Abstract

AbstractThe addition of weak Lewis bases such as NPh3, PPh3, or BiPh3 (Ph=phenyl) to Lewis acidic chloroaluminate ionic liquids yielded efficient cocatalysts for nickel catalyst precursors in highly selective biphasic dimerization reactions of α‐olefins. Triphenylbismuth buffered systems were found to produce up to 96 % dimers from propene. Selectivities and activities were influenced by varying the compositions of the ionic liquids. Furthermore, buffer addition reduced the melting points of the resulting liquids. This effect allowed a screening of many different organic halide salts, which were found to strongly influence the lifetimes and selectivities of the corresponding biphasic olefin dimerization systems. An optimized system dimerized ethene, propene, 1‐butene, and 1‐hexene with high selectivities. It is even possible to recycle amines and buffers used for these compositions by a simple acid base extraction of the spent ionic liquid catalyst systems. We also proposed a mechanism for these NiII catalyzed selective olefin dimerization reactions in alkylaluminum free buffered chloroaluminate melts. The addition of small amounts of BiPh3 to an ionic liquid composition used in the commercial DIFASOL process increased the selectivity to give dimers from a biphasic propene dimerization reaction by 15 %.

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