Nitrogen ligand-containing Rh catalysts for the polymerization of substituted acetylenes

Abstract

The present study deals with the application of Rh complexes possessing a phenoxy-imine ligand ( 1 and 2), a β-diiminate ligand ( 3 and 4), and ammonia ligands ( 5) as catalysts in the polymerization of substituted acetylenes ( 6a– h). All the catalysts ( 1– 5) were effective for the polymerization of monosubstituted acetylenes ( 6a– e) and afforded polymers in moderate to high yields with high molecular weights ( M n = 15,000–93,000), and the presence of cocatalyst was not a strict requisite in the present polymerization systems in contrast to conventional [Rh(nbd)Cl] 2 and [Rh(cod)Cl] 2 catalysts. In the case of phenoxy-imine catalysts, the nbd-bearing one ( 1) was more active than the cod-bearing counterpart ( 2) in accordance to the general behavior of Rh catalysts, while the opposite trend was observed for β-diiminate catalysts ( 3 and 4). Catalyst 2 exhibited the highest activity among all the catalysts examined in the polymerization of phenylacetylene ( 6a) and afforded the highest molecular weight poly( 6a) ( M n = 93,000) in almost quantitative yield. Introduction of electron-donating groups at meta and para positions of 6a (monomers 6b– d) resulted in the decrease of polymer yields. Et 3N and n-C 4H 9Li exerted cocatalytic effects when combined with 1– 5 in the polymerization of 6a, resulting in the increase of both polymer molecular weight and yield.