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

The first three periodic groups
conductance is low. Magnesium migrates both to cathode and anode. Ion
association must be important in solvents of low dielectric constant such as
diethyl ether.
3. 5 Beryllium
Much of the development cf organoberyllium chemistry is due to Coates. The
dialkyls are normally prepared from beryllium chloride and the Grignard reagent.
After removal ofmost ofthe magnesium halide, dialkyls (ethyl to the butyls) are
distilled under reduced pressure as etherates. Ether can be removed only by
prolonged boiling under vacuum. Me 2 Be is purified by repeated sublimation at
low pressure. Small quantities of product free from ether can be made from
beryllium and Me 2 Hg. This method was applied to the preparation of (CDJ 2 Be for
spectroscopic measurements. The slow exchange of alkyl groups between
triarylboranes and diethylberyllium over a period of days at room temperature
has been used to make beryllium diaryls.
2Ph,B + 3Et,Be ------+ 2Et 3 B + 3Ph 2 Be
Pyrolysis of dialkyls which possess /3-hydrogen atoms proceeds mainly by loss of
alkene. This provides a route to the polymeric beryllium hydride itself or to
alkylberyllium hydrides. At higher temperatures Bu~Be decomposes to the metal.
It is possible to plate thin layers of beryllium on to surfaces at 280-300°C
in vacuo.
~ .
(Me 3 C) 2 Be------+ BeH 2 (90-98% punty) + Me 2 C=CH 2
200"
~ l
(Me 2 CHCH 2 ) 2Be ------+ -[Me 2 CHCH 2 BeHJn + Me 2 C=CH 2
200° n
Alkylberyllium hydrides are oligomeric in benzene. They add rapidly to
terminal alkenes (cf boron, p. 66).
Alkylberyllium hydrides can also be obtained in ether by the reaction,
LiH
RBeBr --­
-LiCL
cis
54
t:.H=13 kJ moC 1
t:.S=54 J K-1 moL1