New Developments in the Chemistry of Diborane and the Borohydrides. I. General Summary¹

Abstract

The present is the first of a series of papers describing new developments in the methods of preparation and in the chemistry of diborane and of the borohydrides. New and practical methods for the preparation of borohydrides (a) from diborane, and (b) without the use of diborane are discussed. As a result of the availability of borohydrides, prepared without the use of diborane, methods, far more satisfactoiy than those hitherto known for the preparation of the latter, have been developed. The investigation has led to the preparation of the hitherto unknown borohydrides of sodium, of potassium and of uranium, and some of their derivatives, as well as of a new type of substance, such as sodium trimethoxyborohydride, NaBH(OCH3)3, formed by the addition of compounds of trivalent boron to alkali metal hydrides. Sodium borohydride, as well as sodium trimethoxyborohydride, are of special interest because of their potential usefulness as reducing agents and sources for the generation of hydrogen; uranium(IV) borohydride and its derivatives are of interest because they are the most volatile compounds of uranium except the hexafluoride. The present paper surveys numerous new observations made and organizes the subject matter in the light of the principle which largely guided the research, namely, the application of the Lewis generalized acid-base concept to the reactions of diborane, of the salt-like hydrides and of the borohydrides. Detailed description of the new preparative methods and data confirming the reaction equations herein presented as well as supporting the composition of new substances are deferred to the remaining papers of the series.vestigations carried out under contracts with the National Defense Research Committee, with the Office of Scientific Research and Development and with the Signal Corps, Ground Signal Agency during the years 1940-1944. They were continued under Navy auspices during [1944][1945][1946]. Most of the results were originally described in the final reports on contracts NDC-rc-56, 9820 and 10,421.

Hydrogen Dynamics in Lightweight Tetrahydroborates

“…They may be solved in organic solvents such as tetrahydrofuran (THF). Research on lightweight tetrahydroborates started in world war II during the attempt to find new volatile uranium compounds [8]. Due to their large volumetric and gravimetric hydrogen density they were proposed as solid rocket fuel [9] or as promising candidates for hydrogen storage [10].…”

Tetrahydroborates: Development and Potential as Hydrogen Storage Medium

“…In 1941, H. I. Schlesinger and co-workers [55] were asked to undertake the synthesis of new volatile compounds of uranium. As a consequence of the fact that the tetrahydroborates of aluminum and beryllium are the most volatile compounds of these elements, the synthesis of uranium tetrahydroborate was attempted [53,56].…”

“…After the filtration of the insoluble LiH impurities, the evaporation of the solvent from the filtrate leads to the precipitation of LiBH 4 ·(C 2 H 5 ) 2 O first, and then to high purity LiBH 4 . At that time, it was believed that in the absence of solvents, lithium hydride does not react with diborane even at an elevated temperature [55]. However, recently Friedrichs et al [58] showed that the solvent-free synthesis of LiBH 4 from LiH in a diborane atmosphere at 120 • C is possible.…”

“…In order to circumvent this inconvenience the use of trimethoxyborohydride as hydride ions source was proposed [55,59]. The reaction between trimethoxyborohydride and diborane proceeds rapidly and quantitatively forming sodium tetrahydroborate and trimethylborate, according to reaction (9):…”

“…As a consequence, several new tetrahydroborates were synthesized. Nowadays, the mono-cation tetrahydroborates of 32 chemical elements, plus an undefined number of multi-cation tetrahydroborates are known [23,38,[42][43][44][45][52][53][54][55][56][57][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76][77][78].…”