Ferrocene trimers

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. 

The structure of [Ir(cod)(dppf)]PF6 shows approximately square-planar geometry at Ir, and the cp rings of the dppf ligand are close to parallel and staggered.592 The systems [Ir(cod)(LL)]C104, where LL = dppf, l-diphenylphosphino-2-(7V,7V-dimethylamino)methyl ferrocene and 1,6-diferrocene-2,5-diazahexane, catalytically trimerize PC=CH to 1,3,5-triphenylbenzene.593 The electrochemistry of [Ir(dppf)2]BPh4 shows two one-electron reductions at —1.560 V and -1.755 V vs. ferrocenium/ ferrocene.753... 

Mass spectrometry has proved extremely useful in determining the composition of various polyferrocene products such as those formed by trimerization of ferrocenylacetylenes (180), reactions of ferrocenyl-acetylenes with metal carbonyls (175), oxidative coupling of ferrocenyl polyacetylenes (179), and lithiation of ferrocene (186). The 1,12-dimethyl-[l,l]ferrocenophane (XC) shows a very strong molecular ion and fragments [M—Me]+ [M—2 Me]+ and the doubly charged species M2+, [M —Me]2+, and [M —2 Me]2+ (197). 

Fig. 13.16 Multi-step photoinduced electron [50] and (b) ferrocene-meso, meso-linked transfer in (a) a ferrocene-zinc porphyrin-free porphyrin trimer-fullerene pentad [Fc-base porphyrin-C60 tetrad (Fc-ZnP-H2P-C60) (ZnP)3-C60] Ar = 3,5-Bu 2C6H3 [51].

The best molecule mimicking multi-step electron-transfer processes in the photo synthetic reaction center so far reported is a ferrocene-meso, meso-linked porphyrin trimer-fullerene pentad [Fc-(ZnP)3-C60] in Fig. 13.16b, where the C60 and the ferrocene (Fc) are tethered at both the ends of (ZnP)3 (R = 46.9 A)... 

Scheme 5. Multistep photoinduced ET in a ferrocene-mcio.mcio-linked porphyrin trimer-fullerene pentad [Fc—(ZnP)3 C6o] Ar = 3,5-/-BuC5Fl3 (48).

Simple redox solutes, ferrocene, N, N, N, JV-tetramethyl-l,4-phenylenediam-ine, decamethylferrocene, bis(i-propylcyclopentadienyl) iron(ll), [Ru(phen)j] (0104)2, [Fe(bpy)3](0104)2, [Co(bpy)3](0104)2, and iodine have been studied at electrodes modified with polymeric fullerene films. FuUerene-modified electrodes were prepared by electropolymerization of Cjq initiated by traces of dioxygen or by simultaneous electroreduction of fullerene and Pd(ll) acetate trimer. For the former films, the electrochemical activity decreases upon potential cycling. The electrochemical activity of the film is stabihzed by the redox solute added to the electropolimerization stage due to the catalytic oxidation of the fullerene film by the oxidized form of the redox system. Similarly, positively charged species can also be incorporated into the structure of the film. The reversible behavior of redox solutes decreases with the increase in the thickness of the Pd/C q film. This film also incorporates ferricinium ion, N, N, N, N-tetramethyl-l,4-phenylenediamine cation, decamethylferricinium ion, and to a smaller degree [Co(bpy)3]"+ [53]. 

V vs. Fc+/Fc for the trimer. The AEP values indicated that the interaction energy between ferrocene and ferrocenium sites, m0r is estimated to be — 2 kJ mol-1 based on the neighboring site interaction model,18 and the value was about one-fifth compared with that for oligo(l,l -dihexylferrocenylene)s.15,16... 

Figure 26 Scheme for the functionalized ferrocene moieties with organic radicals as dimers or trimers (a) perchlorotriphenylmethyl, (b) and (o) nitronyl nitroxide. 

The dimeric complex 39 exhibits individual Fe(III)/ Fe(II) redox couples at +0.47 and +0.60 V v. SCE in CH2CI2. The averaged value (+0.54 V) is close to that of the corresponding monomeric complex 38 (+0.51 V). These results are explained by the electronic effect as reported in the literature. The trimer 40 exhibits two redox couples at +0.51 and +0.67 V in a similar condition. The positive peak suggests the presence of significant electronic interaction between two ferrocene units (center and C-terminus). This result indicates the possibility of constructing an expanded conjugation system of polymeric ferrocene amino acid and the development of the conductive devices by partial oxidation. 

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