Dibutylmagnesium

[3988-32-8]  · C8H18Mg (mainly)  · Dibutylmagnesium  · (MW 145 (av))

(magnesiating agent of various activated C-H bonds1 and protic functional groups; can be halogenated to make finely divided anhydrous magnesium chloride or bromide)

Alternate Name: DBM.

Physical Data: waxy solid; for 1 M heptane solution, d 0.72 g cm-3, viscosity 0.91 cP at 25 °C and 0.76 cP at 35 °C.

Solubility: moderately sol (<1.3 M) aliphatic and aromatic hydrocarbons; highly sol ethereal solvents; reacts exothermically with water and protic solvents.

Form Supplied in: available as 0.7-1 M solution in heptane.2

Analysis of Reagent Purity: determined by total alkalinity and magnesium content using standardized EDTA. Will react with oxygen to form soluble alkoxides which could lead to incorrect assay.

Preparative Method: via a two-step process (eq 1).3,4

Handling, Storage, and Precautions: commercial solution is stable indefinitely if kept cool and sealed under inert atmosphere; however, isolated solids are pyrophoric. Main hazard is possibility of solvent ignition due to exothermic reaction between dibutylmagnesium and water in any form (including moist air).

Introduction.

Dibutylmagnesium is a stable and Lewis base-free organomagnesium composition. Hydrocarbon solubility of DBM results from the 1:1 ratio of n-alkyl to s-butyl groups. In synthesis, DBM is used as a metalating or magnesiating agent. Care must be taken to ensure that both equivalents of alkyl groups react because the second equivalent reacts more slowly than the first.

Magnesiation of Hydrocarbyl Substrates.

Cyclopentadiene (eq 2) and phenylacetylene (eq 3) are metalated with DBM.1 Magnesiated substrates of cyclopentadiene undergo metathesis with transition metal halides.5 Although sulfones1 and a-picoline6 derivatives can be magnesiated in heptane, toluene and triphenylmethane cannot.1

Magnesiation of More Acidic Substrates.

Carboxylic acids,7 alcohols,5,8 and amines5,9 can be deprotonated with DBM. Metalation of b-branched secondary amines, such as Diisopropylamine and 2,2,6,6-Tetramethylpiperidine, produce magnesium bis-organoamides which are hydrocarbon soluble.9 Several magnesium organoamides have been used for magnesiation, reduction,10 and amidation.11

Finally, DBM has many uses in polymerization, e.g. it provides a source of magnesium chloride12 for Ziegler-Natta catalysts. For synthesis, anhydrous and Lewis base-free magnesium bromide is easily prepared at 30-45 °C by controlled, sparged addition of anhydrous HBr (2.01 mol) to 0.5 M DBM in heptane (2.0 mol). When the resulting slurry becomes acidic, excess HBr is removed by reflux with proper scrubbing. The solids are isolated, washed with pentane, and dried by an inert gas using an enclosed filter.

Related Reagents.

Bromomagnesium Diisopropylamide; t-Butylmagnesium Chloride; Bromomagnesium Diethylamide; Ethylmagnesium Bromide; Isopropylmagnesium Bromide; Methylmagnesium N-Cyclohexylisopropylamide.


1. Eisch, J. J.; Sanchez, R. JOM 1985, 296, C27.
2. FMC Lithium Division, 449 N. Cox Road, Gastonia, NC 28054, USA.
3. Bryce-Smith, D.; Blues, E. T. OSC 1973, 5, 1141.
4. Kamienski, C. W.; McElroy, B. J.; Bach, R. O. (FMC Lithium Division) US. Patent 4 069 267, 1987.
5. Duff, A. W.; Hitchcock, P. B.; Lappert, M. F.; Taylor, R. G.; Segal, J. A. JOM 1985, 293, 271.
6. Henderson, M. J.; Papasergio, R. I.; Raston, C. L.; White, A. H.; Lappert, M. F. CC 1986, 672.
7. Williams, M. A.; Miller, M. J.; Rath, N. P. JOC 1991, 56, 1293.
8. Kamienski, C. W. (FMC Lithium Division) U.S. Patent 4 748 283 1988; Kamienski, C. W.; Wedinger, R. S. (FMC Lithium Division) U.S. Patent Appl. USSN 252 421, 1988.
9. Mehta, V. C.; Rathman, T. L.; Sanchez, R.; Morrison, R. C. (FMC Lithium Division) U.S. Patent 4 944 894, 1990.
10. (a) Sanchez, R.; Scott, W. TL 1988, 29, 139. (b) Sanchez, R.; Vest, G.; Scott, W.; Engel, P. S. JOC 1989, 54, 4026.
11. Sanchez, R.; Vest, G.; Despres, L. SC 1989, 19, 2909.
12. Knight, G. W.; Lowery, K., Jr.; May, J. A., Jr. (Dow Chemical Co.) U.S. Patent 4 250 288, 1981 (CA 1981, 94 157 570).

Terry L. Rathman

FMC Corporation Lithium Division, Bessemer City, NC, USA



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