Onium Ions. 34: The Methoxydiazonium Ion: Preparation, ¹H, ¹³C, and ¹⁵N NMR and IR Structural Studies, Theoretical Calculations, and Reaction with Aromatics. Attempted Preparation and the Intermediacy of the Hydroxydiazonium Ion

Nitrous oxide is methylated with CH₃F → SbF₅ in SO₂F₂ or with CH₃O⁺SOCIF in SO₂ClF to give the stable methoxydiazonium ion CH₃ON₂⁺ (1), which was characterized by NMR (¹⁵N, ¹³C, ¹H) and FT IR spectroscopic studies. It is stable below -30 °C, above which it decomposes, regenerating N₂O. When reacted with aromatics, such as toluene, 1 gives only methylation products and no methoxy derivatives are formed. Spectroscopic and chemical data indicate that the mesomeric form CH₃O-N=N⁺ is a significant contributor to the overall structure of 1. Consideration of computed charge distribution (4-31 G with full geometry optimization and 4-31 G*) also supports this conclusion. Independent generation of 1 was also studied by solvolysis of methylazoxy triflate and diazotization of methoxylamine with NO⁺BF₄^-. Preparation of the elusive hydroxydiazonium ion HON₂⁺ (4) was attempted by protonation of nitrous oxide in superacids, but no long-lived ion could be observed. Diazotization of hydroxylamine with NO⁺BF₄^- gives nitrous oxide indicative of the intermediacy of 4.