Cyclopentadienyliron moieties

Arenes, on complexation with Cr, Fe, Mn, and so forth, acquire strongly electrophilic character such complexes in reactions with nucleophiles behave as electrophilic nitroarenes.71 Synthesis of aromatic nitriles via the temporary complexation of nitroarenes to the cationic cyclopentadienyliron moiety, cyanide addition, and oxidative demetalation with DDQ has been reported (Eq. 9.43).72... 

Cationic cyclopentadienyl iron fragments have been generated by photolysis of [(C5H5)Fe(C6H6)] [PF6] and shown to form transient cationic triple-decker sandwich complexes with [(t-Bu3C3P2)Fe(r-Bu2P3)]. Similar photolytic removal of cyclopentadienyliron moieties has been utilized as a key step in the synthesis of ether and thioether building blocks for polymer synthesis. ... 

Aromatic and aliphatic spaces have been incorporated into organoiron polymers to determine their affect on the thermal stability and glass transition temperature of the polymers.256 The thermal stability of these polymers increased after the loss of the metallic moieties. The metallated polymer shows two decomposition steps at 245°C, corresponding to decomposition of the cyclopentadienyliron moieties and a second weight loss beginning at 511°C, corresponding to... 

At low concentrations (0.025 M) the photolysis of these polymers resulted in the decoloration due to the degradation of the azo dye.260 After the cationic cyclopentadienyliron moieties are cleaved from the polymer, they form complexes with the azo chromophore, which then leads to photodegradation of the azo chromophore. 

Cationic polyferrocenes containing pendent cyclopentadienyliron moieties as well as azo dyes in their backbone, 210, have been prepared.261 These polymers displayed excellent solubility in polar organic solvents and exhibited max around 419 nm. Electrochemical studies showed that these polymers underwent two redox couples corresponding to the two different iron centers. The oxidation of the ferrocene occurred at Ey2 = 0.89 V and the reduction of the cationic cyclopentadienyliron complex occurred atEV2 = —1.42 V. Photolytic cleavage of the cationic cyclopentadienyliron moieties produced the neutral polyferrocene analogs. 

Star-shaped molecules containing cationic arene complexes of iron and ruthenium have been reported by Astruc and co-workers.298 Utilizing the activating nature of the cyclopentadienyliron moiety on the complexed arene, 260 was converted into 262 via bromobenzylation. The photolysis of 262 gave 263, which was subsequently reacted with 264 to give the hexametallic complex 265. Further nucleophilic aromatic substitution reactions with phenol 266 gave the allyl-substituted complex 267 (Scheme 2.70). 

Star and dendrimer core molecules were prepared by the peralkylation or allylation of cyclopentadienyliron complexes containing methyl-substituted arenes.298,301,302,304-311,333 The preparation of water-soluble metallodendrimers containing six cationic cyclopentadienyliron moieties, 281, has also been reported.301 Dendrimer 281 was tested for potential use as a redox catalyst for the cationic reduction of nitrates and nitrites to ammonia. 

Recently, Abd-El-Aziz and colleagues reported different hyperbranched poly(arylethers) (4,5) and poly(arylthioethers) (6) containing cyclopentadienyliron moieties, which were successfully furnished by nucleophilic substitution of A + Bj type monomers (Scheme 2.3) [54], The polymers were thoroughly characterized by standard spectroscopic analysis techniques, they exhibited generally low viscosities, and the organometallic complexes were stable up to 230 °C, as evaluated by thermal gravimetric analysis (TGA). 

TGA analysis showed that polymers 25 were thermally stable with the first weight loss starting between 225 and 241 °C as a result of the decomplexation of the cyclopentadienyliron moieties as well as partial decomposition of the polymer side chains. The second weight-loss beginning between 400 and 450 °C was attributed to the degradation of the polymer backbone. DSC analysis showed that the organoiron... 

The synthesis of a water-soluhle metallodendrimer containing six cationic cyclopentadienyliron moieties was also reported (249). This dendrimer was examined as a redox catalyst for the cathodic reduction of nitrates and nitrites to ammonia. Star-shaped polyaromatic ether complexes of cyclopentadienyliron were recently reported hy Ahd-El-Aziz and co-workers (250). These complexes contained up to 15 cationic cyclopentadienyliron moieties pendent to aromatic rings in the star branches (111). Electrochemical analysis of these star polymers showed that the iron centers underwent reversible reduction processes. 

The synthesis of polymers containing cyclopentadienyliron moieties within and pendent to their backbones (38) was reported by Abd-El-Aziz and coworkers. The cationic cyclopentadienyliron moieties were pendent to the polymer backbones, while the neutral ferrocene units were incorporated into the polymer backbones. The cationic iron centers underwent reversible reduction processes, while the neutral iron centers underwent reversible oxidation processes. The cationic cyclopentadienyliron moieties were cleaved from the polymer backbones by photolysis however, the ferrocene units in the polymer backbones were not degraded. 

The design of polyether/imines coordinated to cyclopentadienyliron moieties (39) has been achieved via the reaction of a dialdehyde complex of cyclopentadienyliron with a number of aliphatic and aromatic diamines. The polycondensation reactions resulted in the isolation of the polyether/imines in good yields. 

Star polymers and dendrimers have been synthesized by Astruc using cyclopentadienyliron-mediated peralkylation, benzylation, and allylation reactions of cationic tri-, tetra-, and /iexa-methylbenzene cyclopentadienyliron com-plexes. " " These star and dendritic polymers contained cationic cyclopentadienyliron moieties at the core and/or the periphery. The cathodic reduction of nitrates and nitrites to ammonia has been achieved using a water-soluble dendrimer containing six cationic cyclopentadienyliron moieties as a redox catalyst. " The octametallic star (41) was prepared by deprotonation of permethylated iron complexes. ... 

IV POLYMERS CONTAINING NEUTRAL AND CATIONIC CYCLOPENTADIENYLIRON MOIETIES... 

Nucleophilic aromatic substitution reactions of haloarenes complexed to transition metal moieties with oxygen-, sulfin-, and nitrogen-containing nucleophiles allows for the synthesis of a wide variety of aryl ethers, thioethers, and amines. These metal-mediated reactions proceed under very mild conditions and allow for the incorporation of a number of different functional groups. Nucleophilic substitution reactions of chloroarenes complexed to the cyclopentadienyliron moiety have been the focus of many studies directed toward the design of functionalized organic monomers. ... 

The synthesis of polyaromatic ethers coordinated to cyclopentadienyliron moieties was achieved via nucleophilic displacement of the chloro groups from... 

The photolytic demetallation of polymers 3a-h was achieved in solutions of acetonitrile, or acetonitrile/DMF, resulting in the isolation of polymers 4a-h. The photolytic reactions were conducted for 4h, and after that time, there was no evidence of the cyclopentadienyliron moieties in the NMR spectra of the organic polymers... 

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. 

The thermal properties of the carboxylic acid-frmctionalized polymers were compared with the azo-frmctionalized polymers in order to examine the effects of the azobenzene sidechains. In addition, a comparison of the thermal properties of the metallated and demetallated azo-frmctionalized polymers could provide information on the influence of the cyclopentadienyliron moieties on these materials. Thermal analysis of these polymers was performed using thermogravimetric analysis and differential scanning calorimetry. 

Coordination of cyclopentadienyliron moieties to polyether/imines was achieved via reactions of a cyclopentadienyliron dialdehyde complex with various aliphatic and aromatic diamines (scheme 24). ... 

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