Iridium (Ir) nanocrystals were synthesized by reducing (methylcyclopentadienyl)(1,5-cyclooctadiene)lr with hexadecanediol in the presence of four different capping ligand combinations: oleic acid and oleylamine, trioctylphosphine (TOP), tetraoctylammonium bromide (TOAB), and tetraoctylphosphonium bromide (TOPB). The oleic acid/oleylamine-capped nanocrystals were of the highest quality, with the narrowest size and shape distribution. The Ir nanocrystals were tested for their ability to catalyze the hydrogenation of 1-decene as a model reaction. The oleic acid/oleylamine and TOP-capped nanocrystals were both catalytically dead. TOAB and TOPB-coated nanocrystals both catalyzed 1-decene hydrogenation, with the TOPB-coated nanocrystals exhibiting the highest turnover frequencies. Recycling through several catalytic reactions increased the catalytic activity, presumably as a result of ligand desorption and increased exposure of the metal surface, with ligand desorption eventually leading to precipitation and significantly decreased activity.