Reaction of group 14 dimetallenes with alkenes: Electron-rich alkenes

Article abstract of DOI:10.1021/om9606911

The addition reactions of tetramesitylgermasilene with 1-methoxybutadiene, ethyl vinyl ether, vinyl acetate, or styrene were studied. When tetramesitylgermasilene was allowed to react with 1-methoxybutadiene or styrene, formal [2+2] addition products were isolated. The addition of styrene to tetramesitylgermasilene was determined to be completely regioselective. In the presence of ethyl vinyl ether or vinyl acetate, tetramesitylgermasilene undergoes a 1,2-mesityl shift yielding a silylgermylene, at a faster rate than addition to either alkene. Tetramesityldisilene was also found to yield a formal [2+2] adduct with styrene. However, tetramesityldigermene rearranges to a germylgermylene at a faster rate than styrene addition.

Full text of DOI:10.1021/om9606911

Organometallics 1996, 15, 5701-5705
5701
Rea ction of Gr ou p 14 Dim eta llen es w ith Alk en es:
Electr on -Rich Alk en es
Craig E. Dixon, Hui W. Liu, Christopher M. Vander Kant, and Kim M. Baines*
Department of Chemistry, University of Western Ontario, London, Ontario, Canada N6A 5B7
Received August 13, 1996X
The addition reactions of tetramesitylgermasilene with 1-methoxybutadiene, ethyl vinyl
ether, vinyl acetate, or styrene were studied. When tetramesitylgermasilene was allowed
to react with 1-methoxybutadiene or styrene, formal [2+2] addition products were isolated.
The addition of styrene to tetramesitylgermasilene was determined to be completely
regioselective. In the presence of ethyl vinyl ether or vinyl acetate, tetramesitylgermasilene
undergoes a 1,2-mesityl shift yielding a silylgermylene, at a faster rate than addition to
either alkene. Tetramesityldisilene was also found to yield a formal [2+2] adduct with
styrene. However, tetramesityldigermene rearranges to a germylgermylene at a faster rate
than styrene addition.
Sch em e 1
In tr od u ction
Tetramesityldisilene1 and tetramesityldigermene2 are
now well-known examples of stable group 14 dimetal-
lenes. Although both compounds require bulky substit-
uents to gain kinetic stability, the presence of these
sterically demanding groups does not greatly diminish
the reactivity of these species. In fact, it has been shown
that these heavier analogs of alkenes are frequently
more reactive than alkenes. Stable disilenes and di-
germenes react with a variety of compounds to give a
number of previously unknown compounds.3 However,
early in the development of this chemistry, it was
demonstrated that hindered tetraaryldisilenes did not
react with nonpolar alkenes or conjugated dienes. For
example, tetramesityldisilene does not react with 2,3-
dimethylbutadiene4 or isoprene.5
Although hindered tetraaryldisilenes appear to be
unreactive with alkenes or conjugated dienes, hindered
tetraalkyldisilenes have been shown to give addition
products with certain alkenes. Weidenbruch has re-
ported that tetra-tert-butyldisilene will add, in a formal
[2+2] manner, to 2,2′-dipyridine6 or o-methylstyrene7
to yield a disilacyclobutane (see Scheme 1). Tetraalkyl-
disilenes have also been observed to react in a formal
[2+4] manner with conjugated dienes. For example,
tetrakis(1-ethylpropyl)disilene8 and tetra-tert-butyldi-
silene9 give the expected Diels-Alder adducts with 2,3-
dimethylbutadiene. Tetra-tert-butyldisilene also reacts
in a formal [2+4] fashion with cyclopentadiene and
furan.10
X Abstract published in Advance ACS Abstracts, December 1, 1996.
(1) West, R.; Fink, M. J .; Michl, J . Science (Washington, D.C.) 1981,
214, 1343.
(2) (a) Ando, W.; Tsumuraya, T. J . Chem. Soc., Chem. Commun.
1989, 770.; (b) Tsumuraya, T.; Sato, S.; Ando, W. Organometallics 1988,
7, 2015.
(3) For example see: (a) Okazaki, R.; West, R. Adv. Organomet.
Chem. 1996, 39, 231. (b) Raabe, G.; Michl, J . In The Chemistry of
Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: New
York, 1989; p 1015. (c) West, R. Angew. Chem., Int. Ed. Engl. 1987,
26, 1201. (d) Baines, K. M.; Stibbs, W. G. Adv. Organomet. Chem. 1996,
39, 275. (e) Escudie´, J .; Couret, C.; Ranaivonjatovo, H.; Satge´, J . Coord.
Chem. Rev. 1994, 130, 427.
Only one reaction between a digermene and an alkene
or conjugated diene has been reported. Tetramesityl-
digermene has been shown to rearrange via a 1,2-
mesityl shift to give a germylgermylene at a rate faster
than addition of 2,3-dimethylbutadiene. The germylger-
mylene is subsequently trapped by the diene.11
The chemistry of tetramesitylgermasilene has been
shown to be similar in some respects to that of hindered
tetraaryldisilenes and -digermenes. For example, tet-
ramesitylgermasilene does not appear to react with
(4) Fink, M. J .; DeYoung, D. J .; West, R. J . Am. Chem. Soc. 1983,
105, 1070.
(5) Fanta, A. D.; DeYoung, D. J .; Belzner, J .; West, R. Organome-
tallics 1991, 10, 3466.
(6) Weidenbruch, M.; Scha¨fer, A.; Marsmann, H. J . Organomet.
Chem. 1988, 354, C12.
(7) Weidenbruch, M.; Kroke, E.; Marsmann, H.; Pohl, S.; Saak, W.
J . Chem. Soc., Chem. Commun. 1994, 1233.
(9) Masamune, S.; Murakami, S.; Tobita, H. Organometallics 1983,
2, 1464.
(10) Kroke, E.; Weidenbruch, M.; Saak, W.; Pohl, S. Organometallics
1995, 14, 5695.
(8) Masamune, S.; Tobita, H.; Murakami, S. J . Am. Chem. Soc. 1983,
105, 6524.
(11) Baines, K. M.; Cooke, J . A.; Dixon, C. E.; Liu, H. W.; Netherton,
M. R. Organometallics 1994, 13, 631.
S0276-7333(96)00691-7 CCC: $12.00 © 1996 American Chemical Society

5702 Organometallics, Vol. 15, No. 26, 1996
Dixon et al.
Sch em e 2
troscopy (Scheme 4). Compound 3 appears to be derived
from reaction between 1-methoxybutadiene and dimesi-
tylgermylene, consistent with the previously observed
chelotropic [2+4] addition of dimesitylgermylene to 2,3-
dimethylbutadiene11 yielding a germacyclopentene. Un-
der the thermal conditions of reaction, tetramesitylger-
masilene readily rearranges to give the silylgermylene,
which reacts with 1-methoxybutadiene to give com-
pound 4 as a mixture of diastereomers. Interestingly,
compound 5 appears to be the formal [2+2] cycloaddi-
tion product between tetramesitylgermasilene and
1-methoxybutadiene. The presence of four different
Sch em e 3
conjugated dienes such as 2,3-dimethylbutadiene, at
least at a rate faster than the thermal rearrangement
to a silylgermylene.11 While investigating what, if any,
effect changing the electronic character of the diene may
have on the addition reactions of tetramesitylger-
masilene, it was found that tetramesitylgermasilene
yields a formal [2+2] cycloaddition product with 1-meth-
oxybutadiene.12 This result, along with the reports of
tetra-tert-butyldisilene reacting in a formal [2+2] man-
ner with 2,2′-dipyridine and o-methylstyrene, prompted
us to examine the reaction of tetramesitylgermasilene
with a number of substituted alkenes. This paper
reports the results of the reactions between tetramesi-
tylgermasilene and 1-methoxybutadiene, ethyl vinyl
ether, vinyl acetate, or styrene. Also reported are the
results for the reactions of tetramesityldisilene and
tetramesityldigermene with styrene.
1
mesityl groups in the H NMR spectrum of 5 is consis-
tent with a substituted germasilacyclobutane ring, as
is the multiplet observed at 2.95-3.10 ppm, which may
be assigned to the CH of the germasilacyclobutane. In
addition, two alkenyl resonances, which integrate for
two hydrogen atoms, are observed in the chemical shift
range consistent with an alkoxy-substituted vinyl moi-
ety (5.03 and 6.15 ppm) indicating that the terminal
double bond of 1-methoxybutadiene has added to the
Ge-Si double bond of the germasilene. The coupling
constant between these two alkenyl hydrogen atoms
(12.5 Hz) suggests a trans geometry for the double bond.
Taken together, these data support the structural
assignment given for compound 5, which represents the
first example of a formal [2+2] cycloaddition product
between tetramesitylgermasilene and an alkene. The
regiochemistry of the addition is unknown.
In contrast to 2,3-dimethylbutadiene, which reacts
exclusively with the silylgermylene, 1-methoxybutadi-
ene seems to react with the germasilene to some degree.
However, the reaction of 1-methoxybutadiene with the
silylgermylene is still the predominant reaction path-
way. The concurrent formation of the silylgermylene
and the rapid subsequent reaction with the conjugated
diene, polar or not, apparently limits the yield of the
formal [2+2] cycloaddition product. Since germylenes
do not readily add to alkene π-bonds,16 three polar
alkenes, ethyl vinyl ether, vinyl acetate, and styrene,
were selected for reaction with tetramesitylgermasilene
in an attempt to maximize the yield of any formal [2+2]
product.
Resu lts a n d Discu ssion
The thermolysis or photolysis of hexamesitylsiladi-
germirane (1) has been shown to give tetramesitylger-
masilene (2) and dimesitylgermylene, regioselectively13
(Scheme 2). Although the germasilene is stable in
solution at -78 °C, at higher temperatures it rearranges
via a 1,2-mesityl shift to give the corresponding silylger-
mylene13 (Scheme 3). Thus, the relative rate of reaction
of the germasilene with a selected trap versus the rate
of rearrangement to the silylgermylene determines the
products observed. For example, when tetramesitylger-
masilene is generated in the presence of alcohols,14
aldehydes, or ketones,15 the germasilene reacts exclu-
sively with each trap. However, in the presence of 2,3-
dimethylbutadiene11 or triethylsilane,13 the only prod-
ucts detected are those derived from the silylgermylene.
By changing the electronic properties of the alkene or
conjugated diene used in reaction with tetramesitylger-
masilene, we reasoned that the rate of reaction of the
alkene with the Si-Ge double bond of the germasilene
may be increased relative to the rearrangement of the
germasilene to the silylgermylene. Thus, the reaction
between tetramesitylgermasilene and 1-methoxybuta-
diene was investigated.
Photolysis of 1 at -70 °C in the presence of Et3SiH
produces a solution of tetramesitylgermasilene. Sub-
sequent addition of ethyl vinyl ether and slow warming
of the reaction mixture to room temperature produced
compounds 6 and 7 in approximately a one to one ratio
as determined by 1H NMR spectroscopy (Scheme 5).
Compounds 6 and 7 were readily identified by compari-
son to literature data.13 Apparently, the rearrangement
of tetramesitylgermasilene to the corresponding si-
lylgermylene occurs at a faster rate than any reaction
with ethyl vinyl ether. Thermolysis of 1 in the presence
of ethyl vinyl ether gave a very complex reaction
mixture which yielded no identifiable products. Copho-
tolysis of 1 with vinyl acetate and Et3SiH yielded mainly
a mixture of compounds 6 and 7. Again, the 1,2-mesityl
rearrangement appears to occur at a rate greater than
reaction with the alkene. Two additional products were
isolated from the reaction mixture: (triethylsilyl)mesi-
Thermolysis of 1 at 110 °C in the presence of trans-
1-methoxybutadiene yielded three compounds. Com-
1
pounds 3 and 4 were each characterized by IR and H,
13C, and 29Si NMR (for 4) spectroscopy and mass
spectrometry. Compound 5 was produced in low yield
and proved to be unstable in solution and, as a result,
1
was characterized solely by H NMR correlation spec-
(12) Liu, H. W. M.Sc. Thesis, The University of Western Ontario,
1994.
(13) Baines, K. M.; Cooke, J . A. Organometallics 1992, 11, 3487.
(14) Baines, K. M.; Cooke, J . A. Organometallics 1991, 10, 3419.
(15) Baines, K. M.; Cooke, J . A.; Vittal, J . J . Heteroatom Chem. 1994,
5, 293.
(16) Becerra, R.; Boganov, S. E.; Egorov, M. P.; Lee, V. Ya.; Nefedov,
O. M.; Walsh, R. Chem. Phys. Lett. 1996, 250, 111.
(17) Baines, K. M.; Cooke, J . A.; Vittal, J . J . J . Chem. Soc., Chem.
Commun. 1992, 1484.

Group 14 Dimetallenes
Organometallics, Vol. 15, No. 26, 1996 5703
Sch em e 4
tyl(trimesitylgermyl)germane (8) and 4-(2-methyleth-
Ge-H region of the spectrum indicating that methoxide
attacked selectively at the atom adjacent to the CH2
moiety and not the CHPh of the germasilacyclobutane
ring. The IR spectrum shows an absorbance at 2046
cm-1, which is consistent with a Ge-H stretching
vibration. The 1H-29Si HMBC experiment shows a
correlation between the signal at 1.90 ppm in the 29Si
dimension with the OCH3 at 2.78 ppm in the 1H
dimension, which suggests a structure with the 1H
bonded directly to the Ge atom. Furthermore, there
were no 1-bond correlations observed in the standard
1H-29Si HMQC spectra. Taken together, these data
support the structure as assigned for 11. Thus, the
addition of styrene to tetramesitylgermasilene is com-
pletely regioselective with the germanium atom of the
germasilene becoming bonded to the substituted end of
the alkene. Furthermore, attack of methoxide on 10
occurs exclusively at the silicon atom.
enyl)tetramesitylsilagermoxetane (9). Compound 8 ap-
pears to be derived from tetramesityldigermene, which
is a known photoproduct of hexamesitylcyclotriger-
mane,2 a common byproduct in the synthesis of hexa-
mesitylsiladigermirane.14 Under the thermal conditions
of the reaction, the digermene undergoes a 1,2-mesityl
shift to give the germylgermylene which is subsequently
trapped by Et3SiH.17 Compound 9 appears to be the
cycloadduct of tetramesitylgermasilene and crotonalde-
hyde. The regiochemistry of the addition was not
determined; the assigned structure is based upon the
known regiochemistry of the addition of acetone and
pivalaldehyde to tetramesitylgermasilene.15 Crotonal-
dehyde is believed to be generated in small amounts
during the purification of vinyl acetate by distillation
from Li(t-BuO)3AlH.
It is interesting to compare the chemistry of the
heteronuclear dimetallene to that of the homonuclear
analogs, disilenes and digermenes. Photolysis of hex-
amesitylcyclotrigermane18 at -70 °C, in the presence
of Et3SiH, followed by addition of styrene and subse-
quent warming to room temperature yielded two major
compounds, 6 and 8, in a one to one ratio as ascertained
Photolysis of 1 at -70 °C in the presence of Et3SiH,
followed by the addition of styrene and subsequent
warming to room temperature, gave products 6 and 10
in a one to one ratio as determined by 1H NMR
spectroscopy (Scheme 6). Compound 10 appears to be
the formal [2+2] cycloaddition product between tet-
ramesitylgermasilene and styrene. Consistent with this
assignment is the appearance of four mesityl groups and
1
by H NMR spectroscopy (Scheme 8). Tetramesityldi-
germene has been shown to undergo a thermal 1,2-
mesityl rearrangement, similar to that observed with
tetramesitylgermasilene, to give the corresponding ger-
mylgermylene.17 Compound 8 is the result of insertion
of mesityl(trimesitylgermyl)germylene into the Si-H
bond of Et3SiH. Unlike tetramesitylgermasilene, tet-
ramesityldigermene does not appear to add styrene at
a rate faster than the 1,2-mesityl shift. A possible
explanation may be an increased rate of the 1,2-mesityl
rearrangement for the digermene, relative to the ger-
masilene. The increased rate is perhaps due to the
decrease in steric crowding around the germanium atom
in the germylgermylene, compared to the silicon atom
in the corresponding silylgermylene.
1
an ABX spin pattern in the H NMR spectrum of 10.
The 13C NMR, DEPT, HETCOR, and COSY spectra also
support the assignment. Unlike ethyl vinyl ether and
vinyl acetate, it appears that the addition of styrene to
tetramesitylgermasilene occurs at a faster rate than the
1,2-mesityl rearrangement yielding the formal [2+2]
cycloaddition product, 10, completely regioselectively.
The regiochemistry of the adduct was determined by
nucleophilic cleavage of 10 with NaOMe. When a
solution of 10 in THF was refluxed in the presence of
NaOMe, one product, 11, was isolated (Scheme 7). The
1H NMR spectrum of 11 shows one doublet in the Si/
When styrene is added to a solution of tetramesityl-
disilene1 in benzene and heated to 60 °C for several
hours, compound 12 is formed, which is the first
Sch em e 7
Sch em e 5
Sch em e 8
Sch em e 6

5704 Organometallics, Vol. 15, No. 26, 1996
Dixon et al.
1-methoxybutadiene (3 drops, ∼ 40 mg, 0.48 mmol) were
dissolved in toluene (2.0 mL). The reaction mixture was placed
in an oil bath at 105 °C for 4 h. The reaction mixture became
light yellow in color soon after heating began. After 3 h, the
mixture became clear and colorless. The solvents were
evaporated leaving a light yellow viscous residue. The product
mixture was separated by preparative thin-layer chromatog-
raphy using 50% CH2Cl2/hexane as the eluent to give at least
five fractions: Fraction 1, unidentified, appears to be a mixture
of cylcloadducts; fraction 2, compound 5 (3.5 mg, 10%); fraction
3, compound 4 (8 mg, 22%); fraction 4, compound 3 (21 mg,
95%). Compound 5 decomposes if left in solution over a period
of time.
Sch em e 9
example of a formal [2+2] cycloaddition product between
tetramesityldisilene and an alkene (Scheme 9). Again,
the H, 13C NMR, DEPT, HETCOR, and COSY spectra
1
all support the assigned structure for 12. Thus, similar
to tetramesitylgermasilene, tetramesityldisilene adds
styrene in a formal [2+2] fashion.
1,1-Dim esityl-2-m eth oxy-1-ger m a cyclop en t-3-en e (3):
Mp 80-82 °C; IR (thin film, cm-1) 3015 (s), 2922 (s), 2811 (s),
2730 (w), 1603 (s), 1557 (m), 1456 (s), 1411 (m), 1375 (m), 1358
(m), 1087 (s), 1028 (m), 950 (m), 930 (m), 847 (s), 804 (m), 701
(m); 1H NMR (ppm) 6.72, 6.71 (each s, 4 H total, Mes CH),
2.41 (s, 6 H, Mes o-CH3), 2.34 (s, 6 H, Mes o-CH3), 2.12 (s, 3
H, Mes p-CH3), 2.08 (s, 3 H, Mes p-CH3), 3.10 (s, 3 H, OCH3),
In summary, we have shown that tetramesitylger-
masilene yields a formal [2+2] cycloaddition product in
reaction with 1-methoxybutadiene or styrene. It has
been demonstrated that the addition of styrene to
tetramesitylgermasilene is completely regioselective. In
the presence of ethyl vinyl ether or vinyl acetate,
however, it appears that the 1,2-mesityl rearrangement
of tetramesitylgermasilene occurs at a faster rate than
the cycloaddition of either alkene. Furthermore, it has
also been shown that tetramesityldisilene, like tet-
ramesitylgermasilene, adds styrene in a formal [2+2]
manner. In contrast, tetramesityldigermene rearranges
to the corresponding germylgermylene at a faster rate
than styrene addition. We believe that these prelimi-
nary investigations point to a stepwise radical mecha-
nism for the addition of alkenes to tetramesitylger-
masilene, and we are currently exploring this idea.
3
4
5
5
4.77 (dddd, 1 H, J ) 3.2 Hz, J ) 1.1 Hz, J ) 1.1 Hz, J )
3
4
1.8 Hz, CHOCH3), 6.42 (dddd, 1 H, J ) 7.7 Hz, J ) 1.9 Hz,
4J ) 1.6 Hz, J ) 3.2 Hz, dCHCHOCH3), 6.17 (dddd, 1 H, J
3
3
) 7.7 Hz, 3J ) 3.2 Hz, 3J ) 1.9 Hz, 4J ) 1.1 Hz, CH2dCH),
2
3
4
5
2.49 (dddd, 1 H, J ) 17.2 Hz, J ) 3.2 Hz, J ) 1.6 Hz, J )
2
3
4
1.8 Hz, CH2), 1.73 (dddd, 1 H, J ) 17.2 Hz, J ) 1.9 Hz, J )
1.9 Hz, 5J ) 1.1 Hz, CH2); 13C NMR (CDCl3, ppm) 143.95,
142.42, 138.59, 138.15, 138.03, 133.26, (Mes C), 128.78, 128.65
(Mes CH), 134.82, 133.14 (dCH), 81.66 (CHOCH3), 58.66
(OCH3), 24.72 (CH2), 24.39, 24.18, 20.94 (Mes CH3); MS (m/
z) 396 (M+, 10), 312 (GeMes2, 50), 192 (GeMes - H, 100), 119
(Mes, 26), 84 (CH2dCHCHdCHOCH3, 80); high-resolution MS
for C23H30O72Ge: calc, 394.1517; found, 394.1524.
Exp er im en ta l Section
1-Mesityl-2-m eth oxy-1-(tr im esitylsilyl)-1-ger m a cyclo-
p en t-3-en e (4): IR (thin film, cm-1) 2921 (s), 1604 (s), 1448
(s), 1104 (m), 1082 (m), 1027 (m), 848 (s), 784 (s); 1H NMR
(CDCl3, ppm) diastereomeric mixture, 6.62 (s, 6 H, Mes CH),
6.45 (s, 2 H, Mes CH), 6.12-6.21 (m, 1 H, dCH), 5.93-6.03
(m, 1 H, dCH), 4.56-4.63 (m, 1 H, CHOCH3), 3.19 (d, 3 H, J
) 0.7 Hz, OCH3), 2.28-2.38 (m, 1 H, CH2), 2.24 (s, 18 H, Mes
CH3), 2.18, 2.16 (each s, 15 H total, Mes CH3), 2.09 (s, 3 H,
Mes CH3), 1.90-2.07 (m, 1 H, CH2); signals for minor diaste-
reomer apparent at 3.20, 2.25, 2.19, 2.17, 2.10; 13C NMR
(CDCl3, ppm) 144.84, 143.90, 137.90, 136.77, 135.27, 134.59
(Mes C), 129.18, 128.10 (Mes CH), 133.57, 133.06 (dCH), 85.19
(CH-OCH3), 58.62 (OCH3), 24.92 (CH2), 25.57, 24.99, 20.74
(Mes CH3); 29Si NMR (CDCl3, ppm) -19.81; MS (m/ z) 622 (M+
- C3H4, 2), 578 (Mes4GeSi, 10), 385 (SiMes3, 100).
1,1,2,2-Tetr a m esityl-3 (or 4)-(tr a n s-2-m eth oxyeth en yl)-
1,2-sila ger m a cyclobu t a n e (5): 1H NMR (ppm) 6.74, 6.73,
6.71, 6.69 (each s, 8 H total, Mes CH), 6.15 (d, 1 H, J ) 12.5
Hz, dCHOCH3), 5.03 (dd, 1 H, J ) 12.5 Hz, J ) 10.5 Hz,
CHdCHOCH3), 3.13 (s, 3 H, OCH3), 2.95-3.10 (m, 1 H,
CH2CHCd), 2.53 (s), 2.44 (bs), 2.43 (s), 2.30 (s), 2.20-2.60 (m,
25 H total, CH2 and Mes o-CH3), 2.14 (s, 3H, Mes p-CH3), 2.11
(s, 3 H, Mes p-CH3), 2.06 (s, 3 H, Mes p-CH3), 2.03 (s, 3 H,
Mes p-CH3); MS (m/ z) 578 (Mes4GeSi, 18), 385 (SiMes3, 100),
192 (GeMes, 4), 83 (C5H7O, 13).
All experiments were carried out in flame-dried glassware
under an atmosphere of argon. Toluene and benzene were
freshly distilled from sodium/benzophenone. Pentane was
distilled from LiAlH4 prior to use. Styrene was obtained from
BDH and used without any further purification. Ethyl vinyl
ether was obtained from Aldrich Chemical Co. and distilled
from lithium aluminum hydride prior to use. Vinyl acetate
was obtained from Aldrich Chemical Co. and distilled from
lithium tri-tert-butoxyaluminum hydride prior to use. Chro-
matography was carried out using a Chromatotron (Harrison
Research) or on conventional silica gel preparative plates.
NMR spectra were recorded on a Varian Gemini 200 (200.1
MHz for 1H, 50.3 MHz for 13C), an XL-300, a Varian Gemini
300 (299.9 MHz for 1H, 75.4 MHz for 13C, 59.6 MHz for 29Si),
or a Bruker Avance DRX-500 using benzene-d6 as a solvent,
unless otherwise noted. The standards were as follows:
1
residual C6D5H 7.15 ppm for H spectra; C6D6 or CDCl3 central
transition for 13C NMR spectra; Me4Si as an external standard,
0 ppm for 29Si. IR spectra were recorded (cm-1) as thin films
on a Perkin-Elmer System 2000 FT IR spectrometer.
A
Finnegan MAT Model 8230 instrument, with an ionizing
voltage of 70 eV, was used to obtain electron impact mass
spectra (reported in mass-to-charge units, m/ z, with ion
identity and peak intensities relative to the base peak in
parentheses). The 2-D spectra were acquired using standard
techniques.19-21
Photolyses were carried out at 350 nm, unless otherwise
stated, using a Rayonet Photochemical Reactor.
Th er m olysis of SiGe2Mes6 in th e P r esen ce of 1-Meth -
oxybu ta d ien e. SiGe2Mes6 (50 mg, 0.056 mmol) and trans-
Ad d ition of Eth yl Vin yl Eth er to Tetr a m esitylger -
m a silen e. SiGe2Mes6 (50 mg, 0.062 mmol) and Et3SiH (1 mL,
excess) were dissolved in toluene (3 mL) and photolyzed for 6
h at -70 °C. After this time, ethyl vinyl ether (0.5 mL, excess)
was added to the reaction mixture and the solution was
allowed to warm to room temperature. After the solution was
standing at room temperature for several hours, the yellow
color of the germasilene had disappeared. Removal of the
solvents and subsequent purification of the reaction mixture
by preparative thin layer chromatography (20/80 CH2Cl2/
hexanes) yielded compounds 6 (15 mg, 0.035 mmol, 56%) and
7 (17 mg, 0.025 mmol, 40%). There were no compounds
identified as being derived from a reaction between tetramesi-
tylgermasilene and ethyl vinyl ether.
(18) Ando, W.; Tsumuraya, T. J . Chem. Soc., Chem. Commun. 1987,
1514.
(19) Parker, P. B.; Freeman, R. F. J . Magn. Reson. 1985, 64, 334.
(20) Bereton, I. M.; Crozier, S.; Field, J .; Dodrell, D. M. J . Magn.
Reson. 1991, 93, 54.
(21) Von Kienlin, M.; Moonen, C. T. W.; van der Toorn, A.; van Zijl,
P. C. M. J . Magn. Reson. 1991, 93, 423.
(22) While the isolated yield of the formal [2+2] adduct is relatively
low, it appears as a major component in the crude reaction mixture as
determined by 1H NMR spectroscopy.

Group 14 Dimetallenes
Organometallics, Vol. 15, No. 26, 1996 5705
P h ot olysis of SiGe2Mes6 in t h e P r esen ce of Vin yl
Aceta te. Vinyl acetate (1 mL, excess), triethylsilane (1 mL,
excess), and SiGe2Mes6 (100 mg) were dissolved in toluene (5
mL). The reaction mixture was photolyzed for 8 h at -78 °C.
Upon completion of the photolysis, the reaction mixture was
allowed to warm slowly overnight. The product mixture was
then separated by preparative thin layer chromatography to
yield four products: dimesityl(triethylsilyl)germane (6, 31.2
mg), a mixture of mesityl(triethylsilyl)(trimesitylsilyl)germane
(7) and mesityl(triethylsilyl)(trimesitylgermyl)germane (8) in
1,1,2,2-Tet r a m esit yl-3-p h en yld isila cyclob u t a n e (12):
Mp 45-47 °C; IR (thin film, cm-1) 3028 (m) 2962 (s), 2921 (s),
2865 (m), 1604 (s), 1548 (w), 1450 (s), 1409 (m), 1378 (m), 1261
1
(m), 1029 (s), 847 (s), 756 (s), 701 (s); H NMR (ppm, 70 °C)
6.84-7.00 (m, 5 H, Ph H), 6.74 (s, 2 H, Mes H), 6.72 (s, 2 H,
Mes H), 6.66 (s, 2 H, Mes H), 6.63 (s, 2 H, Mes H), 3.46 (X
portion of ABX, 1H, J AX ) 10.7 Hz, J BX ) 12.1 Hz), 2.58 (s, 6
H, Mes o-CH3), 2.51, 2.49 (AB portion of ABX, 2 H, J AB ) 13.7
Hz), 2.43 (s, 6 H, Mes o-CH3), 2.39 (s, 6 H, Mes o-CH3), 2.12
(s, 3 H, Mes p-CH3), 2.10 (s, 3 H, Mes p-CH3), 2.073, 2.068 (s,
6 H total, Mes p-CH3), 1.99 (bs, 6 H, o-CH3); 13C NMR (CDCl3,
ppm) 146.21, 145.36, 143.71 (bs), 143.07 (bs), 138.50, 138.40,
138.34, 138.18, 136.38, 134.31, 132.79, 131.57 (Mes and Ph
C), 129.07 (bs), 128.83 (bs), 128.53 (bs), 128.68, 127.55, 127.44,
124.47 (Ph and Mes CH), 39.88 (CH2-CHPh), 30.09 (CH2-
CHPh), 24.96, 24.71 (bs), 21.03, 20.95, 20.93 (Mes CH3); 29Si
(ppm) -11.06, 7.04; MS (m/ z) 636 (M+, 4), 532 (M+ - CH2-
CHPh, 80), 413 (Mes3Si2, 17) 369 (M+ - Mes2Si, 100), 265
(Mes2Si - H, 50), 147 (MesSi, 38); high-resolution MS for
a
1:3.4 ratio, and 4-(2-methylethenyl)tetramesitylsilager-
maoxetane (9, 19.2 mg, regiochemistry unknown). When
tetramesitylgermasilene was allowed to react with crotonal-
dehyde, compound 9 was isolated in good yield.
4-(2-Meth yleth en yl)tetr a m esitylsila ger m oxeta n e (9):
IR (thin film, cm-1) 3020 (s), 2919 (s), 1604 (s), 1552 (m), 1448
(s), 1410 (m), 1376 (m), 1290 (w), 1233 (w), 1064 (m), 1028
(m), 964 (m), 933 (s), 847 (s), 829 (s), 773 (m), 739 (m); 1H NMR
(ppm) 6.72 (s, 2 H, Mes H), 6.71 (s, 2 H, Mes H), 6.68 (s, 2 H,
Mes H), 6.64 (s, 2 H, Mes H), 5.85-6.05 (m, 2 H, CHCHd),
5.40-5.65 (m, 1 H, CHCH3), 2.67 (s, 6 H, Mes o-CH3), 2.44
(bs, 6 H, Mes o-CH3), 2.35 (s, 6 H, Mes o-CH3), 2.20 (s, 6 H,
Mes o-CH3), 2.11 (s, 6 H, Mes p-CH3), 2.05 (s, 3 H, Mes p-CH3),
2.03 (s, 3, Mes p-CH3), 1.42-1.50 (m, 3 H, CdCCH3); 13C NMR
(ppm) 144.37, 144.26, 143.61, 142.54, 141.03, 139.51, 139.38,
138.27, 138.18, 136.80, 134.65, 133.97 (Mes C), 134.30 (-CHd),
129.70, 129.28, 129.18, 128.83 (Mes CH), 122.83 (CdCH),
87.00 (OCHCHd), 24.96, 24.75, 24.20, 23.47 (Mes o-CH3),
21.08, 20.96, 20.92, 20.85 (Mes p-CH3), 17.48 (dCHCH3); 29Si
NMR (ppm) 28.29 ppm; MS (EI) (m/ z) 648 (M+, 5), 593 (Mes4-
GeSiO(-H), 25), 578 (Mes4GeSi, 11), 475 (Mes3GeSiO, 8), 385
(Mes3Si, 100), 311 (Mes2Ge - H, 11), 193 (MesGe, 9), 84
(SiOC3H3, 73); high-resolution MS calc for C40H50OSi74Ge
648.2843, found 648.2861.
C
44H52Si2 calc 636.3608, found 636.3601.
Ad d ition of Styr en e to Tetr a m esityld iger m en e. Ge3-
Mes6 (50 mg, 0.054 mmol) and Et3SiH (1 mL, excess) were
dissolved in toluene (2 mL) and photolyzed for 8 h at -70 °C.
After this time, styrene (1 mL, excess) was added to the
reaction mixture, and the solution was allowed to warm to
room temperature. After the solution was standing at room
temperature for several hours, the yellow color of the di-
germene had disappeared. Removal of the solvents and
subsequent analysis of the crude reaction mixture by 1H NMR
spectroscopy showed approximately a 1:1 mixture of com-
pounds 6 and 10.
Nu cleop h ilic Clea va ge of 1,1,2,2-Tetr a m esityl-4-p h en -
ylger m a sila cyclobu ta n e (10). Na (20 mg, 0.87 mmol) was
added to MeOH (5 mL) and allowed to stir until all visible
reaction had subsided. 10 (6 mg, 0.008 mmol) was dissolved
in THF (5 mL) and added, in one shot, to the MeONa/MeOH
solution, and the reaction mixture was refluxed for 24 h.
Following the addition of 1 M HCl (approximately 5 mL),
extraction of the aqueous layer with Et2O (3×, 25 mL total),
and removal of the solvents, a white solid was isolated.
Analysis by 1H NMR spectroscopy showed the solid to be
compound 11 (5.8 mg, 0.007 mmol, 94%) in relatively pure
form. Preparative thin-layer chromatography (10/90 CH2Cl2/
hexanes) offered only marginal improvement in purity as
Addition of Styr en e to Tetr am esitylger m asilen e. SiGe2-
Mes6 (30 mg, 0.034 mmol) and Et3SiH (0.5 mL, excess) were
placed in toluene (3 mL) and photolyzed (350 nm) at -70 °C
for 8 h. After this time, styrene (0.5 mL, excess) was added
to the cold reaction mixture and the solution was allowed to
warm to room temperature and stand for several hours.
Following removal of the solvent, the products were separated
by preparative thin layer chromatography (20/80 CH2Cl2/
hexanes), to give two compounds: 10 (11 mg, 33%) and 6 (3
mg, 21%).22
1
determined by H NMR spectroscopy.
1-(Dim esitylger m yl)-1-p h en yl-2-(d im esityl(m eth oxy)-
silyl)eth a n e (11): IR (thin film, cm-1) 2926 (s), 2861 (m), 2046
(w), 1605 (m), 1494 (s), 1451 (m), 1404 (m), 1262 (w), 1050
(m), 825 (m); 1H NMR (ppm) 6.88-7.08, 7.40-7.44 (m, 5 H
total, Ph CH), 6.74 (s, 2 H, Mes CH), 6.71 (s, 2 H, Mes CH),
6.59 (s, 2 H, Mes CH), 6.56 (s, 2 H, Mes CH), 5.82 (d, 1 H, J
) 6.1 Hz, Ge-H), 3.49 (4 lines of ABX, 1 H, CH2CHPh), 2.78
(s, 3 H, OCH3), 2.38 (s, 6 H, Mes p-CH3), 2.34 (s, 6 H, Mes
p-CH3), 2.30, 2.29 (each s, 12 H total, Mes p-CH3), 2.17-2.27
(m, AB of ABX, CH2-CHPh), 2.13 (s, 3 H, Mes o-CH3), 2.10 (s,
3 H, Mes o-CH3), 2.04 (s, 3 H, Mes o-CH3), 1.99 (s, 3 H, Mes
o-CH3); 13C NMR (ppm) 146.07, 144.50, 144.04, 143.86, 143.35,
138.87, 138.83, 138.32, 138.04, 135.13, 134.50, 132.45, 131.67
(Ph and Mes C), 129.80, 129.69, 129.24, 129.14, 128.97, 124.97
(Ph and Mes CH), 49.28 (OCH3), 34.10 (CH2CHPh), 24.87,
24.11, 24.09, 24.02, 23.61, 21.03, 20.95, 20.85 (CH2 and Mes
CH3); 29Si NMR (ppm) 1.90; MS (m/ z) 713 (M+ - H, 12), 595
(M+ - Mes, 24), 312 (GeMes2, 36), 297 (Mes2SiOCH3, 100);
high-resolution MS for C45H55SiGeO calc 713.3234, found
713.3177.
1,1,2,2-Tetr am esityl-4-ph en ylger m asilacyclobu tan e (10):
Mp 66-70 °C; IR (thin film, cm-1) 3022 (m), 2920 (s), 1603
(s), 1551 (w), 1491 (m), 1451 (s), 1047 (m), 1377 (w), 1291 (w),
1031 (m), 848 (s), 756 (s), 700 (s), 626 (s); 1H NMR (ppm) 6.90-
7.10 (m, 5 H, Ph H), 6.73 (s), 6.71 (bs, 6 H total, Mes H), 6.64
(s, 2 H, Mes H), 3.70 (X portion of ABX, 1 H, J AX ) 15.4 Hz,
J BX ) 6.1 Hz, CHPhCH2), 2.66, 2.59 (AB portion of ABX, J AB
) 13.5 Hz, CHPhCH2), 2.57 (s, 8 H total, Mes o-CH3), 2.46
(bs), 2.44 (s, 12 H total, Mes o-CH3) 2.12, 2.11 (each s, 6 H
total, p-CH3), 2.06, 2.05 (each s, 6 H total, Mes p-CH3), 1.93
(bs, 6 H, Mes o-CH3); 13C NMR (CDCl3, ppm) 146.16, 145.13,
144.19, 143.59, 141.92, 138.80, 138.68, 137.60, 137.41, 136.33,
134.32, 132.41 (Mes and Ph C), 129.13, 128.89, 128.45, 128.23,
127.53, 127.13, 124.46 (Mes and Ph CH), 44.35 (CHPhCH2),
30.82 (CHPhCH2), 29.75, 24.84, 24.69, 24.54, 24.46, 21.06,
20.96 (bs, Mes CH3); 29Si NMR (ppm) -1.01; MS (m/ z, CI,
isobutane) 681 (M+ - H, 0.8), 578 (M+ - CH2CHPh, 12), 371
(M+ - Mes2Ge, 28), 313 (M+ - Mes2SiCH2CHPh, 8), 92 (C7H8,
100).
Ad d ition of Styr en e to Tetr a m esityld isilen e. Mes2Si-
(SiMe3)2 (100 mg, 0.24 mmol) was dissolved in pentane (10
mL) and photolyzed (254 nm) at -60 °C for 10 h. At this time,
the pentane was removed, in vacuo, and replaced with
benzene. To this solution was added styrene (0.5 mL, excess),
and the mixture was heated to 60 °C for several hours.
Following removal of the solvent, the reaction mixture was
purified by preparative thin layer chromatography (20/80 CH2-
Cl2/hexanes) to give compound 12 (13.5 mg, 9%).22
Ack n ow led gm en t. We thank the NSERC (Canada)
for financial support and Dr. D. W. Hughes (McMaster
University) for assistance in obtaining the 2-D spectra.
Su p p or tin g In for m a tion Ava ila ble: NMR spectra for
compounds 4, 5, and 10 and the experimental details for the
2-D NMR experiments (49 pages). Ordering information is
given on any current masthead page.
OM9606911