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

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 (Mn = 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) (Mn = 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. Et3N and n-C4H9Li exerted cocatalytic effects when combined with 1–5 in the polymerization of 6a, resulting in the increase of both polymer molecular weight and yield.

Rh complexes possessing a phenoxy-imine ligand (1 and 2), a β-diiminate ligand (3 and 4), and ammonia ligands (5) were used as catalysts in the polymerization of monosubstituted acetylenes (R–CCH; 6a: R = Ph, 6b: R = C6H4–m-NH2, 6c: R = C6H4–p-NH2, 6d: R = C6H4–p-SiMe3, 6e: R = CH2CONH–n-C5H11, 6f: R = COO–n-C6H11, 6g: R = n-C4H9, 6h: R = SiMe3). All the catalysts (1–5) were effective without any cocatalyst for the polymerization of monosubstituted acetylenes (6a–e) and afforded polymers with high molecular weights (Mn = 15,000–93,000) in moderate to high yields. Figure optionsDownload as PowerPoint slide