Tridentate Lewis Acids: Silicon-Functionalised 1,3,5-Triethynylbenzene and 1,3,5-Trivinylbenzene

Article abstract of DOI:10.1002/ejic.201800279

Planar tridentate Lewis acids were synthesised by hydrosilylation reactions of triethynylbenzene with chlorosilanes. Hydrogenation of the rigid triethynylbenzene using hydrogen in the presence of Lindlar's catalyst resulted in the formation of trivinylben

Full text of DOI:10.1002/ejic.201800279

A Journal of
Accepted Article
Title: Tridentate Lewis Acids: Silicon-functionalised 1,3,5-Triethynyl-
benzene and 1,3,5-Trivinylbenzene
Authors: Anna Schwartzen, Lena Siebe, Jan Schwabedissen, Beate
Neumann, Hans-Georg Stammler, and Norbert Werner Mitzel
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201800279
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European Journal of Inorganic Chemistry
10.1002/ejic.201800279
FULL PAPER
Tridentate Lewis Acids: Silicon-functionalised 1,3,5-Triethynyl-
benzene and 1,3,5-Trivinylbenzene
Anna Schwartzen, Lena Siebe, Jan Schwabedissen, Beate Neumann, Hans-Georg Stammler and
Norbert W. Mitzel*
Abstract: Planar tridentate Lewis acids were synthesised by hydro-
silylation reactions of triethynylbenzene with chlorosilanes. Hydroge-
nation of the rigid triethynylbenzene using hydrogen in the presence
of Lindlar’s catalyst resulted in the formation of trivinylbenzene. The
hydrosilylation of this compound enabled the synthesis of flexible
hydrides to the triple bonds depends on the steric shielding of
the alkyl groups. Certain substituents can thus be used to selec-
tively generate compounds with cis- and trans-addition. Further-
more, tetraalkynylbenzene and dialkynylbenzene derivatives
were hydroaluminated by Uhl and co-workers (Scheme 1).[7]
However, there are hardly any reports on hydrosilylated triethy-
nylbenzenes in the literature. Therefore, we have functionalised
the rigid triethynylbenzene framework by hydrosilylation reac-
tions with chlorosilanes.
2 2 3
tridentate Lewis acids with SiClMe , SiCl Me, SiCl groups. In order
to increase the acidity, the chlorine substituents of the tridentate
Lewis acids were substituted by fluorine and compounds with
2 3
SiF Me and SiF groups were obtained. The Lewis acidity of the
isolated compounds was determined with the Gutmann-Beckett
method. The results show the presence of cooperative effects of the
silyl groups.
A more flexible backbone can be achieved starting with 1,3,5-tri-
vinylbenzene as hydrosilylation substrate. This leads to flexible
ethyl functions with Lewis acidic centres in the target molecule.
Until now, trimethylsilyl-functionalised benzenes were not syn-
thesised by hydrosilylation based on trivinylbenzene but by
Friedel-Crafts alkylation of benzene with vinyldichloromethylsila-
Introduction
[8]
ne. However, the product in this process is only a by-product of
the polyalkylation of benzene with dichloromethylvinylsilane and
has not been specifically synthesised and isolated. An alterna-
tive access to 1,3,5-trivinylbenzene is the Stille coupling, in
which organostannanes are palladium-catalysed coupled to
organic halides.[3]
This work is part of a systematic exploring multidentate Lewis
acids based on rigid and oriented backbones.[9] Here we report
the synthesis of flexible tridentate silicon containing Lewis acids
based on 1,3,5-triethynylbenzene. We compare systems with
Triply alkynyl substituted benzenes are used in many fields of
chemistry. Applications include building blocks for the composi-
[
1]
[2]
[3]
tion of dendrimers, macromolecules and polymers. They
are also used for the synthesis of tridentate Lewis acids.[4,5]
Conjugated polymers are required for organic light-emitting
devices (OLED) with light-emissive π-conjugated vinylphenyl
segments in the polymer chain.[6]
2 2
three less flexible –HC=CH- and three more flexible -H C-CH -
spacers between the benzene core and the acid functions.
Results and Discussion
The basic framework was prepared from 1,3,5-tribromobenzene.
Initially, a Sonogashira cross-coupling reaction with trimethyl-
silylacetylene (TMS-acetylene) was conducted based on a litera-
ture protocol[ followed by cleaving the protecting groups under
basic conditions (Scheme 2). The other framework from which
flexible Lewis acids are to be produced was generated starting
from compound 2 by hydrogenation with Lindlar’s catalyst[
(Scheme 3), a palladium-calcium carbonate catalyst deactivated
with lead acetate. The reduced catalytic activity leads predomi-
nantly to trivinylbenzene, but selectivity depends on the reaction
conditions and needed to be optimized. GC/MS analysis of the
product mixture showed 85% of the desired product to be pre-
sent after 18 h reaction time at room temperature. The remain-
ing 15% are the three other compounds shown in Scheme 3.
The gas chromatogram shows the presence of three other com-
pounds resulting from further reduction of the double bonds in 3.
Shorter reaction times, however, lead to incomplete hydrogena-
tion of 1,3,5-triethynylbenzene and the presence of alkynes can
also be detected by GC/MS. Product 3 could be purified by
column chromatography and was isolated as colourless oil.
10]
Scheme 1. Products of triple hydrogallation of 1,3,5-tris[(trimethylsilyl)-ethy-
nyl]benzene (A) and quadruple hydroalumination of 1,2,4,5-tetrakis-[(trimethyl-
silyl)ethynyl]benzene (B) by Uhl et al.
11]
Triethynylbenzene possesses terminal triple bonds which can be
functionalised in hydrometalation reactions. This was already
accomplished in 2006 by Uhl et al. with hydrogallation (Sche-
me 1).[
4,5]
They discovered that the addition of dialkyl gallium
[
a]
M. Sc. A. Schwartzen, B. Sc. L. Siebe, Dr. Jan Schwabedissen,
B. Neumann, Dr. H.-G. Stammler, Prof. Dr. N. W. Mitzel
Universität Bielefeld, Fakultät für Chemie
Lehrstuhl für Anorganische Chemie und Strukturchemie
Universitätsstrasse 25, D-33615 Bielefeld, Germany
E-mail: mitzel@uni-bielefeld.de
Supporting information for this article is given via a link at the end of
the document.
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European Journal of Inorganic Chemistry
10.1002/ejic.201800279
FULL PAPER
Upon extended storage the product becomes increasingly vis-
cous up to a glassy solid. These properties suggest the product
to polymerise at room temperature by ambient light irradiation or
the presence of oxygen similar to styrene. For this reason, the
product was always hydrosilylated directly after purification.
Hydrosilylation reactions
Both framework compounds, 2 and 3, were hydrosilylated with
the chlorosilanes HSiCl , HSiCl Me and HSiClMe (Scheme 4).
Hydrosilylation of triethynylbenzene 2 was conducted in the cor-
responding silane as a solvent in the presence of Karstedt’s ca-
talyst. In the case of substrate 3, this was initially dissolved in
diethyl ether followed by the addition of a small excess of silane
and a drop of catalyst solution.
3
2
2
Scheme 2. Synthesis of 1,3,5-tris[(trimethylsilyl)ethynyl]benzene by Sonoga-
shira cross-coupling reaction of 1,3,5-tribromobenzene and subsequent depro-
tection to 1,3,5-triethynylbenzene. Reagents and conditions: i) 1. TMS-acetyle-
i
ne, Pr
2
NH, CuI, PdCl
2 3 2
(PPh ) , reflux, 1 d; 2. aq. workup, 91%; ii) THF, EtOH,
1
M NaOH, r.t., 1 d, 80%.
Scheme 4. Hydrosilylation reactions of 1,3,5-triethynylbenzene (2) and 1,3,5-
trivinylbenzene (3) with chlorosilanes. Reagents and conditions: i) HSi-
Cl
n n 2
Me(3−n), Karstedt’s catalyst, r.t., 2 d, 98–99%; ii) HSiCl Me(3−n), Et O,
Karstedt’s catalyst, r.t., 3 d, 93–95%.
Table 1. 1H and 29Si NMR chemical shifts [ppm] of compound 4, 5 and 6 in
CDCl solution.
3
Compound
n
Ar–H Ar–CH=
=CH–Si SiCl
6.53 (d)
n
(CH
3
)
(3−n)
n
SiCl Me(3−n)
4
5
6
(SiClMe
2
)
1
2
3
7.51
7.57
7.70
7.11 (d)
7.26 (d)
7.41 (d)
0.59
0.97
–
19.0
17.4
−2.8
(SiCl
(SiCl
2
Me)
)
6.54 (d)
3
6.58 (d)
Scheme 3. Lindlar reduction of 1,3,5-trithynylbenzene and determination of
conversion using GC-MS analysis after 18 h reaction time. Reagents and
All reactions proceeded quantitatively and no by-products were
observed, except for the reaction of trivinylbenzene with
HSiClMe . This reaction was conducted several times, even at
2
conditions: i) 1. EtOAc, Lindlar catalyst, quinoline, H
2%.
2
, r.t., 18 h; 2. aq. workup,
6
higher concentrations of catalyst or silane. But the reactions
produced no product and only the signals for trivinylbenzene
were observed in the H NMR spectrum of the mixtures sugges-
The basic frameworks 2 and 3 have already been reported. The
,3,5-triethynylbenzene has already been completely charac-
1
1
terised and has been described to be isolated over two steps in
ting that this silane is inactive towards hydrosilylation of 3. Besi-
12]
6
4% yield.[ The yield is slightly lower than the 72% we achie-
1
des the resonances for the silyl groups the H NMR spectra of
ved over two steps. The characterisation of 1,3,5-trivinylbenzene
by NMR spectroscopy has already been reported.[13] The yield
obtained via Stille coupling was 92%, while the Lindlar reduction
led to an isolated product with 62% yield.
the obtained vinylsilanes 4, 5 and 6 all show one singlet and two
doublets. This signal pattern is slightly low-field shifted with
increasing number of chlorine substitutes at the silyl functions
(
Table 1).
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European Journal of Inorganic Chemistry
10.1002/ejic.201800279
FULL PAPER
Figure 1. Molecular structure of compound 4 and 6 in the crystalline state. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen atoms are
omitted for clarity. Selected bond lengths [Å] and angles [°] for compound 4: C(1)−C(2) 1.399(2), C(2)−C(3) 1.395(2), C(1)−C(7) 1.471(2), C(7)−C(8) 1.334(2),
C(8)−Si(1) 1.841(2), Si(1)−C(9) 1.850(2), Si(1)−Cl(1) 2.094(1); C(1)−C(2)−C(3) 120.7(1), C(1)−C(7)−C(8) 127.6(2), C(2)−C(1)−C(7) 122.8(1), C(7)−C(8)−Si(1)
122.5(1), C(8)−Si(1)−C(9) 112.1(1), C(8)−Si(1)−Cl(1) 105.4(1). Compound 6: C(1)−C(2) 1.402(6), C(2)−C(3) 1.388(6), C(1)−C(7) 1.472(6), C(7)−C(8) 1.324(6),
C(8)−Si(1) 1.831(4), Si(1)−Cl(1) 2.021(2); C(1)−C(2)−C(3) 121.6(1), C(1)−C(7)−C(8) 127.6(4), C(2)−C(1)−C(7) 122.6(4), C(7)−C(8)−Si(1) 125.5(4),
C(8)−Si(1)−Cl(1) 111.0(2), Cl(1)−Si(1)−Cl(2) 109.0(1).
In addition, the methyl groups of compounds 4 and 5 each gen-
erate a further signal in the region between 0.59 and 0.97 ppm.
The coupling constants of the vinyl protons are in a range be-
tween 18.7 and 19.1 Hz, which is characteristic for a trans-sub-
stitution of the double bond. In the case of compounds 7 and 8,
the protons of the ethyl unit each generate multiplets, slightly
down-field shifted depending on the number of chlorine substitu-
ents of the silyl groups (Table 2). The same parameter deter-
mines the chemical shift in the 29Si NMR spectra, the difference
out of the plane defined by the benzene ring [compound 4 Ar∙∙∙Si
0.202 – 0.481(3) Å; compound 6 Ar∙∙∙Si 0.05(1)ꢀ–ꢀ0.34(1) Å]. The
torsion angles CAr−C=C−Si are all nearly 180 ° for compound 4
[range 175.9(1)° – 177.9(1)°] and 6 [range 178.6(4)° – 180.0(4)°].
Expectedly, the C=C−Si angles in both compounds are wider
than 120° [4: 122.5(1)° – 125.0(1)°; 6: 124.1(4)° – 125.5(4)°]. All
other bond lengths and angles are similar for both compounds
and are in the range of expected values, so they deserve no
detailed discussion.[14]
2 3
between the SiClMe (4) and the SiCl compound (6) being 21.8
ppm. The corresponding difference between compound 7 and 8
is 20.2 ppm.
Table 2. 1H and 29Si NMR chemical shifts [ppm] of compound 7 and 8 in
CDCl
3
solution.
Compound
n
2
3
Ar–H Ar–CH
2
–
–CH
1.46
1.75
2
–Si SiCl
n
(CH
)
3 (3−n)
n
SiCl Me(3−n)
7
8
(SiCl
(SiCl
2
Me)
)
6.91
6.94
2.79
2.87
0.74
32.0
11.8
3
–
Compounds 4 and 6 could be crystallised by evaporation of
concentrated n-pentane solutions and their structure determined
by X-ray diffraction (Figure 1). Both compounds crystallise in the
1
monoclinic space group P2 /n with four (4) and eight (6) mole-
cules per unit cell. In compound 6 disordering of some C=CSiCl
3
groups can be obtained, the following discussion and figures
only refer to the major occupied disordered atoms (for detailed
information see Table 6).
The carbon skeletons of both molecules are almost planar in the
solid state. In both cases, the silicon atoms are slightly twisted
Figure 2. Molecular structure of compound 8 in the crystalline state. Dis-
placement ellipsoids are drawn at the 50% probability level. Hydrogen atoms
are omitted for clarity. Selected bond lengths [Å] and angles [°]: C(1)−C(2)
1.391(2), C(2)−C(3) 1.398(3), C(1)−C(7) 1.514(2), C(7)−C(8) 1.539(2),
C(8)−Si(1) 1.842(2), Si(1)−Cl(1) 2.030(1); C(1)−C(2)−C(3) 121.4(2),
C(1)−C(7)−C(8) 112.8(1), C(2)−C(1)−C(7) 120.3(2), C(7)−C(8)−Si(1) 114.0(1),
C(8)−Si(1)−Cl(1) 112.3(1).
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European Journal of Inorganic Chemistry
10.1002/ejic.201800279
FULL PAPER
Crystals of compound 8 could also be grown and measured by
X-ray diffraction (Figure 2). It crystallises in the monoclinic space
group C2/c with eight molecules per unit cell. In contrast to com-
pounds 4 and 6, the molecules of 8 are not planar in the solid
state: one of the ethylsilyl groups is bent to one side of the ben-
zene plane, the two others to the opposite side. The C–C–C
angles within the ethyl functions are slightly wider than the tetra-
hedral angle for the atoms bound to the benzene rings
Table 4. 1H, 19F and 29Si NMR chemical shifts [ppm] of compounds 12 and
13 in CDCl solution.
3
Compound
2 (SiF Me)
13 (SiF3)
n
2
3
SiF
n
Me(3−n)
Ph–CH
2
–
–CH
2
–Si
n
SiF Me(3−n)
1
2
2.9 (t)
2.73
2.83
1.44
1.35
−135.41
−136.62
−59.6 (q)
[
C(1)−C(7)−C(8) 112.8(1), C(3)−C(9)−C(10) 111.9(2) and
Selected H, 19F and 29Si NMR chemical shifts of the saturated
1
C(5)−C(11)−C(12) 111.4(1)], whereas those bound to the silyl
groups are significantly wider [C(7)−C(8)−Si(1) 114.0(1),
C(9)−C(10)−Si(2) 114.3(1) and C(11)−C(12)−Si(3) 115.3(1)]. All
average bond lengths and angles are in the range of expected
values and deserve no detailed discussion.
fluorosilanes 12 and 13 in CDCl are listed in Table 4. Due to the
fact that the protons of the ethyl bridge are coupling to each
other and to the fluorine substituents of the silyl groups, the
3
1
signal patterns in the H NMR spectrum are more complicated.
The same applies to the 19F NMR spectrum of compound 12,
while fluorosilane 13 generates a triplet with a 3JF,H coupling
constant of 3.0 Hz. The 29Si NMR spectra show the expected
signal patterns, a triplet for fluorosilane 12 (1JSi,F = 297.4 Hz) and
a quartet for compound 13 (1JSi,F = 283.3 Hz)
Fluorination reactions
To increase the Lewis acidity, compounds 4ꢀ–ꢀ8 were reacted
with an excess of SbF to replace the chlorine by fluorine sub-
3
stituents (Scheme 5). Because traces of antimony trichloride
remain in the product after filtration and removal of the solvent,
all fluorosilanes had to be further purified by sublimation. The
formation of complexes of SbCl with molecules that contain
3
chelatingly acting arene groups for complexation of the Sb at-
oms have recently been described by us.[15] Compounds 9, 10
Complexation tests
Chlorosilanes 7 and 8, as well as fluorosilanes 12 and 13, have
three flexible substituents with Lewis acidic functions. Conse-
quently, complexation experiments were conducted with Lewis
bases containing three Lewis basic positions and – exemplarily
– compound 13, which should have the highest Lewis acidity of
the four flexible Lewis acids. The planar nitrate anion was se-
lected expecting that the three arms will catch the anion like
tweezers. The possibility of this type of complexation was exam-
ined by quantum-chemical calculations (B3LYP/6-311G). In an
optimised structure (lowest frequency 20 cm ) of the complex
SiSi distances are between 5.82 and 5.94 Å. According to this
quantum-chemical investigation, the complexation of a nitrate
ion should be possible (see Figure S40 in the Supporting infor-
mation).
and 12 were obtained as colourless viscous oils, while 11 and
1
3 are colourless solids. Selected H, 19F and 29Si NMR chemi-
1
cal shifts and coupling constants of the unsaturated fluorosilanes
, 10 and 11 in CDCl are listed in Table 3.The signals of the
9
3
vinyl protons show a characteristic multiplicity [9 (dd), 10 (dt)
and 11 (dq)] for the fluorine substitution pattern at the silicon
atoms.
−
1
Table 3. 1H, 19F and 29Si NMR chemical shifts [ppm] and coupling con-
stants [Hz] of compounds 9, 10 and 11 in CDCl solution.
3
3JH,H/ 3JF,H
In the corresponding experiment potassium nitrate served as
reactant. It was stirred in dichloromethane with the appropriate
crown ether (18-crown-6) in order to assist in liberating the ani-
ons by complexing the corresponding cations. Compound 13
was added to this mixture. However, the recorded NMR spectra
Compound
n
SiF
n
Me(3−n)
=CH–Si
6.49 (dd)
6.34 (dt)
6.21 (dq)
n
SiF Me(3−n)
9
1
1
(SiFMe
2
)
1
2
3
20.4 (d)
−11.3 (t)
−72.2 (q)
19.3/3.2
19.6/2.9
19.8/2.4
−160.61
−135.43
−139.54
0 (SiF
2
Me)
)
(1
H, 19F and 29Si) did not show any changes in the chemical
1 (SiF
3
shifts relative to the pure compound leading to the conclusion
that no complexation took place.
The values for the coupling constants (~19.6 Hz) between the
vinyl protons confirm the trans-configuration of the double bonds.
The increasing number of fluorine substituents at the silyl groups
has a stronger influence on the chemical shifts of the 29Si chem-
ical shifts compared to the chlorosilane series. The higher the
A neutral compound with three Lewis base functions, 1,3,5-
trimethyl-1,3,5-triazacyclohexane (TMTAC), was also used. After
addition a gel-like solid material was formed. This was not solu-
ble in any deuterated solvent and therefore could not be charac-
terised by NMR. As a direct isolation of an acid base adduct was
not successful so far, we explored the Lewis acidity by standard
methods of acidity measurement: the Gutmann-Beckett test.
number, the stronger the signal is shifted to lower field. The 19
F
NMR signals of compounds 9 and 10 have high multiplicities due
to their coupling to the methyl and vinyl protons. The spectrum
of fluorosilane 9 shows a doublet of septets, that of compound
1
0 a doublet of quartets and fluorosilane 11 generates a doublet
in its 19F NMR spectrum.
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European Journal of Inorganic Chemistry
10.1002/ejic.201800279
FULL PAPER
3
Scheme 5. Fluorination of the chlorinated species 4–8. Reagents and conditions: i) SbF , n-pentane, r.t., 24 h, 97–99%.
Lewis acidity determined by the Gutmann-Beckett method
by fluorine substituents, the effect is stronger and the measured
acidity rises with an increasing number of fluorine functions. The
measured shift of compound 13 is the strongest shift in the 31P
resonance of TEPO compared to the others. Even 12 with obvi-
According to the Lewis acid base concept, all isolated com-
pounds 4ꢀ–ꢀ13 have Lewis acidic functions. The Gutmann-
Beckett method[16,17] was applied to classify the range in which
the acidity of the individual compounds is situated and the influ-
ence of the substitution at silicon. The relative Lewis acidity can
be determined by the 31P NMR shift of the adducts between
TEPO (triethylphosphane oxide) and the Lewis acids (Table 5).
2 3
ously less Lewis acidic individual groups (SiF Me) than 11 (SiF )
exhibits a higher acidity than the latter. Both facts can be at-
tributed to the higher flexibility of fluorosilylethyl compounds 12
and 13, compared to the more rigid fluorosilylvinyl compounds
10 and 11. 12 and 13 can act as Lewis acids in a chelating form,
i. e. with a cooperative effect of the acid functions, whereas for
1
0 and 11 TEPO is too small to be complexed by more than one
Table 5. 31P NMR chemical shifts [ppm] of the complexes of OPEt
with
3
function at a time.
compounds 4–13 with in CDCl
3
solution, shifts due to complexation Δ(δ
3
1P) and calculated acceptor number AN.
Comparison with other Lewis acidities of silicon Lewis acids is
difficult because there are only a few measured values reported
in the literature. Instead, the boranes in this field are well studied
and serve to classify the measured values.[ The well-known
Compound
n
–
1
2
3
2
3
1
2
3
2
3
SiX
n
Me(3−n)
δ 31P
Δ(δ 31P)
AN[a]
18]
TEPO
–
52.3
53.0
52.4
55.0
53.1
54.1
55.1
55.6
56.6
58.7
63.7
–
–
boranes B(C
6
5
F )
3
(CD
2
Cl
2
,
AN = 80)[19] and BF
3
3
(CDCl ,
AN = 84)[ belong to strong Lewis acids. Compared to their
acceptor numbers, the isolated silicon Lewis acids reported here
are rather weak acids. Nevertheless, the acceptor numbers of
compounds 4–12 are between 25 and 39 and are comparable to
18]
4
5
6
7
8
9
SiClMe
2
0.7
0.1
2.7
0.8
1.8
2.8
3.3
4.3
6.4
11.4
27
25
31
27
29
31
32
34
39
50
SiCl
SiCl
SiCl
SiCl
2
3
2
3
Me
3 6 6 2 2 3
the acidities of BEt (C D , AN = 24) and B(OCH CH Cl) (neat,
AN = 31).[20]
Me
SiFMe
2
Conclusions
10
11
12
13
SiF
SiF
SiF
SiF
2
3
2
3
Me
The framework 1,3,5-triethinylbenzene (2) was prepared by So-
nogashira cross-coupling reaction and subsequent deprotection
of the TMS-groups. The 1,3,5-trivinylbenzene was synthesised
from 2 by partial hydrogenation using Lindlar’s catalyst. Both
compounds were equipped with chlorosilyl functions in hydrosi-
lylation reactions. Three new unsaturated (4ꢀ–ꢀ6) and two satura-
ted tris(methyl)chlorosilanes (7ꢀ–ꢀ8) were isolated and character-
ised. The two backbones show different flexibility. The unsatura-
ted chlorosilanes have rather planar structures in the solid state,
while the silylethyl arms of the saturated compounds protrude
from the benzene plane. The chlorosilanes were converted into
the corresponding fluorosilanes (9ꢀ–ꢀ13). The relative Lewis
Me
a] AN = 2.21 × (δ31PLA∙TEPO − 41), Gutmann-Beckett method[17]
[
The shift in the 31P resonance for the chlorinated compounds is
less pronounced and ranges from 0 to 2.7 ppm. However, it can
also be observed that the acidity rises slightly with an increasing
number of chlorine substituents at silicon. By replacing chlorine
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European Journal of Inorganic Chemistry
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FULL PAPER
acidities of the compounds were determined using the Gutmann-
Beckett method. The Lewis acidity increases with the number of
chlorine respectively fluorine substituents, and expectedly, the
chlorosilanes have a lower acidity than the corresponding fluoro-
silanes. The more flexible tris(silylethyl) compounds show higher
Lewis acidities than the corresponding tris(silylvinyl) compounds.
This shows for the small probe molecule triethylphosphane oxi-
de in the Gutmann-Beckett test, that the flexible tris(silylethyl)
compounds are able to use their acid functions in a cooperative
way, whereas the less flexible molecules cannot act in the same
way.
ether (3  30 mL). The combined organic phases were dried over MgSO
and the solvent was evaporated. The crude product was purified by
4
chromatography on silica gel (eluent: n-pentane). R
f
= 0.2 (n-pentane),
): δ = 7.57 (s, 3H, Ar–H),
) δ = 135.8 (CAr-
yield 1.4 g (80%). 1H NMR (300 MHz, CDCl
3
3
.10 (s, 3H, C≡C-H) ppm. 13C{ H} NMR (75 MHz, CDCl
1
3
H), 123.1 (C
q
), 81.7 (C≡C-H), 78.8 (C≡C-H) ppm. MS (EI, 70 eV): m/z
+
[
assignment] = 150.1 [M] , 135, 121.
1,3,5-Trivinylbenzene (3): 1,3,5-Triethynylbenzene (0.50 g, 3.3 mmol)
was dissolved in ethyl acetate (50 mL). Lindlar’s catalyst (0.6 g, 5% Pd)
and quinoline (0.20 mL, 1.7 mmol) were added and the flask was flushed
with hydrogen. The reaction solution was frozen, thawed and then flu-
shed with hydrogen again. This procedure was repeated three times. In
addition, the septum was connected to a hydrogen-filled balloon and the
reaction solution was stirred at ambient temperature for 18 h. The solu-
Experimental Section
4
tion was filtered through Celite, the filtrate was dried over MgSO and the
solvent was evaporated. The crude product was purified by column chro-
Materials and methods
matography on silica gel (eluent: n-hexane). R = 0.5 (n-hexane), yield
f
0
J
.32 g (62%). 1H NMR (300 MHz, CDCl
3
): δ = 7.35 (s, 3H), 6.72 (dd,
NMR spectra were recorded on a Bruker DRX 500, Bruker Avance III 500
and Bruker Avance III 300. The chemical shifts (δ) were measured in
ppm and the spectra were referenced to the residual signal of protonated
3
= 17.6/ 10.9 Hz, 3H), 5.79 (dd, 3J
2
H
,
H
H
,
H
= 17.6 Hz, J
H
,
H
= 0.9 Hz, 3H),
3
= 10.9 Hz, 2J
13
1
5.28 (dd, J
H
,
H
H
,
H
= 0.9 Hz, 3H) ppm. C{ H} NMR (75 MHz,
3
CDCl ) δ = 138.2, 136.7, 123.7, 114.5 ppm.
solvents (CDCl
3
:
1H NMR δ = 7.26 ppm, 13C NMR δ = 77.16 ppm) or
, 29Si: SiMe ; 31P: 85% H
PO in H O). EI mass
externally (19F: CFCl
3
4
3
4
2
General procedure for hydrosilylation
spectra were recorded using an Autospec X magnetic sector spectrome-
ter with EBE geometry (Vacuum Generators, Manchester, UK) equipped
with a standard EI source. Samples were introduced by a push rod in
aluminium crucibles. Ions were generated in EI mode and accelerated by
Triethynylbenzene 2 (0.1 g) was dissolved in diethyl ether (4 mL). The
corresponding chlorosilane (1 mL) and Karstedt's catalyst (2.2−2.4 % Pt
in xylene, 2 drops) were added. The mixture was stirred at ambient tem-
perature for 2 d and all the volatiles were condensed off and the products
were obtained analytically pure as pale yellow solid.
Trivinylbenzene 3 (0.15 g, 0.96 mol) was dissolved in the corresponding
chlorosilane (4 mL) and Karstedt's catalyst (2.2−2.4 % Pt in xylene, 2
drops) was added. The reaction mixture was stirred at ambient tempera-
ture for 3 d and the remaining chlorosilane was removed in vacuo. The
products were obtained analytically pure as colourless solids.
8
kV. CHNS Elemental analyses were performed with HEKAtech EURO
EA (Bielefeld University) and Elementar Model Vario Micro Cube (Micro-
analytical laboratory Kolbe, Mülheim) analyzers (too low values for car-
bon are due to the known formation of silicon carbide and potassium
carbonate).
All operations with air and moisture sensitive compounds were performed
using conventional Schlenk techniques. The reactions were carried out
using freshly distilled and dried solvents from solvent stills (n-pentane
4
over LiAlH4, diethyl ether over LiAlH ). Potassium fluoride (spray dried
1
,3,5-Tris(chlorodimethylsilylvinyl)benzene (4): Yield 425 mg (98%).
quality) was dried in vacuum at about 200 °C before use. Workup and
column chromatography were performed with technical grade solvents.
Column chromatography was performed using silica gel 60 columns
1
): δ = 7.51 (s, 3H, Ar-H), 7.11 (d, 3
9.1 Hz, 3H, Ar-CH=CH-Si), 6.53 (d, 3JH,H = 19.0 Hz, 3H, Ar-CH=CH-Si),
.59 [s, 18H, Si(CH
H NMR (300 MHz, CDCl
3
H,H
J =
1
0
Cl] ppm. 13C{ H} NMR (75 MHz, CDCl
1
3
)
2
3
) δ = 145.7
(0.04−0.063 mm mesh). Trichlorosilane, dichloromethylsilane and chlo-
(
Ar-CH=CH-Si), 138.0 (C
q
), 126.0 (CAr-H), 125.6 (Ar-CH=CH-Si),
rodimethylsilane were purchased from Sigma Aldrich and 1,3,5-
tribromobenzene from Fluorochem.
Cl] ppm. 2 Si NMR (99 MHz, CDCl
9
2
7
3
.0 [Si(CH
3
)
2
3
) δ = 19.0 ppm. MS (EI,
+
+
+
0 eV): m/z [assignment] = 434.1 [M] , 419.1 [M−Me] , 398.1 [M−Cl] ,
40.1 [M−SiMe
+
+
Cl−Cl−Me]+.
2
Cl] , 305.2 [M−SiMe
2
Cl−Cl] , 289.1[M−SiMe
2
Synthetic procedures
+
HRMS: calculated for C18
H27Si
3
Cl
3
: 432.04807; measured: 432.04650.
1
,3,5-Tris[(trimethylsilyl)ethynyl]benzene (1)[1,4]: 1,3,5-Tribromo-ben-
zene (5.0 g, 16 mmol) was dissolved in diisopropylamine (150 mL).
Copper iodide (0.6 g, 3.0 mmol) and trimethylsilylacetylene (8.8 g, 12 mL,
1,3,5-Tris(dichloromethylsilylvinyl)benzene (5): Yield 486 mg (99%).
1H NMR (300 MHz, CDCl ): δ = 7.57 (s, 3H, Ar-H), 7.26 (d, 3JH,H
=
3
18.9 Hz, 3H, Ar-CH=CH-Si), 6.54 (d, 3JH,H = 18.9 Hz, 3H, Ar-CH=CH-Si),
9
0 mmol) were added. The suspension was degassed by three freeze-
pump-thaw cycles and bis(triphenylphosphane)palladium dichloride
0.91 g, 1.3 mmol) was added. The reaction mixture was heated to reflux
for 1 d and saturated aqueous NH Cl solution (50 mL) was added. The
aqueous layer was extracted with diethyl ether (3  50 mL) and the
combined organic phases were dried over MgSO . The solvent was
0.97 [s, 9H, Si(CH
)Cl
3 2
] ppm. 13C{ H} NMR (75 MHz, CDCl
1
3
) δ = 147.9
(
q
(Ar-CH=CH-Si), 137.4 (C ), 127.0 (CAr-H), 123.4 (Ar-CH=CH-Si), 5.8
[Si(CH
3
)Cl
2
]. 29Si NMR (60 MHz, CDCl
3
) δ = 17.4 ppm. MS (EI, 70 eV):
4
+
+
+
m/z [assignment] = 493.9 [M] , 478.9 [M−Me] , 459.0 [M−Cl] , 443.0
[M−Me−Cl]+. Elemental analysis calcd. (%) for
4
15 6 3 r
C H18Cl Si (M =
evaporated and the crude product was purified by column chromatog-
495.26): C 36.38, H 3.66; found: C 36.25, H 3.69.
raphy on silica gel (eluent: n-pentane). The product was isolated as
brownish oil. R
CDCl ): δ = 7.49 (s, 3H, Ar–H), 0.23 [s, 27H, Si(CH
f
= 0.6 (n-pentane), yield 5.4 g (91%). 1H NMR (300 MHz,
1,3,5-Tris(trichlorosilylvinyl)benzene (6): Yield 445 mg (98%). H NMR
(300 MHz, CDCl ): δ = 7.70 (s, 3H, Ar-H), 7.41 (d, JH,H = 18.7 Hz, 3H,
1
3
3
3
)
3
] ppm.
3
Ar-CH=CH-Si), 6.58 (d, 3
NMR (75 MHz, CDCl ) δ = 149.6 (Ar-CH=CH-Si), 137.0 (C
J
H,H = 18.7 Hz, 3H, Ar-CH=CH-Si) ppm. C{ H}
), 128.3 (CAr
) δ = −2.8 ppm.
13
1
1
(
,3,5-Triethynylbenzene (2)[1]: 1,3,5-Tris[(trimethylsilyl)ethynyl]benzene
4.5 g, 12 mmol) was dissolved in THF (30 mL) and ethanol (30 mL). To
3
q
-
29
H), 121.8 (Ar-CH=CH-Si) ppm. Si NMR (60 MHz, CDCl
3
+
]+, 349.0
]+. HRMS: calculated
the solution was added a sodium hydroxide solution (1 M, 30 mL) and the
reaction mixture was stirred at ambient temperature for 1 d. The solvent
was removed in vacuo and the aqueous layer was extracted with diethyl
MS (EI, 70 eV): m/z [assignment] = 555.8 [M] , 420.9 [M−SiCl
3
+
]+, 152.1 [M−3SiCl
[M−SiCl
for C12
3
−2Cl] , 287.0 [M−2SiCl
3
3
+: 551.72033; measured: 551.71951.
9
H Si
3
Cl
9
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800279
FULL PAPER
1
,3,5-Tris(dichloromethylsilylethyl)benzene (7): Yield 457 mg (95%).
1JSi,F = 297.4 Hz) ppm. Elemental analysis calcd. (%) for C15
H F Si (M
24 6 3 r
= 402.60): C 44.75, H 6.01; found: C 41.21, H 6.05.
1
3
H NMR (500 MHz, CDCl
.4 Hz, 6H, Ar-CH -CH
-Si), 1.46 (ddd, 3
CH -Si), 0.74 [s, 9H, Si(CH )Cl
δ = 143.2 (C ) , 125.4 (CAr-H), 28.4 (Ar-CH
Si), 5.2 [Si(CH )Cl
] ppm. 29Si NMR (99 MHz, CDCl
3
): δ = 6.91 (s, 3H, Ar-H), 2.79 (ddd, JH,H = 8.9/
5
2
2
J
H,H = 9.1/ 6.4 Hz, 6H, Ar-CH
2
-
)
] ppm. 13C{ H} NMR (125 MHz, CDCl
1
2
3
2
3
1
,3,5-Tris(trifluorosilylethyl)benzene (13): Yield 386 mg (97%).
q
2 2 2 2
-CH -Si) , 23.6 (Ar-CH -CH -
1
H NMR (500 MHz, CDCl
-Si), 1.35 (m, 6H, Ar-CH
CDCl ) δ = 142.8 (C ), 125.6 (CAr-H), 27.1 (Ar-CH
2JF,C = 18.3 Hz, Ar-CH -Si) ppm. 19F NMR (500 MHz, CDCl
-CH
−136.62 (t, 3JH,F = 3.0 Hz) ppm. 29Si NMR (99 MHz, CDCl
) δ = −59.6 (q,
1JSi,F = 283.3 Hz) ppm. Elemental analysis calcd. (%) for C12
Si (M
3 2
): δ = 6.92 (s, 3H, Ar-H), 2.83 (m, 6H, Ar-CH -
3
2
3
) δ = 32.0 ppm.
CH
2 2
-CH
-Si) ppm. 13C{ H} NMR (125 MHz,
-CH -Si), 9.4 (q,
) δ =
1
2
3
q
2
2
1
1,3,5-Tris(trichlorosilylethyl)benzene (8): Yield 502 mg (93%). H NMR
2
2
3
(
500 MHz, CDCl
3
): δ = 6.94 (s, 3H, Ar-H), 2.87 (m, 6H, Ar-CH
2
-CH
) δ =
-CH -Si)
) δ = 11.8 ppm. Elemental analysis calcd.
= 562.56): C 25.62, H 2.69; found: C 25.79, H
2
-Si),
3
-Si) ppm. 13C{ H} NMR (125 MHz, CDCl
1
H F
15 9
1.75 (m, 6H, Ar-CH
2
-CH
2
3
3
r
142.5 (C
q
2 2
), 125.9 (CAr-H), 28.4 (Ar-CH -CH -Si), 26.3 (Ar-CH
2
2
= 414.49): C 34.77, H 3.65; found: C 35.94, H 3.81 (small contents of
n-pentane explain the slight deviations).
29
ppm. Si NMR (99 MHz, CDCl
%) for C12 Si (M
.89.
3
(
2
H
15Cl
9
3
r
Crystallography
Suitable single crystals of compound 4, 6 and 8 were coated with para-
tone-N oil, mounted onto a glass fibre and cooled in the cryostream of
the diffractometer. Data collections were performed at 100(1) K on a
Rigaku SuperNova diffractometer, using monochromated CuKα radiation
(λ = 1.54178 Å). Using Olex2[21] the structures were solved with the
ShelXS structure solution program applying direct method and the re-
finements were carried out with the refinement package ShelXL.[22]
Crystal and refinement details, as well as CCDC numbers are provided in
table 6. CCDC 1824799ꢀ–1824801 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
General procedure for fluorination
Chlorosilanes 4ꢀ–ꢀ8 were dissolved in n-pentane (2–5 mL) in a glove box.
Antimony trifluoride (2–3 eq) was added and the suspension was stirred
for 24 h at ambient temperature. The solid was filtered off and the solvent
was removed in vacuo. The fluorosilanes were purified by sublimation
(
10−3 mbar, 40 °C). Compound 11 and 13 were isolated as colourless
solids and fluorosilanes 9, 10 and 12 as colourless oils.
1
,3,5-Tris(fluorodimethylsilylvinyl)benzene (9): Yield 377 mg (98%).
1
): δ = 7.50 (s, 3H, Ar-H), 7.06 (d, 3JH,H
from
The
Cambridge
Crystallographic
Data
Centre
via
H NMR (300 MHz, CDCl =
3
9.2 Hz, 3H, Ar-CH=CH-Si), 6.49 (dd, 3
H,H = 19.3 Hz, 3JF,H = 3.2 Hz, 3H,
J
www.ccdc.cam.ac.uk/conts/retrieving.html.
1
Ar-CH=CH-Si), 0.40 [d, 3JF,H = 7.3 Hz, 18H, Si(CH
F] ppm. C{ H}
) δ = 146.0 (d, 3JF,C = 4.0 Hz, Ar-CH=CH-Si), 138.2
JF,C = 17.1 Hz, Ar-CH=CH-Si), 125.4 (CAr-H), −1.1 [d,
13
1
3
)
2
NMR (75 MHz, CDCl
), 125.5 (d, 2
3
Table 6. Crystallographic data for compounds 4, 6 and 8.
(
2
C
J
q
F,C = 15.9 Hz, Si(CH
3
)
2
F] ppm. 19F NMR (300 MHz, CDCl
3
) δ = −160.61
) δ = 20.4 (d,
Si (M
r
Compound
4
6 [a]
8
3
(
1
dsept, JH,F = 7.3/3.2 Hz) ppm. 29Si NMR (99 MHz, CDCl
J
3
Empirical
Formula
Si,F = 274.5 Hz) ppm. Elemental analysis calcd. (%) for C18
H
27
F
3
3
C
18
H
27Cl
3
Si
3
C
12
H
9
Cl
9
Si
3
C
12 9 3
H15Cl Si
=
384.66): C 56.20, H 7.08; found: C 54.35, H 7.16
M
r
434.01
912
monoclinic
556.51
2208
monoclinic
562.56
2256
monoclinic
C2/c
20.2874(2)
11.5184(1)
20.0277(2)
99.476(1)
4616.2(1)
8
F(000) [e]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
1
,3,5-Tris(difluoromethylsilylvinyl)benzene (10): Yield 517 mg (98%).
1
): δ = 7.55 (s, 3H, Ar-H), 7.26 (d, 3JH,H
H NMR (500 MHz, CDCl
3
=
P2 /n
P2 /n
1
1
1
9.6 Hz, 3H, Ar-CH=CH-Si), 6.34 (dt, 3JH,H = 19.6 Hz, 3JF,H = 2.9 Hz, 3H,
6.7814(2)
24.8059(6)
14.7334(4)
102.539(3)
2419.3(1)
4
1.192
4.839
144.2
6.9516(3)
Ar-CH=CH-Si), 0.54 [t, 3
J
F,H = 6.0 Hz, 9H, Si(CH
)F
] ppm. 13C{ H} NMR
1
3
2
23.7724(8)
26.7702(9)
91.332(4)
4422.7(3)
8
1.672
11.966
144.3
3
(
1
125 MHz, CDCl
3
) δ = 149.4 (t, JF,C = 4.0 Hz, Ar-CH=CH-Si), 137.7 (C
q
),
=
26.6 (CAr-H), 119.0 (t, 2
F
,
C
2
β [°]
V [Å ]
J
=
2
0
.
3
H
z
,
A
r
-
C
H
=
C
H
-
S
i
)
,
−
4
.
3
[
t
,
J
F,C
3
] ppm. 19F NMR (500 MHz, CDCl
2
J
0.3 Hz, Si(CH
3
)F
2
3
) δ = −135.43 (dq,
Z
ρ
3
H,F = 6.1/2.8 Hz) ppm. 29Si NMR (99 MHz, CDCl
) δ = −11.3 (d, 1
3
J
Si,F
=
=
calcd. [g cm−3
]
1.619
11.465
150.1
285.2 Hz) ppm. Elemental analysis calcd. (%) for C15
H
18
F
6
Si
3
(M
r
−1
µ [mm
]
396.55): C 45.43, H 4.58; found: C 43.87, H 4.63.
2θ
max [°]
Index range h
Index range k
Index range l
Refl. collected
Indep. refl.
−8 – 8
−8 – 8
−25 – 25
−13 – 14
−25 – 25
42325
−30 – 30
−18 – 18
51430
−23 – 29
−21 – 33
27273
1
,3,5-Tris(trifluorosilylvinyl)benzene (11): Yield 538 mg (99%).
1
): δ = 7.66 (s, 3H, Ar-H), 7.51 (d, 3JH,H = 19.0
H NMR (500 MHz, CDCl
3
Hz, 3H, Ar-CH=CH-Si), 6.21 (dq, 3JH,H = 19.8 Hz, 3JF,H = 2.4 Hz, 3H, Ar-
4775
8641
4668
CH=CH-Si) ppm. 13C{ H} NMR (125 MHz, CDCl
1
) δ = 153.3 (q, 3
), 127.7 (CAr-H), 109.4 (q, 2JF,C = 26.8
Hz, Ar-CH=CH-Si) ppm. 19F NMR (500 MHz, CDCl
) δ = −139.54 (d,
3JH,F = 2.3 Hz) ppm. 29Si NMR (99 MHz, CDCl ) δ = −72.2 (q, 1
59.9 Hz) ppm. Elemental analysis calcd. (%) for C12 Si
08.44): C 35.29, H 2.22; found: C 33.29, H 2.17.
3
F,C
J =
R
int
0.0557
4775/0
223
0.0357
0.0969
0.0396
0.1009
1.045
0.0460
8641/7
482
0.0543
0.1230
0.0744
0.1339
1.037
0.0499
4668/ 0
217
0.0310
0.0828
0.0322
0.0839
1.053
2.2 Hz, Ar-CH=CH-Si), 137.3 (C
q
Data/restraints
Parameters
3
3
J
(M
Si,F
=
=
R , I > 2σ(I)
1
2
4
H Cl1.5F
9 9
3
r
wR
(all data)
wR (all data)
GoF
2
, I > 2σ(I)
R
1
2
1
,3,5-Tris(difluoromethylsilylethyl)benzene (12): Yield 379 mg (98%).
ρ
max/ ρmin [e Å−3
]
0.54/−0.30
1824799
0.86/−0.57
1824800
0.64/−0.44
1824801
1
H NMR (300 MHz, CDCl
3
): δ = 6.88 (s, 3H, Ar-H), 2.73 (m, 6H, Ar-CH
-CH
-Si), 0.29 (t, 3JF,H = 6.4 Hz, 9H,
) δ = 143.7 (C ), 125.3
F,C = 14.9 Hz, Ar-CH -CH -Si),
) δ =
) δ = 2.9 (t,
2
-
CCDC number
CH
Si(CH
Ar-H), 27.5 (Ar-CH
2
-Si), 1.14 (m, 6H, Ar-CH
2
2
13
1
[a] Disorder of Cl(5) and Cl(6) over two sites (88:12). Disorder of C(24),
Si(6), Cl(16), Cl(17) and Cl(18) over three sites (85:7:8), inside this equiva-
lent bond lengths were retrained to be same. The ADP’s of all disordered
atoms were constrained to be equal for the equivalent atoms.
)F
3 2
] ppm. C{ H} NMR (75 MHz, CDCl
3
q
-Si), 15.7 (t, 2
(
C
2
-CH
2
J
19
2
2
−
−
3.9 [t, 2JF,C = 16.0 Hz, Si(CH
3
2 3
)F ] ppm. F NMR (300 MHz, CDCl
135.41 (qt, 3JH,F = 6.4/5.1 Hz) ppm. 29Si NMR (60 MHz, CDCl
3
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800279
FULL PAPER
B. Neumann, N. W. Mitzel, Chem. Commun. 2016, 52, 9949–9952; f) E.
Weisheim, A. Schwartzen, L. Kuhlmann, B. Neumann, H.-G. Stammler,
N. W. Mitzel, Eur. J. Inorg. Chem. 2016, 8, 1257–1266; g) E. Weisheim,
L. Buecker, B. Neumann, H. - G. Stammler, N. W. Mitzel, Dalton Trans.
Acknowledgements
The authors thank Dipl.-Ing. Klaus-Peter Mester for recording
NMR spectra and Heinz-Werner Patruck for measuring the mass
spectra. We gratefully acknowledge financial support from the
Deutsche Forschungsgemeinschaft (DFG).
2016, 45, 198–207; h) E. Weisheim, C. G. Reuter, P. Heinrichs, Y. V.
Vishnevskiy, A. Mix, B. Neumann, H.-G. Stammler, N. W. Mitzel, Chem.
Eur. J. 2015, 21, 12436-12448; J.-H. Lamm, J. Horstmann, J. H. Nissen,
J.-H. Weddeling, B. Neumann, H.-G. Stammler, N. W. Mitzel, Eur. J.
Inorg. Chem. 2014, 4294–4301; i) J.-H. Lamm, P. Niermeier, A. Mix, J.
Chmiel, B. Neumann, H.-G. Stammler, N. W. Mitzel, Angew. Chem. Int.
Ed. 2014, 53, 7938–7942.
Keywords: Triethynylbenzene • Trivinylbenzene • Hydrosilyla-
tion • Tridentate Lewis acids • Solid-State Structures
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This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800279
FULL PAPER
Entry for the Table of Contents
FULL PAPER
Trifunctional Lewis acids with a variety
of chlorinated and fluorinates silyl
groups were investigated for possible
cooperative effects of the groups and
found to be more pronounced for the
more flexible systems.
Poly-Lewis Acids, cooperativity
A. Schwartzen, L. Siebe, B. Neumann,
H.-G. Stammler and N. W. Mitzel*
Page No. – Page No.
Tridentate Lewis Acids: Silicon-
functionalised 1,3,5-Triethynyl-
benzene and 1,3,5-Trivinylbenzene
This article is protected by copyright. All rights reserved.