Chiral Oxazoline Ligands Research Articles

Nickel (II) complexes bearing phosphinoaryl oxazoline ligands as pro-catalysts for Grignard cross-coupling

Ni(II) complexes bearing chiral phosphinoaryl oxazoline ligands are pro-catalysts for cross-coupling of Z-styryl bromide with 1-phenethyl magnesium chloride. Under suitable conditions, there is a dynamic kinetic resolution resulting in moderate enantioselectivity. The nature of the substituent at the stereogenic centre of the oxazoline ligand affects catalysis in two distinct ways: smaller substituents lead to improved rates and selectivities whilst polar substituents reverse the sense of asymmetric induction. The solid state structure of one phosphinoaryl oxazoline Ni(II) pro-catalyst was determined by single crystal x-ray diffraction.

The palladium catalyzed allylic alkylation of bis(trimethylsilyl) substituted propenyl acetates or carbonates in the presence of chiral ligands

Palladium catalyzed asymmetric allylic alkylations of a bis(trimethylsilyl) substituted propenyl acetate and carbonate were investigated using various chiral ligands and reaction conditions. The best enantioselectivity (86% e.e.) was obtained with the substrate 1-phenyl-3,3-bis(trimethylsilyl)propenyl carbonate 13 and the chiral oxazoline ligand 4c.

Chiral oxazoline ligands. Synthesis and characterization of palladium, nickel and manganese complexes containing bidentate N,O and N,P moieties †

Complexes of palladium, nickel and manganese, with the chiral ligand (+)-(4′R)-2-(4′-ethyl-3′,4′-dihydrooxazol-2′-yl)phenol HLOH were synthesized and characterized by 1H, 31P NMR spectroscopy, magnetic susceptibility and including the crystal structure determinations of trans-[PdLOH2] and [PdClLOH(PPh3)]. The LOH moiety is co-ordinated in a bidentate fashion in neutral, cationic and anionic complexes, rigid on the NMR time-scale. Monodentate O-co-ordinated complexes were obtained only in the presence of phosphines. The manganese complex [MnClLOH2] showed little activity in the catalytic epoxidation of styrene. The first phosphinite oxazoline ligand LOP was synthesized from HLOH. Neutral and cationic alkyl and allyl complexes of palladium with it were obtained and characterized. The cationic complexes showed dynamic behaviour.

Synthesis and X-ray structure of a ruthenium cluster with a chiral oxazoline ligand

The cluster Ru 3(CO) 12 reacts with (4 S,5 S)-(-)-2-methyl-5-phenyl-2-oxazoline-4-methanol (HL) to give H 2Ru 6(CO) 14(L) 2; the metal framework consists of two triangles with weak interactions between two edges.

New chiral bis(oxazolinyl)bipyridine ligand (bipymox): Enantioselection in the asymmetric hydrosilylation of ketones

A homochiral chiral 6,6′-bis(oxazolinyl)-2,2′-bipyridine ligand, bipymox ( 1), and its rhodium complex were synthesized to examine the enantioselectivity in the asymmetric hydrosilylation of ketones in comparison to other chiral oxazoline ligands such as bis-(oxazolinyl)pyridine, pybox( 2), and mono(oxazolinyl)pyridine, pymox( 3). The bipymox-rhodium catalyst gave the ( S)-absolute configuration of the product 1-phenylethanol (90 %ee) in the reduction of acetophenone with diphenylsilane the same as the pybox-rhodium system but opposite to the pymox-rhodium system. The reduction of 4-tert-butylcyclohexanone was also described.

Blood transfusions raise man's high-altitude ceiling

Novel chiral monodentate oxazoline ligands have been synthesized in good yields. The catalytic activity of these monodentate oxazoline/Cu catalysts was evaluated in the catalytic asymmetric cyclopropanation of styrene and α-methylstyrene, giving moderate to good enantioselectivities (up to 74% ee for the trans-cyclopropane product) and full conversions (up to 100%). In an attempt to enhance the enantioselectivities of the cyclopropanations, heterocombinations of these ligands were used. Unfortunately, with the data set that was used in this study, no improvements were observed. However, to gain an insight into the nature of the active catalyst present under these circumstances, NMR, mass spectrometric and computational studies were carried out and indicated the presence of bidentate heterocomplexes in the equilibrium mixture. Analysis of the stereoselectivities (ees and des) did not prove very useful in pin-pointing the identity of the active chiral catalyst and only afforded a very weak conclusion. In order to ascertain the importance of the π–π interactions, the monodentate oxazoline ligands 3a and 3b were synthesized and screened in these reactions, and the resulting stereoselectivities were compared to the results obtained using ligands 1a and 1b. There seemed to be very weak π–π interactions at work.