A tetracoordinate rhodium complex, Rh(C⋮CC6H5)(nbd)[P(C6H5)3] (nbd = 2,5-norbornadiene), combined with 4-(dimethylamino)pyridine (DMAP) is an excellent initiator for the stereospecific living polymerization of phenylacetylene and its m- and p-substituted derivatives. The rhodium initiator can be generated efficiently by dissociation of triphenylphosphine from isolable Rh(C⋮CC6H5)(nbd)[P(C6H5)3]2 or by reacting Rh(CH3)(nbd)[P(C6H5)3]2 or [Rh(OCH3)(nbd)]2/P(C6H5)3 with one equivalent of phenylacetylene. The use of a phenylethynyl group, triphenylphosphine, and NBD ligand attached to the rhodium center is crucial for the well-controlled polymerization of phenylacetylenes. An additive, DMAP, is necessary to attain low polydispersities of the polymer products. An active rhodium(I) complex bearing a growing polymer chain, NBD, and P(C6H5)3 was isolated from a reaction mixture and was characterized by NMR, GC−MS, XPS, and elemental analyses. The isolated active polymer initiates the further polymerization of the same monomer or substituted ones with an almost 100% initiation efficiency to give higher molecular weight homopolymers or block copolymers, respectively. Detailed NMR structural analysis of the products indicated that the polymerization with the rhodium(I) complexes proceeds via a 2,1-insertion mechanism to provide stereoregular poly(phenylacetylene)s with cis−transoidal backbone structure.

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Rh+(2,[(í/6-C6H5)B-(C6H5)3], a zwitterionic Rh(I) complex, shows excellent activity for the polymerization of monosubstituted acetylenes under mild conditions. The reaction of phenylacetylene and its p-and m-substituted derivatives proceeds rapidly to give yellow soluble polymers with a cis configuration of the main polymer chain and with a high number-average molecular weight (> 10s) in high yields. The o-substituted derivatives give stereoregular red crystalline polymers which are scarcely soluble in organic solvents. The Rh complex has a moderate activity for the polymerization of íerí-butylacetylene, cyclohexylacetylene, and 3-ethyl-1 -pentyne to afford stereoregular cis polymers in quantitative yields.