclohexa-3,5-diene (5.14 g,
in a Pyrex NMR tube. The NMR tube was degassed under
vacuum and sealed. The sample was irradiated with a 450 W
high-pressure Hg arc lamp for 30 min at room temperature.
NMR, GC, and GC-MS analysis of the resulting mixture
showed 1-germacyclopenta-2,4-diene 5a (100%) was produced.
P h otolysis of 2. A degassed sealed quartz tube containing
a benzene (10 mL) solution of diphenyl derivative 2 (0.3 mg)
was irradiated with a 450 W high-pressure Hg arc lamp for 3
h. NMR, GC, and GC-MS analysis of the resulting mixture
showed the presence of 1-germacyclopenta-2,4-diene 6 (11%),
the three dimeric products 7 (36%), 8 (14%), and 9 (8%), and
2,2,4,4,6,6-hexamethyl-1,3,5-trioxa-2,4,6-trigermacyclohex-
ane (10%), dodecamethylcyclohexagermane (1%), and deca-
methylcyclopentagermane (<1%). 7: NMR (C6D6) δ -0.02 (s,
3H), 0.46 (s, 3H), 4.45 (d, J > 0.1 Hz, 1H), 6.98-7.31 (m, 11H);
13C NMR (C6D6) δ -3.47, -1.99, 47.21, 54.17, 124.15, 126.86,
1
09.1 mmol, 25%): mp 175-176 °C; H NMR (C6D6) δ 0.54 (s,
12H), 6.7-7.3 (m, 20H); 13C NMR (C6D6) δ -3.7, 124.4, 125.5,
127.6, 129.8, 130.0, 140.7, 143.4, 145.1, 149.4; MS m/z 564 (74-
Ge); UV (cyclohexane) λmax 330.4 nm (log ꢀ 3.46). Anal. Calcd
for C32H32Ge2: C, 68.41; H, 5.74. Found: C, 68.58: H, 5.62.
P r ep a r a tion of 1,1,2,2-Tetr a eth yl-3,4,5,6-tetr a p h en yl-
1,2-d iger m a cycloh exa -3,5-d ien e (1b). A mixture of lithium
metal (0.5 g, 0.072 mol) and diphenylacetylene (13 g, 0.072
mol) in anhydrous diethyl ether was stirred for 16 h at room
temperature. To this solution was added anhydrous diethyl
ether (150 mL) and then diethyldichlorogermane (12.0 g, 0.036
mol) in ether (20 mL). After it was refluxed for 3 h, the
mixture was hydrolyzed with water. The organic layer was
extracted with ether and dried over Na2SO4. After the solvent
had been evaporated, the residue was diluted with acetone and
this solution was allowed to stand at room temperature. Pure
1,1,2,2-tetraethyl-3,4,5,6-tetraphenyl-1,2-digermacyclohexa-
3,5-diene (5.14 g, 0.0091 mol, 25%) was obtained: mp 175-
126.98, 128.78, 140.72, 142.75, 144.70, 147.20; IR (KBr, cm-1
)
1236; MS m/z 616 (74Ge). 8: NMR (C6D6) δ -0.12 (s, 3H), 0.58
(s, 3H), 4.26 (d, J > 0.1 Hz, 1H), 6.90-7.21 (m, 11H); 13C NMR
(C6D6) δ -3.50, -2.01, 43.21, 50.17, 122.10, 125.86, 126.98,
128.78, 140.72, 142.75, 144.70, 147.00; IR (KBr, cm-1) 1235;
MS m/z 616 (74Ge); 9: NMR (C6D6) δ 0.04 (s, 3H), 0.08 (s, 3H),
4.36 (d, J > 0.1 Hz, 1H), 6.87-7.20 (m, 11H); 13C NMR (C6D6)
δ -1.47, 0.99, 49.20, 56.16, 125.10, 127.82, 127.96, 129.72,
141.62, 143.55, 145.60, 148.10; IR (KBr, cm-1) 1241; MS m/z
616 (74Ge). The 1H-1H COSY spectra of 7-9 show that the
allylic protons δ 4.26-4.45 ppm couple with the aromatic
protons at δ 6.98-7.31 ppm. The 1H-13C COSY spectra of
7-9 were also observed, but C-H shifts of the aromtic rings
have not yet been confirmed.
P h otolysis of 1-4 in th e P r esen ce of 2,3-Dim eth ylbu ta -
1,3-d ien e. A degassed sealed Pyrex NMR tube containing 1a
(30 mg), 2,3-dimethylbuta-1,3-diene (100 µL), and C6D6 (500
µL) was irradiated with a 450 W high-pressure Hg arc lamp
for 30 min at room temperature. NMR, GC, and GC-MS
analysis of the resulting mixture showed that 5a (96%) and
1,1,2,3-tetramethyl-1-germacyclopent-3-ene (78%) were formed.
P h otolysis of 1-4 in th e P r esen ce of Ch lor ofor m . A
degassed sealed Pyrex NMR tube containing 1a (30 mg),
chloroform (200 µL), and C6D6 (500 µL) was irradiated with a
450 W high-pressure Hg arc lamp for 30 min at room
temperature. NMR, GC, and GC-MS analysis of the resulting
mixture showed that 5a (96%) was formed.
1
176 °C; H NMR (C6D6) δ 1.06-1.12 (m, 4H), 1.21-1.31 (m,
16H), 6.64-7.10 (m, 20H); 13C NMR (C6D6) δ 7.19, 11.28,
124.97, 125.77, 127.31, 128.10, 128.67, 130.27, 141.53, 142.45,
143.67, 153.49; MS m/z 618 (74Ge); UV (cyclohexane) λmax 338.0
nm (log ꢀ 3.72). Anal. Calcd for C34H36Ge2: C, 69.23; H, 6.15.
Found: C, 69.45: H, 6.24.
P r ep a r a tion of 1,1,2,2,3,4,5,6-Octa m eth yl-1,2-d iger m a -
cycloh exa -3,5-d ien e (3). To a solution of (1Z,3Z)-1,4-diiodo-
1,2,3,4-tetramethylbuta-1,3-diene (3.39 g, 9.36 mmol) in 75 mL
of ether at -78 °C was added with stirring 11.5 mL of 1.62 N
n-butyllithium. This solution was stirred at -78 °C for 2 h,
after which time the solution was warmed to 25 °C for 15 min.
To the dilithio compound was added 1,1,2,2-tetramethyldi-
chlorodigermane (2.6 g, 8.5 mmol) in 75 mL of ether. After it
was stirred at room temperature for 90 min, the mixture was
hydrolyzed with water. The organic layer was extracted with
ether and dried over MgSO4. After the solvent had been
evaporated, the residue was distilled under reduced pressure
to give 1,1,2,2,3,4,5,6-octamethyl-1,2-digermacyclohexa-3,5-
1
diene (1.0 g, 3.2 mmol, 37.6%): bp 63 °C/1 mmHg; H NMR
(CDCl3) δ 0.37 (s, 12H), 1.75 (s, 3H), 1.76 (s, 3H), 1.827 (s, 3H),
1.829 (s, 3H); 13C NMR (CDCl3) δ -5.0, 18.4, 18.6, 123.0, 145.0;
MS m/z 314 (74Ge); UV (cyclohexane) λmax 284.8 nm (log ꢀ 2.52).
Anal. Calcd for C12H24Ge2: C, 45.97; H, 7.72. Found: C,
46.12: H, 7.82.
P h otolysis of 1,1-Dim eth yl-2,5-d ip h en yl-1-ger m a cy-
clop en ta -3,5-d ien e. A degassed sealed quartz tube contain-
ing a benzene (10 mL) solution of 1-germacyclopenta-3,5-diene
(0.3 mg) was irradiated with a 450 W high-pressure Hg arc
lamp for 3 h. The reaction mixtures were poured into
methanol. An undissolved white powder remained and was
identified by NMR in C6D6 and MS spectra to be the anti-trans
[2 + 2] dimer (36%). The methanol solution was chromato-
graphed on octadecyl-functionalized silica gel to give the anti-
cis (14%) and syn-cis [2 + 2] dimers (8%).
P r ep a r a tion of 1,1,2,2-Tetr a eth yl-3,4,5,6-tetr a p h en yl-
1-ger m a -2-sila cycloh exa -3,5-d ien e (4). Compound 4 was
prepared according to a method similar to that used for the
preparation of 1. To a solution of 1,4-dilithio-1,2,3,4-tetraphen-
yl-1,3-butadiene was added (diethylchlorosilyl)diethylchlo-
rogermane (11.1 g, 39 mmol) in ether (10 mL). After it was
refluxed for 2 h, the mixture was hydrolyzed with water. The
organic layer was extracted with diethyl ether and dried over
Na2SO4. After the solvent had been evaporated, the residue
was diluted with acetone and this solution was allowed to
stand at room temperature. Pure 1,1,2,2-tetraethyl-3,4,5,6-
tetraphenyl-1-germa-2-silacyclohexa-3,5-diene (10.5 g, 18.4
mmol, 47%) was obtained: mp 152 °C; 1H NMR (C6D6) δ 0.83-
0.93 (m, 2H), 1.02-1.18 (m, 10H), 1.18-1.29 (m, 8H), 6.60-
7.30 (m, 20H); 13C NMR (C6D6) δ 4.8, 6.1, 9.0, 10.7, 124.4,
124.6, 125.2, 125.3, 126.7, 126.8, 127.3, 127.5, 128.0, 128.5,
129.8, 140.1, 141.8, 142.0, 142.9, 143.8, 145.1, 150.1, 153.5;
MS m/z 573 (74Ge); UV (cyclohexane) λmax 338.6 nm (log ꢀ 3.59).
Anal. Calcd for C34H36SiGe: C, 74.88; H, 6.65. Found: C,
74.92: H, 6.72.
Ack n ow led gm en t . We thank Mrs. Takanari
Kayamori and Tokuhisa Ishii of Gakushuin University
for preliminary experiments in this work. We also thank
Dr. Masahiro Kako of the University of Electro-Com-
munication for measuring NMR spectra.
Su p p or tin g In for m a tion Ava ila ble: Tables giving crys-
tallographic data, positional and thermal parameters, and
bond distances and angles and figures giving additional views
and packing diagrams for 1a , 2, and 7-9, additional 2D NMR
spectra for 7, and plots and figures analyzing dihedral angles
(56 pages). Ordering information is given on any current
masthead page.
P h otolysis of 1, 3, a n d 4. As a representative example,
the photochemical reaction of 1a is described. 1,2-Digerma-
cyclohexa-3,5-diene 1 (30 mg) was dissolved in C6D6 (500 µL)
OM970799W