Cationic iron moieties

Abd-El-Aziz. A.S. Todd. E.K. Okasha, R.M. Wood. T.E. Novel approaeh to oligomers and polymers eontaining neutral and cationic iron moieties within and pendent to their backbones. Maeromol. Rapid Commun. 2002. 23. 

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). 

As with homopolymers, block copolymers may incorporate metals such as in the work of Chan and Schrock where palladium-containing norbornene moieties were copolymerized and the metal reduced below the Tg of the polymer to afford metal clusters whose size was modulated by the polymeric composition. Even with fairly labile metals, the gentle reaction conditions of ROMP can incorporate them into polymeric networks. The ROMP of a variety of norbornene derivatives bearing cationic iron moieties was accomplished without loss of the iron, whereas heating above 100 °C resulted in loss of the iron without degradation of the polymer. The norbornene polymer sans iron was also realized via photolysis. ... 

The octasubstituted cored dendrimer 24-FeAr containing 24 cationic aminoarene iron moieties [dendr-( 6-NHC6H4MeFeCp )24] (Cp = rj5-CsMes), i.e. eight tripods, was compared to the analogous mono- and trimetallic amino-arene cationic complexes (resp. 1-FeAr and 3-FeAr, Scheme 9 and Fig. 12) with the same amino-arene iron-sandwich structure for the... 

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. 

Very high endo or cis selectivities have been reported for the reactions of olefins with phenyldiazomethane in the presence of a cationic iron complex11. a-Selenobenzyllithium compounds are carbenoids which transfer the phenylcarbene moiety to olefins with considerable trans preference12. 

In iron reactions where the reagent was equivalent to C, described in Section 8.9.A, the iron moiety was used as an auxiliary. Iron can also stabilize cations, which then react with nucleophiles to generate new carbon-carbon bonds. 08 xhese cations are formed as iron-alkene complexes, usually by reaction of cyclo-pentadienyl dicarbonyl ferrate anion (478) with an allylic halide such as 3-chloro-2-methyl-l-propene. The... 

The ROMP of norbornenes functionalized with neutral ferrocenyl moieties has been reported the aim was to prepare redox-active polymers (218, 219) (eq. 26). The synthesis of polynorbornenes functionalized with cationic cyclopentadienyliron-coordinated aryl ethers has also been reported (220). Demetallation of metallated norbornenes and polynorbornenes led to the liberation of their organic analogues (221-223). Electrochemical analysis of the metallated polymers showed that the cationic iron centers were reduced between -1.2 and -1.4 V. 

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 iron complexes show two-fold reactivity. They react with both strong electrophiles and with strong nucleophiles as the iron can stabilize both the cationic and anionic intermediates. While the electron-withdrawing iron moiety activates the diene to nucleophilic attack, it deactivates it towards electrophilic attack. Electrophilic attack is still useful - the iron stabilizes the diene to all the side reactions that could go along with electrophilic attack, and stabilizes the cationic product. 

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. 

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. 

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. ... 

John, G.R. and Mane-Maguire, A.P, Kinetics of nucleophilic attack on coordinated organic moieties. Part 7. Mechanism of addition of tertiary phosphines to tricarbonyl(dienyl)iron cations, /. Chem. Soc., Dalton, 873, 1979. 

Compound [25] was thus shown to have an unusual affinity for Ag+ cations. X-ray crystallographic determination of the structures of the free ligand, sodium and silver complexes were carried out and are shown in Fig. 17. The Ag-Fe distance in the silver complex of [25] is only 3.37 A, whereas the Na-Fe distance in the sodium complex is 4.39 A. This evidence together with the FAB MS data and UV spectroscopic data suggests that there may be an interaction between the silver cation and the iron present in the ferrocene moiety. 

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