_P.-Powell-auth.-Principles-of-Organometallic-Chemistry-Springer-Netherlands-1988

Akali-metal derivatives
Me
""'"- ~
•·-o( )0-M·
~ ~oEt 2
Cu····Cu 2.42 A
o
Me
(a) (b)
Fig. 3.5 (a) Structure of [Cu(CH,SiMe,)J.. (b) Proposed structure of LiM(C 6 H,Me), in
ether (M =Cu. Ag. Au).
methyl groups and not through carbon (cf. transition metals, 'agostic hydrogen',
p. 22 3 ). Both dibridged and tribridged configurations are present.
Much less is known about the structures of the alkyls of heavier alkali metals.
That of methylsodium is based on (MeNa) 4 tetramers. MeM(M=K. Rb, Cs),
however, possess ionic nickel arsenide structures with isolated methyl anions.
Copper, silver and gold form unstable organo derivatives which show some
relation to those of the compounds discussed above. MeCu decomposes above
-l5°C and MeAg even at -50°C. The compounds [Cu(CH 2 SiMe 3 )] 4 , m.p.
78-9oC and (CuPh)" (decomp. 100') are more robust; the structure ofthe former
has been determined by X-ray diffraction and consists of four coplanar copper
atoms bridged by CH 2 SiMe, groups. Phenyl copper probably bas bridging phenyl
groups. Alkyl or aryl-bridged tetramers are thought to be present in solutions of
Li 2 Cu 2 R 4 (p. 88).
3.3 Alkali-metal derivatives
3.3.1 Preparation of organolithium compounds
The lithium alkyls are extremely reactive. They are very sensitive to oxygen and
moisture. Dry apparatus and dry solvents must be used and air must be excluded
by working under an atmosphere of dry oxygen-free nitrogen or argon. The
following methods of preparation are available.
(a) LITHIUM METAL AND ALKYL HAL!DE. The most direct method of obtaining
a solution of an organolithium reagent is reaction of lithium metal with an
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