Nickel borides preparation

Thiophenes can also be desulfurized to alkenes (RCH2CH=CHCH2R from 115) with a nickel boride catalyst prepared from nickel(II) chloride and NaBILj in methanol.It is possible to reduce just one SR group of a dithioacetal by treatment... 

The halide is not the only metal compound used as source of metal. Metal oxides and sulfides are employed to prepare vanadium, chromium, iron and nickel borides in this way from sulfides at lower reaction T than those required by reaction sintering of the elements . 

Moreover, stable liquid systems made up of nanoparticles coated with a surfactant monolayer and dispersed in an apolar medium could be employed to catalyze reactions involving both apolar substrates (solubilized in the bulk solvent) and polar and amphiphilic substrates (preferentially encapsulated within the reversed micelles or located at the surfactant palisade layer) or could be used as antiwear additives for lubricants. For example, monodisperse nickel boride catalysts were prepared in water/CTAB/hexanol microemulsions and used directly as the catalysts of styrene hydrogenation [215]. 

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-... 

Three new methods for the conversion of alkynes to (Z)-alkenes were reported, although Lindlar semi-hydrogenation still remains as the most convenient method. Copper (I) hydride reagent could reduce alkynes to (Z)-alkenes as shown in Scheme 3 [12]. Yoon employed nickel boride prepared on borohy-dride exchange resin for selective hydrogenation of alkynes to (Z)-alkenes (Scheme 4) [13]. 

In ethanol nickel(II) acetate treated with NaBFLt produces a nearly colloidal black suspension63. Variation of the solvent in the preparation of the nickel catalyst results in an amorphous nickel boride catalyst67,68. This P-2 nickel catalyst is much more sensitive to the double-bond structure69,70. In the hydrogenation of the strained double bonds of nor-bomadienes, P-2 nickel shows high selectivity (95%) and low isomerization characteristics (equations 20 and 21). 

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... 

Another highly active non-pyrophoric nickel catalyst is prepared by reduction of nickel acetate in tetrahydrofuran by sodium hydride at 45° in the presence of tert-amyl alcohol (which acts as an activator). Such catalysts, referred to as Nic catalysts, compare with P nickel boride and are suitable for hydrogenations at room temperature and atmospheric pressure, and for partial reduction of acetylenes to civ-alkenes [49]. 

Hydrogenation using Raney nickel is carried out under mild conditions and gives cis alkenes from internal alkynes in yields ranging from 50 to 100% [356, 357, 358, 359, 360]. Half hydrogenation of alkynes was also achieved over nickel prepared by reduction of nickel acetate with sodium borohydride (P-2 nickel, nickel boride) [349,361,362] or by reduction with sodium hydride [49], or by reduction of nickel bromide with potassium-graphite [363]. Other catalysts are palladium on charcoal [364], on barium sulfate [365, 366], on... 

Nickel boride, formed in situ from sodium borohydride and nickel chloride, has been used to prepare dihydro derivatives from thiothymine 385 <2001JME1853> and thiobarbituric acid derivatives 388 <2002J(P1)2520>. With 4-thiothymine derivatives, an isomeric mixture of 3,4- and 3,6-dihydro derivatives 386 and 387 was obtained <2001JME1853>, but with 2-thiobarbiturates, clean reduction at the 2-position was able to be achieved <2002J(P1)2520>. 

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. 

Nickel boride (prepared by adding NaBH4 to nickel chloride in methanol - THF) is an efficient, non-pyrophoric reagent for the desulfurization of benzo[ Jthiophene and dibenzothiophene (90CC819, 92JOC1986). The reaction proceeds under very mild conditions and is probably mediated by nickel hydride. 

Many other uses of a-sulfinyl carbanions are found in the literature, and in the recent past the trend has been to take advantage of the chirality of the sulfoxide group in asymmetric synthesis. Various ways of preparation of enantiopure sulfoxides have been devised (see Section 2.6.2) the carbanions derived from these compounds were added to carbonyl compounds, nitriles, imines or Michael acceptors to yield, ultimately, with high e.e. values, optically active alcohols, amines, ethers, epoxides, lactones, after elimination at an appropriate stage of the sulfoxide group. Such an elimination could be achieved by pyrolysis, Raney nickel or nickel boride desulfurization, reduction, or displacement of the C-S bond, as in the lactone synthesis reported by Casey [388]. 

When one component of a bimetallic alloy is leached out, a finely divided metal powder of high surface area results. One of the oldest of these so-called skeletal metal catalysts is Raney nickel10,11. Nickel boride is a more recently developed hydrogenation catalyst prepared by the reduction of nickel salts with sodium borohydride12-14. Bimetallic catalysts are often used to achieve selective saturation of a double bond in bifunctional unsaturated systems, e.g. in dienes. Amorphous metal alloys, a newly developed class of metal catalysts15,16, have also been applied in the hydrogenation of alkenes and dienes. 

Nickel boride prepared from Nil2 and two equivalents of LiBH4 [42] was utilized as an oxazaborolidine catalyst support (Scheme 4) [43]. Reaction of nickel boride with 0.1 equivalents of chiral amino alcohol in THF at room temperature gave the anchored catalyst 6, which produced chiral alcohols in optical yields of up to 95%, and which furthermore showed higher activity as regards the reduction of acetophenone derivatives than that of the corresponding homogene-... 

Apart from the above methods, some of which employ drastic conditions, processes close to equilibrium conditions such as pyrolysis and chemical vapor deposition (CVD) have also been employed to prepare BN nanotubes. The CVD growth of hollow, crystalline BN nanotubules by the pyrolysis of borazine on nickel boride catalyst particles maintained at 1270-1370 K, produced nanotubes with bulbous or flag-like caps (Fig. 38). The reaction is given by,... 

Nakano and Fujishige prepared a colloidal nickel boride catalyst by reducing nickel chloride with sodium borohydride in ethanol in the presence of polyvinylpyrrolidone) as a protective colloid.83 Catalytic activity of the colloidal catalyst was higher than P-2 Ni boride for the hydrogenation of acrylamide and markedly enhanced by the addition of sodium hydroxide in the hydrogenation of acetone.84... 

By heating mixtures of nickel and boron in a current of hydrogen at 1100-1200° C., du Jassonneix14 has prepared two borides of nickel,... 

Hydrogenation catalyst. Russell and Hoy have described a nickel boride catalyst which is useful for selective reduction of C=C bonds without hydrogenolysis of liydruxylic subslilueiils or hydrogenation of carbonyl or epoxide groups. The black colloidal catalyst is prepared by reduction of nickel acetate in ethanol with. 0M sodium borohydridc solution. 

Raney nickel and hydrazine hydrate have also been used to prepare 4-(benzyloxy)indoles (16) via reductive cyclization. An improvement can be achieved by using nickel boride instead of Raney nickel the advantages of this method include ease of preparation of the catalyst and its nonpyrophoric nature (equation 14). 

Raney nickel is a stronger desulfurizing agent than nickel boride. On the other hand nickel boride, prepared from nickel(II) chloride and sodium borohydride, is more selective since it does not desulfurize aromatic sulfones. An example of such selectivity is desulfurization of p-phenylsulfonylphenyl p-tolyl sulfide (33), which affords diphenyl sulfone in 91% yield and toluene in 84% yield. In contrast. Raney nickel desulfurizes both the sulfide and the sulfone giving a mixture of benzene and toluene (equation 82). 5... 

As is evident from Table 7, nickel boride does not give as high yields as Raney nickel. However, it offers certain advantages over the latter. In addition to higher selectivity, its preparation is faster and more simple than that of Raney nickel, it allows for better dosage, and is not pyrophoric. ... 

Thiophenes can also be desulfurized to alkenes (RCH2CH=CHCH2R from 49) with a nickel boride catalyst prepared from nickel(II) chloride and NaBELj in methanol.It is possible to reduce just one SR group of a dithioacetal by treatment with borane-pyridine in trifluoroacetic acid or in CH2CI2 in the presence of AlCla. Phenyl selenides RSePh can be reduced to RH with Ph3SnH and with nickel boride. Cleavage of the C—Se bond can also be achieved with Sml2. ... 

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