A Stable and Recoverable Chiral Ru Lewis Acid: Synthesis, Asymmetric Diels-Alder Catalysis and Structure of the Lewis Acid Methacrolein Complex.

Ease of generation, stablity in solution at ambient temperature, high enantioselectivity in Diels-Alder reactions, efficient catalyst recovery, and large rate differences on variation of the anion are all characteristics of the new Ru Lewis acid [CpRu((S,S)-biphop-F)]+ (biphop-F=(C6 F5 )2 POCH2 (Ph)CH2 (Ph)OP(C6 F5 )2 ). The structure of complex 1 (L=methacrolein, Y=SbF6 ) provides evidence for a cooperative binding of the dienophile by both the Lewis acid and the anion.