Polymers Containing Arene Complexes

This chapter was intended to briefly introduce the types of organoiron polymers that have been developed since the early 1950s. Subsequent chapters in this volume will detail some of the advances that have taken place in recent years. The synthesis and properties of ferrocene-based polymers and polymers containing arene complexes of cyclopentadienyliron will be described. The properties and applications of some of these materials will be described, and the reader will hopefully gain an appreciation of organoiron polymers. 

POLYMERS CONTAINING ARENES COORDINATED TO TRANSITION METAL COMPLEXES... 

The Fischer-Hafner synthesis of sandwich compounds (33) does not permit functional groups to be incorporated into the arenes because of side reactions with the Lewis acid catalyst (Friedel-Crafts reducing conditions). This is not the case when metal atoms are used directly. Many metal-arene complexes have been identified that contain F, Cl, CH30, R2N and C02R substituents. It is reasonable to assume that polymer-bound phenyl substituents containing these functional groups will yield similar sandwich complexes. 

The organocobalt polymer 134 was prepared from the reaction of Co2(CO)8 and an acetyl containing polysiloxane.217 Mixed-metal polymers via the reaction of chromium tricarbonyl arene complexes with Mo2Cp2(CO)6 or Co2(CO)8 were also reported. 

Polymers containing aryl groups also react efBdently with metal atoms to yield bis(arene)metal(0) complexes within the polymer chain . Thus, poly(methylphenyl-siloxanes) react at 0°C as a liquid with Ti, V, Cr, Mo and W atoms to give high yields of colored bis( / -arene)metal complexes. In contrast Co, Fe and Ni atoms )deld only metal slurries. Similarly, poly(oxyphenylene) and polystyrene (in a solvent) react with V and Cr atoms to yield colored solutions . By adjusting the metal-atom flux, small, polymer-supported Ti and Mo clusters can be prepared . In some cases the com-plexed metal atoms spontaneously migrate through the polymer fluid to form dimers . 

Cuadrado and co-workers have prepared a pol5uner with Fe—Fe bonds in its structure (19) via reaction of a polysiloxane with Fe(CO)5 (44). The insoluble nature of this pol5uner indicated that cross-linking between polysiloxane chains occurred upon formation of the organoiron polymer. Silicon polymers containing Co—Co bonds (20) have been prepared via the reaction of Co2(CO)s with the triple bonds of a silicon based polymer (45). Mixed metal systems were also described in which complexes containing arenes coordinated to chromium tricarbonyl were reacted with Mo2Cp2(CO)e or Co2(CO)s. 

There has been a great deal of interest in the design of dendrimers using arene complexes of transition metals (246-252). Astruc has developed an efficient route to core molecules suitable for the synthesis of star and dendritic materials via peralkylation or allylation of methyl-substituted arene complexes of cyclopen-tadienyliron. The resulting branched polymers contained cationic cyclopentadi-enyliron moieties at the core and/or the periphery. Complexes containing aryl ethers coordinated to six CpFe+ moieties (110) were synthesized via SNAr reactions (248). 

There are numerous examples of dendrimers and star polymers containing metal coordination complexes (253-259). The synthesis of polypsrridine ruthenium coordination complexes incorporating Fe and Co (113) has been established (255). A ruthenium star-shaped complex with a CpFe" "-coordinated arene as the core has also been reported (254). 

We have reported that norbornene monomers functionalized with arene complexes also undergo ring-opening metathesis polymerization to produce the corresponding cyclopentadienyliron-coordinated polynorbomenes. Scheme 13 shows the synthesis of polymers containing aromatic ether sidechains functionalized with organoiron moieties. ... 

Two different classes of organoiron polymers are the focus of this voliune ferrocene-based macromolecules and polymers containing cationic arene cyclopen-tadienyliron complexes incorporated into their structures. Ferrocene-based polymers are the best-examined class of organo-transition-metal polymer. Since they were first examined in the 1950s, this class of organoiron polymer has been synthesized by almost all imaginable polymerization techniques. 

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