Cobalt(II) Chloride

CoCl2

[7646-79-9]  · Cl2Co  · Cobalt(II) Chloride  · (MW 129.84)

(catalyst for functional group transformations,1-13 C-C bond formations,8,12,14-17 oxidations and reductions,18-27 carbonylations28,29)

Physical Data: mp 86 °C; loses 6H2O at 110 °C; d 3.356 g cm-3.

Solubility: sol alcohol, acetone, ether, cold and hot water.

Form Supplied in: hexahydrate as orange-pink crystals; widely available.

Analysis of Reagent Purity: with alkali, the pink hexaaquacobalt(II) chloride gives a pale blue precipitate of the hydroxide. With excess ammonia this precipitate dissolves and slowly gives a brown solution through oxidation. At room temperature, the orange-pink hexahydrate crystallizes from aq solutions. Anhydrous cobalt chloride is blue in color. It can be prepared by dehydration of the hexahydrate either at 150-160 °C in vacuo or by treatment with thionyl chloride followed by evaporation of the solution and further drying under vacuum at 150 °C for 1 h.

Handling, Storage, and Precautions: anhydrous cobalt chloride should be handled under a N2 atmosphere for strict anhydrous conditions. It should be stored in the absence of moisture, in bottles flushed with N2 in a desiccator for a reasonable period of time. It is toxic and is an irritant. This reagent should be handled in a fume hood.

Introduction.

Cobalt chloride is a useful reagent on its own or in combination with other reagents. Several interesting transformations utilizing cobalt chloride have been reported in recent years.

Functional Group Transformations.

Anhydrous CoCl2 in dry acetonitrile catalyzes several interesting transformations such as cleavage of ethers by acyl chlorides to give esters,1 acylation of alcohols and amines by anhydrides,2 regioselective cleavage of oxiranes with Chlorotrimethylsilane,3 acyl chlorides (eq 1),4 anilines,5 and benzenethiols.6 It also catalyzes addition reactions of alcohols with vinyl ethers to give mixed acetals,7 and the reaction of trimethylsilyl cyanides and acetals or orthoesters to give a-cyano derivatives.8

CoCl2 is also useful for dealkylation of tertiary amines,9 in the synthesis of acid anhydrides from acid chlorides,10 and for thionation of carbonyl compounds in the presence of Bis(trimethylsilyl) Sulfide, providing a simple access to thioketones and thioaldehydes.11

Cobalt hydrides, generated from CoCl2-Sodium Borohydride-Triphenylphosphine in a 1:1:4 ratio, hydrodimerize terminal alkynes to the corresponding trans,trans-1,3-dienes (eq 2).12 This reagent system is also useful for selective isomerization of certain alkenes.13

Carbon-Carbon Bond Forming Reactions.

A catalytic amount of anhydrous CoCl2 in dry acetonitrile is a very useful reagent for condensation reactions involving active methylene compounds (eqs 3 and 4).14-16

Anhydrous CoCl2 also catalyzes the asymmetric cyclopropanation of fumarates with Dibromomethane.17

Oxidations.

Anhydrous CoCl2 catalyzes the oxidation of a variety of aromatic and aliphatic aldehydes to carboxylic acids in the presence of molecular Oxygen and Acetic Anhydride at room temperature.18 The CoCl2/O2 system in 1,2-dimethoxyethane gives lactones from ethers,19 and in diglyme it is an effective system for benzylic group oxidation.20

Reductions.

The combination of anhydrous CoCl2 and complex metal hydrides gives useful reagent systems for deoxygenation of allylic alcohols to alkenes,21 hydroboration or hydrogenation of alkenes,22 and reduction of imines to amines23 and organic halides.24 Reduction of b-sulfenylated unsaturated ketones with NaBH4 in the presence of CoCl2 gives saturated ketones.25 Both aliphatic and aromatic sulfoxides are readily deoxygenated with CoCl2.6H2O/NaBH4/EtOH under a nitrogen atmosphere.26 The same recipe is also useful for the selective reduction of certain disubstituted alkenes (eq 5).27

Carbonylations.

Reduction of anhydrous CoCl2 by NaBH4 in THF under a Carbon Monoxide atmosphere followed by aqueous NaOH treatment gives Sodium Tetracarbonylcobaltate, which is useful for in situ carbonylations of benzyl halides.22b Reduction of anhydrous CoCl2 with Zinc in THF in the presence of alkynes while bubbling CO gives alkyne-Co2(CO)6 complexes (eq 6) which are useful synthetic intermediates28 (e.g. Pauson-Khand cyclopentenone synthesis).

The CoCl2.6H2O reagent, under phase transfer conditions, gives reductive hydroxycarbonylations of gem-dibromocyclopropanes.29

Related Reagents.

Lithium Aluminum Hydride-Cobalt(II) Chloride; Octacarbonyldicobalt; Sodium Tetracarbonylcobaltate.


1. Ahmad, S.; Iqbal, J. CL 1987, 953.
2. Ahmad, S.; Iqbal, J. CC 1987, 114.
3. Iqbal, J.; Khan, M. A. CL 1988, 1157.
4. Iqbal, J.; Khan, M. A. Srivastava, R. R. TL 1988, 29, 4985.
5. Iqbal, J.; Pandey, A. TL 1990, 31, 575.
6. Iqbal, J.; Pandey, A. Shukla, A.; Srivastava, R. R.; Tripathi, S. T 1990, 46, 6423.
7. Iqbal, J.; Srivastava, R. R.; Gupta, K. B.; Khan, M. A. SC 1989, 19, 901.
8. Mukaiyama, T.; Soga, T.; Takenoshita, H. CL 1989, 997.
9. Kai, B. T.; Arcelli, A. JOM 1983, 252, C9.
10. Srivastava, R. R.; Kabalka, G. W. TL 1992, 33, 593.
11. Ricci, A.; Degl'innocenti, A.; Capperucci, A.; Reginato, G. JOC 1989, 54, 19.
12. Satyanarayana, N.; Periasamy, M. TL 1986, 27, 6253.
13. Satyanarayana, N.; Periasamy, M. JOM 1987, 319, 113.
14. Marquet, J.; Moreno-Mañas, M. CL 1981, 173.
15. Iqbal, J.; Srivastava, R. R. TL 1991, 32, 1663.
16. Iqbal, J.; Srivastava, R. R.; Khan, M. A. TL 1990, 31, 1485.
17. Matsuda, H.; Kanai, H. CL 1981, 395.
18. Bhatia, B.; Iqbal, J. TL 1992, 33, 7961.
19. Pei, L.; Alper, H. J. Mol. Catal. 1992, 72, 143.
20. Pei, L.; Alper, H. J. Mol. Catal. 1990, 61, 51.
21. Lee, J.-T.; Alper, H. TL 1990, 31, 4101.
22. (a) Satyanarayana, N.; Periasamy, M. TL 1984, 25, 2501. (b) Satyanarayana, N.; Periasamy, M. JOM 1987, 333, C33.
23. Periasamy, M.; Devasagayaraj, A.; Satyanarayana, N.; Narayana, C. SC 1989, 19, 565.
24. (a) Ashby, E. C.; Lin, J. J. TL 1977, 4481. (b) Ashby, E. C.; Lin, J. J. JOC 1978, 43, 1263.
25. Nishio, T.; Omote, Y. CL 1979, 1223.
26. Chung, S. K.; Han, G. SC 1982, 12, 903.
27. Chung, S.-K. JOC 1979, 44, 1014.
28. Devasagayaraj, A.; Periasamy, M. TL 1989, 30, 595.
29. Grushin, V. V.; Alper, H. TL 1991, 32, 3349.

Mariappan Periasamy & Maddali L. N. Rao

University of Hyderabad, India



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