NMR Reveals That a Highly Reactive Nonheme Fe IV =O Complex Retains Its Six‐Coordinate Geometry and S =1 State in Solution

The [Fe IV (O)(Me 3 NTB)] 2+ (Me 3 NTB=tris[(1‐methyl‐benzimidazol‐2‐yl)methyl]amine) complex 1 has been shown by Mössbauer spectroscopy to have an S =1 ground state at 4 K, but is proposed to become an S =2 trigonal‐bipyramidal species at higher temperatures based on a DFT model to rationalize its very high C−H bond‐cleavage reactivity. In this work, 1 H NMR spectroscopy was used to determine that 1 does not have C 3 ‐symmetry in solution and is not an S =2 species. Our results show that 1 is unique among nonheme Fe IV =O complexes in retaining its S =1 spin state and high reactivity at 193 K, providing evidence that S =1 Fe IV =O complexes can be as reactive as their S =2 counterparts. This result emphasizes the need to identify factors besides the ground spin state of the Fe IV =O center to rationalize nonheme oxoiron(IV) reactivity.