As shown in 15 and 17, element-ligand cooperation through the methylene unit is feasible during radical and hydride processes involving H. To evaluate whether similar reactivity is involved in the activation of N-H bonds, we carried out the activation of cyclohexylamine deuterated (14-d2, 90% D) using 4. As shown in Fig. , both methyl and methylene moieties resulted in an enrichment of deuterium (46% D) after 25 h at 25 °C. However, when the reaction was carried out at -40 °C and monitored by NMR, no obvious incorporation of D in the backbone was detected after complete conversion to 15. Only upon warming the reaction mixture to 25 °C, a clear exchange of H for D in the CH3 and CH2 could be detected. These experiments confirm: 1) the absence of H/D exchange on the ligand by 14-d2 during X-H activation; 2) and that ligand non-innocent reactivity with 3-d is triggered at higher temperatures from amido complex 15. Fig. contains the computed free energy profile for the N-H bond activation step (green-dotted line). Based on the combined experimental evidence and the computational analysis, it is proposed that upon reversible homolysis of the Bi-O bond in 4, NH3 coordinates to the Bi(II) radical through the semi-occupied 6pz orbital to generate II. HAT from II to OAr radical (2) proceeds with a very low energy barrier (TS II- III , ΔG = +1.3 kcal•mol -1 ), resulting in III (ΔG = -4.3 kcal•mol - 1 ). The low energy barrier associated with TS II-III is the result of the remarkably low BDFEN-H = 47.0 kcal•mol -1 calculated for the N-H bond once coordinated to the Bi(II) center. Such coordination-induced bond weakening effect of the Bi(II) was also observed for H2O, CyNH2 and CyOH, with BDFEX-H = 52. . Without hydrogen bonding, 17 is significantly lower in energy (-14.1 kcal mol -1 ) (see SI), permitting its isolation. The hydrogen exchange observed experimentally at the vinylic C-H bonds after the N-H activation was also computationally evaluated (Fig. , blue-dotted line). The computed barrier for the radical hydrogen exchange between III and IV raises to ΔG ‡ = +10.5 kcal•mol -1 , due to the energetic mismatch between IV (BDFEC-H = +51.1 kcal•mol -1 ) and 2 (BDFEO-H = +76.8 kcal•mol -1 ) 3 (Fig. ). Upon single electron transfer (SET) between 1 and 2, the Me C-H bond in the backbone in V also undergoes bondweakening (Fig. , right, BDFEC-H = +60.4 kcal•mol -1 ), resulting in feasible H-abstraction by 2 en route to starting complex 4 (Fig. ). The small energy difference between 4 and III indicates that NH3 activation might be reversible, 5b which was confirmed by the incorporation of deuterium in the CH2 groups of 4 in the presence of ND3 (see SI). Finally, alternative pathways such as direct HAT from 2 to NH3 without the involvement of Bi, or reaction between 4 and NH3 through heterolytic cleavage or polar pathways were discarded due to the highly endergonic profiles obtained (>40 kcal•mol -1 , see SI).