Arene-transition metal polymers

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. 

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. 

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). 

There are a few examples of polymers based on vinylbenzofurans. Vinyldibenzofuran 324 has been patented for use in copolymer formulations with other vinyl arenes, used to prepare light-emitting devices <2004USP6803124>. Benzofuran 325 was developed as one of four polymerizable monomers that contain a built-in antioxidant. The polymerization process was transition metal catalyzed <2003MM8346>. Benzofuran 326 also contains the styrene substructure, but there are few examples of its polymerization. Poly(2,3-benzofuran) films were synthesized by anodic oxidation on stainless steel in the presence of boron trifluoride etherate. The films had good thermal stability and conductivity of lO Scm <2005MI1654>. 

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. 

Transition metal n-complexes can be used in photolabile linkers. The ir-complex 40 was formed from the chromium arene complex 39 and polymer-supported tri-phenylphosphine (38) [60] (Scheme 17.20). The complex 40 tolerated LiAlH4 reduction and acetylation, but released the product 41 in 70% yield when oxidized with air under the influence of UV irradiation. 

Various oxidations with [bis(acyloxy)iodo]arenes are also effectively catalyzed by transition metal salts and complexes [726]. (Diacetoxyiodo)benzene is occasionally used instead of iodosylbenzene as the terminal oxidant in biomimetic oxygenations catalyzed by metalloporphyrins and other transition metal complexes [727-729]. Primary and secondary alcohols can be selectively oxidized to the corresponding carbonyl compounds by PhI(OAc)2 in the presence of transition metal catalysts, such as RuCls [730-732], Ru(Pybox)(Pydic) complex [733], polymer-micelle incarcerated ruthenium catalysts [734], chiral-Mn(salen)-complexes [735,736], Mn(TPP)CN/Im catalytic system [737] and (salen)Cr(III) complexes [738]. The epox-idation of alkenes, such as stilbenes, indene and 1-methylcyclohexene, using (diacetoxyiodo)benzene in the presence of chiral binaphthyl ruthenium(III) catalysts (5 mol%) has also been reported however, the enantioselectivity of this reaction was low (4% ee) [739]. 

POLYMERS CONTAINING ARENES COORDINATED TO TRANSITION METAL COMPLEXES... 

The coordination of transition metal moieties to arenes alters the reactivity of the aromatic ring, making it more susceptible to nucleophilic addition and substitution reactions and also making substituents on the arene more readily deprotonated. Some of the first examples of polymers containing arenes n-coordinated to transition... 

Abd-El-Aziz. A.S. Monomers, oligomers and polymers containing arenes with pendent transition metal moieties. Coord. Chem. Rev. 2002. 233-234. 177-191. 

---