Tris(pentafluorophenyl)borane as a superior catalyst in the synthesis of optically active SiO-coataining polymers

Article abstract of DOI:10.1021/ma050329a

Tris(pentafluorophenyl)borane was found to be an effective catalyst in the synthesis of optically pure and completely diisotactic phenyl- and naphthyl-substituted poly(siloxane)s by the reaction between (R,A)-1,3-dimethyl-1,3-diphenyl {or di(l-naphthyl)}-1,3-disiloxanediol and 1,1,3,3-tetramethyl-1,3-disiloxane, 1,1,6,6-tetramethyl-1,6-disilahexane, or 1,4-bis(dimethylsilyl)benzene under mild reaction conditions. The optically active disloxane units in the produced polymers had better controlled chemical and stereoregular structures than those obtained from the bis(silanol)s and bis(dimethylamino)-dimethylsilane. Homopolymerization of the starting bis(silanol) could be almost completely suppressed. Effects of the structure of the starting bis(silane)s on the yield, molecular weight, optical activity, and thermal properties of the resulting SiOSi-containing polymers were studied.

Full text of DOI:10.1021/ma050329a

6902
Macromolecules 2005, 38, 6902-6908
Tris(pentafluorophenyl)borane as a Superior Catalyst in the Synthesis
of Optically Active SiO-Containing Polymers
Daqing Zhou and Yusuke Kawakami*
School of Materials Science, Japan Advanced Institute of Science and Technology [JAIST],
Asahidai 1-1, Nomi, Ishikawa 923-1292, Japan
Received February 15, 2005; Revised Manuscript Received May 18, 2005
ABSTRACT: Tris(pentafluorophenyl)borane was found to be an effective catalyst in the synthesis of
optically pure and completely diisotactic phenyl- and naphthyl-substituted poly(siloxane)s by the reaction
between (R,R)-1,3-dimethyl-1,3-diphenyl {or di(1-naphthyl)}-1,3-disiloxanediol and 1,1,3,3-tetramethyl-
1,3-disiloxane, 1,1,6,6-tetramethyl-1,6-disilahexane, or 1,4-bis(dimethylsilyl)benzene under mild reaction
conditions. The optically active disloxane units in the produced polymers had better controlled chemical
and stereoregular structures than those obtained from the bis(silanol)s and bis(dimethylamino)-
dimethylsilane. Homopolymerization of the starting bis(silanol) could be almost completely suppressed.
Effects of the structure of the starting bis(silane)s on the yield, molecular weight, optical activity, and
thermal properties of the resulting SiOSi-containing polymers were studied.
Introduction
silsesquioxane gel8 having asymmetric silicon atom
centers in the repeating units using optically pure
silicon-containing monomers.
Nature uses chirality as one of the key structural
factors to perform a series of complicated functionalities,
such as molecular recognition and catalytic activities.1
Syntheses of optically active and/or stereoregular poly-
mers have been a challenging theme in the field of
polymer synthesis in recent years. Optically active
polymers can be obtained by polymerization of optically
active monomers or by stereoselective polymerization
of racemic or prochiral monomers using optically active
catalysts. Configurationally optically active polymers
are interesting as well as conformationally optically
active polymers.2
Stereoregular and/or optically active polysiloxanes
may widen the possible applications of silica, as the
support for optically active compounds, as self-enantio-
recognitive separating membranes, chiral column pack-
ing materials,9 and polymeric supports for asymmetric
catalysts.10 Furthermore, bulky and hydrophobic naph-
thyl groups are expected to stabilize the conformation
of the polymer by supramolecular interaction with
â-cyclodextrin.11 In this article, we described the syn-
thesis and stereochemical characterization of the formed
polymers by the analyses of NMR and optical rotation.
Meanwhile, poly(siloxane)s,3 consisting of [SiRR′O]
repeating units, a class of unique organic-inorganic
hybrid polymers, have been extensively used as one of
the most important thermally stable rubbery and insu-
lating materials. Especially, poly(dimethylsiloxane)s
have been widely used as silicone oil, silicone rubber,
main chain for liquid crystalline polymers,4 and polymer
support for metallocene catalysts by taking advantage
of their highly flexible structure and high thermal
stability.
Polycondensation is considered suitable for prepara-
tion of well-defined polymers. Cross-coupling reactions
of organosilanols with hydrosilanes or aminosilanes are
particularly convenient to synthesize polysiloxanes.
Hydrogen or low molecular weight amine as a byproduct
can be used for foaming and easily removed from the
reaction mixture.
Configurationally optical active poly(siloxane)s are
expected to exhibit novel unique properties different
from those of ordinary poly(siloxane)s without controlled
stereochemistry. It will be very interesting to correlate
the stereoregularity of polysiloxane with their physical
properties, but there are only a few reports on the
control of the stereochemistry of silicon atoms in the
polymer main chains. Recently, we reported the syn-
thesis of stereoregular and/or optically active polycar-
bosilane,5 poly(carbosiloxane)s,6 polysiloxanes,7 and poly-
Experimental Section
General. NMR spectra (1H: 499.4 MHz; 13C: 125.6 MHz;
29Si: 99.2 MHz) were obtained in CDCl3 on a Varian 500 MHz
spectrometer, model Unity INOVA. Chemical shifts are re-
ported in ppm relative to CHCl3 (δ 7.26 for 1H), CDCl3 (δ 77.0
for 13C), and tetramethylsilane (δ 0.0 for 29Si). IR spectra were
obtained on a JASCO VALOR-III spectrophotometer. GC and
DI EI mass analyses were carried out on a Shimazu QP-5000
mass spectrometer. Specific optical rotations were measured
with a JASCO DIP-370S digital polarimeter. Size exclusion
chromatography (SEC) and HPLC analyses were performed
on a JASCO HPLC, model GULLIVER. Combination of Shodex
KF-803L (30 cm, exclusion limit: Mn ) 7.0 × 104, polystyrene)
and KF-804 (30 cm, exclusion limit: Mn ) 4.0 × 105, poly-
styrene) columns (linear calibration down to Mn ) 100) were
used for molecular weight analysis with tetrahydrofuran (THF,
1.0 mL/min) as an eluent. CHIRALCEL OD (0.46 diameter ×
25 cm, cellulose carbamate derivative) or CHIRALPAK AD
(0.46 diameter × 25 cm, amylose carbamate derivative)
optically active stationary phase was used for optical purity
analysis with hexane and 2-propanol as mobile phase at 35
°C (0.4 mL/min, 9-10 kg/cm2) detected by UV (254 nm) and
circular dichroism (CD, 254 nm). For preparative separation,
columns of the size 2.0 diameter × 25 cm with 4.0 mL/min
solvents were used. Elemental analysis (EA) was performed
on a Vario EL III elemental analyzer. Differential scanning
calorimetric (DSC) analysis was performed on a Seiko DSC6200
instrument at a heating rate of 10.0 °C/min. The thermogravi-
metric analysis (TGA) was performed on a Seiko Instruments
TGA/DTA 220 with a heating rate of 10.0 °C/min under
nitrogen flow.
* To whom correspondence should be addressed: Tel +81-761-
51-1630; Fax +81-761-51-1635; e-mail kawakami@jaist.ac.jp.
10.1021/ma050329a CCC: $30.25 © 2005 American Chemical Society
Published on Web 07/06/2005

Macromolecules, Vol. 38, No. 16, 2005
Optically Active SiO-Containing Polymers 6903
Scheme 1. Synthesis and Separation of Optically Active (R,R)-1 and (R,R)-2
Scheme 2
Materials. Bis(dimethylamino)dimethylsilane and 1,3-di-
hydro-1,1,3,3-tetramethyldisiloxane (TMDS) were obtained
from Shin-Etsu Chemical. 1,4-Bis(dimethylsilyl)benzene (BSB)
was prepared according to the literature.12 Tris(pentafluoro-
phenyl)borane [B(C6F5)3] was a gift from Tosoh Finechem Corp.
Chloro(1,5-cyclooctadiene)rhodium(I) dimer [RhCl(cod)]2, tris-
(triphenylphosphine)chlororhodium(I) [RhCl(PPh3)3], and
tris(dibenylideneacetone)dipalladium(0)-chloroform adduct
[Pd2(dba)3‚CHCl3] were purchased from Sigma-Aldrich. THF,
hexane, benzene, and toluene were distilled from sodium prior
to use.
(m/e) 290 (M+), 197 ([M-Me-Ph]+). Calculated for C14H18O3-
Si2 (290.46): C, 57.89; H, 6.25. Found: C, 57.63; H, 7.47.
(R,R)-2: 1,3-Dihydro-1,3-dimethyl-1,3-di(1-naphthyl)disilox-
ane was obtained by the hydrolysis of methyl(1-naphthyl)-
cholorosilane and purified by flash column chromatography
(silica gel 60; eluent, hexane) (4.64 g, 51.8%) as a colorless
liquid. (R,R)-2 was synthesized by the hydrolysis of 1,3-
dihydro-1,3-dimethyl-1,3-di(1-naphthyl)disiloxane with excess
water in the presence of 10% palladium on carbon (0.06 g) in
THF (100 mL). After removal of the catalyst by passing
through a short Celite column, a white solid (4.3 g, 44.1%) was
obtained when the reaction mixture was precipitated into
pentane:CH2Cl2 ) 10:1. Further recrystallization from hexane:
2-propanol ) 10:1 at 0 °C gave a crystal rich in meso-2.
Isolation of optically pure (R,R)-2 was performed by prepara-
tive HPLC on CHIRALAK AD (hexane:2-propanol ) 6:1) using
0.03 g of 2 rich in racemic isomers. The first eluted (R,R)-
isomer was collected (1.22 g, mp 147.3-151.6 °C, [R]23D ) -1.0,
c ) 1.01, CHCl3).
1,4-Bis(dimethylsilyl)butane (BDMSB) was synthesized as
follows: To a 300 mL flask were added Mg tunings (3.6 g, 0.15
mol), dimethylchlorosilane (9.45 g, 0.1 mol), and THF (10 mL).
A THF (50 mL) solution of 1,4-dibromobutane (10.8 g, 0.05
mol) was added slowly to the flask for 2 h. After the reaction
system was stirred for 30 h, the product mixture was diluted
with hexane, filtered to remove the salts, and washed with
water. The organic layer was separated and dried on MgSO4.
Evaporation of the solvent and distillation gave a colorless
liquid (4.28 g, 49.2%); bp 66-68 °C/20 mmHg.
1
NMR (δ) H: 0.05-0.06 (d, J1 ) 3.57 Hz, 12H), 0.56-0.62
(m, 4H), 1.35-1.40 (m, 4H), 3.80-3.86 (m, J1 ) 3.57 Hz, J2 )
3.30 Hz, 2H). 13C: -4.41, 14.03, 28.01. 29Si: -14.3. IR (neat,
cm-1): 2957, 2917, 2113, 1250, 886, 836. Calculated molecular
weight: 174.43. MS (m/e) 173 ([M-H]+), 159 ([M-CH3] +), 144
([M-2CH3]+).
NMR (δ) 1H: 0.52 (s, 6H), 3.26 (br s, 2H), 7.41-7.49 (m, 6H),
7.86 (d, J ) 8.00 Hz, 2H), 7.90 (d, J ) 7.00 Hz, 2H), 8.31 (d,
J ) 8.00 Hz, 2H). 13C: 0.48, 125.02, 125.59, 126.21, 128.25,
128.90, 130.82, 133.37, 134.04, 134.48, 136.40. 29Si: -21.8. IR
(KBr, cm-1): 3198, 3063, 2962, 1590, 1568, 1505, 1428, 1322,
1260, 1220, 1148, 1047, 1024, 988. EI-MS (m/e) 390 (M+).
Calculated for C22H22O3Si2 (390.58): C, 67.65; H, 5.68.
Found: C, 67.59; H, 7.00.
(R,R)-1,3-Dimethyl-1,3-diphenyl- or di(1-naphthyl)-1,3-di-
siloxanediol [(R,R)-1 or -2] was synthesized according to
Scheme 1. (R,R)-1: H2O (0.90 g, 0.05 mol) in THF (30 mL) was
added dropwise to methylphenyldichlorosilane (19.1 g, 0.1 mol)
in THF (150 mL) at 0 °C. The reaction mixture was stirred
for 4 h at room temperature. Removal of the solvent and
distillation afforded 1,3-dichloro-1,3-dimethyl-1,3-diphenyl-
disiloxane (120-125 °C/0.3 mmHg, 6.02 g, yield 36.8%). The
product was hydrolyzed by adding to a two-layer system
consisting of NH4Cl‚NH3 aqueous buffer (150 mL) and Et2O
(150 mL) at 0 °C. The reaction mixture was stirred for 1 h at
the temperature. Organic phase was separated and dried over
anhydrous Na2SO4. Removal of the solvent afforded a crude
product 1. Recrystallization from hexane gave 1 as a colorless
solid. Further recrystallization from hexane:2-propanol ) 10:1
at 0 °C gave meso-1 (1.87 g, 12.9% yield) as a colorless crystal.
Evaporation of the solvent of the filtrate gave 1 rich in racemic
isomers (2.43 g). Optically pure (R,R)-1 was isolated by
preparative HPLC on CHIRALPAK AD (hexane:2-propanol )
10:1, detection at 254 nm, flow rate 4.0 mL/min) using 0.04 g
of 1 rich in racemic isomers as the sample. The first eluted
Deaminative Polycondensation. As a typical example,
polymerization of (R,R)-1 with bis(dimethylamino)dimethyl-
silane (3) was described (Scheme 2). In a 30 mL two-necked
flask, 3 (0.146 g, 1.0 mmol) was added to (R,R)-1 (0.290 g, 1.0
mmol) in toluene (1 mL), and the reaction system was stirred
at 100 °C for 20 h with N2 bubbling. After pouring into
methanol, the precipitate was collected and dried in vacuo to
give the polymer 1 (0.215 g, 63.5% yield, Mn ) 43 300, Mw/Mn
) 2.36, [R]23 ) -1.26, c ) 1.00, CHCl3).
D
NMR (δ) 1H: -0.04 (s, 6H), 0.24 (s, 6H), 7.20 (br, 4H), 7.30
(br, 2H), 7.46 (br, 4H). 13C: -0.23, 1.04, 127.5, 129.5, 133.3,
137.3. 29Si: -34.5, -20.3. IR (neat, cm-1): 3072, 3026, 2963,
2765, 1593, 1429, 1125, 1097, 1021, 906, 849, 798, 731, 700.
Cross-Dehydrocoupling Polymerization. Model Reac-
tion. To a solution of (R,R)-1 (0.029 g, 0.1 mmol) and tris-
(pentafluorophenyl)borane [B(C6F5)3] (0.0002 g, 0.4 mol %) in
toluene (0.4 mL) was slowly added triethylsilane (0.0232 g,
0.20 mmol) at room temperature. After the reaction mixture
was stirred for 2 h, removal of the solvent afforded a crude
product. The product was purified by flash column chroma-
(R,R)-isomer was collected (1.02 g, mp 96.0 ∼ 97.4 °C; [R]23
D
) -6.8, c ) 1.00, CHCl3).
NMR (δ) 1H: 0.40 (s, 6H), 2.86 (br s, 2H), 7.35-7.42 (m, 6H),
7.64 and 7.65 (2d, J ) 6.50 Hz, 4H). 13C: -1.08, 127.9, 130.1,
133.4, 136.40. 29Si: -22.8. IR (KBr, cm-1) 3211, 3072, 3052,
2960, 1592, 1489, 1430, 1262, 1126, 1044, 1029, 997. EI-MS

6904 Zhou and Kawakami
Scheme 3
Macromolecules, Vol. 38, No. 16, 2005
P-6a: Colorless liquid (0.201 g, 38.5% yield): SEC: Mn
)
13 000, Mw/Mn ) 2.55; [R]23 ) -1.30, c ) 1.00, CHCl3. NMR
D
(δ) 1H: -0.22 to -0.19 (d, J ) 4.00 Hz, 12H), 0.40 (s, 6H),
7.17-7.25 (m, 4H), 7.32-7.35 (m, 2H), 7.68-7.70 (br d, 2H),
7.74-7.76 (m, 4H), 8.16-8.17 (br d, 2H). 13C: 0.74, 0.85, 1.16,
124.71, 125.20, 125.52, 128.47, 128.71, 130.21, 133.23, 133.62,
135.32, 136.36. 29Si: -34.0, -21.1. IR (neat, cm-1): 3071, 3039,
2964, 1506, 1261, 1219, 1148, 1094, 1021, 828, 796, 778, 749.
Scheme 4
P-7a: Colorless liquid (0.401 g, 71.4% yield): SEC: Mn
)
91 000, Mw/Mn ) 2.49; [R]23 ) +2.36, c ) 1.00, CHCl3. NMR
D
(δ) 1H: -0.05 to -0.04 (d, J ) 3.4 Hz, 12H), 0.29 (br, 4H),
0.50 (s, 6H), 1.03 (br, 4H), 7.29-7.40 (m, 6H), 7.76-7.85 (m,
6H), 8.25-8.27 (br d, 2H). 13C: 0.01, 0.03, 1.35, 17.78, 26.78,
124.76, 125.23, 125.43, 128.53, 128.89, 130.17, 133.28, 133.53,
135.90, 136.44. 29Si: -34.01, 9.24. IR (neat, cm-1): 3051, 3040,
2956, 2918, 1506, 1457, 1407, 1258, 1218, 1148, 1051, 987, 836,
795, 779, 746.
P-8a: Colorless liquid (0.419 g, 72.1% yield): SEC: Mn
)
12 200, Mw/Mn ) 2.88; [R]23 ) +11.7, c ) 1.00, CHCl3. NMR
D
(δ) 1H: 0.14-0.15 (d, J ) 5.5 Hz, 12H), 0.42 (s, 6H), 7.11-7.15
(m, 2H), 7.22-7.40 (m, 8H), 7.68-7.75 (m, 6H), 8.16-8.18 (d,
2H). 13C: 0.40, 0.44, 1.30, 124.76, 125.27, 125.542, 128.51,
128.81, 130.28, 132.13, 133.24, 133.68, 135.40, 136.34, 140.10.
29Si: -33.0, -1.1. IR (neat, cm-1): 3053, 3005, 2957, 2901,
1589, 1506, 1320, 1259, 1218, 1139, 1046, 987, 825, 779, 748.
tography (Florisil with hexane as an eluent) to give the product
1,1,1,4,4,4-hexaethyl-2,3-dimethyl-2,3-diphenyltetrasiloxane as
a colorless liquid (0.0474 g, 91.4% yield, [R]23 ) -3.55, c )
D
1
1.00, CHCl3).NMR (δ) H: 0.32 (s, 6H), 0.52 (q, J ) 8.00 Hz
12H), 0.88 (t, J ) 8.00 Hz, 18H), 7.29-7.38 (m, 6H), 7.53 (2d,
J1 ) 7.69 Hz, J2 ) 1.65 Hz, 4H). 13C: -0.21, 6.23, 6.67, 127.48,
129.39, 133.30, 138.14. 29Si: -35.3, 11.4. IR (neat, cm-1): 2955,
2911, 2876, 1520, 1485, 1429, 1259, 1238, 1123, 1052, 1005,
972. EI-MS (m/e) 490 ([M-Et]+).
A similar procedure in the presence of rhodium complex
[RhCl(cod)]2 gave the product only in 34% yield at 50 °C, and
side reaction occurred.
Polymerization. As a typical example, the synthetic
procedure to obtain P-3a from (R,R)-1 and 1,3-dihydro-1,1,3,3-
tetramethyldisiloxane (4) was described (Scheme 4). To a
solution of (R,R)-1 (0.290 g, 1.0 mmol) and B(C6F5)3 (0.002 g,
0.4 mmol%) in toluene (1 mL) was slowly added the silane 4
(0.134 g, 1.0 mmol) at room temperature. The reaction mixture
was stirred for 12 h. After pouring into methanol, the
precipitate was collected and dried in vacuo to get the polymer
P-3a (0.105 g, 25.1% yield; SEC: Mn ) 56 600, Mw/Mn ) 1.75;
[R]23D ) -0.90, c ) 1.00, CHCl3).NMR (δ) 1H: -0.02-0.01 (d,
J ) 10.50 Hz, 12H), 0.31 (s, 6H), 7.26-7.29 (m, 4H), 7.32-
7.34 (m, 2H), 7.53-7.55 (m, 4H). 13C: -0.17, 0.98, 1.01, 127.53,
129.503, 133.33, 137.53. 29Si: -34.6, -21.0. IR (neat, cm-1):
3071, 3052, 3015, 2962, 2902, 1654, 1593, 1559, 1429, 1411,
1261, 1098, 1020, 851, 789, 699.
Results and Discussion
The absolute configurations of 1 and 2 were assumed
by referencing the reported (S,S)-1 (ee ) 72%, [R]25
)
D
+3.3).13 The isolated optically pure 1 in this study had
[R]23 ) -6.8, and considered to be (R,R)-1, although
D
the optical rotation was a little too large. Isolated
optically pure 2 also had minus optical rotation of [R]23
D
) -1.0 and was considered as (R,R)-2. Deaminative
polycondensation of optically pure (R,R)-1 with 3 was
carried out to obtain diisotactic and optically active poly-
(siloxane)s (P-1) (Scheme 2). For comparison, polycon-
densation reactions of diastereomer-1 and meso-1 were
also carried out to obtain atactic and meso atactic
polysiloxanes, respectively (Table 1). The resulting
polymers were characterized by 1H, 13C, and 29Si NMR
spectroscopy. 29Si NMR was not sensitive enough to
analyze the stereoregularity of polymers. The 1H signals
of methyl groups of P-1 reflected the stereoregularity
of the polymer (Figure 1). The P-1 prepared from (R,R)-1
showed a strong peak at 0.23 ppm, which was consid-
ered to arise from SiPhMe of racemic disiloxane units.
Only one peak at 0.20 ppm was observed for P-1
prepared from meso-1 assignable to the two equivalent
methyl groups in the meso disiloxane units. Moreover,
two sharp peaks at 0.23 and 0.20 ppm were observed
in P-1 prepared from diastereomer-1, reflecting the
methyl groups from the meso and racemic disiloxane
units. Further evidence for the tacticity of P-1 was given
by the signal of meta-PhSiMe splitting in 13C NMR
(Figure 1). The peaks at 127.56 and 127.52 ppm could
be assigned to meso and racemic disiloxane repeating
unit, respectively. However, there were some unidenti-
fied broad peaks near the main peaks, which might
indicate the presence of a homocondensation product of
P-4a to P-8a were prepared similarly with P-3a.
P-4a: Colorless liquid (0.180 g, 38.9% yield). SEC: Mn
)
12 500, Mw/Mn ) 2.59; [R]23 ) -1.12, c ) 1.00, CHCl3. NMR
D
(δ) 1H: 0.06-0.07 (d, J ) 2.80 Hz, 12H), 0.35 (s, 6H), 0.50 (br,
4H), 1.26 (br, 4H), 7.32-7.39 (m, 6H), 7.57-7.59 (m, 4H). 13C:
-0.03, 0.21, 18.00, 26.94, 127.54, 129.45, 133.32, 138.04. 29Si:
-34.6, 9.1. IR (neat, cm-1): 3070, 3051, 3005, 2957, 2918, 1429,
1410, 1258, 1192, 1124, 1045, 987, 840, 788, 731, 699.
P-5a: Colorless liquid (0.268 g, 55.7% yield): SEC: Mn
)
13 500, Mw/Mn ) 2.19; [R]23 ) +10.4, c ) 1.00, CHCl3. NMR
D
1
(δ) H: 0.33-0.34 (d, J ) 4.00 Hz, 12H), 0.36 (s, 6H), 7.28-
7.31 (m, 4H), 7.35-7.38 (m, 2H), 7.50 (s, br, 4H); 7.55-7.57
(d, 4H). 13C: -0.10, 0.67, 0.69, 127.60, 129.566, 132.26, 133.35,
137.53, 140.43. 29Si: -33.5, -1.1. IR (neat, cm-1): 3071, 3051,
3003, 2958, 2925, 2850, 1592, 1429, 1381, 1259, 1139, 1124,
1081, 1043, 1020, 822, 784, 732, 699.
Table 1. Deaminative Polycondensation of 1 or 2 with 3a
c
run
1 or 2
polymers
atactic
yield (%)b
Mn
Mw/Mn
[R]23D (deg)
1
2
3
4
5
1 diastereomer
meso
67.2
62.1
63.5
47.6
39.0
64 300
52 900
43 300
4 600
2.64
1.87
2.36
1.50
2.36
meso-atactic
(R,R)-diisotactic
atactic
R,R
-1.26
-2.46
2 diastereomer
R,R
(R,R)-diisotactic
4 800
a Aminosilane: 1 mmol, toluene(1 mL), 100 °C. b Isolated yields after reprecipitation into MeOH. c Polystyrene standards.

Macromolecules, Vol. 38, No. 16, 2005
Optically Active SiO-Containing Polymers 6905
Figure 2. 1H NMR spectra of SiPhMe in model compound:
(a) optically active; (b) meso; (c) diastereomer.
Figure 1. 1H NMR spectra of SiPhMe and 13C NMR of meta-
PhSiMe of P-1: (a) (R,R)-diisotactic; (b) meso-atactic; (c)
atactic.
Transition metal catalysts [RhCl(cod)]2, RhCl(PPh3)3,
and [Pd2(dba)3‚CHCl3] showed high activity in the cross-
dehydrocoupling reaction,7b,15 whereas, in this
model reaction, almost no reaction was observed with
[Pd2(dba)3‚CHCl3] and RhCl(PPh3)3 (entries 8-11). [RhCl-
(cod)]2 showed only low activity, and side reaction
occurred (yield 35%, conversion 100%, LiH as additive,
entry 14). Because the reaction temperature was too
high (entry 12), or too basic (entries 13 and 14), a lot of
cyclic oligomers were formed. Thus, rhodium catalysts,
used in the synthesis of poly(methylphenylsiloxane) rich
in syndiotacticity (95% retention of configuration), were
not effective. The substituents on silicon exerted a
significant steric effect on the reactivity of cross-
dehydrocoupling reaction.
the bis(silanol). It is well-known that silanol groups
could undergo self-condensation in high temperature or
under basic conditions. Such reaction will lead to
disruption of the desirable perfectly alternating archi-
tecture. From 1H and 13C NMR spectra and the negative
optical rotation ([R]23 ) -1.26), P-1 prepared from
D
(R,R)-1 with 3 was concluded as a polymer rich in (R,R)-
diisotacticity.
Only low molecular weight polymer (Mn ) 4800, Mw/
Mn ) 2.36) was obtained from the naphthyl derivative,
(R,R)-2, probably due to steric hindrance by the naph-
thyl group attached to the silicon atom.
The dealkylative or dehydrogenative coupling of or-
ganohydrosiloxanes with organomethoxysilanes or or-
ganosilanols by tris(pentafluorophenyl)borane [B(C6F5)3]
reported by Rubinsztajn seems particularly convenient
to synthesize desired polysiloxane due to its high
activity.14 Side reactions, like homocondensation of
silanol groups and disproportionation process, may not
be significant in this system. If the stereochemistry of
the cross-coupling reactions was controlled, this reaction
might be more suitable for the preparation of well-
controlled structure of poly(siloxane)s.
Cross-dehydrocoupling reaction of (R,R)-1 with tri-
ethylsilane, as a model reaction, was carried out in
toluene at room temperature using B(C6F5)3 (Scheme
3), and the results are summarized in Table 2 together
with the data with metallic catalysts.
The condensation reaction took place at room tem-
perature in the presence of very low levels of B(C6F5)3.
The reaction was completed in 2-3 h. The reaction had
very high selectivity and activity when used in nonpolar
solvents, and no byproduct was observed (entries 1-4).
However, when polar solvent was used, no expected
1
product was obtained (entries 5-7). The H NMR of
SiPhMe obviously reflected the reaction was very ste-
reospecific (99% ee retention) (Figure 2). The model
product prepared from optically pure (R,R)-1 or meso-1
showed only one singlet peak at 0.33 or 0.29 ppm,
respectively. The configuration of silicon atoms of
(R,R)-1 was not affected during the cross-dehydrocou-
pling with the hydrosilane. Compared with metallic
catalysts, B(C6F5)3 showed higher reactivity and ste-
reoselectivity in the cross-dehydrocoupling reaction.
Table 2. Cross-Dehydrocoupling Reaction of 1 with Triethylsilanea
entry
1
catalyst
solvent
time, h
yield (conv),%b
stereochemistryc
1
2
diastereomer
meso
B(C6F5)3
toluene
toluene
toluene
pentane
CH2Cl2
THF
3
3
92.1 (100)
91.4 (100)
93.1 (100)
92.3 (100)
- (100)
B(C6F5)3
99% retention
98% retention
99% retention
3
(R,R)
meso
B(C6F5)3
3
4
B(C6F5)3
3
5
meso
B(C6F5)3
10
10
6
6
meso
B(C6F5)3
- (100)
7
meso
B(C6F5)3
ether
- (100)
8
meso
Pd2(dba)3
Pd2(dba)3
Pd2(dba)3
RhCl(PPh3)3
[RhCl(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
toluene
toluene
THF
toluene
toluene
toluene
toluene
12
4
no reaction
no reaction
no reaction
no reaction
33.7 (100)
14.0 (72.6)
35.3 (100)
9
meso
10
11
12
13d
14e
meso
4
meso
5
meso
5
meso
18
18
meso
a 1 (0.1 mmol) with triethylsilane (0.2 mmol) at 20 °C (except for 9-12: 50 °C) in the presence of 0.4 mmol% catalyst. b Isolated yield;
conversions are in parentheses. Yields of 12-14 were determined by NMR. c Determined by NMR. d Additive: 1.0 equiv of Et3N. e Addi-
tive: 1.0 equiv of LiH.

6906 Zhou and Kawakami
Macromolecules, Vol. 38, No. 16, 2005
Table 3. Synthesis of Polymer P-3 to Polymer P-8 by Cross-Dehydrocoupling Reactiona
c
polymer
1 or 2
X
yield (%)b
Mn
Mw/Mn
Tg (°C)d
[R]23D (deg)
-0.90
P-3a 1
P-3b
P-3c
P-4a
P-4b
P-4c
P-5a
P-5b
P-5c
P-6a 2
P-6b
P-7a
P-7b
P-8a
P-8b
(R,R)
meso
diastereomer
(R,R)
meso
diastereomer
(R,R)
meso
diastereomer
(R,R)
diastereomer
(R,R)
-O-
25.1
28.9
27.2
38.9
46.2
48.2
55.7
66.5
72.7
38.5
35.0
71.4
70.2
72.1
81.1
56 600
45 000
17 900
12 500
19 100
14 900
13 500
13 200
7 600
13 000
8 760
9 100
8 100
1.75
3.07
2.18
2.59
4.26
2.66
2.19
2.92
2.18
2.55
2.01
2.49
3.62
2.88
2.64
-69.4
-69.8
-70.0
-63.9
-63.0
-63.6
-34.1
-33.1
-34.1
-16.3
-29.0
-17.6
-19.5
15.6
-(CH2)4-
-1.12
+10.4
-(p-C6H4)-
-O-
-1.30
+2.36
+11.7
-(CH2)4-
-(p-C6H4)-
diastereomer
(R,R)
diastereomer
12 200
6 500
8.34
a [Catalyst]/[silane] ) 0.2%, silane: 1 mmol, catalyst: B(C6F5)3, toluene (1 mL), 20 °C. b Isolated yields after reprecipitation into MeOH.
c Polystyrene standards. d Determined by DSC with heating rate of 10 °C min-1 on the second scan.
Figure 4. 1H NMR spectra of SiNpMe and 13C NMR of
SiNpMe of P-6: (a) (R,R)-diisotactic; (b) atactic.
were very sharp and not contaminated with broad
Figure 3. 1H NMR spectra of SiPhMe and 13C NMR of meta-
unidentified peaks.
PhSiMe of P-3: (a) (R,R)-diisotactic; (b) meso-atactic; (c)
For the naphthyl-substituted poly(siloxane)s, 1H and
atactic.
13C NMR showed the similar results with phenyl-
substituted polymers (Figure 4). The 1H signals of
SiNpMe of P-6a prepared from (R,R)-2 showed a strong
peak at 0.40 ppm. Moreover, two peaks at 0.40 and 0.34
ppm were observed in P-6b prepared from diastereomer-
2, reflecting the methyl groups from the racemic and
meso disiloxane units. The tacticity of P-6 was also
elucidated by the SiNpMe signal in 13C NMR (Figure
4). The peaks at 130.3 and 130.2 ppm were assigned to
meso and racemic disiloxane repeating unit, respec-
tively.
Cross-dehydrocoupling polymerizations of optically
pure (R,R)-1 or (R,R)-2 with the bis(hydrosilane)s were
also carried out (P-3 to P-8) (Scheme 4). The results are
summarized in Table 3.
Although the yield of polymer was not high due to
the unavoidable formation of cyclotetrasiloxane as
byproduct through intramolecular cyclization between
terminal silanol and hydrosilyl groups, homocondensa-
tion of the bis(silanol) was completely suppressed.
Polymers could be purified by reprecipitation.
Purified P-3a, prepared from (R,R)-1 with 4, showed
a strong peak at 0.31 ppm, which is considered to arise
from SiPhMe of racemic disiloxane units. Only one sharp
peak at 0.27 ppm was observed in P-3b prepared from
meso-1 due to the two equivalent methyl groups in the
meso disiloxane units. Moreover, two sharp peaks at
0.31 and 0.27 ppm were observed for P-3c prepared from
diastereomer-1, reflecting the methyl groups in the
racemic and meso disiloxane units. Tacticity of P-3 was
also elucidated by the signal of meta SiPhMe carbon
splitting in 13C NMR (Figure 3). Only one sharp singlet
at 127.5 or 127.6 ppm was observed for the polysiloxane
prepared from (R,R)-1 or meso-1 due to the two equiva-
lent methyl groups in the racemic or meso repeating
disiloxane unit, respectively. On the other hand, two
peaks at 127.6 and 127.5 ppm in almost equal intensity
were observed for the polymer prepared from diastere-
omer-1, reflecting the methyl groups from the meso and
racemic disiloxane units in equal quantity. These peaks
From 1H and 13C NMR spectra, P-3a and P-6a formed
from (R,R)-1 or (R,R)-2, respectively, with 4 were
concluded as predominantly diisotactic polymers. Though
it was not possible to distinguish whether the polymer
was either (R,R)- or (S,S)-diisotactic only by the result
1
of H and 13C NMR, P-3a and P-6a showed negative
optical rotations ([R]23 ) -0.90 and [R]23 ) -1.30,
D
D
respectively); it might be reasonable to consider that the
polymers 3a and 6a are (R,R)-diisotactic as discussed
above.
Thermal properties of the polymer were evaluated
using DSC and TGA. All the poly(siloxane)s exhibited
only one glass transition temperature without any other
transitions. Tg of (R,R)-diisotactic P-3a was -70 °C,
which was a little different from that of meso-atactic
P-3b (-69.8 °C) and atatic P-3c (-69.4 °C). TGA also
showed similar behavior (Figure 5). (R,R)-Diisotactic
P-3a showed an onset decomposition temperature at 487
°C, and for meso-atactic and atactic P-3, no obvious
changes were observed in their onset decomposition

Macromolecules, Vol. 38, No. 16, 2005
Optically Active SiO-Containing Polymers 6907
Table 4. DSC and TGA Data of Optically Active Polymer P-3a to Polymer P-8aa
P-3a
P-4a
P-5a
P-6a
P-7a
P-8a
Tg (°C)
Td(onset) (°C)
char yield (750 °C) (%)
-69.4
487
24
-63.9
468
2.5
-34.1
500
45
-16.3
500
18
-17.6
512
3.6
15.6
534
30
a DSC: second heating (10 °C/min) in air; TGA: 10 °C/min under nitrogen flow (200 mL/min).
Figure 7. 13C NMR spectra of SiNpMe of polymers 6-8: (a)
(R,R)-diisotactic; (b) atactic.
Figure 5. TGA thermograms of polymers 3 and 6.
Figure 6. 13C NMR spectra of SiPhMe in polymers 3-5: (a)
(R,R)-diisotactic; (b) meso-atactic; (c) atactic.
Figure 8. TGA thermograms of polymers 3a-8a.
(P-5a), but introduction of bulky naphthyl group in the
side chain increased the optical rotation only a little.
temperatures (Td ) 478 and 471 °C, respectively). For
the naphthyl-substituted poly(siloxane)s P-6, Tg of
(R,R)-diisotactic P-6a was -16.3 °C, which is a little
different from that of atatic P-6a (-29.0 °C), and onset
decomposition temperature at 500 and 497 °C, respec-
tively. Stereoregularity of the polymers 3 and 6 had only
a small influence on its thermal properties.
Flexible structure (TMDS), long spacer group
(BDMSB), and rigid structure (BSB) were introduced
to the polymers to study the effects of these groups on
their optical and thermal properties (Table 3).
The thermal properties of polymers are represented
in Figure 8 and Table 4. P-3a, a well-known thermally
stable polymer, showed the glass transition temperature
(Tg) at -69.4 °C and the onset decomposition temper-
ature (Td) at 487 °C, and the residual weight was 24%
when heated at 750 °C under nitrogen. As the X group
was changed to -(CH2)4- (P-4a), no obvious change was
observed in its Tg ( -63.9 °C) and Td (468 °C), while
the residual yield after heating was remarkably de-
creased (2.5%). On the other hand, rigid -(p-C6H4)- in
the main chain and bulkier naphthyl group in the side
chains greatly increased the thermal stability: P-5a
(Tg ) -34.1 °C, Td ) 500 °C, residual yield 45%), P-6a
(Tg ) -16.3 °C, Td ) 500 °C, residual yield 18%), and
P-8a (Tg ) 15.6 °C, Td ) 534 °C, residual yield 30%).
From 13C NMR spectra of SiPhMe and the optical
rotation, the polymers prepared from (R,R)-monomers
with the bis(hydrosilane)s by B(C6F5)3 were concluded
to have completely controlled sequence and diisotacticity
(Figures 6 and 7). Introduction of the flexible structure
makes it easy to form the cyclic oligomers as byproducts.
However, introduction of the long spacer group and rigid
structure increased the yields of polymers (Table 3). The
order of molecular weight of the polymers was P-3 >
P-4 > P-5 and P-6 > P-7 > P-8. The reactivity of
hydrosilane groups decreased with the introduction of
the long spacer group [-(CH2)4-], rigid structure [-(p-
C6H4)-], and bulkier group (naphthyl).
Conclusions
Optically pure organosilicon compounds, (R,R)-1,3-
dimethyl-1,3-diphenyl-1,3-disiloxanediol and (R,R)-1,3-
dimethyl-1,3-di(1-naphthyl)-1,3-disiloxanediol, were sepa-
rated by HPLC. Contrary to that, optically active and
diisotactic poly(siloxane)s, but not completely pure, were
prepared by deaminative polycondensation with bis-
(dimethylamino)dimethylsilane; cross-dehydrocoupling
reaction in the presence of B(C6F5)3 under mild reaction
conditions gave polymers with the chiral silicon units
As the X group was changed from -O- to -(CH2)4-
or -(p-C6H4)-, the optical rotation increased remark-
ably from -0.90 (P-3a) to +1.12 (P-4a) and +10.4

6908 Zhou and Kawakami
Macromolecules, Vol. 38, No. 16, 2005
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being completely optically pure and diisotactic. Stereo-
regular, meso-atactic, and atactic polymers showed
similar thermal properties. Introduction of the rigid -(p-
C6H4)- to the main chain increased the optical activity
and improved the thermal properties of polymers. Bulky
naphthyl groups in the side chain had significant effects
on the thermal properties, but not on optical property.
(5) (a) Uenishi, K.; Imae, I.; Shirakawa, E.; Kawakami, Y.
Macromolecules 2002, 35, 2455-2460. (b) Kawakami, Y.;
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Acknowledgment. This work was partly supported
by a Grant-in-Aid for Scientific Research (16205016)
from the Ministry of Education, Science, Sports, Culture
and Technology, Japan. D.-Q. Zhou appreciated the
scholarship from the ministry.
(7) (a) Oishi, M.; Kawakami, Y. Macromolecules 2000, 33, 1960-
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