Abstract
Substituted polyacetylene derivatives are promising π-conjugated materials, which can be synthesized by polymerization of the corresponding substituted acetylenes by transition metal catalysis. Rhodium(I) complexes have been widely used for the polymerization of monosubstituted acetylenes such as phenylacetylene derivatives because they are functional group tolerant and provide cis-stereoregular polymers. There are some examples of well-controlled polymerization of phenylacetylene derivatives using well-defined rhodium(I) complexes as initiators. However, versatile design of polymer end structures is difficult in such known methods because initiators having various functional groups are not easily available. To overcome such a problem, we have developed a new method for well-controlled polymerization of phenylacetylene derivatives using a multicomponent catalytic system composed of bicyclo[2.2.1]hepta-2,5-diene-rhodium(I) chloride dimer [Rh(nbd)Cl]2, arylboronic acids, diphenylacetylene and 50% aqueous solution of KOH. This polymerization method showed a typical living nature, and structures derived from aryl boronic acids and diphenylacetylene were introduced to the initiating end of the obtained polymers. Moreover, functionalization of the polymer terminal end could be achieved by reactions of the living polymer terminus with α,β-unsaturated carbonyl compounds such as acrylates, and various telechelic poly(phenylacetylene)s were obtained. Novel 1,3,5-hexatrienylrhodium(I) complexes were isolated from the present multicomponent catalytic system, and their structures were identified. When [Rh(nbd)Cl]2 was replaced with hydroxy(1,5-cyclooctadiene) rhodium(I) dimer ([Rh(cod)OH]2) in the present catalytic system, cyclobutenylrhodium(I) complexes were exclusively obtained. These complexes provided insights into the initiation mechanism in the living polymerization. The present catalytic system was applied to the living polymerization of water-soluble phenylacetylene derivatives and non-conjugated monosubstituted acetylenes such as N-propargylamides.
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