Carbenes – Formation (Thermal decomposition via hydrazone)

NOTE: Important charges and non-bonding electrons are shown throughout the animation except during the transition phase

^{Click the structures and reaction arrows in sequence to view the 3D models and animations respectively}

Carbenes can be made from diazoalkanes if the diazoalkane is just an intermediate in the reaction and not the starting material. Good starting materials for these reactions are tosylhydrazones (mesylhydrazone is used in the example above for simplicity), which produce transient diazo compounds by base-catalysed elimination of toluenesulfinate (methylsulfinate). The diazo compound is not normally isolated and decomposes to the carbene on heating.

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P. de Frémont, N. Marion and S. P. Nolan, Coord. Chem. Rev., 2009, 253, 862–892.