Organometallic ruthenium(II) arene complexes containing the PTA ligand ([Ru(η⁶-arene)Cl₂(PTA)], PTA = 1,3,5-triaza-7-phosphatricyclo-[3.3.1.1]decane, termed RAPTA) show pharmacologically relevant anti-tumour properties in vitro. Two new enantiomeric pairs of RAPTA compounds, containing the chiral arene (R)- or (S)-2-phenyl-N-(1-phenylethylene)acetamide and either dichlorido or oxalato ligands were synthesised and fully characterised. The stability of the complexes towards hydrolysis was assessed and the dichlorido complexes were found to be more stable towards hydrolysis than the prototype complex RAPTA-C, ([Ru(η⁶-p-cymene)Cl₂(PTA)]). The cytotoxicity of the compounds towards human ovarian cancer cells is moderate to good with a degree of selectivity towards the cancer cells over healthy cells. More significantly, for the first time we were able to establish the influence of a bulky, chiral group attached to the arene on the cytotoxicity of this class of compound, with the S-enantiomer being more cytotoxic than the R-enantiomer.