SEQUENTIAL ELECTROPHILE NUCLEOPHILE ADDITIONS FOR ETA(2)-CYCLOPENTADIENE COMPLEXES OF OSMIUM(II), RUTHENIUM(II), AND RHENIUM(I)/

A series of d(6) transition-metal complexes of the type ML(5)(eta(2)-C pH), where ML(5)=[Os-II(NH3)(5)](2+), [Ru-II(NH3)(5)](2+), and [Re-I(P Ph(3))(PF3)(dien)](+), were synthesized as their triflate salts and co mbined with electrophiles (HOTf, CH2(OMe)(2)) to form eta(3)-allyl com plexes. Treatment of these pi-allyl complexes with the mild carbon nuc leophile 1-methoxy-2-methyl-1-(trimethylsiloxy)propene (MMTP) followed by decomplexation affords substituted eta(2)-cyclopentene derivatives with excellent regio-and stereocontrol. Deuteration and NOE studies f or the pi-allyl complexes along with stereochemical analysis of the or ganic products confirm that both electrophilic and nucleophilic additi on occurs exclusively from the exo face of the ring (opposite to metal coordination) for all three systems.