Importance of the p-Ligand: Remarkable Effect of the Cyclopentadienyl Ring on the Cytotoxicity of Ruthenium PTA Compounds

The water-sol. complexes [(Cp'OR)RuCl(PTA)2] (Cp'OR = h5-1-alkoxy-2,4-di-tert-butyl-3-neopentylcyclopentadienyl; R = Me, Et; PTA = 1,3,5-triaza-7-phosphaadamantane) are considerably more cytotoxic (.apprx.2 orders of magnitude) than the cyclopentadienyl analog [CpRuCl(PTA)2] (i.e., IC50 = 4-10 vs. >1000 mM, depending on the cell line). The structure of [(Cp'OMe)RuCl(PTA)2] is reported, together with that of the precursor [(Cp'OEt)Ru(m-Cl)]2.