Ferrocene FeCp

Such units, together with methyl derivatives of ferrocene and cyclopentadienyl (r 6-arene)-iron(II), [FeCp(r 6-arene)]+, have been extensively used as dendrimer peripheral units, but examples of dendrimers containing metallocene residues both as a core and as terminal units and as a core are also reported.5a,b 17... 

We studied electrochemically induced ET between a ferrocene derivative (FeCp-X) in single oil droplets and hexacyanoferrate(III) (Fe(III)) in the surrounding water phase the reaction system is schematically illustrated in Figure 11 [50,74], Tri-n-butyl phosphate (TBP) containing FeCp-X (ferrocene [X = H] or decamethylferrocene [X = DCM]), a fluorescent dye (perylene [Pe 0.5 mM] or 9,10-diphenylanthracene [DPA 10 mM]), and TBA+TPB (lOmM) is dispersed in an aqueous solution containing TBA+Cr, MgS04 (0.1 M), and potassium hexacyanoferrate(II) (Fe(II) 0.2 mM) with a 1 500 (oil/water) weight ratio as a sample emulsion. 

On the other hand, kET in the FeCp-DCM/Fe(III) system has been determined to be 0.04cmM 1s 1 at r > 5 fim (Figure 14b). The redox potentials of the FeCp-DCM/FeCp-DCM + and FeCp-H/FeCp-H + couples in TBP are 113 and 506 mV (vs. Ag/Ag+ reference electrode), respectively, so the ET rate of FeCp-DCM should be faster than that of FeCp-H. Nonetheless, the ET rate between FeCp-DCM and Fe(III) is almost the same as that of the FeCp-H/Fe(III) system (Figure 14a). One reason may be that FeCp-DCM is a bulky molecule having ten methyl groups on the ferrocene moiety, a relatively long ET distance compared with that between FeCp-H and Fe(III) [76]. 

In the previous section, we demonstrated the micrometer droplet size dependence of the ET rate across a microdroplet/water interface. Beside ET reactions, interfacial mass transfer (MT) processes are also expected to depend on the droplet size. MT of ions across a polarized liquid/liquid interface have been studied by various electrochemical techniques [9-15,87], However, the techniques are disadvantageous to obtain an inside look at MT across a microspherical liquid/liquid interface, since the shape of the spherical interface varies by the change in an interfacial tension during electrochemical measurements. Direct measurements of single droplets possessing a nonpolarized liquid/liquid interface are necessary to elucidate the interfacial MT processes. On the basis of the laser trapping-electrochemistry technique, we discuss MT processes of ferrocene derivatives (FeCp-X) across a micro-oil-droplet/water interface in detail and demonstrate a droplet size dependence of the MT rate. 

A potential difference across the NB/water interface (Ao 0) is determined by the concentrations of TBA+ dissolved in both phases, and calculated to be —131 mV on the basis of Eq. 4. A standard ion transfer potential of ferrocene has been reported to be -75 mV [96]. Therefore, FeCp-EtOH+ is likely to exit quickly to the water phase across the droplet/water interface at the present Ao . Diffusion of FeCp-EtOH + in the NB and water phases is thus concluded to be the rate-determining step of MT from GE to CE across the droplet/water interface. If the Ao value is higher than the ion transfer potential of FeCp-EtOH+ in the NB/water system, a slow MT process, such as migration of the compound across the interface, will be detected. A combination of laser trapping with the microelectrode array methods is highly useful for studying directly MT processes between a droplet and the surrounding solution phase. 

Analogous droplet-size dependence has been observed for electron transfer between ferrocene and hexacyanoferrate(III) across a droplet/water interface with the droplet radius of <5 /an, as described in Section III [80]. In this system, FeCp-X+ transfer is coupled with the electron transfer process and the physical properties of the droplet have been suggested to vary with r. However, droplet size effects on surface capillary waves analogous to those in the MT process may also govern the electron transfer process in the FeCp-X/Fe(IIl) system. 

A powerful route to dithiolene complexes employs alkenedithiolate dianions generated by the hydrolysis of cyclic unsaturated dithiocarbonates, which are formally called l,3-dithiole-2-ones. Representative of the many examples (60), the base hydrolysis route has been used to prepare the ferrocene-substituted dithiolene Ni[S2C2H(C5H4)FeCp]2 (61), the sulfur-rich dithiolene [Ni(S2C2S2-C2H4)2F (62), the cyano(dithiolenes) fra s- Ni[S2C2H(CN)]2 (n = 1, 2) (63), 2,3-thiophenedithiolates [Au(S2C,H2S)21 (64), and the tris(styryldithiolate)... 

Fig. 118. Homogeneous electrode-based enzyme immunoassay. Fecp = ferrocene.

Decamethylferrocene, [FeCp ] (Cp = f/ -CjMes) [26], is the most common alkylated ferrocene derivative used for the preparation of CT complexes. [FeCpf] and its oxidized form, as is the case for most other decamethylmetallocenes [27], has Djj symmetry in the solid state. For use as an electron-donor it has the important advantage that it is resistant towards substitution reactions, ring exchange, and hydrolysis. It is also much more electron-rich than its parent compound, as reflected by the redox data reported in Table 8-1. 

The [Cp(CO)3Fe]+ cation (394) can be prepared from ferrocene by treatment with carbon monoxide, AICI3, A1 powder, and water.One Cp ligand of ferrocene may also be replaced by an arene to form the ( -arene)FeCp+ cations (395) by treatment of ferrocene with the arene in the presence of AICI3, A1 powder, and water (ratio of 1 1 3 1 1). The A1 powder is present to prevent oxidation of ferrocene to the ferricinium cation (292)The chemistry of these (jj -arene)iron cations will be discussed later (Section 8.1.1). Treatment of ferrocene with AICI3 in the absence of a good ligand leads to partial decomposition and formation of unusual bridged ferrocenophanes. ... 

---