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

Bis( arene )complexes
tendency is much more pronounced than in ferrocene. Cr(C 6 H 6 ) 2 is very air
sensitive, while the salts (C 6H 6 ) 2 Cr+x~ are air-stable. Consequently
bis(benzene )chromium does not undergo electrophilic substitution at the arene
rings but becomes oxidized instead.
The arene ligands are displaced only with difficulty; CO or PF 3 yield Cr(C0) 6 or
Cr(PF 3 ) 6 respectively at 200°C/300atm. pressure. Bis(naphthalene)chromium,
made by metal atom synthesis, is much more labile. Two naphthalene ligands are
readily displaced by 6RNC or 3bipy, and one by 3CO, 3PF 3 or 3PR 3 .
Metallation ofthe rings in Cr(C 6 H 6 ) 2 can be achieved using n-pentylsodium or
the n-butyllithium.TMEDA complex. The resulting derivatives react with carbon
dioxide or with aldehydes or ketones. It is difficult, however, to control the
number of metal atoms which enter, so that mixtures of products are formed.
10.1.5 Chemistry of bis(benzene)molybdenum
Bis(benzene)molybdenum, in contrast to the chromium analogue, shows a very
rich and varied chemistry. It has a very low molecular ionization energy in the
H2 C=CHCH2 CL
20°C
HBF,\r
+
[ MoH (C6 H6 )(PR3 l 3]
~
~M~
v(Mo-H) 1915 cm-1
b(Mo-H)-2ppm
Fig. 10.3 Some reactions of bis(benzene)molybdenum.
315