Chemistry Reference
In-Depth Information
2 e
-
RX
Fe(CO)
4
2-
Fe(CO)
5
R
Fe(CO)
4
4.197
4.198
L = CO, PPh
3
O
O
O
R'
I
H
R
Fe(CO)
4
R
Fe(CO)
4
RH
R'
4.199
4.200
Br
2
, MeOH
O
2
O
O
O
R
H
R
OMe
R
'
Scheme 4.71
Br
H
K
2
Fe(CO)
4
NMP
O
H
Br
4.202
4.201
Scheme 4.72
1. K
2
Fe(CO)
4
2.
O
Br
NaOH
O
O
O
4.203
4.204
4.205
Scheme 4.73
alkylated, a reaction that is followed by reductive elimination to generate a ketone. A notable example is the
conversion of the dihalide
4.201
to the cyclic ketone
4.202
(Scheme 4.72). Other carbonyl and carboxylic
derivatives can also be formed: protonolysis of the acyl anion complex gives an aldehyde, oxidation can give
either a carboxylic acid or an ester.
Another useful reaction of these complexes is alkene insertion. This works well with electron-poor alkenes
and may be drawn as a Michael addition. One application is in the synthesis of the perfumery compound,
cis
-jasmone
4.205
(Scheme 4.73).
75
The initial acyl iron complex reacted with methyl vinyl ketone to give a
1,4-diketone
4.204
, which underwent a subsequent intramolecular aldol reaction on treatment with a base.
Intramolecular insertion of simple alkenes is possible (Scheme 4.74). While this is potentially a powerful
cyclization method, it has seen little application beyond a synthesis of aphidicolin
4.209
(Scheme 4.75),
76
and appears to be limited to a small group of alkenes, such as monosubstituted alkenes and cyclopentenes.
77
Cobalt forms a tetracarbonyl anion
4.211
by treatment of dicobalt octacarbonyl
4.210
with sodium amalgam
or sodium hydroxide (Scheme 4.76).
78
In accord with the eighteen-electron rule, this species is a monoanion. It
is much less nucleophilic and less basic than Collman's reagent
4.197
. Indeed, the conjugate acid, HCo(CO)
4
