Cationic organoiron polymers

The synthesis of cationic organoiron containing polymethacrylates and polystyrenes has been reported. The radical polymerization of methacrylate and styrene monomers containing cationic cyclopentadienyliron complexes produced polymers with cationic cyclopentadienyliron complexes in their side chains (Scheme 2.57).265,266 Monomer 216 and polymer 217 were both redox active and underwent reversible reduction processes. An organic analog of the cationic organoiron polymer was obtained by photolytic cleavage of the cationic cyclopentadienyliron... 

Interest in organometallic maaomolecules has grown exponentially ever since Arimoto and Haven first polymerized vinylferrocene in 1955 [1]. Organometallic polymers are known to possess unique optical, magnetic, and thermal properties which allow for potential applications as chemical sensors, electrocatalysts, modified electrodes, and photo-active molecular devices [2-7]. Organoiron polymers are one of the most prevalent classes of organometallic polymers, with many reports on their synthesis and properties published over the past 50 years [8-11]. Of the many varieties of organoiron species, ferrocene and cationic cyclopentadienyliron complexes are most commonly incorporated into polymers. 

Polymers 39 containing both neutral and cationic organoiron moieties as well as azo dyes in their backbone were isolated from the condensation polymerization of azo dye-containing organoiron monomers 37 with various N-, S-, and 0-containing... 

Nishihara has reported the complexation of poly(hexyl phenylene) with cyclopentadienyhron, where approximately 1 in every 1.6 aromatic rings was coordinated to the metalhc moiety. Spectroelectrochemical analysis of this organoiron polymer (40) suggested that a network was formed between the aromatic rings of neighboring polymer chains following reduction of the cationic iron centers to the neutral radicals. 

Monomers 49 and 50 were subsequently reacted with 2d, 7, and lOd in the presence of potassium carbonate in DMF, resulting in the formation of polymers 51a-f as shown in Scheme 14. These polymers are unique in that they bear neutral ferrocenyl units in their backbones and cationic cyclopentadienyliron moieties pendent to their backbones. These polymers were isolated as orange solids in yields ranging from 86 to 91%. These organoiron polymers demonstrated good solubility in polar organic solvents such as DMF and DMSO. 

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. 

Ring-opening metathesis polymerization (ROMP) of norbornene monomers (91) (Scheme 11) fimctionalized with cyclopentadienyliron cations has been accomplished using transition metal catalysts to yield the corresponding organoiron polymer (92). The resulting polynorbomene has the metallic moieties present in the... 

Abd-El-Aziz and coworkers have also reported the preparation of organoiron polymers containing azobenzene chromophores in their sidechains. Scheme 14 shows the synthesis of orange and red-colored cationic polymers (58) that absorbed between 417 and 489 nm. Polymers 58 were subsequently demetallated to produce their corresponding organic analogs (59). Photolysis of polymers 59 in the presence of hydrogen peroxide resulted in the decoloration of these polymers. 

Polymers containing both netural and cationic iron moieties have been prepared from organoiron complexes containing ferrocene and azo dyes in the main chain with pendent cationic iron units. The monomers were prepared by first reacting bifunctional azo dyes 34 with the organoiron complex (1) (Scheme 7.11). 

There have been many studies on this important class of arene iron compound, in part, because they can be used in organic synthesis, polymer synthesis, and for the preparation of a range of new organoiron derivatives that are both mononuclear and polynuclear. Kiindig has written a review on the synthesis of transition metal 77 -arene complexes, which includes a section on [Ee(arene)Gp] cations. 

Polymethacrylates and polystyrenes with cationic cyclopentadienyliron moieties coordinated to their sidechains were prepared by radical polymerization of their corresponding organoiron monomers as shown in Scheme 19. Electrochemical analysis showed that the cyclopentadienyliron coordinated monomers (74) and polymers (75) underwent reversible reduction processes. Photolytic demetallation of die cyclopentadienyliron-coordinated polymethacrylates resrrlted in the corresponding organic analogs with M =48,000-68,000. 

---