When substrate 1a was fluorinated by SF ® in the absence of H-TEDA(BF 4 ) 2 in an in situ irradiation experiment within in an NMR tube in the NMR spectrometer, kinetic studies revealed a trace amount of nascent H-TEDA(BF 4 ) 2 was formed after 5 h. As the concentration of nascent H-TEDA(BF 4 ) 2 increased, a downfield shift of its N-CH 2 -Cl 1 H NMR peak was observed (Scheme 4, A). This occurrence can be explained by aggregation of H-TEDA(BF 4 ) 2 as its concentration increases. The average volume of H-TEDA(BF 4 ) 2 in solution at different concentrations is shown vide infra (Table , entries 1-5), that increases with increasing its concentration, in line with aggregation. The induction period ended as soon as a certain aggregate/chemical shift of H-TEDA(BF 4 ) 2 was reached (~5.275 ppm), and only then significant formation of the product started. This is an indication of H-TEDA(BF 4 ) 2 being involved in a reactive species that drives the reaction towards the fluorinated product. When performing the same experiment with addition of 1.0 eq. exogeneous H-TEDA(BF 4 ) 2 , the chemical shift observed was already ~5.275 ppm, and significant formation of the product started instantly (Scheme 4, B). To evaluate the generality and synthetic efficiency benefit of additive H-TEDA(BF 4 ) 2 on fluorination reactions using SF ® we examined the impact of its presence on a number of reported photochemical/photocatalytic and thermal C(sp 3 )-H fluorinations. We specifically selected substrates which afforded poor/moderate product yields (<20% or <55%) under the standard (unpromoted) reaction conditions. For all subsequent case studies, we evaluated the standard literature conditions without vs with 2.0 equiv. of H-TEDA(BF 4 ) 2 additive present at the start of the reaction for the fixed reaction time period (see the SI file for results with different loadings).