3619-01-0Relevant articles and documents
Inducing Axial Chirality in a Supramolecular Catalyst
Wenz, Katharina Marie,Leonhardt-Lutterbeck, Günter,Breit, Bernhard
, p. 5100 - 5104 (2018)
A new type of ligand, which is able to form axially chiral, supramolecular complexes was designed using DFT calculations. Two chiral monomers, each featuring a covalently bound chiral auxiliary, form a bidentate phosphine ligand with a twisted, hydrogen-bonded backbone upon coordination to a transition metal center which results in two diastereomeric, tropos complexes. The ratio of the diastereomers in solution is very temperature- and solvent-dependent. Rhodium and platinum complexes were analyzed through a combination of NMR studies, ESI-MS measurements, as well as UV-VIS and circular dichroism spectroscopy. The chiral self-organized ligands were evaluated in the rhodium-catalyzed asymmetric hydrogenation of α-dehydrogenated amino acids and resulted in good conversion and high enantioselectivity. This research opens the way for new ligand designs based on stereocontrol of supramolecular assemblies through stereodirecting chiral centers.
Enantiodivergent asymmetric catalysis with the tropos BIPHEP ligand and a proline derivative as chiral selector
Oczipka,Müller,Leitner,Franciò
, p. 678 - 683 (2015/12/30)
A catalytic system based on the tropos ligand BIPHEP and (S)-proline methyl ester as chiral selector was studied for Rh-catalysed asymmetric catalysis. By careful control of the catalyst preformation conditions, the enantioselectivity could be completely reversed in asymmetric hydrogenation of prochiral olefins maintaining the same absolute level in favorable cases. The enantiodivergent asymmetric catalysis could be rationalised by the interplay of the dynamic chirality (tropos) of the phosphine ligand and the coordination of the proline selector. Treating a suitable Rh-BIPHEP precursor with the (Sc)-proline-based ionic liquid led to an equimolar mixture of (RaSc)- and (SaSc)-diastereomers that is kinetically stable at 0 °C. At higher temperature, an irreversible diastereomerisation process was observed resulting in the diastereomerically pure (RaSc)-complex [Rh{(Ra)-BIPHEP}{(Sc)-ProlOMe}]. Whereas the use of the pure (RaSc)-complex led to 51% ee (R) in the hydrogenation of methyl 2-acetamidoacrylate, the S-product was formed with almost identical enantioselectivity when the (RaSc)/(SaSc)-mixture was applied under identical conditions. This inversion was associated with the relative stability of the diastereomers in the equilibria forming the catalytically active substrate complex. The possibility to use this different reactivity to control the direction of enantioselectivity was demonstrated for the hydrogenation of different substrates whereby ee's of up to 80% could be achieved. Moreover, the (RaSc)-complex led to high enantioselectivities of up 86% ee in the asymmetric hydroboration of styrene, approaching the performance of the atropos BINAP ligand for this reaction.
Novel and efficient chiral bisphosphorus ligands for rhodium-catalyzed asymmetric hydrogenation
Tang, Wenjun,Capacci, Andrew G.,White, Andre,Ma, Shengli,Rodriguez, Sonia,Qu, Bo,Savoie, Jolaine,Patel, Nitinchandra D.,Wei, Xudong,Haddad, Nizar,Grinberg, Nelu,Yee, Nathan K.,Krishnamurthy, Dhileepkumar,Senanayake, Chris H.
supporting information; experimental part, p. 1104 - 1107 (2010/06/13)
(Figure Presented) A series of structurally novel, operationally convenient, and efficient chiral 2-phosphino-2,3-dihydrobenzo[d][1,3] oxaphosphole ligands was developed. Applications of ligands 3a and 3b in rhodium-catalyzed asymmetric hydrogenation of α-(acylamlno)acrylates andβ-(acylamino)acrylates provided excellent enantioselectivities (up to >99% ee) and reactivities (up to 10 000 TON).
