Cyclopentadienyliron carbonyl complexes

Arene cyclopentadienylmetal and arene metal carbonyl complexes are two other classes of materials that are metallocene-like in structure. The first report of the synthesis of tiie T) -mesitylene-Ti -cyclopentadienyliron cation in 1957 by Coffield et al. was a seminal event in this research field. However, it was the 1985 report on the polymerization of T -dichlorobenzene-Ti -cyclopentadienylruthenimn with diphe-nohc compounds, forming compounds such as 10, by Segal that caused research in this area to expand. 

Tetrahedral complexes du not exhibit geometrical isomerism. However, they are potentially chiral just as is tetrahedral carbon. The simple form of optical isomerism exhibited by most organic enantiomers, namely four different substituents, is rarely observed because substituents in tetrahedral complexes are usually too labile10 for the complex to be resolved, i.e., they racemize rapidly. However, an interesting series of cyclopentadienyliron phosphine carbonyl compounds (see Chapter 15 for further... 

The occurrence of stable carbene complexes of Groups VI and VII is well documented (87, 96, 202), but the 77-cyclopentadienyliron carbene carbonyl cations (103, 151) appear unstable. 

This procedure is a general preparative method for metalla-0-diketone molecules where the metalla moiety may be either the ra-tetracarbonylrhenium or the carbonyl-7 5 -cyclopentadienyliron fragment.6 In each case the diacylmetallate monanion is prepared from an acyl complex, and then this anion is protonated at low temperature. The synthesis of the metalla-acetylacetone complex presented here utilizes acetylpentacarbonylrhenium as the acyl complex. The preparation of this acetyl complex from acetyl chloride and sodium penta-carbonylrhenium is provided, also. 

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