Lithium Aluminum Hydride-Bis(cyclopentadienyl)nickel

LiAlH4-NiCp2
(LiAlH4)

[16853-85-3]  · AlH4Li  · Lithium Aluminum Hydride-Bis(cyclopentadienyl)nickel  · (MW 37.96) (NiCp2)

[1271-28-9]  · C10H10Ni  · Lithium Aluminum Hydride-Bis(cyclopentadienyl)nickel  · (MW 188.90)

(desulfurization reagent for thiols, thioethers,1,2 thioacetals,1 sulfoxides, and sulfones;2 used as a homogenous catalyst for catalytic hydrogenation3)

Physical Data: see Lithium Aluminum Hydride.

Solubility: see Lithium Aluminum Hydride. Reactions using the mixture are run in THF.

Form Supplied in: prepared in situ from commercially available components.

Preparative Methods: bis(cyclopentadienyl)nickel is added as a THF solution to an equimolar amount of LiAlH4 at rt under nitrogen, resulting in the formation of a dark brown solution after 15 min. A THF solution of the organic substrate is then added to the mixture dropwise. Each carbon-sulfur bond requires at least 1 equiv of the reagent. Catalytic hydrogenation is performed in the presence of 1-5 mol % of the reagent.

Handling, Storage, and Precautions: see Lithium Aluminum Hydride.

Desulfurization.

The mixture of lithium aluminum hydride-bis(cyclopentadienyl)nickel has been used for reductive carbon-sulfur bond cleavage as a homogeneous alternative to the more common reagent, Raney Nickel.4 It has been found to desulfurize thiols, thioethers, and thioacetals effectively (eqs 1-3).1,2

Benzylic, a-acyl substituted, and aryl carbon-sulfur bonds were found to be easily reduced with this reagent, whereas alkyl carbon-sulfur bonds required more vigorous conditions, resulting in lower yields. Carbonyl groups, esters, and alkenes are stable to the reaction conditions, however, similar to Raney nickel,4 and nitro groups are reduced to the corresponding primary amines. In addition, sulfoxides and sulfones can also be desulfurized with this reagent. Longer reaction times and an excess of the reagent are required in order to prevent simple deoxygenation of the sulfoxide or sulfone and achieve complete reduction.2

Catalytic Hydrogenation.

Alkenes and alkynes can also be hydrogenated in the presence of a catalytic amount of LiAlH4-NiCp2.3 This reagent shows selectivity for disubstituted alkenes and conjugated polyenes (eq 4), whereas trisubstituted and sterically hindered alkenes (eq 5) are inert to the reaction conditions. Alkynes may be fully or partially reduced to the corresponding alkanes or alkenes, respectively, giving rise to products derived from cis and trans addition in the latter case.


1. Chan, M.-C.; Cheng, K.-M.; Li, M. K.; Luh, T.-Y. CC 1985, 1610.
2. Chan, M.-C.; Cheng, K.-M.; Ho, K. M.; Ng, C. T.; Yam, T. M.; Wang, B. S. L.; Luh, T.-Y. JOC 1988, 53, 4466.
3. Ho, K. M.; Chan, M.-C.; Luh, T.-Y. TL 1986, 27, 5383.
4. Hauptmann, H.; Walter, W. F. CRV 1962, 63, 347.

Kevin Daniels

The Ohio State University, Columbus, OH, USA



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