Metal template promoted hydroamination of ethynylphosphines and aniline. Asymmetric synthesis, coordination chemistry, and the imine-enamine tautomerism of P-chiral iminophosphines

In the presence of the organopalladium template containing the orthometalat ed (S)-(1-dimethylamino)ethyl)naphthylene auxiliary, both diphenyl(phenylet hynyl)phosphine and di(phenylethynyl)phenylphosphine were reactive toward t he novel hydroamination reaction with aniline to give the corresponding bid entate iminophosphines in high yields. These novel P-N ligands exhibited an interesting imine-enamine tautomerism in solution. Spectroscopic studies c onfirmed that the uncoordinated ligands adopted the stable imino form but c ould be transformed to the enamino form upon complexation with palladium. T he relative stability of the imino and enamino chelates is sensitive to the substituents on the phosphorus donor atoms. When di(phenylethynyl)phenylph osphine was used as the starting material, the hydroamination reaction gave a 4:1 mixture of the chelating diastereomeric P-chiral iminophosphine on t he chiral template. These diastereomeric complexes could be separated effic iently via silica gel column chromatography. A pair of novel and enantiomer ically pure P-chiral iminophosphines was obtained in high yields from the s eparated diastereomeric template complexes by treatment with KCN.