Ruthenium Complexes of Bidentate N,N‐Ligand as Catalyst for Selective N‐Alkylation of Amines with Alcohols

Abstract

AbstractThis report describes the synthesis of a new N‐(4‐(benzo[d]thiazole‐2‐yl)phenyl)‐1‐(pyridine‐2‐yl)methanimine ligand (L1) by the reaction of 2‐(4‐aminophenyl)benzothiazole with pyridine‐2‐carboxaldehyde. The three new ruthenium(II) arene complexes were synthesized by the reaction of L1 with [RuCl2(p‐cymene)]2 (C1), [RuCl2(benzene)]2 (C2), and [RuCl2(hmb)]2 [hmb=hexamethylbenzene] (C3). The new ligand and complexes were characterized with the help of standard analytical techniques like 1H and 13C{1H} Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared (FTIR), Ultraviolet‐visible (UV‐Visible), High‐Resolution Mass Spectrometry (HRMS), cyclic voltammetry, and elemental analysis techniques. The structure of ruthenium complex (C1) and its bonding mode with the ligand were authenticated with the help of single crystal X‐ray diffraction. The complex showed a pseudo‐octahedral half‐sandwich “piano‐stool” type geometry around the Ru center. The ruthenium arene complexes (C1–C3) were used to catalyze the N‐alkylation of aniline derivatives using aliphatic alcohols (EtOH, PrOH, MeOH). Among all three catalysts, C1 showed the highest yield of alkylated derivatives (up to 95%) with 1.0 mol% catalyst loading. The order of alkylation toward alcohol derivatives was EtOH = PrOH > MeOH. The alkylation reaction with ruthenium arene precursors showed poor yields (30–33%), demonstrating ligand design‘s potential in catalysis reactions. The proton NMR of the reaction mixture after 2 h shows the formation of Ru−H intermediate, which gave the desired alkylated products. Overall, these complexes are promising catalyst candidates for organic transformation.