Borohydride reduced metal salts

Catalytically active species have been prepared by the alkali borohydride reduction of a number of different metal salts. Some of these catalysts are metal borides while others appear to be the reduced metal. 

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Despite the previous comments there are dangerous forms of this metal. Thus, the Ru-Zn alloy, when treated by hydrochloric acid leads to zinc dissolving into a very porous ruthenium, which detonates in air spontaneousiy. The same goes for ruthenium, which is obtained by reduction of its salts by sodium borohydride. It is recommended to reduce ruthenium salts using hydrazine, which is reputed to be not dangerous . However, with ruthenium trichioride this reaction seems to be not dangerous only when hydrazine has a very low molar ratio (0.9 mol per cent). If it is not the case, a huge volume of gas could constitute an important pressure risk. 

Colloidal metals are usually prepared by reduction of a salt with a reducing agent, such as phosphorus, acetone, tannin, or carbon monoxide. Platinum metals can also be prepared as finely divided very active blacks by reducing the metal salt in an aqueous solution of sodium or potassium borohydride. 

Use of borohydride solutions to reduce ruthenium salt solutions to the metal or an alloy gave solid products (possibly hydrides), which when dry, exploded violently in contact with water or when disturbed by a spatula. Hydrazine appears to be a safe reducant for ruthenium salt solutions. 

Highly active nickel, platinum and palladium catalysts can also be prepared by reducing the metal salts with sodium borohydride. 

A number of metals salts can be used as the source of electrophiles in reactions with alkenes. One of the most interesting of these involves the attack of mercury(II) acetate in acetic acid. Reductive cleavage of the organomercury compound with sodium borohydride leads to the overall hydration of the alkene in a Markownikoff sense. There are a number of preparative advantages, such as a reduced tendency to rearrange, associated with this and similar relatively mild procedures when compared to the direct protonation of a double bond (Scheme 3.14)... 

Attempts to reduce the 3-oxo-group in the ketol pyridinium sulphate (181), using sodium borohydride in anhydrous methanol, afforded instead the stable 3,3-dimethoxy-derivative (182), The pyridinium ion is sufficiently acidic to promote this acetalization, although alkali-metal salts of the ketol sulphate were... 

A solution of appropriate salts can also be reduced in the liquid phase by the addition of an appropriate reducing agent. Sodium borohydride has been used but care must be taken to remove the boron from the catalyst, particularly for the mixed noble metals. This has been accomplished by adding a dilute borohydride solution to the mixed metal salt solution under rapid agitation followed by a thorough washing of the precipitated metal black with warm water.The use of hydrazine, formaldehyde or formic acid is preferred to borohydride since the byproducts of the reduction do not contaminate the catalyst. Another procedure is to use a ternary alloy and to leach out one component as in the preparation of Raney nickel and similar catalysts. 

Fig. 9.2. Cartoon showing the seed-mediated growth approach to the synthesis of metallic nanorods of controllable aspect ratio. In the first step, metal salts are reduced with sodium borohydride, a strong reducing agent, to metal nanospheres ( seeds ) that are 3-4 nm in diameter. In the subsequent growth steps.

Sulfones and sulfoxides are not affected by borohydrides in alcohol media [RJl] except in the presence of transition metal salts such as FeClg, C0CI2, or TiCl4 [CH3, G02, KT2, LZl, W4] (Figure 5.8). The sulfides obtained are not reduced under these conditions but are desulfurized in the presence of the NP+ salts [G02]. Another possibility is to treat the sulfoxides with NaCNBHg in MeOH. This reduction takes place via the sulfoxonium salt [PSl] (Figure 5.8). 

In the nanowater pools (called nano reactors), nanosized metals and metallic salts can be conveniently synthesised. In the case of synthesis of metals, metal ions from their salts are reduced by different agents like sodium borohydride, ascorbic acid etc. Metallic salts are generally prepared by exchange reactions. The addition or mixing can be done in two ways. 

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