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 moieties were incorporated into an amorphous silicon nitride network via chemical modification of a polysilazane followed by pyrolysis in ammonia (NH) at 1000 °C. Emphasis is placed on the mechanisms of hydrogen (H) activation within Na-doped a-SiBN structure. This material design approach allows the homogeneous distribution of Na and B moieties surrounded by SiN units contributing to the transformation of the B moieties into 4-fold coordinated geometry upon encountering H, potentially serving as frustrated Lewis acid (FLA) sites. Exposure to H 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⋅⋅⋅H⋅⋅⋅H⋅⋅⋅:N(Na)=). Reversible H adsorption-desorption behavior with high activation energy for H desorption (124 kJ mol) suggested the H 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.