Methyllithium and related compounds

Molecular structure of (a) methyllithium tetramer (Li4Me4) (H atoms have been omitted) and (b) vinyllithium-THF tetramer (LiHC=CH2-THF)4 (THF ligands have been omitted). 

Methyllithium, the simplest organolithium compound, is tetrameric. The Li4(CH3)4 molecule with T symmetry may be described as a tetrahedral array of four Li atoms with a methyl C atom located above each face of the tetrahedron, as shown in Fig. 12.3.1(a). The bond lengths areLi-Li 268 pm andLi-C 231 pm, and the bond angle Li-C-Li is 68.3°. 

Vinyllithium, LiHC=CH2, has a similar tetrameric structure in the crystalline state with a THF ligand attached to each lithium atom [Fig. 12.3.1(b)], In THF solution vinyllithium is tetrameric as well. The internuclear Li-H distances are in agreement with those calculated from the two-dimensional NMR 6Li, XH HOSEY spectra. 

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