Spontaneous reduction of mixed 2,2′-bipyridine/methylamine/chloro complexes of Pt^IV in water in the presence of light is accompanied by complex isomerization, loss of methylamine, and formation of a strong oxidant, presumably HOCl

Three 2,2′-bipyridine (2,2′-hpy) complexes of Pt^IV have been synthesized, characterized by X-ray crystallography, and their solution behavior in D₂O studied by ¹H NMR spectroscopic analysis: mer-[PtCl₃(2,2′-bpy)-(MeNH₂)] Cl·H₂O (4), trans-[PtCl₂(2,2′-bpy)(MeNH ₂)₂]Cl₂ (5), and trans-[Pt (2,2′-bpy) (MeNH₂)₂(OH)₂]Cl₂ (6; MeNH ₂ = methylamine). Complexes 4 and 5 undergo hydrolysis of the Cl ions, both in the dark and daylight, as evident from a drop in the pH value. Two solvolysis products were detected in the case of 4, which is indicative of species with equatorial and axial OH^- groups. The hydrolysis reaction of 5 implies that an axial Cl group is replaced by an OH^- moiety; in contrast. 6 remains virtually unaffected. Ordinary daylight, in particular irradiation with a 50-W halogen lamp, initially causes ligand-isomerization processes, which are followed by the reduction of 4 and 5 to Pt^II species. This reduction of 4 and 5 is accompanied by the formation of hypochlorous acid, as demonstrated qualitatively in the decoloration test of indigo, and loss of MeNH₂, which is particularly pronounced in the case of 5. The formation of Pt^II compounds is established on the basis of the J coupling constants of ¹⁹⁵Pt with selected ¹H NMR resonances. The results obtained herein are possibly also relevant to the chemistry of Cl-containing Pt^IV antitumor agents and their reactions with DNA.