Poly-ferrocenylenes

There is one report of the redox properties of poly(ferrocenylene) by Oyama et al. noting that the cyclic voltammetry of low molecular weight poly(ferrocenylene) (Mw 900) dissolved in CH2C12 or electrodeposited on Pt gives a broad redox wave with two (or three) peaks between 0.2 and 0.8 V vs. SSCE (70). 

Jakle and Wagner have communicated the synthesis of bromo-substituted, boranediyl-bridged poly(ferrocenylene)s (40) (Fig. 28) by the reaction of Fc(BBr2)2 with three equivalents of HSiEt3. The polymer 40 was transformed into the corresponding mesityl-substituted polymer (40Mes) by treating its slurry in toluene with... 

Figure 28 Synthesis of bromo-substituted, boranediyl-bridged poly(ferrocenylene)s (40) from Fc(BBr2)2. (Adapted from ref. 62.)...

Poly(ferrocenylalkylsilanes), glass transitions, 12, 330 Poly(ferrocenylarylsilanes), glass transitions, 12, 330 Polyferrocenyl dendrimers, synthesis, 6, 195—196 Polyferrocenylenedivinylenes, synthesis, 12, 345 Poly(ferrocenylene persulfides), synthesis, 12, 345 Polyferrocenylenes, via condensation, 12, 317 Poly(ferrocenylene—vinylene) via polycondensation, 12, 321—322 synthesis, 12, 344—345... 

The structure of poly(ferrocenylene), 50, involved conformations where the directly bonded cyclopentadienyl rings were canted (rotated) to create sizable dihedral angles, which interfered with extended conjugation. We synthesized poly(ethynylferrocene), 54.86 This poly... 

Poly(ferrocenylene vinylene) derivatives 68 with values of 3,000-10,000 and polydispersities of ca. 2.2-2.8 (determined by GPG) were synthesized in 1995 in high yields via a titanium-induced McMurry coupling reaction of the corresponding alkylferrocenyl carbaldehyde monomers (Equation (26)). " Gharacterization of these soluble polymers by NMR and IR revealed the presence of trans-Yinylcnc units. The UV-VIS spectra of the polymers are similar to those of the monomers and this indicates a fairly localized electronic structure in the former. The relatively limited electron localization is also reflected in the electrical and optical properties. For example, the values for iodine-doped conductivity a= 10 Scm ) and non-linear third-order optical susceptibility (x = 1-4 x 10 esu) are lower than those of linear conjugated polymers such as poly(l,4-phenylene-vinylene) (a = 2.5x 10 Scm" = 8 X 10 esu). 

The synthesis of poly(ferrocenylene-vinylene) via ROMP of the vinylene-bridged [2]ferrocenophane 109 was reported in 1997 263 monomer was obtained from the McMurry coupling of l,l -ferrocenedicarbaldehyde. In the presence of a molybdenum ROMP catalyst, 109 was found to undergo polymerization (Scheme 11) to give an insoluble orange powder 110, which exhibited a conductivity of 10 S cm after iodine doping. Partially soluble block co-polymers 111 were also... 

This atom-abstraction route was also used for the preparation of polymeric networks from alkylated [3,3 ]bis-(trithia)ferrocenophanes. A bimodal molecular weight distribution, with maxima at 4/n 5,000 and 5 x 10, was obtained by GPC for the material from which a polymer fraction was isolated (4/ = 8.5 x 10 ). Low molecular weight poly(ferrocenylene perselenides) have also been prepared from the selenium analog of 114. These materials also undergo photodegradation upon exposure to UV light in air. ... 

Figure 20 Cyclic voltammogram of poly(ferrocenylene persulfides) 115 (top R = R = f-Bu bottom R = t-Bu, R" = H) showing two reversible oxidation waves separated by a redox ooupling AE 2 of oa. 0.29 V for both polymers (in 0.1 M [BU4NKPF6] in CH2CI2). (Reproduced with permission of The Amerioan Chemical Society from Compton, D. L. and Rauchfuss, T. S., Organometallics, 1994, 13, 4367.)...

Other approaches to prepare poly(ferrocenylene)s have been to use dehalogenation reactions of l,r-dibromoferrocene or l,r-diiodoferrocene using magnesium. Virgin poly(ferrocenylene)s are also insulators [25-26]. 

The presence of at least one alkyl group on the cyclopentadienyl motif is required to induce solubility in these poly(ferrocenylene persulfide)s. These polymers show two reversible oxidations. This type of electrochemical behavior is fairly common in ferrocene polymers where the ferrocene units are separated by short spacers as will be pointed out in the next section. 

In early 1992, it was reported that [3]trithiaferrocenophanes, which are essentially unstrained, function as precursors to poly(ferrocenylene persulfides) via a novel atom abstraction polymerization route (eq. 34) (173). Thus, reaction of [3]-trithiaferrocenophanes (53) with P(C4H9)3 led to the formation of the phosphine sulfide S=P(C4Hg)3 and the polymers (54). 

Electrochemistry of oligo- and poly-ferrocenylenes is an intriguing subject for research because ferrocene is a representative molecule that undergoes reversible le oxidation and thus the polyferrocenylene system is an ideal model to show how the sequence of the redox site interaction dominates the redox property of the whole system. Electrochemical properties have been reported on oligoferrocenylene with 4 by Brown et al. [59] and a soluble component of polyferrocenylene by Oyama et al. [61], The oligomers give the same number of le oxidation waves to that of ferrocene units. 

Grubbs and coworkers [6] studied ROMP of strained [4]ferrocenophanes as a plausible route to poly(ferrocenylene-divinylene) and related poly(ferrocenylenebutenylene) (Scheme 12.2, R = H) employing a W-initiator. The obtained polymers (R = H) with n> 10 displayed somewhat limited solubility in common organic solvents. Gel permeation chromatography (GPC) analyses of the CH2Cl2-soluble fractions showed oligomeric structure of these products with chain lengths of circa 10. 

The ptdymer XXX in the Fe(II) state has a low ccmductivity (10 —10 crfun" cm ) but subsequent to partial oxMation with picric acid, benzoquinone, chloranil TCNQ produces intensely cdouied salts with maximum conductivities at 70% oxidaticm of lO times that of tiie parent Such increases also occur with poly(ferrocenylene) (XXXI) polymer (XXXII) ptdj ethynyl-ferrocene) (XXXIV) and pdy(3-vinylbisfulvalenedi-iron) (XXXIIl) upcm partial oxidation. Polymer XXXIV incorporates both a conjugated n and redox tems. 

The introduction of what are essentially diffused orbitals from the metal can allow the orbital overlap such as between two molecules in adjacent layers of crystal. Alternatively, d orbitals may enhance the intramolecular conduction paths by their conjugation with the orbitals of the polymer. Even if the polymer chain is not conjugated, enhanced conductivity may still be achieved, because with transition metals, a mixed valence system may be formed, allowing transport of electrons by redox behaviour between metal atoms in different oxidation states. An example of this type of behaviour occurs in the poly(ferrocenylene) polymers. The standard, unoxidized poly(ferrocenylene) is effectively an insulator, but oxidation of ferrocenium (Fe(II)) to ferricenium (Fe(III)) with I as counteranion results in a large increase in conductivity. If around 5% ferricenium is present, a 10-fold increase in conductivity occurs, while a maximum increase of 10-100 times has been reported with 35-65% ferrocenium [63]. The structure of the poly(ferrocenylene) polymer and two of its analogues are shown in Fig. 1.11. 

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