Platinum(IV)-Mediated Nitrile–Amidoxime Coupling Reactions: Insights into the Mechanism for the Generation of 1,2,4-Oxadiazoles

Authors

  • Dmitrii S. Bolotin,

    1. Department of Chemistry, St. Petersburg State University, Universitetsky Pr. 26, 198504 Stary Petergof (Russian Federation)
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  • Dr. Nadezhda A. Bokach,

    Corresponding author
    1. Department of Chemistry, St. Petersburg State University, Universitetsky Pr. 26, 198504 Stary Petergof (Russian Federation)
    • Department of Chemistry, St. Petersburg State University, Universitetsky Pr. 26, 198504 Stary Petergof (Russian Federation)
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  • Prof. Dr. Matti Haukka,

    1. Department of Chemistry, University of Eastern Finland, P.O. Box 111, 80101 Joensuu (Finland)
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  • Prof. Dr. Vadim Yu. Kukushkin

    Corresponding author
    1. Department of Chemistry, St. Petersburg State University, Universitetsky Pr. 26, 198504 Stary Petergof (Russian Federation)
    2. Institute of Macromolecular Compounds of Russian Academy of Sciences, V.O. Bolshoii Pr. 31, 199004 St. Petersburg (Russian Federation)
    • Department of Chemistry, St. Petersburg State University, Universitetsky Pr. 26, 198504 Stary Petergof (Russian Federation)
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Abstract

The nucleophilic addition of amidoximes R′C(NH2)[DOUBLE BOND]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){HN[DOUBLE BOND]C(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{HN[DOUBLE BOND]C(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 717 bear nitrogen-bound O-iminoacylated amidoxime groups. The addition of one equivalent of the corresponding amidoxime to each of 710 leads to 12, 13, 16, and 17, respectively. Complex [PtCl4(NCNMe2){HN[DOUBLE BOND]C(NMe2)ONC(Ph)NH2}] (10), when dissolved in MeNO2, gave mer-[PtCl3{HN[DOUBLE BOND]C(NMe2)ONC(Ph)NHC(NMe2)[DOUBLE BOND]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)[DOUBLE BOND]NOCR([DOUBLE BOND]NH) (1925) were liberated from the corresponding complexes 1117 by treatment with excess NaCN and these metal-free species were characterized by 1H and 13C{1H} NMR spectroscopy. The conversion of 1925 into the 3,5-substituted 1,2,4-oxadiazole compounds OaN[DOUBLE BOND]C(R′)N[DOUBLE BOND]Cb(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′.

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