Tetrahydroborate ion

Gmelin Handbook Volumes on Boron and its Compounds (a) Main Volume (1926) (b) Supplement vol. 1 (1954) (c) Compounds 8 (NSSV 33), The tetrahydroborate ion and its derivatives (1976) (d) Compounds 9 (NSSV 34), Boron-halogen compounds , Part 1 (1976) (e) Compounds 10 (NSSV 37), Boron compounds with coordination number 4 (1976) (f) Compounds 15 (NSSV 46), Amine-boranes (1977) (g) Compounds 19 (NSSV 53), Boron-halogen compounds , Part 2 (1978) (h) Supplement Volumes (1980-82), Springer-Verlag, Berlin. 

The simplest hydrogen compounds are salts of the tetrahydroborate ion BH4- which is tetrahedral and isoelectronic with methane. LiBH4 is prepared by reducing BF3, with LiH. It is more widely used as the... 

Tetrahydroborate ion exchanges hydrogen with water only slowly. Thus, about 13 % exchange was found over24hat 90 °Cin 10 M NaOD in D2O. Rates mea-... 

In alkaline aqueous solution, reduction of iodate ion by tetrahydroborate ion has been found to compete with hydrolysis, the rate law being of the form... 

There are few useful reactions in which new B—H bonds are formed. Although the formation of boranes from the protolysis of borides or the reduction of boron compounds with Hj, either in electrical discharges or in the presence of active metals, have historical importance, these methods have no importance or utility today. Indeed, the preparation of boranes is so dominated by the single common starting material, the tetrahydroborate ion, that the only important reactions in which B—H bonds are formed are those in which hydride ion either reduces species with B—O or B-halogen bonds to form boranes or adds to trifunctional boron compounds to form hydroborates. 

These reaction mixtures may be used to form the tetrahydroborate ion e.g., LiH and BFj react in nonethereal organic liquids to afford LiBH LiBH is available in 90% yield in the presence of B(OCH3)3 as catalyst via the intermediacy of B H, and similar yields arise from the reaction in an autoclave at 120°C. 

Earlier kinetic studies on the acid hydrolysis of the tetrahydroborate ion (BH4 ) in moist acetonitrile were interpreted in terms of the accumulation of an intermediate complex of acetic acid and the tetrahydroborate anion. However, nmr measurements and kinetic isotope effects now show that while this intermediate is formed, and allows isotope exchange between BH4 and CH3COOD, it does not accumulate. The rate-determining step involves a second intermediate CHaCOOBHa", so that the earlier study on the hydrolysis of tetrahydroborate actually related to the hydrolysis of this species. It is suggested that this occurs... 

Treatment of thiiranes with lithium aluminum hydride gives a thiolate ion formed by attack of hydride ion on the least hindered carbon atoms (76RCR25), The mechanism is 5n2, inversion occurring at the site of attack. Polymerization initiated by the thiolate ion is a side reaction and may even be the predominant reaction, e.g. with 2-phenoxymethylthiirane. Use of THF instead of ether as solvent is said to favor polymerization. Tetrahydroborates do not reduce the thiirane ring under mild conditions and can be used to reduce other functional groups in the presence of the episulfide. Sodium in ammonia reduces norbornene episulfide to the exo thiol. 

A flow-injection system with electrochemical hydride generation and atomic absorption detection for the determination of arsenic is described. This technique has been developed in order to avoid the use sodium tetrahydroborate, which is capable of introducing contamination. The sodium tetrahydroborate (NaBH ) - acid reduction technique has been widely used for hydride generation (HG) in atomic spectrometric analyses. However, this technique has certain disadvantages. The NaBH is capable of introducing contamination, is expensive and the aqueous solution is unstable and has to be prepared freshly each working day. In addition, the process is sensitive to interferences from coexisting ions. 

Hydroborate Reduction. Lithium or sodium tetrahydroborate and diborane can be used for reduction of metal ions, especially light transition metal ions, to produce colloidal metals. For example, colloidal copper protected by polymer was prepared by reduction of copper(II) sulfate by a large excess of sodium tetrahydroborate in the presence of PVP or other polymers (12). A similar procedure for nickel(III) chloride produced nickel boride, not zero-valence nickel metal particles. 

The one-electron electrochemical reduction of NP (57) is a reversible process in aqueous solution, provided the measurements are performed at pH > 8 (—0.123 V vs. NHE) (57a,57b). Different chemical reductants such as sodium in liquid ammonia, tetrahydroborate, ascorbic acid, quinol, dithionite, superoxide or thiolates are also known to generate the [Fen(CN)5NO]3 ion (48,57). However, care must be taken in the products analysis, because the negative redox potentials of some of these reductants allow for further nitrosyl reduction (57a). Also, the reduced product is unstable toward cyanide... 

Method. Solutions of amino acids in phosphate buffer (pH 9.3) are mixed with an equal volume of freshly prepared 0.4 M pyridoxal solution (adjusted to pH 9.3) and permitted to stand at 8 °C for 30 min. (The molar ratio of pyridoxal to amino acid should be >75 1.) At this point, 1 ml of sodium tetrahydroborate solution (100 mg/ml in 0.1 N sodium hydroxide) is added and the contents are gently shaken. Excess of sodium tetrahydroborate is destroyed by addition of sufficient hydrochloric acid (pH 1-2) prior to column chromatography. The pyridoxal derivatives are separated on a column (100 X 0.6 cm) of Aminex A-5 ion-exchange resin (Bio-Rad) at a mobile phase flow-rate of 33 ml/h. The eluting solvents consist of 0.2 N buffers at pH 3.40,4.44 and 4.86 and a 0.35 N buffer at pH 5.86 (all of the buffers are sodium citrate). The separation of a number of pyridoxyl-... 

Speciation of lead in air and atmospheric particulates is still a topic of great environmental relevance. Sodium tetrahydroborate may be used to hydrogenate inorganic lead ions and alkyl-lead species.60 As in the study by Balls outlined above, cryogenic trapping may again be used to trap temporarily the plumbane and alkyl- and tetraalkyl-lead compounds, which are then released sequentially by heating for detection by flame AAS. 

With this repertoire of bonding possibilities at our disposal, we car construct the molecular structures of various boron-hydrogen compounds, both neutral species and anions. The simplest is the tetrahydroborate 26 or borohydride ion, BH. Although borane is unstable with respect to dimerization, the addition of a Lewis base, H . satisfies the fourth valency of boron and provides a stable entity. Other Lewis bases can coordinate as well. 

A mechanistic study of the role of the lanthanide cations suggests that they catalyze decomposition of borohydride by the hydroxylic solvent to afford alkoxyborohydrides, which may responsible for the observed regioselectivity. The stereoselectivity of the process is also modified by the presence of Ln " ions, in that axial attack of cyclohexenone systems is enhanced. a,p-Unsaturated aldehydes are regio-selectively reduced to allylic alcohols by bis(triphenylphosphine)copper(I) tetrahydroborate in the presence of Lewis acid catalyst. ... 

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