Remarkable Cocatalytic Effect of Alkali Metal Amides and Alkoxides in the Rhodium-Catalyzed Polymerization of Phenylacetylene

Polymerizations of phenylacetylene ( 1 ) with [(nbd)RhCl] 2 (nbd: 2,5-norbornadiene) in the presence of alkali metal amides ( 2 − 5 ) in toluene at 30 °C reached completion almost instantaneously. These polymerizations are much faster than the polymerization catalyzed by the well-known conventional catalyst system, [(nbd)RhCl] 2 /triethylamine (Et 3 N) (polymer yield is 75% after 1 h under the same conditions). The molecular weights of the formed polymers ( 2, M n = 270 000; 3, M n = 297 000; 4, M n = 310 000; 5, M n = 396 000; after 1 h) were clearly higher than that with the [(nbd)RhCl] 2 /Et 3 N system ( M n = 118 000). KO- t Bu ( 6 ) also served as cocatalyst but it was less effective than were 2 − 5 . In the polymerization of 1 with [(nbd)RhCl] 2 / 4 − 6, toluene was the optimal solvent in terms of polymer yield and molecular weight. The stoichiometric amount of cocatalyst to the Rh metal was found to be the most suitable with respect to polymer yield, beyond which there was no discernible change in the polymerization behavior. The increase in monomer-to-rhodium ratio ([M] 0 /[Rh]) resulted in the increase of molecular weight to provide very high molecular weight polymers ( 4, M n = 721 000; 5, M n = 766 000) in high yields ( 4, yield = 79%; 5, yield = 100%) at [M] 0 /[Rh] of 5000.