The Supporting Information for this article contains detailed experimental procedures, preparation of the ammonium salts, ionic liquids, and complex 1, as well as a catalyst concentration series, and is available on the WWW under http://dx.
The solubility of NbCl 5 , TaCl 5 , TiCl 4 , ZrCl 4 , and HfCl 4 in neutral [BMIM][AlCl 4 ] (BMIM = 1-butyl-3-methylimidazolium) was determined. While TiCl 4 was immiscible with the neutral ionic liquid, 0.80 molar equivalents of ZrCl 4 and stoichiometric amounts of HfCl 4 dissolved in the melt at ambient temperature. The crystal structures and the unit cell parameters of [BMIM]
We have developed a new buffered silica‐based Lewis acid cocatalyst for olefin dimerization and polymerization reactions with nickel complexes. The Lewis acidities of EtAlCl2 and Et2AlCl‐modified silicas were adjusted by the addition of BiPh3 or N‐methylpyrrole buffers. The buffered heterogeneous cocatalysts were employed to activate nickel complexes for selective propene dimerization reactions to give dimers in 91 % yield. Buffer addition also reduced the rate of ligand abstraction from the catalytically active nickel center. In combination with a nickel diimine complex, ethene was polymerized to give 69 wt % polyethylene and 31 wt % oligomers. The polyethylene displayed a molecular mass of 154 kg mol−1 and a polydispersity index (PDI) of 3.26. The oligomers consisted of 93 % butenes, 46 % thereof being 1‐butene. Furthermore, triphenylbismuth‐buffered Lewis acidic chloroaluminate ionic liquids were coated on surface‐modified silica to yield a supported ionic liquid phase (SILP) system. Dimer selectivities of up to 94 % were obtained with the SILP system in nickel‐catalyzed propene dimerization reactions. The newly developed silica‐based cocatalysts provide promising new olefin dimerization systems suitable for fixed bed applications.
A binary cocatalyst system based on simple aluminum chloride and weak Lewis bases such as triphenylbismuth or N‐methylpyrrole has been developed. A donor–acceptor interaction kept aluminum chloride dissolved in toluene or methylene chloride. The systems were investigated by use of 27Al NMR spectroscopy and were used as cocatalysts in nickel‐catalyzed dimerization and polymerization reactions of α‐olefins. Their Lewis acidities correlated to the line width of the 27Al NMR signals and were influenced by the solvent and the type and amount of buffer. For propene dimerization reactions, dimer selectivities of up to 95 % were achieved. Ethene was dimerized to give butenes (up to 92 %), of which 79 % were 1‐butene. With a Brookhart‐type nickel diimine complex, ethene was polymerized with a cocatalyst solely based on aluminum chloride. Up to 38 wt % of the reaction products were polyethylene with a typical molecular weight of 140 kg mol−1. The donor–acceptor interactions of triphenylbismuth and N‐methylpyrrole with aluminum chloride were successfully transferred to Lewis acidic chloroaluminate ionic liquids. Ethene was polymerized with a nickel diimine complex dissolved in buffered chloroaluminate ionic liquids in the absence of alkylaluminum groups.
The addition of triphenylbismuth (BiPh 3 ) 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 BiPh 3 -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.
Abstract:We describe the facile synthesis of new, cationic triphenylphosphine derivatives containing para-trimethylammonium substituents. The ionic phosphines were successfully employed in nickel-catalyzed propene dimerization reactions in highly Lewis acidic chloroaluminate ionic liquids. Buffering of such liquids is achieved by an interaction of the Lewis basic phosphine with the Lewis acidic aluminum centers. The P À Al interaction of triarylphosphines and tri-tert-butylphosphine with the highlyÀ was monitored by 31 P and
27Al NMR spectroscopy. Coupling of tri-tert-butylphosphine with 27 Al resulted in an expected but unusual sextet in the 31 P NMR spectrum and a doublet in the 27 Al NMR spectrum.
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