Orbitals-Driven Insights on the Reactivity of Boron Oxide with Dioxygen for Methane Oxidation on Singlet and Triplet Spin States

Abstract

Boron-based compounds such as frustrated Lewis pairs and borylenes that mimic transition-metal(TM)-like reactivity have attracted significant interest in recent years. This work examines the reactivity of boron oxide (B2O3) towards dioxygen for methane activation. Density functional theory in combination with orbital analysis were utilized to derive mechanistic pathways for methane-to-formaldehyde conversion over B2O3 in presence of closed-shell singlet and triplet O2. Multiple pathways were screened on the triplet spin state. Best route via the triplet spin state depicts the interaction of B2O3 with dioxygen (O1=O2) and CH4 at a barrier of 49.8 kcal mol−1, to produce an intermediate having a B−O1−O2H unit and a free CH3 radical, which later react together at a barrier of 57.6 kcal mol−1, to finally yield HCHO. In the singlet spin state, a free CH3 radical does not form instead an intermediate with a B−O1−O2−CH3 unit is found after crossing a barrier of 41.1 kcal mol−1, which further undergoes via a relatively lower barrier of 23.4 kcal mol−1 to yield HCHO. Thus, the singlet pathway is energetically preferred over the triplet one. Orbitals further capture that at singlet and triplet states, methane activation follows a hydride and a hydrogen-atom-transfer mechanism, respectively.