Diiron nonacarbonyl
Diiron nonacarbonyl is an organometallic compound with the formula Fe29. This metal carbonyl is a reagent in organometallic chemistry and of occasional use in organic synthesis. It is a more reactive source of Fe than Fe(CO)5. This micaceous orange solid is virtually insoluble in all common solvents.
Synthesis and structure
Following the original method, photolysis of an acetic acid solution of Fe5 produces Fe29 in good yield:Fe29 consists of a pair of Fe3 centers linked by three bridging CO ligands. Although older textbooks show an Fe-Fe bond consistent with the 18 electron rule, theoretical analyses have consistently indicated the absence of a direct Fe-Fe bond: this latter model proposes an Fe-C-Fe three-center-two-electron "banana bond" for one of the bridging carbonyls. The minor isomer has been crystallized together with C60. The iron atoms are equivalent and octahedral molecular geometry. Elucidation of the structure of Fe29 proved to be challenging because its low solubility inhibits growth of crystals. The Mößbauer spectrum reveals one quadrupole doublet, consistent with the D3h-symmetric structure.
Reactions
is a precursor to compounds of the type Fe4L and Fe3. Such syntheses are typically conducted as tetrahydrofuran slurries. In these conversions, it is proposed that small amounts of Fe29 dissolve according to the following reaction:Alkene complexes arise by direct reaction of a suspension in warm benzene:
In related reaction (benzylideneacetone)iron tricarbonyl, with the formula is prepared by the reaction of diiron nonacarbonyl with benzylideneacetone. This complex is a source of the Fe3 fragment.
Oxidative addition of allyl bromide to diiron nonacarbonyl gives the allyl iron derivative:
Cyclobutadieneiron tricarbonyl is prepared similarly using 3,4-dichlorocyclobutene, as described in the following idealized equation:
has also been employed in the synthesis of cyclopentadienones via a net -cycloaddition from dibromoketones, known as the Noyori reaction.
Low temperature UV/vis photolysis of Fe29 yields the unsaturated complex Fe28, which exists as both CO-bridged and unbridged isomers.