Ruthenium Polyaminocarboxylate Complexes

taining polyaminocarboxylate (pac) ligands (Ru-pac) is of continuing interest. The donor character of the pac ligand is comparable with that of many biological enzymes which make use of the carboxylate and amine donors from amino acids to bind to a metal centre. The pac ligand can form very stable 1:1 (metal : ligand) complexes with ruthenium. Early studies (1-3), later confirmed by crystallographic evidence (4-8), showed that the pac ligands in Ru-pac complexes function as pentadentate ligands, see Figure 1. The sixth coordination site of the ruthenium centre in Ru-pac complexes is occupied by a water molecule at low pH or by an hydroxide ion at high pH. Figure 1 shows structures and formulae of some [Ru(pac)(H2O)] complexes, and Table I contains data on spectral, electrochemical and acid-dissociation constants for these [Ru(pac)(H2O)] complexes. The chemistry of [Ru(pac)(H2O)] complexes is dominated by their lability towards the aquosubstitution reaction, which affords a facile and straightforward synthesis to mixed-ligand complexes (8). The reasons that ruthenium complexes containing ‘pac’ ligands demonstrate potential applications in metallodrugs are because of: • the number of stable and accessible oxidation states they possess, • their rapid rate of ligand exchange, and • their ability to bind to certain biological molecules. Furthermore, these Ru-pac complexes exhibit catalytic properties, in homogeneous conditions in the presence of oxygen atom donors, that mimic the biological enzymatic oxidation of hydrocarbons by cytochrome P-450 (8). Although the significance of Ru-pac complexes as chemotherapeutic agents has been reviewed (9), this article aims to examine the prospects of Ru-pac complexes for promoting studies towards the development of Ru-pac based pharmaceuticals, for a range of diseases. A glossary of terms used in the review is appended at the end of the paper.