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- Title
Phosphane-Phosphite Chelators Built on a α-Cyclodextrin Scaffold: Application in Rh-Catalysed Asymmetric Hydrogenation and Hydroformylation.
- Authors
Jouffroy, Matthieu; Sémeril, David; Armspach, Dominique; Matt, Dominique
- Abstract
Four hybrid phosphane-phosphite ligands were synthesised by regioselective A,B-functionalisation of a methylated α-cyclodextrin (α-CD) scaffold. In all these ligands the phosphite part comprises a 2,2′-bisaryloxyphosphanyloxy group. The ligands, which display inherent chirality, readily form 12-membered chelate rings with d8-metal ions. In the most flexible chelates (those with an unsubstituted 2,2′-bisphenoxy group), the metal plane describes a fan-like motion about the P ···P′ axis with concomitant fast atropisomerisation of the biaryl unit. When the latter is blocked, as in the 2,2′-binaphthyloxyphosphites, the fan-like motion no longer takes place. Rhodium complexes of the CDs were assessed in asymmetric hydrogenation of α-dehydroamino acid esters and hydroformylation of styrene. Poor enantiodiscrimination was observed for the highly mobile chelate complexes, whereas the more rigid ones all resulted in significant ee values. The best performing hydrogenation catalyst is the one in which both chiral components - CD and ( S)-binaphthyl - behave in a synergistic way.
- Subjects
PHOSPHINES; ORGANIC compounds; SOLUTION (Chemistry); INTERMEDIATES (Chemistry); PROPERTIES of matter
- Publication
European Journal of Organic Chemistry, 2013, Vol 2013, Issue 27, p6069
- ISSN
1434-193X
- Publication type
Article
- DOI
10.1002/ejoc.201300854