Preparative and Structural Chemistry of Diastereomeric Derivatives of 3-PhosphanylpyrroIidine and Their Palladium(II) Complexes -Asymmetric Grignard Cross-Coupling Reaction

Article abstract of DOI:10.1002/cber.19971300729

The preparation of both diastereomeric derivatives of 3-(diphenylphosphanyljpyrrolidine with chiral (tetrahydrofuran2-yl}methyl and [(/V-neopentyl)pyrrolidin-2-yl]methyl groups as substituents on the pyrrolidine nitrogen atom and of (2S,4S)-l-benzyl-4-(diphenylphosphanyl)-2-(methoxymethyljpyrrolidine is reported. [3S,P(fiS)]-3-(phenylphosphanyljpyrrolidine, bearing an additional chiral center on phosphorus, is the starting material for the preparation of phosphanes, in which one phenyl group of the PPh2 moiety is substituted by an 2-methoxyphenyl (= An) or 2,4,6-trimethoxyphenyl (= TMP) group. PdI₂ complexes of these ligands were separated into diastereomers by chromatography on silica gel columns. The structural chemistry of these novel phosphane diastereomers and their PdI₂ complexes is investigated by X-ray crystallography and NMR. At the P,N-coordinated palladium center displacement of an iodide anion is found for P,N,N' ligands only. In the nickel complex catalysed cross-coupling reaction, yielding 3-phenyl-l-butene, we obtain the highest enantioselectivities in the case of simple l-alkyl-3-(diphenylphosphanyl)pyrrolidine ligands. The enantioselectivity obtained with diastereomeric derivatives, bearing additional ether or amine ligating sites is mainly determined by the chiral center in 3-position of the 3-(phosphanyl)pyrrolidine part of these ligands. Optimisation of enantioselectivity with these ligands can be carried out by a variation of the ligand to nickel ratio and by the choice of the vinyl halide used as starting compound. The catalytic cycle must contain at least one catalytically active species, bearing more than one ss-aminoalkylphosphane ligand. VCH Verlagsgesellschaft mbH,.