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

Complexes of arenes
(Q)-R
Cr cr­
(C0)3
R = CMe 2 CN, CH 2 CN, CH 2 C0 2 Bu 1
Very strong nucleophiles such as phenyllithium, however, attack a carbonyl
ligand to form carbene complexes, as described on p. 2 34.
10.2.2 Other reactions
Coordination of an arene to Cr(C0) 3 has further consequences which are valuable
in synthesis. On account of its electron withdrawing nature the acidity of both
ring (Hr) and side chain (Ha, HP) hydrogens is enhanced relative to the free arene.
(C 6 H 6 )Cr(C0)3' for example, is metallated by n-butyllithium in THF at -40°C,
whereas benzene itself is not under similar conditions. The stabilization of side
chain anion sites is illustrated by the following reactions:
Cr
(C0) 3
~o
""'-cMe 3
ButoK/Mei ~1 ~O
DMSO \.l) '-..._ CH
3
Cr
DMF
(C0) 3
Mel/NaH
U--~0
Ţ c""'-cHMe2
Cr
(C0) 3
The uncomplexed ketone is inert to NaH/Mei in dimethylformamide.
10.2.3 Stabilization of a-carbonium Ions
The stabilization of carbonium ions adjacent to a ferrocenyl group was noted on
p. 285. Compared with the a-ferrocenyl group the stabilization arising from an a-
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