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

Abstract

We report the synthesis and characterization of a RuII 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). Treatment of ligands L1–L3 with [Ru(p-cymene)Cl2]2 afforded the corresponding complexes [(RuCl)(η6-p-cymene)(L1-3)-k2-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 varying the 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.