NICKEL CATALYSTS (HETEROGENEOUS)

1

Nickel Catalysts (Heterogeneous)

Ni

0

[7440-02-0]

Ni

(MW 58.71)

InChI = 1/Ni
InChIKey = PXHVJJICTQNCMI-UHFFFAOYAH

(hydrogenolyses and hydrogenations

1

)

Physical Data:

mp 1453

◦

C; bp 2730

◦

C; d 8.908 g cm

−3

.

Form Supplied in:

powder, rod, wire, foil, or pellet; 75% nickel

on graphite is available.

Preparative Methods:

nickel on alumina can be prepared from

Ni(NO

3

)

2

·6H

2

O slurried with Alumina and then dried at

120

◦

C. The catalyst is activated before use by heating at 400

◦

C

for 30 min.

2

Handling, Storage, and Precautions:

nickel is stable to air, yet

care should be taken to avoid moisture when using finely divided
nickel catalysts. Nickel is a possible carcinogen. Use in a fume
hood.

Heterogeneous Nickel Catalysts. This class of compounds

covers Ni

0

on a variety of supporting media. Raney nickel and

Urushibara nickel are discussed under separate headings (see
Raney Nickel and Urushibara Nickel). There have been many
significant contributions to this field, yet a comprehensive study
of reactions involving these heterogeneous processes has not been
produced. Therefore, many of the catalysts described have been
applied to only a limited subset of substrates.

Hydrogenolyses.

Hydrogenolysis reactions have been the

subject of many studies involving heterogeneous nickel cata-
lysts.

3

–

6

Most of these reactions have involved the use of substi-

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,
hydroxymethylenes, and halomethylenes.

3

The removal of alkyl

groups from substituted adamantanes at elevated temperatures is
even possible.

4

Eq 1 demonstrates the temperature dependence of

hydrogenolyses utilizing nickel on alumina.

5

(1)

CN

30% Ni/Al

2

O

3

30% Ni/Al

2

O

3

H

2

(1 atm)

180 °C

99%

H

2

(1 atm)

235 °C

80%

At lower temperatures the nitrile is hydrogenolyzed to a methyl

group, yet at higher temperatures the resulting methyl group can be
removed. Similar hydrogenolysis reactions have been performed
using platinum and palladium catalysts; however, these reactions
tend to be low yielding (<10%) due to random cracking of the
parent hydrocarbon.

6

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
(Z)-alkenes using notably mild conditions (eq 2).

7

OTHP

Bu

OTHP

Bu

Bu

OTHP

Ni/graphite

EDA, THF

(2)

+

97.4:2.6

H

2

(1 atm)

rt, 140 min

97%

Similar hydrogenations have been performed using supported

palladium with similar stereoselectivity. However, nickel on
graphite offers a reasonably priced alternative that can produce
results comparable with, and in some cases better than, those with
palladium catalysts. Further, nickel catalysts are nonpyrophoric,
making filtration during workup safer than with other catalysts. A
disadvantage of nickel on graphite is that the catalyst should be
prepared fresh prior to each hydrogenation.

Caubere

8

has described a heterogeneous catalyst (Nic), which

is a complex reducing agent of the type NaH–RONa–NiX

2

(see

Nickel Complex Reducing Agents). Nic is highly reactive, capable
of rapidly reducing alkenes, alkynes, and carbonyls. Reduction of
alkynes occurs with high stereoselectivity to the corresponding
(Z)-alkene. Nic offers several advantages over Raney nickel in
that it is nonpyrophoric, stable to long-term storage, and provides
higher stereoselectivity.

There have also been reports of aromatic saturation in excellent

yields by passing hydrogen and gaseous substrate over nickel on
alumina.

9

Hydrogenation of nitriles to the corresponding amines

are known. For example, hydrogenating propionitrile with nickel
on silica in methanolic ammonia at 125

◦

C for 45 min resulted in

a 97% yield of n-butylamine.

10

1.

Bartok, M. Stereochemistry of Heterogeneous Metal Catalysis; Wiley:
New York, 1985.

2.

Maier, W. F.; Bergmann, K.; Bleicher, W.; Schleyer, P. v. R., Tetrahedron
Lett. 1981

, 22, 4227.

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.
1979, 20, 181.

5.

Maier, W. F.; Grubmuller, P.; Thies, I.; Stein, P. M.; McKervey, M. A.;
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.

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.

9.

Ciborowski, S., Przem. Chem. 1960, 39, 228 (Chem. Abstr. 1961, 55,
4387e).

10.

Greenfield, H., Ind. Eng. Chem., Prod. Res. Develop. 1967, 6, 142.

Christopher R. Sarko & Marcello DiMare

University of California, Santa Barbara, CA, USA

Avoid Skin Contact with All Reagents