Understanding the Origins of Nucleophilic Hydride Reactivity of a Sodium Hydride–Iodide Composite

Abstract

Sodium hydride (NaH) has been commonly used as a Brønsted base in chemical syntheses, while it has rarely been employed to add hydride (H(-) ) to unsaturated electrophiles. We previously developed a procedure to activate NaH through the addition of a soluble iodide source and found that the new NaH-NaI composite can effect even stereoselective nucleophilic hydride reductions of nitriles, imines, and carbonyl compounds. In this work, we report that mixing NaH with NaI or LiI in tetrahydrofuran (THF) as a solvent provides a new inorganic composite, which consists of NaI interspersed with activated NaH, as revealed by powder X-ray diffraction, and both solid-state NMR and X-ray photoelectron spectroscopies. DFT calculations imply that this remarkably simple inorganic composite, which is comprised of NaH and NaI, gains nucleophilic hydridic character similar to covalent hydrides, resulting in unprecedented and unique hydride donor chemical reactivity.

Reduction of N,N‐Dimethylcarboxamides to Aldehydes by Sodium Hydride–Iodide Composite

“…Despite the recent progress, there is still ample room to develop methods for reducing simple amides into aldehydes, that can be conducted in operationally simple and cost‐effective manners under milder reaction conditions. We recently disclosed that sodium hydride (NaH) could act as a hydride donor in the presence of NaI or LiI in THF, capable of performing a series of unprecedented hydride reduction such as hydrodecyanation of carbonitriles ( Scheme ,a ), hydrodehalogenation of haloarenes ( Scheme ,b ), and dearylation of arylphosphine oxides ( Scheme ,c ) . In this context, we envisioned that use of the sodium hydride–iodide composite for the reduction of amides results in unique outcomes .…”

N‐Silylation of Amines Mediated by Et3SiH/KOtBu

“…When the reactions were carried out with NaO t Bu as base, no silylated products were produced, while NaH was found to be effective, although in low‐to‐moderate yields (see Table S1 in Supporting Information file). Interestingly, KH was also ineffective in producing silylated products and this point comes up for comment later in this article …”

“…This may initially seem curious, as commercial KH was not effective in promoting the reactions in the laboratory. However, a strong difference in reactivity between a free KH molecule and the commercial solid aggregate is expected …”

Mechanistic Insights on Reduction of Carboxamides by Diisobutylaluminum Hydride and Sodium Hydride−Iodide Composite

“…The amide reduction by the NaH−NaI composite empirically gave the corresponding aldehydes ( Schemes ,b and 4,b ). We assume that counter ion metathesis between NaH and NaI in THF allows for generation of activated, nanomeric units of NaH, that possesses enhanced nucleophilic hydridic character to promote the present process . Thus, using a NaH dimer as an appropriate model of the active species, the possibility of the pathways for the C−O and C−N bonds scission from the anionic carbinol amine intermediate II was investigated by the same DFT method.…”