Ferrocenylsilanes

Closely related reactions have been accomplished by photoelectron-transfer reactions of allylsilanes and benzylsilanes, and a similar mechanism involving the cation radical intermediate is suggested [29]. Chemical oxidation of allylsilanes [27] and ferrocenylsilanes [30] also cleaves the C-Si bond and mechanism of these reactions seem to closely relate to that of the electrochemical process. 

Gohy JE, Lohmeijer BGG, Alexeev A, Wang XS, Manners 1, Winnik MA, Schubert US (2004) Cylindrical micelles from the aqueous self-assembly of an amphiphilic poly(ethylene oxide)-b-poly(ferrocenylsilane) (PEO-b-PES) block copolymer with a metallo-supramolecular linker at the block junction. Chem Eur J 20 4315 323... 

For the unusual reactivity of ferrocenylsilanes toward 5u in THF, affording ketones instead of the expected tertiary alcohols, a mechanism was proposed including the inner-sphere electron transfer from 5u within a reactant complex. The proposition was based on an electrochemical CV examination, which indicated that the outer-sphere process is thermodynamically unfavorable. 

Corriu, R. J., Larcher, F., and Royo, G., J. Organomet. Chem. 104, 161 (1976) (Synthesis of chiral ferrocenylsilanes stereochemistry of their reactions). 

Another impressive example is the facile cleavage of Si—C(Cp) bonds in strained [1]-ferrocenophanes with bridging silicon. This behaviour is the basis for the synthesis of high-molecular-weight poly(ferrocenylsilanes) (equation 47) and will be described in more detail in Section II.E.l. 

Comparable effects have been described for silicon-bridged species with up to eight ferrocenyl units176 and also for poly(ferrocenylsilanes) of type 68163. The difference in the electrochemical behaviour of carbon and silicon substituted multiferrocenes may be explained by the different electron donating or withdrawing effects exerted by these substituents on a ferrocene unit. The phenomena described show that a proper choice of the bridges allows one to determine whether a molecule with three or more ferrocenyl units is first oxidized in the center or at the periphery151. 

The electrochemical behavior of poly(ferrocenylsilanes) has been studied at three levels—in solution by cyclic voltammetry, as films deposited on electrodes, and in the solid state via iodine doping. Solution cyclic voltammetric oxidation and reduction has shown that the polymer, where R/R is Me/Me, reversibly oxidizes in methylene chloride in two stages, apparently with the first oxidation being on alternating iron atoms along the chain.29 Films cast on electrodes behave in a similar way and also show an electrochromic response to oxidation and reduction.30... 

Poly(ferrocenylsilanes) with methoxyethoxyethoxy or quaternary ammonium groups on silicon are hydrophilic or soluble in water and display lower critical solution temperature (LSCT) behavior—again, a similarity to polyphosphazenes26 3233 (see Chapter 3). 

Attempts have been made to deposit water-soluble poly(ferrocenylsilanes) on surfaces via layer-by-layer self assembly.17 Block copolymers of poly(ferrocenylsilanes) with poly (ethylene oxide) self-assemble in aqueous media to form redox active micelles.17... 

Manners, Winnick, and their collaborators22 have studied the self-assembly into cylindrical micelles of block copolymers formed from poly(ferrocenylsilanes) (R/R = Me/Me) and poly(dimethylsiloxane). By ensuring that the poly(dimethylsiloxane)... 

Figure 6.1 Cylindrical micelles of a poly(ferrocenyldimethylsilane)/poly(dimethylsiloxane) or polyisoprene block copolymer showing the central core of the ferrocenylsilane units and the corona of the organic polymer blocks. Reproduced by permission of Prof. I. Manners.

Pannell and coworkers34 described the use of poly(ferrocenylsilanes) as coatings in optical fiber gas sensors. In these devices a small change in refractive index of the polymer film results in a large change in the optical transmission of a tapered optical fiber. This is useful for remote sensing of ammonia or carbon dioxide. Polymers of type 6.20 with R/R = Me/Ph and copolymers from monomers with R/R = Me/Ph and Me/Me were found to be effective for this application. 

Pt-catalyzed copolymerization of ferrocenylsilane and SCB, disilacyclobutane, or cyclic silane monomers can be accomplished to provide random copolymers (Scheme 17) <1996MAR319, 1995MM401>. 

We have a specific interest in the self-assembled structures formed by poly(ferrocenylsilane) block copolymers, such as poly(ferrocenyldimethylsilane-Z -dimethyl-siloxane) (PFS-PDMS) and (ferrocenyldimethylsilane-Z>-isoprene) (PFS-PI). The PFS block contains an iron atom in the main chain repeat unit. These polymers are particularly promising for novel applications, since they can be used as charge-transport materials and, by pyrolysis, as precursors to ferromagnetic ceramics [4-6], Moreover, they can by synthesized with a very narrow molar mass distribution, with excellent control over chain length and composition [7], An important feature of PFS is that the polymers bearing two methyl groups on the silane unit are crystalline, whereas polymers with two different substituents on each silane (methyl, ethyl methyl, phenyl) are atactic and remain amorphous. This feature of the polymer composition has a strong influence on the type of self assembled structures that these poly-... 

Figure 2.13. Photograph of the shaped magnetic ceramics obtained from crosslinked poly(ferrocenylsilane) precursor materials. Reproduced with permission from [96],...

Raez J, Manners I et al (2002) Nanotubes from the self-assembly of asymmetric crystalline — coil poly(ferrocenylsilane — siloxane) block copolymers. J Am Chem Soc 124 10381-10395... 

Massey JA, Temple K et al (2000) Self-assembly of organometallic block copolymers the role of crystallinity of the core-forming polyferrocene block in the micellar morphologies formed by poly(ferrocenylsilane-b-dimethylsiloxane) in n-alkane solvents. J Am Chem Soc 122 11577-11584... 

Table 7-3. Formal electrode potentials (m. SCE) for the sequential oxidation of the ferrocenylsilane-chromium complexes (> -C5H5)Fe[(> -C5H4)- SiMe2 (> -C6H5)Cr(CO)3] shown in Scheme 7-2. Dichloromethane solution. Fc = (C5H5)Fe(CjH4)...

Additional work has shown that it is also possible to induce the ROP of [IJsilaferrocenophanes in solution at ambient temperatures by using anionic initiators (55). For example, the reaction of 13 (R = R = Me) with approximately 10 mol % ferrocenyllithium (FcLi) followed by hydrolytic workup yields a moderate molecular weight poly(ferrocenylsilane) 15 (R = R = Me) with A/ 9500 and Mn 8000. With approximately equimolar... 

The poly(ferrocenylsilanes) synthesized to date by either thermal or anionic ROP are listed in Table I. 

The glass transitions (Tg values) for poly(ferrocenylsilanes) (Table 1) are, generally, significantly higher than those for the analogous polysi-... 

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