Details

Autor(en) / Beteiligte

• Trabesinger, Gerald
• Albinati, Alberto
• Feiken, Nantko
• Kunz, Roland W
• Pregosin, Paul S
• Tschoerner, Matthias

Titel

Enantioselective Homogeneous Catalysis and the “3,5-Dialkyl Meta-Effect”. MeO−BIPHEP Complexes Related to Heck, Allylic Alkylation, and Hydrogenation Chemistry

Ist Teil von

• Journal of the American Chemical Society, 1997-07, Vol.119 (27), p.6315-6323

Ort / Verlag

American Chemical Society

Erscheinungsjahr

1997

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• The enantioselectivities arising from a Pd-catalyzed Heck reaction (>98% ee) and an allylic alkylation (>90% ee) using a 3,5-di-tert-butyl-MeO−BIPHEP chiral auxiliary (1) are reported. Higher ee's are observed with the 3,5-dialkyl substituents than with the unsubstituted parent MeO−BIPHEP. It is proposed that the observed dialkyl “meta-effect”, on enantioselectivity, is the combined result of a more rigid and slightly larger chiral pocket and that this effect will have some generality in homogeneous catalysis. Detailed NMR studies on the allyl complex [Pd(PhCHCHCHPh)(1)]PF6 (5), and the model hydrogenation catalyst [RuH(cymene)(1)]BF4 (6), reveal restricted rotation about several of the P−C(ipso) bonds of the phosphorus substituents containing the 3,5-di-tert-butyl groups. The X-ray structure of 6 reveals that the cymene ligand is not symmetrically bound to the Ru atom. This observation is interpreted as an expression of the chiral pocket of 1. MM3* calculations on 6 support the NMR findings and reproduce the X-ray results.