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

Abstract

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)(Ph 2 PCH 2 CH 2 NHCH 2 CH 2 PPh 2 )] also produce sec-buta-nol and, in optimized conditions (120 °C, 10 mol% NaOEt base), achieve 71 % selectivity to this butanol isomer. The same triand 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.

Backbone-functionalised ruthenium diphosphine complexes for catalytic upgrading of ethanol and methanol to iso-butanol

“…selectivity, TOF) are targeted, this performance is similar to the best existing examples. 29–33,39,43…”

“…24 The reaction pathway includes dehydrogenation of simple alcohol, base-catalyzed aldol condensation reaction and rehydrogenation of the aldol product. 25 Our group [26][27][28][29][30][31][32][33] and others [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] have been seeking new homogeneous catalysts for ethanol upgrading via Guerbet chemistry. Despite these recent advances, there is still significant scope for further catalyst development.…”

Valorization of Lignocellulosic Molecules through Homogeneous Ru‐Catalyzed C−C and C−N Bond Forming Reactions

“…Wass and coworkers showed that trans ‐ Ru ‐ 13 and Ru‐14 complexes supported by small bite angle diphosphines and by mixed donor P−N ligands, respectively, are effective catalysts leading to the product with fair to good conversion and very high selectivity (Scheme 14). [49a,c] In 2017, trans ‐ Ru‐13 in combination with NaOH (200 mol %) was also applied to a mixture of ethanol and methanol containing the same amount of water present in the fermentation broth (85 %) [49b] . The reaction performed at 180 °C for 2 h led to isobutanol in 36 % yield and 78 % selectivity.…”

Tuning Ethanol Upgrading toward Primary or Secondary Alcohols by Homogeneous Catalysis

“…Herein, we demonstrate the catalytic transformation of ethanol to 2-butanol with pincer complexes Ru-MACHO ( Ru-1 ) and Ru-MACHO-BH ( Ru - 2 ), as well as the formation of low amounts of 2-butenes/butane (≤5%) under mild conditions (Figure , lower pathway) . Simply shifting to the analogous complex Ru - 5 , with the P -substituents changing to t -butyl groups, leads to the production of 1-butanol instead (Figure , upper pathway).…”