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 and 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 structure analyses. The exo isomer undergoes a sequence of ligand substitutions to give the 'chiral-at-rhenium' derivatives [PCpReNO(CO)PPh(3)]BF4 and PCpReNO(CH3)PPh(3) as a 1:1 inseparable mixture of diastereomers. The latter compound has also been characterized by an X-ray structure analysis with both diastereomers occupying unique positions in the crystal lattice.