NICKEL CATALYSTS (HETEROGENEOUS) 1
Nickel Catalysts (Heterogeneous) Hydrogenations. Supported nickel catalysts have been used
to hydrogenate both alkynes and alkenes in high yield. Nickel on
graphite has been used extensively to semihydrogenate alkynes to
Ni0
(Z)-alkenes using notably mild conditions (eq 2).7
Ni/graphite
[7440-02-0] Ni (MW 58.71)
Bu
EDA, THF
InChI = 1/Ni
OTHP
H2 (1 atm)
InChIKey = PXHVJJICTQNCMI-UHFFFAOYAH
rt, 140 min
97%
(hydrogenolyses and hydrogenations1)
Bu
ć% ć% + (2)
Physical Data: mp 1453 C; bp 2730 C; d 8.908 g cm-3. Bu OTHP
OTHP
Form Supplied in: powder, rod, wire, foil, or pellet; 75% nickel
97.4:2.6
on graphite is available.
Preparative Methods: nickel on alumina can be prepared from
Similar hydrogenations have been performed using supported
Ni(NO3)2·6H2O slurried with Alumina and then dried at
ć% ć% palladium with similar stereoselectivity. However, nickel on
120 C. The catalyst is activated before use by heating at 400 C
graphite offers a reasonably priced alternative that can produce
for 30 min.2
results comparable with, and in some cases better than, those with
Handling, Storage, and Precautions: nickel is stable to air, yet
palladium catalysts. Further, nickel catalysts are nonpyrophoric,
care should be taken to avoid moisture when using finely divided
making filtration during workup safer than with other catalysts. A
nickel catalysts. Nickel is a possible carcinogen. Use in a fume
disadvantage of nickel on graphite is that the catalyst should be
hood.
prepared fresh prior to each hydrogenation.
Caubere8 has described a heterogeneous catalyst (Nic), which
is a complex reducing agent of the type NaH RONa NiX2 (see
Heterogeneous Nickel Catalysts. This class of compounds
Nickel Complex Reducing Agents). Nic is highly reactive, capable
covers Ni0 on a variety of supporting media. Raney nickel and
of rapidly reducing alkenes, alkynes, and carbonyls. Reduction of
Urushibara nickel are discussed under separate headings (see
alkynes occurs with high stereoselectivity to the corresponding
Raney Nickel and Urushibara Nickel). There have been many
(Z)-alkene. Nic offers several advantages over Raney nickel in
significant contributions to this field, yet a comprehensive study
that it is nonpyrophoric, stable to long-term storage, and provides
of reactions involving these heterogeneous processes has not been
higher stereoselectivity.
produced. Therefore, many of the catalysts described have been
There have also been reports of aromatic saturation in excellent
applied to only a limited subset of substrates.
yields by passing hydrogen and gaseous substrate over nickel on
alumina.9 Hydrogenation of nitriles to the corresponding amines
Hydrogenolyses. Hydrogenolysis reactions have been the
are known. For example, hydrogenating propionitrile with nickel
subject of many studies involving heterogeneous nickel cata-
ć%
on silica in methanolic ammonia at 125 C for 45 min resulted in
lysts.3 6 Most of these reactions have involved the use of substi-
a 97% yield of n-butylamine.10
tuted adamantanes in the gas phase over supported nickel catalysts
(i.e. 30% nickel on alumina). These gas phase hydrogenolyses
have been performed upon a variety of functional groups such as
halides, amines, alcohols, carboxylic acids, esters, nitriles, ethers,
1. Bartok, M. Stereochemistry of Heterogeneous Metal Catalysis; Wiley:
hydroxymethylenes, and halomethylenes.3 The removal of alkyl
New York, 1985.
groups from substituted adamantanes at elevated temperatures is
2. Maier, W. F.; Bergmann, K.; Bleicher, W.; Schleyer, P. v. R., Tetrahedron
even possible.4 Eq 1 demonstrates the temperature dependence of Lett. 1981, 22, 4227.
hydrogenolyses utilizing nickel on alumina.5 3. Andrade, J. G.; Maier, W. F.; Zapf, L.; Schleyer, P. v. R., Synthesis 1980,
802. (b) Pines, H.; Shamaiengar, M.; Postl, W. S., J. Am. Chem. Soc.
1955, 77, 5099.
4. Grubmuller, P.; Schleyer, P. v. R.; McKervey, M. A., Tetrahedron Lett.
30% Ni/Al2O3 30% Ni/Al2O3
1979, 20, 181.
H2 (1 atm) H2 (1 atm)
CN
5. Maier, W. F.; Grubmuller, P.; Thies, I.; Stein, P. M.; McKervey, M. A.;
180 °C 235 °C
99% 80% Schleyer, P. v. R., Angew. Chem., Int. Ed. Engl. 1979, 18, 939.
6. Grubmuller, P.; Maier, W. F.; Schleyer, P. v. R.; McKervey, M. A.;
Rooney, J. J., Chem. Ber. 1980, 113, 1989.
(1)
7. Savoia, D.; Tagliavini, E.; Trombini, C.; Umani-Ronchi, A., J. Org.
Chem. 1981, 46, 5340.
8. Brunet, J. J.; Gallois, P.; Caubere, P., J. Org. Chem. 1980, 45, 1937.
At lower temperatures the nitrile is hydrogenolyzed to a methyl
9. Ciborowski, S., Przem. Chem. 1960, 39, 228 (Chem. Abstr. 1961, 55,
4387e).
group, yet at higher temperatures the resulting methyl group can be
removed. Similar hydrogenolysis reactions have been performed 10. Greenfield, H., Ind. Eng. Chem., Prod. Res. Develop. 1967, 6, 142.
using platinum and palladium catalysts; however, these reactions
tend to be low yielding (<10%) due to random cracking of the Christopher R. Sarko & Marcello DiMare
parent hydrocarbon.6 University of California, Santa Barbara, CA, USA
Avoid Skin Contact with All Reagents