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)]+
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Reactions of halide complexes (η5-C5H5)Re(NO)(PPh3)(X) (X = I, 7; X = Br, 8) and AgBF4in refluxing benzene gives bridging halide complexes (RR,SS)-[(7r-C5H5)Re(NO)(PPh3)]2X+BF4“ exclusively as dl diastereomers (X = I, (RR,SS)-4, 59%; X = Br, (RR,SS)-5, 54%). Reaction of optically active (+)-(R)-7 and dichloromethane complex (S)-[(η5-C5H5)Re(NO)(PPh3)(ClCH2Cl)]+BF4~ ((S)-l) gives a complex mixture of products, including species derived from -CH2C1 transfer from (S)-l to (+)-(R)-7. In no case is evidence for a meso diastereomer of a bridging halide complex observed. The structure of solvate (RR,5S)-4-(CHCl2CHClo)a7is verified by X-ray crystallography (monoclinic, P2(l)/c (No. 14), a = 14.975 (4) A, b = 18.219 (4) A, c = 20.855 (4) A, β = 108.20 (2)°, Z = 4). A “W” conformation is found for the P-Re-I-Re-P bonds, and a stereoelectronic rationale is given. Models show that if meso bridging halide complex diastereomers were to adopt analogous “W” conformations, severe steric interactions would occur between two syn cyclopentadienyl ligands. Complexes (RR,SS)-4 and (RR,SS)-5 react with acetonitrile (95 °C, 1.25 and 0.25 h, respectively) to give [(η5-C5H5)Re(NOHPPh3)(NCCH3)]+BF4~ and halide complexes (η5-C5H5)Re(NO)(PPh3)(X) (93-99% of theory). © 1989, American Chemical Society. All rights reserved.
author list (cited authors)
Winter, C. H., Arif, A. M., & Gladysz, J. A.