AbstractA 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.