Mesityllithium1,2

(1; R1 = R2 = Me)

[5806-59-7]  · C9H11Li  · Mesityllithium  · (MW 126.14) (2; R1 = R2 = i-Pr)

[74226-59-8]  · C15H23Li  · 2,4,6-Triisopropylphenyllithium  · (MW 210.32) (3; R1 = R2 = t-Bu)

[35383-91-6]  · C18H29Li  · 2,4,6-Tri-t-butylphenyllithium  · (MW 252.41) (4; R1 = R2 = t-BuCH2)

[76804-36-9]  · C21H35Li  · 2,4,6-Trineopentylphenyllithium  · (MW 294.50) (5; R1 = R2 = CF3)

[444-40-6]  · C9H2F9Li  · 2,4,6-Tris(trifluoromethyl)phenyllithium  · (MW 288.05) (6; R1 = R2 = (SiMe3)2CH)

[125444-10-2]  · C27H59LiSi6  · 2,4,6-Tris[bis(trimethylsilyl)methyl]phenyllithium  · (MW 559.34) (7; R1 = Me, R2 = t-Bu)

[126062-41-7]  · C12H17Li  · 4-t-Butyl-2,6-dimethylphenyllithium  · (MW 168.23) (8; R1 = Et, R2 = t-Bu)

[149266-65-9]  · C14H21Li  · 4-t-Butyl-2,6-diethylphenyllithium  · (MW 196.29) (9; R1 = R2 = Me, .Et2O)

[119088-34-5]  · C13H21LiO  · Mesityllithium  · (MW 200.28) (10; R1 = R2 = i-Pr, .Et2O)

[107742-58-5]  · C19H33LiO  · Mesityllithium  · (MW 284.46) (11; R1 = R2 = t-Bu, .3THF)

[149764-17-0]  · C30H53LiO3  · Mesityllithium  · (MW 468.77) (12; R1 = R2 = Et, .Et2O)

[107742-59-6]  · C16H22LiO  · Mesityllithium  · (MW 237.32) (13; R1 = R2 = Ph, .2Et2O)

[133777-60-3]  · C32H37LiO2  · Mesityllithium  · (MW 460.63)

(used for the generation of other amine-free organolithium compounds; derivatives are also synthetic building blocks for the preparation of compounds containing low-coordinate main Group element functional groups which are otherwise not stable, i.e. steric protection)

Alternate Name: 2,4,6-trimethylphenyllithium.

Preparative Methods: the corresponding bromobenzene derivative is treated with 2 equiv t-Butyllithium3 in THF solution,4,5 a method which leads to a 1:1 mixture of the desired Li derivatives (1)-(8) and Lithium Bromide (no alkyl halide is present under these conditions; eq 1).

According to X-ray structure determinations and molecular weight measurements in solution, the highly hindered organolithium compounds in the series (1)-(13) are monomeric,6,7 i.e. not aggregated as are most other Li derivatives.

Handling, Storage, and Precautions: solutions of (1)-(8) may be kept under Ar or N2 in a refrigerator; normally they are used right away; with (1), (2), and (4), a transmetalation from the nuclear to a benzylic position would lead to thermodynamically more stable Li compounds (such rearrangements8 are catalyzed by tertiary amines, for instance N,N,N,N-Tetramethylethylenediamine).

Use of o,o-Disubstituted Compounds as Bases.

Two examples are shown in eqs 2 and 3.3,4 The 1:1 acylation of Li enolates shown in the first reaction gives best yields of diketones such as (14) at -75 °C when the enolate solutions are amine-free (see Methyl 4-Nitrobutanoate and Methyl 3-Nitropropanoate). The enolate formation from benzyl methyl ketone produces the thermodynamically less stable isomer (15) preferentially over the more stable one (16).4,9

Preparation of Low-Coordinate Main Group Element Derivatives.

Due to the steric hindrance, especially in the 2,4,6-tri-t-butyl aryl compounds (3) and (11), called supermesityllithium, it is possible to prepare derivatives of types of compounds which are otherwise not stable because they would be too reactive to be isolated. Three examples are the selenoaldehyde (17),10 the dibora-allene anion derivative (18),11 and the diphosphene (19).12 A literature search reveals that this technique of steric protection was used all over the Periodic Table, including transition metals (consider also the principle of sterically protected but electronically effective functional groups,13 and compare also the stabilization of tetrahedrane by t-butyl substitution14).

Related Reagents.

Lithium Diisopropylamide; Lithium 2,2,6,6-Tetramethylpiperidide; Phenyllithium.


1. Brandsma, L.; Verkruijsse, H. Preparative Polar Organometallic Chemistry; Springer: Berlin, 1987; vol 1.
2. Wakefield, B. J. Organolithium Methods; Academic: London, 1988.
3. (a) Seebach, D.; Neumann, H. CB 1974, 107, 847 (CA 1974, 80, 145 527p). (b) Neumann, H.; Seebach, D. TL 1976, 4839. (c) Neumann, H.; Seebach, D. CB 1978, 111, 2785 (CA 1978, 89, 162 560x).
4. (a) Beck, A. K.; Hoekstra, M. S.; Seebach, D. TL 1977, 1187. (b) Seebach, D.; Weller, T.; Protschuk, G.; Beck, A. K.; Hoekstra, M. S. HCA 1981, 64, 716 (CA 1981, 95, 186 681n).
5. Yoshifuji, M.; Nakamura, T.; Inamoto, N. TL 1987, 28, 6325.
6. Maetzke, T.; Seebach, D. HCA 1989, 72, 624 (CA 1990, 112, 55 649e).
7. (a) Olmstead, M. M.; Power, P. P. JOM 1991, 408, 1. (b) Girolami, G. S.; Riehl, M. E.; Suslick, K. S.; Wilson, S. R. OM 1992, 11, 3907. (c) Ruhlandt-Senge, K.; Ellison, J. J.; Wehmschulte, R. J.; Pauer, F.; Power, P. P. JACS 1993, 115, 11353.
8. See for instance: Meyer, N.; Seebach, D. CB 1980, 113, 1304 (CA 1980, 93, 71 166q).
9. Another method of obtaining thermodynamically less stable Li enolates is the trapping of in situ generated ketenes by RLi: (a) Häner, R.; Laube, T.; Seebach, D. JACS 1985, 107, 5396. (b) Seebach, D.; Amstutz, R.; Laube, T.; Schweizer, W. B.; Dunitz, J. D. JACS 1985, 107, 5403.
10. (a) Okazaki, R.; Ishii, A.; Inamoto, N. CC 1986, 71. (b) Ishii, A.; Okazaki, R.; Inamoto, N. BCJ 1986, 59, 2529. (c) Ishii, A.; Okazaki, R.; Inamoto, N. BCJ 1987, 60, 1037.
11. Hunold, R.; Allwohn, J.; Baum, G.; Massa, W.; Berndt, A. AG(E) 1988, 27, 961.
12. Yoshifuji, M.; Shima, I.; Inamoto, N. JACS 1981, 103, 4587.
13. (a) Schlecker, R.; Seebach, D.; Lubosch, W. HCA 1978, 61, 512 (CA 1978, 89, 59 583h). (b) Seebach, D.; Hassel, T. AG(E) 1978, 17, 274. (c) Hassel, T.; Seebach, D. AG(E) 1979, 18, 399. (d) Seebach, D.; Locher, R. AG(E) 1979, 18, 957. (e) Seebach, D.; Ertas, M.; Locher, R.; Schweizer, W. B. HCA 1985, 68, 264 (CA 1985, 103, 123 099s). (f) Seebach, D.; Häner, R.; Vettiger, T. HCA 1987, 70, 1507 (CA 1988, 108, 150 938z). (g) Vettiger, T.; Seebach, D. LA 1990, 195 (CA 1990, 112, 139 774e). (h) Suzuki, K.; Seebach, D. LA 1992, 51. (i) Seebach, D.; Pfammatter, E.; Gramlich, V.; Bremi, T.; Kühnle, F.; Portmann, S.; Tironi, I. LA 1992, 1145.
14. Maier, G. AG(E) 1988, 27, 309.

Albert K. Beck, Robert Dahinden & Dieter Seebach

Eidgenössische Technische Hochschule, Zürich, Switzerland



Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.