Intramolecularly donor-stabilized silenes: Part 6. the synthesis of 1-[2,6-bis(dimethylaminomethyl)phenyl]silenes and their reaction with aromatic aldehydes

Article abstract of DOI:10.1016/j.jorganchem.2005.02.049

The intramolecularly donor-stabilized silenes ArR¹SiC(SiMe ₃)₂ (3a-d) (3a: R¹ = Me; 3b: R¹ = t-Bu; 3c: R¹ = Ph; 3d: R¹ = SiMe₃; Ar = 2,6-(Me₂NCH₂

Full text of DOI:10.1016/j.jorganchem.2005.02.049

Journal of Organometallic Chemistry 691 (2006) 229–239
www.elsevier.com/locate/jorganchem
Intramolecularly donor-stabilized silenes: Part 6. The synthesis
of 1-[2,6-bis(dimethylaminomethyl)phenyl]silenes and their
q
reaction with aromatic aldehydes
*
Ute Baumer, Helmut Reinke, Hartmut Oehme
¨
Fachbereich Chemie der, Universita¨t Rostock, Buchbinderstrasse 9, D-18051 Rostock, Germany
Received 29 November 2004; accepted 9 February 2005
Available online 10 October 2005
Abstract
The intramolecularly donor-stabilized silenes ArR1Si@C(SiMe3)2 (3a–d) (3a: R1 = Me; 3b: R1 = t-Bu; 3c: R1 = Ph; 3d:
R1 = SiMe3; Ar = 2,6-(Me2NCH2)2C6H3) were prepared by treatment of the (dichloromethyl)oligosilanes (Me3Si)2R1Si–CHCl2
(1a–d), with 2,6-bis(dimethylaminomethyl)phenyllithium (molar ratio 1:2). For 3c and 3d, X-ray structural analyses were performed
indicating that only one dimethylamino group of the tridentate ligand is coordinated to the electrophilic silene silicon atoms, i.e., the
central silicon atoms are tetracoordinated. The N ! Si donation leads to pyramidalization at the silene silicon atoms; the configu-
ration at the silene carbon atoms is planar. For a chemical characterization 3a and 3c were treated with water to give the silanols
ArR1Si(OH)–CH(SiMe3)2 (5a,c). Studies of the reactions of 3a and 3c with benzaldehyde, 4-chlorobenzaldehyde or 4-methoxybenz-
aldehyde, respectively, revealed an unexpected reaction path leading to the substituted 2-oxa-1-sila-1,2,3,4-tetrahydronaphthalenes
12a, 12c, 13 and 14. Both 12a and 12c were structurally characterized by X-ray analyses. The formation of these six-membered cyclic
compounds, which is discussed in detail, gives support to a dipolar mechanism for the general reaction of silenes with carbonyl
derivatives.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Donor–acceptor systems; 2-Oxa-1-sila-1,2,3,4-tetrahydronaphthalenes; Silaethenes; Silenes; Silicon
1. Introduction
lyl)silene (3d) [5]. The compound is obtained in a multi-
step but simple one-pot reaction by treatment of
(dichloromethyl)tris(trimethylsilyl)silane (1d) with 2,6-
bis(dimethylaminomethyl)phenyllithium (molar ratio
1:2). The reaction path leading to 3d, which similarly ap-
plies to a series of further intramolecularly donor-stabi-
lized silenes bearing other dialkylaminoaryl substituents,
was discussed in detail [6] and is outlined in an abbrevi-
ated form in Scheme 1. NMR studies as well as the
X-ray structural analysis of 3d revealed a strong intra-
molecular coordination, but only one dimethylamino
group of the ligand is coordinated to the silene Si atom
of 3d, i.e., the silene silicon atom is tetracoordinated in
solution as well as in the solid state.
Intramolecular amine coordination proved to be an
effective tool in stabilizing derivatives of three-coordi-
nate silicon, such as silanthiones [2], silanimines [3], sil-
aphosphenes [3] as well as silylium ions [4]. In this
context, the tridentate 2,6-bis(dimethylaminomethyl)-
phenyl ligand is of particular interest, since one or both
amino groups may coordinate to the electrophilic silicon
atom. Recently, we were able to describe the synthesis of
the isolable intramolecularly donor-stabilized 1-[2,6-
bis(dimethylaminomethyl)phenyl]-1,2,2-tris(trimethylsi-
q
For Part 5, see [1].
Corresponding author. Tel.: +49 381 498 6400; fax: +49 391 498
*
In the case of silyl cations, substituted and stabilized
by the 2,6-bis(dimethylaminomethyl)phenyl ligand,
6382.
E-mail address: hartmut.oehme@chemie.uni.rostock.de (H. Oehme).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.02.049

230
U. Ba¨umer et al. / Journal of Organometallic Chemistry 691 (2006) 229–239
phenyllithium (molar ratio 1:2) to give the stable silenes
3a–d (Scheme 1). As discussed previously [5], the reac-
tion proceeds through a deprotonation of the dichlo-
romethyl group of 1a–d, lithium chloride elimination
and trimethylsilyl migration producing the transient si-
lenes 2a–d. Addition of a second molar equivalent of
2,6-bis(dimethylaminomethyl)phenyllithium across the
polar Si@C bond of 2a–d, repeated loss of LiCl and a
further Si–C shift of a Me3Si group, affords the silenes
3a–d. Using the same method, treatment of 1d with
2,6-bis(diethylaminomethyl)phenyllithium gave 4, the
diethylaminomethyl analogue of 3d. Complexes 3a,c,d
and 4 were isolated as pale yellow crystalline solids
(yields between 49% and 78%). Complex 3b was ob-
tained only in an impure oily form, but could be identi-
fied by characteristic NMR data.
ArLi
ArH
Me3Si
Me3Si Si CHCl2
R1
Me3Si
SiMe3
Cl
Me3Si
Me3Si Si
R1
Li
Cl
Cl
+
–
Si
R1
C
C
LiCl
–
rearr.
1a-d
2a-d
a: R1= Me
b: R1 = tBu
c: R1 = Ph
+
ArLi
d: R1 = SiMe3
SiMe3
Li
Cl
Ar
Me3Si Si
C
R1
-
LiCl
rearrangement
NMe2
SiMe3
Si C
R1
SiMe3
Me2N
For 3c and 4 X-ray structural analyses were per-
formed, which unambiguously confirm the proposed
structures. The results of the structural elucidation of
3d were reported previously [5]. The structural data ob-
tained reveal, that in all compounds investigated only
one dimethylamino group (in 4 one diethylamino group)
is coordinated to the silene silicon atom. This is clearly
to be seen in Fig. 1, which exemplarily shows the results
of the X-ray analysis of 3c.
3a-d
Me2N
ArLi = Li
Me2N
a: R1= Me
b: R1 = tBu
c: R1 = Ph
d: R1 = SiMe3
Scheme 1. The reaction of the (dichloromethyl)oligosilanes (1a–d)
with 2,6-bis(dimethylaminomethyl)phenyllithium (1:2) producing the
intramolecularly donor-stabilized silenes 3a–d.
Some characteristic bond parameters are summarized
in Table 1. The data obtained for the new compounds 3c
and 4 largely agree with those already reported for 3d [5]
pentacoordination at the central silicon atom was ob-
served. Thus, silyl cations bearing at least one Si–H
bond are siliconium ions with chelation of both dimeth-
ylamino groups to the silicon atom. But generally, the
number of dimethylamino groups coordinated to the sil-
icon atom is varying depending on substituents, the
counterion and the solvent [4b].
In the present paper, we pursue the question, whether
a change in the substitution pattern of silene 3d, e.g., the
replacement of the 1-trimethylsilyl group by a more elec-
tronegative carbon substituent, may increase the coordi-
nation number at the silene silicon atom. For that
purpose, we synthesized some new silenes bearing the
2,6-bis(dimethylaminomethyl)phenyl group (3a–c) using
the established method mentioned above. Furthermore,
we studied the behavior of these Si@C-systems towards
aromatic aldehydes and describe an unexpected reaction
path leading to products whose structures shed some
light on the mechanism of the general reaction of silenes
with carbonyl compounds.
2. Results and discussion
Fig. 1. Molecular structure of 3c in the crystal (ORTEP, 30%
probability level, H atoms omitted for clarity; see also Table 2 for
˚
additional crystallographic information). Selected bond lengths (A):
2.1. Synthesis and structure of the 1-[bis(dimethylamino-
methyl)phenyl]silenes 3a–d
Si(1)–C1 1.744(2), Si1–C8 1.888(2), Si1–C20 1.891(2), Si1–N1 2.043(2),
Si1–N2 4.709; C1–Si2 1.840(2), C1–Si3 1.838(2). Selected bond angles
(ꢁ): C1–Si1–C8 122.01(10), C1–Si1–C20 120.14(10), C8–Si1–C20
106.70(10), Si1–C1–Si2 123.04(13), Si1–C1–Si3 121.47(12), Si2–C1–
Si3 114.87(11).
The (dichloromethyl)oligosilanes (Me3Si)2R1Si–CH-
Cl2 (1a–d) (a: R1 = Me; b: R1 = t-Bu; c: R1 = Ph; d:
R1 = Me3Si) react with 2,6-bis(dimethylaminomethyl)

U. Ba¨umer et al. / Journal of Organometallic Chemistry 691 (2006) 229–239
231
Table 1
Selected structural data of the silenes 3c, 3d and 4 and, for comparison, of the acyclic silene amine adduct Me2EtN Æ Me2Si@C(SiMe2Ph)2 [7]
˚
Distances (A)
Compound
Sum of angles (ꢁ)
Si@C
Si1–N1
Si1
C1
3c
3d [5]
1.744(2)
1.759(3)
1.764(2)
1.761(4)
2.043(2)
2.035(3)
2.077(2)
1.988(4)
348.9
348.5
345.7
341.8
359.4
359.9
359.5
359.2
4
Me2EtN Æ Me2Si@C(SiMe2Ph)2 [7]
Atomic numbering analogously 3c.
and are similarly consistent with those reported by Wi-
berg et al. [7] for the acyclic silene amine adduct Me2Et-
N Æ Me2Si@C(SiMe2Ph)2. For all compounds Si1–N1
and 4 were recovered unchanged. Similar results were
obtained after treatment of the stable silenes with 2,3-di-
methyl-1,3-butadien. The reaction, which in case of
uncomplexed silenes through a [2 + 4] cycloaddition step
normally leads to silacyclohexenes, is frequently used for
the chemical characterization of silenes [8]. But in this
particular case no reaction occurred.
˚
distances of approximately 2.04 A were found. These
figures appear to be typical for amine-coordinated si-
lenes. The distances between the silene silicon atoms
and the nitrogen atoms of the second dimethylamino
˚
group are considerably longer (for 3c 4.709 A). The
The addition of water across the Si@C double bond
to give silanols is considered to be a typical reaction of
silenes [8]. Actually, the reaction of 3a and 3c with ex-
cess water produced the expected silanols ArR1-
Si(OH)CH(SiMe3)2 (5a,c) (5a: R1 = Me; 5c: R1 = Ph;
Ar = 2,6-(Me2NCH2)2C6H3). The silene 3a proved to
be extraordinarily moisture sensitive and is converted
by traces of water into the disiloxane [(Me3Si)2CH]-
ArMeSi–O–SiMeAr[CH(SiMe3)2] (6a) (Ar = 2,6(Me2-
NCH2)2C6H3). Addition of water to the silene 4 gave
the silanol [2,6-(Et2NCH2)2C6H3](Me3Si)[(Me3Si)2CH]-
SiOH (7). In these reactions, the behavior of 3a–c and
4 is in full agreement with the previously described prop-
erties of 3d [5]. For 5c and 6a also X-ray structural anal-
yses were performed. Details of the synthesis and
structure of 5–7 are given below (see Section 3).
Particularly, high hopes we had of studies on the
interaction of the newly synthesized silenes with car-
bonyl compounds. Normally, silenes react with alde-
hydes and ketones in a formal [2 + 2] cycloaddition
step to give 1,2-oxasiletanes [8]. Only in a few cases these
four-membered ring systems can be isolated [6a,9]. Usu-
ally, they undergo spontaneous cycloreversions into an
olefin and a transient silanone, which rapidly forms olig-
omeric products.
As already verified for other derivatives of three-
coordinate silicon, also silanones are expected to be
stabilized by amine coordination to the electrophilic
silanone silicon atom. While intramolecularly donor-
stabilized silanethiones could be isolated and proved
to be stable [2], comparable Si@O systems are unknown.
Expectations on the stabilization of silanones by intra-
molecular amine coordination must not be exaggerated.
Belzner et al. [2b] succeeded in the generation of the sila-
none Ar2Si@O (Ar = 2-dimethylaminomethylphenyl) by
the reaction of the silylene Ar2Si: with isocyanates, but
the compound proved to be labile and the product
isolated he identified as the respective cyclotrisiloxane
(Ar2SiO)3, the silanone trimer. Silanones bearing a
donation of the nitrogen lone pair to the silene silicon
atom leads to pyramidalizations at the Si1 atoms. In
contrast, the configuration at the silene carbon atoms
is trigonal planar. The similarities also apply to the
Si1–C1 distances. Si@C bond lengths of approximately
˚
1.75 A prove to be standard values for amine coordi-
nated silenes (see also [6b]). A comparison of these struc-
tural data with those of kinetically stabilized
uncomplexed silenes was discussed previously [6b].
Tetracoordination of the silene silicon atoms was
proved for 3a–d also in solution. Whereas the 1H
NMR spectra of 3a–d at room temperature show only
one signal for both NMe2 groups, at low temperatures
two signals for the dimethylamino groups appear and,
additionally, one of the NMe2 signals is split into two
peaks (for 3d in THF-d8 the coalescence temperature
was found to be 233 K). Thus, the signal pattern of
1
the low temperature H NMR spectra agrees with the
solid-state structure. At room temperature rapid ex-
change processes lead to the magnetic equivalence of
the two dimethylamino groups.
Summarizing the results of the structural investiga-
tions, we have to conclude that independent of the sec-
ond substituent at the silene silicon atoms in 3a–d and
4, respectively, only one dialkylamino group is coordi-
nated to the electrophilic Si1 atoms, i.e., in the solid
state as well as in solution the silene silicon atoms are al-
ways tetracoordinated.
2.2. Reactivity of the intramolecularly donor-stabilized
silenes 3a–d
Compared with uncomplexed silenes, the reactivity of
3a–d or 4, respectively, is reduced dramatically. Rapid
dimerization is a typical behavior of reactive Si@C sys-
tems [8], but even after prolonged heating, no dimers of
the newly synthesized silenes could be detected; 3a–d

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U. Ba¨umer et al. / Journal of Organometallic Chemistry 691 (2006) 229–239
2,6-bis(dialkylaminomethyl)phenyl substituents might
be interesting model compounds, and additional kinetic
stabilization by suitable bulky substituents may finally
lead to stable silanones. In this context the reaction of
3a–d and 4 or any related silene with aldehydes or
ketones might be a promising route to intramoleculaly
donor-stabilized silanones.
mer, 12c could be separated into the two stereoisomers
trans,cis-12c and cis,trans-12c, which differ in the rela-
tive configurations of the 4-dimethylamino groups and
the 3-phenyl groups with reference to the substituents
at the ring silicon atoms. All three isolated species are
colorless solids, whose structures were elucidated on
the basis of NMR and MS studies and, in particular,
by X-ray structural analyses. Fig. 2 shows the results
of the X-ray analysis of trans,cis-12c, the outcome of
the X-ray analysis of cis,trans-12c is demonstrated in
Fig. 3. Complex 12a may similarly be described as the
trans,cis-derivative, however, there are two symmetry
independent molecules in the asymmetric unit, hence
the number of molecules within the triclinic unit cell is
4. The six membered rings are slightly folded (torsional
angles O1–Si1–C8–C9: 12a 13.34(19)ꢁ and ꢀ6.7(2)ꢁ for
the corresponding atoms O31–Si31–C38–C39 in the sec-
ond molecule; trans,cis-12c 10.1(3)ꢁ, cis,trans-12c
26.98(12)ꢁ; C8–C9–C17–C20: 12a 17.5(3)ꢁ and 24.5(3)ꢁ
for the corresponding atoms C38–C39–C47–C50 in the
second molecule, trans,cis-12c 28.9(5)ꢁ, cis,trans-12c
ꢀ55.32(15)ꢁ; atomic numbering for 12a analogously
12c). In all structures the obtained bond lengths and an-
gles are in agreement with standard values. The reaction
of 3d with benzaldehyde gave 8d and 9 exclusively.
Our proposal on the reaction path to 12a,c is summa-
rized in Scheme 3. Obviously, the aldehyde attacks the
silene system of 3a,c with the nucleophilic carbonyl oxy-
gen atom at the silene silicon atom to form the zwitter-
ionic structures 15a,c. Ring closure to 16a,c is the
expected way of stabilization of 15a,c, and the oxasile-
tane systems formed undergo spontaneous cyclorever-
sions leading finally to the olefin 9 and the silanone
Unfortunately, the reactivity of the silenes 3a–d and 4
towards carbonyl compounds is very low. This, obvi-
ously, is due to the strong N ! Si coordination. Com-
plexes 3a, 3c and 3d were chosen for studies of their
reaction with benzaldehyde. The components were dis-
solved in heptane and the solutions were heated for
three days at 80 ꢁC. Aqueous workup of the heptane
solutions and chromatographic separation of the reac-
tion mixtures always gave the olefin 9 in yields of 33–
69%. Its analytical data proved to be identical with those
described for 2,2-bis(trimethylsilyl)styrene in the litera-
ture [10]. The silanone oligomers 8a, 8c and 8d, respec-
tively, were not isolated as pure compounds, but
NMR and IR studies of the chromatographically sepa-
rated product mixtures strongly refer to the proposed
structures. In most cases varying quantities of the
respective silanols 5a,c,d were isolated, indicating that
considerable quantities of the starting silenes remained
unchanged. Both 8a,c,d and 9 are the expected products
of the reaction of the silenes 3a, 3c and 3d with benzal-
dehyde (Scheme 2).
In case of the reaction of 3a and 3c, respectively, with
benzaldehyde, besides 8a, 8c and 9 two unexpected
products were isolated, to which we assign the structures
of the 2-oxa-1-sila-1,2,3,4-tetrahydronaphthalenes (12a
and 12c). Whereas 12a was isolated as a pure diastereo-
R1
R2
CH=C(SiMe3)2
9 (R2 = H)
10 (R2 = Cl)
11 (R2 = OCH3)
Si O
+
n
C6H3(CH2NMe2)2
NMe2
Si C
CHO
R2
8a,c,d
SiMe3
+
R1
SiMe3
Me2N
NMe2
CH
CH
3a,c,d
R2
O
Si
R1 CH(SiMe3)2
Me2N
12a (R1 = Me; R2 = H)
12c (R1 = Ph; R2 = H)
13 (R1 = Ph; R2 = Cl)
14 (R1 = Ph; R2 = OCH3)
Scheme 2. The reaction of the intramolecularly donor-stabilized silenes 3a and 3c, respectively, with benzaldehyde.

U. Ba¨umer et al. / Journal of Organometallic Chemistry 691 (2006) 229–239
233
oligomers 8a,c (Way A). But in a competing reaction
one proton is abstracted intramolecularly from the ben-
zylic methylen group by the tris(silyl)carbanionic centres
of 15a,c to produce the new zwitterions 17a,c, which sta-
bilize under ring closure to give 12a,c (Way B).
The proposed mechanism is supported by studies of
the reaction of 3c with benzaldehyde in different sol-
vents. Increasing polarity of the solvent should enhance
the stability of the zwitterion 15c, facilitating the proton
transfer 15c ! 17c, thus favoring Way B and the forma-
tion of 12c. Actually, the results of the reactions of 3c
with benzaldehyde in heptane, toluene and THF, respec-
tively, indicate that with increasing polarity of the sol-
vent used the yield of 12c (i.e., the mixture of the
isomers) increases on the expense of the olefin 9 [yields
in heptane: 9 33%, 12c 24%; in toluene: 9 12%, 12c
49% (mixture of isomers); in THF: 9 4%, 12c 52% (mix-
ture of isomers)]. After the reaction of 3d with benzal-
dehyde neither in heptane nor in THF the expected
six-membered system 12d could be found, i.e., the reac-
tion proceeds along Way A exclusively. Probably, due to
the extraordinary steric congestion at the central silicon
atom in 15d (R = SiMe3) and a restricted rotation
around the Si–CSi2 bond a suitable conformation neces-
sary for the proton transfer is excluded.
Fig. 2. Molecular structure of trans,cis-12c in the crystal (ORTEP,
30% probability level, H atoms omitted for clarity; see also Table 2 for
˚
additional crystallographic information). Selected bond lengths (A):
Si1–C1 1.874(4), Si1–C27 1.887(4), Si1–O1 1.654(3), C8–C9 1.418(5),
C9–C17 1.556(5), C17–C20 1.541(5), C20–O1 1.440(4). Selected bond
angles (ꢁ): O1–Si1–C8 102.65(15), O1–C20–C17 108.7(3), C9–C17–C20
112.2(3), C20–O1–Si1 123.4(2).
Moderately stable ‘‘silenes of the Brook type’’ [8b] re-
act with aromatic aldehydes to give mixtures of diaste-
reomeric oxasiletanes [9]. Concerning the reaction
path, three alternative ways were taken into consider-
ation: a concerted one-step [2 + 2] addition or two-step
processes involving either a diradical intermediate or a
dipolar intermediate both resulting from primary inter-
actions of the carbonyl oxygen atom with the silene sil-
icon atom. The radical mechanism could widely be
excluded, and Brook et al. [9] favor a dipolar mechanism
with intermediates structurally comparable with 15a,c,d,
but were unable to present any trapping products. The
formation of the intermediates 17a,c by an irreversible
proton transfer from 15a,c, identified by the isolation
of 12a,c, may be considered as an indication of a dipolar
intermediate in the course of the reaction of 3a,c,d with
benzaldehyde. Despite a considerable weakening of the
electrophilic properties of the central silicon atoms due
to the intramolecular amine coordination in 3a,c,d, the
primary attack of the aldehyde with its nucleophilic oxy-
gen atom is directed towards the silene silicon atoms.
Thus, the reasonable interpretation of the formation of
12a,c strongly supports a dipolar mechanism for the
reaction of silenes with carbonyl compounds, as pro-
posed by Brook et al. [9].
Fig. 3. Molecular structure of cis,trans-12c in the crystal (ORTEP,
30% probability level, H atoms omitted for clarity; see also Table 2 for
˚
additional crystallographic information). Selected bond lengths (A):
In view of the ylidic character of intramolecularly
amine coordinated silenes and the proved pronounced
nucleophilic properties of their silene carbon atoms
[6c], one may also assume the reaction of 3a,c,d with
benzaldehyde to proceed through an initial attack of
the silene carbon atom at the carbonyl carbon atom,
Si1–C1 1.8686(15), Si1–C8 1.8983(15), Si1–C27 1.8811(15), Si1-O1
1.6594(10), C8–C9 1.417(2), C9–C17 1.517(2), C17–C20 1.540(2), C20–
O1 1.4282(17). Selected bond angles (ꢁ): O1–Si1–C8 101.27(6), O1–
C20–C17 111.23(12), C9–C17–C20 110.35(12), C20–O1–Si1 127.45(9).

234
U. Ba¨umer et al. / Journal of Organometallic Chemistry 691 (2006) 229–239
NMe2
NMe2
SiMe3
C(SiMe3)2
+
Si C
PhCHO
Si
R1
SiMe3
R1
O
CHPh
Me2N
Me2N
3a,c,d
15a,c,d
A
B
NMe2
CH
NMe2
CH(SiMe3)2
Si C(SiMe3)2
Si
R1
R1
O
CHPh
Me2N
O
CHPh
Me2N
17a,c
16a,c,d
NMe2
CH
8a,c,d +
9
CH Ph
O
Si
R1 CH(SiMe3)2
Me2N
12a,c
Scheme 3. Proposed reaction path of the formation of the 2-oxa-1-sila-1,2,3,4-tetrahydronaphthalenes (10a and 10c) by the interaction of the silenes
3a and 3c, respectively, with benzaldehyde.
and 8a,c,d and 9 might be produced through the inter-
mediate oxasiletanes 16a,c,d along a Peterson-type
mechanism. Under these circumstances no 12a,c can
be formed, i.e., 8a,c,d and 9 on the one hand and
12a,c on the other are products of different reaction
paths. But this idea could easily be excluded by studies
of the reaction of 3c with 4-chlorobenzaldehyde or 4-
methoxybenzaldehyde, respectively. Whereas the con-
version of the intermediate zwitterions of the type 15
(Way A or B) should not be significantly influenced
by the nature of the carbonyl compound used, 4-chloro-
benzaldehyde should favor a Peterson-type mechanism,
4-methoxybenzaldehyde should favor the mechanism
described in Fig. 3. Actually, the reaction of 3c with
4-chlorobenzaldehyde in heptane produced 32% of the
2-oxa-1-silatetrahydronaphthalene 13 besides 9% of
the olefin 10. Under the same conditions, complex 3c
was converted with 4-methoxybenzaldehyde to give
19% of 14 and 46% of 11 (Scheme 2). Both 13 and 14
proved to be pure diastereomers and X-ray structural
analyses, performed for the two compounds, justify a
description as c-3-(4-chlorophenyl)-t-4-dimethylamino-
8-(dimethylaminomethyl)-1-phenyl-r-1-[bis(trimethylsi-
lyl)methyl]-2-oxa-1-sila-1,2,3,4-tetrahydronaphthalene
(13) and c-3-(4-methoxyphenyl)-t-4-dimethylamino-8-
(dimethylaminomethyl)-1-phenyl-r-1-[bis(trimethylsilyl)-
methyl]-2-oxa-1-sila-1,2,3,4-tetrahydronaphthalene (14),
respectively. The results of these experiments unambigu-
ously exclude a significant role of a Peterson-type mech-
anism and support the proposed pathway described in
Scheme 3.
As the outcome of the reaction of 3d with 4-chloro-
benzaldehyde and 4-methoxybenzaldehyde, respectively,
the olefins 10 and 11 were isolated besides considerable
quantities of the silanol ArR1Si(OH)CH(SiMe3)2 (5d)
(R1 = Me3Si, Ar = 2,6(Me2NCH2)2C6H3). Again, the
formation of the respective 2-oxa-1-sila-tetrahydronaph-
thalene systems did not occur.
3. Experimental
All reactions involving organometallic reagents were
carried out under purified argon. NMR: Bruker AC
250 or Bruker ARX 300, temperature 30 ꢁC, tetrameth-
ylsilane as internal standard. IR: Nicolet 205 FT-IR.
MS: Intectra AMD 402 (EI with 70 eV or chemical
ionization with isobutane). (Dichloromethyl)methyl-
bis(trimethylsilyl)silane (1a) [6a], tert butyl(dichloro-
methyl)bis(trimethylsilyl)silane(1b)[11], (dichloromethyl)

U. Ba¨umer et al. / Journal of Organometallic Chemistry 691 (2006) 229–239
235
phenylbis(trimethylsilyl)silane (1c) [6a], (dichloro-
methyl)tris(trimethylsilyl)silane (1d) [12] as well as
2,6-bis(dimethylaminomethyl)phenyllithium [13] were
prepared as described in the literature. The synthesis
of 3d and 5d previously [5]. All yields given refer to
amounts obtained after chromatographic separation
and purification or recrystallization.
NMR (benzene-d6): d = 0.28 and 0.62 (2s, Si(CH3)3,
2 · 9H), 1.99 (s, NCH3, 12H), 3.13 and 3.66 (2d,
2J = 14.0 Hz, CH2, 2 · 2H), 6.93–7.70 (m, aryl-CH,
8H). 13C NMR (benzene-d6): d = 7.68 and 9.1
(Si(CH3)3), 22.7 (Si@C), 46.4 (NCH3), 64.2 (CH2),
125.6, 127.1, 129.1, 130.0, 136.7, 137.0, 138.0 and
144.5 (arom. C). 29Si NMR (benzene-d6): d = ꢀ9.6 and
ꢀ8.9 (SiMe3), 23.9 (Si@C). MS (EI, m/z, %): 454 (44)
[M+], 439 (75) [M+ ꢀ CH3]. Anal. Calc. for C25H42N2Si3
(454.27): C, 66.01; H, 9.31; N, 6.16. Found: C, 65.82; H,
9.58; N, 6.17%.
3.1. General procedure for the synthesis of the silenes 3a–c
and 4
At 0 ꢁC, the respective (dichloromethyl)tris(trimeth-
ylsilyl)silane 1a, 1b or 1c, respectively, was added to
an ethereal suspension of 2,6-bis(dimethylaminom-
ethyl)phenyllithium (in case of 4 to a solution of 2,6-
bis(diethylaminomethyl)phenyllithium). The mixture
was stirred for 48 h at room temperature, and after
evaporation of the solution in vacuo pentane was added
and the lithium chloride formed was separated by filtra-
tion. The residue obtained by evaporation of the filtrate
was recrystallized from pentane.
3.1.4. 1-[2,6-Bis(diethylaminomethyl)phenyl]-1,2,2-
tris(trimethylsilyl)silene (4)
Following the procedure described above, 0.65 g
(1.97 mmol) of 1d and 1.00 g (3.94 mmol) of 2,6-
bis(diethylaminomethyl)phenyllithium gave 0.48
g
(49%) of 4. Pale yellow crystals, m.p. 74–78 ꢁC. 1H
NMR (benzene-d6): d = 0.19, 0.28 and 0.57 (3s, SiCH3,
3 · 9H), 0.90 (t, 3J = 7.2 Hz, CCH3, 12H), 2.58 (dq,
2J = 13.0 Hz, 3J = 7.0 Hz, CCH2N, 4H), 2.79 (dq,
2J = 13.1 Hz, 3J = 7.0 Hz, CCH2N, 4H), 3.64 (d,
2J = 15.3, ArCH2, 2H), 3.73 (d, 2J = 15.3, ArCH2,
2H), 7.23–7.24 (m, aryl-CH, 3H). 13C NMR (ben-
zene-d6): d = 3.1 (SiSiCH3), 7.1 and 8.1 (CSiCH3),
10.5 (CCH3), 21.7 (Si@C), 46.4 (CCH2), 58.7
(ArCH2N), 124.5, 129.6, 140.3 and 143.5 (arom. C).
29Si NMR (benzene-d6): d = ꢀ20.0 (SiSi Me3), ꢀ8.35
and 8.40 (CSiMe3), 36.7 (Si@C). MS (EI, m/z, %):
506 (3) [M+], 477 (38) [M+ ꢀ CH2CH3]. Anal. Calc.
for C26H54N2Si4 (507.06): C, 61.59; H, 10.73; N,
5.52. Found: C, 61.65; H, 10.99; N, 5.62%.
3.1.1. 1-[2,6-Bis(dimethylaminomethyl)phenyl]-1-
methyl-2,2-bis(trimethylsilyl)silene (3a)
1.00 g (3.65 mmol) of 1a and 1.45 g (7.32 mmol) of
2,6-bis(dimethylaminomethyl)phenyllithium gave 0.77 g
1
(78%) of 3a. Colorless crystals, m.p. 190–194 ꢁC. H
NMR (benzene-d6): d = ꢀ0.15 and 0.18 (2s, Si(CH3)3,
2 · 9H), 0.13 (s, SiCH3, 3H), 1.80 (s, NCH3, 12H),
2
2.75 and 3.41 (2d, J = 13.4 Hz, CH2, 2 · 2H), 6.77–
6.93 (m, aryl-CH, 3H). 13C NMR (benzene-d6):
d = 1.7 (SiCH3), 6.8 and 8.0 (Si(CH3)3), 22.7 (Si@C),
45.9 (NCH3), 64.2 (CH2), 125.7, 127.7, 128.3, 129.7,
139.6 and 143.4 (arom. C). 29Si NMR (benzene-d6):
d = ꢀ10.6 and ꢀ7.7 (SiMe3), 30.3 (Si@C). MS (EI,
m/z, %): 392 (100) [M+], 377 [M+ ꢀ CH3]. Anal. Calc.
for C20H40N2Si3 (392.80): C, 61.15; H, 10.26; N, 7.13.
Found: C, 60.95; H, 10.52; N, 7.31%.
3.2. General procedure for the reaction of 3a, 3c or 4 with
water
Ethereal solutions of the respective silenes were
added to excess water/THF mixtures (1:1). After stir-
ring for half an hour the organic layer was separated
and the aqueous phase extracted with ether. The col-
lected and dried organic solutions were evaporated
and the residues obtained were purified by recrystalli-
zation from heptane (5c) or by Kugelrohr-distillation
(5a and 7).
3.1.2. 1-tert-Butyl-1-[2,6-bis(dimethylaminomethyl)-
phenyl]-2,2-bis(trimethylsilyl)silene (3b)
The compound could not be isolated in a pure form.
Therefore, only the characteristic NMR data are given.
1H NMR (benzene-d6): d = 0.14 and 0.53 (2s, SiCH3,
2 · 9H), 1.11 (s, CCH3, 9H), 2.15 (s, NCH3, 12H),
3.57 (pseudo-t, 2J = 15.6 Hz, CH2, 4H), 6.88–7.42
(aryl-CH, 3H). 13C NMR (benzene-d6): d = 7.1 and 8.4
(SiCH3), 26.8 (Si@C), 29.6 (CCH3), 44.1 (NCH3), 63.9
(CH2), 124.2–147.5 (aryl-C). 29Si NMR (benzene-d6):
d = ꢀ10.6 and ꢀ8.8 (SiMe3), 39.0 (Si@C).
3.2.1. [2,6-Bis(dimethylaminomethyl)phenyl]-methyl-
[bis(trimethylsilyl)methyl]-silanol (5a)
1.25 g (3.19 mmol) of the silene 3a produced 0.88g
(67%) of 5a. Colorless oil. 1H NMR (benzene-d6):
d = 0.24 and 0.47 (2s, SiCH3, 2 · 9H), 0.31 (s, SiCH,
1H), 0.70 (s, OSiCH3, 3H), 1.96 (s, NCH3, 12H),
3.32 and 3.64 (2d, 2J = 12.2 Hz, 2 · 2H), 6.84–7.30
(m, aryl-CH, 3H), 8.0 (br s, OH, 1H). 13C NMR (ben-
zene-d6): d = 1.4 (OSiCH3), 3.2 and 3.8 (CSiCH3),
5.3 (SiCH), 44.4 (NCH3), 65.9 (CH2), 126.0, 127.8,
128.1, 131.5, 143.4 and 143.8 (arom. C). 29Si NMR
3.1.3. 1-[2,6-Bis(dimethylaminomethyl)phenyl]-1-
phenyl-2,2-bis(trimethylsilyl)silene (3c)
2.09 g (6.22 mmol) of 1c and 2.46 g (12.45 mmol) of
2,6-bis(dimethylaminomethyl)phenyllithium
1.80 g (54%) of yellow crystals, m.p. 189–193 ꢁC. H
afforded
1

236
U. Ba¨umer et al. / Journal of Organometallic Chemistry 691 (2006) 229–239
2
4.11 (dd, J = 11.9 Hz, PhCH2N, 2H), 3.66 and 3.97
(benzene-d6): d = 0.5 and 0.6 (SiMe3), 1.9 (SiOH). MS
(EI, m/z, %): 410 (3) [M+], 395 (81) [M+ ꢀ CH3], 393
[M+ ꢀ OH]. Anal. Calc. for C20H42N2OSi3 (410.26):
C, 58.47; H, 10.30; N, 6.82. Found: C, 58.20; H,
10.20; N, 6.74%.
2
(dd, J = 14.9 Hz, PhCH2N, 2H), 6.87–7.92 (m, aryl-
CH, 3H) 8.38 (br s, OH, 1H). 13C NMR (benzene-d6):
d = 1.4, 3.8 and 4.3 (SiCH3), 6.7, 10.0, 12.2 and 12.9
(CCH3), 30.2 (SiCH), 44.8 and 46.8 (CH2CH3), 59.5
and 61.2 PhCH2N, 126.2, 127.2 and 132.1 (arom. CH),
127.7, 128.5 and 143.6 (quart. arom. C). 13C NMR (ben-
zene-d6): d = ꢀ19.7 (SiSiMe3), 0.8 and 1.5 (CSiMe3), 2.3
(SiOH). MS (EI, m/z, %): 524 (1) [M+], 509 (29)
[M+ ꢀ CH3], 496 (6) [M+ ꢀ C2H5]. Anal. Calc. for
C26H56N2OSi4 (525.08): C, 59.47; H, 10.75; N, 5.34.
Found: C, 59.65; H, 10.78; N, 5.55%.
3.2.2. [2,6-Bis(dimethylaminomethyl)phenyl]-phenyl-
[bis(trimethylsilyl)methyl]-silanol (5c)
1.43 g (3.15 mmol) of silene 3c gave 0.67 g (88%) of
5c, colorless crystals (from heptane), m.p. 168–171 ꢁC.
1
ꢀ1
~
IR (nujol): m ¼ 3424 cm (SiOH). H NMR (benzene-
d6): d = 0.21 and 0.37 (2s, SiCH3, 2 · 9H), 0.64 (s, CH,
1H), 1.98 (s, NCH3, 12H), 2.73 and 4.00 (2br d, CH2,
2 · 2H), 6.84–7.30 (m, aryl-CH, 8H), 9.7 (br s, SiOH,
1H). 13C NMR (benzene-d6): d = 3.2 and 3.4 (SiCH3),
4.7 (SiCH), 44.3 and 45.5 (NCH3), 63.4 and 65.4
(CH2), 125.6, 127.8, 129.1, 130.0, 136.7, 137.0, 138.0
and 144.5 (arom. CH). 29Si NMR (benzene-d6):
d = ꢀ8.7 (SiOH), 0.2 and 1.1 (SiMe3). MS (EI, m/z,
%): 472 (76) [M+], 457 (100) [M+ ꢀ CH3], 412 (38)
[M+ ꢀ CH2NMe2]. Anal. Calc. for C25H44N2OSi3
(472.89): C, 63.50; H, 9.38; N, 5.92. Found: C, 63.86;
H, 9.49; N, 5.41%.
3.4. General procedure of the reaction of the silenes 3a, 3c
and 3d, respectively, with aromatic aldehydes
The reactions were carried out in heptane, THF or
toluene. Approximately 2 mmol of the respective silene
were dissolved in 100 ml of the solvent and after addi-
tion of the equimolar quantity of the aldehyde the mix-
ture was heated under stirring for 3 days (reaction
temperature in heptane 80 ꢁC, in THF 61 ꢁC, in toluene
105 ꢁC). Subsequently, the solvent was removed in va-
cuo and the residue was separated by column chroma-
tography. The respective styrenes were eluted with
pure hexane. The silanols were obtained by elution with
heptane/ethyl acetate (50:1), and elution with heptane/
ethyl acetate (5:1) gave the 2-oxa-1-silatetrahydronaph-
thalenes. The products obtained were recrystallized
from acetonitrile.
3.3. 1,3-Bis[2,6-bis(dimethylaminomethyl)phenyl]-1,3-
dimethyl-1,3-bis[bis(trimethylsilyl)methyl]disiloxane
(6a)
Wet ether was added to an ethereal solution of 2.0 g
(5.51 mmol) of 3a until the solution had completely
decolorized. Evaporation and recrystallization of the
residue from acetonitrile gave colorless crystals, m.p.
3.4.1. Reaction of 3a with benzaldehyde in heptane
Separation of the product mixture obtained after the
reaction of 1.06 g (2.71 mmol) of 3a with 0.29 g (2.71
mmol) of benzaldehyde afforded 0.46 g (69%) of 9,
0.05 g (4.5%) of 5a and 0.15 g (11.5%) of 12a.
1
168–173 ꢁC, yield 3.87 g (84%). H NMR (benzene-d6):
d = 0.05 and 0.49 (2s, SiCH3, 2 · 18H), 0.29 (s, OSiCH3,
6H), 1.30 (s, CH, 2H), 2.04 and 2.23 (2s, NCH3, 2 · 6H),
2
2.75 and 3.08 (2d, J = 13.4 Hz, CH2, 2 · 2H), 3.01 and
4.55 (2d, 2J = 12.5 Hz, CH2, 2 · 2H), 7.07–7.37 (m,
arom CH). 13C NMR (benzene-d6): d = 1.4 (OSiCH3),
3.4 and 5.3 (SiCH3), 8.3 (SiCH), 45.4 and 45.5
(NCH3), 65.4 and 65.8 (CH2), 130.4, 132.6 and 147.6
(arom. CH), 143.5, 144.1 and 144.5 (quart. arom. C).
13C NMR (benzene-d6): d = ꢀ1.51, 0.12 and 0.93 (SiMe3
and SiO). MS (EI, m/z, %): 802 (33) [M+], 787 (35)
[M+ ꢀ CH3], 758 (31) [M+ ꢀ NMe2], 611 (62)
[M+ ꢀ C6H3(NMe3)2]. Anal. Calc. for C40H82N4OSi6
(803.62): C, 59.78; H, 10.28; N, 6.97. Found: C, 58.58;
H, 10.37; N, 6.72%.
3.4.1.1. c-4-Dimethylamino-8-(dimethylaminomethyl)-1-
methyl-c-3-phenyl-r-1-bis(trimethylsilyl)-2-oxa-1-sila-1,
2,3,4-tetrahydronaphthalene (12a). Colorless crystals,
ꢀ1
~
m.p. 98–100 ꢁC. IR (nujol): m ¼ 1034 cm
(SiOC).
1H NMR (benzene-d6): d = 0.13 and 0.29 (2s,
Si(CH3)3, 2 · 9H), 0.035 (s, Si3CH, 1H), 0.76 (s,
SiCH3, 3H), 1.96 (s, NCH3, 6H), 2.11 (s, NCH3,
6H), 3.42 and 3.92 (2d, 2J = 12.8 Hz, NCH2,
2 · 1H), 4.40 (d, 3J = 9.9 Hz, NCH, 1H), 5.19 (d,
3J = 9.9 Hz, OCH, 1H), 7.12–7.86 (m, aryl-H, 8H).
13C NMR (benzene-d6): d = 2.9 (SiCH3), 3.1 and 3.8
(Si(CH3)3), 4.6 (Si3C), 41.4 and 45.2 (NCH3), 65.8
(NCH2), 71.3 (NCH), 75.0 (OCH), 127.0, 127.9,
128.2, 128.7, 129.3 and 130.0 (arom. CH), 132.9,
138.4 143.2 and 149.5 (arom. quart. C). 29Si NMR
(benzene-d6): d = 0.44 (SiO), 0.83 and 2.96 (SiMe3).
MS (CI, m/z, %): 498 (M+), 483 [M+ ꢀ CH3]. Anal.
Calc. for C27H46N2OSi3 (498.92): C, 65.00; H, 9.29;
N, 5.61. Found: C, 65.58; H, 9.41; N, 5.56%.
3.3.1. [2,6-Bis(diethylaminomethyl)phenyl]-
trimethylsilyl-[bis(trimethylsilyl)methyl]silanol (7)
Treatment of 1.04 g (2.05 mmol) of 4 with water pro-
duced 0.77 g (77%) of 7 in form of a colorless oil. IR
1
ꢀ1
~
(nujol): m ¼ 3350–3500 cm (br, SiOH) H NMR (ben-
zene-d6): d = 0.16, 0.30 and 0.49 (3s, SiCH3, 3 · 9H),
0.84 and 1.03 (2t, J = 7.02 Hz, CCH3, 2 · 6H), 0.96
(s, CH, 1 H), 2.40–2.70 (m, NCH2C, 8H), 3.26 and
3

U. Ba¨umer et al. / Journal of Organometallic Chemistry 691 (2006) 229–239
237
3.4.2. Reaction of 3c with benzaldehyde
3.4.3. Reaction of 3c with 4-chlorobenzaldehyde
The reaction of 1.2 g (2.6 mmol) of 3c with 0.28 of
benzaldehyde in heptane gave 0.21 g (33%) of 9 and
0.36 g (24%) of trans,cis-12c. The same reaction carried
out with 0.90 g (2.0 mmol) of 3c and 0.21 g of benzalde-
hyde in toluene afforded 0.06 g (12.5%) of 9, 0.06 g (3%)
of 5c, 0.30 g (27%) of trans,cis-12c and 0.04 g (3%) of cis
trans- 12c. In THF 1.0 g (2.2 mmol) of 3c and 0.23 g (2.2
mmol) of benzaldehyde produced 0.02 g (4.0%) of 9,
0.38 g (31%) of trans,cis-12c and 0.11 g (8%) of cis trans-
12c.
0.85 g (1.9 mmol) of 3c and 0.25 g (1.9 mmol) of 4-
chlorobenzaldehyde gave besides unidentified material
0.05 g (9.5%) of 10 and 0.60 g (32%) of 13.
3.4.3.1. 1-(4-Chlorophenyl)-2,2-bis(trimethylsilyl)ethyl-
ene (10). Colorless oil. 1H NMR (benzene-d6): d = 0.01
and 0.21 (2s, SiCH3, 2 · 9H), 7.68 (s, CH, 1H), 6.85 (d,
3
3J = 8.0 Hz, aryl-CH, 2H), 7.04 (d, J = 8.0 Hz, aryl-
CH, 2H). 13C NMR (benzene-d6): d = 0.6 and 2.2
(SiCH3), 30.2 (Si2C), 113.5 and 129.6 (arom. CH),
155.6 and 155.8 (arom. quart. C), 159.5 (olef. C). 29Si
NMR (benzene-d6): d = ꢀ8.1 and ꢀ0.7 (SiCH3). MS
(CI, m/z, %): 282 (44) [M+], 267 (76) [M+ ꢀ CH3], 209
(20) [M+ ꢀ SiMe3]. Anal. Calc. for C14H23ClSi2
(282.96): C, 59.43; H, 8.19. Found: C, 59.55; H, 8.36%.
3.4.2.1.
t-4-Dimethylamino-8-(dimethylaminomethyl)-
1,c-3-diphenyl-r-1-[bis(trimethylsilyl)methyl]-2-oxa-1-
sila-1,2,3,4-tetrahydronaphthalene (trans,cis-12c). Col-
orless crystals, m.p. 137–141 ꢁC. IR (nujol):
(SiOC). 1H NMR (benzene-d6):
ꢀ1
~
m ¼ 1035 cm
3.4.3.2. c-3-(4-chlorophenyl)-t-4-dimethylamino-8-(di-
methylaminomethyl)-1-phenyl-r-1-[bis(trimethylsilyl)-
methyl]-2-oxa-1-sila-1,2,3,4-tetrahydronaphthalene (13)
Colorless crystals, m.p. 123–127 ꢁC. IR (nujol):
d = 0.10 and 0.26 (2s, SiCH3, 2 · 9H), 0.74 (s, Si3CH,
1H), 1.96 and 2.11 (2s, NCH3, 2 · 6H), 3.42 (d,
2J = 12.8 Hz, 1H), 3.95 (d, 2J = 12.8 Hz, 1H), 4.40
(d, 3J = 9.9 Hz, NCH, 1H), 5.18 (d, 3J = 10.0 Hz,
OCH, 1H), 7.09–7.86 (m, aryl-CH, 13H). 13C NMR
(benzene-d6): d = 3.3 and 3.7 (SiCH3), 4.7 (SiO), 41.1
and 45.0 (NCH3), 65.3 (CH2), 70.7 (NCH), 76.1
(OCH), 121.4, 128.7, 129.8, 135.3, 136.3, 139.9,
143.2, 144.5 and 149.8 (arom. CH), 128.2, 128.3,
128.8, 129.7 and 135.4 (quart. arom. C). 29Si NMR
(benzene-d6): d = ꢀ3.48 (SiO), 0.39 and 1.25 (SiMe3).
MS (CI, m/z, %): 560 (15) [M+], 545 (32)
[M+ ꢀ CH3], 516 (23) [M+ ꢀ N(CH3)2], 454 (100)
[M+ ꢀ C6H5CHO]. Anal. Calc. for C32H48N2OSi3
(560.99): C, 68.51; H, 8.62; N, 4.99. Found: C,
67.05; H, 8.78; N, 4.46%.
1
ꢀ1
~
m ¼ 1062 cm (SiOC). H NMR (benzene-d6): d = 0.10
and 0.24 (2s, SiCH3, 2 · 9H), 0.74 (s, Si3CH, 1H), 1.89
and 2.10 (2s, NCH3, 2 · 6H), 3.39 and 3.93 (2d,
2J = 12.82 Hz, CH2, 2H), 4.25 (d, 3J = 10.07 Hz,
3
NCH, 1H), 5.04 (d, J = 10.07 Hz, OCH, 1H), 7.16–
7.82 (m, aryl-CH, 12 H). 13C NMR (benzene-d6):
d = 3.3 and 3.7 (SiCH3), 4.6 (Si3C), 41.1 and 44.9
(NCH3), 65.3 (CH2), 70.7 (NCH), 75.3 (OCH), 119.8,
128.1, 128.6, 129.0, 129.3, 129.8, 135.2 and 135.4 (arom.
CH), 133.6, 136.2, 139.6, 143.1, 143.2, 149.3 (quart.
arom. C). 29Si NMR (benzene-d6): d = ꢀ3.1 (SiO), 0.4
and 1.2 (SiMe3). MS (CI, m/z, %): 594 (3) [M+], 579
[M+ ꢀ CH3], 550 (3) [M+ ꢀ N(CH3)2]. Anal. Calc. for
C32H47ClN2OSi3 (595.44): C, 64.55; H, 7.96; N, 4.70.
Found: C, 63.49; H, 7.96; N, 4.57%. HRMS calc.:
594.2685; found: 594.2665.
3.4.2.2. c-4-Dimethylamino-8-(dimethylaminomethyl)-1,
t-3-diphenyl-r-1-[bis(trimethylsilyl)methyl]-2-oxa-1-sila-
1,2,3,4-tetrahydronaphthalene (cis,trans-12c). Colorleꢀs1s
~
crystals, m.p. 120–126 ꢁC. IR (nujol): m ¼ 1040 cm
3.4.4. Reaction of 3c with 4-methoxybenzaldehyde
0.85 g (1.9 mmol) of 3c and 0.25 g (1.9 mmol) of 4-
methoxybenzaldehyde gave besides unidentified material
0.24 g (46%) 11 and 0.21 g (19%) of 14.
1
(SiOC). H NMR (benzene-d6): d = 0.24 and 0.33 (2s,
SiCH3, 2 · 9H), 1.35 (s, Si3CH, 1H), 1.97 and 2.14 (2s,
NCH3, 2 · 6H), 3.41 (d, 3J = 14.0 Hz, CH2, 1H),
3.51 (d, 3J = 14.0 Hz, CH2, 1H), 3.33 (d, 3J = 3.7
Hz, NCH, 1H), 5.58 (d, 3J = 3.7 Hz, OCH, 1H),
6.95–7.99 (m, aryl-H, 13H). 13C NMR (benzene-d6):
d = 3.7 and 4.0 (SiCH3), 7.1 (SiO), 43.3 and 47.9
(NCH3), 64.8 (CH2), 74.2 (NCH), 75.4 (OCH),
121.0, 122.7, 125.6, 127.4, 127.5, 128.1, 129.6, 135.8
and 136.0 (arom. CH), 137.6, 141.0, 143.6, 144.8
and 145.7 (quart. arom. C). 29Si NMR (benzene-d6):
d = ꢀ9.11 (SiO), ꢀ1.55 and ꢀ0.58 (SiMe3). MS (CI,
m/z, %): 560 (2) [M+], 545 (17) [M+ ꢀ CH3], 516
(2) [M+ ꢀ N(CH3)2], 454 (100) [M+ ꢀ C6H5CHO].
Anal. Calc. for C32H48N2OSi3 (560.99): C, 68.51;
H, 8.62; N, 4.99. Found: C, 67.80; H, 8.67; N,
4.79%.
3.4.4.1. 1-(4-Methoxyphenyl)-2,2-bis(trimethylsilyl)eth-
ylene (11). Colorless oil. 1H NMR (benzene-d6):
d = 0.14 and 0.27 (2s, SiCH3, 2 · 9H), 3.38 (s,
OCH3, 3H), 6.71 (d, 3J = 8.55 Hz, arom. CH, 2H),
7.12 (d, 3J = 8.55 Hz, arom. CH, 2H), 7.90 (s, CH,
1H). 13C NMR (benzene-d6): d = 0.8 and 2.4 (SiCH3),
30.2 (Si2C), 54.7 (OCH3), 113.5 (CH), 113.5 and 129.6
(arom. CH), 155.6 and 155.8 (quart. arom. C), 159.5
(olef. C). 29Si NMR (benzene-d6): d = ꢀ8.3 and ꢀ1.0
(SiCH3). MS (CI, m/z, %): 278 (44) [M+], 263 (28)
[M+ ꢀ CH3], 205 (16) [M+ ꢀ SiMe3]. Anal. Calc. for
C15H26OSi2 (278.15): C, 64.68; H, 9.41. Found: C,
64.28; H, 9.53%.

238
U. Ba¨umer et al. / Journal of Organometallic Chemistry 691 (2006) 229–239
Table 2
Crystal and structure refinement data for 3c and isomers of 12c
Compound
3c
trans,cis-12c
cis,trans-12c
Formula weight
T (K)
Crystal system
454.88
200(2)
Triclinic
560.99
293(2)
560.99
173(2)
Monoclinic
P21/n
Monoclinic
C2/c
ꢀ
Space group (H.-M.)
Space group (Hall)
Unit cell dimensions
P1
ꢀP 1
ꢀP 2yn
ꢀC 2yc
˚
a (A)
8.8750(18)
10.725(2)
15.473(3)
10.600(3)
18.7836(4)
19.7861(5)
17.8214(4)
90
˚
b (A)
27.508(11)
12.341(4)
90
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
101.71(3)
105.03(3)
109.990(10)
90
3382(2)
91.7680(10)
90
6620.2(3)
101.35(3)
1343.5(5)
3
˚
V (A )
Z
2
1.124
4
1.102
8
1.126
Dcalc (Mg mꢀ3
)
Absorption coefficient (mmꢀ1
F(000)
Crystal size (mm3)
)
0.191
496
0.166
1216
0.169
2432
0.4 · 0.3 · 0.3
2.01–24.21
ꢀ10 6 h 6 9,
ꢀ12 6 k 6 12,
0 6 l 6 17
4019
0.58 · 0.4 · 0.24
1.91–22.00
ꢀ1 6 h 6 11,
ꢀ28 6 k 6 1,
ꢀ13 6 l 6 12
5189
0.68 · 0.36 · 0.22
3.10–25.00
ꢀ22 6 h 6 22,
ꢀ22k 6 23,
ꢀ21 6 l 6 21
32067
h Range for data collection (ꢁ)
Index ranges
Reflections collected
Independent reflections (Rint
Completeness to h/(%)
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
)
4019
4128 (0.0338)
22.00ꢁ/100
4128/0/343
1.062
5833 (0.0252)
25.00ꢁ/99.8
5833/0/343
1.084
24.21ꢁ/92.7
4019/0/271
0.998
R1 = 0.0385, wR2 = 0.0953
R1 = 0.0533, wR2 = 0.1000
0.291/ꢀ0.188
R1 = 0.0471, wR2 = 0.1070
R1 = 0.0914, wR2 = 0.1385
0.277/ꢀ0.223
R1 = 0.0345, wR2 = 0.0900
R1 = 0.0412, wR2 = 0.0977
0.297/ꢀ0.204
ꢀ3
˚
Largest difference in peak/hole (e A
)
3.4.4.2. c-3-(4-methoxyphenyl)-t-4-dimethylamino-8-(di-
methylaminomethyl)-1-phenyl-r-1-[bis(trimethylsilyl) me-
thyl]-2-oxa-1-sila-1,2,3,4-tetrahydronaphthalene (14)
Colorless crystals, m.p. 150–156 ꢁC. IR (nujol):
of 12c a Bruker P4 four-circle diffractometer and for all
other compounds an X8Apex area detector system was
used. All investigations were carried out with Mo Ka-
radiation (graphite monochromator). The structures
were solved with the Bruker SHELXTL software package
and refined with full-matrix least-squares methods (Bru-
ker SHELXTL) on F2. All non-hydrogen atoms were re-
fined anisotropically, while the hydrogens were put
into theoretical positions and refined according to the
riding model. Due to the low absorption coefficients
no absorption correction was performed. Further, crys-
tallographic and structure refinement data for the com-
pounds shown in Figs. 1–3 can be taken from Table 2.
CCDC Nos. 252260–252262 contain the corresponding
supplementary crystallographic data.
1
ꢀ1
~
m ¼ 1061 cm (SiOC). H NMR (benzene-d6): d = 0.12
and 0.28 (2s, SiCH3, 2 · 9H), 0.74 (s, Si3CH, 1H), 2.02
and 2.11 (2s, NCH3, 2 · 6H), 3.30 (s, OCH3, 3H), 3.43
and 3.96 (2d, 2J = 12.8 Hz, CH2, 2H), 4.41 (d,
3
3J = 10.0 Hz, NCH, 1H), 5.19 (d, J = 9.8 Hz, OCH,
1H), 6.83–7.91 (m, aryl-CH, 12H). 13C NMR (ben-
zene-d6): d = 3.3 and 3.7 (SiCH3), 4.6 (Si3C), 41.1 and
44.9 (NCH3), 54.7 (OCH3), 65.3 (CH2), 70.7 (NCH),
75.6 (OCH), 113.9, 127.4, 128.8, 129.1, 129.7, 129.9,
135.3 and 135.4 (arom. CH), 136.3, 136.6, 140.1,
143.2, 150.0 and 159.8 (arom. quart. C). 29Si NMR (ben-
zene-d6): d = ꢀ3.6 (SiO), 0.4 and 1.3 (SiMe3). MS (CI,
m/z, %): 590 (1) [M+], 575 (12) [M+ ꢀ CH3]. Anal. Calc.
for C33H50N2O2Si3 (591.02): C, 67.06; H, 8.53; N, 4.74.
Found: C, 67.21; H, 8.72; N. 4.54%.
4. Supplementary material
CCDC Nos. 252263–252268 contain the supplemen-
tary crystallographic data for compounds 4, 5c, 6a,
12a, 13 and 14. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/conts/retrieving.html
(or from the CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK; fax +44 1223 336 033; e-mail: deposit@
ccdc.cam.ac.uk).
3.5. Crystal structure determination of 3c, trans,cis-12c
and cis,trans-12c
The X-ray investigations were performed with three
different diffractometer systems. For 3c and 4, a STOE
imaging plate detecting system, for the trans–cis isomer

U. Ba¨umer et al. / Journal of Organometallic Chemistry 691 (2006) 229–239
239
Acknowledgements
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´
(b) M. Chauhan, C. Chuit, R.J.P. Corriu, A. Mehdi, C. Reye,
Organometallics 15 (1996) 4326.
We gratefully acknowledge the support of our work
by the Fonds der Chemischen Industrie. We thank Prof.
Michalik, Dr. W. Baumann and Prof. N. Stoll for
recording NMR and mass spectra and Prof. R. Kempe
and Dr. A. Spannenberg for their help in performing
several X-ray structural analyses.
[5] M. Po¨tter, U. Ba¨umer, M. Mickoleit, R. Kempe, H. Oehme, J.
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