Organometallic cis-Dichlorido Ruthenium(II) Ammine Complexes

Abstract

Bifunctional neutral half-sandwich Ru^II complexes of the type [(η⁶-arene)Ru(NH₃)Cl₂] where arene is p-cym (1) or bip (2) were synthesised by the reaction of N,N-dimethylbenzylamine (dmba), NH₄PF₆ and the corresponding Ru^II arene dimer, and were fully characterised. X-ray crystallographic studies of [(η⁶-p-cym)Ru(NH₃)Cl₂]·{(dmba–H)(PF₆)} (1a) and [(η⁶-bip)Ru(NH₃)Cl₂] (2) show extensive H-bond interactions in the solid state, mainly involving the NH₃ and the Cl ligands, as well as weak aromatic stacking interactions. The half-lives for the sequential hydrolysis of 1 and 2 determined by UV/Vis spectroscopy at 310 K ranged from a few minutes for the first aquation to ca. 45 min for the second aquation; the diaqua adducts were the predominant species at equilibrium. Arene loss during the aquation of complex 2 was observed. Upon hydrolysis, both complexes readily formed mono- and di-9-ethylguanine (9-EtG) adducts in aqueous solution at 310 K. The reaction reached equilibrium after ca. 1.8 h in the case of complex 1 and was slower but more complete for complex 2 (before the onset of arene loss at ca. 2.7 h). Complexes 1 and 2 were not cytotoxic towards A2780 human ovarian cancer cells up to the maximum concentration tested (100 μM).