GENERATION AND REACTIVITY OF THE CHIRAL RHENIUM CHLOROBENZENE COMPLEX [ETA-5-C5H5)RE(NO)(PPH3)(CIC6H5)]+BF4- - AN IMPROVED FUNCTIONAL EQUIVALENT OF THE CHIRAL LEWIS ACID [(ETA-5-C5H5)RE(NO)(PPH3)]+BF4-
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abstract
Reaction of (5-C5H5)Re(NO)(PPh3)(CH3) (1) and HBF4 OEt2 in C6H5Cl at -45C gives the chlorobenzene complex [(5-C5H5)Re(NO)(PPh3)(ClC6H5)]+BF-4 (5). The rhenium is bound chiefly to chlorine in 5, but other species, possibly 2-arene isomers, are apparent by 31P NMR. The relative amounts change upon warming, and new species appear. Complex 5 reacts with neutral donor ligands L (CH3CN, C6H5CH2CH=CH2, THF) to give the corresponding adducts [(5-C5H5)Re(NO)(PPh3)(L)]+BF-4, halide ions X- to give halide complexes (5-C5H5)Re(NO)(PPh3)(X), and HSi(OEt)3 to give hydride complex (5-C5H5)Re(NO)(PPh3)(H) (74-91%). When 5 is generated from optically active 1, analogous reactions with L ((-)-(S)-2-phenylbutyronitrile, benzaldehyde) give adducts in high optical yields and with overall retention of configuration at rhenium. For example, carboxylate complex (+)-(RR)-(5-C5H5)Re(NO)(PPh3)(O(C=O)-CH(OAc)C6H5) forms in > 99% d.e. upon treatment of 5 derived from (+)-(S)-1 with (-)-(R)-C6H5CH(OAc)COOH and then base. Thus, 5 serves as a functional equivalent of the chiral Lewis acid [(5-C5H5)Re(NO)(PPh3)]+-superior in many aspects to the analogous dichloromethane complex reported earlier. 1990.
