Syntheses, structures, and anticancer activity of novel organometallic ruthenium-maltol complexes

Abstract Organometallic ruthenium complexes containing two dehydrogenated maltol ligands Ru 3 (CO) 8 (2 L –2H) 1 , Ru 3 (CO) 7 PPh 3 (2 L –2H) 2 , [Ru 3 (CO) 7 (2 L –2H)] 2 (dppm or dppe) 3 , 4 ( L  = Maltol) have been synthesized and characterized. The in vitro anticancer activity of compounds 1 – 4 against seven types of human cancer cell lines was assessed and compared to clinically used drug cisplatin. The anticancer activity of compound 1 ( Fig. 3 ) is many times more potent than cisplatin against seven types of human cancer cell lines. There is a correlation between substituting a CO ligand in 1 with different phosphines decreases the activity following the order 1  >  2  >  3  >  4 . The X-ray crystal structures of complexes 1 and 2 are reported. The single crystal X-ray diffraction structure of 1 consists of a triangular ruthenium metal framework in which a Ru–Ru bond is bridged by two maltolate ligands with their two oxygen atoms in a μ − η 2 -bonding mode. The dihedral angle between Ru 3 and maltol planes is 40.2°. The two ruthenium atoms bridged by maltol ligands each have two carbonyl ligands and the third ruthenium atom is bonded to four carbonyl ligands. The greatest structural difference between 1 and 2 is the angle between the best planes of the two coordinated C 6 H 5 O 3 −1 ligands; in 1 it is 27.1° while in 2 it is 42.8°. It is interesting to note that the phosphine substitution occurs at the ruthenium atom not bound by maltol ligands.