Novel cyclic α phosphino α amino acids and α phosphonium glycolates P O ̄ligands and nickel complexes : syntheses structural characterization properties and use in catalysis Novel heterocyclic alpha phosphinoamino acids by structural relationship named 3 phosphaprolines were obtained by cyclocondensation of 2 phenylphosphinoethylamines with glyoxylic pyruvic or phenylglyoxylic acid at room temperature in diethylether. The reactions proceed via primary attack of the P lone electron pair as shown by the synthesis of phosphonium glycolates from tertiary phosphines and glyoxylic acid and addition of PH at the carbonyl group. The ring closure proceeds by replacement of the hydroxy by the amino group and is kinetically controlled. NMR monitoring of the phosphaprolines in CD3OD over several days indicates changes of the diastereoisomer ratios leading to higher contents of the more stable trans diastereoisomers. The zwitterionic compounds are soluble in part in CD3OD DMF or DMSO are somewhat sensitive to air in solution and may undergo hydrolysis with larger amounts of water. The structures are proved by multinuclear NMR spectra and two crystal structure analyses. Suitable phosphaprolines as well phosphonium glycolates and Ni(COD)2 allow to generate precatalysts activated by NaH for the oligomerisation of ethylene to mainly linear products with methyl and vinyl end groups. Some additional investigations with phosphinophenolates another type of P C C O ligands were performed for comparison. Precatalysts prepared from 2 phosphinophenolesters and Ni(COD)2 at room temperature were characterized by multinuclear NMR but decomposed on ... Phosphine Aminosäuren Phosphoniumsalze Nickel Oligomerisation Phosphino amino acids Phosphaprolines Phosphonium glycolates Nickel catalysts Ethylene oligomerisation