Upon addition of half an equivalent of model substrate 1a to Fe(HMDS)2 in C6D6 at ambient temperature, an immediate color change was observed from pale green to pale yellow, attributed to coordination of the azide substrate and formation of complex 2 (Fig. ). In 1 H NMR spectroscopy, the signals for 1a experience paramagnetic perturbation and the singlet for Fe(HMDS)2 shifts from 63 ppm upfield to 55 ppm (Fig. ). When using one or two equivalents of 1a, comparable yet slightly shifted paramagnetic signals evolved in the 1 H NMR spectrum, though no diamagnetic signals for the substrate were observed (Fig. ). The most significant change pertains to the SiMe3 signal of iron-bound HMDS, which shifted further upfield to 43 and 32 ppm, respectively. Notably, when using 10 eq substrate, broadening of the substate signals are observed in the diamagnetic region, indicating interaction with the paramagnetic iron center (Fig. ). We attribute these observation to an equilibrium between Fe(HMDS)2-coordinated azide 2 and non-coordinated substrate 1a, which is fast on the NMR time scale and gradually shifts to the product side as more substrate equivalents are used (Fig. ). This assignment was further supported by IR spectroscopy.