Chemistry Reference
In-Depth Information
CHO
H
2
, CO, acacRh(CO)
2
, L
*
MeO
MeO
4.191
4.192
CO
2
H
KMnO
4
MeO
4.193
t
-Bu
t
-Bu
O
O
O
O
MeO
OMe
P
P
L*=
4.194
O
O
t
-Bu
t
-Bu
MeO
OMe
Scheme 4.69
EtO
OEt
Cat., H
2
, CO,
SnCl
2
, HC(OEt)
3
MeO
MeO
4.191
4.195
Cl
2
Pt
Ph
2
P
PPh
2
Cat. =
4.196
N
t
-Boc
Scheme 4.70
4.5 Stoichiometric Carbonylation using Carbonyl Complexes
4.5.1
Iron and Cobalt Carbonyl Anions
Iron pentacarbonyl can be reduced by various reagents, such as sodium amalgam, to generate the anion
Fe(CO)
4
2
−
4.197
. Its sodium salt, known as Collman's reagent, is commercially available as a complex with
1,4-dioxane.
73
This material is pyrophoric and must be handled under an inert atmosphere. The potassium
salt can also be prepared.
74
The dianion acts as a nucleophile and participates in various S
N
2 reactions
(Scheme 4.71). Tight ion pairing has been demonstrated and, as a consequence, reaction rates are markedly
higher in polar solvents, which break up the ion pairs and free the anion.
N
-Methyl pyrrolidine has been widely
used. Additionally, the tetracarbonylferrate dianion is quite basic, so, in line with this familiar situation with
less-exotic nucleophiles, efficient alkylation reactions appear to be limited to primary halides and secondary
tosylates; other substrates give the products of elimination. The initial products of nucleophilic substitution,
alkyl tetracarbonyl iron monoanions
4.198
, are generally not isolated. Addition of another ligand, typically
CO or triphenylphosphine, results in CO insertion to give the acyl complex anion
4.199
. This can be further
