The directed, chemoselective hydrogenation of olefins has been established using iridium(I) catalysts which feature a tuned NHC/phosphine ligand combination. This selective reduction process has been demonstrated in a wide array of solvents, including more environmentally acceptable media, also allowing further refinement of hydrogenation selectivity.
Kerr, W. J., Mudd, R. J., & Brown, J. A. (2016). Iridium(I) NHC/phosphine catalysts for mild and chemoselective hydrogenation processes. Chemistry - A European Journal, 22(14), 4738–4742. https://doi.org/10.1002/chem.201504825