Iron-oleate complex

Hai, H.T., Yang, H.T., Kura, H Hasegawa, D., Ogata, Y., Takahashi, M. and Ogawa, T. (2010) Size control and characterization of wustite (core)/spinel (shell) nanocubes obtained by decomposition of iron oleate complex. Journal of Colloid and Interface Science, 346 (1), 37-42. 

The precursors used for the iron oxide nanocrystal synthesis via the heat-up method are various iron carboxylatc complexes, including the most widely used iron-oleate complex. Generally, when heated, metal carboxylatc complexes thermally decompose at temperatures near 300°C or higher to produce metal oxide nanocrystals along with some byproducts, such as CO, CO2, H2, water, ketones, esters, and various hydrocarbons. It is thought that the decomposition reaction proceeds via the formation of thermal See radicals liom metal carboxylatc (26, 27) ... 

In the synthesis of the nanocrystals, a homogeneous iron-oleate solution prepared at room temperature is heated to 320°C, which is the thermal decomposition temperature of iron-oleate complex, and held at that temperature (24). As shown in Figure 6.13, the curve for the reaction extent of the thermal decomposition of iron-oleate complex in the solution shows a sigmoidal shape, which is typical of autocatalytic reactions. Interestingly, there is a time lag between the onset of the reaction extent curve and the initiation of the nanocrystal formation. As shown in the right of the figure, when the solution temperature just reaches 320°C, there is a trace amount of nanocrystals in the solution while about half of the iron-oleate complex has already been decomposed. This implies that iron oxide crystal is not a direct product of the thermal decomposition of iron-oleate complex. Rather, when iron-oleate complex is thermally... 

Interest in iron carbonyl as a precursor for nanomaterials has been revived during the past decade such that, in 2001, Hyeon et al. reported the synthesis of monodisperse 4—16 nm Y-Fe203 nanocrystals from iron pentacarbonyl in octyl ether in the presence of either oleic or lauric adds as surface ligands [68]. In this approach, highly reactive Fe(CO)5 first formed iron-oleate complexes, the subsequent decomposition of which at 300 ° C led to the formation of transient metallic iron spedes or strongly reduced iron oxocomplexes, followed by their oxidation to the y-FezOs phase by introducing (CH3)3NO into the reaction mixture. 

The ready hydrogenation and isomerization of methyl oleate and palmitoleate with Fe(CO)s confirm the results of Ogata and Misono (18) with monounsaturated aliphatic compounds. In the isomerization of monoolefins Manuel (15) suggested the occurrence of equilibria involving either 7r-olefin HFe(CO)3 and a-alkyl Fe(CO)3 complexes, or TT-olefin Fe(CO)3 and 7r-allyl HFe(CO)3 complexes. The formation of olefin-iron tetracarbonyl complexes has been reported (19). The reaction of butadiene and Fe2(CO)9 has been observed to lead to the formation of butadiene-Fe(CO)4 and butadiene-[Fe(CO)4]2 complexes in which one or both double bonds are pi-bonded to the iron (16). A mechanism involving both monoene-Fe(CO)4 (I) and allyl-HFe(CO)3 complexes (II) is postulated for the isomerization of methyl oleate (Scheme II) and for its homogeneous hydrogenation. 

If monoolefin-Fe(CO)4 complexes are involved in oleate hydrogenation, similar complexes may be invoked as intermediates in the formation of diene-Fe(CO).3 complexes from linoleate (Scheme III). Iron tetracarbonyl complexes were also suggested by Pettit and Emerson (19) in the formation of conjugated diene-Fe(CO)a from nonconjugated dienes. 

The mechanism for homogeneous hydrogenation of methyl linoleate by Fe(CO)s based on kinetic evidences and radioactive tracers involves monoene- and diene-Fe(CO)4 and diene-Fe(CO)3 complexes as important intermediates. Contrary to our previous postulate (7) the free conjugated diene is only a minor intermediate. Confirmatory evidence is needed for the occurrence of oleate- and linoleate-Fe(CO)4 complexes during hydrogenation and isomerization with Fe(CO)r>. Also, the species of iron carbonyl hydrides formed during hydrogenation should be elucidated. 

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