Reaction of N,C,N organobismuth(I) 1 with 2.0 equiv. of alkoxide radical 2 in THF, led to the isolation of 4 in 95% yield as an orange solid, with concomitant formation of 3 (Fig. ). Single crystal XRD reveals 4 as monomeric structure and a fourfold coordinated Bi center (Fig. , and SI). The bond distances of C7-C8 (1.355(6) Å) and C7-N1 (1.379(5) Å) clearly indicate a double C=C bond and a single C-N bond, respectively. The angles between Bi with the distinct three anionic ligands (C1, N1, O) vary from 75.48( )° to 95.07(12)°, with a sum of angles up to 256.2°, pointing to a major contribution of the 6p Bi orbitals in the Bi-X bonds (X = C1, N1, O). Importantly, the Bi-O distance is considerably large (2.178(3) Å) and the angle of C47-O-Bi (136.2(3)°) is larger than the closely related BiCl(O-2,4,6-t Bu3C6H2)2. This implies a poor overlap between the lone pair in the sp 2 hybridized orbital of the O atom and the diffuse p orbital of the Bi center, indicating a weak Bi-O bond. EPR analysis of 4 at room temperature resulted in the clear detection of the signal for the known radical 2 (Fig 2C, top), which could be characterized with high resolution. Due to the relatively high temperature (>100 K) for the Bi-O bond homolytic cleavage, only 2 was detected, as the EPR signal for Bi(II) ( ) is assumed to be too broad to be detectable, because of a fast relaxation caused by large spin-orbit coupling. When 4 (13.08 mM) was subjected to successive cycles of temperature changes within the range of 243-293 K, the concentration of 2 remained constant at a given temperature, supporting the reversibility of the homolytic cleavage (see SI). The thermodynamic parameters of the equilibrium in PhMe (ΔH = +28.0 ± 0.3 kcal•mol -1 and ΔS = +58.7 ± 1.2 cal•mol -1 •K -1 ) are consistent with a dissociative mechanism (Fig. , bottom). 19f Importantly, the large contribution of the entropy compensates for the unfavorable enthalpy and results in ΔG = +10.5 ± 0.67 kcal•mol -1 at 298 K between the diamagnetic and the paramagnetic species. Computed singlet and triplet bond dissociation potential energy profiles of 4 at the PBE0/Def2-TZVP (ZORA) 24 level of theory are shown in Fig. . Upon elongation of the Bi-O bond, the triplet state crosses the singlet state at around ~3.1 Å, indicating that splitting into two radical species is energetically favorable by 37.2 kcal•mol -1 . Spin density analysis indicates a considerable spin polarization on the Bi center when the Bi-O bond is elongated to 2.3 Å (see SI). Orbital analysis of the singlet state for 4 shows that the HOMO is predominantly located on the alkoxide ligand and the LUMO on the N,C,N ligand and neighboring Bi. The Bi-O cleavage is essentially completed at ca 4.5 Å. Importantly, values of ΔH = +25.0 kcal•mol -1 and ΔS = +62.1 cal•mol -1 •K -1 for the Bi-O scission are in good agreement with the experimental thermodynamic data obtained by EPR. The considerable entropic contribution is attributed to high translational and rotational entropy components resulting in a rather small computed ΔG = +6.5 kcal•mol -1 (ΔGexp = +10.5 ± 0.67 kcal•mol -1 ). In comparison, the heterolytic bond cleavage of the Bi-O bond, is highly endergonic with ΔG = +43.7 kcal•mol -1 , supporting the energetic preference for the formation of radical 2 and 5. It is important to highlight that the weak Bi-O bond is a consequence of the relativistic effect of Bi, which combined with the stability of the Bi(II) by the pincer framework, the stability of radical 2 and the large entropic gain, results in a mild homolytic cleavage. The BDFE of X-H on a ligand is influenced by the oxidation potential at the metal center and a pKa value of X-H. Therefore, coordination to Bi(II) will increase the population at the anti-bonding orbitals, making RBi(II)-X-H a strong reductant. Hence, the Bi(II)/Bi(III) redox couple presents itself as a good candidate for coordination-induced bond weakening. When 4 was mixed with 1.0 equiv. of phenol (6, BDFEO-H = 79.8 kcal•mol -1 ), rapid formation of 7 was obtained in 92% isolated yield (Figure ). Interestingly, the reaction with 1.0 equiv. of H2O (BDFEO-H = 113.0 kcal•mol -1 ) led to rapid conversion to the corresponding hydroxy bismuth 9 (86%), which has recently been characterized in the context of N2O activation. Cyclohexanol afforded the corresponding bismuth alkoxide 11 in 98% yield. Similarly, when primary α-monoalkyl (12, BDFEN-H = 95.0 kcal•mol -1 ) and α-dialkyl amines (14, BDFEN-H = 90.7 kcal•mol -1 ) were mixed with 4, the corresponding bismuth amides were obtained in 78% ( ) and 95% ( ) yields, respec-tively. Similar yields were observed in apolar non-protic solvents, as shown for the 95% yield of 15 in PhMe. Finally, when 4 was mixed with 1.0 equiv. of dry ammonia, 17 was isolated in 76% yield. It is important to mention that Bi(III) complexes bound to a free NH2 group are rare, and therefore, 17 represents a unique example of such pnictogen-pnictogen bond. 7, 9, 11, 13, 15 and 17 are diamagnetic and no signal was detected by EPR in toluene at various temperatures. In all cases, solidstate structures reveal the bismuth center to be fourfold coordinated, and residing in a distorted plane formed by the imine, amido and phenyl ring (see SI). The -OH, -OPh, -NHCy, and -NH2 groups in 7, 9, 15 and 17 are perpendicular to this plane, and they localize on either side. The bond distances of C7-C8 and C7-N1 clearly indicate that the double C=C bonds and single C-N bonds are preserved. Generally, main group elements beyond group 14 have a reduced tendency to form stable complexes with NH3; 5b and therefore represent excellent candidates for NH3 activation and direct conversion to added-value chemicals beyond the stable MG-NH2 compounds. In order to explore their reactivity, 15 and 17 were mixed with various X-H sources (Scheme 1). Initially, the basicity of the Bi-NH2 and Bi-NHCy bond was confirmed by the immediate reaction at -80 °C with 6, leading to 7 and 14/16. Such basicity is also demonstrated by the reaction with H2O, leading quantitatively to 9. When 6 was replaced by 6-d, no deuteration of the ligand was observed, pointing to reactivity occurring solely at the Bi center. Additionally, when 15 and 17 were mixed with a chromium hydride with a weak Cr-H bond ( ) (BDFECr-H = 53.0 kcal•mol -1 ), reduction to 1 rapidly occurred at -80 °C, with no intermediates detected. Concomitantly, Cr-Cr dimer 19 and 14/16 resulted, which point to a radical reaction of 15 and 17 with a weak H • source. 19d, e 1 was also produced selectively when 15 and 17 were mixed with 2 equiv. of 2-naphthalenethiol (20) (BDFES-H = 75.9 kcal•mol -1 , see SI), which formed 2-naphthyl disulfide ( ) and 14/16. Interestingly, when 15 and 17 were mixed with an alternative hydride source with a much larger BDFEB-H = 108.6 kcal•mol -1 , 30 reduction to 1 occurred with the formation of 21/22. However, in this case, a Bi(III)-H (int-BiH) could be detected at -50°C, featuring the characteristic signal in the 1 H NMR at +26.0 ppm. 31 Int-BiH slowly converted into 1 at -50 °C, with the migration of the H atom to the methylene backbone. Incorporation of one deuterium in the methyl groups on the backbone using DBpin further confirmed such migration (see SI). Moreover, reduction of 15 and 17 to 1-d could also be accomplished using BD3. Collectively, these bismuth-amido complexes feature chemically non-innocent reactivity (element-ligand cooperation), 32 as well as reactivity towards radical species.