Ferrocene dimers

Effects of spacer groups on the formation and properties of the mixed-valence states of conjugated ferrocene dimers have been extensively studied by both electrochemical and spectroscopic methods. It should be noted that a characteristic feature in the electronic spectra of ferrocene dimers with conjugated spacer groups is the appearance of metal-to-ligand charge transfer (MLCT) bands in the neutral form as well as IT bands in the mixed-valence state. The dimer Fc — CH=CH — Fc... 

The electrochemistry of some single-atom bridged ferrocene dimers gives a separation of two le waves. The carbon atoms in CROH and C = 0 can communicate between ferrocene units in 32 and 33 (101). Diferrocenyl sulfide, 34, shows significant AE° values, 0.29-0.33 V, indicating the presence of strong internuclear interactions (102,103). 

Azo-bridged ferrocene oligomers also show a marked dependence on the redox potentials and IT-band characteristics of the solvent, as is usual for class II mixed valence complexes 21,22). As for the conjugated ferrocene dimers, 2 and 241 the effects of solvents on the electron-exchange rates were analyzed on the basis of the Marcus-Hush theory, in which the t/max of the IT band depends on (l/Dop — 1 /Ds), where Dop and Ds are the solvent s optical and static dielectric constants, respectively (155-157). However, a detailed analysis of the solvent effect on z/max of the IT band of the azo-bridged ferrocene oligomers, 252,64+, and 642+, indicates that the i/max shift is dependent not only on the parameters in the Marcus-Hush theory but also on the nature of the solvent as donor or acceptor (92). 

Azoferrocene, 77, is a jr-conjugated ferrocene dimer and one of the simplest analogues of azobenzene, having two redox-active metal complex units. 

In 2005, Moyano et al. [60] reported a new type of chiral dimeric ferrocene palladacycle 43 that lacked the element of planar chirality and involved three... 

Table IV lists the redox potentials of conjugated ferrocene oligomers (mainly dimers with a single bridge). Potential values are denoted against different reference electrodes as given in the references. The values can be primarily compared using the relationship mentioned in the footnote of the table, although care should be taken with some errors derived from junction potentials which depend on experimental conditions. There have been several reports on the quantitative estimation of structural factors affecting internuclear electron delocalization.

Thia-crown ethers incorporating propan-2-one units and dimeric silver(I) compounds as (176) and other polymeric species have been prepared.1132,1133 Other substituents can be diisopropyl idene groups which form complexes of the type [AgL(PPh3)]OTf (177),1134 pyridazine,1133 phthalazine1136 ligands or even organometallic compounds as ferrocene in (178).1137... 

In order to determine the multiplicity of the reactive species, the photodimerization was carried out in the presence of the triplet quenchers oxygen and ferrocene. The results of these experiments are shown in Table 10.4.<41) It is obvious that the presence of oxygen exerts a large quenching effect on the production of the tram dimer and a smaller but significant effect on the formation of the cis dimer (the formation of tram dimer is decreased by oxygen by a factor of 25, while the cis dimer is decreased by a factor of 1.2). As with oxygen, the production of the tram dimer was quenched in the... 

The quenching of the trans dimer with oxygen and ferrocene indicates that this product is formed almost entirely from the triplet state. It is possible to calculate the amount of triplet-derived product in benzene by subtracting the amount of product obtained in the presence of oxygen from the amount of product obtained in the absence of oxygen. Such a calculation indicates that acenaphthylene triplets in benzene give both trans and cis dimers in the ratio of 74 26. The triplet state accounts for almost all of the trans product and about 10% of the cis product. The break in the slope of the Stem-Volmer plot for the trans dimer (Figure 10.3) may be attributed to the presence of two excited species which are quenched at different rates. These two species could be (a) two different monomeric acenaphthylene triplet states 7 and T2 or (b) a monomeric acenaphthylene triplet state 7 and a triplet excimer. This second triplet species is of relatively minor importance in the overall reaction since less than 5% of the total product in an unquenched reaction is due to this species. 

Figure 10.3. Stem-Volmer plot of the quenching of acenaphthylene dimer formation by ferrocene. (Reproduced with permission from Ref. 41.)...

A2 is the dimer, HA is ethyl iodide, and Q is ferrocene. This mechanism is essentially the same as that proposed for the dimerization of acenaphthylene. The steps involving possible singlet excimer formation and singlet dimerization have been excluded since they are at best relatively unimportant processes in heavy-atom solvents. Using the steady-state approximation, we can... 

The dithiophosphonic acid monoesters, RP(OR )(S)SH can be conveniently prepared by cleavage of dimeric, cyclic diphosphetane disulfides, [RP(S)S]2 with alcohols, silanols, or trialkylsilylalcohols180 and then can be converted into metal complexes M[SPR(OR )]2 without isolation.181 The substituted ferrocenyl anion, (N3C6H4CH20)(CpFeC5H4)PS2 has been prepared in two steps from P4Sio, ferrocene and hydroxymethylbenzotriazole (and its salt was used for the preparation of some nickel and rhodium complexes).182 Zwitter-ionic ferrocenylditiophosphonates,... 

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