Nickel Boride
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Nickel boride is the common name of materials composed chiefly of the elements
nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to ...
and
boron Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the ''boron group'' it has th ...
that are widely used as
catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
s in
organic chemistry Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J.; ...
. Their approximate
chemical composition A chemical composition specifies the identity, arrangement, and ratio of the elements making up a compound. Chemical formulas can be used to describe the relative amounts of elements present in a compound. For example, the chemical formula for ...
is Ni2.5B, and they are often incorrectly denoted "" in organic chemistry publications. Nickel boride catalysts are typically prepared by reacting a
salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
of nickel with
sodium borohydride Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula Na BH4. This white solid, usually encountered as an aqueous basic solution, is a reducing agent that finds appli ...
. The composition and properties vary depending on the specific preparation method. The two most common forms, described and evaluated in detail by
Herbert C. Brown Herbert Charles Brown (May 22, 1912 – December 19, 2004) was an American chemist and recipient of the 1979 Nobel Prize in Chemistry for his work with organoboranes. Life and career Brown was born Herbert Brovarnik in London, to Ukrainian Jewis ...
and
Charles Allan Brown Charles is a masculine given name predominantly found in English language, English and French language, French speaking countries. It is from the French form ''Charles'' of the Proto-Germanic, Proto-Germanic name (in runic alphabet) or ''*k ...
in 1963, are known as P−1 nickel and P−2 nickel. These catalysts are usually obtained as black granules (P−1) or colloidal suspensions (P−2). They are air-stable, non-
magnetic Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particle ...
and non-
pyrophoric A substance is pyrophoric (from grc-gre, πυροφόρος, , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolith ...
, but slowly react with water to form
nickel hydroxide Nickel(II) hydroxide is the inorganic compound with the formula Ni(OH)2. It is an apple-green solid that dissolves with decomposition in ammonia and amines and is attacked by acids. It is electroactive, being converted to the Ni(III) oxy-hydroxi ...
. They are insoluble in all solvents, but react with concentrated
mineral acids A mineral acid (or inorganic acid) is an acid derived from one or more inorganic compounds, as opposed to organic acids which are acidic, organic compounds. All mineral acids form hydrogen ions and the conjugate base when dissolved in water. Char ...
. They are claimed to be more effective
hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a Catalysis, catalyst such as nickel, palladium or platinum. The process is commonly employed to redox, reduce or S ...
catalysts than Raney nickel.


History

These catalysts originate during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
with the work of a research group led by Hermann I. Schlesinger, discoverer of borohydrides. They noted that reaction of with salts of certain transition metals yielded black precipitates, and that the
cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, pr ...
product catalyzed the decomposition of borohydride. However, their research was focused on war-related applications, and the black precipitate was not investigated further. In 1951,
Raymond Paul Raymond Rudolf Valentine Paul (21 November 1928 – 23 December 2013) was a British fencer. Fencing career He competed at the 1952 and 1956 Summer Olympics with the best individual result of eighth place in the foil in 1956. He won four na ...
and others investigated the reaction of with nickel chloride, sulfate, and acetate in various solvents and measured their performance as hydrogenation catalysts. In 1963, H. C. Brown and Charles A. Brown reported the synthesis and performance of two similar catalysts, which they denoted by "P-1" (the same as Paul's) and "P-2", obtained by reacting sodium borohydride with nickel acetate in water and ethanol, respectively.


Preparation

In contrast with other
boride A boride is a compound between boron and a less electronegative element, for example silicon boride (SiB3 and SiB6). The borides are a very large group of compounds that are generally high melting and are covalent more than ionic in nature. Some bor ...
s, which require high temperatures, preparation of these nickel boride catalysts can be carried out at ambient temperature, without special equipment. Ineded, they are usually generated ''in situ''. The P−1 catalyst can be generated by reacting a nickel(II) salt, such as
sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ar ...
,
chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...
,
nitrate Nitrate is a polyatomic ion A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zer ...
, or
acetate An acetate is a salt (chemistry), salt formed by the combination of acetic acid with a base (e.g. Alkali metal, alkaline, Alkaline earth metal, earthy, Transition metal, metallic, nonmetallic or radical Radical (chemistry), base). "Acetate" als ...
, and
sodium borohydride Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula Na BH4. This white solid, usually encountered as an aqueous basic solution, is a reducing agent that finds appli ...
in alkaline aqueous solutions. The product precipitates as a fine, black granular powder. The chemistry is very similar to that of
electroless nickel-boron plating Electroless nickel-boron coating (often called NiB coating) is a metal plating process that can create a layer of a nickel- boron alloy on the surface of a solid substrate, like metal or plastic. The process involves dipping the substrate in a wat ...
, and yields
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
gas and the corresponding
sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
salt as byproducts. The borohydride must be added gradually to the nickel salt solution, not the other way around, because the product catalyzes the hydrolysis of borohydride to hydrogen and hypoborate . The catalytic activity of P-1 is enhanced by adding small amount of salts of other metals (but not
cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, pr ...
) to the nickel salt during preparation. Benzene however reduces its activity somewhat. The P−2 form is prepared similarly from
nickel(II) acetate Nickel(II) acetate is the name for the coordination compounds with the formula Ni(CH3CO2)2·x H2O where x can be 0, 2, and 4. The green tetrahydrate Ni(CH3CO2)2·4 H2O is most common. It is used for electroplating. Synthesis and structure The ...
and sodium borohydride in
ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
. An inert atmosphere was found necessary for maximum catalytic activity. The result was an almost colloidal suspension of the black catalyst. Another method uses
nickel chloride Nickel(II) chloride (or just nickel chloride) is the chemical compound NiCl2. The anhydrous salt is yellow, but the more familiar hydrate NiCl2·6H2O is green. Nickel(II) chloride, in various forms, is the most important source of nickel for che ...
NiCl2 instead of acetate.


Structure and composition

The P-1 and P-2 "nickel boride" catalyst have been suggested to be amorphous compounds, composed of nickel bonded to individual boron centres. However, that structure was later found to be incorrect. An
X-ray diffraction X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...
analysis of P-1 by L. Hofer and others in 1964 indicated that the nickel and boron contents were in 2.5:1 ratio, but the solid contained 11% of strongly bound water and other compounds. was amorphous when freshly prepared (with crystalline
nanoparticle A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 1 ...
s about 1.5 nm across), but even heating at 90 °C caused the formation of some crystalline nickel. Heating at 250 °C caused it to separate into two phases: metallic nickel, and crystalline trinickel boride with the
cementite Cementite (or iron carbide) is a compound of iron and carbon, more precisely an intermediate transition metal carbide with the formula Fe3C. By weight, it is 6.67% carbon and 93.3% iron. It has an orthorhombic crystal structure. It is a hard, brit ...
structure, stable at least up to 750 C. No trace of the true dinickel boride was seen. The authors concluded that P-1 was an intimate mixture of metallic nickel and some amorphous boron-containing compound. The true structure of these "nickel borides" was elucidated only in 2007. They consist of small grains of crystalline nickel boride embedded in an amorphous nickel matrix. The two forms P−1 and P−2 differ in terms of amount of their contamination by NaBO2
adsorbed Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a ...
on the surface. P−1 Ni2B has an oxide to boride ratio of 1:4, whereas that of P−2 Ni2B is 10:1. Their properties differ in terms of catalytic efficiency and substrate specificity.


Applications

Ni2B is an efficient
catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
and
reducing agent In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are commonly reducing agents include the Earth meta ...
. It is used as a heterogeneous hydrogenation catalyst.


Catalytic hydrogenation

The catalytic activity of P−1 is insensitive to
steric hindrance Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape ( conformation) and reactivity of ions ...
of side chains on the substrate and thus more active, and seldom affects protecting groups. In contrast, P−2 is very sensitive to steric factors. For these reasons, P−1 is usually used for the complete reduction of unsaturated
hydrocarbons In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...
under mild conditions, while P−2 is useful in partial reductions such as converting
alkyne \ce \ce Acetylene \ce \ce \ce Propyne \ce \ce \ce \ce 1-Butyne In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and n ...
s to
alkene In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
s in high yields: The H2/Ni2B system will not hydrogenolyse
ether In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again be c ...
s,
alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...
s,
aldehyde In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...
s,
amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituen ...
s and
amide In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it is ...
s as it reduces alkenes in preference, even under forcing conditions. It leaves
epoxide In organic chemistry, an epoxide is a cyclic ether () with a three-atom ring. This ring approximates an equilateral triangle, which makes it strained, and hence highly reactive, more so than other ethers. They are produced on a large scale for ...
s unaffected, but affects
cyclopropane Cyclopropane is the cycloalkane with the molecular formula (CH2)3, consisting of three methylene groups (CH2) linked to each other to form a ring. The small size of the ring creates substantial ring strain in the structure. Cyclopropane itself ...
s occasionally. Most
ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...
s are stable to Ni2B, except for benzylic, allylic and propargylic esters which are cleaved by hydrogenolysis:


Desulfurization

The NiCl2/NaBH4 system desulfurizes
thioamide A thioamide (rarely, thionamide, but also known as thiourylenes) is a functional group with the general structure R–CS–NR′R″, where R, R′, and R″ are organic groups. They are analogous to amides but they exhibit greater multiple bond ch ...
s,
thioether In organic chemistry, an organic sulfide (British English sulphide) or thioether is an organosulfur functional group with the connectivity as shown on right. Like many other sulfur-containing compounds, volatile sulfides have foul odors. A sul ...
s,
thioester In organic chemistry, thioesters are organosulfur compounds with the functional group . They are analogous to carboxylate esters () with the sulfur in the thioester playing the role of the linking oxygen in the carboxylate ester, as implied by t ...
s,
thiol In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl gro ...
s and
sulfide Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds lar ...
s. Organic sulfides,
disulfide In biochemistry, a disulfide (or disulphide in British English) refers to a functional group with the structure . The linkage is also called an SS-bond or sometimes a disulfide bridge and is usually derived by the coupling of two thiol groups. In ...
s, thiols, and
sulfoxide In organic chemistry, a sulfoxide, also called a sulphoxide, is an organosulfur compound containing a sulfinyl () functional group attached to two carbon atoms. It is a polar functional group. Sulfoxides are oxidized derivatives of sulfides. E ...
s are reduced by NiCl2/NaBH4 to
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...
s. Illustrated is the reduction of
phenothiazine Phenothiazine, abbreviated PTZ, is an organic compound that has the formula S(C6H4)2NH and is related to the thiazine-class of heterocyclic compounds. Derivatives of phenothiazine are highly bioactive and have widespread use and rich history. T ...
to
diphenylamine Diphenylamine is an organic compound with the formula (C6H5)2NH. The compound is a derivative of aniline, consisting of an amine bound to two phenyl groups. The compound is a colorless solid, but commercial samples are often yellow due to oxidized ...
: Ni2B can also be used to cleave
thioacetal In organosulfur chemistry, thioacetals are the sulfur (''thio-'') analogues of acetals (). There are two classes: the less-common monothioacetals, with the formula , and the dithioacetals, with the formula (symmetric dithioacetals) or (asymm ...
s. Since Ni2B is non-pyrophoric, stable in air, and give high yields in many cases, it is proposed as a safer alternative to Raney Nickel for removal of cyclic thioacetals. Desulfurization catalyzed by Ni2B proved to occur with retention of configuration by
isotopic labeling Isotopic labeling (or isotopic labelling) is a technique used to track the passage of an isotope (an atom with a detectable variation in neutron count) through a reaction, metabolic pathway, or cell. The reactant is 'labeled' by replacing specific ...
.


Reduction of nitrogenous groups

The NiCl2/NaBH4 system reduces aliphatic
nitro group In organic chemistry, nitro compounds are organic compounds that contain one or more nitro functional groups (). The nitro group is one of the most common explosophores (functional group that makes a compound explosive) used globally. The nitr ...
s,
nitrile In organic chemistry, a nitrile is any organic compound that has a functional group. The prefix ''cyano-'' is used interchangeably with the term ''nitrile'' in industrial literature. Nitriles are found in many useful compounds, including met ...
s and
oxime In organic chemistry, an oxime is a organic compound belonging to the imines, with the general formula , where R is an organic side-chain and R’ may be hydrogen, forming an aldoxime, or another organic group, forming a ketoxime. O-substituted ...
s completely to
amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituen ...
s. For aryl amines,
nitrobenzene Nitrobenzene is an organic compound with the chemical formula C6H5 NO2. It is a water-insoluble pale yellow oil with an almond-like odor. It freezes to give greenish-yellow crystals. It is produced on a large scale from benzene as a precursor t ...
s are converted to
aniline Aniline is an organic compound with the formula C6 H5 NH2. Consisting of a phenyl group attached to an amino group, aniline is the simplest aromatic amine In organic chemistry, an aromatic amine is an organic compound consisting of an aroma ...
s, and
azoxy In chemistry, azoxy compounds are a group of chemical compounds sharing a common functional group with the general structure . They are considered N-oxides of azo compounds. Azoxy compounds are 1,3-dipoles. They undergo 1,3-dipolar cycloaddit ...
benzenes to
azobenzene Azobenzene is a photoswitchable chemical compound composed of two phenyl rings linked by a N=N double bond. It is the simplest example of an aryl azo compound. The term 'azobenzene' or simply 'azo' is often used to refer to a wide class of simi ...
s.
Azide In chemistry, azide is a linear, polyatomic anion with the formula and structure . It is the conjugate base of hydrazoic acid . Organic azides are organic compounds with the formula , containing the azide functional group. The dominant applic ...
s are cleanly reduced to amines in preference to
sterically hindered Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape ( conformation) and reactivity of ions ...
aliphatic nitro groups:


Dehalogenation

Most organic
fluorides Fluoride (). According to this source, is a possible pronunciation in British English. is an inorganic, monatomic anion of fluorine, with the chemical formula (also written ), whose salts are typically white or colorless. Fluoride salts typi ...
and
chlorides The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...
are unaffected by Ni2B,
bromides A bromide ion is the negatively charged form (Br−) of the element bromine, a member of the halogens group on the periodic table. Most bromides are colorless. Bromides have many practical roles, being found in anticonvulsants, flame-retardant ...
show variable reactivity, and
iodides An iodide ion is the ion I−. Compounds with iodine in formal oxidation state −1 are called iodides. In everyday life, iodide is most commonly encountered as a component of iodized salt, which many governments mandate. Worldwide, iodine defic ...
are often completely reduced to hydrocarbons. With Ni2B in
dimethylformamide Dimethylformamide is an organic compound with the formula ( CH3)2NC(O)H. Commonly abbreviated as DMF (although this initialism is sometimes used for dimethylfuran, or dimethyl fumarate), this colourless liquid is miscible with water and the majo ...
, α-bromoketones are reduced to the parent ketones. Vicinal bromides are dehalogenated to alkenes: For aryl bromides, the modified system in dimethylformamide is used for clean debromination. Reductive cleavage of iodides occurs with retention of configuration.


Safety

Nickel compounds are possible carcinogens and contact with skin should be avoided. Particular care should be taken whenever is used in dimethylformamide as
sodium borohydride Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula Na BH4. This white solid, usually encountered as an aqueous basic solution, is a reducing agent that finds appli ...
may spontaneously ignite in dimethylformamide.


See also

*
Cobalt boride Cobalt borides are inorganic compounds with the general formula CoxBy. The two main cobalt borides are CoB and Co2B. These are refractory materials. Applications Materials science Cobalt borides are known to be exceptionally resistant to oxidati ...
*
Urushibara nickel Urushibara nickel is a nickel based hydrogenation catalyst, named after Yoshiyuki Urushibara. History It was discovered by Yoshiyuki Urushibara in 1951, while doing research on the reduction of estrone to estradiol. Preparation First nickel is pr ...


References

Raymond Paul, Paul Buisson, and Nicole Joseph (1952): "Catalytic activity of nickel borides". ''Industrial and Engineering Chemistry'', volume 44, issue 5, pages 1006-1010. Hermann Irving Schlesinger, Herbert C. Brown, A. E. Finholt, James R. Gilbreath, Henry R. Hoekstra, and Earl K. Hyde (1953): "Sodium borohydride its hydrolysis and its use as a reducing agent and in the generation of hydrogen". ''Journal of the American Chemical Society'', volume 75, issue 1,pages 215-219. Charles A. Brown and Herbert C. Brown (1963): "The reaction of sodium borohydride with nickel acetate in aqueous solution—a convenient synthesis of a nickel hydrogenation catalyst of low isomerization tendency". ''Journal of the American Chemical Society'' (Communications to the Editor), volume 85, issue 7, pages 1003-1005. Herbert C. Brown and Charles A. Brown (1963): "The reaction of sodium borohydride with nickel acetate in ethanol solution: a highly selective nickel hydrogenation catalyst". ''Journal of the American Chemical Society'' (Communications to the Editor), volume 85, issue 7, pages 1005-1006. L. J. E. Hofer, J. F. Shultz, R. D. Panson, and R. B. Anderson (1964): "The nature of the nickel boride formed by the action of sodium borohydride on nickel salts". ''Inorganic Chemistry'', volume 3, issue 12, pages 1783–1785. Charles Allan Brown (1970): "Catalytic hydrogenation. V. Reaction of sodium borohydride with aqueous nickel salts. P-1 nickel boride, a convenient, highly active nickel hydrogenation catalyst". ''
The Journal of Organic Chemistry ''The Journal of Organic Chemistry'', colloquially known as ''JOC'', is a peer-reviewed scientific journal for original contributions of fundamental research in all branches of theory and practice in organic and bioorganic chemistry. It is publ ...
'', volume 35, issue 6, pages 1900–1904.
Charles Allan Brown and Vijay K. Ahuja (1973): "Catalytic hydrogenation. VI. Reaction of sodium borohydride with nickel salts in ethanol solution. P-2 Nickel, a highly convenient, new, selective hydrogenation catalyst with great sensitivity to substrate structure". ''Journal of Organic Chemistry'', volume 38, issue 12, pages 2226–2230. Chemicals & Reagents, 2008-2010 {{cite book, title = Encyclopedia of Inorganic Chemistry, chapter = Boron: Inorganic Chemistry, author1 = Robert A. Scott, publisher = Wiley, year = 2011, isbn = 9780470862100, page = 401
Borides Nickel compounds Hydrogenation catalysts