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

Alkali-metal derivatives
addition of butadiene and styrene monomers. Furthermore lithium alkyls afford
linear polymers, whereas the materials produced via free radical initiation are
highly branched. (see Table 3.4).
3.3.3 Organosodium and potassium compounds
The organic group in these compounds has considerable carbanionic character.
In general, paraffin hydrocarbons are the only sui table reaction media. Ethers are
cleaved and aromatic hydrocarbons metallated. To prepare small quantities of
organosodium or potassium compounds, the mercury alkyl method can be used.
petroleum
R,Hg + 2Na(excess) _ ___:___ __ ____. 2RNal + Na. Hg (amalgam)
Exchange between sodium or potassium tert-butoxide and organolithium in
paraffins is preferable. as the lithium alkoxide remains in solution.
RLi + Bu 1 0Na----> RNal + Li0Bu 1 (soluble)
Direct reaction between sodium or potassium and alkyl and aryl halides is
complicated by exchange and coupling reactions, which can lead to mixtures of
products. These complications can be reduced by rapid stirring and the use of
finely divided metal or amalgams. Phenylsodium can be made in this way: PhCI
+ Na--+ PhNa + NaCI. Acidic hydrocarbons react with alkali metals in ether
solvents. Cyclopentadiene, for example, affords sodium cyclopentadienide in
tetrahydrofuran (p. 279). Triphenylmethylpotassium is obtained as a deep red
solution from triphenylmethane and potassium in 1, 2-dimethoxyethane. These
carbanions, in which the negative charge is delocalized over severa! carbon
atoms, do not attack ethers, in contrast to the simple alkyl or aryl carbanions
present in methylsodium or phenylpotassium.
3C,H 6 + 2Na ----> 2C,H,- Na' + C,H.
Ph ,CH + K ----> Ph,C K.,. + iH,
Caesium reacts directly with toluene and even with alkanes.
(a) HYDROCARBON ANIONS. Aromatic hydrocarbons containing two or more
benzene rings joined (biphenyl. terphenyls ). conjugated ( 1, 4-diphenylbutadiene)
or fused (naphthalene, anthracene, phenanthrene) react with alkali metals
without loss or transfer of hydrogen. The formation of these addition compounds
is facilitated by donor solvents such as tetrahydrofuran or 1, 2-dimethoxyethene.
The products are highly coloured; their formation is accompanied by the transfer
of one or more electrons from the alkali metal to the lowest unoccupied molecular
orbita! (LUMO) of the hydrocarbon.
Solutions of sodium naphthalene in tetrahydrofuran are dark green. electrically
conducting because the compound consists of ions Na(THF)" + (C, 0 H,)- · and
paramagnetic because ofthe unpaired electron in a singly occupied n-orbital. The
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