Metal complexation synthetic polymers

Based on the models of natural metal complexes synthetic metal complexes have been developed for different purposes. They consist of a synthetic polymer, which is the replacement of the biopolymer protein in the natural metal complexes, and a specific synthetic ligand that is able to bind the metal ions. The basic model of synthetic metal complexes is shown in Figure 7. 

Metal-acetylide complexes have been used as a unit of organometallic polymers that have metallic species in the main chain [20]. Representative examples are metal-poly(yne) polymers (19) of group 10 metals depicted in Scheme 5. These polymers are easily prepared from M(PR3)2Cl2 (M=Pt, Pd) and dialkynyl compounds catalyzed by Cu(I) salts in amine. Recently, this synthetic method was successfully applied to the construction of metal-acetylide dendrimers. 

We shall focus here on the synthesis of the isocyanide-containing polymer. Several reactions of the polymer with the metal vapors of Cr, Fe and Ni using a matrix-scale modeling technique, as well as synthetic-scale metal vapor methods, are then presented in order to demonstrate the reactivity of the isocyanide groups on the polymer. Finally, preliminary studies of the reactivity of the polymer-based metal complexes are described. 

In the present paper we describe the catalytic mechanisms of synthetic polymer-Cu complexes a catalytic interaction between the metal ions which attached to a polymer chain at high concentration and an environmental effect of polymer surrounding Cu ions. In the latter half, the catalytic behavior is compared with the specific one of tyrosinase enzyme in the melanin-formation reaction which is a multi-step reaction. To the following polymers Cu ions are combined. 

Figure 3 Schematic illustration of a hybrid hydrogel system—genetically engineered coiled-coil protein domains used to crosslink synthetic water-soluble polymers. Divalent transition metal ions are shown to form complexes with nitrogen-oxygen-donor ligands on the synthetic polymer side chains and the terminal histidine residues in the coiled coils.

While in most of the reports on SIP free radical polymerization is utihzed, the restricted synthetic possibihties and lack of control of the polymerization in terms of the achievable variation of the polymer brush architecture limited its use. The alternatives for the preparation of weU-defined brush systems were hving ionic polymerizations. Recently, controlled radical polymerization techniques has been developed and almost immediately apphed in SIP to prepare stracturally weU-de-fined brush systems. This includes living radical polymerization using nitroxide species such as 2,2,6,6-tetramethyl-4-piperidin-l-oxyl (TEMPO) [285], reversible addition fragmentation chain transfer (RAFT) polymerization mainly utilizing dithio-carbamates as iniferters (iniferter describes a molecule that functions as an initiator, chain transfer agent and terminator during polymerization) [286], as well as atom transfer radical polymerization (ATRP) were the free radical is formed by a reversible reduction-oxidation process of added metal complexes [287]. All techniques rely on the principle to drastically reduce the number of free radicals by the formation of a dormant species in equilibrium to an active free radical. By this the characteristic side reactions of free radicals are effectively suppressed. 

Abstract This review describes recent results in the field of poly(aryleneethynylene)s (PAEs) that contain metal ions in the polymer backbone, or in the polymer side chain. This work is focused primarily on polymers possessing ligands of metal complexes as part of the aryle-neethynylene chain. PAEs with porphyrinylene in the backbone have also been addressed. Synthetic routes toward the polymers, as well as their photochemical, photophysical, and electrochemical properties, are presented. Monodisperse oligo(phenyleneethynylene)s with terminal metal complexes or with a ferrocene and thiol at each end are mentioned. 

Conjugated dienes such as 1,3-butadiene very readily polymerize free radically. The important thing to remember here is that there are double bonds still present in the polymer. This is especially important in the case of elastomers (synthetic rubbers) because some cross-linking with disulfide bridges (vulcanization) can occur in the finished polymer at the allylic sites still present to provide elastic properties to the overall polymers. Vulcanization will be discussed in detail in Chapter 18, Section 3. The mechanism shown in Fig. 14.3 demonstrates only the 1,4-addition of butadiene for simplicity. 1,2-Addition also occurs, and the double bonds may be cis or trans in their stereochemistry. Only with the metal complex... 

In order to gain more control over this reaction, chromium salphen dimers were synthesized. The synthetic route was developed in such a manner that the bridging length between the two salphen units can easily be varied and that the synthesis of heteronuclear metal complexes is possible. Since the ligand substitution pattern is highly important for the activity of the catalyst as well as the characteristics of produced polymer, an analogous monomeric Cr(lll) complex was synthesized for comparison [102] (Fig. 35). 

Synthetic polymers stabilize metal colloids as important catalysts for multi-electron reactions. Polynuclear metal complexes are also efficient catalysts for multielectron processes allowing water photolysis. 

A polymer ligand might be expected to protect the dioxygen-metal complex against autoxidation in much the same way as the globin protein does. In this chapter, we describe how polymer-metal complexes react with molecular oxygen and introduce attempts to construct synthetic oxygen carriers. 

As mentioned above, in metal ion-catalyzed oxidations many polymer-metal complexes have been found to exhibit high catalytic efficiency in comparison with their low-molecular-weight analogs. Table 12 summarizes the catalytic activity of the Cu complexes of synthetic polymers. It is noteworthy that high efficiency is observed for complexes composed of simple synthetic polymers arch as poly-(ethyleneimine), poly(vinylpyridine) and poly(acrylic add). 

The characteristics of synthetic polymer-metal complexes having uniform structure were illustrated. The chemical reactivity of a metal complex is often affected by the addition of a polymer ligand that exists outside the coordination sphere and air-rounds the metal complex. The effects of polymer ligands have been summarized under two heads steric effects, and environmental effects. 

Hydroxy- and 1,8-dihydroxy-anthraquinones form neutral 2 1 complexes (209) with divalent metals such as copper and zinc, whilst 1,4- and 1,5-dihydroxyanthraquinones form polymeric complexes (210) and (211), respectively. The latter are virtually insoluble in a wide range of organic solvents and have been used for the mass pigmentation of synthetic polymers. The parent compounds have also found application as mordant dyestuffs, e.g. (212), (213) and (214). 

These new complexes and polymers are related to the square-planar palladium and platinum polyynes which have recently been shown (25-28) to exhibit interesting X ) behavior. We have not yet measured the %(3) properties of our rhodium complexes, or the molecular weights of the polymers. Current synthetic work is directed towards understanding the influence of the linker groups on electronic communication between the metal centers, and on designing new linkers with low-lying 7i levels to improve conjugation. 

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