On the many roles of NH3 ligands in mono- and multinuclear complexes of platinum

Abstract

The role of the NH₃ ligands in the highly successful antitumour agents cisplatin and carboplatin is not fully understood. Suggestions that the ammonia ligands are involved in target recognition through hydrogen bond formation, e.g. with guanine-O6, have been questioned. Here, we review the roles and functions of NH₃ ligands of cis-PtCl₂(NH₃)₂ and likewise of its trans-isomer in complexes with model nucleobases as well as other N-heterocyclic ligands. Specifically, their roles in hydrogen bonding interactions with nucleobases as well as anions, the influence on acid–base properties of co-ligands, their involvement in condensation reactions, as well as a variety of displacement reactions will be examined. As a result, it can be stated that the ammonia ligands in cis- and trans-Pt^II(NH₃)₂ entities display additional features to those generally discussed in the last four decades since the discovery of the antitumour activity of cisplatin.