Four Ru(II)-arene thioamide complexes of the type [(η6-cymene)Ru(PPh3)(L)]+ (L = bidentate monoanionic thioamide ligand) have been synthesized and isolated as their hexafluorophosphate salts. All these complexes are fully characterized by spectroscopic methods. Molecular structures of the ligands (HL2 and HL3) and complex (3) were determined by single crystal X-ray crystallography. The ligands coordinated to Ru center through phenolic O and thioamide S atoms. All the four complexes were tested as catalysts in the one pot synthesis of 1,5-diketones from aromatic ketones and alcohols in the presence of KOtBu, and the products were analyzed by GC/GC–MS/1H NMR. Complexes 1 and 2 behaved as catalysts to produce 1,5-diketones while complexes 3 and 4 catalyzed the reactions to form alkylated ketones. Scope of the reaction was extended to various substituted alcohols and ketones to prepare 1,5-diketones with catalyst 1.