OPTICALLY-ACTIVE TRANSITION-METAL COMPLEXES .2. RHENIUM COMPLEXES WITH THE OPTICALLY-ACTIVE CYCLOPENTADIENYL LIGAND PCP - X-RAY STRUCTURES OF THE EXO AND ENDO ISOMERS OF PCPRE(CO)(3) AND OF THE DERIVATIVE PCPRENO(CH3)PPH(3)

The synthesis of the optically active exo and endo isomers of PCpRe(CO )(3) [PCp = 'pinene-fused cyclopentadienyl'] is described. The yield a nd relative ratio of the two isomers is strongly dependent on solvent, temperature and the various starting materials Re(CO)(3)L(2)X [X = Cl , L = CO, THF, pyridine, CH3CN, DME] as well as the derivative MPCp [M = Li, Tl] used. Both isomers have been characterized by crystal struc ture analyses. The exo isomer undergoes a sequence of ligand substitut ions to give the 'chiral-at-rhenium' derivatives [PCpReNO(CO)PPh(3)]BF 4 and PCpReNO(CH3)PPh(3) as a 1:1 inseparable mixture of diastereomers . The latter compound has also been characterized by an X-ray structur e analysis with both diastereomers occupying unique positions in the c rystal lattice.