Gerlinde Mehler

Mixtures of chiral and achiral monodentate ligands in asymmetric Rh-catalyzed olefin hydrogenation: reversal of enantioselectivity

The recently described method of combinatorial asymmetric transition metal catalysis based on the use of mixtures of chiral monodentate P-ligands has been extended to include mixtures of chiral and achiral monodentate P-ligands, reversal of enantioselectivity in Rh-catalyzed olefin hydrogenation being possible in appropriate cases.

Enantioselective hydrogenation of enamides catalyzed by chiral rhodium-monodentate phosphite complexes

Chiral monophosphites derived from BINOL are cheap and efficient ligands in the Rh-catalyzed hydrogenation of N-acyl enamides, providing amines with high degrees of enantioselectivity (up to 97.0% ee).

Chiral heterobimetallic complexes of carbodiphosphoranes and phosphinidene–carbene adducts

Heterobimetallic complexes derived from carbodiphosphoranes or phosphinidene-carbene adducts are reported, in which the central atom accepts two lone-pairs from two different donor ligands and - at the same time - donates two lone-pairs to two different metal centers. Therefore these complexes are carbogenic yet captodative chiral entities.

Alkinkomplexe des η5-Cyclopentadienylnickelmethyls und deren Thermolyse

Abstract Cp 2 Ni reacts at −78°C with MeLi and RCCR to give thermolabile complexes of the type CpNiMe(η 2 -RCCR) (R = Me ( 1 ), SiMe 3 ( 2 )). 2-Butyne dissociates from 1 above −30°C and ethane is liberated to give (CpNi) 2 (MeCCMe) ( 6 ) via (CpNiMe) 2 (MeCCMe) ( 3 ), which is present in only small concentrations. 2 is more stable and reacts above 0°C to give both the known compounds (CpNi) 2 (Me 3 SiCCSiMe 3 ) ( 7 ) and the [bis(1,1-trimethylsilyl)-η 3 -allyl]nickel compound 5 as a result of the addition of the MeNi bond to the CC bond of the coordinated alkyne in 2 followed by various rearrangements. The alkyne can be displaced from 1 and 2 in an equilibrium reaction with acetonitrile to give CpNiMe(MeCN) ( 4 ).

Bis(cyclopropenium)phosphines: Synthesis, Reactivity, and Applications

A straightforward route for the preparation of a set of bis(cyclopropenium)-substituted phosphines is reported. Due to their dicationic nature, these ligands depict an excellent π-acceptor character. The effect of the ligand substituent pattern on the catalytic activity of the metal complexes thereof derived is also studied. Whereas sterically demanding biaryl groups directly attached to the phosphorus atom seem to facilitate elementary steps such as the product release from the catalyst, long chain dialkylamino groups on the cyclopropenium units maximize the catalysts solubility and, thus, allow the use of typical apolar solvents such as toluene. Importantly, all new ligands prepared can be easily handled in air. Finally, the impact of the newly prepared dicationic phosphines in hydroarylation reactions is demonstrated. In particular, their use in the synthesis of several naphtho[1,2-b]furanes and naturally occurring naphthalene derivatives such as Calanquinone C is reported.

Preparation of novel HIV-protease inhibitors

The synthesis and biological properties of new HIV-1-protease inhibitors involving amino acids or dipeptides attached to binaphthol, biphenol or embonic acid are described.