Spontaneous Reduction of Mixed 2,2′‐Bipyridine/Methylamine/Chloro Complexes of PtIV in Water in the Presence of Light Is Accompanied by Complex Isomerization, Loss of Methylamine, and Formation of a Strong Oxidant, Presumably HOCl

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Abstract
Three 2,2′‐bipyridine (2,2′‐bpy) complexes of PtIV 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)(MeNH2)2]Cl2 (5), and trans‐[Pt (2,2′‐bpy)(MeNH2)2(OH)2]Cl2 (6; MeNH2=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 PtII 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 PtII 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 PtIV antitumor agents and their reactions with DNA.