Studies on Pt–S bonds. Competition of chelating methylsulfanyl- or methylsulfinyl-acetate, -benzoate and -phenolate for Pt^II(H₂NCH₂CH₂NH₂)

Abstract

The reactions of [Pt(en)(L-S,O)]⁺ (en = ethane-1,2-diamine) with L′, where both L and L′ are the anionic chelating ligands methylsulfanylacetate, 2-(methylsulfanyl)benzoate, 2-(methylsulfanyl)phenolate and their methylsulfinyl analogues, have been studied by ¹H NMR spectroscopy in D₂O solutions at 40 °C. Thioethers bind more strongly than sulfoxides to Pt(en) and within each series the order of affinity towards Pt is ^-OC₆H₄SMe > ^-O₂CCH₂SMe > ^-O₂CC₆H₄SMe and ^-OC₆H₄S(O)Me > ^-O₂CCH₂S(O)Me > ^-O₂CC₆H₄ S(O)Me. The first step of the reactions is substitution of the Pt–O bond of L by the Pt–S bond of L′ to give [Pt(en)(L-S)(L′-S)], with both ligands monodentate, S-co-ordinated, followed by closure of the chelate ring of L′, to give [Pt(en)(L′-S,O)]⁺, which occurs by displacement of the Pt–S bond of L by the oxygen atom of L′. The disubstituted species [Pt(en)(O₂CCH₂SMe)₂], [Pt(en)(O₂CC₆H₄SMe)₂] and [Pt(en)(O₂CCH₂SMe){OC₆H₄ S(O)Me}] are stable at 40 °C and present at the end of the reactions in equilibrium with the reactants and the products. Only the former, however, could be isolated as a pure compound.

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