Sodium Hydride-Nickel(II) Acetate-Sodium t-Pentoxide

NaH + Ni(OAc)2 + NaO-t-C5H11
(NaH)

[7646-69-7]  · HNa  · Sodium Hydride-Nickel(II) Acetate-Sodium t-Pentoxide  · (MW 24.00) (Ni(OAc)2.4H2O)

[6018-89-9]  · C4H14NiO8  · Sodium Hydride-Nickel(II) Acetate-Sodium t-Pentoxide  · (MW 248.87) (NaO-t-C5H11)

[14593-46-5]  · C5H11NaO  · Sodium Hydride-Nickel(II) Acetate-Sodium t-Pentoxide  · (MW 110.15)

(highly active and selective nickel hydrogenation catalyst at atmospheric pressure; allows semihydrogenation of alkynes to cis-alkenes1,2 and stereoselective reduction of ketones9)

Physical Data: see Sodium Hydride and Nickel(II) Acetate; the t-pentoxide salt is prepared in situ.

Solubility: sol THF, DME.

Preparative Methods: the nickel catalyst (referred to as NiC) is easily prepared by addition of the alcohol, the sodium salt of which has been chosen as an activating agent (in this case, sodium t-pentoxide), to a stirred suspension of Ni(OAc)2 and a calculated excess of NaH in THF at 45 °C. Before hydrogenation, EtOH is used to wash NiC to eliminate excess soluble alkoxide.

Handling, Storage, and Precautions: when long storage is required, the excess sodium hydride must not be neutralized, but rather destroyed before use in hydrogenation. Simple washing with EtOH can eliminate excess alkoxide. Store under argon. Use in a fume hood.

Hydrogenation.

It was observed that, at room temperature and atmospheric pressure, alkenes and alkynes could be reduced to alkanes and cis-alkenes, respectively, over this NiC catalyst. Until most of the alkyne is converted to the alkene, only minor amounts of alkane are formed, even when further hydrogenation of the alkene is the faster reaction.1,2 It was also found that NiC could promote hydrogenation of carbonyl compounds under ambient conditions. In reductions of ethylenic unsaturations, NiC catalysts are very sensitive to steric hindrance about the carbonyl groups (eqs 1-4).3

Other Reductions.

NiC can also be activated by Chlorotrimethylsilane; selective reduction of polyunsaturated ketones is easily performed with this reagent.4 NiC is useful in desulfurizing organic compounds such as sulfur-containing heteroaromatic substrates, aryl thioethers, dithioacetals, sulfoxides, and sulfones.5,8 NiC combined with 2,2-bipyridine (the nickel complex reducing agent NiCRA-bipy) is also very efficient in the desulfurization of organic compounds.8

Homocoupling of aryl bromides and chlorides is effected with NiCRA-bipy; the presence of alkali iodides improves the procedure. Yields are very high; however, a number of functional groups in the substrate may cause loss of reactivity.6 NiCRA-bipy is the first nickel-containing reagent that allows Ullmann-type cross-coupling to occur in good yield and under mild conditions.7

NiCRAs and other metal complex reducing agents are among the reagents known for epimerization of alcohols. By varying the metal used, and by using additives such as Magnesium Bromide or Me3SiCl, preferential formation of axial and equatorial alcohols from ketones is achieved. NiCRAs may be used to transform a given alcohol into its thermodynamically less stable epimer.9 This method, complementary to the familiar Meerwein-Ponndorf-Verley-Oppenauer and Raney nickel processes, employs substrate-activated agents ((SA)NiCRA) or other additives (eq 5) (DMHDNa = sodium salt of 2,5-dimethylhexane-2,5-diol).

Related Reagents.

Nickel Complex Reducing Agents; Sodium Hydride; Sodium Hydride-Copper(II) Acetate-Sodium t-Pentoxide; Sodium Hydride-Palladium(II) Acetate-Sodium t-Pentoxide; Zinc Complex Reducing Agents.


1. Brunet, J. J.; Gallois, P.; Caubere, P. TL 1977, 3955.
2. Brunet, J.-J.; Gallois, P.; Caubere, P. JOC 1980, 45, 1937.
3. Gallois, P.; Brunet, J.-J.; Caubere, P. JOC 1980, 45, 1946.
4. Fort, Y.; Vanderesse, R.; Caubere, P. TL 1986, 27, 5487.
5. Becker, S.; Fort, Y.; Vanderesse, R.; Caubere, P. TL 1988, 29, 2963.
6. Lourak, M.; Vanderesse, R.; Fort, Y.; Caubere, P. JOC 1989, 54, 4840.
7. Lourak, M.; Vanderesse, R.; Fort, Y.; Caubere, P. JOC 1989, 54, 4844.
8. Becker, S.; Fort, Y.; Vanderesse, R.; Caubere, P. JOC 1989, 54, 4848.
9. Vanderesse, R.; Feghouli, G.; Fort, Y.; Caubere, P. JOC 1990, 55, 5916.

Edward J. Parish & Haoyu Qin

Auburn University, AL, USA



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