Efficient Solvent-Free Hydrogenation of Levulinic Acid to γ-Valerolactone by Pyrazolylphosphite and Pyrazolylphosphinite Ruthenium(II) Complexes

Abstract

Solvent-free conversion of bioderived levulinic acid (LA) to γ-valerolactone (GVL) has been achieved by new pyrazolylphosphite and pyrazolylphosphinite ruthenium(II) complexes as catalyst precursors, using both formic acid and molecular hydrogen as hydrogen sources. The reactions were very efficient at moderate temperatures of 100−120 °C. With a catalyst loading of 0.1%, 100% LA conversion (with hydrogen gas) was achieved with 100% GVL selectivity at 110 °C and 15 bar. The catalyst was recyclable up to three times without significant loss of activity and selectivity. The catalyst precursors are found to be more efficient when the hydrogen source was molecular hydrogen as compared to formic acid. NMR studies of reactions involving formic acid as a hydrogen source indicate that the initial step in the reaction involves the decomposition of formic acid to CO 2 and H 2 .

xNi–yCu–ZrO2 catalysts for the hydrogenation of levulinic acid to gamma valorlactone

“…The hydrogenation of LA to GVL has been reported using both homogeneous and heterogeneous catalysts [4,5]. Re, Ru, Pd, and Pt have been the generally explored precious metal heterogeneous catalysts for the synthesis of GVL from LA with a particular focus on Ru due to its excellent performance for the liquid phase hydrogenation of this substrate [6][7][8][9]. High turnover numbers can also be achieved using well dispersed Pd nanoparticles deposited on SiO 2 supports [10].…”

Multidentate Pyridyl‐Aminophosphinite and Pyridyl‐Phosphoramidite Ruthenium(II) Complexes: Synthesis, Structure and Application as Levulinic Acid Hydrogenation Pre‐Catalysts

“…The observation is further highlighted when the performance of monometallic cationic catalyst precursors, with P ^ N donor ligands, are compare to the current bimetallic systems ( 5–8 ). The former (at 0.1 mol‐% loading) displayed LA conversions in the range of 37 % to 68 % in 16 h, while in this works the same loading of the pre‐catalysts 5 – 8 gave conversions in the range of 87 % to 100 % in 8 h.…”

“…Triethylamine was chosen as the base for the reaction due to its effectiveness as reported previously , . The reactions involving 1 and the rest of the catalyst precursors were accompanied by CO 2 and H 2 generation as observed previously , , . This was characterized by a rise in the pressure gauge reading and prolonged fizzing of the reaction mixture after opening the reactors.…”

“…When comparing the current bimetallic catalysts with similar monometallic systems which we previously used for LA hydrogenation,, [19a] it becomes clear that there is merit to introducing two active sites in the catalyst structure. For example, monometallic phosphorus‐donor (phosphinite and phosphite) ruthenium catalysts precursor (at 0.1 mol‐% loading) showed 70 % to 96 % conversion of LA in 16 h, while similar catalysts precursors ( 1–4 ) coordinated in a monodentate fashion produced 93 % to 98 % conversion in half the time. Furthermore, the latter required more base additive (20 mmol) while in this report we have established that lower base additive (5 mmol) is sufficient.…”

“…Our group has reported application of P ^ N pyrazolyl‐phosphite ruthenium(II) and pyrazolyl‐phosphinite ruthenium(II) complexes for LA hydrogenation and noticed the catalysts are effective and selective for GVL formation using molecular hydrogen . By carefully selecting phosphinocarboxylate ligands, we were able to design another heterometallic Ru ^ Zn‐based catalyst system.…”