László Markó

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.

Study of carbon monoxide insertion into the carbon—cobalt bond

(Triphenylphosphine)benzylcobalt tricarbonyl can be carbonylated at atmospheric pressure and room temperature to form (triphenylphosphine)(phenylacetyl)cobalt tricarbonyl. Using 13CO as carbonylating agent it was shown, that the acyl group is formed by incorporation of a carbonyl ligand, whereas the carbon monoxide from the gas phase enters the coordination sphere of the cobalt atom as a new ligand. The acyl complex can be easily decarbonylated at somewhat elevated temperatures.

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.

AsCo3(CO)9, its cyclic trimer, As3Co9(CO)24 and the phosphorus-containing analog P3Co9(CO)24☆

The AsCo3(CO)9 trigonal pyramidal cluster, its cyclic “trimer” As3Co9(CO)24 and the phosphorus-containing analog of the latter, P3Co9(CO)24 have been prepared and characterized. A reversible equilibrium between the arsenic-containing monomer and trimer was found to depend on p(CO). Such an equilibrium could not be observed in the case of P3Co9(CO)24.

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 .

Transformations of the heteronuclear clusters En[Co(Co)3]4−n (E = P, As; n = 1–3) when treated with soft lewis acids and bases

Abstract The tetrahedral pnigogenic clusters E n [Co(CO) 3 ] 4 - n (EP, As; n = 1–3) react with soft Lewis acids and bases to give products of substitution and transformation of the cluster. Lewis acids promote transformations to clusters containing more cobalt atoms and Lewis basis to clusters containing fewer such atoms.

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.

Transition-metal alkyls and hydrides : III. Alkyl-olefin exchange reaction of grignard reagents catalyzed by nickel chloride☆

Abstract Anhydrous nickel chloride catalyzes the alkyl-olefin exchange reaction between Grignard reagents and α-olefins. The catalyst is especially effective in the case of gaseous olefins and long-chain alkylmagnesium halides. Olefins with internal double bonds do not undergo the reaction, while primary alkylmagnesium halides react more easily than secondary and tertiary ones. The reaction may involve a hydridic transition state or a direct hydride-ion migration between the ligands in the catalyst complex.

Catalytic and stoichiometric reduction of ketones and aldehydes by the hydridotetracarbonyl ferrate anion

Abstract Acetone is catalytically reduced to isopropyl alcohol by carbon monoxide and water in the presence of iron carbonyls and triethylamine at 100°C and 100 bar. Use of NaOH in place of triethylamine gives a much less efficient catalyst system. The Et 3 NH·HFe(CO) 4 system also catalyses the reduction of n-butyraldehyde to n-butyl alcohol at room temperature in a fast stoichiometric reaction, whereas NaHFe(CO) 4 is inactive under the same conditions. The Et 3 NH + cation is necessary for the transfer of a proton to the carbonyl group, while the HFe(CO) 4 − anion carries out nucleophilic attack on carbonyl group and supplies the hydride ion.