¹H‐NMR and UV studies of Rh complexes as a stereoregular polymerization catalysts for phenylacetylenes: Effects of ligands and solvents on its catalyst activity

Abstract

Phenylacetylene and its homologues bearing methoxy or chloro groups in the para position of the phenyl ring were stereoregularly polymerized by Rh complex catalysts, e.g., [Rh (norbornadiene) Cl]2, in the presence of various solvents. The 1H‐NMR and UV study of the Rh complex showed that the activity of the Rh catalysts greatly depends upon not only the ligand in the Rh catalyst but also on the solvent used, e.g., polyphenylacetylene with a highly cis‐transoidal content was quantitatively obtained when norbornadiene was coordinated as the ligand, and triethylamine (TEA) was used as solvent, whereas tetrahydrofuran (THF) and benzene reduced the cis content. It was also found that the Rh catalyst as a dimer complex dissociates into the monomeric species not only when TEA was used but also when alcohol, benzene, and THF were used. The resulting monomeric species was considered as the important propagation species in this polymerization. The sharp line width observed in the 1H‐NMR spectrum of polyphenylacetylene and its homologues which were prepared in ethanol or TEA was interpreted by the narrow chemical shift distribution arising from the high cis content. © 1994 John Wiley & Sons, Inc.

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

“…We have reported 12,13,15,16,18) that the Wilkinson type catalysts, such as [Rh(L-L)Cl] 2 , L-L = norbornadiene (NBD) or cyclooctadiene (COD), are extremely effective for the formation of aromatic polyacetylenes (Scheme 2) to produce the corresponding cis-transoid polyacetylenes, when amine or alcohol was used as the solvent under mild conditions (Tab. 1).…”

“…On the other hand, using the [Rh(NBD)Cl] 2 catalyst at room temperature produces the cis-isomer almost quantitatively, forming light yellow and amorphous material bearing a fairly high molecular weight when poor solvents such as alcohol or amine were used in the polymerization. We found that the most outstanding features of the resulting polyacetylene, which was stereospecifically prepared using the simple Rh complex catalyst, are first: 1 H and 13 C NMR spectra of the resulting polymers have extremely sharp line widths compared with those of the trans-isomers 16,18,20) , which makes an unequivocal assignment of each signal impossible and may be correlated with the polymer structures and/or the concentration of p-radicals involved in the trans-conjugated polymer [23][24] and second: the formation of a pseudohexagonal, columnar structure, representing self-assembly or a superstructure, which is associated with useful and anisotropic physicochemical properties 19,20) . Therefore, these characteristics may be a proof of the highly stereospecific polymerization of monosubstituted acetylenes.…”

“…Recently, analogues of the Wilkinson catalyst, e. g. [Rh(norbornadiene)Cl] 2 , were extensively developed in order to selectively produce cis-PEB even at room temperature 12,18,21,22) , although the complete cis-polyacetylene can be generated at a lower temperature, ca. -78 8C in the case of Ziegler-Natta catalysts 1 b) .…”

“…However, except for the precise control of the molecular weight and its dispersity, there has been no clear and unequivocal assignment (Scheme 1) of the geometry and/ or regularity of the resulting polymers regarding the C2C bond in the main chain of the polymer, including few stereospecific polymerizations of cis-and/or transmonosubstituted polyacetylenes (i), copolymerization (ii), isomerization (iii) of cis-to-trans geometrical isomer with its mechanism (iv), generation of p-conjugated radicals as solitons through the rotational scission of the cisdouble-bond, and the role of the radical in the conductivity and/or magnetism of the polymer (v). In this report, we describe the stereospecific polymerization to yield selectively the cis-form using the [Rh(norbornadiene)Cl] 2 ([Rh(NBD)Cl] 2 ) catalyst [12][13][14][15][16][17][18] , leading to a control method of molecular orientation and/or spin order in solid polymers, i. e., the formation of pseudohexagonal structures [19][20][21] , aggregation of the radical spins as a source of magnetism [20][21] , pressure-induced cis-trans isomerization [14][15][16] , and generation of the p-radical through rotational scission of the cis-double-bonds (Scheme 1).…”

Pressure-inducedcis totrans isomerization of aromatic polyacetylenes prepared using a Rh complex catalyst: A control of ?-conjugation length

“…2 It has been proposed that the effect of the solvents is to promote In a previous article we reported that phenylacetthe efficient dissociation of the dimer complex ylene (PA), 1 its homologues, 2 a-naphthylacety-[Rh(NBD)Cl] 2 into the monomeric species, which lene, 3 and alkylpropiolates, 4,5 and pentynoate 6 may be an important initiation species for this can be stereospecifically polymerized in the prespolymerization, 1,7 as shown in Scheme 1. Further, ence of a Rh complex, [Rh(norbornadiene)Cl] 2 , the structural differences observed between poly-[Rh(NBD)Cl] 2 , when triethylamine (TEA) or an pentynoates prepared with the Rh complex cataalcohol is used as the polymerization solvent and lyst and with metathesis catalysts such as WCl 6 that the helical cis-transoid isomer were selecwas interpreted in terms of the difference in geotively formed in high yields under mild conditions.…”