The diazidation of alkenes through an iron-catalyzed, ligand-free system has been established, providing straightforward access to structurally vicinal diazides in good yields at room temperature with TMSN3 as the azido source. The ratio of tBuOOH to TMSN3 was essential for the reaction: one equivalent TMSN3 was needed to react with tBuOOH to form HN3 as a nucleophile in the reaction ultimately achieving the diazidation of alkenes.