Quinaphos and Dihydro-Quinaphos phosphine-phosphoramidite ligands for asymmetric hydrogenation.
New derivatives of the Quinaphos ligands and the related Dihydro-Quinaphos ligands based on the more flexible 1,2,3,4-tetrahydroquinoline backbone have been prepared and fully characterised. A general and straightforward separation protocol was devised, which allowed for the gram-scale isolation of the R(a),S(c) and S(a),R(c) diastereomers. These new phosphine-phosphoramidite ligands have been applied in the Rh-catalysed asymmetric hydrogenation of functionalised olefins with the achievement of excellent enantioselectivities (> or = 99%) in most cases and turnover frequency (TOF) values of up to > or = 20,000 h(-1). These results substantiate the practical utility of readily accessible Quinaphos-type ligands, which belong to the most active and selective category of ligands for Rh-catalysed hydrogenation known to date.
Pullmann
Thomas
T
Institut für Technische und Makromolekulare Chemie, RWTH Aachen University, Worringerweg 1, 520274 Aachen, Germany.
Engendahl
Barthel
B
Zhang
Ziyun
Z
Hölscher
Markus
M
Zanotti-Gerosa
Antonio
A
Dyke
Alan
A
Franciò
Giancarlo
G
Leitner
Walter
W