We begin by examining intermediates in the first half of the reaction coordinate: the resting state species and the metal-oxo intermediate. At the resting state, we find that Ru catalysts generally have positive DEI-L(resting) values (ca. 13 kcal/mol on average) suggesting a strong preference for Ru catalysts to remain in the LS state regardless of the nature of the ligands present (Figure and Supporting Information Figures and). On the contrary, most Fe catalysts exhibit negative DEI-L(resting) values (ca. -8 kcal/mol on average) suggesting that the IS state is better stabilized (Figure and Supporting Information Figures and). After excluding outliers, for Fe we generally observe that ligand field strength influences the ground state spin with weak-field ligands (oxygen-and sulfur-coordinating e.g., pyran, water, and thiopyran) favoring the IS state and strong-field ligands (carbon-coordinating e.g., methyl isocyanide and carbonyl) favoring the LS state (Supporting Information Figure ). Consistent with this trend, many Fe catalysts exhibit near-zero DEI-L(resting) values (< |5 kcal/mol| for 38% of Fe catalysts), most of which comprise moderate-field nitrogen-coordinating ligands (e.g., acetonitrile and ammonia) (Figure and Supporting Information Figures and). This suggests facile interconversion between the LS and IS states at the resting state for Fe catalysts (Figure and Supporting Information Figures and). At the metal-oxo intermediate, the IS state is preferable over the LS state for both Fe and Ru catalysts by 28 kcal/mol for Fe and 22 kcal/mol for Ru on average (Figure and Supporting Information Figure ). The stabilization of the IS state metal-oxo relative to the LS metal-oxo in Fe catalysts is only slightly greater (i.e., by ca. 6 kcal/mol) than that in Ru catalysts. Thus, the high favorability of metal-oxo formation in Ru catalysts, particularly in the IS state, can be attributed to the destabilization of the IS resting state species coupled with the stabilization of the Ru IS metal-oxo species.