Cyclisierung und fragmentierung aliphatischer azide an metall-metall-dreifachbindungen: Neuartige reaktionswege gegenüber ihrer thermischen zersetzung ln der gasphase [1,2]

The organoazides 4a-4c react with the dinuclear molybdenum and tungsten compounds of composition [(η⁵-C₅R₅)M(CO)₂]₂ (R = H, M = Mo: 1; CH₃, Mo: 2; CH₃, W: 3) at temperatures between 200 and 300 K to yield the novel organoimido derivatives 5-7 in quantitative yields. The dominating structural characteristics of the products are fused 3 5-membered metallacycles that originate from addition of the aliphatic azides to the metal-metal multiple bonds of the precursor organometallics 1-3 with consecutive ring closure via nucleophilic attack of the coordinated azide upon one of the metalcarbonyl ligands. Another azide molecule undergoes metal-induced nitrogen elimination, with the remaining organoimido fragment being coordinated as a linear terminal ligand through a molybdenum-nitrogen triple bond (172.6(9) pm). The thermal decomposition of allyl azides monitored in the gas phase by the changes in photo-electron spectroscopic ionization patterns, underlines the dominating effect of the multiply bonded metalmetal coordination sphere: N₂ is eliminated only at temperatures above 650 K. As exemplified for allyl azide, the red-hot tube pyrolysis is dominated by a 1,2-hydrogen shift accompanying the N₂ elimination and yields the corresponding imine, H₂CCHC(H)NH.