Synthesis of Dowex functionalised half-sandwich Ru (II) (η6-p-cymene) complex as effective and selective hydrogenation of furfural to levulinic acid

Abstract

The ruthenium(II) complex [(η6-p-cymene)Ru(Cl)(8-amino quinoline)] and [η6-p-cymene)Ru(OH2)(8-amino quinoline)] were synthesised, charactrised, and used to prepare novel ruthenium(II) based Dowex resin polymer [(η6-p-cymene)Ru(Cl / or OH2)(8-amino quinoline)]@Dowex. The ruthenium(II) comlex based Dowex catalyst is synthesisedby treatment of [(η6-p-cymene)Ru(Cl)(8-amino quinoline)] or [η6-p-cymene)Ru(OH2)(8-amino quinoline)] with Dowex@Na via ion exchange synthesis, in the presence of DCM as a solvent forming [(η6-p-cymene)Ru(Cl / OH2)(8-amino quinoline)]@Dowex, respectively. The developed Dowex polymer were caractrised by IR spectroscopy, ICP analysis, and 13C Solid-State NMR. The ICP proved the presence of Ru in the polymer resien with 63 and 61 wt% respectively. The catalytic transfer hydrogenation of furfural over both Ru(II) comlex based Dowex catalyst were investigated with formic acid as the hydrogen donor and water as the solvent at 80 oC after 19 h. The [(η6-p-cymene)RuCl (8-amino quinoline)]@Dowex and [(η6-p-cymene)RuOH2(8-amino quinoline)]@Dowex catalysts were shown to exhibit high activity in the transfer hydrogenation of furfural to form a sole levulinic acid (Lv) giving good conversion and excellent selectivity under mild reaction conditions. The [(η6-p-cymene)RuOH2(8-amino quinoline)]@Dowex catalyst showed high stability and reactivity in four catalyst recycling runs, which presents a completed selectivity of levulinic acid and enhancement of yield to 66%. Therefore, recyclability and leaching tests confirmed [η6-p-cymene)Ru(OH2)(8-amino quinoline)] complex to function as a heterogeneous catalyst which could be reused for at least four consecutive reaction runs without significant loss of catalytic activity.