Enantioselektive Katalyse, XI. Darstellung von optisch reinen Diphosphanen mit vier Stereozentren

Enantioselective Catalysis, XI. – Preparation of Optically Pure Diphosphanes with Four Stereogenic Centers We synthesized a number of new diphosphanes with four stereogenic centers and two different aryl groups on each phosphorus atom. Starting with the diastereomeric mixture of [P(R,S),3R,4R,P′(R,S)]-1-(tert-butoxycarbonyl)-bis(phenyl-phosphanyl)pyrrolidine (1a,b,c) we prepared the corresponding chlorophosphanes by use of chlorotrimethylsilane followed by treatment with hexachloroethane. The chlorophosphanes react with Grignard. or organolithio compounds to the target molecules. For the chromatographic separation and purification of the diastereomers we transformed them into their Pdl2 complexes (Pd-4a,b,c to Pd-12a,b,c). The structures of Pd-4a, Pd-4c, Pd-6c, Pd-8b and Pd-9a were determined by X-ray diffraction analysis. A correlation between structural parameters of these Pd complexes and the enantio-selection for rhodium complexes of the same ligands as hydrogenation catalysts is suggested.