Ligand structures systems

Besides structure and substructure searches, Gmclin provides a special search strategy for coordiuation compouuds which is found in no other database the ligand search system, This superior search method gives access to coordination compounds from a completely different point of view it is possible to retrieve all coordination compounds with the same ligand environment, independently of the central atom or the empirical formula of the compound. 

The scaffolding technique still requires intense validation studies to develop and optimize the different synthesis conditions required for the different backbones and ligand systems. Different electronic and steric properties may lead to synthetic conditions and in some cases even to alternative synthetic routes to arrive at a given ligand structure. 

Asymmetric hydrosilylation of ketones has developed enormously since these early reports and probably there are few catalytic reactions for which the variety in ligand structure is so immense as for this reaction. Numerous reports have been published and in general oxazoline-based ligand systems seem to give the highest enantioselectivities. In the following we will mention a few... 

The interplay between solvent polarity and boron ligand structure in the enhancement of aldol stereoselection has been examined in several systems (6). The representative trends that have been noted for the boryl enolates derived from both cyclohexanone and tert-butyl thiopropionate (eqs. [49] and [50]) are summarized in Table 21. 

Kruger, H.-J., Peng, G. and Holm, R. H. (1991) Low-potential nickel(III,II) complexes - new systems based on tetradentate amidate thiolate ligands and the influence of ligand structure on potentials in relation to the nickel site in [NiFe]-hydrogenases. Inorg. Chem., 30, 734-42. 

Designing potential DNA intercalators has led to an investigation of a series of [Ru([9]aneS3)LCl] complexes where L is a didentate polypyridyl ligand. Structural data for the complexes are discussed in terms of hydrogen-bonded interactions and rr-stacking between extended aromatic systems, e.g., dppz and 4,7-Ph2phen. " ... 

A variable-temperature Li, C, NMR spectroscopy study was carried out on the ligand structure and association behavior of [ Li, N]-enriched lithium bis(trimethylsilyl)-amide in hydrocarbon solntion. The system behaves as shown, for example, in equation 38, with the solnte adopting a dimeric form (209), which tnms to the monomeric 210 on... 

These, in turn, can be condensed with amines to give imines 4 or ketimines 5 and 6, or reduced to give amino alcohols 7-9, respectively. The ligand structure is therefore vastly variable. Steric factors, such as flexibility of backbone and side-chains, as well as electronic factors (for example sp versus sp conflguration of the N-donors) can be easily modulated. The introduction of central chirality via chiral amine side-chains is also possible. The interaction of planar and central chirality, usually referred to as chiral cooperativity [11-13], can thus be studied in a ligand system which has both planar and central chiral elements. 

A series of earlier papers on complexes of indium(III) with porphyrins,265 and phthalocyanines266-268 has been summarized earlier.7 The structures InLX (L = substituted porphyrin X = Cl, OAc, OPh) imply a square pyramidal stereochemistry with the indium atom situated above the ligand N4 system, and this has been confirmed by X-ray crystallography for X = C1269 and X = Me,270 but for X = MeOS02, the indium atom is in the plane of the four nitrogen atoms.271 A number of Schiff base derivatives have recently been described.272... 

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