Separation of optically active ethynylsilane derivatives and their polymerization by transition-metal catalysts

Article abstract of DOI:10.1021/ma0301101

Optically pure (-)-(4-bromophenyl)ethynylmethyl(1-naphthyl)silane[(-)-1], (-)-1,2-diethynyl-1,2-dimethyl-1,2-di(1-naphthyl)disilane [(-)-2], and (+)-1,2-diethynyl-1,2-dimethyl-1,2-diphenyldisilane [(+)-3] were separated by a chromatographic technique on a

Full text of DOI:10.1021/ma0301101

Macromolecules 2003, 36, 7461-7468
7461
Separation of Optically Active Ethynylsilane Derivatives and Their
Polymerization by Transition-Metal Catalysts
Yu su k e Ka w a k a m i,* Ma sa k a tsu Om ote, Ich ir o Im a e, a n d Eiji Sh ir a k a w a
Graduate School of Materials Science, J apan Advanced Institute of Science and Technology,
1-1 Asahidai, Tatsunokuchi, Ishikawa 923-1292, J apan
Received February 13, 2003; Revised Manuscript Received J uly 14, 2003
ABSTRACT: Optically pure (-)-(4-bromophenyl)ethynylmethyl(1-naphthyl)silane [(-)-1], (-)-1,2-diethy-
nyl-1,2-dimethyl-1,2-di(1-naphthyl)disilane [(-)-2], and (+)-1,2-diethynyl-1,2-dimethyl-1,2-diphenyldisilane
[(+)-3] were separated by a chromatographic technique on an optically active stationary phase.
Polymerization via Heck reaction or dimerization of bis(ethynyl) groups of these compounds gave optically
active polymers. The structures of the polymers were characterized by 1H, 13C, and 29Si NMR
spectroscopies. Poly(1) and poly(2) have regular chemical structure. In poly(3), (E)-ene-yne is mixed
with (E)-ene-(E)-ene and yne-yne structures. All the polymers are considered stereoregular concerning
the configuration of the silicon atoms. The optical properties in solution were measured. Although the
electronic absorption and fluorescence spectra of optically active polymers did not change compared with
those of racemic polymers, the circular dichroism spectra showed a negative Cotton effect.
Sch em e 1. Syn th esis a n d Sep a r a tion of Op tica lly
In tr od u ction
Active (-)-1, (-)-2, a n d (+)-3
There has been much attention given to organosilicon
polymers such as polysilanes and polycarbosilanes as
functional materials, such as photoresists, semiconduc-
tors, and hole-transporting materials. Among these
polymers, those having an oligosilane unit sandwiched
by a carbon-carbon conjugated system are especially
interesting to elucidate electrical and optical properties
of the polymers arising from σ-π conjugation. Ishikawa,
Corriu, and West reported the preparation of such
disilane-containing polymers through dimerization or
palladium-catalyzed Heck coupling reaction of ethynyl-
silyl compounds, and mentioned their electrical and
optical properties.1-5 However, characterization of the
polymer structure is not well-done, which makes it
difficult to understand their properties on the basis of
the chemical structure.
Meanwhile, we have developed a stereospecific syn-
thesis of optically active silicon compounds to obtain
stereoregular and/or optically active poly(carbosilane)s,6,7
poly(carbosiloxane)s,8,9 and poly(siloxane)s.10 These re-
actions contribute very much to the clarification of the
polymer structure and stereochemical pathway of the
reaction. If the chirality of the silicon atoms is con-
trolled, characterization of the polymer by spectroscopic
methods will become easier compared with that of the
racemic polymer, and unambiguous identification of the
structure might be made. However, no such stereoreg-
ular poly(carbosilane)s conjugated with a π-system have
been reported.
In this paper, we describe the separation of optically
pure (-)-(4-bromophenyl)ethynylmethyl(1-naphthyl)si-
lane, (-)-1,2-diethynyl-1,2-dimethyl-1,2-di(1-naphthyl)-
disilane, and (+)-1,2-diethynyl-1,2-dimethyl-1,2-diphen-
yldisilane on optically active stationary phases,11 and
structural analyses of the polymers obtained via Heck
reaction or dimerization of ethynyl functions.
are reported in parts per million relative to the peaks for
CHCl3 (δ 7.26 for 1H), CDCl3 (δ 77.00 for 13C), and tetrameth-
ylsilane (δ 0.00 for 29Si). IR spectra were obtained on a J ASCO
VALOR-III spectrophotometer. Specific optical rotations were
measured with a J ASCO DIP-370S digital polarimeter. Size
exclusion chromatography (SEC) and HPLC analysis were
performed on a J ASCO HPLC apparatus, model GULLIVER,
with a combination of Shodex KF-803L (30 cm, exclusion limit
Mn ) 7 × 104, polystyrene) and KF-804 (30 cm, exclusion limit
Mn ) 4 × 105, polystyrene) columns (linear calibration down
to Mn ) 100) using tetrahydrofuran (THF; 1 mL/min) as the
mobile phase for molecular weight analysis, and with a
CHIRALCEL OD (25 cm, cellulose tris(3,5-dimethylphenyl)-
carbamate coated on silica gel, Daicel) column with hexane/
2-propanol (100:0 to 1500:1 v/v) as the mobile phase at 35 °C
(0.4 mL min-1, 9-11 kg cm-2) detected by UV (254 nm) and
circular dichroism (CD; 254 nm) for optical purity analysis.
Separation by HPLC was performed on a CHIRALCEL OD
column (25 cm × 2 cm) with hexane/2-propanol (100:0 to 750:1
v/v) as the mobile phase (4.0 mL min-1, 16-20 kg cm-2). High-
resolution mass spectra were taken on a Bruker DALTONICS
Exp er im en ta l Section
1
Gen er a l P r oced u r es. NMR spectra (500 MHz, H; 125.7
MHz, 13C; 99.3 MHz, 29Si) were obtained in CDCl3 on a Varian
500 MHz spectrometer, model Unity INOVA. Chemical shifts
10.1021/ma0301101 CCC: $25.00 © 2003 American Chemical Society
Published on Web 09/11/2003

7462 Kawakami et al.
Macromolecules, Vol. 36, No. 20, 2003
was added trifluoromethanesulfonic acid (80 mmol), and the
solution was warmed to room temperature over 40 min and
stirred for 30 min. Naphthylation at -20 °C, followed by
distillation of the residue after the removal of volatile materi-
als by heating to 200 °C at 2.2 mmHg gave 1,2-dimethyl-1,2-
di(1-naphthyl)disilane (9.12 g, 67% yield).
Passing excess chlorine gas over 1,2-dimethyl-1,2-dinaph-
thyldisilane in CCl4 gave 1,2-dichloro-1,2-dimethyl-1,2-dinaph-
thyldisilane without cleavage of the Si-Si bond. Ethynylation
afforded diastereomeric 2 (5.56 g, 14.2 mmol, 57% yield). Pure
isomers, (-)-2 and meso-2, were separated by preparative
chromatography (100:1) by recycling three times (Figure 1a-
c). Data for (-)-2: 1H NMR δ 0.75 (s, 6H, SiCH3), 2.83 (s, 2H,
SiCtCH), 7.10-7.95 (m, 14H, naphthyl protons); 13C NMR δ
-2.51 (SiCH3), 86.64 (SiCtCH), 98.72 (SiCtCH), 125.10,
125.39, 125.45, 128.29, 128.53, 130.38, 131.54, 133.07, 134.89,
136.58 (naphthyl carbons); 29Si NMR δ -36.89; HRMS m/z
found 390.1273, calcd for C26H22Si2, M, 390.1260; [R]25 ) -
D
26.53° (c 1.01, CHCl3). Data for meso-2: 1H NMR δ 0.72 (s,
6H, SiCH3), 2.65 (s, 2H, SiCtCH), 7.27-8.12 (m, 14H, naph-
thyl protons); 13C NMR δ -2.33 (SiCH3), 86.45 (SiCtCH),
98.75 (SiCtCH), 125.20, 125.51, 125.60, 128.69, 128.72,
130.46, 131.77, 133.24, 134.98, 136.75 (naphthyl carbons).
(+)-1,2-Dieth yn yl-1,2-dim eth yl-1,2-diph en yldisilan e [(+)-
3]. Similar chlorination of 1,2-dimethyl-1,2-diphenyldisilane
and ethynylation afforded diastereomeric 3 (69% yield). After
recrystallization two times from ethanol, meso-3 was isolated1e
as a pure isomer. Optically active antipode (+)-3 was sepa-
rated with hexane/2-propanol (750:1) as the mobile phase. By
recycling five times, optically pure disilane was isolated
(Figure 1d,e). Data for (+)-3: 1H NMR δ 0.57 (s, 6H, SiCH3),
2.68 (s, 2H, SiCtCH), 7.28-7.52 (m, 10H, phenyl protons);
13C NMR δ -4.42 (SiCH3), 85.48 (SiCtCH), 97.71 (SiCtCH),
127.89, 129.44, 133.19, 134.35 (phenyl carbons); 29Si NMR δ
F igu r e 1. HPLC chromatograms of (a) meso-2, (b) (-)-2, (c)
diastereomeric 2 (n-hexane:2-propanol ) 100:1), (d) diastereo-
meric 3, and (e) optically pure (+)-3 (n-hexane:2-propanol )
1500:1).
Bio-Apex 70E. Electronic absorption, fluorescence, and circular
dichroism spectra were obtained on a J ASCO V-570 UV/VIS/
near-IR spectrometer, J ASCO FP-6500 spectrofluorometer,
and J ASCO J -720 spectropolarimeter, respectively.
Ma ter ia ls. Synthetic routes and chromatograms of the
monomers are shown in Scheme 1 and Figure 1.
(-)-(4-Br om op h e n yl)e t h yn ylm e t h yl(1-n a p h t h yl)si-
la n e [(-)-1]. Dropwise addition of a solution of 4-bromophen-
ylmagnesium bromide (105 mmol) in diethyl ether (120 mL)
to a solution of methyltrimethoxysilane (13.62 g, 100 mmol)
in diethyl ether (100 mL) afforded (4-bromophenyl)dimethoxy-
methylsilane (15.62 g, 60 mmol). Naphthylation (naphthyl-
magnesium bromide in THF) and ethynylation (ethynylmag-
nesium bromide in THF) gave (4-bromophenyl)ethynylmethyl(1-
naphthyl)silane (5.97 g, 17% yield). Optically pure (-)-1 was
separated by preparative HPLC (750:1)
-38.63; [R]26 ) +8.17° (c 2.33, CHCl3).
D
(R)-Ethynylmethyl(1-naphthyl)phenylsilane was synthe-
sized as a model compound to study regio- and stereoselectivity
in the dimerization of an ethynyl group from (S)-methyl(1-
naphthyl)phenylchlorosilane13 (1.13 g, 4.0 mmol, 99% ee).
Optically pure compound was separated with hexane as the
mobile phase from the crude product with 60% ee:
1H NMR δ 0.88 (s, 3H, SiCH3), 2.73 (s, 1H, SiCtCH), 7.34-
8.14 (m, 12H, naphthyl and phenyl protons); IR (KBr) 2035 (γ
(CtCH)) cm-1; HRMS m/z found 272.1026, calcd for C19H16Si,
M, 272.1021; [R]27 ) +6.00° (c 1.00, CHCl3).
D
P olym er iza tion . Polymerization schemes are shown in
Scheme 2.
:
1H NMR δ 0.86 (s, 3H, SiCH3), 2.74 (s, 1H, SiCtCH),
P olym er iza tion by Heck Rea ction . A typical procedure
is given. 1,4-Diiodobenzene (0.33 g, 1 mmol), 2 (0.39 g, 1 mmol),
(Ph3P)2PdCl2 (35.1 mg, 0.05 mmol), CuI (9.5 mg, 0.05 mmol),
triethylamine (1.5 mL), and toluene (10 mL) were placed in a
flask and stirred at 80 °C for 2 days. The resulting solution
was filtered, concentrated, and purified by reprecipitation from
7.40-8.06 (m, 11H, naphthyl and phenyl protons); 13C NMR
δ -1.19 (SiCH3), 86.63 (SiCtCH), 97.42 (SiCtCH), 124.85,
125.12, 125.72, 126.10, 128.20, 129.01, 130.99, 131.25, 131.29,
133.41, 133.88, 135.61, 136.08, 136.49 (naphthyl and phenyl
carbons); 29Si NMR δ -25.23; HRMS m/z found 352.0128, calcd
for C19H15SiBr, M, 352.0106; [R]25 ) -8.80° (c 1.00, CHCl3).
CHCl3 into methanol two times. Data for poly((-)-1): Mw )
D
1
(-)-1,2-Dieth yn yl-1,2-d im eth yl-1,2-d i(1-n a p h th yl)d isi-
la n e [(-)-2]. To a cooled solution of 1,2-dimethyl-1,2-diphen-
yldisilane12 (9.59 g, 39.5 mmol) in CH2Cl2 (40 mL) at -20 °C
4900; Mn ) 3300; H NMR δ 0.88 (s, 6H, SiCH3), 7.23-8.17
(m, 11H, naphthyl and phenylene protons); 13C NMR δ -1.09
(SiCH3), -1.00 (SiCH3 terminal), 91.56 (SiCtC-), 109.11
Sch em e 2. P olym er iza tion of (-)-1, (-)-2, a n d (+)-3

Macromolecules, Vol. 36, No. 20, 2003
Separation of Ethynylsilane Derivatives 7463
(SiCtC-), 123.81, 125.10, 125.63, 125.99, 126.01, 128.41,
128.91, 131.04, 131.08, 131.22, 131.40, 131.45, 131.56, 131.90,
132.10, 133.41, 134.43, 135.51, 136.19, 136.62, 137.12 (naph-
thyl and phenylene carbons); 29Si NMR δ -25.73 (half-height
peak width 2.28 Hz), -25.60 (terminal); [R]25 ) +11.40° (c
D
1.00, CHCl3); yield 76%. Data for poly(rac-1): Mw ) 4000; Mn
) 2800; 29Si NMR δ -25.73 (half-height peak width 3.76 Hz),
-25.60 (terminal); yield 48%. Data for
poly((-)-2): Mw ) 13000; Mn ) 5900; 1H NMR δ 0.84 (s,
6H, SiCH3), 7.08-8.22 (m, 18H, naphthyl and phenylene
protons); 13C NMR δ -2.25 (SiCH3), 93.39 (SiSiCtC-), 110.05
(SiSiCtC-), 123.27, 125.18, 125.40, 125.45, 128.59, 128.64,
130.30, 131.73, 131.82, 131.93, 132.37, 133.19, 134.92, 135.20,
136.78 (naphthyl and phenylene carbons); 29Si NMR δ -36.95;
[R]25 ) -80.20° (c 1.00, CHCl3); yield 78%.
D
Data for poly(diastereo-2): Mw ) 15300; Mn ) 6000; yield
71%. Data for poly(meso-2): Mw ) 19600; Mn ) 8300; yield
73%.
P olym er iza tion by Dim er iza tion . Typically, a solution
of 0.185 g (0.64 mmol) of 3 and 5 mol % chlorotris(triph-
enylphosphine)rhodium(I) in 0.6 mL of toluene was stirred for
2 days at room temperature. The residue was reprecipitated
twice from chloroform to 2-propanol to give 33.6 mg (18% yield)
of poly(3).1c
1
Data for poly((+)-3): Mw ) 17300; Mn ) 5400; H NMR δ
0.48-0.59 (m, 6H, SiCH3), 6.05 (d, 1H, J ) 19.0 Hz, olefinic
protons), 6.68 (d, 1H, J ) 19.0 Hz, olefinic protons), 7.06-
7.74 (m, 10H, phenyl protons); 13C NMR δ -5.76, -5.52, -3.91,
-3.77 (SiCH3), 91.19, 91.34, 91.42, 91.57 (SiSiCtC-), 109.61,
109.71, 109.77, 109.88 (SiSiCtC-), 125.79, 125.83, 125.90,
125.93 (SiSiCdC-), 127.72, 127.87, 127.92, 128.02, 128.59,
129.23, 134.09, 134.36, 134.45, 134.64, 134.71, 133.19, 134.87
(phenyl carbons), 142.55, 142.59, 142.75, 142.79 (SiSiCdC-);
29Si NMR δ -39.29 (SiSiCtC-), -26.25 (SiSiCdC-). Data
for poly(meso-3): Mw ) 22600; Mn ) 8200; yield 62%. Data
for poly(diastereo-3): Mw ) 12300; Mn ) 5600; yield 59%.
Resu lts a n d Discu ssion
F igu r e 2. 29Si NMR spectra of (a) poly(rac-1) and (b) poly-
((-)-1).
A model reaction to obtain poly(1) or poly(2) from
ethynylsilanes and haloaryl compounds, by treatment
of a toluene solution of meso-31c with iodobenzene under
the Heck condition, afforded 1,2-dimethyl-1,2-diphenyl-
1,2-bis(2-phenylethynyl)disilane. Only one isomer was
produced, evidenced by HPLC, which suggests that the
reaction has proceeded with retention of stereochemistry
of the asymmetric silicon center.
Poly(1) and poly(2) obtained from rac-1, (-)-1, dia-
stereomeric 2, meso-2, and (-)-2 were light-yellow, and
soluble in common organic solvents such as toluene,
THF, and CHCl3. In the 13C NMR spectrum of poly(1),
the signal at 91 ppm is assigned to the ethynyl carbon
adjacent to the silicon atom, and the signal at 109 ppm
to the ethynyl carbon bonded to phenylene groups. No
dimerization of the ethynyl group was observed. In the
29Si NMR spectra shown in Figure 2, two peaks (-25.73
and -25.60 ppm) were observed.
The signal at -25.73 ppm is assigned to the internal
silicon atom of the polymer chain, and the signal at
-25.60 ppm to the terminal silicon atom. The terminal
signals were observed because of the low molecular
weight of the product. Thus, poly(1) is determined as
poly[{methyl(1-naphthyl)silylene}(ethynylene)(1,4-phe-
nylene)]. However, unfortunately, no definite peak
separation which reflects the stereoregularity of the
polymer was observed in the NMR spectra of poly(rac-
1) and poly((-)-1). The half-height peak width at -25.73
ppm in the 29Si spectrum measured after deconvolution
was narrower for poly((-)-1) (2.28 Hz) than that of poly-
(rac-1) (3.76 Hz). This probably suggests that poly((-
)-1) is isotactic because the model reaction proceeded
with 100% retention of configuration at the silicon atom.
Poly((-)-1) showed optical activity ([R]25 ) +11.40° (c
D
1.00, CHCl3).
The 1H NMR spectra of poly(2) show two singlet peaks
assignable to methyl protons and multiplet peaks as-
signable to 1-naphthyl and phenylene protons in the
ratio 3:3:14:4. The 13C NMR spectra show peaks of the
methyl carbon, ethynylene carbon, and aromatic car-
bons. In the 29Si NMR spectra, only one peak could be
observed. Although the two silicon atoms could not be
distinguished, the chemical structure of poly(2) is as-
signed as poly[{1,2-di(1-naphthyl)-1,2-dimethyldisilan-
ylene}(ethynylene)(1,4-phenylene)(ethynylene)] as shown
in Scheme 2. Poly(2) has a high enough molecular
weight; therefore, no terminal signal was observed.
However, no definite difference was observed in the 29
spectra among poly(diastereo-2), poly(meso-2), and poly-
((-)-2).
Si
The splitting pattern of poly(2) should reflect the
relation of configuration of two successive disilane units.
There are six distinguishable stereochemical relations
concerning two successive disilane units for poly(dia-
stereo-2), as shown in Figure 3.
The information about the stereochemistry of the
disilane unit in the polymer could be obtained by the
1
analysis of the H and 13 C signals of the SiCH3Np unit.
Two peaks were observed for the methyl proton of poly-
(diastereo-2) as shown in Figure 4a.
The peak at 0.84 ppm should be assigned to the signal
of the R-R disilane unit (Figure 4c), and the signal at
0.75 ppm to the R-S (S-R) unit. The 13C NMR methyl
1
signal showed a trend similar to that of the H NMR

7464 Kawakami et al.
Macromolecules, Vol. 36, No. 20, 2003
F igu r e 3. Stereochemical relations concerning two successive
disilane units of poly(diastereo-2) (R and S indicate the
absolute configuration of the silicon atom).
F igu r e 5. 13C NMR spectra of SiCH3 of (a) poly(diastereo-2),
(b) poly(meso-2), and (c) poly((-)-2).
The peak of SiCH3Np at -2.27 ppm could be assigned
to the R-R disilane unit, and that at -2.09 ppm to the
R-S (S-R) disilane unit. The 1H and 13C NMR analysis
of poly((-)-2) proved the complete retention of asym-
metric silicon atoms in the polymerization. It is impor-
tant to note that the areas of the two peaks of poly-
(diastereo-2) are not equal. The ratio of the R-R (S-S)
and R-S (S-R) disilane units in poly(diastereo-2) is
roughly estimated to be 60:40 by 13C NMR. In compari-
son with poly(1), it is possible to observe an environ-
mental difference around the Si atom of poly(2) by NMR
spectroscopy. In the 1H NMR spectrum of poly(diastereo-
2), two doublet signals were observed at 8.28 and 8.14
ppm for one of the naphthyl protons (Figure 6a). Poly-
(meso-2) showed the signal at 8.28 ppm (Figure 6b), and
poly((-)-2) the signal at 8.14 ppm (Figure 6c). The peaks
of poly(diastereo-2) at 8.28 and 8.14 ppm are reasonably
considered to reflect the relative concentration of the
meso and racemo diads of the disilane units. The ratio
is estimated to be (R-R + S-S):(R-S + S-R) ) 69:
31. If the polymerization proceeds statistically, these
signals must be equal. This means racemo diads are
more contained in the isolated poly(diastereo-2). It is
reasonable to consider that the fractions which contain
more racemo diads would be less soluble in methanol,
precipitated, and separated as the product. Some stereo-
selection should be occurring in the polymerization.
F igu r e 4. 1H NMR spectra of SiCH3 of (a) poly(diastereo-2),
(b) poly(meso-2), and (c) poly((-)-2).
spectrum; namely, two peaks were observed in poly-
(diastereo-2) (Figure 5a).

Macromolecules, Vol. 36, No. 20, 2003
Separation of Ethynylsilane Derivatives 7465
F igu r e 6. 1H NMR spectra of SiNp-H of (a) poly(diastereo-
2), (b) poly(meso-2), and (c) poly((-)-2).
Poly((-)-2) is considered optically pure (>99%).
It is not clear at this point whether a successive
relation among R-R, S-S, R-S, and S-R can be
distinguished or not. Precise analysis of the regularity
concerning the two successive disilane units can be
obtained by the analysis of the ethynyl carbon directly
attached to the silicon atom.
F igu r e 7. 13C NMR spectra of SiCtC of (a) poly(diastereo-2),
(b) poly(meso-2), and (c) poly((-)-2).
The 13C NMR spectra of poly(meso-2) and poly((-)-2)
showed ethynylene carbon signals at 93.17 and 110.16
ppm and at 93.40 and 110.06 ppm, respectively. Peaks
around 93 ppm are assigned to the ethynylene carbon
directly attached to the silicon atom (SiSiCtC, R-car-
bon), and the peaks around 110 ppm to the ethynylene
carbon adjacent to the p-phenylene ring (SiSiCtC-Ar-,
â-carbon). Poly(diastereo-2) showed two broad multiplet
signals at around 93 ppm in different strengths, namely,
at 93.44, 93.39 (shoulder), 93.27, and 93.23 (shoulder)
ppm, and two signals at around 110 ppm. The â-carbon
from the monomer with the stereoisomer ratio RR:SS:
RS:SR ) 43:43:7:7 were analyzed. The crude polymer
showed three peaks (93.44, 93.39, and 93.27 ppm)
reflecting the small theoretical concentration of the
R-carbon of relation vi; namely, the signal at 93.23 ppm
was weak. This peak ratio was roughly determined as
8:2:1:0 after deconvolution of the peaks at 93.44, 93.39,
93.27, and 93.23 ppm. This fact partially guarantees the
appropriateness of the above assignment. After repre-
cipitation, the signal at 93.27 ppm became even weaker
than the crude polymer.
If the polymerization proceeds statistically, the four
signals in Figure 7a must be in a ratio of 2:1:1:2.
However, the peaks originating from the racemo rela-
tion were strong, and those originating from the meso
relation were weaker than the calculated value. This
indicates nonstatistical distribution of the disilane diad
in the isolated polymer. However, the precise concentra-
tion of the successive diad of poly(diastereo-2) could not
be estimated quantitatively because of the signal over-
lap.
signals around 110 ppm are not well separated. The 13
C
peaks of the R-carbon around 93 ppm are shown in
Figure 7.
The shoulder peaks at 93.39 and 93.23 ppm are
assigned to the R-carbon signals of the racemo relation
i and the meso relation v (mirror relation) + vi (center
of symmetry) (Figure 3). The R-carbon signals of relation
iv (center of symmetry) seem to appear at slightly lower
field than that of relation i around 93.44 ppm. The peaks
of the two R-carbons in relations ii and iii are not equal,
and seem to slightly downfield shift from the signals
related to the racemo (93.39 ppm) or meso (93.23 ppm)
disilane unit, and appear around 93.44 and 93.27 ppm,
respectively. Thus, the signals at 93.44 and 93.27 ppm
are considered as overlapped signals of R-carbons at-
tached to the racemo and meso units in relations ii-iv.
To confirm the assignment, signals of poly(2) obtained
To examine the more complicated case of a σ-π
conjugated polymer, the polymer was synthesized via
dimerization reaction of ethynyl functions. A model
reaction of polymerization by dimerization was studied
by the treatment of a toluene solution of (R)-ethynyl-
methyl(1-naphthyl)phenylsilane with a catalytic amount
of chlorotris(triphenylphosphine)rhodium(I) at room

7466 Kawakami et al.
Macromolecules, Vol. 36, No. 20, 2003
temperature for 24 h, which afforded 1,4-bis(methyl(1-
naphthyl)phenylsilyl)but-1-en-3-yne in 84% yield. The
coupling constants (J ) 19.0 Hz) of the olefinic protons
1
at δ 6.11 and 7.02 in the H NMR clearly indicate the
compound has an E configuration of the olefinic group.
On HPLC analysis, only one stereoisomer was observed.
The product is reasonably considered an (R,R) isomer.
The dimer from rac-ethynylsilane showed four peaks
assignable to the (R,R), (R,S), (S,R), and (S,S) isomers
in equal quantities. The reaction is considered to
proceed with retention of the stereochemistry of the
asymmetric silicon centers.
To study the structure of poly(3), poly((+)-3), poly-
(meso-3), and poly(diastereo-3) were prepared from (+)-
3, meso-3, and diastereomeric 3, respectively, for com-
1
parison. In the H NMR spectra of poly(meso-3), olefin
protons were observed as doublets at 6.05 (d, 1H, J )
19.0 Hz) and 6.68 (d, 1H, J ) 19.0 Hz) ppm. The
appearance of two peaks for the olefin protons with
trans-coupling indicates that the polymers have ene-
ene and ene-yne structures with (E)-configuration
concerning the CdC bond. In the 13C NMR spectra, two
olefin and two ethynylene carbons were observed at 125
(SiSiCdC-) and 142 (SiSiCdC-) ppm and and at 91
(SiSiCtC-) and 110 (SiSiCtC-) ppm, respectively. The
signal of the ethynylene carbon at 110 ppm (SiSiCtC-)
split into two peaks (109.82 and 109.91 ppm), which also
indicates that the polymer has yne-yne and yne-ene
structures. The olefin carbon at 142 ppm (SiSiCdC-)
also split into two peaks (142.50 and 142.82 ppm), which
indicates that the polymer has ene-ene and ene-yne
structures. Thus, it is concluded that the polymer has
three kinds of basic structure, yne-yne, (E)-ene-yne,
and (E)-ene-(E)-ene, similar to those reported by Ish-
ikawa and as shown in Scheme 2.1b,c
F igu r e 8. 29Si NMR spectra of (a) poly(diastereo-3), (b) poly-
(meso-3), and (c) poly((+)-3).
Ta ble 1. Str u ctu r e of -R1-CtC-[m eso-Si-Si]-R2- a n d
th e Ch em ica l Sh ifts of Silicon a n d Ca r bon Atom s
(In d ica ted )
Whether poly((+)-3) has regular structure or not
depends on the stereo- and regiospecificity of the dimer-
ization reaction. Chemical shifts of poly(3) are deter-
mined by the geometrical structure of carbon 4 units
formed by dimerization, namely, (E)-ene-(E)-ene, (E)-
ene-yne, and yne-yne structure, and the configuration
of asymmetric silicon centers. The 29Si NMR spectra of
poly(3) are shown in Figure 8.
chemical shift
of Si (ppm)
chemical shift
of C (ppm)
substituent
R1
R2 poly(meso-3) poly((+)-3) poly(meso-3) poly((+)-3)
yne yne
yne ene
01/16
91.30
91.45
91.57
91.19
91.34
91.42
91.57
a
39.12
∼39a
ene
ene
yne
ene
In poly(3), silicon atoms are attached to an ene or yne
carbon, and the ene or yne group is further attached to
an ene or yne group. The 29Si chemical shifts are
considered to be determined principally by which carbon
of the C4 unit formed by dimerization the silicon atom
is attached to, which will be further split by the
stereochemistry of the disilane unit (meso, racemo). This
is also true for silicon atoms attached to an olefinic
carbon. Such possible structures with a meso-disilane
unit are shown in Table 1.
a
Not separated.
for poly(meso-3) (Figure 8b). A shoulder signal was
observed for poly((+)-3) (Figure 8c). Some distinction
was made by the difference between the structures of
the C4 units, but the difference between the ene-ene
and ene-yne structures of the C4 unit could not be
clearly distinguished. There may be influences by higher
order regularity on the broadness of these two peaks.
The ratio of the peaks at -39 and -26 ppm of poly-
(meso-3) is roughly 1:1, which, with the 60:40 ratio of
yne-yne and yne-ene structures, strongly indicates
that the ratio of the ethynylene and olefin carbons
attached to the silicon atom is roughly 1:1.
The signals for the silicon atoms adjacent to the
carbon-carbon double bond appeared as only one peak,
and did not give any information about the ratio of the
concentration of the ene-yne and ene-ene structures.
In poly(diastereo-3), the signal for each silicon atom was
observed as two peaks (SiCdC, -26.11 and -26.23 ppm;
SiCtC, -39.00 and -39.27 ppm) (Figure 8a). These
peaks are basically overlapped signals of poly((+)-3) and
poly(meso-3).
In the spectra, the signal of SiCtC adjacent to the
yne-yne [R1 ) yne] and yne-ene [R2 ) ene] structures
of poly(meso-3) appeared as two peaks (-38.98 and
-39.12 ppm). The signal at -39.12 ppm is assigned to
the silicon atom attached to the yne-yne C4 unit, and
the signal at -38.98 ppm to that attached to the yne-
ene C4 unit at present, taking the magnetic anisotropy
effect into account. The ratio of the yne-yne and yne-
ene is roughly estimated to be 60:40. These signals
appeared as broad and at a little higher field than the
peaks for poly((+)-3). The signal was not separated for
the silicon atom attached to yne-yne and yne-ene
structures. The signal of SiCdC in the ene-ene and
ene-yne structures appeared as one peak (-26.12 ppm)

Macromolecules, Vol. 36, No. 20, 2003
Separation of Ethynylsilane Derivatives 7467
F igu r e 10. Electronic absorption (a), fluorescence (b), and
circular dichroism (c) spectra of poly((-)-2) in cyclohexane.
The assignments are similar to those of poly(meso-3).
Atactic poly(diastereo-3) showed six peaks at 91.42,
91.55, 91.13, 91.17, 91.29, and 91.32 ppm (Figure 9a).
The signals are basically overlapped peaks of poly(meso-
3) and poly((+)-3). Although complete analysis could not
be made, detailed structural analysis of poly(3) became
possible with the aid of optically active poly((+)-3).
F igu r e 9. 13C NMR spectra of SiCtC of (a) poly(diastereo-3),
(b) poly(meso-3), and (c) poly((+)-3).
In the 13C NMR spectra, the signal for the ethynylene
carbon of poly(meso-3) not directly adjacent to the silicon
atom (SiCtC) was observed at 109 ppm as two peaks.
The signal for the ethynylene carbon adjacent to the
silicon atom (SiCtC) was observed around 91 ppm, split
into four peaks, and gave more information about the
structure of the polymers. Analysis of the structures of
poly(3) was made using the signal of SiCtC.
The signal for the ethynylene carbon attached to the
silicon atom should ideally split into eight peaks reflect-
ing the chemical structure, and that for the ene carbon
into four peaks, for poly(meso-3). The chemical shift of
the ethynylene carbon (SiCtC) is considered to reflect
the structure of consecutive -R1-CtC-Si-Si-R2-
units (R1, R2 ) yne or ene shown in Table 1). The 13C
NMR spectra of poly(3) are shown in Figure 9.
In the spectrum of poly(meso-3), the signal of the
ethynylene carbon with R1 ) yne and R2 ) yne is
considered to appear at 91.16 ppm, and that of the
ethynylene carbon with R1 ) yne and R2 ) ene at 91.30
ppm. The signals of the ethynylene carbon with R1 )
ene and R2 ) yne will appear at 91.45 ppm, and that of
the ethynylene carbon with R1 ) ene and R2 ) ene at
91.57 ppm, respectively. Poly((+)-3) also showed four
peaks at 91.57, 91.42, 91.34, and 91.19 ppm (Figure 9c).
The optical properties of the polymer were investi-
gated. Typical spectra are shown for poly((-)-2) in
Figure 10. The electronic absorption spectrum showed
two absorption maxima at around 300 and 225 nm,
which are ascribed to the absorptions of the π-π*
transition of the pendant naphthyl group and the
transition of the σ-π-conjugated backbone system,
respectively. In the fluorescence spectrum, a broad peak
was observed around 375 nm, when the polymer was
excited at 265 nm. These spectra in cyclohexane did not
differ remarkably between optically active and racemic
polymers. However, negative Cotton effects at both
absorption bands were observed in the circular dichro-
ism spectra of optically active polymers, but not for
racemic polymers. Recently, we reported that Cotton
effects of optically pure oligosilanes having chiral cen-
ters on the silicon atoms are well-related to their crystal
structures by X-ray analysis.14 The stereochemistry of
the disilane units in poly((-)-2) can be assumed an S,S
relationship. The optical properties of the polymer in
the solid film state are under study.

7468 Kawakami et al.
Macromolecules, Vol. 36, No. 20, 2003
(2) (a) Corriu, R. J . P.; Douglas, W. E.; Yang, Z.-X. J . Polym.
Sci., Part C: Polym. Lett. 1990, 28, 431. (b) Corriu, R. J . P.;
Douglas, W. E.; Yang, Z. -X.; Garnier, F.; Yassar, A. J .
Organomet. Chem. 1991, 417, C50. (c) Corriu, R. J . P.;
Douglas, W. E.; Yang, Z. -X.; Karakus, Y.; Cross, G. H.; Bloor,
D. J . Organomet. Chem. 1993, 455, 69.
(3) (a) Yuan, C.-H.; West, R. Appl. Organomet. Chem. 1994, 8,
423. (b) Li, H.; West, R. Macromolecules 1998, 31, 2866.
(4) Kunai, A.; Toyoda, E.; Horata, K.; Ishikawa, M. Organome-
tallics 1995, 14, 714.
(5) Kwak, G.; Masuda, T. Macromolecules 2002, 35, 4138.
(6) Kawakami, Y.; Nakao, K.; Shinke, S.; Imae, I. Macromolecules
1999, 32, 6874.
(7) Uenishi, K.; Imae, I.; Shirakawa, E.; Kawakami, Y. Chem.
Lett. 2001, 986.
Con clu sion
Polymerization of optically pure (-)-1 and (-)-2 via
Heck reaction gave polymers with regular chemical
structure, while the polymer from dimerization of (+)-3
had a mixture of (E)-ene-yne, (E)-ene-(E)-ene, and
yne-yne structures.
1
The H, 13C, and 29Si NMR spectra of the polymers
from optically pure monomers showed sharper signals
compared with those of the polymers from racemic
monomers, suggesting that the polymers from optically
pure monomers are highly stereoregular. The optically
active polymers showed negative Cotton effects in the
wavelength region of both the σ-main chain and π-side
chain, reflecting their stereochemical structures.
(8) Li, Y.; Kawakami, Y. Macromolecules 1999, 32, 548.
(9) Murano, M.; Li, Y.; Kawakami, Y. Macromolecules 2000, 33,
3940.
(10) Oishi, M.; Kawakami, Y. Macromolecules 2000, 33, 1960.
(11) Shinke, S.; Kawakami, Y. Chromatographia 2001, 53, 140.
(12) Corey, J . Y.; Kraichely, D. M.; Huhmann, J . L.; Braddock-
Wilking, J .; Lindeberg, A. Organometallics 1995, 14, 2704.
(13) Sommer, L. H.; Frye, C. L.; Parker, G. A.; Michael, K. W. J .
Am. Chem. Soc. 1964, 86, 3271.
(14) (a) Oh, H.-S.; Imae, I.; Kawakami, Y. Chirality 2003, 15, 231.
(b) Oh, H.-S.; Imae, I.; Kawakami, Y.; Raj, S. S. S.; Yamane,
T. J . Organomet. Chem., in press. (c) Suzuki, K.; Kawakami,
Y. Organometallics 2003, 22, 2367. (d) Oh, H.-S.; Park, L.
S.; Kawakami, Y. Chirality, in press.
Refer en ces a n d Notes
(1) (a) Ohshita, J .; Furumori, K., Matsuguchi, A.; Ishikawa, M.
J . Org. Chem. 1990, 55, 3277. (b) Ohshita, J .; Furumori, K.;
Ishikawa, M.; Yamanaka, T., Organometallics 1989, 8, 2084.
(c) Ohshita, J .; Matsuguchi, A.; Furumori, K.; Hong, R. F.;
Ishikawa, M.; Yamanaka, T.; Koike, T.; Shioya, J ., Macro-
molecules 1992, 25, 2134. (d) Ohshita, J .; Hamaguchi, T.;
Toyoda, E.; Kunai, A.; Komaguchi, K.; Shiotani, M.; Ishikawa,
M.; Naka, A. Organometallics 1999, 18, 1717. (e) Tsutsui, S.;
Toyoda, E.; Hamaguchi, T.; Ohshita, J .; Kanetani, F.; Kunai,
A.; Naka, A.; Ishikawa, M. Organometallics 1999, 18, 3792.
MA0301101