Dienyl-iron tricarbonyls

The reactions of cationic (ii -dienyl)iron-tricarbonyl complexes with nucleophiles have been studied extensively by Birch and Pearson. These complexes are prepared by abstraction of an allylic hydride from riMiene complexes, which are readily available from the reaction of 1,3- or 1,4-dienes with Fe fCO),. The parent pentadienyl complex reacts with a variety of nucleophiles exclusively at the termineil carbon, and this reaction generates a new T -diene complex (Equation 11.50). ... 

The electrophilic character of the dienyl iron tricarbonyl complex 65 as such [109] or masked in the form of the labile pyridinium complex 64 [110] was exploited to label several enzymes in aqueous medium. Nucleophilic addition of the imidazole of histidine residues and/or the primary amine of lysine residues (depending on their accessibility) was shown to occur by spectroscopic methods (Scheme 6.17). 

The generic structure is indicative of random incorporation of dienyl iron tricarbonyl moieties, corresponding to 1,3 octadiene-, 2,4 octadiene- and 3 5 octadiene-iron tricarbonyl. We have found that a derivative of constant stoichiometry is obtained ia the thermal decomposition of an excess of Fe(C0)5 dilute xylene solution of c/5-poly(butadiene). The polymer is a bright yellow, air-stable, solid which was conveniently isolated from benzene by lyophilization (see Experimental). The purification procedure detailed in the Experimental Section is a key factor in the stability of the product. 

In order to identify the structure of the polymer, we compared the spectral characteristics (IR/NMR) of this product with those of an appropriate octadiene derivative. Based on the work of Pettit, et al.- it would be predicted that octadienes could react with Fe(C0)5 to yield as many as six isomeric dienyl iron tricarbonyl compounds. 

Fe(C0)5 and c/5-polybutadiene is much simpler, consisting only of six principal resonances. We have assigned the three high field peaks at 34, 32 and 29 ppm to beta to the dienyl iron tricarbonyl moiety,... 

In light of the surprising cis substitution proposed for some of the dienyl iron tricarbonyl residues in the polymer, we wanted to corroborate our spectral evidence for the structure of the polymer by some additional analytical technique. In 1963> Mahler and Pettit -effectively demonstrated that the pentadienyliron tricarbonyl cation, which displays characteristic carbonyl bands at 2120 cm" and 2050 cm" can only be generated from cis diene iron tricarbonyl precursors. 

Organoiron chemistry 1 ferrocene and dienyl iron tricarbonyl cation... 

This chapter deals with two differing applications of organoiron chemistry to organic synthesis. In the first section the chemistry of ferrocene is examined, in particular the reactions required for the construction of ferrocene-based ligands, which have found wide usage in asymmetric catalysis. In contrast, the cationic dienyl iron tricarbonyl complexes studied in the second section have been employed directly in many elegant total syntheses of complex organic structures. 

Fundamental to the development of dienyl iron tricarbonyl chemistry has been the availability of substituted cyclohexadiene precursors arising from the Birch reduction. In this process, a wide range of aromatic compounds are readily reduced to their corresponding unconjugated cyclohexa-1,4-dienes without further reduction to a cyclohexane. The reaction is typically performed by adding sodium to a liquid ammonia solution of the substrate in the presence of an added alcohol. 

Some reactions of cyclohepta- and cyclohexa-dienyl iron tricarbonyl complexes resemble the reactions of the jr-cyclopentadienyl iron analogues. However, ring addition reactions which give diene derivatives occur more readily [263c], e.g. 

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