Asymmetric catalysis using niobium and tantalum complexes

TL;DRAbstract

Niobium and tantalum have been used for a number of catalytic reactions. These mclude carbon monoxide reduction, dimensation and polymerisation of olefins, oligomerisation and polymerisation of acetylenes, nucleophilic Wittig-type reactions, hydrogenation of arenes and aryl phosphmes, hydrodemtrogenation and hydroboration reactions.
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\nIn this work their potential as enantioselective catalysts was investigated. The metal chlorides displayed Lewis-acid activity and they were used, in conjunction with a number of chiral ligands, in the catalysis of the Diels-Alder reaction between cyclopentadiene and either crotonaldehyde or methacrolem. A number of ammo acids were investigated and, although Lewis-acid activity was evident from the yield at low temperature and from the endo.exo ratios, no chiral induction was achieved. When Cisymmetncal tartrate esters were used ee’s of 22 and 40% m the presence of niobium pentachlonde were achieved for the ethyl and i-propyl esters respectiv

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