X‐ray Structure of the Isodiazomethane Complex Cr(CO) 5 C≡N‐NH 2 and [3+2]‐Cycloadditions to the Metallo‐Nitrile‐Imine [Cr(CO) 5 C≡N‐NH] – [1]

The structure of [Cr(CO) 5 CNNH 2 ] ( 1a ) containing Eugen Müller’s “isodiazomethane” as a ligand has been determined by X‐ray diffraction. In its deprotonated form 1a acts as a 1,3‐dipole of the (metallo) nitrile imine type, i.e., undergoes [3+2]‐cycloaddition reactions with acetylenes (MeO 2 CC≡CCO 2 Me), trifluoroacetonitrile,carbon disulfide and isocyanate (PhNCO). The new 16‐electron ligand [C≡N–NH] – is isoelectronic with isocyanomethanide [C≡N–CH 2 ] – and the fulminate anion [C≡N–O] – . Further relations and derivations within these classes of compounds are discussed.