Synthesis, characterization and anticancer studies of Osmium-cymene complexes with O,O'- and P,P'-chelators as well as monodentate N- and P-donar ligands

Abstract

Seventeen novel osmium cymene complexes with O,O′- and P,P′-chelating ligands as well as N- and P-monodentate ligands are reported. The osmium cymene complexes were synthesised and characterised by spectroscopic techniques (NMR, IR and Raman), elemental analysis, thermal analysis, conductivity studies and X-ray crystallography. The molecular structures of complexes 1(b), 2, 4, 6, 7(a)-(d) and 11 in this study are reported. The cymene rings of these complexes show different conformations due to loss of planarity influenced by the ancillary ligands as a result of ML back bonding. Osmium cymene complexes of the type [Os(η6-p-cymene)BrL2]+ (where L2 = chelating P,P′ ligand) and binuclear [{Os(η6-p-cymene)Br2}2 L2] (where L2 = bridging P,P′ ligand) were evaluated for anticancer activity against renal, melanoma, breast and HeLa cancer cells. The chelated-diphosphine osmium cymene complexes exhibited significant anticancer activities relative to the bridged-diphosphine osmium analogues. A series of O,O′-chelated osmium complexes exhibited moderate and poor anticancer activities.