HIGHLY STEREOSELECTIVE COORDINATION OF MONOSUBSTITUTED ETA-3-ALLYL GROUPS TO CHIRAL (BIS(OXAZOLINE)) PALLADIUM CATIONS

Stereoselectivity in coordination of various eta3-1-monosubstituted-allyl groups to chiral ((R,R)-bis(oxazoline))palladium(II) cations was investigated by H-1 NMR spectroscopy. When the eta3-1-phenylallyl, 1-(1-naphthyl)allyl, and 1-(silylcarbonyl)allyl groups coordinated to the palladium cation, two diastereomers arose in which the substituent occupied the syn position with respect to the eta3-allyl framework. In the major diastereomer (73-93% selectivity), the substituent at the allyl carbon was located so as to stagger the substituent at the oxazoline ring, while, in the minor diastereomer, the former eclipsed the latter. The diastereoselectivity increased in the sequence of the size of the substituent at allyl group: Ph < 1-naphthyl < COSiMe2Ph. In the case of the eta3-1-(trimethylsilyl)allyl group coordination, the diastereomer in which the Me3Si group occupied the anti position and staggered the ring substituent dominated (greater-than-or-equal-to 95 % selectivity). A slow isomerization process between the three diastereomers of the (eta3-1-(trimethylsilyl)allyl)(bis(oxazoline))palladium complex was observed.