New approaches to the synthesis of substituted derivatives of the [B₃H₈]⁻ anion

Objectives. To develop methods for the synthesis of substituted derivatives of the octahydrotriborate anion. Such compounds can be considered as hydrogen storage, components of ionic liquids, precursors for the production of boride coatings using the traditional chemical vapor deposition method, and also as a building material for the production of higher boron hydrogen clusters.

Methods. Since substitution reactions are sensitive to moisture and atmospheric oxygen, the syntheses were carried out in a direct flow of argon or in a dry, sealed SPEKS GB02M glove box with a double gas purification unit and two airlocks. The reaction was initiated by cooling to 0°C, in order to avoid the formation of by-products. All the results were characterized using infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies.

Results. The study presents a detailed study of the known methods for preparing substituted derivatives of the octahydrotriborate(1−) anion using dry hydrogen chloride as an electrophilic inductor and makes recommendations for improvement. In this method it is advisable to use cesium octahydrotriborate which facilitates the yield of the target product. New methods were proposed to initiate the substitution reaction in the [B₃H₈]⁻-anion using N-chlorosuccinimide and bromine. Using these inductors, new substituted derivatives of the octahydrotriborate anion with N-nucleophiles were obtained and defined by means of IR and NMR spectroscopies: [B3H7NCR], (R = Et, i-Pr, Ph) and [B₃H₇NH₂R], (R = C₉H₁₉ (INA), Bn), [B₃H₇NHEt₂], as well as Bu₄N[B₃H₇Hal], Bu₄N[B₃H₆Hal₂], where Hal = Cl, Br. It was also established that hydrogen bromide is released during the reaction with bromine and amines. This immediately protonates the amine which requires additional heating of the reaction mixture. The study also established that the reaction mechanism with N-chlorosuccinimide is not radical.

Conclusions. The main factors influencing the course of the substitution reaction are the possible occurrence of side interactions between the nucleophile and the inducer, steric possibilities, and subsequent isolation of the reactive reaction products.

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