Synthesis, structure and cytotoxicity of a series of Dioxidomolybdenum(VI) complexes featuring Salan ligands

Abstract

Seven hexacoordinated cis-dioxidomolybdenum(VI) complexes [MoO2L1–7] (1‐7) derived from various tetradentate diamino bis(phenolato) “salan” ligands, N,N′-dimethyl-N,N′-bis-(2-hydroxy-3-X-5-Y-6-Z-benzyl)-1,2-diaminoethane {(X=Br, Y=Me, Z=H (H2L1); X=Me, YCl, Z=H (H2L2); X=iPr, Y=Cl, Z=Me (H2L3)} and N,N′-bis-(2-hydroxy-3-X–5-Y-6-Z-benzyl)-1,2-diaminopropane {(X=Y=tBu, Z=H (H2L4); X=Y=Me, Z=H (H2L5); X=iPr, YCl, Z=Me (H2L6); X=Y=Br, Z=H (H2L7)} containing O‐N donor atoms, have been isolated and structurally characterized. The formation of cis-dioxidomolybdenum(VI) complexes was confirmed by elemental analysis, IR, UV–vis and NMR spectroscopy, ESI-MS and cyclic voltammetry. X-ray crystallography showed the O2N2 donor set to define an octahedral geometry in each case. The complexes (1–7) were tested for their in vitro antiproliferative activity against HT-29 and HeLa cancer cell line. IC50 values of the complexes in HT-29 follow the order 6<7<<1<2<5<<3<4 while the order was 6<7<5<1<<3<4<2 in HeLa cells. Some of the complexes proved to be as active as the clinical referred drugs, and the greater potency of 6 and 7 (IC50 values of 6 are 2.62 and 10.74μM and that of 7 is 11.79 and 30.48μM in HT-29 and HeLa cells, respectively) may be dependent on the substituents in the salan ligand environment coordinated to the metal.