Selective hydrodeoxygenation of oxygenated aromatic molecules using a molecular palladium catalyst covalently bound to a solid SiO2 support†

The selective hydrodeoxygenation of lignin derived aromatics represents an important step towards the valorization of biomass. With this goal in mind, we synthesized a hybrid molecular/heterogeneous catalyst comprised of a (2,6-bis(1-methylbenzimidazolyl)pyridine-4′-aminopropyltrisiloxane)palladium(II) molecular catalyst covalently bound to a solid silica support through the siloxane functional group. A series of model complexes containing C–O bonds typically found in lignin biomass were explored and varying degrees of C–O bond hydrogenation were achieved. The stable covalent binding of the catalyst to the support was attributed to the observed long catalyst lifetimes which led to over 6000 catalytic turnovers without catalyst deactivation. Spectroscopic characterization of the catalyst pre- and post-catalytic reactions shows the catalyst maintains molecular integrity under the reaction conditions examined. The catalyst also exhibited complete selectivity for hydrodeoxygenation over ring hydrogenation of oxygenated aromatic molecules.