Complexation/chelation

Ferric ammonium citrate [1185-57-5]—A mixture of complex chelates prepared by the iateraction of ferric hydroxide with citric acid ia the presence of ammonia. The chelates occur ia brown and green forms, are dehquescent ia air, and are reducible by light. 

Scheme 27 Rigid chiral carbene complex chelates in diastereoselective benzannulation...

Several groups have reported the use of rare earth complexes as catalysts for asymmetric Diels-Alder reaction. Qian and Wang described thus the preparation and use of Yb complexes chelated by Pr-PyBOx to successfully achieve the hetero-Diels-Alder reaction of methyl glyoxylate with Danishefsky s diene in 77% ee and 73% yield (Scheme 37) [98]. 

It is for long known that all aforementioned acids form stable complex (chelate) compounds with numerous, especially transition metal cations (see, e.g., Refs. [21, 22]). This fact is pointed out in practically all papers on the subject. However, the composition of complex compounds, their stability, the type of bonding between metal cations and carboxylic anions on various stages of the synthesis, and possible role of steric factors in these phenomena are discussed in a very small number of publications. 

Ion-association complexes may be classified into three types non-chelated complexes chelated complexes oxonium systems. 

The question of which pathway is preferred was very recently addressed for several diimine-chelated platinum complexes (93). It was convincingly shown for dimethyl complexes chelated by a variety of diimines that the metal is the kinetic site of protonation. In the system under investigation, acetonitrile was used as the trapping ligand L (see Fig. 1) which reacted with the methane complex B to form the elimination product C and also reacted with the five-coordinate alkyl hydride species D to form the stable six-coordinate complex E (93). An increase in the concentration of acetonitrile led to increased yields of the methyl (hydrido)platinum(IV) complex E relative to the platinum(II) product C. It was concluded that the equilibration between the species D and B and the irreversible and associative1 reactions of these species with acetonitrile occur at comparable rates such that the kinetic product of the protonation is more efficiently trapped at higher acetonitrile concentrations. Thus, in these systems protonation occurs preferentially at platinum and, by the principle of microscopic reversibility, this indicates that C-H activation with these systems occurs preferentially via oxidative addition (93). 

Free metal ions Inorganic ion pairs complexes Organic complexes chelates Metals species bound to high molecular weight DOM Metals in colloids Metals sorbed onto colloids Precipitates... 

Binding of metal ion/ complex/ chelate at a macromolecular chain, network or surface... 

Metal complex/ chelate as part of a polymer via the metal or the ligand... 

Physical interaction of metal complexes/ chelates/ clusters with organic and inorganic macromolecules... 

Type 3 metal complexes involve the physical interaction of a metal complex, chelates, or metal cluster with an organic polymer or inorganic high molecular weight compound. The preparation of type 3 compounds differs from those of type 1 and type 2, as they are ultimately achieved through the use of adsorption, deposition by evaporation, microencapsulation, and various other methods. 

To some extent, the aqueous metal silicate complexes constitute an entire class of placeholders. There is ample evidence that silica forms strong complexes with several metals, but the stoichiometry of such complexes has not yet been established. Different speciation schemes have been proposed to interpret experimental data, for example, 1 2 complexes, chelates, or mixed hydroxide silicate complexes. Despite these ambiguities we decided to include several metal silicate complexes in the data base as guidelines for modellers. Should such complexes turn out to be of crucial importance in particular systems, additional experimental studies would be called for. 

The reaction of hexacyanometalates with metal complexes chelated by penta-dentate ligands may afford polynuclear complexes. The presence of the penta-dentate ligand precludes the polymerization that leads to extended systems. The preparation of a representative heptanuclear, mixed-valance iron complex, [Fe (CNFe° (salmeten))6]Cl2 6H20, is detailed herein. 

Lewis Base Complexes, Chelated Metal Amides and Heteroleptic Amido Complexes... 

The number and variety of coordination complexes of palladium(II) with sulfur-containing bidentate or multidentate ligands is legion, and it is possible here only to summarize the different kinds of complexes formed and to guide the reader into the literature. Table 2 contains a selection of typical palladium(II) complexes of bi- or multi-dentate sulfur or selenium donor ligands, and comments on pertinent aspects of particular complexes. Chelate... 

The C3F7COCHCOBul ligand (often abbreviated as fod) has both a high fluorine content and bulky side chains, a combination of features which leads to quite high volatility in its complexes. Chelates of this ligand are often isolated as hydrates but these can be readily desolvated without significant decomposition.349... 

Free Metal Inorganic Organic Complexes, Ions Complexes Chelates... 

Getty, A. D. Goldberg, K. I. Reaction of a Pd(II) complex chelated by a tridentate PNC ligand with water to produce a [(PN)Pd(w-OH)]22+ dimer a rare observation of a well-defined hydrolysis of a Pd(II)—aryl compound. Organometallics 2001, 20, 2545—2551. 

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