Ferrocene-coordination polymers

Figure 23 Charge transfer coordination polymers (33) obtained from diborylated ferrocenes with 4,4 -bipyridine (bipy) or 1,2-bis(4-pyridyl)ethane (pyetpy) bridges. (Adapted from ref. 55.)...

An enormous number of polymers have been used to prepare chemically modified electrodes. Some examples are given in Table 13.2 Albery and Hillman provide a more extensive list [8]. As indicated in Table 13.2, these polymers can be divided into three general categories—redox polymers, ion-exchange and coordination polymers, and electronically conductive polymers. Redox polymers are polymers that contain electroactive functionalities either within the main polymer chain or in side groups pendant to this chain. The quintessential example is poly(vinylferrocene) (Table 13.2). The ferrocene groups attached to the polymer chain are the electroactive functionality. If fer-... 

Boron—nitrogen coordination polymers, with ferrocene, 6, 208 Boron nucleophiles, in conjugate additions asymmetric 1,4-additions, 10, 388 mechanisms, 10, 384 to nitroolehns, 10, 388 to a,/3-unsaturated amides, 10, 386 to a,/3-unsaturated esters, 10, 386 to a,/3-unsaturated ketones, 10, 384 Boron-silicon bonds, addition to alkenes, 10, 760 to alkynes, 10, 758 to allenes, 10, 760 to carbenoids, 10, 766 to 1,3-dienes, 10, 762 to isocyanides, 10, 765... 

Borylated ferrocenes have been exploited by Wagner as building blocks for the assembly of macrocycles and coordination polymers (Scheme 15). Treatment of the diborylated ferrocene l,L-fc(BMe2)2 with the bifunctional aromatic amines pyrazine and 4,4 -bipyridine, respectively, led to spontaneous and reversible formation of (89) and related ferrocenylborane polymers.The polymeric nature of... 

Organometallic polymers, in contrast to coordination polymers, have metal-to-carbon bonds. They are the topic of this chapter. Three seminal events provided the foundation for the field of organometallic polymers to develop. The landmark discovery of ferrocene by Kealy and Pauson in 1951 marked the first organometallic compound.11 This was quickly followed by the full elucidation of its structure and an understanding of its reactivity by Wilkinson, Rosenblum, Whiting, and Woodward.12,13 This history was celebrated in a 2001 feature article in Chemical and Engineering News 4 Finally, the first polymerization of an organometallic compound was reported by Arimoto and Haven at Dupont Co. in 1955.15,16 Vinylferrocene 1... 

Mochida and co-workers have constructed coordination networks by using ferrocene-based bidentate ligands, 1,1 -(4-dipyridinethio)ferrocene and l,l -(2-dipyridinethio)ferrocene. In order to obtain coordination polymers, these... 

A few other examples of chain-forming coordination polymers are mentioned. A polymer 31 was obtained under inert conditions by the reaction of 4,4, 5,5 -tetramethyl-2,2 -bisphosphinine with naphthalene/Na in dimethoxy-ethane [85]. The bisphosphinine is reduced two-fold. In the deep purple oxygen-sensitive crystals the chain is held together by electrostatic interactions through alternation between three and one Na(I) cations. The reaction of pentaphosphaferrocene with CuX (X = Cl, Br, I) was used to prepare yellow-brown crystals of one- and two-dimensional poljmiers in which the phospha-ferrocene units are connected by CuX units [86]. One-, two- and three-dimensional tubes were prepared by employing dimetal building units [87]. For example, a one-dimensional tube was obtained from a Rh2 compound with malonic acid and linkers such as tra 5-l,2-bis(4-pyridyl)ethylene. 

BpyP = 3,6-bis(4 -pyridyl-l -pyridinio) pyridazine) consists of 1-D infinite chains (1-D linear chain Scheme 5a), in which photoelectron transfer from Cl to BPyP occurs, generating the pyridyl radical. Solid state cyclic voltammograms of several 1-D coordination polymers containing ferrocene-based bidentate ligands (1-D linear chain Scheme 5a) have been reported. ... 

Horikoshi, R., and T. Mochida. 2010. Ferrocene-containing coordination polymers ligand design and assembled structures. European Journal of Inorganic Chemistry (34) 5355-5371. 

Boron-nitrogen coordination polymers with ferrocene in the main chain have also been obtained by reacting... 

Much work has been undertaken to modify electrode surfaces with films which are themselves conducting. The most promising approaches involve organic charge transfer and radical ion polymers. Coordination chemistry has, to date, played little part in this work (a good recent review is available),67 but one example relating to ferrocene chemistry can be quoted. In this example a well known electron acceptor, 7,7, 8,8 -tetracyanoquinodimethane (TCNQ 27), is modified and incorporated into polymer (28) in which the iron(II) of the ferrocene unit is the electron donor. The electrical conductivity of such a film will depend on partial electron transfer between ion and TCNQ centres as well as on the stacking of the polymer chains. The chemistry of other materials, based on coordination compounds, which have enhanced electrical conductivity is covered in Chapter 61. 

Finally, ferrocenyl units have been incorporated into the perimeter of dcndrimcric polymers by Astruc and coworkers.40 Gold nanoparticles form the core of the dendrimers, with the branched units with terminal ferrocene units coordinated to the gold surface via... 

In other examples, compounds in which a metal atom is already coordinated in a molecule can be used as a comonomer in an addition polymerization. Two examples involve the ferrocenes discussed in Chapter 6. The vinyl ferrocene molecule is shown in 7.14, and a similar vinyl manganese complex in 7.15.30 An alternative approach involves condensation polymerization. For example, if the R group in the ferrocene unit shown in 7.16 contains a hydroxyl group, it can be copolymerized with a diacid chloride. If it is an acid chloride, it can be copolymerized with a diamine. (This type of polymer is called a heteroannular chain if only one of the rings in the repeat unit is in the backbone, the polymer is called homoannular.)7 Similarly, the titanium complex shown in 7.17 is copolymerized with diacids or diols.30 Numerous other examples involving ferrocenes are discussed in Chapter 6. 

While dicyclopentadienyl compounds of transition metals (see Transition Metals) typically have a ferrocene-hke (see Ferrocene) sandwich structure, the electron-deficient cyclopentadienides of the main group metals tend to form polymers with bridging cyclopentadienyl (Cp) groups. Although exceptions are known, the tendency is rather consistent. The element zinc, owing to its borderline position between transition metals and main group metals, presents a variety of coordination (see Coordination Numbers Geometries) modes with the Cp anion. 

Other reference electrodes have been proposed for use in the nonaqueous solvents that are widely used in coordination chemistry. Their main advantage is that they allow one to work with a single solvent. Among these electrodes, the Ag+/Ag electrode is reversible in many solvents.4 Ag+ ions are introduced as salts, such as AgCl or AgBF4. However, the inner solution has to be refreshed due to the reactivity of Ag+. Another class consists of redox electrodes in which the two components are in solution, such as ferrocenium ion/ferrocene Fc+/Fc.5 Since the potential is dependent on the concentration ratio of the redox couple, this ratio must be kept constant. An attractive solution to prevent the use of a junction lies in the preparation of a functionalized-polymer coated electrode such as poly(vinylferrocene).6 The polymer is deposited by electrooxidation in its oxidized form, polyFc+, and then partially reduced to yield poly Fc+/Fc. Their use is limited by their relative stability in the different solvents. 

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