Steady-state photolysis of dimesitylbis(trimethylsilyl)germane

Article abstract of DOI:10.1139/V07-039

The photolysis of dimesitylbis(trimethylsilyl)germane (3) in hexanes or THF, at low temperature, has been investigated as a potential method for the preparative-scale synthesis of tetramesityldigermene (5). A product mixture, consisting of hexamethyldisilane, mesitylene, 2-trimethylsilylmesitylene (7), a new germacyclobutene (8), and an unidentified polymer, was obtained. No evidence for the formation of tetramesityldigermene (5) was observed.

Full text of DOI:10.1139/V07-039

668
Steady-state photolysis of
dimesitylbis(trimethylsilyl)germane1
Krysten L. Hurni and Kim M. Baines
Abstract: The photolysis of dimesitylbis(trimethylsilyl)germane (3) in hexanes or THF, at low temperature, has been
investigated as a potential method for the preparative-scale synthesis of tetramesityldigermene (5). A product mixture,
consisting of hexamethyldisilane, mesitylene, 2-trimethylsilylmesitylene (7), a new germacyclobutene (8), and an un-
identified polymer, was obtained. No evidence for the formation of tetramesityldigermene (5) was observed.
Key words: diaryldisilylgermane, digermene, germylene, germacyclobutene, photolysis.
Résumé : On a étudié la photolyse du dimésitylbis(triméthylsilyl)germane (3) dans les hexanes ou le THF, à de faibles
températures, comme méthode potentielle de la synthèse à l’échelle préparative de tétramésityldigermène (5). On a ob-
tenu un mélange de produits formé d’hexaméthyldisilane, de mésitylène, de 2-triméthylsilylmésitylène (7), d’un nou-
veau germacyclobutène (8) et d’un polymère non identifié. On n’a observé aucune formation du tétramésityldigermène
(5).
Mots-clés : diaryldisilylgermane, digermène, germylène, germacyclobutène, photolyse.
[Traduit par la rédaction] Hurni and Baines 674
Introduction
been carried out in a matrix at low temperature on an analyt-
ical scale. The presence of the digermene under these condi-
tions has been inferred by the observation of appropriate
signals by UV–vis or NMR spectroscopy (7a–7e). On
one occasion, the photolysis of bis(2,4,6-triisopropyl-
phenyl)bis(trimethylsilyl)germane was carried out at room
temperature in solution for the subsequent preparation of an
adduct of tetrakis(2,4,6-triisopropylphenyl)digermene; how-
ever, the adduct was isolated in very low yield (7f). The irra-
diation of diphenylbis(trimethylsilyl)germane (1) in solution
at room temperature has been investigated, primarily as a
source of diphenylgermylene (2) for kinetic studies (8); the
synthesis of tetraphenyldigermene was not the goal of these
studies. Although the generation of diphenylgermylene (2)
was shown to be the primary reaction pathway followed in
the steady-state photolysis of germane 1 at room tempera-
ture, the occurrence of other minor reaction pathways was
noted (8b–8c). Similarly, dimesitylbis(trimethylsilyl)ger-
mane (3) has been investigated as a photochemical precursor
of dimesitylgermylene (4) for solution-state kinetic studies
(9). Both dimesitylgermylene (4) and tetramesityldigermene
(5) were readily detected by UV–vis spectroscopy; however,
the weakness of the absorptions precluded the use of ger-
mane 3 as an effective source of germylene 4 for kinetic
measurements. To date, the viability of using the irradiation
Since the synthesis of the first solid digermene 30 years
ago by Lappert et al. (1), followed six years later by the
preparation of the first solution-stable digermene by
Masamune et al. (2), several methods for the preparation of
digermenes have been realized (3). These heavier alkene an-
alogues are important not only because they are useful sub-
strates for the preparation of a variety of organogermanium
compounds, but also because they are the molecular ana-
logues of the germanium dimers found on the Ge(100)-2 × 1
surface (3i). For some time, our research group has been
extensively engaged in the study of the reactivity of diger-
menes (4). This, and the interest in the emerging applica-
tions of digermene chemistry (3i, 5), have continuously
driven a need for the development of efficient routes for the
preparation of digermenes.
In almost every review on digermene chemistry published
since 1990, the preparation of tetraaryldigermenes by the ir-
radiation of a diarylbis(trimethylsilyl)germane has been de-
scribed as one of the primary methods for the synthesis of
digermenes (Scheme 1) (3a–3f, 3h). An analogous method is
frequently employed in the preparative-scale synthesis of a
variety of disilenes (3b, 3e, 6); however, in the case of
tetraaryldigermenes, the photolyses have, in general, only
Received 21 January 2007. Accepted 19 April 2007. Published on the NRC Research Press Web site at canjchem.nrc.ca on 7 June
2007.
This article is dedicated to G. Michael Bancroft in recognition of his outstanding contributions not only to science and to Canada,
but also to the Department of Chemistry at The University of Western Ontario.
K.L. Hurni and K.M. Baines.2 Department of Chemistry, The University of Western Ontario, London, ON N6A 5B7, Canada
1This article is part of a Special Issue dedicated to Professor G. Michael Bancroft.
2Corresponding author (e-mail: kbaines2@uwo.ca).
Can. J. Chem. 85: 668–674 (2007)
doi:10.1139/V07-039
© 2007 NRC Canada

Hurni and Baines
669
Scheme 1.
Scheme 3.
Scheme 2.
Table 1. Relative ratios of volatile products formed by irradia-
tion of 3 for different time periods, as determined by GC.
Time (h)
Mesitylene
7
8
10
11
3
of diarylbis(trimethylsilyl)germanes as a means for the prep-
aration of practical quantities of a digermene has not been
demonstrated.
0.5a
12
19
37
44
55
70
4
14
22
44
45
33
17
6
n/a
n/a
n/a
n/a
n/a
n/a
n/ac
16
n/a
n/a
n/a
n/a
n/a
n/a
7
72
54
12
2
2
3
7
9
1a
3a
Many of our studies on the reactivity of digermenes em-
ploy tetramesityldigermene (5) as the prototypical diger-
mene (4). We generate digermene 5 either by thermolysis or
by photolysis of hexamesitylcyclotrigermane (6) (10). A dis-
advantage of this method is the concomitant formation of an
equivalent of dimesitylgermylene (4). In general, germylene
4 and digermene 5 are trapped during the course of the reac-
tion, and the two products are separated by chromatography
(Scheme 2) (4c). The irradiation of germane 3 as a possible
route to tetramesityldigermene (5) is particularly attractive,
since hexamethyldisilane is a volatile, relatively inert
coproduct, which could easily be removed in vacuo from
digermene 5 (or the products derived from it) at the end of
the procedure. The formation of 5 could be determined
either directly, using UV–vis or NMR spectroscopy, or indi-
rectly, by the reaction with a well-known trapping reagent
(e.g., methanol). We now report on the results of our investi-
gations of this reaction on a preparative scale.
6a
24a
48a
1b
11
12
6
21
23
0
0
n/ac
18
0
5b
13
21
15
21
17
17
20b
17
Note: n/a: not applicable.
aIrradiation (254 nm) of 3 at –70 °C in hexanes.
bIrradiation (254 nm) of 3 at –70 °C in hexanes in the presence of 2,3-
dimethylbutadiene.
cGermane 3 and germacyclopentene 10 initially co-elute in the gas
chromatogram. Together, they account for 76%.
fied as mesitylene, 2-trimethylsilylmesitylene (7), germ-
acyclobutene 8, and hexamethyldisilane. An uncharacterized
germanium-containing polymer was also obtained
(Scheme 3). The relative ratios of the products were deter-
mined by GC analysis of the reaction mixture before expo-
sure to air and are given in Table 1. A GC–MS of the
headspace gas revealed no additional volatile products. Be-
cause of the difficulties encountered during the separation of
and loss by evaporation of several products, we were unable
to determine the isolated yields.4 Hexamethyldisilane was
identified as a component of the product mixture (prior to its
Results
A colourless solution of 3 was photolyzed (254 nm) at
–70 °C for 24 h.3 The product mixture obtained after re-
moval of the solvent was quite complex. Similar results were
obtained when either hexanes or THF were used as the sol-
vent for the photolysis. In the early stages of the photolysis,
the colourless solution became yellow and, by the end of the
photolysis, the colour of the solution was orange. The crude
product mixture was separated by preparative TLC. Five
products were isolated, and four were unambiguously identi-
1
removal in vacuo) by comparison of its H chemical shift
with that of an authentic sample. The relative amount of
hexamethyldisilane could not be determined by GC, since it
eluted with the solvent in the gas chromatogram; however, it
3 Previous work from this laboratory has shown that tetramesityldigermene (5) rearranges to (trimesitylgermyl)mesitylgermylene between –
70 °C and room temperature (4a, 4b, 4e).
4 Mesitylene and hexamethyldisilane partially evaporate under ambient conditions. Complete loss of mesitylene occurs upon chromatography.
2-Trimethylsilylmesitylene (7) slowly evaporates after extended periods in vacuo.
© 2007 NRC Canada

670
Can. J. Chem. Vol. 85, 2007
1
Scheme 4.
could be determined by H NMR spectroscopy prior to re-
moval of the solvent.5 Mesitylene was identified in the crude
1
product mixture by H NMR spectroscopy and by compari-
son of the GC retention time with that of an authentic sam-
ple. Compounds 7 and 8 could not be completely separated.
An authentic sample of 2-trimethylsilylmesitylene (7) was
prepared by treatment of bromomesitylene with BuLi, fol-
lowed by the addition of trimethylsilyl chloride, a variation
on the published procedure (11). Thus, 7 was unambigu-
ously identified in the mixture by comparison of the 1H
NMR spectroscopic data and of the GC retention time with
that of the prepared authentic sample.
1
The H NMR spectrum of germacyclobutene 8 contained
six signals: a singlet at 0.23 ppm assigned to two equivalent
trimethylsilyl groups, two singlets (6.85 and 6.70 ppm) as-
signed to two aryl-H’s, and three singlets at 2.19, 2.23, and
2.52 ppm, which were consistent with the presence of two
CH3–Ar groups and a CH2 group, respectively. Clearly, the
1
mesityl group is no longer symmetric. The H–29Si gHMBC
spectrum of 8 displayed a correlation between the signal as-
signed to the trimethylsilyl groups in the 29Si dimension and
1
the signal assigned to the CH2 group in the H dimension.
The highest-mass ion was located at m/z 338 in the mass
spectrum of 8. Moreover, the precise mass of m/z 338 agrees
well with the calculated mass of 8. The structure of 8 is
completely consistent with the spectroscopic data.
retention time and the 1H NMR chemical shifts with those of
an authentic sample (12).
The relative amount of germacyclobutene 8 in the product
mixture varied greatly depending on the length of the irradi-
ation time. The photolysis of germane 3 was monitored
hourly by GC; a steady increase in the relative amounts of
mesitylene, 7, and 8 was observed as 3 was consumed, up to
a given time period. Interestingly, prolonged irradiation of
the sample (24 h) led to a reduction in the relative amount of
8 and an increase in the relative amount of mesitylene (Ta-
ble 1). Photolysis of a mixture of 7 and 8, isolated from the
reaction mixture, showed complete loss of germacyclobutene
8 by 1H NMR spectroscopy and the appearance of
mesitylene by GC, while 7 remained unchanged. Thus,
germacyclobutene 8 is photolytically unstable and decom-
poses to produce mesitylene and other unidentified, non-
volatile products.
The addition of methanol to the reaction solution (prior to
exposure to the ambient atmosphere) at low temperature or
at room temperature led to the production of trace amounts
of dimesitylmethoxygermane (9), identified by comparison
1
of the H chemical shifts with the published data (13). No
evidence for the formation of the methanol adduct of
digermene 5, (Mes2Ge(OMe)GeHMes2), and hence, no evi-
dence for the formation of digermene 5 was observed. Co-
photolysis of germane 3 with methanol also produced
methoxygermane 9 in low yield in addition to mesityl-
methoxy(trimethylsilyl)germane, identified by GC–MS anal-
ysis (Scheme 4).
In an attempt to trap any transient germylenes, germane 3
was co-photolyzed with 2,3-dimethylbutadiene, a well-
known and efficient trapping agent for germylenes (8b, 14,
15). The solution remained clear and colourless throughout
the entire irradiation. The resulting product mixture con-
tained both 1,1-dimesityl-3,4-dimethyl-1-germacyclopent-3-
ene (10) and 1-mesityl-3,4-dimethyl-1-(trimethylsilyl)-1-
germacyclopent-3-ene (11) in addition to the previously ob-
served products (Scheme 5). There was also a noticeable in-
crease in the relative amount of 7 produced under these
conditions (Table 1).
A yellow solid precipitated from the crude product mix-
ture (exposed to air) upon the addition of methanol. The sig-
1
nals in the H NMR spectrum of this solid were very broad.
The chemical shifts of the signals were consistent with the
presence of both mesityl groups and trimethylsilyl groups.
The same material was also isolated by chromatography
from the product mixture in yields of 10–20 wt%. Elemental
analysis of the solid by Energy Dispersive X-ray analysis
(EDX) confirmed the presence of germanium and silicon in
the sample. These observations are consistent with the for-
mation of a polymer, which has been tentatively assigned the
structure (GeR2)n (R = Mes, Me3Si).
Germacyclopentene 10 was identified by comparison of
1
the GC retention time and the H NMR chemical shifts with
those of an authentic sample (4b, 16). Germacyclopentene
11 was characterized by NMR spectroscopy and mass spec-
trometry as part of a mixture of 11 with trace amounts of 7
Photolysis of germane 3 at 10 °C produced the same prod-
ucts in approximately the same ratios. Mes2GeH2 was also
identified in trace amounts based on a comparison of the GC
1
and 8. The most diagnostic feature of the H NMR spectrum
of 11 is the two sets of doublets at 1.90 and 2.23 ppm, as-
5 Supplementary data for this article are available on the journal Web site (canjchem.nrc.ca) or may be purchased from the Depository of Un-
published Data, Document Delivery, CISTI, National Research Council Canada, Ottawa, ON K1A 0S2, Canada. DUD 5172. For more in-
formation on obtaining material, refer to http://cisti-icist.nrc-cnrc.gc.ca/irm/unpub_e.shtml.
© 2007 NRC Canada

Hurni and Baines
671
Scheme 5.
diene reveals many similarities. The structures of com-
pounds 10 and 11 are analogous to those of compounds 12
and 13. Hexamethyldisilane and an aryltrimethylsilane were
observed in both reactions. Although the formation of
mesitylene is observed during the irradiation of 3, benzene
was not reported as a product of the photolysis of 1. Not sur-
prisingly, an analogous compound to germacyclobutene 8
was not formed during the photolysis of 1. Since dienes are
known triplet quenchers, and thus, may suppress radical for-
mation (8c), the co-photolysis of germane 1 with methanol
was also examined. The formation of both methoxy-
diphenylgermane (14) and 1,1,2,2-tetraphenylbis(trimethyl-
silyl)digermane (15) was observed under these conditions in
addition to other unidentified products (Scheme 6). Germane 14
was believed to be formed by the insertion of germylene 2
into the OH bond of methanol. On the other hand, the for-
mation of digermane 15 was rationalized by the coupling of
two Ph2(Me3Si)Ge radicals, which result from the homolysis
of a Ge–Si bond (8c). An analogous digermane was not ob-
served by 1H NMR spectroscopy or GC–MS upon the
photolysis of germane 3 in the presence of methanol. The
photolysis of germane 1 in the absence of a trapping agent
was not examined.
On the basis of the relative amounts of hexamethyldisilane
and 7 formed, the extrusion of a germylene from 3 appears
to be a minor reaction pathway. We propose a radical-based
mechanism to explain the formation of germacyclobutene 8
from the irradiation of dimesitylbis(trimethylsilyl)germane
(3). Homolysis of the Ge–Mes bond produces a germyl and
a mesityl radical. Abstraction of a benzylic hydrogen by the
mesityl radical results in the formation of a benzylic radical
and mesitylene. Germacyclobutene 8 is reasonably formed
by ring closure of the resulting 1,4-biradical (Scheme 7). We
note that, at low conversions, mesitylene and 8 are formed in
approximately equal amounts, consistent with this proposal
(Table 1). To provide some evidence for the proposed mech-
anism, 3 was irradiated for 5 h in THF-d8. After irradiation,
THF-d8 was removed and replaced with C6H6. A signal at
6.71 ppm, which we attribute to 1,3,5-(CH3)3C6H2D, was
1
signed to the non-equivalent H’s of the CH2 groups. A cor-
1
relation was observed between these two signals in the H
dimension of the 13C–1H gHSQC spectrum of 11 and one
signal in the 13C dimension at 27.59 ppm. The 1H–1H
gCOSY spectrum of 11 revealed a correlation between the
signals assigned to the CH2 groups and the signal assigned
to equivalent methyl groups, consistent with the structure of
11. The mass spectrum of one component of the crude prod-
uct mixture (separated by GC) exhibited a highest-mass ion
at m/z 347, corresponding to the molecular ion of 11. Fur-
thermore, the precise mass determination of m/z 347 agrees
with the calculated precise mass of 11.
2
observed in the H NMR spectrum of the product. The for-
mation of the deuterated mesitylene is consistent with a
cage-escaped mesityl radical, which, at least to some extent,
abstracts a deuterium from the solvent. We acknowledge that
the mesityl radical may result from homolysis of the
Ge–Mes bond of 3 or during the secondary photolysis of 8.
Discussion
Clearly, a quick evaluation of the results shows that ger-
mane 3 is not a clean source of germylene 4, and thus, is not
a viable precursor for the preparation of digermene 5. The
results can be better understood if we consider the previous
report of the steady-state irradiation of the corresponding
phenyl derivative, diphenylbis(trimethylsilyl)germane (1)
(8c). Co-photolysis of 1 with 2,3-dimethylbutadiene resulted
in the formation of germacyclopentenes 12 (major product)
and 13 (minor product) in addition to hexamethyldisilane
and trimethylsilylbenzene (Scheme 6) (8c). The products are
believed to be formed by extrusion of either diphenyl-
germylene (2) or phenyl(trimethylsilyl)germylene, with the
concomitant formation of the disilane or arylsilane, respec-
tively, followed by addition of the germylene to the diene
(8c). Examination of the structures of the products formed
during the photolyses of both 1 and 3 in the presence of the
On the other hand, homolysis of the Ge–Si bond could
produce a trimethylsilyl and a germyl radical. By following
a similar reaction pathway, the formation of germylenes 4
and 16 in addition to 7 and hexamethyldisilane can be ac-
counted for. However, the formation of hexamethyldisilane
and 7 by concerted elimination of 4 or 16 is also plausible
(Scheme 8) and, perhaps, more likely given that the relative
amount of 7 increased when 2,3-dimethylbutadiene was used
as a trapping agent.
Photolysis of germane 3 in the presence of either 2,3-
dimethylbutadiene or methanol gives 10 and 11 or 9, respec-
tively. This provides convincing evidence for the formation
of germylenes 4 and 16 during the reaction. In the absence
of a germylene trap, the germylenes may indeed couple to
produce digermenes. However, under the given reaction con-
© 2007 NRC Canada

672
Can. J. Chem. Vol. 85, 2007
Scheme 6.
Scheme 7.
Scheme 8.
held belief that the photolysis of diarylbis(trimethyl-
silyl)germanes is a useful method for the preparation of
tetraaryldigermenes. However, our results appear reasonable,
given that the observed products of the steady-state solution
photolyses of diphenylbis(trimethylsilyl)germane (1) demon-
strated that cleavage of the germanium–phenyl bond was oc-
curring, at least to some extent, during irradiation, since
products, formally derived from phenyl(trimethyl-
silyl)germylene, were isolated (8b, 8c). Previous studies of
the photolysis of dimesitylbis(trimethylsilyl)germane (3), in
which both dimesitylgermylene (4) and tetramesityl-
digermene (5) were characterized by UV–vis spectroscopy,
showed no evidence for the formation of additional products
or alternate reaction pathways (7b–7e, 9). It is unlikely that
the absorptions originally assigned to the germylene 4 and
digermene 5 are erroneous, as has been shown in the di-
phenyl case (8c, 15), since the assignments for the mesityl
system, both in a matrix and in solution, have been corrobo-
rated in at least three independent studies (7b–7d, 9, 17).
Possibly, at the low conversions used in the previous experi-
ments, the absorptions of potential radical species could not
be observed and (or) are too weak to be observed.
ditions, any digermenes formed apparently polymerize,
yielding a germanium-based polymer.
Clearly, our results indicate that the steady-state
photolysis of germane 3 in solution is not a feasible route
for the preparation of synthetic quantities of digermene 5.
The results were somewhat surprising, given the commonly
The low yields of germacyclopentenes 10 and 11 obtained
© 2007 NRC Canada

Hurni and Baines
673
during the photolysis of 3 in the presence of 2,3-dimethyl-
butadiene are most likely due to secondary photolysis of the
germacyclopentene rings (17). However, even at low con-
version, the irradiation still yields only relatively low ratios
of 10 and 11 (Table 1). Unfortunately, there are few re-
agents that are known to react quickly with dimesityl-
germylene (4) under photolytic conditions to give a stable
product, and thus, we were limited in our selection of
germylene trapping agents.
In summary, the steady-state irradiation of germane 3 in
solution is not a feasible route for the preparation of practi-
cal quantities of tetramesityldigermene (5), contrary to what
may be expected based on the numerous reviews written on
digermene chemistry (3). Thus, for tetramesityldigermene
(5), the thermolysis or photolysis of hexamesitylcyclotri-
germane (6) continues to be the best method for the prepara-
tion of this useful digermene. We are continuing our search
for alternate large-scale, practical syntheses of tetramesityl-
digermene (5).
the photolysis and reverted to yellow when the solution was
warmed to room temperature. Gas chromatograms of both
the reaction mixture and the headspace gas were recorded
prior to exposure to the ambient atmosphere. In some reac-
tions, methanol was added to the solution either at room
temperature or in the cold (dry ice – acetone bath). The sol-
vent was removed by rotary evaporation, yielding a yellow
oil. Hexamethyldisilane and mesitylene were removed in
vacuo. The resulting crude mixture was purified by prepara-
tive TLC (silica gel; hexanes) to give a polymer as a yellow
solid and a liquid mixture of 7 (11) and 8.5
2-Trimethylsilylmesitylene (7)
1H NMR (C6D6) δ: 6.73 (s, 2H, Mes CH), 2.34 (s, 6H,
Mes o-CH3), 2.12 (s, 3H, Mes p-CH3), 0.34 (s, 9H,
Si(CH3)3). 13C NMR (C6D6) δ: 144.12 (o-MesC), 138.34 (p-
MesC), 132.90 (i-MesC), 129.48 (Mes CH), 24.86 (Mes o-
CH3), 20.89 (Mes p-CH3), 3.67 (Si(CH3)3). 29Si NMR
(C6D6) δ: –6.1 (Si(CH3)3). GC–MS (m/z): 192 (M+, 25), 177
(M+ – CH3, 100), 162 (M+ – (CH3)2, 12), 149 (M+ – SiCH3,
10), 119 (Mes, 4), 73 (Si(CH3)3, 5).
Experimental
1,1-Bis(trimethylsilyl)-4,6-dimethyl-1-germadihydro-
benzocyclobutene (8)
General details
Unless otherwise indicated, all reactions were carried out
in flame-dried glassware under an inert atmosphere of argon
using a dual manifold vacuum line or prepared under a nitro-
gen atmosphere using an MBraun Labmaster 130 glovebox.
THF and hexanes were purged with nitrogen and then
passed through an alumina column (Innovative Technology
Inc., Newburyport, Massachusetts) prior to use. Trimethyl-
silyl chloride was distilled from calcium hydride prior to
use. 2,3-Dimethylbutadiene, BuLi, and 1-bromo-2,4,6-
trimethylbenzene were purchased from the Aldrich Chemi-
cal Co. and used without further purification. Chromatogra-
phy was carried out on conventional silica-gel preparative
plates. Dimesitylbis(trimethylsilyl)germane (3) was prepared
according to the previously reported procedure (7d).
NMR spectra were recorded on a Varian Mecury 400, a
Varian Inova 400, or a Varian Inova 600 NMR spectrometer.
The standards used were as follows: residual C6D5H
(7.15 ppm) for 1H NMR spectra, C6D6 central transition
(128.00 ppm) for 13C NMR spectra, and Me4Si as an exter-
nal standard (0.00 ppm) for 29Si spectra. Mass spectra were
recorded on a Finnegan MAT model 8400 mass spectrometer
with an ionizing voltage of 70 eV (reported in mass-to-
charge units (m/z) with ion identity and intensity relative to
the base peak in parentheses). GC analyses were performed
on a polydimethylsiloxane column using an Agilent 6850
Series GC. Photolyses were performed at 254 nm using a
Rayonet Photochemical Reactor (Southern New England
Co.) typically equipped with 10 bulbs. Samples were cooled
by circulating methanol through a vacuum-jacketed quartz
immersion well using an Endocal model ULT–70 low-
temperature external bath circulator.
1H NMR (C6D6) δ: 6.85 (s, 1H, CH), 6.70 (s, 1H, CH),
2.52 (s, 2H, GeCH2), 2.23 (s, 3H, 6-CH3), 2.19 (s, 3H, 4-
CH3), 0.23 (s, 18H, Si(CH3)3). 13C NMR (C6D6) δ: 153.77
(CH2–C), 140.59 (CH2–Ge–C), 140.04 (6-CH3C), 138.16 (4-
CH3C), 128.29 (5-CH), 124.96 (3-CH), 21.84 (4-CH3),
21.45 (6-CH3), 13.69 (CH2), 0.20 (Si(CH3)3). 29Si NMR
(C6D6) δ: –7.3 (Si(CH3)3). GC–MS (m/z): 338 (M+ 74Ge,
25), 323 (M+ – CH3, 30), 265 (M+ – Si(CH3)3, 37), 249
(M+ – Si(CH3)3 – CH2, 15), 73 (Si(CH3)3, 100). Exact mass
calcd. for C15H2870Ge28Si2: 334.0973; found: 334.0979.
Co-photolysis of dimesitylbis(trimethylsilyl)germane (3)
with 2,3-dimethylbutadiene
A clear, colourless solution of germane 3 (100 mg,
0.219 mmol) and 2,3-dimethylbutadiene (0.1 mL, excess),
dissolved in hexanes (8 mL), was irradiated at –70 °C for
24 h. The solution remained clear and colourless throughout
the irradiation. The solvent was removed by rotary evapora-
tion to yield a clear, slightly yellow liquid. The crude prod-
uct mixture was separated by chromatography (silica gel;
hexanes) to give a polymer, germacyclopentene 10, and a
mixture of 7, 8, and 11.5 Compounds 7, 8, and 11 were fur-
ther separated from the mixture using preparative TLC (sil-
ica gel; hexanes). Compound 7 was removed under high
vacuum to give 11, which remained contaminated with small
amounts of 8.
1-Mesityl-3,4-dimethyl-1-(trimethylsilyl)-1-germacyclopent-
3-ene (11)
1H NMR (C6D6) δ: 6.80 (s, 2H, Mes CH), 2.30 (s, 6H,
Mes o-CH3), 2.23 (d, 2H, CHH, J = 15 Hz), 2.17 (s, 3H,
Mes p-CH3), 1.90 (d, 2H, CHH, J = 15 Hz), 1.75 (s, 6H,
CH3), 0.13 (s, 9H, Si(CH3)3). 13C NMR (C6D6) δ: 142.95 (o-
Mes C), 137.39 (p-Mes C), 135.75 (i-Mes C), 131.04 (C=C),
128.44 (Mes CH), 27.59 (CH2), 24.83 (Mes o-CH3), 21.05
(Mes p-CH3), 19.32 (CH3), –1.07 (Si(CH3)3). 29Si NMR
(C6D6) δ: –10.9 (Si(CH3)3). EI-MS (m/z): 348 (M+ 74Ge,
Photolysis of dimesitylbis(trimethylsilyl)germane (3)
A clear, colourless solution of germane 3 (100 mg,
0.219 mmol), dissolved in hexanes or THF (8 mL), was
placed in a quartz Schlenk tube fitted with a septum. The so-
lution was photolyzed at –70 °C for 24 h; the colour of the
solution changed from light yellow to deep orange during
© 2007 NRC Canada

674
Can. J. Chem. Vol. 85, 2007
14), 266 (M+ – C6H10, 44), 193 (Mes74Ge, 28), 177 (Mes
Si(CH3)2, 100), 119 (Mes, 8), 73 (Si(CH3)3, 36). Exact mass
calcd. for C18H3070Ge28Si: 344.1360; found: 344.1366.
B: Condens. Matter, 68, 115436 (2003); (d) Y.-J. Xu, Y.-F.
Zhang, and J.-Q. Li. J. Phys. Chem. B, 110, 3197 (2006);
(e) M.A. Filler, J.A. van Deventer, A.J. Keung, and S.F. Bent.
J. Am. Chem. Soc. 128, 770 (2006); (f) J.-H. Cho, K.S. Kim,
and Y. Morikawa. J. Chem. Phys. 124, 024716 (2006).
6. (a) R. West. Angew. Chem., Int. Ed. Engl. 26, 1201 (1987);
Acknowledgements
(b) M. Weidenbruch. Coord. Chem. Rev. 130, 275 (1994);
(c) T.L. Morkin, T.R. Owens, and W.J. Leigh. In The chemis-
try of organic silicon compounds. Vol. 3. Edited by Z.
Rappoport and Y. Apeloig. John Wiley and Sons Ltd.,
Chichester. 2001. p. 949; (d) K.M. Baines and M.S. Samuel. In
Science of synthesis. Vol. 4. Edited by I. Fleming. Georg
Thieme Verlag, Stuttgart. 2002. p. 117; (e) M. Kira. J.
Organomet. Chem. 689, 4475 (2004); (f) H. Ottosson and P.G.
Steel. Chem. Eur. J. 12, 1576 (2006).
We thank the Natural Sciences and Engineering Research
Council of Canada (NSERC), The University of Western
Ontario, and the Ontario Photonics Consortium (OPC) for fi-
nancial support. We also thank Teck Cominco Ltd. for a
generous gift of GeCl4. Finally, we also thank a referee for a
useful suggestion.
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