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

This report describes synthesis of a new N-(4-(benzo[d]thiazole-2-yl)phenyl)-1-(pyridine-2-yl)methanimine ligand (L1) and its three ruthenium(II) arene complexes with RuCl4(p-cymene)2 (C1), RuCl4(benzene)2 (C2), and RuCl4(hmb)2 [hmb = hexamethylbenzene] (C3). The new ligand and complexes were characterized with the help of standard analytical techniques like 1H and 13C{1H} NMR, FTIR, UV-Visible, HRMS, cyclic voltammetry and elemental analysis techniques. The structure of ruthenium complex (C1) and its bonding mode with ligand were authenticated with the help of single crystal X-ray diffraction. The complex showed pseudo-octahedral half-sandwich “piano-stool” type geometry around Ru center. The ruthenium arene complexes (C1-C3) were used as catalyst for N-alkylation of aniline derivatives using aliphatic alcohols (EtOH, PrOH, MeOH). Among all three catalysts, C1 showed 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 less yield (30-33%), which clearly demonstrates the potential of ligand design in catalysis reactions. The mechanistic studies showed the formation of Ru-H intermediate and imine species, which gave the desired alkylated products. Overall, these complexes are promising catalyst candidates for organic transformation.