AbstractThe nucleophilic addition of amidoximes R′C(NH2)NOH (4: R′=Me, 5: CH2Ph, 6: Ph) to coordinated nitriles in the platinum(IV) complexes trans‐[PtCl4(RCN)2] (1: R=Et, 2: Ph, 3: NMe2) proceeds in a 1:1 molar ratio and leads to the monoaddition products [PtCl4(RCN){HNC(R)ONC(R′)NH2}] (7: R/R′: Et/CH2Ph, 8: Et/Ph, 9: NMe2/CH2Ph, 10: NMe2/Ph). Meanwhile, if the nucleophilic addition proceeds in a 2:1 molar ratio the reaction gives the bisaddition species [PtCl4{HNC(R)ONC(R′)NH2}2] (11: R/R′=Et/Me, 12: Et/CH2Ph, 13: Et/Ph, 14: Ph/Ph, 15: NMe2/Me, 16: NMe2/CH2Ph, 17: NMe2/Ph). All complexes 7–17 bear nitrogen‐bound O‐iminoacylated amidoxime groups. The addition of one equivalent of the corresponding amidoxime to each of 7–10 leads to 12, 13, 16, and 17, respectively. Complex [PtCl4(NCNMe2){HNC(NMe2)ONC(Ph)NH2}] (10), when dissolved in MeNO2, gave mer‐[PtCl3{HNC(NMe2)ONC(Ph)NHC(NMe2)NH}] (18) with the newly formed tridentate ligand derived from an unexpected coupling between two Me2NCN ligands and the N and the O centers of the amidoxime. The O‐imidoylamidoxime compounds R′C(NH2)NOCR(NH) (19–25) were liberated from the corresponding complexes 11–17 by treatment with excess NaCN and these metal‐free species were characterized by 1H and 13C{1H} NMR spectroscopy. The conversion of 19–25 into the 3,5‐substituted 1,2,4‐oxadiazole compounds OaNC(R′)NCb(R)(a–b) (26: R/R′=Me/Et, 27: PhCH2/Et, 28: Ph/Et, 29: Ph/Ph, 30: Me/NMe2, 31: PhCH2/NMe2, 32: Ph/NMe2) occurs at room temperature and the cyclization is promoted by strong acceptor substituents R′.