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

Complexes of arenes
- BH 3
~j
Cr
(C0) 3
- ~'',oH
Cr
(C0) 3
10.3 Chemistry of some arene complexes of iron
Salts of bis( arene )iron cations can be prepared by a rather remarkable reaction in
which anhydrous iron(II) chloride, aluminium(III) chloride and the arene are
heated under reflux in cyclohexane
FeCI 2 + 2AICI 3 + 2arene -----> Fe(arene); +AICI_;
The tetrachloroaluminate is then converted into the more tractable hexafluorophosphate
by treatment with aqueous NH 4 PF 6 • The dications are susceptible
to attack by nucleophiles including cyanide and various carbanions, which add
exo to one of the rings.
Nu
Nu
H
H
Fe
H
Nu
Alkyl or aryllithium reagents can add either to o ne ring or to both, depending on
the ratio of reactants. The addition of aryllithium followed by oxidation of the
bis(cyclohexadienyl)iron adduct provides a route to unsymmetrical biphenyls.
When ferrocene is heated with an arene in the presence of aluminium and
aluminium(III)chloride, arene(cyclopentadienyl)iron cations are produced together
with 'ferrocenophane' biproducts. Following hydrolysis of the reaction
mixture the cations are precipitated as hexafluorophosphates, leaving the
320