Mono- and dinuclear thiophene-based palladium(ii) complexes bearing phosphorus ylides: synthesis, catalytic activity,...

Two new thiophene-based palladium(ii) complexes, the mononuclear [Pd(L)₂(Cl)₂] (M) and [Pd(L)(µ-Cl)]₂ (D), were synthesized in good yield (73-90%) by reacting equimolar palladium(ii) salts with the thiophene-derived Schiff base ligand, C₁₀H₇N[double bond, length as m-dash]C(H)(C₄H₃S) (L). The reactivity of complex D with unsymmetrical phosphorus ylides [Ph₂P(CH₂)₂PPh₂C(H)C(O)C₆H₄X] (X = Cl (Y¹), NO₂ (Y²), OCH₃ (Y³), Br (Y⁴)) was also investigated via chloride bridge-splitting reactions, affording a new family of mononuclear thiophene-based Pd(ii) complexes (D¹-D⁴). L and its Pd(ii) complexes were characterized by elemental analysis, FT-IR, and NMR (¹H, ¹³C, and ³¹P) spectroscopy. Single-crystal X-ray diffraction confirmed the molecular structures of L and complex M, and DFT calculations were additionally performed to support the structural analysis of L. Complexes D¹-D⁴ exhibited excellent catalytic activity in Suzuki-Miyaura cross-coupling reactions under aerobic conditions in EtOH. MTT assays revealed cytotoxic activity against human carcinoma cell lines HT-29 and A549, with D⁴ showing the highest cytotoxicity. Molecular docking with SARS-CoV-2 (PDB ID: 6Y2F) and transcription factor STAT3B/DNA (PDB ID: 1BG1) indicated that L, complexes M and D¹ effectively interact with the active sites via stable non-covalent interactions, suggesting their potential as anticancer and anti-COVID-19 agents; D¹ showed superior inhibitory activity against COVID-19.