Chelating atoms

Metal-directed self-assembly of two- and three-dimensional synthetic receptors (macroheterocycles involving transition metal atoms, among them chelated atoms) 98CSR417. 

Structure of the EDTA ion the chelating atoms, six in all, have color screens. 

Figure 33 shows the octahedral geometry of the Mn(II) complex with the ligand dithio-methyl-triazene-1 -oxide, [MeN(0)N-NHC6H4S]2 (CH2)2. Because of the presence of different N202S2 chelating atoms the complex is considerably distorted.48... 

This can be achieved by cyclization (crown ethers), by the formation of an intramolecular hydrogen bond (Taddol and Nobin), or by use of a second metal ion to correctly position the chelating atoms within its coordination sphere (metal (salen) complexes). 

Cheletropic reactions are cyclizations - or the reverse fragmentations - of conjugated systems in which the two newly made o bonds terminate on the same atom. However, a cheletropic reaction is neither a cycloaddition nor a cycloreversion. The reason is that the chelating atom uses two AOs whereas in cycloadditions, each atom uses one and only one AO. Therefore, Dewar-Zimmerman rules cannot apply to cheletropic reactions. Selection rules must be derived using either FO theory or correlation diagrams 38 The conjugated fragment39 of 4n + 2 electron systems reacts in a disrotarory (conrotarory) mode in linear (nonlinear) reactions. In 4n electron systems, it reacts in a disrotarory (conrotarory) mode in nonlinear (linear) reactions. 

When chelation is possible, this is the conformation to consider—the one with the carbonyl O and the other chelating atom almost eclipsing one another. It is the most populated because it is stabilized by the chelation, and it is also the most reactive, because the Lewis-acidic metal atom increases the reactivity of the carbonyl group. Attack is still along the less hindered pathway, but this now leads to the other face of the carbonyl group, and the stereochemical outcome is reversed. 

These solvents dissolve the chalcogen elements sulfur, selenium, and tellurium, and therefore can be used for the solvothermal synthesis of metal chalcogenides by the reaction of metal oxalate with chalcogens at 120°C-200°C. It has been reported that the reaction also proceeds in tetrahydrofuran or pyridine, but the reaction in polyamines having more than two chelating atoms proceeds more completely. ... 

It has even been noted that deprotonation of some chiral, nonracemic carbonyl compounds by an achiral base affords an enolate that is chiral (having a chirality axis or a chelating atom that becomes stereogenic upon coordination to the lithium, for example) and nonracemic, and which affords nonracemic products upon alkylation [144-146], but a mechanistic rationale has not been established. 

J Structural Studies. As was true in the case of the halide anion recognition, important support for the proposed phosphate anion binding interaction has come from single crystal X-ray diffraction analyses. As shown in Figures 6 and 7, respectively, the diprotonated form of sapphyrin binds the monobasic forms of both phosphoric and phenylphosphoric acid. While, at least from the perspective of the coordinated atoms, these two structures bear a striking resemblance to those of the mono- and dihydrochloride salts alluded to above, in both cases it is of interest to note that in each relevant comparison pair, the phosphate oxyanion is far closer to sapphyrin plane. Specifically, in the case of the H2P04 structure, this chelated atom is found to reside 0.83 A (only ) above the macrocylic plane. Similarly, in the case of the 1 2 complex formed between diprotonated sapphyrin and... 

The words nitrogen, oxygen, sulphur, selenium indicate the type of chelating atom. 

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