Highly selective and efficient solvent-free transformation of bio-derived levulinic acid to γ-valerolactone by Ru(II) arene catalyst precursors

The selective and efficient solvent-free hydrogenation of bio-based levulinic acid (LA) to γ-valerolactone (GVL)was achieved with new pyridylimine ruthenium(II) complexes as catalyst precursors. The hydrogenation reactionswere performed in the presence of formic acid as hydrogen source using a catalyst loading as low as 0.1 mol% with potassium hydroxide or triethylamine (Et3N). 4-Hydroxyvaleric acid (HVA) was produced only whenKOH was used, whereas reactions involving Et3N were selective to GVL. At 150 °C,>96% LA conversions wereachieved with 100% GVL selectivity. Recyclability of catalyst precursors was demonstrated by running threeconsecutive reactions where 100% conversion and selectivity was maintained. In-situ NMR studies show thathydrogen gas is formed by the decomposition of formic acid to carbon dioxide and hydrogen. Ru-hydride specieshave been detected, by 1H NMR, and are believed to be the catalytically active species, and a mechanism of thereaction has been proposed.

利用新型吡啶亚胺钌(II)配合物作为催化剂前驱体，实现了基于生物来源的糠醛酸（LA）的精选且高效的溶剂化氢化反应，转化为γ-丁内酯（GVL）。氢化反应在甲酸作为氢源的存在下进行，催化剂负载量低至0.1 mol%，并使用氢氧化钾或三乙胺（Et3N）。仅当使用氢氧化钾时，才产生4-羟基戊酸（HVA），而涉及Et3N的反应则对GVL具有选择性。在150°C的温度下，实现了超过96%的LA转化率，同时保持了100%的GVL选择性。通过连续进行三次反应，展示了催化剂前驱体的可回收性，在这三次反应中均保持了100%的转化率和选择性。原位核磁共振研究表明，甲酸分解产生二氧化碳和氢气，形成了氢化钌物种，通过1H NMR检测到，并被认为是催化活性物种，同时提出了该反应的机理。