Homogeneous Tetradentate Ruthenium Hydrogenation Catalysts for the Deoxygenation of Biomass-Derived Substrates in Aqueous Acidic Media
This thesis is an investigation of tetradentate ruthenium catalyst systems incorporating metal-ligand bifunctionality for the deoxygenation of biomass-derived substrates. Tridentate systems employed by the Schlaf group are proven catalysts for the partial deoxygenation of biomass-derived substrates. It was postulated that tetradentate systems would exhibit increases in temperature stability and catalytic activity relative to analogous tridentate systems. Ru(6,6′-bis(aminomethyl)-2,2′-bipyridine)(OH2)22 was synthesized in situ using the catalyst platform Ru(DMF)63 and fully characterized. The catalyst system was stable to temperatures of 200°C, and was effective for the conversion of the model substrate 2,5-hexanedione, but was not recyclable. When tested in water against the more complex substrate 2,5-dimethylfuran, substrate polymerization was observed, an effect that was minimized in alternative solvent systems at the cost of catalytic activity. The addition of a strong acid co-catalyst also decreased the overall catalytic activity. A structurally analogous catalyst system was also investigated, but proved inactive for the conversion of the model substrate. This was likely due to flexibility of the ligand, so the synthesis of a rigid analog of this ligand was attempted, but ultimately proved unsuccessful.