Ferrocenyl electron donor substituent

It would also be interesting to check the ability of the ruthenocene acrylonitrile cation-radical to rotate around the ethylene bond Ruthenocenyl is weaker than ferrocenyl as a donor substituent (Laus et al. 2005). The particular property of rotating around the ethylenic bond in cation-radicals is a method of elucidating an electronic structure. 

Several additional studies have confirmed interannular electronic interactions in ferrocene. Early investigations by Nesmeyanov and coworkers and by others demonstrated the electron-donor properties of the ferrocenyl group (71). Aminoferrocene, for example, is approximately 20 times as strong a base as aniline, while benzoic acid is several times more acidic than ferrocenecarboxylic acid. Moreover, acidities and basicities of this sort are markedly affected by substituents on the opposite cyclopentadienyl ring. 

Crabtree and coworkers used the disappearance of color to monitor the activity of 12 potential catalysts for hydrosilation reactions [6], The group used alkenes and imines with ferrocenyl and pyrimidyl substituents at either end as colored reactants. On hydrosilation the color is bleached, because conjugation between the electron donor and acceptor groups is reduced. The bleaching is easily observed by eye and can be recorded quantitatively by means of a digital camera (Figure 5.4.1). By use of this method, the known Wilkinson catalyst was identified in a proof-of-concept experiment. A palladacycle, [ Pd (o-tolylfi PQ H4 OAc 2, usually used in Heck reactions, was also found to be catalytically active. 

Fig. 9 Scheme showing a a bis-porphyrin connected by ferrocene core [40] b a zinc porphyrin with a mero-methyl-imidazolyl substituent and possessing an appended ferrocenyl as electron donor group [52] and c a scheme of a mixed SAM of 1-butanethiol and 5-[l -(6-thioacetylhexanoyl) ferrocenyl]-10,15,20-triferrocenylporphyrin on gold surface [49]... 

A series of slipped cofacial zinc(II)porphyrin dimers formed through axial coordination of a wieso-methyl-imidazolyl substituent and possessing an appended ferrocenyl as electron donor groups were realized as photosynthetic models (Fig. 9b) [52]. Directly bond and methyl-bridged ferrocene derivatives show good electronic coupling whereas phenylene-ethylene and phenylene-ethynylene spacers decreased the electronic communication. Those electronic effects were reflected on the absorption and fluorescence properties, as well as on the porphyrin ring redox properties. 

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). 

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]. 

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