The isomerization reaction of the head-to-head α-pyridonato-bridged ethylenediamineplatinum(II) binuclear complex (HH-[Pt2(en)2(α-pyridonato)2]2+, HH dimer) to the head-to-tail isomer and the decomposition reactions of the HH and HT dimers to monomers in aqueous solution were studied in detail at various pH values using 1H NMR. It was found that the isomerization reaction proceeded preferentially at pH ~ 7. In contrast, the isomerization reaction and decomposition reactions preferentially proceeded at lower pH. An initial Pt–O (α-pyridonate) bond-breaking mechanism was proposed for both the isomerization and the acid-decomposition reactions based on the acid dependency of the detected reaction intermediate. The protonation of the dissociated oxygen atom of the monodentated α-pyridonate in the intermediate plays a vital role in determining isomerization or decomposition.
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