Bipyrimidine ruthenium(II) arene complexes: structure, reactivity and cytotoxicity.

The synthesis and characterization of complexes [(η-arene)Ru(N,N′)X][PF], where arene is para-cymene ( p-cym), biphenyl (bip), ethyl benzoate (etb), hexamethylbenzene (hmb), indane (ind) or 1,2,3,4-tetrahydronaphthalene (thn), N,N′ is 2,2′-bipyrimidine (bpm) and X is Cl, Br or I, are reported, including the X-ray crystal structures of [(η- p-cym)Ru(bpm)I][PF], [(η-bip)Ru(bpm)Cl][PF], [(η-bip)Ru(bpm)I][PF] and [(η-etb)Ru(bpm)Cl][PF]. Complexes in which N,N′ is 1,10-phenanthroline (phen), 1,10-phenanthroline-5,6-dione or 4,7-diphenyl-1,10-phenanthroline (bathophen) were studied for comparison. The Ru arene complexes undergo ligand-exchange reactions in aqueous solution at 310 K; their half-lives for hydrolysis range from 14 to 715 min. Density functional theory calculations on [(η- p-cym)Ru(bpm)Cl][PF], [(η- p-cym)Ru(bpm)Br][PF], [(η- p-cym)Ru(bpm)I][PF], [(η-bip)Ru(bpm)Cl][PF], [(η-bip)Ru(bpm)Br][PF] and [(η-bip)Ru(bpm)I][PF] suggest that aquation occurs via an associative pathway and that the reaction is thermodynamically favourable when the leaving ligand is I > Br ≈ Cl. p K* values for the aqua adducts of the complexes range from 6.9 to 7.32. A binding preference for 9-ethylguanine (9-EtG) compared with 9-ethyladenine (9-EtA) was observed for [(η- p-cym)Ru(bpm)Cl][PF], [(η-hmb)Ru(bpm)Cl], [(η-ind)Ru(bpm)Cl], [(η-thn)Ru(bpm)Cl], [(η- p-cym)Ru(phen)Cl] and [(η- p-cym)Ru(bathophen)Cl] in aqueous solution at 310 K. The X-ray crystal structure of the guanine complex [(η- p-cym)Ru(bpm)(9-EtG- N7)][PF] shows multiple hydrogen bonding. Density functional theory calculations show that the 9-EtG adducts of all complexes are thermodynamically preferred compared with those of 9-EtA. However, the bmp complexes are inactive towards A2780 human ovarian cancer cells. Calf thymus DNA interactions for [(η- p-cym)Ru(bpm)Cl][PF] and [(η- p-cym)Ru(phen)Cl][PF] consist of weak coordinative, intercalative and monofunctional coordination. Binding to biomolecules such as glutathione may play a role in deactivating the bpm complexes. [ABSTRACT FROM AUTHOR]