Organometallics
Article
(OSO2CF3)(Cl)L] (3) with four silyl and {[L(Cl)Si](Me3Si)-
CCCC(SiMe3)[Si(Cl)L]}2+·2[ClB(C6F5)3]− (4) hav-
ing two silyl and two silyliumyl substituents, respectively
(Scheme 2). Both these transformations are unknown in the
field of silene reaction chemistry.
Scheme 2. Reactions of 2 with AgOSO2CF3 and B(C6F5)3
Figure 1. X-ray crystal structure of 2 with thermal ellipsoids at 30%
probability level. The hydrogen atoms are omitted for clarity.
178.6(2)° and C(2)−C(3)−C(4) = 179.1(2)°). This array is
coplanar to Si(1) (the least-squares plane Δ = 0.0027 Å) and
according to Si(2) (Δ = 0.0017 Å), but these two planes have a
torsion angle of 32.5°. These data indicate clearly π-electrons’
conjugation over the two terminal SiC bonds and one
central CC bond.
Oxidative addition reactions of the silylenes with alkynes are
well-known.1a,b,4a tBu2Si:, in situ generated, reacts with tBuC
CCCtBu to produce sequentially [1 + 2] oxidative
cycloaddition compound [tBu2Si(η2-C2)tBu]2.4a It is then
reasoned that the formation of 2 from 1 and Me3SiCCC
CSiMe3 might proceed through a similar route to form
[L(Cl)Si(η2-C2)SiMe3]2 which underwent further bond
isomerization over the two jointed Si(η2-C2)-cycles. This
shows a route different from hv-induced conversion of
[tBu2Si(η2-C2)tBu]2 to 2,5-disilabicyclohexadiene.4a This
might be due to the different reactivities, when tBu2Si: is
compared with silylene 1. In the latter the amidinate donor
ligand at the Si atom strongly promotes the stable SiC bond
formation. A comparable case is known for a smooth synthesis
of the N-donor stabilized silene (Me3Si)(9-NMe2C10H6)Si
C(SiMe3)2.6
C6D6 was added to a mixture of 1 and 1,4-bis-
(trimethylsilyl)-1,3-butadiyne in a 2:1 molar ratio at room
temperature, immediately forming a deep brown solution.
After storing the flask for 1 h, the 1H NMR data confirmed the
reaction came to completion. Large-scale reaction in toluene
formed 2 as a red-brown solid (81% yield) by removal of
toluene followed with washing using n-hexane (Scheme 1). X-
ray quality single crystals of 2 were obtained by storing the
solution in solvent mixture of toluene and n-hexane at −20 °C
for 24 h. Compound 2 has a good solubility in aromatic solvent
(benzene and toluene), but is sparingly soluble in n-hexane. It
is highly air- and moisture-sensitive. Under inert atmosphere
like N2 and Ar, it can be stored for a long time at room
temperature. The melting point measurement indicated that
upon heat treatment up to 150 °C 2 started to decompose as
indicated by its color change from brown to black. Compound
2 has been characterized by NMR (1H, 13C, 29Si), CHN
elemental analysis, and X-ray crystallography. The 29Si NMR
spectrum shows two resonances, and the small broad one at δ
−6.38 ppm is assignable to the SiC which appears upfield
when compared with that of L(Cl)Si: in 1 (δ 14.6 ppm).8a
Actually, the 29Si NMR resonances are shown in a wide range
for the silenes (δ −59.9 to −78.7 and 17.5−144.2 ppm),1c,5−7,9
and the value for 2 is comparable to that of Tip2SiC[η2-
Si(Tip)(Ph)N(tBu)] (δ −6.9 ppm, Tip = 2,4,6-iPr2C6H2).9b
However, the 13C NMR spectrum does not display the SiC
resonance, although the acetylenic carbon resonance is clearly
found at δ 82.19 ppm. X-ray single-crystal diffraction study of 2
clearly discloses the composition and structure (Figure 1). The
Si(1)−C(1) and Si(2)−C(4) bond lengths are 1.723(2) and
1.724(2) Å, which are a little longer than that in Wiberg’s
Me2SiC(SiMe3)SiMetBu2 (1.702(5) Å)10 but shorter than
those of other silenes (1.726(4)−1.778(3) Å).1c,9 The C(1)−
C(2) and C(3)−C(4) bond lengths are 1.437(3) and 1.434(3)
Å, whereas the C(2)−C(3) bond length exhibits 1.214(3) Å.
The former two are a little shorter than that of the C−C single
bond, while the latter is a little longer than that of the CC
triple bond. It is noteworthy that the C(1)−C(2)−C(3)−C(4)
unit is in an almost linear array (C(1)−C(2)−C(3) =
The SiC bond in the silenes is known to be highly
polarized indicative of a high reactivity.1c,2 We performed
further reactions using 2 with AgOSO2CF3, B(C6F5)3, and
[Ph3C]+[B(C6F5)4]−, respectively. At room temperature,
CD3CN was added to a mixture of 2 and 2 equiv of
1
AgOSO2CF3. After 10 min the H NMR spectrum indicated
that the reaction was complete. It was clearly observed that the
silver mirror was spontaneously generated. The following
filtration to remove the mirror and then storing the filtrate at
−20 °C in a freezer for 24 h led to formation of complex 3
(Scheme 2) as light-yellow crystals (68% yield). Reaction of 2
and 2/3 equiv of B(C6F5)3 was conducted in a mixture of
CDCl3 and C6D6 at room temperature and finalized within 10
1
min. However, the H NMR data indicated formation of a
mixture of products. The flask was stored in a freezer at −20
°C for 2 weeks to produce 4 as light-pink crystals (19% yield).
Interestingly, the mother solution after separation of 4 was
again kept at −20 °C for 2 days affording compound 5 as
purple crystals (30% yield) (Scheme 2). For comparison, the
reaction of 2 with [Ph3C]+[B(C6F5)4]− in CD3CN was
accomplished. The reaction also occurred immediately at
1
room temperature and was complete within 10 min. The H
NMR data showed formation of several new species. Storing
the solution after addition of pyridine and n-hexane at −20 °C
in a freezer for 2 weeks resulted in products [L2(Cl)Si]+[B-
B
Organometallics XXXX, XXX, XXX−XXX
Chen, Yilin
