Enantioselective Catalysts for the Diels–Alder Reaction between Methacrolein and Cyclopentadiene Based on the Chiral Fragment (η5-C5Me5)M(chiral diphosphane) (M = Rh, Ir)
摘要:
The aqua complexes [(eta(5)-C5Me5)M(PP*)-(H2O)][SbF6](2) (M = Rh, Ir; PP* = chiral diphosphane) (1-10) are prepared and characterized. These complexes efficiently catalyze the Diels-Alder reaction between methacrolein and HCp with enantioselectivities of up to 96% e.e. The norphos complexes 9 and 10, which are obtained as diastereomeric mixtures of the two epimers at the metal, afford the highest e.e. values. The intermediate complexes [(eta(5)-C5Me5)M(PP*)-(methacrolein)] [SbF6](2) (11-20) are also isolated and characterized, including the molecular structure determination of the [(eta(5-CMe5)-Me-5)M(benphos)(methacrolein)][SbF6](2) (M = Rh (13), Ir (14)) derivatives. An NMR study of the reactivity of the metallic intermediates under catalytic conditions explains the high enantioselectivities achieved with the norphos systems.