Nickel borides

Reduction and desulfurization of hetarenes with participation of nickel boride 970PP1. 

Catalysts show remarkable product variation in hydrogenation of simple nitriles. Propionitrile, in neutral, nonreactive media, gives on hydrogenation over rhodium-on-carbon high yields of dipropylamine, whereas high yields of tripropylamine arise from palladium or platinum-catalyzed reductions (71). Parallel results were later found for butyronitrile (2S) and valeronitrile (74) but not for long-chain nitriles. Good yields of primary aliphatic amines can be obtained by use of cobalt, nickel, nickel boride, rhodium, or ruthenium in the presence of ammonia (4J 1,67,68,69). 

Methyl a-D-mannopyranoside was treated in succession with p-toluene-sulfonyl chloride, carbonyl chloride, and benzoyl chloride, and, without isolating the intermediates, there was obtained in 37% yield methyl 4-0-l enzoyl-2,3-O-carbony 1-6-0-(p-tolylsulfonyl ) -D-mannoside. The tos-yloxyl group of the latter was replaced by iodine, and hydrogenation of the 6-iodo derivative in the presence of a nickel boride catalyst gave methyl 4-0-benzoyl-2,3-0-carbonyl-6-deoxy- -D-mannoside. Treatment of the latter with hydrogen bromide in acetic acid gave crystalline 4-0-benzoyl-2,3-0-carbonyl-6-deoxy-a-D-mannosyl bromide (8) (16). The... 

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-... 

In some cases it is necessary to hydrogenate allylic compounds to saturated molecules without hydrogenolysis. It was found that nickel boride is a good catalyst for this purpose.46... 

A reagent of nickel boride/hydrazine hydrate reduces both aromatic and aliphatic nitro compounds. For example, it has been used for synthesis of 4-(benzyloxy)indole and -alky ltryp-... 

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]. 

A catalyst that permits hydrogenation of an alkyne to an alkene is the nickel boride compound called P-2 catalyst. 

Desulfurization of phosphonylated thioamides has been achieved by nickel boride.71 73... 

The reductive cleavage of the N-O bond in the isoxazolidine 162 unmasks the 1,3-amino alcohol moiety. Thus, isoxazolidines can be viewed as direct precursors of 7-amino alcohols. The reductive cleavage of the cycloadduct proved difficult. W2 Raney-Ni and nickel boride were both ineffective. In contrast, nickel-aliminium alloy in an alkaline medium efficiently reduced the N-O bond at room temperature in the presence of a base (Equation 27) <1997TA109>. 

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). 

Chlordane (1 mM) in methyl alcohol (30 mL) underwent dechlorination in the presence nickel boride (generated by the reaction of nickel chloride and sodium borohydride). The catalytic dechlorination of chlordane by this method yielded a pentachloro derivative as the major product having the empirical formula C10H9CI5 (Dennis and Cooper, 1976). 

Sodium hydrogen telluride reacts with epoxides, in accordance with an S 2 displacement, giving rise to telluro-alcohols. These products are useful intermediates since they are easily converted into the corresponding alcohols and ketones by treatment with nickel boride followed by oxidation (reaction (a)) or to alkenes via the corresponding tosylates (reaction b)). ... 

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]. 

If the double bonds are structurally different to such an extent that their rates of hydrogenation differ considerably they can be reduced selectively. Monosubstituted double bonds are saturated in preference to di- and trisub-stituted ones [13, 348, 349]. When 2-methyl-1,5-hexadiene was hydrogenated over nickel boride with one mole of hydrogen only the unbranched double bond was reduced, giving 95% yield of 2-methyl-1-hexene [349]. 

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... 

Aliphatic and aromatic sulfides undergo desulfurization with Raney nickel [673], with nickel boride [673], with lithium aluminum hydride in the presence of cupric chloride [675], with titanium dichloride [676], and with triethyl phosphite [677]. In saccharides benzylthioethers were not desulfurized but reduced to toluene and mercaptodeoxysugars using sodium in liquid ammonia [678]. This reduction has general application and replaces catalytic hydrogenolysis, which cannot be used [637]. 

Partial desulfurization of disulfides to sulfides was accomplished by treatment with tris(diethylamino)phosphine in good yields [303]. 1,2-Dithiacy-clohexane was thus quantitatively converted to thiophane (tetrahydrothio-phene) at room temperature [303]. Complete desulfurization to hydrocarbons resulted when disulfides were refiuxed in ethanol with Raney nickel or nickel boride (yields 86 and 72%, respectively) [673]. 

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