Preparationof <i>trans</i>,<i>trans</i>-[Pt(py)₂(N₃)₂(OH)₂]via Photoinduced Reactivity of [Pt(NO₃)₆]^2– Anion

The photoinduced reaction of [Pt­(NO₃)₆]^2– with pyridine or its derivatives (L) was found to result in the formation of [PtL₄]­(NO₃)₂ salts in high yield. This transformation was successfully probed for methyl- and carboxyethyl-substituted pyridines, and the corresponding [PtL₄]­(NO₃)₂ salts were isolated and fully characterized using single-crystal X-ray diffraction (SCXRD). Anation of the [Pt­(py)₄]²⁺ cationic complex with N₃^– was studied by ¹H NMR spectroscopy in aqueous and water/dimethyl sulfoxide solutions of [Pt­(py)₄]­(NO₃)₂. A mixture of cis- and trans-[Pt­(py)₂(N₃)₂] complexes was determined as the final product of this interaction with the domination of the trans-isomer (cis to trans ratio is about 1:8) due to its preferable formation from the transient [Pt­(py)₃(N₃)]⁺ cationic complex. The difference observed for the experimentally determined activation parameters of trans- and cis-paths of anation was supported by DFT calculations. Finally, the new three-stage Ag-free synthetic procedure for the preparation of the trans,trans-[Pt­(py)₂(N₃)₂(OH)₂] prodrug (potential agent for the photodynamic anticancer therapy) was found using (i) light-induced formation of [Pt­(py)₄]­(NO₃)₂ from (Bu₄N)₂[Pt­(NO₃)₆] followed by (ii) anation of [Pt­(py)₄]²⁺ with azide and (iii) accomplished by oxidation of the resulting mixture of cis- and trans-[Pt­(py)₂(N₃)₂] with H₂O₂. Efficient separation of cis,trans-[Pt­(py)₂(OH)₂(N₃)₂] and trans,trans-[Pt­(py)₂(N₃)₂(OH)₂] produced at the last stage was achieved by simple recrystallization from water.