Mercury(II) Acetate-Sodium Trimethoxyborohydride1

Hg(OAc)2-NaBH(OMe)3
(Hg(OAc)2)

[1600-27-7]  · C4H6HgO4  · Mercury(II) Acetate-Sodium Trimethoxyborohydride  · (MW 318.69) (NaBH(OMe)3)

[16940-17-3]  · C3H10BNa  · Mercury(II) Acetate-Sodium Trimethoxyborohydride  · (MW 170.83)

(organomercury acetates are powerful reagents for radical carbon-carbon bond formation in combination with borohydrides1)

Physical Data: mp 178-180 °C (overheating results in decomposition); d 3.27 g cm-3.

Solubility: sol ethanol, methanol, acetic acid, ethylene glycol, hot water; slightly sol acetone, ethyl acetate, water.

Form Supplied in: white solid; widely available.

Purification: recrystallization from a mixture of hot ethanol, water, and acetic acid (10:10:1).

Handling, Storage, and Precautions: mercury(II) acetate has a slight acetic odor; forms white light-sensitive crystals. Keep well closed and protected from light. Inhalation of mercury(II) acetate dust should be avoided: wearing of protecting gloves for handling this compound is recommended. Extremely toxic. Use in a fume hood.

Reduction of Organomercury Acetates.

Reaction of Mercury(II) Acetate with alkenes, cyclopropanes, ketones, organoboron and metalloorganic compounds leads to organomercury acetates.2 On reduction with Sodium Borohydride or Sodium Trimethoxyborohydride they give organomercury hydrides,3 which are potential precursors for carbon radicals. In the presence of alkenes, crossed-coupled products are formed in a radical chain process. To achieve high yields, electron-poor alkenes like acrylonitrile, vinyl ketones, acrylates, fumarodinitrile, or maleic anhydrides should be used.4 Compared with the tin method, the mercury method has the advantages of mild reaction conditions (20 °C), short reaction times (30-60 min), and easy workup procedures (after filtration of the precipitated mercury, distillation of the residual product).

Alkenes.

Alkenes with an electron-rich terminal double bond can be coupled with electron-poor alkenes in a one pot reaction.5 The reaction proceeds via hydroboration of the alkene, transformation of the boron-carbon into a mercury-carbon bond, and reaction with NaBH4 and alkene. The reaction conditions tolerate substituents like Br, Cl, OH, OAc, OTs, OR, and CO2R. Alkenes with two different substituted double bonds react regioselectively (eq 1).5 An example of the high stereoselectivity of this method is demonstrated in the reaction of b-pinene (eq 2).5

The reaction of mercury salts with electron-rich alkenes yields different b-substituted organomercury acetates via addition of the electrophilic mercury ion to the double bond and subsequent trapping by nucleophilic solvent (water, alcohol, acids).6 The addition reaction follows the Markovnikov rules (eq 3).7

Alkenes with nucleophilic neighboring groups such as alcohols (eq 4), carboxylates (eq 5), amides, amines, and alkenes, lead to cyclic products in the mercuration/reductive coupling sequence.8 The nucleophiles act as intramolecular traps for the mercurated alkenes.

Cyclopropanes.

The ring opening of cyclopropanes proceeds by attack of mercury acetate at the least substituted ring position and ring opening towards the most substituted position. Different functional groups are introduced into the products by varying solvents (see above).9 The acyclic organomercury salt can be coupled with an alkene (eq 6).10

Carbonyl compounds can act as precursors for cyclopropanes. An aldehyde or ketone is converted to its trimethylsilyl enol ether which is then subjected to the Simmons-Smith cyclopropanation reaction (eq 7).11

Ketones.

Ketones can be coupled with electron-poor alkenes via hydrazones.12,13 A large variety of ketones can be used; the bulky t-butyl group is tolerated (eq 8).14 With sterically hindered starting materials or less reactive alkenes, as a side reaction the reduction products are formed.

The reactions of norcamphor derivatives illustrate how an electrophilic carbon of a carbonyl group can be coupled with electron-poor alkenes (umpolung) (eq 9).15


1. (a) Giese, B. Radicals in Organic Synthesis: Formation of Carbon-Carbon Bonds; Pergamon: Oxford, 1986. (b) Barluenga, J., Yus, M. CRV 1988, 88, 487. (c) Regitz, M.; Giese, B. MOC 1989, E19a.
2. (a) MOC 1974, 13/2b. (b) Larock, R. C. Organomercury Compounds in Organic Synthesis; Springer: Berlin, 1985.
3. Russell, G. A.; Guo, D. TL 1984, 25, 5239.
4. (a) Giese, B. AG(E) 1985, 24, 553. (b) Giese, B.; Kretzschmar, G. CB 1982, 115, 2012.
5. Giese, B.; Kretzschmar, G. AG(E) 1981, 20, 965.
6. (a) Giese, B.; Heuck, K. CB 1979, 112, 3759. (b) Giese, B.; Heuck, K. TL 1980, 21, 1829. (c) Giese, B.; Lüning, U. S 1982, 735.
7. Kozikowski, A. P.; Nieduzak, T. R.; Scripko, J. OM 1982, 1, 675.
8. (a) Giese, B.; Heuck, K. CB 1981, 114, 1572. (b) Danishefsky, S.; Taniyama, E.; Webb, R. R. TL 1983, 24, 11. (c) Stevens, R. V.; Albizati, K. F. JOC 1985, 50, 632.
9. Giese, B.; Zwick, W. CB 1983, 116, 1264.
10. Giese, B.; Zwick, W. CB 1982, 115, 2526.
11. (a) Giese, B.; Horler, H.; Zwick, W. TL 1982, 23, 931. (b) Giese, B.; Horler, H. T 1985, 41, 4025.
12. Nesmeyanov, A. N.; Reutov, O. A.; Loseva, A. S.; Khorlina, M. Y. IZV 1959, 50 (CA 1959, 53, 14 965).
13. Giese, B.; Erfort, U. AG(E) 1982, 21, 130.
14. Giese, B.; Erfort, U. CB 1983, 116, 1240.
15. Giese, B.; Engelbrecht, R.; Erfort, U. CB 1985, 118, 1289.

Bernd Giese & Joachim Dickhaut

University of Basel, Switzerland



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