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

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.