Bálint Heil

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.

Rhodium phosphine complexes as homogeneous catalysts: 14. Asymmetric hydrogenation of a Schiff base of acetophenone — effect of phosphine and catalyst structure on enantioselectivity

Abstract Using catalysts prepared in situ from [Rh(NBD)Cl] 2 and chiral diphosphines of the type Ph 2 PCHRCH 2 PPh 2 (R = Ph, i-Pr, PhCH 2 ) optical yields above 60% were achieved in the hydrogenation of PhMeCNCH 2 Ph. Although reproducibility of the results was poor, it can be concluded that the chiral diphosphines DIOP and diPAMP are much less effective, and that the halide ligand is necessary for good enantioselectivity.

Phosphinerhodium complexes as homogeneous catalysts

Abstract The enantioselectivity of catalysts obtained in situ from [Rh(nbd)Cl] 2 , (+)-DIOP and triethyl amine for the hydrogenation of aryl ketones is significantly increased if benzene is used as a solvent. Optical yields of 55–84% were achieved at 50° C and 70 bar H 2 .

1,4:3,6-dianhydro-2,5-dideoxy-2,5-bis(diphenylphosphino)-l-iditol. A new chiral ligand for asymmetric hydrogenation with rhodium complexes as catalysts

Abstract A new chiral 1,4-diphosphine, 1,4:3,6-dianhydro-2,5-dideoxy-2,5-bis(diphenylphosphino)- l -iditol, has been prepared from d -mannitol. Rhodium complexes of this ligand are asymmetric homogeneous hydrogenation catalysts for dehydroamino acids, giving ( S )-amino acids in 21–58% optical yields.

Phosphinerhodium complexes as homogeneous catalysts : VIII. Enantioselective hydrogenation of ketones: evidence for several mechanisms with catalysts containing diop

Abstract Optical yields obtained in the hydrogenation of acetophenone with cationic and in situ rhodium complex catalysts depend on the P/Rh ratio and on the ionic or non-ionic character of the active species. The enantioselectivity of the in situ catalyst containing (+)-DIOP is reversed by addition of achiral tri-n-alkyl-phosphines. On the basis of these observations and the amount of H 2 consumed in preforming the catalysts, several different mechanisms are suggested: for example: cycles involving cationic rhodium complexes containing two (or three) phosphorus ligands and cycles involving non-ionic rhodium complexes with two phosphorus ligands in cis or trans positions. In the in situ catalyst with a Rh/(+)-DIOP/P-n-Bu 3  1/1/1 ratio (+)-DIOP functions as a monodentate ligand.

Hydroformylation of chiral terpenes with PtCl(SnCl3)-(bis-phosphine) as catalyst

Abstract (+)- R -Limonene and (−)- R -carvone undergo hydroformylation in the presence of catalytic Pt-bisphosphine-SnCl 2 systems to yield exclusively the linear products. The internal double bond and the carbonyl group remain intact in both substrates during the reaction. The variation of the diastereomeric composition of the aldehydes upon variation of the chelating phosphine in the catalyst has been investigated.