Catalytic Tetrazole Synthesis via [3+2] Cycloaddition of NaN 3 to Organonitriles Promoted by Co(II)-complex: Isolation and Characterization of a Co(II)-diazido Intermediate.

The [3+2] cycloaddition of sodium azide to nitriles to give 5-substituted 1H-tetrazoles is efficiently catalyzed by a Cobalt(II) complex ( 1 ) with a tetradentate ligand N , N -bis(pyridin-2-ylmethyl)quinolin-8-amine. Detailed mechanistic investigation shows the intermediacy of the cobalt(II) diazido complex ( 2 ), which has been isolated and structurally characterized. Complex 2 also shows good catalytic activity for the synthesis of 5-substituted 1H-tetrazoles. These are the first examples of cobalt complexes used for the [3+2] cycloaddition reaction for the synthesis of 1H-tetrazoles under homogeneous conditions.