Hydrogen Liberation from Formic Acid Mediated by Efficient Iridium(III) Catalysts Bearing Pyridine-Carboxamide Ligands

Herein it is shown that complexes [Cp*Ir(R-pica)Cl] {R-pica = R-picolinamidate = (2)-R-pyridine-2-carboxamide ion (-1), 1 R = H and 2 R = Me} catalyze the liberation of H-2 from formic acid (FA) in water, at ambient temperature and pressure, in the absence of any addictive/promoter, with performances comparable with those of the best catalysts reported so far. TOF values approaching 30000 h(-1) were observed for 1 and 2 (pH = 3.7, [HCOOH] + [HCOO-] = 1 m, [Cat] = 250 mu m, T = 60 degrees C), whereas the TON was only limited by the amount of HCOOH used and by the increase of pH with the progress of reaction, which makes the protonation of Ir-H less probable.