Yoshikazu Sadahiro

Precise synthesis of monosubstituted polyacetylenes using Rh complex catalysts. Control of solid structure and π‐conjugation length

Stereospecific polymerization of monosubstituted acetylenes was successfully performed using a Rh complex, [Rh(norbornadiene)Cl] 2 , as a catalyst, and the resulting polyacetylenes were characterized in detail by 1 H NMR, ESR, laser Raman, diffuse reflective UV, and wide-angle X-ray diffraction. The Rh complex was found to yield selectively the cis-transoid isomer even at room temperature in high yields when alcohol or triethylamine was used as the solvent. Additionally, the resulting cis-polyacetylenes were found to form a pseudohexagonal, columnar self-assembly or superstructure. Further compression of the cis-polymers induced cis-trans isomerization even at room temperature under vacuum, breaking rotationally the cis-C=C bonds and, thus, giving π-radicals as the origin of magnetic properties.

Pressure‐induced cis to trans isomerization of aromatic polyacetylenes prepared using a Rh complex catalyst: A control of π‐conjugation length

This study reports that stereospecific polymerization of aromatic acetylenes, e.g., p-methoxyphenylacetylene (pMOPA) and p-ethoxyphenylacetylene (pEOPA) was successfully performed to give polyacetylene selectively bearing cis-transoid forms in high yield when a Rh complex catalyst, [Rh(norbornadiene)Cl] 2 was used in the presence of triethylamine as the polymerization solvent together with a detailed characterization of the resulting polymers, before and after compression. Compression of these polymers induced a cis-trans isomerization at room temperature under vacuum even in the solid state. Based on data collected before and after compression it is estimated that the trans conjugated length, (C=C) n , produced as a result of the compression is n = 26 for PpMOPA and n = 40 for PpEOPA polymers, respectively. We further found that g values in the ESR spectra of the pristine polymer were shifted to higher magnetic field by compression, indicating that unpaired electrons called solitons are stabilized in the trans conjugation length as mobile electrons, although in the pristine polymers the unpaired electrons are stabilized in the less conjugated chain, showing large g value, suggesting a magnetic interaction between oxygen in the alkoxy group of phenyl moiety and unpaired electrons in the cis form.

Pressure-induced cis to trans isomerization of poly(ortho- and para-methoxyphenylacetylene)s prepared by [Rh(norbornadiene)Cl]2 catalyst. A Raman, UV, and ESR study

The stereospecific polymerization of o- and p-methoxyphenylacetylenes (MOPAs) with [Rh(norbornadiene)Cl] 2 as a catalyst in the presence of an organic base (triethylamine) at 30°C is reported, together with the detailed characterization using resonance Raman, diffuse reflection UV, and ESR spectroscopic methods. The resulting polymers were shown to selectively have a cis-transoid form. It was found, interestingly, that the resultant aromatic polyacetylenes in the cis form are easily isomerized to those in the trans form when a pressure of ca. 100∼200 kg/cm 2 was exerted on the solid polymers at room temperature.

Columnar Assemblies of Aliphatic Poly(acetylene ester)s Prepared with a [Rh(norbornadiene)Cl]2 Catalyst.1H and13C NMR, X-Ray Diffraction and AFM Studies

Alkyl propiolates: HC≡CCOOn-C m H 2m+1 (m = 2∼4), acetylene esters were polymerized with a [Rh(norbornadiene)Cl] 2 catalyst in methanol as the polymerization solvent to produce poly(n-alkyl propiolate)s, PAPAs, called polyacetylene esters, in relatively high yields. The resulting PAPAs were characterized in detail using 1 H and 13 C NMR spectroscopy, X-ray diffraction, and atomic force microscope methods. The data showed that the resulting polymers selectively have cis-transoid form. The cis-transoid isomer is not amorphous but holds a pseudohexagonal structure called a columnar assembly the diameter of which agrees with those estimated by the semiempirical calculation method (AM1). The crystalline ratios of the columnar assemblies were also estimated to be ca. 60∼70%. In the case of poly(ethyl propiolate), PEPA, the crystalline size was found to approximately agree with that estimated from the AFM images of the cast film of PEPA.

Columnar Formation from Polyethynylbenzene and Poly-(p-Methylethynylbenzene) Polymerized Using [Rh(norbornadiene)CI]2 as a Catalyst. An X-ray and ESR Study

Abstract Stereoregular polymerization of p-methylethynylbenzene (MEB) was successfully performed using a [Rh(norbornadiene)CI]2 catalyst in alcohol and triethylamine. Polymers which have a cis-transoid structure were selectively formed in fairly high yields. The structure and properties of the resulting polymers were compared with those of polyethylnylbenzene (PEB) by means of x-ray diffraction and ESR techniques. The data showed that both pristine amorphous polymers are converted to pseudohexagonal structures called columnar when they were treated with toluene at room temperature. The line width, ΔH msl in the ESR spectrum of PMEB polymer was found to be increased from 10.5–12.5 gauss to 13.1–15.8 gauss when the solvent was changed from alcohols, e.g., ethanol or tert-butanol, to cyclic alcohols, e.g., cyclopentanol. The increase of the observed ΔH msl was explained in terms of magnetically inhomogeneous broadening arising from heterogeneous aggregations of radical spins in the columnar polymer phase.

Radiation-induced Cis to Trans isomerization of poly(n-butylpropiolate) prepared with a [Rh(norbornadiene)Cl]2 complex as a stereospecific catalyst

Abstract Normal alkylpropiolate, i.e., n -butylpropiolate: HCCCOO n C 4 H 9 was polymerized with [Rh(norbornadiene)Cl] 2 catalyst in methanol solvent to produce poly( n -butylpropiolate), (PBPA) polymer called polyacetylene esters in relatively high yields. The obtained polymer was characterized in detail using 1 HNMR, gel permeation chromatography (GPC), diffuse reflective UV methods. Consequently, the data showed that the resulting polymers selectively have cis-transoid form. We also found that γ -ray irradiation of the cis isomer resulted in isomerization to the trans isomer even at room temperature in air to generate the extended trans sequences which can stabilize mobile unpaired electrons as π -radicals called solitons.

Formation of Columnar from Poly(p-Methylethynylbenzene) Polymerized Using [Rh(norbornadiene)Cl]2 as a Catalyst. An X-Ray and ESR Study

Columnar polymers of p-methylethynylbenzene (MEB) were synthesized using [Rh(norbornadiene)Cl]2 as a catalyst in alcohol. Polymers having a cis-transoid structure were selectively formed at high yields. The structure and properties of the polymers were analyzed by means of X-ray diffraction and ESR methods. The data showed that the pristine amorphous polymer was converted to a pseudohexagonal columnar one when it was treated with toluene at room temperature. Formation of columnar polymers was also demonstrated by the increase in the linewidth in the ESR spectra of the polymer obtained by the toluene treatment of the pristine amorphous polymer, indicating that a magnetically inhomogeneous line broadening mechanism operates among the radical spins which are heterogeneously distributed in the columnar phase.

Unusually facil cis to trans isomerization of a polypropiolate bearing a long alkyl chain polymerized using a [Rh(norbornadiene)Cl]2 catalyst : An ESR study

Alkylpropiolate having n-hexadecyl moiety in the ester group was stereospecifically polymerized with a [Rh(norbornadiene)Cl] 2 complex catalyst in alcohol to give rise to cis-transoid polyacetylenes in high yields. The unusually facile cis to trans isomerization for the polymer was found to be induced when the polymer was warmed to even less than ca. 57°C, Under these conditions ESR spectra bearing hyperfine structures due to the radicals generated by the rotational scission in the cis-π bond were observed. This isomerization induced a large g value shift in the ESR spectra together with an increase of the radical concentration during the isomerization, indicating formation of planar conjugated trans sequences that stabilize mobile unpaired electrons as solitons.

Synthesis of Sulfur Atom-Substituted Poly(phenylacetylene) Using Rh Complex Catalyst-Columnar Formation and cis-to-trans Isomerization

硫黄原子を側鎖に含む置換アセチレンは, トリエチルアミン溶媒の存在下, ロジウム (Rh) 錯体触媒によって, 立体規則的に重合が進行し, シス体の置換ポリアセチレンが選択的かつ高収率で生成する. このシス体ポリアセチレン主鎖はらせん構造を有し, 分子集合体であるカラムナー結晶を形成していることを見いだした. このシス体ポリマーに約200kg/cm2の圧力をかけると, シス体の二重結合が回転解裂し, シス体とトランス体の2種類のラジカルが生成し, 前者の不対電子はベンゼン環のパラ位についているアルキルスルホキシド部位まで移動し, その結果非常に大きなg値, すなわちg=2.0081, 線幅ΔHmsl=11GのtripletのESRのスペクトルを示すことを見いだした. スルホキシド硫黄の隣のメチレンにスピン密度が現われることは半経験的量子化学的計算法, AM1法を用いて確認した. 一方, トランス体ラジカルは共役平面構造を有し, スピン密度はその主鎖に非局在化し速い運動性を示すソリトン様の磁気的な振舞いを示すことを見いだした.