Head-to-head versus head-to-tail dimerizations of transient silenes - the generation and dimerization behavior of 2-(2-dimethylaminoaryl)-1,1-bis(trimethylsilyl)silenes

Article abstract of DOI:10.1016/S0022-328X(99)00740-8

The transient silenes (Me₃Si)₂Si=CR¹R² (4: R¹=H, R²=2-Me₂N-5-Me-C₆H₃; 11: R¹=Me, R²=2-Me₂N-C₆H₄; 15: R¹=3,5-Me₂-C₆H₃, R²=2-Me₂N-C₆H₄; 18: R¹=Me, R²=2-Me₂N-5-Me-C₆H₃) were generated following the mechanism of the sila-Peterson reaction. Thus, 4 was obtained by base-induced trimethylsilanol elimination from (2-dimethylamino-5-methylphenyl)tris(trimethylsilyl)silylmethanol (3). Addition of methyllithium or 3,5-dimethylphenyllithium, respectively, to the carbonyl group of 2-dimethylaminobenzoyl-tris(trimethylsilyl)silane (10) and subsequent elimination of Me₃SiOLi led to 11 and 15, respectively. Similarly, (2-dimethylamino-5-methylbenzoyl)-tris(trimethylsilyl)silane (17) and MeLi gave 18. The silene 4 underwent a spontaneous head-to-tail cyclodimerization to give a 1,3-disilacyclobutane (5), whereas 11 afforded a linear head-to-head dimer (12). The dimerization rates of 15 and 18 proved to be slow, thus, under the conditions of the sila-Peterson reaction readdition products of eliminated trimethylsilanolate to the Si=C bond of the silenes were obtained (16, 19). The structures of the compounds prepared were elucidated on the basis of comprehensive NMR and MS studies; for 5 also the results of an X-ray structural analysis are given. Possible reasons for the different behavior of the similarly structured silenes are discussed.

Full text of DOI:10.1016/S0022-328X(99)00740-8

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Journal of Organometallic Chemistry 598 (2000) 395–402
Head-to-head versus head-to-tail dimerizations of transient
silenes — the generation and dimerization behavior of
2-(2-dimethylaminoaryl)-1,1-bis(trimethylsilyl)silenes
Douglas Hoffmann a, Thoralf Gross a, Rhett Kempe b, Hartmut Oehme a,*
a Fachbereich Chemie der Uni6ersita¨t Rostock, D-18051 Rostock, Germany
b Institut fu¨r Organische Katalyseforschung an der Uni6ersita¨t Rostock e. V., D-18055 Rostock, Germany
Received 24 September 1999; accepted 22 November 1999
Dedicated to Professor Manfred Meisel on the occasion of his 60th birthday
Abstract
The transient silenes (Me3Si)2SiꢀCR1R2 (4: R1=H, R2=2-Me2N-5-Me–C6H3; 11: R1=Me, R2=2-Me2N–C6H4; 15: R1=3,5-
Me2–C6H3, R2=2-Me2N–C6H4; 18: R1=Me, R2=2-Me2N-5-Me–C6H3) were generated following the mechanism of the
sila-Peterson reaction. Thus,
4 was obtained by base-induced trimethylsilanol elimination from (2-dimethylamino-5-
methylphenyl)tris(trimethylsilyl)silylmethanol (3). Addition of methyllithium or 3,5-dimethylphenyllithium, respectively, to the
carbonyl group of 2-dimethylaminobenzoyl-tris(trimethylsilyl)silane (10) and subsequent elimination of Me3SiOLi led to 11 and
15, respectively. Similarly, (2-dimethylamino-5-methylbenzoyl)-tris(trimethylsilyl)silane (17) and MeLi gave 18. The silene 4
underwent a spontaneous head-to-tail cyclodimerization to give a 1,3-disilacyclobutane (5), whereas 11 afforded a linear
head-to-head dimer (12). The dimerization rates of 15 and 18 proved to be slow, thus, under the conditions of the sila-Peterson
reaction readdition products of eliminated trimethylsilanolate to the SiꢀC bond of the silenes were obtained (16, 19). The
structures of the compounds prepared were elucidated on the basis of comprehensive NMR and MS studies; for 5 also the results
of an X-ray structural analysis are given. Possible reasons for the different behavior of the similarly structured silenes are
discussed. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Silicon; Silenes; Silene dimerization; 1,2-Disilacyclobutanes; 1,3-Disilacyclobutanes
fording products whose individual structures depend on
the substitution pattern of the transient SiꢀC system
[2–5]. The unusual behavior of 1 was attributed to the
donor properties of the 2-dimethylamino group of the
2-aryl substituent causing an intermolecular interaction
with the electrophilic silene silicon atom of a neighbor-
ing silene molecule, thus initiating a head-to-tail dimer-
ization through a cyclic seven-membered transition
state [1,5]. This picture could successfully be applied to
the dimerization behavior of 2-(dimethylaminonaph-
thyl)-1,1-bis(trimethylsilyl)silenes [6] and proved to be
worthwhile in understanding the solvent-dependent re-
giospecifity of the cyclodimerization of 2-(2-
methoxyphenyl)-1,1-bis(trimethylsilyl)silene [5]. In this
paper we describe the generation of some new transient
2 - (dimethylaminophenyl) - 1,1 - bis(trimethylsilyl)silenes
and demonstrate that slight changes in the molecular
1. Introduction
In a recently published paper we described the gener-
ation of the transient 2-(2-dimethylaminophenyl)-1,1-
bis(trimethylsilyl)silene (1) by a modified Peterson
reaction and its spontaneous dimerization to 2,4-bis(2-
dimethylaminophenyl) - 1,1,3,3 - tetrakis(trimethylsilyl)-
1,3-disilacyclobutane (2) [1]. The formation of the 1,3-
disilacyclobutane 2, the formal head-to-tail cyclodimer
of the silaethene 1, was a rather unexpected result of
the studies, since 1,1-bis(trimethylsilyl)silenes were gen-
erally found to dimerize in a head-to-head mode, af-
* Corresponding author. Tel.: +49-381-4981765; fax: +49-381-
4981763.
E-mail address: hartmut.oehme@chemie.uni-rostock.de (H.
Oehme)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00740-8

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D. Hoffmann et al. / Journal of Organometallic Chemistry 598 (2000) 395–402
structure of the silaethenes may lead to a fundamentally
different reaction behavior.
meric 1,3-disilacyclobutanes E-5 and Z-5 in a total
yield of 82%.
The structures of E-5 and Z-5, which are indicative
for the head-to-tail mode of the dimerization of 4, were
elucidated on the basis of NMR and MS studies. For
E-5 also an X-ray structural analysis was performed,
which revealed a planar 1,3-disilacyclobutane system
(Fig. 1). Apart from slightly elongated ring Si–C dis-
tances, which are considered as being due to steric
congestion, the bond parameters are in the expected
region.
The 1,3-disilacyclobutane 5 is the expected dimer of
4, since its formation is fully consistent with the conver-
sion of 1 into 2, and the observed regiospecifity of the
dimerization can easily be explained following the pro-
posed mechanism outlined in the introductory remarks.
Obviously, the unusual head-to-tail dimerization is ef-
fected by the ortho-dimethylamino group of the phenyl
substituent in 4. With the intention to confirm the
concept and to possibly reverse the dimerization re-
giospecifity of the SiꢀC system by ruling out the donor
properties of the dimethylamino group through com-
plexation, the procedure used for the generation of 4
was repeated in the presence of triethylborane as a
lone-pair acceptor. Actually, deprotonation of 3 with
methyllithium in ether in the presence of equimolar
quantities of Et3B·THF gave no head-to-tail cycload-
duct 5 nor the head-to-head dimer of the silene 4, but
afforded the hexasilane 9 in a yield of 63% (Schemes 1
and 2). Its structure was elucidated by comprehensive
NMR and MS studies (see Section 3).
2. Results and discussion
2-(2-Dimethylamino-5-methylphenyl)-1,1-bis(trime-
thylsilyl)silene (4) was prepared according to our stan-
dard method by deprotonation of (2-dimethylamino-5-
methylphenyl)-tris(trimethylsilyl)silylmethanol (3) with
methyllithium in ether following the mechanism of the
modified Peterson reaction. In the absence of scavenger
reagents, silene 4 proved to be unstable and underwent
rapid cyclodimerization to afford the two stereoiso-
The formation of 9 as the outcome of the conversion
of deprotonated 3 was really surprising and the ob-
served reaction course unique for all reactions of the
sila-Peterson type we studied. The generation of 9 can
easily be understood following the sequence given in
Scheme 2. Deprotonation of 3, isomerization of 6 by a
1,3-Si,O-trimethylsilyl migration to give 7 and subse-
quent trimethylsilanolate elimination leads to the silene
4, which is trapped by addition of the silyl lithium
compound 7 to the SiꢀC group resulting in the forma-
tion of 8. Hydrolysis of 8 during the aqueous workup
affords 9. The lithium silanide 7 is considered to be an
intermediate in the course of the silene generation. We
suppose, in presence of triethylborane, the elimination
of trimethylsilanolate from 7 under formation of 4 to
be a comparatively slow process due to the complexa-
tion of the silaanion by Et3B. Thus, the transient silene,
forming gradually, always meets an effective excess of
nucleophilic 7 and adduct formation dominates prior to
silene dimerization.
Fig. 1. Molecular structure of 5 in the crystal (ORTEP, 30% probabil-
ity, H atoms, except ring-CH, omitted for clarity); selected bond
,
lengths (A) and angles (°): C1–Si1, 1.922(2); Si1–Si2, 2.3616(11);
Si1–Si3, 2.6365(10); C1–Si1–C1A, 91.60(9); Si1–C1-Si1A, 88.40(9).
The isolation of compound 9, i.e. the proof of the
intermediate formation of the organolithium derivative
8, is of particular interest with respect to the general
discussion of the mechanism of the formation of 1,2-
disilacyclobutanes as the formal head-to-head dimers of
Scheme 1. Generation and head-to-tail cyclodimerization of the tran-
sient silene 4.

D. Hoffmann et al. / Journal of Organometallic Chemistry 598 (2000) 395–402
397
But under conditions of the sila-Peterson reaction also
the addition of silene precursors of type 7 to the SiꢀC
bond of the transient silene and subsequent ring closure
with intramolecular elimination of lithium trimethylsi-
lanolate might be a way conceivable to 1,2-disilacy-
clobutanes. But, actually, in the case of the reaction of
3 with MeLi in presence of Et3B no head-to-head
cyclodimer of 4 was found. Also, prolonged heating of
the reaction mixture prior to hydrolysis — even after
exchange of the solvent from ether to toluene and
refluxing for several hours — always gave compound 9
(after aqueous workup) as the final product exclusively.
Consequently also, the related mechanism proposed by
Auner and co-workers [10], for the formation of the
formal [2+2] and [2+4] cyclodimers of 2-mesityl-1,1-
bis(trimethylsilyl)silene [9], appears not to be very
likely.
2-Methyl-2-(2-dimethylaminophenyl)-1,1-bis(trime-
thylsilyl)silene (11) was generated by addition of
methyllithium to the carbonyl function of 2-dimethy-
laminobenzoyl-tris(trimethylsilyl)silane (10), giving an
intermediate alkoxide, which spontaneously eliminated
lithium trimethylsiloxide establishing the Si=C system.
Also silene 11 is unstable and as the final product of the
reaction we isolated 1-[1-(2-dimethylaminophenyl)-
ethenyl] - 2[1 - (2 - dimethylaminophenyl)ethyl] - 1,1,2,2-
tetrakis(trimethylsilyl)disilane (12), a product of an ob-
vious head-to-head dimerization of 11 (Scheme 3). This
type of silene dimerization is not uncommon; it is
typical for 1,1-bis(trimethylsilyl)silenes with ‘allylic’ hy-
drogen atoms [3,4,8,9]. But the remarkable point is that
the replacement of one hydrogen atom at the silene C
atom of compound 1 by a methyl group leads to a
reversed regiospecifity of the silene dimerization. The
reason for this surprising behavior is not clear, and in
view of the small difference in the spacial demand of
the hydrogen atom in 1 and the methyl group in 11,
respectively, a change of the dimerization mode due to
steric reasons is hardly conceivable.
Scheme 2. Generation of the silene 4 by a sila-Peterson reaction and
addition of the precursor lithium silanide 7 to the SiꢀC bond.
Depending on the substitution pattern, the biradicals
formed by Si–Si coupling of transient silenes may
stabilize to afford 1,2-disilacyclobutanes, tetrahydro-
2,3-disilanaphthalenes or (in the presence of ‘allylic
hydrogen’) linear dimers of type 12, respectively [5,7].
For some cases it was proved that both 1,2-disilacy-
clobutanes and tetrahydro-2,3-disilanaphthalenes exist
in
a temperature-dependent equilibrium with the
monomeric silenes [11,12]. Recently we found that on
heating to 200°C, the formerly described 1,2-disilacy-
clobutane 13, the formal [2+2] head-to-head cy-
clodimer of 2-(4-dimethylaminophenyl)-1,1-bis(trime-
thylsilyl)silene [1], is quantitatively converted into the
linear dimer 14 (Scheme 4).
Scheme 3. Generation of the transient silene 11 and its spontaneous
head-to-head reaction affording the linear dimer 12.
transient silenes. It is generally accepted that the dimer-
ization involves Si–Si bond formation as a first step
giving a carbon centered 1,4-biradical, which subse-
quently stabilizes to give the four-membered ring [7].
In the case of the dimerization of 11, hydrogen
transfer in the above mentioned 1,4-biradical under

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D. Hoffmann et al. / Journal of Organometallic Chemistry 598 (2000) 395–402
formation of 12 makes the reaction irreversible and the
formation of alternative products is excluded. Methyl-
lithium is an unfavourable reagent in the reaction with
10, since in this way ‘allylic’ hydrogen is introduced
into the silene structure. To avoid this disadvantage,
lithium derivatives possessing no hydrogen at the car-
banionic C-atom were used in the addition reaction
with the acylsilane 10. But after treatment of 10 with
tertbutyllithium or mesityllithium, respectively, the
acylsilane was recovered unchanged. Obviously, the
nucleophilic attack of the bulky organolithium reagents
at the sterically encumbered carbonyl group of 10 is
completely prevented. The reaction of 10 with phenyl-
lithium gave a complex mixture of unidentified, pre-
sumably oligomeric or polymeric products. This is in
agreement with our general experience that silenes with
an unsubstituted phenyl group at the silene C-atom do
not undergo a clean dimerization but give complex
mixtures of products. 3,5-Dimethylphenyllithium reacts
with 10 to afford the siloxane 16 (Scheme 5).
Scheme 4. Thermal isomerization of a 1,2-disilacyclobutane 13, the
formal [2+2] cyclodimer of 2-(4-dimethylaminophenyl)-1,1-
bis(trimethylsilyl)silene, into the linear silene dimer 14.
The structure of 16 is easily understood as the result
of an addition of trimethylsilanolate, just eliminated
from the lithium alkoxide obtained through addition of
3,5-dimethylphenyllithium to the carbonyl group of 10,
at the SiꢀC bond of the generated silene 15. The
readdition of trimethylsilanolate is a general and ex-
pected side reaction of the silene synthesis according to
the sila-Peterson process and was observed several
times, particularly in the case of sterically highly con-
gested silenes [4b,13]. Due to the kinetic stabilization,
the dimerization of these silenes becomes a compara-
tively slow reaction, making the silanolate addition the
dominant process. Summarizing the results of these
experiments, we have to state that silenes, obtained by
replacement of the 2-hydrogen atom in 1 by other
groups, do not dimerize in a head-to-tail mode follow-
ing the mechanism discussed above, and the question
concerning the reason for the opposite regiospecifity of
the two similarly structured silenes 1 and 11 remains
unanswered.
Scheme 5. Generation of the transient silene 15 by a sila-Peterson
reaction and readdition of Me3SiOLi to the SiꢀC bond.
Interestingly, the reaction of (2-dimethylamino-5-
methylbenzoyl)-tris(trimethylsilyl)silane
(17)
with
methyllithium under the same conditions applied in the
reaction of 10 with MeLi, gave no silene dimer, but
again a readdition product of eliminated trimethylsi-
lanolate at the SiꢀC bond of the generated silene 18
(Scheme 6).
The insignificant increase of the steric bulk, caused
by introduction of a methyl group into the 5-position of
the aryl substituent of 11 (giving 18), again leads to a
fundamental change in the behavior of the respective
silene.
The conclusion drawn from the experiments de-
scribed in this paper is that slight variations in the
structures of the 2-(dimethylaminophenyl)silenes funda-
Scheme 6. Generation of the transient silene 18 by a sila-Peterson
reaction and readdition of Me3SiOLi to the SiꢀC bond.

D. Hoffmann et al. / Journal of Organometallic Chemistry 598 (2000) 395–402
399
mentally influence the mode of dimerization. Deviating
from the usual dimerization behavior of 1,1-bis-
(trimethylsilyl)silenes, 2-(2-dimethylaminophenyl)-1,1-
bis(trimethylsilyl)silene (1) and 2-(2-dimethylamino-5-
methylphenyl)-1,1-bis(trimethylsilyl)silene (4) undergo a
formal [2+2] head-to-tail dimerization to give the 1,3-
disilacyclobutanes 2 and 5, respectively. On the other
hand, 2-methyl-2-(2-dimethylaminophenyl)-bis(trime-
thylsilyl)silene (11) affords a linear head-to-head dimer,
a behavior that was similarly also observed for the
4-dimethylaminophenyl isomer [1]. Unfortunately, at-
tempts to replace the 2-methyl substituent in 11 by a
group bearing no a-hydrogen atom were unsuccessful.
Thus, the idea that hydrogen transfer in the biradical
Si–Si coupling product of 11, leading to the linear
dimer 12, might be a trap in the silene dimerization
equilibria preventing the formation of head-to-head or
head-to-tail cyclodimers, could not be deepened. In-
creasing steric protection of the SiꢀC system reduces the
dimerization rate and in the case of a silene generation
according to the sila-Peterson reaction, the readdition
of trimethylsilanolate gains importance. Thus, for 15
and 18, this reaction type dominates.
CH3, 3H), 2.40 (s, NCH3, 6H), 3.37 (br s, COH, 1H),
5.62 (s, HCO, 1H), 6.81–6.83 (m, aryl-H, 2H), 7.31 (s,
aryl-6CH, 1H). 13C-NMR (benzene-d6): l=1.8
(SiCH3), 2.7 (aryl-CH3), 45.5 (NCH3), 65.4 (HCO),
119.9, 127.9 and 130.6 (aryl-CH), 133.3, 141.1 and
148.7 (quart. aryl-C). 29Si-NMR (benzene-d6): l= −
68.9 (SiSiMe3), −12.5 (SiMe3). MS m/z (%): 411 (5)
[M+], 396 (7) [M+–CH3], 338 (10) [M+–SiMe3], 164
(100) [M+–Si(SiMe3)3]. Anal. Found: C, 55.34; H, 9.96;
N, 3.31. Calc. for C19H41NOSi4 (411.88): C, 55.41; H,
10.03; N, 3.40%.
3.2. 2,4-Bis(2-dimethylamino-5-methylphenyl)-
1,1,3,3-tetrakis(trimethylsilyl)-1,3-disilacyclobutane (5)
To a stirred solution of 0.5 g (1.2 mmol) of 3 in 30 ml
of ether, the equimolar quantity of methyllithium was
added at −78°C. After warming up to r.t., water was
added, the ethereal layer was separated, dried with
magnesium sulfate and evaporated. After treatment of
the residue with some n-heptane E-5 separated in the
form of colorless crystals (0.19 g). Chromatographic
separation of the evaporated mother liquor (silica gel;
heptane–ethyl acetate, 20:1) gave 0.13 g of the Z-iso-
mer. Total yield 0.32 g (82%).
3. Experimental
1
E-5: m.p. \230°C dec. H-NMR (benzene-d6): l=
0.29 (s, SiCH3, 36H), 2.36 (s, aryl-CH3, 6H), 2.55 (s,
All reactions involving organometallic reagents were
carried out under purified argon. NMR: Bruker AC
250 or Bruker ARX 300, tetramethylsilane as internal
standard. IR: Nicolet 205 FT-IR. MS: Intectra AMD
402, chemical ionization with isobutane as the reactant
gas. (Me3Si)3SiLi·3THF was prepared as reported in
the literature [14]. All yields given refer to amounts
obtained after chromatographic separation and
purification.
3
NCH3, 12H), 4.14 (s, ring-CH, 2H), 6.77 (dd, J=7.93
4
3
Hz, J=2.13 Hz, aryl-4CH, 2H), 6.88 (d, J=7.95 Hz,
aryl-3CH, 2H), 7.62 (d, J=2.15 Hz, aryl-6CH). 13C-
4
NMR (benzene-d6): l=0.7 (SiCH3), 8.9 (ring-C), 20.6
(aryl-CH3), 45.6 (NCH3), 119.9, 124.5 and 131.6 (aryl-
CH), 132.5, 140.9 and 149.1 (quart. aryl-C). 29Si-NMR
(benzene-d6): l = −14.2 (SiMe3), −8.7 (ring-Si). MS
m/z (%): 642 (29) [M+], 627 (10) [M+–CH3], 569 (100)
[M+–SiMe3], 321 (62) [(Me3Si)2SiꢀCH(C6H3Me-
NMe2)+]. Anal. Found: C, 59.47; H, 9.67; N, 4.36.
Calc. for C32H62N2Si6 (643.37): C, 59.74; H, 9.71; N,
4.35%.
3.1. (2-Dimethylamino-5-methylphenyl)-
tris(trimethylsilyl)silylmethanol (3)
Z-5: m.p.=205°C dec. 1H-NMR (benzene-d6):
l=0.25 and 0.36 (2s, SiCH3, 2×18 H), 2.36 (s, aryl-
CH3, 6H), 2.57 (s, NCH3, 12H), 3.80 (s, ring-CH, 2H),
A total of 5.00 g (10.6 mmol) of (Me3Si)3SiLi·3THF,
dissolved in 30 ml of ether, were added to a suspension
of an equimolar quantity (2.75 g) of MgBr2·OEt2 in 20
ml of ether. After stirring for 0.5 h at room temperature
(r.t.), the mixture was cooled to −78°C and 1.73 g
(10.6 mmol) of 2-dimethylamino-5-methylbenzalde-
hyde, dissolved in 20 ml of ether, were added within 1
h. The stirred solution was allowed to warm up
overnight, water was added, the ethereal extracts were
dried with MgSO4 and the solvent was removed in
vacuo. Chromatographic purification of the residue (sil-
ica gel; heptane–ethyl acetate, 20:1) and recrystalliza-
tion from acetonitrile afforded 2.6 g (59%) of 3, m.p.
72–75°C. IR (nujol): w˜ =3552 cm−1 (OHfree). 1H-NMR
(benzene-d6): l=0.33 (s, SiCH3, 27H), 2.22 (s, aryl-
3
4
6.77 (dd, J=8.23 Hz, J=2.13, aryl-4CH, 2H), 6.89
(d, 3J=7.93, aryl-3CH, 2H), 7.62 (d, 4J=1.83 Hz,
aryl-6CH, 2H). 13C-NMR (benzene-d6): l= −0.1 and
1.7 (SiCH3), 10.1 (ring-C), 20.6 (aryl-CH3), 45.7
(NCH3), 119.8, 124.8 and 132.2 (aryl-CH), 132.4, 139.9
and 149.3 (quart. aryl-C). 29Si-NMR (benzene-d6):
l= −14.4 and −13.9 (SiMe3), −6.9 (ring-Si). MS
m/z (%): 642 (44) [M+], 627 (10) [M+–CH3], 569 (100)
[M+–SiMe3], 321 (39) [(Me3Si)2SiꢀCH(C6H3Me-
NMe2)+]. Anal. Found: C, 59.50; H, 9.57; N, 4.33.
Calc. for C32H62N2Si6 (643.37): C, 59.74; H, 9.71; N,
4.35%.

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D. Hoffmann et al. / Journal of Organometallic Chemistry 598 (2000) 395–402
3.3. 1-(2-Dimethylamino-5-methylbenzyl)-2-
[2-dimethylamino-5-methyl-(h-trimethylsiloxy)benzyl]-
1,1,2,2-tetrakis(trimethylsilyl)disilane (9)
3.5. 1-[1-(2-Dimethylaminophenyl)ethenyl]-
2[1-(2-dimethylaminophenyl)ethyl]-
1,1,2,2-tetrakis(trimethylsilyl)disilane (12)
A total of 0.5 g (1.2 mmol) of 3 were dissolved in 30
ml of ether. The solution was cooled to −78°C and
equimolar quantities of first BEt3·THF and then of
methyllithium were added. After stirring for 0.5 h the
solution was allowed to warm up gradually to r.t.,
water was added and the ethereal phase was separated,
dried and concentrated. Chromatography of the residue
(silica gel; heptane–ethyl acetate, 20:1) gave 0.28 g
(63%) of 9, m.p. 132–134°C. 1H-NMR (benzene-d6):
l=0.08, 0.13, 0.36, 0.44 and 0.66 (5s, SiSiCH3 and
OSiCH3, 5×9H), 2.26 and 2.29 (2s, aryl-CH3, 2×3H),
2.51 and 2.57 (2s, NCH3, 2×6H), 2.90 and 2.98 (2d,
2J=13.0 Hz, SiCH2, 2×1H), 6.07 (s, SiCH, 1H),
An equimolar quantity of methyllithium was added
to a stirred solution of 0.5 g (1.27 mmol) of 10 in 20 ml
of ether at −78°C. After gradual warming up to r.t.,
water was added and the organic layer separated, dried
with MgSO4 and evaporated. Chromatographic separa-
tion (silica gel; heptane–ethyl acetate, 20:1) of the
residue afforded 0.29 g (71%) of 12 as a colorless oil,
1
which gradually crystallized, m.p. 95–98°C. H-NMR
(benzene-d6): l=0.10, 0.32, 0.38 and 0.56 (4s, SiCH3,
3
4×9H), 1.78 (d, J=7.63 Hz, CHCH3, 3H), 2.49 and
2.55 (2s, NCH3, 2×6H), 3.76 (q, 3J=7.63 Hz,
2
CHCH3, 1H), 5.93 and 6.25 (2d, J=3.05 Hz, CCH2,
2H), 6.89–7.51 (m, aryl-CH, 8H). 13C-NMR (benzene-
d6): l=2.9, 3.1 and 4.8 (two signals) (SiCH3), 20.2
(CHCH3), 24.8 (CHCH3), 45.6 and 46.2 (NCH3), 119.4,
119.9, 123.0, 124.3, 126.1, 127.5, 130.9, 131.0, 134.6,
143.2, 144.0, 149.8, 151.5 and 151.8 (olef. and aromat.
C). 29Si-NMR (benzene-d6): l= −62.7 and-52.2
(SiSiMe3), −13.6, −12.9, −12.3 and −12.2 (SiMe3).
MS m/z (%): 642 (7) [M+], 627 (3) [M+–CH3], 494 (5)
[M+–Me2NC6H4CHCH3], 322 (70) [Si(SiMe3)2-
CHCH3C6H4NMe+2 ], 320 (100) [Si(SiMe3)2CCH2-
C6H4NMe+2 ]. Anal. Found: C, 59.71; H, 9.70; N, 4.32.
Calc. for C32H62N2Si6 (643.37): C, 59.74; H, 9.71; N,
4.35%.
4
6.86–6.88 (m, aryl-CH, 4H), 7.27 (d, J=1.8 Hz, aryl-
CH, 1H), 7.59 (s, aryl-CH, 1H). 13C-NMR (benzene-
d6): l=2.1, 2.6, 2.9 and 3.0 (SiSiCH3), 4.2 (OSiCH3),
15.5 and 20.8 (aryl-CH3), 45.6 and 46.5 (NCH3), 66.9
(SiCH2), 119.7, 120.4, 126.3, 127.6, 127.8, 128.3, 131.8,
132.7, 133.1, 137.9, 141.9, 147.8 and 149.8 (aromat-C
and SiCH). 29Si-NMR (benzene-d6): l= −64.8 and
−51.1 (SiSiMe3), −13.5, −12.6 and −12.3 (two
signals) (SiSiMe3), 14.5 (OSiMe3). MS m/z (%): 732
(23) [M+], 717 (28) [M+–CH3], 643 (25) [M+–
OSiMe3], 584 (17) [M+–CH2C6H3MeNMe2], 236 (100)
[Me3SiOCHC6H3MeNMe+2 ]. Anal. Found: C, 57.17; H,
10.04; N, 3.82. Calc. for C35H72N2OSi7 (733.57): C,
57.31; H, 9.89; N, 3.82%.
3.6. [(2-Dimethylaminophenyl)(3,5-dimethylphenyl)-
methyl]-trimethylsiloxy-bis(trimethylsilyl)silane (16)
3.4. 2-Dimethylaminobenzoyl-tris(trimethylsilyl)silan
(10)
To 0.5 g (1.27 mmol) of 10, dissolved in 20 ml of
ether, an equimolar quantity of an ethereal 3,5-
dimethylphenyllithium solution was added at −78°C.
After gradual warming up to r.t., water was added and
the organic layer was separated, dried with MgSO4 and
evaporated. Chromatography of the residue (silica gel;
heptane–ethyl acetate, 20:1) gave 16 in form of a pale
yellow oil, yield 0.39 g (61%). IR (cap.): w˜ =1053 cm−1
(SiO). 1H-NMR (benzene-d6): l=0.05 and 0.11 (2s,
SiSiCH3, 2×9H), 2.55 (s, OSiCH3, 9H), 2.21 (s, aryl-
CH3, 6H), 2.46 (s, NCH3, 6H), 4.72 (s, SiCH, 1H), 6.69
(s, aryl-CH, 1H), 6.94–6.98 (m, aryl-CH, 1H), 7.08–
7.12 (m, aryl-CH, 2H), 7.30 (s, aryl-CH, 2H), 7.78–7.82
(m, aryl-CH, 1H). 13C-NMR (benzene-d6): l= −0.8
and −0.6 (SiSiCH3), 2.5 (OSiCH3), 21.5 (aryl-CH3),
40.1 (SiCH), 45.5 (NCH3), 120.4, 123.5, 126.4, 126.8,
126.9 132.4, 137.6, 138.0, 144.0 and 153.2 (aromat. C).
29Si-NMR (benzene-d6): l= −19.7 and −19.6
(SiSiMe3), −13.1 (SiSiMe3), 7.0 (OSiMe3). MS m/z
(%): 501 (4) [M+], 486 (13) [M+–CH3], 428 (100)
[M+–SiMe3], 263 (85) [Me3SiOSi(SiMe3)+2 ]. Anal.
Found: C, 61.65; H, 9.24; N, 2.98. Calc. for
C26H47NOSi4 (502.01): C, 62.21; H, 9.44; N, 2.79%.
At r.t., 5.00 g (10.6 mmol) of (Me3Si)3SiLi·3THF,
dissolved in 30 ml of ether, were added to an ethereal
solution of 1.90 g (10.6 mmol) of methyl 2-dimethyl-
aminobenzoate. After 2 h, stirring water was added, the
organic layer separated, the aqueous phase extracted
with ether, and the combined ethereal solutions were
dried with MgSO4 and evaporated. Chromatographic
separation (silica gel; heptane–ethyl acetate, 20:1) of
the residue gave 2.6 g (62%) of a yellow oil, which
gradually crystallized. IR (cap.): w˜ =1599 cm−1 (CO).
1H-NMR (benzene-d6): l=0.28 (s, SiCH3, 27H), 2.47
(s, NCH3, 6H), 6.66–7.21 (m, aryl-CH, 4H). 13C-NMR
(benzene-d6): l=1.3 (SiCH3), 45.3 (NCH3), 117.5,
120.7, 126.8 and 130.0 (aryl-CH), 142.9 and 149.3
(quart. aryl-C), 209.0 (CO). 29Si-NMR (benzene-d6):
l= −71.8 (SiSiMe3), −11.8 (SiMe3). MS m/z (%):
395 (8) [M+], 380 (60) [M+–CH3], 322 (17) [M+–
SiMe3], 73 (100) [SiMe3+]. Anal. Found: C, 53.70; H,
9.44; N, 3.29. Calc. for C18H37NOSi4 (395.84): C, 54.62;
H, 9.42; N, 3.54%.

D. Hoffmann et al. / Journal of Organometallic Chemistry 598 (2000) 395–402
401
3.7. (2-Dimethylamino-5-methylbenzoyl)tris-
(trimethylsilyl)silane (17)
0.223 mm−1, F(000)=1408, [ range 1.9–24.33°; index
ranges −235h523, −185k518, −145l514;
−3
,
d
calc=1.034 g cm−3, peak/hole 0.65/−0.43 e A
,
As described for the synthesis of 10, 5.0 g (10.6
mmol) of (Me3Si)3SiLi·3THF and 2.1 g (10.6 mmol) of
methyl 2-dimethylamino-5-methylbenzoate gave 2.4 g
(55%) of 17 in the form of a yellow oil, which slowly
crystallized. IR (Nujol): w˜ =1606 cm−1 (CO). 1H-NMR
(benzene-d6): l=0.29 (s, SiCH3, 27H), 2.13 (aryl-CH3,
measured reflections 10 815, independent reflections
3305, observed reflections 2344, Rint 0.04, number of
parameters 212, R1 [I=2|(I)] 0.043, wR2 (all data)
0.110. The structure was solved by direct methods
(
SHELXS-86) [15] and refined by full-matrix least-
squares techniques against F2
(SHELXL-93) [16]. XP
3
3H), 2.50 (s, NCH3, 6H), 6.67 (d, J=8.25 Hz, aryl-
(Siemens Analytical X-ray Instruments, Inc.) was used
for structure representations.
CH, 1H), 6.90 (dd, 3J=8.23 Hz, 4J=2.43 Hz, aryl-CH,
1H), 6.99 (d, 4J=2.35 Hz, aryl-CH, 1H). 13C-NMR
(benzene-d6): l=1.3 (SiCH3), 20.3 (aryl-CH3), 45.5
(NCH3), 117.8, 127.1, 130.2, 130.4, 143.4 and 147.2
(aromat. C), 208.7 (CO). 29Si-NMR (benzene-d6): l=
−72.1 (SiSiMe3), −11.9 (SiMe3). MS m/z (%): 409 (3)
[M+], 394 (22) [M+–CH3], 336 (6) [M+–SiMe3], 247
(2) [Si(SiMe3)+3 ], 73 (100) [SiMe+3 ]. Anal. Found: C,
55.43; H, 9.60; N, 3.46. Calc. for C19H39NOSi4 (409.87):
C, 55.68; H, 9.59; N, 3.42%.
4. Supplementary material
Crystallographic data (excluding structure factors)
for the structure reported in this paper have been
deposited with the Cambridge Crystallographic Data
Centre, CCDC no. 132657. Copies of the information
may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(Fax:
+44-1223-336033;
e-mail:
deposit@ccdc.
3.8. [2-Dimethylamino-5-methyl(h-methyl)benzyl]-
trimethylsiloxy-bis(trimethylsilyl)silane (19)
cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
To 0.5 g (1.22 mmol) of 17, dissolved in 20 ml of
ether, the equimolar quantity of methyllithium was
added at −78°C. After gradual warming up to r.t.,
water was added and the organic phase was separated,
dried with MgSO4 and evaporated. Chromatographic
separation (silica gel; heptane–ethyl acetate, 20:1) af-
forded the siloxane 19 in the form of a colorless oil,
Acknowledgements
We gratefully acknowledge the support of our re-
search by the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie. We thank Profes-
sor M. Michalik, Dr W. Baumann and Professor N.
Stoll for recording the NMR and MS spectra, respec-
tively.
1
yield 0.23 g (44%). H-NMR (benzene-d6): l=0.11 (s,
OSiCH3, 9H), 0.20 and 0.21 (2s, SiSiCH3, 2×9 H),
3
1.61 (d, J=7.65 Hz, CHCH3, 3H), 2.26 (s, aryl-CH3,
3
3H), 2.51 (s, NCH3, 6H), 3.19 (q, J=7.63, SiCH, 1H),
6.86–7.22 (m, aryl-CH, 3H). 13C-NMR (benzene-d6):
l= −0.8 and −0.6 (SiSiCH3), 2.3 (OSiCH3), 19.0
(CHCH3), 20.9 (SiCH), 24.5 (aryl-CH3), 45.4 (NCH3),
119.3, 126.3, 130.4, 132.6, 141.5 and 149.2 (aromat. C).
29Si-NMR (benzene-d6): l= −20.4 and −19.7
(SiSiMe3), 2.3 (SiSiMe3), 6.9 (OSiMe3). MS m/z (%):
425 (2) [M+], 410 (10) [M+–CH3], 352 (100) [M+–
SiMe3], 263 (30) [Me3SiOSi(SiMe3)+2 ]. Anal. Found: C,
56.69; H, 10.07; N, 3.54. Calc. for C20H43NOSi4
(425.91): C, 56.64; H, 10.18; N, 3.30%.
References
[1] C. Krempner, D. Hoffmann, H. Oehme, R. Kempe,
Organometallics 16 (1997) 1828.
[2] A.G. Brook, K.M. Baines, Adv. Organomet. Chem. 25 (1986) 1.
[3] D. Bravo-Zhivotovskii, V. Brande, A. Stanger, M. Kapon, Y.
Apeloig, Organometallics 11 (1992) 2326.
[4] (a) J.Ohshita, Y. Masaoka, M. Ishikawa, Organometallics 10
(1991) 3775. (b) J. Ohshita, Y. Masaoka, M. Ishikawa, T.
Takeuchi, Organometallics 12 (1993) 876.
[5] K. Schmohl, M. Blach, H. Reinke, R. Kempe, H. Oehme, Eur.
J. Inorg. Chem. (1998) 1667 and literature cited therein.
[6] D. Hoffmann, H. Reinke, H. Oehme, J. Organomet. Chem. 585
(1999) 189.
[7] T. Mu¨ller, W. Ziche, N. Auner, in: Z. Rappoport, Y. Apeloig
(Eds.), The Chemistry of Organic Silicon Compounds, vol. 2,
John Wiley, New York, 1998, p. 927.
[8] (a) A.G. Brook, J.W. Harris, J. Lennon, M. ElSheikh, J. Am.
Chem. Soc. 101 (1979) 83. (b) K. Baines, A.G. Brook,
Organometallics 6 (1987) 692.
[9] C. Krempner, H. Reinke, H. Oehme, Chem. Ber. 128 (1995) 143.
[10] T. Mu¨ller, W. Ziche, N. Auner, in: Z. Rappoport, Y. Apeloig
(Eds.), The Chemistry of Organic Silicon Compounds, vol. 2,
John Wiley, New York, 1998, p. 919.
3.9. Crystal-structure determination of 5
X-ray diffraction data were collected with a STOE-
IPDS diffractometer using graphite-monochromated
Mo–Ka radiation. Crystals from heptane, crystal size
0.4×0.3×0.3 mm3, formula C32H62N2Si6, formula
weight 643.38, monoclinic, space group C2/c, a=
,
20.655(4), b=12.581(3), c=16.066(3) A; i=98.32(3)°;
3
,
V=4131.0(15) A ; Z=4; temperature 293(2) K, v=
.

402
D. Hoffmann et al. / Journal of Organometallic Chemistry 598 (2000) 395–402
[11] A.G. Brook, S.C. Nyburg, W.F. Reynolds, Y.C. Poon, Y.-M.
Chang, J.-S. Lee, J. Am. Chem. Soc. 101 (1979) 6750.
[12] C. Krempner, R. Kempe, H. Oehme, Z. Naturforsch. 52b (1997)
815.
[14] G. Gutekunst, A.G. Brook, J. Organomet. Chem. 225 (1982)
1.
[15] G.M. Sheldrick, SHELXS-86, University of Go¨ttingen, Germany,
1986.
[13] F. Luderer, H. Reinke, H. Oehme, J. Organomet. Chem. 510
(1996) 181.
[16] G.M. Sheldrick, SHELXL-93, University of Go¨ttingen, Germany,
1983.
.