Transient Overcoordination Unlocks C-H Bond Activation in Boron-Based Oxidative Dehydrogenation

The identification of the true active site in boron-catalyzed oxidative dehydrogenation of propane (ODHP) remains deeply contested. Prevailing models attempt to describe a molten or quasi-molten boron oxide phase using static, high-energy BO_x species, yet they do not resolve a central paradox that explains how a formally nonreducible B(III) center can mediate efficient C-H activation while sustaining exceptional propylene selectivity. Here, by combining exhaustive thermodynamic screening of 9700 BO_x/Ni(111) configurations with enhanced sampling ab initio molecular dynamics (AIMD), we show that activity is mediated not by any pre-existing structure but by transiently accessible overcoordinated [BO₄] generated through continuous [BO₃] ⇌ [BO₄] interconversions. This dynamic sp²-to-sp³ rehybridization provides crucial coordination-charge compensation, acting as an electronic buffer that allows the strictly +3 boron center to activate C-H bonds without localized reduction. Furthermore, mapping the catalytic cycle provides a mechanistic framework for the selectivity paradox. The structurally adaptive boron centers thermodynamically favor the adsorption of gas-phase oxygenated radicals, suppressing chain propagation and thereby preventing deep oxidation to CO_x. Finally, AIMD trajectories and free-energy barriers across N-doped, C-doped, metal-free, and h-BN-derived BO_x systems show that this coordination-fluxionality mechanism is general across the BO_x systems examined here, shifting catalyst design from identifying a single "active site" to engineering the thermodynamic accessibility and lifetime of transient coordination states.