Precursors ferrocene

Of course, commercially available transition metal complexes are stable at room temperature because they have achieved an 18-electron noble gas-like electronic configuration. Thus, molecules like iron pentacarbonyl [Fe(CO)s], ferrocene [Fe(C5H5)2], as well as piano-stool complexes such as C5H5Co(CO)2 are chemically quite inert. In order to study bimolecular reactions, it is necessary to first prepare unsaturated complexes. For studies using molecular beams, one approach is through photolysis of a stable volatile precursor in a supersonic nozzle. 

At first sight, these strong effects might not seem to be predictable, given that the ferrocene reactant is uncharged and thus the formation of the precursor complex should be unaffected by the charge of the other reactant. The reaction of the ion-paired species, however, is not a simple electron-transfer reaction, because transfer of the anion must also occur. A detailed understanding of the dynamics of the process remains to be developed. 

Let us suppose we have a ferrocene molecule bearing a peripheral functional group able to complex a cationic species. The one-electron oxidation of the ferrocene complex, Figure 35b, undergoes an anodic shift with respect to the ferrocene precursor, Figure 35a, simply because of the electrostatic effect to remove electrons from a cationic complex with respect to the neutral original molecule. 

The ligands discussed so far all contained C2 symmetry. An important new class of ligands having Ci symmetry was introduced by Togni [22] (see Figure 4.19). They can be easily made from an enantiomeric amine as the precursor in a few steps. Different substituents can be introduced at the phosphorus atoms. In addition to the chiral carbon atom the molecule has planar chirality as well. The chiral carbon atom is used to introduce the planar chirality, i.e. lithiation of the ferrocenyl amine takes place at a specific side of the amine at the ferrocene moiety. 

Following the same strategy, Landis prepared the l,l -ferrocenyldi-phosphines 53a-c featuring pendant benzoxaborolidine moieties (Scheme 33). 63 Reaction of 2-aminophenol with the ferrocene precursor 51 afforded 52 which was subsequently coupled with various boronic acids to give compounds 53a-c in good yields. Monomeric open structures were supported by 31P NMR spectroscopy and crystallography for 53a. 

In 1951, ferrocene was synthesized by Pauson [17] and Miller [18]. Soon after this synthesis, two groups led by Wilkinson and Fischer, independently reported that ferrocene has a stable carbon-iron 7r-bond [19]. This was the first example of a true organotransition metal complex containing a carbon-metal bond. Since then, numerous organotransition metal complexes have been prepared. The importance of these complexes as intermediates of many synthetic reactions has been discovered. More importantly, some transition metal complexes were found to behave as precursors of active catalysts. 

Receptor 93 incorporates a zinc porphyrin backbone with four ferrocene amides [65]. This shares the design of the cobaltocenium receptor 4, except that now a zinc atom occupies the centre of the porphyrin. The Lewis acid metal centre provides an additional binding site for anion recognition. In dichloro-methane solution no significant anion-induced shifts in the lH NMR signals of the amide protons were seen in the free-base precursor of 93, whereas the... 

Enantio-enriched enol esters - potential precursors of enantiopure a-arylalkanoic acids - have been prepared by asymmetric coupling of ketenes with aldehydes, using a chiral ferrocene bearing a dimethylaminopyridine function.20... 

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