To gain more insights into the mechanism, kinetic experiments were performed. Firstly, the initial concentration of substrate 1a was varied under otherwise identical conditions. Time-dependent monitoring of the yields does not show any observable initiation period (Fig. ). The pertinent time-conversion profiles clearly indicate a first order rate dependance on the initial substrate concentration for the first 10 minutes. Moreover, a gradual decrease of the reaction rate at longer reaction times was noted. The higher the initial substrate concentration, the faster this rate decrease occurs. This behavior is attributed to product inhibition, as more amine product will be formed at higher initial substrate concentrations. In addition, the gradual loss of activity might also originate from catalyst decomposition. Such a process is supported by the observation of the protonated ligand, H-N(SiMe3)2, by a singlet at 0.08 ppm in 1 H NMR spectroscopy. The first order dependence in substrate concentration is in line with the previously reported cobalt porphyrin system by de Bruin et al. and our iron mesoionic carbene catalyst, which show substrate coordination or loss of dinitrogen to be rate limiting. Contrastingly, all other reported systems display a zero-order dependance on substrate concentration, suggesting hydrogen atom abstraction by the nitrene as the rate limiting step. The turnover frequency (TOF) of Fe(HMDS)2 at the highest substrate concentration reached 110 h -1 , which is even faster than the previously reported mesoinoic carbene iron complex as the most active system so far (cf. TOFmax = 70 h -1 under identical conditions). The reaction order in catalyst was investigated by varying the catalyst concentration under otherwise identical conditions. Analysis of the time-dependent yields of 1b showed no observable dependance of the catalyst concentration on the initial rate of the reaction (Fig. ), suggestion an apparent zero-order dependance in catalyst. While these data might insinuate that the catalyst is not involved in the turnover-limiting step, there are other scenarios that can lead to such behavior. In particular, reversible product inhibition of the catalyst at the beginning of the reaction may result in a negative dependance and a net cancelling of the catalyst concentration in the rate law. Such a scenario is supported by the observation that at advanced stages of the reaction and increasing product concentration, the order in catalyst is not zero anymore. competition experiments were performed, by reacting a 1:1 mixture of 1a and 1a-d2 (Fig. ). The observation of equal ratios of 1b and 1b-d2 throughout the reaction indicates an absence of a KIE, commensurate with C-H/D bond breaking is not involved in the rate-determining step. This conclusion is in line with the kinetic data. Notably, the total rate of the intermolecular KIE competition experiment is significantly lower than the rate when using exclusively 1a (Fig. ).