Synthesis, structures, and cytotoxicity insights of organotin(IV) complexes with thiazole-appended pincer ligand

Diorganotin complexes of the compositions [Me₂Sn(L)] (1), [n-Bu₂Sn(L)] (2), [Ph₂Sn(L)]⋅C₆H₆ (3), [Bz₂Sn(L)]⋅C₆H₆ (4) and [n-Oct₂Sn(L)] (5) were synthesized by reacting R₂SnO (R = Me, n-Bu, Ph, Bz or n-Oct) with the N²,N⁶-di(thiazol-2-yl)pyridine-2,6-dicarboxamide (H₂L, where H₂ denotes the two acidic protons) in refluxing toluene. Additionally, the mono-n-butyltin complex [n-BuSn(HL)Cl₂]·H₂O (6) was synthesized from n-BuSnCl₃ and H₂L in acetonitrile. Compounds were characterized by FT-IR, ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy, while their solid-state structures were examined using single-crystal X-ray diffraction studies. In diorganotin compounds 1-5, the dianionic tridentate ligands (N_py, N^-, N^-) act as κ-N³ chelators. In 6, the L moiety (O, N_py, N^-) acts as a κ-ON² tridentate chelator, with involvement of one of the carboxamide oxygen atoms. The coordination polyhedron around the Sn(IV) ion is completed either by two axial Sn-R ligands in compounds 1-5 or by n-Bu and Cl ligands in compound 6, giving rise to distorted trigonal bipyramid or octahedral structures, respectively. The tin NMR results show that the penta-coordinated structures of compounds 1-5 and the hexacoordinated structure of compound 6, observed in the solid-state, are retained in solution. The in vitro antitumor activities of 1-5 were tested on T-47D breast cancer cells. Of these, diphenyltin compound 3 showed the highest anti-proliferative effect, with an IC₅₀ of 10 ± 1.60 μM. Compound 3 exhibited selective toxicity, potentially inducing apoptosis via reactive oxygen species generation and nuclear changes, indicating promise as a breast cancer treatment. This study is the first to explore thiazole-appended organotin compounds for cytotoxicity.