Borohydride complex ion

The borohydride complex ion, BH4, is used not only to generate hydrogen but also for a new class of fuel cell by applying it directly as the liquid source of protide. Protide in BH4 can release two electrons per protide individually and a total of eight electrons when it is transformed to proton ... 

Borohydride Complex Ions in Aqueous Alkaline Solution... 

Practically, the hydrolysis as given in Eq. (6.35) does not happen. NaB02 as spent fuel is unable to exist as anhydrous NaB02 in aqueous solutions. NaBH4 gives an alkaline solution with a very high pH value, even diluted to a level of 1 % NaBH4 in water (pH = 11) and it exists as a borohydride complex ion in the form of BH4 once it is diluted in aqueous solution ... 

Reaction of free-base porphyrin compounds with iron(II) salts in an appropriate solvent results in loss of the two N—H protons and insertion of iron into the tetradentate porphyrin dianion ligand. Five-coordinate iron(III) porphyrin complexes (hemins), which usually have the anion of the iron(II) salt for the fifth or axial ligand, are isolated if the reaction is carried out in the presence of air. Iron(II) porphyrin complexes (hemes) can be isolated if the reaction and workup is conducted under rigorously anaerobic conditions. Typically, however, iron(II) complexes are obtained from iron(III) porphyrin complexes by reduction with dithionite, thiolate, borohydride, chromous ion, or other reducing agents. 

A complex ion, tetrahydridoborate(III) (borohydride, BH4"), can be formed it has very strong reducing properties. Other, more complex, borohydride ions exist. 

Reduction ultimately involves transfer of a hydride to a silyloxonium ion. It remains unclear whether this involves direct reaction of a second borohydride complex 2 with 5, with a tetrahedral oxonium ion 6 or some other process. Irrespective, the data does not support the intermediacy of a free silylium ion intermediate [24]. 

The majority of borohydride complexes have been prepared by ion exchange in non-aqueous solvents. For example, the nitrato copper(I) complex, [Cu(N03)(PPh3)2l, reacts sodium borohydride in a mixture of... 

Semenenko and coworkers have proposed a method for the synthesis of tungsten and molybdenum polyhydride complexes, [M(H)4(PR3)4] (M = W, Mo PR3 = phosphine or phosphite). The method involves ion exchange between [Md ] and Ca[BH4l2 in dimethoxyethane and results in the formation of the borohydride complexes, [M(ti2-BH4)J, which were identified in situ by IR spectroscopy. Addition of PR3 leads to the decomposition of the i]2-borohydride complexes and isolation of the polyhydrides, [M(H)4(PR3)4]. 

Cationic rings are readily reduced by complex hydrides under relatively mild conditions. Thus isoxazolium salts with sodium borohydride give the 2,5-dihydro derivatives (217) in ethanol, but yield the 2,3-dihydro compound (218) in MeCN/H20 (74CPB70). Pyrazolyl anions are reduced by borohydride to pyrazolines and pyrazolidines. Thiazolyl ions are reduced to 1,2-dihydrothiazoles by lithium aluminum hydride and to tetrahydrothiazoles by sodium borohydride. The tetrahydro compound is probably formed via (219), which results from proton addition to the dihydro derivative (220) containing an enamine function. 1,3-Dithiolylium salts easily add hydride ion from sodium borohydride (Scheme 20) (80AHC(27)151). 

Reduction of ketones to triphenylsilyl ethers is effected by the unique Lewis acid perfluorotriphenylborane. Mechanistic and kinetic studies have provided considerable insight into the mechanism of this reaction.186 The salient conclusion is that the hydride is delivered from a borohydride ion, not directly from the silane. Although the borane forms a Lewis acid-base complex with the ketone, its key function is in delivery of the hydride. 

In other cases, the borate complexes were decomposed prior to acetylation, either by distillation with acidified methanol, or with methanol after removal of cations. In a study of the former method, it was concluded that, when the excess of borohydride is decomposed with acetic acid, five evaporations with methanol are required for optimal results.39 The methanol must be added to the residue obtained on concentrating the aqueous solution to dryness, as, otherwise, trimethyl borate will not be formed. It has been stated that removal of borate is more efficient when hydrofluoric acid (instead of hydrochloric acid) is used to neutralize the excess of borohydride.113 Alternatively, borate complexes have been decomposed by removing cations with an ion-exchange resin, followed by distillation with methanol. Acetylation may then be conducted at 100° for 20 minutes, or at room temperature overnight91 or for shorter periods.26 It should, however, be noted that, when cations were removed and the product was acetylated without prior distillation with methanol, 4 hours of refluxing was still required, and irreproducible results were obtained when this time was lessened to 30 min to 1 hour.219... 

Considerable inter-element interference effects have been reported on the actual hydride-forming step. Elements easily reduced by sodium borohydride (e.g. silver, gold, copper, nickel) give rise to the greatest suppressions. These interfering ions may be removed by the addition of masking agents that complex with them. 

Pd/Sn bimetallic nanoparticles were synthesized from SnCl2 and Pd(N03)2 (47). In this case, the authors presented the pretreatment of the mixed solution. This pretreatment may produce the double complexes of Sn and Pd ions. The procedure is as follows Separate boiled clear solutions of SnCl2 and Pd(N03)2 with a small portion of concentrated HC1 were mixed and evaporated to dryness. The dry solids were digested with concentrated HNOj and HC1, forming an orange-red solution, which was again evaporated. The dry solid was then extracted with water and reduced by borohydride in the presence of surfactant. In the Pd-Sn bimetallic nanoparticles thus prepared, tin exists as Sn11 or Sn,v ions, as confirmed by XPS. 

---