(Trimethylsilyl)methyllithium

(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 [LiCH2TMS]6, akin to some polymorphs of methyllithium. Many adducts have been characterized including the diethyl ether complexed cubane [Li4(μ3-CH2TMS)4(Et2O)2] and [Li2(μ-CH2TMS)2(TMEDA)2].

Preparation
(Trimethylsilyl)methyllithium, which is commercially available as a THF solution, is usually prepared by treatment of (trimethylsilyl)methyl chloride with butyllithium:
 * (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.

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):
 * Petersen Olefination Scheme V.1.png

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.

Related compounds

 * bis(trimethylsilyl)methyllithium
 * tris(trimethylsilyl)methyllithium