On-Water Polymerization of Phenylacetylene Catalyzed by Rh Complexes Bearing Strong π-Acidic Dibenzo[a,e]cyclooctatetraene Ligand

A series of new mononuclear neutral and water-soluble cationic rhodium (Rh) complexes bearing strong π-acidic dibenzo[a,e]cyclooctatetraene (dbcot) diene ligand have been synthesized and structurally characterized. In the polymerization of phenylacetylene, the dbcot Rh complex exhibits higher catalytic activity than the corresponding cod-based Rh complex in both of organic solvent and aqueous media, affording the high cis-transoidal PPAs with up to 99% of cis-contents, moderate molecular weights, and moderate to broad molecular weight distributions. Moreover, on-water polymerization of substituted phenylacetylenes is achieved by these complexes under air atmosphere, in which 3- to 163-fold acceleration of the polymerization rate is observed in aqueous polymerization compared to that in organic solvents. The nature of the Rh complex, solvent, polymerization temperature, and substituted group on the phenylacetylene impact on the polymer's yield, stereoselectivity, molecular weight, and molecular weight distribution. In addition, the water-soluble cationic Rh complexes can be reused for three times.