A sustainable supply chain: The controlled transformation of the biomass‐derived platform compounds levulinic acid (LA) and itaconic acid (IA) into the corresponding lactones, diols, or cyclic ethers (see picture) by using a multifunctional molecular catalyst is described.

Selective hydrogenation of biogenic carboxylic acids is an important transformation for biorefinery concepts based on platform chemicals. We herein report a mechanistic study on the homogeneously ruthenium/phosphine catalyzed transformations of levulinic acid (LA) and itaconic acid (IA) to the corresponding lactones, diols, and cyclic ethers. A density functional theory (DFT) study was performed and corroborated with experimental data from catalytic processes and NMR investigations. For [Ru(TriPhos)H](+) as the catalytically active unit, a common mechanistic pathway for the reduction of the C═O functionality in aldehydes, ketones, lactones, and even free carboxylic acids could be identified. Hydride transfer from the Ru-H group to the carbonyl or carboxyl carbon is followed by protonation of the resulting Ru-O unit via σ-bond metathesis from a coordinated dihydrogen molecule. The energetic spans for the reduction of the different functional groups increase in the order aldehyde < ketone < lactone ≈ carboxylic acid. This reactivity pattern as well as the absolute values are in full agreement with experimentally observed activities and selectivities, forming a rational basis for further catalyst development.

Eine nachhaltige Versorgungskette: Die kontrollierte Überführung der aus Biomasse erhaltenen Plattformverbindungen Lävulinsäure (LA) und Itaconsäure (IA) in die entsprechenden Lactone, Diole oder cyclischen Ether (siehe Bild) wird durch einen multifunktionellen molekularen Katalysator möglich.

Coordinatively unsaturated ruthenium complexes with a tethered SDmp (Dmp=2,6-dimesitylphenyl) ligand, [(DmpS)Ru(PR(3))][BAr(F) (4)] (3 a: R=Et; 3 b: R=Ph; Ar(F)=3,5-(CF(3))(2)C(6)H(3)), were synthesized by the reactions of [{(p-cymene)RuCl}(2)(mu-Cl)(2)], LiSDmp, phosphines, and NaBAr(F) (4). The Ru--S bonds in 3 a and 3 b were found to serve as the polarized reactive site in reactions with alkyl halides, diazoalkanes, (p-tosyliminoiodo)benzene, phenylacetylene, and H(2). Alkylation of 3 a and 3 b with methyl iodide or ethyl bromide occurred instantaneously to give the thioether complexes [(DmpSR')RuX(PR(3))][BAr(F) (4)] (4 a: R=Et, R'=Me, X=I; 4 b: R=R'=Et, X=Br; 4 c: R=Ph, R'=Me, X=I; 4 d: R=Ph, R'=Et, X=Br). Treatment of 3 a with diazoalkanes N(2)CHR (R=CO(2)Et, SiMe(3)) led to the cycloaddition of carbenes to the Ru--S bond to form [DmpS(CHR)Ru(PEt(3))][BAr(F) (4)] (5 a: R=CO(2)Et; 5 b: R=SiMe(3)), whereas the reaction with (p-tosyliminoiodo)benzene gave rise to [DmpS{NS(O)(C(6)H(4)-4-CH(3))O}Ru(PEt(3))][BAr(F) (4)] (6), which contains a five-membered ruthenacycle of RuSNSO. Addition of phenylacetylene to the Ru--S bond occurred reversibly to produce the vinyl sulfide complexes [DmpS(PhCCH)Ru(PR(3))][BAr(F) (4)] (7 a: R=Et; 7 b: R=Ph). On the other hand, the phenylacetylene at ruthenium slowly isomerized to vinylidene and bridged Ru and S in the products, [DmpS{C(CHPh)}Ru(PR(3))][BAr(F) (4)] (8 a: R=Et; 8 b: R=Ph). Complex 3 a catalyzed the hydrogenation of acetophenone, in which the heterolytic H-H splitting at the Ru-S site is suggested to be involved in the mechanism.

Less is more: The integrated development and optimization of catalysts and reaction media led to a highly selective decarbonylation of 5‐(hydroxymethyl)furfural (HMF) to furfuryl alcohol (FFA) with an iridium/phosphine catalyst in the presence of compressed carbon dioxide. Subsequent hydrogenation over ruthenium nanoparticles (RuNPs) led to tetrahydrofurfuryl alcohol (THFA), a possible solvent for the decarbonylation reaction (see scheme).