Tailoring C–H amination activity via modification of the triazole-derived carbene ligand

Two new C,O-bidentate chelating triazolylidene-phenolate ligands were synthesized that feature a diisopropylphenyl (dipp) and an adamantyl (Ad) substituent respectively on the triazole scaffold. Subsequent metalation afforded iron(ii) complexes [Fe(C^O)2] that are active catalysts for the intramolecular C–H amination of organic azides. When compared to the parent complex containing a triazolylidene with a mesityl substituent (Mes) the increased steric bulk led to slightly lower activity (TOFmax = 23 h−1vs. 30 h−1), however selectivity towards pyrrolidine formation increases from 92% up to >99%. Kinetic studies indicate that the mechanism is similar in all three complexes and includes a half-order dependence in [Fe(C^O)2], congruent with the involvement of a dimetallic catalyst resting state within this catalyst class. Structural analysis suggests that enhanced bulkiness disfavors N2 loss and nitrene formation, yet shields the nitrene from intermolecular processes and thus favors intramolecular nitrene insertion into the C–H bond. This model rationalizes the high selectivity and the lower reaction rate observed with dipp and with Ad substituents on the ligand.


L3
Figure      Figure S14: Evans method of 7.5 mM solution of complex 2 in C6D6 and toluene as internal standard at 299 K.

Figure S15:
Evans method of 7.5 mM solution of complex 2 in C6D6 with toluene as internal standard at 299 K, zoomed in on the CH3 signal of the toluene (internal standard)

Variable Time Normalisation Analysis
As an alternative method for elucidating reaction orders, variable time normalisation analysis (VTNA) S2 was performed on the kinetic data for complex 2 (Fig. S24-S28).The data was cut after the first data point with yield >75% to remove data points beyond the linear regime, in which decreasing substrate concentrations lead to a decrease in reaction rate.
reaction order in catalyst

Figure S16 :
Figure S16: Evans method of 16.4 mM solution of complex 3 in C6D6 and toluene as internal standard at 299 K.

Figure S17 :
Figure S17:Evans method of 16.4 mM solution of complex 3 in C6D6 with toluene as internal standard at 299 K, zoomed in on the CH3 signal of the toluene (internal standard). 0

Figure S19 :Figure S22 :
Figure S19: Zoom of the stacked plots (cf Fig. S18), highlighting the signals relevant to determine the yield of the reaction (* marks internal standard).

Figure S24 :
Figure S24: Selected area of the time conversion plot with product (M) and [Cat.]normalised against time, assuming 0.5 order.

Figure S27 :
Figure S27: Selected area of the time conversion plot with complex 2 with product (M) and [Sub] normalised against time assuming 1st order in substrate.