Cyclopentadienyliron complexes

Thus, reaction of cyclopentadienyliron complex 1, containing a cr-bound but-3-enyl unit, with radical or proton-source (e.g. trifluoroacetic acid) reagents leads to regioselective cyclopropane formation with high yields. ... 

Stereochemical investigations of the above mentioned reactions of cyclopentadienyliron complexes have been helpful in understanding the mechanism of [2+1] cyclopropanation of alkenes with cationic cyclopentadienyliron carbene complexes. Based on the results of these investigations, the cyclopropanation is believed to occur due to electrophilic attack by the carbene center of metallacarbenoid 5 at the less substituted position of the alkene to produce cationic complex 6 which undergoes back-side ring closure to alford 7 or front-side ring closure to afford 8 depending on cation stability, lifetime and rotation of the fS-y bond in 6. ... 

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. 

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... 

Cationic star-shaped molecules containing cyclopentadienyliron complexes, where the organo-metallic cations are evenly distributed throughout the molecule branches, 250, have been reported (Scheme 2.67).295 296 291 Electrochemical studies of these materials indicated that the iron centers underwent reversible reductions. For the hexametallic star-shaped molecule (n = 1), two redox potentials were observed at KU2 = I -20 and —1.30 V. 

Various first-generation dendrimers and star-shaped molecules were generated from the nucleophilic aromatic substitution of chlorosubstituted arenes coordinated to cyclopentadienyliron complexes (Schemes 2.68 and 2.69). These compounds contained either ether or ester bridges. The star-shaped molecules prepared with ether bridges showed a decrease in solubility with an increase in star size, whereas the incorporation of ester bridges resulted in a decrease... 

A number of research groups have reported the preparation of a large number of star-shaped molecules and dendrimers containing ferrocenyl or arene cyclopentadienyliron complexes at the core or the peripheries.300-320 A number of these dendrimers were prepared via cyclopentadienyliron-mediated per-alkylation, -benzylation and -allylation reactions of cationic tri-, tetra- and hexamethylbenzene complexes. These dendrimers were multifunctional materials and have been used in the synthesis of branched organic and organometallic polymers. 

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. 

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. 

Figure 23 Schematic representations of the photochromism of (a) diarylethene-biidged dinuclear bis(bipyridyl)ruthenium(II) complex, (b) diaiylethene-bridged dinuclear cyclopentadienyliron complex, and (c) diethynylethene-bridged dinuclear ferrocene complex.

A route to non-racemic P-stereogenic vinylphosphine-boranes, e.g., (100), is afforded by the addition of methylphenylphosphine-borane with alkynes in the presence of a chiral diphosphine-palladium catalyst. The ehiral diphosphine-platinum complex-catalysed addition of diethylphosphine to the diene cis,cis-muco-nitrile has given the new diphosphine (101) as a 3 2 mixture of diastereoisomers. Further work has been reported on the use of cyclopentadienyliron complexes that act as metal templates for the intramolecular hydrophosphination of coordinated vinylphosphines with 1,2-diphosphino-alkanes and -benzenes, leading to 1,4,7-triphosphacyclononanes, e.g., (102), capable of further elaboration to form new cyclic phosphines. 

The synthesis of polyaromatic ethers (37) and thioethers containing azobenzene dyes in their sidechains has been achieved. These polymers were prepared by reaction of cyclopentadienyliron-complexed azobenzene monomers with various dinucleophiles. These organoiron polymers were bright orange or red, and could be bleached by irradiating the polymer in a solution containing hydrogen peroxide. 

The electrochemical properties of the trimetallic monomers were examined using cyclic voltammetry. It has been established that cationic cyclopentadienyliron complexes undergo reduction processes, while ferrocene and functionalized ferro-cenes undergo oxidation processes. Figure 25 shows the cyclic voltammogram of complex 49. The 1/2 value obtained for the oxidation of the neutral iron center was 0.994 y and the 1/2 value obtained for the reduction of the two terminal cationic iron centers was -1.12 V... 

Good agreement has been observed by Wrackmeyer et between the DFT calculated and experimental Vhfc and /cFe couplings in a series of ferrocenes and cyclopentadienyliron complexes. 

Polymers containing pendent cationic cyclopentadienyliron complexes, as well as ferrocene and azo dyes in the backbone 71 have also been reported. These brightly... 

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