Novel Rh complexes, Rh[C(C6H5)=C(C6H5)(2)](nbd)(4-XC6H4)(3)P (1a: X = F; 1b: X= Cl), were isolated from mixtures of [(nbd)RhCl](2), (C6H5)(2)C=C(C6H5)Li, and (4-XC6H4)(3)P, and the polymerization of phenylacetylene thereby was investigated. The polymerization by la in toluene at 30 degrees C in the presence of (4-FC6H4)(3)P (5 equiv to Rh or more) proceeded with virtually quantitative initiation efficiency to give polymer with low polydispersity (M-w/M-n similar to 1.05). The living character of this polymerization was confirmed by means of both the time profile of polymerization and the multistage polymerization. Toluene, benzene, and THF were particularly useful as polymerization solvents; the polydispersity remained 1.05-1.06, while the larger the dielectric constant of the solvent, the slower the polymerization. This polymerization smoothly proceeded in the temperature range 15-60 degrees C.