Nickel boride catalysts

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... 

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]. 

O-p-tolylsulfonyl-a-D-mannoside (39) in 37% yield. Treatment of (39) with sodium iodide in acetone gave the 6-iodo derivative (40), which underwent reduction with hydrogen in the presence of a nickel boride" catalyst" to give methyl 4-0-benzoyl-2,3-0 carbonyl-6-deoxy-o>-D-manno-side (41) in 95% yield. Reaction of (41) with hydrogen bromide in acetic acid effected replacement of the methoxyl group at C-l, affording crystalline... 

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. 

There have been a considerable number of papers reporting the properties of sulphur-resistant methanation catalysts, i.e., catalysts which can operate successfully in significant partial pressures of H2S. Most of these report work using catalysts containing vanadium, molybdenum, and such metals. However, attempts have been made to find nickel-based catalysts containing suitable additives to allow them to operate in such atmospheres. For example, Bartholomew and Uken115 have compared the deactivation behaviour of a range of nickel catalysts in 10 p.p.m. H2S. They found that nickel boride catalysts and Raney nickel materials deactivated more slowly than did unsupported nickel and alumina-supported nickel. They attributed this improvement to two factors ... 

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,... 

A root-growth mechanism has been proposed for the growth of BN nanotubes, wherein the nanotubes nucleate on the nickel boride catalyst particle often with irregular initiation caps and... 

Comparison of the site densities from Table XIX with metal areas determined from H2 adsorption provides important insights into the nature of H2S adsorption on these catalysts. For example, the sulfur site density of 213 /tmol/g compared to the metal site density of 182 /rmol/g (from H2 adsorption) for 14% Ni/Al203 is equivalent to S/Nis = 0.6, in reasonable agreement with the earlier discussed studies (Section III,C) which show values of 0.5-0.8 and consistent with the value 0.6 determined for pure unsupported Ni. However, in the case of a typical molybdenum-containing catalyst, e.g., 10% Ni/20% Mo/A1203, the sulfur site density and H2 uptake are 693 and 72 /imol/g, respectively (S/Nis = 4.8), providing evidence that a considerable amount of sulfur adsorbs on molybdenum oxide sites which do not adsorb H2 a similar behavior is also observed for Raney Ni and nickel-boride catalysts. 

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... 

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. 

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. ... 

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. 

Using diborane as the reducing agent gave a nickel boride catalyst significantly different from those prepared using borohydride. This DBNi catalyst... 

Fig. 12.2. The promoting effect of adding chromium to the P-1 nickel boride catalyst in the hydrogenation of various substrates.

Fig. 12.4. Hydrogenation of 1-heptene over nickel boride catalysts.

A) P-2 nickel boride catalyst B) preformed P-2 nickel boride added to a micelle suspension C) nickel boride formed in the presence of a reversed phase micelle medium. (Redrawn using data from Ref 46.)... 

While a nickel boride catalyst preferentially saturates the carbon-carbon double bond of a,p-unsaturated aldehydes, the cobalt borides have a tendency to favor carbonyl group hydrogenation. Cinnamaldehyde was hydrogenated to cinnamoyl alcohol in 97% selectivity at 50% conversion and 86% selectivity at 74% conversion over a P-2 cobalt boride (Eqn. 12.7).5 With a P-2W cobalt boride the unsaturated alcohol was produced in 97% selectivity at 73% conversion. The presence of the aromatic ring enhances selectivity in this reaction since the hydrogenation of crotonaldehyde to 2-buten-l-ol occurred with only about a 25% selectivity at under 20% conversion over either catalyst (Eqn. 12.8).54... 

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... 

In ethanol nickcl(II) acetate treated with NaBH4 produces a nearly colloidal black suspension. Variation of the solvent in the preparation of the nickel catalyst results in an amorphous nickel boride catalyst . This P-2 nickel catalyst is much more sensitive to the double-bond structure . 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). 

The simplest and most straightforward use of acetylenes in leukotriene synthesis is as a protected cis double bond. Scheme 2.1 shows the use of 3-nonyne-l-ol as a starting material which will eventually become the C-12 to C-20 chain of LTA4 (Scheme 3.20). Semihydrogenation over a Lindlar or nickel boride catalyst ensures a high yield of the cis olefin 1. Scheme 2.2 shows a limitation... 

Selective hydrogenation of C=C. Corey has used P-1 type nickel boride catalyst for selective hydrogenation of C-C triple bonds in the presence of C-C double bonds. Thus in a total synthesis of the sesquiterpene sesquicarene (3) Corey and Achiwa3 hydrogenated (1) to (2) in 90% yield. 

A small amount of nickel boride (0.05 equiv) is enough to fulfill the coupling reaction at ambient temperatures with methyl crotonate 31. However, the coupling reaction with methyl acrylate 32 requires larger amounts of nickel boride (0.2 equiv) for better yields, presumably because alkyl iodides cannot compete with acrylates for the small amount of nickel boride catalyst, since the double bond of acrylates is rapidly hydrogenated even at 0°C by this system [16]. 

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