Polymeric Ligands

As discussed in detail in Section 2.4, the pronounced tendency of tellurium to participate in both hypervalent bonding and secondary 5p - 5a interactions can lead to the construction of polymeric telluride networks. 

Two extreme formulations can be considered for such metal chalcogenides ME3 with linear E chains (i) [M E (E2 )] implying Ei dumbbells as structural fragments ( 2 di) and semiconducting behaviour or (ii) 1oP ]2 implying chains of equidistant E ions d = di) and metallic properties. The former description clearly applies to ZrSe3 di = 

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In polymerizing these compounds, a reaction between a-TiCls and triethylaluminum produces a five coordinate titanium (111) complex arranged octahedrally. The catalyst surface has four Cl anions, an ethyl group, and a vacant catalytic site ( ) with the Ti(lll) ion in the center of the octahedron. A polymerized ligand, such as ethylene, occupies the vacant site ... 

Bipyridines were efficiently used in supramolecular chemistry [104], Since the molecule is symmetric no directed coupling procedure is possible. In addition, 2,2 6/,2//-terpyridine ligands can lead to several metal complexes, usually bis-complexes having octahedral coordination geometries [105,106], Lifetimes of the metal-polymeric ligand depend to a great extent on the metal ion used. Highly labile complexes as well as inert metal complexes have been reported. The latter case is very important since the complexes can be treated as conventional polymers, while the supramolecular interaction remains present as a dormant switch. 

In case of the complexes with polymeric ligands II and III C-0 coupling could be further promoted by changing the solvent and increasing the ratio 1igand/copper ( I 3,J 5). Both factors seem to force the substrates... 

We always applied the polymeric ligands in concentrations below those for homogeneous segmental distribution. In other words we dealt with separate polymer coils containing the active centers, which... 

Unmodified poly(ethyleneimine) and poly(vinylpyrrolidinone) have also been used as polymeric ligands for complex formation with Rh(in), Pd(II), Ni(II), Pt(II) etc. aqueous solutions of these complexes catalyzed the hydrogenation of olefins, carbonyls, nitriles, aromatics etc. [94]. The products were separated by ultrafiltration while the water-soluble macromolecular catalysts were retained in the hydrogenation reactor. However, it is very likely, that during the preactivation with H2, nanosize metal particles were formed and the polymer-stabilized metal colloids [64,96] acted as catalysts in the hydrogenation of unsaturated substrates. 

Water soluble polymeric ligands in aqueous hydroformylation... 

An interesting family of polymeric ligands show inverse temperature dependence of solubihty in water, i.e. they can be precipitated from aqueous solutions by increasing the temperature above the so-called cloud point. Typically these ligands contain poly(oxyalkylene) chains, but the phenomenon can be similarly observed with poly(N-isopropyl acrylamide) derivatives (e.g. 132) and methylated cyclodextrins, too. At or above their cloud points these compounds fall off the solution, due to the break-up and loss of the hydration shell which prevents aggregation and precipitation of their molecules. Conversely, upon cooling below this temperature (also called the lower critical solution temperature, LCST) these substances dissolve again. 

Complex comprising a metal and one or more polymeric ligands. 

Additional ligands, (I), and ringopening polymerization ligand polymers, (II), prepared in the current application are illustrated below. 

A polymeric ligand having pendant sulfide and imidazolyl groups binds Cu2+ to give an efficient oxidation catalyst [35]. The base polymer is a free radical copolymer of ethylvinylsulfide and vinylimidazole. 

A novel approach to electrode design using polymeric ligands was recently illustrated using the nickel—triphenylphosphine system.80 An effective homogeneous electroactive catalyst (Ni/PPh3) is solubilized with 2% crosslinked polystyrene phenylphosphine. The complexed polymer is then... 

Complex formation of poly(amino acid)s and poly(amine)s with several metal ions has been studied by means of potentiometry, colorimetry, and spectrometry in aqueous solutions. In most cases, conformational change of the polymeric ligand is induced as the result of complex formation, leading to changes in reactivity. 

The effect of polymeric ligands on the acid and base hydrolyses of ds-[Co(en)2PVPCl]2+ (PVP = poly-4-vinylpyridine, en = ethylenediamine) (70) and... 

Selective and reversible adsorption of gaseous molecules such as dioxygen, carbon monoxide, ethylene, acetylene, and dinitrogen have been performed by the use of suitable macromolecule-metal complexes. Selective adsorption of metal ions such as UO has also been studied using polymeric ligands. 

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