Synthesis, structure, and reactivity of bridging halide complexes of the formula [(.eta.5-C5H5)Re(NO)(PPh3)]2X+ BF4-. Preferential binding of one enantiomer of halide complexes (.eta.5-C5H5)Re(NO)(PPh3)(X) by the chiral Lewis acid [(.eta.5-C5H5)Re(NO)(PPh3)]+