Herein, we report the simple iron(II) complex Fe(HMDS)2 (HMDS = -N(SiMe3)2) as a new catalyst for the intramolecular C-H amination using organic azides. The complex is conveniently synthesized in one single step using commercially available starting materials only, making it particularly interesting for utilization, as no ligand synthesis is required. This complex is catalytically active without the use of Boc2O or any other additive. The simplicity of the catalytic system provides a unique opportunity to investigate the catalytic mechanism in order to understand and rationally improve the catalytic process. We have therefore used both experimental and computational methods to elucidate this iron-catalyzed C-H amination reaction and also to identify critical decomposition pathways.