Improved synthetic methods ligands

New synthetic routes have therefore been developed in order to improve the purity of the precipitates. Thus pure tetrakis complexes (see fig. 55, bottom) could be isolated using ligand 57 in ethanol with a large excess of sodium ions in slightly basic conditions (method D, table 12), whereas method B seems to be the more appropriate synthetic way to obtain pure trimeric complexes. Pure tris complexes could not be isolated however mixtures with up to 75% of tris complex could be obtained by using as little ammonium hydroxide as possible and a mixture of dichloromethane and water as biphasic solvent (improved A method). 

Finally, while the new synthetic methods for technetium compounds in the oxidation states I, II and V will undoubtedly play an important role in the development of improved radioscintigraphic agents, there remains a need to understand the chemical mechanisms involved in these syntheses, particularly with regard to ligand substitution reactions and atom transfer redox processes. Mechanistic studies to complement the increasing body of structural knowledge is essential to the further development of technetium radiopharmaceuticals. 

Aromatic amines are found in biologically active natural products, common pharmaceuticals, dyestuffs, materials with conductive and emissive properties, and ligands for transition-metal-catalyzed reactions. For these reasons much effort has been spent for more than a century on methods to prepare aromatic amines. The synthetic methods to obtain these materials range from classical methods, such as nitration and reduction of arenes, direct displacement of the halogens in haloarenes at high temperatures, or copper-mediated chemistry, as well as modem transition-metal-catalyzed processes and improved copper-catalyzed processes. The following sections describe each of these synthetic routes to aromatic amines, including information on the scope and mechanism of most of these routes to anilines and aniline derivatives. 

An improved synthetic route to bis(indenyl)dimethyl metallocenes 653 involves treatment of the neutral ligand with a twofold excess of MeLi followed by the reaction of the resulting mixture with MC14 (M = Zr, Hf) in pentane477 (Scheme 151). This simple, one-pot method produces the metallocene dimethyl complexes in high overall yields... 

Vicinal amino alcohols are highly useful molecules. Vicinal amino alcohols find use as synthetic intermediates, ligands for metal catalyzed reactions, and as biologically interesting molecules. It is not surprising that considerable effort has gone into the synthesis of useful vicinal amino alcohols as well as the development of new and improved methods for their synthesis. 

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