Second Sphere Ligand Promoted Organoiridium Catalysts for Methanol Dehydrogenation under Mild Conditions

Hydrogen produced from renewable resources is a potential source of clean energy. And Methanol is a liquid at room temperature and has a hydrogen content of up to 12.6 wt%, makes it a promising hydrogen source and can provide great benefits for sustainable hydrogen production. In this work, the modification of the picolinic acid ligand along with changes in the type and substituent position of the groups enhances the activity in iridium-catalyzed methanol dehydrogenation catalysis. These second sphere ligand modifications are found to be effective for achieving highly active organoiridium catalysts for methanol dehydrogenation reaction under mild conditions, i. e. 1 atm, 78 degrees C, with a weak base and without using an organic solvent, exhibiting a TOF of 377 h(-1). The electronic population analysis of each ligand is theoretically calculated, which shows that catalytic activity is dramatically affected by modifications to the metal's secondary coordination sphere environment, and the high activity originates from appropriate coordination by the picolinic acid ligand and carboxylic acid moiety in addition to the hydroxyl functionality. Moreover, kinetic experiments suggest that the C-H bond of methanol is linked to the iridium core and broken in the rate-determining step of the reaction. This study will be valuable for catalyst development in the field of methanol dehydrogenation.