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

Seven hexacoordinated cis-dioxidomolybdenum(VI) complexes [MoO2 L1-7 ] (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 (H2 L1 ); X=Me, YCl, Z=H (H2 L2 ); X=i Pr, Y=Cl, Z=Me (H2 L3 )} and N,N'-bis-(2-hydroxy-3-X-5-Y-6-Z-benzyl)-1,2-diaminopropane {(X=Y=t Bu, Z=H (H2 L4 ); X=Y=Me, Z=H (H2 L5 ); X=i Pr, YCl, Z=Me (H2 L6 ); X=Y=Br, Z=H (H2 L7 )} 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 O2 N2 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.