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.

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