Disilene Fluoride Adducts versus β-Halooligosilanides

Article abstract of DOI:10.1021/acs.inorgchem.9b02223

Extending the chemistry of disilene fluoride adducts studied earlier by us, we investigated the formation of 1,1-bis(trimethylsilyl)fluorodiphenylsilylsilanide, which was prepared by reaction of (Me₃Si)₃SiSiPh₂F with KO^tBu. The formed FPh₂SiSi(Me₃Si)₂K displays distinctively different structural and spectroscopic features compared to the earlier reported F(Me₃Si)₂SiSi(SiMe₃)₂K. While the latter eliminates metal fluoride upon reaction with MgBr₂, the respective magnesium silanide is formed from FPh₂SiSi(Me₃Si)₂K. Reaction of (Me₃Si)₃SiSiPh₂Cl with KO^tBu proceeded similarly, but the formed ClPh₂SiSi(Me₃Si)₂K easily undergoes potassium chloride elimination to the disilene Ph₂SiSi(SiMe₃)₂. Compared to F(Me₃Si)₂SiSi(SiMe₃)₂K, which can be regarded as a disilene fluoride adduct, structural, spectroscopic, and reactivity properties of FPh₂SiSi(Me₃Si)₂K distinguish it as a β-fluorodisilanide.

Full text of DOI:10.1021/acs.inorgchem.9b02223

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Disilene Fluoride Adducts versus β‑Halooligosilanides
̈
Istvan Balatoni, Johann Hlina, Rainer Zitz, Alexander Pocheim, Judith Baumgartner,*
and Christoph Marschner*
Institut fur Anorganische Chemie, Technische Universitat Graz, Stremayrgasse 9, 8010 Graz, Austria
̈
̈
S
* Supporting Information
ABSTRACT: Extending the chemistry of disilene fluoride adducts studied
earlier by us, we investigated the formation of 1,1-bis(trimethylsilyl)-
fluorodiphenylsilylsilanide, which was prepared by reaction of
(Me3Si)3SiSiPh2F with KOtBu. The formed FPh2SiSi(Me3Si)2K displays
distinctively different structural and spectroscopic features compared to the
earlier reported F(Me3Si)2SiSi(SiMe3)2K. While the latter eliminates metal
fluoride upon reaction with MgBr2, the respective magnesium silanide is
formed from FPh2SiSi(Me3Si)2K. Reaction of (Me3Si)3SiSiPh2Cl with KOtBu
proceeded similarly, but the formed ClPh2SiSi(Me3Si)2K easily undergoes
potassium chloride elimination to the disilene Ph2SiSi(SiMe3)2. Compared to F(Me3Si)2SiSi(SiMe3)2K, which can be
regarded as a disilene fluoride adduct, structural, spectroscopic, and reactivity properties of FPh2SiSi(Me3Si)2K distinguish it as
a β-fluorodisilanide.
An interesting feature of β-fluorodisilanyl potassium
compounds 2a and 2b is that attempts to transmetallate by
metathesis reaction with MgBr2 or Cp2ZrCl2 do not proceed as
expected but lead via the elimination of metal fluorides to the
formation of disilenes (Scheme 1), which depending on the
bulk of substituents are either stable or undergo 2 + 2
cycloaddition.13,14
INTRODUCTION
■
Over the last few years, the development of methods for the
preparation of silanides1−5 has promoted a tremendous
progress of organosilicon chemistry. The availability of a
wide variety of nucleophilic silicon compounds in combination
with long known silyl electrophiles has brought us much closer
to a mature organic chemistry of silicon, where Si−Si bond
formation is not mainly restricted to Wurtz-type coupling of
halosilanes.
A logical next step in this development is the introduction of
functionalized silanides with the chemistry of α-functionalized
silyl anions (silylenoids) being pioneered by Kawachi and
Tamao6−9 as well as a few others.10−12
Our own contribution to this topic started out from the
reaction of methoxytris(trimethylsilyl)silane with KOtBu to
bis(trimethylsilyl)methoxysilyl potassium,10 which displays
silylenoid character. This led us further to the synthesis of a
β-fluorodisilanyl potassium compound (2a) from fluorosilane
1a, which forms via the condensation of two molecules of
transient fluorosilylenoids (Scheme 1).13,14 Both of our
synthetic approaches exploit silanide formation via Me3Si−Si
bond cleavage with KOtBu.15,16
While condensation of fluorosilylenoids is a good and high
yielding method to β-fluorodisilanides, it suffers from two
disadvantages. First, it only works well starting out from a
trisilylated silylfluoride. Our attempts to replace one of the silyl
groups with other substituents were met only with very limited
t
success. Reactions of R(Me3Si)2SiF (R = Me, Ph, Bu) with
KOtBu gave the expected KR(SiMe3)SiSi(SiMe3)RF only for
the R = tBu case with poor selectivity.14 The second issue with
the condensation reaction is that as a consequence of its
nature, the substituents on the central silicon atoms are
identical. To obtain access to β-fluorodisilanides with different
substituents on the two silicon atoms, we decided to avoid the
condensation step by introducing the Si−Si bond formed
initially by silylenoid dimerization already into a substrate for
silanide formation. The metalation then can occur in a separate
step under conditions preserving the Si−Si bond.
In analogy to work by Wiberg and co-workers on Lewis base
adducts of silenes,17 we regarded the β-fluorodisilanides as
fluoride adducts of tetrakis(trimethylsilyl)disilene. This view is
supported by a rather short central Si−Si bond of 2.293(2) Å
of 2a, indicating partial double bond character and very short
Si−F bonds of 1.411(4)/1.437(4) Å.13 Extending this
chemistry to a case where one of the trimethylsilyl groups
was replaced by a triisopropylsilyl group confirmed the
transient formation of silylenoid (Me3Si)(iPr3Si)Si(F)K,
which dimerized to (Me3Si)(iPr3Si)(F)SiSi(K)(SiMe3)(SiiPr3)
(2b) (Scheme 1).14
RESULTS AND DISCUSSION
■
In a first attempt to implement this strategy, by reaction of
(Me3 Si)3 SiSiMe2 Cl1 8 with ZnF2 . we prepared
(Me3Si)3SiSiMe2F.18,19 Treatment of the latter with KOtBu
was supposed to give (Me3Si)2(K)SiSiMe2F, but instead clean
substitution of fluoride was observed to yield
Received: July 25, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.9b02223
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Inorganic Chemistry
Article
Scheme 1. Synthesis of Potassium β-Fluorodisilanides and Subsequent Disilene Formation upon Attempted Transmetallation
(Me3Si)3SiSiMe2OtBu. This outcome clearly indicates that the
SiMe2F group is both sterically and electronically more
susceptible to reaction with the alkoxides than the
trimethylsilyl group. To suppress this reaction, the methyl
groups of the SiMe2F substituent need to be replaced by
bulkier groups.
A straightforward way to introduce the bulkier Ph2SiX group
and in addition avoid a subsequent halide exchange step is the
reaction of silanide (Me3Si)3SiK with Ph2SiX2 (X = F, Cl). We
thus obtained (Me3Si)3SiSiPh2X (X = F, Cl) (3a, 3b) in
excellent yields (Scheme 2).
2). Compared to the previously reported K(Me3Si)2SiSi-
(SiMe3)2F (2a),13 the bond distance between Si1 and Si2
(2.2970(15) Å) is very similar. This shortening of the central
Si−Si bond by ca. 0.04 Å reflects the disilene contribution of
the structure. The angles around the negative silicon atom sum
up to 299.8 deg, thus exhibiting a more pronounced pyramidal
silicon than the 333.2 deg observed for 2a.13 This coincides
with a Si−F bond length of 1.639(2) Å for 4a, featuring an
elongation from the respective distance for 3a (1.6194(17) Å),
which is surprising as the Si−F bond of K(Me3Si)2SiSi-
(SiMe3)2F (2a) is very short (1.411(4)/1.437(4) Å).13
It can be assumed that the Si−F interaction is strongly
connected to the polarity of the associated Si−Si double bond
of the respective disilene. In their seminal paper, Wiberg and
co-workers argue: “A prerequisite for adduct formation seems
to be a polar SiX double bond as neither Brook’s sila enol
ether (Me3Si)3Si = C(OSiMe3)(1-adamantyl),21,22 which has a
largely nonpolar silicon−carbon double bond nor West’s23 or
Masamune’s24 (symmetrical) disilenes have been reported to
form stable adducts.” Despite the fact that our synthesis of
K(Me3Si)2SiSi(SiMe3)2F (2a) has disproved Wiberg’s argu-
ment, it is still reasonable that adducts of polar disilenes such
as (Me3Si)2SiSiPh2 should be more stable. During their
quest for the synthesis of a disilyne,25 Wiberg et al. later
reported some examples of β-halooligosilanides such as tBu3Si-
(H)(Br)SiSi(H)(Na)SitBu3, which however are very reactive
even at low temperature and could not be rigorously
characterized.26,27
Scheme 2. Preparation of Oligosilanyl Halides 3a and 3b
The solid-state structures in the crystals of 3a and 3b
(Figure 1, Table 1) are inconspicuous with typical Si−F
(1.6194(17) Å) and Si−Cl (2.0984(19) Å) distances and fairly
short central Si−Si bonds of 2.3386(11) and 2.342(2) Å,
respectively. Also, the NMR features of 3a are rather
predictable (Table 2). The 29Si resonances at 21.1 (SiPh2F),
−9.7 (SiMe3) and −134.8 ppm (Siq) are typical for a
1
neopentasilane and so is the JSi−F = 319 Hz for the
SiPh2F20 group.
The structural differences between 4a and 2a are consistent
with the NMR spectroscopic analysis. The stronger silanide
character, which is evident in the stronger pyramidalization of
the anionic silicon atom of 4a, is reflected by a more shielded
resonance at −201.6 ppm, which is decisively different from
the −169.3 ppm observed for 2a (Table 2). Even more
significant is the fact that for K(Me3Si)2SiSi(SiMe3)2F (2a) a
Starting out from (Me3Si)3SiSiPh2F (3a), reaction with
KOtBu in the presence of 18-crown-6 selectively cleaved off a
trimethylsilyl group as silyl ether leading to the desired β-
fluorodisilanide 4a (Figure 2, Scheme 3).
The solid state structure of 4a (Figure 2) reveals a fairly
typical silanide with the potassium ion in a crown-ether unit
coordinating to the negatively charged silicon atom Si2 (Figure
Figure 1. Molecular structures of 3a (left) and 3b (right) (thermal ellipsoid plot drawn at the 30% probability level). All hydrogen atoms are
omitted for clarity (bond lengths in Å, angles in deg). 3a: Si(1)−F(1) 1.6194(17), Si(1)−C(1) 1.873(3), Si(1)−Si(2) 2.3386(11), Si(2)−Si(5)
2.3508(12), Si(2)−Si(3) 2.3530(12), Si(2)−Si(4) 2.3535(12), F(1)−Si(1)−Si(2) 105.85(7), Si(1)−Si(2)−Si(5) 103.97(4), Si(1)−Si(2)−Si(3)
116.59(4). 3b: Si(1)−C(1) 1.876(5), Si(1)−Si(2) 2.342(2), Si(2)−Si(3) 2.353(2), Si(1)−Cl(1) 2.0984(19), C(1)−C(3) 1.386(7), Cl(1)−
Si(1)−Si(2) 107.69(7), Si(1)−Si(2)−Si(3) 112.91(7).
B
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Table 1. Structural Bond Distances of Starting Materials 3a and 3b, as well as β-Halodisilanides 4a, 4b, 5, 6, 7 and Related
Compound 2a
compound
Si1−F(X)
1.6194(17)
2.0984(19) X = Cl
1.639(2)
2.153(2) X = Cl
1.639(3)
1.653(5)
Si1−Si2
2.3386(11)
2.342(2)
2.2970(15)
2.315(2)
2.3006(17)
2.318(3)
2.3593(19)/2.355(2)
2.293(2)
Si2−SiMe3
Si2−M
3a
3b
4a
4b
5
2.3508(12)/2.3535(12)
2.353(2)/2.354(1)
2.341(1)/2.347(1)
2.356(2)/2.360(2)
2.339(2)/2.351(2)
2.346(3)/2.345(3)
2.361(2)−2.378(1)
2.350(2)
n.a.
n.a.
3.5609(14) M = K
n.a.
n.a.
6
2.609(3) M = Mg
2.799(1)/2.803(1) M = Zr
3.944(2)
7
2a
1.625(3)/1.621(3)
1.437(4)/1.411(4)
a
a
Data taken from ref 13.
Table 2. NMR Chemical Shift and Coupling Data of 3a, 4a,
5, 6, 7 and the Related Compounds (Me3Si)3SiSi(SiMe3)2F,
2a, and 2b
δ
29Si1−X
δ
29Si2
δ
29SiMe3
compound
1JSi−F
2JSi−F
3JSi−F
δ
19F
3a
21.1
319 Hz
15.8
41.4
356 Hz
39.7
42.0
358 Hz
32.1
320 Hz
25.1
322 Hz
41.3
338 Hz
58.6
314 Hz
62.3
342 Hz
72.3
292 Hz
−134.8
19 Hz
−127.3
−201.6
5 Hz
−195.7
−202.5
n.d.
−171.1
15 Hz
−90.9
12 Hz
−129.1
14 Hz
−169.3
79 Hz
−175.8
53 Hz
−162.1
91 Hz
−9.7
4 Hz
−9.6
−4.4
9 Hz
−5.7
−3.9
7 Hz
−7.4
6 Hz
−6.5
4 Hz
−12.1
5 Hz
−6.5
18 Hz
−171.2
3b
4a
n.a.
−162.6
4b
5
n.a.
−164.5
6
7
−164.8
−166.8
−235.0
−213.5
−200.1
−195.8
Figure 2. Molecular structure of 4a (thermal ellipsoid plot drawn at
the 30% probability level). All hydrogen atoms are omitted for clarity
(bond lengths in Å, angles in deg). K(1)−Si(2) 3.5609(14), Si(1)−
F(1) 1.639(2), Si(1)−C(13) 1.888(3), Si(1)−Si(2) 2.2970(15),
F(1)−Si(1)−Si(2) 120.26(9), Si(1)−Si(2)−Si(3) 97.89(5), Si(1)−
Si(2)−K(1) 112.74(5).
a
(Me3Si)3SiSi(SiMe3)2F
a
2a·18-c-6
a
2b·18-c-6
Scheme 3. Reaction of (Me3Si)3SiSiPh2F (3a) with KOtBu
in the Presence of 18-crown-6 or [2.2.2] Cryptand to
Potassium β-Fluorodisilanides 4a and 5 and Subsequent
Transmetallation to a Magnesium β-Fluorodisilanide (6)
a
2b·(THF)6
a
Data taken from refs 13 and 14.
2
rather pronounced JSi−F coupling of 79 Hz was observed,
2
whereas the JSi−F coupling of 4a amounts only to 5 Hz.
While the crystal structure of 4a still reveals an interaction
between the negatively charged silicon atom Si1 and the
potassium ion, the reaction of 3a and KOtBu in the presence of
[2.2.2] cryptand gave product 5 as a separated ion pair. The
structural properties of the anionic part of 5 (Figure 3) are
quite similar to those of 4a (Table 1). The sum of angles
around the negatively charged silicon atom (297.8 deg) is even
slightly smaller than that for 4a. This picture is congruent with
the NMR spectroscopic results. The diminished ionic
interaction results in a slightly more shielded silanide chemical
shift of −202.5 ppm, and the more pure silanide character is
also reflected by other spectroscopic features such as 1JSi−F and
the chemical shifts of the SiPh2F and the SiMe3 groups (Table
2).
fluorodisilanide 6 in a clean reaction (Scheme 3).28,29 29Si
NMR spectroscopic analysis of 6 shows rather typical chemical
shifts for a trisilylated magnesium silanide of −171.1 ppm for
the negatively charged silicon atom and −7.4 ppm for the
trimethylsilyl groups.28,29 This again is consistent with the
structural data obtained from single crystal XRD analysis
(Figure 4). The diminished silanide character of 6 is reflected
by a less pyramidal silanide silicon atom with a sum of angles
of 313.6 deg. The central Si−Si bond (2.318(3) Å) is also
elongated compared to 4a and 5 but still shorter than that of
3a.
Reaction of 4a with Cp2ZrCl2 did also not give the expected
disilene. Instead, clean formation of the silylzirconocene 7
(Scheme 4, Figure 5) was observed.30,31 Again this outcome
emphasizes the silanide character of 4a compared to the
disilene fluoride adduct character of 2a. The 29Si NMR
Reactions of 2a with MgBr2·Et2O and Cp2ZrCl2 were found
to cause the formation of disilene (Me3Si)2SiSi(SiMe3)2.13,14
Therefore, we reacted compound 4a with these reagents in the
expectation of an analogous disilene formation. However,
reaction of 4a with MgBr2·Et2O instead gave magnesium β-
C
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Figure 5. Molecular structure of 7 (thermal ellipsoid plot drawn at the
30% probability level). All hydrogen atoms are omitted for clarity
(bond lengths in Å, angles in deg). Zr(1)−Cl(1) 2.4044(15), Zr(1)−
Si(2) 2.7993(14), F(1)−Si(1) 1.624(3), Si(2)−Si(1) 2.3593(19),
Si(2)−Si(3) 2.3641(18), Si(2)−Si(4) 2.3771(18), Si(1)−C(17)
1.868(5), Cl(1)−Zr(1)−Si(2) 94.28(5), Si(1)−Si(2)−Si(3)
101.62(7), F(1)−Si(1)−Si(2) 108.91(12).
Figure 3. Molecular structure of 5 (thermal ellipsoid plot drawn at the
30% probability level). All hydrogen atoms are omitted for clarity
(bond lengths in Å, angles in deg). Si(1)−F(1) 1.639(3), Si(1)−C(1)
1.908(4), Si(1)−Si(2) 2.3006(17), K(1)−O(1) 2.802(3), K(1)−
N(1) 3.066(4), F(1)−Si(1)−Si(2) 120.79(12), Si(1)−Si(2)−Si(3)
97.49(6), O(1)−K(1)−N(1) 121.06(10).
independent molecules in the asymmetric unit was determined.
The Si−Zr distance of 2.799(1)/2.803(1) Å is close to that of
related oligosilanyl Zr(X)Cp2 (X = Cl, Br) compounds,33−36
and the Si−F bond length is close to that of 3a. The Zr−Si−
Si−F torsional angles of the two independent molecules of 7
are 145.6 and 162.56, indicating a transoid arrangement with
no direct interaction between F and Zr. The sum of angles
around the metalated of 7 is 310.5 deg, which is very close to
what was found for 6, whereas the central Si−Si bond
(2.3593(19) Å) is substantially longer than what was observed
for 3a and 6. However, this elongation might be caused not
only by a less polar Si−Zr bond but also by the relatively large
Cp2Zr(Cl) substituent.
When we studied the reaction of (Me3Si)3SiF with KOtBu to
2a (Scheme 1), it was evident that we ought to study also the
analogous reaction with (Me3Si)3SiCl.13,14 However, this
reaction is not clean at all, which we attribute to the propensity
of the transient bis(trimethylsilyl)chlorosilylenoid to release
bis(trimethylsilyl)silylene and maybe also the fact that the Si−
Cl is weaker than the Si−F bond. In order to exploit the
weaker Si−Cl bond we checked on the reaction of tris-
(trimethylsilyl)(chlorodiphenylsilyl)silane (3b) with KOtBu.
And indeed it was possible to detect the formation of β-
chlorodisilanide 4b (Scheme 5). As expected, the compound is
Figure 4. Molecular structure of 6 (thermal ellipsoid plot drawn at the
30% probability level). Only the anion part of the molecule is shown.
All hydrogen atoms are omitted for clarity (bond lengths in Å, angles
in deg). Si(2)−Si(1) 2.318(3), Si(2)−Mg(1) 2.609(3), Si(1)−F(1)
1.653(5), Si(1)−C(1) 1.877(7), Mg(1)−O(1) 2.019(5), Mg(1)−
Br(1) 2.460(3), Si(1)−Si(2)−Mg(1) 111.54(10), F(1)−Si(1)−Si(2)
112.11(18), O(2)−Mg(1)−O(1) 99.7(2), O(1)−Mg(1)−Br(1)
103.90(18), O(1)−Mg(1)−Si(2) 111.18(18), Br(1)−Mg(1)−Si(2)
122.41(11).
Scheme 5. Synthesis of β-Chlorodisilanide 4b, Followed by
Chloride Elimination and Cyclotetrasilane (8) Formation
Scheme 4. Formation Fluorosilyl Zirconocene Chloride 7 by
Reaction of 4a with Zirconocene Dichloride
spectrum of 7 features the Si-Zr resonance at −90.9 ppm,
which is only slightly shifted to higher field compared to a
number of related isotetrasilanyl zirconocene chlorides, which
typically resonate close to −85 ppm.31,32
less stable than 4a. While the latter turned out to be stable in
solution at temperatures up to 100 °C, compound 4b
eliminates chloride slowly already at ambient temperature as
well as under transmetalation conditions. The thus formed
disilene (Me3Si)2SiSiPh2 could not be observed directly as it
undergoes head-to-tail [2 + 2] cycloaddition to give 1,1,3,3-
The solid state structure of 7 (Figure 5), which crystallizes in
̅
the triclinic space-group P1 with two crystallographically
D
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Figure 6. Molecular structure of 4b (thermal ellipsoid plot drawn at the 30% probability level). All hydrogen atoms are omitted for clarity (bond
lengths in Å, angles in deg). Si(1)−Cl(1) 2.153(2), Si(1)−Si(2) 2.315(2), Si(2)−Si(4) 2.356(2), Si(2)−Si(3) 2.360(2), Si(3)−C(36) 1.889(7),
K(1)−O(8) 2.665(5), K(1)−O(7) 2.695(5), K(1)−O(6) 2.792(4), Cl(1)−Si(1)−Si(2) 119.30(9), Si(1)−Si(2)−Si(4) 102.89(8), Si(4)−Si(2)−
Si(3) 103.09(8), O(8)−K(1)−O(7) 166.80(17).
tetrakis(trimethylsilyl)tetraphenylcyclotetrasilane 8 (Scheme
5).
4a. Whereas the 1JSi−F coupling of 2a (314 Hz) is some 25 Hz
reduced compared to the neutral analog (Me3Si)3SiSi-
1
(SiMe3)2F, the JSi−F coupling constant of 4a (356 Hz) is
Crystal structure analysis of 4b (Figure 6) revealed it to be
another separated ion pair. The main structural properties are
very similar to what was found for 5 (Table 1). Even more
than was observed for the fluorosilanides, the Si−Cl distance of
4b is elongated to 2.153(2) Å compared to the 2.0984(19) Å
detected for 3b. The central Si−Si bond (2.315(2) Å) is still
shortened but to a lesser degree than was found for 4a and 5
(Table 1).
NMR spectroscopic analysis of 4b (Table 2) reveals the
silanide signal (−195.7 ppm) to be distinctly less shielded
compared to fluorosilanides 4a and 5. This is consistent with
the chemical shifts of the trimethylsilyl groups of 4b (−5.7
ppm) which are not shifted so far downfield as the ones of 4a
and 5 (−4.4 and −3.9 ppm, respectively).
almost 40 Hz larger than that of (Me3Si)3SiSiPh2F. Given the
fact that J-coupling is strongly dependent on the s-orbital
contribution, this behavior proves that the fluoride in 2a is
bonded via π-type orbitals with a smaller s-orbital contribution
than in 4a. This is further substantiated by the values of the
2JSi−F coupling constants. While we observe an unusually large
2JSi−F = 79 Hz for 2a the respective value is as small as 5 Hz for
4a and could not even be determined for the separated ion pair
in 5. This clearly shows that the fluoride in 2a interacts with
the disilene unit (i.e., the two doubly bound silicon atoms),
whereas 4a and 5 can be categorized as β-fluorodisilanides with
the fluorides interacting mostly with the directly attached
silicon atoms. The stronger disilene character in 2a is also
evident in its reactivity. Reactions of 2a with metal halides
favor the elimination of metal fluorides with concurrent release
of a disilene; analogous conversions with 4a cleanly lead to
transmetalated compounds.
CONCLUSION
■
Some time ago, we encountered the formation of disilene
fluoride adducts which form by condensation of two molecules
of potassium bis(trimethylsilyl)fluorosilylenoid. These disilene
adducts behave as nucleophiles in reactions with classical
electrophiles such as silyl or alkyl halides. However, in attempts
to transmetallate with metal halides such as MgBr2, LiCl, or
Cp2ZrCl2, release of the disilene was observed. The current
account deals with an extension of the chemistry of disilene
fluoride adducts to compounds with different substituents in 1-
and 2-positions.13,14
EXPERIMENTAL SECTION
■
General Remarks. All reactions involving air-sensitive compounds
were carried out under an atmosphere of dry nitrogen using either
Schlenk techniques or a glovebox. All solvents were dried using
column based solvent purification system.37 Tetrakis(trimethylsilyl)-
silane,38 1-chloro-1,1-diphenyl-2,2-bis(trimethylsilyl)-
trimethyltrisilane,39 MgBr2·OEt2,40 and [2.2.2] cryptand41 have been
prepared following published procedures. All other used chemicals
were obtained from different suppliers and used without further
Starting from tris(trimethylsilyl)fluorodiphenylsilylsilane
(3a), reaction with KOtBu gave a disilene fluoride adduct
with phenyl instead of trimethylsilyl groups at the fluoride
bearing silicon atom.
Structural and spectroscopic characterization of the new
adduct K(Me3Si)2SiSiPh2F (4a, 5) show surprising differences
to K(Me3Si)2SiSi(SiMe3)2F (2a) with respect to the
interaction between the disilene and the fluoride. The Si−F
bond of 2a is almost 0.2 Å shorter than a regular Si−F bond, in
contrast to this, the Si−F bond of 4a is slightly elongated
compared to the starting material. This observation needs to
be regarded in the context of JSi−F coupling constants of 2a and
1
purification. H (300 MHz), 13C (75.4 MHz), 19F (75.4 MHz), and
29Si (59.3 MHz) NMR spectra were recorded on a Varian INOVA
300 spectrometer. Spectra are referenced to tetramethylsilane (TMS)
for H, 13C, and 29Si and to CFCl3 for 19F typically using the known
1
positions of residual solvent signals.42 If not noted otherwise, all
samples were measured in C6D6. To compensate for the low isotopic
abundance of 29Si, the INEPT pulse sequence was used for the
amplification of the signal.43,44 Frequently, this does not allow
observing diphenylsilyl Si signals; therefore, the Varian s2pul
sequence (a simple inverse-gated single pulse experiment) was used
for those cases. Elementary analysis were carried out using a Heraeus
VARIO ELEMENTAR instrument. As potassium and magnesium
E
DOI: 10.1021/acs.inorgchem.9b02223
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
silanides usually give poor analysis data, the purity of these
compounds is confirmed by 1H, 13C, and 29Si NMR spectra (see
Supporting Information).
8.24 (m, 4H), 7.40 (m, 4H), 3.76 (18-cr-6), 0.53 (s, 18H, SiMe3).
2
2
13C: 148.5 (d, JC−F = 19 Hz), 138.1 (d, JC−F = 5 Hz), 134.8, 126.8,
1
70.2 (18-cr-6), 7.5. 29Si: 41.4 (d, JSi−F = 356 Hz, SiPh2F), −4.4 (d,
2
3JSi−F = 9 Hz, SiMe3), −201.6 (d, JSi−F = 5 Hz, Siq). 19F: −162.6
X-ray Structure Determination. For X-ray structure analyses,
the crystals are mounted onto the tip of glass fibers, and data
collection was performed with a BRUKER-AXS SMART APEX CCD
diffractometer using graphite-monochromated Mo Kα radiation
(1JF−Si = 353 Hz).
Method B. Compound 3a (280 mg, 0.623 mmol), 18-crown-6 (173
mg, 0.654 mmol), and KOtBu (73 mg, 0.654 mmol) were dissolved in
toluene (5 mL). The reaction mixture was stirred for 6 h, after which
the solvent was removed in vacuo, and some byproducts were
removed by sublimation. Product 4a (204 mg, 45%) crystallized as
deep orange crystals from THF/pentane at −60 °C.
2-Chloro-2,2-diphenyl-1,1-bis(trimethylsilyl)disilanyl Potas-
sium 18-Crown-6 (4b). A precooled (−30 °C) solution of KOtBu
(112 mg, 1.00 mmol) and 18-crown-6 (265 mg, 1.00 mmol) in THF
(5 mL) was added to a precooled solution of compound 3b (466 mg,
1.00 mmol) in THF (3 mL). After vigorous shaking, the clear yellow
reaction mixture was stored at −30 °C for 6 h. Reaction monitoring
by NMR spectroscopy showed reaction completion. NMR (δ in ppm,
in THF with an acetone-d6 capillary at 243 K): 1H: 7.10 (d, 4H, JH−H
= 6 Hz, PhH), 6.20−6.36 (m, 4H, PhH), 2.81 (s, 24H, 18-cr-6), 0.83
(SiMe3). 13C: 146.3, 133.9, 125.5, 125.1, 69.4 (18-cr-6), 5.3. 29Si: 39.7
(SiPh2Cl), −5.7 (SiMe3), −195.7 (Siq).
2-Fluoro-2,2-diphenyl-1,1-bis(trimethylsilyl)disilanyl Potas-
sium Cryptand (5). Crypt[2.2.2] (377 mg, 1.00 mmol) and KOtBu
(113 mg, 1.00 mmol) were dissolved in benzene (2 mL) and added to
a stirred solution of compound 3a (449 mg, 1.00 mmol) in benzene
(3 mL). After 2 h, stirring was discontinued upon which two liquid
phases separated. The top layer was separated, and the orange ionic
phase below was dried under a vacuum. The orange residue was
washed with pentane, yielding the title compounds as an orange solid
(351 mg, 43%). NMR (δ in ppm, C6D6): 1H: 7.79−7.85 (m, 4H, Ph),
(0.71073 Å). The data were reduced to F2 and corrected for
o
absorption effects with SAINT45 and SADABS,46,47 respectively. The
structures were solved by direct methods and refined by full-matrix
least-squares method (SHELXL97).48 If not noted otherwise, all non-
hydrogen atoms were refined with anisotropic displacement
parameters. All hydrogen atoms were located in calculated positions
to correspond to standard bond lengths and angles. All diagrams are
drawn with 30% probability thermal ellipsoids, and all hydrogen
atoms were omitted for clarity. Crystallographic data (excluding
structure factors) for the structures of compounds 3a, 3b, 4a, 4b, 5, 6,
and 7 reported in this paper are deposited with the Cambridge
Crystallographic Data Center as supplementary publication no.
CCDC-1920634 (3a), 1920635 (3b), 1920633 (4a), 1920637 (4b),
1920638 (5), 1920639 (6), and 1920636 (7). Copies of data can be
obtained free of charge at http://www.ccdc.cam.ac.uk/products/csd/
request/. Figures of solid state molecular structures were generated
using Ortep-3 as implemented in WINGX49 and rendered using POV-
Ray 3.6.50
1-Fluoro-1, 1-diphenyl-2, 2-bis(trimethylsilyl)-
trimethyltrisilane (3a). Tetrakis(trimethylsilyl)silane (200 mg,
0.623 mmol) and KOtBu (73 mg, 0.654 mmol) were dissolved in
THF (4 mL). After 6 h, MgBr2·OEt2 (169 mg, 0.654 mmol) was
added. Stirring was continued for 30 min after which precipitated KBr
was removed by filtration. Difluorodiphenylsilane (0.654 mmol, 144
mg) was added dropwise within 3 min to the colorless solution, and
the precipitated white MgBrF was removed again by filtration after 30
min. The solvent was removed in vacuo, and the yellow residue was
crystallized from pentane yielding colorless crystalline 3a (252 mg,
90%). Mp.: 75−77 °C. NMR (δ in ppm): 1H: 7.73 (m, 4H), 7.10 (m,
7.02−7.19 (m, 6H, Ph), 3.64 (s, 12H, cryptand), 3.60 (t, 12H, JH−H
=
4 Hz, cryptand), 2.62 (t, 12H, JH−H = 4 Hz, cryptand), 0.00 (s, 18H,
1
SiMe3). 19F: −164.5 (1JSi−F = 359 Hz). 29Si (s2pul): 42.0 (d, JSi−F
=
3
358 Hz, SiPh2F), −3.9 (d, JSi−F = 6 Hz, SiMe3), −202.6 (Siq).
2-Fluoro-2,2-diphenyl-1,1-bis(trimethylsilyl)disilanyl Mag-
nesiumbromide (6). A cold solution of 3a (1.00 mmol, 449 mg)
(stored at −35 °C prior to the reaction) in THF (2 mL) was added to
a cold solution of KOtBu (1.05 mmol, 118 mg) in THF (2 mL), and
the resulting yellow reaction mixture was kept cold for another 6 h.
Then the silanide solution was added dropwise to a cold suspension
of magnesium bromide etherate (1.05 mmol, 272 mg) in THF (6
mL) under vigorous stirring. The off-white suspension was stored at
−35 °C for another 2 h followed by evaporation of the solvent under
reduced pressure. The remaining off-white solid was extracted with
benzene/pentane (1:2 ratio), and the combined extracts were
concentrated under a vacuum to a volume of about 1 mL. Addition
of pentane (10 mL) afforded precipitation of the magnesium silanide
which was washed with pentane (2 × 2 mL) and dried under a
vacuum giving analytically pure 6 as a white microcrystalline solid
(230 mg, 57%). Colorless single-crystals of 6 suitable for X-ray
diffraction analysis were obtained from the pentane solutions used to
2
6H), 0.21 (s, 27H, SiMe3). 13C: 138.4 (d, JC−F = 13 Hz), 134.0 (d,
1
3JC−F = 3 Hz), 130.3, 128.3, 2.9. 29Si: 21.1 (d, JS2i−F = 319 Hz,
3
SiPh2F), −9.7 (d, JSi−F = 4 Hz, SiMe3), −134.8 (d, JSi−F = 19 Hz,
Siq). 19F: −171.2 (1JF−Si = 319 Hz). Anal. Calcd. for C21H37FSi5
(448.95): C 56.18, H 8.31. Found: C 55.97, H 8.23.
1-Chloro-1, 1-diphenyl-2, 2-bis(trimethylsilyl)-
trimethyltrisilane (3b). Tetrakis(trimethylsilyl)silane (62.3 mmol,
20.0 g) and KOtBu (65.5 mmol, 7.35 g) were dissolved in DME (40
mL) and stirred for 6 h. The solution was added dropwise within 2 h
to dichlorodiphenylsilane (169.5 mmol, 17.6 g) in toluene (150 mL)
and stirring was continued for 12 h. The solvent was removed in
vacuo, and the residue was extracted with pentane three times. After
removal of the solvent, 3b was obtained as a colorless semicrystalline
solid (28.7 g, 99%). Mp.: 175−176 °C. NMR (δ in ppm): 1H: 7.80−
7.87 (m, 4H, Ph), 7.10−7.20 (m, 6H, Ph), 0.28 (s, 27H, SiMe3). 13C:
137.4 (Ph), 135.0 (Ph), 130.3 (Ph), 128.2 (Ph), 2.9 (SiMe3). 29Si
(s2pul): 15.8 (SiPh2Cl), −9.6 (SiMe3), −127.3 (Siq). Anal. Calcd. for
C21H37ClSi5 (465.40): C 54.20, H 8.01. Found: C 54.19, H 8.12.
2-Fluoro-2,2-diphenyl-1,1-bis(trimethylsilyl)disilanyl potas-
sium 18-crown-6 (4a). Method A. Compound 3a (300 mg, 0.668
mmol), 18-crown-6 (185 mg, 0.702 mmol), and KOtBu (73 mg, 0.702
mmol) were dissolved in a minimum amount of benzene or DME.
The color of the mixture immediately turned to yellow in DME and to
orange in benzene/18-crown-6. After a few minutes, the reaction was
finished as could be determined by NMR spectroscopic analysis. The
solvent was removed, and pentane was added to the residue. The
insoluble salts were removed by filtration. Tetrakis(trimethylsilyl)-
silane (in the case of both solvents) and tris(trimethylsilyl)silyl
potassium (just when benzene/18-crown-6 was employed as solvent)
were observed as byproducts. Sublimation at 60 °C to remove
Si(SiMe3)4 followed by crystallization of the residue from pentane
yielded pure orange crystalline 4a (in case of DME: 258 mg, 65%
(calculated with 2 DME); in benzene/18-crown-6:204 mg, 45%).
1
wash the product. NMR (δ in ppm, C6D6): H: 8.04 (m, 4H, Ph),
7.22−7.32 (m, 4H, Ph), 7.15 (m, 2H, Ph), 3.63 (br s, 8H,
OCH2CH2), 1.19 (br s, 8H, OCH2CH2), 0.49 (s, 18H, SiMe3).
13C: 142.1 (d, JC−F = 15 Hz, Ph), 134.5 (d, JC−F = 3 Hz, Ph), 129.2,
69.8 (OCH2CH2), 25.0 (OCH2CH2), 5.6 (SiMe3). 19F: −164.8. 29Si
1
3
(s2pul): 32.1 (d, JSi−F = 320 Hz, SiPh2F), −7.4 (d, JSi−F = 6 Hz,
SiMe3), −171.1 (d, JSi−F = 15 Hz, SiMg).
2-Fluoro-2,2-diphenyl-1,1-bis(trimethylsilyl)disilanyl Zirco-
nocene Chloride (7). A cold solution of 3a (1.00 mmol, 449 mg)
(stored at −35 °C prior to the reaction) in THF (2 mL) was added to
a cold solution of KOtBu (1.05 mmol, 118 mg) in THF (2 mL), and
the resulting yellow reaction mixture was kept cold for another 6 h.
Then, this silanide solution was added dropwise to a cold solution of
Cp2ZrCl2 (1.05 mmol, 307 mg) in THF (5 mL) under vigorous
stirring. After the addition, the orange reaction mixture was kept at
−35 °C for another 1 h, followed by evaporation of all volatiles under
reduced pressure. The orange residue was extracted with benzene/
pentane (1:2 ratio), the combined solutions were evaporated to
1
NMR (δ in ppm, in DME with a D2O capillary): H: 8.44 (m, 2H),
F
DOI: 10.1021/acs.inorgchem.9b02223
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
dryness, and the solid yellow residue was washed with pentane (3 × 5
mL). The remaining solid was taken up in benzene (3 mL) and the
solution layered with pentane which afforded orange crystals of 7
(394 mg, 62%). NMR (δ in ppm, C6D6): 1H: 7.94 (m, 4H, Ph), 7.22
(m, 4H, Ph), 7.09−7.16 (m, 2H, Ph), 5.96 (s, 10H, Cp), 0.42 (s, 18H,
SiMe3). 13C: 140.7 (d, JC−F = 13 Hz, Ph), 134.4 (d, JC−F = 3 Hz, Ph),
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129.9, 128.2, 111.8 (Cp), 5.1 (SiMe3). 19F: −166.8 (d, JSi−F = 323
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36H, SiMe3). 13C: 139.2 (Ph), 137.2 (Ph), 129.2 (Ph), 128.1 (Ph),
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ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.9b02223.
Tabulated crystallographic data for compounds 3a, 3b,
4a, 4b, 5, 6, and 7. NMR spectra (1H, 13C, 19F, and 29Si)
for compounds 3a, 3b, 4a, 4b, 5, 6, 7, and 8 (PDF)
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Formation of Formal Disilene Fluoride Adducts. J. Am. Chem. Soc.
2008, 130, 17460−17470.
Accession Codes
CCDC 1920633−1920639 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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AUTHOR INFORMATION
■
Corresponding Authors
*(J.B.) E-mail: baumgartner@tugraz.at. Phone: (+43) 316 873
32107. Fax: (+43) 316 873 1032112.
*(C.M.) E-mail: christoph.marschner@tugraz.at. Phone: (+43)
316 873 32112. Fax: (+43) 316 873 1032112.
́
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ORCID
Judith Baumgartner: 0000-0002-9938-1813
Christoph Marschner: 0000-0001-8586-2889
Funding
Support for this study was provided by the Austrian Fonds zur
Forderung der wissenschaftlichen Forschung (FWF) via
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Projects P-19338 (C.M.) and P-30955 (J.B.).
Notes
The authors declare no competing financial interest.
G
DOI: 10.1021/acs.inorgchem.9b02223
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DOI: 10.1021/acs.inorgchem.9b02223
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