Tandem Oligomerization-Hydrogenation Using Brønsted Acidic Iridium Hydride Catalysts

Cationic iridium complexes bearing the tris[3,5-bis(trifluoromethyl)phenyl]phosphine ligand unexpectedly give acidic metal hydrides. Net-dihydrogen heterolysis at such complexes provides hydrogenation catalysis by an ionic mechanism. The direct reduction of isobutene competes with cationic oligomerization to give the gasoline additive isooctane (2,4,4-trimethylpentane) as a major product of a tandem oligomerization/hydrogenation sequence. Mechanistic experiments argue for the role of neutral iridium hydrides generated by the proton transfer of a cationic hydride precursor to an olefin substrate.