Ferrocenyl derivatives protonation

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. ... 

For the stereoselective formation of diastereomeric products, it was recognized at an early stage that the U-4CR can proceed stereoselectively if chiral primary amines and aldehydes are employed as the reactive components. The peptide derivatives 17 can only be formed if the amino component 14 contains an alkyl group that can be replaced by a proton in 16 producing 17 (Scheme 3).P l The essential problems were first solved separately by a variety of experimental investigations.It was found that chiral, a-ferrocenyl-substituted alkyl-amines 18 are able to fulfill all the requirements of peptide synthesis by stereoselective U-4CRs (Scheme 4).hi New, efficient methods were developed for the preparation of alkyl-amines in order to investigate their role in the synthesis of peptide derivatives by the... 

In poly(methylphenylphosphazene), [Ph(Me)P=N] 58, both the phenyl and methyl substituents are potential sites for formation of derivatives [65]. Deprotonation of ca. half of the methyl substituents on this polymer was carried out in THF at — 78 °C using n-BuLi. On treatment of the intermediate polymer anion with ferrocenyl ketones and subsequent quenching with a mild proton source, phos-phazenes 59 containing the OH functional group were prepared. The amount of substitution, determined by NMR and elemental analysis, was found to be 45 and 36%, respectively, for polymers 59a and 59b (Scheme 10-27). For these substituted polymers was 187000 and 154000, respectively, and no degradation of the parent polymer occurred. 

The deprotonated form, 1-FcAq, shows reversible two-step 1 e reduction at = -1.26 and -1.71 V versus ferrocenium/ferrocene (Fc /Fc) derived from the anthraquinone moiety, and reversible 1 e" oxidation at = 0.22 V due to the fer-rocenyl moiety in BU4NCIO4-CH2CI2 (Table 3.4). The first reduction potential shifts dramatically in the positive direction to E = -0.06 V, and the oxidation potential shifts moderately in the positive direction to E = 0.33 V in the protonation product, [1-FvAqH], whereas the second reduction potential is little changed. These results correspond to the structural changes in both ferrocenyl and anthraquinone moieties by protonation. 

Interestingly, an isotope effect of 1.8 was determined in the phenylation of pal-ladacycles 49 derived from ferrocenyl oxazoHnes, which is also consistent with a proton-abstraction by the base in the C—C bond-forming step (Scheme 11.17) [46]. 

Electrochemistry of the protonated compounds supported the reactions given in Scheme 2. The series of monoprotonated complexes exhibits a reversible two-step one-electron reduction of the protonated anthraquinone moiety (AqH) in the cyclic voltammograms, whose potentials are largely shifted in the more positive direction than those of nonprotonated forms (Table 1). The reversible oxidation waves of non-and monoprotonated complexes are derived from the metal-centered oxidation of the ferrocenyl and ftilvene complex moieties. In [l,5-Fc FvAqH2 ], the redox reaction... 

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