Catalytic Conversion of Ethanol to n‑Butanol Using Ruthenium P–N Ligand Complexes

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 [RuCl₂(η⁶-p-cymene)]₂ and 2-(diphenylphosphino)­ethylamine (1) shows enhanced activity at initial water concentrations higher than those of our previously reported diphosphine systems. Preliminary mechanistic studies (electrospray ionization mass spectrometry and nuclear magnetic resonance spectroscopy) suggest the possibility of ligand-assisted proton transfer in some derivatives.