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

The first three periodic groups
pulses may be required (in FT n.m.r.) to obtain a reasonable signal. even with
broad-band proton decoupling. The quadrupolar relaxation rate decreases with
increasing temperature. At low temperatures therefore, relaxation is relatively
fast, so that sharp resonance signals are observed, but with loss of 11 B- 13 C
coupling. As the tempera ture is raised, broadening occurs, followed by resolution
into a 1:1:1:1 quartet from which the 11 B- 13 C coupling constant can be
measured.
3.9 Organometallic compounds of aluminium, gallium,
indium and thallium
3.9.1 Alkylaluminium compounds
Alkylaluminium compounds are produced on a very large scale industrially. This
is somewhat remarkable considering their extreme susceptibility to oxidation and
hydrolysis, which makes handling hazardous. In 19 7 5 about 20 000 tonnes
were produced worldwide for sale and a further 90 000 tonnes were used
as intermediates in the manufacture of linear alcohols and 1-alkenes. Their
preparation depends on 'hydroalumination', or the addition of Al-H to an
alkene. The key to the success of this method, which is much more suitable to
industrial than to laboratory use, is the production of metal with an active
surface. One way of achieving this is ball-milling the powder in contact with the
metal alkyl.
The two main discoveries, both due to K. Ziegler, were first that Al-H
bonds add to olefins, particularly in the absence of ethers and other bases, and
second, that although aluminium metal does not form AlH 3 by direct reaction
with hydrogen, it does take up hydrogen in the presence of aluminium alkyl.
With reactive alkenes such as ethene, the process is usually carried out in two
stages, using preformed trialkylaluminium.
1 50°C C H
2Al + 3H 2 + Et,Al ------+ 6Et 2 AIH ____2___4 Et,Al
With less reactive, bulky alkenes such as 2-methyl-1-propene, a single step
suffices.
110-160 c
/0°C
2Al + 3H 2 + 6Me 2 C=CH 2 -----> 2(Me 2 CHCH 2 ),Al
50-200atm
Some reactions of organoaluminium compounds are summarized in Fig. 3.18. By
far the most important from a commercial standpoint are (1), the insertion of
alkene into an aluminium-carbon bond
and (2) transalkylation, the displacement of one alkene by another.
80
::.:::: AICH 2 CH 2 R + H 2 C=CHR' ----> :::::AICH 2 CH 2 R' + RCH=CH 2