Arene metal polymers

Apart from the metal atom aggregation reactions described below, bis(arene)metal complexes of the early transition metals are resistant to ligand displacement The rings on the corresponding bis(naphthalene)metal species (41) are by, contrast, labile. Polymer-supported analogs of these naphthalene compounds with vanadium and chromium are known (42), but Ti atoms attack the polymer at the silicon ether linkage. These and other hybrid polymers can be further modified once the metal atom is incorporated. Thus a-methyl naphthalene is displaced from the hybrid organometallic polymer shown in Scheme 7 (43). 

The free or polymer-bound bis(arene)metal complex can also react with metal atoms. Francis et al. (44) first published evidence that the siloxane-bound ic-complexes are converted to dimers and higher nuclearity clusters by additional metal atoms. Their experiments were conducted on quiescent thin liquid films of polymer applied to the optical window of a cryotip (see above, Small Scale Syntheses). Low nuclearity polymer-encapsulated molecules of Tin, Vn, Crn and Mon (n = 2-5) were inferred from quantitative studies of the metal atom aggregation process. The initial reaction appears to occur as follows ... 

The ability of n-arene metal complexes to coordinate additional metal atoms may be significant in the early stages of metallization of some phenyl-rich polymers. At the lowest coverages of say chromium on polystyrene, (arene)2Cr may be formed. With continued accumulation of metal these compounds may rapidly convert to thermally unstable organometallic cluster species that eventually expel the metal core. 

A modern series of new plastics are based on transition metals (e.g. Fe, Ti, Cr, Zn, V) to form polymers and possess unusual properties such as variable oxidation states, and ligand exchange on the metal atom. They have reduced UV absorption and visible radiation and exhibit electrical conductivity. Examples include cyclopentadienyl and arene metal n polymeric complexes that act as electron rich aromatic system and are very reactive to a range of monomers to form polymers. 

The organocobalt polymer 134 was prepared from the reaction of Co2(CO)8 and an acetyl containing polysiloxane.217 Mixed-metal polymers via the reaction of chromium tricarbonyl arene complexes with Mo2Cp2(CO)6 or Co2(CO)8 were also reported. 

Polymers containing aryl groups also react efBdently with metal atoms to yield bis(arene)metal(0) complexes within the polymer chain . Thus, poly(methylphenyl-siloxanes) react at 0°C as a liquid with Ti, V, Cr, Mo and W atoms to give high yields of colored bis( / -arene)metal complexes. In contrast Co, Fe and Ni atoms )deld only metal slurries. Similarly, poly(oxyphenylene) and polystyrene (in a solvent) react with V and Cr atoms to yield colored solutions . By adjusting the metal-atom flux, small, polymer-supported Ti and Mo clusters can be prepared . In some cases the com-plexed metal atoms spontaneously migrate through the polymer fluid to form dimers . 

Tabakei, M. and Yilmaz, M. (2008). Synthesis of a ehitosan-linked ealix[4]arene ehelating polymer and its sorption ability toward heavy metals and diehromate anions. Bioresour. Technol. 99(14), 6642-6645. 

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. 

Recently, Deligoz and Yilmaz [51] prepared three polymeric calix[4]arenes, which were synthesized by reacting chloromethylated polystyrene with 25,26,27-tribenzoyloxy-28-hydroxy calix[4]arene (2a, 3a) and po-lyacryloyl chloride with 25,26,27,28-tetraacetoxy ca-lix[4]arene (4a). After alkaline hydrolysis of the polymers, they were utilized for selective extraction of transition metal cations from aqueous phase to organic phase. 

Selective extraction experiments were then performed to see transference of some transition elements (Cu ", Ni ", Co ", and Fe " ) from the aqueous phase to the organic phase by the synthesized polymeric calixarenes. Phase-transfer studies in water-chloroform confirmed that polymer 2b and 3b were Fe ion-selective as was its monomer (1). Extraction of Fe " cation with 2b and 3b was observed to be maximum at pH 5.4. Only trace amounts of other metal cations such as Cu, Ni ", and Co " were transferred from the aqueous to the organic phase (Table 3). Furthermore, the extracted quantities of these cations remained unaffected with increasing pH. The effect of pH on the extraction of 3b was lower and 56% extraction was accomplished even at pH 2.2. The extraction experiments were also performed with calix[4]arene (1) the ratio was 8.4% at pH 2.2. The polymeric calix[4]arenes were selective to extract Fe " from an aqueous solution, which contained Cu +, Ni, Co ", and Fe " cations, and it was observed that the... 

Tullock C.W. et al.. Polyethylene and elastomeric polypropylene using alumina-supported bis(arene) titanium, zirconium, and hafnium catalysts, J. Polym. Sci, Part A, Polym. Chem., 27, 3063, 1989. Mueller G. and Rieger R., Propene based thermoplastic elastomers by early and late transition metal catalysis. Prog. Polym. Sci., 27, 815, 2002. 

The same polymeric arenes that served as metallation catalysts in equation 119 can also be used for silylation in Barbier-type reactions (equation 131). The polymer is presumably converted to a lithium arene adduct that activates metallic lithium for metallation of the halogenated substrates, before addition of an electrophile to achieve the synthetic goal. Equations 132-135 illustrate some of the cases investigated. The products can be characterized by the usual spectroscopic methods . 

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