A significant activation of the C≡N group in organonitriles upon their coordination to a platinum(IV) center has been found in the reaction of [PtCl₄(RCN)₂] (R = Me, Et, CH₂Ph) with the nitrile oxides 2,4,6-R′3C6H2CNO (R′ = Me, OMe) to give the (1,2,4-oxadiazole)platinum(IV) complexes [PtCl₄{N=C(R)ON=CC₆H₂R′₃}] (R = Me, R′ = Me (1); R = Et, R′ = Me (2); R = Et, R′ = OMe (3); R = CH₂Ph, R′ = Me (4)); the [2 + 3] cycloaddition was performed under mild conditions (unless poor solubility of [PtCl₄(RCN)₂] precludes the reaction) starting even from complexed acetonitrile and propionitrile, which exhibit low reactivity in the free state. The reaction between complexes 2-4 and 1 equiv of Ph₃P=CHCO₂Me in CH₂Cl₂ leads to the appropriate platinum(II) complexes [PtCl₂{N=C(R)-ON=CC₆H₂R′₃}] (5-7); the reduction failed only in the case of 1 insofar as this complex is insoluble in the most common organic solvents. All the platinum compounds were characterized by elemental analyses, FAB mass spectrometry, and IR and ¹H, ¹³C{¹H}, and ¹⁹⁵Pt NMR spectroscopies, and three of them also by X-ray crystallography. The oxadiazoles formed in the course of the metal-mediated reaction were liberated almost quantitatively from their Pt(IV) complexes by reaction of the latter (complexes 2-4) with an excess of pyridine in chloroform, giving free 1,2,4-oxadiazoles and trans-[PtCl₄(pyridine)₂]; the sequence of the Pt(IV)-mediated [2 + 3] cycloaddition and the liberation opens up an alternative route for the preparation of this important class of heterocycles.