Catalytic conversions in water: Part 14. The alternating copolymerization of ethene and CO catalyzed by water-soluble Pd catalysts Original Research Article

The alternating copolymerization of ethene and carbon monoxide proceeds efficiently in aqueous media in the presence of the water-soluble Pd/DPPPr-S/HOTs (DPPPr-S: C3H6-1,3-(P(C6H4-m-SO3Na)2)2, HOTs: p-toluenesulfonic acid) catalyst system. A maximum catalyst activity of 7.7 kg copolymer (g Pd)−1 h−1 was observed at 90°C and 60 bar. The molecular weights of the copolymer samples increased with increasing pressure and decreasing temperature and ranged from Mn=50.0 kg mol−1 (50°C, 40 bar) to Mn=9.6 kg mol−1 (90°C, 40 bar). High reaction rates were observed when ethene/CO mixtures richer in CO (optimum at 64% v/v CO) were used, but the highest molecular weights were obtained when the ethene/CO ratio was 1.0. The water-soluble catalysts containing the water-soluble ligands 1,2-bis(di(m-sodiumsulfonatophenyl)phosphino)ethane (DPPEt-S), 1,4-bis(di(m-sodiumsulfonatophenyl)phosphino)butane (DPPBu-S) and (s, s) 2,4-bis(di(m-sodiumsulfonatophenyl)phosphino)pentane (2,4-DPPPen-S), having a C2H4, n-C4H8 or 2,4-n-C5H10 bridge between the phosphorus atoms, respectively, were also tested in the copolymerization. Pd/DPPEt-S/HOTs was less stable, Pd/2,4-DPPPen-S/HOTs also exhibited a lower catalyst activity, while Pd/DPPBu-S/HOTs was more active compared to the catalyst system based on DPPPr-S. In all cases, the average molecular weights of the products were considerably lower compared to those of samples obtained with Pd/DPPPr-S/HOTs.