Addition of phenylacetylene to germasilenes

Article abstract of DOI:10.1021/om981017h

Phenylacetylene has been found to add regioselectively to both tetramesitylgermasilene and Si,Si-di-tert-butyldimesitylgermasilene to give the 3-phenyl-1-sila-2-germacyclobut-3-enes, exclusively. The regioselectivity of the adducts was established by nucl

Full text of DOI:10.1021/om981017h

2206
Organometallics 1999, 18, 2206-2209
Ad d ition of P h en yla cetylen e to Ger m a silen es
Kim M. Baines,* Craig E. Dixon, J onathon M. Langridge, Hui Wen Liu, and
Fagen Zhang
Department of Chemistry, University of Western Ontario, London, Ontario, Canada N6A 5B7
Received December 15, 1998
Phenylacetylene has been found to add regioselectively to both tetramesitylgermasilene
and Si,Si-di-tert-butyldimesitylgermasilene to give the 3-phenyl-1-sila-2-germacyclobut-3-
enes, exclusively. The regioselectivity of the adducts was established by nucleophilic cleavage
of the Si-Ge bond using sodium methoxide or hydroxide, respectively, to give the (methoxy-
or hydroxysilyl)germylethenes.
In tr od u ction
toluene at 105 °C. Under these conditions, the siladi-
germirane cleaves to give tetramesitylgermasilene and
dimesitylgermylene, regioselectively.12 Compounds 2, 3,
and 4 were isolated from the reaction mixture (eq 1).
The addition of alkynes to both stable (and relatively
stable) disilenes,1-6 and digermenes,7-11 yields disila-
cyclobutenes and digermacyclobutenes, respectively.
Whereas only phenylacetylene has been reacted with
stable digermenes, a variety of alkynes, ranging from
the unsubstituted acetylene5 to a diyne6 have been
reacted with disilenes. The addition of alkynes to
disilenes is believed to occur in a stepwise manner,2,5
although there has been some debate over the nature
of the intermediate. The fact that tetramesityldisilene
only reacts with polar terminal alkynes is evidence for
a zwitterionic intermediate;5 however, a biradical in-
termediate has also been proposed.2
We have been successful in the synthesis of two
heteronuclear group 14 dimetallenes, namely, tetrames-
itylgermasilene12,13 and Si,Si-di-tert-butyldimesitylger-
masilene.14 The germasilenes provide an opportunity to
examine the regiochemistry of the addition of an un-
symmetrical alkyne, and thus, the addition of phenyl-
acetylene to both germasilenes has been examined.
The 1H NMR spectral data of compound 2 are
remarkably similar to those of the phenylacetylene
adducts of Mes2SidSiMes2, 5,1 and Mes2GedGeMes2,
6.7 The chemical shift of the vinylic hydrogen is quite
Resu lts
Thermolysis of cyclo-SiGe2Mes6 in the presence of
phenylacetylene was carried out in (or without) dry
(1) Fink, M. J .; DeYoung, D. J .; West, R. J . Am. Chem. Soc. 1983,
105, 1070-1071.
(2) Nakadaira, Y.; Sato, R.; Sakurai, H. Chem. Lett. 1985, 643-646.
(3) Scha¨fer, A.; Weidenbruch, M.; Pohl, S. J . Organomet. Chem.
1985, 282, 305-313.
(4) De Young, D. J .; West, R. Chem. Lett. 1986, 883-884.
(5) De Young, D. J .; Fink, M. J .; Michl, J .; West, R. Main Group
Met. Chem. 1987, 1, 19-43.
diagnostic at 7.87 ppm for 2 compared to 8.08 ppm for
51 and 8.07 ppm for 6.7,15 Only one isomer of 2 was
formed. An attempt was made to determine the regio-
chemistry of the adduct by spectroscopic means; how-
ever, the results were ambiguous. To identify the
regiochemistry of the adduct, 2 was treated with sodium
methoxide followed by treatment with water (eq 2). The
reaction was remarkably clean, giving essentially one
product, 7, which was identified by NMR spectroscopy
and mass spectrometry. The absence of the typically
shielded 13C resonance of a RO-CdC moiety and the
absence of a geminal or a vicinal alkenyl coupling
pattern in the 1H NMR spectrum of 7 led us to conclude
(6) Kirmaier, L.; Weidenbruch, M.; Marsmann, H.; Peters, K.; von
Schnering, H. G. Organometallics 1998, 17, 1237-1240.
(7) Ando, W.; Tsumuraya, T. J . Chem. Soc., Chem. Commun. 1989,
770-771.
(8) Batcheller, S. A.; Masamune, S. Tetrahedron Lett. 1988, 29,
3383-3384.
(9) Tsumuraya, T.; Ando, W. Organometallics 1990, 9, 869-871.
(10) Tsumuraya, T.; Kabe, Y.; Ando W. J . Organomet. Chem. 1994,
482, 131-138.
(11) Weidenbruch, M.; Hagedorn, A.; Peters, K.; von Schnering, H.
G. Angew. Chem., Int. Ed. Engl. 1995, 34, 1085-1086.
(12) Baines, K. M.; Cooke, J . A. Organometallics 1991, 10, 3419-
3421.
(13) Baines, K. M.; Cooke, J . A. Organometallics 1992, 11, 3487-
3488.
(14) Kollegger, G. M.; Stibbs, W. G.; Vittal, J . J .; Baines, K. M. Main
Group Metal Chem. 1996, 17, 317-330.
(15) All chemical shifts in C6D6.
10.1021/om981017h CCC: $18.00 © 1999 American Chemical Society
Publication on Web 05/06/1999

Addition of Phenylacetylene to Germasilenes
Organometallics, Vol. 18, No. 11, 1999 2207
data and the MS fragmentation pattern are also con-
sistent with the structure as shown.
The formation of compounds 2-4 can be explained
by initial thermal degradation of cyclo-SiGe2Mes6 to give
Mes2SidGeMes2 and Mes2Ge:. Mes2SidGeMes2 under-
goes a cycloaddition reaction with PhCtCH, yielding
only one isomer, the 2,3-silagermacyclobutene, regiose-
lectively. To confirm that 2 is indeed the product from
the direct reaction of the germasilene with the alkyne,
a solution of the germasilene was generated by pho-
tolysis of the siladigermirane in the presence of Et3SiH
at -70 °C.13 Phenylacetylene was then added to the
germasilene in the cold, and the solution was warmed
to room temperature. In addition to the expected Et3-
SiGeHMes2, 2 was isolated (eq 3).
that cleavage had indeed occurred at the Si-Ge bond
and not the Si-C or Ge-C bond. The signal at 5.86 ppm
in the 1H NMR spectrum can be assigned to a MH
moiety. The absence of a large coupling in the 1H-
coupled 29Si NMR spectrum of 7 allowed us to assign
the MH signal as a GeH, and thus, the methoxide anion
appears to have become attached to the silicon atom.
Consistent with this conclusion, the base peak in the
mass spectrum of 7 occurs at m/z 297, corresponding to
[Mes2SiOCH3]+. The regiochemistry of the cleavage of
this Si-Ge bond is in agreement with the regiochem-
istry of other nucleophilic cleavage reactions of silylger-
manes.16 Most importantly, the absence of any splitting
of the Ge-H signal indicates that the vinylic hydrogen
atom is vicinal to the germanium atom and not geminal.
Thus, the terminal carbon of the phenylacetylene is
attached to the silicon atom of the germasilene, and the
phenyl group is attached to the carbon atom adjacent
to the germanium.
The yield of digermin 3 was low. In both the 1H
(CDCl3 and C6D6) and the 13C NMR spectra, there is
only one kind of mesityl group present in the molecule.
The ratio of the vinyl hydrogen atoms to the phenyl
group and mesityl aryl hydrogen atoms is 1:5:4. From
the MS, the highest mass ion was found at 826.2830.
There are two structures consistent with these data:
If the formation of the dimetallacyclobutene ring
occurs in two steps via a biradical or a zwitterionic
intermediate, the regiochemistry is most likely governed
by the preferential formation of a germanium-centered
radical or ion and stabilization of a vinylic radical or
ion by the phenyl substituent.
The formation of 1,4-digermins and germoles such as
3 and 4, respectively, from the reaction between ger-
mylenes and alkynes is well-known.17 Although the
mechanism for the formation of both the digermin and
the germole is still open to scrutiny, the initial formation
of a transient germirene followed by either dimerization
to give the digermin or reaction with a second equivalent
of alkyne to give the germole has been proposed.17
To investigate not only the generality of the addition
of phenylacetylene to germasilenes but also the regio-
chemistry of the reaction, the addition of phenylacety-
lene to Si,Si-di-tert-butyldimesitylgermasilene14 was
investigated. Cophotolysis of Si,Si-di-tert-butyltetrames-
itylsiladigermirane (8) and phenylacetylene at ambient
temperatures also gave three compounds (eq 4).
A fragment corresponding to Mes2GePhCCPh or PhC-
CPh was not apparent in the mass spectrum of 3.
Furthermore, only the loss of PhCCH (and not PhCCPh)
was observed. Considering the known reactivity of Me2-
Ge: toward phenylacetylene and other alkynes (in
particular cyclooctyne), where structures analogous to
3 but not 3a have been isolated,17 the structure 3 is
assigned to the compound.
With toluene as the reaction solvent, only traces of
1
the germole 4 were observed in the H NMR spectrum
of the product mixture. By using phenylacetylene itself
as the reaction solvent,17 a small amount of compound
4 could be isolated. The 1H NMR spectrum of compound
4 has one type of mesityl group in a 1:1 ratio with the
phenyl group. There are two correlated doublets at 6.20
and 5.68 ppm with a coupling constant of 1.7 Hz,
consistent with a homovinylic long-range coupling. The
highest mass ion was found at 516.1884. From these
data, the structure of 4 has been assigned. The 13C NMR
(16) (a) Kabaki, M.; Inoue, S.; Nagata, Y.; Sato, Y. Synth. Commun.
1990, 20, 3245-3252. (b) Mochida, K.; Suzuki, H.; Nanba, M.; Kugita,
T.; Yokoyama, Y. J . Organomet. Chem. 1995, 499, 83-88. (c) Dixon,
C. E.; Liu, H. W.; Vander Kant, C. M.; Baines, K. M. Organometallics
1996, 15, 5701-5705.
(17) Billeb, G.; Brauer, H.; Neumann, W. P.; Weisbeck, M. Orga-
nometallics 1992, 11, 2069-2074.
Compound 3 was isolated in 28% yield from the
reaction mixture. A second compound, also believed to

2208 Organometallics, Vol. 18, No. 11, 1999
Baines et al.
Th er m olysis of cyclo-SiGe2Mes6 in t h e P r esen ce of
P h en yla cetylen e. cyclo-SiGe2Mes6 (50 mg, 0.056 mmol) and
phenylacetylene (0.25 mL, 45× excess) were placed in toluene
(2.5 mL). The mixture was heated to 105 °C for 5 h. Shortly
after the thermolysis was started, the mixture turned yellow
in color. After 3-4 h, the color faded to light yellow. After 4 h,
the solvents were evaporated, leaving a yellow, viscous oil. The
product mixture was separated by preparative thin-layer
chromatography (Chromatotron; 10% CH2Cl2/hexane) to yield
two major compounds, compound 2 (19 mg, contaminated with
a trace of an unknown compound) and compound 3 (10 mg,
43%), and a trace amount of compound 4 (<2 mg). When neat
phenylacetylene is used as the solvent, the following yields
were obtained: compound 2 (23 mg, 61%), compound 3 (14 mg,
61%), and compound 4 (6 mg, 21%).
be derived from the addition of phenylacetylene to Mes2-
Ge:, was obtained in low yield but could not be identi-
fied.
Only one compound derived from reaction between
phenylacetylene and the germasilene was isolated in
high yield. The silagermacyclobutene structure was
1
apparent from the singlet at 7.08 ppm in the H NMR
spectrum of 9. An attempt was made to determine the
regiochemistry of the adduct by cleavage of the Si-Ge
bond with sodium methoxide; however, the cleavage of
the dimetallacyclobutene was not clean. The bulk of the
tert-butyl groups on silicon may hinder the approach of
the methoxide nucleophile, leading to a less selective
cleavage. Hence, a smaller nucleophile, sodium hydrox-
ide, was employed (eq 5). In this case, the reaction was
3-P h en yl-1,1,2,2-tetr a m esityl-1-sila -2-ger m a cyclobu t-
3-en e (2): white solid; mp 82-84 °C; IR (thin film, cm-1) 3047
(m), 2971 (s), 2920 (s), 2857 (m), 1603 (s), 1558 (m), 1542 (m),
1507 (m), 1450 (s), 1412 (m), 1380 (m), 1291 (m), 1237 (w),
1194 (w), 1062 (w), 1038 (m), 879 (m), 850 (s), 815 (m), 753
(s), 696 (m); 1H NMR (CDCl3, 300 MHz, ppm) 7.63 (s, 1 H,
vinyl-H), 7.15 (m, 5 H, Ph-H), 6.67 (s, 4 H, Mes-H), 6.64 (s, 4
H, Mes-H), 2.22 (s, 12 H, Mes-CH3), 2.19 (bs, 12 H, Mes-CH3),
1.99 (s, 12 H, Mes-CH3); 1H NMR (C6D6, 200 MHz, ppm) 7.87
(s, 1 H, vinyl-H), 7.4-7.0 (2m, 5 H, H-Ph), 6.66 (s, 8 H, Mes-
H), 2.41 (s, 12 H, CH3), 2.29 (s, 12 H, CH3), 2.06 (s, 12 H, CH3);
13C NMR (75 MHz, CDCl3, ppm) 153.89 (HCdCPh), 174.11,
145.31, 144.05, 143.10, 139.15, 138.59, 137.65, 133.32 (Ar-C
and vinyl Cd), 128.70, 128.44 (Mes-H), 127.89, 126.62, 126.31
(Ph-H), 24.74, 24.56 (o-CH3), 21.02, 20.97 (p-CH3); 29Si NMR
(CDCl3, ppm) -2.79, J Si-H ) 11 Hz; MS (m/z) 680 (59, M+),
561 (6, M+ - Mes), 533 (8, M+ - SiMes), 412 (16, M+ - SiMes2
- 2H), 385 (100, SiMes3), 367 (58, M+ - GeMes2 - H), 312
(24, GeMes2), 279 (11), 235 (8), 192 (28, GeMes - H), 147 (12,
SiMes), 125 (14); high-resolution MS calcd for C44H50Si74Ge
680.2894, found 680.2896.
quantitative, with only a trace of impurities being
visible in the crude reaction mixture by 1H NMR
analysis. The presence of a signal assignable to a
hydroxyl hydrogen and the absence of any signals with
1
a geminal or a vicinal alkenyl coupling in the H NMR
spectrum of 10 led to the conclusion that cleavage of
the Si-Ge bond occurred. The 1H-coupled 29Si NMR
spectrum of 10 lacked any large coupling, leading to the
1
assignment of the signal at 6.43 ppm in the H NMR
spectrum to a GeH. The regiochemistry of the cleavage
is the same as was observed previously. The GeH signal
is a singlet, confirming that the benzylidenylic carbon
is adjacent to the germanium atom. It follows that the
regiochemistry shown for compound 9 is correct.
In summary, the regioselective addition of phenyl-
acetylene to germasilenes appears to be a general
reaction. We continue to design experiments to help us
determine the factors controlling the regiochemistry of
the reaction.
Compound 2 can also be synthesized by addition of phenyl-
acetylene to the preformed germasilene. A solution of cyclo-
SiGe2Mes6 (150 mg, 0.17 mmol) dissolved in toluene (2 mL)
and Et3SiH (1 mL) was photolyzed at -70 °C for 8 h.
Phenylacetylene (0.5 mL) was then added to the yellow
solution in the cold. The color of the solution faded almost
immediately. The solvent was removed in vacuo, and the
product mixture was separated by chromatography (85:15
hexanes/CH2Cl2) to yield 2 (23 mg, 20%) in addition to Mes2-
GeH(SiEt3) and recovered siladigermirane.
Exp er im en ta l Section
2,5-Diph en yl-1,1,4,4-tetr am esityl-1,4-diger m acycloh exa-
2,5-d ien e (3): white solid; mp 246-248 °C; 1H NMR (300 MHz,
CDCl3, ppm) 7.64 (s, 2 H, vinyl-H), 7.03-7.23 (m, 10 H, Ph-
H), 6.55 (s, 8 H, Mes-H), 2.19 (s, 12 H, o-CH3), 2.07 (s, 24 H,
All experiments were carried out in flame-dried glassware
under an atmosphere of argon. Toluene and Et2O were freshly
distilled from sodium/benzophenone. Phenylacetylene was
obtained from the Aldrich Chemical Co. and distilled before
use. Chromatography was carried out using a Chromatotron
(Harrison Research) or on conventional silica gel preparative
plates. Photolyses were carried out at 350 nm using a Rayonet
photochemical reactor. Hexamesitylsiladigermirane12 and Si,-
Si-di-tert-butyltetramesitylsiladigermirane14 were synthesized
according to published procedures.
1
p-CH3); H NMR (300 MHz, C6D6, ppm) 7.89 (s, 2 H), 7.55-
7.50, 7.05-6.85, (total 10 H), 6.59 (s, 8 H), 2.29 (s, 24 H), 2.08
(s, 12 H); 13C NMR (50 MHz, CDCl3, ppm) 147.68 (HCdCPh),
155.77, 144.02, 143.40, 137.70, 135.11 (Ar-C and vinyl Cd),
128.88, 127.72, 127.19, 126.43 (Mes-H, Ph-H), 24.02, 20.98
(Mes-CH3); MS (m/z): 825 (28, M+ - H), 724 (63, M+
-
CHCPh), 707 (7, M+ - Mes), 604 (11, M+ - PhCCH - Mes),
533 (34, Mes3GeCHCPh), 431 (72, GeMes3), 413 (44, Mes2-
GeCCPh), 363 (28), 311 (48, GeMes2 - H), 293 (24), 220 (24),
193 (100, GeMes), 120 (30, Mes + H); high-resolution MS calcd
for C52H5672Ge74Ge 826.2815, found 826.2841.
NMR spectra were recorded on a Varian Gemini 200 (200.1
1
MHz for H, 50.3 MHz for 13C), an XL-300, or a Varian Gemini
300 (299.9 MHz for 1H, 75.4 MHz for 13C, 59.6 MHz for 29Si)
using benzene-d6 as solvent, unless otherwise noted. The
standards were as follows: residual C6D5H 7.15 ppm for 1H
spectra; C6D6 or CDCl3 central transition for 13C NMR spectra;
and 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 peak intensities relative to the base
peak and the ion identity in parentheses).
1,1-Dim esityl-2,4-diph en yl-1-ger m acyclopen tadien e (4):
white solid; 1H NMR (300 MHz, CDCl3, ppm) 7.3-7.7 (m, Ph),
7.20 (s, Ph), 6.81 (s, 4 H, Mes), 6.20 (d, 1 H, J ) 1.7 Hz), 5.68
(d, 1 H, J ) 1.7 Hz, vinyl-H), 2.36 (s, 12 H, Mes-CH3), 2.25 (s,
6 H, Mes-CH3); 13C NMR (50 MHz, CDCl3, ppm) 143.93,
141.96, 138.79, 133.48, 131.38, 129.86, 129.31, 128.11, 128.07,
127.99, 127.68, 127.61, 127.21, 24.32, 21.06; MS (m/z) 516 (38,
M+), 413 (100, Mes2GeCCPh), 397 (10, M+ - Mes), 295 (40,

Addition of Phenylacetylene to Germasilenes
Organometallics, Vol. 18, No. 11, 1999 2209
MesGe - CPhCH), 191 (52), 169 (52), 147 (34), 119 (82), 103
(90); high-resolution MS calcd for C34H3474Ge 516.1872, found
516.1884.
cm-1) 3060 (w), 3020 (w), 2960 (s), 2920 (s), 2860 (s), 1600 (m),
1460 (s), 1290 (s), 1280 (s), 1180 (w), 1140-980 (br, s), 880
(w), 850 (m), 860 (m), 800 (s), 750 (s), 700 (s); 1H NMR (C6D6,
300 MHz, ppm) 7.28-7.23, 7.14-7.00 (m, 5 H, Ph), 7.08 (s, 1
H, CHd), 6.75 (s, 4 H, Mes-CH), 2.50 (s, 12 H, o-CH3), 2.09 (s,
Rea ction of Com p ou n d 2 w ith Sod iu m Meth oxid e. To
a solution of compound 2 (20 mg, 0.0294 mmol) dissolved in
THF (1 mL) was added a solution of NaOMe, prepared by
dissolving Na (25 mg) in MeOH (1 mL). The solution was then
refluxed overnight. The reaction mixture was then cooled and
added to water (2 mL). The mixture was then extracted with
diethyl ether, and the solvents were evaporated to yield a light
yellow residue, which was then purified by preparative thin-
layer chromatography (Chromatotron; 50% CH2Cl2/hexane) to
yield one major product, compound 7 (19 mg, 91%).
1-Dim esitylger m yl-2-(d im esitylm eth oxysilyl)-1-p h en -
1
6 H, p-CH3), 1.14 (s, 18 H, t-Bu); H NMR (CDCl3, 300 MHz,
ppm) 7.27-7.15, 7.11-7.06 (m, 5 H, Ph), 7.05 (s, 1 H, CHd),
6.74 (s, 4 H, Mes-CH), 2.31 (s, 12 H, o-CH3), 2.21 (s, 6 H,
p-CH3), 1.08 (s, 18 H, t-Bu); 13C NMR (CDCl3, ppm): 181.15
(HCdCPh), 150.26 (HCdCPh), 146.23, 142.56, 139.00, 137.40
(Ar-C), 128.54, (d, Mes-CH), 127.72, 126.32, 126.20 (Ph-CH),
29.48, 25.13, 20.92 (CH3), 23.00 (C(CH3)3); 29Si NMR (ppm)
30.79; MS (m/z) 556 (35, M+), 499 (100, M - t-Bu), 311 (34,
GeMes2 - H), 281 (25), 193 (88, GeMes), 105 (36), 91 (69), 73
(70); high-resolution MS calcd for C34H46Si74Ge 556.2581, found
556.2587.
Rea ction of Com p ou n d 9 w ith Sod iu m Hyd r oxid e. A
solution of compound 9 (30 mg, 0.054 mmol) in 1,4-dioxane (8
mL) was added dropwise to a clear, colorless, homogeneous
solution of NaOH (2 pellets; approximately 75 mg) in aqueous
dioxane (8 mL, approximately 40% H2O). The solution was
heated for 20 h, after which time the reaction mixture was a
clear yellow in color. After the reaction cooled to room
temperature, water (5 mL) was added and the reaction mixture
was left to stir for 25 min. The reaction mixture was then
extracted with hexanes. The solvent was removed from the
combined organic layers to give a sticky white solid, 10 (24
mg, 77%). If left for any period of time, or if chromatographed,
compound 10 is slowly converted to a new compound whose
structure has not yet been determined.
2-(Di-ter t-b u t ylh yd r oxysilyl)-1-(d im esit ylger m yl)-1-
p h en yleth en e (10): IR (thin film; cm-1) 3608 (OH); 1H NMR
(C6D6, 300 MHz, ppm) 7.34-7.39, 6.88-7.03 (m, 6 H, Ph-H
and CHd), 6.69 (s, 4 H, Mes-CH), 6.43 (s, 1 H, GeH), 2.39 (s,
12 H, o-Me), 2.04 (s, 6 H, p-Me), 1.54 (s, 1 H, OH), 1.13 (s, 18
H, t-Bu); 13C NMR (CDCl3, ppm) 161.78, 146.71, 143.56,
142.83, 138.65, 134.02, 128.90, 127.52, 127.25, 126.53, 28.06,
23.99, 21.12, 21.04; 29Si NMR (1H-coupled, ppm) 3.13 (bm); MS
(m/z) 574 (6, M+), 517 (50, M+ - t-Bu), 455 (46, M+ - Mes),
397 (100, M+ - t-Bu - Mes - H), 313 (33, Mes2GeH), 277 (30),
193 (25, MesGe), 163 (23), 119 (12), 84 (52).
1
yleth en e (7): white solid; H NMR (300 MHz, CDCl3, ppm)
7.2-6.5 (m, 5 H, Ph), 7.09 (s, 1 H, vinyl-H), 6.74 (s, 4 H, Mes-
H), 6.66 (s, 4 H, Mes-H), 5.86 (s, 1 H, GeH), 2.92 (s, 3 H, OCH3),
2.27 (s, 12 H, Mes-CH3), 2.23 (s, 6 H, Mes-CH3), 2.19 (s, 6 H,
1
Mes-CH3), 1.99 (s, 12 H, Mes-CH3); H NMR (C6D6) 7.5-6.8
(m, Ph), 6.73, 6.72, 6.24, 3.02, 2.43, 2.28, 2.12, 2.09; 13C NMR
(50 MHz, CDCl3, ppm) 149.43 (vinyl-CH), 157.54, 147.82,
144.36, 143.24, 138.97, 137.51, 135.54, 132.13 (vinyl and ArC),
129.14, 128.22, 127.35, 127.19, 125.97 (ArCH), 50.05 (OCH3),
24.16, 23.54, 21.08 (Mes-CH3); 29Si NMR (CDCl3, ppm) -16.37
(bm); MS (m/z) 712 (1, M+), 697 (1, M+ - CH3), 635 (<1, M+
-
Ph), 592 (40, M+ - Mes), 577 (7, M+ - Mes - CH3), 547 (14,
M+ - Mes - CH3 - CH3O), 531 (11, M+ - Mes - OCH3
2CH3), 516 (5, M+ - Mes - OCH3 - 3CH3), 473 (4, M+
-
-
2Mes), 457 (9, M+ - 2Mes - CH3), 413 (21, M+ - Mes2-
SiOCH3), 399 (30, M+ - Mes2GeH), 368 (18, Mes2SiCPhCH),
311 (31, Mes2Ge - H), 297 (100, Mes2SiOCH3), 279 (24, Mes2-
SiCH), 265 (20, Mes2Si - H), 193 (12 MesGe), 105 (9), 59 (18);
high-resolution MS calcd for C54H54OSi73Ge 711.3179, found
711.3149.
P h otolysis of cyclo-Si(t-Bu )2Ge2Mes4 in th e P r esen ce
of P h en yla cetylen e. A solution of cyclo-Si(t-Bu)2Ge2Mes4 (50
mg, 0.065 mmol) and phenylacetylene (0.5 mL) in toluene (2
mL) was photolyzed (350 nm) 18 h at room temperature.
Within 1 h, the pale yellow cloudy reaction mixture became
dark yellow in color. At the end of the photolysis, the reaction
mixture was a bright orange, clear solution. The solvent was
removed under vacuum to give a viscous orange oil, which
became a dark orange solid when a stream of argon was blown
over it for 1.5 h. The product mixture was separated by
preparative thin-layer chromatography (Chromatotron) using
1:9 CH2Cl2/hexanes as the eluent. The polarity of the eluent
was gradually changed to 25:75 CH2Cl2/hexanes. Three prod-
ucts were isolated and identified, 9, which was purified by
recrystallization from pentane (27.8 mg, 77%), (7.7 mg, 29%),
and a third compound observed in low yield, which appeared
to be derived from the addition of Mes2Ge: to phenylacetylene.
However, this third compound could not be unambiguously
identified.
Ack n ow led gm en t. Financial assistance from the
Natural Sciences and Engineering Research Council of
Canada in the form of a Summer Research Assistant-
ship to J .M.L. and a grant to K.M.B. is gratefully
acknowledged.
Su p p or tin g In for m a tion Ava ila ble: 1H and 13C NMR
spectra of 2-4, 7, 9, and 10, and 29Si NMR spectra of 2, 7, 9,
and 10. This material is available free of charge via the
Internet at http://pubs.acs.org.
3-P h en yl-1,1-d i-ter t-bu tyl-2,2-d im esityl-1-sila -2-ger m a -
cyclobu t-3-en e (9): white solid; mp 190-193 °C; IR (thin film,
OM981017H