Synthesis and Catalytic Application of Ru(II) Complexes Supported by Zwitterionic Triazol(in)ium-5-dithiocarboxylates (MIC·CS2) and Isothiocyanates (MIC·CSNPh)

In recent years, NHC-derived zwitterions [NHC·CS(X)] (X = S and NR) have gained a great deal of attention owing to their various applications in fields such as organic synthesis, organometallics, and more recently in catalysis. In this work, we report that the reaction of free triarylated triazol-5-ylidenes (MIC) with equimolar amounts of dithiocarboxylate and isothiocyanate derivatives allows for the preparation of a series of MIC·SC₂ and MIC·CSNAr zwitterions in good yields. Their potential as ligands for transition metals was demonstrated by the synthesis of ruthenium(II) complexes with the general formulas [RuCl(p-cymene)(MIC·CS₂)]PF₆ and [RuCl(p-cymene)(MIC·CNSAr)]PF₆. The zwitterions and the ruthenium complexes were fully characterized by NMR spectroscopy, X-ray crystallography, TGA, and elemental analysis. The new ruthenium complexes were successfully applied as catalysts in the transfer hydrogenation of a series of aldehydes and ketones showing good efficiency under low catalyst loadings and providing excellent conversions.