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 .

New Ru(ii) complexes (1 and 2) have been synthesized and reacted with Zn(OAc)2 to form hexanuclear complexes (3 and 4) containing four Ru(ii) and two Zn(ii) centres. The latter are highly active and recyclable catalyst for the conversion of levulinic acid to GVL.

The new compounds and potential ligands 2-(3,5-di-tert-butyl-1H-pyrazol-1-yl)ethyldiphenlyphosphinite (L1), 2-(3,5-di-tert-butyl-1H-pyrazol-1-yl)ethyldiethylphosphite (L2), 2-(3,5-di-tert-butyl-1H-pyrazol-1-yl)ethyl-diethylphosphite (L3) and 2-(3,5-diphenyl-1H-pyrazol-1-yl)ethyldiethylphosphite (L4) were prepared from the reaction of (3,5-(disubstituted)pyrazol-1H-yl)ethanol and the appropriate phosphine chloride. The phosphinite (L1) and phosphites (L2-L4) and 2-(3,5-diphenyl-1H-pyrazol-1-yl)ethyldiphenylphosphinite (L5) were reacted with [Ru(p-cymene)Cl2]2 to afford the ruthenium(ii) complexes [Ru(p-cymene)Cl2(L1)] (1), [Ru(p-cymene)Cl2(L2)] (2), [Ru(p-cymene)Cl2(L3)] (3), [Ru(p-cymene)Cl2(L4)] (4), and [Ru(p-cymene)Cl2(L5)] (5). All ruthenium complexes were characterized by a combination of NMR spectroscopy, elemental analysis and, in selected cases, by single crystal X-ray crystallography. Complexes 1-5 and [Ru(p-cymene)Cl2(L6)] (6) (prepared from 2-(3,5-dimethyl-1H-pyrazol-1-yl)ethyldiphenylphosphinite (L6)) were investigated as catalysts for both transfer and molecular hydrogenation of acetophenone to 1-phenylethanol. At 80 °C the percent conversion of acetophenone in transfer hydrogenation was moderate to high over 10 h (42-87%); for molecular hydrogenation acetophenone, conversions were as high as 98% in 6 h.

Novel multidentate pyridyl‐aminophosphinite (L1) and pyridyl‐phosphoramidite (L2) ligands of N^P^P^N‐donor system have been synthesized via a series of simple steps. The ligands are symmetrical and as a result, their reactions with [Ru(p‐cymene)Cl2]2 and [Ru(benzene)Cl2]2 lead to the formation of four monodentate bimetallic complexes (1–4) that retain the symmetry of the ligands. Meso and racemic mixtures (rac) of bidentate bimetallic complexes 5–8 were formed from the monodentate complexes through coordination of the pyridine nitrogen atoms to the two metal centers. The isomerism occurs at each metal center, which was evidenced by 31P{1H}, 1H NMR spectroscopy and single‐crystal X‐ray diffraction. The complexes were active towards hydrogenation of levulinic acid (LA) to γ‐valerolactone (GVL) using formic acid as the hydrogen source. The complexes are active at relatively low temperatures and are able to perform the hydrogenation in the absence of any additional solvent apart from the reagents to give high TON of 3 600. The catalysts are recyclable up to the fourth cycle, following which 20 % loss of activity is seen.

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