RuII-phosphine catalysed direct synthesis of benzimidazoles via acceptorless dehydrogenative coupling of alcohols with aromatic diamines

Abstract

We report the synthesis and characterization of Ru^II complexes containing amide-based phosphine ligands [o-Ph₂P(C₆H₄)C(O)N(H)C₆H₄(o-OR)] (L1 R = Me; L2 R = Et; L3 R = ⁱPr). Reaction of ligands L1–L3 with [Ru(p-cymene)Cl₂]₂ afforded the corresponding complexes [(RuCl)(η⁶-p-cymene)(L1–3)-κ²-P,O][Cl] (1 R = Me, 2 R = Et, and 3 R = ⁱPr). These complexes exhibit excellent catalytic activity in the selective synthesis of 2-substituted and 1,2-disubstituted benzimidazoles, with product selectivity governed by alcohol concentration. Control experiments revealed the operation of both acceptorless dehydrogenative and oxidative coupling pathways. Furthermore, the catalytic protocol was successfully extended to a broad range of substrates, delivering diverse benzimidazole derivatives in moderate to excellent yields.