Synthesis and catalytic activity of water-soluble ruthenium(II) p-cymene complexes in tandem nitroarene reduction/N-methylation and transfer hydrogenation

In this study, a series of water-soluble ruthenium(II) p-cymene complexes bearing carboxylic acid-functionalized ligands (Ru1–Ru3) were synthesized, fully characterized (1H NMR, 13C NMR, and FT-IR), and evaluated in two distinct catalytic transformations: tandem nitroarene reduction/N-methylation and transfer hydrogenation. Of the catalysts tested, Ru1 exhibited superior catalytic activity in both systems. Under optimized conditions (1 mol% Ru1, 8 mmol NaBH4, 110 °C, 2 h in methanol), Ru1 promoted the one-pot tandem transformation of nitrobenzene to N-methylaniline with up to 93% conversion using methanol as a sustainable C1 and H2 source. Furthermore, Ru1 proved highly effective in the transfer hydrogenation of acetophenone and various structurally diverse ketones using isopropanol as the hydrogen donor (0.5 mol% catalyst, 0.5 mmol KOH, 82 °C, 1.5 h), delivering the corresponding secondary alcohols in moderate to excellent yields (51%–98%). These protocols offer atom-economical, sustainable, and versatile catalytic routes for both amine functionalization and carbonyl reduction.