Polymetallocenylenes

The earliest routes to polyferrocenylene involved poorly defined free-radical recombination processes (Eq. 3.1). In 1960, the polymerization of molten ferrocene at 200 °C in the presence of approximately stoichiometric amounts of t-butyl peroxide, t-BuOOt-Bu, as the radical source was described [12-14]. The yields of soluble material of idealized structure 3.4 were low (ca. 5-15%), as were the molecular weights ( 7000). 

Subsequently, a series of different radical reactions were reported, such as mixed Ullmann reactions of halo- and l,l -dihaloferrocene with copper bronze [17,18], coupling reactions of lithio- and l,l -dilithioferrocene with cobalt chloride in the pres- 

The conductivity of unoxidized oligo(l,l -ferrocenylene), prepared by the radical recombination of ferrocene, was studied, and this led to the conclusion that the material was an insulator [27-29]. However, upon partial oxidation with iodine or quinones, the presence of mixed-valence states led to a dramatic increase in conductivity from a value of Scm for the pristine material to a maximum of 10 -10 Scm at room temperature. Similar values have been determined for biferrocenylene and biferrocene salts ]30-32]. 

Arguably the most impressive early results on polyferrocenylenes in terms of product yield, molecular weight, and purity were obtained in 1979 using the step- 

Apart from the case of polyferrocenylenes, very little work has been reported on analogous materials containing directly linked metallocene units. The synthesis of very low molecular weight polyruthenocenylenes 3.9 (M as 1400) using, for example, Ullmann coupling has been briefly described (Eq. 3.5). The few results on oli- 

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Polymetallocenylenes and Polymetallocenes with Short Spacers via Condensation Routes... 

In contrast to the continuous progress in the study of poly(l,l -ferrocenylene), there are few investigations of other relating polymetallocenylenes. 01igo(l,2-ferro-cenylene)s (14, = 2-5) have been synthesized by the Ullmann coupling of iodoferrocene and 1,2-diiodofer-... 

Theoretical studies of polymetallocenylene-related polymers have been carried by Burdett and Canadell [67]. There are two different electron counts associated with a bandgap corresponding to iron and chromium polymers in the band structure of a naphthalene-bridged sandwich complex polymer, 16 [67], whereas one bandgap is found in the band structure of polyferroce-nylene [60]. This is due to a three-orbital interaction between the and d y of metal and the LUMO of naphthalene, causing three bands in the band structure. 

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