1415631-75-2Relevant academic research and scientific papers
Supramolecular hybrid bidentate ligands in asymmetric hydrogenation
Bellini, Rosalba,Reek, Joost N. H.
, p. 4684 - 4693 (2012)
In this study we introduce a novel class of supramolecular bidentate hybrid ligands and their application in the rhodium-catalysed asymmetric hydrogenation of prochiral olefins. A new supramolecular strategy is reported in which the two nonequivalent phosphorus atoms are linked covalently to a chiral scaffold, and the supramolecular interactions are used to control the second coordination sphere of the transition-metal catalyst. The supramolecular assembly is formed in situ by selective interaction between the nitrogen-donor atoms and the zinc(II) template, which is essential for obtaining high activity and selectivity. The investigations of the different zinc(II) and ruthenium(II) templates on the reaction parameters revealed a dependence of the activity and selectivity on the association constant between the supramolecular template and the pyridyl ligands. The scope of the supramolecular assemblies was explored in the Rh-catalysed asymmetric hydrogenation of α-dehydroamino acid esters and Roche ester derivatives. High activities and good to excellent enantioselectivities up to 99 % ee were obtained with the supramolecular ligands. Application of the supramolecular strategy on the basis of variations of the steric and electronic properties of zinc(II) templates demonstrate that these changes can influence key reaction parameters such as activity and selectivity. Copyright
Application of supramolecular bidentate hybrid ligands in asymmetric hydroformylation
Bellini, Rosalba,Reek, Joost N. H.
, p. 13510 - 13519,10 (2020/09/14)
In this study we report a novel class of supramolecular bidentate hybrid ligands in which the two inequivalent phosphorus units and pyridine moieties are covalently attached to a chiral scaffold and the supramolecular interactions are used as a second handle to control the coordination sphere around the transition-metal centre. The coordination chemistry of these ligands was investigated under hydroformylation conditions by high-pressure NMR and IR spectroscopy, revealing the formation of a single active species in which the phosphane ligand is in the axial position and the phosphoramidite adopts the equatorial position. These ligands were applied in the asymmetric Rh-catalysed hydroformylation of styrene and para-substituted analogues. In these hydroformylation reactions, modification of the electronic and steric properties of the zinc(II)-templates appear to have a significant influence on the activity and selectivity of the catalysis. In particular, zinc(II)-templates bearing more electron-withdrawing substituents led to an increase in enantioselectivity.
