Crown ether adducts of light alkali metal triphenylsilyls: Synthesis, structure and hydrosilylation catalysis

Article abstract of DOI:10.1039/c4dt00916a

Alkali metal triphenylsilyls [Li(12-crown-4)SiPh₃]·(thf)_0.5(2), [Na(15-crown-5)SiPh₃]·(thf)_0.5(3) and [K(18-crown-6)SiPh₃(thf)] (4) were synthesized using 1,1,1-trimethyl-2,2,2-triphenyldisilane (Ph

Full text of DOI:10.1039/c4dt00916a

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Crown ether adducts of light alkali metal
triphenylsilyls: synthesis, structure and
hydrosilylation catalysis†
Cite this: Dalton Trans., 2014, 43,
14315
Valeri Leich, Kevin Lamberts, Thomas P. Spaniol and Jun Okuda*
Alkali metal triphenylsilyls [Li(12-crown-4)SiPh3]·(thf)0.5 (2), [Na(15-crown-5)SiPh3]·(thf)0.5 (3) and [K(18-
crown-6)SiPh3(thf)] (4) were synthesized using 1,1,1-trimethyl-2,2,2-triphenyldisilane (Ph3SiSiMe3) and
isolated in high yields. Solid state structures were determined by single crystal X-ray diffraction. These
alkali metal silyls catalyzed the regioselective hydrosilylation of 1,1-diphenylethylene to give the anti-
Markovnikov product. The presence of crown ethers enhanced the reactivity of the metal silyls in hydro-
silylation catalysis.
Received 27th March 2014,
Accepted 7th May 2014
DOI: 10.1039/c4dt00916a
www.rsc.org/dalton
Introduction
Organosilicon compounds are valuable intermediates of con-
siderable interest in materials science.1 Applications in syn-
thetic chemistry include their use as protecting groups in
organic chemistry and for regio- and stereoselective C–C bond
formation under mild conditions.2 Prominent examples of
organosilicon mediated reactions are the Sakurai reaction,3
the Mukaiyama aldol reaction,4 Peterson olefination5 and
Hiyama cross coupling.6 Reactivity studies of organometallic
silicon compounds provided insight into the mechanisms of
these reactions. Therefore isolation and full characterization of
organometallic silicon compounds help to understand the
nature of the metal–silicon bond. In this regard alkali metal
silyls could serve as precursors for transition metal silyls or
model complexes itself.
The synthesis of alkali metal silyls often requires specific
silanes as starting materials limiting their general application.
Reproducible protocols to produce these metal silyls in high
yields from commercially available chemicals could benefit
their application. Procedures reported in the literature are
compiled in Scheme 1.
Scheme 1 Syntheses of alkali metal silyls reported in the literature.
Examples are [MSiPh3] (M
=
Li, Na, K),7 [LiSiPh2Me],8
[LiSiPhMe2],8 [KSiPh2 Bu],9 [KSiPh2H]10 and [KSiPhH2].11 The
cleavage of symmetrical or unsymmetrical disilanes with alkali
metal alkoxides (Scheme 1b) was used to synthesize [MSiMe3]
(M = Na, K)12 and [KSiR3] (R3 = Me3, Ph2Me, Ph3).12c The use of
HMPA, DMI or DMPU as solvents limited the application of
these procedures. The reaction of a silane with an alkali metal
or alkali metal hydride under dihydrogen release was reported
only for a few compounds (Scheme 1c). Examples are [LiSi-
(GePh3)3],13 [LiSiPh3],7b [KSiR3] (R3 = Et3, Ph3)14 and [MSiH3]
(M = K, Rb, Cs).15 This straightforward strategy is hampered by
low yields, side reactions and the preparation of highly acti-
vated alkali metals. Alkali metal “hypersilyls” [MSi(SiMe3)3]
(M = Li–Cs) have attracted some interest due to their stability,
simple and high yield syntheses.16 They can be prepared from
t
The cleavage of a symmetrical disilane, which contains one
or more aryl groups on the silicon, with alkali metals is the
most common method to prepare metal silyls (Scheme 1a).
The increase in reactivity from lithium to cesium comes along
with the decrease in the solubility of the alkali metal silyls.
Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, D-52056
Aachen, Germany. E-mail: jun.okuda@ac.rwth-aachen.de; Fax: +49 241 80 92 644
†Electronic supplementary information (ESI) available: NMR spectra, X-ray
crystallographic details and data. CCDC 993779 (2β), 993780 (3β) and 993781
(4). For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c4dt00916a
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Si(SiMe3)4 and common alkali metal reagents17 or by trans- hexaphenyldisilane with sodium metal in 71% yield. To the
metalation18 (Scheme 1d).
best of our knowledge, it was never isolated or characterized.
In many cases the metal silyls were not isolated and charac-
[K(18-crown-6)SiPh3(thf)] (4) was synthesized reacting disi-
terized fully due to their high reactivity towards water and lane 1 with potassium tert-butoxide/18-crown-621 in THF for
oxygen. Reactivity studies or applications in catalysis of alkali 1 h following a modified procedure.12c Potassium silyl 4 was
metal silyls remain still scarce. We report here the synthesis, isolated in quantitative yield (99%) as analytically pure orange
characterization and application in catalytic hydrosilylation of powder (Scheme 2). Recently published synthesis of [K(18-
[Li(12-crown-4)SiPh3]·(thf)0.5 (2), [Na(15-crown-5)SiPh3]·(thf)0.5 crown-6)SiPh3]22 reported a yield of 88% (16 h) and 75% for
(3) and [K(18-crown-6)SiPh3(thf)] (4).
[KSiPh3].23
Characterization of alkali metal silyls
1H NMR spectra of 2, 3 and 4 in d8-THF displayed one singlet
at δ ∼ 3.5 ppm for the crown ether methylene protons and
three multiplets at δ ∼ 6.8–7.4 ppm for the para-, meta- and
ortho-Ph protons of the phenyl substituents (see ESI†). 13C{1H}
and 29Si{1H} NMR data are listed in Table 1 and are compar-
able to the data published for [LiSiPh3] and [KSiPh3].24
The metal cation and complexation with crown ethers has
only a small influence on the 13C NMR shifts of the ortho-,
meta- and para-Ph carbons. Going from Li to K, a small down-
field shift of the ipso carbon atom from 156.30 ppm to
160.95 ppm was observed.
Results and discussion
Synthesis and isolation of alkali metal silyls
All metal silyls were synthesized from 1,1,1-trimethyl-2,2,2-tri-
phenyldisilane7d 1 as a starting material. The use of disilane 1
offers some advantage over established preparation methods:
(1) 1,1,1-trimethyl-2,2,2-triphenyldisilane can be prepared
from commercially available chemicals in high yield and
purity; (2) nucleophilic attack at the SiMe3- is favored over the
SiPh3-silicon center, thus giving one silyl species selectively;
t
(3) the coupling products CH2(SiMe3)2 and BuOSiMe3 are low
It was stated before that the NMR data are consistent with a
strong M–Si interaction with covalent character, forming
monomeric metal silyl species in ethereal solvents.24 Recently,
DFT calculations indicated a highly polar localized Ca–Si bond
in [Ca(SiPh3)2(thf)4].25 The solution structure of 2, 3 and 4
appears to be similar to that of alkali metal silyls [MSiPh3]
(M = Li and K).
Crystals of 2, 3 and 4 were grown from THF–hexane at
−30 °C. X-ray diffraction at low temperature for compounds
2 and 3 resulted only in low resolution data that could not be
indexed with only one unit cell. Heating the crystals to 220 K
revealed a reversible solid state phase transition. Data collec-
tions were performed at 100 K and 220 K.
boiling, stable compounds, which suppress the back reaction
to the starting materials.
In all cases the procedures were simple. To a solution of 1 a
solution of the appropriate nucleophile/crown ether was added
slowly and stirred for 1–12 h. After the time indicated the
product crystallized from THF–hexane solution. [Li(12-crown-
4)SiPh3]·(thf)0.5 (2) was prepared from lithium alkyl LiCH2-
SiMe3/12-crown-4 in 80% yield (Scheme 2). In the case of 2
only a slight increase in yield compared to [LiSiPh3(thf)]19
(63%) was achieved. Common lithium reagents such as
lithium methyl, n-butyl and tert-butoxide were not able to
cleave 1 selectively. Addition of 12-crown-4 to the reaction
solution reduced the reaction time from 24 h to 12 h.
Evaluation of the low temperature data of [Li(12-crown-4)-
SiPh3]·(thf)0.5 (2α) did not allow satisfactory indexing of the
unit cell. Weak diffraction power and twinning with several
independent domains suggest a unit cell of approximately
7808 Å3 with trigonal metrics. The high temperature data (2β)
allowed for a structure solution in the trigonal space group
[Na(15-crown-5)SiPh3]·(thf)0.5 (3) was synthesized in quanti-
tative yield starting from disilane 1 and sodium tert-butoxide/
15-crown-5 within 2 h (Scheme 2). Without addition of crown
ether no conversion to the sodium silyl was observed. Sodium
triphenylsilyl [NaSiPh3]20 was synthesized before by cleavage of
ˉ
P3c1 with a unit cell four times smaller than the low tempera-
ture phase. Despite the low diffraction power, a restrained but
satisfactory structure model was obtained. [Li(12-crown-4)-
SiPh3] units cocrystallized with 0.5 equivalents of the solvate
thf in agreement with the 1H NMR spectrum.
Table 1 13C{1H} and 29Si{1H} NMR data of 2, 3 and 4 in ppma
ipso
ortho
meta
para
29Si{1H}
2
3
4
156.30
157.70
160.95
137.11
137.30
137.20
126.96
126.72
126.46
124.61
124.13
123.10
−8.60
−6.60
−8.24
Scheme 2 Synthesis of crown ether adducts of Li/Na/K-triphenylsilyls.
14316 | Dalton Trans., 2014, 43, 14315–14321
a NMR spectra were recorded at 25 °C in d8-THF solutions.
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pentagonal pyramidal coordination is found for the sodium
cation (Fig. 2). The tip is occupied by the ordered triphenyl-
silyl, the base is formed by the C5-symmetric crown ether, dis-
ordered over the three symmetry equivalent positions. The
Si1–Na1–O1–5 angles range from 99.9(3)° to 124.8(3)° but have
to be interpreted with care as the structure model is based on
a
heavily restrained and constructed model that barely
included the assignment of electron density maxima in
Fourier maps.
[K(18-crown-6)SiPh3(thf)] (4) crystallizes in the monoclinic
space group Cc with Z = 4. The molecular connectivity differs
from that in Li and Na analogues by an extended coordination
sphere. The larger size of the potassium cation allows the
coordination of one thf molecule (K1–O7 = 2.810(5) Å) (Fig. 3).
Fig. 1 Ball and stick model of the main residue of 2β. Hydrogen atoms
and solvent molecules are omitted for clarity. Selected bond lengths [Å]
and angles [°]: Li1–Si1 2.650(9), Li1–O1–4avg 2.11(1), Si1–C9 1.923(5),
Li1–Si1–C9 116.43(9), Si1–Li1–O1 118.9(3), Si1–Li1–O2 113.8(3), Si1–Li1–
O3 112.4(3), Si1–Li1–O4 115.0(2).
Li is enclosed in a distorted square pyramidal geometry
with the crown ether occupying the square plane (Fig. 1). The
Li–Si contact is located along a 3-fold axis resulting in a
heavily disordered structure model for the C4 symmetric crown
ether. The 3-fold rotation axis of the silyl group is compatible
with the crystal symmetry. The Li1–Si1 bond length of 2.650(9)
Å and Si1–Li1–O1–4 angles from 112.4(3)° to 118.9(3)° indicate
a similar interaction between lithium and the silyl anion as in
literature known compounds ([(LiSiMe3)2(TMEDA)3] = 2.70(1)
Å,26 [Li(thf)3SitBuPh2] = 2.675(5) Å,27 [Li(thf)3SiPh3] = 2.672(13)
Å,19 [Li(thf)3Si(SiMe3)3] = 2.672 Å,28 [Li(thf)3Si(SiMe3)3]2
=
Fig. 2 Ball and stick model of the main residue of 3β. Hydrogen atoms
and solvent molecules are omitted for clarity. Selected bond lengths [Å]
and angles [°]: Na1–Si1 2.983(4), Na1–O1–5avg 2.53(1), Si1–C21 915(6),
Si1–Na1–O1 105.9(3), Si1–Na1–O2 117.7(3), Si1–Na1–O3 99.9(3), Si1–
Na1–O4 124.8(3), Si1–Na1–O5 112.9(3).
2.689(4)29). Crystal data and refinement results for all struc-
tures are given in Table 3; details of the low temperature phase
2α are given in the ESI.†
Low temperature diffraction data of [Na(15-crown-5)-
SiPh3]·(thf)0.5 (3α) were of slightly better intensity and could
be indexed as twin with at least three components in a nearly
trigonal unit cell (a = 25.313(15) Å, b = 25.329(15) Å, c = 10.576(7)
Å, α = 89.673(14)°, β = 90.506(15)°, γ = 117.638(13)°) with
pseudo translation symmetry along the a-axis. A structure solu-
ˉ
tion was obtained in P1 and the basic connectivity of the mole-
cule could be derived using an isotropic model with an average
Na–Si distance of 2.99(1) Å.
ˉ
The high temperature phase 3β crystallizes in P3 and is
similar to 2β with respect to connectivity and packing. The
lower crystal symmetry is compensated by a smaller unit cell,
resulting in a closely related asymmetric unit when compared
to 2β, including 0.5 equivalents of cocrystallized thf. The Na–
Si contact extends along the 3-fold axis with a bond length of
2.983(4) Å, which is comparable to known sodium silyl radical
([NaSi(SitBu2Me)2] = 3.0744(8) Å30) or silyls [NaSi(SiMe3)3]2
3.049(1) Å,18a [NaSitBu3]2 = 3.073(4) Å,31 [Na(thf)2SitBu3]2
=
=
Fig. 3 Ball and stick model of the asymmetric unit of 4. Hydrogen
atoms are omitted for clarity. Selected bond lengths [Å] and angles [°]:
K1–Si1 3.460(3), K1–O7 2.810(5), K1–O1–6avg 2.819(5), Si1–K1–O7
172.75(11), Si1–K1–O1–6avg 94.75(12), K1–Si1–C10 118.3(2), K1–Si1–C11
2.919(1) Å,31 [Na(PMDTA)SitBu3] = 2.967(2) Å,31 [NaSitBu2Ph]2 =
2.8811(19) Å,32 [Na(thf)SitBu2Ph] = 2.9910(2) Å33). A distorted 111.9(2), K1–Si1–C12 124.1(2).
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A K1–Si1 bond length of 3.460(3) Å and an average Si1–K1–
O1–6 angle of 94.75(12)° (measured at 100(2) K) suggest a
stronger interaction between potassium cation and the silyl
anion compared to [K(18-crown-6)SiPh3]22,34 (K–Si = 3.5404(5)
Å at 100(2) K). In this compound, [K(18-crown-6)SiPh3] units
are connected by intermolecular π-interactions between a pot-
assium atom and one of the phenyl rings of the silyl anion to
form chains. In 4 the thf ligand disrupts these chains to form
monomeric units in the solid state. This results in higher
nucleophilicity of the triphenylsilyl anion in solution.
Table 3 Crystal data and refinement results for 2β, 3β and 4
Compound
2β
3β
4
Empirical
formula
C
28H35LiO4.5Si
C30H39NaO5.5Si
C34H47KO7Si
M (g mol−1
Temperature (K)
Crystal system
Space group no.
a (Å)
)
478.59
220(2)
538.69
220(2)
634.90
100(2)
Monoclinic
Cc (9)
19.801(6)
14.731(4)
12.752(4)
112.535(5)
3435.6(18)
4
Trigonal
Trigonal
ˉ
ˉ
P3c1 (165)
P3 (147)
11.9898(9)
—
21.5449(17)
—
2682.2(5)
4
0.120
12.858(5)
—
10.756(5)
—
1540.1(14)
2
0.126
b (Å)
c (Å)
β (°)
V (Å3)
Z
Catalytic hydrosilylation with alkali metal silyls
μ (mm−1
)
0.234
Total/unique
reflections
Variables refined
30 183/1837
4593/1817
12 783/7033
The alkali metal silyls 2, 3 and 4 were tested in the catalytic
hydrosilylation of 1,1-diphenylethylene (1,1-DPE) and their activity
compared to that of known metal silyls (Table 2). Using potass-
ium silyl [KSiPh3(thf)]25 (2.5 mol% catalyst loading) quantitat-
ive hydrosilylation of 1,1-DPE was observed at 40, 60 and 80 °C
within 174, 83 and 39 h, without any catalyst deactivation
(Table 2, entries 1–3).
114
(17 restraints)
0.0543
0.3126/0.2733
0.1287/0.0961
1.040
123
(76 restraints)
0.0308
0.2141/0.1900
0.1661/0.1155
1.005
389
(2 restraints)
0.0765
0.1944/0.1862
0.0803/0.0715
1.080
Rint
wR2 (all/obs)
R1 (all/obs)
GOF on F2
Diff. peak/hole
0.397/−0.403
0.450/−0.436
0.751/−0.469
(e Å−3
)
Use of diphenylsilane (H2SiPh2) and phenylsilane (H3SiPh)
shortened reaction times, but the yield of the product
decreased to 87 and 78%, respectively (Table 2, entries 4–5).
Interestingly, known [LiSiPh3(thf)3]19 also catalyzed the hydro-
silylation of 1,1-DPE within 40 h at 80 °C to give the product in
96% yield (Table 2, entry 6). The catalyst is deactivated after
this time. Using alkali metal silyls 2, 3 and 4 in the catalytic
hydrosilylation shortened reaction times without catalyst de-
activation (Table 2, entries 9–11). In all cases quantitative con-
version was observed at 80 °C after 15–20 h. Alkali metal
triphenylsilyls synthesized by established methods showed
comparable activities in the hydrosilylation of 1,1-DPE
(Table 2, entries 7/8). Complexation of alkali metal with crown
ethers increased both reactivity and stability of the resulting
Flack parameter
CCDC
—
993779
—
993780
0.00(9)
993781
metal silyls. Hydrosilylation of styrene, 1-octene and cyclo-
hexene with 2, 3 and 4 as catalysts was not observed.
In comparison with hydrosilylation catalysts based on the
alkaline earth metals ([M(DMAT)2(thf)2] and [K(DMAT)], M =
Ca, Sr, DMAT = CH(SiMe3)C6H4-2-(NMe2), reaction times:
2–24 h)35 reaction times are longer for alkali metal silyls.
Regioselectivity changed to give anti-Markovnikov hydrosilyl-
ation products. As proposed by Harder et al., hydrosilylation
catalyzed by metal silyls might operate through a different
mechanism.35,36 A silyl migration mechanism, established for
transition metal-catalyzed hydrosilylation,37 could be feasible
(Scheme 3). The first step of the catalytic cycle involves a fast
insertion of an alkene into the metal silicon bond to give a
resonance stabilized metal alkyl. This undergoes rate-determin-
ing σ-bond metathesis with a silane to regenerate the silyl and
the hydrosilylated product.25
Table 2 Hydrosilylation of 1,1-DPE with alkali metal silyls
Entrya Silane
Cat.
T [°C] t [h]
Conversionb
1
2
3
4
5
6
7
HSiPh3
HSiPh3
HSiPh3
[KSiPh3(thf)]25
[KSiPh3(thf)]25
[KSiPh3(thf)]25
40
60
80
80
80
80
80
174
83
39
2
2
40
16
>99
>99
>99
87c
78c
96c
>99
H2SiPh2 [KSiPh3(thf)]25
H3SiPh
HSiPh3
HSiPh3
[KSiPh3(thf)]25
[LiSiPh3(thf)3]19
[LiSiPh3(thf)3]19
12-crown-4
+
8
HSiPh3
[KSiPh3(thf)]25
+
80
20.5 >99
18-crown-6
9
10
11
HSiPh3
HSiPh3
HSiPh3
2
3
4
80
80
80
15
18
20
>99
>99
>99
a Reaction conditions: catalyst (2.5 μmol), alkene (0.1 mmol), silane
(0.11 mmol). b Determined by 1H NMR spectroscopy. c Catalyst
deactivation after time indicated.
Scheme 3 Proposed silyl migration mechanism.
14318 | Dalton Trans., 2014, 43, 14315–14321
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(12-crown-4), 124.61 (para-Ph), 126.96 (meta-Ph), 137.11
Conclusions
(ortho-Ph), 156.30 (ipso-Ph). 29Si{1H} NMR (d8-THF, 25 °C,
7
In conclusion, a series of light alkali metal triphenylsilyls were 79.5 MHz): δ −8.60 (LiSi). Li{1H} NMR (d8-THF, 155.5 MHz):
synthesized from 1,1,1-trimethyl-2,2,2-triphenyldisilane (Ph3Si- δ 0.59 (s, Li(12-crown-4)Si). Anal. calc. for C28H35LiO4.5Si
SiMe3) and characterized by spectroscopic and X-ray diffraction (478.59 g mol−1): C, 70.27, H, 7.37; Li, 1.45. Found: C, 69.37;
methods. They catalyze the anti-Markovnikov hydrosilylation H, 7.08; Li, 1.45%.
of activated olefins, supporting the active role of metal silyls in
Synthesis of [Na(15-crown-5)SiPh3]·(thf)0.5 (3). A solution of
this type of catalysis. Thus coordination of alkali metal silyls sodium tert-butoxide (96 mg, 1.00 mmol) in THF (2 mL)
with crown ethers enhances both stability and reactivity of the was added to a solution of 15-crown-5 (220 mg, 1.00 mmol) and
resulting complexes.
1,1,1-trimethyl-2,2,2-triphenyldisilane (333 mg, 1.00 mmol) in
THF (2 mL). The reaction mixture turned yellow and was stirred
for 2 h at r.t. The solvent was removed under reduced pressure
and the crude product washed with pentane (3 × 3 mL). After
drying under reduced pressure, [Na(15-crown-5)SiPh3]·(thf)0.5
(538 mg, 0.99 mmol, 99%) was obtained as pale yellow powder.
Crystals of [Na(15-crown-5)SiPh3]·(thf)0.5 suitable for single
Experimental
General experimental remarks
All operations were performed under an inert atmosphere of crystal X-ray analysis were grown from THF–hexane at −30 °C
dry argon using standard Schlenk line or glove box techniques. over a period of 24 h.
d8-THF was distilled under argon from sodium/benzophenone
1H NMR (d8-THF, 400.1 MHz): δ 1.78 (m, 2H, thf), 3.58 (s,
ketyl prior to use. 1,1-Diphenylethene and 1,4,7,10-tetraoxa- 20H, 15-crown-5), 3.62 (m, 2H, thf), 6.82–6.86 (m, 3H, para-
cyclododecane (12-crown-4) were dried over CaH2 and distilled Ph), 6.93–6.97 (m, 6H, meta-Ph), 7.37–7.39 (m, 6H, ortho-Ph).
under argon prior to use. Triphenylsilane, 1,4,7,10,13-pentaoxa- 13C{1H} NMR (d8-THF, 100.6 MHz): δ 26.43 (thf), 68.26 (thf),
cyclopentadecane (15-crown-5) and 1,4,7,10,13,16-hexaoxa- 69.86 (15-crown-5), 124.13 (para-Ph), 126.72 (meta-Ph), 137.30
cyclooctadecane (18-crown-6) were purified by vacuum (ortho-Ph), 157.70 (ipso-Ph). 29Si{1H} NMR (d8-THF, 25 °C,
sublimation. THF and pentane were purified using a MB 79.5 MHz): δ −6.60 (NaSi). Anal. calc. for C30H39NaO5.5Si
SPS-800 solvent purification system. The metal content was (538.69 g mol−1): Na, 4.27. Found: Na, 3.83%.
determined by atom absorption spectroscopy (Shimadzu
Synthesis of [K(18-crown-6)SiPh3(thf)] (4). A solution of pot-
AA-6200, 460.7 nm, air/acetylene flame). NMR spectra were assium tert-butoxide (112 mg, 1.00 mmol) in THF (1 mL)
recorded on a Bruker Avance II 400 and a Bruker Avance III HD was added to a solution of 18-crown-6 (264 mg, 1.00 mmol) and
400 spectrometer at 25 °C in J. Young type NMR tubes. Chemi- 1,1,1-trimethyl-2,2,2-triphenyldisilane (333 mg, 1.00 mmol) in
1
cal shifts for H, 13C{1H} and 29Si{1H} NMR spectra were refer- THF (2 mL). The reaction mixture immediately turned yellow/
enced internally using the residual solvent resonance and are orange and was stirred for 1 h at r.t. The solvent was removed
reported relative to tetramethylsilane. 7Li{1H} spectra were under reduced pressure and the crude product was washed
referenced to LiCl in D2O (1 M). The resonances in 1H and 13
C
with pentane (3 × 3 mL). After drying under reduced pressure,
NMR spectra were assigned on the basis of two-dimensional [K(18-crown-6)SiPh3(thf)] was obtained as yellow powder
NMR experiments (COSY, HSQC, HMBC). 1,1,1-Trimethyl- (634 mg, 1.00 mmol, 99%). Crystals of [K(18-crown-6)SiPh3(thf)]
2,2,2-triphenyldisilane7d and [LiCH2SiMe3]38 were prepared suitable for single crystal X-ray analysis were grown from THF–
according to literature procedures.
Synthesis of [Li(12-crown-4)SiPh3]·(thf)0.5 (2). A solution of
hexane at −30 °C over a period of 12 h.
1H NMR (d8-THF, 400.1 MHz): δ 1.78 (m, 4H, thf), 3.52 (s,
[LiCH2SiMe3] (47 mg, 0.50 mmol) in THF (1 mL) was added to 24H, 18-crown-6), 3.62 (m, 4H, thf), 6.73–6.77 (m, 3H, para-
a solution of 1,1,1-trimethyl-2,2,2-triphenyldisilane (167 mg, Ph), 6.87–6.91 (m, 6H, meta-Ph), 7.36–7.39 (m, 6H, ortho-Ph).
0.50 mmol) in THF (1 mL). The reaction mixture turned 13C{1H} NMR (d8-THF, 100.6 MHz): δ 23.26 (thf), 68.27 (thf),
yellow and was stirred for 12 h at r.t. After 12 h 12-crown-4 71.09 (18-crown-6), 123.10 (para-Ph), 126.46 (meta-Ph), 137.20
(44 mg, 0.50 mmol) in THF (1 mL) was added and [Li(12- (ortho-Ph), 160.95 (ipso-Ph). 29Si{1H} NMR (d8-THF, 25 °C,
crown-4)SiPh3]·(thf)0.5 precipitated from the reaction mixture. 79.5 MHz): δ −8.24 (KSi). Anal. calc. for C34H47KO7Si (634.90 g
The solvent was removed under reduced pressure and the mol−1): K, 6.16. Found: K, 6.12%.
crude product was washed with pentane (3 × 3 mL). After
drying under reduced pressure, [Li(12-crown-4)SiPh3]·(thf)0.5
was obtained as pale yellow powder (193 mg, 0.40 mmol,
Hydrosilylation of 1,1-diphenylethene
80%). Crystals of [Li(12-crown-4)SiPh3]·(thf)0.5 suitable for Hydrosilylation experiments were performed as follows: a solu-
single crystal X-ray analysis were grown from THF–hexane at tion of catalyst (2.5 μmol) in d8-THF (0.5 mL) in a Young’s
−30 °C over a period of 24 h.
NMR tube was treated with 1,1-DPE (0.10 mmol). Immediately
1H NMR (d8-THF, 400.1 MHz): δ 1.78 (m, 2H, thf), 3.61 (m, the reaction mixture turned deep red. Silane (0.11 mmol) was
2H, thf), 3.62 (s, 16H, 12-crown-4), 6.86–6.91 (m, 3H, para-Ph), added and the reaction mixture was heated for the indicated
6.96–7.00 (m, 6H, meta-Ph), 7.33–7.36 (m, 6H, ortho-Ph). 13C- period of time. The conversion of the substrate was deter-
{1H} NMR (d8-THF, 100.6 MHz): δ 26.44 (thf), 68.28 (thf), 71.37 mined by 1H NMR spectroscopy.
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Crystal structure determination
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X-ray diffraction data were collected on
a
Bruker
D8 goniometer with APEX CCD area-detector in ω-scan mode.
Mo-Kα radiation (multilayer optics, λ = 0.71073 Å) from an
Incoatec microsource was used. Temperature control was
achieved with an Oxford cryostream 700.
Determination of the unit cells of 2β, 3β and 4 and frame
processing was done with SAINT+.39 The low temperature
structures were indexed with CELL NOW.40 Multiscan absorp-
tion corrections were applied with SADABS41 for single crystal
data and TWINABS42 for the twinned data. Structures were
solved by direct methods (SHELXS40) and refined against F2
with SHELXL-13.40 Hydrogen atoms were included as riding
on calculated positions with Uiso(H) = 1.2Ueq.(non-H). Non-
hydrogen atoms were refined with anisotropic displacement
parameters in the well ordered parts. The disordered parts
were modeled using one isotropic displacement parameter for
all atoms in the disordered molecular fragment. In 2β all non-H
atoms of the crown ether could be found in the difference
Fourier map. In 3β only 1 reasonably high electron density
maximum could be found and the crown ether was con-
structed based on this position. Restraints were slowly released
to allow for stable refinement. In the final model of both struc-
tures C–C distances are restrained to be close to 1.42 Å and
C–O distances to 1.50 Å. The disordered thf molecules are
based on a constructed model that was placed in the void with
diffuse electron density and refined with the same distance
restraints. Full details of the refinement are given as ESI.†
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Acknowledgements
We thank Prof. U. Englert for helpful discussions regarding
single crystal X-ray diffraction. Financial support by the
Cluster “Tailor Made Fuels from Biomass” and the Fonds der
Chemischen Industrie is gratefully acknowledged. This paper
is dedicated to the memory of Prof. M. F. Lappert.
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