Catalytic Trimerization of Bis-silylated Diazomethane

(Me3Si)2CNN isomerizes upon addition of traces of [Me3Si]+ ions to give (Me3Si)2NNC, which then undergoes an unusual trimerization reaction to give exclusively 4-diazenyl-3-hydrazinylpyrazole. As catalyst the isonitrilium ion, [(Me3Si)2NNC­(SiMe3)]+, was identified and fully characterized. Experiments and computations indicate a three-step reaction including isomerization of diazomethane, a C–C or N–C coupling, and a formal cycloaddition reaction. The kinetics and thermodynamics are discussed on the basis of DFT calculations.