Non-catalyzed addition reactions of Cl3SiSiCl3 with 1,2-diketones, 1,2-quinones and with a 1,4-quinone

Article abstract of DOI:10.1016/S0022-328X(02)01193-2

The first uncatalyzed reactions of a disilane with 1,2-diketones, 1,2-quinones and with a 1,4-quinone are reported. Thus, Si₂Cl₆ reacts under mild conditions with such substrates to give bis-trichlorosiloxy addition compounds. The structure of the corresponding addition compound of benzyl, namely, cis-PhC(OSiCl₃)=C(OSiCl₃)Ph was structured by X-ray diffraction analysis. Evidence for the intermediacy of five-coordinate species in these reactions is discussed. A reaction of Si₂Cl₆ with LiNMeC(O)Et aimed at making a hypercoordinate silicon complex led to the disproportionation product cis-Cl₂Si[NMeC(O)Et]₂ (whose structure was also determined by X-ray diffraction analysis) in which the amide ligands chelate the silicon via the nitrogen and oxygen to form five-membered rings whose bond lengths suggest substantial electron delocalization.

Full text of DOI:10.1016/S0022-328X(02)01193-2

Journal of Organometallic Chemistry 651 (2002) 15–21
www.elsevier.com/locate/jorganchem
Non-catalyzed addition reactions of Cl3SiSiCl3 with 1,2-diketones,
1,2-quinones and with a 1,4-quinone
Jinchao Yang, John G. Verkade *
Department of Chemistry, Iowa State Uni6ersity, Gilman Hall, Ames, IA 50011-3111, USA
Received 1 October 2001; received in revised form 15 January 2002; accepted 23 January 2002
Dedicated to Academician Mikhail Voronkov on the occasion of his eightieth birthday
Abstract
The first uncatalyzed reactions of a disilane with 1,2-diketones, 1,2-quinones and with a 1,4-quinone are reported. Thus, Si2Cl6
reacts under mild conditions with such substrates to give bis-trichlorosiloxy addition compounds. The structure of the
corresponding addition compound of benzyl, namely, cis-PhC(OSiCl3)ꢀC(OSiCl3)Ph was structured by X-ray diffraction analysis.
Evidence for the intermediacy of five-coordinate species in these reactions is discussed. A reaction of Si2Cl6 with LiNMeC(O)Et
aimed at making a hypercoordinate silicon complex led to the disproportionation product cis-Cl2Si[NMeC(O)Et]2 (whose
structure was also determined by X-ray diffraction analysis) in which the amide ligands chelate the silicon via the nitrogen and
oxygen to form five-membered rings whose bond lengths suggest substantial electron delocalization. © 2002 Published by Elsevier
Science B.V.
Keywords: 1,2-Diketones; 1,2-Quinones; 1,4-Quinone; Disilane; Addition reactions
In earlier publications, we showed that alkynes are
trimerized to benzene derivatives at ca. 200 °C in the
presence of Si2Cl6 (1) as a catalyst [3]. In the past, such
reactions of alkynes have been universally carried out
with the aid of transition metal catalysts. We report
here the use of the activated disilane Si2Cl6 (1) for the
double silylation of a,b-diketones (2a,b); the ortho-
quinones (3a,b) and the para-quinone (4). All of these
reactions proceed well in the absence of a catalyst to
give the corresponding products 5a,b; 6a,b and 7.
Whereas, alkyne trimerization catalyzed by 1 at ca.
200 °C occurs by a free radical mechanism [3], the
1. Introduction
Organosilicon compounds are important because of
their versatile synthetic utility and their unique physical
and chemical properties [1]. One method for their
preparation involves the transition metal-catalyzed ad-
dition of disilanes [2] to unsaturated compounds such
as acetylenes, olefins, dienes, allenes, a diyne, 1,2-unsat-
urated ketones, quinones, an a-keto ester, aldehydes,
isocyanides and imines [1]. Although the formation of
p-bis(dimethylfluorosiloxy)benzene
from
p-benzo-
quinone and FMe2SiSiMe2F is known [2], this reaction
is the only example involving an activated disilane.
Moreover, this reaction required the presence of
Pd(PPh3)2Cl2 or Pd(PPh3)4 as a catalyst. To our knowl-
edge, no disilane–1,2-diketone; disilane–1,4-quinone or
disilane–1,2-quinone reactions not catalyzed by a tran-
sition metal catalyst have been reported.
* Corresponding author. Tel.: +1-515-294-5023; fax: +1-515-294-
0105.
E-mail address: jverkade@iastate.edu (J.G. Verkade).
0022-328X/02/$ - see front matter © 2002 Published by Elsevier Science B.V.
PII: S0022-328X(02)01193-2

16
J. Yang, J.G. Verkade / Journal of Organometallic Chemistry 651 (2002) 15–21
wise noted. Products were analyzed by 1H-, 13C-,
29Si-NMR and HRM spectroscopies.
2.2. Adduct formation of 1 with
N,N,N%,N%-tetramethylethylenediamine
In a 50 ml flask pre-flushed with nitrogen and
equipped with a magnetic stirrer, Et2O (ca. 20 ml) was
added with a syringe, followed by N,N,N%,N%-te-
tramethylethylenediamine (2.32 g, 20.0 mmol). Disilane
1 (2.69 g, 10.0 mmol) was then introduced dropwise
with stirring at r.t. whereupon a white precipitate was
observed to form immediately which was accompanied
by a mild exotherm. The reaction mixture was stirred
for 2 h and then the precipitate was filtered off and
washed with 3×10 ml of Et2O. Drying the precipitate
under vacuum gave 4.70 g of product as a white
powder in 93% yield assuming a 1:1 adduct had
formed. The product was analyzed as a hypercoordi-
reactions described herein, which proceed at room tem-
perature, are likely to proceed via formation of a
hypercoordinate intermediate followed by molecular re-
arrangement involving SiꢁSi bond cleavage. The notion
that five-coordinate silicon intermediates possessing
CꢀO“Si linkages are involved in these reactions is
amply supported by the considerable number of reports
of such complexes in recent years [4,5]. These com-
plexes contain one chelate ring per silicon, and a six-co-
ordinate silicon complex with a CꢀO“Si linkage in a
six-membered ring has also been described recently [6].
Here we report the molecular structure of novel six-co-
ordinate 8 in which two CꢀO“Si linkages are present,
each in a four-membered ring.
nated silicon adduct of
1
with N,N,N%,N%-te-
tramethylethylenediamine by 29Si-NMR spectroscopy.
29Si MAS-NMR (solid, hexamethylcyclotrisiloxane) for
1
the adduct: l −79.24; H-NMR (CDCl3): l 2.87 (s,
4H), 2.61 (s, 12H); 13C-NMR (CDCl3); l 55.14, 46.57.
Mass spectra revealed only the presence of decomposi-
tion products. Efforts to obtain crystals of this adduct
failed.
2. Experimental
NMR spectra were measured on Bruker AC-200
(29Si), Bruker DRX-400 (1H and 13C) and Bruker MSL-
300 (solid 29Si MAS) instruments. The NMR solvent
was CDCl3 unless otherwise noted. Chemical shifts
were calibrated to CDCl3 for 1H- and 13C-NMR spectra
and to SiMe4 for 29Si-NMR spectra. High resolution
mass spectral and elemental analyses were performed at
Iowa State University by the Chemistry Department
Instrument Services Unit.
Diethyl ether and THF were dried with Na, DMF
was distilled under nitrogen, after stirring with CaH2,
and were stored over molecular sieves. Hexachlorodisi-
lane (1) was purchased from Aldrich and was used as
received. Benzyl (2a), 1-phenyl-1,2-propanedione (2b),
2.3. Adduct formation of 1 with DMF
To a 50 ml flask pre-flushed with nitrogen, Et2O (ca.
20 ml) was added by syringe, followed by DMF (1.46 g,
20.0 mmol). Disilane 1 (2.69 g, 10 mmol) was then
introduced dropwise at r.t., whereupon a white precipi-
tate was observed which was accompanied by a mild
exotherm. The reaction mixture was stirred for 3 h and
then the precipitate was filtered and washed with 5×10
ml of Et2O. Drying the precipitate under vacuum af-
forded 3.10 g product (90% yield) assuming the forma-
tion of a 1:1 adduct. The product analyzed as a
hypercoordinated adduct of 1 with DMF by 29Si-NMR
spectroscopy. 29Si MAS-NMR (solid hexamethylcyclo-
tetrachloro-1,2-benzoquinone
(3a),
phenanthrene-
quinone (3b), p-benzoquinone (4) N,N,N%,N%-te-
tramethylethylenediamine (tmeda), N-methylpropi-
onamide and N-methyltrimethylacetamide were
purchased from Aldrich Chemical Co. and were used as
received unless otherwise noted.
1
trisiloxane): l −184.71, −192.10; H-NMR (CDCl3):
l 8.02 (s, 1H), 2.95 (s, 3H), 2.87 (s, 3H); 13C-NMR
(CDCl3) l 162.69, 36.68, 31.61. Mass spectra revealed
only the presence of decomposition products. Efforts to
purify the product failed and no crystals were obtained.
2.1. General description of reactions
2.4. Reaction of 1 with 2a (method A: at 100 °C
without a sol6ent)
Reactions of hexachlorodisilane (1) with DMF and
N,N,N%,N%-tetramethylethylenediamine were carried out
at room temperature (r.t.) in Et2O or C5H12 under
nitrogen. Each reaction of 1 with a quinone was carried
out in an NMR tube under nitrogen either at r.t. in
CHCl3 or at 80–120 °C without a solvent. The conver-
sions in all the reactions were quantitative unless other-
A nitrogen-flushed NMR tube was charged with 2a
(42.0 mg, 0.200 mmol) followed by the introduction of
1 (64.0 mg, 0.240 mmol). The NMR tube was stoppered
with a septum and the mixture was heated to 100 °C
for 1 h. After cooling to r.t., a yellow solution was

J. Yang, J.G. Verkade / Journal of Organometallic Chemistry 651 (2002) 15–21
17
1
obtained which when analyzed by H-, 13C-, 29Si-NMR
sity, ion) 418.0 [8.97, M+(2 37Cl, 4 35Cl)], 416.0 [11.13,
M+(37Cl, 5 35Cl)], 265.0 (4.50, [M−OSiCl3]+). HRMS
(EI): Calc. for C9H8Cl6O2Si2: 413.81941. Found:
413.81935. Attempts to purify the product were
unsuccessful.
and HR mass spectroscopies revealed the product 5a in
which
a
vinylic fragment had formed. 1H-NMR
(CDCl3): l 7.25 (m, 10H); 13C-NMR (CDCl3): l 136.60,
133.04, 129.46, 129.01, 128.27. 29Si-NMR (CDCl3,
SiMe4):
l
−21.27. HRMS (EI): Calc. for
C14H10Cl6O2Si2: 475.83506. Found: 475.83527. Purify-
ing the product (to remove 1) by evaporation under
vacuum afforded pure 5a. Anal. Calc. for
C14H10Cl6O2Si2: C, 35.07; H, 2.08; Cl, 44.46; Si, 11.69.
Found: C, 35.84; H, 2.16; Cl, 44.19; Si, 11.65%.
2.8. Reaction of 1 with 3a
An NMR tube pre-flushed with nitrogen was charged
with 3a (49.0 mg, 0.200 mmol). Disilane 1 (60.0 mg,
0.220 mmol) was introduced with a syringe and then
the tube was stoppered with a septum and heated to
80 °C for 2 h, during which time a homogenous light
2.5. Reaction of 1 with 2a (method B: at r.t. in
CHCl3)
brown solution was obtained. The H-, 13C-, 29Si-NMR
1
and HR mass spectra of the product were consistent
with the formation of 6a. 13C-NMR (CDCl3): l 140.18,
129.51, 129.97, 125.97; 29Si (CDCl3, SiMe4): l −20.17.
MS (70 eV, EI): m/z (relative intensity, ion) 518.0 [4.48,
M+(4 37Cl, 6 35Cl)], 516.0 [8.67, M+(3 37Cl, 7 35Cl)],
514.0 [9.66, M+(2 37Cl, 8 35Cl)], 344.0 [8.16, M−
(SiCl3+Cl)]+. HRMS (EI): Calc. for C6Cl10O2Si2:
509.63222. Found: 509.63227. Efforts to purify the
product were unsuccessful.
In a nitrogen-flushed NMR tube was charged with 2a
(42.0 mg, 0.200 mmol) followed by the introduction of
1 (64.0 mg, 0.240 mmol). The NMR tube was stoppered
with a septum and 0.70 ml of CDCl3 was added with a
syringe. A light yellow solution was obtained after 2a
had dissolved. Taking the NMR spectra immediately
after adding the CDCl3 showed the absence of starting
material 2a. 1H- and 13C-NMR spectroscopies confi-
rmed that methods A and B both gave 5a.
2.9. Reaction of 1 with 3b
2.6. Reaction of 1 with 2a at 0 °C
This procedure is the same as that of the reaction of
In a glass tube equipped with a magnetic stirrer, and
cooled by an ice bath was charged with 2a (0.42 g, 2.0
mmol) followed by the introduction of (0.64 g, 2.4
mmol) of 1. The tube was then cooled with liquid
nitrogen and flame sealed under vacuum. The mixture
was then allowed to warm to 0 °C in an ice bath and
stirred until a homogeneous mixture was obtained.
Shaking the reaction mixture occasionally was essential
to ensure good mixing. The tube was then left undis-
turbed for 2 days at 0 °C, during which time colorless
crystals of 5a formed which were suitable for X-ray
diffraction studies.
1 with 3a, so only the characterization of the product
6b is given. H-NMR (CDCl3): l 8.67–8.69 (m, 2H),
1
8.21–8.23 (m, 2H), 7.70–7.71 (m, 4H); 13C-NMR
(CDCl3): l 134.88, 128.87, 127.43, 127.03, 126.66,
122.91, 122.84; 29Si-NMR (CDCl3, SiMe4): l −20.09.
MS (70 eV, EI): m/z (relative intensity, ion) 482.0 [1.18,
M+(4 37Cl, 2 35Cl)], 480.0 [4.23, M+(3 37Cl, 3 35Cl)],
478.0 [9.55, M+(4 37Cl, 2 35Cl)], 476.0 [12.38, M+(37Cl,
5
35Cl)], 474.0 [6.18, M+(6 35Cl)], 135.0 (6.64, SiCl3).
HRMS (EI): Calc. for C14H8Cl6O2Si2: 473.81941.
Found: 473.81953. Attempts to purify the product were
unsuccessful.
2.7. Reaction of 1 with 2b
2.10. Reaction of 1 with 4
In a nitrogen-flushed NMR tube, 2b (30.0 mg, 0.200
mmol) was added by a syringe. The NMR tube was
cooled to 0 °C by an ice bath and then disilane 1 (64.0
mg, 0.240 mmol) was introduced. The reaction was
exothermic judging from the boiling of the mixture and
Compound 4 (purified by recrystallization from
C6H14 (22.0 mg, 0.220 mmol) was introduced by syringe
into an NMR tube. The tube was closed with a septum
and then it was heated to 80 °C for 2 h, during which
time the reaction mixture became a clear light yellow
1
1
the warm-up of the tube. The product analyzed by H-,
solution. The product analyzed by H-, 13C-, 29Si-NMR
13C-, 29Si-NMR and HRMS spectroscopies as 5b. For-
mation of the cis-isomer was inferred from the
analogous reaction of 1 with 2a to give 5a whose
structure was determined by X-ray diffraction analysis.
1H-NMR (CDCl3): l 7.40 (m, 5H), 2.07 (s, 3H); 13C-
NMR (CDCl3): l 134.70, 134.15, 133.07, 129.22,
129.10, 128.41, 17.70; 29Si-NMR (CDCl3, SiMe4): l
−21.79, −22.74. MS (70 eV, EI): m/z (relative inten-
and HR mass spectroscopies as 7. H-NMR (CDCl3): l
1
7.04 (s, 4H); 13C-NMR (CDCl3): l 147.62, 121.00;
29Si-NMR (CDCl3): l −22.02. MS (70 eV, EI): m/z
(relative intensity, ion) 380.0 [5.34, M+(4 37Cl, 2 35Cl)],
378.0 [11.75, M+(3 37Cl, 3 35Cl)], 376.0 [17.21, M+(2
37Cl, 4 35Cl)], 241.0 [1.01, [M−SiCl3]+]. HRMS (EI):
Calc. for C6H4Cl6O2Si2: 373.7881. Found: 373.78780.
This reaction was also carried out in CHCl3 at r.t.,

18
J. Yang, J.G. Verkade / Journal of Organometallic Chemistry 651 (2002) 15–21
giving 7 in 100% conversion immediately after mixing 1
and 4. Purification of the product by removal of 1
under vacuum afforded pure product. Anal. Calc. for
C6H4Cl6O2Si2: C, 19.09; H, 1.19; Cl, 56.49; Si, 14.77.
Found: C, 19.31; H, 1.19; Cl, 56.01; Si, 14.48%.
A total of 22 002 (for 5a) and 11 557 (for 8) data were
harvested by collecting three sets of frames with 0.3°
scans in ꢀ with an exposure time 30 (for 5a) and 20 s
(for 8) per frame. These highly redundant data sets
were corrected for Lorentz and polarization effects. The
absorption correction was based on fitting a function to
the empirical transmission surface as sampled by multi-
ple equivalent measurements [7].
2.11. Synthesis of hexacoordinated bicyclic silicon
compound 8
The systematic absences in the diffraction data were
uniquely consistent for the space groups P21/c (for 5a)
and P21/n (for 8) that yielded chemically reasonable
and computationally stable results of refinement [8]. A
successful solution by the direct methods provided the
positions of most atoms from the E-map. The remain-
ing non-hydrogen atoms were located in an alternating
series of least-squares cycles and difference Fourier
maps. All non-hydrogen atoms were refined with an-
isotropic displacement coefficients. All hydrogen atoms
were included in the structure factor calculation at
idealized positions and were allowed to ride on the
neighboring atoms with relative isotropic displacement
coefficients. Crystallographic data and pertinent bond
lengths and angles are given in Tables 1 and 2,
respectively.
In a 250 ml flask equipped with a magnetic stirrer,
Et2O (100 ml) was added under nitrogen, followed by
N-methylpropionamide (2.61 g, 30.0 mmol). The solu-
tion was cooled to 0 °C, and tert-butyllithium (1.7 M
in pentane, 18.0 ml) was added dropwise under nitro-
gen with a syringe. A white suspension was observed to
form during the addition of t-BuLi. After the addition
of t-BuLi solution, the reaction mixture was stirred at
0 °C for 1 h, and then at r.t. for another 2 h. Then the
reaction mixture was re-cooled to 0 °C and 1 (2.01 g,
7.50 mmol) or SiCl4 (2.55 g, 15 mmol) was added
dropwise to the suspension. The reaction mixture was
allowed to warm to r.t. where it was stirred for another
2 h and then refluxed overnight. The reaction mixture
was filtered, and colorless crystals of 8 (3.13 g) suitable
for X-ray diffraction were observed to form in the
1
filtrate during filtration. H-NMR (CDCl3): l 2.99 (s,
3H), 2.40–2.47 (q, 2H), 1.17–1.22 (t, 3H); 13C-NMR
(CDCl3): l 183.31, 29.27, 21.09, 8.02; 29Si MAS-NMR
(solid hexamethylcyclotrisiloxane): l −159.89. MS (EI)
m/z (intensity, ion): 270.9 (19.46, M+).
4. Results and discussion
4.1. SiꢁSi bond clea6age during adduct formation
In an effort to detect silyl radicals in our alkyne
trimerization reactions catalyzed by 1 [3], 1,2-quinones
and 1,4-quinones (which are commonly used as efficient
radical traps [9]) were utilized in the reactions reported
herein. When benzil (2a) was introduced in the reac-
tions of 1 with alkynes, no cyclotrimerizations product
was detected, however, the new product 5a was formed
as a viscous liquid. Lowering the reaction temperature
to 80 °C, or by simply mixing 1 and 2a in CHCl3 (or
toluene) at room temperature gave 5a in quantitative
3. X-ray molecular structure solution of 5a and 8
A colorless crystal with approximate dimensions
0.43×0.31×0.14 mm3 was selected from oil under
ambient conditions and was attached to the tip of a
glass capillary. The crystal was mounted in a stream of
cold nitrogen at 173(2) K and centered in the X-ray
beam by using a video camera. The crystal evaluation
and data collection were performed on a Bruker CCD-
1
conversion, as confirmed by H-, 13C- and 29Si-NMR
,
1000 diffractometer with Mo–Ka (u=0.71073 A) radi-
ation and the diffractometer to crystal distance of 5.08
cm.
spectroscopies. The 1,2-diones 2b and 3a,b also resulted
in the formation of the corresponding products 5b and
6a,b in quantitative conversions. Similarly, the 1,4-qui-
none 4 led to the quantitative formation of 7 whether
the reaction was carried out at 100 °C or by mixing the
reagents in CHCl3 at room temperature. Although this
compound was reported in 1940 [10], it had been
synthesized from the reaction of para-cresol with SiCl4,
and only a density, index of refraction and a partial
elemental analysis (Cl and Si) was reported.
The strength of SiꢁSi linkage in disilanes is expected
to be weakened when electron withdrawing substituents
are present, thus facilitating the generation of SiCl3
radicals at elevated temperatures (ca. 200 °C) [3]. We
therefore suspected that the radical generation might
The initial cell constants were obtained from three
series of ꢀ scans at different starting angles. Each series
consisted of 20 frames at intervals of 0.3° in a 6° range
about ꢀ with the exposure time of 10 s per frame. A
total of 43 reflections were obtained. The reflections
were successfully indexed by an automated indexing
routine built in the SMART program. The final cell
constants were calculated from a set of 6921 strong
reflections from the actual data collection.
The data were collected by using the hemisphere data
collection routine. The reciprocal space was surveyed to
the extent of 1.8 hemisphere to a resolution of 0.80 A.
,

J. Yang, J.G. Verkade / Journal of Organometallic Chemistry 651 (2002) 15–21
19
account for the occurrence of the reaction of 2a with 1
to form 5a at 100 °C. However, the following observa-
tion militates against this possibly. When 1 and 2a were
mixed in chloroform or toluene, we observed immediate
formation of 5a even under ambient conditions, at which
temperature the concentration of SiCl3 radicals,
if any, would be expected to be too low to cause the
reaction to occur so rapidly.
We suggest that the disilane–1,2-diketones, –quinone
and –1,4-quinone reactions reported herein are proba-
bly initiated by the formation of pentacoordinated sili-
con species, the presence of which becomes more
prominent when electron withdrawing groups such as
halogens are attached to the silicon. Although hyperco-
ordinated silicon compounds have been extensively in-
vestigated [11], similar compounds formed from
disilanes are lacking. In an effort to elucidate the
pathway for the reactions reported here, we now de-
scribe some observations that lend credence to the
formation of hypercoordinate species with 1.
possessing electron lone pairs [11,12]. Formation of the
adducts was detected in solution by 29Si-NMR and
supported by characteristic catalytic reactions [11,12].
When Si2Cl6 was added to a solution of tmeda in Et2O
at room temperature (or at −78 °C), a white precipitate
formed immediately. Filtering off the solvent and drying
the product under vacuum afforded a white powdery
material in 93% yield based on the assumed formation
1
of a 1:1 adduct. Only slight changes in the H- and
13C-NMR spectra were observed upon adduct formation
but evidence for the presence of hypercoordinated silicon
species was obtained from the solid state 29Si-NMR
spectrum, in which only a strong upfield signal at l
−79.24 ppm was observed. The lack of other 29Si peaks
was consistent with the idea of a stoichiometric reaction.
The presence of a single 29Si-NMR chemical shift sug-
gests the possibility of a six-membered ring structure for
this adduct as shown below.
4.2. Si2Cl6 adduct formation with tmeda and DMF
The reaction of Si2Cl6 with DMF further supports the
notion of the formation of hypercoordinated disilane
species. In this case, although we could not obtain pure
Silanes such as methyltrichlorosilane have long been
known to be able to form adducts with compounds
Table 1
Crystal data and structure refinement for 5a and 8
Empirical formula
Formula weight
Temperature (K)
C28H20Cl18O4Si6
1227.08
173(2)
C8H16Cl2N2O2Si
271.22
173(2)
,
Wavelength (A)
0.71073
Monoclinic
P21/c
0.71073
Monoclinic
P21/n
Crystal system
Space group
Unit cell dimensions
,
a (A)
19.5119(10)
5.9456(5)
22.7893(12)
90
110.493(1)
90
2476.5(3)
2
1.646
10.3238(5)
9.0982(5)
14.3632(7)
90
103.822(1)
90
1310.04(12)
4
1.375
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
V (A )
3
,
Z
Dcalc (mg m−3
)
Absorption coefficient (mm−1
F(000)
)
1.173
1220
0.572
568
Crystal size (mm3)
0.43×0.31×0.14
1.11–26.37
−245h522, 05k57, 05l528
22 002
0.45×0.45×0.45
2.67–26.36
−125h512, 05k511, 05l517
11 557
q range for data collection (°)
Index ranges
Reflections collected
Independent reflections
Completeness to q=26.37°
Absorption correction
Max/min transmission
Refinement method
5077 [Rint=0.0385]
99.8%
Empirical with SADABS
0.8530 and 0.6324
Full-matrix least-squares on F2
5077/0/253
R1=0.0397, wR2=0.1122
R1=0.0574, wR2=0.1247
1.081
2669 [Rint=0.0170]
99.9%
Empirical with SADABS
0.7830 and 0.7830
Full-matrix least-squares on F2
2669/0/140
R1=0.0250, wR2=0.0914
R1=0.0288, wR2=0.0948
1.006
Data/restraints/parameters
Final R indices [I\2|(I)]
R indices (all data)
Goodness-of-fit on F2
−3
,
Largest difference peak and hole (e A
)
0.694 and −0.543
0.239 and −0.219

20
J. Yang, J.G. Verkade / Journal of Organometallic Chemistry 651 (2002) 15–21
Table 2
solid 29Si-NMR spectrum (despite the similarity in the
1H- and 13C-NMR spectra of the adduct to DMF
itself). The proposed structure of this adduct is shown
below. Although five- and six-membered ring structures
are shown for the DMF and tmeda adducts, respec-
tively, we are unable to rule out a polymeric structure
or a larger cyclic oligomer.
,
Bond lengths (A) and angles (°) for 5a and 8
5a
8
Bond lengths
Cl(1)ꢁSi(1)
Cl(2)ꢁSi(1)
Cl(3)ꢁSi(1)
Cl(4)ꢁSi(2)
Cl(5)ꢁSi(2)
Cl(6)ꢁSi(2)
Si(1)ꢁO(1)
Si(2)ꢁO(2)
O(1)ꢁC(1)
O(2)ꢁC(2)
2.0061(12)
2.0096(12)
2.0086(12)
1.9914(13)
2.0107(13)
2.0085(14)
1.603(2)
1.614(2)
1.397(3)
1.400(3)
SiꢁN(1)
SiꢁN(2)
SiꢁO(2)
SiꢁO(1)
SiꢁCl(1)
SiꢁCl(2)
SiꢁC(5)
SiꢁC(1)
1.8303(11)
1.8345(11)
1.8850(10)
1.8859(10)
2.1447(5)
2.1542(5)
2.2886(14)
2.2896(14)
4.3. Si2Cl6 reactions with 1,2-diketones and a quinone
1,2-Diketones (2a,b) and (3a,b) and the quinone (4)
react at moderate temperature (80 °C or below), to give
5a,b; 6a,b and 7, respectively, in excellent conversions.
We propose that adduct formation (as an unstable
intermediate) between disilane 1 and a 1,2-diketone or a
1,2-quinone is the initial step for these reactions as
depicted in the structure below. In an effort to obtain
evidence for such an adduct, a mixture of 1 and 2a
(with 1 in 20% excess) was sealed in a glass tube. As
described in Section 2, crystals were grown from this
reaction mixture.
Bond angles
Cl(1)ꢁSi(1)ꢁCl(3)
O(1)ꢁSi(1)ꢁCl(2)
Cl(1)ꢁSi(1)ꢁCl(2)
Cl(3)ꢁSi(1)ꢁCl(2)
Cl(4)ꢁSi(2)ꢁCl(6)
O(2)ꢁSi(2)ꢁCl(5)
Cl(4)ꢁSi(2)ꢁCl(5)
Cl(6)ꢁSi(2)ꢁCl(5)
C(1)ꢁO(1)ꢁSi(1)
C(2)ꢁO(2)ꢁSi(2)
C(2)ꢁC(1)ꢁO(1)
109.59(6)
108.72(9)
110.08(6)
108.20(6)
111.34(7)
111.63(9)
110.29(7)
106.58(6)
130.39(18)
127.41(18)
118.5(3)
N(1)ꢁSiꢁN(2)
N(1)ꢁSiꢁO(2)
N(2)ꢁSiꢁO(2)
N(1)ꢁSiꢁO(1)
N(2)ꢁSiꢁO(1)
O(2)ꢁSiꢁO(1)
N(1)ꢁSiꢁCl(1)
N(2)ꢁSiꢁCl(1)
O(2)ꢁSiꢁCl(1)
O(1)ꢁSiꢁCl(1)
N(1)ꢁSiꢁCl(2)
N(2)ꢁSiꢁCl(2)
O(2)ꢁSiꢁCl(2)
O(1)ꢁSiꢁCl(2)
Cl(1)ꢁSiꢁCl(2)
N(1)ꢁSiꢁC(5)
158.86(6)
94.50(5)
69.14(5)
69.48(5)
95.47(5)
86.76(4)
98.00(4)
96.92(4)
165.49(3)
90.74(3)
95.97(4)
97.45(4)
90.58(4)
164.92(4)
95.40(2)
128.07(5)
N(2)ꢁSiꢁC(5)
O(2)ꢁSiꢁC(5)
O(1)ꢁSiꢁC(5)
Cl(1)ꢁSiꢁC(5)
Cl(2)ꢁSiꢁC(5)
C(1)ꢁO(1)ꢁSi
C(5)ꢁO(2)ꢁSi
34.57(5)
34.58(4)
91.95(4)
131.43(4)
94.26(4)
89.72(8)
89.96(6)
Analysis of these crystals by X-ray diffraction means,
however, (Fig. 1) showed the compound to be cis-1,2-
diphenyl-1,2-bis(trichlorosiloxy)ethylene 5a (with 1 as
an inclusion). Moreover, monitoring the reaction with
29Si-NMR spectroscopy in toluene at −50 °C showed
instant formation of 5a. These results suggest that any
intermediate adduct formed must be too short-lived to
allow isolation or detection by NMR spectroscopy.
Examples of coordination of an acetyl group (via
oxygen) to a silicon atom are well known [13]. It has
been reported [12] that in 9–12 the SiꢁX as well as the
SiꢁO bond distances vary with different X groups, with
,
the shortest SiꢁO bond (1.74 A) observed for X=
SO3CF3. This bond distance (not unexpectedly) is
,
longer than the SiꢁO bond in 5a [1.609(2) A, Fig. 1].
4.4. Synthesis of a new hexacoordinated silicon species
Fig. 1. Computer drawing of 5a.
When we performed the reaction between 1 and four
equivalents of the lithium salt of N-methylpropi-
onamide (obtained by reacting equimolar amounts of
product from the reaction, two high-field signals (l
−184.71 and −192.10 ppm) were observed in the

J. Yang, J.G. Verkade / Journal of Organometallic Chemistry 651 (2002) 15–21
21
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 172400 and 172401 for com-
pounds 5a and 8. Copies of this 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.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
Acknowledgements
The authors thank the NSF and the Donors of the
Petroleum Research Fund administered by the Ameri-
can Chemical Society for grant support.
Fig. 2. Computer drawing of 8.
References
N-methylpropionamide and t-BuLi in Et2O) we ob-
tained the novel hexacoordinated silicon compound 8
(Fig. 2). It is interesting to note that the SiꢁN and SiꢁO
bond lengths in this compound [1.8324(11) and
[1] H. Yamashita, N.P. Reddy, M. Tanaka, Organometallics 16
(1997) 5223.
[2] K. Tamao, S. Okazaki, M. Kumada, J. Organomet. Chem. 146
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[3] (a) J. Yang, J.G. Verkade, J. Am. Chem. Soc. 120 (1998) 3855;
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5095;
,
1.8855(11) A, respectively] are fairly similar, and that
the OꢁC and ring NꢁC links are essentially the same
,
length [1.2987(15) and 1.3014(18) A, respectively] indi-
cating rather compete delocalization of the electrons
within the four-membered ring systems.
(b) I.D. Kalikhman, I.B. Bannikova, L.P. Petuchov, V.A. Pes-
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87.
The synthesis of 8 was carried out by the reaction of
LiNMeC(O)Et with Si2Cl6 or SiCl4 using the stoi-
chiometries shown in reactions (1) and (2), respectively.
Reaction (1) was originally performed with the inten-
tion of making 14 in reaction (3).
[5] (a) I.D. Kalikhman, V.A. Pestunovich, B.A. Gostevskii, O.B.
Banikova, M.G. Voronkov, J. Organomet. Chem. 338 (1988)
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5095.
4LiNMeC(O)Et+Si2Cl6“cis-Si[NMeC(O)Et]2Cl2
8
+[:Si[NMeC(O)Et]2]x+4LiCl
(1)
(2)
13
2LiNMeC(O)Et+SiCl4“8+2LiCl
4LiNMeC(O)Et+Si2Cl6
[6] I. Kalikhman, O. Girshberg, L. Lameyer, D. Stalke, D. Kost,
Organometallics 19 (2000) 1927.
[7] R.H. Blessing, Acta Crystallogr. A51 (1995) 33.
[8] All software and sources of the scattering factors are contained
in the SHELXTL (version 5.1) program library (G. Sheldrick,
Bruker Analytical X-Ray System, Madison WI).
[9] (a) K. Creber, T. Ho, Can. J. Chem. 60 (1982) 1054;
(b) B. Adeleka, J. Wan, J. Chem. Soc. Perkin Trans. 2 1 (1980)
225.
“Cl[NMeC(O)Et]2SiSi[NMeC(O)Et]2Cl
(3)
14
The formation of disproportionation product 8 (instead
of 14) suggests that silylene 13, its siliconꢁsilicon double
bonded dimer or a cyclic oligomer had formed. Al-
though we have been unable to isolate and characterize
13, further efforts are underway to do so.
[10] Yu.N. Volynov, B.N. Dolgov, Zhurnal obschei Khimii 10 (1940)
550.
[11] For reviews on hypercoordinated silicon chemistry, see: (a) C.
Chuit, R.J.P. Corriu, J.C. Young, Chem. Rev. 93 (1993) 1371;
(b) R.R. Holmes, Chem. Rev. 96 (1996) 927.
[12] S. Kobayashi, K. Nishio, J. Org. Chem. 59 (1994) 6620.
[13] A. Bassindale, M. Borbaruah, S. Glynn, D. Parker, P. Taylor, J.
Chem. Soc. Perkin Trans. 2 110 (1999) 2099.
5. Supplementary material
Crystallographic data for the structural analysis have