Chelates and chelation

Amperometric titrations involving chelates and chelating agents. J. Dolezal, K. Stulik and J. Zyka, Chelates Anal. Chem., 1972, 3, 57-150 (300). 

Chelates and chelating agents in the analytical chemistry of niobium and tantalum. E. Lassner and R. Puschel, Chelates Anal. Chem., 1969, 2, 213-340 (311). 

Conductometric and high frequency impedimetric titrations involving chelates and chelating agents. 

Sec also Chelates and Chelation Cobalt Copper Gold Hydrate Iron Manganese and Molybdenum (In Biological Systems). 

LIGAND. Any atom, radical, ion, or molecule in u complex ipnly-ulomic group) which is hound lo the central aiorn. Thus, the ammonia molecules in Co(NH-,l(,, ". and ihe chlorine atoms in PtCIn) arc ligands. Ligands are also eomplcxing agents, as for example. EDTA. ammonia, etc. See also Chelates and Chelation. 

Hexacoordinated structures prevail in the case of complexonates of the triamine series [764]. However, a great variety of CN of metals is also observed. Moreover, many coordination modes are observed for the complexones of the triamine series, penta-, hexa-, hepta-, and octa-types with chelate and chelate-bridge function of mono-, di-, tri-, and tetra-deprotonated ligands. As a result, a number of metal-cycles are formed. Thus, maximum dentacity of diethylenetriami-noacetic acid 431 (m = n = p = q = 1), with respect to a metal atom, equals 8 (3N+50), leading to seven metal-cycles (two ethylenediamine and five glycine) being formed [764]. 

R. Piischel and E. Lassner, Chelates and Chelating Agents in the Analytical Chemistry of Molybdenum and Tungsten, in Chelates in Analytical Chemistry, Vol. 1 (H. A. Flaschka and A. J. Barnard, eds.), Marcel Dekker, New York (1967). 

The chiral sulphoxide, (S)-(+)-2-(4-tolylsulphinyl)-2-cyclopentenone, has been used as a ring D component to effect an asymmetric Michael addition with 91-94% diastereoselectivity by reaction in the chelated form with the a,a-disubstituted lithium enolate from 2-bromo-6-methoxytetral-1-one while the (R)-(-) antipode reacts in a non-chelated form with the a-monosubstituted lithium enolate of 6-methoxytetralone (ref. 147). This synthesis makes use of earlier experience in the use of a-mono and a,a-disubstituted lithium enolates in the ethyl acetoacetate series with the non-chelated and chelated forms respectively of a p-ketosulphoxide (ref. 148). Eight futher steps were involved to produce (+)-estrone methyl ether in an overall yield of 6.3%. 

In 1955 Mellor was appointed Professor of Chemistry at the Univeraty of New South Wales. Unfortunately, he did no more experimental research, but he was the author of four books The Rdle of Science and Industry in Australia in the War of 1939-194509), Chelating Agents and Metal Chelates 20),The Evolution of the Atomic Theory (21), and Chemistry of Chelation and Chelating Agents (22). 

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