Cationic iron complexes ferrocene

Although the mercuration of ferrocene has been reported for many years, only recently has the mechanism of this reaction been elucidated. Recent studies indicate that the soft mercuric cation undergoes complexation to the Lewis-basic iron center prior to mercuration. This event is followed by the rate-limiting endo-attack of the cyclopentadienyl ring and subsequent product formation (Scheme 7).103... 

Cationic polyferrocenes containing pendent cyclopentadienyliron moieties as well as azo dyes in their backbone, 210, have been prepared.261 These polymers displayed excellent solubility in polar organic solvents and exhibited max around 419 nm. Electrochemical studies showed that these polymers underwent two redox couples corresponding to the two different iron centers. The oxidation of the ferrocene occurred at Ey2 = 0.89 V and the reduction of the cationic cyclopentadienyliron complex occurred atEV2 = —1.42 V. Photolytic cleavage of the cationic cyclopentadienyliron moieties produced the neutral polyferrocene analogs. 

Cationic arene cyclopentadienyl iron complexes were first isolated from the reaction of CpFe(CO)2Cl with arenes in the presence of AICI3 [80]. Subsequently, Nesmeyanov developed the ferrocene route (Scheme 9) and for most arenes this is more convenient and efficient and has become the standard synthesis for this class of compounds [81]. It has drawbacks in that it requires a stoichiometric... 

Polymers containing both netural and cationic iron moieties have been prepared from organoiron complexes containing ferrocene and azo dyes in the main chain with pendent cationic iron units. The monomers were prepared by first reacting bifunctional azo dyes 34 with the organoiron complex (1) (Scheme 7.11). 

Metallocenes of these metals are exceptionally stable because they achieve lie configuration of the valence shell. They are stable in air in the solid state. They undergo reduction with difficulty by contrast, in acidic media, they are easily oxidized to the [MCP2] cations. Dilute, acidic solutions of Fecp are blue-green, while more concentrated solutions are blood red. Neutral and even more basic solutions of the ferrocenium cation Fecp undergo decomposition to give ferrocene and iron hydroxide. Ferrocene forms charge transfer complexes with nitrobenzene, tetracyanoethylene, and 2, 3-dichloro-5, 6-dicyanoquinone. 

The electrochemical properties of the trimetallic monomers were examined using cyclic voltammetry. It has been established that cationic cyclopentadienyliron complexes undergo reduction processes, while ferrocene and functionalized ferro-cenes undergo oxidation processes. Figure 25 shows the cyclic voltammogram of complex 49. The 1/2 value obtained for the oxidation of the neutral iron center was 0.994 y and the 1/2 value obtained for the reduction of the two terminal cationic iron centers was -1.12 V... 

Interestingly, the sulfur-linked bis-crown ligand [8] shows an unprecedented cathodic potential shift upon addition of K+ cations to the electrochemical solution (Table 3). It is believed to be a conformational process that causes the anomalous shift of the ferrocene/ferrocenium redox couple and not a through-space or through-bond interaction, as these effects would produce the expected anodic potential shift of the ferrocene redox couple. The origin of the effect may be a redirection of the lone pairs of the sulfur donor atoms towards the iron centre upon complexation. This would increase the electron density... 

Compound [25] was thus shown to have an unusual affinity for Ag+ cations. X-ray crystallographic determination of the structures of the free ligand, sodium and silver complexes were carried out and are shown in Fig. 17. The Ag-Fe distance in the silver complex of [25] is only 3.37 A, whereas the Na-Fe distance in the sodium complex is 4.39 A. This evidence together with the FAB MS data and UV spectroscopic data suggests that there may be an interaction between the silver cation and the iron present in the ferrocene moiety. 

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