Ni boride

Ring strain can also exert an important influence on the regioselectivity the hydrogenation of 5-methylenenorbornene over a Ni-boride catalyst (P-2) resulted in preferential... 

Various active nickel catalysts obtained not via reduction of nickel oxide with hydrogen have been described in the literature. Among these are the catalysts obtained by the decomposition of nickel carbonyl 10 by thermal decomposition of nickel formate or oxalate 11 by treating Ni-Si alloy or, more commonly, Ni-Al alloy with caustic alkali (or with heated water or steam) (Raney Ni) 12 by reducing nickel salts with a more electropositive metal,13 particularly by zinc dust followed by activation with an alkali or acid (Urushibara Ni) 14-16 and by reducing nickel salts with sodium boro-hydride (Ni boride catalyst)17-19 or other reducing agents.20-24... 

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... 

P-1 Ni Boride 77 Nickel acetate tetrahydrate (1.24 g, 5.0 mmol) in 50 ml distilled water is placed in a 125-ml Erlenmeyer flask connected to a mercury bubbler and flushed with nitrogen. To the magnetically stirred solution, 10 ml of a 1.0M solution of sodium borohydride in water is added over 30 s with a syringe. When gas evolution has ceased, a second portion of 5.0 ml of the borohydride solution is added. The aqueous phase is decanted from the granular black solid and the latter washed twice with 50 ml of ethanol, decanting the wash liquid each time. 

P-2 Ni Boride. 78 Nickel acetate tetrahydrate (1.24 g, 5.0 mmol) is dissolved in approximately 40 ml of 95% ethanol in a 125-ml Erlenmeyer flask. This flask is attached to a hydrogenator, which is then flashed with nitrogen. With vigorous stirring, 5.0 ml of 1M sodium borohydride solution in ethanol is injected. When gas evolution from the mixture has ceased, the catalyst is ready for use. 

Besides Urushibara Ni and Ni boride catalysts, various finely divided nickel particles have been prepared by reaction of nickel salts with other reducing agents, such as sodium phosphinate 20,85 alkali metal/liquid NH3 21 NaH-f-AmOH (designated Nic) 22,86Na, Mg, and Zn in THF or Mg in EtOH 24 or C8K(potassium graphite)/THF-HMPTA (designated Ni-Grl) 23,87 Some of these have been reported to compare with Raney Ni or Ni borides in their activity and/or selectivity. 

P-1 Ni16 and P-1 Co17 boride catalysts have also proved to be good catalysts for the hydrogenation of aromatic hydrocarbons. Table 11.3 compares the activities of these nickel and cobalt catalysts in the hydrogenation of some aromatic hydrocarbons in hydrocarbon solvent at 80°C and the initial hydrogen pressure of 7.8 MPa.18 It is noted that, as in the cases of Raney Ni and Raney Co, P-1 Co boride is generally more active than P-1 Ni boride, except for o-xylene. 

Catalytic reduction of acetates (tertiary or allylic) with Ni boride (reaction (e)) may serve as a shortcut option to achieve the transition from oxidation level 1 to oxidation level 0. This pathway eliminates the necessity first to prepare sulfur-containing derivatives. 

The desulfurizations illustrated in Scheme 5 show that Ni boride may tolerate hindered alkenes, alcohols (without oxidoreduction), ketones and esters. However, under certain conditions. 

Ni-Boride. To circumvent the shortcomings of Ra-Ni, thioacetals may be reduced in the presence of a Ni-reagent, such as Ni-boride generated in situ from NiCl2 or Ni(OAc)2 and NaBH4. Ni-boride is more conveniently prepared and handled than Ra-Ni and reduces thioacetals without concomitant formation of olefin by-products. " ... 

NiCl2 (1 eq) + NaBH4 (2 eq) Ni-boride + thioacetal reduction product... 

Nickel is used for high-pressure hydrogenations. Supported-Ni catalysts such as Raney-Ni and Ni-Boride are employed for hydrogenolysis of the C-S bonds in... 

Ni-Boride, readily prepared by reduction of Ni(OAc)2 with NaBH4, is more reactive than Raney-Ni." Treatment of NiCl2 with NaBH4 in methanol followed by heating yields a stable suspension of M2B, which catalyzes the regioselec-tive 1,4-reduction of a, 3-unsaturated aldehydes and ketones. ... 

Selectivity is put in use, e.g., in the synthesis of santal derivatives. Hydrogenation of 3 over Ni boride affords selectively 4 in 98% yield ... 

Ni boride (obtained from sodium borohydride reduction of Ni acetate in ethanol) exhibits sensitivity to substitution on the double bond, and to strained double bonds , and hence is useful for selective half-hydrogenation of dienes. Ni boride selectively hydrogenates the strained double bond of norbonene and dicyclopentadiene. Thus, a synthesis of 13-santalene involves the selective saturation of the endocyclic double bond of 7 over Ni boride, to afford 8 in 98% yield ... 

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