Szilárd Tőrös

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.

Rhodium phosphine complexes as homogeneous catalysts. part 3. Homogeneous ssymmetric hydrogenation of schiffs bases

SummaryComplexes formed from [Rh(norbornadiene)Cl]2 and tertiary phosphines under hydrogen are active catalysts for the homogeneous hydrogenation of Schiff bases at 30–80° and 1-70 bars. Using chiral phosphines some optical induction can be achieved, but the optical yields are rather low.

Homogenkatalytische asymmetrische hydrierung von ketonen

Zusammenfassung Complexes formed from [Rh(1,5-hexadiene)Cl] 2 and tertiary phosphines under hydrogen are active catalysts for the homogeneous hydrogenation of ketones. Using chiral phosphines optical yields up to 51% were achieved.

Phosphinerhodium complexes as homogeneous catalysts. XVI: Stereoselective hydrogenation of cyclic ketones

Abstract Cyclic ketones have been hydrogenated stereoselectively with various phosphphinerhodium complexes as catalysts. Systems containing phosphines of high basicity and consequently forming Rh III dihydrides as active species yielded mainly the thermodynamically more stable alcohol isomers. Catalysts prepared from aryl-type phosphines of low basicity and modified with Et 3 N, which contain Rh I monohydrides as active complexes, afforded the less stable alcohol isomers as the major products. The ratio of Rh III and Rh I hydrides, which determines the stereoselectivity of the catalysts prepared in situ could be changed by suitable choice of base.

Phosphinorhodium complexes as homogeneous catalysts XIII. Enantioselective hydrogenation of aminoalkyl aryl ketones with a rhodium-diop catalytic system*

Summary The catalyst formed in situ from [Rh(NBD)Cl]2 + DIOP catalyses the hydrogenation of α-(N,N-dialkylamino)alkyl aryl ketones to give enantioselectivities of up to 95%.

HOMOGENEOUS CATALYTIC HYDROAMINOMETHYLATION OF STEROIDS WITH AMINOALCOHOLS

Abstract Rhodium-catalyzed carbonylation of several Δ 16 steroids was carried out in the presence of aminoalcohols and new hydroxy-aminomethyl derivatives have been obtained in moderate to good yields. The multi-step reaction is highly chemo- and regioselective. The new compounds containing the hydroxy function can serve as starting materials for further functionalization of the steroid skeleton.

Comparative investigation of the regioselectivity in styrene and α-methylstyrene hydroalkoxycarbonylation as a function of palladium catalyst structure

Abstract Catalytic pathways of the styrene and α-methyl-styrene hydroalkoxycarbonylation in the presence of Pd(PPh 3 ) 2 Cl 2 and Pd(PPh 3 ) 2 Cl 2 /SnCl 2 catalyst precursors have been suggested. As a method, deuterium labelling with EtOD has been applied and it resulted in mixtures of mono- and polydeuterated reaction products, detected and determined by NMR methods. Comparative elucidation of the mechanisms governing these systems does support the assumption that the hydrido route is operative. The different behaviour of the metal–alkyl intermediates accounts for the observed strong influence of catalyst and substrate structure on regioselectivity.

Phosphinerhodium complexes as homogeneous catalysts. XV: Hydrogenation of ketones with PPh3-containing rhodium catalysts

Abstract Wilkinson-type complexes containing PPh 3 ligands and modified by Et 3 N can be successfully used as catalysts for the homogeneous hydrogenation of ketones. The reaction is first order in substrate and rhodium and the rate does not depend on the partial pressure of hydrogen. Excess of the ligand (PPh 3 /Rh > 3) does not inhibit the reduction. The reaction between HRh(PPh 3 ) 3 and the ketone is regarded as the rate-determining step, and this is followed by a fast reaction with H 2 . The activity of the catalyst is not very sensitive to the structure of the substrate.

Hydrogenation Reactions of CO and CN Functions Using Rhodium Complexes

Stimulating results achieved in hydrogenation of C==C double bonds with phosphinerhodium complexes led to the application of these compounds for the catalytic reduction of C==O and C==N double bonds. The present review summarizes the results in this area reported up until now. To give a more complete picture of the subject, some reports on iridium and ruthenium phosphine complex catalysts have been included as well.