Can an Elusive Platinum(III) Oxidation State be Exposed in an Isolated Complex?

Platinum(IV) complexes are extensively studied for their activity against cancer cells as potential substitutes for the widely used platinum(II) drugs. Pt^IV complexes are kinetically inert and need to be reduced to Pt^II species to play their pharmacological action, thus acting as prodrugs. The mechanism of the reduction step inside the cell is however still largely unknown. Gas-phase activation of deprotonated platinum(IV) prodrugs was found to generate products in which platinum has a formal +3 oxidation state. IR multiple photon dissociation spectroscopy is thus used to obtain structural information helping to define the nature of both the platinum atom and the ligands. In particular, comparison of calculations at DFT, MP2 and CCSD levels with experimental results demonstrates that the localization of the radical is about equally shared between the d_xz orbital of platinum and the p_z of nitrogen on the amino group, the latter acting as a non-innocent ligand.