Single-point energy calculations on the optimized geometries of active-site intermediates and their isomers were performed using domain-localized pair natural orbital coupled cluster with singles, doubles and perturbative triples (i.e., DLPNO-CCSD(T) ) in ORCA v4.0.1.2. Two-point extrapolation to the complete basis set (CBS) limit was carried out using Dunning-style correlation-consistent double-z and triple-z (i.e., aug-cc-pVDZ and aug-cc-pVTZ) basis sets. All reported DLPNO-CCSD(T)/CBS energies were obtained using tight PNO thresholds, consistent with prior work (Supporting Information Table ). Mayer bond order analysis to quantify the strength of binding of aKG, monodentate, and bidentate succinate ligands to iron was performed using Multiwfn 100 .