Mechanistic insight into CO2 hydrogenation
Reversible H2 storage near room temperature and pressure with pH as the ‘switch’ for controlling the direction of the reaction has been demonstrated using a bio-inspired proton-responsive Ir(III) dimer. Several similar mononuclear Ir(III) catalysts for CO2 hydrogenation were prepared to gain mechanistic insight through investigation of the factors that control the effective generation of formate. These factors include: (1) kinetic isotope effects by water, hydrogen, and bicarbonate; (2) position and number of hydroxyl groups on bpy-type ligands; and (3) mono- vs di-nuclear iridium complexes. We have, for the first time, obtained clear evidence from kinetic isotope effects and computational studies of the involvement of a water molecule in the rate-determining heterolysis of H2, and accelerated proton transfer by formation of a water bridge in CO2 hydrogenation catalyzed by bio-inspired complexes bearing a pendent base. A more significant enhancement of the catalytic activity was observed from electron donation by the ligand than on the number of the active metal centers.
ACS Catal. 2013, 3, 856-860, DOI: 10.1021/cs400172j.
Last Modified: November 4, 2013