Ferrocene and derivatives

A study of the relaxational transitions and related heat capacity anomalies for galactose and fructose has been described which employs calorimetric methods. The kinetics of solution oxidation of L-ascorbic acid have been studied using an isothermal microcalorimeter. Differential scanning calorimetry (DSC) has been used to measure solid state co-crystallization of sugar alcohols (xylitol, o-sorbitol and D-mannitol), and the thermal behaviour of anticoagulant heparins. Thermal measurements indicate a role for the structural transition from hydrated P-CD to dehydrated P-CD. Calorimetry was used to establish thermodynamic parameters for (1 1) complexation equilibrium of citric acid and P-CD in water. Several thermal techniques were used to study the decomposition of p-CD inclusion complexes of ferrocene and derivatives. DSC and derivative thermogravimetric measurements have been reported for crystalline cytidine and deoxycytidine. Heats of formation have been determined for a-D-glucose esters and compared with semiempirical quantum mechanical calculations. ... 

Cunnane, V., Geblewicz, G. and Schiffrin, D. (1995) Electron and ion transfer potentials of ferrocene and derivatives at a liquid-liquid interface. Eiectrochimica Acta, 40 (18), 3005-3014. 

Although analytical SFC was demonstrated in the early 1960s, it has only been in recent years that the availability of adequate high resolution packed and capillary SFC columns and instrumentation has led to renewed interest in the technique. Plasma emission is a natural development because of its use in GC and HPLC. A surfatron MIP sustained in helium has been employed for SFC detection, giving sulfur-specific detection at 921.3 nm with a 25 pg s limit for thiophene [28]. An argon high efficiency MIP has been interfaced with packed column SFC and the separation and detection of ferrocene and derivatives achieved with iron specific detection. Methanol modifier concentrations to 5% were tolerated in the carbon dioxide mobile phase [29]. 

Since ferrocene and many of its derivatives are easily oxidized by air in the presence of acids, nitrogen is passed in at a rate sufficient to exclude air from the system. 

Arenas such as benzene and its derivatives can form complexes precisely analogous to ferrocene and related species. Though particularly exciting when first recognized as rj complexes in 1955 these compounds introduce no new principles and need only be briefly considered here. Curiously, the first such compounds were made as long ago as 1919 when F. Hein reacted CrCL with PhMgBr to give compounds which he formulated as polyphenylchromium compounds [CrPh ]°- + (n = 2, 3, or 4) their true nature... 

The biradical catalysts described previously for double-base propints (Ref 80) are also effective for hydrocarbon propints. Table 34 shows how p,p,-biphenylene-bis(diphenylmethyl) compares to n butyl ferrocene as a catalyst in a carboxy-terminated polybutadiene. These catalysts are claimed to overcome all of the processing difficulties, chemical stability and volatility disadvantages attributed to catalysts based on ferrocene and carborane derivatives. Another somewhat similar functioning catalyst, the free radical compd, 2,2-diphenylpicrylhydrazyl,... 

Nesmeyanov et a/.545 used a mixture of ferrocene, deuterated trifluoroacetic acid and benzene in the molar ratios 1 2 20 in a preliminary investigation of the reactivity of ferrocene and its derivatives. At 25 °C, rate coefficients were 1,620 x 10-7 (ferrocene) and 19.3 xlO-7 (acetylferrocene). In a subsequent publication by Alikhanov and Shatenshtein543 these values were altered to 1,600 x 10-7 and 1.5 x 10 7, respectively, and a value of 0.77 x 10"7 added for 1,1-diacetylferrocene. Under the same conditions, toluene gave a value of 0.3 x 10-7 so that the activating effects of these compounds relative to benzene can be approximately determined. 

Nesmeyanov et a/.546 have also measured the effects of substituents in deuteration of ferrocene by deuterated trifluoroacetic acid in dichloromethane at 25 °C. Rate coefficients were measured for ferrocene and its derivative in a range of such acid mixtures, the composition of which was omitted, and in some cases the rate of exchange for ferrocene was calculated on the basis of a linear relationship between log and —H0. Results including the calculated knl values are given in Table 161. It should be noted that, in discussing those results, the authors quoted the incorrect partial rate factors for dedeuteration of toluene arising from the use of the incorrect data for benzene (see p. 199). This should be taken into account... 

Numerous chemical reactions have been carried out on ferrocene and its derivatives.317 The molecule behaves as an electron-rich aromatic system, and electrophilic substitution reactions occur readily. Reagents that are relatively strong oxidizing agents, such as the halogens, effect oxidation at iron and destroy the compound. 

The electroactive units in the dendrimers that we are going to discuss are the metal-based moieties. An important requirement for any kind of application is the chemical redox reversibility of such moieties. The most common metal complexes able to exhibit a chemically reversible redox behavior are ferrocene and its derivatives and the iron, ruthenium and osmium complexes of polypyridine ligands. Therefore it is not surprising that most of the investigated dendrimers contain such metal-based moieties. In the electrochemical window accessible in the usual solvents (around +2/-2V) ferrocene-type complexes undergo only one redox process, whereas iron, ruthenium and osmium polypyridine complexes undergo a metal-based oxidation process and at least three ligand-based reduction processes. 

Derivatives of calicene that are unsubstituted at the five-membered ring are unknown with the exception of the cationic complex 105 prepared from ferrocene and 3,3-dichloro-1,2-diphenyl-cyclopropene97 ... 

Since the first report on the ferrocene mediated oxidation of glucose by GOx [69], extensive solution-phase studies have been undertaken in an attempt to elucidate the factors controlling the mediator-enzyme interaction. Although the use of solution-phase mediators is not compatible with a membraneless biocatalytic fuel cell, such studies can help elucidate the relationship between enzyme structure, mediator size, structure and mobility, and mediation thermodynamics and kinetics. For example, comprehensive studies on ferrocene and its derivatives [70] and polypy-ridyl complexes of ruthenium and osmium [71, 72] as mediators of GOx have been undertaken. Ferrocenes have come to the fore as mediators to GOx, surpassing many others, because of factors such as their mediation efficiency, stability in the reduced form, pH independent redox potentials, ease of synthesis, and substitutional versatility. Ferrocenes are also of sufficiently small size to diffuse easily to the active site of GOx. However, solution phase mediation can only be used if the future biocatalytic fuel cell... 

Apart from electron promoters a large number of electron mediators have long been investigated to make redox enzymes electrochemically active on the electrode surface. In the line of this research electron mediators such as ferrocene and its derivatives have successfully been incorporated into an enzyme sensor for glucose [3]. The mediator was easily accessible to both glucose oxidase and an electron tunnelling pathway could be formed within the enzyme molecule [4]. The present authors [5,6] and Lowe and Foulds [7] used a conducting polymer as a molecular wire to connect a redox enzyme molecule to the electrode surface. 

Figure 16.10 Diagram showing how values of the standard electrode potential of the couple R/R- referenced to several standard electrode potentials (SHE, Agl/Ag,l-, and ferrocenium/ferrocene) are derived. See equations 16.34 and 16.35.

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