Synthesis of Polymers Containing Group 15 Elements via Bismetallation of Acetylenic Compounds

Abstract

Carbon-element bond formation is a key point of synthetic methodology for incorporating a wide variety of metallic or metalloid elements in polymer main chains. Radical ‘bismetallation’ to carbon-carbon triple bonds based on homolytic cleavage of element-element single bonds is one of the most useful and highly atom-economical methods for carbon-element bond formation. Syntheses of novel polymers containing group 15 elements have been achieved by ring-collapsed radical alternating copolymerization (RCRAC) of homocyclic compounds with rings built exclusively of group 15 elements with acetylenic compounds. Poly(vinylene-arsine)s were successfully prepared by a radical reaction between pentamethylpentacycloarsine (cyclo-(MeAs)5) or hexaphenylhexacycloarsine (cyclo-(PhAs)6) and mono-substituted acetylenic compounds using 2,2′-azobisisobutyronitrile (AIBN) as a radical initiator or irradiation with xenon lamp at room temperature. Without any radical initiator at 25 °C, cyclo-(MeAs)5 caused cleavage of the arsenic-arsenic bond spontaneously and copolymerized with phenylacetylene to give poly(vinylene-arsine)s. The copolymers obtained showed fluorescence properties which were influenced by the substituents of the acetylenic compounds. Poly(vinylene-phosphine)s and poly(vinylene-stibine)s were also prepared by RCRAC of cyclo-(MeP)5 and cyclo-(PhSb)6 with alkynes, respectively. Different reactivity of pnictogen radicals made it possible to construct the periodic vinylene-arsine-vinylene-stibine backbone. The radical terpolymerization of cyclo-(MeAs)5, phenylacetylene, and a vinyl monomer and radical copolymerization of cyclic diarsine with vinyl monomers were also described.