Exchanging conformations of a hydroformylation catalyst structurally characterized using two-dimensional vibrational spectroscopy.

Catalytic transition-metal complexes often occur in several conformations that exchange rapidly ( View Article and Find Full Text PDF

Application of supramolecular bidentate hybrid ligands in asymmetric hydroformylation.

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.

Coordination studies on supramolecular chiral ligands and application in asymmetric hydroformylation.

In this study we introduce a series of monodentate pyridine-based ligands for which the phosphorus coordination mode to rhodium can be controlled by the binding of Zn(II)-templates to the pyridyl group. A series of monodentate phosphoroamidite and phosphite ligands have been prepared and studied under hydroformylation conditions by in situ high-pressure NMR and IR techniques. These studies reveal the exclusive formation of rhodium hydride complexes in which the phosphorus atom of the ligand resides in an axial position, trans to the hydride, but only after addition of Zn(II)-template.

Highly selective asymmetric Rh-catalyzed hydroformylation of heterocyclic olefins.

A small family of new chiral hybrid, diphosphorus ligands, consisting of phosphine-phosphoramidites L1 and L2 and phosphine-phosphonites L3a-c, was synthesized for the application in Rh-catalyzed asymmetric hydroformylation of heterocyclic olefins. High-pressure (HP)-NMR and HP-IR spectroscopy under 5-10 bar of syngas has been employed to characterize the corresponding catalyst resting state with each ligand. Indole-based ligands L1 and L2 led to selective ea coordination, while the xanthene derived system L3c gave predominant ee coordination.

Self-assembly of a confined rhodium catalyst for asymmetric hydroformylation of unfunctionalized internal alkenes.

A chiral supramolecular ligand has been assembled and applied to the rhodium-catalyzed asymmetric hydroformylation of unfunctionalized internal alkenes. Spatial confinement of the metal center within a chiral pocket results in reversed regioselectivity and remarkable enantioselectivities.

Highly enantioselective hydroformylation of dihydrofurans catalyzed by hybrid phosphine-phosphonite rhodium complexes.

Unprecedented regio- and enantioselectivities (>91%) are reported for the Rh-catalyzed asymmetric hydroformylation of 2,3- and 2,5-dihydrofuran using tunable hybrid phosphine-phosphonite ligands.

Monoaryl-substituted salicylaldoximes as ligands for estrogen receptor beta.

Salicylaldoximes possess a hydrogen-bonded pseudocyclic A' ring in place of the typical phenolic A ring that is characteristic of most estrogen receptor (ER) ligands. Monoaryl-substituted salicylaldoximes were obtained by replacing the phenol moiety (ring A) of the ERbeta pharmacophore with the pseudocycle A' ring, which has previously been shown to behave as a bioequivalent of phenols in nonselective ER ligands. In this series, small substituents (CH 3, CN, Cl) were introduced into the central phenyl scaffold.