Highly active and robust rhodium(I) catalyst for the polymerization of arylacetylenes in polar and aqueous medium under air atmosphere

A catalytic system consisting of Rh2nbd2Cl2 (nbd = norbornadiene) and a hydrophilic, neutral phosphinopyrazine ligand showed a great catalytic activity for the polymerization of phenylacetylene (PA) as well as other terminal arylacetylenes in alcohol and water under air atmosphere at room temperature. The catalyst proved to be highly stable and robust without loss of the catalytic activity in recycle runs. The influence of an external base, the effect of solvent and monomer/catalyst molar ratio has been studied. In general, the addition of a base resulted in an increase of the molecular weight of the polymer. However, weakly coordinating bases such as Et3N gave a unimodal molecular weight distribution, whilst strongly coordinating hydroxide/alkoxide gave bimodal polymers. Highly crystalline red-brown samples of PPA obtained in water with the above catalyst revealed a high molecular weight (58,500 Da) with a bimodal molecular weight distribution. The polymers were characterized by 1H NMR spectroscopy as highly stereoregular cis−transoidal with >99% of cis-content.