The iridium(I) compounds HIr(cod)(PR3)(2) (cod: 1,5-cyclooctadiene; PR3: Ph-3, P(p-MeOC6H4)(3), P(o-MeOC6H4)Ph-2, PCyPh2, PCy2Ph) were employed as catalyst precursors for the polymerization of phenylacetylene. The polyene was formed as the major product with all the catalysts except the PCy2Ph derivative, which promoted preferential formation of oligomers. In all cases the polymerization reactions were highly stereoselective, yielding 100% trans-polyphenylacetylene. From the catalytic mixtures the iridium(III) derivatives fac-HIr(CdropCPh)(2)(PR3)(3) (PR3: PPh3, P(p-MeOC6H4)(3)) were isolated. The results of spectroscopic studies are also reported, which provide information on the evolution of the iridium precursors during the catalytic reaction. (C) 2003 Elsevier B.V. All rights reserved.