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Biphasic, Homogeneous, and Heterogeneous Hydrocarbon Conversion Reactions with Novel Aluminum Chloride Based Catalyst Systems
(2011)
- The aim of this thesis was the development of novel cocatalysts for nickel catalyzed olefin dimerization and oligomerization reactions. For this purpose, cheap and air stable Lewis acidic chloroaluminate ionic liquids were the starting point for our investigations. Chloroaluminate melts are immiscible with hydrocarbon phases, and thus, biphasic oligomerization reactions allow a simple product separation by decantation. Unmodified chloroaluminate melts containing excess aluminum chloride predominantly catalyze non selective, cationic olefin oligomerization reactions. We found that the addition of triphenylamine, triphenylphosphine, or triphenylbismuth donors efficiently suppressed these side reactions to yield an ideal cheap and air stable ionic liquid cocatalyst for common nickel complexes used for olefin dimerization reactions. Especially triphenylbismuth was able to buffer slightly acidic chloroaluminate melts as well as highly acidic compositions. For nickel catalyzed dimerization reactions, we found that high buffering levels led to very high selectivities to give dimers, while systems with lower buffer contents were less selective but extremely active. Further, the melting points of acidic chloroaluminate melts were reduced upon addition of BiPh3. Thus, room temperature ionic liquid compositions derived from 100 different organic halide salts were screened towards their performances in nickel catalyzed selective propene dimerization reactions. Amines and BiPh3 used for such systems can be easily recovered by acid base extraction. Subsequently, an optimized composition was successfully employed to dimerize ethene, propene, 1-butene, and 1-hexene with high activities and selectivities. In order to minimize leaching effects and to investigate the interactions of a donor additive with the ionic liquid, a cationic para-trimethylammonium substituted triphenylphosphine derivative was synthesized and its interaction with the ionic liquid was monitored by means of 31P NMR spectroscopy. The concept of buffering highly Lewis acidic aluminum chloride centers was also transferred to binary homogeneous systems. In combination with stoichiometric amounts of BiPh3 or N-methylpyrrole buffer, aluminum chloride readily dissolved in toluene and methylene chloride to form a highly efficient, cheap and air stable cocatalyst for nickel catalyst precursors. Furthermore, the Lewis acidities of these binary homogeneous cocatalyst solutions could be tuned precisely by the choice of the solvent and the type and amount of buffer. Also, buffer addition efficiently suppressed isomerization reactions of the 1-olefinic products. The interaction of BiPh3 and N-methylpyrrole with AlCl3 was monitored by 27Al NMR spectroscopy. Further, the concept of buffering highly Lewis acidic aluminum species was extended to heterogeneous systems. The Lewis acidities of EtAlCl2 or Et2AlCl modified silicas were reduced by the addition of BiPh3 or N-methylpyrrole buffers. Buffered surface modified silica cocatalysts were successfully employed to activate nickel complexes for highly selective olefin dimerization reactions. Also, surface modified silica proved to be an ideal substrate for the formation of supported ionic liquid phase (SILP) cocatalyst systems used in nickel catalyzed olefin dimerization reactions. Buffered aluminum based cocatalysts were also able to activate a nickel diimine complex for biphasic, homogeneous, and heterogeneous ethene polymerization reactions. The polymer yields, molecular weights and polydispersities of the polyethylenes could be influenced by varying the solvent or the type and amount of buffer. We developed the first air stable cocatalyst systems solely based on aluminum chloride. With the right combination of solvent, type and amount of buffer, and process parameters, tailor-made homogeneous, heterogeneous and biphasic cocatalysts for numerous catalyst precursors can be designed. The systems proved to be highly active, long term stable and very selective for olefin dimerization or polymerization reactions. Due to the cheap components and the possibility to recycle buffers or halide salts, these new systems provide promising alternatives to established alkylaluminum based cocatalyst systems.
