1,2,4-triazole-derived N-heterocyclic carbene complexes of platinum(II) as catalysts for hydroamination reactions and active anticancer agents

A series of five platinum(II) complexes of 1,2,4-triazole derived N-heterocylcic carbenes (R-tazy) with generic formula cis-[PtCl2(R-tazy)(DMSO)] (DMSO = dimethyl sulfoxide) have been successfully synthesized. The complexes feature the carbenes with the same benzyl wingtip, but are differed by their N-4 substituent (R = isopropyl (1), cyclohexyl (2), phenyl (3), mesityl (4) and 2,6-diisopropylphenyl (5)). The two new compounds 1 and 2 were characterized by means of multinuclear (H-1, C-13{H-1}) magnetic resonance spectroscopy, mass spectrometry, elemental analysis and single crystal X-ray diffraction (for 2). The hindered rotations of the benzyl and kappa-S-dimethyl sulfoxide were elucidated using NMR spectroscopy and rationalized with density functional theory (DFT) calculation. Notably, the five complexes were found active catalysts for intermolecular hydroamination of phenylacetylene using aromatic amines in the presence of silver(I) triflate additive. In addition, all the five complexes display high cytotoxicity toward human carcinoma in the mouth (KB), human breast carcinoma (MCF-7) and human colorectal carcinoma (HT-29) cell lines with IC50 concentration in the 3.0 +/- 0.4-14.3 +/- 1.3 mu M range. Interestingly, compound 1 and 3 display lower cytotoxicity toward non-cancerous human embryonic kidney cell (HEK-293A).