A mechanistic investigation of the ruthenium porphyrin catalysed aziridination of olefins by aryl azides

A mechanism for the aziridination of olefins by aryl azides (ArN3), promoted by ruthenium(ii) porphyrin complexes, is proposed on the basis of kinetic and theoretical studies. All the recorded data support the involvement of a mono-imido ruthenium complex as the active intermediate in the transfer of the nitrene moiety "ArN" to the olefin. The selectivity of the aziridination vs. the uncatalysed triazoline formation can be enhanced by fine-tuning the electronic features of the porphyrin ligand and the olefin/azide catalytic ratio. The DFT study highlights the importance of an accessible triplet ground state of the intermediate ruthenium mono-imido complex to allow the evolution of the aziridination process.