The reaction of group 14 dimetallenes with alkenes: Electron-poor alkenes

Article abstract of DOI:10.1021/om970638s

The addition reactions of tetramesitylgermasilene with methyl vinyl ketone (MVK), crotonaldehyde, and acrylonitrile were studied. When tetramesitylgermasilene was allowed to react with MVK, [2 + 4] cycloaddition and nonregioselective carbonyl [2 + 2] cycloaddition products were isolated. When tetramesitylgermasilene was allowed to react with crotonaldehyde, the carbonyl [2 + 2] adduct was produced exclusively. The regiochemistry was not determined. The addition of acrylonitrile to tetramesitylgermasilene yielded a germasilacyclobutane, which is the formal [2 + 2] cycloadduct between the germasilene and the C-C double bond of acrylonitrile. Tetramesityldisilene was also found to yield a formal [2 + 2] adduct with acrylonitrile. However, tetramesityldigermene rearranges to a germylgermylene at a faster rate than acrylonitrile addition.

Full text of DOI:10.1021/om970638s

Organometallics 1997, 16, 5437-5440
5437
Th e Rea ction of Gr ou p 14 Dim eta llen es w ith Alk en es:
Electr on -P oor Alk en es
Craig E. Dixon, J effrey A. Cooke, and Kim M. Baines*
Department of Chemistry, University of Western Ontario, London, Ontario, Canada N6A 5B7
Received J uly 28, 1997X
The addition reactions of tetramesitylgermasilene with methyl vinyl ketone (MVK),
crotonaldehyde, and acrylonitrile were studied. When tetramesitylgermasilene was allowed
to react with MVK, [2 + 4] cycloaddition and nonregioselective carbonyl [2 + 2] cycloaddition
products were isolated. When tetramesitylgermasilene was allowed to react with crotonal-
dehyde, the carbonyl [2 + 2] adduct was produced exclusively. The regiochemistry was not
determined. The addition of acrylonitrile to tetramesitylgermasilene yielded a germasila-
cyclobutane, which is the formal [2 + 2] cycloadduct between the germasilene and the C-C
double bond of acrylonitrile. Tetramesityldisilene was also found to yield a formal [2 + 2]
adduct with acrylonitrile. However, tetramesityldigermene rearranges to a germylgermylene
at a faster rate than acrylonitrile addition.
In tr od u ction
dition products have also been isolated from reactions
between tetramesitylgermasilene and trans-1-methox-
ybutadiene7 as well as between tetra-tert-butyldisilene
and 2,2′-dipyridine,8 o-methylstyrene,9 or furan.10 In
each case where reaction between the dimetallene and
the alkene is observed, the alkene reacting has been
electron-rich. To our knowledge, the only electron-poor
alkene that has been allowed to react with a dimetal-
lene, namely tetramesityldisilene, has been an R,â-
unsaturated ketone. Although the reactivity of dimet-
allenes toward ketones and aldehydes is well-known,
the effect of the C-C double bond in conjugation with
the carbonyl on this observed reactivity was not. When
tetramesityldisilene was allowed to react with acrolein,
methyl vinyl ketone, or ethyl vinyl ketone, the only
products isolated were the corresponding disilaoxetanes
from addition of the carbonyl moiety to the Si-Si double
bond.11 Apparently, the presence of the C-C double
bond in conjugation with the carbonyl did not affect the
reactivity between the disilene and the ketone.
To further explore what effect substitution of an
electron-withdrawing group on an alkene may have on
its reactivity with tetramesitylgermasilene, three elec-
tron-poor alkenes were selected for study. The results
of the reactions between tetramesitylgermasilene and
methyl vinyl ketone, crotonaldehyde, or acrylonitrile are
reported in this paper. Also reported are the results of
the reactions between tetramesityldisilene and -di-
germene and acrylonitrile.
The chemistry of stable and relatively stable tet-
raaryldisilenes and -digermenes has been extensively
documented,1 and the reactivity of tetramesitylger-
masilene, the first relatively stable germasilene, has
been demonstrated to closely follow that of its homo-
nuclear analogs tetramesityldisilene and tetramesityl-
digermene. In many cases, these heavier analogs of
olefins have displayed an increased reactivity toward
many reagents relative to alkenes. For example, tet-
ramesityldisilene,2 -digermene,3 and -germasilene3
smoothly add alcohols across the double bond without
need of a catalyst. This increased level of reactivity of
the heavier group 14 double bonds, relative to the C-C
double bond, is responsible for some interesting behavior
that has no direct parallel in carbon chemistry. For
example, the C-O double bond of ketones and aldehydes
reacts rapidly with the M1-M2 double bond of tet-
ramesityldisilene,2 -digermene,4 and -germasilene,5 in
a formal [2 + 2] manner, to fashion the corresponding
metallaoxetane.
Surprisingly, stable and relatively stable tetraaryldi-
metallenes have proven to be, for the most part, unre-
active toward conjugated dienes. For example, tet-
ramesityldisilene,2 -digermene,6 and -germasilene6 are
each unreactive toward 2,3-dimethylbutadiene. How-
ever, tetramesityldisilene and -germasilene will add
styrene in a formal [2 + 2] manner.7 [2 + 2] cycload-
Resu lts a n d Discu ssion
X Abstract published in Advance ACS Abstracts, November 1, 1997.
(1) 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.
(2) Fink, M. J .; DeYoung, D. J .; West, R. J . Am. Chem. Soc. 1983,
105, 1070.
(3) Baines, K. M.; Cooke, J . A. Organometallics 1991, 10, 3419.
(4) Ando, W.; Tsumuraya, T. J . Chem. Soc., Chem. Commun. 1989,
770.
Photolysis of hexamesitylsiladigermirane (1) in the
presence of methyl vinyl ketone (MVK) at 22 °C yielded
compounds 3-5 in a 8:1:4 ratio (Scheme 1). Compounds
(7) Dixon, C. E.; Liu, H. W.; Vander Kant, C. M.; Baines, K. M.
Organometallics 1996, 15, 5701.
(8) Weidenbruch, M .; Flintjer, B.; Pohl, S.; Hasse, D.; Martens, J .
J . Organomet. Chem. 1988, 338, C1.
(9) Weidenbruch, M.; Kroke, E.; Marsmann, H.; Pohl, S.; Saak, W.
J . Chem. Soc., Chem. Commun. 1994, 1233.
(10) Weidenbruch, M.; Kroke, E.; Saak, W.; Pohl, S. Organometallics
1995, 14, 5695.
(5) Baines, K. M.; Cooke, J . A.; Vittal, J . J . Heteroat. Chem. 1994,
5, 293.
(6) Baines, K. M.; Cooke, J . A.; Dixon, C. E.; Liu, H. W.; Netherton,
M. R. Organometallics 1994, 13, 631.
(11) Fanta, A. D.; DeYoung, D. J .; Belzner, J .; West, R. Organome-
tallics 1991, 10, 3466.
S0276-7333(97)00638-9 CCC: $14.00 © 1997 American Chemical Society

5438 Organometallics, Vol. 16, No. 25, 1997
Dixon et al.
Sch em e 1
Sch em e 2
Sch em e 3
Interestingly, crotonaldehyde, despite its structural
similarity to MVK, failed to produce a similar product
mixture when allowed to react with tetramesitylger-
masilene. Photolysis of hexamesitylsiladigermirane in
the presence of crotonaldehyde, at -78 °C, yielded one
product, 6, the formal [2 + 2] cycloaddition product
between the carbonyl moiety of crotonaldehyde and
tetramesitylgermasilene (Scheme 2). Compound 6 was
previously isolated as a minor byproduct from the
photolysis of SiGe2Mes6 in the presence of vinyl acetate
distilled from LiAlH(O-t-Bu)3.7 The spectroscopic data
for compound 6 agree completely with the literature
data.7 The regiochemistry of the adduct was not
determined; the assigned structure is based on the
known regiochemistry for the addition of pivalaldehyde
and acetone to the germasilene.5 It is noteworthy to
mention that another product is observed in the 1H
NMR spectrum of the crude reaction mixture, which is
presumably derived from the reaction between dimesi-
tylgermylene and crotonaldehyde. However, compound
6 was the only compound isolated from the reaction
mixture, indicating that the germylene-derived product
may have decomposed during chromatography. In fact,
compounds derived from reaction between dimesitylger-
mylene and ketones or aldehydes have been found to
be notoriously difficult to purify by conventional chro-
matographic techniques; therefore, this observed de-
composition is not unexpected.14 The observed reactiv-
ity of tetramesitylgermasilene with MVK or croton-
aldehyde is consistent with the reactivity observed
between tetramesityldisilene and R,â-unsaturated ke-
tones or aldehydes. Not surprisingly, the cycloaddition
of the germasilene to the carbonyl moiety of MVK or
crotonaldehyde occurs preferentially over reaction with
the C-C double bond.
1
3 and 5 were characterized by H, 13C, and 29Si NMR
and IR spectroscopy and mass spectrometry. Compound
4 could not be isolated free of compound 3 and as a
result was characterized soley by 1H NMR spectroscopy,
as a mixture of 3 and 4.
Compounds 3 and 4 appear to be the [2 + 2] adducts
of tetramesitylgermasilene, generated by photolysis of
the siladigermirane,12 and the carbonyl group of MVK.
Consistent with this assignment, as determined by
1
thorough H NMR spectroscopic examination of 3, is the
presence of four nonequivalent mesityl groups, a single
resonance, and the characteristic splitting pattern for
a terminal vinyl moiety: three doublets of doublets at
6.32, 5.19, and 4.82 ppm with J trans ) 16.9 Hz, J cis
)
10.7 Hz, and J gem ) 1.92 Hz. Furthermore, the 25.45
ppm signal in the 29Si NMR spectrum is consistent with
the 2-sila-3-germaoxetane structure.5 Although the
regiochemistry of 3 was not determined, we are confi-
dent that 3 is the major regioisomer on the basis of
molecular structure determinations of similar adducts.
Acetone and pivalaldehyde each gave a [2 + 2] adduct
with tetramesitylgermasilene and were shown to give
a single regioisomer: the 2-sila-3-germaoxetane.5 Com-
pound 5 is the [2 + 4] cycloadduct of tetramesitylger-
masilene and MVK. Consistent with this assignment
are the two distinct mesityl groups, as determined by
1H NMR spectroscopy, as is the presence of a triplet at
4.50 ppm (J ) 6.5 Hz), corresponding to the vinyl
moiety. The regiochemistry of the molecule was not
determined. No product derived from the reaction
between dimesitylgermylene and MVK was detected.
The reactivity of metallenes and dimetallenes with
ethylenic ketones has been shown to follow a certain
order, loosely based upon the polarity of the reacting
double bond. For example, nonpolar disilenes11 exclu-
sively undergo [2 + 2] additions with the carbonyl
double bond, whereas the more polar germenes undergo
[2 + 4] cycloadditions, regioselectively, as the sole mode
of reaction.13 The reactivity of tetramesitylgermasilene
toward MVK falls between the observed reactivity of
disilenes and digermenes, which would be consistent
with the slight polarity of the silicon-germanium
double bond.
Thermolysis of hexamesitylsiladigermirane at 110 °C,
in the presence of Et3SiH and acrylonitrile, yielded
1
compounds 7-9 in a 3:1:2 ratio, as determined by H
NMR spectroscopy (Scheme 3). Compounds 7 and 8 are
the products obtained by trapping dimesitylgermylene
and mesityl(trimesitylsilyl)germylene (from rearrange-
ment of Mes2GedSiMes2) with Et3SiH, respectively, and
were identified by comparison to the literature data.12
Compound 9 is the cycloaddition product between
tetramesitylgermasilene and the C-C double bond of
acrylonitrile. Consistent with this assignment is the
(12) Baines, K. M.; Cooke, J . A. Organometallics 1992, 11, 3487.
(13) Lazraq, M.; Escudie´, J .; Couret, C.; Satge´, J . Organometallics
1992, 11, 555.
(14) Cooke, J . A. Ph.D. Thesis, The University of Western Ontario,
1994.

Reaction of Group 14 Dimetallenes with Alkenes
Organometallics, Vol. 16, No. 25, 1997 5439
Sch em e 4
however, tetramesitylgermasilene yields the formal [2
+ 2] cycloaddition product in reaction with the C-O
double bond, exclusively. Furthermore, it has also been
shown that tetramesitylgermasilene and -disilene add
across the C-C double bond of acrylonitrile in a formal
[2 + 2] manner. In the case of tetramesitylgermasilene
the addition of acrylonitrile is not entirely regioselective,
with the major regioisomer produced being 9. In
contrast, tetramesityldigermene rearranges to the cor-
responding germylgermylene at a faster rate than
addition of acrylonitrile, perhaps a reflection of the
greater ease for migration of the mesityl group across
the Ge-Ge double bond in comparison to the ger-
masilene system.
Sch em e 5
In combination with the results of our previous
investigations,7 tetramesitylgermasilene and/or -disilene
react with the following alkenes: 1-methoxybutadiene,
styrene, and acrylonitrile. However, no reaction was
observed between the germasilene and ethyl vinyl ether,
vinyl acetate, allyltrimethylsilane, trans-phenylvinyl-
cyclopropane, and 2,3-dimethylbutadiene. The reac-
tions between the germasilene and R,â-unsaturated
carbonyl compounds such as crotonaldehyde and methyl
vinyl ketone are dominated by reaction with the carbo-
nyl moiety. As a result, we cannot consider these
alkenes in our examination of the reactivity of dimet-
allenes toward alkenes. We believe that this trend in
reactivity suggests a mechanism of addition which
proceeds through a biradical intermediate. We will
report on our findings in due course.
appearance of four mesityl groups and an ABX spin
pattern in the 1H NMR spectrum of 9. The IR spectrum
shows an absorbance at 2217 cm-1, which is assigned
to the CN stretching vibration. The 13C (spin sort
method), COSY, HSQC (heteronuclear spin quantum
coherence; 1H/13C), and HMBC (heteronuclear multiple
1
bond correlation; 1H/13C and H/29Si) NMR spectra also
1
support the assignment. The H/29Si HMBC spectrum
shows a two-bond correlation between the signal at 10.1
ppm in the 29Si dimension and the methylene protons
at 2.48 and 2.57 ppm in the 1H dimension, which
suggests the regiochemistry of compound 9 is that which
is shown. There is also evidence to suggest the presence
of another regioisomer of 9. There appears to be an
additional four lines in the 1H NMR spectrum (3.04
ppm), consistent with an ABX spin system. Further-
more, the 29Si NMR spectrum shows a second signal
very close to that which was assigned to 9 (approxi-
mately 10.1 ppm). The ratio of these two regioisomers
is approximately 8:1, with the major component being
9.
Exp er im en ta l Section
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. Acrylonitrile was obtained
from BDH and used without any further purification. Cro-
tonaldehyde was base-washed, dried and filtered from MgSO4,
and distilled prior to use. MVK was simply distilled under
an atmosphere of argon prior to 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.
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 Advance DRX-500 using benzene-d6 as a solvent.
The standards were as follows: residual C6D5H 7.15 ppm for
1H spectra; C6D6 central transition for 13C NMR spectra; Me4-
Si as an external standard, 0 ppm for 29Si. The 2-D spectra
were acquired using standard techniques.16-18 IR spectra were
recorded (cm-1) as thin films on a Perkin-Elmer System 2000
FT IR spectrometer. A Finnegan MAT Model 8230 instru-
ment, 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).
It is interesting to compare the chemistry of the
heteronuclear dimetallene to that of the homonuclear
analogs, disilenes and digermenes. When acrylonitrile
is added to a solution of tetramesityldisilene in benzene
and this mixture is allowed to stand at 22 °C for several
1
hours, compound 10 is formed (Scheme 4). The H, 13
C
(spin sort method), COSY, HSQC (1H/13C), and HMBC
(1H/13C and 1H/29Si) NMR spectra all support the
assigned structure for 10. Thus, similar to the case for
tetramesitylgermasilene, tetramesityldisilene adds acry-
lonitrile in a formal [2 + 2] fashion.
Thermolysis of hexamesitylcyclotrigermane in the
presence of Et3SiH and acrylonitrile yielded compounds
7 and 12, which were readily identified by referral to
the literature data15 (Scheme 5). Tetramesityldi-
germene has been shown to undergo a thermal 1,2-
mesityl shift to give the corresponding germylger-
mylene.15 Compound 12 results from insertion of
mesityl(trimesitylgermyl)germylene into the Si-H bond
of Et3SiH. Unlike tetramesitylgermasilene and tet-
ramesityldisilene, tetramesityldigermene does not ap-
pear to add acrylonitrile at a faster rate than the 1,2-
mesityl shift to the corresponding germylgermylene.
In summary, we have shown that tetramesitylger-
masilene yields formal [2 + 2] and [2 + 4] cycloaddition
products in reaction with the C-O double bond of MVK
and that the [2 + 2] reaction does not occur entirely
regioselectively. In the presence of crotonaldehyde,
P h otolysis of SiGe2Mes6 in th e P r esen ce of Meth yl
Vin yl Keton e (MVK). A solution of SiGe2Mes6 (75 mg, 0.084
mmol) and freshly distilled MVK (0.75 mL, excess) in dry
toluene was photolyzed for 6.5 h at 22 °C. During the
photolysis, the reaction mixture developed a yellow color which
faded as the reaction proceeded. Following the photolysis, the
solvent was removed, yielding a tan semisolid. Trituration of
(16) Parker, P. B.; Freeman, R. F. J . Magn. Reson. 1985, 64, 334.
(17) Bereton, I. M.; Crozier, S.; Field, J .; Dodrell, D. M. J . Magn.
Reson. 1991, 93, 54.
(15) Baines, K. M.; Cooke, J . A.; Vittal, J . J . J . Chem. Soc., Chem.
Commun. 1992, 1484.
(18) Von Kienlin, M.; Moonen, C. T. W.; van der Toorn, A.; van Zijl,
P. C. M. J . Magn. Reson. 1991, 93, 423.

5440 Organometallics, Vol. 16, No. 25, 1997
Dixon et al.
this mixture with either hexanes or diethyl ether caused
precipitation of a white, intractable solid. Removal of the
solvent from the triturate yielded a mixture of both regioiso-
mers of 4-methyl-2,2,3,3-tetramesityl-4-vinylgermasilaoxetane
(3 and 4) and 5-methyl-2,2,3,3-tetramesitylgermasilacyclohex-
1-ene (5). Separation of the components was accomplished
using preparative thin-layer chromatography (Chromatotron)
with hexanes/CH2Cl2 as the eluent. Compounds 3 and 5 were
isolated in 38% and 18% yields, respectively. The minor
isomer, 4, could not be separated from the major isomer, 3.
Compound 5 contained traces of, perhaps, a regioisomeric
compound. No product derived from the reaction of MVK with
Mes2Ge: was detected.
raphy (50/50 CH2Cl2/hexanes), to give compound 9 (3 mg,
6%).19
1,1,2,2-Tet r a m esit yl-4-cya n o-1-ger m a -2-sila cyclob u -
ta n e (9). IR (thin film, cm-1): 3016 (m), 2964 (s), 2927 (s),
2860 (s), 2217 (m, CN), 1611 (s), 1458 (s), 1417 (m), 1383 (m),
1039 (m), 856 (m). 1H NMR (ppm): 6.70 (s, 2 H, Mes H), 6.63
(s, 2 H, Mes H), 6.61 (s, 2 H, Mes H), 6.59 (s, 2 H, Mes H),
3.14 (X portion of ABX, 1 H, CH2CHCN, J AX ) 8 Hz, J BX ) 13
Hz), 2.57, 2.48 (AB portion of ABX, CH2CHCN, J AB ) 15.1 Hz),
2.35 (s, 6 H, Mes o-CH3), 2.31 (s, 6 H, Mes o-CH3), 2.24 (s, 6
H, Mes o-CH3), 2.09 (s, 6 H, Mes o-CH3), 2.07 (s, 3 H, Mes
p-CH3), 2.04 (s, 6 H, Mes p-CH3), 2.01 (s, 3 H, Mes p-CH3). 13
C
NMR (ppm): 145.37, 144.58, 143.64, 142.25, 139.73, 139.52,
139.20, 138.54, 135.40, 130.87 (Mes C), 129.95, 129.79, 129.31,
129.24 (Mes CH), 124.44 (CN), 26.30 (CH2), 25.41, 24.68, 24.36,
24.32 (Mes o-CH3), 21.48 (CH), 21.05, 20.96, 20.87 (Mes p-CH3).
4-Met h yl-2,2,3,3-t et r a m esit yl-4-vin ylger m a sila oxet -
a n e (3). IR (thin film, cm-1): 2957 (s), 2919 (s), 1605 (s), 1553
(w), 1442 (s), 1410 (m), 1377 (w), 1070 (w), 1029 (w), 997 (w),
940 (m), 900 (w), 847 (s), 790 (w). 1H NMR (ppm): 6.72, 6.71,
29Si NMR (ppm): 10.1. MS (m/z): 631 (M+, 25), 616 (M+
-
CH3, 39), 512 (M+ - Mes, 24), 385 (Mes3Si, 100), 339 (Mes2-
SiGe, 74), 310 (Mes2Ge, 31), 265 (Mes2Si - H, 36), 191 (MesGe,
55), 147 (MesSi, 68). High-resolution MS (m/z): calcd for
6.66, 6.64 (s, 8 H total, Mes H), 6.32 (dd, 1 H, CHdCH2, J cis
10.6 Hz, J trans ) 16.9 Hz), 5.19 (dd, 1 H, CHdCHHtrans, J gem
1.9 Hz, J trans ) 16.9 Hz), 4.82 (dd, 1 H, CHdCHcisH, J gem
)
)
)
C
39H47SiGeN, 631.2683; found, 631.2690.
1.9 Hz, J cis ) 10.6 Hz), 2.65 (bs), 2.46 (vbs), 2.37 (s), 2.19 (s)
(24 H total, Mes o-CH3), 2.118, 2.114 (6 H total), 2.06 (3 H),
2.01 (3 H) (each s, Mes p-CH3), 1.62 (s, 3 H, CH3). 13C NMR
(ppm): 148.01 (CHdCH2), 143.90 (vbs), 142.76, 142.37, 141.69,
139.23, 137.95, 135.42, 134.55 (Mes C), 129.82 (bs), 129.24 (bs),
129.13, 128.91 (Mes CH), 108.03 (CHdCH2), 94.38 (CsO),
30.53 (OCsCH3), 26.65 (vbs), 24.93 (bs), 24.24, 23.92 (vbs) (o-
CH3), 21.06, 20.96, 20.92 (p-CH3). 29Si NMR (ppm): 25.45. MS
(m/z): 648 (M+, 9), 578 (Mes4SiGe, 4), 528 (M+ - Mes, 8), 385
(Mes3Si, 69), 312 (Mes2Ge, 100), 265 (Mes2Si, 6), 192 (MesGe,
21). High-resolution MS (m/z): calcd for C40H50GeSiO, 648.2843;
found, 648.2828.
Addition of Acr ylon itr ile to Tetr am esityldisilen e. Mes2-
Si(SiMe3)2 (100 mg, 0.24 mmol) was dissolved in pentane (8
mL) and photolyzed (254 nm) at -60 °C for 12 h. At this time,
the pentane was removed, in vacuo, and replaced with toluene.
To this solution was added acrylonitrile (0.25 mL, excess), and
the mixture was allowed to stand at 22 °C for 12 h. Following
removal of the solvent, the reaction mixture was purified by
preparative thin-layer chromatography (50/50 CH2Cl2/hexanes)
to give compound 10 (14 mg, 10%).19
1,1,2,2-Tetr am esityl-4-cyan o-1,2-disilacyclobu tan e (10).
Mp: 178-180 °C. IR (thin film, cm-1): 3032 (m), 2965 (s),
2920 (s), 2224 (m, CN), 1611 (s), 1555 (w), 1454 (s), 1413 (m),
1379 (w), 1293 (w), 1271 (w), 1237 (w), 1064 (w), 1036 (m),
856 (s). 1H NMR (ppm): 6.69 (s, 2 H, Mes CH), 6.65 (s, 2 H,
Mes CH), 6.58 (s, 2 H, Mes CH), 6.57 (s, 2 H, Mes CH), 3.04
(X portion of ABX, 1 H, CH2CHCN, J AX ) 8.2 Hz, J BX ) 13.6
Hz), 2.45, 2.35 (AB portion of ABX, CH2CHCN, J AB ) 14.8 Hz),
2.38 (s, 6 H, Mes o-CH3), 2.35 (s, 6 H, Mes o-CH3), 2.27 (s, 6
H, Mes o-CH3), 2.08 (s, 3 H, Mes p-CH3), 2.06 (s, 6 H, Mes
o-CH3), 2.024 (s, Mes p-CH3), 2.018 (s, Mes p-CH3) (9 H total).
13C NMR (ppm): 146.15, 145.45, 143.81, 143.47, 140.15,
139.39, 139.275, 139.265, 136.25, 135.82, 131.43, 129.07 (Mes
C), 130.02, 129.85, 129.31 (Mes CH), 123.76 (CN), 25.75 (Mes
o-CH3), 25.13 (CH2), 24.69, 24.53, 24.47 (Mes o-CH3), 21.00,
20.89, 20.80 (Mes p-CH3), 20.15 (CH). 29Si NMR (ppm): 7.50
(SiCHCN), -1.60 (SiCH2). MS (m/z): 585 (M+, 25), 570 (M+
- CH3, 74), 466 (M+ - Mes, 15), 293 (Mes2Si2 - H, 95), 266
(Mes2Si, 34), 147 (MesSi, 100). High-resolution MS (m/z):
calcd for C39H47Si2N, 585.3247; found, 585.3243.
4-Met h yl-2,2,3,3-t et r a m esit yl-4-vin ylger m a sila oxet -
a n e (4, Min or Isom er ). 1H NMR (ppm): 6.72, 6.71, 6.66, 6.62
(each s, Mes H), 6.39 (dd, 1 H, CHdCH2, J cis ) 10.7 Hz, J trans
) 16.9 Hz), 5.37 (dd, 1 H, CHdCHHtrans, J gem ) 2.0 Hz, J trans
) 16.9 Hz), 4.91 (dd, 1 H, CHdCHcisH, J gem ) 2.0 Hz, J cis
)
10.7 Hz), 2.65 (bs), 2.46 (vbs), 2.32 (s), 2.21 (s) (o-CH3), 2.12,
2.09, 2.05, 2.03 (s, p-CH3), 1.54 (s, CH3).
2-Meth yl-4,4,5,5-tetr a m esityloxa sila ger m a cycloh ex-1-
en e (5). IR (thin film, cm-1): 3022 (s), 2976 (s), 2919 (s), 2731
(w), 1661 (m), 1604 (s), 1551 (m), 1449 (s), 1409 (s), 1376 (m),
1313 (m), 1289 (w), 1264 (m), 1210 (s), 1132 (s), 1063 (m), 1008
(s), 915 (m), 848 (s), 788 (w), 739 (s), 693 (s), 620 (m). 1H NMR
(ppm): 6.72 (s, 4 H, Mes H), 6.69 (s, 4 H, Mes H), 4.51 (dt, 1
H, CdCH, J ) 6.9 Hz, J ) 0.9 Hz), 2.55 (bs, 12 H total, Mes
o-CH3 and CH2), 2.22 (s, 12 H, Mes o-CH3), 2.09, 2.08 (each s,
12 H total, Mes p-CH3), 1.70 (d, 3 H, CH3, J ) 0.9 Hz). 13C
NMR (ppm): 148.54 (CH3CdCH), 144.80, 143.43, 139.34,
138.54, 137.45, 133.69 (Mes C), 129.82, 129.41 (Mes CH),
102.20 (CH3CdCH), 25.06, 24.06 (Mes o-CH3), 23.11 (CH3),
20.96, 20.89 (Mes p-CH3), 19.10 (CH2). 29Si NMR (ppm):
-4.22. MS (m/z): 648 (M+, 16), 578 (Mes4SiGe, 2), 385 (Mes3-
Si, 48), 312 (Mes2Ge, 100), 267 (Mes2Si, 13), 192 (MesGe, 48),
147 (MesSi, 14), 84 (53), 49 (60). High-resolution MS (m/z):
calcd for C40H50GeSiO, 648.2843; found, 648.2857.
Th er m olysis of Ge3Mes6 in th e P r esen ce of Acr ylon i-
tr ile. Ge3Mes6 (50 mg, 0.054 mmol) and Et3SiH (1 mL, excess)
were dissolved in toluene (2 mL), and the mixture was heated
to 110 °C for 8 h. After this time, the solvents were removed
1
and subsequent analysis of the crude reaction mixture by H
NMR spectroscopy showed a mixture of compounds 7 and 12
as the major product. There were no products detected from
a reaction between tetramesityldigermene and acrylonitrile.
P h otolysis of SiGe2Mes6 in th e P r esen ce of Cr oton a l-
d eh yd e. A solution of SiGe2Mes6 (48 mg, 0.054 mmol) and
crotonaldehyde (1 mL, excess) in dry toluene (3 mL) was
photolyzed for 6 h at -78 °C. The solution remained colorless
during the given reaction time. After removal of the solvent,
the oily mixture was separated by preparative thin-layer
chromatography (Chromatotron) with a CH2Cl2/hexanes mix-
ture as the eluent. Compound 6 was isolated as the major
product (35 mg, 63%) and identified by comparison to the
literature data.5
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 and mass
spectra for compounds 3, 5, 9, and 10 and IR spectra for 5, 9,
and 10 (27 pages). Ordering information is given on any
current masthead page.
Th er m olysis of SiGe2Mes6 in th e P r esen ce of Acr y-
lon itr ile. SiGe2Mes6 (40 mg, 0.045 mmol), acrylonitrile (0.5
mL, excess), and Et3SiH (0.5 mL, excess) were placed in
toluene (3 mL), and the mixture was heated to 110 °C for 8 h.
The solvents were then removed to yield a yellow solid. This
mixture was separated by preparative thin-layer chromatog-
OM970638S
(19) While the isolated yield of the cycloadduct is low, it appears as
a major component of the crude reaction mixture, as determined by
1H NMR spectroscopy. Loss of material appears to occur during the
separation and purification of the compounds.