Alkenes Nickel boride

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... 

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. 

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)). ... 

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... 

Reduction of derivatives of ally lie alcohols. Nickel boride can effect reduction of allylic alcohols to alkenes, but yields are generally improved by reduction of the acetates, benzoates, or trifluoroacetates.1 Reduction of allylic benzyl ethers to alkenes is effected in higher yield with Raney nickel. Methyl ethers are not reduced by either reagent. The trimethylsilyl ethers of allylic alcohols are reduced to alkenes by nickel boride in diglyme.2... 

Dehalogenation a-Bromo or a-chloro ketones are reduced by nickel boride in DMF to ketones in 70-95% yield. Wc-Dibromides are reduced to alkenes in 80-90% yield. 

Unsaturated aldehydes.4 A nickel boride catalyst similar to P-2 nickel boride is obtained by reaction of NiCl2 and excess NaBH4 in C2H5OH. It effects selective hydrogenation of a,P-alkynal acetals to the (Z)-a,p-alkenal acetals. 

Palladium catalysts, 230 of alkyl silyl ethers to alkanes Nickel boride, 197 of alkyl sulfonates to alkanes Lithium triethylborohydride, 153 of alkynes to cis-alkenes... 

Arene(tricarbonyl)chromium complexes, 19 Nickel boride, 197 to trans-alkenes Chromium(II) sulfate, 84 of anhydrides to lactones Tetrachlorotris[bis(l,4-diphenyl-phosphine)butane]diruthenium, 288 of aromatic rings Palladium catalysts, 230 Raney nickel, 265 Sodium borohydride-1,3-Dicyano-benzene, 279 of aryl halides to arenes Palladium on carbon, 230 of benzyl ethers to alcohols Palladium catalysts, 230 of carboxylic acids to aldehydes Vilsmeier reagent, 341 of epoxides to alcohols Samarium(II) iodide, 270 Sodium hydride-Sodium /-amyloxide-Nickel(II) chloride, 281 Sodium hydride-Sodium /-amyloxide-Zinc chloride, 281 of esters to alcohols Sodium borohydride, 278 of imines and related compounds Arene(tricarbonyl)chromium complexes, 19... 

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. 

Ni-Gr I.1 This nickel catalyst reduces disubstituted alkynes to cis-alkenes the stereoselectivity is comparable to that observed with Lindlar catalyst or nickel boride (3, 208 -210 5,471-472). 

Nickel boride, generated in situ from nickel chloride and sodium borohydride, is an efficient reagent for debromination of vie-dibromides to the corresponding ( >alkenes... 

Hydrogenation of an alkyne can be stopped at the alkene stage by using a poisoned (partially deactivated) catalyst made by treating a good catalyst with a compound that makes the catalyst less effective. Lindlar s catalyst is a poisoned palladium catalyst, composed of powdered barium sulfate coated with palladium, poisoned with quinoline. Nickel boride (Ni2B) is a newer alternative to Lindlar s catalyst that is more easily made and often gives better yields. 

TABLE 3.1 Rates of Hydrogenation of Alkenes over P-1 and P-2 Nickel Boride and Nic Catalysts... 

In contrast to Lindlar catalyst we have found that the hydrogenation of an alkyne over ethylenediamine-poisoned "P-2" nickel boride or quinoline-poisoned palladium-on-barium sulfate always gives a minor amount of the saturated hydrocarbon in addition to the olefin. The ratio of saturated hydrocarbon to olefin (about 0.01) also is nearly constant throughout the hydrogenation until the alkyne is consumed, and then it increases. Further reaction of the alkene on the catalyst surface before desorption would explain these results. 

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. ... 

The more ethanol in the reduction solvent, the greater the amount of BOj found in the resulting nickel boride precipitate.This ion is formed by the hydrolysis of borohydride but, since it is not very soluble in ethanol, it is not kept in solution in alcoholic solvents. The BO2 is apparently responsible for the decreased activity and increased selectivity of the P-2 nickel boride. 3,35 Vvt]ien the P-2 catalyst was isolated and washed with water before use, the resulting P-2W catalyst was more active than both the P-2 and P-1 nickel borides but it became less selective in alkene hydrogenation than the P-2 catalyst. ... 

While various borohydride nickel ratios have been used in these nickel boride preparations maximum P-2 catalytic activity was observed with a 2 1 BH4 Ni ratio.However, when the reduction was run under a hydrogen atmosphere using a 4 1 BH4 Ni ratio, a hydrogenated nickel boride catalyst, the P-3 nickel boride, was obtained.27 This catalyst was somewhat more active than the P-2 catalyst for alkene hydrogenation but it induced signifieantly more double bond isomerization during the reaction. 

As shown by the data in Fig. 12.4 these micelle stabilized catalysts were considerably more active for alkene hydrogenation than the P-2 nickel borides. The hydrogenation run using a preformed P-2 catalyst in a reversed micelle medium proceeded at a faster rate than the reaction run over P-2 nickel boride in... 

The borohydride reduction of nickel decanoate in cyclohexane also produced a reversed micelle stabilized nickel boride cateilyst.37 The most active catalyst was formed using a 3 1 BH4 Ni ratio. This gave a catalyst that was about as active as the P-2 catalyst for alkene hydrogenation. The use of other BH4 Ni ratios gave less active catalysts. 

Nickel boride catalysts have been considered viable alternatives to Raney nickel since they are non-pyrophoric, are easily prepared and the preparation procedure is reproducible. In addition these catalysts appear to be somewhat more active than W2 Raney nickel for the hydrogenation of alkenes and nitriles but both types of catalyst have about the same activity for carbonyl group hydrogenation. While nickel boride and Raney nickel are both more resistant to... 

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