Synthesis and characterization of spirosilanes - 1,2-hydroboration and 1,1-carboboration

Article abstract of DOI:10.1002/ejic.201402286

Starting from dichloro(divinyl)silane, the dialkynyl(divinyl)silanes (CH₂=CH)₂Si(C≡CR)₂ (R = tBu, p-tolyl, 3-thienyl, CH₂NMe₂) were prepared. These silanes were treated with 9-borabicyclo[3.3.1]nonane (9-BBN) for 1,2-hydroboration of the vinyl groups. The hydroboration products rearranged quickly and quantitatively by intramolecular 1,1-carboboration into the respective target compounds, the axially chiral 5-silaspiro[4.4]nona-1,6-dienes bearing boryl groups at the 2- and 7-positions and the R substituents at the 1- and 6-positions. Simple protodeborylation with acetic acid proved possible, except for R = tBu. The remaining Si-C function in (CH₂=CH)₂Si(Cl)C≡CtBu opens the way to new spirosilanes after a sequence of hydroboration/ carboboration/hydroboration, for which a first example was studied. The products were characterized by X-ray diffraction in the solid state and NMR spectroscopy in solution (¹H, ¹¹B, ¹³C, ¹⁵N, ²⁹Si), complemented by optimization of gas-phase structures and calculation of NMR parameters by DFT methods. The dialkynyl(divinyl)silanes (CH₂=CH)₂Si(C≡CR)₂ and the alkynyl(chloro)(divinyl)silane (CH₂=CH)₂Si(Cl)C≡CtBu are obtained from dichloro(divinyl)silane and converted into spirosilanes. The spirosilanes are used for successful protodeborylation reaction. The characteristic NMR spectroscopic data for all compounds are collected, and the X-ray structures of some examples are determined. Copyright

Full text of DOI:10.1002/ejic.201402286

FULL PAPER
DOI:10.1002/ejic.201402286
Synthesis and Characterization of Spirosilanes –
1,2-Hydroboration and 1,1-Carboboration
Ezzat Khan,*[a] Bernd Wrackmeyer,[b] Cristian Döring,[b] and
Rhett Kempe[b]
Keywords: Spiro compounds / Hydroboration / Carboboration / Silanes / Structure elucidation
Starting from dichloro(divinyl)silane, the dialkynyl(divinyl)-
silanes (CH2=CH)2Si(CϵCR)2 (R = tBu, p-tolyl, 3-thienyl,
CH2NMe2) were prepared. These silanes were treated with
9-borabicyclo[3.3.1]nonane (9-BBN) for 1,2-hydroboration of
the vinyl groups. The hydroboration products rearranged
quickly and quantitatively by intramolecular 1,1-carbobor-
ation into the respective target compounds, the axially chiral
5-silaspiro[4.4]nona-1,6-dienes bearing boryl groups at the 2-
and 7-positions and the R substituents at the 1- and 6-posi-
tions. Simple protodeborylation with acetic acid proved pos-
sible, except for R = tBu. The remaining Si–C function in
(CH2=CH)2Si(Cl)CϵCtBu opens the way to new spirosilanes
after a sequence of hydroboration/carboboration/hydrobor-
ation, for which a first example was studied. The products
were characterized by X-ray diffraction in the solid state and
NMR spectroscopy in solution (1H, 11B, 13C, 15N, 29Si), com-
plemented by optimization of gas-phase structures and cal-
culation of NMR parameters by DFT methods.
Introduction
1,1-Carboboration and more recently the combination of
1,2-hydroboration and 1,1-carboboration have opened at-
tractive routes to Group 14 metallacycles.[1–3] With silicon,
heterocycles such as 1-silacyclobutenes,[4–6] 1-silacyclopent-
2-enes,[7,8] 1-silacyclohex-2-enes,[7,9] and silole derivatives
are particularly noteworthy.[10–12] Addressing 1-silacyclo-
pent-2-enes, numerous derivatives bearing functionalities
such as Si–organyl, Si–Cl, and Si–H at a chiral silicon atom
have become available (Figure 1, example A). The processes
of 1,2-hydroboration[13] and 1,1-carboboration[14] are sim-
ple, efficient, and cost effective. Although they require care-
ful purification of the starting silanes, the following reac-
tions afford the desired pure products in high yield.
In addition to simple silicon heterocycles, a few examples
of silane derivatives with the silicon atom in the center of a
spiro structure have been reported.[15–19] Most routes
towards spirosilanes appear to be rather inconvenient and
narrow, particularly if the rings contain C=C bonds or
Figure 1. Examples of 1-silacyclopent-2-ene derivatives A and B.
other functional groups attached to the carbon atoms of tions appears to be versatile in synthesis.[4–9,20,21] In the
the ring. Recently, we have characterized a few spirosilane present work, further examples are given to emphasize the
derivatives as first examples, namely, the 4-silaspiro[3.3]- simple and general route to 5-silaspiro[4,4]nona-1,6-diene
hepta-1,5-dienes[20] and the axially chiral 5-silaspiro[4.4]- derivatives. Furthermore, a route to other types of spiro-
nona-1,6-dienes (Figure 1, example B),[21] through consecu- silanes containing the 1-silacyclopent-2-ene unit is explored.
tive 1,2-hydroboration and 1,1-carboboration reactions.
The combination of these stereo- and regioselective reac-
Results and Discussion
[a] Department of Chemistry, University of Malakand,
18550 Chakdara, Khyber Pakhtunkhwa, Pakistan
Synthesis of Starting Silanes
E-mail: ekhan@uom.edu.pk
www.uom.edu.pk
Divinyl(dichloro)silane was treated with 2 equiv. of the
[b] Anorganische Chemie II, Universität Bayreuth,
95440 Bayreuth, Germany
respective lithiated alkyne at low temperature (–78 °C)[22–24]
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to afford the required dialkynyl(divinyl)silanes 1. For the a heteroaryl group (1c), and a potentially coordinating
tBu derivative, the reaction afforded a mixture of 1a and 2a Lewis base (1d).
(Scheme 1). The components of the mixture were separated
by fractional distillation under vacuum (ca. 10–3 Torr). The
purity of the new dialkynyl(divinyl)silanes was checked by
NMR spectroscopy (see Exp. Section), and the compounds
1,2-Hydoboration and 1,1-Carboboration
were used in further reactions when the required purity
(Ն99%) was achieved. The substituents R were selected to
provide a bulky alkyl group (1a and 2a), an aryl group (1b),
The dialkynyl(divinyl)silanes 1a–1d fulfill all of require-
ments to combine 1,2-hydroboration and 1,1-organobor-
ation for the syntheses of spirosilanes of type B.[21] In the
present study, it is shown that different substituents R do
not have an appreciable influence on the course of the reac-
tions, which consist of twofold intermolecular 1,2-hydro-
borations and twofold intramolecular 1,1-vinylborations.
All of the reactions were performed by following the litera-
ture procedure,[7,8,21] and the required products were ob-
tained in reasonable quantity and with sufficient purity of
Ͼ98% (Scheme 2).
The proposed mechanism of the reaction for the synthe-
sis of the spirosilanes given in Scheme 2 has already been
discussed in greater detail,[21] supported by theoretical cal-
Scheme 1. Syntheses of dialkynyl(divinyl)silanes 1a–1d and alkynyl-
(divinyl)silane 2a.
Scheme 2. Syntheses of spirosilanes bearing tBu, 4-Me-C6H4, and 3-thienyl substituents at the 1- and 6-positions.
1
Figure 2. Contour plot of (part of the aliphatic region) the 2D H–13C correlated spectrum of spirosilane 3a [recorded by the gradient-
selected heteronuclear single quantum coherence (gs)HSQC method].[27]
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culations.[25] In a first step, silanes bearing vinyl and alkynyl
groups at the Si atom react with 9-borabicyclo[3.3.1]nonane
(9-BBN) selectively by 1,2-hydroboration of the C=C bond,
and the boron atom preferably becomes linked to the ter-
minal carbon atom of the vinyl group (intermediate C,
Scheme 2). This is a unique property of 9-BBN, which pre-
fers the terminal C=C bond over the CϵC bond, if we com-
pare it with other dialkylboranes.[26] The first intermediate
C (not observed) from twofold 1,2-hydroborations pos-
sesses a suitable geometry for intramolecular 1,1-vinylbor-
ation. In the next step, an interaction between the electron-
deficient boron atoms and the CϵC units (Si–C activation
indicated by dashed lines) causes cleavage of the Si–Cϵ
bonds and the formation of a zwitterionic alkynylborate-
like intermediate D (not detected). Finally 1,1-vinylboration
leads to the spirosilane by twofold ring closure.[21] Usually,
the intermolecular 1,1-organoboration of alkynylsilanes
with trialkylboranes (BR3) requires harsh conditions and
long reaction times.[14] By contrast, the intramolecular 1,1-
organoboration proceeds quickly and more smoothly, as
studied for vinylsilanes.[7,8,21] The results of the present
study lead us to conclude that the consecutive 1,2-hydro-
boration and 1,1-vinylboration reactions proceed smoothly
and selectively independent of the R group. All of the spiro-
silanes bearing boryl groups at the 2- and 7-positions were
colorless oily or crystalline materials, and their structures
could be deduced from a consistent set of solution-state
NMR spectroscopic data (Figure 2 and Table 1) and also
by X-ray diffraction (Figures 3 and 4).
Figure 3. Molecular structure of spirosilane 3a. Drawn at 40%
probability level; hydrogen atoms are omitted for clarity; see
Table 2 for selected bond lengths and angles.
Figure 4. Molecular structure of spirosilane 3c. Drawn at 40%
probability level; hydrogen atoms are omitted for clarity; see
Table 2 for selected bond lengths and angles.
Table 1. 13C, 11B, and 29Si NMR spectroscopic data[a] of spirosilane
derivatives 3–5.
For 1d, derived from propargylamine, the reaction with
2 equiv. of 9-BBN proceeded in the same way as those of
1a–1c. The major difference in the final polycyclic product
4d arises from coordinative N–B bonding (Scheme 3), as
deduced from the 11B and 29Si NMR spectroscopic data
(see below). Compound 4d is a white, amorphous powder.
δ13C
(C-1,6)
δ13C
(C-2,7)
δ13C
(C-3,8)
δ13C
(C-4,9)
δ11B δ29Si
3a[b] 151.0
(59.9)
167.2 br. 34.1
172.4 br. 35.3
173.2 br. 34.9
194.6 br. 35.9
10.9
(51.6)
85.1 32.8
3b[c] 149.8
(59.0)
9.3 (51.8) 84.4 36.3
8.9 (51.8) 85.4 37.0
3c[d] 143.0
(59.3)
4d[e] 132.4
(64.8)
11.3
(53.1)
8.0 (50.5)
6.9
–
17.8
29.8
30.2
5b[f] 142.2
(60.8)
148.2
(11.4)
148.3
(11.0)
31.1
31.1
5c[g] 136.3
(61.1)
7.5 (52.3)
–
Scheme 3. Synthesis of the polycyclic spirosilane derivative 4d.
[a] NMR spectroscopic data measured in C6D6 at 23Ϯ1 °C, the
values in brackets represent coupling constants 1J
and
29Si,13
C
The spirosilane derivatives discussed so far contain boryl
groups. As they are active functional groups, they invite fur-
2J
[Hz], br. stands for a broad 13C signal owing to partially
29Si,13
C
relaxed 13C–11B spin–spin coupling.[28] [b] Measured in CDCl3,
other 13C NMR spectroscopic data: δ = 33.7 (Me), 35.3 (tBu), 35.1, ther chemistry such as oxidation, hydrolysis, or Suzuki-type
35.2, 32.2 (br), 23.4 (9-BBN) ppm. [c] Other 13C NMR spectro-
coupling reactions.[29] Here, we describe the protodeboryl-
ation of 3b and 3c as representative examples. The treat-
ment of 3b and 3c with an excess of glacial acetic acid by
the literature procedure[30] afforded the desired protodebor-
ylated spirosilanes (Scheme 4). Compounds 5b and 5c were
obtained as crystalline materials, and the structure of 5b
(Figure 5) was determined by X-ray diffraction (see below).
The same reaction to remove the boryl substituents failed
for 3a, presumably owing to the bulk of the tBu group.
29Si,13
scopic data: δ = 34.4, 34.9, 32.6 (br), 23.8 (9-BBN), 140.8 (J
= 6.1 Hz), 129.2, 128.3, 135.8, 21.1 (4-Me-C6H4) ppm. [d] OtheCr
13C NMR spectroscopic data: δ = 34.3, 34.7, 32.6 (br), 23.7 (9-
29Si,13
BBN), 144.4 (J
C= 6.9 Hz), 128.0, 125.7, 120.3 (3-thienyl) ppm.
[e] Other 13C NMR spectroscopic data: δ = 69.9 (J
C = 11.0 Hz,
29 13
NCH2), 48.7 (Me), 48.6 (Me), 34.2, 34.1, 30.6, 30.5,S2i,4.3, 24.0, 22.4
(br), 22.1 (br., 9-BBN) ppm. [f] Other 13C NMR spectroscopic data:
29Si,13
δ = 21.1, 137.4 (J
= 5.3 Hz), 129.6, 126.9, 136.2 (Me, i-, o-,
C
m-, p-4-Me-C6H4) ppm. [g] Other 13C NMR spectroscopic data: δ
= 141.4 (J = 5.4 Hz), 126.1, 125.7, 120.7 (3-thienyl) ppm.
29Si,13
C
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synthetic potential. Thus, another equivalent of 9-BBN can
still be reacted to afford 1-silacyclopent-2-ene derivative 7a
(Scheme 5, b), which now contains Si–Cl and C–B function-
alities. In a first attempt to make use of these functions, the
nonagostic complex 7a was treated with N-(trimethylsilyl)-
pyrazole at ambient temperature (Scheme 5, c). The reac-
tion proceeded by elimination of Me3SiCl, and new Si–N
and B–N bonds were formed to give the spirosilane 8a in
high purity (Ͼ99%). The structure of 8a in solution follows
from the NMR spectroscopic data (1H, 13C, 15N, 11B, and
29Si) and was confirmed by single-crystal X-ray diffraction
(see below).
Scheme 4. Protodeborylation of the spirosilanes 3b and 3c with an
excess of acetic acid.
NMR spectroscopy and DFT Calculations
All of the NMR spectroscopic data (Table 1 and
Exp. Section) strongly support the proposed solution-state
structures, including the persistence of the axial chirality of
the 5-silaspiro[4.4]nona-1,6-dienes. The latter is shown by
the splitting of the relevant 1H and 13C NMR signals
(shown for some examples in Figure 2). Other convincing
arguments for the structural assignments such as the 11B,
13C, and 29Si chemical shifts and spin–spin coupling con-
stants, in particular nJ
29Si,13
C, have been discussed previously
for related derivatives.[21] As the X-ray diffraction studies
indicated negligible intermolecular interactions, the com-
parison between calculated gas-phase structures and direct
structural evidence from the solid state is meaningful.
Therefore, the geometries of the gas-phase structures of 3,
4, 5, and 8a were optimized at the B3LYP/6-311+(G/d,p)
level of theory,[31] and satisfactory agreement was observed.
This prompted us to calculate some chemical shifts[32] and
coupling constants,[33] in particular δ11B, δ15N, and δ29Si as
Figure 5. Molecular structure of spirosilane 5b, an example of a
protodeborylated spirosilane. Drawn at 50% probability level;
hydrogen atoms are omitted for clarity. See Table 2 for selected
bond lengths and angles.
A New Spirosilane
well as nJ
C at the same level of theory. Again the agree-
29Si,13
The 1,2-hydroboration and 1,1-carboboration of 2a leads
to the 1-silacylopent-2-ene derivative 6a with Si–vinyl and
Si–Cl functions (Scheme 5, a), both of which enhance its
ment with the experimental data was encouraging. This is
well known for δ11B[34] and appears to be helpful with
δ29Si[35] [in the present case, the increased 29Si nuclear
shielding in 4d (δ29Si = 17.8 ppm) is correctly predicted] and
it serves to assign the different 15N NMR signals of 8a to
the Si–N (δ15N
= =
–165.2 ppm) and B–N (δ15N
–117.7 ppm) bonds. As shown recently for other 1-silacy-
clopent-2-enes,[8b] the sign and magnitude of calculated
nJ
C coupling constants correspond closely to the exper-
29Si,13
imental data.[35]
X-ray Structural Analyses of 3a, 3c, 5b, and 8a
The molecular structures of silanes 3a, 3c, 5b, and 8a are
represented in Figures 3–6. The structural data pertinent to
3a, 3c, and 5b compare well with the reported structures,
and there is a negligible influence of the R group. All bond
lengths and angles (Table 2) are within the expected ran-
ges.[21] In 3a, the carbon atoms around the silicon atom are
arranged in a distorted tetrahedral fashion with the ex-
pected small endocyclic C1–Si1–C4 angle of 92.7°. The ge-
ometry around the boron atoms is close to trigonal planar.
The distortion seems to be caused by the proximity to the
Scheme 5. Stepwise synthesis of spirosilane 8a.
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Table 2. Selected bond lengths [pm] and angles [°] of boryl-substituted spirosilanes 3a and 3c and protodeborylated spirosilane 5b.
3a (R = tBu)
3c (R = 3-thienyl)
5b (R = 4-Me-C6H4)
C1–Si1
C4–Si1
C1–C2
C2–C3
C3–C4
C3–B2
C4–C5
C2–C1–Si1
C3–C2–C1
C4–C3–C2
C4–C3–B2
C3–C4–Si1
C5–C4–Si1
C1–Si1–C4
C1–Si1–C9
C1–Si1–C12
C4–Si1–C9
187.5(15)
187.3(13)
154.0(2)
153.8(19)
135.2(2)
156.5(2)
153.6(18)
105.5(9)
110.8(11)
116.5(12)
129.5(12)
110.6(10)
126.1(10)
92.7(6)
C4–Si1
C1–Si1
C3–C4
C2–C3
C1–C2
C2–B1
C1–C5
C3–C4–Si1
C2–C3–C4
C1–C2–C3
C1–C2–B1
C2–C1–Si1
C5–C1–Si1
C1–Si1–C4
C1–Si1–C1A
C4–Si1–C1A
C1–Si1–C4A
187.4(3)
186.8(2)
154.1(3)
152.6(3)
135.7(3)
156.4(4)
146.3(3)
106.58(17)
112.0(2)
C1–Si1
C4–Si1
C1–C2
C2–C3
C3–C4
–
C4–C5
C2–C1–Si1
C3–C2–C1
C4–C3–C2
–
C3–C4–Si1
C5–C4–Si1
C1–Si1–C4
C1–Si1–C1
C4–Si1–C1
C1–Si1–C4
187.8(3)
187.6(3)
154.9(4)
150.8(4)
134.6(4)
–
148.3(4)
105.4(2)
109.9(2)
120.1(3)
–
108.4(2)
128.5(2)
119.9 (13)
118.7(2)
93.6(13)
119.9(13)
116.5(2)
124.7(2)
111.30(18)
126.81(18)
119.82(11)
118.30(16)
93.16(11)
93.16(11)
115.0(7)
119.7(6)
119.7(6)
tBu group. Both five-membered rings of the molecule are
The molecular structure of 8a suffers from a little disor-
considerably twisted with Si1–C9–C10–C11 and Si1–C1– der, but it can be solved unambiguously (Figure 6). The
C2–C3 torsion angles of –14.1 and –19.2°, respectively. The data obtained for the five-membered 1-silacyclopent-2-ene
silicon and boron atoms are trans to each other and are ring are within the expected range.[5,8,21] The silicon atom
almost coplanar at the C=C bonds (torsion angles: B1– has two different ring structures at either side, and its sur-
C11–C12–Si1 174.7°, B2–C3–C4–Si1 175.2°). The same fea- roundings correspond to a distorted tetrahedron, as ex-
tures were observed in the molecular structure of 3c.
pected (bond angles: N1–Si1–C9 104.4°, C1–Si1–C4 95.0°,
C1–Si1–N1 108.3°, and C4–Si1–C9 123.8°). The molecule
bears two boron centers, one is tricoordinate, and the other
is tetracoordinate. All of the carbon atoms attached to the
B2 center adopt trigonal planar surroundings with bond
angles of C26–B2–C3 124.2°, C22–B2–C3 123.3°, and C22–
B2–C26 110.5°. The four-coordinate boron atom adopts a
tetrahedral geometry with bond angles of N2–B1–C10
103.0°, C18–B1–C14 104.8°, N2–B1–C18 110.1°, and C10–
B1–C14 113.7°.
All positions of the atoms of the five-membered rings
deviate slightly from a plane with torsion angles of Si1–C1–
C2–C3 15.8° and Si–C4–C3–C2 1.9°. The six-membered
ring containing the silicon atom is markedly nonplanar as
far as the Si1–C9–C10–B1 unit is concerned (torsion angle
–47.9°). By contrast, the atoms in the fragment Si1–N1–
N2–B1 almost form a plane (torsion angle 7.4°).
Figure 6. Molecular structure of spirosilane derivative 8a. Drawn
at 40% probability level; hydrogen atoms are omitted for clarity.
Selected bond lengths [pm] and angles [°]: C1–C2 154.4(2), C1–Si1
185.4(19), C2–C3 153.1(3), C3–C4 135.6(2), C3–B2 157.2(3), C4–
C5 152.8(2), C4–Si1 186.7(17), C9–C10 155.2(2), C9–Si1 185.9(19),
C10–B1 164.2(3), N1–Si1 181.7(14), N2–B1 162.7(2); C4–C3–C2
117.08(15), C4–C3–B2 130.9(16), C3–C4–Si1 108.79(13), N1–Si1–
C1 108.30(8), N1–Si1–C9 104.38(7), C1–Si1–C9 119.49(9), N1–
Si1–C4 104.50(7), C1–Si1–C4 94.99(8), C9–Si1–C4 123.8(8).
Conclusions
Axially chiral 5-silaspiro[4.4]nona-1,6-dienes bearing
boryl groups at the 2- and 7-positions and various R sub-
The molecular structure of 5b is shown in Figure 5, it stituents at the 1- and 6-positions are accessible in essen-
has a distorted tetrahedral geometry around the silicon tially quantitative yield by combining consecutive intermo-
atom with bond angles of 93.6, 119.9, 118.7, and 113.3°. lecular 1,2-hydroboration and intramolecular 1,1-carbo-
The five-membered rings of the spiro structure are slightly boration reactions; the results were fairly independent of
distorted with respect to a plane (torsion angles: Si1–C1– the R group. In the absence of extreme steric hindrance,
C2–C3 16.5° and Si1–C4–C3–C2 –0.7°). The p-tolyl moie- protodeborylation with acetic acid can be achieved by fol-
ties are twisted by 31° with respect to the five-membered lowing a simple protocol. The products, including a new
rings of the spiro structure. All other bond lengths and spirosilane, were characterized in the solid state by X-ray
angles are within the expected ranges.
diffraction and in solution by multinuclear magnetic reso-
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29Si,13
C
29Si,13
= 20.2 Hz, ϵC), 132.9 (J
C
= 105.5 Hz, SiCϵ), 109.0 (J
nance techniques; in addition, the gas-phase structures were
optimized by DFT methods, which also served for the cal-
culation of NMR spectroscopic parameters.
= 82.1 Hz, SiC=), 136.4 (=C), 119.9, 132.4, 129.3, 139.4, 21.3 (4-
Me-C6H4) ppm. 29Si NMR: δ = –52.8 ppm.
1c: Yield 98%. 1H NMR (400 MHz, C6D6): δ = 6.1 (m, 2 H,
SiCH=), 6.3 (m, 4 H, =CH2), 6.6, 6.9, 7.1 (m, m, m, 6 H, 3-thienyl)
ppm. 13C NMR: δ = 87.5 (J
= 104.9 Hz, SiCϵ), 103.7
29Si,13
C
29Si,13
C
29Si,13
(J
= 20.2 Hz, ϵC), 132.5 (J
= 82.3 Hz, SiC=), 136.6
C
Experimental Section
(=C), 131.1, 130.1, 125.5, 122.0 (3-thienyl) ppm. 29Si NMR: δ =
General: All preparative work and the handling of air- and moist-
ure-sensitive chemicals were performed under a dry argon atmo-
sphere. Dialkyn-1-ylsilanes were prepared and purified by following
the reported procedures[13,14] and fully characterized by multinu-
clear NMR spectroscopy. Other commercial chemicals such as
dichloro(divinyl)silane, n-butyllithium (1.6 m in hexane), propar-
gylamine, pyrazole, 9-borabicyclo[3.3.1]nonane, and glacial acetic
acid were used as received without further purification. The NMR
spectra were recorded at 23Ϯ1 °C with Varian Inova 300 and 400
spectrometers and a Bruker AMX 500 spectrometer (15N NMR),
all equipped with multinuclear units; C6D6 or CDCl3 solutions (ca.
10–15% v/v) in 5 mm o.d. tubes were used. Chemical shifts (in
ppm) are given relative to SiMe4 [TMS; δ1H (C6D5H) = 7.15 ppm,
δ 13C (C6D6) = 128.0 ppm, δ1H (CHCl3) = 7.23 ppm, δ 13C (CDCl3)
–52.8 ppm.
1
1d: Yield 97%. H NMR (400 MHz, CDCl3): δ = 2.14, 3.17 (s, s,
16 H, CH2NMe2), 5.94–6.00 (m, 6 H, Si–vinyl) ppm. 13C NMR: δ
29Si,13
= 82.8 (J
C
29Si,13
C
= 19.3 Hz, ϵC),
= 104.2 Hz, SiCϵ), 104.0 (J
C = 81.8 Hz, SiC=), 135.6 (=C), 43.7 (Me), 48.5 (CH2)
29Si,13
132.0 (J
ppm. 29Si NMR: δ = –54.3 ppm.
2a: Yield 30%; b.p. 32–35 °C/0.1 Torr. 1H NMR (400 MHz, C6D6):
δ = 1.0 (s, 9 H, tBu), 6.0 (dd, J1H,1H = 6.5, 11.4 Hz, 2 H, SiCH=),
6.1 (m, 4 H, =CH2) ppm. 13C NMR: δ = 75.9 (J
= 114.8 Hz,
= 87.2 Hz,
C
29Si,13
C
29Si,13
C
29Si,13
= 21.4 Hz, ϵC), 133.0 (J
SiCϵ), 120.7 (J
SiC=), 136.7 (=C), 28.4, 30.5 (tBu) ppm. 29Si NMR: δ = –23.8
ppm.
Hydroboration of Silanes 1a–1d: A pure sample of silane 1a (0.73 g,
2.99 mmol) was dissolved in THF, and a twofold excess of 9-BBN
(0.75 g, 5.98 mmol) was added in one portion. The reaction mixture
was stirred at 23 °C for 2 h. After the reaction was complete, the
solvent and other readily volatile materials were removed. The oily
residue was dissolved in pentane (3 mL) and kept at r.t. After 3–
4 d, colorless crystals were separated from the mother liquor. A few
crystals were dissolved in C6D6, and their NMR spectroscopic data
were collected; a crystal of suitable dimensions was studied by X-
ray diffraction. The other spirosilanes were prepared in the same
way. Colorless crystals of spirosilane 3c were grown in an analogous
way. The hydroboration of silane 1d, followed by intramolecular
donor–acceptor interactions, afforded 4d. The solid powder was
dissolved in CH2Cl2, and 4d was extracted in its pure form with a
Soxhlet extractor. Our attempts to grow crystals were not success-
ful.
=
77.0 ppm,
δ
29Si
=
0 ppm for SiMe4 with Ξ(29Si)
=
=
19.867187 MHz], MeNO2 (neat) for 15N [Ξ(15N)
10.136767 MHz], and BF3–OEt2 for 11B [δ 11B = 0 ppm with Ξ(11B)
= 32.083971 MHz]. The 29Si NMR spectra were recorded by using
the refocused insensitive nuclei enhanced by polarization transfer
(INEPT) pulse sequence with 1H decoupling[21] based on nJ
29Si,1Hvinyl
≈ 12–20 Hz (n = 2,3) and 3J29Si,1H(C4) ≈ 25 Hz (after optimization of
the respective refocusing delays). Melting points were determined
by using a Büchi 510 melting point apparatus.
All quantum chemical calculations were performed by using the
Gaussian 09 program package.[36] The optimized geometries at the
B3LYP/6-311+G(d.p) level of theory[31] were found to be minima
by the absence of imaginary frequencies. The NMR parameters
were calculated[32,33] at the same level of theory. The calculated nu-
clear magnetic shielding constants σ11B were converted by
δ11B(calcd.) = σ(11B) – σ(11B, B2H6) with σ(11B, B2H6) = +84.1
[δ11B(B2H6) = 18 and δ11B (BF3–OEt2) = 0] and the calculated
σ(29Si) values were converted to chemical shifts δ29Si by δ29Si
(calcd.) = σ(29Si, TMS) – σ(29Si) with σ(29Si, TMS) = +340.1 and
δ29Si(TMS) = 0.
3a: Yield 96%; m.p. 220–224 °C. 1H NMR (400 MHz): δ = 0.8
(ddd, J1H,1H = 7.5, 9.5 Hz, 2 H, 4-H, 9-H), 1.0 (ddd, J1H,1H = 2.3,
9.4 Hz, 2 H, 4-H, 9-H), 1.0 (s, 18 H, tBu), 1.5, 1.6, 1.9–2.1 (m, m,
m, 28 H, 9-BBN), 2.6 (m, J1H,1H = 2.3, 7.5 Hz, 4 H, 3-H, 8-H) ppm.
1
3b: Yield 89%. H NMR (400 MHz): δ = 1.4, 1.7, 1.7–1.9 (m, m,
m, 28 H, 9-BBN), 1.1, 1.2 (m, m, 4 H, 4-H, 9-H), 2.8, 2.9 (m, m,
4 H, 3-H, 8-H), 2.0, 6.9, 7.1 (s, m, m, 14 H, 4-Me-C6H4) ppm.
Dialkyn-1-yldivinylsilanes 1a–1d and Dialkyn-1-ylvinylsilane 2a: A
suspension of LiCϵCtBu (20 mmol, in pentane) was prepared at
–78 °C. To this suspension at the same temperature, an equimolar
amount of dichlorodivinylsilane was added. The reaction mixture
was stirred for 1 h and then warmed to room temperature. The
solid material (LiCl) was removed by filtration, and all volatiles
were removed under reduced pressure (20 Torr). The remaining oily
residue was identified as a mixture of 1a, 2a, and some amount of
unreacted silane. Pure samples of 1a and 2a were obtained by frac-
tional distillation. The other silanes 1b, 1c, and 1d were prepared
and purified in the same way.
3c: Yield 95%; m.p. 122–124 °C. 1H NMR (400 MHz): δ = 1.0
3
2
(ddd, J1H,1H = 4.9, 9.0 Hz, J1H,1H = 15.5 Hz, 2 H, 5-H), 1.2 (ddd,
3J1H,1H = 3.9, 9.0 Hz, 2J1H,1H = 15.5 Hz, 2 H, 5-H), 2.7 (ddd, 3J1H,1H
= 4.9, 9.0 Hz, 3J1H,1H = 18.2 Hz, 2 H, 4-H), 2.8 (ddd, 3J1 H,1H = 3.9,
9.0 Hz, 3J1H,1H = 18.2 Hz, 4-H), 1.3, 1.7–1.9 (m, m, 28 H, 9-BBN),
6.8, 6.9, 7.0 (m, m, m, 6 H, C4H3S) ppm.
1
4d: Yield 92%. H NMR: δ = 1.1, 1.3, 1.9 (m, m, m, 9-BBN, 4-H),
2.1, 2.2 (s, s, 6 H, NMe2), 2.3 (m, 2 H, 3-H), 3.0 (m, 2 H, NCH2)
ppm.
1
1a: Yield 65%. H NMR (400 MHz, C6D6): δ = 1.0 (s, 18 H, tBu),
Hydroboration of Silanes 2a: Chlorodivinylsilane 2a (1.09 g,
5.48 mmol) was dissolved in THF, and 9-BBN (0.50 g, 4.09 mmol)
was added in one portion. The reaction proceeded at r.t. After 2 h,
all readily volatile materials were removed under vacuum
(10–2 Torr). The remaining oily compound was studied by NMR
spectroscopy and identified as mixture of 6a (major product; ca.
90%) and 7a (minor product; ca. 10%). Then, a further amount of
9-BBN (2 equiv.) was added, and the reaction was performed under
6.0 (dd, J1H,1H = 6.6, 11.3 Hz, 2 H, SiCH=), 6.2 (m, 4 H, =CH2)
ppm. 13C NMR: δ = 76.5 (J
29Si,13
C
29Si,13
106.6 Hz, SiCϵ), 118.5 (J
C
29Si,13
C
= 19.5 Hz, ϵC), 134.1 (J
= 81.6 Hz, SiC=), 135.2 (=C), 28.4,
30.8 (tBu) ppm. 29Si NMR: δ = –53.9 ppm.
1
1b: Yield 96%. H NMR (400 MHz, C6D6): δ = 6.1 (m, J1H,1H
=
9.0 Hz, 1 H, SiCH), 6.4 (m, J1H,1H = 9.4, 8.3 Hz, 2 H, H2C=), 1.9,
6.7, 7.3 (s, m, m, 7 H, 4-Me-C6H4) ppm. 13C NMR: δ = 87.1(J
29Si,13
C
Eur. J. Inorg. Chem. 2014, 3411–3419
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FULL PAPER
identical conditions. The compound was worked-up, and the oily
residue obtained was pure 7a in reasonably good yield and purity
(Ͼ95% by NMR spectroscopy).
4-H), 2.48 (m, 4 H, 3-H), 6.84 (t, J1H,1H = 3.0 Hz, J29Si,1H = 12.7 Hz,
2 H, 2-H), 6.87 (dd, J1H,1H = 2.9, 5.0 Hz, 2 H, 3-thienyl), 6.97 (m,
J1H,1H = 1.0, 2.9 Hz, 2 H, 3-thienyl) 7.08 (dd, J1H,1H = 1.0, 5.0 Hz,
2 H, 3-thienyl) ppm.
1
6a: Yield 97%. H NMR (400 MHz): δ = 1.05 (s, 9 H, tBu), 0.94
(m, 2 H, 5-H), 2.45 (m, 2 H, 4-H), 1.44, 1.57–1.96 (m, 14 H, BBN),
Silane 8a: A Schlenk tube was charged with pure silane 7a (1.32 g,
3.0 mmol) and hexane (10 mL). To this solution, an equimolar
amount of N-trimethylsilylpyrazole was slowly added with constant
stirring. The reaction proceeded at 23 °C and was constantly moni-
tored by 29Si NMR spectroscopy (7a: δ = +40.9 ppmǞ8a: δ =
+32.1 ppm). After 4–5 h, the reaction was complete, and all readily
volatile materials and solvent were removed under vacuum; the so-
lid residue (pure 8a) was dissolved in hot hexane (2 mL). Colorless
crystals were grown after 3 d, yield 70%. 1H NMR (400 MHz,
CDCl3): δ = 0.58 (s, 9 H, tBu), 0.01, 0.40, 0.62, 0.93, 1.16–1.68 (m,
9-BBN, 5-H, CH2CH2), 6.86 (s, 1 H, =CH), 5.95, 7.10, 7.70 (m, m,
5.93 (dd, 1 H, SiCH), 6.06 (dd, 2 H, =CH2) ppm. 13C NMR
29Si,13
(100.5 MHz): δ = 147.8 (J
= 73.4 Hz, C-2), 171.4 (br., C-3),
C
29Si,13
C
29Si,13
C
= 62.0 Hz, C-5), 136.6 (J = 72.2 Hz,
33.1 (C-4), 12.2 (J
SiCH2), 134.9 (H2C=), 28.5 (q), 30.5 (Me, tBu), 35.5, 32.7 (br),
23.7 (9-BBN) ppm. 11B NMR (128.3 MHz): δ = 85.4 ppm. 29Si
NMR (59.6 MHz): δ = 24.6 ppm.
1
7a: Yield 96%. H NMR (400 MHz): δ = 1.21 (s, 9 H, tBu), 1.27,
1.48 (m, m, 2 H, 5-H), 2.49 (m, 2 H, 4-H), 1.61–2.03 (m,
SiCH2CH2, 9-BBN) ppm. 13C NMR (100.5 MHz):
δ
=
29Si,13
147.6 (J
C
= 69.6 Hz, C-2), 171.1 (br., C-3), 33.8 (C-4), 11.3
m, 3 H, pyrazole) ppm. 13C NMR: δ = 147.3 (J
= 67.6 Hz,
29Si,13
C
29Si,13
29Si,13
C = 56.6 Hz,
(J
C = 59.5 Hz, C-5), 20.5 (br., BCH2), 13.4 (J
29Si,13
C
C-1), 174.8 (br., C-2), 33.0 (C-3), 12.1 (J
= 59.9 Hz, C-4), 7.1
SiCH2), 35.5, 32.7, 31.5 (br), 23.67, 23.65 (9-BBN), 33.7 (Me tBu),
35.3 (Cq tBu). 11B NMR (96.2 MHz): δ = 85.4 ppm. 29Si NMR
(59.6 MHz): δ = 40.9 ppm.
29Si,13
(J
C
= 59.7 Hz, SiCH2), 15.3 (br., CH2), 33.4 (Me tBu), 34.8
(Cq, tBu), 139.7, 137.4, 105.5 (pyrazole), 35.2, 35.1, 34.4, 32.2, 32.5
(br), 31.5, 30.9, 24.8, 24.6, 23.3 (2ϫ BBN) ppm. 15N NMR
(50.7 MHz): δ = –165.2 (SiN), –117.7 (BN) ppm. 11B NMR
(96.2 MHz): δ = 85.0, –2.8 ppm. 29Si NMR (59.6 MHz): δ = 32.1
ppm.
Protodeborylation of 3b and 3c: The protodeborylation and purifi-
cation of 3b and 3c were performed by following the literature pro-
cedure.[30] Compound 5b was dissolved in pentane (3ϫ 5 mL), and
the solvent and all other volatiles were removed. The suspension
obtained was dissolved in hot hexane and kept at 23 °C. Crystals
of appropriate dimensions were grown, and their X-ray diffraction
and NMR spectroscopic data were collected. Exactly the same pro-
cedure was practiced for spirosilane 5c, except that the crystals were
obtained from a solution in THF.
Crystal Structure Determinations of Spirosilanes 3a, 3b, 5b, and 8a:
Details pertinent to the crystal structure determinations are listed
in Table 3. Crystals of appropriate size were selected (in perfluori-
nated oil[37] at room temperature), and the data collections were
performed at 133 K by using a STOE IPDS II system equipped
with an Oxford Cryostream low-temperature unit. The structure
solutions and refinements were accomplished by using SIR97,[38]
SHELXL-97,[39] and WinGX.[40] CCDC-992918 (for 3a), -992919
(for 3c), -992921 (for 5b), and -992920 (for 8a) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
5b: Yield 82%. 1H NMR (300 MHz): δ = 0.7, 0.9 (ddd, ddd, 2J1H,1H
3
= 15.6 Hz, J1H,1H = 4.8, 9.2 Hz, 4 H, 4-H, 9-H), 2.2–2.4 (m, 4 H,
3
3-H, 8-H), 1.9, 6.7, 7.2 (s, m, m, 14 H, 4-Me-C6H4), 6.8 (t, J1H,1H
= 3.0 Hz, 2 H, 2-H, 7-H) ppm.
1
5c: Yield 87%. H NMR (400 MHz): δ = 0.82 (ddd, J1H,1H = 4.9,
8.9, 15.8 Hz, 2 H, 4-H), 1.05 (ddd, J1H,1H = 4.9, 8.9, 15.8 Hz, 2 H, Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Table 3. Data pertinent to the crystal structure determinations of 3b, 3c, 5b, and 8a.
3a (R = tBu)
3c (R = 3-thienyl)
5b (R = 4-Me-C6H4) 8a (R = tBu)
Formula
Crystal shape
Dimensions [mm]
Crystal system
Space group
C32H54B2Si
prism
0.62ϫ0.27ϫ0.18
triclinic
P1
C32H42B2S2Si
prism
0.56ϫ0.38ϫ0.32
monoclinic
P2/c
C22H24Si
platelike
0.34ϫ0.32ϫ0.09
monoclinic
C2/c
C29H48B2N2Si
prism
0.62ϫ0.50ϫ0.34
triclinic
P1
a [pm]
b [pm]
c [pm]
α [°]
β [°]
γ [°]
Z
1075.8(8)
1138.1(8)
1242.5(9)
77.7(6)
78.7(6)
83.7(6)
670.0(5)
687.7(5)
3098.9(3)
90
94.0(0)
90
2253.1(9)
558.0(3)
1652.4(8)
90
124.9(6)
90
783.3(7)
1324.5(13)
1490.0(14)
109.8(7)
102.3(7)
100.1(7)
2
2
2
4
Absorption coefficient μ [mm–1]
Diffractometer
Measuring range [°]
Reflections collected
Independent reflections [IϾ2σ(I)]
Absorption correction
Refined parameters
wR2/R1 [F2 Ͼ2σ(F2)]
Max./min. residual electron density
[epm–3 ϫ10–6]
0.10
0.25
0.14
0.11
STOE IPDS II, Mo-Kα, λ = 71.069 pm, graphite monochromator
1.7–25.8
19253
4723
none
316
0.110/0.057
0.52/–0.21
1.3–25.7
12539
2377
none
168
0.139/0.057
0.44/–0.32
2.2–25.65
10830
1328
none
106
0.161/0.056
0.45/–0.26
1.52–25.71
17090
3611
none
341
0.101/0.044
0.49/–0.24
Eur. J. Inorg. Chem. 2014, 3411–3419
3417
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FULL PAPER
West, Angew. Chem. Int. Ed. 2006, 45, 2578–2581; Angew.
Chem. 2006, 118, 2640.
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