Methyl lithium
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Methyl lithium is an s-block organometallic compound. It has a polymeric structure in solution and in the solid state. Two aggregates exist:
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[edit] Tetrahedron of lithium atoms
This cluster has a distorted cube structure.
Colour code: Li- blue C- black H- white
[edit] Octahedron of lithium atoms
This cluster has a distorted hexagonal prism with Li and C atoms at alternate corners.
Colour code: Li- blue C- black H- white
These structures have been determined by 6Li, 7Li and 13C NMR spectroscopy.
The degree of aggregation depends upon the solvent. A hydrocarbon solvent will favour formation of the hexamer whereas methyl lithium dissolved in an ether will adopt the tetramer form.
These clusters are electron deficent, that is, there is not enough electrons for two per bond. The hexamer is a 30 electron compound (30 valence electrons.) The C-H bonding takes 18 electrons from the cluster, leaving 12 electrons to hold the structure together. There are six electrons for six metal-metal bonds and one electron per methyl-eta3 lithium interaction.
[edit] Synthetic route
Direct synthesis: Treatment of an organic halide with lithium.
2Li + MeBr ---> LiMe + LiBr The solvent must be dry to prevent the product hydrolysing.
[edit] Reactivity
Methyl lithium is strongly basic and nucleophilic due to the partially negative carbon and is therefore particularly reactive towards electron donors. For example, ferrocene can be metallated by treatment with methyl lithium
