Fe catalysts predominantly underwent spin-allowed C-H hydroxylation pathways on the IS state surface, although changes in the ligand chemistry for Fe catalysts could more readily destabilize spin-allowed pathways in favor of spin-forbidden pathways. These proposed spin-reactivity trends were corroborated in the full free energy landscapes that we computed for six representative Fe and Ru catalysts. The spin-allowed pathways in Fe catalysts with comparable energetic spans to their Ru analogues suggested that Fe catalysts provide a better opportunity for tuning C-H activation reactivity over Ru catalysts. Kinetic information obtained from the full free energy landscapes was used to validate the existence of a strong BEP relationship for the metal-oxo formation and slightly weaker BEP for the HAT step. The presence of BEP relations suggested that knowledge of reaction energetics is sufficient in finding optimal C-H activation catalysts. Fe catalysts that outperform Ru catalysts should minimize metal-oxo formation energies without sacrificing relatively favorable HAT energies for Fe catalysts. Our high-throughput study, thus, reveals that Fe catalysts demonstrate promise for polyolefin functionalization. The discovery of realizable Fe catalysts, however, may also require optimization of reaction conditions in addition to reaction energetics to harness their complete potential for polyolefin functionalization. complexes for free energy landscape calculations; free energy landscape of complex A referenced to oxidant-bound species; free energy landscape of complex B referenced to oxidant-bound species; free energy landscape of complex C referenced to oxidant-bound species; free energy landscape of complex E referenced to oxidantbound species; free energy landscapes of complexes D and F referenced to resting state; free energy landscape of complex A referenced to resting state; free energy landscape of complex B referenced to resting state; free energy landscape of complex C referenced to resting state; free energy landscape of complex E referenced to resting state; details on transition state searching; MECPs for complexes D and F with Ru; energetic span analysis of complexes D and F; outliers omitted from metal-oxo formation and HAT BEP plots; free energy changes and barriers for b-HAT in complexes A-F with Fe (PDF)