Novel Lewis Acid‐Base Interactions in Polymer‐Derived Sodium‐Doped Amorphous Si−B−N Ceramic: Towards Main‐Group‐Mediated Hydrogen Activation

Interest is growing in transition metal-free compounds for small molecule activation and catalysis. We discuss the opportunities arising from synthesizing sodium-doped amorphous silicon-boron-nitride (Na-doped a-SiBN). Na⁺ cations and 3-fold coordinated B^III moieties were incorporated into an amorphous silicon nitride network via chemical modification of a polysilazane followed by pyrolysis in ammonia (NH₃) at 1000 °C. Emphasis is placed on the mechanisms of hydrogen (H₂) activation within Na-doped a-SiBN structure. This material design approach allows the homogeneous distribution of Na⁺ and B^III moieties surrounded by SiN₄ units contributing to the transformation of the B^III moieties into 4-fold coordinated geometry upon encountering H₂, potentially serving as frustrated Lewis acid (FLA) sites. Exposure to H₂ induced formation of frustrated Lewis base (FLB) N^-= sites with Na⁺ as a charge-compensating cation, resulting in the in situ formation of a frustrated Lewis pair (FLP) motif (≡B^FLA⋅⋅⋅H^δ-⋅⋅⋅H^δ+⋅⋅⋅:N^-(Na⁺)=). Reversible H₂ adsorption-desorption behavior with high activation energy for H₂ desorption (124 kJ mol^-1) suggested the H₂ chemisorption on Na-doped a-SiBN. These findings highlight a future landscape full of possibilities within our reach, where we anticipate main-group-mediated small molecule activation will have an important impact on the design of more efficient catalytic processes and the discovery of new catalytic transformations.