Disodium tetracarbonylferrate

Disodium tetracarbonylferrate is the organoiron compound with the formula Na₂[Fe(CO)₄]. It is always used as a solvate, e.g., with tetrahydrofuran or dimethoxyethane, which bind to the sodium cation.^[1] An oxygen-sensitive colourless solid, it is a reagent in organometallic and organic chemical research. The dioxane solvated sodium salt is known as Collman's reagent, in recognition of James P. Collman, an early popularizer of its use.^[2]

Disodium tetracarbonylferrate

Names
IUPAC name disodium tetracarbonylferrate
Systematic IUPAC name disodium tetracarbonylferrate
Other names disodium iron tetracarbonyl, Collman's reagent
Identifiers
CAS Number	14878-31-0 Y
3D model (JSmol)	Interactive image
ECHA InfoCard	100.035.395
EC Number	238-951-0
PubChem CID	73357794
InChI InChI=1S/4CHO.Fe.2Na/c4*1-2;;;/h4*1H;;;/q4*-1;+2;2*+1 Key: JSMIGIAJTPRDEQ-UHFFFAOYSA-N
SMILES [Na+].[Na+].[O+]#[C][Fe-6]([C]#[O+])([C]#[O+])[C]#[O+]
Properties
Chemical formula	C4FeNa2O4
Molar mass	213.87
Appearance	Colorless solid
Density	2.16 g/cm3, solid
Solubility in water	Decomposes
Solubility	tetrahydrofuran, dimethylformamide, dioxane
Structure
Crystal structure	Distorted tetrahedron
Coordination geometry	Tetrahedral
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Pyrophoric
Related compounds
Related compounds	Iron pentacarbonyl
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Structure

The dianion [Fe(CO)₄]²⁻ is isoelectronic with Ni(CO)₄.^[3][4] The iron center is tetrahedral, with Na⁺---OCFe interactions. It is commonly used with dioxane complexed to the sodium cation.

Synthesis

The reagent was originally generated in situ by reducing iron pentacarbonyl with sodium amalgam.^[5] Modern synthesis use sodium naphthalene or sodium benzophenone ketyls as the reducants:^[1][6]

Fe(CO)₅ + 2 Na → Na₂[Fe(CO)₄] + CO

When a deficiency of sodium is used, the reduction affords deep yellow octacarbonyl diferrate:^[1]

2 Fe(CO)₅ + 2 Na → Na₂[Fe₂(CO)₈] + 2 CO

Some specialized methods do not start with iron carbonyl.^[7]

Reactions

It is used to synthesise aldehydes from alkyl halides.^[8] The reagent was originally described for the conversion of primary alkyl bromides to the corresponding aldehydes in a two-step, "one-pot" reaction:^[5]

Na₂[Fe(CO)₄] + RBr → Na[RFe(CO)₄] + NaBr

This solution is then treated sequentially with PPh₃ and then acetic acid to give the aldehyde, RCHO.

Disodium tetracarbonylferrate can be used to convert acyl chlorides to aldehydes. This reaction proceeds via the intermediacy of iron acyl complex.

Na₂[Fe(CO)₄] + RCOCl → Na[RC(O)Fe(CO)₄] + NaCl

Na[RC(O)Fe(CO)₄] + HCl → RCHO + "Fe(CO)₄" + NaCl

Disodium tetracarbonylferrate reacts with alkyl halides (RX) to produce alkyl complexes:

Na₂[Fe(CO)₄] + RX → Na[RFe(CO)₄] + NaX

Such iron alkyls can be converted to the corresponding carboxylic acid and acid halides:

Na[RFe(CO)₄] + O₂, H⁺ →→ RCO₂H + Fe...

Na[RFe(CO)₄] + 2 X₂ → RC(O)X + FeX₂ + 3 CO + NaX