Adducts of sila-, germa-, and stannaethenes Me2E=C(SiMe3)2 (E = Si, Ge, Sn) with anthracene: Syntheses, structures, thermolyses

Article abstract of DOI:10.1139/v00-095

The [4 + 2] cycloadducts of Me₂E=C(SiMe₃)₂ (E = Si, Ge, Sn) and anthracene are prepared by reaction of an excess of anthracene in benzene with the [2 + 2] cycloadduct of Me₂Si=C(SiMe3)2 and Ph₂C=NSiMe

Full text of DOI:10.1139/v00-095

1412
Adducts of sila-, germa-, and stannaethenes
Me2E=C(SiMe3)2 (E = Si, Ge, Sn) with anthracene:
syntheses, structures, thermolyses1
Nils Wiberg, Susanne Wagner, Sham-Kumar Vasisht, and Kurt Polborn
Abstract: The [4 + 2] cycloadducts of Me2E=C(SiMe3)2 (E = Si, Ge, Sn) and anthracene are prepared by reaction of
an excess of anthracene in benzene with the [2 + 2] cycloadduct of Me2Si=C(SiMe3)2 and Ph2C=NSiMe3 at 130°C,
with Me2Ge(OPh)-CLi(SiMe3)2 at 100°C, and with Me2SnBr-CNa(SiMe3)2 at 80°C, respectively. The mentioned ad-
ducts act as sources for the ethenes Me2E=C(SiMe3)2 above 100°C, the intermediate formation of which has been
demonstrated by trapping experiments with 2,3-dimethylbutadiene (formation of a [4 + 2] and an ene reaction product).
The half life time of the anthracene adducts with E = Si, Ge, and Sn in the presence of DMB (= 2,3-dimethylbutadiene)
in benzene on thermolysis at 130°C (first order reactions) is found to be 141, 12, and 0.3 h, respectively. In the
absence of DMB, thermolysis of the cycloadducts leads in benzene as reaction medium exclusively to the dimers of
the Me2E=C(SiMe3)2 intermediates. In toluene as reaction medium ene products of Me2E=C(SiMe3)2 are observed in
addition to the dimers. The ene products are not isolable as such, but only after migration of the Me2E–CH(SiMe3)2
substituents. The formed derivatives C6H5CH2EMe2CH(SiMe3)2 of toluene in part give a second ene reaction with
another Me2E=C(SiMe3)2 molecule. X-ray structure analyses of the mentioned sources in fact prove the latter to be
normal [4 + 2] cycloadducts of Me2E=C(SiMe3)2 and anthracene.
Key words: silaethene, germaethene, stannaethene, [4 + 2] anthracene adducts, [4 + 2] cycloadditions and reversions,
ene reactions, X-ray structure analyses.
Résumé : On a préparé les cycloadduits [4 + 2] du Me2E=C(SiMe3)2 (E = Si, Ge, Sn) avec l’anthracène en faisant
réagir un excès d’anthracène, en solution dans le benzène, avec respectivement le cycloadduit [2 + 2] du Me2Si=C(SiMe3)2
et le Ph2C=NSiMe3 à 130°C, avec le Me2Ge(OPh)-CLi(SiMe3)2 à 100°C et avec le Me2SnBr-CNa(SiMe3)2 à 80°C. À
des températures supérieures à 100°C, les produits mentionnés agissent comme sources d’éthènes Me2E=C(SiMe3)2
dont on a démontré la formation par des expériences de piégeage à l’aide de 2,3-diméthylbutadiène qui donne lieu à la
formation d’un produit d’addition [4 + 2] ainsi que d’un produit de réaction ène. On a trouvé que les temps de demi-
vie des adduits de l’anthracène avec E = Si, Ge et Sn en présence de DMB (= 2,3-diméthylbutadiène), en solution dans
le benzène, lors d’une thermolyse à 130°C (réactions du premier ordre) sont respectivement de 141, 12 et 0,3 h. En ab-
sence de DMB, la thermolyse des cycloadduits dans le benzène comme milieu réactionnel conduit exclusivement aux
dimères des intermédiaires Me2E=C(SiMe3)2. Lorsque le milieu réactionnel est le toluène, on observe aussi des produits
de réaction ène, en plus de la formation des dimères. Il n’est pas possible d’isoler les produits ène comme tels,
uniquement après la migration des substituants Me2E-CH(SiMe3)2. Une partie des dérivés qui se forment dans le
toluène, C6H5CH2EMe2CH(SiMe3)2, donne lieu à une deuxième réaction ène, avec une autre molécule
Me2E=C(SiMe3)2. Une analyse des structures déterminées par diffraction des rayons X pour les sources mentionnées
prouve en fait que ces derniers sont des cycloadduits [4 + 2] normaux des Me2E=C(SiMe3)2 avec l’anthracène.
Mots clés : silaéthène, germaéthène, stannaéthène, adduits [4 + 2] de l’anthracène, cycloadditions et
cycloréversions [4 + 2], réactions ène, détermination de structures par diffraction des rayons X.
Wiberg et al. 1420
Received July 8, 1999. Published on the NRC Research Press website on October 20, 2000.
This paper is dedicated to Professor A.G. Brook on the occasion of his 75th birthday.
N. Wiberg,2 S. Wagner, S.-K. Vasisht, and K. Polborn.3 Department Chemie der Universität München, Butenandtstr. 5–13 (Haus
D), D-81377 München, Germany.
1Compounds of silicon and homologues, part 130, and unsaturated compounds of silicon and homologues, part 55. Part 129:
N. Wiberg, T. Blank, A. Purath, G. Stößer, H. Schnöckel. Angew. Chem. Int. Ed. Engl. 38, 2563 (1999); Part 54: N. Wiberg,
H.-W. Lerner, S.-K. Vasisht, S. Wagner, K. Karaghiosoff, H. Nöth, W. Ponikwar. Eur. J. Inorg. Chem. 1211 (1999).
2Author to whom correspondence should be addressed: Telephone: +49(0)89-2180-7456. Fax: +49(0)89-2180-7865.
e-mail: Niw@cup.uni-muenchen.de
3X-ray structure analyses.
Can. J. Chem. 78: 1412–1420 (2000)
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Wiberg et al.
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Scheme 1. Generation of 1, 2, 3 by thermal salt elimination.
ethenes from 1·LiX, 2·LiX, and 3·LiX with appropriate
reactants, able to fix the unsaturated compounds at low tem-
peratures and able to set them free at slightly higher temper-
atures.
An example are the adducts 1·Ph2C=NSiMe3, which can
be generated from 1 (from 1·LiF) and benzophenonimine
Ph2C=NSiMe3 at room temperature via [2 + 2] and [4 + 2]
cycloadditions (Scheme 2, first equation). Above 60°C the
cycloadducts decompose reversibly into 1 and comparatively
unreactive5 Ph2C=NSiMe3 (8). Unfortunately it is impossible
to “store” 2 and 3 with Ph2C=NSiMe3. Meanwhile we suc-
ceeded in synthesizing the [4 + 2] cycloadducts 1a, 2a, and
3a from 1, 2, 3 and anthracene (a). They act as “stores” for
silaethene as well as germaethene and stannaethene, and are
able to decompose above 100°C via thermal cycloreversion
into the unsaturated compounds 1, 2, and 3 which dimerize
in a fast reaction (Scheme 2, second equation).
Syntheses of the anthracene adducts 1, 2, and 3
The adducts 1a, 2a, and 3a must be synthesized at higher
temperatures because of the low reactivity of the ethenes 1,
2, 3 towards anthracene. Due to the decreasing reactivity in
the order 3, 2, 1, the applied reaction temperature is higher
for 1 than for 2, and for 2 higher than for 3. The adduct 3a is
prepared from Me2SnBr–CBr(SiMe3)2 and sodium (forma-
tion of 3 via 3·NaBr, see Schemes 1 and 2) in the presence
of excess anthracene at 80°C using toluene as solvent (molar
ratio Me2SnBr–CBr(SiMe3)2:sodium:anthracene = 1:2:20;
benzophenone is added to the reaction mixture for activation
of sodium; nearly quantitative formation of 3a). Compound
2a can be prepared by adding a –50°C cold solution of
2·LiOPh in tert-butylbenzene to a 100°C hot solution of
anthracene (added in excess) in tert-butylbenzene (molar ra-
tio 2·LiOPh to anthracene = 1:2; ca. 50% yield of 2a besides
(2)2, see Schemes 1 and 2). The adduct 1a is synthesized by
heating a solution of 1·Ph2C=NSiMe3 and an excess of
anthracene in benzene at 130°C for 14 h (molar ratio
1·Ph2C=NSiMe3 to anthracene = 1:2, nearly quantitative for-
mation of 1a, see Scheme 2).
In this context it should be mentioned that the rate con-
stants for the formation of the anthracene adducts increase in
the order 1a < 2a < 3a (see above), as do the rate constants
for the thermal cycloreversions of the adducts, leading to 1,
2, 3 and anthracene (ratio of the rate constants about
1:10:100; see below). Thus, going from 1 over 2 to 3, both
activation energies for the formation of the source and for
the decomposition of the source are decreasing. Therefore,
the absolute reaction enthalpies (equivalent to the difference
in both activation energies) for the presumably exothermic
formation of the ”sources” are obviously very similar. In
contrast to 2a and 3a, the adduct 1a shows a low tendency
towards cycloreversion even at 130°C. Therefore, it is favor-
able to use the adducts 1·Ph2C=NSiMe3, 2a, and 3a as
”sources” for 1, 2, and 3 (5–7) to perform reaction studies
for sila-, germa-, and stannaethenes at temperatures between
100 and 130°C.
Introduction
In the past years we attempted to generate silaethene
Me2Si=C(SiMe3)2 (1), germaethene Me2Ge=C(SiMe3)2 (2)
and stannaethene Me2Sn=C(SiMe3)2 (3) as short-lived reac-
tion intermediates, which immediately dimerize to (1)2, (2)2,
and (3)2. If a solution of PhLi in ether is added to a cold so-
lution of Me2EX-CBr(SiMe3)2 (E = Si, Ge, Sn; X = Br, F,
OPh) in ether, 1, 2, and 3 will be formed (1–3). According
to Scheme 1, the compounds Me2EX-CBr(SiMe3)2 react by
exchange of bromine bonded to carbon for lithium; thus the
sila-, germa-, and stannaethene sources Me2EX-CLi(SiMe3)2
(1·LiX, 2·LiX, 3·LiX)4 are formed. The latter decompose via
thermal salt elimination to ethenes 1, 2, and 3. The reaction
rate is found to increase in the order 1·LiX < 2·LiX < 3·LiX
and depending on X in the order X = OPh < F < Br (1, 2, 3).
Thus, salt elimination takes place for 1·LiBr at –78°C dur-
ing hours (1), for 2·LiBr at –78°C during minutes (2), for
1·LiF at +8°C during hours (1), and for 2·LiOPh at –40°C
during one hour (2). The reactive intermediates 1, 2, and 3
react with their precursors Me2EX-CLi(SiMe3)2 via the in-
sertion products Me2EX-C(SiMe3)2-EMe2-CLi(SiMe3)2 to
(1)2, (2)2, and (3)2 (Scheme 1, (4)).
The intermediate formation of 1, 2, and 3 could be proved
by trapping experiments among others, with organic dienes
and enes (formation of Diels–Alder and ene reaction prod-
ucts (5–7)). Due to the high dimerization tendency (even
growing in the direction 1, 2, 3, see above) and the reduced
reactivity of dienes and enes at lower temperatures, the
cycloadditions and ene reactions have to be carried out with
an excess of the trapping reagent and not at too low reaction
temperatures (see Experimental).
The less reactive dienes and enes are by no means effec-
tive trapping reagents for 1, 2, and 3 even when the relevant
ethenes are released from more stable sources 1·LiX, 2·LiX,
and 3·LiX. In the latter case it is advantageous to use
“stores” of 1, 2, and 3, which are formed by reaction of the
4 The also possible (but unwanted) exchange of X bonded to silicon, germanium, or tin for phenyl under formation of Me2EPh–CBr(SiMe3)2
is only important for Me2EX–CBr(SiMe3)2 with X = Br at reaction temperatures above –78°C (E = Si, Ge) and at –78°C (E = Sn).
5 Ph2C=NSiMe3 slowly and irreversibly traps 1 by formation of the insertion product Ph2C=N–SiMe2-C(SiMe3)3 (8).
© 2000 NRC Canada

1414
Can. J. Chem. Vol. 78, 2000
Scheme 2. Generation of 1, 2, 3 by thermal cycloreversion.
Fig. 1. Kinetic (first order presentation) of the thermolyses of 3a
in the absence or presence of DMB (mol ratio 3a:DMB = 1:10)
in C6D6 at 130°C.
Fig. 2. Kinetic (first order presentation) of the thermolyses of
1a, 2a, and 3a in the presence of DMB (mol ratio adduct: DMB
= 1:10) in C6D6 at 130°C.
Thermolyses of 1a, 2a, and 3a
It is difficult to determine the reaction order and the rate
constants for the thermolysis of 1a, 2a, and 3a in benzene,
leading to dimers (1)2, (2)2, (3)2, and anthracene. The reason
for this fact is the increasing rate of the reverse reaction (that
is to say, the rate for the adduct formation from 1, 2, 3, and
anthracene) due to the increase of free anthracene in the re-
action mixture in the course of the reaction (Scheme 2, sec-
ond equation). If ln (c/co) (c = adduct concentration at time
t, co = sum of concentration of adduct and dimer) is plotted
against time t in the sense of a first order reaction, a graph
with a significant decrease in the ascent will be obtained in-
stead of a straight line (Fig. 1). If the decomposition of 1a,
2a, and 3a is carried out in the presence of a suitable trap-
ping reagent like DMB (= 2,3-dimethylbutadiene), which re-
moves the sila-, germa-, and stannaethene 1, 2, and 3 from
the adduct equilibrium (Scheme 2, second equation), the
thermolysis of the adducts takes place according to a first
order reaction as expected (Fig. 2). At the starting point the
ascents of first order plots of adduct thermolysis in the pres-
ence and the absence of DMB are similar (Fig. 1).
In the presence of DMB, the thermal cycloreversion reac-
tions of the adducts 1a, 2a, and 3a in benzene at 100–130°C
lead to [4 + 2] cycloadducts 4 and ene reaction products 5
(Scheme 3). Rate constants and half life times for these
thermolyses are shown in Table 1.
Using toluene as solvent instead of benzene for the 130°C
thermolyses of 1·Ph2C=NSiMe3, 2a, and 3a; the ene prod-
ucts of 1, 2, and 3 with toluene are formed to our surprise,
together with the dimers (1)2, (2)2, and (3)2. The highly reac-
tive compounds 1, 2, and 3 force the chemically quite
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Wiberg et al.
1415
Scheme 4. Thermolyses of 1a, 2a, 3a in toluene (in addition to
Scheme 3. Thermolyses of 1a, 2a, 3a in the presence of DMB.
8 and 10, the dimers (1)2, (2)2, (3)2 are formed).
Table 1. Rate constants k and half life times τ1/2 of the
thermolyses of 1a, 2a, and 3a in C6D6 at variable temperatures
in the presence of DMB (mol ratio adducts: DMB = 1:10).
k (s–1)
τ1/2 (h)
Table 2. Relative yields of dimers (1)2, (2)2, (3)2, and products
8, 10 [mole %] after complete thermolysis of 0.08 molar solu-
tions of 1·Ph2C=NSiMe3, 2a and 3a in toluene at 130°C.
1a
2a
3a
(130°C)
(130°C)
(130°C)
(100°C)
1.37 × 10–6
1.60 × 10–5
6.60 × 10–4
2.44 × 10–5
141
12
0.3
7.9
Sources
T (°C)
t (d)
dimers
8
10
1·Ph2C=NSiMe3
2a
3a
130
130
130
9
44
1
37%
12%
83%
57%
49%
13%
6%
39%
4%
unreactive toluene to act as an ene reagent. Certainly 1, 2,
and 3 (generated from 1·Ph2C=NSiMe3, 2a, 3a) first form
the ene products 6 (Scheme 4). These are only intermedi-
ates, which finally react to the toluene derivatives 8 and 10.
The products 8 are obtained from 6 via rearrangement of
Me2E–CH(SiMe3)2 groups, whereas there are three possible
ways that may lead to 10 as the product (Scheme 4):
(i) Products 6 rearrange to the non-isolable products 7 (ac-
cording to experimental studies a rearrangement of 8 to 7
does not occur), whereby the latter reacts with 1, 2, or 3 via
ene products 9 to isolable compounds 10 (as no traces of
products 7 were found, reaction path (i) is less probable).
(ii) Products 10 are formed by reaction of 8 with 1, 2, or 3
via the ene products 11 (according to preliminary studies
these reactions do not occur, therefore reaction path (ii) is
less probable). (iii) Products 6, which certainly are very re-
active intermediates, form directly with 1, 2, or 3 the ene
products 10.
Table 2 shows the yields of the products after complete
thermolysis of 1·Ph2C=NSiMe3, 2a, and 3a at 130°C in tolu-
ene. It reveals that if complete educt thermolysis needs a
long time, a decrease in the yields of dimers (1)2, (2)2, and
(3)2 will be observed. This fact can be explained as follows:
the stationary concentration of intermediates 1, 2, and 3 de-
creases with decreasing rate for the decomposition of the
sources 1a, 2a, 3a. As a consequence, the ene reactions of 1,
2, and 3 with toluene (which take place according to a first
order reaction) are more dominant than the dimerization re-
actions (which represents a second order reaction). This im-
portant result indicates that the formation of (1)2, (2)2, and
(3)2 — via the thermal cycloreversion of 1·Ph2C=NSiMe3,
1a, and 2a, respectively — takes place through a direct
dimerization of 1, 2, and 3 (compare however the formation
of dimers in the course of salt elimination of 1·LiX,
Scheme 1).
Of course, both the ratio of yields of dimers to ene reac-
tion products and the ratio of yields of 8 to 10, in addition
depend on the relative reactivity of ethenes 1, 2, or 3 to-
wards themselves, toluene and toluene derivatives 6, 7, and
8, respectively. Obviously, on going from toluene to 6, 7, or
8, the ene reactivity has significant effect in the case of the
germaethene 2, a smaller effect in the case of the
stannaethene 3 and the smallest effect in the case of the
silaethene 1, regarding the ratio of yields of 8 to 10 (Ta-
ble 2). Nevertheless, for direct formation of 10 from 6 – be-
ing the most favoured reaction course – the stationary
concentrations of 1, 2, or 3 are important, as the transforma-
tions of 6 into 8 and 10, respectively, are zero order in the
first and first order in the second case concerning the men-
tioned ethenes.
Structures of 1a, 2a and 3a
The anthracene adducts 1a, 2a, and 3a precipitate from
benzene as colourless, moisture- and air-insensitive crystals,
which melt at 144, 136, and 140°C, respectively, and are
thermolabile above 100°C. Figure 3 shows their molecular
structure in the crystal determined by X-ray structure analysis.
© 2000 NRC Canada

1416
Can. J. Chem. Vol. 78, 2000
Table 3. Selected bond distances (Å) and angles (°) for 1a, 2a, and 3a (for atom numbering see Fig. 3). The unit cells of the adducts
contain one, three, or two independent molecules in the case of 1a, 2a, or 3a.
1a, 2a, 3a
E = Si
E = Ge
E = Sn
E—C9
E—C1
C1—C2
E—C17
E—C16
Si1—C1
Si2—C1
C9—C8
1.907(2)
1.905(2)
1.612(2)
1.875(3)
1.873(3)
1.923(2)
1.923(2)
1.498(3)
1.386(3)
1.515(3)
1.515(3)
1.392(4)
1.496(4)
104.4(2)
117.8(1)
117.6(1)
111.1(2)
105.9(1)
99.4(1)
109.1(1)
114.1(1)
105.6(1)
107.3(2)
115.2(2)
115.5(2)
103.8(2)
114.7(2)
115.8(2)
1.999(5), 1.982(5), 1.993(5)
2.001(4), 2.001(5), 1.998(5)
1.603(6), 1.619(7), 1.619(6)
1.956(6), 1.961(6), 1.947(6)
1.940(6), 1.954(6), 1.962(7)
1.911(5), 1.921(6), 1.933(5)
1.930(5), 1.914(5), 1.915(5)
1.506(7), 1.501(7), 1.492(7)
1.389(7), 1.385(7), 1.402(7)
1.517(7), 1.514(7), 1.509(7)
1.524(6), 1.522(7), 1.516(6)
1.391(7), 1.386(7), 1.391(7)
1.502(7), 1.509(7), 1.501(7)
104.6(3), 104.5(3), 104.4(4)
117.8(2), 117.1(3), 118.0(3)
118.2(2), 119.0(3), 117.8(3)
113.3(3), 111.4(3), 107.6(3)
104.8(3), 107.0(3), 114.4(3)
97.5(2), 97.3(2), 97.3(2)
108.4(2), 111.7(2), 111.9(2)
112.8(2), 109.2(3), 110.3(2)
104.0(3), 105.1(3), 104.8(3)
107.8(4), 108.0(4), 108.7(4)
115.6(4), 115.7(5), 115.5(4)
115.6(4), 116.2(5), 115.7(4)
105.0(4), 104.9(4), 105.2(4)
115.4(4), 115.7(5), 116.6(4)
115.9(4), 115.8(5), 115.0(4)
2.194(4), 2.199(4)
2.201(3), 2.206(3)
1.604(5), 1.621(4)
2.147(5), 2.141(5)
2.133(4), 2.149(5)
1.897(3), 1.911(3)
1.914(4), 1.900(4)
1.498(5), 1.491(5)
1.409(5), 1.399(5)
1.523(5), 1.512(5)
1.521(5), 1.521(5)
1.401(5), 1.397(5)
1.501(5), 1.497(5)
107.1(2), 104.8(3)
117.9(2), 118.8(2)
117.3(2), 120.5(2)
115.6(2), 109.9(2)
106.2(2), 109.9(2)
91.7(1), 91.7(1)
108.8(2), 110.3(2)
108.6(1), 108.7(2)
105.4(2), 105.0(2)
107.7(3), 109.7(3)
117.4(3), 116.6(3)
116.4(3), 117.4(3)
103.7(3), 104.7(3)
117.0(3), 117.0(3)
117.2(3), 116.7(3)
C8—C3
C3—C2
C2—C15
C15—C10
C10—C9
C17-E-C16
C16-E-C1
C17-E-C1
C16-E-C9
C17-E-C9
C1-E-C9
E-C1-Si1
E-C1-Si2
E-C1-C2
C8-C9-C10
C3-C8-C9
C2-C3-C8
C15-C2-C3
C10-C15-C2
C9-C10-C15
Fig. 3. View of the molecular structures of 1a, 2a, and 3a (E =
Si, Ge, Sn) in the crystal (ORTEP plot; 25% thermal probability
ellipsoids; local symmetry of the molecules ≈ cn) (for clarity hy-
drogen atoms are not shown) and atom numbering scheme. For
selected bond lengths and angles see Table 3.
of the roof are planar (each angular sum at C3, C8, C10, and
C15 is about 360°). The ridge is bridged with a Me2E–
C(SiMe3)2 group (Fig. 4). The exchange of silicon for ger-
manium and of germanium for tin practically doesn’t change
most of the bond lengths and angles in 1a, 2a, and 3a, ex-
cept the E—C bond length and C-E-C bond angles (Fig. 5).
Experimental
All experiments were carried out in the absence of air and
moisture. According to literature procedures were prepared:
1·Ph2C=NSiMe5 (8), Me2Ge(OPh)-CBr(SiMe3)2 (2),
Me2SnBr-CBr(SiMe3)2 (3). The NMR-spectra were recorded
on multinuclear instruments Jeol GSX 270 and Jeol EX 400.
The product seperation was done by preparative HPLC on
Waters 600 (column 21.2 mm × 250 mm; Zorbax C18; flow
21 mL/min.; detection: UV at 230 nm and refractometer).
Mass spectrometry (EI): Varian CH7; found and calculated
isotopic patterns were in perfect agreement.
Thermolyses of 1·LiBr, 2·LiBr, 3·LiBr in the presence
of DMB at low temperatures
To a solution of x mmol Me2EBr-CBr(SiMe3)2 and
y mmol DMB in ether, x mmol PhLi in ether are added
dropwise at temperature T (Table 4). After warming up to
ambient temperature the types and yields of products formed
In Table 3, selected bond length and angles are given. It is
evident from Fig. 3 that the anthracene part is bent roof-
shaped at the central C-atoms in 1a, 2a, and 3a. Both parts
1
were identified by H NMR (Table 4) and by comparison of
© 2000 NRC Canada

Wiberg et al.
1417
Table 4. Reactions of Br/Br (Me2EBr–CBr(SiMe3)2, E = Si, Ge, Sn) with PhLi in the presence of DMB at
low temperatures T; (dimers = (1)2, (2)2, (3)2, Ph/Br = Me2EPh–CBr(SiMe3)2, for 4 and 5 see Scheme 3;
% = reaction yields).
Me2EBr-CBr(SiMe3)2, E =
Si
Ge
Sn
Br/Br (mmol)
DMB (mmol)
Et2O (mL)
T (°C)
Dimers (%)
4 (%)
0.45
13.5
9
–78
14
75
11
—
0.27
0.27
10
–78
80
16
4
0.27
0.27
10
–40
7
54
11
28
0.76
8.8
25
–40
6
56
5
33a
3.2
32
10
–78
60
10
—
30
3.2
64
10
–40
19
18
—
63
5 (%)
Ph/Br (%)
—
anBuLi was used instead of PhLi, therefore Me2GeBu–CBr(SiMe3)2 (2) was formed.
Fig. 4. Projection of 1a, 2a, and 3a in the direction of the mid-
dle C atoms of the anthracene parts of the molecules. Dihedral
and folding angles in (°) (first data for E = Si, second for E =
Ge and third for E = Sn, see the legend of Table 3).
Fig. 5. Projection of 1a, 2a, and 3a in the direction of the nor-
mals of the two benzene rings. Bond distances in (Å) and bond
angles in (°) (first data for E = Si, second for E = Ge and third
for E = Sn, mean values in case of 2a and 3a, see Table 3).
the NMR data with those of authentic compounds (dimers of
1, 2, 3, Diels-Alder adducts 4, ene reaction products 5, and
Me2EPh-CBr(SiMe3)2 (1–3)).
SiMe3), 12.51 (Si3C), 43.27 (SiCH), 50.68 (CCH),
124.5/125.4/126.0/126.4 (8 =CH-), 143.4/143.5 (4 =C<).
29Si NMR (C6D6, eTMS) δ: 1.68 (SiMe2), 3.16 (2 SiMe3).
MS: m/z 394 (M+). Anal. calcd. for C23H34Si3: C 69.98, H
8.68; found: C 69.54 H 8.46.
Synthesis of 1a
A solution of 0.132 g (0.28 mmol) 1•Ph2C=NSiMe3 and
0.100 g (0.56 mmol) anthracene in 2.4 mL benzene was
1
heated for 14 h at 130°C. According to H NMR, 94% 1a,
2% (1)2 and 4% Ph2C=N-SiMe2-C(SiMe3)3 were formed.
The reaction mixture was treated with 0.5 mL MeOH –
1.0 mL tBuOMe, and separation was done by HPLC using
MeOH and tBuOMe as mobile phase (0–8 min: 100%
MeOH, 8–20 min with gradient to 80% MeOH – 20%
tBuOMe, 20–25 min with gradient to 100% MeOH). Reten-
tion time: 5.1 min (anthracene), 9.2 min (1a), 14.7 min
(Ph2C=N–SiMe2–C(SiMe3)3).
Synthesis of 2a
A solution of 1.17 mmol Me2Ge(OPh)–CLi(SiMe3)2 in
tBuC6H5 (synthesized by reaction of 1.17 mmol
Me2Ge(OPh)-CBr(SiMe3)2 with 1.17 mmol nBuLi in Et2O at
–78°C, ether replaced by tBuC6H5 at –78°C) at –50°C, was
added dropwise (over a period of one hour) to a solution of
0.456 g (2.56 mmol) anthracene in 20 mL tBuC6H5, which
1
9,10-Dihydro-9,10-[11,11-dimethyl-12,12-bis(trimethylsilyl)-
11-silaethano]-anthracen (1a): colourless solid, mp 144°C.
1H NMR (C6D6, iTMS) δ: –0.083 (s; 2 SiMe3), 0.085 (s;
SiMe2), 3.51 (s, SiCH), 4.56 (s; CCH), 6.90–7.10 (m; =CH).
13C{1H} NMR (C6D6, iTMS) δ: 1.91 (SiMe2), 4.52 (2
was heated to 100°C. According to H NMR, 2a and (2)2
were formed in the molar ratio 1.2:1, besides Me2GeR–
CH(SiMe3)2 (R = OPh, nBu) (2). The reaction mixture was
allowed to cool to room temperature, 0.3 mL Me3SiCl (to
form Me3SiOPh of LiOPh) were added, and all volatile
© 2000 NRC Canada

1418
Can. J. Chem. Vol. 78, 2000
fractions (tBuC6H5, Me3SiCl, Me3SiOPh) were condensed in
oil pump vacuum at 30°C. The residue was dissolved in
8 mL benzene and insoluble LiBr was removed. The solu-
tion was concentrated to 4 mL, and 1.5 mL MeOH – 2.5 mL
tBuOMe were added. Some hours later anthracene and (2)2
had crystallized partially and were removed by decantation.
The further separation of the reaction mixture was done by
HPLC using MeOH as mobile phase. Retention times:
6.0 min (anthracene), 11.4 min (2a), 41.6 min ((2)2).
21 min: 57% 3a, 43% (3)2. In the further course of the reac-
tion (3)2 precipitates.
Thermolysis of anthracene adducts 1a, 2a, 3a in
presence of DMB at 100°C and 130°C
Sealed NMR tubes containing 0.016 g (0.04 mmol) of 1a
and 0.045 mL (0.40 mmol) DMB in 0.5 mL C6D6 (A);
0.018 g (0.04 mmol) of 2a and 0.045 mL (0.40 mmol) DMB
in 0.6 mL C6D6 (B); 0.029 g (0.06 mmol) of 3a and
0.068 mL (0.60 mmol) DMB in 0.6 mL C6D6 (C); 0.029 g
(0.06 mmol) of 3a and 0.081 mL (0.72 mmol) DMB in
0.6 mL C6D6 (D); were heated at 130°C (A, B, C) and
100°C (D). The progress of the reaction was monitored by
9,10-Dihydro-9,10-[11,11-dimethyl-12,12-bis(trimethylsilyl)-
11-germaethano]-anthracene (2a): colourless solid, mp
136°C. 1H NMR (C6D6, iTMS) δ: –0.102 (s; 2 SiMe3), 0.232
(s; GeMe2); 3.66 (s; GeCH), 4.69 (s; CCH), 6.90–7.10 (m;
=CH–). 13C{1H} NMR (CDCl3, iTMS) δ: 2.19 (GeMe2),
3.96 (2 SiMe3), 13.57 (Si2C), 42.38 (GeCH), 50.19 (CCH),
124.0/124.5/125.6/126.5 (8 =CH–), 142.1/143.2 (4 =C<).
29Si NMR (CDCl3, eTMS) δ: 3.49 (2 SiMe3). MS: m/z 440
(M+).
1
1H NMR. The intensities of the H NMR signals as resulting
from the evaluation of the integrals were determined for 1a,
2a, 3a, 4, and 5. To determine the reaction order, –ln (c/c0)
1
was plotted against time t, with c being the H NMR signal
area of anthracene adducts and c0 being the sum of 1H NMR
signal areas of anthracene adducts + 4 + 5. For the plots, rate
constants, and half life times see Table 1 and Fig. 2.
Synthesis of 3a
A mixture of 0.23 g (10.0 mmol) sodium metal, 9.10 g
(50.0 mmol) benzophenone and 17.80 g (100 mmol)
anthracene in 200 mL toluene was stirred and heated to
100°C for 1/2 hour to obtain a deep blue coloured solution.
The reaction mixture was cooled to 80°C and a solution of
2.33 g (5.00 mmol) of Me2SnBr-CBr(SiMe3)2 in 50 mL tolu-
Thermolysis of 1·Ph2C=NSiMe3 in toluene
A solution of 0.075 g (0.16 mmol) 1·Ph2C=NSiMe3 in
2.0 mL toluene was heated at 130°C for 9 d in a sealed,
evacuated NMR tube. The 1H NMR spectrum indicated
complete conversion to Ph2C=N–SiMe2–C(SiMe3)3 (59%),
(1)2 (15%), 8 (23%), and 10 (3%). After removal of volatile
constituents, the residue was treated with 1.0 mL tBuOMe –
0.5 mL MeOH and separation was done by HPLC using
MeOH as mobile phase. Retention times: 10.2 min (8),
18.1 min (Ph2C=N–SiMe2–C(SiMe3)3), 34.4 min (10), and
44 min ((1)2).
1
ene was added over a period of two hours. According to H
NMR 88% 3a, 10% (3)2 and 2% 8 were formed. The reac-
tion mixture was cooled down to 0°C, unsoluble compounds
(NaBr, anthracene) were separated, solvent was removed and
benzophenone was sublimed out at 60°C and 10–3 mbar over
2 days. The residue was treated with 5 mL MeOH – 10 mL
tBuOMe and separation of the reaction mixture was done by
HPLC using MeOH and tBuOMe as mobile phase (0–8 min:
100% MeOH, 8–14 min with gradient to 80% MeOH – 20%
tBuOMe, 20–25 min with gradient to 100% MeOH). Reten-
tion times: 5.0 min (anthracene), 8.4 min (3a), and 18.5 min
((3)2).
Benzyldimethylsilyl-bis(trimethylsilyl)methane (8, E = Si):
colourless liquid. 1H NMR (C6D6, iTMS) δ: –0.750 (s,
Si3CH), 0.078 (s; 2 SiMe2), 0.148 (s; 2 SiMe3), 2.17 (s;
SiCH2), 6.99–7.15 (m; o-/p-/m-CH of Ph). 13C{1H} NMR
(C6D6, iTMS) δ: 0.645 (SiMe2), 2.28 (Si3C), 3.35 (2 SiMe3),
28.76 (SiCH2), 124.3/128.2/128.5/140.4 (p-/o-/m-/i-C of Ph).
29Si NMR (C6D6, eTMS) δ: –0.15 (2 SiMe3), 0.68 (SiMe2).
MS: m/z 308 (M+).
9,10-Dihydro-9,10-[11,11-dimethyl-12,12-bis(trimethylsilyl)-
11-stannaethano]-anthracene (3a): colourless solid, mp
140°C. 1H NMR (C6D6, iTMS) δ: –0.098 (s; 2 SiMe3), 0.166
(s; SnMe2), 3.92 (s, SnCH), 4.90 (s; CCH), 6.83–7.15
(m; =CH). 13C{1H} NMR (C6D6, iTMS) δ: – 4.18 (SnMe2),
3.87 (2 SiMe3), 16.93 (SnSi2C), 39.33 (SnCH), 50.60
(CCH), 123.6/123.8/125.7/127.3 (8 =CH-), 141.0/143.5
(4 =C<). 29Si NMR (C6D6, eTMS) δ: = 3.01 (2 SiMe3).
119Sn NMR (C6D6, eTMS) δ: = –3.14 (SnMe2). MS: m/z 486
(M+). Anal. calcd. for C23H34Si2Sn: C 57.06, H 7.03; found:
C 56.73 H 6.82.
1-[1,1-Dimethyl-2,2-bis(trimethylsilyl)-1-silaethyl]-2-[2,2-
dimethyl-3,3-bis(trimethylsilyl)-2-silapropyl]-benzene (10,
1
E = Si): colourless solid, mp 96°C. H NMR (C6D6, iTMS)
δ: = –0.458 (s, Si3CH), –0.041 (s, Si3CH), 0.148 (s; 2 SiMe3),
0.199 (s; 2 SiMe3), 0.199 (s; SiMe2), 0.521 (s; SiMe2), 2.56
(s; SiCH2), 7.06 (t; J = 7 Hz; 1 CH of Ph), 7.12 (d; J = 7 Hz;
1 CH of Ph), ? (1 CH of Ph; hidden by solvent), 7.50 (d; J =
1
7 Hz; 1 CH of Ph). H NMR (d6-acetone, iTMS) δ: –0.410
(s, Si3CH), –0.105 (s, Si3CH), 0.064 (s; 2 SiMe3), 0.179 (s;
2 SiMe3), 0.105 (s; SiMe2), 0.450 (s; SiMe2), 2.44 (s;
SiCH2), 7.04 (t; J = 7 Hz; 1 CH of Ph), 7.09 (d; J = 7 Hz; 1
CH of Ph), 7.21 (t; J = 7 Hz; 1 CH of Ph), 7.42 (d; J = 7 Hz;
1 CH of Ph). 13C{1H} NMR (CDCl3, iTMS) δ: 1.71 (SiMe2),
3.25 (SiMe2), 3.44 (2 SiMe3), 3.61 (2 SiMe3), 3.18 (Si3C),
4.58 (Si3C), 29.53 (SiCH2), 123.4/128.5/128.5/135.2 (=CH
of Ph), 139.3/146.4 (=C< of Ph). 29Si NMR (C6D6, eTMS)
δ: –4.79 (SiMe2), 0.15 (2 SiMe3), 0.69 (2 SiMe3), 1.84
(SiMe2). MS: m/z 509 (M+ – CH3).
Thermolysis of 3a in benzene at 130°C
A sealed NMR tube, containing 0.029 g (0.06 mmol) of
3a in 0.6 mL C6D6, was heated at 130°C. The progress of
1
the reaction was monitored by H NMR after 10, 15, 17,
1
21 min. The intensities of the H NMR signals as resulting
from the evaluation of the integrals were determined for 3a
and the dimer of 3 as follows: 10 min: 72% 3a, 28% (3)2;
15 min: 64% 3a, 36% (3)2; 17 min: 62% 3a, 38% (3)2;
© 2000 NRC Canada

Wiberg et al.
1419
Table 5. Summary of crystal data collections for 1a, 2a, and 3a.
1a
2a
3a
Empirical formula
Formula weight (g mol–1)
C23H34Si3
394.77
C23H34GeSi2
439.27
C23H34SnSi2
483.36
Temperature (K)
293(2)
293(2)
293(2)
Wavelength (Å), (MoKα)
0.71073
monoclinic
Cc
0.71073
triclinic
P-1
0.71069
monoclinic
P21/n
Crystal system
Space group
a (Å)
b (Å)
c (Å)
11.752(2)
14.575(2)
13.6361(13)
90.000(10)
93.585(11)
90.000(14)
2331.0(6)
4
9.5615(8)
15.430(2)
25.350(4)
89.063(14)
81.005(14)
73.980(11)
3549.2(9)
6
16.621(2)
9.6809(14)
30.447(6)
90.000(14)
101.979(13)
90.000(12)
4792.3(13)
8
α (°)
β (°)
γ (°)
Volume (Å3)
Z
Density (calculated) (Mg/m3)
Absorption coefficient (mm–1)
F (000)
1.125
0.209
856
1.233
1.401
1392
1.340
1.171
1984
Crystal size (mm)
Theta range for data collection (°)
Index ranges
0.53 × 0.43 × 0.13
2.23 to 25.01
–13 ≤ h ≤ 13,
–17 ≤ k ≤ 0,
–16 ≤ l ≤ 16
6225
0.53 × 0.47 × 0.20
2.16 to 23.97
–10 ≤ h ≤ 10,
–17 ≤ k ≤ 0,
–28 ≤ l ≤ 28
11551
0.53 × 0.37 × 0.27
2.45 to 24.97
–19 ≤ h ≤ 0,
–11 ≤ k ≤ 0,
–35 ≤ l ≤ 36
8717
Reflections collected
Independent reflections
Max. and min. transmission
Data / restraints / parameters
Goodness-of-fit on F2
R1 (I > 2σ(I))
4092
11078
8402
0.9993 and 0.9474
4092 / 2 / 243
1.064
0.0353
0.0882
0.9945 and 0.7262
11078 / 0 / 727
1.103
0.0535
0.1148
0.9987 and 0.9525
8402 / 6 / 485
1.113
0.0345
0.0818
wR2
Largest diff. peak and hole (e/Å3)
0.193 and –0.180
0.862 and –0.665
0.718 and –0.636
δ: –0.326 (s, Si2CH), –0.090 (s, Si2CH), 0.055 (s; 2 SiMe3),
0.152 (s; 2 SiMe3), 0.211 (s; GeMe2), 0.560 (s; GeMe2),
2.53 (s; GeCH2), 7.04 (t; J = 7 Hz; 1 CH of Ph), 7.06 (d; J =
7 Hz; 1 CH of Ph), 7.20 (t; J = 7 Hz; 1 CH of Ph), 7.37 (d;
J = 7 Hz; 1 CH of Ph). 13C{1H} NMR (C6D6, iTMS) δ: 1.23
(GeMe2), 2.89 (GeMe2), 3.15 (2 SiMe3), 3.19 (2 SiMe3),
3.50 (GeSi2C), 4.41 (GeSi2C), 30.30 (GeCH2),
124.1/128.4/128.5/134.3 (=CH of Ph), 141.1/146.0 (=C< of
Ph). 29Si NMR (C6D6, eTMS) δ: 0.76 (2 SiMe3), 1.28 (2
SiMe3). MS: m/z 509 (M+ – SiMe3 – 2CH4 – H2).
Thermolysis of 2a in toluene
A solution of 0.026 g (0.06 mmol) 2a in 0.75 mL toluene
was heated at 130°C for 44 d in a sealed, evacuated NMR
1
tube. The H NMR spectrum indicated complete conversion
to (2)2 (12%), 8 (49%), and 10 (39%). After removal of vol-
atile constituents, the residue was treated with 1.0 mL
tBuOMe – 0.5 mL MeOH and separation was done by
HPLC using MeOH as mobile phase. Retention times:
10.1 min (8), 34.2 min (10), and 41.0 min ((2)2).
Benzyldimethylgermyl-bis(trimethylsilyl)methane (8, E = Ge):
colourless liquid. 1H NMR (C6D6, iTMS) δ: –0.659 (s, Si2CH),
0.137 (s; 2 SiMe3), 0.185 (s; GeMe2), 2.30 (s; GeCH2),
6.99–7.15 (m; o-/p-/m-CH of Ph). – 13C{1H} NMR (CDCl3,
iTMS) δ: 0.244 (GeMe2), 2.80 (GeSi2C), 3.15 (2 SiMe3),
28.52 (GeCH2), 123.9/127.9/128.1/141.0 (p-/o-/m-/i-C of
Ph). 29Si NMR (C6D6, eTMS) δ: 0.53 (2 SiMe3). MS: m/z
339 (M+ – CH3).
Thermolysis of 3a in toluene
A solution of 0.097 g (0.200 mmol) 3a in 2.5 mL toluene
was heated at 130°C for 26 h in a sealed, evacuated NMR
1
tube. The H NMR spectrum indicated complete conversion
to (3)2 (83%), 8 (13%), and 10 (4%). After removal of vola-
tile constituents, the residue was treated with 1.0 mL
tBuOMe/0.5 mL MeOH, and separation was done by HPLC
using MeOH as mobile phase. Retention times: 10.7 min (8),
36.6 min ((3)2), and 40.4 min (10).
1-[1,1-Dimethyl-2,2-bis(trimethylsilyl)-1-germaethyl]-2-
[2,2-dimethyl-3,3-bis(trimethylsilyl)-2-germapropyl]-ben-
zene (10, E =Ge): colourless solid. H NMR (C6D6, iTMS)
1
δ: –0.374 (s, Si2CH), –0.037 (s, Si2CH), 0.142 (s; 2 SiMe3),
0.182 (s; 2 SiMe3), 0.287 (s; GeMe2), 0.620 (s; GeMe2),
2.64 (s; GeCH2), 7.04 (t; J = 7 Hz; 1 CH of Ph), 7.07 (d; J =
7 Hz; 1 CH of Ph), ? (1 CH of Ph; hidden by solvent), 7.44
Benzyldimethylstannyl-bis(trimethylsilyl)methane (8, E = Sn):
colourless liquid. 1H NMR (C6D6, iTMS) δ: –0.672 (s, Si2CH),
0.108 (s; 2 SiMe3), 0.289 (s; SnMe2), 2.35 (s; SnCH2), 6.99–
7.29 (m; o-/p-/m-CH of Ph). 13C{1H} NMR (CDCl3, iTMS)
δ: –6.85 (SnMe2), 0.13 (SnSi2C), 3.27 (2 SiMe3), 23.19
1
(d; J = 7 Hz; 1 CH of Ph). H NMR (d6-acetone, iTMS)
© 2000 NRC Canada

1420
Can. J. Chem. Vol. 78, 2000
(SnCH2), 123.4/127.0/128.4/142.7 (p-/o-/m-/i-C of Ph). 29Si
NMR (C6D6, eTMS) δ: 0.33 (2 SiMe3). 119Sn NMR (C6D6,
eTMS) δ: 8.00 (SnMe2). MS: m/z 385 (M+ – CH3).
diffractometer was used. All structures were solved by
SHELXS86 and refined with SHELXL93. The non-
hydrogen atoms were refined anisotropically. The H atoms
were considered as a riding model. Crystallographic parame-
ters and details of the data collection are summarized in
Table 5.6
1-[1,1-Dimethyl-2,2-bis(trimethylsilyl)-1-stannaethyl]-2-
[2,2-dimethyl-3,3-bis(trimethylsilyl)-2-stannapropyl]-benzene
1
(10, E = Sn): colourless solid. H NMR (C6D6, iTMS) δ:
–0.408 (s, Si2CH), –0.197 (s, Si2CH), 0.150 (s; 2 SiMe3),
0.158 (s; 2 SiMe3), 0.181 (s; SnMe2), 0.507 (s; SnMe2), 2.64
(s; SnCH2), 7.02 (t; J = 7 Hz; 1 CH of Ph), 7.06 (d; J =
7 Hz; 1 CH of Ph), ? (1 CH of Ph; hidden by solvent), 7.46
(d; J = 7 Hz; 1 CH of Ph). 13C{1H} NMR (CDCl3, iTMS) δ:
–6.18 (SnMe2), –4.47 (SnMe2), 1.11 (SnSi2C), 1.32 (SnSi2C),
3.32 (4 SiMe3), 22.76 (SnCH2), 122.9/127.9/128.2/134.9
(=CH of Ph), 142.5/146.6 (=C< of Ph). 29Si NMR (C6D6,
eTMS) δ: 1.48 (2 SiMe3), 1.88 (2 SiMe3). 119Sn NMR
(CDCl3, eTMS) δ: –28.58 (SnMe2), 9.88 (SnMe2). MS: m/z
603 (M+ – SiMe3 – C2H6).
Acknowledgements
We are grateful to the Deutsche Forschungsgemeinschaft,
Bonn, for the generous financial support.
References
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(1986).
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93 (1991).
4. N. Wiberg, T. Passler, S. Wagner, and K. Polborn. Unpub-
lished.
Thermolysis of 8 in benzene
A solution of 0.022 g (0.07 mmol) 8 (E = Si) in 0.6 mL
benzene was heated at 160°C for 5 d and at 170°C for 11 d.
1
According to H NMR spectrum no reaction (formation of
7) occurred.
5. N. Wiberg, K. Schurz, and G. Fischer. Chem. Ber. 119, 3498
(1986) and 120, 1605 (1987); N. Wiberg, G. Fischer, and S.
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Wagner. Z. Naturforsch. 51b, 629, (1996).
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7. N. Wiberg, S. Wagner, and S.-K. Vasisht. Chem. Eur. J. 2571
(1998).
Thermolysis of 8 and 1·Ph2C=NSiMe3 in benzene
A solution of 0.008 g (0.026 mmol) 8 and 0.016 g
(0.034 mmol) 1·Ph2C=NSiMe3 1in 0.6 mL C6D6 was heated
at 130°C for 9 d. According to H NMR spectrum no forma-
tion of 10 occurred.
8. N. Wiberg, G. Preiner, G. Wagner, H. Köpf, and G. Fischer. Z.
Naturforsch. 42b, 1055 (1987); N. Wiberg, G. Preiner, G.
Wagner, and H. Köpf. Z. Naturforsch. 42b, 1062 (1987).
Crystal structures of 1, 2 and 3
Single crystals were crystallized from benzene as colour-
less plates. For structure determinations a Nonius CAD4
6 Crystallographic data for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre (CCDC
127654 for 1a, 127655 for 2a, and 127656 for 3a). Copies of the data can be obtained, free of charge, on application to the Director, CCDC,
12 Union Road, Cambridge CB2 1EZ, U.K. (Fax: 44-1223-336033 or e-mail: deposit@ccdc.cam.ac.uk).
© 2000 NRC Canada