Catalytic Disproportionation of Formic Acid to Methanol by an Iridium Complex Immobilized on Bipyridine-Periodic Mesoporous Organosilica

We report the first example of using heterogeneous Iridium (Ir) catalysts under atmospheric pressure conditions to achieve the catalytic disproportionation of formic acid to methanol. IrCp* complex (Cp*=pentamethylcyclopentadienyl (eta(5)-C5Me5)) was immobilized on the pore surface of the periodic mesoporous organosilica synthesized from a precursor mixture of ethane (Et) and 2,2'-bipyridine (BPy)-bridged organosilanes (Ir-Et-BPy-PMO). Ir-Et-BPy-PMO showed unique catalysis with higher selectivity of methanol compared to homogeneous Ir-BPy complexes. Furthermore, Ir-Et-BPy-PMO exhibited high reusability without any noticeable decrease in activity for at least five times with no leaching of Ir species during the reaction. The increase in methanol selectivity of Ir-Et-BPy-PMO would be attributed to the unique confinement effect in the mesochannels with their high aspect ratio for the retention of generated H-2/CO2, which suppresses the competing formic acid dehydrogenation and promotes the formic acid hydrogenation.