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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
Author(s) -
Nakabayashi Yasuo,
Erxleben Andrea,
Létinois Ulla,
Pratviel Geneviève,
Meunier Bernard,
Holland Lars,
Lippert Bernhard
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200601271
Subject(s) - chemistry , methylamine , isomerization , medicinal chemistry , stereochemistry , ligand (biochemistry) , moiety , photochemistry , crystallography , organic chemistry , catalysis , biochemistry , receptor
Three 2,2′‐bipyridine (2,2′‐bpy) complexes of Pt IV have been synthesized, characterized by X‐ray crystallography, and their solution behavior in D 2 O studied by 1 H NMR spectroscopic analysis: mer ‐[PtCl 3 (2,2′‐bpy)(MeNH 2 )]Cl⋅H 2 O ( 4 ), trans ‐[PtCl 2 (2,2′‐bpy)(MeNH 2 ) 2 ]Cl 2 ( 5 ), and trans ‐[Pt (2,2′‐bpy)(MeNH 2 ) 2 (OH) 2 ]Cl 2 ( 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 MeNH 2 , 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 195 Pt with selected 1 H 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.