Ferrocenyl substituent

Oxadiazole 220 bearing a ferrocenyl substituent was reacted with ammonium ethanoate and hydrazine to yield the corresponding 1,2,4-triazoles 221 and 222 in reasonable yield (Scheme 19) <2003JOM(675)1>. 

In contrast, ferrocene, l,T-dimethylferrocene, decamethylferrocene, and 1,2-diferrocenylethane all react with DDQ forming a dark green 1 1 ion-radical salt. Both (DDQ) and ferrocenium constituents of the salts were characterized by their typical electron spectra (Salman et al. 2004). Sometimes, even a weak charge transfer can transform the ferrocenyl substituent into the full-value hole reservoir acting intramolecularly. Scheme 1.31 gives two such examples. One of them describes the effect of charge-transfer coordination between Sc + as an acceptor and a ferrocene derivative as a donor (Qkamoto et al. 2003). The other example introduces the effect of charge-transfer coordination between pyridine as a donor and a ferrocenium derivative as an acceptor (Hillard et al. 2006). 

Chinese researchers reported a synthetic route to photochrome 16 (Scheme 7), in which the aldehyde functions are then transformed into cyclic acetals and thioacetals, methylol and dicyanoethylene groups (07T5437, 08T2576). Scheme 7 also gives (at the bottom) symmetrical photochrome 17 (where R are ferrocenyl substituents), which does not exhibit fluorescence in the initial state, but shows fluorescence in the cyclic form and which is also synthesized starting from dialdehyde 16 (08AFM302). 

The copolymers of type 67 exhibit the characteristic photochemical depolymerization noted for polysilanes, a source of their potential as photoresist materials. However, the presence of the ferrocenyl substituents results in a significant retardation of this depolymerization, presumably due to the ability of ferrocene to quench the triplet state responsible for the polysilane photochemistry164. Polymers of type 67 can be regarded as polysilanes with reversible redox behaviour. 

The benzannulation approach has also been used to generate a steroid D ring bearing both a tunable donor (ferrocenyl substituent) and an acceptor site (benzoquinone functionality), which allows for modification of the electron-transfer properties [94]. 

Carbodiimides are widely used to mediate the attachment of biomarkers to polypeptides. Examples include carbodiimides with ferrocenyl substituents. Also, peptides are covalently modified with ferrocenecarboxylic acid using EDCCl and N-hydroxy-succinimide to promote the coupling to surface lysines. They also mediate the attachment of substituents to single walled nanotubes (SWNTs) and multiwalled nanotubes (MWNTs). Also, microdots are attached to virus molecules using a water soluble carbodiimide. The attachment of viral DNA to gold particles is used in the manufacture of a new type of vaccine. 

On the basis of an X-ray structure analysis [110], cyclic voltammetry [110] and MoBbauer data [111], BFC4 is best described as a zwitterion containing one cationic ferrocenyl substituent and a negative charge at boron [110]. 

Removal of the first electron occurs at E° = -1-0.31 V, which is lower than that of ferrocene (E° = 4-0.40 V) removal of the second electron occurs at = 4- 0.65 V [80]. As expected, the ferrocenyl substituent is more electron-donating than the hydrogen atom. 

Scheme 7-17 shows a series of cyclobutadiene-cobalt complexes bearing ferrocenyl substituents. 

Figure 7-30 shows the cyclic voltammetric response exhibited by trans-CpCo[Fc2Ph2C4] [116]. Two reversible one-electron oxidations, which are probably centered on the two ferrocenyl substituents, precede the irreversible oxidation of the cobalt center. 

The occurrence of discrete oxidation steps for each ferrocenyl substituent in the diferrocene complex indicates that the biscarbyne cobalt core CC03C does not constitute an impassable barrier to electronic interaction between the two redox centers. 

Many derivatives have been prepared from ferrocene monocarboxylic acid (S). Acetylferrocene was reduced by lithium aluminum hydride to the carbinol, and this was then converted into vinylferrocene. From this, polymers and copolymers with other polymerizable substances have been obtained. The polymers are easily obtainable in the cationic form and in the reduced, uncharged form, which are interconvertible (5). Urethanes (3), amino acids and urea, hydantoin and pyrazoline derivatives with ferrocenyl substituents have also been prepared (100, 178). 

In tra 5-[Cl(dppm)2Ru = C = C = C(SeFc)(C2H4CH = CH2)], the redox-active ferrocenyl substituent is directly attached to the allenylidene ligand. Oxidation of the ferrocenylselenyl group caused a redshift of the allenylidene IR band by 10 cm This result fully conforms to what one would expect of the replacement of a substituent ER by a weaker donor. Such substitution... 

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