Formation of Crystalline Sodium Hydride Nanoparticles Encapsulated Within an Amorphous Framework
A major research theme to emerge in the science and technology of materials is the incorporation of nanostructure into the functionality of properties. Such nanostructured materials can offer distinct advantages over bulk materials, partly because the physical properties of the material itself can vary in a tunable, size-dependent fashion. Of course, in addition, nanoparticles offer a greatly increased surface area for chemical reaction. Typical methods for nanoparticle synthesis include: reaction in the liquid phase using the sol–gel approach and mechanical ball-milling of the bulk material; both of these approaches are somewhat problematic for the preparation of reactive nanostructured materials which are sensitive to air and/or moisture. We report here the formation of crystalline nanoparticles of sodium hydride encapsulated in a host amorphous silica gel matrix. These nanoparticles are formed by in situ hydrogenation of a precursor material—Na loaded silica gel—under mild conditions. The resulting material is considerably less pyrophoric and less air-sensitive than the bulk hydride. We anticipate that this formation method of in situ modification of reactive precursor material may have wide applications.
In synthetic organic chemistry, sodium hydride (NaH) has been utilized almost exclusively as a routine Brønsted base, while sodium hydride has not been considered to work as a hydride donor. Recently, our group has serendipitously found that sodium hydride can function as a unique hydride donor by its solvothermal treatment with sodium iodide (NaI) or lithium iodide (LiI) in tetrahydrofuran (THF) as a solvent. This discovery led to the development of unprecedented reductive molecular transformations such as hydrodecyanation of α-quaternary benzyl cyanides, controlled reduction of amides into aldehydes, dearylation of arylphopsphine oxides, and hydrodehalogenation of haloarenes. Moreover, this concise protocol allows for the use of sodium hydride as enhanced Lewis acid and Brønsted base, enabling directed aromatic C-H sodiation, nucleophilic amination of methoxy arenes, and C2-amination of pyridines (the Chichibabin amination).
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