Borohydride, sodium with nickel salts

Nickel borides are usually prepared by reduction of nickel salts with sodium or potassium borohydride. Two types are used. PI nickel boride is prepared by the reaction between aqueous solutions of nickel salts and a borohy-... 

Nickel of activity comparable to Raney nickel is obtained by reduction of nickel salts, e.g. nickel acetate, with 2 mol of sodium borohydride in an aqueous solution and by washing the precipitate with ethanol [13, 47] Procedure 7, p. 205). Such preparations are designated P-1 or P-2 and can be conveniently prepared in situ in a special apparatus [4] Procedure 2, p. 202). They contain a high percentage of nickel boride, are non-magnetic and non-pyrophoric and can be used for hydrogenations at room temperature and... 

It has also been found that highly active catalysts can be prepared in situ by reducing a platinum, palladium, or rhodium salt with sodium borohydride in the presence of a carbon support. Similar reductions of nickel salts produce colloidal nickel-boron, which is highly selective toward olefins of different structural types. The normal order of reactivity—i.e., terminal > disubstituted > trisubstituted—is observed, but the reactivity spread is sufficiently large that selective hydrogenation of polyenes is possible, as illustrated by a step in a synthesis of the natural product... 

Partial reduction of alkynes to Z-alkenes is another important synthetic application of selective hydrogenation catalysts. The transformation can be carried out under heterogeneous or homogeneous conditions. Among heterogeneous catalysts, the one that is most successful is Lindlar s catalyst, which is a lead-modified palladium-CaCOa catalyst.A nickel-boride catalyst prepared by reduction of nickel salts with sodium borohydride is also useful.A homogeneous rhodium catalyst has also been reported to show good selectivity. 

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

Highly active platinum, palladium, and nickel catalysts also can be obtained by reduction of metal salts with sodium borohydride (NaBH4). 

Reduction of aqueous or ethanolic solutions of inorganic salts with sodium or potassium borohydride is now the most useful procedure for catalyst activation. Reduction is fast and efficient at room temperature, and, particularly in the case of nickel, a catalyst more active than Raney nickel can be obtained.66 Instead of borohydride, silicon hydrides such as tribenzylsilane have been used for the reduction to produce active platinum catalysts.75... 

Quinoxaline derivatives give, after reduction with sodium borohydride-transition-metal salt system, e.g. nickel(II) chloride, 1,2,3,4-tetrahydroquinoxaline derivatives. ... 

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. 

Silyl and stannyl hydrides effect high yield reduction of aryl diazonium salts, and are compatible with a wider range of solvents than is HaP02. NaH prepared situ has been found to be much more active than the commercial product. Using the more active NaH, hydrogenolysis of benzylic halides is possible. Sodium borohydride has been reported to reduce nitriles to amines if Raney nickel is used as catalyst. 

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