Generation and reactivity of the chiral rhenium chlorobenzene complex 5-C5H5)Re(NO)(PPh3)(ClC6H5)>+ BF4- : an improved functional equivalent of the chiral Lewis acid 5-C5H5)Re(NO)(PPh3)>+BF4-

Article abstract of DOI:10.1016/0022-328X(90)85333-T

Reaction of (η⁵-C5H5)Re(NO)(PPh3)(CH3) (1) and HBF4*OEt2 in C6H5Cl at -45 deg C gives the chlorobenzene complex <(η⁵-C5H5)Re(NO)(PPh3)(ClC6H5)>⁺BF4^- (5).The rhenium is bound chiefly to chlorine in 5, but other species, possibly η²-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 <(η⁵-C5H5)Re(NO)(PPh3)(L)>⁺BF4^-, halide ions X^- to give halide complex (η⁵-C5H5)Re(NO)(PPh3)(X), and HSi(OEt)3 to give hydride complexes (η⁵-C5H5)Re(NO)(PPh3)(H) (74-91percent).When 5 is generated from optically active 1, analogous reactions with L ((-)-(S)-2-phentylbutyronitrile, benzaldehyde) give adducts in high optical yields and with overall retention of configuration at rhenium.For example, carboxylate complex (+)-(RR)-(η⁵-C5H5)Re(NO)(PPh3)(O(C=O)-CH(OAc)C6H5) forms in >99percent 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 <(η⁵-C5H5)Re(NO)(PPh3)>⁺ -- superior in many aspects to the analogus dichloromethane complex reported ealier.