(Trimethylsilyl)methyllithium explained
(Trimethylsilyl)methyllithium is classified both as an organolithium compound and an organosilicon compound. It has the empirical formula LiCH2Si(CH3)3, often abbreviated LiCH2TMS. It crystallizes as the hexagonal prismatic hexamer [LiCH<sub>2</sub>TMS]6, akin to some polymorphs of methyllithium.[1] Many adducts have been characterized including the diethyl ether complexed cubane [Li<sub>4</sub>(μ<sub>3</sub>-CH<sub>2</sub>TMS)<sub>4</sub>(Et<sub>2</sub>O)<sub>2</sub>][2] and [Li<sub>2</sub>(μ-CH<sub>2</sub>TMS)<sub>2</sub>([[Tetramethylethylenediamine |TMEDA]])2].[3]
Preparation
(Trimethylsilyl)methyllithium, which is commercially available as a THF solution, is usually prepared by treatment of (trimethylsilyl)methyl chloride with butyllithium:[4]
(CH3)3SiCH2Cl + BuLi → (CH3)3SiCH2Li + BuCl
(Trimethylsilyl)methylmagnesium chloride is often functionally equivalent to (trimethylsilyl)methyllithium. It is prepared by the Grignard reaction of (trimethylsilyl)methyl chloride.[5]
Use in methylenations
In one example of the Peterson olefination, (trimethylsilyl)methyllithium reacts with aldehydes and ketones to give the terminal alkene (R1 = Me, R2 & R3 = H):
Metal derivatives
(Trimethylsilyl)methyllithium is widely used in organotransition metal chemistry to affix (trimethylsilyl)methyl ligands. Such complexes are usually produced by salt metathesis involving metal chlorides. These compounds are often highly soluble in nonpolar organic solvents, enjoying stability due to their steric bulk and resistance to beta-hydride elimination. In these regards, (trimethylsilyl)methyl is akin to neopentyl.
Bis(trimethylsilyl)methylmagnesium is used as an alternative to (trimethylsilyl)methyllithium.[6]
Related compounds
- bis(trimethylsilyl)methyllithium[7]
- tris(trimethylsilyl)methyllithium[8]
Notes and References
- 10.1016/0022-328X(86)80537-X. X-ray Crystal Structure of Trimethylsilylmethyllithium. 1986. Tecle'. Berhan. Maqsudur Rahman. A.F.M.. Oliver. John P.. Journal of Organometallic Chemistry. 317. 3. 267–275.
- 10.1039/c002504f. The First Asymmetric Organolithium Tetramers with Simple Ether Donor Bases. 2010. Tatic. Tanja. Meindl. Kathrin. Henn. Julian. Pandey. Sushil Kumar. Stalke. Dietmar. Chemical Communications. 46. 25. 4562–4564. 20502820.
- 10.1002/ejic.200800610. Deaggregation of Trimethylsilylmethyllithium. 2008. Tatic. Tanja. Ott. Holger. Stalke. Dietmar. European Journal of Inorganic Chemistry. 2008. 24. 3765–3768.
- Encyclopedia: 2019 . Trimethylsilylmethyllithium . Encyclopedia of Reagents for Organic Synthesis . 10.1002/047084289X.rt321 . Werth . Jacob . David J. . Age. 978-0471936237 .
- Book: 10.1002/9780470132562.ch15. 1989. Inorganic Syntheses. 2007. Brennan. David J.. Graaskamp. James M.. Dunn. Beverly S.. Allcock. Harry R.. Organosilicon Derivatives of Cyclic and High Polymeric Phosphazenes . 25 . 60–68. 9780470132562.
- Book: Richard A. Andersen, Geoffrey Wilkinson . . Bis[(Trimethylsilyl)Methyl] Magnesium . 10.1002/9780470132500.ch61 . 1979 . 19 . 262–265. 9780470132500 .
- 10.1039/C39840001163. Molecular structures of Bis(trimethylsilyl)methyl-lithium [(LiR), R = CH(SiMe<sub>3</sub>)<sub>2</sub>] in the Vapour (Gas-Phase Electron Diffraction: a Monomer, n= 1) and the Crystal (X-ray: a Polymer, n=∞). Journal of the Chemical Society, Chemical Communications. 1984. 1163–1165. Jerry L. Atwood . Torgny Fjeldberg . Michael F. Lappert . N. Tuyet Luong-Thi . Riz Shakir . Andrew J. Thorne . 17.
- 10.1039/C39830000827. Crystal structure of the Tetrahydrofuran Adduct of Tris(trimethylsilyl)-Methyl-Lithium, [Li(thf)<sub>4</sub>][Li{C(SiMe<sub>3</sub>)<sub>3</sub>}<sub>2</sub>], an Ate Derivative of Lithium. Journal of the Chemical Society, Chemical Communications. Colin Eaborn . Peter B. Hitchcock . J. David Smith . Alice C. Sullivan. 1983. 827–828.
