EPR spectroscopy elucidates the electronic structure of [FeV(O)(TAML)] complexes

Multifrequency, multitechnique pulse EPR spectroscopy was employed to unravel the spin Hamiltonian parameters of O-17 in the [Fe-V 00000000 00000000 00000000 00000000 11111111 00000000 11111111 00000000 00000000 00000000 O] moiety with two different tetraamido macrocyclic ligands (TAMLs), [Fe-V(O)(TAML-1)](-) (1, H-4(TAML-1) = 3,4,8,9-tetrahydro-3,3,6,6,9-hexamethyl-1H-1,4,8,11-benzotetraazocyclotridecane-2,5,7,10-(6H,11H)-tetrone) and [Fe-V(O)(TAML-2)](-) (2, H-4(TAML-2) = H-4[(Me2CNCOCMe2NCO)(2)CMe2]), to investigate the electronic structure of Fe-V-oxo species. Although rigorous computational studies on high-valent iron-oxo species have been reported recently, experimental evidence to explicate the electronic structure of Fe-V-oxo species is sparse. In particular, a complete hyperfine tensor of O-17 can hardly be detected. Herein, we successfully probed the hyperfine tensor of O-17 of the Fe-V-oxo moiety using ENDOR spectroscopy. Hence, the EPR spectroscopic results reported here provide a conclusive experimental basis for elucidating the electronic structure of the Fe-V-oxo complex. Moreover, the reactivity of the two different complexes is very distinct, and our results may provide insight into how their electronic structure contributes to their reactivity.