Understanding the Polymerization of Diphenylacetylenes with Tantalum(V) Chloride and Cocatalysts: Production of Cyclic Poly(diphenylacetylene)s by Low-Valent Tantalum Species Generated in Situ

Abstract

A systematic investigation of the polymerization of representative diphenylacetylenes with TaCl 5 and cocatalysts suggested that low-valent Ta species, which are formed by in situ reduction of TaCl 5 by the cocatalysts, are involved in the polymerization and that the polymerization reaction proceeds by an insertion ring expansion mechanism via the formation of tantalacyclopentadiene intermediates, rather than the previously considered metathesis mechanism. This polymerization mechanism indicates the production of unprecedented cis-stereoregular cyclic poly(diphenylacetylene)s. Indeed, the possibilities of a cyclic structure and high cis-stereoregularity of the resulting polymers were reasonably supported by the results of their detailed atomic force microscopy (AFM) and NMR analyses, respectively.

Applications of Vanadium, Niobium, and Tantalum Complexes in Organic and Inorganic Synthesis

“…Taniguchi, Asakawa, Maeda, and co-workers systematically investigated the polymerization of diphenylacetylenes with low-valent Ta species (Scheme ), which were formed in situ after reduction of TaCl 5 . The mechanism of TaCl 5 –Ph 4 Sn system is an insertion ring expansion.…”

“…Taniguchi, Asakawa, Maeda, and co-workers systematically investigated the polymerization of diphenylacetylenes with low-valent Ta species (Scheme 27), which were formed in situ after reduction of TaCl 5 . 199 The mechanism of TaCl 5 −Ph 4 Sn system is an insertion ring expansion. The polymeric degree produced by this system was much higher than that with the WCl 6 −Ph 4 Sn system, and the best result was M n = 22.0 × 10 4 , M w /M n = 2.31.…”

Azobenzene functionalized poly(diphenylacetylene): Polymer synthesis and tunable fluorescent emission

“…Fourier transform infrared (FTIR) spectra were recorded on a Bruker VECTOR 22 spectrometer. 1 H and 13 C NMR spectra were measured on a Bruker ARX 500 spectrometer using CDCl 3 as solvent and tetramethylsilane as internal standard. The thermal stability of the polymers was evaluated on a Perkin-Elmer Pyris thermogravimetric analyzer TGA 6.…”

“…Poly(disubstituted acetylenes)(PDSAs) has become one of the most attractive topics in the research area of polyacetylenes, due to the observations of colossal circular polarized fluorescence emission, super-high gas permeability, as well as the significantly improved stability in comparison with the mono-substituted polyacetylene counterparts. [1][2][3][4][5][6][7][8][9][10] Regarding these advanced functions, the interactions between the polyene main-chain and the side chains play important roles. The "jacked effect", for instance, is considered as the basic reason for the enhanced thermal stability of PDSAs.…”

Nickel-catalysed cycloaddition oligomerisation of 1,6-diynes to medium-size cyclic polyenes

“…22 In particular, conjugated macrocyclic polyenes have attracted considerable research interest. However, except for elegant works reported by Veige 23 and Maeda, 24 who synthesized substituted cyclic polyenes with high molecular weight from terminal monoalkynes using tungsten catalysts and fully substituted cyclic polyenes via TaCl 5 / Bu 4 Sn-catalysed polymerisation of 1,2-diarylacetylene, respectively, cyclic polyenes have been scarcely explored owing to the difficulty of their synthesis. Herein, we report the selective synthesis of 2 via the nickel-catalysed cycloaddition oligomerisation of 1 through consecutive intermolecular/intramolecular insertion reactions and the conversion of 2 to regio-isomeric cyclic polyene 3 (type II) via thermal isomerisation (Scheme 1).…”