Der Widerspenstigen Zähmung: Ein Rutheniumdiphosphan‐Katalysator ermöglichte eine beispiellose Selektivität von über 94 % bei gutem Umsatz (20 %+) in der Ethanolveredelung zu 1‐Butanol (siehe Bild; P orange, Ru blau). Mechanistische Studien zeigen, dass die Acetaldehyd‐Aldolkondensation vermutlich am Metall stattfindet und ihre gezielte Kontrolle entscheidend für die hohe Selektivität ist.

The catalytic conversion of (bio)ethanol into butanol is an attractive route to upgrade the modest fuel characteristics of this widely available bioderived substrate into a molecule that has properties much closer to conventional gasoline. The Guerbet reaction, known for more than 100 years, provides an ideal mechanism for this transformation. However, despite the apparently simple nature of this reaction for ethanol, it provides formidable challenges, especially in terms of achieving high selectivity. There have been advances in both heterogeneous and homogeneous catalysis in this regard, and this Perspective focuses on the very recent reports of homogeneous catalysts that describe encouraging results in terms of achieving high selectivity, mechanistic understanding, and widening scope.

We report several ruthenium catalysts incorporating mixed donor phosphine-amine ligands for the upgrade of ethanol to the advanced biofuel n-butanol, which show high selectivity (90%+) at good (up to 31%) conversion. In-situ formation of catalysts from mixtures of [RuCl 2 (η 6 -p-cymene)] 2 and 2-(diphenylphosphino)ethylamine (1) show enhanced activity at higher initial water concentrations than our previously reported diphosphine systems. Preliminary mechanistic studies (ESI-MS and NMR spectroscopy) suggest the possibility of ligand assisted proton transfer in some derivatives.

The synthesis of a range of chiral palladium bis(phosphite) pincer complexes has been achieved via C-H activation of the parent ligands and one of the complexes formed shows good activity in the catalytic allylation of aldehydes.

Catalysts based on ruthenium diphosphine complexes convert methanol/ethanol mixtures to the advanced biofuel isobutanol, with extremely high selectivity (>99%) at good (>75%) conversion via a Guerbet-type mechanism.