Synthesis and structural elucidation of cytotoxic mono and dinuclear rhenium carbonyl complexes bearing bis-{1,3-(imino pyrrolyl)-m-chloro phenyl)} ligand

A mononuclear and dinuclear rhenium tricarbonyl compounds were synthesized by the one-pot condensation reaction of [Re(CO)₅Br], pyrrole-2-carboxaldehyde and 4‑chloro-m-phenylene diamine. The mononuclear rhenium tricarbonyl complex containing {3-(imino pyrrolyl)-6‑chloro phenylamine)} ligand (IPP) with formula {[Re(CO)₃Br(IPP)], (1), was obtained by refluxing stoichiometric quantities of amine, aldehyde and rhenium metal precursor in methanol solution. Similarly, dinuclear rhenium tricarbonyl compound {[Re(CO)₃Br]₂(BIPP)], BIPP = bis-{1,3-(imino pyrrolyl)-m-chlorophenyl)}, (2) has been synthesized by refluxing appropriate amounts of aldehyde, and rhenium metal precursor in the presence of one equivalent of amine ligand. Compounds 1 and 2 were characterized by FT-IR, ¹H NMR, and UV–Vis spectroscopy, elemental analysis, and mass spectrometry. The luminescence properties of the formed complexes were studied in solution at room temperature, revealing an extended lifetime for the dinuclear complex 2 in comparison to 1. DFT calculations for the optimized structures helped to understand the geometry of the complexes, whereas TD-DFT revealed the vertical transitions responsible for the photophysical properties of the complexes. The cytotoxicity of such complexes against MCF-7 breast cancer has been also reported, revealing a dose-dependent growth inhibition attributed to a DNA-intercalating mode of binding for both complexes. The pronounced effect of the two metals on the cytotoxic studies and lifetime of the excited species were investigated. The greater intercalation ability of the complex 2 in comparison to complex1 obtained from circular dichroism studies also indicates the greater efficacy of Re complex 2.