Structural chemistry chelate complexes

Transition metal hydroxyoxime complexes have been reviewed very recently.2507 Their use in both analytical chemistry and extraction metallurgy is well known. The square planar structure of the bis chelate complex NiL (347) with the deprotonated 2-hydroxybenzaldoxime (HL) is typical of this series of nickel complexes.2508 Their bis adducts, NiLJ, with bases such as py, substituted pyridines and cyclomethyleneimines, are six-coordinate.2509 The acyl oxime (H2L) complexes are similar to the aforementioned complexes being either square planar bis chelates Ni(HL)2 (348) or octahedral bis adducts, Ni(HL)2B2.2507 When the acyl oxime acts as a dibasic ligand L, the corresponding (NiL) complexes are insoluble and involve extensive polymerization. 

My first incursion into organo-transition metal chemistry occurred because of my interest in chemical bonding. How did olefins with no lone pair of electrons form coordinate bonds to metal atoms The position in 1941 can be read in Keller s review on olefin complexes 54). During the war years I was able to assemble a card index of all references to olefin complexes and I convinced myself that they should be formulated as chelate complexes of, for example, structure (VII) for Zeise s ion if chlorine could bridge metal atoms why should it not bridge carbon to a metal Nature rejected my letter on this topic as being... 

Equation (12) illustrates the following general principle electrophiles able to form a chelated complex with the Lewis acid e.g. 28) control (usually invert) the simple stereoselection of the reaction . The major isomer (29) is, in fact, syn. Adducts (29) and (30) were then transformed, by simple functional group chemistry, into (+)-PS-5, a carbapenem antibiotic. Transition structure models for this process are discussed in detail in Section 2.4.4.1. 

In a review of the stereochemistry of a-hydroxycarboxylate complexes, Tapscott includes the structural chemistry of complexes that contain ligands in which a sulfur atom is attached to a carbon a to a carboxylic group. This includes both a-mercapto and a-thioether groups. Lists of structural bonding parameters for a-thiocarboxylate complexes are given together with parameters for chelate rings. 

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