New ruthenium(II) isocyanide catalysts for the transfer hydrogenation of ethyl levulinate to γ-valerolactone in C2-C6 alcohols

• New ruthenium (II) isocyanide complexes were synthesized from simple precursors. • The complexes were characterized and tested in the transfer hydrogenation reactions. • The transfer hydrogenation of ethyl levulinate to γ-valerolactone was optimized. • Several biomass-derived alcohols (2-butanol etc) were studied under green conditions. • The recycling of the best catalyst was investigated, improving the sustainability. Transfer hydrogenation (TH) processes are receiving great attention for biomass valorization and ruthenium(II) complexes are renowned TH catalysts both on laboratory and industrial scale. Only a few homogeneous catalytic precursors are available in the literature for the TH of ethyl levulinate (EL) to γ-valerolactone (GVL). Herein, starting from simple, commercially available isocyanides, two classes of air-stable ruthenium(II) complexes were synthesized and tested as catalytic precursors. First, an optimized preparation of Ru(II) p -cymene isocyanide complexes was developed. Then, the thermally induced p -cymene/DMSO substitution gave access to unprecedented ruthenium isocyanide-DMSO complexes. All the complexes were characterized and tested in TH of EL to GVL showing promising performances, adopting 2-propanol as hydrogen donor, a low catalyst (Ru) and co-catalyst (KOH) amount, working under microwave heating for 1 h at 150 °C. The most selective systems were also successfully tested with different biomass-derived alcohols, including 2-butanol. Finally, the recycling of the best catalyst was also investigated, thus improving the efficiency of the entire process.