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

Organocopper and -silver compounds
those of zinc, mercury or tin, but except in rather special cases (e.g. allylzinc
bromides + allyl halides), they are insufficiently reactive for coupling to occur.
Such coupling, however, is catalysed by nickel and palladium complexes (p. 22 7).
Organocopper reagents add in a 1,4-fashţon to a/3-unsaturated ketones. This
contrasts with' the behaviour of organolithiums, for which 1, 2-addition predominates
and of Grignard reagents, which are rather unpredictable (p. 46 ). Such
additions have proved valuable in the syntl,lesis, for example, of terpene and
steroid derivatives. They can be used to introduce interannular substituents.
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3.10.2 Complexes of copper(I) and silver(I) with alkenes and arenes
Copper(I) and silver(I) compounds form adducts with alkenes both in the solid
state and in solution. With simple monoalkenes these are rather unstable, the
bonding being much weaker than that present in palladium and platinum
complexes (p. 19 6 ). Ethene and AgBF 4 are said to form four solid complexes of
compositions 3:1,2:1, 3:2 and 1:1 C 2 H 4 :AgBF 4 • Solid silver nitrate takes up
ethene forming C 2 H 2 .2AgNO~ as white needles which decompose above - 30°C.
Stability constants for complex formation in many of these systems have been
obtained by, for example, measuring the distribution of alkene between an
organic solvent such as carbon tetrachloride and aqueous silver nitrate.
The ability of aqueous copper(I) solutions to absorb alkenes and alkynes is used
industrially. In the steam cracking of naphtha into alkenes, which is carried out
at 770°Cjl atm, the main product is ethene. Propene and lesser amounts of
alkynes, 1, 3-butadiene and butenes are also produced. A chilled aqueous
ammoniacal copper(I) acetate solution is used as the absorber. The more
unsaturated the hydrocarbon, the more stable is the complex. In the first stage the
alkynes combine with copper, the complex is withdrawn and the alkynes
liberated by heating. The copper solution is then recycled ata lower tempera ture
to remove the 1, 3-butadiene, allowing butanes and butenes to pass on. The 1. 3-
butadiene is freed by heating the solution of complex in a desorber and is finally
fractionated.
Gas chromatographic columns in which the stationary phase consists of silver
nitrate dissolved in a polyethylene glycol are useful for separating alkenes. These
are specifically retarded with respect to alkanes of the same carbon number.
The bonding of alkenes to copper and silver probably resembles that found in
palladium or platinum complexes. The interactions are much weaker, probably
on account ofthe filled d 10 configuration ofthe former elements which lowers the
participation of d-orbitals.
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