Enantioselective Catalysts
for the Diels–Alder
Reaction between Methacrolein and Cyclopentadiene Based on the Chiral
Fragment (η5-C5Me5)M(chiral
diphosphane) (M = Rh, Ir)
posted on 2011-12-26, 00:00authored byDaniel Carmona, Fernando Viguri, Ainara Asenjo, M. Pilar Lamata, Fernando Lahoz, Pilar Garcı́a-Orduña, L. A. Oro
The aqua complexes [(η5-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 [(η5-C5Me5)M(PP*)(methacrolein)][SbF6]2 (11–20) are also isolated and characterized,
including the molecular structure determination of the [(η5-C5Me5)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.