Synthesis, structural characterization, antimicrobial and cytotoxic effects of aziridine, 2-aminoethylaziridine and azirine complexes of copper(ii) and palladium(ii)

Abstract

The synthesis, spectroscopic and X-ray structural characterization of copper(II) and palladium(II) complexes with aziridine ligands as 2-dimethylaziridine HNCH₂CMe₂ (a), the bidentate N-(2-aminoethyl)aziridines C₂H₄NC₂H₄NH₂ (b) or CH₂CMe₂NCH₂CMe₂NH₂ (c) as well as the unsaturated azirine NCH₂CPh (d) are reported. Cleavage of the cyclometallated Pd(II) dimer [μ-Cl(C₆H₄CHMeNMe₂-C,N)Pd]₂ with ligand a yielded compound [Cl(NHCH₂CMe₂)(C₆H₄CHMe₂NMe₂-C,N)Pd] (1a). The reaction of the aziridine complex trans-[Cl₂Pd(HNC₂H₄)₂] with an excess of aziridine in the presence of AgOTf gave the ionic chelate complex trans-[(C₂H₄NC₂H₄NH₂-N,N′)₂Pd](OTf)₂ (2b) which contains the new ligand b formed by an unexpected insertion and ring opening reaction of two aziridines (“aziridine dimerization”). CuCl₂ reacted in pure HNC₂H₄ or HNCH₂CMe₂ (b) again by “dimerization” to give the tris-chelated ionic complex [Cu(C₂H₄NC₂H₄NH₂-N,N′)₃]Cl₂ (3b) or the bis-chelated complex [CuCl(C₂H₂Me₂NC₂H₂Me₂NH₂-N,N′)₂]Cl (4c). By addition of 2H-3-phenylazirine (d) to PdCl₂, trans-[Cl₂Pd(NCH₂CPh)₂] (5d) was formed. All new compounds were characterized by NMR, IR and mass spectra and also by X-ray structure analyses (except 3b). Additionally the cytotoxic effects of these complexes were examined on HL-60 and NALM-6 human leukemia cells and melanoma WM-115 cells. The antimicrobial activity was also determined. The growth of Gram-positive bacterial strains (S. aureus, S. epidermidis, E. faecalis) was inhibited by almost all tested complexes at the concentrations of 37.5–300.0 μg mL⁻¹. However, MIC values of complexes obtained for Gram-negative E. coli and P. aeruginosa, as well as for C. albicans yeast, mostly exceeded 300 μg mL⁻¹. The highest antibacterial activity was achieved by complexes 1a and 2b. Complex 2b also inhibited the growth of Gram-negative bacteria.