Platinum-Catalyzed Reactions of 2,3-Bis(diisopropylsilyl)thiophene with Alkynes

Abstract

The reactions of 2,3-bis(diisopropylsilyl)thiophene (1) with diphenylacetylene, phenylacetylene, trimethylsilylacetylene, and mesitylacetylene have been reported. The reactions of 1 with diphenylacetylene and phenylacetylene in the presence of a catalytic amount of tetrakis(triphenylphosphine)platinum(0) at 80 °C gave [1,4]disilino[2,3-b]thiophene derivatives. With trimethylsilylacetylene, 1 afforded two types of products arising from sp-hybridized C–H bond activation of the acetylene, together with [1,3]disilolo[4,5-b]thiophene derivatives. A similar treatment of 1 with mesitylacetylene produced two regioisomers of products arising from the C–H bond activation of mesitylacetylene. Theoretical calculations for the intramolecular reactions of 10a and 10b are also discussed.

Full text

Platinum-Catalyzed Reactions of 2,3-Bis(diisopropylsilyl)thiophene
with Alkynes
Akinobu Naka,*
,†
Takashi Mihara,
†
Hisayoshi Kobayashi,*
,‡
and Mitsuo Ishikawa
§
†
Department of Life Science, Kurashiki University of Science and the Arts, Nishinoura, Tsurajima-cho, Kurashiki, Okayama 712-8505,
Japan
‡
Professor Emeritus Kyoto Institute of Technology, Matsugasaki, Kyoto 606-8585, Japan
§
Professor Emeritus Hiroshima University, Higashi-Hiroshima 739-8527, Japan
*
SSupporting Information
ABSTRACT: The reactions of 2,3-bis(diisopropylsilyl)-
thiophene (1) with diphenylacetylene, phenylacetylene,
trimethylsilylacetylene, and mesitylacetylene have been
reported. The reactions of 1with diphenylacetylene and
phenylacetylene in the presence of a catalytic amount of
tetrakis(triphenylphosphine)platinum(0) at 80 °C gave [1,4]-
disilino[2,3-b]thiophene derivatives. With trimethylsilylacety-
lene, 1afforded two types of products arising from sp-
hybridized C−H bond activation of the acetylene, together
with [1,3]disilolo[4,5-b]thiophene derivatives. A similar treat-
ment of 1with mesitylacetylene produced two regioisomers of products arising from the C−H bond activation of
mesitylacetylene. Theoretical calculations for the intramolecular reactions of 10a and 10b are also discussed.
1. INTRODUCTION
It is well-known that reactions of organosilanes with unsaturated
compounds in the presence of a catalytic amount of transition-
metal complexes can be employed for the synthesis of various
organosilicon compounds.
1
In these reactions, the silyl-
transition-metal complexes would be formed as reactive species.
For example, the benzodisilaplatinacyclopentene derivatives are
produced by reactions of 1,2-bis(hydrosilyl)benzenes with
platinum complexes, and their chemical properties have been
widely examined by Tanaka et al., Nagashima et al., and other
chemists.
2−8
We have reported that the platinum-catalyzed reactions of
tetraethyl-substituted benzodisilacyclobutene with alkynes such
as diphenylacetylene, 3-hexyne, and phenylacetylene readily
produce the respective 1:1 adducts, benzodisilacyclohexadiene
derivatives, in high yield.
9−11
On the other hand, platinum-
catalyzed reactions of tetraisopropyl-substituted benzodisilacy-
clobutene with the same alkynes afford two types of products,
benzodisilacyclohexadienes and benzodisilacyclopentenes.
12,13
Recently, we have demonstrated that the platinum-catalyzed
reactions of 2,3-bis(diethylsilyl)thiophene with alkynes such as
diphenylacetylene, 3-hexyne, and phenylacetylene afford the
respective [1,4]disilino[2,3-b]thiophenes.
14
In these reactions,
[1,2,5]platinadisilolo[3,4-b]thiophene derivatives would be
formed as the reactive intermediates.
It is of considerable interest to us to investigate the chemical
behavior of 2,3-bis(silyl)thiophene with bulky substituents on
the silicon atoms toward alkynes in the presence of a platinum
catalyst. In this article, we report the platinum-catalyzed reactions
of 2,3-bis(diisopropylsilyl)thiophene with mono- and disub-
stituted alkynes.
2. RESULTS AND DISCUSSION
The starting compound, 2,3-bis(diisopropylsilyl)thiophene (1),
was prepared by the reaction of 2-bromo-3-iodothiophene with
magnesium and chlorodiisopropylsilane in the presence of a
catalytic amount of copper(I) cyanide in tetrahydrofuran (THF)
(Scheme 1).
15
We first examined the reactions of 1with diphenylacetylene.
Treatment of compound 1with diphenylacetylene in the
presence of Pt(PPh3)4in refluxing benzene for 96 h gave
1,1,4,4-tetraisopropyl-2,3-diphenyl-1,4-dihydro-[1,4]disilino-
[2,3-b]thiophene (2) in 80% yield (Scheme 2). The structure of
2was verified by spectroscopic analysis. The mass spectrum for 2
shows parent ions at m/z488, corresponding to the calculated
molecular weight of C30H40Si2S. The 1H NMR spectrum of 2
Received: October 24, 2017
Accepted: November 21, 2017
Published: November 30, 2017
Scheme 1. Synthesis of Compound 1
Article
Cite This: ACS Omega 2017, 2, 8517−8525
© 2017 American Chemical Society 8517 DOI: 10.1021/acsomega.7b01628
ACS Omega 2017, 2, 8517−8525
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shows septet signals at 1.33 and 1.34 ppm, attributable to the
methine protons in the isopropyl groups at silicon; four doublet
signals at 0.80, 0.81, 1.04, and 1.09 ppm, attributable to the
methyl protons of the isopropyl groups; two doublet signals at
7.39 and 7.76 ppm, attributable to the thienylene protons; and
signals attributed to the phenyl protons. The 29Si NMR spectrum
for 2shows signals at −10.6 and −9.2 ppm.
On the basis of the results obtained from the platinum-
catalyzed dehydrogenative double silylation
2−6,14
of various
unsaturated compounds with bis(hydrosilane)s, the formation of
adducts 2obtained from the platinum-catalyzed reaction of 1
with diphenylacetylene may be explained as follows: (1)
oxidative addition of the platinum species to one of the Si−H
bonds in 1; (2) dehydrogenation to give the bis(silyl)platinum
complex (3); (3) insertion of a triple bond of alkynes into a
platinum−silicon bond to produce the platinum complex (4);
(4) reductive elimination of 2from the Pt complex (4)(Scheme
3).
Unfortunately, compound 1did not react with phenyl-
trimethylsilylacetylene and bis(trimethylsilyl)acetylene. The
starting compound 1was recovered quantitatively.
Next, we investigated the platinum-catalyzed reaction of 1with
monosubstituted alkynes under the same conditions as described
above. Treatment of 1with phenylacetylene at 80 °C indicated
that 1:1 cyclic adducts as a mixture of two regioisomers, namely,
1,1,4,4-tetraisoproyl-3-phenyl-1,4-dihydro-[1,4]disilino[2,3-b]-
thiophene (5a) and 1,1,4,4-tetraisopropyl-2-phenyl-1,4-dihydro-
[1,4]disilino[2,3-b]thiophene (5b), were produced in a ratio of
3:1 in 60% yield, along with unreacted starting compound 1
(40%) (Scheme 4). All attempts to separate 5a and 5b were
unsuccessful, but their structures were verified by spectroscopic
analysis of the mixture.
The regioselective formation of 5a and 5b in the platinum-
catalyzed reaction of 1with monosubstituted alkynes can be best
explained by a series of reactions similar to the reaction shown in
Scheme 3. Namely, the regioselective addition of a Pt−Si bond in
the intermediate similar to 3to the carbon−carbon triple bond of
monosubstituted acetylene affords predominantly 1,1,5,5-
tetraisopropyl-3-phenyl-1,5-dihydro-[1,2,5]platinadisilepino-
[3,4-b]thiophene as the intermediate. It has been reported that
the introduction of electron-withdrawing substituents on the
silicon atom in the silyl−platinum complexes enhances the Pt−Si
bond.
14,16,17
In the present reactions, the Pt−Si bond of the Pt−
Si−C−C moiety is probably weaker than that of the Pt−Si−C−S
moiety (sulfur has higher electronegativity than carbon) and the
former migrates to the less hindered carbon atom in the
coordinated monosubstituted alkyne to produce insertion
product 5a.
When a mixture of 1and trimethylsilylacetylene in the
presence of Pt(PPh3)4catalyst was heated to reflux in benzene for
20 h, four products were obtained. We separated these products
Scheme 2. Reactions of 1 with Diphenylacetylene
Scheme 3. Proposed Mechanism for the Production of
Compound 2
Scheme 4. Reactions of 1 with Phenylacetylene and Trimethylsilylacetylene
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from the reaction mixture by column chromatography and
identified them as (E)- and (Z)-1,1,3,3-tetraisopropyl-2-
((trimethylsilyl)methylene)-2,3-dihydro-1H-[1,3]disilolo[4,5-
b]thiophene (6a,b), (2-((diisopropyl)silyl)thiophen-3-yl)-
diisopropyl((trimethylsilyl)ethynyl)silane (7), and (3-
((diisopropyl)silyl)thiophen-2-yl)diisopropyl((trimethylsilyl)-
ethynyl)silane (8) by mass spectrometry (MS) and 1H, 13C, and
29Si NMR spectroscopy (Scheme 4). Unfortunately, all attempts
Scheme 5. Reaction Mechanism for the Production of 7 and 8
Scheme 6. Production of 6a and 6b from 7 and 8
Scheme 7. Reaction Mechanism of 6a and 6b from 7 and 8
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to separate 6a and 6b were unsuccessful. The ratio of 6a and 6b
was determined to be 1.6:1 by 1H NMR spectrometric analysis.
Compounds 7and 8were isolated by column chromatography.
The 1H NMR spectrum of 7shows a singlet signal at 0.22 ppm
attributed to trimethylsilyl protons and a triplet signal at 4.28
ppm attributed to a proton on the silicon atom along with
isopropyl and thienyl protons. The 13C NMR spectrum of 7
reveals a resonance at −0.16 ppm, attributed to trimethylsilyl
carbons, and two resonances at 108.70 and 118.17 ppm,
attributed to sp-hybridized carbons as well as isopropyl and
thienyl carbons. The 1H NMR spectrum of 8shows a singlet
signal at 0.21 ppm, attributed to trimethylsilyl protons, and a
double of triplet signal at 4.46 ppm (4J= 3.6 Hz, 5J= 0.8 Hz),
attributed to an Si−H proton along with isopropyl and thienyl
protons. The 13C NMR spectrum of 8reveals a resonance at
−0.10 ppm, attributed to trimethylsilyl carbons, and two
resonances at 109.90 and 119.38 ppm, attributed to the sp-
hybridized carbons as well as isopropyl and thienyl carbons.
Scheme 5 illustrates a possible mechanistic interpretation of
the observed reaction course for products 7and 8. The formation
of 7and 8can be understood in terms of insertion of the Pt atom
into the sp-hybridized C−H bond of the acetylene leading to 9,
followed by the reductive elimination of the C−Si bond to give
complexes 10a and 10b.
To confirm whether or not compounds 6a and 6b were
produced from compounds 7and 8by intramolecular hydro-
silation, we carried out reactions of 7and 8with a catalytic
amount of the platinum complex. Thus, the reaction of 7with 6
mol % of tetrakis(triphenylphosphine)platinum(0) at 80 °C for
130 h produced 6a and 6b in the ratio of 1.2:1 in 47% combined
yield, in addition to the starting compound 7and its isomer 8in
the ratio of 3:1 (Scheme 6). The presence of 8in this reaction
obviously indicates the production of intermediates 11a and 11b
(Scheme 7). A similar reaction of 8in the presence of the
platinum catalyst produced 6a and 6b in the ratio of 1.3:1 in 49%
combined yield, along with the starting compound 8and its
isomer 7in the ratio of 5:1. These reactions indicate that
compounds 6a and 6b must come from the intramolecular
hydrosilation of 7and 8.
Next, we investigated the reaction of 1with mesitylacetylene.
Thus, when a mixture of 1and mesitylacetylene in the presence
of the same catalyst was heated to reflux in benzene for 4 h, a
mixture of the regioisomers was obtained in an almost
quantitative yield (Scheme 8). The regioisomers were separated
using column choromatography and assigned as [2-
(diisopropylsilyl)thiophen-3-yl]diisopropyl(mesitylethynyl)-
silane (12) and [3-(diisopropylsilyl)thiophen-2-yl]diisopropyl-
(mesitylethynyl)silane (13) by MS and 1H, 13C, and 29Si NMR
spectroscopy.
2.1. Theoretical Calculations. We carried out density
functional theory (DFT) calculations to investigate the energy
and structural changes from 7and 8to 6a and 6b. Gaussian09
program package
18
was employed together with the Becke-three-
parameter-Lee−Yang−Parr hybrid functional.
19
The Los Alamos
effective core potentials were used for Si, S, and Pt atoms along
with the corresponding valence basis sets.
20
For the H and C
atoms, the Dunning−Huzinaga full double-basis set was
employed.
21
Scheme 8. Reaction of 1 with Mesitylacetylene
Scheme 9. Species Evaluated by DFT Calculation
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The calculated species are Pt complexes, that is, 10a,10b,11a,
and 11b, shown in Scheme 7, and their transition states (TS’s)
are labeled as TS(10−11a) and TS(10−11b). Furthermore, 10a
and 10b mutually convert through TS(10−14a), 14a, TS(14a−
14b), 14b, and TS(14−10b), as shown in Scheme 9, and these
structures were also investigated. In the calculations, TS is
searched first. Then, the intrinsic reaction coordinate (IRC)
analysis is carried out at each TS for both directions, that is, the
reactant and product sides. Because the IRC analysis for the
whole reaction path is very time consuming, it is limited to the
Figure 1. Optimized structures for 10a, TS(10−11a), and 11a (left) and 10b, TS(10−11b), and 11b (right). Total energy of 10a is taken as the zero of
relative energy.
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neighborhood of TS’s, and normal optimization runs are
followed at the end points of IRC analysis. Finally, we confirmed
that the reaction path is seamlessly connected from the reactant,
via TS, to the product.
Figure 2. Optimized structures for TS(10−14a) and 14a (left), TS(10−14b) and 14b (right), and TS(14a−14b) (bottom center). Total energy of 10a
is taken as the zero of relative energy.
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The optimized structures for 10a, TS(10−11a), and 11a are
shown in the left column and 10b, TS(10−11b), and 11b are
shown in the right column of Figure 1.Figure 2 shows the
optimized structures for TS(10−14a) and 14a in the left column
and TS(10−14b) and 14b in the right column. TS(14a−14b)is
a junction between the a- and b-series and shown at the center.
For all of the intermediate species, the optimized structures are
well-described by the line drawing structures shown in Schemes 7
and 9. A noticeable point is that a weak interaction between the
CC group and the Pt atom is suggested in 10a and 10b.
The energy changes for all reaction paths are shown in Figure
3. The total energy of 10a is taken as zero. Among the TS’s,
TS(10−11a)andTS(10−11b) are the highest, and the
conversions from 10a to 11a and 10b to 11b are the rate-
determining step. This means that compounds in the a- and b-
series can mix with each other because the energies for TS(10a−
14a), TS(14a−14b), and TS(10−14b) are lower than those for
TS(10−11a) and TS(10−11b). The conversion from 14a to
14b proceeds by an internal rotation of the Si−C−Pt group. The
energy difference between the corresponding compounds in the
a- and b-series is relatively small (at maximum, 16.3 kJ mol−1
between 10a and 10b). Thus, the energetics for the a- and b-
series reactions resemble each other, and the two sets of reactions
occur in parallel.
3. CONCLUSIONS
We describe here the preparation and platinum-catalyzed
reactions of 2,3-bis(diisopropylsilyl)thiophene. The reactions
of 2,3-bis(diisopropylsilyl)thiophene 1with diphenylacetylene in
the presence of a catalytic amount of Pt(PPh3)4proceeded to
give cyclic products such as 2. A similar treatment of 1with
monosubstituted alkynes bearing less bulky substituents such as
phenylacetylene afforded regioisomers of the cyclic products,
whereas with alkynes bearing bulky substituents, 1gives products
arising from sp-hybridized C−H bond activation of the alkynes.
In the intramolecular reactions of 10a and 10b, the theoretical
calculations indicate that the conversion from 14a to 14b or 14b
to 14a proceeds with the internal rotation of the Si−C−Pt group.
4. EXPERIMENTAL SECTION
4.1. General Procedure. All reactions of 2,3-bis-
(isopropylsilyl)thiophene 1were carried out under an
atmosphere of dry nitrogen. Yields of the products were
determined by analytical gas−liquid chromatography (GLC)
with the use of tridecane or pentadecane as an internal standard
on the basis of the starting compound used. NMR spectra were
recorded on a JMN-ECS400 spectrometer. Low- and high-
resolution mass spectra were recorded on a JEOL model JMS-
700 instrument. Column chromatography was performed using
Wakogel C-300 (WAKO).
4.2. Preparation of 2,3-Bis(diisopropylsilyl)thiophene
1. In a 200 mL three-necked flask fitted with a stirrer, a reflux
condenser, and a dropping funnel were placed 1.75 g (72.0
mmol) of magnesium, 11.2 g (74.3 mmol) of chlorodiisopro-
pylsilane, and 0.411 g (4.59 mol) of copper(I) cyanide in 10 mL
of dry THF. To this mixture was added dropwise a solution of
5.94 g (20.6 mmol) of 2-bromo-3-iodothiophene in 10 mL of dry
THF. The mixture was heated to reflux for 4 h. The resulting
magnesium salts were removed by filtration and washed with
ether. The solvent was evaporated, and the residue was distilled
under reduced pressure to give 2.35 g (37% yield) of 2,3-
bis(diisopropylsilyl)thiophene 1:bp77−80 °C/2 torr; anal.
calcd for C16H32Si2S: C, 61.46; H, 10.32. Found: C, 61.16; H,
10.01. MS m/z312 (M+); 1H NMR δ(CDCl3) 0.96 (d, 6H,
MeCH, J= 7.6 Hz), 1.01 (d, 6H, MeCH, J= 7.6 Hz), 1.06 (d, 6H,
MeCH, J= 7.6 Hz), 1.07 (d, 6H, MeCH, J= 7.6 Hz), 1.15−1.28
(m, 4H, CHMe), 4.24 (t, 1H, HSi, J= 3.6 Hz), 4.36 (t, 1H, HSi, J
= 3.6 Hz), 7.29 (d, 1H, thienyl ring proton, J= 4.4 Hz), 7.67 (d,
1H, thienyl ring proton, J= 4.4 Hz); 13C NMR δ(CDCl3) 12.25,
11.72 (CHMe); 18.79 (2C), 18.84, 18.93 (MeCH); 130.05,
134.29, 142.04, 143.82 (thienyl ring carbons); 29Si NMR
δ(CDCl3)−3.52, −3.09.
4.2.1. Platinum-Catalyzed Reaction of 1with Diphenyla-
cetylene. In a 30 mL two-necked flask fitted with a reflux
condenser were placed 0.310 g (0.991 mmol) of 1, 0.355 g (1.99
mmol) of diphenylacetylene, and 0.0658 g (0.0529 mmol) of
Pt(PPh3)4in 15 mL of dry benzene. The mixture was heated to
reflux for 96 h. The mixture was analyzed by GLC as being 2
(80% yield), along with starting compound 1(20% yield). The
solvent benzene was evaporated, and the residue was chromato-
graphed on a silica gel column using hexane as the eluent: HR-
MS: calcd for C30H40Si2S 488.2389, found: 488.2378. MS m/z
488 (M+); 1H NMR δ(CDCl3) 0.80 (d, 6H, MeCH, J= 7.6 Hz),
0.81 (d, 6H, MeCH, J= 7.6 Hz), 1.04 (d, 6H, MeCH, J= 7.6 Hz),
1.09 (d, 6H, MeCH, J= 7.6 Hz), 1.33 (sep, 2H, CHMe, J= 7.6
Hz), 1.34 (sep, 2H, CHMe, J= 7.6 Hz), 6.85−6.90 (m, 4H,
phenyl ring protons), 6.91−6.96 (m, 2H, phenyl ring protons),
7.04 (dt, 4H, phenyl ring protons, J= 7.8, 0.9 Hz), 7.39 (d, 1H,
thienyl ring proton, J= 4.4 Hz), 7.76 (d, 1H, thienyl ring proton, J
= 4.4 Hz); 13C NMR δ(CDCl3) 11.98, 12.44 (CHMe), 17.62,
17.85, 17.87, 18.04 (MeCH), 125.14, 125.22, 127.28, 127.31,
128.47, 128.56, 129.87, 132.75, 141.44, 143.99, 144.05, 144.16,
156.36, 157.62 (phenyl, thienyl ring and olefinic carbons); 29Si
NMR δ(CDCl3)−10.6, −9.2.
Figure 3. Energies for all optimized structures along the a- and b-reaction paths. Total energy of 10a is taken as the zero of relative energy.
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4.2.2. Platinum-Catalyzed Reaction of 1with Phenyl-
acetylene. In a 30 mL two-necked flask fitted with a reflux
condenser were placed 0.312 g (0.998 mmol) of 1, 0.205 g (2.01
mmol) of phenylacetylene, and 0.0649 g (0.0522 mmol) of
Pt(PPh3)4in 15 mL of dry benzene. The mixture was heated to
reflux for 73 h. The mixture was analyzed by GLC as being 5a and
5b (60% combined yield), together with starting compound 1
(40% yield). The solvent benzene was evaporated, and the
residue was chromatographed on a silica gel column using hexane
as the eluent. The ratio of 5a and 5b was determined to be 3:1 by
1H NMR spectroscopic analysis. For 5a and 5b: HR-MS: calcd
for C24H36Si2S 412.2076, found: 412.2055. MS m/z412 (M+);
1H NMR δ(CDCl3) 0.79 (d, 3H, MeCH, J= 7.2 Hz (5b)), 0.80
(d, 3H, MeCH, J= 7.2 Hz (5a)), 0.986 (d, 3H, MeCH, J= 7.2 Hz
(5b)), 0.992 (d, 3H, MeCH, J= 7.2 Hz (5a)), 1.02 (d, 6H,
MeCH, J= 7.2 Hz (5b)), 1.03 (d, 6H, MeCH, J= 7.2 Hz (5a)),
1.24 (sep, 1H, CHMe, J= 7.2 Hz (5a), overlapped with 5b), 1.36
(sep, 1H, CHMe, J= 7.2 Hz (5a)), 1.37 (sep, 1H, CHMe, J= 7.2
Hz (5b)), 6.75 (s, 1H, HCC(5b)), 6.77 (s, 1H, HCC
(5a)), 7.19−7.27 (m, 3H, phenyl ring protons (5a), overlapped
with 5b), 7.30−7.34 (m, 2H, phenyl ring protons (5a),
overlapped with 5b), 7.35 (d, 1H, thienyl ring proton, J= 4.4
Hz (5a)), 7.36 (d, 1H, thienyl ring proton, J= 4.4 Hz (5b)), 7.74
(d, 1H, thienyl ring proton, J= 4.4 Hz (5b)), 7.75 (d, H, thienyl
ring proton, J= 4.4 Hz (5a)); 13C NMR δ(CDCl3) 12.38 (5a),
12.53 (5b), 12.70 (5b), 12.96 (5a) (CHSi), 17.68 (5a), 17.90
(5a), 17.98 (5b), 18.09 (3C) (5b), 18.33 (5a), 18.40 (5a)
(MeCH), 126.42 (2C) (5a and 5b), 126.68 (5b), 126.72 (5a),
128.15 (5b), 128.18 (5a), 129.97 (5b), 130.18 (5a), 132.34 (5a),
133.17 (5b), 141.23 (5b), 141.85 (5a), 143.82 (5a), 144.00 (5b),
144.15 (5b), 145.30 (5a), 149.25 (5a), 160.74 (5a), 162.08 (5b)
(phenyl and thienyl ring and olefinic carbons); 29Si NMR
δ(CDCl3)−10.4 (5a), −8.84 (5b), −8.76 (5b), −7.51 (5a).
4.2.3. Platinum-Catalyzed Reaction of 1with Trimethylsi-
lylacetylene. In a 30 mL two-necked flask fitted with a reflux
condenser were placed 0.309 g (0.988 mmol) of 1, 0.215 g (2.19
mmol) of trimethylsilylacetylene, and 0.0640 g (0.0514 mmol) of
Pt(PPh3)4in 15 mL of dry benzene. The mixture was heated to
reflux for 20 h. The mixture was analyzed by GLC as being 6a and
6b (22% combined yield) and 7and 8(71% combined yield).
The ratio of 6a and 6b in the reaction mixture was determined to
be 1.6:1 by 1H NMR spectroscopic analysis. The ratio of 7and 8
in the reaction mixture was determined to be 1:1 by 1H NMR
spectroscopic analysis. The solvent benzene was evaporated, and
the residue was chromatographed on a silica gel column using
hexane as the eluent. For 6a and 6b: HR-MS: calcd for
C21H40Si3S 408.2159, found: 408.2141. MS m/z408 (M+); 1H
NMR δ(CDCl3) 0.19 (s, 9H, Me3Si (6a and 6b)), 0.82 (d, 6H,
MeC, J= 7.6 Hz (6a)), 0.83 (d, 6H, MeC, J= 7.6 Hz (6b)), 0.98
(d, 6H, MeC, J= 7.6 Hz (6b)), 1.00 (d, 6H, MeC, J= 7.6 Hz
(6a)), 1.05 (d, 6H, MeC, J= 7.6 Hz (6b)), 1.07 (d, 6H, MeC, J=
7.6 Hz (6a)), 1.17 (d, 6H, MeC, J= 7.6 Hz (6b)), 1.19 (d, 6H,
MeC, J= 7.6 Hz (6a)), 0.95−1.28 (m, 4H, HC (6a), overlapped
with 6b), 7.34 (d, 1H, thienyl ring proton, J= 4.0 Hz (6b)), 7.35
(d, 1H, thienyl ring proton, J= 4.0 Hz (6a)), 7.64 (s, 1H, HCC
(6a), overlapped with 6b), 7.75 (d, 1H, thienyl ring proton, J=
4.0 Hz (6a)), 7.77 (d, 1H, thienyl ring proton, J= 4.0 Hz (6b));
13C NMR δ(CDCl3)−0.49 (6a and 6b) (Me3Si), 13.12 (6a),
13.19 (6b), 14.34 (6b), 14.58 (6a) (HCSi), 18.41 (6a), 18.57
(6b), 18.66 (6a), 18.82 (6b), 19.38 (6b), 19.50 (6a), 19.53 (6b),
19.75 (6a) (MeC), 130.93 (6b), 132.24 (6a), 133.19 (6a),
133.69 (6b), 147.52 (6b), 148.17 (6a), 151.61 (6a), 152.09 (6b),
163.92 (6b), 164.07 (6a), 167.91 (6a), 167.97 (6b) (thienyl ring
and olefinic carbons); 29Si NMR δ(CDCl3)−9.70 (6b), −9.64
(6a), −2.36 (6b), −2.08 (6b), −0.62 (6a), −0.46 (6a). For 7:
HR-MS: calcd for C18H33Si3S 365.1611, found: 365.1614. MS m/
z365 (M+-(i-Pr)); 1H NMR δ(CDCl3) 0.22 (s, 9H, Me3Si), 0.96
(d, 6H, MeC, J= 7.6 Hz), 0.98 (d, 6H, MeC, J= 7.6 Hz), 1.06 (d,
6H, MeC, J= 7.6 Hz), 1.12 (d, 6H, MeC, J= 7.6 Hz), 1.20 (dsep,
2H, HC, J= 7.6 Hz, 3.6 Hz), 1.33 (sep, 2H, HC, J= 7.6 Hz), 4.28
(t, 1H, SiH, J= 3.6 Hz), 7.29 (d, 1H, thienyl ring proton, J= 4.4
Hz), 7.65 (d, 1H, thienyl ring proton, J= 4.4 Hz) 13C NMR
δ(CDCl3)−0.16 (Me3Si), 11.95, 13.88 (HC), 18.23, 18.60,
19.00, 19.14 (MeC), 108.70, 118.17 (CC), 130.48, 134.75,
142.60 (2C), (thienyl ring carbons); 29Si NMR δ(CDCl3)
−18.19, −11.07, −3.71. For 8: HR-MS: calcd for C18H33Si3S
365.1611, found: 365.1592. MS m/z365 (M+-(i-Pr)); 1H NMR
δ(CDCl3) 0.21 (s, 9H, Me3Si), 0.92 (d, 6H, MeC, J= 7.6 Hz),
1.02 (d, 6H, MeC, J= 7.6 Hz), 1.08 (d, 6H, MeC, J= 7.6 Hz),
1.09 (d, 6H, MeC, J= 7.6 Hz), 1.25 (dsep, 2H, HC, J= 7.6 Hz, 3.6
Hz), 1.26 (sep, 2H, HC, J= 7.6 Hz), 4.46 (dt, 1H, SiH, J= 3.6 Hz,
0.8 Hz), 7.51 (d, 1H, thienyl ring proton, J= 4.4 Hz), 7.65 (dd,
1H, thienyl ring proton, J= 4.4 Hz, 0.8 Hz); 13C NMR δ(CDCl3)
−0.10 (Me3Si), 12.58, 13.56 (HC), 18.21, 18.49, 18.79, 18.96
(MeC), 109.90, 117.38 (CC), 129.56, 136.54, 141.43, 143.69
(thienyl ring carbons); 29Si NMR δ(CDCl3)−18.52, −10.61,
−3.23.
4.2.4. Platinum-Catalyzed Reaction of 7.In a 30 mL two-
necked flask fitted with a reflux condenser were placed 0.1110 g
(0.271 mmol) of 7and 0.0190 g (0.0152 mmol) of Pt(PPh3)4in
9 mL of dry benzene. The mixture was heated to reflux for 130 h.
The mixture was analyzed by GLC as being 6a and 6b (47%
combined yield) and 7and 8(53% combined yield). The ratio of
6a and 6b in the reaction mixture was determined to be 1.2:1 by
1H NMR spectroscopic analysis. The ratio of 7and 8in the
reaction mixture was determined to be 3:1 by 1H NMR
spectroscopic analysis. All spectral data for 6a,6b,7, and 8were
identical to those of the authentic samples.
4.2.5. Platinum-Catalyzed Reaction of 8.In a 30 mL two-
necked flask fitted with a reflux condenser were placed 0.0979 g
(0.239 mmol) of 8and 0.0168 g (0.0135 mmol) of Pt(PPh3)4in
6 mL of dry benzene. The mixture was heated to reflux for 130 h.
The mixture was analyzed by GLC as being 6a and 6b (49%
combined yield) and 7and 8(51% combined yield). The ratio of
6a and 6b in the reaction mixture was determined to be 1.3:1 by
1H NMR spectroscopic analysis. The ratio of 7and 8in the
reaction mixture was determined to be 1:5 by 1H NMR
spectroscopic analysis. All spectral data for 6a,6b,7, and 8were
identical to those of the authentic samples.
4.2.6. Platinum-Catalyzed Reaction of 1with Mesitylace-
tylene. In a 30 mL two-necked flask fitted with a reflux condenser
were placed 0.306 g (0.979 mmol) of 1, 0.312 g (2.16 mmol) of
mesitylacetylene, and 0.0653 g (0.0525 mmol) of Pt(PPh3)4in
15 mL of dry benzene. The mixture was heated to reflux for 4 h.
The mixture was analyzed by GLC as being 12 and 13 (97%
combined yield). The ratio of 12 and 13 in the reaction mixture
was determined to be 1:1 by 1H NMR spectroscopic analysis.
The solvent benzene was evaporated, and the residue was
chromatographed on a silica gel column using hexane as the
eluent. For 12: HR-MS: calcd for C24H35Si2S 411.1998, found:
411.2005. MS m/z411 (M+-(i-Pr)); 1H NMR δ(CDCl3) 0.99 (d,
6H, MeCH, J= 7.2 Hz), 1.00 (d, 6H, MeCH, J= 7.2 Hz), 1.07 (d,
6H, MeCH, J= 7.2 Hz), 1.15−1.25 (m, 2H, HC), 1.20 (d, 6H,
MeCH, J= 7.2 Hz), 1.43 (sep, 2H, HC, J= 7.2 Hz), 2.29 (s, 3H,
Mes), 2.51 (s, 6H, Mes), 4.29 (t, 1H, SiH, J= 3.2 Hz), 6.89 (s,
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2H, Mes-H), 7.32 (d, 1H, thienyl ring proton, J= 4.4 Hz), 7.66
(d, 1H, thienyl ring proton, J= 4.4 Hz); 13C NMR δ(CDCl3)
11.98, 14.26, (HCMe), 18.53, 18.90, 18.98, 19.11 (MeCH),
21.31, 21.36 (Mes-Me), 96.45, 106.24 (CC), 120.17, 127.53,
130.59, 134.78, 138.05, 141.07, 142.05, 143.63 (mesityl and
thienyl ring carbons); 29Si NMR δ(CDCl3)−9.20, −3.57. For
13: HR-MS: calcd for C24H35Si2S 411.1998, found: 411.2000.
MS m/z411 (M+-(i-Pr)); 1H NMR δ(CDCl3) 0.97 (d, 6H, MeC,
J= 7.2 Hz), 1.02 (d, 6H, MeC, J= 7.2 Hz), 1.06 (d, 6H, MeC, J=
7.2 Hz), 1.18 (d, 6H, MeC, J= 7.2 Hz), 1.60−1.25 (m, 2H, HC),
1.38 (sep, 2H, HC, J= 7.2 Hz), 2.29 (s, 3H, p-Mes), 2.48 (s, 6H,
o-Mes), 4.50 (brt, 1H, SiH, J= 3.2 Hz), 6.89 (s, 2H, Mes-H), 7.65
(s, 2H, thienyl ring protons); 13C NMR δ(CDCl3) 12.59, 13.97
(CHSi), 18.51, 18.72, 18.76, 18.90 (CH3), 21.30, 31.35 (Mes-
Me), 97.68, 105.65 (CC), 120.32, 127.55, 129.54, 137.01,
137.93, 140.82, 140.97, 144.60 (thienyl and mesityl ring
carbons); 29Si NMR δ(CDCl3)−8.86, −3.32.
■ASSOCIATED CONTENT
*
SSupporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acsomega.7b01628.
1H, 13C, and 29Si NMR spectra for all products (PDF)
■AUTHOR INFORMATION
Corresponding Authors
*E-mail: anaka@chem.kusa.ac.jp (A.N.).
*E-mail: hisabbit@yahoo.co.jp (H.K.).
ORCID
Akinobu Naka: 0000-0003-0019-9104
Notes
The authors declare no competing financial interest.
■ACKNOWLEDGMENTS
We thank grants-in-aid or Scientific Research program (No.
26410061) from the Ministry of Education, Science, Sports, and
Culture of Japan, and Wesco Science Promotion Foundation.
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