Interactions of chloromethyldisilanes with tetrakis(dimethylamino)ethylene (TDAE), formation of [TDAE] [Si3Me2Cl7]

Article abstract of DOI:10.1016/S0022-328X(02)01856-9

The chlorodisilanes SiClMe₂-SiClMe₂ (1), SiCl₂Me-SiCl₂Me (2), SiCl₃-SiCl₃ (3) and a 9:1 mixture of 2 and SiCl₃-SiCl₂Me (4) were reacted with the electron-rich alkene tetrakis-(dimethylamino)-ethylene (TDAE) in n-hexane as well as in polar solvents. While 1 gave no reaction at all, 3 underwent a disproportionation reaction into SiCl₄ and Si(SiCl₃)₄. Also 2 and mixtures of 2 and 4 were disproportionated into MeSiCl₃ (2a) and methylchlorooligosilanes. Additionally a crystalline mixture of Si₃Me₃Cl₆ -TDAE (5a) plus Si₃Me₂Cl₇ -TDAE (5b) was obtained by reaction of a 9:1 mixture of 2 and 4 with TDAE in n-hexane as well as in 1,2-dimethoxyethane. The reaction of 2 with TDAE in acetonitrile (MeCN) led to a crystalline precipitation of [TDAE]Cl₂ -MeCN (6.MeCN) in addition to MeSiCl₃ and methylchlorooligosilanes. The structures of 5b and 6.MeCN were determined by X-ray crystallography beside their NMR and IR spectroscopic characterization. Compound 5b crystallizes in the monoclinic space group P2/c (Z = 4), 6.MeCN in the orthorhombic space group Pna2₁ (Z = 4). The structure of 5b reveals a [TDAE]^.+ radical cation and a 1, 2-Me₂Si₃Cl₇^- anion with a pentacoordinated central silicon atom.

Full text of DOI:10.1016/S0022-328X(02)01856-9

Journal of Organometallic Chemistry 662 (2002) 14ꢃ22
/
www.elsevier.com/locate/jorganchem
Interactions of chloromethyldisilanes with
tetrakis(dimethylamino)ethylene (TDAE), formation of [TDAE]
[Si3Me2Cl7]ꢁ
+ꢀ
C. Knopf a,*, U. Herzog a, G. Roewer a, E. Brendler b, G. Rheinwald c, H. Lang c
a Institut fur Anorganische Chemie, TU Bergakademie Freiberg, Leipziger Straße 29, D-09596 Freiberg, Germany
¨
b Institut fur Analytische Chemie, TU Bergakademie Freiberg, Leipziger Straße 29, D-09596 Freiberg, Germany
¨
c Institut fur Chemie, Lehrstuhl Anorganische Chemie, TU Chemnitz, Straße der Nationen 62, D-09111 Chemnitz, Germany
¨
Received 25 September 2001; accepted 17 July 2002
Abstract
The chlorodisilanes SiClMe2Ã
were reacted with the electron-rich alkene tetrakis-(dimethylamino)-ethylene (TDAE) in n-hexane as well as in polar solvents. While
/
SiClMe2 (1), SiCl2MeÃ
/
SiCl2Me (2), SiCl3Ã
/
SiCl3 (3) and a 9:1 mixture of 2 and SiCl3Ã
/
SiCl2Me (4)
1 gave no reaction at all, 3 underwent a disproportionation reaction into SiCl4 and Si(SiCl3)4. Also 2 and mixtures of 2 and 4 were
disproportionated into MeSiCl3 (2a) and methylchlorooligosilanes. Additionally a crystalline mixture of Si3Me3Cl6×
Si3Me2Cl7×TDAE (5b) was obtained by reaction of a 9:1 mixture of 2 and 4 with TDAE in n-hexane as well as in 1,2-
dimethoxyethane. The reaction of 2 with TDAE in acetonitrile (MeCN) led to a crystalline precipitation of [TDAE]Cl2×MeCN (6×
MeCN) in addition to MeSiCl3 and methylchlorooligosilanes. The structures of 5b and 6×MeCN were determined by X-ray
crystallography beside their NMR and IR spectroscopic characterization. Compound 5b crystallizes in the monoclinic space group
/TDAE (5a) plus
/
/
/
/
+ ꢀ
P2/c (Zꢂ
/
4), 6×
/
MeCN in the orthorhombic space group Pna21 (Zꢂ
/
4). The structure of 5b reveals a [TDAE]
radical cation and
a 1; 2-Me2Si3Clꢁ7 anion with a pentacoordinated central silicon atom.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Chlorosilane; Disilane; TDAE; Hypercoordination; Silicon
1. Introduction
finally polysilanes. Oligosilanes containing up to seven
silicon atoms were isolated and identified by Herzog et
al. [5]. Hildebrandt and Engels [6] studied theoretically
the mechanism of the Lewis-base catalyzed dispropor-
tionation of chlorodisilanes. From their calculations
they concluded that the activation energy of the
disproportionation as well as the location and the
geometry of the transition state on the reaction co-
ordinate are significantly influenced by the used Lewis-
base. But besides this, their computation results do not
support the common assumption that the disproportio-
nation is initiated by the preformation of a disilane-
donor complex. However, they have found a strong
stabilization effect of the intermediate silylene by
coordination of Lewis-bases.
Chloromethyldisilanes are by-products of the
¨
MULLERꢃ
/
ROCHOW process [1,2]. Via a catalytic dispro-
portionation reaction they can be converted into oligo-
or polysilanes, which represent promising precursor
compounds of silicon carbide ceramics. Key steps of
the disproportionation of SiCl2MeÃ
are outlined in Scheme 1.
Most probably the catalytic disproportionation pro-
ceeds via a 1,2-shift of one of the chlorine substituents at
the donor coordinated Si-atom followed by the subse-
/
SiCl2Me (2) [3ꢃ5]
/
quent cleavage of the SiÃ
/
Si bond. Insertion reaction of
the as-formed donor stabilized silylene into a SiÃ
/Cl
bond of a further molecule of 2 leads to oligo- and
Previously applied disproportionation catalysts are
electron-pair donors such as amines, phosphanes,
AgCN, hexamethylphosphoric acid triamide or N-
* Corresponding author
E-mail address: claudia.knopf@chemie.tu-freiberg.de (C. Knopf).
heterocycles like N-methylimidazol [7ꢃ9]. In contrast
/
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 8 5 6 - 9

C. Knopf et al. / Journal of Organometallic Chemistry 662 (2002) 14ꢃ
/
22
15
Scheme 1. Supposed mechanism of the Lewis-base catalyzed disproportionation of 2.
to these types of catalytically active compounds, which
SiCl3 (3) and a 9:1 mixture of 2 and SiCl2MeÃ
/SiCl3 (4)
represent electron pair donors, tetrakis(dimethylamino)-
ethylene (TDAE) should be able to transfer either one or
two electrons to the disilane molecule. Thus it may form
radical cation or dication salts. Based on this behavior
towards TDAE.
Compound 1 gave no reaction when a mixture with
TDAE n-hexane was heated to reflux for 2 h.
On the other hand, the higher chlorofunctionalized
disilanes 2 and 3 reacted with TDAE under dispropor-
tionation, see Table 1.
Additionally in case of the reaction of TDAE with 2 a
dark red precipitation was observed. MAS NMR
spectra of this highly air sensitive product revealed the
formation of 5a but in mixture with smaller amounts of
a second compound which was later found to be 5b. The
formation of 5b is understandable by the fact that the
of the TDAE Burger and Moritz [10] converted poly-
¨
halomethanes into halomethanide anions. This
prompted us to find out, whether an eꢁ-transfer to
the disilane is able to initiate the disproportionation
process of disilanes. A specific N-coordination of the
TDAE to a disilane molecule or silylene species is
sterically hindered by the bulky dimethylamino groups
[11,12]. Some steps of the redox process should be
affected significantly by the used solvent.
used 2 contained small amounts (1ꢃ2%) of methylpen-
/
tachlorodisilane (4) as was detected by 29Si NMR
2. Results and discussion
2.1. Disproportionation of disilanes with TDAE in n-
hexane
In order to reveal mechanistic details of the dispro-
portionation process we have investigated the reactivity
of SiClMe2Ã
/
SiClMe2 (1), SiCl2MeÃ
/
SiCl2Me (2), SiCl3Ã
/
Table 1
29Si-NMR spectroscopic identification of the products of the reaction
of TDAE with chlorosubstituted disilanes in n-hexane
Educt disilanes
Identified products
Relative amount (%)
1
SiClMe2ÃSiClMe2 (1)
(no reaction)
100
2
SiCl2MeÃSiCl2Me (2)
MeSiCl3 (2a)
SiClMe(SiCl2Me)2 (2b)
97
1
2
3
SiCl3ÃSiCl3 (3)
SiCl4 (3a)
Si(SiCl3)4 (3b)
46
48
6
2/4 (9:1)
SiCl2MeÃSiCl2Me (2)
MeSiCl3 (2a)
69
21
5
Fig. 1. (A) ORTEP plot of the molecular structure of 5b. (B) ORTEP plot
of the trisilanide ion Si3Me2Clꢁ7 in 5b. Positions of C1, Cl3 and Cl4
marked by an apostrophe have an occupation factor of 36.5%, the
positions without an apostrophe have an occupation factor of 63.5%.
SiClMe(SiCl2Me)2 (2b)
SiMe(SiCl2Me)3 (2c)
5

16
C. Knopf et al. / Journal of Organometallic Chemistry 662 (2002) 14ꢃ22
/
Table 2
˚
Selected bond lengths (A), bond angles (8) and dihedral angles (8) of 5b
Bond lengths
Si(1)ÃSi(2)
Si(1)ÃCl(1)
Si(2)ÃC(1)
Si(2)ÃCl(3)
Si(2)ÃCl(4)
Si(2)ÃSi(3)
Si(3)ÃCl(6)
C(4)ÃC(5)
N(2)ÃC(5)
N(3)ÃC(10)
2.326(2)
2.079(2)
1.80(4)
Si(1)ÃC(2)
Si(1)ÃCl(2)
Si(2)ÃC(1)?
Si(2)ÃCl(3)?
Si(2)ÃCl(4)?
Si(3)ÃCl(5)
Si(3)ÃCl(7)
N(1)ÃC(4)
C(10)ÃC(11)
N(4)ÃC(11)
1.892(6)
2.081(3)
2.04(6)
2.498(13)
2.328(9)
2.325(2)
2.008(3)
1.416(10)
1.365(6)
1.367(6)
2.583(15)
2.140(20)
2.079(3)
2.021(3)
1.353(6)
1.408(11)
1.363(6)
Bond angles
Cl(1)ÃSi(1)ÃCl(2)
C(2)ÃSi(1)ÃCl(2)
Cl(1)ÃSi(1)ÃSi(2)
Si(1)ÃSi(2)ÃSi(3)
C(1)?ÃSi(2)ÃCl(3)?
C(1)?ÃSi(2)ÃCl(4)?
Cl(3)?ÃSi(2)ÃCl(4)
C(1)?ÃSi(2)ÃSi(1)
Cl(3)?ÃSi(2)ÃSi(1)
Cl(4)?ÃSi(2)ÃSi(1)
C(1)?ÃSi(2)ÃSi(3)
Cl(3)?ÃSi(2)ÃSi(3)
Cl(4)?ÃSi(2)ÃSi(3)
Cl(6)ÃSi(3)ÃSi(2)
Cl(5)ÃSi(3)ÃCl(6)
Cl(6)ÃSi(3)ÃCl(7)
N(1)ÃC(4)ÃC(5)
N(1)ÃC(4)ÃN(1b)
N(3)ÃC(10)ÃC(11)
N(3)ÃC(10)ÃN(3a)
103.66(10)
105.6(2)
106.01(9)
118.15(9)
84.8(20)
98.8(18)
172.6(4)
116.1(16)
73.6(5)
C(2)ÃSi(1)ÃCl(1)
C(2)ÃSi(1)ÃSi(2)
Cl(2)ÃSi(1)ÃSi(2)
C(1)ÃSi(2)ÃCl(3)
C(1)ÃSi(2)ÃCl(4)
Cl(3)ÃSi(2)ÃCl(4)
C(1)ÃSi(2)ÃSi(1)
Cl(3)ÃSi(2)ÃSi(1)
Cl(4)ÃSi(2)ÃSi(1)
C(1)ÃSi(2)ÃSi(3)
Cl(3)ÃSi(2)ÃSi(3)
Cl(4)ÃSi(2)ÃSi(3)
Cl(5)ÃSi(3)ÃSi(2)
Cl(7)ÃSi(3)ÃSi(2)
Cl(5)ÃSi(3)ÃCl(7)
108.1(2)
120.9(3)
111.27(10)
93.8(10)
95.7(11)
170.2(4)
120.1(13)
82.4(6)
94.7(3)
99.0(5)
118.9(20)
85.3(4)
121.0(12)
85.4(3)
87.8(3)
98.4(12)
114.38(16)
105.19(15)
106.12(16)
120.5(3)
119.0(7)
121.0(3)
117.9(7)
105.47(9)
117.97(12)
106.75(13)
N(2)ÃC(5)ÃC(4)
N(2)ÃC(5)ÃN(2b)
N(4)ÃC(11)ÃC(10)
N(4)ÃC(11)ÃN(4a)
120.2(3)
119.6(7)
120.8(4)
118.5(7)
Dihedral angles
N(1)ÃC(4)ÃC(5)ÃN(2)
36.2(3)
N(3)ÃC(10)ÃC(11)ÃN(4)
37.1(3)
Positions of C1, Cl3 and Cl4 marked by an apostrophe have an occupation factor of 36.5%, the positions without an apostrophe have an
occupation factor of 63.5%.
spectroscopy. We were not able to obtain single crystals
of 5a suitable for X-ray analysis. However, if the
reaction was repeated with a 9:1 molar mixture of 2
and 4 a crystalline mixture of 5a and 5b containing
larger amounts of 5b was obtained. In this case single
crystals of 5b could be isolated and characterized by
crystal structure analysis (Fig. 1A and B). Selected bond
lengths and angles are listed in Table 2.
positions with an occupancy ratio of 63.5:36.5%.
Although the geometry of the hypervalent central silicon
atom can be described as a distorted trigonal bipyramid,
individual bond lengths and angles should be regarded
Compound 5b crystallizes in the monoclinic space
group P2/c with four formula units in the unit cell. The
asymmetric unit contains two halves of a [TDAE]
+ ꢀ
radical cation resulting in two crystallographically
independent cations each having crystallographic C2
symmetry. The anion clearly consists of the trisilane
[Cl2MeSiÃ
/
SiMeCl2Ã
/
SiCl3]ꢁ, i.e. the central silicon
atom Si2 of the trisilane has picked up an additional
chloride ion.
Refinement of the structure was hampered by a
disorder of the methyl and chlorine substituents at Si2
which was modeled with these atoms in two alternative
Fig. 2. EPR spectrum of the red precipitation of 5a and 5b resulting
from the disproportionation of a 9:1 molar mixture of 2 and 4 with
TDAE.

C. Knopf et al. / Journal of Organometallic Chemistry 662 (2002) 14ꢃ
/
22
17
Fig. 3. (A) 29Si CP MAS NMR spectrum of 5aꢀ
to the unpaired electron in the [TDAE]
units at 10 and 14 ppm.
/
5b. (B) 13C CP MAS NMR spectrum of 5aꢀ
/
5b (rotational sidebands are marked by asterisks). Due
radical cation the signals at 157 and 45 ppm are broadened in comparison with the signals of the SiMe
+ ꢀ
with caution due to the disorder. However, the data
strongly suggest that the coordination geometry consists
of two silyl groups and one methyl substituent in
equatorial and two chlorine atoms in axial positions.
There is one further example of an chlorinated
oligosilane coordinated by additional chloride anions,
namely the Si6Cl214ꢁ anion reported by Boudjouk and
coworkers [13]. But in that case the two additional
chloride ions are above and below the centre of a planar
is the dihedral angle NÃ
the methyl groups gives rise to nonzero dihedral angles
in TDAE0 of 288 [15]. The increased dihedral angles of
/
CÃ
/
CÃ
/
N. Mutual repulsion of
36ꢃ
/
378 in 5b reflects the decreased energy gain of the p-
bond which is occupied by only one electron in the
+ꢀ
radical cation TDAE
To the best of our knowledge the crystal structure
.
analysis of 5b is the first structural characterization of a
TDAE
+ꢀ
radical cation. A compound [TDAE]C60
Si6 ring with equal distances to all silicon atoms.
which shows superconductivity and ferromagnetism
[16], has been known for some time and a structural
characterization has been reported in [17], but the
internal coordinates of the TDAE unit could not be
refined due to the quality of the X-ray data. So far it is
+ꢀ
The CÃ
/
C distance of the TDAE
corresponds to the values calculated by Hino et al. [14]
cation in 5b
0
for the mono cation (1.337 A in TDAE , 1.417 A in
˚
˚
+ ꢀ
TDAE
and 1.539 A in TDAE2ꢀ). Another indicator
˚

18
C. Knopf et al. / Journal of Organometallic Chemistry 662 (2002) 14ꢃ22
/
Scheme 2. Proposal of a mechanism regarding the reaction of chloromethyldisilanes with TDAE in n-hexane.
+ꢀ
still to decide whether this compound contains
or a mixture of TDAE0 and TDAE2ꢀ besides
The unpaired electron of the TDAE radical cation
in 5a and 5b gives rise to an EPR signal with a g-factor
+ ꢀ
TDAE
Cꢁ60 [18,19].
of 2.006 (Fig. 2). Due to the hyperfine structure coupling
1
with the H and 14N nuclei a splitting into 1521 lines
In the TDAE2ꢀ dication there is no electron left in
should be expected. But like in [20] and [21] we could
only observe a partial resolution.
the p-orbital resulting in an even larger dihedral angle
NÃ
/
CÃ
/
CÃ
/N, see also compound 6, Section 2.2).
The 29Si CP MAS NMR spectrum of the mixture of
5a and 5b shows six lines (Fig. 3A). There are three
resonances in the region of SiCl2Me units, one is caused
by the SiCl2Me unit of 5b, the other two must be
correlated with compound 5a, which contains two such
units. The assignment of the signals of the 29Si CP MAS
NMR spectrum (Fig. 3A) as well as a 13C CP MAS
NMR spectrum (Fig. 3B) is given in Table 3. The signal
Table 3
29Si and 13C MAS NMR data of the obtained TDAE salts of trisilanes
(5a, 5b)
Compound
d (ppm)
29Si
13C
of the carbon atoms of the CÄ
131.2 ppm) is shifted to dCꢂ156.5 ppm in the spectrum
of 5aꢀ5b. This drastic effect is a result of the formation
of the radical cation [TDAE] . Despite of the radical
/
C unit (TDAE0 dCꢂ
/
[Cl2MeSiAÃSiBCl2MeÃSiACl2Me]ꢁ A: 38.9/33.9 SiMe: 10.1; 14.5
/
+ ꢀ
[(Me2N)2CÃC(NMe2)2]
(5a)
[Cl2MeSiAÃSiBCl2MeÃSiCCl3]ꢁ
B: ꢁ56.3
A: 30.5
CÃC: 156.5
NMe2: 45.0
/
+ꢀ
+ ꢀ
+ ꢀ
[(Me2N)2CÃC(NMe2)2]
(5b)
B: ꢁ75.6
C: 16.5
properties of the [TDAE]
NMR signals could be observed, however they are
cation its 13C CP MAS

C. Knopf et al. / Journal of Organometallic Chemistry 662 (2002) 14ꢃ
/
22
19
broadened to a line width of several ppm. As already
stated in [20], the unpaired electron is largely delocalized
across the whole radical cation resulting in a low
probability density at each carbon atom. In the 29Si
CP MAS NMR spectrum the signals of the central Si
atoms of the trisilane units exhibit the expected highfield
The analogous reaction in acetonitrile led to the
formation of two liquid phases plus a precipitation of
[TDAE]Cl2 (6×
/
MeCN). The result of the X-ray structure
analysis is presented in Fig. 4. Selected bond lengths and
angles are listed in Table 4.
The crystal structure of 6×
/
MeCN consists of the
TDAE2ꢀ cation plus two isolated chloride ions. The
˚
shifts of 50ꢃ
comparison with the parent trisilanes SiACl-
Me(SiBCl2Me)2 (dSi: ꢁ
4.9 (A), 23.8 ppm (B) [5]) and
Cl3SiAÃSiBClMeÃSiCCl2Me (dSi: 5.9 (A), ꢁ
4.7 ppm (B),
/
70 ppm due to pentacoordination in
C(1)Ã
/
C(2) distance (1.502 A) as well as the dihedral
/
angles NÃ
agreement with the calculated CÃ
in TDAE2ꢀ [14] as well as the experimental values for
other TDAE2ꢀ compounds: [TDAE]Cl2×
2H2O (CÃC:
2H2O (CÃC: 1.51
N: 678) [22], [TDAE](PF6)2 (CÃC: 1.511 A,
N: 728) [23], [TDAE][TCNE]2 (CÃ
N: 61.58) [24], [TDAE][TCNE] (CÃ
N: 71.38), [TDAE][TCNQ]2 (CÃC: 1.515 A,
N: 63.98) [25] and [TDAE](SCF3)2 [26].
/
CÃ
/
CÃN of 71.2 and 72.08 in 6 are in good
/
˚
C distance of 1.539 A
/
/
/
/
21.9 ppm (C) [4]). However, while dSi of the central
silicon atoms in both trisilanes are almost equal, the 29Si
NMR signal of the central silicon atom in 5b is almost
20 ppm upfield from that of 5a revealing a stronger
coordination of the additional chloride substituent in 5b
in accordance with a higher chlorofunctionalization and
hence a higher acceptor strength of the trisilane frag-
ment in 5b.
/
/
˚
1.52 A, NÃ
/
CÃ
CÃ
CÃ
CÃ
CÃ
CÃ
/
CÃ
/
N: 768), [TDAE]Br2×
/
/
˚
˚
A, NÃ
NÃCÃ
NÃCÃ
NÃCÃ
NÃCÃ
/
CÃ
/
/
/
˚
C: 1.513 A,
C: 1.516 A,
/
/
/
/
˚
˚
/
/
/
/
/
/
/
/
/
/
/
On the other hand the signals of the terminal silicon
Obviously two electrons from the TDAE were trans-
ferred to the disilane molecule and chloride ions were
split off.
As demonstrated, the pathway of the disproportiona-
tion and the kind of the products depend strongly on the
properties like polarity or donor strength of the used
solvent. In nonpolar solvents, such as n-hexane, the
reaction of TDAE with chloromethyldisilanes 2 and 4
gives reactive isolable intermediates (5a and 5b). In the
atoms in 5a and 5b are shifted downfield by 10ꢃ
compared to the trisilanes SiClMe(SiCl2Me)2 and
Cl3SiÃSiClMeÃSiCl2Me.
/15 ppm
/
/
Obviously 5a and 5b are reactive intermediates of the
base catalyzed disproprotionation of 2 and 4.
Starting from these results a proposal concerning the
mechanistic pathway of the reaction of chloromethyldi-
silanes with TDAE in n-hexane can be developed, see
Scheme 2.
more polar solvent DME the intermediates (5aꢀ
/
5b) as
The process should be initiated by an electron transfer
step from the TDAE to the disilane. The as-formed
well as the known disproportionation products 2a, 2b
+ꢀ
[TDAE]
radical cation is stabilized by the electron
donating dimethylamino groups. The disilane radical
intermediate may decay into a silyl radical plus a
chloride stabilized silylene that may also be understood
as a dichlorosilanide anion. The latter can insert into a
SiÃ
/
Cl bond of a further disilane molecule leading to a
trisilane species. A subsequent 1,2-shift of a chloride to
the middle silicon atom could create the anions found in
5a (Rꢂ
/
Me) or 5b (RꢂCl). The silyl radical should be
/
able either to disproportionate into trichloromethylsi-
lane (2a) and the corresponding silylene or to undergo a
recombination step.
Fig. 4. ORTEP plot of the molecular structure of 6×MeCN.
/
2.2. Disproportionation of chloromethyldisilanes with
TDAE in polar solvents
Table 4
˚
Selected bond lengths (A), bond angles (8) and dihedral angles (8) of
6×MeCN
The reaction of TDAE with a 9:1 mixture of 2 and 4
Bond lengths
in 1,2-dimethoxyethane (DME) yielded an orangeꢃred
/
C(1)ÃC(2)
N(2)ÃC(1)
N(4)ÃC(2)
1.502(2)
1.317(2)
1.326(2)
N(1)ÃC(1)
N(3)ÃC(2)
1.323(2)
1.317(2)
precipitation consisting of 5a and 5b besides the mono-
silane 2a plus the oligomers 2b as well as 2c.
It should be noted that the 29Si-NMR signal of the
central SiClMe moiety of the trisilane 2b was shifted to
Bond angles
N(1)ÃC(1)ÃC(2)
N(3)ÃC(2)ÃC(1)
116.12(14) N(2)ÃC(1)ÃC(2)
116.83(13) N(4)ÃC(2)ÃC(1)
116.85(14)
116.50(13)
ꢁ
/
12.2 ppm (in CDCl3 or n-hexane a signal at ꢁ4.9 ppm
/
is observed). This may be explained by a partial
coordination of additional chloride ions at the central
silicon atom in solution.
Dihedral angles
N(1)ÃC(1)ÃC(2)ÃN(3) 71.2(2)
N(2)ÃC(1)ÃC(2)ÃN(4) 72.0(2)

20
C. Knopf et al. / Journal of Organometallic Chemistry 662 (2002) 14ꢃ22
/
Table 5
Crystallographic parameters and experimental details for the compounds 5b and 6×MeCN
5b
6×MeCN
Empirical formula
Molecular mass (g molꢁ1
T (K)
C
12H30Cl7N4Si3
C12H27Cl2N5
312.29
173(2)
)
562.82
173(2)
˚
Radiation (l, A)
Moꢃ/Ka (0.71073)
MoꢃKa (0.71073)
/
Crystal system
Space group
Unit cell dimensions
Monoclinic
P2/c
Orthorhombic
Pna21
˚
a (A)
19.921(4)
9.550(17)
14.136(3)
92.784 (4)
2686.3(8)
1.392
13.1709(3)
12.1745(3)
10.5631(3)
˚
b (A)
˚
c (A)
b (8)
3
V (A )
˚
1693.78(7)
1.225
Dcalc (g cmꢁ3
)
Z
4
4
Crystal size (mm3)
0.38ꢄ0.18ꢄ0.16
0.880
v-Scan
1.0ꢄ0.60ꢄ0.35
0.380
v-Scan
m (mmꢁ1
Scan mode
)
u Range for collection (8)
Index range
1.02ꢃ
/
30.86
2.28ꢃ30.36
ꢁ185h 510, ꢁ165k 515, ꢁ75l 515
7651
/
ꢁ285h 527, ꢁ135k 511, ꢁ205l 520
20 882
Measured reflections
Independent reflections
Observed reflections
Completeness to umax (%)
Final R1/wR2 [I ꢀ2s(I)]
R1/wR2 (all data)
7745
3445
3053
2785
91.5
87.3
0.0855/0.2598
0.1931/0.3234
1.097
0.0272/0.0655
0.0320/0.0682
1.030
Goodness-of-fit on F2
˚
Max/min e-density (e A
ꢁ3
)
0.908/ꢁ1.438
0.157/ꢁ0.231
and 2c result. In this medium the disproportionation
reactivity is higher than in n-hexane. Obviously the
more polar solvent acetonitrile promotes the transfer of
two electrons from TDAE delivering the ionic
300 spectrometer at 59.672 (29Si) and 75.467 MHz (13C)
using MAS CP techniques.
EPR spectra were recorded on a BRUKER ESP 300 E
spectrometer. Microwave frequency: 9722.051 MHz (X-
band), microwave power: 2000 W, temperature: 25 8C,
modulation frequency: 100 kHz, modulation amplitude:
1.995 G.
[TDAE]Cl2×
/
MeCN (6×
/
MeCN). With increasing dielec-
tric constant (DC; n-hexane: 1.88, DME: 7.2 [27]) the
+ꢀ
formation of the monocation TDAE
(5aꢀ5b) is
/
changed to the production of the dication TDAE2ꢀ
(acetonitrile: DC: 37.5 [27]). Thus by means of the
properties of the solvents used it seems possible to
control and adjust a defined state of the electron transfer
process.
IR spectra (4000ꢃ
/
400 cmꢁ1) were measured with a
NICOLET-FT-IR spectrometer using pressed KBr pel-
lets.
3.2. X-ray crystal analyses
X-ray structure analysis measurements were per-
formed on a BRUKER AXS SMART 1K CCD. Crystal
3. Experimental
data of 5b and 6×
/
MeCN as well as data collection and
3.1. General
refinement details are given in Table 5.
The unit cells were determined with the program
SMART [28]. For data integration and refinement of the
All reactions were carried out under an inert gas
atmosphere (argon) applying standard Schlenk techni-
ques. Solvents were dried prior to use.
The measurements of the liquid samples were per-
formed on a BRUKER DPX 400 spectrometer at 79.495,
100.613 and 400.130 MHz for 29Si, 13C and 1H,
respectively. All spectra were recorded using external
CDCl3 and Me4Si as internal reference. The measure-
ments of the solids were performed on a BRUKER MSL
unit cells the program SAINT [28] was used. The space
groups were determined using the program XPREP [28].
All data were corrected for absorption using SADABS
[29]. The structures were solved using direct methods
(SHELX-97 [30]) and refined using least-squares-methods
(SHELX-97). Molecular structure representations were
done with ZORTEP [31]. The ellipsoides at the nonhydro-
gen atoms are at the 50% probability level. The positions

C. Knopf et al. / Journal of Organometallic Chemistry 662 (2002) 14ꢃ
/
22
21
of the hydrogen atoms of 6 were taken from the electron
density difference map and refined freely. The hydrogen
atoms of 5b were positioned as riding model to their
neighboring atom.
at 0 8C. The reaction mixture discolored, and a red
solid was obtained immediately. The solution was
stirred for 1 h. After that the solution was investigated
by 29Si NMR spectroscopy (see Table 1).
3.3. Synthesis of methylchlorodisilanes
3.4.3. Disproportionation of 2
Compound 2 (2.54 g, 11.14 mmol, containing 1ꢃ2% 4,
/
3.3.1. 1,2-Dichlorotetramethyldisilane (1)
Section 3.3.2) was dissolved in 3 ml n-hexane. TDAE
(2.23 g, 11.14 mmol) was added dropwise at room
temperature with stirring. The color of the solution
changed to orange, and a red solid of 5a (containing
small amounts of 5b; characterized by 29Si MAS NMR)
was obtained immediately. 29Si- and 13C NMR spectra
of the filtrated solution showed only the signals of the
educts [29Si NMR: d 17.3 ppm (2); 13C NMR: d 4.9 (2),
Compound 1 was prepared by chlorination of hexa-
methyldisilane (28.1 g, 191.9 mmol) with aluminum
chloride (50.7 g, 380.0 mmol) and acetyl chloride (33.8 g,
430.5 mmol) at 0 8C [32]. After stirring for 20 h 1 was
condensed into a trap at ꢁ
/
78 8C. Redistillation gave 28
g (78%) of 1 [29Si NMR [32]: 17.4 ppm; 13C NMR: 1.2
1
1
ppm; H NMR: 0.55 ppm; JSiC: 48.7 Hz]. Bp. 148 8C.
41.0 (N(CH3)2), 131.5 ppm (CÄ
/
C)]. The experiment was
3.3.2. 1,1,2,2-Tetrachlorodimethyldisilane (2) and
methylpentachlorodisilane (4)
repeated, but additionally the solution was refluxed for
2 h. 29Si- and 13C NMR spectra of the separated liquid
product mixture were recorded (29Si NMR assignment:
see Table 1; 13C NMR: d 4.9 (2), 9.6 (2a), 41.0
The preparation of 2 by chlorination of technical
disilane fraction with acetyl chloride and aluminum
chloride at 125 8C was carried out as described in [32].
The resulting product was in fact a mixture of 90 mol%
1,1,2,2-tetrachlorodimethyldisilane (2) (29Si NMR: 17.6
ppm; 13C NMR: 5.8 ppm; 1H NMR: 0.99 ppm [32]) and
10 mol% pentachloromethyldisilane (4) [29Si NMR [33]:
(N(CH3)2), 131.5 ppm (CÄ
/
C)].
3.4.4. Disproportionation of a 9:1 mixture of 2 and 4 in
n-hexane
Ten grams of the mixture of 2 and 4 was diluted with
30 ml n-hexane and 8.77 g (43.8 mmol) TDAE was
added dropwise under stirring at 0 8C. A red precipita-
tion of 5a and 5b was observed immediately. After
stirring for 2 h a part of the solution was separated and
29Si and 13C NMR spectra were recorded [29Si NMR
assignment: see Table 1; 13C NMR: d 5.1 ppm (2), d 6.9
ppm (SiACH3 of [(Cl2CH3SiA)2SiBCH3Cl]), broad sig-
dA 13.7 ppm, dB
ꢁ
/
0.8 ppm (CH3Cl2SiAÃ
/
SiBCl3); 13C
1
1
NMR: 5.01 ppm; H NMR: 1.06 ppm; JSiC: 60.7 Hz].
In a second experiment the reaction mixture (same as
above) was heated up to 115 8C only. Separation and
distillation of the crude product gave almost pure 2,
containing 1ꢃ2% 4, Bp. 153 8C.
/
3.3.3. Hexachlorodisilane (3)
nals at d 41.0 ppm (N(CH3)2) and d 131.9 ppm (CÄ
/
C)].
Compound 3 was obtained by the chlorination of
hexaphenyldisilane (15 g, 28.95 mmol), diluted in n-
hexane, with aluminum chloride (27.1 g, 202.7 mmol)
and acetyl chloride (15.9 g, 202.7mmol). After stirring
overnight 10 ml n-hexane was added, the upper phase
separated and the n-hexane removed in vacuo. Redis-
tillation gave 4.3 g (55%) of pure 3 (29Si NMR [34]: ꢁ
6.8 ppm). Bp. 144 8C.
Besides 13C and 29Si MAS NMR, EPR and an X-ray
structure analysis the red precipitate of 5a and 5b was
characterized by IR and elemental analysis. IR (KBr,
cmꢁ1): nCÄC: 1671 (s), nSiCl: 514, 498 and 416 cmꢁ1 29Si
;
and 13C MAS NMR: see Table 3; Anal. Calc. for
C13H33Cl6N4Si3 (5a) (542.36 g molꢁ1); C, 28.8; H, 6.1;
Cl, 39.2; N, 10.3; Si, 15.5 and C12H30Cl7N4Si3 (5b)
(562.82 g molꢁ1); C, 25.6; H, 5.3; Cl, 44.1; N, 9.9; Si,
14.9. Found: C, 29.1; H, 5.6; Cl, 40.0; N, 10.7; Si, 14.3%.
/
3.4. Homogeneous disproportionation of chlorodisilanes
3.4.5. Disproportionation of 2 in 1,2-dimethoxyethane
3.4.1. Disproportionation of 1
Compound 2 (5.06 g, 22.2 mmol) (containing 1ꢃ2% 4)
/
Compound 1 (2 g, 10.74 mmol) was diluted with 3 ml
n-hexane. TDAE (2.15 g, 10.74 mmol) was added
dropwise with stirring to this solution at room tempera-
ture. After stirring for 5 h 29Si- and 13C NMR spectra of
the solution were recorded which revealed the starting
materials only. There was no further reaction when the
mixture was heated to reflux for 2 h.
was diluted in 20 ml DME. TDAE (4.44 g, 22.2 mmol)
was added dropwise with stirring at room temperature.
Discoloring of the solution and precipitation of a yellow
solid took place. The solution was separated and 29Si-
and 13C NMR spectra were recorded [29Si NMR: d 13.6
(2a),
d
18.8 (2), dA 24.4, dB
ꢁ
ꢁ
/
12.2 ppm
((Cl2CH3SiA)2SiBCH3Cl, 2b), dA 31.7, dB
/62.9 ppm
((Cl2CH3SiA)3SiBCH3, 2c); 13C NMR: d 9.2 (2a), d 4.8
(2), dA 7.3 ppm (Cl2CH3SiA)2SiBCH3Cl, 2b), dA 9.1, dB
3.4.2. Disproportionation of 3
Compound 3 (3.12 g, 11.6 mmol) was dissolved in 10
ml n-hexane, and 2.32 g (11.6 mmol) TDAE was added
ꢁ
12.5 ppm (Cl2CH3SiA)3SiBCH3, 2c), broad signals at
/
d 41.2 (N(CH3)2) and 131.7 ppm (CÄ
/
C)].

22
C. Knopf et al. / Journal of Organometallic Chemistry 662 (2002) 14ꢃ22
/
[3] R. Richter, G. Roewer, U. Bohme, K. Busch, F. Babonneau, H.P.
¨
3.4.6. Disproportionation of a 9:1 mixture of 2 and 4 in
acetonitrile
Martin, E. Muller, Appl. Organomet. Chem. 11 (1997) 71.
¨
[4] U. Herzog, N. Schulze, K. Trommer, G. Roewer, Main Group
Met. Chem. 22 (1999) 19.
The 9:1 molar mixture of 2 and 4 (4.44 g, 22.2 mmol)
were diluted in 20 ml acetonitrile. TDAE (4.44 g, 22.2
mmol) was added dropwise with stirring at room
temperature. The formation of two phases and a
discoloring of the solution occurred. Both phases were
investigated by 29Si- and 13C NMR [29Si NMR: upper
[5] U. Herzog, R. Richter, E. Brendler, G. Roewer, J. Organomet.
Chem. 507 (1996) 221.
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339 (1997) 145.
phase d 14.7 (2a), 20.0 (2), dA 22.3 and dB ꢁ
53.0 ppm
/
(no assignment), lower phase: d 12.5 (2a), 17.9 ppm (2);
13C NMR: upper phase: d 5.9 (2), 10.0 ppm (2a); lower
[10] H. Burger, P. Moritz, Organometallics 12 (1993) 4930.
¨
[11] N. Wiberg, J.W. Buchler, Chem. Ber. 96 (1963) 3223.
[12] N. Wiberg, Angew. Chem. 20 (1968) 809.
phase: d 5.2 (2), 9.8 (2a), 41.2 (N(CH3)2, 131.4 ppm (CÄ
C)]. Additionally we obtained colorless crystals (6×
MeCN). M.p. 243ꢃ
245 8C; (KBr, cmꢁ1): nCÄC: 1670
(s); 13C NMR (D2O): d 41.5, 42.4 (N(CH3)2), d 154.9
ppm (CÃ
C); 1H NMR (D2O): d 3.30, 3.59 ppm
/
[13] S.-B. Choi, B.-K. Kim, P. Boudjouk, D.G. Grier, J. Am. Chem.
Soc. 123 (2001) 8117.
/
/
[14] S. Hino, K. Umishita, K. Iwasaki, K. Tanaka, T. Sato, T.
Yamabe, K. Yoshizawa, K. Okahara, J. Phys. Chem. Sect. A 101
(1997) 4346.
/
[15] H. Bock, H. Borrmann, Z. Havlas, H. Oberhammer, K. Ruppert,
A. Simon, Angew. Chem. 103 (1991) 1733.
(N(CH3)2) [22], 2.06 ppm (CH3CN); Anal. Calc. for
C12H27Cl2N5 (312.29): C, 46.1; H, 8.7; Cl, 22.7; N, 22.4,
Found: C, 44.8; H, 8.6; Cl, 22.5; N, 18.7%.
[16] P.-K. Allemand, K.C. Khemani, A. Koch, F. Wudl, K. Holczer,
S. Donovan, G. Gruner, J.D. Thompson, Science 253 (1991) 301.
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M. Allemand, A. Hirsch, K. Holczer, Q. Li, J.D. Thompson, F.
Wudl, Nature 355 (1992) 331.
4. Supplementary material
[18] K. Tanaka, T. Sato, T. Yamabe, J. Phys. Chem. Sect. A 100
(1996) 3980.
Crystallographic data (excluding structure factors) for
the structures in this paper have been deposited at the
Cambridge Crystallographic Data Centre, CCDC nos.
[19] Y. Deligiannakis, G. Papavassiliou, M. Fardis, G. Diamanto-
poulos, F. Milia, C. Christides, K.I. Pokhodnia, V. Barchuk,
Phys. Rev. Lett. 83 (1999) 1435.
179841 and 179842 for compounds 5b and 6×
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
/
MeCN.
[20] K. Kuwata, D.H. Geske, J. Am. Chem. Soc. 86 (1964) 2105.
[21] M. Fujitsuka, C. Luo, O. Ito, J. Phys. Chem. Sect. B 103 (1999)
445.
[22] H. Bock, K. Ruppert, K. Merzweiler, D. Fenske, H. Goesmann,
Angew. Chem. 101 (1989) 1715.
Cambridge CB2 1EZ, UK (Fax: ꢀ44-1223-336033; e-
mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk)
/
[23] K. Elbl-Weiser, C. Krieger, H.A. Staab, Angew. Chem. 102 (1990)
183.
[24] M.T. Johnson, C.F. Campana, B.M. Foxman, W. Desmarais,
M.J. Vela, J.S. Miller, Chem. Eur. J. 6 (2000) 1805.
[25] J.R. Fox, B.M. Foxman, D. Guarrera, J.S. Miller, J.C. Calabrese,
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Acknowledgements
[26] A. Kolomeitsev, M. Medebielle, P. Kirsch, E. Lork, G.-V.
Roschenthaler, Perkin 1 (2000) 2183.
[27] C. Reichardt, Solvent Effects in Organic Chemistry, vol. 3, VCH,
We are grateful to the Deutsche Forschungsge-
meinschaft, the Graduiertenkolleg ‘‘Crystal Engineering
and Crystallisation’’ and Fonds der Chemischen Indus-
trie for financial support. We thank F. Wirbeleit for
carrying out the EPR measurements and B. Kutzner for
recording the NMR spectra.
Weinheim, 1979, pp. 270ꢃ272.
/
[28] Bruker AXS Inc., Madison, WI, USA, 1998.
[29] G.M. Sheldrick, SADABS V2.01, Program for Empirical Absorp-
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¨
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[30] G.M. Sheldrick, SHELX-97, Programs for Crystal Structure
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¨
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