Rhodium-Catalyzed Polycyclotrimerization of Diphenylpropiolates: A Facile Strategy toward Ester-Functionalized Hyperbranched Polyarylenes

Abstract

Alkyne polycyclotrimerizations have become efficient synthetic tools for constructing hyperbranched polyphenylenes. However, the polycyclotrimerization reactions of internal alkynes are rarely reported. Herein, we present the first example of RhCl 3 -catalyzed polycyclotrimerization of activated internal diynes to prepare hyperbranched polymers. The polymerization reactions of diphenylpropiolates (1a−c) were performed in toluene under reflux in the presence of RhCl 3 •3H 2 O and N,N-diisopropylethylamine (DIPEA), affording soluble hyperbranched poly-(triphenylbenzoate)s (hb-PTPBs), hb-P1a−c, with high molecular weights (up to 187000) and high regioregularities (fraction of 1,2,4-triphenylbenzoate isomer up to 88.2%) in satisfactory yields. The degree of branching of hb-P1a was determined to be 0.73. The resultant hb-PTPBs are thermally stable, with 5% weight loss temperatures higher than 330 °C. The hb-PTPBs are weakly emissive in their dilute solutions but become intensively emissive upon aggregate formation, showing aggregation-induced emission features.

Metal-free polycyclotrimerization of trimethylsilyl-protected diynes: a facile strategy toward regioregular hyperbranched polyarylenes

“…Nevertheless, polycyclotrimerizations of internal alkynes have been rarely employed to prepare HBPs. [34][35][36] This is mainly caused by the low reactivity and high steric hindrance of internal alkynes. Recently, we have developed a rhodium-catalyzed polycyclotrimerization of diphenylpropiolates for the synthesis of ester-functionalized HBPs.…”

“…Recently, we have developed a rhodium-catalyzed polycyclotrimerization of diphenylpropiolates for the synthesis of ester-functionalized HBPs. 34 However, the used internal alkyne monomers are limited to activated alkynes and the products are the mixtures of 1,2,4- and 1,3,5-trisubstituted benzene isomers (the ratio of the 1,2,4-isomer to the 1,3,5-isomer is close to 22 : 3). Moreover, the metallic catalyst residues in the HBPs can make their photophysical performance worse.…”