| A series of ruthenium-based homogeneous ionic hydrogenation catalysts and their application in the selective deoxygenation under acidic conditions of glycerol, levulinic acid, anhydroerythritol, and 5-hydroxymethylfurfural was investigated. The syntheses of the five acid- and water-stable catalysts cis-[Ru(N--N)2(OH2)2](OTf) 2, [Cp*Ru(OH2)(N--N)](OTf), and mer-[Ru(OH 2)3(terpy)](OTf)2 (Cp* = C5Me 5-; N--N = 2,2'-bipyridine, 1,10-phenanthroline; OTf = CF3SO3-; terpy = 2,2':6',2"-terpyridine) are described. An improved, two-step synthesis of 6,6'-diamino-2,2'-bipyridine (dabp) was developed and synthetic efforts towards cis-[Ru(dabp) 2(OH2)2](OTf)2 and [Cp*Ru(OH2 )(dabp)](OTf) are discussed.;The five catalysts were tested as hydrogenation catalysts for carbonyl model substrates. Aldehydes were readily hydrogenated, while activity in ketone hydrogenations scaled inversely with the steric demand of the catalyst and ketone. The [Cp*Ru(OH2)(N--N)](OTf) catalysts were the least active while [Ru(OH2)3(terpy)](OTf)2 was the most active. Deoxygenation studies of the model substrate 1,2-hexanediol showed that [Ru(N--N)2(OH2)2](OTf) 2 and [Ru(OH2)3(terpy)](OTf)2 were stable to 175 °C, while the [Cp*Ru(OH2)(N--N)](OTf) systems were stable to at least 200 °C. Substrate condensation reactions dominated at reaction temperatures greater than 150 °C. The addition of water alleviated this problem to a certain extent, but also resulted in decreased catalytic activity. [Ru(OH2)3(terpy)](OTf) 2 was found to be very active, completely deoxygenating 1,2-hexanediol to hexane.;The [Cp*Ru(OH2)(N--N)](OTf) and [Ru(OH2) 3(terpy)](OTf)2 catalysts were tested for the selective deoxygenation of glycerol to 1,3-propanediol. 1-Propanol was produced in up to 18% yield, but no 1,3-propanediol was observed. The bulk of the glycerol was consumed in condensation reactions. Control experiments proved that the desired pathway of glycerol to 1,3-propanediol (and further deoxygenation to 1-propanol or even propane) was not the operative pathway. Instead, glycerol was dehydrated to acrolein, which was subsequently hydrogenated to 1-propanol.;Levulinic acid was hydrogenated to gamma-valerolactone in 80% yield. Trace amounts of tetrahydrofuran were obtained from anhydroerythritol, but in general, little hydrogenation activity was observed for this substrate.;The presence of high concentrations of acid and/or water in reaction mixtures containing 5-hydroxymethylfurfural led either to hydration and fragmentation to levulinic acid and subsequent hydrogenation to gamma-valerolactone, or to polymerization and decomposition. With less acid, nearly complete conversion of 5-hydroxymethylfurfural was observed. Identified hydrogenation products included 2,5-hexanedione and 2,5-bis(hydroxymethyl)furan. |
