Polymerization of Phenylacetylenes with Rhodium Zwitterionic Complexes: Enhanced Catalytic Activity by π-Acidic Diene Ligands

Zwitterionic Rh catalysts bearing a series of tetrafluorobenzobarrelene (tfb) ligands proved to be highly active in the polymerization of phenylacetylenes. The highest catalytic activity for the polymerization of phenylacetylene was observed with (tfb)Rh⁺[(η⁶-Ph)B⁻Ph₃] (1). Catalyst 1 displayed higher activity to produce higher molecular weight polymer than the conventional nbd analogue, (nbd)Rh⁺[(η⁶-Ph)B⁻Ph₃] (5, nbd = 2,5-norbornadiene). In the case of other zwitterionic Rh catalysts bearing polymethylated tfb ligands [tfb-Me₂, 2; tfb-Me₃, 3; tfb-Me₄, 4], the catalytic activity tended to decrease with increasing number of the incorporated methyl groups. Catalyst 1 also showed high activity in the polymerization of phenylacetylene derivatives irrespective of electron-donating or -withdrawing nature of ring-substituents of the monomers.