The rate of the reaction significantly decreases over time, combined with formation of H-N(SiMe3)2 (vide supra). We hypothesized a catalyst decomposition pathway, in which a coordinated HMDS group deprotonates the coordinated amine in the resting state 4, leading to decoordination of H-N(SiMe3)2 and pyrrolidinyl bonding to iron. According to DFT calculations this transformation is 9.7 kcal/mol uphill, only slightly higher than the substitution with another substrate molecule and therefore potentially competitive as a decomposition pathway (Schemes S1, S2). Attempts to isolate and characterize any degradation product have not been successful so far, though the decoordinated H-N(SiMe3)2 was unambiguously identified by 1 H NMR spectroscopy.