Control in Advanced Biofuels Synthesis via Alcohol Upgrading: Catalyst Selectivity to n-Butanol, sec-Butanol or Isobutanol

Ruthenium complexes with tetradentate PNNP donor ligands demonstrate a marked change in selectivity compared to analogous bis bidentate PN complexes in Guerbet catalysis, producing mixtures of n-butanol (17 %), sec-butanol (14 %) and ethyl acetate (66 %) rather than the usual 90 %+ selectivity to n-butanol. Tridentate PNP ruthenium complexes such as [Ru(H)(Cl)(CO)(Ph2PCH2CH2NHCH2CH2PPh2)] also produce sec-butanol and, in optimized conditions (120 degrees C, 10 mol% NaOEt base), achieve 71 % selectivity to this butanol isomer. The same tri- and tetradentate complexes are efficient catalysts for the conversion of methanol/ethanol mixtures to isobutanol (up to 97 % selectivity). In this way, judicious choice of ligand within this general catalyst family allows selectivity to three butanol isomers of interest as fuel molecules.

Automated summary

Ruthenium complexes with tetradentate PNNP donor ligands exhibit different selectivity in Guerbet catalysis compared to bis bidentate PN complexes, producing a mixture of n-butanol (17%), sec-butanol (14%) and ethyl acetate (66%) instead of the usual 90%+ selectivity to n-butanol. Tridentate PNP ruthenium complexes also produce sec-butanol and achieve 71% selectivity to this isomer in optimized conditions. The same tri- and tetradentate complexes are efficient catalysts for converting methanol/ethanol mixtures to isobutanol with up to 97% selectivity.