Strong Lewis Base Ga₄B₂O₉: Ga-O Connectivity Enhanced Basicity and Its Applications in the Strecker Reaction and...

Heterogeneous solid base catalysis is valuable and promising in chemical industry, however it is insufficiently developed compared to solid acid catalysis due to the lack of satisfied solid base catalysts. To gain the strong basicity, the previous strategy was to basify oxides with alkaline metals to create surficial vacancies or defects, which suffers from the instability under catalytic conditions. Monocomponent basic oxides like MgO are literally stable but deficient in electron-withdrawing ability. Here we prove that a special connectivity of atoms could enhance the Lewis basicity of oxygen in monocomponent solids exemplified by Ga₄B₂O₉. The structure-induced basicity is from the μ₃-O linked exclusively to five-coordinated Ga³⁺. Ga₄B₂O₉ behaved as a durable catalyst with a high yield of 81% in the base-catalyzed synthesis of α-aminonitriles by Strecker reaction. In addition, several monocomponent solid bases were evaluated in the Strecker reaction, and Ga₄B₂O₉ has the largest amount of strong base centers (23.1 μmol/g) and the highest catalytic efficiency. Ga₄B₂O₉ is also applicable in high-temperature solid-gas catalysis, for example, Ga₄B₂O₉ catalyzed efficiently the dehydrogenation of n-propanol, resulting in a high selectivity to propanal (79%). In contrast, the comparison gallium borate, Ga-PKU-1, which is a Brönsted acid, preferred to catalyze the dehydration process to obtain propylene with a selectivity of 94%.