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Nickel-Catalyzed Propene Dimerization Reactions in Triphenylbismuth-Buffered Chloroaluminate Ionic Liquids: High Performance with Unconventional Cations
The addition of triphenylbismuth (BiPh3) efficiently buffers Lewis acidic chloroaluminate ionic liquids over a wide range of compositions. Since the melting points of these ternary mixtures are lower compared to unbuffered chloroaluminate systems, the scope of cations for the formation of buffered room temperature ionic liquids is greatly extended. The buffered ionic liquids were used to activate nickel complexes for selective biphasic propene dimerization reactions. Lifetimes, selectivities and productivities of such dimerization catalysts could be adjusted by the choice of the cation and the composition. At lower reaction temperatures, the selectivities to give dimers increased significantly. Propene dimers were obtained with selectivities of up to 98%. A cation screening with 100 ammonium and phosphonium halide salts was performed. N‐Methylpyrrolidine hydrochloride gave the best results in terms of selectivity and lifetime. Propene dimerization reactions in BiPh3‐buffered chloroaluminate melts were catalyzed by various soluble nickel compounds with similar performances. The introduction of basic, sterically demanding tricyclohexylphosphine ligands led to higher degrees of branching, however, at the expense of lower dimer selectivities.