Imre Péter Tóth

A facile method for the preparation of 2,4-bis(diphenylphosphino)pentane (BDPP) enantiomers and their application in asymmetric hydrogenation

Abstract Asymmetric heterogeneous hydrogenation of acetylacetone was applied for the preparation of both enantiomers (2 R ,4 R and 2 S ,4 S ) of 2,4-bis(diphenylphosphino)pentane (BDPP). Among the chiral phosphines prepared up to now BDPP appears to be unique in the sense that its rhodium(I) complexes serve as effective homogeneous asymmetric hydrogenation catalysts not only for the reduction of Z -α-amidoacrylic acids but also for the reduction of α-ethylstyrene, acetophenone, and acetophenonebenzylimine. The analogous phosphinite ligand BDPOP yields a less selective catalyst.

Catalytic and structural studies of RhI complexes of (−)-(2S,4S)-2,4-bis(diphenylphosphino)pentane. Asymmetric hydrogenation of acetophenonebenzylimine and acetophenone

Abstract Rhodium(I) complexes formed by (−)-(2 S ,4 S )-2,4-bis(diphenylphosphino)pentane (BDPP) are efficient catalysts for the hydrogenation of acetophenone and acetophenonebenzylimine. The composition of the solvent mixture and the reaction temperature have a marked influenced on the enantioselectivity. These effects are thought to be related to the enhanced conformational flexibility of six-membered rings when simple substrates without functional groups are coordinated to the rhodium. X-ray crystallographic studies reveal that in [Rh(( S , S )-BDPP)NBD] + ( 1 ) the ligand is in a chair conformation, and that in [Rh(( S , S )-BDPP)COD] + ( 2 ) the chelate ring is in a δ-skew conformation. Studies of Rh(( S , S )-BDPP)(NBD)Cl ( 3 ) in solution indicate a trigonal bipyramidal structure with a chair conformation of the ring in aromatic solvents and a conformationally labile ring in methanol.

Temperature dependence of the asymmetric induction in the PtCl(SnCl3)[(−)-(2S,4S)-2,4-bis(diphenylphosphino)pentane]-catalyzed enantioselective hydroformylation reaction

Abstract Asymmetric hydroformylation of some prochiral olefins has been shown to be catalyzed by a new (preformed) PtCl(SnCl 3 )[( S , S )-BDPP] (( S , S )-BDPP = (−)-(2 S ,4 S )-2,4-bis(diphenylphosphino)pentane) catalyst. Vinylidene carboxylic esters are hydroformylated regioselectively but with rather moderate enantioselectivity. In hydroformylation of styrene the linear non chiral regioisomer 3-phenylpropanal is the main product, but the enantioselective formation of 2-phenylpropanal is strongly influenced by the reaction temperature, The S -enantiomer predominate at lower and the R -species at higher temperatures. Appropriate choices of the partial pressure of CO and H 2 led to a relatively high (76.5%) enantiomeric excess.

Asymmetric hydroformylation with Pt-phosphine-SnCl2 and Pt-bisphosphine-CuCl2 (or CuCl) catalytic systems

Abstract A study has been made of asymmetric hydroformylation of styrene with PtCl 2 (PPh 3 ) 2 + bisphosphine + SnCl 2 (bisphosphine: BDPP = (−)-(2 S ,4 S )-2,4-bis(diphenylphosphino)pentane or DIOP = (−)-(4 R ,5 R )-2,2-dimethyl-4,5-bis(diphenylphosphinomethyl)-1,3-dioxolane) and PtCl 2 (bisphosphine) + PPh 3 + SnCl 2 catalysts prepared “in situ”. The presence of an excess of the phosphine ligand slightly lowered the reaction rate, but the enantioselectivity of these systems is significantly higher than those involving PtCl(SnCl 3 )(bisphosphine) catalysts. Under mild reaction conditions 88.8% enantiomeric excess was achieved. Replacing SnCl 2 in these catalysts by CuCl 2 or CuCl gave a new homogeneous catalytic system which is active at higher reaction temperature (> 100°C), but has a rather moderate enantioselectivity.

Chiral sulphonated phosphines: II. Influence of water on the enantioselectivity in the reduction of dehydro-aminoacids☆

For the reduction of dehydro aminoacids in various media with rhodium complexes containing chiral ligands, a linear correlation of log %S/%R with the solvophobicity parameter Sp has been observed. The decrease in enantioselectivity in water is due to the high interfacial energy of this solvent.

The landscape of Comet Halley

Abstract In this paper the three-dimensional model of P/Halleys nucleus is constructed based on the results of the imaging experiments. It has the following major characteristics: the overall sizes are 7.2, 7.22, and 15.3 km; its volume is 365 km 3 ; the ratios of the inertial momenta are 3.5:3.4:1, the longest inertial axis is slightly inclined to the geometrical axis of the body, 3.3° latitude and 1.1° longitude if the geometrical axis is at zero latitude and longitude. The shape is very irregular; it is not close to any regular body, e.g., to a tri-axial ellipsoid. Several features on the images are interpreted as local slope variations of the nucleus.

Asymmetric hydroformylation of styrene using rhodium and platinum complexes of diphosphites containing chiral chelate backbones and chiral 1,3,2-dioxaphosphorinane moieties

Abstract Several chiral diphosphite ligands containing six stereogenic centres were synthesised and tested in order to study chiral cooperativity in the Rh- and Pt-catalysed asymmetric hydroformylation of styrene. The ligands were prepared either by the reaction of 2,4-pentanediol enantiomers with (4R,6R)-4,6-dimethyl-2-chloro-1,3,2-dioxaphosphorinane or that of (1S,3S)-1,3-diphenyl-1,3-propanediol with 4,6-dimethyl-2-chloro-1,3,2-dioxaphosphorinane enantiomers. Thus the chirality was varied both in the chelate backbone and in the terminal groups of the ligands. In case of Pt-catalysed hydroformylation, the stereogenic elements in the bridge have been found to be determinate for the product configuration with a cooperative effect from the terminal groups when the constellations are matched with 40% e.e. maximum enantioselectivity. Some coordination chemistry and the crystal structure determination of these ligands are also reported.

Asymmetric hydrogenation using chiral phosphinite rhodium complexes

Abstract The Cu(I) complex of (1R,3R)-bis(diphenylphosphinoxy)-1,3-diphenylpropane (BDPODP) has been prepared and used for the transfer of the ligand to Rh(I). The Rh(I) complexes of this new phosphinite obtained by this method act as efficient asymmetric homogeneous hydrogenation catalysts for (Z)-α-(acylamino)-cinnamic acids.

Exploring the circumstellar environment of the young eruptive star V2492 Cygni

Context. V2492 Cyg is a young eruptive star that went into outburst in 2010. The near-infrared color changes observed since the outburst peak suggest that the source belongs to a newly defined sub-class of young eruptive stars, where time-dependent accretion and variable line-of-sight extinction play a combined role in the flux changes. Aims. In order to learn about the origin of the light variations and to explore the circumstellar and interstellar environment of V2492 Cyg, we monitored the source at ten different wavelengths, between 0.55 μm and 2.2 μm from the ground and between 3.6 μm and 160 μm from space. Methods. We analyze the light curves and study the color−color diagrams via comparison with the standard reddening path. We examine the structure of the molecular cloud hosting V2492 Cyg by computing temperature and optical depth maps from the far-infrared data. Results. We find that the shapes of the light curves at different wavelengths are strictly self-similar and that the observed variability is related to a single physical process, most likely variable extinction. We suggest that the central source is episodically occulted by a dense dust cloud in the inner disk and, based on the invariability of the far-infrared fluxes, we propose that it is a long-lived rather than a transient structure. In some respects, V2492 Cyg can be regarded as a young, embedded analog of UX Orionis-type stars. Conclusions. The example of V2492 Cyg demonstrates that the light variations of young eruptive stars are not exclusively related to changing accretion. The variability provided information on an azimuthally asymmetric structural element in the inner disk. Such an asymmetric density distribution in the terrestrial zone may also have consequences for the initial conditions of planet formation.

Chiral sulfonated phosphines. Rhodium(I)-catalyzed asymmetric hydrogenolysis of epoxides

Abstract Rhodium(I) complexes of sulfonated (−)-(2S,4S)-2,4-bis(diphenylphosphino)pentane ((S,S)-(BDPP)) are effective as catalyst for asymmetric hydrogenolysis of sodium cis -epoxysuccinate to sodium hydroxysuccinate in aqueous-organic two phase solvent system or in aqueous solution. It has been shown by deuterium labelling studies that both hydrogen and water participate in the aqueous hydrogenolysis as reactants and the reaction proceeds via the direct CO bond cleavage of the epoxy group. High pressure NMR studies show the presence of rhodaoxetane-BDPP complexes as catalytic intermediates, which are formed by the oxidative addition of the epoxide to unsaturated Rh(I) species. Accordingly, a reaction mechanism has been proposed for the aqueous catalytic process. The use of a racemic substrate, sodium trans -phenylglycidate with the aqueous Rh-sulfonated (S,S)-BDPP system results in the kinetic resolution of the (2S,3R)-epoxide enantiomer. Thus, asymmetric aqueous catalytic hydrogenolysis could be a useful synthetic approach not only to chiral α-hydroxycarboxylic acid derivatives but also to chiral trans -substituted epoxides.