Reaction strategies using functionalized polyethylenes as ligands for homogeneous palladium catalysis

Abstract

Diphenylphosphine functionalized ethylene oligomers were used as supports for palladium(0) and palladium(II) catalysts. An advantage of using these ethylene oligomer ligated catalysts was their temperature dependent solubility in common organic solvents. Following homogeneous reactions at elevated temperatures, the ethylene oligomer ligated catalysts were quantitatively separated by thermal precipitation from the reaction solution. Diphenylphosphine functionalized ethylene oligomer ligated palladium(0) complexes have been used to catalyze the nucleophilic substitution of allylic compounds, decarboxylative rearrangement of allylic acetoacetates, and alkylation of β-keto and β-cyanocarboxylates. Ethylene oligomer ligated palladium(0) catalysts were recycled up to ten times with no detectable loss in catalytic activity. Tetrakis(triphenylphosphine)palladium(0) was used for the alkylation of β-keto- and β-cyanocarboxylates with allylic alcohols. This reaction was carried out without the addition of base or any prior activation of the allylic hydroxyl group. High yields of the products were obtained. Comparison of the reaction rates of palladium(0) catalyzed reactions of allyl alcohols and active methylene compounds in the presence of various amounts of triphenylphosphine, alkyldiphenylphosphines and diphenylphosphine functionalized ethylene oligomer indicated that the functionalized ethylene oligomer closely imitated the behavior of an alkyldiphenylphosphine ligand. Diphenylphosphine functionalized ethylene oligomer ligated palladium(II) catalysts have been used to catalyze the dimerization and acetoxylation of butadiene. The ethylene oligomer ligated palladium(II) catalysts were recycled successfully up to four times. The ethylene oligomer ligated palladium(II) catalysts' activity and product distribution were comparable to those obtained when the homogeneous catalysts were used.