Rhodium(I) Complexes Bearing an Aryl‐Substituted 1,3,5‐Hexatriene Chain: Catalysts for Living Polymerization of Phenylacetylene and Potential Helical Chirality of 1,3,5‐Hexatrienes

Unique bench‐stable rhodium(I) complexes bearing an aryl‐substituted 1,3,5‐hexatriene chain have been synthesized by reactions of (bicyclo[2.2.1]hepta‐2,5‐diene)rhodium(I) chloride dimer ([Rh(nbd)Cl]2) with aryl boronic acids and diphenylacetylenes in the presence of a 50 % aqueous solution of KOH. X‐ray crystallographic analysis of the isolated complexes indicated a square‐planar structure stabilized by a strong interaction with one of the aryl groups on the 1,3,5‐hexatriene chain, which has a helical structure. The helical chirality of the isolated rhodium complexes was confirmed to be sufficiently stable to be resolved into enantiomers by HPLC on a chiral stationary phase at room temperature. It was confirmed that the isolated rhodium complexes functioned as initiators for living polymerization of phenylacetylene to give cis‐stereoregular poly(phenylacetylene) with a well‐controlled molecular weight. Isolable chiral rhodium(I) complexes bearing a helical aryl‐substituted 1,3,5‐hexatriene chain were synthesized by one‐pot reactions of [Rh(nbd)Cl]2 with aryl boronic acids and diphenylacetylenes in the presence of 50 % aqueous KOH (see scheme). The persistent helical chirality of the complexes enabled their separation into enantiomers by HPLC on a chiral stationary phase. The complexes served as bench‐stable catalysts for living polymerization of phenylacetylene.