We have synthesized chiral amino alcohol tantalum(V) catalysts for the asymmetric intramolecular hydroamination of aminoallenes to produce chiral pyrrolidine products. Previous studies using tris(dimethylamido) tantalum amino alcohol complexes produced the pyrrolidine product with an enantioselectivity up to 76 %ee. In an attempt to improve the selectivity, we proposed the addition of a pentamethylcyclopentadiene (Cp*) group to the complex.  This  extra steric bulk should increase selectivity in the asymmetric bond-forming step. Attempts to append the Cp* ligand onto TaCl(NMe2)4 using salt metathesis have thus far been unsuccessful, so we have turned our attention to using Cp*Ta(CH3)4 as a catalyst precursor.   We have recently developed a library of chiral ?2 amino alcohol ligands (H2X2) derived from phenylalanine and valine. Protonolysis of two methyl groups on the precursor form the desired chiral tantalum(V) amino alcohol complexes. Results from hydroamination reactions using these catalysts will be presented.

Sterically congested tantalum(V) complexes for the asymmetric hydroamination of aminoallenes

239th National Meeting (2010)

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