Metal complexes bearing phosphine ligands are attracting increasing attention for their applications in medicinal chem. In particular, organometallic ruthenium-phosphine complexes have been found to exhibit promising antitumor activity. The synthesis, anticancer activity and reactivity of a novel bis-phosphine complex, [Ru(η6-cymene)(PPh2(o-C6H4O)-κ2-P,O)(pta)]Cl (pta = 1,3,5-triaza-7-phosphatricyclo[220.127.116.11.]decane), is presented. The complex appears to exhibit its anticancer effect via a different mechanism to other ruthenium-arene pta complexes with labile co-ligands.