Macrocyclic NHC complexes of group 10 elements with enlarged aromaticity for biological studies

Abstract

Two sets of macrocyclic, bio-inspired, non-heme ligands are utilized for the synthesis of Ni^II, Pd^II and Pt^II complexes. The ligands consist of a 16-atom macrocycle, formed by four methylene bridged NHC moieties, with imidazole or benzimidazole as building blocks. The complexes exhibit a square planar coordination geometry and are characterized by NMR, ESI-MS, elemental analysis, SC-XRD and UV/Vis. For complexes incorporating benzimidazole, an evaluation of luminescence properties is performed, and is found that phosphorescence is present for the Pd^II derivative and there is fluorescence for the Pt^II derivative. Stability studies in cell culture medium are performed for subsequent MTT assays. Here, the Ni^II complexes show low to no activity, and Pd^II and Pt^II complexes exhibit remarkable low IC₅₀ values in cisplatin resistant A2780cisR cells.