Ferrocenyl group

Third, metallocene units, such as ferrocene or ruthenocene, have been linked to phosphazene cyclic trimers or tetramers and these were polymerized and substituted to give polymers of the type mentioned previously (41). Polyphosphazenes with ferrocenyl groups can be doped with iodine to form weak semiconductors. Polymer chains that bear both ruthenocenyl and ferrocenyl side groups are prospective electrode mediator systems. 

In 3, the amino functional group is two methylene units removed from the ferrocene nucleus. It appears from the instantaneous and quantitative formation of h from 3 that this feature minimizes steric effects and also enables 3 to undergo the Schotten-Baumann reaction readily without the classical a-metallocenylcarbenium ion effects providing any constraints. The IR spectrum of showed the characteristic N-H stretch at 3320 cm" (s), the amide 1 (carbonyl) stretch at 1625 an - -(s), the amide II (N—H) stretch at 1540 cm (s), and the amide III band at 1310 cm 1(m). In addition, characteristic absorptions of the ferrocenyl group were evident at 1100 and 1000 cm l (indicating an unsubstituted cyclopentadienyl ring) and at 800 cm"l. 

Macrocycles attached to redox responsive groups such as ferrocene (78) can give selective transition metal ion receptors. The X-ray structure reveals a five-coordinate zinc with distorted square-pyramidal geometry bound to the four macrocycle nitrogens and an iodide. In the solid state the two ferrocenyl groups are positioned on the same side of the ligand with distances to the metal center of 5.347(7) and 6.120(8) A and these distances can be related to the redox behavior.689... 

In addition to the well-known luminescent Re(NAN)(GO)3 moieties, the electrochemically active ferrocenyl groups were employed as building blocks for the construction of polynuclear silver(i) alkynyl complexes. Yip reported the synthesis, structural characterization, and electrochemistry of a tetranuclear complex, [Ag3(dppm)3(C=CFc)(OTf)]OTf 96 (Figure 43), with the Ag3(dppm)3 skeletal unit being capped by a ferrocenylethynyl ligand on one side and an OTP anion on the other, all in a /Z3-771-bonding mode.170... 

P)GeFc2 compounds, suggesting delocalization of electron density from the porphyrin to the ferrocenyl group. The conclusion is that the stability of Ge—C bonds is higher in the ferrocenyl complexes than in the alkyl complexes165. 

The ferrocenyl group is a very good electron donor. The a-ferrocenyl P-silyl substituted carbocation 20 is accessible by protonation of ( )-1 -ferrocenyl-2-(triisopropylsilyl)alkene 21 with trifluoroacetic acid in SO2CIF at - 95 °C (13, 22). 

We consider now the bis(ferrocenyl) molecule in which the two ferrocenyl subunits are separated by a methylene group, namely diferro-cenylmethane. The molecular structure of this molecule is known. The two ferrocenyl subunits occupy two positions of the tetrahedral coordination of the bridging methylene carbon atom. In each ferrocenyl group, the cyclopentadienyl rings assume an eclipsed disposition.28... 

It is reasonable to assume that the first two-electron process result in the simultaneous oxidation of the two outer ferrocenyl units of the molecule (which are quite distant from each other, and hence not electrostatically interacting), whereas the second one-electron oxidation should be centred on the central ferrocenyl group (that can interact electrostatically with the now positively charged lateral subunits). 

Therefore, one can infer that the central 1,3,5-triethynylbenzene fragment does not allow any electronic communication among the ferrocenyl groups. In fact, such a consideration is too simplistic and one must take into account that the ability of the fragment interposed between redox active centres to block the charge flow cannot be... 

It is important to note that the appearance of a single oxidation process for PVF indicates that there is no interaction between the ferrocene subunits in the polymer chain, which means that the carbon chain creates a barrier blocking the electronic communication between the ferrocenyl groups. 

This complex exhibits in DMF solution a one-electron reduction (Eal = -1.60 V vs. SCE) which is centred on the central [Fe(f 5-C5H5)(/ 6-C6R-6)]"1" core, as well as a single six-electron oxidation (Eo1 = -1-0.44 V), which is centred on the outer, not-interacting ferrocenyl groups. 

As the latter were not easily accessible by chemical synthesis at that time, new methods of preparing these ferrocene derivatives were developed and introduced in 1969. It was then proved that the U-4CRs of chiral a-ferrocenyl-alkylamines can form diastereomeric a-aminoacid derivatives stereo-selectively, and it was further shown that after the reaction the a-ferrocenyl groups of the products can be replaced by protons, thus resynthesizing the chiral a-ferrocenyl-alkylamines simultaneously." Later, the development of this ferrocene chemistry was given up since such syntheses cannot form the products in sufficient quantity and stereoselective purity. ... 

It should be pointed out that the treatment of phosphorus or sulfur donors bearing ferrocenyl groups with diiodine results in the formation of molecular charge-transfer adducts without simultaneous oxidation of the ferrocenyl groups (Durfey et al. 2000, Gridunova et al. 1982). At the same time, the reaction of 4-ferrocenyl-l,3-dithiolene-2-thione with diiodine leads to a charge-transfer complex in which the iron has been oxidized from Fe" to Fe ". This was confirmed by magnetic measurements and Moessbauer spectroscopy (Allen et al. 2003). 

In a similar manner, introduction of the ferrocenyl group drastically changes the reactivity of the mesityl enol ester cation-radicals. These cation-radicals undergo a bond scission in solution according to the following equation (Mes = mesityl) ... 

The preparation of a series of ferrocenyl carbene complexes [(CO)5CrC(X)-C5H4FeC5H5] (X = O - NMe4% OMe, OEt, NH2, NMc2, or NC4H8) has been reported. The presence of a ferrocenyl group adjacent to the carbene... 

J> = CittHsFe. This symbol shall be used for the ferrocenyl group throughout the rest of this review. 

Ferrocenyl groups are useful tools for stereoselective syntheses. Hayashi and coworkers have discovered a novel class of ferrocenyl catalysts allowing the kinetic resolution of benzylic zinc derivatives, such as 448 . The racemic mixture of the benzylic zinc reagent... 

SCHEME 112. Ferrocenyl groups in cross-coupling reactions... 

In 1969, Elschenbroich and Cais reported the ESR spectra of several ferrocenyl anion radicals, including benzoyl, p-tolyl, p-carbomethoxy-benzoyl, p-nitrophenyl, p-cyanophenyl, and nitroferrocene, prepared by electrolytic reduction in either acetonitrile or DMF (5S). In general, the ferrocenyl group destabilizes the anion radicals compared to a phenyl substituent. When both groups are present, delocalization of the unpaired electron into the phenyl substituent is more extensive, and the ESR spectra resemble, for the most part, anion radicals of substituted aromatics. There is small spin density in the ferrocenyl moiety, which appears as small hyperfine couplings for the cyclopentadienyl protons ortho to the point of substitution (38). 

Similarly, the fluorescence intensity of the 1,4-disubstituted azine with ferrocene and pyrene units (17) can be reversibly modulated by sequential redox reactions of ferrocene moiety. In the neutral state, compound 17 displays weak fluorescence owing to the electron transfer from the ferrocenyl group to the excited pyrene unit or by energy transfer from the excited pyrene unit to the ferrocenyl unit. Oxidation of the ferrocenyl unit, however, leads to remarkable fluorescence enhancement. This is because the ferrocenium cation shows weak electron donating ability and also the corresponding spectral overlap becomes small.27... 

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