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 (5-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)-[(5-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, = 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 [(5-C5H5)Re(NOHPPh3)(NCCH3)]+BF4~ and halide complexes (5-C5H5)Re(NO)(PPh3)(X) (93-99% of theory). 1989, American Chemical Society. All rights reserved.
