Surface-Enhanced and Electric Field-Modulated Reactivity of Fe(IV)=O Complexes: Unveiling the Synergy of Lewis Acid Additives, Au(111), and Graphene Surfaces in Biomimetic C–H Activation

Abstract

Achieving high reactivity and maintaining selectivity simultaneously is one of the holy grails of catalytic transformations; while metalloenzymes perform this task effortlessly, synthetic models to mimic their reactivity often struggle to achieve either of the goals set. High-valent FeIV=O species are highly reactive oxidants, but their elevated activity often limits catalytic turnover due to rapid catalyst degradation and over-oxidation of substrates. To overcome these shortcomings, here we have explored electrostatic and surface effects in tuning the reactivity of [(F8)FeIV(O)] (1) and [(F8)FeIV(O)](LutH)+ (2) using density functional theory (DFT) and periodic DFT calculations. To begin with, the effect of Lewis acid (LutH+ 2,6–lutidinium triflate), which is found to induce a local electric field and diminishes the kinetic barrier by ~15 kJ mol⁻¹ . As the addition of adduct and their direct role in the oxidation process are difficult to control, we explored the possibility of employing oriented external electric fields (OEEFs) to gain control over the reactivity and the oxidation process. Our results demonstrate that applying an OEEF along the Fe-O direction reduces the kinetic barrier further by ~29 kJ mol⁻¹, while along the the O-Fe direction, proton transfer was preferred, offering an intriguing way to channelise selectivity. Surface interactions provide additional control: Au(111) lowers the barrier by ~58 kJ mol⁻¹ under OEEFs, whereas graphene inhibits reactivity, requiring an OEEF along +Z-direction to reduce the barrier by ~49 kJ mol⁻¹. By integrating chemical modifications and external control, this study offers a general framework for designing next-generation oxidation catalysts across diverse catalytic systems.