Polymers ferrocene-based

Ferrocene-Based Polymers, and Additional Phosphorus- and Boron-Containing Polymers 

2 Addition Polymerization of Vinylferrocenes and Other Vinyl Organometallics 

Considerable effort in the 1970s by Pittman, George, Hayes, Korshak, and others was applied to exploring the addition polymerization of vinylferrocene 6.1 to give organic polymers with pendent ferrocenyl side groups (6.2 in reaction (l)).1 6 This type of polymerization reaction has been attempted with the use of free radical, cationic, anionic, and Ziegler-Natta methods. 

For free radical polymerization reactions, the initiating radicals must be generated from azo-initiators because peroxides cause oxidation of the metal. In polymerizations of the type shown in reaction (2) the side group ferrocene units are the source of both the 

Related organometallic monomers, such as the cyclopentadienylchromium complexes, shown as 6.7 and 6.8, have also been homo- and copolymerized, using free radical initiation.7 Here, too, the transition metal in 6.7 generates an electron-rich vinyl group which deactivates the monomer. 

The same reasons for the interest in incorporating ferrocene units into the side group structure have also provided motivation for the synthesis of polymers in which ferrocenyl moieties are part of the main chain. An important additional reason for the synthesis of polymers with skeletal ferrocenyl units is provided by the observation that in molecular species in which two ferrocene units are linked together in close proximity the iron atoms can often interact to yield delocalized, mixed-valent species on one-electron oxidation. For example, the mixed-valence cations derived 

Previous attempts to synthesize ferrocene-backbone macromolecules of type 4 (y 0) in which the ferrocene units are separated via a spacer group have also focused on the use of condensation reactions. Polymers 4 (y 3) in which the spacer is very long have been successfully prepared (36), but well-characterized materials of substantial molecular weight where the ferrocene units are held in close proximity to one another are extremely rare. Previous work on such polymers and other ferrocene- 

This chapter presents an overview of ad classes of macromolecules containing iron-carbon bonds and highlights some examples of these materials. The methods utilized to synthesize and characterize these polymers are described and the properties of some of the organoiron-based polymers are noted. This chapter focuses on the diversity formd in the area of organoiron polymer chemistry and briefly introduces the materials covered in the remaining chapters in this volume. 

Soon after the monumental discovery and elucidation of the structure of ferrocene, the homo- and copolymerization of vinylferrocene was reported using a number of different catalysts. The solution and bulk synfliesis of polyvinylferrocene (1) has been studied in detail, as have the properties of polyvinylferrocene. While many of these studies were undertaken in the 1960s and 1970s, the polymerization of vinylferrocene continues to be an active area of research. The copolymerization of vinylferrocene with styrene using a living radical initiator (viz., TEMPO) was also reported.  

It has also been reported that polymers containing ferrocene units in the main-chain or sidechains may possess liquid crystalline characteristics. Ferrocene-based liquid crystalline polyesters (3) containing phosphorous groups in their backbones have been reported by Senthd and Kannan.  

Polymers containing sidechain and mainchain ferrocenyl moieties have also been reported to possess nonlinear optical (NLO) properties. By incorporating 5 mol% of the organometaUic monomer into the polymethacrylate (4), it was possible to generate NLO properties.  

Similarly, Neuse and coworkers have reported that the incorporation of a small amount of a ferrocene-containing sidechain into polyaspartamide introduces antipro- 

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The electrochemical behavior of ferrocene-based polymers [15] and of complexes containing a large, well defined number of ferrocene-type units [16] had already been reported when several groups became interested in dendrimer research. In the past few years several dendrimers of different chemical nature and structure carrying ferrocene-type units in the periphery have been synthesized... 

There is an enormous number of ferrocene derivatives ranging from monoferrocenes to ferrocene-based polymers. 

Over the past 10 years, research into water-soluble ferrocene-based polymers and polyelectrolytes has increased.168-175 Vancso and co-workers have reported the preparation and self-assembly of anionic and cationic polyelectrolytes.171,172 Polyanionic, 89, and polycationic, 90, ferrocene-based electrolytes are two examples of such polyelectrolytes.170... 

In addition to solution measurements, several bulk measurements have been made on ferrocene chromophores incorporated into poled polymer films." These measurements have shown that there are no special problems associated with poling ferrocene chromophores. The best bulk performance achieved for a ferrocene-based polymer material was an EO coefficient, of 25pmV (1,300 nm) for a film of 18 incorporated at 20 wt.% into amorphous polycarbonate " this is not, however, competitive with the performance of state-of-the-art all-organic poled polymer systems. In some cases, the chromophores have been covalently linked to the polymer chain. Bulk SHG measurements have also been made on self-assembled Langmuir-Blodgett films incorporating ionic ferrocene-based chro-... 

More recently, a soluble polymer (32) was prepared via reaction of l,l -ferrocenedimethanol with 4,4 -biphenyltetraamine in the presence of [RuCl2(P(C6115)3)3] (70). Approximately 20% of the iron centers were foimd to be in the Fe(III) state as a result of oxidation by ruthenium complexes formed during the polycondensation reaction. Wright and co-workers have reported the synthesis of ferrocene-based polymers possessing nonlinear optical properties (33) (71-73). These polymers were formed by polycondensation of a difunctionabzed ferrocene monomer (71). 

The synthesis of conjugated polymers containing ferrocene units in their backbones has received much attention in recent years (78-81). Bochmann and co-workers have described the synthesis of ferrocene-based polymers via palladium-catalyzed coupling reactions of dihalide or divinyl functionalized ferrocene monomers with aromatic spacers (37) (78). 

Ring-opening metathesis polymerization (ROMP) of ferrocenophanes containing bridging olefinic groups (45, 46 48) has been examined in order to synthesize conjugated ferrocene-based polymers (93-95). The poljuners synthesized... 

Mainchain ferrocene-based polymers have also been synthesized by polyaddition reactions." For example, the reaction of l,l -dimercaptoferrocene with 1,4-butandiyl dimethacrylate resulted in the isolation of polymer 13. 

Copolymerization reactions with ferrocenophanes using transition metal catalysts have also been accomplished. The self-assembly of block copolymers has been examined, and polymers with dimethylsiloxane or ethyleneoxide blocks have been found to be soluble in aqueous solution. These ferrocene-based polymers have been found to self-assemble in solution, and their morphologies have been investigated. A number of water-soluble anionic (26) and cationic (27) polyelectrolytes have also been produced by sidechain functionalization. 

The synthesis and properties of star polymers and dendrimers functionalized with ferrocene units has attracted a great deal of attention. The synthesis of high-generation dendrimers functionalized with chiral ferrocenyl units in their structures has been reported. The chiroptical properties of this class of dendrimer was dependent on the number of ferrocenyl groups and their chemical environment, but not on their position within the dendrimer. Deschenaux has reported the synthesis of hquid crystalline ferrocene-based polymers prossessing an enantiotropic smectic A phase. Ferrocene-functionahzed cyclic siloxane (29) and silsesquioxane branched polymers have also been reported. A hyperbranched polymer with a cubic silsesquioxane core was used to mediate the electrocatalytic oxidation of ascorbic acid. 

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. 

Photolysis of polymers 51a-f (Scheme 15) resulted in loss of the CpFePFs moieties, and polymers 52a-f, containing only neutral ferrocene groups in their backbones, were isolated. This methodology represents a new route to the production of ferrocene-based polymers containing aryl ether and thioether spacers. 

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