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

Abstract

Diorganotin complexes of the compositions [Me<inf>2</inf>Sn(L)] (1), [n-Bu<inf>2</inf>Sn(L)] (2), [Ph<inf>2</inf>Sn(L)]⋅C<inf>6</inf>H<inf>6</inf> (3), [Bz<inf>2</inf>Sn(L)]⋅C<inf>6</inf>H<inf>6</inf> (4) and [n-Oct<inf>2</inf>Sn(L)] (5) were synthesized by reacting R<inf>2</inf>SnO (R = Me, n-Bu, Ph, Bz or n-Oct) with the N2,N6-di(thiazol-2-yl)pyridine-2,6-dicarboxamide (H<inf>2</inf>L, where H<inf>2</inf> denotes the two acidic protons) in refluxing toluene. Additionally, the mono-n-butyltin complex [n-BuSn(HL)Cl<inf>2</inf>]·H<inf>2</inf>O (6) was synthesized from n-BuSnCl<inf>3</inf> and H<inf>2</inf>L 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<inf>py</inf>, N−, N−) act as κ-N3 chelators. In 6, the L moiety (O, N<inf>py</inf>, 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 IC<inf>50</inf> 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. © 2024 Elsevier Inc.