STEREOCHEMICAL PATTERN OF PHOSPHINE OXIDATION BY A PEROXOMETALLACYCLIC PLATINUM COMPLEX - EVIDENCE OF AN INTRAMOLECULAR PROCESS

The prochiral peroxometallacyclic ketenyl platinum complex [(PPh3)2Pt- O-O-C(O)-C=C=O] (1) reacts with (S)-(-)-alpha-methylbenzylamine to giv e the diastereomeric amidic derivatives, 2. One of the two possible di asteromers, 2a, has been obtained pure and the absolute configuration at the carbon atom sigma-bonded to the metal is inferred from its CD s pectrum. Compound 2a has been used to oxidize the chiral racemic phosp hine (RS)-PPhCyPr using a molar ratio, PPhCyPr 2a = 2:1. The reaction products contains an enantiomeric excess of (S)-(-)-OPPhCyPr whereas u nreacted PPhCyPr shows the prevalent (S) configuration, indicating tha t the reaction occurred with asymmetric induction. These findings are rationalized by a mechanism based on the coordination to the metal of PPhCyPr mainly in the (R) configuration, followed by an intramolecular oxidation by the peroxide moiety.