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

Abstract

SUMMARY: 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-C2C bonds and, thus, giving p-radicals as the origin of magnetic properties.

Substituted polyacetylenes

“…Use of the cocatalysts in the polymerization of 1-phenyl-1-alkynes(4) catalyzed by TaCl 5 and NbCl 5 generally accelerated the reaction, and increased the polymer M w up to about 1.5 Â 10 6 . 40 Although diphenylacetylene (12) did not polymerize with TaCl 5 alone, this monomer produced an insoluble yellow polymer quantitatively in the presence of appropriate cocatalysts (Me 4 Sn, Et 3 SiH, etc.) despite its remarkable steric crowding.…”

“…16 Further, Tabata and other researchers studied the Rh-catalyzed polymerization of 1. 12,13 The molecular weight of poly(1) is 5 Â 10 3 -1 Â 10 5 with W and Mo catalysts, while that with Rh catalysts is higher and 1 Â 10 4 -1 Â 10 6 . Zieglertype and other catalysts yield partly insoluble poly(1) and/or oligomers.…”

“…Poly(diphenylacetylene) [poly (12)] is thermally very stable, but insoluble in any solvent. In general, aliphatic polyacetylenes from unsymmetrically disubstituted acetylenes (e.g., 2-octyne) are soluble, whereas those from symmetrical monomers (e.g., 4-octyne) are insoluble.…”

“…81 These monomers were more reactive than 12 in copolymerization. Unlike poly (12), these polymers were soluble in toluene, CHCl 3 , and so forth owing to the high configurational entropy induced by the para-substituents. Their M w values determined by GPC were in the range of 6 Â 10 5 -36 Â 10 5 , and membranes could be obtained by solution casting.…”

“…In parallel to these catalyst developments, Rh catalysts were found to polymerize monosubstituted acetylenes to give stereoregular cis-transoidal polymers. 12,13 A comprehensive and informative review article has recently been published concerning the living polymerization of substituted acetylenes. 14,15 The above-stated progress of various transition metal-based polymerization catalysts enabled the synthesis of a wide variety of polymers from acetylene derivatives including monosubstituted and disubstituted acetylenes, [8][9][10][11][16][17][18] and a,x-diynes.…”