Catalytic role of ruthenium(III) complexes bearing cystamine-based disulfide ligands on the N-alkylation of o-substituted anilines

Ruthenium(III) complexes of cystamine-based disulfide ligands with the general formula [RuXL1-4] (X = Cl or Br; L1-4 = pentadentate Schiff base ligands) were synthesized from ruthenium precursor complexes [RuX3(AsPh3)(3)] (X = Cl or Br) and disulfide ligands derived from cystamine and 2-hydroxy-substituted aromatic aldehydes, viz., salicylaldehyde, 5-chlorosalicylaldehyde, o-vanillin, and 2-hydroxynaphthaldehyde for L-1-L-4, respectively. The ligands and their complexes were structurally characterized by elemental, spectral (UV-Vis, IR, NMR, EPR, and ESI-mass) and cyclic voltammetry methods. The new complexes have shown effective hydrogen transfer properties, which were studied in the catalytic transfer hydrogenation of some secondary alcohols using gas chromatography. The catalytic properties of the complexes toward the N-alkylation of o-substituted anilines were analyzed in detail showing that this catalytic reaction involved two important hydrogen transfer steps. Hence, a new suitable and efficient catalytic system has been investigated for the synthesis of various benzazoles in a one-pot reaction.